Latent heat-assisted cooling for high-efficiency solar-driven freshwater production

Domain: physics
Published: 2025-11-28
Editorial outcome: major_revision

Abstract
Solar-driven interfacial evaporation has shown great potential in freshwater production due to its minimal carbon footprint and adaptability to diverse water sources. However, while significant progress has been made in enhancing vapor generation rates, limited heat dissipation during condensation continues to constrain overall water production efficiency. Here, we introduce a latent heat-assisted evaporative cooling (LHEC) strategy that effectively dissipates condensation heat by harnessing water’s latent heat. Using delignified wood as the demonstrating LHEC substrate, we achieved a 2.5-fold increase in heat dissipating heat flux and accelerated vapor diffusion from the evaporation region toward the condensation interface. This approach improves solar water production efficiency to 0.76 (versus 0.49 in conventional systems) and demonstrates robust salt resistance for long-term operation. Notably, the plug-and-play design of the LHEC substrate enables seamless integration into a range of solar evaporation architectures, including single/multi-stage systems, all of which benefit from its enhanced condensation performance. This universality offers a fully passive, single solar-powered solution. This LHEC strategy represents a significant step forward in scalable, efficient and environmentally sustainable freshwater production.

Introduction
Freshwater is essential for life, agriculture, and industry. However, its scarcity, intensified by climate change, population growth, and industrial expansion, demands urgent solutions through sustainable technologies1,2. Amongst, solar-driven clean water production is particularly attractive due to the abundant and eco-friendly nature of solar energy3. In particular, interfacial solar driven water evaporation strategy which demonstrates excellent solar energy utilization efficiency (>90%) has emerged as a promising sustainable approach, in which solar energy is the only driving force4–7. To date, numerous solar-driven interfacial vapor generation strategies have been developed to enhance vapor generation rates (J vapor ), now reaching values of over 1kgm−2h−18–10. However, despite these advancements, the actual clean water production rate (J prod ) remain significantly lower, typically in the range of 0.3–0.5kgm−2h−111–14. This discrepancy arises primarily from inefficiencies in the vapor-to-liquid condensation process, which is critical for determining the final J prod . For effective condensation, the water vapor must first achieve saturation15. Unlike the evaporation process typically conducted in open environments, vapor condensation often requires a closed environment to enable vapor saturation (Fig. 1a). However, this closed environment unavoidably increases relative humidity (φ) near the solar evaporator, thereby diminishing the evaporation driving force and, consequently, the evaporation flux (J vapor /\propto C sat(T(E)) - φC sat(T(S))) Here, C sat-T(E) and C sat-T(S) refer to the vapor saturation concentrations at the temperature of the solar evaporator (T E) and the surroundings (T S), respectively16,17. To address this limitation, efficient heat dissipation during condensation can lower C sat-T(S), thereby increasing the evaporation flux and final freshwater production16–20. As illustrated in the psychrometric chart with the closed-air cycle from evaporation to condensation21 (Fig. 1b), unlike volumetric evaporation, interfacial solar-vapor generation produces more vapor at a higher temperature. Additionally, the heat generated during the saturation of vapor (step 3→4) and vapor-to-liquid phase change (step 4→1) is even significantly greater than in conventional volumetric water heating systems, further amplifying the need for effective heat release. Therefore, a strategy that can efficiently dissipate the heat involved in the above steps is critical to maintaining effective condensation and ultimately boosting the clean water production rate in the interfacial solar clean water production system.

To date, various strategies have been proposed to enhance heat dissipation in solar clean water production systems (Fig. 1c)14. A widely adopted approach involves using high-thermal-conductivity materials, such as metals (e.g., Cu, Al), in the condensing section to improve convective and conductive heat dissipation (Q con)20,22–26. However, this metal-based strategy is expensive, prone to corrosion in water environments, and becomes less effective at elevated ambient temperature due to the reduced temperature difference between the condenser surface and the surrounding air27–29. Additionally, metals tend to generate parasitic photothermal heat under direct solar irradiation, leading to self-heating and further inhibits heat dissipation, which becomes more severe under hot climates30,31. Another approach utilizes passive daytime radiative cooling (PDRC), which radiates heat into outer space32–35. While PDRC can enhance efficiency to some extent, its overall performance remains low and relies highly on weather conditions36–38. Additionally, the complex material preparation involved increases implementation challenges, hindering large-scaled deployment and maintenance39. Therefore, it still remains as a challenge to develop a highly efficient, cost-effective and easily scalable heat dissipation strategy that can perform effectively under high ambient temperature and cloudy weather conditions.

In a typical solar-driven interfacial water evaporation process, heat is absorbed to overcome water’s large latent heat of vaporization (~2450Jg−1), facilitating efficient vaporization40. Given the considerable latent heat and continuous water supply, this latent heat can also be harnessed as an effective cooling power source through spontaneous phase transition, to be adopted to dissipate heat and promote vapor condensation (Fig. S14). Unlike ambient cooling and PDRC strategies, the cooling power of latent heat-assisted evaporative cooling (LHEC) increases with the saturated vapor concentration corresponding to the ambient temperature (C sat(T amb)). At a given relative humidity, elevated ambient temperatures lead to higher C sat(T amb), making LHEC particularly effective in hot climates (Fig. 1c) where conventional cooling methods are less efficient41–43. To evaluate its potential, we conducted theoretical simulations comparing the heat flux of the LHEC process with that of ambient cooling and PDRC (Fig. 1d, see Supplementary Note S1 for detailed calculation)44. The results reveal that LHEC achieves a higher heat dissipation flux than both ambient cooling and PDRC, with its cooling advantage becoming more pronounced at elevated surface temperatures. Thus, developing an all-passive LHEC strategy can overcome the key bottleneck of limited heat dissipation in solar water production systems, offering a promising solution to enhance the solar clean water production efficiency.

In this work, we designed a LHEC strategy by using a delignified wood as the substrate. The wood was chosen for its intrinsic micro-scale tracheids that facilitate water transport and its environmental sustainability. The delignification process significantly enhances water transport capability while reducing solar absorption, minimizing parasitic heat that would otherwise consume additional cooling power. These properties collectively enhance the substrate’s heat dissipation performance. Theoretical simulation revealed that the LHEC substrate not only thermodynamically improves heat dissipation, but also kinetically accelerates vapor diffusion from the evaporator interface to the condensation surface, thereby collectively boosting clean water production efficiency. When integrated into a conventional solar interfacial evaporator setup, the LHEC substrate increased the system’s heat dissipation capacity by 2.5-fold compared to conventional air cooling. Under solar irradiation of 1.4kWm−2, the LHEC-assisted system achieved a solar water production efficiency of ~76%, compared to ~49% for conventional air-cooling systems. Additionally, this LHEC substrate demonstrates high versatility, seamlessly integrating with various solar interfacial evaporation setups, including single-stage, multi-stage, and geometrically diverse configurations, all of which exhibited improved water production rates. Furthermore, its microporous structure offers resistance to salt accumulation during seawater use, ensuring stable heat dissipation and long-term operational reliability. Compared to existing cooling strategies, the LHEC approach delivers superior efficiency, low cost, sustainability, and environmental adaptability, representing a significant advancement toward practical and scalable solar water production systems.

Results
Design, fabrication and characterization of a wood based latent heat-assisted evaporative cooling substrate
An efficient LHEC process requires substrates that fulfill several key criteria. First, they must exhibit excellent capillary water transport and a large surface area to ensure rapid and stable water evaporation. Second, to minimize parasitic heat accumulation caused by solar energy absorption, the substrates should exhibit low absorption efficiency across the full solar spectrum (0.2–2.5μm), maintaining a stable and relatively low surface temperature under solar radiation45. Third, considering that seawater constitutes around 97% of Earth’s water resources, the substrate must have good anti-salt accumulation performance to enable long-term operational stability in marine environments46. Considering these requirements, natural wood was chosen as the model material due to its earth-abundant availability and massive intrinsic interconnected channels, which are advantageous for capillary water transport and salt resistance. To further enhance its performance, a delignification treatment was applied to remove lignin, for lowering solar energy absorption capability as well as improving hydrophilicity47. The delignified wood exhibits a notably improved whiteness appearance, suggesting its non-absorbing and scattering towards the visible light (Fig. 2a and Fig. S15)48,49. Scanning electron microscopy (SEM) was used to investigate the dilignified wood’s structure. Cross-sectional SEM images revealed a multi-scale channel network composed of large vessels (~200μm in diameter) and smaller fiber tracheids (~20μm in diameter) (Fig. 2b, Figs. S16, S17a). The removal of lignin exposed numerous nanopores (~100nm in diameter) within the wood cell walls, significantly increasing the water transportation channels for water evaporation and enhancing its hydrophilicity (Fig. 2c)50. Longitudinal SEM images further revealed the low-tortuous alignment of fiber tracheids, as well as the presence of bordered pits (~1μm in diameter) distributed across the cell walls (Fig. 2d and Fig. S17b). These pits created interconnections between adjacent vessels and fiber tracheids, facilitating efficient water transport throughout the structure.

The water transport capability of delignified wood was assessed next through dynamic water contact angle tests, showing a contact angle of approximately 57° at 200ms and complete water droplet absorption within 0.8sec, confirming its excellent hydrophilicity (Fig. S18). Capillary height measurements further demonstrated the wood’s ability to transport water up to 13.2cm, highlighting its efficient water absorption and transport for LHEC (Fig. 2e). The corresponding thermal-infrared image revealed that after water spread across the delignified wood surface, its temperature dropped to approximately 18°C, with a ΔT of 4°C compared to ambient temperature. The above characteristics indicated that delignified wood can serve as an effective substrate for evaporative cooling.

In addition to supporting evaporative cooling, the hierarchical structure of interconnected channels enhances solar light scattering, reducing parasitic heat detrimental to the LHEC process. Finite-difference-time-domain (FDTD) simulations (Fig. 2f, Note S2) showed that pores with diameter of 10–30μm can scatter light across the full solar spectrum (0.2–2.5μm), aligning with the size of the wood’s microscale tracheids. This indicates the substrate’s ability to effectively scatter sunlight across the entire spectrum. Besides, it shows that nanopores around 1μm contribute to light scattering, particularly in the visible to near-infrared range. The alignment of these pore sizes with the wood’s pits and nanopores further enhances overall light scattering efficiency.47 These multiscale structural features synergistically enhance the substrate’s light scattering efficiency, which is critical for reducing parasitic heat51,52. To verify this, solar absorption spectrum of the delignified wood substrate was measured (Fig. 2g), showing a lower solar absorbance (A solar) of approximately 0.11 compared to natural wood (0.46). This result aligns with the above FDTD simulations, demonstrating the substrate’s ability to maintain a stable surface temperature and minimize parasitic heat under solar irradiation, thereby supporting efficient LHEC performance.

Besides the above demonstrated potential for efficient LHEC process, the delignified wood can also enhance heat dissipation through radiative cooling, leveraging its intrinsic chemical composition47. Fourier transform infrared (FTIR) spectra (Fig. 2h) confirm the removal of lignin, as indicated by the absence of lignin-specific peaks at 1590 and 1501cm−1. The strong O-H stretching vibration peak at 3350cm−1 reflects abundant hydrophilic sites, consistent with the above water contact angle measurement. The absorption peak at 1103cm−1 corresponds to the numerous C-O skeletal bonds in the wood structure. This peak falls within the long-wave infrared (LWIR) absorption range (667–1250cm−1), indicating the wood’s ability to radiate heat effectively in this spectrum53. To validate this, we conducted the infrared spectroscopy measurement (Fig. 2i). It shows that the wood substrate achieves a high emittance of ~0.96 across the LWIR range, covering the atmospheric transparent window (8–13μm), which confirms its strong radiative cooling performance. Furthermore, in typical interfacial vapor condensation scenarios, the heat dissipation surface temperature ranges from 30 to 50°C54,55. Theoretical calculation in Fig. 2i indicates that the blackbody radiation peak within this temperature range aligns with the LWIR range, matching the wood’s high emittance and further supporting efficient heat dissipation during condensation. By combining the constant evaporative cooling power, low solar absorption and high LWIR emission, the delignified wood demonstrates significant potential as an ideal LHEC substrate for heat dissipation during solar interfacial vapor condensation (Fig. 2j).

Evaluation of the latent heat-assisted evaporative cooling performance
To comprehensively evaluate the delignified wood’s performance as an LHEC substrate, its evaporative heat dissipation and anti-parasitic heat capabilities were tested using a self-customized setup (Fig. 3a and Fig. S19). In this setup, an electro heater was used to simulate the heat input (Q TEI) from the solar evaporator, and a thermal flux meter was fixed to the back to record the thermal heat loss and facilitate faster attainment of thermal equilibrium. A thermal flux meter on the electro heater recorded the corresponding thermal input (Q TEI). On the opposite side, a piece of delignified wood was attached to the glass plate, with a thermocouple placed on the interface to continuously monitor the “condensation interface” temperature. The bottom side of the wood was immersed in water to ensure a steady water supply for evaporation. A solar simulator was used to irradiate the wood substrate, with its power intensity (Q solar) adjusted to match Q TEI, replicating practical conditions.

As shown in Fig. 3b, the steady LHEC power (Q LHEC) increased proportionally with the thermal energy input (Q TEI), demonstrating the substrates’ ability to dissipate heat efficiently through the LHEC process (see Note S3 for detailed LHEC power calculation). To quantify the cooling contribution of the LHEC, we defined the ratio (α) as the proportion of LHEC cooling flux to the total heat input, comprising both the thermal energy input from the electric heater (Q TEI) and the absorbed portion of solar irradiation (Q solar). Therefore, energy ratio α = Q LHEC / (Q TEI + Q solar), where Q solar is the absorbed solar energy. The ratio α remained relatively stable, ranging from 0.8 to ~1.0 at the thermal input increased from 0.2 to 1kWm−2 (Fig. 3c), indicating that the entire heat dissipation process is predominantly governed by LHEC instead of convective and radiative cooling (Fig. S20). Moreover, the delignified wood can continuously support this evaporative heat dissipation through rapid water transport, even under high heat loads. It should be mentioned that, under solar irradiation, the LHEC power increased slightly compared to non-irradiated conditions, reflecting the cooling power required to dissipate parasitic heat from solar absorption. Due to the substrate’s low solar absorbance, solar irradiation at 1kWm−2 required only ~100Wm−2 of additional cooling (Fig. 3b). This highlights the substrate’s ability to scatter solar radiation effectively, as corroborated by its low solar absorbance in Fig. 2f, confirming its resistance to parasitic heat and suitability for efficient LHEC.

Effective heat dissipation can lower the “condensation interface” temperature, which is a critical parameter for thermal management56. As shown in Fig. 3d, the interface temperature of LHEC substrate rose more slowly with increasing thermal input and plateaued at higher heat levels. By comparison, a reference glass substrate, which is a common condensation material used in solar interfacial evaporation systems, exhibited consistently higher interface temperature, with the difference becoming more pronounced at higher thermal inputs. These results demonstrate the superior heat dissipation capabilities of delignified wood as LHEC substrate.

Improvement of solar interfacial clean water production by latent heat-assisted evaporative cooling
We integrated the wood-based LHEC substrate into a conventional solar interfacial evaporation setup to evaluate its contribution to clean water production. Considering cost, versatility, earth-abundance and anti-salt fouling, a polypyrrole (PPy)-coated wood interfacial evaporator covered with a conventional glass cover was fabricated as a representative and accessible solar water production setup (see Note S4 for detailed preparation). The PPy-coated evaporator achieved high solar absorption (95%) and a vapor generation rate (J evap) of ~1.11kgm−2h−1 under 1kWm−2 irradiation in an open environment (Figs. S21, S22). The wood-based LHEC substrate was attached to one wall of the cubic glass cover, while a bulk water reservoir below ensured continuous water supply for both solar vapor generation and the LHEC process. The system was tested under simulated solar irradiation to replicate practical real-world conditions (Fig. 4a).

The heat dissipation capability of the LHEC-assisted setup was assessed by comparing heat flux at the LHEC interface to a setup without LHEC. Under varying solar irradiation intensities, both setups showed increasing heat fluxes that stabilized over time (Figs. S23, S24). However, the LHEC-assisted setup consistently demonstrated higher stabilized heat fluxes, with a heat dissipation rate approximately 2.5 times greater than the bare glass surface across different irradiation levels (Fig. 4b). This experimentally highlights the LHEC’s significant enhancement of condensation heat dissipation. Additionally, as unveiled by Fig. 4c, temperature monitoring revealed that the LHEC surface was consistently 4–6°C cooler than the bare glass surface, while the vapor temperature in the LHEC-assisted setup was only slightly lower (<1°C) than in the bare setup. This resulted in a greater temperature difference (ΔT) between the vapor and the condensation wall. Without LHEC, ΔT values ranges from 6.5 to 11.1°C, whereas with LHEC, ΔT increased to 10.0–16.4°C. This improvement in ΔT enhances heat exchange between the vapor and the condensation wall, thereby promoting the condensation process.

The wood-based LHEC substrate not only can enhance heat dissipation but also can accelerate vapor diffusion from the evaporator surface to the condensation section, collectively leading to a higher vapor collection rate. To validate this, we utilized a COMSOL model to simulate the vapor concentration distribution above the evaporator surface, using experimentally measured surface temperature and heat flux values as boundary conditions (see Note S5 and Table S1 for details). As shown in Fig. 4d, the vapor concentration gradient in the LHEC-assisted setup was steeper than in the setup without LHEC. This steeper gradient confirms faster vapor diffusion in the LHEC-assisted system. The steady vapor diffusion rate (J diff) was calculated using J diff = −D∇C, where D is the water vapor diffusion coefficient. Figure 4e shows that J diff in the LHEC-assisted setup was significantly higher, demonstrating enhanced vapor mass transfer from the evaporator surface to the condensation section, which directly benefits the condensation process. Additionally, J diff increased with rising irradiation intensities, consistent with the enlarged temperature difference (ΔT) shown earlier in Fig. 4c.

Clean water generation rates of the two setups were also evaluated. Under 1kWm−2 solar irradiation, the LHEC-assisted setup achieved a freshwater production rate of 0.90kgm−2h−1, representing a 34.3% improvement over the setup without LHEC (Fig. 4f). To evaluate the impact of LHEC coverage, substrates were applied to different sides of the glass cover (Fig. S25). Two-sided coverage yielded the highest water generation rate, while further extension caused evaporator overcooling. Considering this trade-off, along with cost, structural complexity, and potential shading, we adopted the single-sided configuration for subsequent studies. To reveal the contribution of LHEC to energy conversion, we calculated the solar water production efficiency, which is defined as η = (J prod × H cond) / I solar, where J prod denotes the water generation rate (kgm−2s−1), and H cond is the enthalpy of vapor condensation (Jkg−1), I solar is the solar irradiation intensity (Wm−2). Without LHEC, the solar water production efficiency remained around 45%, which is comparable to the performance of conventional systems57,58. In contrast, the LHEC-assisted setup achieved efficiencies of up to 76% under 1.4kWm−2, promoting the conversion of solar energy into freshwater (Fig. 4g). Notably, efficiency of the LHEC-assisted setup increased gradually with higher solar intensities, which can be attributed to the increasing heat dissipation benefits of the evaporative cooling mechanism as the heat load increases (Figs. 1d, 3d).

To evaluate the versatility and plug-and-play compatibility of the wood-based LHEC substrate, we integrated it with five representative condensation setups: a single slope device (SSD), an inversed-structure device (ISD), a droplet-wise condensation device (DWD), a film-wise condensation device (FWD), and a three-stage distillation device (TSDD) (see Note S6 for detailed design and preparation). Figure 4h shows that the implementation of the wood based LHEC substrate significantly enhanced water production rates in all setups. Among them, the ISD exhibited the greatest improvement, with a water production rate increase of up to 35.5% under 1 sun irradiation. Meanwhile, the TSDD-LHEC configuration achieved the highest water production rate, reaching 1.99kgm−2h−1. These results demonstrate the LHEC’s versatility and effectiveness in enhancing condensation performance across various system designs, highlighting its potential as a robust and adaptable solution for interfacial freshwater production.

Practical performance evaluation of the latent heat-assisted evaporative cooling strategy
An outdoor experiment was conducted to evaluate the practical applicability of the LHEC-assisted solar water production strategy. The experimental setup (Fig. 5a, b) was deployed on the Zijingang Campus of Zhejiang University, Hangzhou, China, from February to May, 2023, under various weather conditions. Thermocouples and a pyranometer were used to continuously monitor and record the ambient temperature and solar intensity profiles. Results for sunny and cloudy conditions both showed that the LHEC-assisted setup consistently outperformed the bare glass setup. On sunny days, the LHEC-assisted system achieved a peak freshwater production rate of 0.85kgm−2h−1 under solar radiation of ~0.9kWm−2, representing a ~25% increase over the bare setup (Fig. 5c). On cloudy days (~0.6kWm−2), the average freshwater production rate improved from 0.40 to 0.54kgm−2h−1, achieving a ~35% improvement (Fig. S26). To further validate the environmental robustness of LHEC strategy, we conducted performance comparisons in a controlled environment chamber with temperatures ranging from 15 to 40°C and humidity from 25 to 75% RH (Fig. S27). Under these varying conditions, the LHEC strategy consistently provided over a 19% improvement in solar water generation performance. These results demonstrate that the LHEC-assisted strategy can effectively enhance the solar freshwater production under various outdoor conditions.

To test its durability in seawater, simulated seawater (3.5% salinity) was used to evaluate heat dissipation stability (Fig. S28). The wood based LHEC substrate maintained a stable heat dissipation flux of ~1kWm−2 over 120h, under a continued heat load of 1kWm−2, with no performance decline (Fig. 5d). This stability is attributed to the interconnected multi-scale channel structure of the delignified wood, which facilitates salt re-diffusion and prevents salt accumulation (Fig. S29)59. To further validate its practical application, the LHEC-assisted setup was floated on seawater for outdoor testing (Fig. 5e and Fig. S30). It achieved maximum freshwater production rate of 1.08kgm−2h−1 under peak solar irradiance of approximately 1.1kWm−2 (Fig. 5f and Fig. S31). To evaluate scalability, two large-scale solar distillation setups were constructed and tested outdoors using saline water (see Supplementary Note S7 for details). The LHEC-assisted system consistently achieved an average of ~35% increase in water production, confirming its effectiveness at larger scales. Additionally, the water purification performance of the LHEC-assisted setup was evaluated using natural lake water and seawater as raw water sources. The produced freshwater from these sources showed significantly reduced salt ion concentration and total organic carbon (TOC) levels, satisfying World Health Organization (WHO) drinking water standards (Fig. 5g).

We compared the solar water production efficiency of the LHEC-assisted strategy with previously reported approaches (Fig. 5h). The results reveal that despite the simplicity of prototype, the LHEC-assisted system still achieves a notable solar water production efficiency, comparable to state-of-the-art devices. Additionally, we performed an economic analysis of the wood-based LHEC substrate over a one-year operational cycle (Fig. S32 and Table S2 and 3). The results demonstrate that a modest additional investment of 12.7% in materials and maintenance yields a 35% increase in freshwater output, ultimately leading to an 18.2% reduction in the cost per liter of water (Fig. 5i). This low cost suggests that integrating the LHEC strategy into a traditional solar vapor generation system requires minimal investment, yet provides a significant solar water production boost. In summary, the wood-based LHEC strategy demonstrates comparable solar water production efficiency, environmental friendliness, low cost and portability (Tables S4 and 5). These advantages make it an excellent candidate for practical solar water production applications.

Methods
Chemicals and materials
Balsa wood was purchased from Sinokiko Balsa wood Trading Co., Ltd. (Guangzhou, China). Sodium chlorite (NaClO 2, 80 wt%) was purchased from Aladdin Ltd. (Shanghai, China). Acetic acid (CH 3COOH, >99.7%) was purchased from RCI Labscan. Sodium acetate (CH 3COONa, >99 wt%) was purchased from J&K Chemical Co., Ltd. (China). Pyridine (C 5H 5N, >99.5%) was purchased from MACKLIN Co., Ltd., (China). Ammonium persulfate ((NH 4) 2S 2O 8, >98 wt%), Hydrochloric acid (HCl, 36–38%), Octadecyltrichlorosilane (C 18H 37SiCl 3, 95%) and Hexane (C 6H 14, >97%) were purchased from Sinopharm Chemical Reagent Co. Ltd. (China). The glass was purchased from Shunlong Quartz Co., Ltd. (Jiangsu, China). All the chemicals and materials were used directly unless otherwise specified.

Fabrication of delignified wood based latent heat-assisted evaporative cooling substrate
To prepare the delignified wood, 2 wt% NaClO 2 solution was first prepared by dissolving NaClO 2 in deionized water. The pH of the solution was adjusted to 4.8 by adding CH 3COOH and CH 3COONa. Original balsa wood blocks (12cm×14cm) were immersed in this solution and heated at 90°C for 6h. This process was repeated three times to ensure effective delignification. After treatment, the wood blocks were sequentially rinsed with ethanol and deionized water to remove residual chemicals. The samples were then frozen at −20°C for 12h, followed by lyophilization for 24h to obtain dry delignified wood.

Characterization
SEM was performed on a field emission scanning electron microscope (Gemini SEM 300, Germany). FTIR spectrometer (AVA TAR370, NICOLET, USA) was employed to conduct the infrared (IR) spectra measurement. The solar absorption spectrum was measured using a UV–vis–NIR spectrophotometer (Cary 5000) with an integrating sphere. The long wavelength IR emittance spectrum was determined using an FTIR spectrometer with an integrating sphere (iS50 FT-IR, NICOLET). The water contact angles were performed using an optical angle meter system (OCA20, DataPhysics, Germany). The capillary rise height was determined by the color difference in IR photographs that were taken by an IR camera (FLUK, Ti450, USA).

Quantification of the latent heat-assisted evaporative cooling performance
The latent heat evaporative cooling performance was evaluated using a custom-assembled apparatus. A ceramic heating plate (resistance=48Ω) simulated condensation heat, with the heat flux controlled by a DC power supply (Wanptek, GPS305D, China). A heat flux meter (Hukseflux, HFH04-02, Holland) monitored the heat flow density. The LHEC wood substrate was tightly attached to the glass plate (5cm×5cm). Temperature on the inner surface of the glass was measured using thermocouples (CEM, DT8891E, China). The bottom of the LHEC wood substrate was submerged in water contained in a beaker. The mass changes of whole system were measured using an analytical balance (Mettler Toledo, ME204E, USA) to calculate the evaporation rate. A xenon lamp (CEL-AAAS50, Aulight) simulated solar irradiation, with intensity adjusted via current and calibrated by an optical power meter (CEL-NP2000-2, Aulight). The experiments were conducted in a laboratory environment with room temperature around 25°C and relative humidity of ~50%. For each thermal energy input condition, the mass changes of the LHEC substrate were measured in three independent tests, and the error bars represent the arithmetic mean±standard deviation. The inner surface temperature data under different thermal energy inputs were measured once.

Measurement of solar fresh clean water generation
A typical experiment setup consisted of a delignified wood as the LHEC substrate, a PPy coated wood as the solar evaporator, and a glass cover with a water collection trough. Two thermocouples were placed to measure steam temperature: one on the glass wall at the wood-based LHEC substrate attachment point and the other above the evaporator. A heat flux meter was positioned between the glass wall and the LHEC substrate to measure thermal flux at the condensation surface. The setup was placed over a beaker with deionized water for steam generation and LHEC. Indoor water production experiments were conducted at 25°C with ~50% relative humidity, while the outdoor experiments were performed on the Zijingang Campus of Zhejiang University, Hangzhou, China, as well as in Meishan Bay, Ningbo, China. A solar radiometer (RS485, China) was employed to record real-time solar radiation, and thermocouples tracked temperature fluctuations. Data were wirelessly transmitted to a personal computer, with the system powered by a portable energy source. Experiments were conducted in triplicate, and the error bars represent the arithmetic mean±standard deviation.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "This manuscript presents a latent heat-assisted cooling (LHEC) strategy using delignified wood to enhance condensation in solar-driven freshwater production systems. While the experiments are generally well-executed, the overall novelty and scientific contribution are limited. The key performance claims—particularly the reported 93% efficiency—are not adequately supported or benchmarked against state-of-the-art systems. Moreover, several physical assumptions appear oversimplified, and the lack of long-term data raises concerns regarding practical relevance and scalability.\n\nMajor Comments\n1.The term “water production efficiency” used throughout the manuscript is ambiguous and potentially misleading. Based on the context, it appears to represent the ratio of condensed water to the evaporated vapor (i.e., vapor-to-water conversion efficiency), rather than the commonly used solar-to-water efficiency that accounts for the total solar energy input. I strongly recommend renaming this metric to “vapor-to-water efficiency” to avoid confusion. Furthermore, if solar-to-water efficiency is calculated based on the total solar input, the actual efficiency of the improved system is approximately 60% when the input is 1kW.m-2.h-1, which is in line with typical values reported for solar distillation systems. Therefore, the claim of exceptional performance (~93% efficiency) appears overstated and should be critically re-evaluated or rephrased with proper benchmarking.\n2.The key idea of this work appears to be enhancing condensation by leveraging the latent heat of water evaporation to passively cool the condensation surface. However, similar latent heat recycling principles have long been implemented in multistage solar distillation systems, where condensation heat is reused to drive evaporation in subsequent stages. The authors should explicitly clarify what practical or thermodynamic advantages the proposed LHEC strategy offers over such multistage systems. Is it more efficient, simpler to construct, or more scalable? Without a clear comparison or justification, the novelty and contribution of this work remain questionable.\n3.The performance of the proposed LHEC-assisted system appears to be highly dependent on ambient environmental conditions, particularly temperature and humidity, which significantly influence the evaporation rates. However, the current manuscript only presents limited outdoor data, collected over a narrow time window (February to May), without adequate seasonal variation. To convincingly demonstrate the robustness and practical applicability of this strategy, it is essential to include or discuss performance under diverse environmental conditions, such as low-temperature or high-humidity scenarios. Without such data, the claimed universal applicability of the system remains unsubstantiated.\n4.Scaling up the delignified wood substrate presents challenges, as the capillary-driven water supply is typically limited to just a few centimeters. This significantly restricts the large-scale manufacturing and application of the proposed approach.\n5.Other capillary wicks and porous materials can offer similar performance and functionality to delignified wood and are already commercially available. Moreover, although wood is a sustainable resource, the chemical-intensive processes involved in its fabrication may raise environmental concerns.\n6.The water collection rate under 1.4 kW m⁻² irradiation was below 1.6 kg m⁻² h⁻¹, corresponding to an energy conversion efficiency of approximately 70%. However, the water production efficiency shown in Fig. 4g approaches 90%, revealing a discrepancy. Similar mismatches between reported efficiencies and actual water production rates are observed under other irradiation intensities as well.\nMinor Comments:\n1.\"Second, Second, to minimize parasitic...\" remove the repetition.\n2.\"This indicates the substrate’s ability to effectively scatter sunlight across the entire spectrum.\" How does the wood scatter sunlight?\n3.Avoid using abbreviation in subtitles and figure captions.", "reviewer_2": "In this work, Guo et al. has proposed using evaporative cooling, in which they termed “Latent Heat-Assisted Evaporative Cooling (LHEC), to enhance the water production efficiency in solar stills by incorporating a delignified wood structure on the outer wall of the condenser. Their main arguments are that the substrate has achieved a 2.5-fold increase in heat dissipation, accelerated vapor diffusion flux inside the solar still, and improved water production by 93%. This is an interesting proposal, and it seems that the addition does lead to improvements in device performance in multiple different configurations. I think that the idea can merit publication, but their metrics are very misleading and many experiments are not satisfactory to support their claims. As a result, I suggest major revisions before the manuscript can be considered for acceptance.\n1. They claim that their device has a water production efficiency of 0.93 in the abstract. However, this metric is quite misleading because they defined it in pg. 8 that it is “the production rate (Jprod) against the natural solar evaporation rate (Jevap). This comparison is not meaningful because the boundary conditions that govern solar evaporation without condensation (depends on ambient humidity, temperature, and wind flow) are completely different from that in a solar still (depends on condenser design, condenser/evaporator configuration, etc.). The common metric used in literature for water production efficiency is the heat of evaporation/condensation compared to total solar energy input. Using their data in Fig. 4f, their true water production efficiency is around 59% under 1 sun. This value is still reasonably high for the solar still configuration they have, and more in line with other papers in the field. The authors should remove all data and claims that correspond to their 90% efficiency claim and use the correct metric.\n2. In Fig. 3, they compared the effectiveness of dissipating heat using the LHEC substrate vs glass. However, the configurations they used don’t reflect how the LHEC would be implemented in a real device. The authors should be comparing the performance of a ceramic heater and then a piece of glass as their control experiment (what they currently report for the gray bars). Then afterwards, they should have the ceramic heater, the same piece of glass, and finally the LHEC substrate on the outside to reflect the configurations deployed in a solar still device. The authors should revise all data corresponding to Fig. 3 and conduct the correct experimental comparisons between the two.\n3. Adding on to point 2, Fig. 3e's thermal resistance was calculated by using the temperature difference between the ambient and the environment. However, with the LHEC, there is a cooling potential happening due to phase change between the thermal resistance associated with the LHEC thermal conductance and the ambient convection. You cannot calculate the effective thermal resistance over this entire series when there is cooling happening in the middle. Fig. 3d, showing the temperature at the interface between the ceramic heater and the glass in the scenario described in Comment 2 above, would be a more appropriate measurement to illustrate the enhanced cooling from the LHEC. Another separate metric that would be more meaningful is characterizing what proportion of the cooling flux comes from evaporation as opposed to convection and radiation on the LHEC side.\n4. Adding onto points 2 and 3, is the backside of the ceramic heater properly insulated? If so, how was it done? Otherwise the heat flux from the ceramic heater would be two parallel networks (frontside through the glass/LHEC and backside through whatever the ceramic heater is in contact with).\n5. On page 2, the authors claim that metal-based condensers “become less effective at elevated ambient temperatures”. However, the thermophysical properties of the metal doesn’t change significantly (thermal conductivity) over the temperature range expected in solar stills and its thermal resistance should consequentially remain the same at elevated temperatures. The authors need to clarify why this statement was made and justify their argument.\n6. In Fig. 1d for their calculated theoretical heat dissipation power and SI Note 1, the current mass transfer correlation of vapor km = 25+19v doesn’t have an explanation for its physical basis. The cited paper (Ref. 6) referred to an Engineering Toolbox website rather than a reputable correlation source. Furthermore, the units that the authors used for the vapor concentration (g/m3) doesn’t match the units for their cited km (kg/m2-h, which should lead to the vapor concentrations being described in a dimensionless units). The authors should refer to a Heat and Mass Transfer textbook and redo these calculations with a correct correlation for their system size and check their units properly.\n7. Their current system configuration has a lot of benefits due to the small device scale they built. If the device is made taller, the salt diffusion in the LHEC will become more challenging because the ion transport resistance would increase. If the device is made wider, the LHEC condenser wall will be further away from the evaporator and the vapor transport resistance would be higher. To prove that this idea has real world potential, the authors should build a larger scaled version of the LHEC solar still device (with the evaporator surface area an order of magnitude larger, on the order of 0.1 m2 or greater) and measure the water production performance difference between the bare device and the LHEC device using salt water over extended periods of time (a few days to prove the anti-salting capabilities of the LHEC).\n7. Fig 5i shows the comparison of different traits between each strategy and Table S1 shows their rating scale. However, the grading scale seems quite arbitrary. For example, for energy neutrality, grade 3 “requires a temperature gradient” and grade 4 is “energy independent”. However, any cooling strategy will naturally form a temperature gradient. Another example is for adaptability, Grade 3 “requires cooler condition but easy to achieve” and Grade 2 is “requires cooler condition but harder to achieve.” The authors need to think more carefully about this comparison grade standards that rely on real metrics because its current form is not very meaningful.\n8. Delignified wood is usually much weaker than untreated wood. What is the mechanical strength of the delignified wood? Will it crack if salt crystals crystallize inside of the pore?\n9. Their Note S5 discusses their COMSOL simulation setup, however it is missing many details that can influence their simulation results. The authors should clearly list in a table all the values they used for their boundary conditions (boundary temperature, boundary heat flux, etc) and describe what all terms actually encompass in their note (for example dzQted accounts for additional heat sources, but what does this actually mean?).\n10. In the COMSOL simulation, they have written that dzG is the generation or removal of water vapor. Where was this condition placed inside of the simulation and how were these values determined?\n11. Their current COMSOL simulation doesn’t illustrate if the heat of evaporation or heat of condensation is correctly coupled in the simulation, which can have large effects on the temperature gradients and corresponding vapor gradients. The authors should clarify this point.\n12. On page 1, the authors cite Ref. 8 and 9 that achieve evaporation rates on the order of 10 kg/m2-h and use it as a reference point in comparison to the water production rate. However, these high evaporation rates in Ref. 8 and 9 are due to environmental heat absorption, which is a different mechanism from solar evaporation in solar stills. The authors should look for other references that provides a better comparison of the 0.3-0.5 kg/m2-h water production rate.\n13. Their manuscript and SI has many typos (for example in the heat equation in the SI, they wrote µ instead of u for velocity). The authors should go through their writings carefully and fix their notations.\n14. Fig 5h is quite misleading because there is no x-axis, but they placed their LHEC assisted setup on the right most side. In conjunction with point 1 above, the authors should revise this figure either with proper x-axis labels (maybe with a bar chart or an actual metric on the x-axis) as opposed to their current data representation.", "reviewer_3": "This study proposes a latent heat-assisted evaporative cooling (LHEC) strategy using delignified wood to improve the efficiency of solar water production systems. A multi-scale interconnected channel structure with microscale tracheids, nanopores, and bordered pits was created, which enables efficient capillary water transport and low solar absorbance. These properties minimize parasitic heat accumulation and enhance heat dissipation. The substrate increases the heat dissipation capacity by 2.5 times compared to conventional air cooling. This strategy outperforms existing methods in multiple metrics, offering an economical and eco-friendly solution for scalable solar water production with significant practical potential. I think the work demonstrates a certain level of innovation, yet there are still some issues that need to be addressed, as presented below.\n1.The manuscript contains several minor typographical errors. For instance, in the fifth line of page 4, the word “second” appears twice. Moreover, throughout the manuscript, the minus sign is incorrectly written as a hyphen. The authors are advised to carefully proofread the text to avoid such errors in future revisions.\n2.To enhance the clarity of the research presented in this paper, it is recommended to include a schematic diagram illustrating the principle behind the latent heat-assisted evaporative cooling (LHEC) strategy.\n3.For Figure 2g, to show the superiority of wet delignified wood in reducing spectral absorbance, the absorbance data of natural wood should be provided as a comparative reference.\n4.Figure 5d requires longer experimental time (7 days of continuous or intermittent operation) to further demonstrate the stability of the LHEC structure.\n5.Regarding Figures 5a and 5b, the authors need to explain why only a single-sided LHEC structure was adopted instead of a 2 or 3-sided structure. To make the work more comprehensive, data comparisons for other structural configurations are better to be provided.\n6.The authors should place the economic analysis table in the main text. Additionally, it is better to consider the lifespan of the LHEC structure in the economic analysis.\n7.For Figure 5g, the authors should provide a performance comparison between the system with and without the LHEC substrate.\n8.To clarify the accuracy and for better understanding, it’s recommended to introduce how to obtain water production efficiency. Moreover, the proposed LHEC structure induces additional seawater input for the system, how to interpret the rationality of calculating the water production efficiency using the same method as traditional water production systems?\n9.In Section S5, the models utilized in COMSOL software are introduced, and the governing equations are thoroughly explained. To facilitate the reproduction of this study, the author should provide a comprehensive table of the boundary conditions necessary for solving these equations and specify the interface types employed.\n10.To ensure the reliability of the numerical simulation results, it is essential to present the outcomes of a mesh independence study.", "reviewer_4": "I co-reviewed this manuscript with one of the reviewers who provided the listed reports. This is part of the Nature Communications initiative to facilitate training in peer review and to provide appropriate recognition for Early Career Researchers who co-review manuscripts."}, "author_response": "Responses to the reviewers’ comments (Manuscript number NCOMMS-25-15552)\nChanges in the revised manuscript as a response to the reviewers’ comments are\nhighlighted in red color and clarifications regarding the reviewer’s comments are\nprovided in blue color.\nReviewer #1 (Remarks to the Author):\nThis manuscript presents a latent heat-assisted cooling (LHEC) strategy using delignified wood\nto enhance condensation in solar-driven freshwater production systems. While the experiments\nare generally well-executed, the overall novelty and scientific contribution are limited. The key\nperformance claims—particularly the reported 93% efficiency—are not adequately supported\nor benchmarked against state-of-the-art systems. Moreover, several physical assumptions\nappear oversimplified, and the lack of long-term data raises concerns regarding practical\nrelevance and scalability.\nResponse: We sincerely thank you for the constructive comments and for acknowledging the\nquality of our experimental work. In response to the concerns raised, we have made several\nsubstantial revisions to strengthen the scientific rigor and practical relevance of the study.\nSpecifically, we have:\n Clarified the performance matrices by rephrasing the terminology used in efficiency\nreporting. The previously used term \"solar water production efficiency\" has been revised\nto \"solar vapor-to-water efficiency,\" with clear definitions and corresponding calculations\nprovided. We have also added the conventional solar-to-water energy conversion\nefficiency for benchmarking purposes.\n Provided comparative analysis with multistage solar distillation systems through both\nexperimental demonstrations and mechanistic discussion. This addresses concerns\nregarding novelty and differentiates our strategy from existing approaches that utilize\nlatent heat primarily for vapor generation rather than condensation enhancement.\n Added environmental adaptability and scalability experiments, including testing the\nperformance enhancement of LHEC under various environmental conditions and\nconducting scale-up demonstrations using modified delignified wood and supplementary\nheat-transfer configurations. These efforts help confirm the robustness and practical\nfeasibility of our system.\nPlease refer to the following detailed point-to-point response below as well as the revised\nmanuscript for the detailed revision. We hope these additions can address your concerns about\nour work.\nQ1 The term “water production efficiency” used throughout the manuscript is ambiguous and\npotentially misleading. Based on the context, it appears to represent the ratio of condensed\nwater to the evaporated vapor (i.e., vapor-to-water conversion efficiency), rather than the\ncommonly used solar-to-water efficiency that accounts for the total solar energy input. I\n1 / 48\nstrongly recommend renaming this metric to “vapor-to-water efficiency” to avoid confusion.\nFurthermore, if solar-to-water efficiency is calculated based on the total solar input, the actual\nefficiency of the improved system is approximately 60% when the input is 1 kW m-2 h-1, which\nis in line with typical values reported for solar distillation systems. Therefore, the claim of\nexceptional performance (~93% efficiency) appears overstated and should be critically re-\nevaluated or rephrased with proper benchmarking.\nResponse: We thank you for this important and constructive suggestion. To improve clarity and\navoid potential misinterpretation, we have revised the term “solar water production efficiency”\nto “solar vapor-to-water efficiency” throughout the revised manuscript. This matric is defined\nas the ratio of the freshwater generation rate to the vapor generation rate by evaporator. It serves\nto evaluate the effectiveness of the condensation process, which is the primary focus of our\nstudy. Given that our work emphasizes condensation enhancement through latent heat-assisted\ncooling (LHEC), we believe solar vapor-to-water efficiency is an appropriate and targeted\ndescriptor.\nTo further address your concern and enable benchmarking with conventional systems, we have\nadditionally calculated the solar-to-water energy conversion efficiency, which considers the\ntotal solar energy input. As shown in Figure R1, the control setup without LHEC achieves a\nsolar-to-water efficiency of approximately 0.45 under 1.0 kW m−2 irradiation. With the LHEC\nintegration, this value increases to approximately 0.60, and further rises to 0.76 under higher\nsolar input. These values are consistent with those reported for high-performing solar\ndistillation systems and support the validity of our approach.\nWe have included the above solar-to-water efficiency values and the corresponding calculations\nas Note S6 into the revised Supporting Information. A discussion to clarify the distinction\nbetween solar vapor-to-water efficiency and solar-to-water efficiency has also been updated on\npage 9, to avoid any overstatement of performance, as shown below:\n“To reveal the contribution of LHEC for condensation, we normalized the production rate (J )\nprod\nagainst the natural solar evaporation rate (J ) as solar vapor-to-water efficiency…”\nevap\n“…the LHEC-assisted setup achieved solar vapor-to-water efficiency of up to 93% under 1.4\nkW m−2 solar irradiation, corresponding to a solar-to-water efficiency of 0.76…”\nFigure R1 The comparison of calculated solar-to-water efficiency of our setup with and without\n2 / 48\nLHEC assistance under different solar irradiation intensities.\nQ2 The key idea of this work appears to be enhancing condensation by leveraging the latent\nheat of water evaporation to passively cool the condensation surface. However, similar latent\nheat recycling principles have long been implemented in multistage solar distillation systems,\nwhere condensation heat is reused to drive evaporation in subsequent stages. The authors should\nexplicitly clarify what practical or thermodynamic advantages the proposed LHEC strategy\noffers over such multistage systems. Is it more efficient, simpler to construct, or more scalable?\nWithout a clear comparison or justification, the novelty and contribution of this work remain\nquestionable.\nResponse: We sincerely appreciate your insightful comment. The core innovation of our study\nlies in introducing a latent heat–assisted evaporative cooling (LHEC) strategy to passively\nenhance the condensation efficiency of solar-generated vapor. While multistage solar\ndistillation systems indeed utilize latent heat recycling, their primary focus is on reusing\ncondensation heat to drive additional evaporation stages within closed space, rather than\nimproving the condensation process itself (see Figure R2a below)\nIn contrast, our LHEC approach targets the vapor condensation step by facilitating heat\ndissipation to outer environment through passive water evaporation from a substrate placed\nat the condenser surface. This strategy enables a localized cooling effect that reduces condenser\ntemperature and enlarge temperature difference between evaporator and condensation surface,\nthereby enhancing overall water yield.\nIn the original manuscript, we have demonstrated advantages of the LHEC strategy in\nimproving the vapor condensation performance towards single-stage solar distillation sets with\ndifferent structures, which all showed improved efficiencies ranging from 11% to 43%. (Figure\n4h of the original manuscript, which has also been shown as Figure R3i, ii, iii and iv below).\nTo further clarify its practical potential, we implemented our LHEC design in a three-stage solar\ndistillation setup by attaching a wood-based evaporative substrate to the finned condenser\nsurface (Figure R2b and d). Infrared imaging revealed that the LHEC integration reduced the\ncondenser temperature from 25 to 19 °C (Figure R2e), resulting in an increase in water\nproduction from 1.619 to 1.995 kg m−2 h−1, with an approximately 23% improvement (Figure\nR2f).\nThese results demonstrate that, beyond its structural simplicity and ease of integration, the\nLHEC strategy offers a distinct thermodynamic advantage by directly enhancing condensation\nperformance.\nThe performance comparison of three-stage distillation (Figure R2f) has been incorporated into\nFigure R3 as Figure R3v. Figure R2b and 2d have been added into Note S7 of the revised\nSupporting information with detailed manufacture process of the three-stage distillation device.\nFigure R3 has been updated as Figure 4h into the revised manuscript, along with a proper\ndescription as shown below.\n“…, we integrated it with five representative condensation setups: a single slope device (SSD),\n3 / 48\nan inversed-structure device (ISD), a droplet-wise condensation device (DWD), a film-wise\ncondensation device (FWD), and a three-stage distillation device (TSDD) (see Note S7 for\ndetailed design and preparation)…”\n“…the TSDD-LHEC configuration achieved the highest absolute water production rate,\nreaching 1.99 kg m−2 h−1…”\nFigure R2 a, The schematic diagram of multistage solar distillation system. b, Schematic of LHEC\nsubstrate integrated into multistage solar distillation for improving heat dissipation. The assembly\nthree-stage solar distillation setup without (c) and with (d) LHEC substrate. e, Infrared image\ncomparison of three-stage solar distillation setup with and without LHEC substrate. f, The clean\nwater generation rate comparison between three-stage solar distillation setup without and with\nLHEC assistance.\n4 / 48\nFigure R3 The Incremental solar water production rates with LHEC assistance across various\nstrategies.\nActually, we did not prioritize the multistage distillation demonstration in the main study due\nto considerations of fabrication cost and practical feasibility. As shown in Figures R4 below,\nduring the initial two hours, the freshwater generation rate of the three-stage system remains\nlower than that of the single-stage system. This indicates a longer startup time before reaching\na steady-state output, which reduces its effectiveness in time-sensitive scenarios such as\nemergency water supply.\nMoreover, the multistage system involves more complex assembly, leading to substantially\nhigher costs. As illustrated in Table R1, the unit cost of the multistage setup is approximately\n$2.00 per device, or $617 m−2, whereas the single-stage setup costs only $0.043 per device, or\n$48.6 m−2. This highlights the better scalability and cost-effectiveness of the single-stage\nLHEC-integrated design for practical deployment.\nFigure R4 The comparison of water generation rates over time between LHEC assisted single-stage\nsetup and three-stage solar distillation setup.\n5 / 48\nTable R1 Materials cost of three-stage solar distillation setup and single-stage setup with LHEC\nQ3 The performance of the proposed LHEC-assisted system appears to be highly dependent on\nambient environmental conditions, particularly temperature and humidity, which significantly\ninfluence the evaporation rates. However, the current manuscript only presents limited outdoor\ndata, collected over a narrow time window (February to May), without adequate seasonal\nvariation. To convincingly demonstrate the robustness and practical applicability of this strategy,\nit is essential to include or discuss performance under diverse environmental conditions, such\nas low-temperature or high-humidity scenarios. Without such data, the claimed universal\napplicability of the system remains unsubstantiated.\nResponse: Your suggestion has been well taken. To further access the broader applicability of\nthe LHEC strategy, we conducted controlled experiments in an environmental chamber under\nsimulated solar irradiation (1 kW m−2), covering a range of ambient temperatures (15 °C, 25 °C,\n40 °C) and relative humidity levels (25%, 50%, 75%) (Figure R5a below). As shown in Figure\nR5b, the LHEC strategy enhanced solar water production rates across all tested environments.\nThe solar water production improvement by LHEC strategy was presented in Figure R5c. Under\nlow-temperature (15 °C, 50% RH) and high-humidity (25 °C, 75% RH) conditions, the LHEC\nstrategy achieves solar water production improvements of 27.9% and 22.3%, respectively.\nNotably, even in the in the most challenging scenario, (15 °C, 75% RH), the water generation\nrate increased by approximately 15% compared to the control. This enhancement becomes more\npronounced at higher temperatures and lower humidity levels, aligning with the expected\nbehavior of evaporative cooling. These results confirm that the LHEC strategy maintains\neffectiveness across a wide range of environmental conditions, supporting its potential for year-\nround operation in diverse climatic regions.\nFigure R5 have been added as Figure S28 into the revised manuscript, with a proper description\npage 10 to better reflect the system’s environmental adaptability, as shown below.\n6 / 48\n“…To further validate the environmental robustness of LHEC strategy, we conducted\nperformance comparisons in a controlled environment chamber with temperatures ranging from\n15 to 40 °C and humidity from 25% to 75% RH (Fig. S28). Under these varying conditions, the\nLHEC strategy provided over a 19% improvement in solar water generation performance…”\nFigure R5. a, Photographs of setup with LHEC assistance operating in controlled environment\nchamber for solar water production under solar irradiation of 1 kW m−2. b, The solar water\nproduction comparison between setup with and without LHEC under different temperature and\nhumidity. c, The solar water production improvement by LHEC under different temperature and\nhumidity.\nQ4 Scaling up the delignified wood substrate presents challenges, as the capillary-driven water\nsupply is typically limited to just a few centimeters. This significantly restricts the large-scale\nmanufacturing and application of the proposed approach.\nResponse: We thank you for this valuable comment. The core focus of our study is to\ndemonstrate the effectiveness of the LHEC strategy, for which delignified wood was selected\ndue to its low solar absorption, salt resistance and natural abundance. While delignified wood\ndoes have limitations in capillary height, its water transport performance can be substantially\nenhanced through appropriate surface modifications.\nFor instance, we grafted acrylic acid on delignified wood for improving hydrophilicity [J. Appl.\nPolym. Sci. 2021, 80, 2267-2272]. Specifically, the delignified wood was immersed in 30%\nhydrogen peroxide (H O ) solution, heated to 95 °C for 30 minutes to promote the generation\n2 2\nof free radicals, followed by the addition of acrylic acid monomer (1.5 mol L−1) for surface\ngrafting and polymerization at 60 °C for 12 hours. This treatment increased the capillary height\nto approximately 41 cm, as shown in Figure R6 below, thereby addressing concerns regarding\nvertical water supply in scaled-up applications.\nTo further demonstrate scalability, we constructed two large-scale solar distillation systems\nusing poly (methyl methacrylate) (PMMA) chambers (35 cm × 35 cm × 35 cm), each equipped\nwith a 25 cm × 25 cm PPy-modified wood evaporator (Figure 7a). In one setup, the\ncondensation surface was lined with the modified delignified wood substrate. Both systems\nwere placed above a bulk water source and tested under outdoor conditions. As shown in\nFigures R7b and c, the modified wood maintained effective water transport across its surface\nthroughout the experiment. Under an average solar intensity of ~0.8 kW m−2, the system with\nthe modified condensation surface achieved a ~29% increase in water production rate (Figure\nR7d and e). These results support the feasibility of using treated delignified wood for large-\nscale LHEC applications.\nFigure R6 Infrared images demonstrating capillary rise of water on delignified wood grafted with\npolyacrylic acid.\n8 / 48\nFigure R7 a, Photograph of the experimental large-scale solar water production setups with and\nwithout LHEC. b-c, Infrared images of both setups at 10:00 AM and 12:00 AM. d, The recorded\nsolar radiation intensity and ambient temperature. e, Comparison of solar water production rates\nbetween setups with and without LHEC.\nIn addition to the above surface modification method, we also explored a chemical-free strategy\nto overcome capillary limitations. As illustrated in Figure R8a, we attached a thin aluminum\nfoil (100 μm) to the outer surface of the PMMA cover to facilitate heat transfer from areas\nbeyond the capillary-active zone to the LHEC region. This design enables effective thermal\nregulation over extended surface areas without requiring direct water contact. We also conduct\noutdoor experiment with this configuration, conducted under solar intensity of 0.9 kW m−2,\nshowed a ~25% increase in water yield (Figure R8b-d), further demonstrating the feasibility of\nthis solution.\nTogether, these two approaches show that the capillary constraint of delignified wood can be\neffectively addressed and does not pose a fundamental limitation for the scalable\nimplementation of the LHEC strategy. We hope these clarifications address your concern.\n9 / 48\nFigure R8 a, Photograph of aluminum foil incorporation strategy for transferring heat from regions\nbeyond the capillary reach to the LHEC region. b, Photograph of the experimental large-scale solar\nwater production setups with and without LHEC. c, The recorded solar radiation intensity and\nambient temperature. d, Solar water production rates of setup with and without LHEC.\nQ5 Other capillary wicks and porous materials can offer similar performance and functionality\nto delignified wood and are already commercially available. Moreover, although wood is a\nsustainable resource, the chemical-intensive processes involved in its fabrication may raise\nenvironmental concerns.\nResponse: We appreciate your comment regarding alternative materials and environmental\nconsiderations associated with the delignified wood.\nThe selection of delignified wood was based on its functional advantages and suitability under\nrealistic operating conditions. The LHEC strategy requires a stable water supply to drive\nevaporative cooling, particularly in saline environments where salt accumulation can impede\nlong-term operation. Delignified wood possesses vertically aligned microchannels that support\nboth efficient capillary water transport and salt ion rediffusion [Energy Environ. Sci. 2019, 12,\n1558-1567]. This structure effectively mitigates surface salt crystallization. In contrast, most\ncommercially available porous wicks lack such alignment and are more prone to salt buildup,\nas illustrated in Figure R9a.\nTo validate this, we conducted comparative experiments using two typical commercial\nmaterials: nonwoven cotton fabric and melamine sponge. As shown in Figure R9b, both\nmaterials showed visible salt crystallization after evaporating 50 mL of 3.5 wt% saline water,\n10 / 48\nwhile delignified wood maintained a clean interface. We also measured their solar absorptance,\nwhich was 0.25 for nonwoven fabric and 0.47 for melamine sponge, significantly higher than\nthe 0.11 measured for delignified wood (Figure R9c). These higher solar absorption values lead\nto increased parasitic heat gain, which is detrimental to the condensation cooling performance\ncentral to the LHEC system.\nOther materials with aligned channels, such as ice-templated hydrogels, were also considered.\nHowever, these typically require freezing-based fabrication processes that are energy-intensive\nand less practical for scalable, sustainable applications.\nTo address the environmental concerns associated with the delignification process, we adopted\nan alternative treatment method using 30 wt% H O at 100 °C. This oxidative process\n2 2\nselectively removes lignin and generate only water and oxygen as byproducts. It avoids\nintroducing residual salts or persistent chemical pollutants [Green Chem. 2021, 23, 2198-2232].\nAs shown in Figure R10, the treated wood exhibits a white appearance consistent with lignin\nremoval. The degraded lignin components are readily biodegradable through microbial activity\nin natural environments. This method therefore offers a cleaner and more environmentally\nfriendly pathway to obtain delignified wood.\nTogether, these findings support the choice of delignified wood as a practical and sustainable\nsubstrate for the LHEC strategy. We hope the above illustration can answer your concern.\nFigure R9 a, Schematic illustration of salt rediffusion pathway in low-tortuosity and high-tortuosity\nporous structure. b, The picture of salt accumulation in cotton fabric and melamine foam after\ntreatment of 50 mL-saline water. c, Solar absorption spectra of wet cotton fabric and melamine foam.\n11 / 48\nFigure R10 Appearance comparison between raw wood and delignified wood treated by hydrogen\nperoxide solution.\nQ6 The water collection rate under 1.4 kW m−² irradiation was below 1.6 kg m−² h−¹,\ncorresponding to an energy conversion efficiency of approximately 70%. However, the water\nproduction efficiency shown in Fig. 4g approaches 90%, revealing a discrepancy. Similar\nmismatches between reported efficiencies and actual water production rates are observed under\nother irradiation intensities as well.\nResponse: We thank you for this important observation and apologize for any confusion caused\nby the terminology used in the original manuscript.\nTo clarify, the term \"solar water production efficiency\" previously used in the text has now been\nrevised to \"solar vapor-to-water efficiency \" throughout the manuscript. This matric is defined\nas the ratio of water condensation rate to natural evaporation rate by solar absorber. It is\nintended to reflect the effectiveness of the condensation cooling performance and the system’s\ncapacity to convert solar-driven vapor into liquid water, which is the core focus of our LHEC\nstrategy.\nWe recognize that this solar vapor-to-water efficiency metric differs from the conventional\nsolar-to-water energy conversion efficiency, which is calculated based on the total solar input\nenergy and the latent heat required for water condensation. To improve clarity and facilitate\ndirect comparison, we have now included the solar-to-water efficiency values in the revised\nmanuscript alongside the solar vapor-to-water efficiency data.\nPlease refer to the response to Q1 above for the calculated solar-to-water efficiency, as well as\nthe detailed change in the revised manuscript.\nQ7 \"Second, Second, to minimize parasitic...\" remove the repetition.\nResponse: We thank you for pointing out the typographical error. The repeated word has been\nremoved, and the corrected sentence in the revised manuscript has also been shown below:\n“…Second, to minimize parasitic heat accumulation caused by solar energy absorption…”\n12 / 48\nQ8 \"This indicates the substrate’s ability to effectively scatter sunlight across the entire\nspectrum.\" How does the wood scatter sunlight?\nResponse: We thank you for this important question. The ability of wood to scatter sunlight\noriginates from its intrinsic multiscale porous structure [Science 2019, 364, 760-763]. The cell\nwalls of delignified wood are composed of cellulose fibers with a refractive index (n) of\napproximately 1.52 [RSC Adv. 2020, 10, 40719-40724]. These fibers are interspersed with air-\nfilled or water-filled pores, which have lower refractive indices (n ≈1.00, n ≈1.33). This\nair water\nrefractive index contrast causes incident light to undergo multiple scattering events within the\nmaterial. Scattering is particularly effective when the pore sizes are comparable to the\nwavelengths of incoming solar radiation. In our case, pore size analysis revealed a broad\ndistribution, with dominant pore diameters centered around 0.8 μm and 18 μm (Figure S14 of\nthe original manuscript, now shown as Figure R11 below). These dimensions cover much of\nthe solar spectrum, enabling broadband light scattering.\nTo further support this mechanism, we conducted Finite-Difference Time-Domain (FDTD)\nsimulations to model the electric field distribution as light interacts with the pore structures.\nAs shown in Figure R12, the simulated electric field patterns clearly demonstrate light scattering\nand confinement within the wood matrix, confirming its ability to diffusely reflect and scatter\nsolar radiation across a wide spectral range.\nFigure R11 a, Pore diameter distribution of pits, with the pore sizes primarily concentrated around\n0.8 μm. b, Channel diameter distribution of tracheids, with the pore sizes primarily concentrated\naround 18.5 μm.\nFigure R12 Electric field distribution of light propagating through pores of different sizes, with (a)\n13 / 48\nrepresenting air-filled pores surrounded by cellulose material, and (b) representing water-filled\npores surrounded by cellulose material. The simulations were conducted for different incident\nwavelengths (λ), ranging from 0.3 to 2.5 μm. The pore sizes, indicated by the black circles, are\n0.8 μm and 18 μm, which correspond to effective scattering when the incident light wavelength\nmatches the pore size.\nQ9 Avoid using abbreviation in subtitles and figure captions.\nResponse: We appreciate your helpful suggestion. We have removed all abbreviations from\nsubtitles and figure captions throughout the revised manuscript to ensure clarity and improve\nreadability.\n14 / 48\nReviewer #2 (Remarks to the Author):\nIn this work, Guo et al. has proposed using evaporative cooling, in which they termed “Latent\nHeat-Assisted Evaporative Cooling (LHEC), to enhance the water production efficiency in\nsolar stills by incorporating a delignified wood structure on the outer wall of the condenser.\nTheir main arguments are that the substrate has achieved a 2.5-fold increase in heat dissipation,\naccelerated vapor diffusion flux inside the solar still, and improved water production by 93%.\nThis is an interesting proposal, and it seems that the addition does lead to improvements in\ndevice performance in multiple different configurations. I think that the idea can merit\npublication, but their metrics are very misleading and many experiments are not satisfactory to\nsupport their claims. As a result, I suggest major revisions before the manuscript can be\nconsidered for acceptance.\nResponse: We sincerely thank you for recognizing the potential of our proposed latent heat-\nassisted evaporative cooling (LHEC) strategy and for your thoughtful evaluation of our\nmanuscript. We are encouraged that you find the approach promising and acknowledge its\npositive impact on device performance across multiple configurations.\nWe have carefully addressed each of your detailed comments in the point-by-point responses\nbelow. All revisions have been implemented in the updated manuscript and Supporting\nInformation. We hope that the strengthened data, clearer terminology, and revised discussion\nnow provide a more solid foundation for the conclusions and improve the overall quality of the\nwork.\nQ1 They claim that their device has a water production efficiency of 0.93 in the abstract.\nHowever, this metric is quite misleading because they defined it in pg. 8 that it is “the\nproduction rate (Jprod) against the natural solar evaporation rate (Jevap). This comparison is\nnot meaningful because the boundary conditions that govern solar evaporation without\ncondensation (depends on ambient humidity, temperature, and wind flow) are completely\ndifferent from that in a solar still (depends on condenser design, condenser/evaporator\nconfiguration, etc.). The common metric used in literature for water production efficiency is\nthe heat of evaporation/condensation compared to 12. Using their data in Fig. 4f, their true\nwater production efficiency is around 59% under 1 sun. This value is still reasonably high for\nthe solar still configuration they have, and more in line with other papers in the field. The\nauthors should remove all data and claims that correspond to their 90% efficiency claim and\nuse the correct metric.\nResponse: We sincerely thank you for this critical and constructive comment. Here, we have\ncalculated the solar-to-water efficiency, which is defined as the ratio of the energy of freshwater\ngeneration to the input solar energy, for setups under various solar irradiation (Figure R13). For\nthe solar distillation setup with the assistance of LHEC, the solar-to-water efficiency was 0.56,\n0.60, 0.68, and 0.76 under solar irradiation intensities of 0.8, 1.0, 1.2, and 1.4 kW m−2,\nrespectively. In contrast, the solar-to-water efficiency of the setup without LHEC remained\naround 0.45. These results demonstrate that LHEC can effectively enhance the solar-driven\nfreshwater production performance.\n15 / 48\nIn addition, to avoid any potential confusion for the readers, we have changed the original term\n“solar water production efficiency” to “solar vapor-to-water efficiency”. This parameter\nnormalizes the water generation rate against the natural evaporation rate of the solar absorber,\neliminating performance differences in the evaporator during solar distillation. We hope this\nparameter can reflect the condensation performance in solar distillation process, which aligns\nwith the focus of this study.\nTo support above viewpoint, we conducted comparative experiments using two more different\nevaporators (natural wood and AgNPs/PPy/wood) under the same solar intensity (1000 W m−2),\nwith and without LHEC assistance. As shown in Figure R14, the solar-to-water efficiency\nvaried significantly across the three evaporators even under identical cooling conditions, due\nto differences in solar absorption and evaporation performance. In contrast, the solar vapor-to-\nwater efficiency values remained much more consistent across the same set of evaporators with\nidentical cooling conditions, indicating that this metric more directly reflects condensation\nbehavior rather than evaporator design.\nFor these reasons, we have decided to retain the solar vapor-to-water efficiency metric in the\nrevised manuscript, with clear definitions and supporting discussion, while ensuring that it is\nnot misrepresented as an energy conversion efficiency. And we hope this clarification resolves\nyour concern.\nWe have changed term “solar water production” to “solar vapor-to-water efficiency” in revised\nmanuscript. The calculation of solar-to-water efficiency has been added into revised manuscript\nas Note S6, with a proper description in revised manuscript on page 9 as shown below.\n“…To reveal the contribution of LHEC to condensation, we normalized the production rate\n(J ) against the natural solar evaporation rate (J ) as solar vapor-to-water efficiency…”\nprod evap\n“…the LHEC-assisted setup achieved solar vapor-to-water efficiency of up to 93% under 1.4\nkW m−2 solar irradiation, corresponding to a solar-to-water efficiency of 0.76…”\nFigure R13 The comparison of calculated solar-to-water efficiency of our setup with and without\nLHEC assistance under different solar irradiation intensities.\n16 / 48\nFigure R14 The comparison of solar-to-water efficiency (a) and solar vapor-to-water efficiency (b)\nof our setup with and without LHEC assistance under solar irradiation of 1000 W m−2.\nQ2 In Fig. 3, they compared the effectiveness of dissipating heat using the LHEC substrate vs\nglass. However, the configurations they used don’t reflect how the LHEC would be\nimplemented in a real device. The authors should be comparing the performance of a ceramic\nheater and then a piece of glass as their control experiment (what they currently report for the\ngray bars). Then afterwards, they should have the ceramic heater, the same piece of glass, and\nfinally the LHEC substrate on the outside to reflect the configurations deployed in a solar still\ndevice. The authors should revise all data corresponding to Fig. 3 and conduct the correct\nexperimental comparisons between the two.\nResponse: We sincerely thank you for this insightful comment. To better reflect the actual\nimplementation of the LHEC strategy in a solar distillation device, we have revised the\nexperimental configuration as suggested. Specifically, we reconstructed the setup by inserting\na 1 mm thick glass plate between the aluminum heating surface and the LHEC substrate,\nconsistent with the thickness of the transparent cover used in our device. This updated\nconfiguration is now shown in the revised picture (Figure R15a).\nUsing this setup, we re-measured the steady-state evaporation rates under both solar and non-\nsolar conditions (Figure R15b). Since the introduction of additional thermal resistance does not\naot\naffect the steady-state heat flux of the system, the newly measured evaporation rates closely\nmatch our original data. The evaporation rate under solar conditions is slightly higher than that\nunder non-solar conditions, which is attributed to the minor parasitic heat generation from the\nLHEC substrate.\nWe also redrew the schematic based on the revised experimental configuration (Figure R16a),\nand remeasured and updated all data reported in Figure 3 of the original manuscript, including\nthermal power dissipation by LHEC, energy ratio analysis and interface temperature profiles.\nThe revised results are presented in Figures R16b-d. These data reconfirm the LHEC substrate’s\neffectiveness in dissipating heat.\nUnder 1.0 kW m−2 solar irradiation, the thermal dissipation from the LHEC increased by\napproximately 100 W m−2 compared to the non-irradiated case, aligning with the measured\nsolar absorptance of the substrate (A =~0.11). We further recalculated the ratio of heat\nsolar\n17 / 48\ndissipated by the LHEC relative to total thermal input. As shown in Figure R16c, this ratio\napproached unity at 200 W m−2 input and remained above 80% even at higher input levels,\nindicating that LHEC remains the dominant cooling pathway across a wide thermal load range.\nLastly, we compared the interface temperatures of the bare glass and the glass with LHEC\nassistance under varying heat inputs. As shown in Figure R16d, the LHEC-assisted interface\nconsistently maintained a lower surface temperature, with the temperature difference increasing\nunder higher thermal loads. Moreover, the LHEC interface temperature showed minimal\nchange under solar exposure, demonstrating strong resistance to parasitic heating.\nFigure R15a and Figure R15b have been updated as Figure S20 and Figure S2 into the revised\nSupporting information. Figure R16 have been updated as Figure 3 into the revised manuscript,\nwith proper description on page 6, as shown below.\n“…On the opposite side, a piece of delignified wood was attached to the glass plate…”\nThe quantification of the latent heat-assisted evaporative cooling performance in Method\nsection on page13 of revised manuscript has been updated as shown below.\n“…The LHEC wood substrate was tightly attached to the glass plate (5 cm × 5 cm)…”\n“…Temperature on the inner surface of the glass was measured using thermocouples…”\nFigure R15 a, Digital picture of the assembled setup for measuring the LHEC performance. b,\nRecorded evaporation rate of LHEC substrate with and without simulated solar irradiation.\n18 / 48\nFigure R16 Performance evaluation of delignified wood as an LHEC substrate. a, Schematic\nof the self-assembled experimental setup for measuring the LHEC performance of delignified wood.\nAmbient conditions were maintained at 25 °C and 50% relative humidity to simulate typical\nscenarios. b, LHEC power profiles of the delignified wood under progressively increased thermal\nenergy inputs, with and without solar irradiation. c, Energy ratio (α) of the LHEC power to the total\nheat input, with and without solar irradiation. d, Monitored condensation interface temperature\nunder different thermal energy input, comparing conventional ambient cooling with the LHEC-\nassisted cooling strategy with and without solar irradiation.\nQ3 Adding on to point 2, Fig. 3e's thermal resistance was calculated by using the temperature\ndifference between the ambient and the environment. However, with the LHEC, there is a\ncooling potential happening due to phase change between the thermal resistance associated with\nthe LHEC thermal conductance and the ambient convection. You cannot calculate the effective\nthermal resistance over this entire series when there is cooling happening in the middle. Fig.\n3d, showing the temperature at the interface between the ceramic heater and the glass in the\nscenario described in Comment 2 above, would be a more appropriate measurement to illustrate\nthe enhanced cooling from the LHEC. Another separate metric that would be more meaningful\nis characterizing what proportion of the cooling flux comes from evaporation as opposed to\nconvection and radiation on the LHEC side.\nResponse: We appreciate your insightful comment. In response, we have removed the original\nthermal resistance data (Figure 3e) from the manuscript, as we agree that calculating an\n19 / 48\neffective thermal resistance across the entire system, which includes a local cooling region due\nto evaporation, may lead to misleading interpretations.\nTo better represent the contribution of the LHEC substrate to heat dissipation, we have revised\nour analysis. First, we corrected the formula used to calculate the energy ratio (α), which was\npreviously defined as the ratio of evaporative cooling power (Q ) to the thermal energy input\nLHEC\n(Q ). In the revised version, we account for both thermal energy input from the electric heater\nTEI\nand the solar irradiation input (Q ). The updated formula is:\nsolar\n“\n𝑄𝑄𝐿𝐿𝐿𝐿𝐿𝐿𝐶𝐶\n𝛼𝛼 = 𝑄𝑄𝑇𝑇𝐿𝐿𝑇𝑇+𝐴𝐴𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠×𝑄𝑄𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠\nwhere α is the energy ratio of evaporative cooling flux to total heat dissipation flux, Q is\nLHEC\nthe LHEC power, Q is the thermal energy input from the electric heater, A is the solar\nTEI solar\nabsorbance of delignified wood, Q denotes the solar irradiance intensity”\nsolar\nWe have recalculated this ratio under a range of heat inputs and present the results in Figure\nR17a. To further quantify the relative contribution of evaporation compared to convective and\nradiative cooling, we introduced a new metric:\n𝑄𝑄𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿 𝛼𝛼\n=\nAt a thermal energy input of 200 W m𝑄𝑄−𝑐𝑐2,𝑐𝑐 𝑐𝑐α+ a𝑟𝑟p𝑟𝑟𝑟𝑟proac1h−es 𝛼𝛼1.0, indicating that nearly all the input\nenergy is dissipated via the LHEC pathway. This observation is supported by infrared imaging\n(Figure R17b), which shows that the LHEC interface temperature is nearly equal to the ambient\ntemperature under these conditions, implying minimal convective and radiative losses.\nUsing this metric, we evaluated the evaporative cooling contribution under both non-irradiated\nand solar-irradiated conditions. As shown in Figure R17c, without solar input, the LHEC\ncooling flux is approximately 3–5 times higher than the combined convective and radiative flux\nwhen the thermal input exceeds 200 W m−2. Under solar irradiation, the Q /Q ratio\nLHEC con+rad\nreaches around 11 at 400 W m−2 and gradually declines to approximately 4 at 800 and\ndominant pathway for thermal dissipation under realistic operating conditions.\nFigure R16a and Figure R16c have been updated as Figure 3c and Figure S21 into the revised\nmanuscript, with prober description on page 7.\n“…, we defined the ratio (α) as the proportion of LHEC cooling flux to the total heat input,\ncomprising both the thermal energy input from the electric heater (Q ) and the absorbed\nTEI\nportion of solar irradiation (Q )…”\nsolar\n“…The measured energy ratio α remained relatively stable, ranging from 0.8 to ~1.0 at the\nthermal input increased from 0.2 to 1 kW m−2 (Fig. 3c), indicating that the entire heat dissipation\nprocess is predominantly governed by LHEC instead of convective and radiative cooling (Fig.\nS21)…”\n20 / 48\nFigure R17 a, Energy ratio of LHEC power in total heat dissipation with and without solar\nirradiation. b, The infrared image of LHEC substrate under thermal energy input of 200 W m−2.\nc, Energy ratio of LHEC power opposed to convective and radiative cooling flux on the LHEC\nside.\nQ4 Adding onto points 2 and 3, is the backside of the ceramic heater properly insulated? If so,\nhow was it done? Otherwise, the heat flux from the ceramic heater would be two parallel\nnetworks (frontside through the glass/LHEC and backside through whatever the ceramic heater\nis in contact with).\nResponse: We appreciate your thoughtful concern. In our original experiments, the ceramic\nheater was not thermally insulated on the backside. However, the thermal energy input in our\nsetup was not estimated based on the electrical input to the heater. Instead, we used a heat flux\nsensor placed at the front interface to directly measure and control the thermal power delivered\nto the LHEC side, thereby minimizing uncertainty related to backside heat loss.\nHere, to enhance the environmental stability of setup and accelerate its reaching thermal\nequilibrium, we placed heater onto a polystyrene (PS) foam with 3 cm thickness in above\nexperiments, which serves as a thermal insulator (Figure R14a and Figure R15a). To verify the\neffectiveness of heat insulation, we measured the heat flux from the heater into the PS foam\nunder thermal energy input of 1000 W m−2. The recorded backside heat flux was only\n~50 W m−2, confirming that the PS foam provided adequate insulation and that the majority of\nthe heat was directed toward the LHEC side (Figure R18).\nThe relevant description has been rephrased on page 6 of revised manuscript, as shown below.\n“…A polystyrene (PS) foam was affixed to the backside to reduce heat loss and facilitate faster\n21 / 48\nattainment of thermal equilibrium…”\nFigure R18 The recorded heat flux from electrical heater toward PS foam under thermal energy\ninput of 1000 W m−2.\nQ5 On page 2, the authors claim that metal-based condensers “become less effective at elevated\nambient temperatures”. However, the thermophysical properties of the metal doesn’t change\nsignificantly (thermal conductivity) over the temperature range expected in solar stills and its\nthermal resistance should consequentially remain the same at elevated temperatures. The\nauthors need to clarify why this statement was made and justify their argument.\nResponse: We thank you for this insightful comment and apologize for the lack of clarity in the\noriginal statement.\nThe statement \"become less effective at elevated ambient temperatures\" was not intended to\nsuggest that the intrinsic thermophysical properties of metals, such as thermal conductivity,\nchange significantly within the temperature range encountered in solar distillation. Rather, we\naimed to highlight the cooling effectiveness of metal-based condensers decreases at elevated\nambient temperatures due to a diminished temperature gradient between the condenser surface\nand the surrounding environment.\nMetal-based condensers, particularly those with finned structures, dissipate heat primarily\nthrough passive convection and conduction to the ambient air. The efficiency of this heat\ntransfer process depends strongly on the temperature difference between the condenser surface\nand ambient air. As ambient temperature rises, this temperature difference narrows, leading to\na reduction in overall heat dissipation capability (as illustrated in Figure R19a below).\nTo experimentally verify this effect, we respectively placed three solar distillation setups inside\nan environmental chamber under controlled humidity (RH=50%) and varied the ambient\ntemperature (Figure R19b). The three sets include: a bare glass solar distillation setup, a solar\ndistillation setup equipped with a metal fin condenser, and a setup assisted by the LHEC\nsubstrate. As shown in Figure R19c, both the metal fin condenser and the LHEC substrate\nimproved water collection rates compared to the bare-glass setup. However, as ambient\n22 / 48\ntemperature increased, the performance enhancement provided by the metal condenser\ngradually declined. In contrast, the LHEC-assisted system exhibited increased water production\nwith rising ambient temperature (Figure R19d), demonstrating greater resilience under high-\ntemperature conditions.\nThese results confirm that while metal conductors retain their thermal conductivity, their\nfunctional cooling performance becomes less effective at higher ambient temperatures due to\nreduced convective heat transfer. To avoid further misunderstanding, we have revised this\nsentence in the revised manuscript (page 2), as shown below:\n“…However, this metal-based strategy is expensive, prone to corrosion in water environments,\nand becomes less effective at elevated ambient temperature due to the reduced temperature\ndifference between the condenser surface and the surrounding air…”\nFigure R19 a, The schematic of solar distillation setups with assistance of metal fined condenser\nand LHEC substrate, respectively. b, Picture of solar distillation setup equipped with metal fined\ncondenser in environment-controlled chamber. c, Measured water collection rates of different setups\nunder 50% RH and different ambient temperature. d, The water collection improvement by finned\nmetal condenser and LHEC substrate respectively.\nQ6. In Fig. 1d for their calculated theoretical heat dissipation power and SI Note 1, the current\nmass transfer correlation of vapor km = 25+19v doesn’t have an explanation for its physical\n23 / 48\nbasis. The cited paper (Ref. 6) referred to an Engineering Toolbox website rather than a\nreputable correlation source. Furthermore, the units that the authors used for the vapor\nconcentration (g/m3) doesn’t match the units for their cited km (kg/m2-h, which should lead to\nthe vapor concentrations being described in a dimensionless units). The authors should refer to\na Heat and Mass Transfer textbook and redo these calculations with a correct correlation for\ntheir system size and check their units properly.\nResponse: We sincerely thank you for pointing this issue. We agree that the previously adopted\nempirical expression for the vapor mass transfer may lack a clear physical foundation. In\nresponse, we have revised the calculation using a classical mass transfer model based on Fick's\nlaw of diffusion, following guidance from the textbook Fundamentals of heat and mass\ntransfer (Incropera, F. P., DeWitt, D. P., Bergman, T. L., & Lavine, A. S. 1996, Wiley). In the\nrevised approach, the water vapor mass flux is defined as:\n𝐷𝐷\n∆𝑚𝑚 = ×(𝐶𝐶𝑠𝑠 −𝐶𝐶𝑟𝑟)\nwhere D (m2 s−1) is the vapor diffusion coe𝛿𝛿fficient, is the vapor concentration\ndifference (kg m−3) between saturation vapor concentration in LHEC surface ( ) and the actual\n𝛥𝛥𝐶𝐶 = 𝐶𝐶𝑠𝑠 −𝐶𝐶𝑟𝑟\nvapor concentration in environment ( ). is the thickness of boundary layer (m).\n𝐶𝐶𝑠𝑠\nThe vapor concentration difference (𝐶𝐶𝑟𝑟) ca𝛿𝛿n be calculated as\n𝛥𝛥𝐶𝐶\n𝑀𝑀𝑤𝑤 𝑃𝑃𝑠𝑠(𝑇𝑇) 𝑃𝑃𝑠𝑠(𝑇𝑇𝑟𝑟𝑎𝑎𝑎𝑎)\n𝛥𝛥𝐶𝐶 = 𝐶𝐶𝑠𝑠 −𝐶𝐶𝑟𝑟 = ( −𝑅𝑅𝑅𝑅 )\nwhere (g mol−1) is the molar mass of w𝑅𝑅ater, 𝑇𝑇R (J mol−1 K𝑇𝑇−𝑟𝑟1)𝑎𝑎 𝑎𝑎is the universal gas constant,\nT (K) and T (K) are the temperature of LHEC surface and ambient, respectively. P (Pa) is\n𝑀𝑀𝑤𝑤 atm s\nthe saturation vapor pressure, and RH is the air relative humidity (50%). The vapor pressure P\ns\n(Pa) is computed using the Clausius-Clapeyron relation as:\n𝑅𝑅𝑒𝑒𝑒𝑒𝑟𝑟𝑒𝑒𝑀𝑀𝑤𝑤 1 1\n𝑃𝑃𝑆𝑆(𝑇𝑇) = 611exp ( ( − ))\nThe vapor diffusion coefficient (D) can be para𝑅𝑅meteriz2e7d3 base𝑇𝑇d on ambient temperature as\nfollow:\n−7 −5\nThe thickness of boundary𝐷𝐷 la=ye(r1 .(49 ) ×ca1n0 be )c𝑇𝑇a𝑟𝑟l𝑎𝑎c𝑎𝑎ula−te1d. 9a6cc×or1d0ing classical convective mass\ntransfer theory as below\n𝛿𝛿\n𝐿𝐿\n𝛿𝛿 =\nin which is the characteristic length of the L𝑆𝑆Hℎ𝐿𝐿EC surface (m), and is the Sherwood\nnumber over the length . Here, we assume the LHEC surface is a vertical plane (0.05 m ×\n𝐿𝐿 𝑆𝑆ℎ𝐿𝐿\n0.05 m). For natural convection mass transfer from a vertical plate in the laminar flow regime,\n𝐿𝐿\nthe Sherwood number can be estimated by [Bejan, A. Convection heat transfer. 2013, John\nwiley & sons]:\n24 / 48\n1\n4\n𝑆𝑆ℎ𝐿𝐿 = 0.6×(𝑅𝑅𝑅𝑅𝑎𝑎)\nwhere is the mass transfer Rayleigh number, which can be calculated as:\n𝑅𝑅𝑅𝑅𝑎𝑎\nin which Gr and Sc are the Grashof nu𝑅𝑅m𝑅𝑅b𝑎𝑎er= fo𝐺𝐺r 𝐺𝐺m×as𝑆𝑆s 𝑆𝑆transfer and Schmidt number. The both\ncan be estimated as follow:\n3\n𝑔𝑔𝑔𝑔𝛥𝛥𝐶𝐶𝐿𝐿\n𝐺𝐺𝐺𝐺 = 2\n𝑣𝑣\n𝑣𝑣\n𝑆𝑆𝑆𝑆 =\nin which denotes the gravity acceleration (m s−𝐷𝐷2), is the volumetric expansion coefficient\nfor mass transfer (m3 kg−1), approximated as , where is the air density. is the\n𝑔𝑔 𝑔𝑔\nkinematic viscosity of ambient air (m2 s−1), is t−h1e molecular diffusion coefficient of water\n𝜌𝜌𝑟𝑟𝑎𝑎𝑟𝑟 𝜌𝜌𝑟𝑟𝑎𝑎𝑟𝑟 𝑣𝑣\nvapor in ambient air (m2 s−1).\n𝐷𝐷\nBased on above formulas, we recalculated the theoretical water evaporation rates of LHEC\nunder different surface temperatures, which are now presented in Figure R20 below. Meanwhile,\nwe have carefully reviewed the units in the updated calculation process to ensure that they are\nconsistent and correct throughout. Based on the updated water evaporation rate, the theoretical\nLHEC power have been updated accordingly (Figure R21). It still shows that compared to\nradiative cooling and convective cooling, LHEC exhibits th flux, and as the surface temperature\nincreases, the performance of LHEC improves further.\nThe above complete derivation and step-by-step calculation of the water evaporation rate using\nthis new model has been updated into the revised Supporting Information (Note S1). Figure\nR20 and 21 have been updated as Figure S1 and Figure 1d into the revised manuscript, with\nprober description on Page 3, as shown below.\n“…The results revealed that LHEC achieves a higher heat dissipation flux than both ambient\ncooling and PDRC, with its cooling advantage becoming more pronounced at elevated surface\ntemperatures…”\nFigure R20 Estimated water evaporation rate from LHEC surface under different surface\n25 / 48\ntemperature.\nFigure R21 Theoretical calculation of cooling power achieved by different strategies as a function\nof surface temperature.\nQ7 Their current system configuration has a lot of benefits due to the small device scale they\nbuilt. If the device is made taller, the salt diffusion in the LHEC will become more challenging\nbecause the ion transport resistance would increase. If the device is made wider, the LHEC\ncondenser wall will be further away from the evaporator and the vapor transport resistance\nwould be higher. To prove that this idea has real world potential, the authors should build a\nlarger scaled version of the LHEC solar still device (with the evaporator surface area an order\nof magnitude larger, on the order of 0.1 m2 or greater) and measure the water production\nperformance difference between the bare device and the LHEC device using salt water over\nextended periods of time (a few days to prove the anti-salting capabilities of the LHEC).\nResponse: We sincerely thank you for this valuable suggestion. To test the scalability and\npractical applicability of the LHEC strategy, we constructed two large-scale solar distillation\nsetups and performed outdoor solar water production experiments using saline water (3.5 wt%).\nEach system consisted of a transparent acrylic cover, a polypyrrole (PPy) modified wood\nevaporator (25 cm × 25 cm), and a built-in groove as collection channel for condensed water.\nIn one of the setups, we attached the LHEC substrate with height around 20 cm to one side of\nthe acrylic cover to facilitate condensation cooling (Figure R22a).\nTo address the challenges of limited capillary rise height and to ensure effective salt backflow\nin LHEC substrate, we implemented a thermally conductive aluminum foil (100 μm thickness)\non the outer surface of the acrylic wall. This layer enables efficient heat transfer from the top\nof the chamber to the LHEC region, thereby extending the cooling effect vertically while\nminimizing the diffusion path length for salt ions (Figure R22b).\n26 / 48\nFigure R22 a, Picture of components for assembling outdoor solar distillation setups. b, Assembly\nof the LHEC-assisted large-scale solar distillation setup, illustrating the heat transfer by thermal-\nconductive aluminum foil to LHEC substrate.\nThe two systems were tested under natural sunlight for six consecutive days on the rooftop of\nZijingang Campus of Zhejiang University, Hangzhou, China (Figure R23a). Water collection\nwas carried out at regular intervals. Infrared thermal imaging confirmed that the LHEC region\nmaintained a lower surface temperature than the bare acrylic region, which is favorable for\nimproved condensation (Figure R23b). As recorded, under the average natural solar irradiance\nof 730 W m−2 (Figure R23c), the LHEC-assisted setup showed a ~33% increase in water\nproduction compared to the control (Figure R23d).\nAlthough the absolute water production rates in the large-scale setups were lower than those of\nthe small-scale systems (0.43 kg m−2 h−1 vs 0.65 kg m−2 h−1), this reduction is mainly attributed\nto the higher thermal resistance of the thicker acrylic cover and the increased vapor boundary\nlayer associated with larger geometries. Nevertheless, the relative performance enhancement\nprovided by the LHEC substrate remained consistent, with a ~30% improvement in the large-\nscale configuration, which is comparable to the 26% enhancement observed in the small-scale\nsystem under comparable solar irradiation (0.8 kW m−2).\n27 / 48\nFigure R23 a, Photograph of outdoor solar water production test by the LHEC-assisted solar\ndistillation setup and bare acrylic solar distillation setup. b, Infrared image of LHEC-assisted solar\ndistillation setup and bare acrylic solar distillation setup. c, Outdoor environment condition data in\na clear sunny day. d, Comparison of water production rates by setups with and without LHEC.\nTo further assess the long-term reliability and anti-salt-accumulation performance, we\nconducted continuous outdoor solar distillation experiment for six days. As shown in Figure\nR24a-e, the LHEC-assisted setup consistently outperformed the control across varying solar\nirradiance levels: Day 2 (500 W m−2): ~45% increase, Day 3 (860 W m−2): ~27% increase, Day\n4 (900 W m−2): ~25% increase, Day 5 (780 W m−2): ~44% increase, and Day 6 (890 W m−2):\n~39% increase, respectively. These results confirm that the LHEC strategy remains effective at\nlarger scales, with consistent performance enhancement under saline conditions.\nIn large-scale configurations, we agree that the vapor diffusion path becomes longer, which will\ndelay the initial rise in freshwater yield due to the longer time required to reach vapor saturation.\nHowever, this does not impact the subsequent solar distillation performance. It is supported by\nthe observation that increasing the collection interval from 1 hour (date in day 1, day 2, day 3)\nto 2 hours (date in day 4, day 5, day 6) led to increased water production in both setups.\nThis\nindicates that the initial lag in vapor saturation can be offset over time, without negatively\naffecting long-term performance.\nTo further evaluate salt accumulation, we performed SEM imaging on the top cross-section of\nthe LHEC substrate after the six-day operation. As shown in Figure R24f and g, no significant\nsalt deposition was observed within the wood tracheid structures. Only a few isolated salt\ncrystals were found on the surface walls, confirming that the substrate effectively suppresses\ninternal salt accumulation even under prolonged saline exposure.\nFigures R22-R24 have been incorporated into the revised manuscript as Figures S12-S14. The\ncorresponding discussion has been added to Supplementary Note S8, and a concise description\nhas been included in the main text on page 11, as shown below.\n“…To evaluate scalability, two large-scale solar distillation setups were constructed and tested\noutdoors using saline water (see Supplementary Note S8 for details). The LHEC-assisted\nsystem consistently achieved an average ~35% increase in water production, confirming its\neffectiveness at larger scales…”\n28 / 48\nFigure R24 a-e, Water production rates by solar distillation setups with and without LHEC under\noutdoor conditions. f-g, The scanning electron microscope images of cross-section LHEC substrate\nafter six-day solar distillation operation.\nQ8 Fig 5i shows the comparison of different traits between each strategy and Table S1 shows\ntheir rating scale. However, the grading scale seems quite arbitrary. For example, for energy\nneutrality, grade 3 “requires a temperature gradient” and grade 4 is “energy independent”.\nHowever, any cooling strategy will naturally form a temperature gradient. Another example is\nfor adaptability, grade 3 “requires cooler condition but easy to achieve” and grade 2 is “requires\ncooler condition but harder to achieve.” The authors need to think more carefully about this\ncomparison grade standards that rely on real metrics because its current form is not very\nmeaningful.\nResponse: We thank you for this valuable comment. In response, we have redesigned the\nevaluation framework using parameterized and metric-based standards. The revised\ncomparison concludes four representative cooling strategies: (1) the LHEC substrate used in\nthis work (delignified balsa wood); (2) a finned aluminum condenser representing an air-\ncooled metallic surface; (3) a finned aluminum condenser with epoxy coating, representing a\nmetallic water-cooled interface; and (4) a radiative cooling membrane, as reported in Proc. Natl.\nAcad. Sci. U. S. A. 2021, 118, 2019292118, as a representative radiative cooler. We evaluated each\nstrategy across five criteria:\n Solar vapor-to-water efficiency, values were obtained from reported data (water metal\ncooler and radiative cooler) or measured performance (air metal cooler and LHEC\nsubstrate).\n Material cost (USD per m2).\n Portability (kg per m2)\n Eco-friendliness, evaluated by scoring the number of the following attributes met: (i)\nbiodegradability, (ii) recyclability, (iii) resource abundance.\n Manufacturing complexity, scored based on whether the process meets: (i) no need for\nlarge-scale equipment, (ii) scalability, (iii) single-step processing.\nThis revised system uses clearly defined and traceable indicators, replacing the previous\nsubjective descriptors such as \"requires temperature gradient\" or \"easy to achieve.\" Each\nstrategy was graded on a 1–4 scale for each criterion, based on these specific and repeatable\nstandards.\nThe updated grading results have been presented as Table R2 and visualized in Figure R25\nbelow. Table R2 and Figure R25 haven been incorporated as Table S4 and Figure 5j of the\nrevised manuscript, with a proper description. We believe this revision have enhanced the\ntransparency, objectivity, and comparative value of our evaluation, and we thank you again for\nthis important suggestion.\nTable R2. The comparison grade of different cooling strategy\n29 / 48\nFigure R25 Evaluation of the delignified wood based LHEC strategy against other reported\ncondensation techniques.\nQ9 Delignified wood is usually much weaker than untreated wood. What is the mechanical\nstrength of the delignified wood? Will it crack if salt crystals crystallize inside of the pore?\nResponse: We thank you for this insightful comment. It is true that delignified wood generally\nexhibits reduced mechanical strength compared to untreated wood. In our study, the\ndelignification treatment was intentionally applied to reduce parasitic heat absorption from\nsolar irradiation and to enhance the hydrophilicity of the substrate, thereby facilitating\ncapillary-driven water transport and salt rediffusion.\nTo characterize the mechanical strength, we performed tensile strength tests on delignified\nwood, which was found to be ~6.5 MPa (Figure R26a). Then, we subjected the delignified wood\nto 120 hours of evaporative heat dissipation under 1000 W m−2 in 3.5 wt% saltwater (Figure\nR26b). After such long-time salt accumulation, the SEM images revealed that no significant\nsalt accumulation occurred inside the tracheid channels, with salt crystals primarily\naccumulating on the cell wall surface (Figure R26c). Then, we performed tensile tests on this\nsample. The tensile fracture strength showed no significant change (~4%), indicating that long-\nterm operation in saltwater condition does not substantially affect the mechanical strength of\nthe delignified wood (Figure R26d). These results confirm that the delignified wood possesses\ngood salt resistance and maintains its mechanical strength under prolonged operating conditions.\n31 / 48\nFigure R26 a, Tensile strength-strain curves of delignified wood. b, Heat dissipation flux under\nthermal load of 1000 W m−2 in 3.5 wt% brine over 120 hours. c, Scanning electron microscope\nimages of the delignified wood after salt accumulation. d, Fracture strength comparison of\ndelignified wood before and after salt accumulation.\nQ10 Their Note S5 discusses their COMSOL simulation setup, however it is missing many\ndetails that can influence their simulation results. The authors should clearly list in a table all\nthe values they used for their boundary conditions (boundary temperature, boundary heat flux,\netc) and describe what all terms actually encompass in their note (for example dzQted accounts\nfor additional heat sources, but what does this actually mean?).\nResponse: Thank you for your valuable suggestion. In response, we have revised the COMSOL\nsimulation section and systematically rechecked all the boundary conditions. To clarify convey\nthe simulation setup, we have labeled all relevant boundaries and domains in the simulation\ngeometry for the LHEC assisted configuration, as shown in Figure R27 below. Subsequently,\nwe have compiled a complete list of boundary conditions in a structured table (Table R3 below),\nincluding values used for boundary temperature and boundary heat flux. This allows readers to\neasily reference and replicate the setup. It is worth noting that, for the control setup without\nLHEC, the only modification is the boundary condition at Boundary 1, which has been adjusted\nto a convective heat flux matching Boundary 3. This difference is now explicitly noted.\nFigure R27 has been updated as Figure S3 in the revised Supporting information (Note S5).\nTable R3 has been added as Table S1 in the revised Supporting Information.\n32 / 48\nFigure R27 The labels of different boundaries and domains for setup with LHEC assistance.\nTable R3. Boundary conditions for setup with LHEC assistance\nIn addition, we sincerely apologize for the confusion caused by the term \"dzQted as additional\n as additional\n as additional\nheat sources.\" This parameter was inherited from the default heat transfer structure in COMSOL,\nwhich includes placeholders for internal heat sources. However, in our actual model, no\nadditional internal heat sources were used. We have now revised the heat transfer equation\napplied in Domain b, and clarified its components as follows:\nWhere is the velocity vector of\n𝐮𝐮\nm\n⋅\no\n∇\ni\n\ns\n𝜌𝜌\nt\n𝐶𝐶\nai𝑒𝑒r\n𝑇𝑇\n, = \nis\n∇\nth\n⋅\ne\n( 𝑘𝑘\nfl\\∇\nu\n𝑇𝑇\n)id\ndensity is the temperature,\n𝐮𝐮 𝜌𝜌 𝑇𝑇\n33 /\n𝐶𝐶\n4𝑒𝑒8\nis the specific heat capacity, is the thermal conductivity.\nThis revised formulation refle𝑘𝑘cts the actual energy transport in our system and removes unused\nor irrelevant source terms. We have updated all the COMSOL-related equations and parameter\ndefinitions in Note S5 of the revised manuscript.\nQ11 In the COMSOL simulation, they have written that dzG is the generation or removal of\nwater vapor. Where was this condition placed inside of the simulation and how were these\nvalues determined?\nResponse: We thank you for this insightful comment. In the original equation, the term d G\nz\nreferred to the generation or removal of water vapor, was incorrectly included. Given that no\nexternal sources or sinks of water vapor are involved in our simulation, and since our model is\na two-dimensional setup, we have removed this term and updated the corresponding equation\nas shown below.\n𝐮𝐮⋅∇𝑆𝑆𝑒𝑒 = ∇⋅(𝐷𝐷∇𝑆𝑆𝑒𝑒)\nwhere is the velocity vector of moist𝑆𝑆 𝑒𝑒ai=r, 𝑅𝑅𝑅𝑅 𝑆𝑆iss the mass concentration of water vapor,\nis the relative humidity, is the saturation concentration of water vapor dependent on\n𝐮𝐮 𝑆𝑆v\nlocal pressure and temperature, and is the diffusivity of moist air.\n𝑅𝑅𝑅𝑅 𝑆𝑆s\n𝐷𝐷\nQ12 Their current COMSOL simulation doesn’t illustrate if the heat of evaporation or heat of\ncondensation is correctly coupled in the simulation, which can have large effects on the\ntemperature gradients and corresponding vapor gradients. The authors should clarify this point.\nResponse: We thank you for raising this important point. In our model, we used the Moist Heat\nmodule in COMSOL, which provides a built-in mechanism to couple the heat of evaporation\nand heat of condensation through the heat source term defined as:\nwhere is the water-vapor transition mass flux and is the latent heat.\n𝑞𝑞 = −∆𝑚𝑚 𝑅𝑅\nThis cou∆p𝑚𝑚ling directly links the vapor transport to the ther𝑅𝑅mal field by accounting for the energy\nconsumed or released during phase change. The module also allows manual toggling of this\ncoupling effect for comparison and validation.\nTo verify that the latent heat coupling was correctly implemented and that it affects temperature\ngradients meaningfully, we conducted a control simulation. As shown in Figure R28a, when\nlatent heat coupling is enabled, the predicted surface temperatures on the condenser sides are\napproximately 28 °C and 33 °C, respectively. These values are consistent with our experimental\nobservations. By contrast, when the coupling is disabled, the simulated temperatures drop\nsignificantly (to 16 °C and 28 °C), as shown in Figure R28b, which no longer matches the\nexperimental data. This deviation confirms that the latent heat term has a substantial influence\non the heat and mass transfer behavior and that its inclusion is essential for realistic simulation.\nThese results demonstrate that our model properly includes and couples the heat of\ncondensation, ensuring accurate representation of thermal-mass transfer interactions in the\n34 / 48\nsystem.\nFigure R28 a, The temperature distribution in model with (left) and without (right) LHEC assistance\nwhen coupled with condensation heat. b, The temperature distribution in model with (left) and\nwithout (right) LHEC assistance when ignored condensation heat.\nQ13 On page 1, the authors cite Ref. 8 and 9 that achieve evaporation rates on the order of 10\nkg/m2-h and use it as a reference point in comparison to the water production rate. However,\nthese high evaporation rates in Ref. 8 and 9 are due to environmental heat absorption, which is\na different mechanism from solar evaporation in solar stills. The authors should look for other\nreferences that provides a better comparison of the 0.3-0.5 kg/m2-h water production rate.\nResponse: Thank you very much for raising this point. In response, we have removed Refs. 8\nand 9 and replaced them with three more appropriate references that report purely solar-driven\nevaporation systems: Sci. Adv. 2019, 5, eaaw5484; Energy Environ. Sci. 2020, 13, 2087-2095;\nand J. Am. Chem. Soc. 2022, 144, 3083-3090.\nAdditionally, we have also revised the corresponding sentence in the introduction to reflect this\ncorrection, as shown below:\n“…To date, numerous solar-driven interfacial vapor generation strategies have been developed\nto enhance vapor generation rates (J ), with reported values exceeding 3 kg m−2 h−1 8-10…”\nvapor\nQ14 Their manuscript and SI has many typos (for example in the heat equation in the SI, they\nwrote µ instead of u for velocity). The authors should go through their writings carefully and\nfix their notations.\n35 / 48\nResponse: We sincerely apologize for these typos. We have carefully reviewed and revised the\nentire manuscript and Supporting Information, correcting all identified issues. This includes the\nreplacement of the incorrect symbol \"µ\" instead of \"u\" for velocity in the heat equation, along\nwith other typographic inconsistencies. We appreciate your attention to detail, and we have\nmade sure that all notations are now consistent and accurate throughout the manuscript.\nQ15 Fig 5h is quite misleading because there is no x-axis, but they placed their LHEC\nassisted setup on the right most side. In conjunction with point 1 above, the authors should\nrevise this figure either with proper x-axis labels (maybe with a bar chart or an actual metric on\nthe x-axis) as opposed to their current data representation.\nResponse: We appreciate your comment. The x-axis in previous Figure 5h does not represent a\nmetric. It only indicates different reference comparisons and their categorization. Therefore, we\nhave revised the figure to a bar chart according your comment as shown in Figure R29.\nFigure R29 has been incorporated into the revised manuscript as the updated Figure 5h.\nFigure R29 Comparison of the solar vapor-to-water efficiency between the LHEC assisted setup\nand other previously reported works assisted by representative cooling strategies.\n36 / 48\nReviewer #3 (Remarks to the Author):\nThe authors have revised the manuscript extensively according to reviewer's comments.My concerns about the\npaper have been addressed. Therefore,I recommend the publication of the paper.\nResponse: We greatly appreciate your positive feedback on the innovation and potential of our\nwork. At the same time, we appreciate the constructive comments you provided. We have\ncarefully reviewed each of the points raised and revised the manuscript accordingly to address\nyour concerns. Detailed responses and corresponding modifications are presented in the point-\nby-point replies below.\nWe believe these revisions have strengthened the clarity, rigor, and completeness of our study.\nThank you again for your thoughtful feedback and valuable suggestions.\nQ1 The manuscript contains several minor typographical errors. For instance, in the fifth line\nof page 4, the word “second” appears twice. Moreover, throughout the manuscript, the minus\nsign is incorrectly written as a hyphen. The authors are advised to carefully proofread the text\nto avoid such errors in future revisions.\nResponse: We sincerely thank the reviewer for pointing out the typographical and formatting\nissues in our manuscript. In response, we have removed the repeated word “second” from the\nfifth line of page 4 in the revised manuscript. Furthermore, we have carefully proofread the\nentire manuscript and Supporting Information, correcting all identified grammatical errors and\ntypographical inconsistencies. In particular, we have replaced all incorrectly used hyphens with\nproper minus signs where required in mathematical expressions and data reporting. These\ncorrections have been applied consistently throughout the text to ensure clarity and accuracy.\nWe appreciate your attention to detail, which has helped us improve the overall quality and\npresentation of the manuscript.\nQ2 To enhance the clarity of the research presented in this paper, it is recommended to include\na schematic diagram illustrating the principle behind the latent heat-assisted evaporative\ncooling (LHEC) strategy.\nResponse: Thank you for your valuable suggestion. To improve the clarity of the research,\nwe\nhave included a schematic diagram (Figure R30) illustrating the principle behind the latent heat-\nassisted evaporative cooling (LHEC) strategy. As shown in the diagram, when a moist surface\n37 / 48\nis exposed to external non-saturated air, a water concentration gradient is created between the\nmoist surface (C ) and the surrounding air (C ). According to Fick's law of diffusion,\nmoist surface air\nthis gradient drives the natural departure of water molecules from the liquid water surface into\nthe surrounding gaseous air. During this phase transition, the water molecules must overcome\nthe hydrogen bonding forces, which requires the absorption of latent heat (~2400 J g−1) for\nphase change. This heat uptake leads to the effective cooling of the moist surface. This process\nis fundamental to the LHEC strategy, where the absorbed latent heat plays a key role in\nenhancing the cooling effect.\nFigure R30 have been added as Figure S15 into the revised Supporting Information, with a\nproper description on page 3 of the revised manuscript, as shown below.\n“…, this latent heat can also be harnessed as an effective cooling power source through\nspontaneous phase transition…”\nFigure R30 Schematic diagram of latent heat-assisted evaporative cooling driven by water vapor\nconcentration gradient between moist surface and environment. During phase transition, latent heat\nis absorbed for overcoming the hydrogen bonding force.\nQ3 For Figure 2g, to show the superiority of wet delignified wood in reducing spectral\nabsorbance, the absorbance data of natural wood should be provided as a comparative reference.\nResponse: We thank you for your valuable comment. In response, we have measured the solar\nabsorbance spectra of natural raw wood in wet state to provide a direct comparison. As shown\nin Figure R31 below, the solar absorbance of wet natural wood is approximately 0.46, which is\nsignificantly higher than that of wet delignified wood (0.11) under the same conditions. This\nresult confirms that delignification markedly reduces solar absorbance, thereby enhancing the\nsubstrate’s ability to suppress parasitic heat gain.\nFigure R31 has been incorporated into the revised manuscript as Figure 2g, with the\n38 / 48\ncorresponding description added on page 5, as shown below.\n“…To verify this, solar absorption spectrum of the delignified wood substrate was measured\n(Fig. 2g), showing a lower solar absorbance of approximately 0.11 compared to natural wood\n(~0.46)…”\nFigure R31 Absorbance spectra of natural wood and delignified wood at wet state across solar\nspectrum.\nQ4 Figure 5d requires longer experimental time (7 days of continuous or intermittent operation)\nto further demonstrate the stability of the LHEC structure.\nResponse: Thank you for this valuable suggestion. In response, we extended the experiment\noriginally shown in Figure 5d to a total duration of 10 days. Each day, the LHEC substrate was\nimmersed in 3.5 wt% saline water and subjected to continuous evaporative cooling for 12 hours,\nunder a constant thermal input of 1000 W m−2 provided by an electric heater.\nAs shown in Figure R32, the measured heat dissipation flux remained stable around\nmaintained stable salt-resistant performance, even under extended exposure to saline conditions\nand high thermal load.\nFigure R32 has been updated into the revised manuscript as Figure 5d, along with a proper\ndescription on page 10, as shown below.\n“…The wood based LHEC substrate maintained a stable heat dissipation flux of ~1 kW m−2\nover 120 hours, under a continued heat load of 1 kW m−2, with no performance decline (Fig.\n5d)…”\n39 / 48\nFigure R32 Measured heat flux fluctuation of LHEC substrate in brine operation for 10 days.\nQ5 Regarding Figures 5a and 5b, the authors need to explain why only a single-sided LHEC\nstructure was adopted instead of a 2 or 3-sided structure. To make the work more\ncomprehensive, data comparisons for other structural configurations are better to be provided.\nResponse: We thank you for this thoughtful suggestion. To access the impact of LHEC\ncoverage area on system performance, we conducted additional experiments by applying LHEC\nsubstrates to different numbers of sides of the glass cover. As shown in Figure R33a, the\nmaximum water collection rate was achieved when LHEC substrates were applied to two sides,\nresulting in an enhancement of ~21% compared to the single-sided configuration.\nHowever, extending the LHEC coverage to three or more sides led to a decline in performance.\nTo understand this effect, we measured the surface temperatures of both the glass condenser\nwall and the evaporator under varying LHEC configurations. As shown in Figure R33b,\nincreasing the number of LHEC substrates resulted in a progressive decrease in the temperature\nof both surfaces. The maximum temperature difference between the glass wall and evaporator\n(T −T ) was observed when LHEC was applied to two sides. Adding more LHEC\nglass wall evaporator\nsubstrates caused overcooling of the evaporator surface, thereby reducing vapor generation and\nultimately lowering overall condensation efficiency. Considering the performance trade-off,\nalong with practical factors such as material cost, structural complexity, and potential solar\nshading effects, we selected the single-sided LHEC configuration as a representative and\nscalable design for this study.\nFigure R33 has been incorporated into the revised manuscript as Figure S26, along with a\nproper discussion added on page 9, as shown below.\n“…To evaluate the impact of LHEC coverage, substrates were applied to different sides of the\nglass cover (Fig. S26). Two-sided coverage yielded the highest water generation rate, while\nfurther extension caused evaporator overcooling. Considering this trade-off, along with cost,\nstructural complexity, and potential shading, we adopted the single-sided configuration for\nsubsequent studies...”\n40 / 48\nFigure R33 a, Water generation rates by applying LHEC substrates to different numbers of sides of\nthe glass cover. b, Temperature profiles of the evaporator and condensation wall for different LHEC\nconfigurations.\nQ6 The authors should place the economic analysis table in the main text. Additionally, it is\nbetter to consider the lifespan of the LHEC structure in the economic analysis.\nResponse: Thank you for your valuable suggestion. In response, we re-evaluated the fabrication\ncost of both solar water production setup ($47.5 m−2, Table R4 below) and the LHEC substrate\n($1.25 m−2, Table R4), with consideration of more factors including materials cost, chemicals\ncost and electricity cost, as shown in Figure R34. In our experiments, it was found that\ndelignified wood used as the LHEC substrate can operate for at least one month, while the non-\ndelignified wood solar evaporator remains effective after four months. However, considering\nthe potential increase in parasitic heat over time and the risk of biofouling on the evaporator\nsurface, we conservatively assume a replacement cycle of one month for LHEC substrate and\nfour months for the PPy wood evaporator. Based on these assumptions, the annualized\noperational cost over one-year operation is estimated to be $117.74 m−2 for the bare setup and\n$132.75 m−2 for the LHEC-assisted setup (Table R5).\nWhen normalized by the annual freshwater output, the unit water production cost is calculated\nto be $0.11 per liter for the bare system and $0.09 per for the LHEC-assisted system, indicating\na 18.2% reduction in cost per liter. This demonstrates that the additional 12.7% investment in\nmaterial and maintenance enables an approximately 35% improvement in freshwater yield and\na substantial decrease in per-liter cost, highlighting the economic viability of the LHEC strategy.\nWe have integrated the above economic comparison into Figure R35 for clarity.\nFigure R34 as well as Table R4-R6 have been included as Figure S33 and Table S2-3 in revised\nSupporting Information, respectively. Figure R35 has been updated as Figure 5i in revised\nmanuscript, with prober description on page 11 as shown below.\n“…Additionally, we performed an economic analysis of the wood-based LHEC substrate over\na one-year operational cycle (Fig. S33 and Table S2-3). The results demonstrate that a modest\nadditional investment of 12.7% in materials and maintenance yields a 35% increase in\nfreshwater output, ultimately leading to an 18.2% reduction in the cost per liter of water (Fig.\n5i) …”\n41 / 48\nFigure R34 Schematic diagram showing the fabrication process and associated costs for the solar\nwater generator setup.\nTable R4 The respective calculation of the fabrication cost for solar water generation setup and\nLHEC substrate\nNote: 1Prices of the chemicals were determined based on the average prices on website. 2Price of\nthe electricity was determined according to the average electricity price in China.\n42 / 48\nTable R5 Cost comparison between the setup with and without LHEC over one year operation.\nNote: 1Based on our experimental observations, the delignified wood substrate can be used\ncontinuously for at least one month, and the solar evaporator remains functional for at least four\nmonths. 2Eastern China receives ~1600 kWh m−2 of solar radiation annually [Appl. Energy 2022,\n315, 119045].\nFigure R35 Economic analysis for setup with and without LHEC over one year operation.\nQ7 For Figure 5g, the authors should provide a performance comparison between the system\nwith and without the LHEC substrate.\nResponse: Thank you for your suggestion. The LHEC substrate is positioned on the outside of\nthe glass cover, for enhancing heat dissipation during the condensation process. Therefore, we\nconsider that it does not significantly impact the purification effectiveness of the solar\ndistillation setup. To validate this, we tested the concentrations of salt ions and total organic\ncarbon (TOC) in the treated water and condensed water for the setup without LHEC assistance.\nAs shown in Figure R36, the absence of the LHEC substrate does not significantly affect the\nwater purification performance, confirming that the LHEC enhances condensation cooling\n43 / 48\nwithout altering the purification capabilities of the setup.\nFigure R36 Comparison of ion concentrations and TOC concentrations in raw sea and lake water,\nand purified water using setup with (a) and without (b) LHEC assistance.\nQ8 To clarify the accuracy and for better understanding, it’s recommended to introduce how to\nobtain water production efficiency. Moreover, the proposed LHEC structure induces additional\nseawater input for the system, how to interpret the rationality of calculating the water\nproduction efficiency using the same method as traditional water production systems?\nResponse: Thank you for your valuable comment. We appreciate your insightful question\nregarding the calculation of water production efficiency. In this work, we calculated this metric\nby normalizing water production rate against the natural solar evaporation rate (J /J ). J\nprod evap evap\nrefers to the evaporation rate of the solar evaporator in an open environment, which serves as\nan indicator of the evaporator’s performance. Here, J /J serves as a reference baseline that\nprod evap\nreflects the intrinsic condensation performance in solar distillation system. This approach\nallows us to decouple the contribution of the condensation enhancement from that of the\nevaporator performance, and thus more accurately evaluate the role of the LHEC substrate in\nimproving the vapor-to-liquid conversion process.\nTo avoid confusion, we have rephrased the “solar production efficiency” with “solar vapor-to-\nwater efficiency,” throughout the revised manuscript to better reflect the nature of this\nparameter, as shown below.\n“…To reveal the contribution of LHEC for condensation, we normalized the production rate\n(J ) against the natural solar evaporation rate (J ) as solar vapor-to-water efficiency…”\nprod evap\n“…the LHEC-assisted setup achieved solar vapor-to-water efficiencies of up to 93% under 1.4\nkW m−2 solar irradiation…”\nFor setup with/without LHEC assistance, the solar vapor generated inside comes from the same\nevaporator indicating that both setups possess same solar vapor generation performance. The\nadditional seawater input does not enter the primary vapor condensation loop. Therefore, it does\nnot contribute to the solar-to-vapor conversion efficiency and should not be included in the\ncalculation of J . Accordingly, the method used to calculate solar vapor-to-water efficiency\nevap\nremains valid in LHEC structure, and the resulting parameter can be used to compare the\n44 / 48\ncondensation performance between the two systems. We sincerely hope that you agree with this\napproach and rationale.\nQ9 In Section S5, the models utilized in COMSOL software are introduced, and the governing\nequations are thoroughly explained. To facilitate the reproduction of this study, the author\nshould provide a comprehensive table of the boundary conditions necessary for solving these\nequations and specify the interface types employed.\nResponse: Thank you for your valuable suggestion. To ensure the clarity and reproducibility of\nour simulation, we have labeled all relevant boundaries and domains in the simulation geometry\nfor the LHEC assisted configuration, as shown in Figure R37 below. Subsequently, we have\ncompiled a complete list of boundary conditions in a structured table (Table R6 below),\nincluding values used for boundary temperature, convective heat flux. This allows readers to\neasily reference and replicate the setup. It is worth noting that, for the control setup without\nLHEC, the only modification is the boundary condition at Boundary 1, which has been adjusted\nto a convective heat flux matching Boundary 3. This difference is now explicitly noted.\nFigure R37 and Table R6 have been incorporated into the revised manuscript as Figure S3 and\nTable S1, respectively.\nFigure R37 The labels of different boundaries and domains for setup with LHEC assistance.\n45 / 48\nTable R6. Boundary conditions for setup with LHEC assistance\nQ10 To ensure the reliability of the numerical simulation results, it is essential to present the\noutcomes of a mesh independence study.\nResponse: Thank you very much for your valuable suggestion. We have conducted a mesh\nindependence study by applying three different mesh resolutions to our models (see Figure R38\nbelow): regular mesh (1738 elements), fine mesh (2805 elements), and finer mesh (7081\nelements).\nAs shown in Figure R38b and c, the water vapor concentration distribution for both the LHEC-\nassisted and control configurations remain consistent across all three different mesh resolutions.\nThese results confirm that our simulation outputs are mesh-independent, reinforcing the\ncredibility of the numerical analysis.\nFigure R38 has been included in the revised Supporting Information as Figure S5, along with a\ncorresponding description in Note S5.\n46 / 48\nFigure R38 a, Mesh distributions for the three different resolutions: regular mesh (1738 elements),\nfine mesh (2805 elements), and finer mesh (7081 elements). b, Water vapor concentration\ndistribution of LHEC assisted model for the three mesh resolutions. c, Water vapor concentration\ndistribution of model without LHEC assistance for the three mesh resolutions.\n47 / 48\nReviewer #4 (Remarks to the Author):\nI co-reviewed this manuscript with one of the reviewers who provided the listed reports. This\nis part of the Nature Communications initiative to facilitate training in peer review and to\nprovide appropriate recognition for Early Career Researchers who co-review manuscripts.\nResponse: We sincerely thank you for the effort you put into reviewing our manuscript and for\nthe valuable feedback you provided.\n48 / 48\nResponses to the reviewers’ comments (Manuscript number NCOMMS-25-15552A)\nChanges in the revised manuscript as a response to the reviewers’ comments are\nhighlighted in red color and clarifications regarding the reviewer’s comments are\nprovided in blue color.\nReviewer #1 (Remarks to the Author):\nAlthough the authors have tried to revise the content, the metrics and methodology for vapor-\nto-water efficiency are still in chaos and misleading. Moreover, this is a metric created by the\nauthors, but not important for the community. The vapor/water production rate is the real\nperformance indictor needed, while it is only ~0.9 kgm-2h-1 even with additional cost from\nLHEC. This is quite low, comparing to many other literatures. More importantly, the fixed\ncooling temperature with LHEC is not reasonable for year-round operation with variable\nambient temperature. We have plenty of choices to reduce the condensation temperature, but\nthe idea of using LHEC is not reasonable at all.\nResponse: Thank you for your continued feedback and thoughtful critique. In response to your\nconcerns, we have carefully revised the manuscript and made the following clarifications:\n We have removed the “solar vapor-to-water efficiency” metric and adopted the more\nwidely accepted “solar water production efficiency”. This change is reflected throughout\nthe revised manuscript.\n As for the water production rate, the reported ~0.9 kg m−2 h−1 was measured using a\ndeliberately simplified demonstration system. This design allowed us to isolate and\nevaluate the effect of the LHEC strategy on condensation enhancement, heat dissipation,\nand temperature regulation. Our intention was not to optimize the device for peak\nperformance, but to understand the mechanism and practical value of LHEC.\n To illustrate the broader applicability of the LHEC concept, we further integrated it into\nvarious system configurations. These include a film-wise condensation setup (yielding\n~0.98 kg m−2 h−1), a three-stage distillation system (~2.0 kg m−2 h−1), and modified setups\ninvolving multiple LHEC substrates (~1.1 kg m−2 h−1) or enhanced evaporator materials\n(~1.2 kg m−2 h−1). These results support the strategy’s compatibility with different solar\ndistillation architectures.\n Regarding concerns about its functionality under varying environmental conditions, we\nwould like to clarify that the LHEC strategy does not impose a fixed cooling temperature.\nInstead, it passively absorbs heat through the evaporation of water from its surface, which\ndynamically adjusts with ambient temperature and humidity. Experiments under controlled\nconditions show consistent reduction in condenser surface temperature compared to bare\nsurface, with temperature drops observed across a wide range of scenarios (e.g. −9°C in\n75% RH and 40°C ambient; −12.4°C in 25% RH and 40°C ambient; −4.4°C in 75% RH\nand 15°C ambient; −5.5°C in 25% RH and 15°C ambient), thereby boosting freshwater\nproduction.\n Finally, we provide a comparative discussion between the LHEC substrate and\n1 / 26\nconventional metal-based cooling elements. While metallic structures may offer efficient\nheat conduction, they are also associated with higher cost, parasitic heat gain, and\ncorrosion issues when exposed to saline environments. In contrast, the LHEC substrate\noffers a low-cost, parasitic heat-resistant, and passive cooling alternative. We further\ndemonstrate that the LHEC approach can be used in conjunction with seawater cooling to\nenhance heat dissipation without mutual interference.\nPlease refer to the following detailed point-to-point response below as well as the revised\nmanuscript for the detailed revision.\nWe respectfully clarify that the core main of our study is not to propose a highly engineered\nsolar distillation set for peak performance under s specific condition. Rather, we introduce a\ngeneralizable condensation enhancement strategy that is cost-effective, structurally simple, and\nadaptable to a wide range of solar distillation designs. We hope with the above clarifications\nyou can agree with us on that.\nQ1 Chaos in metric and methodology. The current methodology using water production rate\nratio cannot describe the vapor-to-water efficiency. Currently, such efficiency is calculated\nbased on solar water production rates with setups with/without LHEC, which will have different\ntemperature and humidity inside the device. This makes the evaporation rate/efficiency\ndifferent in two setups, making the water production rate not directly comparable. In general,\nit is more likely a performance degradation ratio. If the term efficiency is used, the ratio between\nevaporation rate and water collection rate should be evaluated within the same device, and there\nwill be two “vapor-to-water efficiency” for both setups with/without LHEC.\nResponse: We sincerely thank you for your insightful feedback regarding the methodology and\nthe use of the \"solar vapor-to-water efficiency\" metric. After carefully considering your\ncomments, we have decided to remove the “solar vapor-to-water efficiency” from the\nmanuscript, and adopted “solar water production efficiency” (the energy of freshwater\ngeneration vs. solar energy input) as the primary evaluation parameter, to keep consistent with\nother studies in the research community [e.g. Joule 2021, 5, 1971-1986, Nature Water 2023, 1,\n790-799].\nAccordingly, we changed the y-axis label of Figure 4g to “solar water production efficiency”,\nwhich has been shown as Figure R1 below. As can be seen, the solar water production efficiency\nof our demo setup with LHEC assistance is obviously higher than that of the bare setup.\nMoreover, this improvement by LHEC becomes more pronounced under higher solar intensities,\ndemonstrating the contribution of LHEC for enhancing the condensation process and the overall\nenergy conversion in system.\nFigure R1 has been updated as Figure 4g into the revised manuscript on page 17, along with a\nproper description as shown below.\n“To reveal the contribution of LHEC to energy conversion, we calculated the solar water\nproduction efficiency, which is defined as η =(J ×H )/I where J denotes the\nsolar-water prod cond solar prod\nwater generation rate (kg m−2 s−1), H is the enthalpy of vapor condensation (J kg−1), and I\ncond solar\n2 / 26\nis the solar irradiation intensity input (W m−2) . Without LHEC, the solar water production\nefficiency remained around 45%, which is comparable to the performance of conventional\nsystems57,58. In contrast, the LHEC-assisted setup achieved efficiencies of up to 76% under 1.4\nkW m−2, promoting the conversion of solar energy into freshwater (Fig. 4g). Notably, efficiency\nof the LHEC-assisted setup increased gradually with higher solar intensities, which can be\nattributed to the increasingly heat dissipation benefits of the evaporation cooling mechanism as\nthe heat load increases (Fig. 1d and 3d).”\nFigure R1. Comparison of solar water production efficiency in setup with and without LHEC\nassistance.\nQ2 Low water production rate. The vapor-to-water efficiency is a metric created in this work,\nbut not a common performance indicator the community cares. With even LHEC, the water\nproduction rate under one sun is only ~0.9 kgm-2h-1, which is quite low comparing with many\nprevious works: 1.6 kg m−2 h−1 in Nature Nanotechnology, 2018, 13(6): 489-495; 1.063 kg m−2\nh−1 in Joule, 2021, 5(6): 1602-1612; 1.72 kg m−2 h−1 in Nature Communications, 2020, 11(1):\n521.\nResponse: Thank you for your valuable comment. As noted in our response to Q1 above, we\nhave removed the “vapor-to-water efficiency” metric throughout the manuscript and instead\nadopted the widely used “solar water production efficiency” to evaluate system performance.\nWe would also like to clarify that the main objective of our study is not to achieve the highest\nabsolute water production rate, but to establish a broadly applicable condensation enhancement\nstrategy (the latent heat evaporative cooling, LHEC), that passively improves condensation\nperformance. To isolate and quantify the effect of LHEC, we deliberately adopted a simple solar\ndistillation set in Figures 4 and 5. This approach enabled us to directly track changes in heat\nflux, temperature gradients, and mass transfer behavior attributable to LHEC, which serves as\na proof-of-concept platform.\nTo further demonstrate the broader applicability of the LHEC strategy, we integrated it\ninto other distillation architectures. For example, in a film-wise condensation device (FWD),\nthe LHEC-assisted system achieved ~0.98 kg m−2 h−1 freshwater production, with improvement\n3 / 26\nof 32% (Figure 4h of the manuscript, shown as Figure R2a below); in a three-stage distillation\ndevice (TSDD), the production increased to ~2.0 kg m−2 h−1 with improvement of 25% (Figure\n4h of the manuscript, shown as Figure R2b below). Additional configurations, such as applying\nLHEC to two surfaces or replacing the PPy wood evaporator with a PPy/Ag/Wood evaporator\ndesign, yielded rates of ~1.1 and ~1.2 kg m−2 h−1 with improvement of 64% and 43%,\nrespectively (Figure S26 in SI, shown as Figure R2c and R2d below).\nWe fully acknowledge the significance of the references you provided. However, direct\ncomparison of absolute water production rates can be misleading, as these values are\nstrongly influences by system-specific variables such as evaporator design, thermal\ninsulation, condenser structure/size and system design, which are often not identical. For\ninstance, the first reference you mentioned [Nature Nanotechnology, 2018, 13(6): 489-495]\nreached a freshwater production rate of 1.6 kg m−2 h−1, it was achieved by lowering the latent\nheat of water evaporation, but it used a conventional glass condenser. We believe that\nintegrating our LHEC into such a design may also can help to further enhance its output. For\nthe second citation you mentioned [Joule, 2021, 5(6): 1602-1612], the reported rate of 1.063\nkg m−2 h−1 was achieved using a nanostructured hydrophobic condenser and active heat\nconduction via metallic materials. The total set design is different, and although the freshwater\nproduction rate in the latter study is lower than in the former, this does not mean that the metal\nair cooler strategy proposed is not meaningful. Regarding the third citation [Nature\nCommunications, 2020, 11(1): 521], we were unable to locate the referenced article and suspect\nthere may have some information error.\nWe have rephrased the corresponding description in the Abstract, the fourth paragraph of the\nIntroduction as well as the Discussion section to better illustrate this point, which has been\nshown as below.\n“…Notably, the plug-and-play design of the LHEC substrate enables seamless integration into\na range of solar evaporation architectures, including single/multi-stage systems, all of which\nbenefit from its enhanced condensation performance…”\n“…Additionally, this LHEC substrate demonstrates high versatility, seamlessly integrating with\nvarious solar interfacial evaporation setups, including single-stage, multi-stage, and\ngeometrically diverse configurations…”\nWe hope this explanation helps clarify the intent and relevance of our work. We would like to\nrespectfully reiterate that our aim is to propose a modular, low-cost, and energy-\nindependent solution that can be coupled with a wide range of solar distillation systems.\nRather than focusing solely on maximizing performance in a specific configuration. This work\nseeks to balance cost, ease of fabrication, and environmental compatibility, we sincerely hope\nyou can agree with us on it.\n4 / 26\nFigure R2 The schematic diagram of LHEC application in film-wise condensation device (a) and\nthree-stage distillation device (b) with corresponding water generation rates in respective device. c,\nSchematic diagram of setup assisted by two LHEC substrates with corresponding water generation\nrate. d, Schematic diagram of LHEC assisted setup driven by PPy/AgNPs/wood evaporator, with\ncorresponding water generation rate.\nQ3 Not suitable for year-round operation. To ensure the use of LHEC could enhance the\ncondensation, its temperature should be above the ambient temperature but lower than the\noriginal condensation temperature without LHEC. If the LHEC temperature is lower than\nambient, it will just cool the ambient rather than the condensation. If the LHEC temperature is\nhigher than original condensation temperature, it is not effective. However, the gap between\nambient temperature and original condensation temperature is small and will vary around the\nyear. This makes the latent heat based LHEC with constant working temperature not suitable.\nThe use of LHEC could bring benefits in the selected condition shown in this paper, but will\nbecome disadvantages in other conditions.\nResponse: Thank you for your comment. We would like to respectfully clarify that the LHEC\nstrategy does not operate by maintaining a constant surface temperature. Rather, its cooling\neffect arises from enhanced heat dissipation via phase-change evaporation, which absorbs a\nlarge amount of latent heat (~2450 J g−1). Unlike bare surfaces that rely primarily on air\nconvection for cooling, the LHEC surface dissipates heat more effectively, resulting in a\nconsistently lower steady-state temperature under the same heat flux, as verified through both\ncalculations and experiments (Figure R3a-d).\nSpecifically, the original condensation surface is cooled only through natural air convection\n(Figure R3a), whereas the LHEC strategy draws heat away by enabling continuous phase\nchange water evaporation process on surface (Figure R3b). As shown in Figure R3c, this\nmechanism provides a higher heat dissipation rate across a wide range of surface temperatures.\nFigure R3d further confirms that the LHEC surface maintains a lower temperature than the bare\nglass surface at steady state, without requiring fixed or externally controlled temperature\nsettings.\nIn our solar distillation experiments, the LHEC-assisted setup exhibited a 2.5-fold increase in\nheat dissipation flux compared to the bare surface (Figure R3e), which effectively reduced the\ncondensation surface temperature and increased the temperature gradient with the evaporator\n(Figure R3f). This enhancement translated into a measurable increase in freshwater production.\nTo assess the adaptability of LHEC under different environmental conditions, we conducted\nadditional experiments in a controlled climate chamber simulating seasonal variations\n(temperature: 15–40 °C; relative humidity: 25–75%) (Figure R4a). Across all tested conditions,\nthe LHEC-assisted surface consistently maintained a lower temperature than the bare surface\n(Figure R4b), resulting in an increased temperature difference with the evaporator and higher\nfreshwater output (Figure R4c–d). These results confirm that the LHEC cooling effect is not\nfixed at a specific temperature but instead responds dynamically to environmental variations,\nsupporting its potential for year-round operation.\nFigure R4 has been updated into the revised Supporting Information as Figure S27, with a\nproper description.\n6 / 26\nFigure R3 The schematic diagram of solar distillation setup cooling by air convection (a) and LHEC\nstrategy (b). c, The calculated heat dissipation flux comparison between air convection and LHEC\nunder different surface temperature. d, The measured condensation surface temperature of glass\nsurface cooling by air convection and LHEC surface under certain heat dissipation flux. e, The\ncomparison of measured heat dissipation flux in solar distillation setup cooling by air convection\nand LHEC, respectively. f, The measured temperatures of solar vapor and condensation surface\ncooling by air convection and LHEC strategy, respectively.\n7 / 26\nFigure R4 a, Photograph of solar distillation setup operation in temperature- and humidity-\ncontrolled chamber. b, Condensation surface temperature comparison between original setup and\nLHEC assisted setup under different temperature and humidity. c, The solar water production\ncomparison between setup with and without LHEC under different temperature and humidity. d,\nThe solar water production improvement by LHEC under different temperature and humidity.\nQ4 Following the previous comment, seawater cooling to enhance condensation could be a\nlow-cost and much more effective way.\nResponse: Thank you for your comment. We would first like to clarify what the “seawater\ncooling” strategy you meant. Based on our understanding, there are two possible approach\nstrategies that utilize seawater to enhance condensation, and we would like to respond\naccordingly.\nOne possible approach involves the active circulation of seawater to the condenser surface\nusing pumps or fluidic systems. While this can enhance heat transfer, this approach would\ninevitably require additional energy input and the continuous operation of electrically driven\ndevices, which increases both the operational cost and system complexity (Figure R5a).\nAnother passive approach relies on metallic materials to conduct condensation heat into the\nseawater, with configurations generally categorized as inverted (Figure R5b) or upright (Figure\nR5c) structures. In inverted systems, metal plates or containers dissipate heat downward into\n8 / 26\nthe seawater reservoir. However, published results [e.g., Desalination 2022 544, 116132\n(ref.23); Appl. Therm. Eng. 2022, 201, 117834 (ref.24)] show that their solar water production\nefficiency remains lower than that achieved in our LHEC-assisted demo setup (see Figure R5d).\nUpright configurations using heat pipes can achieve comparable or higher efficiencies [J. Mater.\nChem. A 2022,10, 11784-11792 (ref 25)], but they require more sophisticated assembly and\ncome at a significantly higher cost (e.g., $616 m−2), compared to our LHEC substrate ($0.41\nm−2). Additionally, metal-based systems are considerably heavier (~35 kg m−2 vs. ~0.32 kg m−2\nfor LHEC), reducing their suitability for portable or modular applications (Figure 6a). In\naddition, the upright structure is highly susceptible to solar irradiation, as it directly exposed to\nsunlight. Metal condensers tend to absorb significant amounts of sunlight [Sol. Energy 1984,\n32, 211-222], and the parasitic heat generated under direct sunlight is detrimental to the\ncondensation process (Figure R6b). More importantly, metal based coolers are prone to\ncorrosion in high-salinity seawater, and their use requires strict sealing during assembly to\nprevent seawater intrusion [J. Mater. Sci. Technol. 2022, 112, 230-238; Corrosion 2003, 59,\n1112-1119]. These limitations have already been discussed in our introduction to highlight why\nmetal-based seawater cooling, despite its potential, poses challenges for low-cost, scalable\ndeployment.\nFinally, we would like to clarify that the two cooling strategies are not mutually exclusive or\niterative. As demonstrated in three-state distillation setup (Figure R6c and d), both cooling\nmethods can be used simultaneously, ultimately enhancing the condensation performance\ntogether (Figure R6e).\nWe sincerely hope these clarifications can address your concerns and explain why we chose to\nfocus on the LHEC strategy. Our aim is to offer a passive, broadly applicable cooling solution\nthat balances performance with simplicity, cost and compatibility across diverse solar\ndistillation systems.\n9 / 26\nFigure R5 Schematic diagram of the active seawater cooling solar distillation setup, in which\nseawater is delivered to the condenser glass surface by water pump to reduce its temperature.\nSchematic diagram of passive seawater cooling solar distillation setup with inversed structure (a)\nand upright structure (b) cooling by seawater. c, Solar water production efficiency comparison\nbetween solar distillation setups cooling by seawater and LHEC.\n10 / 26\nFigure R6 a, Comparison of components, estimated materials cost and portability comparison\nbetween LHEC substrate and water metal cooler in ref. 25. b, Schematic showing solar parasitic\nheat generation and metal corrosion on water metal cooler when applied for solar distillation.\nPhotograph (c) and schematic (d) showing three-stage distillation setup cooling by bulk water and\nLHEC synergistically. e, freshwater water generation improvement by LHEC application compared\nto three-stage distillation setup solely cooling by bulk water.\n11 / 26\nReviewer #2 (Remarks to the Author):\nThe revised manuscript by Guo et al. has been significantly improved and their level of effort\nin this revised version should be commended. Almost all my concerns have been addressed by\ntheir revised manuscript. However, there are a few more problems that should be addressed\nbefore the manuscript can be considered for publication. I want to especially emphasize my\nconcerns with Point 1 especially below.\nResponse: We sincerely thank you for your recognition of the improvements made in our revised\nmanuscript. We also deeply appreciate your constructive feedback, which has been instrumental in\nfurther enhancing the quality of our work. We have carefully addressed your remaining concerns as\ndetailed in the point-by-point response below as well as the revised manuscript.\nQ1 Point 1, The solar vapor-to-water efficiency is defined as Jprod/J_evap from the authors’\nmanuscript and it is highlighted as a key metric in their paper. In the authors’ response to my\ncomments from the original Q6, they have written the similar equation.\nJ=k(C_s(T)-C_a)\nWhere k describes the convective mass transfer coefficient, C_s is the saturated vapor\nconcentration in kg/m3 at temperature T, and C_a is the vapor concentration in the environment.\nk is related to the Sherwood number Sh through\nk=ShD/L\nWhere D is the diffusion coefficient of vapor in air and L is the characteristic length scale of\nthe evaporation configuration. We can rewrite the previous equation as\nJ_evap=k(C_s(T_E )-RH*C_s(T_amb))\nWhere T_E is the evaporator surface temperature, T_amb is the ambient temperature, and RH\nis the relative humidity. This is similar to the equation the authors wrote in page 2. Transport\nfrom the evaporator to the condenser inside of the solar still will follow\nJ_prod=k'(C_s(T_E )-C_s(T_C ))\nWhere T_C is the condenser temperature and k’ is the convective mass transfer coefficient\ninside of the still. What this means then is that the solar vapor-to-water efficiency just describes\nJ_prod/J_evap =(k'(C_s(T_E)-C_s (T_C)))/(k(C_s(T_E )-RH*C_s(T_amb)))\nThe convective mass transfer coefficients for k and k’ will not deviate significantly from each\nother because both are in natural convective conditions with similar operating temperature. The\nsample temperature T_E may deviate a little bit as well. However, both the variations in k and\nT_E will be small (for a given solar intensity) relative to the possible variation in the laboratory\nRH. As a result, this metric primarily<\b> reflects how similar your condenser’s vapor\npressure inside of the solar still is with your laboratory ambient vapor pressure. The condenser\ntemperature (T_C) will be lower with the LHEC, leading C_s(T_C) to approach\nRH*C_s(T_amb). This metric is not meaningful because the second boundary condition for\n12 / 26\nJ_evap in open laboratory conditions is completely independent of the solar still performance,\nwhich will always have an internal humidity close to 100% RH at steady state. Experimentalists\nwho test their evaporation rates in drier laboratory conditions will be arbitrarily penalized based\non this metric. Furthermore in a solar still, the evaporator and condenser temperatures are\ninherently coupled if the rigorous control volume analysis is conducted and the authors’\ndescriptions of a mismatch between evaporation and condensation performance is incorrectly\nattributed in the main text.<\b>\nA similar but more meaningful metric could be to measure the evaporation rate of water inside\nof the solar still and compare it with the liquid water produced at the condenser as vapor leakage\nout of the device is a common loss in systems. However, I will strongly reiterate<\b> that the\ncurrent metric is not useful especially if it is being highlighted as a key metric in the abstract.\nThe new figure R14b for natural wood, ppy/wood, and AgNPS/PPy/wood does not support the\nusefulness of the metric. The authors should use more meaningful metrics such as the solar to\nwater production efficiency described in both Reviewer 1’s and my comments from the\nprevious round and remove references to the solar vapor-to-water efficiency. I strongly re-\nemphasize<\b> the improvement in water production efficiency due to the addition of the\nLHEC in the solar still has enough merit to stand on its own. I strongly urge<\b> against\ncreating this new arbitrary metric when existing and meaningful metrics are more representative\nof their device performance.\nResponse: We sincerely thank you for your thorough and insightful analysis of the solar vapor-\nto-water efficiency metric. Your detailed critique of the proposed metric and the mass transfer\nprocesses involved in solar still systems have been very helpful. We greatly appreciate the time\nand effort you invested in providing such comprehensive feedback.\nAfter careful consideration, we fully agree with your assessment. Following your and Reviewer\n#1’s suggestions, we have removed the \"solar vapor-to-water efficiency\" metric throughout the\nmanuscript and adopted \"solar water production efficiency\" (based on latent heat of\ncondensation vs. solar input) as the primary evaluation parameter. Accordingly, we changed the\ny-axis label of Figure 4g to “solar water production efficiency”, which has been shown as\nFigure R7 below. The description in the revised manuscript has also been updated, as shown\nbelow.\n“To reveal the contribution of LHEC to energy conversion, we calculated the solar water\nproduction efficiency, which is defined as η =(J ×H )/I , where J denotes the\nsolar-water prod cond solar prod\nwater generation rate (kg m−2 s−1), H is the enthalpy of vapor condensation (J kg−1), and I\ncond solar\nis the solar irradiation intensity input (W m−2) . Without LHEC, the water production efficiency\nremained around 45%, which is comparable to the performance of conventional systems57,58. In\ncontrast, the LHEC-assisted setup achieved efficiencies of up to 76% under 1.4 kW m−2,\npromoting the conversion of solar energy into clean freshwater (Fig. 4g). Notably, efficiency\nof the LHEC-assisted setup increased gradually with higher solar intensities, which can be\nattributed to the increasingly heat dissipation benefits of the evaporation cooling mechanism as\nthe heat load increases (Fig. 1d and 3d).”\n13 / 26\nFigure R7. Comparison of solar water production efficiency in solar distillation setup with and\nwithout LHEC assistance.\nQ2 Point 6, The transport of vapor molecules is through both convection and diffusion, not\njust diffusion as the authors have written. The boundary layer thickness delta comes from the\nbalance between the two due to the Sherwood number dependence. In fact, the Sherwood\nnumber is defined as the improvement in mass transfer rate due to convection and diffusion\nwhen compared to pure diffusion. The authors should rewrite this section to better reflect this.\nThe author should also write the equation as a general convective mass transfer coefficient\nthrough the Sherwood relationship rather than expressing it as D/delta due to the transport not\nonly occurring through diffusion.\nResponse: We sincerely thank you for your insightful suggestion. We apologize for not clearly\nreflecting the influence of convection in our previous calculations. Actually, in our earlier\ncalculation of the Sherwood number, we had considered natural convection with a heat transfer\ncoefficient (h =10 m s−1) under environmental conditions. According to your comments, to\nc\nbetter reflect that, we have now revised the mass transfer coefficient (k ) to explicitly account\nL\nfor both convection and diffusion. Additionally, based on the calculated Sherwood number,\nwe have provided the mass transfer coefficient (k ) values under different environmental conditions\nL\nin calculations.\nThe revised water vapor mass flux is now expressed as follows:\nwhere (m s−1) is the mass tra∆n𝑚𝑚sf=er 𝑘𝑘c𝐿𝐿o×eff(i𝐶𝐶c𝑠𝑠ie−nt𝐶𝐶 𝑎𝑎th)at includes both convection and\ndiffusion effects, is the vapor concentration difference (kg m−3) between\n𝒌𝒌𝑳𝑳\nsaturation vapor concentration in LHEC surface ( ) and the actual vapor concentration in\n𝛥𝛥𝐶𝐶 = 𝐶𝐶𝑠𝑠 −𝐶𝐶𝑎𝑎\nenvironment ( ).\n𝐶𝐶𝑠𝑠\nThe vapor con𝐶𝐶c𝑎𝑎entration difference ( ) can be calculated as\n𝛥𝛥𝐶𝐶\n𝑀𝑀𝑤𝑤 𝑃𝑃𝑠𝑠(𝑇𝑇) 𝑃𝑃𝑠𝑠(𝑇𝑇𝑎𝑎𝑎𝑎𝑎𝑎)\n𝛥𝛥𝐶𝐶 = 𝐶𝐶𝑠𝑠 −𝐶𝐶𝑎𝑎 = ( −𝑅𝑅𝑅𝑅 )\n𝑅𝑅 𝑇𝑇 𝑇𝑇𝑎𝑎𝑎𝑎𝑎𝑎\n14 / 26\nwhere (g mol−1) is the molar mass of water, R (J mol−1 K−1) is the universal gas constant,\nT (K) and T (K) are the temperature of LHEC surface and ambient, respectively. P (Pa) is the\n𝑀𝑀𝑤𝑤atm s\nsaturation vapor pressure, and RH is the air relative humidity (50%). The vapor pressure P\ns\n(Pa) is computed using the Clausius-Clapeyron relation as:\n𝑅𝑅𝑒𝑒𝑒𝑒𝑎𝑎𝑒𝑒𝑀𝑀𝑤𝑤 1 1\n𝑃𝑃𝑆𝑆(𝑇𝑇) = 611exp ( ( − ))\nThe mass transfer coefficient ( ) was is derived f𝑅𝑅rom th2e 7S3herw𝑇𝑇ood number ( ) as follows:\n𝑘𝑘𝐿𝐿 𝑆𝑆ℎ𝐿𝐿\n𝑆𝑆ℎ𝐿𝐿 ×𝐷𝐷\n𝑘𝑘𝐿𝐿 =\nwhere D (m2 s−1) is the vapor diffusion coefficien𝐿𝐿t in ambient air, is the characteristic length\nof the LHEC surface (m). Here, we assume the LHEC surface is a vertical plane (0.05 m × 0.05\n𝐿𝐿\nm).\nThe vapor diffusion coefficient (D) can be parameterized based on ambient temperature as\nfollow:\n−7 −5\nThe calculation of Sherw𝐷𝐷oo=d (n1u.m49be×r 1is0 jo)in𝑇𝑇𝑎𝑎tl𝑎𝑎y𝑎𝑎 d−et1er.9m6in×ed1 0by diffusion and convection\nprocesses, based on the Rayleigh number ( ). Here, we assume that LHEC operates under\nnatural convection conditions from a vertical plate, with the convective heat transfer coefficient\n𝑅𝑅𝑅𝑅𝑎𝑎\n(h =10 W m−2 K−1). Accordingly, Sherwood number can be estimated by [Bejan, A. Convection\nc\nheat transfer. 2013, John Wiley & Sons]:\n1\n4\n𝑆𝑆ℎ𝐿𝐿 = 0.6×(𝑅𝑅𝑅𝑅𝑎𝑎)\nwhere is the mass transfer Rayleigh number, which can be calculated as:\n𝑅𝑅𝑅𝑅𝑎𝑎\n3\n𝑔𝑔𝑔𝑔𝛥𝛥𝐶𝐶𝐿𝐿\n𝑅𝑅𝑅𝑅𝑎𝑎 =\nin which denotes the gravity acceleration (m s− 𝑣𝑣 2)𝐷𝐷, is the volumetric expansion coefficient\nfor mass transfer (m3 kg−1), approximated as , where is the air density. is the\n𝑔𝑔 𝑔𝑔\nkinematic viscosity of ambient air (m2 s−1), is th−e 1molecular diffusion coefficient of water\n𝜌𝜌𝑎𝑎𝑎𝑎𝑎𝑎 𝜌𝜌𝑎𝑎𝑎𝑎𝑎𝑎 𝑣𝑣\nvapor in ambient air (m2 s−1). Accordingly, the mass transfer coefficient ( ) is calculated\n𝐷𝐷\nto be 0.004593, 0.005167, 0.005637, 0.006049, and 0.006527 m s−1, corresponding to\n𝒌𝒌𝑳𝑳\nambient temperatures of 30, 35, 40, 45, and 50°C, respectively.\nWe have incorporated the revised calculation process and the mass transfer coefficient values\n(k ) into Note S1 of revised Supporting Information. The modified formulation emphasizes that\nL\nthe transport of water vapor through both convection and diffusion. We believe this improved\ntreatment will enhances the rigor of the calculation process, and we thank you again for your\nsuggestion.\n15 / 26\nQ3 Point 7, I would like to first thank the authors for the commendable efforts on building\nthe larger solar still to illustrate the scalability of the device as this is an endeavor. I am satisfied\nwith the main results of their work. However, there are some smaller details that need to be\npointed out and potentially corrected.\n1. I agree that the initial rise in freshwater yield to reach vapor saturation will cause the water\nproduction to decrease and in fact this is a general challenge with scaling solar still devices for\nreal world deployment.\n2. However, it is incorrect to say that the increased vapor transport path does not impact\nsubsequent distillation performance. In fact, the authors correctly pointed out that the increased\nvapor boundary layer will lead to a reduction in performance, which is consistent with this\nviewpoint. It is well appreciated that internal natural convection velocities decrease with\nincreased system size (refer to Adrian Bejan’s Convection Heat Transfer textbook for an\nauthoritative description on this). This translates to slower vapor transport and will lead to a\ndecrease in steady state performance as seen from the lower production rates with the larger\nstill when compared to the smaller device.\n3. Regardless of bullet points 1 and 2, the authors have successfully shown that the LHEC\nmechanism scales favorably in terms of improving the water production rates in larger devices,\nwhich will add strong support for their paper.\n4. I don’t think the aluminum foil is an effective design choice. For the top half condensation\nthat is covered by the aluminum foil, the heat can either travel in parallel through\nconvection/radiation into the ambient environment or through conduction through the\naluminum foil to the LHEC. The resistances are roughly (I am using estimates on the\ndimensions of the device)\nR_env ~ 1/(wH*(h_conv+h_rad)) ~ 1/((35 cm)*(17.5 cm)*(10+5)) ~ 1 K/W\nR_cond ~ (H/2)/(wt*k_alum) ~ (8.75 cm)/((35 cm)*(100 um)*(237)) ~ 10 K/W\nThis analysis shows that the heat rejected is primarily directly to the environment through\nconvection and radiation and not by conduction to the LHEC through the aluminum due to the\norder of magnitude difference. The authors can do their own in-depth analysis to clarify if the\naluminum foil does anything as mine is just an order of magnitude simple estimate. Otherwise,\nthey should qualify their statement in Note S8 on the limits of the height scalability of the\nLHEC device. It is also important to note that the temperature reading of the aluminum foil\nthrough IR camera is not accurate because aluminum foils are generally highly reflective in the\nrelevant IR spectrum.\nResponse: We sincerely thank you for your positive evaluation of our efforts to demonstrate\nthe scalability of the system, and for your recognition that the LHEC mechanism maintains its\nenhancement effect even in larger devices. This acknowledgment is very much appreciated.\nWe agree with your viewpoint that larger sizes not only extend the time required for the vapor\nto reach saturation, but also reduce internal natural convection, which slows the transfer of solar\nvapor from the evaporation surface to the condensation surface. In this section, we have revised\nthe explanation accordingly, adding the reduction in internal convection as a key factor\n16 / 26\ncontributing to the lower performance of larger devices.\nRegarding point 4 on the aluminium foil, we are grateful for your clear thermal resistance\nestimation. Your analysis shows that the thermal resistance associated with conduction through\nthe current thin (100 µm) aluminium layer is significantly higher than that for heat rejection to\nthe ambient via convection and radiation. We agree that under the present configuration, the\ncontribution of the aluminium foil to lateral heat transfer is limited. Nevertheless, we believe\nthis does not represent a fundamental design constraint. As you rightly pointed out, increasing\nthe thickness of the conductive layer could meaningfully reduce its thermal resistance and allow\nmore efficient lateral heat redistribution. Preliminary calculations on increasing the aluminium\nthickness to approximately 1 mm indicate that the thermal resistance could become comparable\nto that of environmental dissipation, which would facilitate improved coupling between the\ncondensation zones.\nWe have revised the discussion in Note S8 to reflect these insights. The updated text clarifies\nthe limitations observed in the current system and outlines future directions to address them,\nincluding improving internal convection and enhancing cross-sectional conduction through\nredesign of the condenser materials, as shown below.\n“This is attributed to the higher thermal resistance of the acrylic cover and increased vapor\ntransport path present in larger geometries. The increased vapor transport path leads to a thicker\nvapor boundary layer, which suppresses internal convection and weakens the transfer of vapor\nfrom the evaporation surface to the condensation surface. Furthermore, thermal resistance\ncalculations indicate that the 100 µm aluminum foil provided limited support for heat transfer\nfrom the LHEC to the non-LHEC region. Increasing the thickness, for example to ~1 mm, could\nsubstantially improve the heat transfer performance and achieve a more comparable level of\nheat dissipation from the LHEC to the non-LHEC region.”\nWe also acknowledge your comment regarding the limitations of using infrared thermography\nto measure the surface temperature of reflective materials like aluminium. We have added a\nnote in the revised Supporting Information to caution against over-interpreting the thermal\nimages of the aluminium-covered section, and have re-expressed the associated claims with\nmore appropriate qualifiers, as shown below.\n“Infrared thermal imaging confirmed that the LHEC substrate applied region maintained a\nlower surface temperature than the bare acrylic region, which is favorable for improved\ncondensation”\nThank you again for your constructive suggestions, which have helped us refine both the\ninterpretation and presentation of our scale-up experiments.\nQ4 Point 8, I still have general doubts about the comparisons grade, although it is an\nimprovement from before. My general comment is that the authors should tone down their\nclaims about how much better the LHEC substrate and there is a general lack of citations on\nhow they arrived at each number.\n1. My concerns about solar vapor to water efficiency is already outlined in Point 1. Furthermore,\n17 / 26\nan apples-to-apples comparison requires the same solar still device configuration and testing\nthe difference by just replacing the cooling strategy. I don’t have any doubt that the LHEC is\nprobably better in water production efficiency (latent heat of evaporation vs solar energy input),\nbut the authors should not use the solar vapor to water efficiency. If the authors want to rely on\na literature review, they should really include a range of studies with similar configurations and\nadded citations.\n2. I don’t necessarily agree that the LHEC substrate will be large-equipment free in\nmanufacturing when you are considering scaled up manufacturing at a large scale. (The\nmanufacturing will require a way to efficiently distribute heat on a large scale (their method\nuses 90 oC), a significant volume of acidic solutions to be dispensed, and subsequent washing.\nI think claiming it as a Grade 4 is too optimistic given their grading.\n3. Why would the LHEC be recyclable? Aluminum is one of the most recycled materials in the\nworld and I doubt that delignified wood can reach the same level. Again, based on their grading\nscale, it should really be lower than aluminum fins.\n4. Again there are not citations for how these costs are arrived at.\n5. These values seem possible, but again the authors should show how they arrive at these\nnumbers.\nResponse: We sincerely thank you for the constructive suggestions. Your comments helped us\nreflect carefully on how to present comparative performance more rigorously and objectively.\nIn response, we have made several revisions and would like to clarify the following points:\nFirst, regarding the radar chart and the associated “grade” classification in our original\nmanuscript: we fully understand your concerns. At present, there is no widely accepted or\nstandardized definition for how such grades should be assigned in the context of solar\ndistillation systems. Different studies have adopted various grading criteria based on differing\nunderstandings of cost, scalability, recyclability, and performance, which leads to substantial\ninconsistency in interpretation across the field. As a result, such radar diagrams are typically\nused in the literature for general, symbolic illustration of a material or method’s potential rather\nthan for strict quantitative comparison. Our original intent was to qualitatively demonstrate the\ncomprehensive performance of the LHEC strategy across multiple dimensions, not to claim\nabsolute superiority based on precise scoring.\nHowever, we agree that without a clear and unified grading framework, the figure may be prone\nto misinterpretation and, more importantly, does not directly impact the core findings of our\nwork. After careful consideration, we have decided to remove the radar chart (previous Figure\n5j or Figure R8) from the revised manuscript. The relevant textual content has been updated\naccordingly to avoid any overstatement.\nRegarding the specific indicators used in the comparison:\n1. Solar water production efficiency has replaced the “solar vapor-to-water efficiency”\nthroughout the manuscript. The data sources of the solar water production efficiency are as\nfollows: a, LHEC data comes directly from this work. b, Air metal cooler data also comes\nfrom our own experiments, where we replaced the LHEC substrate with a finned aluminum\n18 / 26\ncooler as shown in Table R1. c, Radiative cooler data comes from previously published\npapers [Desalination 2025, 593, 118241] [Mater. Today Energy 2022, 28, 101072] [Appl.\nEnergy 2024, 355, 122254]. d, Water metal cooler data is taken from our previous work [J.\nMater. Chem. A 2022,10, 11784-11792]. However, this literature related to radiative\ncoolers does not provide information on their condensation area or details of the radiative\nmaterials. Therefore, we have selected another study [Proc Natl Acad Sci U S A 2021, 118,\n2019292118], which also investigates radiative cooling aiding steam condensation, for\ncomparison. The respective models and key relevant parameters are summarized in Table\nR1 for comparison.\n2. Manufacturing scalability: We acknowledge that the delignification process requires\nelevated temperature and acid treatment, which may involve heating and washing\nequipment at large scale. Therefore, we no longer describe the LHEC fabrication as free\nfrom large-scale equipment, and the relevant description has been adjusted.\n3. Recyclability: Although prior studies have reported delignified wood as biodegradable or\nreusable under certain conditions [e.g., Nat. Sustainability 2022, 5, 628], we agree that for\naquatic applications, such recyclability is limited. In contrast, aluminium is well-known for\nits mature and high-efficiency recycling process. We have corrected the comparison to\nreflect this point.\n4. Cost and weight: The LHEC cost was calculated based on raw material and chemical\nconsumption used in this work. The values for other cooling materials are estimated from\nmaterial unit prices in the Chinese market, combined with the reported device designs.\nWeight and density data were measured directly or estimated based on material properties\nand geometries in Table R1.\nIn summary, we have retained Tables S1 and S2 (incorporated as Table S4 and S5 of the revised\nmanuscript) to provide transparent and source-supported comparison, while removing the radar\nchart to avoid any misleading interpretation. These changes ensure that our conclusions are\nsupported by verifiable data and that the discussion remains focused on the actual contribution\nof the LHEC strategy. Importantly, we would like to emphasize that this figure removal does\nnot affect the overall findings or the significance of our work.\nThe relevant statement in the revised manuscript now reads:\n“…the wood-based LHEC strategy demonstrates comparable solar water production efficiency,\nenvironmental friendliness, low cost and portability (Table S4-5).”\nWe appreciate your helpful feedback and believe that these revisions have further improved the\nrigour and clarity of our work.\n19 / 26\nTable R1 Comparison of representative materials and key parameters for different cooling\nstrategies.\nTable R2 The comparison of different cooling strategy\n20 / 26\nFigure R8. Evaluation of the delignified wood based LHEC strategy against other reported\ncondensation techniques.\nQ5 Point 10, Their COMSOL simulation is potentially not coupled correctly in its current form.\nTheir governing equations are fine, but they modeled the evaporation rate and condensation\nrate using convective mass transfer coefficients K for boundary 5. Like how they didn’t\nexplicitly model convective heat transfer coefficients at the boundaries and included its effects\nimplicitly through the coupling between Navier-Stokes and the heat transfer equations, the mass\ntransfer coefficients should also naturally arise from the coupling between Navier-Stokes and\nthe vapor transfer equations. I have two different suggestions here and the authors can decide\nwhich one makes more sense:\n1. The authors should extract the effective heat transfer coefficient, h, from internal natural\nconvection based on their current simulation. They should then report their chosen value of K\nin the simulations. Using the heat and mass transfer analogies (which are covered in their\nreferenced textbooks), they should illustrate that the simplified K is a possible value. The\ncorrect convective conditions transport equations for heat and mass transfer using these\ngeneralized convective conditions really should be (T_Evap – T_Cond) and (c_sat(T_Evap) –\nc_sat(T_cond)) respectively as these boundaries are what drive the natural convection inside of\nthe device. The authors should clarify if Boundary 5’s c_v in their written equation in Table R3\nis coupled to the correct surface based on this. Since the simulation is only a supporting piece\nof evidence rather than the main objective of this work, this can be sufficient if the chosen\nvalues are reasonable.\n2. Alternatively, the authors can redo the simulations and don’t explicitly set K. Instead, let the\nnatural couplings between Navier-Stokes and the vapor transport equation determine the rate\nof condensation, which would be more correct. The authors can even extract the effective K’s\nthis way as a numerical supporting piece of evidence in their work.\nResponse: We sincerely appreciate your continued response and the valuable suggestions you\nprovided to address this issue. We agree that the value of convective mass transfer coefficients\n(K) was not sufficiently clarified in our original description. Following your first suggestion,\nwe aimed to verify the reasonableness of our chosen K value through regression analysis.\nFirstly, we clarified that the value of K is set as 0.005 m s−1, which is consistent with previously\nreported literature describing the water evaporation and condensation process under closed and\nnatural convection conditions [Sol. Energy 1996, 57, 459-464], [Int. J. Heat Mass Transfer 1997,\n40, 2963-2973], and the subsequent simulations were conducted under this parameter.\nSubsequently, we extracted the convective heat transfer coefficient (h ) from the current\neff\nsimulation, as shown below.\n𝑞𝑞\nℎeff =\n𝑇𝑇𝐸𝐸𝑒𝑒𝑎𝑎𝑒𝑒 −𝑇𝑇𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶\nwhere denotes the average heat flux on condensation surface. and are average\ntemper𝑞𝑞ature of evaporation and condensation surface, respec𝑇𝑇tiv𝐸𝐸𝑒𝑒e𝑎𝑎ly𝑒𝑒. Bas𝑇𝑇e𝐶𝐶d𝐶𝐶 𝐶𝐶o𝐶𝐶n the above\nequation, the effective heat transfer coefficients (h ) obtained under solar intensities of 800,\neff\n1000, 1200, and 1400 W m−2 were 6.89, 7.23, 7.58, and 7.94 W m−2 K−1, respectively, in the\nbare setup. In contrast, the LHEC-assisted setup exhibited higher values of 7.70, 8.08, 8.53, and\n8.91 W m−2 K−1 under the same irradiance conditions.\nThereafter, the obtained heat transfer coefficients were incorporated into the heat–mass transfer\nanalogy (Chilton–Colburn/Lewis correlation) to determine the regressed K’ value, as shown\nbelow [Appl. Therm. Eng. 2013, 50, 422-428]:\n1\n′ 𝐷𝐷 𝑆𝑆𝑆𝑆 3\n𝐾𝐾 = ℎeff ( )\nwhere D denotes the water vapor diffusion coef𝑘𝑘ficie𝑃𝑃n𝑃𝑃t, k is thermal conductivity of moist air,\nPr and Sc are Prandtl number and Schmidt number respectively, which can be calculated as\nbelow:\n𝜇𝜇 𝑆𝑆p\n𝑃𝑃𝑃𝑃 =\n𝑘𝑘\n𝜇𝜇\n𝑆𝑆𝑆𝑆 =\nwhere denotes the dynamic viscosity of mois𝜌𝜌t 𝐷𝐷air, is the specific heat capacity, is the\nfluid density. Using the above equation, the calculated K’ values in bare setup were 0.0064,\n𝜇𝜇 𝑆𝑆p 𝜌𝜌\n0.0067, 0.0070 and 0.0073 m s−1 under solar irradiation of 800, 1000, 1200, and 1400 W m−2,\nrespectively. In the LHEC-assisted setup, the corresponding values increased to 0.0071, 0.0075,\n0.0079, and 0.0083 m s−1. These results are in close agreement with the initially prescribed K\nvalue (0.005 m s−1), and fall within the reported range for natural convection in closed systems\n(10−3-10−2 m s−1), thereby confirming the plausibility of our chosen parameter.\nIn addition to verifying the appropriateness of the selected K value, we have also revised the\nboundary conditions for both heat and mass transfer to explicitly adopt the generalized\nconvective driving potentials as shown below:\n∆𝑚𝑚 = 𝐾𝐾𝑀𝑀𝑒𝑒𝑆𝑆sat(𝑇𝑇𝐸𝐸𝑒𝑒𝑎𝑎𝑒𝑒)−𝑆𝑆sat(𝑇𝑇𝐶𝐶 𝐶𝐶𝐶𝐶𝐶𝐶)\n22 / 26\n𝑞𝑞𝑐𝑐𝐶𝐶𝐶𝐶𝑒𝑒 = ℎ 𝑇𝑇𝐸𝐸𝑒𝑒𝑎𝑎𝑒𝑒 −𝑇𝑇𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶\nWhere denotes the saturation vapor concentration at the corresponding surface\ntemperature. Regarding the expression of c , we have revised the notation to avoid ambiguity.\n𝑆𝑆sat(𝑇𝑇) v\nWe now clarify that it explicitly represents the saturation vapor concentration at the condensing\nsurface temperature ( . Thus, Boundary 5 is directly coupled to the condensing\nsurface, in accordance with the generalized convective condition.\n𝑆𝑆sat(𝑇𝑇𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶)\nAbove derivation confirm the reasonableness of our initially prescribed K value. We have\nincorporated the above verification of the K value together with the revised boundary conditions\ninto Note S5 of the revised Supporting Information. We sincerely hope that these clarifications\nand modifications can address your concerns and further strengthen the reliability of our\nsimulation approach. Thank you again for your constructive suggestions.\nQ6 Point 13, The newly cited papers are part of a controversial debate in the community on\ncluster evaporation and reduced latent heat. See [Ducker, W.A., “Decreasing the energy of\nevaporation using interfacial water: is this useful for solar evaporation efficiency?, ACS Omega,\n8(22), 19706-19707, 2023], [Zhang, J.H. et al, “Superthermal solar interfacial evaporation is\nnot due to reduced latent heat of water”, Energy Environ. Sci., 18(4), 1707-1721, 2025], and\n[Lemmens, A.K. et al, “VUV Photoionization Dynamics and Reactivity of Heterogeneous\nWater Clusters”, J. Phys. Chem. A, 2025]. For the evaporation rate to be so high and break\nenergy conservation using single vapor latent heat of evaporation, this must occur through a\ndifferent mechanism from thermal evaporation as being shown by Guo et al’s work here. If the\nauthors insist on using these papers as citations, they need to further qualify this statement\nbecause the evaporation mechanisms are different. Otherwise, I would more strongly suggest\nthat the authors restrict their paper citations to works that don’t violate energy conservation\nbased on single vapor latent heat of evaporation because this is more in line with their\nexperimental work.\nResponse: Thank you for your continued feedback. We have removed Refs. 8-10 and replaced\nthem with other three appropriate references: [Adv. Mater. 2017, 29, 1604031; Adv. Energy\nMater. 2018, 8, 1702884; Nat. Commun. 2022, 13, 849]. These works adhere to energy transfer\nbased on the single vapor latent heat of evaporation, and are more in line with our current work.\nAdditionally, we have also revised the corresponding sentence in the introduction on page 2 to\nreflect this correction, as shown below:\n“…To date, numerous solar-driven interfacial vapor generation strategies have been developed\nto enhance vapor generation rates (J ), with reported values exceeding 1 kg m−2 h−1 8-10.”\nvapor\nQ7 Point 15, This point has been addressed. However, I will re-iterate again that solar vapor-\nto water efficiency is not a meaningful metric as outlined in Point 1. The authors should replace\nthe graph with a water production efficiency metric (latent heat of phase change vs solar energy\ninput) or a different more meaningful metric.\nResponse: Thank you for your continued feedback. As suggested, we have replaced the original\ngraph with a revised comparison based on solar water production efficiency (Figure R9 below).\n23 / 26\nIt shows that, despite the simplicity of our setup, the LHEC-assisted system still ranks among\nthe top-performing state-of-the-art devices, demonstrating the effectiveness of our strategy.\nFigure R9 has been updated as Figure 5h into the revised manuscript on page 22, along with a\nproper description as shown below.\n“The results reveal that despite the simplicity of prototype, the LHEC-assisted system still\nachieves a notable solar water production efficiency, comparable to state-of-the-art devices.”\nFigure R9 Comparison of the solar water production efficiency between the LHEC assisted setup\nand other previously reported works assisted by representative cooling strategies.\nQ8 Minor New Comments, Figure 1a should be diffusion + natural convection, not just\ndiffusion.\nResponse: Thank you very much for your helpful suggestion. As shown in Figure R10, we have\nadded the natural convection in the diagram to provide a more accurate description of the vapor\nmovement in solar distillation setup.\nFigure R10 has been updated as Figure 1a into the revised manuscript on page 17.\nFigure R10 Schematic illustration of the key steps involved in solar-driven freshwater production\nin a closed environment, highlighting the critical role of heat dissipation.\n24 / 26\nReviewer #3 (Remarks to the Author):\nThe authors have revised the manuscript extensively according to reviewer's comments. My\nconcerns about the paper have been addressed. Therefore, I recommend the publication of the\npaper.\nResponse: We sincerely thank you for your acknowledgement of the efforts we conducted,\nas\nwell as the positive assessment and recommendation for publication. We are grateful for the\nconstructive comments and suggestions you provided, which have greatly helped us improve\nthe quality of the manuscript.\n25 / 26\nReviewer #4 (Remarks to the Author):\nI co-reviewed this manuscript with one of the reviewers who provided the listed reports. This\nis part of the Nature Communications initiative to facilitate training in peer review and to\nprovide appropriate recognition for Early Career Researchers who co-review manuscripts.\nResponse: Thank you for your time and effort in co-reviewing our manuscript, and for the\nvaluable feedback provided. We have carefully addressed the comments and hope the revisions\nmeet your expectations.\n26 / 26\nResponses to the reviewers’ comments (Manuscript number NCOMMS-25-15552B)\nChanges in the revised manuscript as a response to the reviewers’ comments are\nhighlighted in red color and clarifications regarding the reviewer’s comments are\nprovided in blue color.\nReviewer #1 (Remarks to the Author):\nThe authors have addressed all my comments. The integration of LHEC substrate with different\nsolar desalination devices and analyses under different ambient conditions provide satisfactory\nresults, The manuscript can be accepted\nResponse: Thank you for your positive assessment and recommendation for acceptance. We\nare grateful for the constructive comments and suggestions provided during your review\nprocess, which have greatly helped us improve the quality of the manuscript.\nReviewer #2 (Remarks to the Author):\nThe newly revised manuscript by Guo et al. is now much more rigorous and thorough. All my\nmajor concerns from the previous round have been fixed. After addressing my additional minor\ncomments below, I think the manuscript will be suitable for publication.\nResponse: Thank you very much for your positive feedback. We have carefully addressed your\nremaining comments as detailed in the point-by-point response below as well as the revised\nmanuscript.\nQ1 On page 3, the authors highlight weather resilient as being a challenge. The LHEC is not\nweather-resilient because it depends on ambient humidity, so this point may not be appropriate\nto highlight\nResponse: Thank you for your kind consideration. We have replaced the term \"weather-resilient\"\nwith a more specific description, emphasizing the challenges associated with heat dissipation under\nhigh ambient temperatures and cloudy conditions. The revised manuscript has been updated\naccordingly, as shown below:\n“…Therefore, it still remains as a challenge to develop a highly efficient, cost-effective and\neasily scalable heat dissipation strategy that can perform effectively under high ambient\ntemperature and cloudy weather conditions.”\nQ2 On page 3, the authors highlight that the LHEC cooling power increases with rising ambient\nsaturated vapor concentration. However, this phrasing isn't very clear because the evaporative\ncooling should be very small if the ambient RH is near 100%. The authors should clarify their\npoint here.\n1 / 3\nResponse: Thank you very much for pointing out this issue. We apologize for the confusion\ncaused by our imprecise wording.\nTo clarify, what we intended to express is that the cooling power of LHEC increases with the\nsaturated vapor concentration corresponding to the ambient temperature (C (T )), rather\nsat amb\nthan the actual ambient vapor concentration at near-saturation. At a given relative humidity, a\nhigher ambient temperature corresponds to a higher saturated vapor concentration at that\ntemperature. This creates a larger vapor concentration gradient between the evaporating surface\nand the ambient air, which provides a stronger driving force for evaporation and enhances the\ncooling power. Accordingly, we have updated the revised manuscript as shown below:\n“…the cooling power of latent heat-assisted evaporative cooling (LHEC) increases with the\nsaturated vapor concentration corresponding to the ambient temperature (C (T )). At a given\nsat amb\nrelative humidity, …”\nQ3 On page 6, the authors highlight the radiative cooling potential of the material. In literature\nthe term \"radiative cooling\" usually refers to heat exchange with space through the atmospheric\nwindow (what the authors called PDRC in their radiative cooling potential and many of the\nLHEC configurations would have a small view factor with the atmosphere. The emissivity of\n0.96 manuscript). However, the author's analysis is more related to its blackbody emissivity\nrather pretty in line with untreated wood, water, and other organic materials as well. The authors\nshould replace radiative cooling phrases and qualify their claims.\nResponse: Thank you for your thoughtful comment and for pointing out the potential ambiguity\nin our terminology. We agree that in the literature “radiative cooling” is most commonly used\nto describe heat dissipation through the atmospheric transparency window (8–13 µm), typically\nwhen the surface temperature is below the ambient temperature [Appl. Phys. Rev. 2019, 6,\n021306].\nTo clarify, our analysis refers to the case where the condensation surface during solar distillation\ngenerally remains slightly above the ambient temperature. In this condition, heat can still be\neffectively dissipated not only through the atmospheric window but also to the surrounding\nenvironment, and thus high emissivity across both the atmospheric window and the broader\nblackbody spectrum is beneficial [Proc. Natl. Acad. Sci. U. S. A. 2021, 118, e2019292118]. The\nLHEC substrate exhibits high emissivity over 3–16 µm, covering both the atmospheric window\nand the blackbody radiation range.\nIn light of your comment, we have revised the manuscript to avoid potential misunderstanding\nby explicitly stating that the observed effect relates to “broadband infrared emissivity” rather\nthan strictly “radiative cooling” in the conventional sense. We have also qualified the\ncorresponding claims to make clear that the term in this context refers to enhanced infrared heat\ndissipation covering both spectral regions. Please refer to the changes below:\n“…It shows that the wood substrate achieves a high emittance of ~0.96 across the LWIR range,\ncovering the atmospheric transparent window (8-13 μm), which confirms its strong radiative\ncooling performance…”\n2 / 3\nQ4 There are a number of typos still in the manuscript, page 5 \"features synergistically to\",\npag3 \"even severe\", and etc. The authors should do a careful read through of the manuscript\nbefore publication.\nResponse: Thank you very much for identifying these errors. We have carefully corrected all\nthe issues you pointed out as shown below.\n“…These multiscale structural features synergistically enhance the substrate’s light scattering\nefficiency…”\n“…metals tend to generate parasitic photothermal heat under direct solar irradiation, leading to\nself-heating and further inhibits heat dissipation, which becomes more severe under hot\nclimates…”\nAdditionally, we have conducted a thorough line-by-line review of the entire manuscript to\nidentify and correct any remaining typos and grammatical errors.\n3 / 3\nResponses to the reviewers’ comments (Manuscript number NCOMMS-25-\n15552C)\nChanges in the revised manuscript as a response to the reviewers’ comments are\nhighlighted in red color and clarifications regarding the reviewer’s comments are\nprovided in blue color.\nReviewer #2 (Remarks to the Author):\nThe authors have addressed my final comments. The manuscript can be accepted in its current\nform.\nResponse: Thank you for your positive assessment and recommendation for acceptance. We\nare grateful for the constructive comments and suggestions provided during your review\nprocess, which have greatly helped us improve the quality of the manuscript.\n1 / 1"}]

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