Femtosecond laser synthesis of multiscale high-entropy alloys/graphene composites for high-performance Joule heating

Domain: chemistry
Published: 2026-03-03
Editorial outcome: major_revision

Abstract
High-entropy alloy nanoparticles (HEA-NPs) have garnered significant interest across diverse fields. However, thus far, research on their applications has predominantly focused on electrocatalysis. Expanding the applications of HEA-NPs beyond current fields is timely and desirable but remains a challenge. Here, we demonstrate the successful femtosecond laser synthesis of HEA-NPs on the laser-induced graphene (LIG) for realizing high-performance Joule heating applications. This prepared composites (HEAs/LIG) exhibits exceptional electrothermal conversion ability with efficiency up to ~285.4°C cm2 W−1. Furthermore, the HEAs/LIG also shows high broadband infrared emissivity of ~0.98 across the wavelength range from 2.5 to 20 μm. Finally, we present the applications of HEAs/LIG as an efficient Joule heater, which consumes ~49.1% less energy compared to conventional electrical heaters in winter. This work expands the application of HEA-NPs into the Joule heating field, and underlining the importance of further development in efficient energy utilization technology.

Introduction
Since the concept of high-entropy alloys (HEAs) was first proposed in 2004, the HEAs have emerged as a frontier in materials science due to their unique properties1–5. The multicomponent solid-solution alloys results in high configurational entropy and synergism among multiple components, which endows HEAs with remarkable mechanical6, thermal7, and chemical properties8,9. Driven by advances in nanotechnology, the preparation of HEA nanoparticles (HEA-NPs) has become convenient. HEA-NPs exhibit unique properties, including elevated specific surface areas, compositional tunability, and pronounced lattice distortions. Tunable electronic structures and abundant active sites render HEA-NPs particularly attractive to be used as a versatile platform10–12. Consequently, HEA-NPs play an essential role in numerous applications including catalysis8,13, batteries14, solar evaporation15,16, and electromagnetic shielding17, among many others (Supplementary Fig. 1). The combination of these structural and functional advantages highlights their potential and nanoscale derivatives in next-generation material applications.

Joule heating applications impose a demanding combination of high broadband infrared (IR) emissivity and high conductivity. To date, most research of HEA-NPs has concentrated on their catalytic activity, with comparatively limited exploration of other functional applications. Leveraging the inherent metallic characteristics, HEA-NPs typically demonstrate good electrical conductivity18,19. For the optical properties, recent studies have indicated that HEA-NPs exhibit strong absorption through d-d interband transitions in the visible range20, while high-entropy oxides (HEOs) can demonstrate both high absorption and IR emissivity21–24. These findings reveal the potential for coupling the conductivity of HEA-NPs with enhanced IR radiative performance, also establishing the foundation for their Joule heating application. However, a high-performance Joule heater based on HEA-NPs is timely and desirable yet difficult to realize due to the demanding higher requirements for HEA-NPs emissivity. Thus, it is attractive to develop an effective approach to synthesize multifunctional HEA-NPs for high-performance Joule heating.

Herein, a solid-phase synthesis method based on femtosecond laser processing is proposed, enabling the successful synthesis of HEA-NPs on laser-induced graphene (LIG). Using LIG as the substrate, the high peak temperature and heating/cooling rates drive the formation of HEA-NPs within nanosecond timescale. Density functional theory (DFT) calculations verify that the mechanism of electrical resistance reduction originates from the HEA-NPs loading and deoxidation renovating effect on LIG. Notably, the multiscale composite material (HEAs/LIG) can serve as Joule heating material, achieving a heater energy efficiency of ~285.4°C cm2 W−1. Besides exceptional electrothermal performance, the HEAs/LIG also exhibits an excellent IR emissivity of ~0.98 across a broad wavelength range of 2.5–20 μm. Therefore, the HEAs/LIG was ~49.1% more energy efficient when used as an electric heater in winter compared to a commercial electric heater (CEH). These findings highlight the strong competitiveness of HEAs-based multifunctional materials for developing high-performance Joule heaters.

Results
Femtosecond laser synthesis
The synthesis process of HEAs/LIG by femtosecond laser is illustrated (Fig. 1a and Supplementary Fig. 2). Based on the suitable mixing enthalpy and atomic radius, Fe, Co, Ni, Cr, Mn, and Ru were chosen as the metallic precursors (Supplementary Tables 1 and 2). According to the calculation, the mixing entropy of FeCoNiCrMnRu HEA-NPs could jump to 1.79R (Supplementary Note 1). We also prepared low-entropy (FeCo) and medium-entropy (FeCoNiCr) that were named as LEAs/LIG and MEAs/LIG, respectively. For the HEA-NPs system, femtosecond laser can break through the thermodynamic energy barrier and prepare FeCoNiCrMnRu HEA-NPs with uniform element distribution (Supplementary Fig. 3). The pristine LIG (P-LIG) substrate exhibited superwetting behavior to the mixed precursor solution, making homogeneous loading of metal ions (Supplementary Figs. 4, 5). The femtosecond laser (~350 fs) was employed in ambient air to prepare HEA-NPs (Supplementary Fig. 6). In this study, P-LIG was selected as the substrate because its super-black offers a high laser absorption of ~98% (Supplementary Figs. 7, 8). The resulting superior photothermal conversion efficiency, coupled with the low specific heat capacity and synthesis time of femtosecond laser prepared HEA-NPs reported in the literature (see Supplementary Table 4 for more details). Moreover, under the transient high-temperature conditions generated by femtosecond laser, the P-LIG layer can act as a micro-reactor that effectively blocks the binding of oxygen and metals, promoting the formation of single-phase HEA-NPs25. The temperature variation was simulated using COMSOL simulations (Fig. 1b and Supplementary Note 2). The simulated temperature-time curve on the surface demonstrated a heating time of 350 fs (one femtosecond laser pulse) to reach up to ~3081 K (Fig. 1c) with a heating rate of ~8.0 × 1015 K s−1. Obviously, the high temperature far exceeded the pyrolysis temperatures of all metal salts, causing all precursors to decompose simultaneously (Supplementary Table 3). Subsequently, rapid alloy phase fixation was achieved with a cooling rate of ~5.6 × 1011 K s−1 to avoid phase separation. The highly localized femtosecond laser pulse could facilitate rapid cooling and help preserve the single-phase random atomic configuration to promote the formation of uniform HEA solid solutions3,9,10. Additionally, the transient high temperature accelerated the nucleation process, restrict further particle growth, and form smaller particles (Supplementary Fig. 10 and Note 3). According to the simulation, the duration within a single femtosecond laser-induced thermal pulse that exceeds the pyrolysis temperatures of all metallic salts, which corresponds to the synthesis time of HEA-NPs, is ~10 ns. In addition, the high temperature only acted on the surface and did not damage the P-LIG substrate (Supplementary Fig. 11). It is noted that the classical heat diffusion model employed here provides an estimate of the extreme thermal cycle but does not capture the initial electron-lattice non-equilibrium. The predicted temperatures and heating/cooling rates should be interpreted as the qualitative conditions of the extreme conditions that facilitate rapid melting and solidification, consistent with the formation of HEA-NPs. While the exact numerical value is determined by the model, the phenomenon of rapid heating/cooling and its consequence is physically reasonable.

Femtosecond laser synthesis presents an effective route for the fabrication of HEA-NPs. This method leverages energy deposition on a femtosecond timescale, enabling the high heating rate and rapid synthesis durations26–31. Compared to previously reported methods for synthesizing HEA-NPs, such as prior laser ablation32–35, carbothermal shock36–41, microwave heating42, flame spray pyrolysis43,44, and flash irradiation45–47, femtosecond laser has made progress in both heating rate and synthesis time (Fig. 1d and Supplementary Table 4). Furthermore, our method realized convenient synthesis of HEA-NPs, benefiting from non-contact processing, precise pattern control, and tunable parameters (Supplementary Table 5)48–50. Notably, compared with other research on the laser heating for HEAs, we successfully achieved the synthesis of multiscale HEAs/LIG and explored the electrical and IR radiation properties, significantly broadening the application of HEA-based materials. The femtosecond laser demonstrates obvious advantages over nanosecond and continuous wave (CW) lasers for the synthesis of HEA-NPs (Supplementary Table 6). Femtosecond laser synthesis enables the formation of significantly smaller HEA-NPs compared to those typically obtained with CW laser51. This is a direct consequence of the high heating and cooling rates, which rapidly freeze the nucleated liquid droplets, effectively suppressing coalescence that leads to coarse and irregular particles under the slower thermal cycles of CW laser. A key practical advantage is the ability to synthesize HEA-NPs directly in ambient atmosphere without requiring liquid environments or chemical reductants. Many nanosecond laser methods or other techniques for producing non-oxide HEA-NPs necessitate such controlled conditions32–35,52–54. The femtosecond laser achieves this through non-equilibrium energy deposition, while the short interaction time minimizes oxidation of HEA-NPs despite being performed in air. Our strategy for achieving high-performance Joule heating incorporated utilizing the high conductivity of HEA-NPs and high emissivity of LIG (Fig. 1e). Stable anchoring of HEA-NPs onto LIG synergistically enhanced the electrothermal conversion performance while retaining the high IR emissivity of LIG substrate. Owing to its excellent Joule heating property, the HEAs/LIG exhibited promising potential for diverse heating applications, such as heaters and de-icing/snow-melting systems (Fig. 1f). Based on the concentration of the FeCoNiCrMnRu precursor solution (0.1 M), the used volume (160 μL) and the coated area (20 mm × 20 mm), we can estimate the mass loading of the FeCoNiCrMnRu HEA-NPs on the LIG to be ~1.5 mg cm⁻2. Therefore, even if Ru was used with considering its cost and supply, its contribution to device-level cost is limited. However, it is also desirable to investigate a wider range of low-cost and abundant elements, such as Cu, Zn, Mo, and Sn, to either replace Ru or further increase the configurational entropy, which is anticipated to correspondingly enhance the electrothermal performance of the HEAs/LIG composite. We also fabricated a HEAs/LIG sample with an active area of 40 mm × 40 mm, and the infrared thermal image of this sample under an applied voltage revealed a highly uniform temperature distribution (Supplementary Fig. 12). This excellent uniformity is achieved by our femtosecond laser direct writing process, which involves point-by-point material transformation followed by a continuous line-scanning strategy. Laser systems with large-field lenses and higher-power lasers will be available for industrial-scale processing. We also evaluated the batch-to-batch reproducibility by measuring the sheet resistance at multiple locations across five independent HEAs/LIG samples fabricated over a span of eight month (Supplementary Fig. 13). The results show a very narrow distribution in sheet resistance (Supplementary Fig. 14). This remarkably low variation displayed the exceptional batch-to-batch reproducibility of our method. The processing time for our method preparing HEAs/LIG samples is directly proportional to the area. This represents a highly efficient and single-step process that simultaneously synthesizes the HEAs/LIG in ambient air. The most promising route for industrial-scale throughput is parallelization, which uses beam shaping with a spatial light modulator (SLM) to create multiple focused spots or a homogeneous flat-top beam, allowing for the parallel writing of multiple lines or large areas in a single pass.

Structural properties and surface chemistry
The HEAs/LIG also exhibited excellent flexibility (Fig. 2a). The first femtosecond laser applied to the PI substrate surface produced fibrous porous micro/nanostructures, which was beneficial for uniformly loading metal precursors (Supplementary Figs. 15, 16). Following the second femtosecond laser, scanning electron microscopy (SEM) images revealed the formation of abundant irregular micrometer-scale protuberances covered with reticulated nanostructures on the HEAs/LIG surface (Fig. 2b and Supplementary Fig. 17). Experimental results demonstrated that as the laser scanning speed increased, the density of protuberances decreased (Supplementary Fig. 18). Instead, ordered and groove-like microstructures emerged. Correspondingly, confocal laser scanning microscopy (CLSM) measurements indicated a higher surface roughness with an arithmetical mean roughness (Sa) of ~21.82 μm and root mean square roughness (Sq) of ~25.72 μm (Fig. 2c and Supplementary Fig. 19). This roughened surface morphology would work to enhance absorption within the IR spectral band.

The Raman spectra exhibited three characteristic D (~1329 cm−1), G (~1559 cm−1), and 2D (~2680 cm−1) peaks of defective graphene (Fig. 2d). The P-LIG possessed abundant defects, which could facilitate interactions with the formed HEA-NPs. Interestingly, micro-Raman spectra of HEA/LIG revealed the coexistence of two distinct forms of graphene. The Raman spectra of the protuberances indicated reduced graphene defects and the presence of metal oxides. In contrast, the spectra at the remaining positions were similar to those of the P-LIG. These finds were verified by the Raman spectra of other locations across different samples surfaces (Supplementary Fig. 20). By calculations, the crystalline sizes (La) of these two sites were ~32.5 nm and ~15.5 nm (Supplementary Note 4 and Supplementary Fig. 21). The LEAs/LIG and MEAs/LIG also exhibited analogous results but with higher defect levels in the graphene relative to the HEAs/LIG (Supplementary Fig. 22). From a perspective of surface chemistry, both energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) results further confirmed the existence of expected metal compositions (Fig. 2e and Supplementary Fig. 23). The deconvolution of O 1s spectra revealed that the second laser scan, while generating HEA-NPs, also resulted in the formation of few metal oxides (Supplementary Fig. 24−28). Meanwhile, a reduction in LIG oxygen defects was observed. This finding was consistent with the above Raman analysis. The X-ray diffraction (XRD) data of LIG displayed a characteristic peak (~26.2°) of the graphene C(002) plane. Differently, the HEAs/LIG had an additional broad peak (~43.1°), proving the (111) plane of a face-centered cubic (FCC) structure and small grain size of HEA-NPs (Fig. 2f). The C(002) peak in the HEAs/LIG sample shifted to a higher angle of ~26.5°, suggesting an enhanced degree of graphitization. The transmission electron microscopy (TEM) images of P-LIG and LIG further showed the typical graphene layer of ~0.34 nm (Supplementary Figs. 29, 30). In contrast, the size distribution of the FeCoNiCrMnRu HEA-NPs mainly ranged from 5 to 30 nm (Fig. 2g and Supplementary Fig. 31). There were few large-sized FeCoNiCrMnRu HEA-NPs with a ~200 nm size (Supplementary Fig. 32). High-resolution TEM (HRTEM) images showed that the FeCoNiCrMnRu HEA-NPs were enveloped by multilayer graphene (Fig. 2h). An interplanar spacing of 0.225 nm for the (111) plane was observed, which corresponded to the (111) plane of FeCoNiCrMnRu HEA-NPs and was in accord with the results obtained from XRD data. It is noteworthy that observed expansion in the (111) interplanar spacing of FeCoNiCrMnRu, compared to its Ru-free counterpart, serves as indirect evidence for the successful incorporation of Ru atoms into the lattice. Owing to the competition of HEA-NPs for the adsorption of oxygen in LIG, a small amount of high-entropy oxide nanoparticles (HEO-NPs) with spinel structure were discovered (Supplementary Fig. 33). The formation of these HEO-NPs originated from the renovation of highly defective LIG by the metallic nanoparticles under the femtosecond laser-induced high-temperature and high-pressure environment. Given that the detection limit of XRD technology for crystalline phases is within the range of 1-5 wt%, the volume fraction of these surface HEOs may be well below this detection threshold. Critically, the HEO-NPs usually exhibited excellent infrared emissivity across a broadband due to efficient electron transitions and enhanced lattice vibration absorption21. Therefore, the transformation ultimately contributed positively to the overall infrared emissivity of the HEAs/LIG composite material. Their presence helps to enhance the overall infrared emissivity of the device, thereby improving the infrared radiation capability and Joule heating performance. The high-angle annular dark-field scanning TEM (HAADF-STEM) and element mappings indicated that the distribution of each metallic element was highly uniform (Fig. 2i, Supplementary Figs. 34, 35). The reason for the lower Mn content compared to other elements might be attributed to the temperature during femtosecond laser treatment exceeding the boiling point of Mn, resulting in partial evaporation. Furthermore, the particle size of the FeCoNiCrMnRu HEA-NPs was found to decrease with increasing laser scanning speed (Supplementary Fig. 36). This trend can be attributed to the reduced interaction time and effective growth time for the nanoparticles at higher scanning speeds, which limits the coalescence.

Electrical properties and electronic structure
We explored the influence of precursors and laser parameter on the sheet resistance. The direct secondary femtosecond laser scanning fabricated laser-induced graphene (S-LIG) exhibited significantly increased sheet resistance (Fig. 3a). In contrast, samples added the metal precursor prior to the secondary laser scanning consistently demonstrated sheet resistance values lower than both P-LIG and S-LIG. Among all alloy nanoparticles/LIG, the HEAs/LIG exhibited the lowest sheet resistance (~51.8 Ω sq−1). The ternary FeCoNiCrMnRu sample also showed a slightly lower sheet resistance compared to both quinary FeCoNiCrRu (~60.2 Ω sq−1) and FeCoNiCrMn (~59.9 Ω sq−1) (Supplementary Figs. 37, 38). Furthermore, as the precursor volume increased, the sheet resistance of HEAs/LIG decreased rapidly (Fig. 3b). Besides the precursor compositions, laser parameters also play a crucial role. Experimental results demonstrated that across all laser parameter sets, samples added with HEA precursor solution showed lower sheet resistance than the non-additive samples. Moreover, reducing both the scanning spacing and speed led to decreased sheet resistance (Fig. 3c, 3d). Narrower spacing or slower speed would increase the overlap of scanning paths, resulting in enhanced thermal accumulation and higher thermal cycling frequency. Therefore, Therefore, in order to avoid damage to the sample, we selected the parameters of 15 μm and 50 mm s−1 for obtaining the HEAs/LIG with the lowest sheet resistance.

Then, we studied the electronic structure of HEAs/LIG using DFT calculations (see more detailed parameter settings in Supplementary Note 5). DFT calculations were conducted to evaluate the effect the interaction between HEA-NPs and LIG, as well as their impacts on conductivity. The high temperature not only produced HEA-NPs but also drove the removal of heteroatoms from LIG. In the presence of metal nanoparticles acting as catalysts, competitive binding to oxygen accelerates the shift of oxygen heteroatoms (Fig. 3e). Calculation results confirmed the binding energies between oxygen and LIG, as well as between oxygen and Fe, Co, Ni, Cr, Mn, Ru metals (Supplementary Figs. 39−44). The metal-oxygen interaction was obviously stronger than LIG-oxygen55, indicating that free oxygen atom was preferentially adsorbed on the metals, which was consistent with Raman and XPS results (Fig. 3f). We further examined how removing oxygen heteroatoms modified the band structures of LIG (Supplementary Fig. 45). In contrast to ideal graphene with zero band gap, the intrinsic defects made the LIG present natural semiconducting behavior (Fig. 3g). The band gap of LIG (~0.46 eV) was narrower than P-LIG (~0.99 eV) (Fig. 3h, i), which significantly reduced the energy required for electron transitions from the valence band to the conduction band. Under excitation by an external electric field, more electrons could be excited to the conduction band, thereby effectively enhancing the conductivity. Both P-LIG and LIG were direct band gap semiconductors, while the LIG possessed notably conduction and valence bands dispersion, leading to a smaller effective mass and enhanced conductivity. While the DFT calculation results indicate that this transformation consumes some HEAs by converting them into HEOs, resulting in a decrease in conductivity. But it also facilitates the renovation of LIG, which concurrently enhanced its overall electrical conductivity. Considering both oxygen-heteroatom removal and the loading of HEA-NPs, we calculated the density of states (DOS) of P-LIG and HEAs/LIG (Fig. 3j and Supplementary Fig. 46). Compared with P-LIG, the HEAs/LIG heterostructure showed increased electronic states near the Fermi level in the spin-up and spin-down states (Figs. 3k, l). The significant change at the Fermi level was mainly attributed to the orbital contributions of various metal (Supplementary Fig. 47)56. DFT results clearly clarified the basic reason for the observed decrease in sheet resistance.

Electrothermal conversion and infrared emissivity
The low sheet resistance of HEAs/LIG endowed it with good electrothermal conversion performance (Supplementary Note 6). Both P-LIG and HEAs/LIG exhibited linear I–V characteristics consistent, with fitted resistances of ~39.7 Ω and ~25.1 Ω (Fig. 4a). At 8 V voltage, the HEAs/LIG could reach ~205.2°C, whereas P-LIG only realized ~146.8°C (Fig. 4b, 4c). Infrared camera images directly showed the equilibrium temperatures at different voltages and the uniform temperature fields of P-LIG and HEAs/LIG surfaces (Supplementary Fig. 48). Moreover, a linear correlation of the equilibrium temperature with the square of voltage for both P-LIG and HEAs/LIG has been found (Supplementary Fig. 49). At a given voltage, the HEAs/LIG responded markedly faster than P-LIG (Fig. 4d). As for the high entropy samples, the FeCoNiCrMnRu showed a performance improvement in equilibrium temperatures at the 8 V voltage compared to both FeCoNiCrRu and FeCoNiCrMn. Specifically, the equilibrium temperatures of the FeCoNiCrMnRu, FeCoNiCrRu, and FeCoNiCrMn were ~204.1°C, ~183.4°C, and ~185.3°C, respectively (Supplementary Figs. 50, 51). The temperature variation of HEAs/LIG was recorded in-time at an interval of 2 V, indicating an excellent temperature response to voltage change (Fig. 4e). Under a constant voltage applied for 20 min, the surface temperature of HEAs/LIG remained nearly unchanged, demonstrating reliable stability and reliability for electric heating (Fig. 4f). Overall, the electrothermal performance of HEAs/LIG composite was highly competitive with other recent reports (Supplementary Fig. 52). We further established the relationship between equilibrium temperature and input power density, and summarized the heater energy efficiency of other advanced electrothermal materials. This comparison was intended to provide a performance standard for our prepared HEAs/LIG within the landscape of reported advanced film and flexible electrothermal devices. It was acknowledged that some of the compared devices were developed for multifunctional applications. Heater energy efficiency can be interpreted as a comparative performance metric, representing the electrical power density required to achieve a specified surface temperature under identical input conditions. As for the HEAs/LIG, the fitting calculation showed a heater energy efficiency of up to ~285.4°C cm2 W−1, indicating superior performance that surpassed most electrothermal materials (Fig. 4g and Supplementary Table 7)57–61. The high heater efficiency of HEAs/LIG represents an objective outcome derived after accounting for both infrared radiation and convective heat transfer. The higher heater efficiency of HEAs/LIG may also be plausibly attributed to the disruption of air convection by their surface structural morphology. The bending stability of HEAs/LIG heater was examined. We performed 200 cycles bending tests and monitored the evolution of its electrothermal performance metrics (Supplementary Fig. 53). The electrothermal response remained unchanged after testing. This exceptional durability under mechanical deformation originated from the synergistic combination of the flexible LIG substrate and the anchored HEA-NPs.

The IR emissivity quantifies the strength of the thermal radiation capacities. To investigate the radiation properties, we measured the IR emission spectra (2.5–20 μm) and emissivity of HEAs/LIG and P-LIG, with low-emissivity aluminum (Al) as a reference (Supplementary Note 7). After loading HEA-NPs, the HEAs/LIG still displayed high average emissivity across the full IR band (Fig. 4h), with the average emissivity calculated as 0.980, whereas the Al exhibited only 0.058 (Supplementary Figs. 54, 55). The infrared emissivity was consistently high across all the FeCoNiCrMnRu, FeCoNiCrRu, and FeCoNiCrMn samples, further indicating that this property is predominantly governed by the LIG carrier rather than the specific HEA composition (Supplementary Fig. 56). Although the spectral distribution of thermal radiation varies with temperature (Wien displacement law), the broadband high emissivity across the entire infrared spectrum of HEAs/LIG samples ensures excellent radiative performance at different applied voltages. The exceptional radiative performance originated from the rougher laser-induced hierarchical microstructures with feature sizes exceeding IR wavelength. These microstructures can promote multi reflections and absorptions of light, which greatly boosted the light-substrates interaction and achieve high emissivity (Fig. 4i). COMSOL optical simulation was adopted to investigate the electric field distribution of P-LIG, HEAs/LIG, and Al at different wavelengths (Supplementary Note 8). The simulation results suggested strong IR absorption of P-LIG and HEAs/LIG, which was consistent with our experimental measurements (Fig. 4j, Supplementary Figs. 57, 58). On a hot stage, both P-LIG and HEAs/LIG showed radiative temperatures closest to the set temperature, while the Al almost only slightly increased (Fig. 4k and Supplementary Fig. 59). Conventional high-entropy materials were usually limited in restricted band and emissivity21. Our HEAs/LIG composites overcame these constraints and outperformed most high emissivity materials, including graphene62–66, high-entropy21,23,24,67,68, and other materials69–74 (Fig. 4l and Supplementary Table 8)23,52,53. Furthermore, the HEAs/LIG samples also showed excellent durability and stability during the air exposure, high humidity, and repeated heating/cooling test. The sheet resistance and surface emissivity of both tested samples almost remained unchanged after stability test (Supplementary Fig. 60). This exceptional oxidation resistance was attributed to the unique core-shell structure formed during our femtosecond laser processing (Supplementary Fig. 61). The formed graphene shell encapsulating the HEA-NPs provides an excellent barrier against oxidation and moisture (Supplementary Fig. 62). The porous and robust LIG substrate firmly anchors the HEA-NPs, preventing their migration and agglomeration under repeated thermal treatment. Contact angle measurements revealed the hydrophobicity of P-LIG and HEAs/LIG with water contact angles of 152.8° and 145.3°, which further expanded their multifunctionality (Supplementary Figs. 63, 64).

High-performance Joule heating
Finally, experiments validated the exceptional radiative heating ability of HEAs/LIG (Fig. 5a, Supplementary Figs. 65−68). Due to the high heater energy efficiency and infrared emissivity, the HEAs/LIG could achieve a higher surface temperature under the same electrical power input. This elevated temperature, coupled with the high emissivity, enables efficient radiative heating of objects. The real-time temperature curves of heated object indicated that HEA/LIG could maintain a steady-state temperature ~11.2°C higher than CEH with the distance of 4 mm and 5 V voltage (Fig. 5b). At different distances, the HEAs/LIG expectedly achieved the highest stable temperature and fastest heating speed, demonstrating superior heating performance (Fig. 5c, Supplementary Figs. 69, 70). This was due to the broadband high IR emissivity and superior electrothermal conversion performance. It was worth noting that the HEAs/LIG heater showed excellent stability during the rapid on/off cycling test (Supplementary Fig. 71). The reliable cycling stability comes from the robust interface between the HEA-NPs and the LIG substrate, as well as the intrinsic high-temperature stability and anti-oxidation properties of the graphene shell-encapsulated HEA-NPs composition. Similarly, HEAs/LIG could be applied to de-icing, snow removal, and warming in cold environments (Fig. 5d). The HEAs/LIG heater realized complete ice melting within 3 min, demonstrating excellent melting efficiency (Fig. 5e, 5f, Supplementary Fig. 72, and Movie 1). Here, RT indicates that the ice melting occurred naturally at room temperature with no heater used. In cold environments, HEAs/LIG heater also enabled energy-efficient personal warming (Fig. 5g). At 5 V voltage, the HEAs/LIG heater could lift the upper surface temperature of the heated object from ~−7.5°C to a human-comfortable level of ~24.0°C, while CEH failed under the same conditions (Fig. 5h and Supplementary Fig. 73). Crucially, the HEAs/LIG required only ~1.17 W to maintain thermal comfort, whereas the CEH demanded ~2.3 W, yielding a notable ~49.1% energy saving (Fig. 5i). Under the tested specific geometric and enclosed conditions (housing model), HEAs/LIG heaters achieved a measurable reduction in the electrical energy consumption required to reach the same target object temperature, thereby demonstrating an energy-saving effect. Energy saving efficiency of HEAs/LIG in winter was further evaluated75,76. The energy savings of provincial capitals in China was given in Fig. 5j. The detailed assumptions, parameters, and methodology of the energy saving calculation could be found in Supplementary Note 9. Using the computational models, we mainly calculated the winter energy savings potential across China. Compared to using CEH, HEAs/LIG heater delivers markedly higher energy saving performance. For example, Harbin can save roughly 1134.99 MJ m−2. The projected energy savings of some Chinese and global cities further prove the potential of HEAs/LIG heater (Fig. 5k). The experimental and complementary simulations prove that the HEAs/LIG heater offers an exceptional pathway toward sustainable thermal management, positioning them as strong candidates for energy-efficient heating technologies.

Methods
Materials and reagents
Polyimide (PI) film with a thickness of 200 μm was supplied by Zhongshan Chenxi Electronics Co., Ltd. (Guangdong, China). Titanium (Ti) substrates with a thickness of 1 mm and aluminum (Al) sheets were bought from Anhui Zhengying Technology Co., Ltd (Anhui, China). The plane model (Fig. 5d) and house model (Supplementary Fig. 73) were purchased from Taobao e-commerce platform. Absolute alcohol, FeCl3·6H2O (>99%), CoCl2·6H2O (>99.9%), NiCl2·6H2O (>99.9%), CrCl3·6H2O (>98%), MnCl2·4H2O (>99%), and RuCl3·xH2O (>98%) were purchased from Shanghai Macklin Biochemical Co., Ltd (Shanghai, China). Contact-angle testing on all materials was performed using deionized water. Commercial electric heaters (CEH) with the size of 20 mm × 20 mm × 2 mm were purchased online. The CEH was covered with Al. Therefore, Al sheets were chosen as a reference to test the infrared (IR) emissivity. The laser-treated Ti substrate was used as the heated object in the radiative thermal transfer experiment (Figs. 5b and 5h). All chemicals were used as received without further purification.

Preparation of P-LIG
Pristine LIG (P-LIG) was prepared using femtosecond laser direct writing technology. The laser beam (pulse width: 350 fs; central wavelength: 1035 nm; repetition rate: 400 kHz) originated from a commercial femtosecond fiber laser (HR-Femto-IR-50-40B, Huaray, China) and was used to perform ablation operations. During the processing, the laser beam was directed onto the PI film surface via a two-mirror galvanometric scanning system (basiCube 10, Scanlab, Germany) equipped with an f-θ lens (focal length 125 mm), thereby achieving laser focusing and scanning along the x-y axis directions. For P-LIG preparation, the laser scanning spacing was set to 15 μm, power to 2.6 W, and scanning speed to 100 mm s−1. The size of the as-prepared sample area was 20 mm × 20 mm.

Precursor loading on P-LIG
In a typical preparation process, various metal chlorides were mixed in absolute alcohol at 0.1 M for each metallic element. The mixed solution was directly dropped onto the P-LIG surface with different volume. Then, the P-LIG with precursor was dried at room temperature.

Preparation of LEAs/LIG, MEAs/LIG, HEAs/LIG, and S-LIG
Then, the P-LIG with precursor were was irradiated by the same laser as mentioned above. The laser synthesis was conducted with a variation of scanning spacing (15, 20, 25, 30, 35, and 40 μm) and scanning speed (50, 70, 90, 110, 130, and 150 mm s−1), and fixed laser power of 2.0 W. Finally, the FeCoNiCrMnRu HEA-NPs loaded on the LIG (HEAs/LIG) were obtained. Similarly, the samples prepared using low-entropy (FeCo) and medium-entropy (FeCoNiCr) mixed precursor solutions were named LEAs/LIG and MEAs/LIG, respectively. Moreover, the high-entropy samples (FeCoNiCrRu and FeCoNiCrMn) were prepared to verify the influence of Ru and configurational entropy on the Joule heating performance. Samples subjected to a second direct writing scan using the femtosecond laser without dispensing the precursor solution are named as secondary processed LIG (S-LIG). Furthermore, the LIG referred to the laser-induced graphene section in the HEAs/LIG composite materials. Unless otherwise specified, the scanning spacing and scanning speed adopted in this work were 15 μm and 50 mm s−1, respectively.

Characterization
The morphology and microstructure of the samples were examined by a field emission scanning electron microscope (FESEM, MIRA3 LMU, TESCAN, Czech Republic) equipped with an energy-dispersive X-ray spectroscopy (EDS, TESCAN, Czech Republic). The 3D surface morphology, cross-sectional profile and surface roughness were characterized by a confocal laser scanning microscope (CLSM, Axio LSM700, Zeiss, Germany). A field-emission transmission electron microscope (FETEM, Tecnai G2 F20 S-TWIN, FEI, America) with EDS was utilized to study the morphology and elemental distribution of the as-prepared samples with an acceleration voltage of 200 kV. The elemental states on the sample surface were analyzed via an X-ray photoelectron spectroscopy (XPS, Thermo Scientific, K-Alpha, America) with a monochromatic Al Kα X-ray radiation. The crystal structure of samples was characterized by an X-ray diffractometer (XRD, XRD-6100, Shimadzu, Japan) with a scanning speed of 1°/min using the Cu Kα radiation (λ=1.54 Å). The Raman spectroscopy was collected with a Invia Qontor Raman Spectrometer (Renishaw, UK) and the excitation wavelength was 532 nm. The reflectance and transmittance spectra were measured by an ultraviolet–visible spectrophotometer (UV-2600, Shimadzu, Japan) equipped with a diffuse integrating sphere. The IR spectra of samples in the range of 2.5–25 μm was measured by a Bruker Vertex 70 Fourier transform infrared (FTIR) spectrometer with an integrating sphere (A562). The emissivity of mid-infrared band (2.5−20 μm) was measured by a Fourier transform infrared spectrometer with a gold integrating sphere (PIKE). The microstructure of samples was observed by a metallurgical microscope (CX40M-T/RT, Ningbo Sunny Instruments Co., Ltd., China). Contact angle and dynamic wetting behavior were recorded using a contact angle goniometer (SDC-200S, Sindin) at ambient temperature. A direct current (DC) power source (SPPS1203D, Shenzhen Kuaiqu Electronics Co., Ltd., China) was applied to performing the electric heating experiments. The surface temperature distribution was investigated using an infrared thermal camera (UTi320E, UNI-T). The temperature data was acquired by a multi-channel temperature collecting system (UT3208, UNIT, China). The temperature change during femtosecond laser irradiation and electric field intensity of sample surfaces were studied using the finite element COMSOL Multiphysics software. Spin-polarized density functional theory (DFT) calculations were performed using the CASTEP module within the Materials Studio platform. All error bars in SD (standard deviation) are obtained by statistically repeating independent identical experimental results at least three times, and data are presented as mean values ± SD.

Thermal radiation measurements
Radiative heating experiments were performed using different samples (including HEAs/LIG, P-LIG, and CEH), with laser-treated Ti as the object to be heated (Supplementary Fig. 66). A DC power supply was used to apply direct current to the electric heater, and the HEAs/LIG side faced the surface of the laser-treated Ti, while the temperature on the back side of the laser-treated Ti was recorded using a multi-channel temperature collecting system (Fig. 5a and Supplementary Fig. 65). The temperature-time curves at different distances between heated object and heater was also measured to obtain heating rates by curve fitting. For Fig. 5e, an ice cube was used as the heated object for radiative melting tests. For Fig. 5g, radiative space-heating tests were conducted in a closed house (house model shown in Supplementary Fig. 73) under an ambient temperature of −7.5°C following the same procedure as Fig. 5a with the back-side temperature of the laser-treated Ti recorded. For Fig. 5i, the steady-state electrical power required for the HEAs/LIG and CEH heaters to heat the object to a comfortable temperature was measured.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "The manuscript reports the femtosecond-laser, in-situ synthesis of FeCoNiCrMnRu high-entropy alloy (HEA) nanoparticles on laser-induced graphene (LIG), forming a multiscale HEA/LIG hybrid for electro-thermal heating and broadband infrared emission. However, several critical elements of the evidence chain are incomplete. I therefore recommend major revision.\n1. Air exposure, high humidity, and repeated heating/cooling can lead to oxidation, migration, or agglomeration of metal nanoparticles, affecting electrical and radiative properties. Stability under these conditions should be substantiated.\n2. The presence of HEO observed by TEM should be quantified. The manuscript should clarify their fraction and discuss their influence on emissivity and conductivity, and thus on the overall device performance.\n3. Where blackbody radiation curves are shown (e.g., Fig. 4h), the corresponding blackbody temperature should be explicitly annotated.\n4. Thermal/optical modeling requires clear disclosure of material constants (e.g., ρ, c_p, k, n, k) and boundary conditions, along with a brief uncertainty/sensitivity discussion.\n5. Given the local nature of femtosecond direct writing, the manuscript should address large-area uniformity, batch-to-batch reproducibility, and practical scalability/throughput considerations.\n6. Bending/adhesion/abrasion durability data are important for flexible device claims and should be presented with clear before/after performance metrics.\n7. If energy-efficiency advantages over commercial heaters are asserted, the underlying assumptions, parameters, and calculation approach should be transparent.\n8. The use of Ru raises questions about cost and supply. A brief discussion of material criticality and potential substitutions would improve the practicality narrative.\n9. A direct comparison between FeCoNiCrMn (high-entropy) and FeCoNiCrMnRu is needed to reveal whether performance gains arise from Ru itself or from marginally higher configurational entropy.\n10. For Joule-heating use cases, rapid on/off cycling stability should be demonstrated, with tracking of sheet resistance, heating metrics, and emissivity over extended cycles.", "reviewer_2": "This manuscript presents the synthesis of high-entropy alloy nanoparticles (HEA-NPs) on laser-induced graphene (LIG) using femtosecond (fs) laser irradiation, aiming to demonstrate enhanced Joule heating performance. However, This reviewer finds several fundamental concerns that undermine the validity and significance of the reported results.\nThe justification for using a femtosecond laser is insufficient. While the authors claim a thermal mechanism for HEA nanoparticle formation, femtosecond lasers are typically associated with non-thermal, \"cold\" ablation processes. The manuscript does not demonstrate clear advantages of fs lasers over more accessible alternatives like nanosecond or CW lasers, raising concerns about the method’s practicality and relevance.\nThe thermal simulation based on the classical heat diffusion equation is also problematic. It fails to capture ultrafast non-equilibrium dynamics occurring in the first few picoseconds after fs-laser exposure, leading to questionable predictions such as a ~3000 K peak temperature and a cooling rate of ~5.6 × 10^11 K/s. Figures 1b–d rely heavily on this model, without addressing material phase stability or the validity of such extreme thermal conditions. Key physical effects such as laser ablation, evident in Fig. S13, and heat accumulation from pulse overlap are neglected in the simulation. These omissions limit the credibility of the thermal analysis and the claimed mechanism of HEA nanoparticle formation.\nLastly, the metric of “electrothermal efficiency” appears equivalent to area-normalized thermal resistance, which may overstate performance for thinner films. The comparison in Fig. 4g seems not fair, as many cited devices were designed for multifunctionality, not optimized heating.\nGiven the above issues, this reviewer finds that the manuscript contains critical scientific flaws. Therefore, unfortunately, this manuscript is not recommended for publication.", "reviewer_3": "In this manuscript, they achieved the successful fabrication of FeCoNiCrMnRu HEA-NPs on LIG by using femtosecond laser ultrafast solid-phase synthesis. It is a novel research.Some parts should be revised.It can be accepted after revisions.\n1. Pristine LIG (P-LIG) was prepared using femtosecond laser direct writing technology. How much of the yield of the nanoparticles should be menthened? How many grams did you prepared?\n2. How to control the particle size to make it uniform by so fast laser processing. A TEM image of the nano HEA particles should be added.\n3. How can you find it for high-performance Joule heating applications? occasionally?\n4. Why did you choose FeCoNiCrMnRu? Ru is very expensive? Why must you add Ru? How about the property without Ru?\n5. High-performance Joule heating applications of the eCoNiCrMnRu HEA-NPs shold consider the oxidation problems of the particles. It will be oxided quikly in air,"}, "author_response": "The Response to the Reviewer’s Comments\nManuscript Number: NCOMMS-25-66444\nTitle: Ultrafast achieving multiscale high-entropy alloys/graphene for high-performance Joule\nheating\nAuthors: Lingxiao Wang, Kai Yin, Jianqiang Xiao, Xinghao Song, Jiaqing Pei, Jun He, Ji-An\nDuan\nNature Communications\nWe are indebted to the reviewers for their time and effort in reviewing our paper. The\ndetailed comments from the referees are very impressive and greatly valued. We are happy to\nhave such excellent advice for improving the paper’s quality. With our best efforts and best\nknowledge, we have made changes by following the referees’ comments. This report\nsummarizes our understanding of the recommendations and the changes we have made in\nresponse. The reviewers’ comments are reproduced following by the corresponding\nmodifications to the manuscript.\nIn this report, some reference numbers, equations, and figures are marked by an R, for\nexample, Figure R1, to distinguish them from those numbers for Figures in our original paper,\nfor examples, Figure 1 and Figure S1. Different descriptions are also marked with different\ncolors: Reviewer’s comments are black; Our response is marked with blue and red; The part\ninvolved the revised manuscript in our response is red.\nREVIEWER #1\nReviewer’s Comments\nThe manuscript reports the femtosecond-laser, in-situ synthesis of FeCoNiCrMnRu high-\nentropy alloy (HEA) nanoparticles on laser-induced graphene (LIG), forming a multiscale\nHEA/LIG hybrid for electro-thermal heating and broadband infrared emission. However,\nseveral critical elements of the evidence chain are incomplete. I therefore recommend major\nrevision.\nOur Response\nWe greatly appreciate the reviewer’s positive comments on our manuscript. These insightful\nsuggestions/comments will significantly help to improve the scientific quality and presentation\nof this work. Below are our detailed responses to each raised concern and suggestion.\nReviewer’s Comments\n1. Air exposure, high humidity, and repeated heating/cooling can lead to oxidation, migration,\nor agglomeration of metal nanoparticles, affecting electrical and radiative properties. Stability\nunder these conditions should be substantiated.\nOur Response\nWe sincerely appreciate the reviewer’s professional comment regarding the stability of\nHEAs/LIG samples under air, humidity, and thermal cycling conditions. These factors\nincluding oxidation, migration, and agglomeration are critical challenges that can degrade\nelectrical and radiative properties. In our revised manuscript, we have taken a comprehensive\nstability assessment to substantiate the robustness of our FeCoNiCrMnRu HEAs/LIG.\nThe emissivity of mid-infrared band (2.5−20 μm) was measured by a Fourier transform infrared\nspectrometer with a gold integrating sphere (PIKE).\nSpecifically, we compared the electrical and radiative properties of the pristine HEAs/LIG\nsample with two tested samples. A sample stored for six months under ambient conditions with\nthe temperature 20–25 °C and relative humidity of ~70%, while the other subjected to extensive\nJoule heating-cooling cycles after 100 cycles.We found that both the aged and thermally cycled\nsamples retained their electrical and radiative properties with negligible change compared to\nthe pristine sample. The sheet resistance and surface emissivity of both tested samples almost\nremained unchanged after stability test (Figure R1). Then, we performed detailed TEM and\nEDS analysis on these aged samples (Figure R2). This exceptional oxidation resistance was\nattributed to the unique core-shell structure formed during our femtosecond laser processing\n(Figure R3). The formed graphene shell encapsulating the HEA-NPs provides an excellent\nbarrier against oxidation and moisture (Figure R4) [Adv. Mater., 2024, 36, 2402391]. The\nporous and robust LIG matrix firmly anchors the HEA-NPs, preventing their migration and\nagglomeration under repeated thermal treatment. These comprehensive stability data strongly\nverify the durability of the HEAs/LIG.\nFigure R1. (a) Sheet resistance and (b) infrared emissivity of the HEAs/LIG in the wavelength\nrange of 2.5 to 20 μm before and after stability test. A sample stored for eight months under\nambient conditions with the temperature 20–25 °C and relative humidity of ~70%, while the\nother subjected to extensive Joule heating-cooling cycles after 100 cycles.\nFigure R2. TEM images of HEA-NPs after stability test.\nFigure R3. HRTEM images of HEA-NPs after stability test, showing the multilayer graphene\nencapsulating the HEA-NPs.\nFigure R4. HAADF-STEM images and the corresponding EDS elemental mappings for HEA-\nNPs (Fe, Co, Ni, Cr, Mn, Ru, and O) after stability test.\nWe have added a discussion about the stability of HEA-NPs in therevised manuscript. We also\nincluded Figure R1 as Figure S60, Figure R3 as Figure S61, and Figure R4 as Figure S62\nin the supplementary information, as follows:\nFurthermore, the HEAs/LIG samples also showed excellent durability and stability during the\nair exposure, high humidity, and repeated heating/cooling test. The sheet resistance and surface\nemissivity of both tested samples almost remained unchanged after stability test\n(Supplementary Fig. 60). This exceptional oxidation resistance was attributed to the unique\ncore-shell structure formed during our femtosecond laser processing (Supplementary Fig. 61).\nThe formed graphene shell encapsulating the HEA-NPs provides an excellent barrier against\noxidation and moisture (Supplementary Fig. 62). The porous and robust LIG substrate firmly\nanchors the HEA-NPs, preventing their migration and agglomeration under repeated thermal\ntreatment. (Page 13, Manuscript)\nReviewer’s Comments\n2. The presence of HEO observed by TEM should be quantified. The manuscript should clarify\ntheir fraction and discuss their influence on emissivity and conductivity, and thus on the overall\ndevice performance.\nOur Response\nWe sincerely appreciate the reviewer’s insightful observation regarding the HEOs detected in\nour TEM analysis. Furthermore, we agree that a detailed discussion on their fraction and\ninfluence is crucial for understanding the device performance. In our experiments, TEM and\nRaman data confirmed the presence of trace HEOs (Figure R5), while XRD showed no\ndiscernible crystalline oxide peaks (Figure R6). Providing an exact quantitative fraction of\nthese oxides from TEM alone is challenging due to the statistical limitations. However, based\non the extensive TEM observation, Raman, and XRD results, we can provide a qualitative\nestimate of the presence of HEOs.\nOur TEM images detected the presence of HEOs. The Raman spectroscopy data, which\nwas highly sensitive to surface species and chemical bonds, provided complementary evidence\nfor the presence of metal-oxygen bonds, further supporting the TEM observations. In view of\nthe locality of TEM and sensitivity of Raman, we estimate that the primary reason for the\nabsence of distinct metal oxide peaks in the XRD pattern is their exceptionally low content and\nhigh degree of dispersion. Given that the detection limit of XRD technology for crystalline\nphases is within the range of 1-5 wt%, the volume fraction of these surface HEOs may be well\nbelow this detection threshold.\nThe formation of these HEOs originated from the renovation of highly defective LIG by\nthe metallic nanoparticles under the femtosecond laser-induced high-temperature and high-\npressure environment. While the DFT calculation results indicate that this transformation\nconsumes some HEAs by converting them into HEOs, resulting in a decrease in conductivity\n[ACS Nano, 2024, 18, 34492-34530]. But it also facilitates the renovation of LIG, which\nconcurrently enhanced its overall electrical conductivity. Critically, related literature [Adv.\nFunct. Mater., 2023, 33, 2303197; Adv. Mater., 2025, e08636] confirms that the HEOs usually\nexhibited excellent infrared emissivity across a broad band due to efficient electron transitions\nand enhanced lattice vibration absorption. Therefore, the transformation ultimately contributes\npositively to the overall infrared emissivity of the HEAs/LIG composite material. Therefore,\nwe believe that trace HEOs are generally beneficial within our HEAs/LIG. Their presence helps\nto enhance the overall infrared emissivity of the device, thereby improving the infrared\nradiation capability and Joule heating performance.\nFigure R5. Raman spectra of HEAs/LIG and P-LIG.\nFigure R6. XRD spectra of HEAs/LIG and P-LIG.\nWe have also added corresponding discussion about the influence of HEOs in the revised\nmanuscript:\nThe formation of these HEO-NPs originated from the renovation of highly defective LIG by\nthe metallic nanoparticles under the femtosecond laser-induced high-temperature and high-\npressure environment. Given that the detection limit of XRD technology for crystalline phases\nis within the range of 1-5 wt%, the volume fraction of these surface HEOs may be well below\nthis detection threshold. Critically, the HEO-NPs usually exhibited excellent infrared\nemissivity across a broad band due to efficient electron transitions and enhanced lattice\nvibration absorption21. Therefore, the transformation ultimately contributed positively to the\noverall infrared emissivity of the HEAs/LIG composite material. Their presence helps to\nenhance the overall infrared emissivity of the device, thereby improving the infrared radiation\ncapability and Joule heating performance. (Page 8, Manuscript)\nWhile the DFT calculation results indicate that this transformation consumes some HEAs by\nconverting them into HEOs, resulting in a decrease in conductivity. But it also facilitates the\nrenovation of LIG, which concurrently enhanced its overall electrical conductivity. (Page 10,\nManuscript)\nReviewer’s Comments\n3. Where blackbody radiation curves are shown (e.g., Fig. 4h), the corresponding blackbody\ntemperature should be explicitly annotated.\nOur Response\nWe sincerely thank the reviewer for the insightful comments. We have annotated the\ncorresponding blackbody temperature for Figure 4h in the manuscript, Figure S45, and Figure\nS48 in the supplementary information, as follows:\nFig. 4h, Infrared emissivity of P-LIG and HEAs/LIG in the wavelength range of 2.5 to 20 μm.\nSupplementary Figure 54. Infrared emissivity of Al in the wavelength range of 2.5 to 20 μm.\nSupplementary Figure 58. Simulated infrared emissivity of (a) P-LIG, HEAs/LIG, and (b) Al\nin the wavelength range of 3 to 20 μm.\nIn addition, we have also added corresponding explanations in therevised manuscript:\nAlthough the spectral distribution of thermal radiation varies with temperature (Wien\ndisplacement law), the broadband high emissivity across the entire infrared spectrum of\nHEAs/LIG samples ensures excellent radiative performance at different applied voltages.\n(Page 13, Manuscript)\nReviewer’s Comments\n4. Thermal/optical modeling requires clear disclosure of material constants (e.g., ρ, c_p, k, n,\nk) and boundary conditions, along with a brief uncertainty/sensitivity discussion.\nOur Response\nWe appreciate the reviewer’s rigorous attention to the methodological details of our simulation\nframework. We have now supplemented the manuscript with a detailed description of the\nparameters, boundary conditions, and an uncertainty analysis related to our thermal/optical\nmodeling. The revisions can be found in the revised supplementary information.\nCOMSOL thermal modeling: In this thermal simulation, the initial temperature of the entire\nsystem was set to the ambient temperature of 293.15 K. The A, ε, k, ρ, and C of LIG were set\np\nas 0.977, 0.98, 129 W (m K)−1, 2200 kg m−3, and 1150 J (kg K)−1. The primary uncertainty in\nour thermal model stems from the precise thermophysical properties of the LIG composite. As\na porous material, these properties can vary within a certain range based on the laser processing\nparameters and the distribution of HEA-NPs. While these variations introduce minor\nquantitative errors in the absolute temperature values predicted, they do not alter the overall\nconclusions of our study. The simulated trends, which include the rapid thermal response,\ncooling process and uniform temperature distribution, are in qualitative agreement with our\nexperimental results. (Supplementary Note 2, supplementary information)\nCOMSOL Optical modeling: The electric displacement field is described using the refractive\nindex model:\n(S )\n2\nwhe r e n i s t h e r e f r a c t i v e i n d e x , a n d k i\n𝜀\ns 𝑟th\n=\ne e\n(\nx\n𝑛\nti\n−\nnc\n𝑖\nt\n𝑘\nio\n)\nn coefficient. The structure parame\n2\nte\n2\nrs for\nsimulation were based on experimental CLSM profiles. The plane wave source with a\nwavelength from 3 to 20 μm (with a spacing of 0.05 μm) was incident along the y axis and the\nperiodic boundary condition (PBC) was applied to the surfaces along the x axis:\n(S )\n𝐸𝑑𝑠𝑡 = 𝐸𝑠𝑟𝑐 (S 23 )\nThe i n c i d e n t b o u n d a r y i s s e t u s i n g t h e s c\n𝐻\na𝑑tt𝑠e𝑡r\n=\ning\n𝐻\nb𝑠𝑟o𝑐undary condition:\n24\n(S )\nIn addition, perfectly matched layer (PML) absorbing boundary conditions were applied in the\n𝒏×(∇×𝐄)−𝑗𝑘𝑛×(𝐄×𝒏) = 0 25\ny axis to the top and bottom of the air and materials layer, which effective simulated an open\nfree-space environment. Along the x axis, the width was set to 300 μm in all simulations. The\nn and k of air was set as 1 and 0. The n and k of Al model adopted the material parameters\nbuilt-in in COMSOL software (Rakic 1998: Lorentz-Drude model; n,k 0.0620-248 μm). The n\nand k of graphene parts in the P-LIG and HEAs/LIG models adopted the material parameters\nbuilt-in in COMSOL software (Querry 1985: Pyrolytic carbon; n,k 0.21-55.6 μm). For the\nmetal parts of HEAs/LIG, the n and k used the Fe as example, which also adopted the built-in\nparameters in COMSOL software (Querry 1985: n,k 0.21-55.6 μm). For the optical modeling\nand the calculation of emissivity, the main sources of uncertainty are the n and k of the\ncomposite, as well as the simplification of modeling the metallic inclusions primarily based on\nFe as a representative element. In addition, the minor contribution from the metal oxides, whose\nvolume fraction was below the detection limit of XRD, was omitted. All of the factors could\nintroduce a degree of approximation. Considering these, our model likely provided a lower-\nbound estimate of the performance of HEAs/LIG composite. While the absolute values from\nour optical simulations carried a degree of uncertainty, the key physical insights and the\nsuperior radiation performance of our HEA/LIG composite were demonstrated and are not\ncompromised by these approximations. (Supplementary Note 8, supplementary information)\nReviewer’s Comments\n5. Given the local nature of femtosecond direct writing, the manuscript should address large-\narea uniformity, batch-to-batch reproducibility, and practical scalability/throughput\nconsiderations.\nOur Response\nWe sincerely thank the reviewer for these critical questions regarding large-area uniformity,\nreproducibility, and scalability, which are essential for assessing the practical potential of our\ntechnology. We have conducted systematic evaluations to address each of these points, and the\nresults demonstrate the robustness of our femtosecond laser direct writing process.\nTo demonstrate large-area uniformity, we fabricated a HEAs/LIG sample with an active\narea of 40 mm × 40 mm (Figure R7a). The infrared thermal image of this sample under an\napplied voltage of 16 V revealed a highly uniform temperature distribution (Figure R7b).This\nexcellent uniformity is achieved by our femtosecond laser direct writing process, which\ninvolves point-by-point material transformation followed by a continuous line-scanning\nstrategy. The overlapping of laser spots and scans ensures consistent energy delivery, leading\nto homogeneous formation of both the LIG substrates and HEA-NPs. However, fabricating\neven larger areas (e.g., beyond 100 mm × 100 mm) with our current lab-scale setup is limited\nby the scanning field of the galvanometer and the laser power. These are not fundamental\nlimitations of the technology itself. Laser systems with large-field lenses and higher-power\nlasers will be available for industrial-scale processing.\nWe evaluated the batch-to-batch reproducibility by measuring the sheet resistance at\nmultiple locations across five independent HEAs/LIG samples fabricated over a span of eight\nmonths (including samples from our earlier studies) (Figure R8). The results show a very\nnarrow distribution in sheet resistance (Figure R9). This remarkably low variation displayed\nthe exceptional batch-to-batch reproducibility of our method. The digital and programmable\nnature of laser writing ensures consistent energy delivery and patterning across different\nbatches.\nRegarding throughput, the processing time for our method is directly proportional to the\narea. For instance, fabricating a 20 mm × 20 mm sample takes ~20 minutes in our current\nconfiguration. This represents a highly efficient and single-step process that simultaneously\nsynthesizes the LIG support and the HEA-NPs in ambient air. The current high uniformity and\nreproducibility are achieved using a Gaussian laser beam. However, the current single-beam\nscanning speed may present a throughput challenge for very large-scale fabrication. The most\npromising route for industrial-scale throughput is parallelization, which uses beam shaping\nwith a spatial light modulator (SLM) to create multiple focused spots or a homogeneous flat-\ntop beam, allowing for the parallel writing of multiple lines or large areas in a single pass. This\nwould dramatically increase the throughput and makes the process compatible with roll-to-roll\nmanufacturing for flexible electronics. It is also a key focus of our ongoing research.\nFigure R7. (a) Optical photo and (b) infrared camera image of a larger HEAs/LIG sample. The\nsize of the as-prepared sample area was 40 mm × 40 mm.\nFigure R8. Optical photos of HEAs/LIG prepared at different time point in 2025.\nFigure R9. Sheet resistance of HEAs/LIG prepared at different time point in 2025.\nWe have added the discussion about the large-area uniformity, batch-to-batch reproducibility,\nand practical throughput in the revised manuscript. We also included Figure R7 as Figure S12,\nFigure R8 as Figure S13, and Figure R9 as Figure S14 in the supplementary information, as\nfollows:\nWe also fabricated a HEAs/LIG sample with an active area of 40 mm × 40 mm, and the infrared\nthermal image of this sample under an applied voltage revealed a highly uniform temperature\ndistribution (Supplementary Fig. 12). This excellent uniformity is achieved by our femtosecond\nlaser direct writing process, which involves point-by-point material transformation followed\nby a continuous line-scanning strategy. Laser systems with large-field lenses and higher-power\nlasers will be available for industrial-scale processing. We also evaluated the batch-to-batch\nreproducibility by measuring the sheet resistance at multiple locations across five independent\nHEAs/LIG samples fabricated over a span of eight month (Supplementary Fig. 13). The results\nshow a very narrow distribution in sheet resistance (Supplementary Fig. 14). This remarkably\nlow variation displayed the exceptional batch-to-batch reproducibility of our method. The\nprocessing time for our method preparing HEAs/LIG samples is directly proportional to the\narea. This represents a highly efficient and single-step process that simultaneously synthesizes\nthe HEAs/LIG in ambient air. The most promising route for industrial-scale throughput is\nparallelization, which uses beam shaping with a spatial light modulator (SLM) to create\nmultiple focused spots or a homogeneous flat-top beam, allowing for the parallel writing of\nmultiple lines or large areas in a single pass. (Page 5, Manuscript)\nReviewer’s Comments\n6. Bending/adhesion/abrasion durability data are important for flexible device claims and\nshould be presented with clear before/after performance metrics.\nOur Response\nWe sincerely thank the reviewer for this valuable comment regarding the durability of flexible\nHEAs/LIG electric heater. Following your suggestion, we have conducted a series of\nstandardized mechanical tests, including bending, adhesion, and abrasion tests, to\nquantitatively evaluate the durability.\nTo evaluate the flexibility, the HEAs/LIG sample was subjected to 200 repeated bending\ncycles (Figure R10a). The equilibrium temperature was recorded during the bending test\n(Figure R10b). Figure R10c further shows the temperature-time curves of the HEAs/LIG\nheater at a constant voltage of 8 V before and after 200 bending cycles. The saturation\ntemperature remained nearly unchanged. This excellent bending stability demonstrated that the\nHEA-NPs were firmly anchored on the flexible LIG network. The LIG substrate itself could\naccommodate strain without fracture, and our fabrication method ensured that the composite\nstructure maintains its electrothermal performance under repeated mechanical deformation.\nThis result supports the flexibility for applications involving bending.\nWe further assessed the mechanical robustness including adhesion and abrasion, which are\ncritical for skin-wearable or frequently handled devices. A standard tape test using a 3M\ntransparent tape was performed for 30 cycles. The tape was firmly pressed onto the HEAs/LIG\nsurface and then peeled off (Figure R11). The sample was subjected to a linear abrasion test\nover a total path length of 10 cm under a normal load of 100 g with 800 mesh sand paper\n(Figure R12). Every each test was recorded as one cycle. The results indicated that these tests\nled to a noticeable performance degradation. The equilibrium temperature decreased from\n~202 °C to ~29 °C. The current HEAs/LIG structure exhibits limited resistance to mechanical\nwear and strong adhesion forces. The performance is owing to the physical removal of the top-\nlayer LIG flakes and HEA-NPs. For applications requiring adhesion and abrasion resistance,\nencapsulation with a thin and flexible polymer layer, such as Polydimethylsiloxane (PDMS)\nand Ecoflex, would be a highly effective solution.\nFigure R10. (a) Optical photo, (b) equilibrium temperature change, and (c) temperature-time\ncurves of bending test for the HEAs/LIG over 200 cycles at the voltages of 8 V.\nFigure R11. (a) Optical photo of the HEAs/LIG after 30 adhesion cycles. (b) Equilibrium\ntemperature change of the HEAs/LIG over 30 cycles at the voltages of 8 V.\nFigure R12. (a) Illustration of one abrasion cycle. (b) Optical photo of the HEAs/LIG after 5\nabrasion cycles. (c) Equilibrium temperature change of the HEAs/LIG over 5 cycles at the\nvoltages of 8 V.\nWe have added the discussion about the bending durability in the revised manuscript. We also\nincluded Figure R10 as Figure S53, in the supplementary information, as follows:\nThe bending stability of HEAs/LIG heater was examined. We performed 200 cycles bending\ntests and monitored the evolution of its electrothermal performance metrics (Supplementary\nFig. 53). The electrothermal response remained unchanged after testing. This exceptional\ndurability under mechanical deformation originated from the synergistic combination of the\nflexible LIG substrate and the anchored HEA-NPs. (Page 12, Manuscript)\nReviewer’s Comments\n7. If energy-efficiency advantages over commercial heaters are asserted, the underlying\nassumptions, parameters, and calculation approach should be transparent.\nOur Response\nWe thank the reviewer for this rigorous attention to the calculation details of our energy-\nefficiency framework. We fully agree that claims of energy efficiency must be supported by\ntransparent calculations. Our claim of energy-efficiency advantage is primarily based on a\nlower steady-state power consumption for achieving a comparable surface temperature. We\nhave revised the manuscript to include a dedicated section (Supplementary Note 9,\nsupplementary information) detailing the following assumptions, parameters, and methodology.\nThe revisions can be found in the revised manuscript and supplementary information:\nThe detailed assumptions, parameters, and methodology of the energy saving calculation could\nbe found in Supplementary Note 9. Using the computational models, we mainly calculated the\nwinter energy savings potential across China. Compared to using CEH, HEAs/LIG heater\ndelivers markedly higher energy saving performance. For example, Harbin can save roughly\n1134.99 MJ m−2. (Page 15, Manuscript)\nA comprehensive Python-based simulation framework was used to evaluate the winter energy-\nsaving performance of HEAs/LIG as a Joule heater compared with CEH. First, we set several\ncommon parameters. The climate data used includes the dataset for mean air temperature over\nthe main terrestrial lands of China 2020. At the same time, building density and roof area ratios\nwere set based on statistical data from various provinces in China. For example, Beijing's\nbuilding density was set at 0.35, and roof area accounted for 30% of the building land area.\nThe energy-efficiency analysis was based on the experimental data in Fig. 5i. When raising the\nambient temperature from –7.5 °C to the winter indoor comfort level of 24 °C, the required\npower for the HEAs/LIG and CEH are 1.17 W and 2.30 W, respectively, over the same area.\nUsing 24 °C as the target indoor temperature, power density scaling was performed based on\nthe above temperature difference, where the scaling factor equals the heating demand divided\nby the baseline temperature difference. This yielded the difference in power consumption\nbetween HEAs/LIG and the CEH when used as electric heating devices. Assuming continuous\noperation over 24 hours without considering differences in building insulation, the total\ndifference in energy savings density over a 90-day period was ultimately determined.\n(Supplementary Note 9, supplementary information)\nReviewer’s Comments\n8. The use of Ru raises questions about cost and supply. A brief discussion of material\ncriticality and potential substitutions would improve the practicality narrative.\nOur Response\nWe sincerely thank the reviewer for this insightful comment regarding the cost and supply risk\nof Ru. Ru is a platinum-group metal typically obtained as a by-product. In our initial design,\nRu was selected primarily to modestly increase configurational entropy rather than to leverage\nany Ru-specific noble-metal functionality. However, we fully acknowledge the practical\nlimitations of Ru, as rightly pointed out by the reviewer. To address this, we have already\nidentified promising substitution strategies by referring literatures.\nCu is a highly viable candidate, as it is inexpensive and possesses excellent electrical\nconductivity. In addition to extending the versatility of the femtosecond laser synthesis for\nHEA-NPs, we will aim to leverage higher conductivity for achieving uniform heating and rapid\nthermal response. This can also ensure high performance while enhancing practicality and\nscalability. Furthermore, we will also screen Zn, Mo, and Sn as alternative or additional\nelements to prepare single-phase HEAs while avoiding cost and supply risk. It is worth\nmentioning that our femtosecond laser process forms HEA-NPs directly on the LIG, the areal\nloading of every element (Fe, Co, Ni, Cr, Mn, and Ru) is very low, with an expected total\nloading density of ~1.5 mg cm⁻2. Therefore, even if Ru was used, its contribution to device-level\ncost is limited.\nTo improve the practicality narrative of HEAs/LIG Joule heater, we have added the discussion\nabout the material criticality and potential substitutions in the revised manuscript:\nBased on the concentration of the FeCoNiCrMnRu precursor solution (0.1 M), the used volume\n(160 μL) and the coated area (20 mm × 20 mm), we can estimate the mass loading of the\nFeCoNiCrMnRu HEA-NPs on the LIG to be ~1.5 mg cm⁻2. Therefore, even if Ru was used\nwith considering its cost and supply, its contribution to device-level cost is limited. However,\nit is also desirable to investigate a wider range of low-cost and abundant elements, such as Cu,\nZn, Mo, and Sn, to either replace Ru or further increase the configurational entropy, which is\nanticipated to correspondingly enhance the electrothermal performance of the HEAs/LIG\ncomposite. (Page 5, Manuscript)\nReviewer’s Comments\n9. A direct comparison between FeCoNiCrMn (high-entropy) and FeCoNiCrMnRu is needed\nto reveal whether performance gains arise from Ru itself or from marginally higher\nconfigurational entropy.\nOur Response\nWe sincerely thank the reviewer for this insightful comment regarding the role of Ru.To verify\nthe significance of Ru and configurational entropy (ΔS ), we fabricated and tested three\nconf\nHEAs/LIGcomposites: FeCoNiCrMnRu (with Ru and high ΔS ), FeCoNiCrRu (low ΔS ),\nconf conf\nand FeCoNiCrMn (no Ru) (Figure R13). The comprehensive results were presented in Figure\nR14 (sheet resistance), Figure R15 (Joule heating performance), Figure R16 (infrared camera\nimages),and Figure R17 (infrared emissivity). The senary FeCoNiCrMnRu sample (~51.8 Ω\nsq−1) also showed a slightly lower sheet resistance compared to both quinary FeCoNiCrRu\n(~60.2 Ω sq−1) and FeCoNiCrMn (~59.9 Ω sq−1). Furthermore, the FeCoNiCrMnRu showed a\nperformance improvement in equilibrium temperatures at the 8V voltage compared to both\nFeCoNiCrRu and FeCoNiCrMn. The equilibrium temperatures of FeCoNiCrMnRu,\nFeCoNiCrRu, and FeCoNiCrMn were ~204.1 °C, ~183.4°C, and ~185.3°C, respectively. The\ninfrared emissivity was consistently high across all three samples, indicating that this property\nis predominantly governed by the LIG carrier rather than the specific HEA composition. These\nresults suggested that the metallic elements in this system contributed in a largely equivalent\nmanner to the electrical and thermal properties. The slight performance advantage of the senary\nFeCoNiCrMnRu was more accurately attributed to its higher configurational entropy rather\nthan to the specific chemical identity of Ru.\nFigure R13. Optical photos of (a) FeCoNiCrMnRu HEAs/LIG, (b) FeCoNiCrRu HEAs/LIG,\nand (c) FeCoNiCrMn HEAs/LIG surfaces.\nFigure R14. Sheet resistance of FeCoNiCrMn the HEAs/LIG, FeCoNiCrRu HEAs/LIG, and\nFeCoNiCrMnRuHEAs/LIG.\nFigure R15. Temperature-time curves of the FeCoNiCrMn HEAs/LIG, FeCoNiCrRu\nHEAs/LIG, and FeCoNiCrMnRu HEAs/LIG at the voltages of 8 V.\nFigure R16. Corresponding infrared camera images of the FeCoNiCrMn HEAs/LIG,\nFeCoNiCrRuHEAs/LIG, and FeCoNiCrMnRuHEAs/LIG at the voltages of 8 V.\nFigure R17. Infrared emissivity of the FeCoNiCrMn HEAs/LIG, FeCoNiCrRu HEAs/LIG,\nand FeCoNiCrMnRuHEAs/LIG in the wavelength range of 2.5 to 20 μm.\nWe have revised the manuscript to incorporate this new data and the refined discussion. We\nalso included Figure R13 as Figure S37, Figure R14 as Figure S38, Figure R15 as Figure\nS50, Figure R16 as Figure S51, and Figure R17 as Figure S56 in the supplementary\ninformation.\nThe senary FeCoNiCrMnRu sample also showed a slightly lower sheet resistance compared to\nboth quinary FeCoNiCrRu (~60.2 Ω sq−1) and FeCoNiCrMn (~59.9 Ω sq−1) (Supplementary\nFigs. 37 and 38). (Page 9, Manuscript)\nAs for the high entropy samples, the FeCoNiCrMnRu showed a performance improvement in\nequilibrium temperatures at the 8V voltage compared to both FeCoNiCrRu and FeCoNiCrMn.\nSpecifically, the equilibrium temperatures of the FeCoNiCrMnRu, FeCoNiCrRu, and\nFeCoNiCrMn were ~204.1 °C, ~183.4°C, and ~185.3°C, respectively (Supplementary Figs. 50\nand 51). (Page 12, Manuscript)\nThe infrared emissivity was consistently high across all the FeCoNiCrMnRu, FeCoNiCrRu,\nand FeCoNiCrMn samples, further indicating that this property is predominantly governed by\nthe LIG carrier rather than the specific HEA composition. (Supplementary Fig. 56). (Page 13,\nManuscript)\nReviewer’s Comments\n10. For Joule-heating use cases, rapid on/off cycling stability should be demonstrated, with\ntracking of sheet resistance, heating metrics, and emissivity over extended cycles.\nOur Response\nWe greatly appreciate the reviewer’s insightful and constructive suggestion. We fully agree\nthat the cycling stability is a critical performance metric for practical Joule-heating applications.\nWe have conducted additional experiments to systematically evaluate the rapid on/off cycling\nstability of our HEAs/LIG heater. The HEAs/LIG sample was subjected to 100 consecutive\nrapid heating-cooling cycles under a constant DC voltage of 8 V. Each cycle consisted of 60\nseconds of heating followed by 60 seconds of natural cooling in ambient conditions. During\nthis long-term cycling test, we tracked the sheet resistance, equilibrium temperature, and\ninfrared emissivity (Figure R18). The HEAs/LIG heater exhibits exceptional operational\nstability. The sheet resistance remained remarkably stable, which indicated that the conductive\nLIG network and the anchored HEA-NPs maintained excellent structural and electrical\nintegrity without significant oxidation, cracking, or delamination. Correspondingly, the\nequilibrium temperature also showed negligible degradation. The infrared emissivity of the\nsample remained constant throughout the stability test, confirming the surface chemical and\nmorphological stability, which is crucial for radiation-based heating applications. The\noutstanding cycling stability can be attributed to the robust interface between the HEA-NPs\nand the LIG substrate, as well as the intrinsic high-temperature stability and anti-oxidation\nproperties of the graphene shell-encapsulated HEA-NPs composition.\nFigure R18. (a) Temperature-time curve of HEAs/LIG sample during the rapid on/off cycling\nstability test at the voltage of 8 V. (b) Evolution of sheet resistance over 100 cycles. (c)\nEquilibrium temperature change over 100 cycles. (d) Infrared emissivity of the heater at the\ninitial, 20th, 40th, 60th, 80th, and 100th cycles in the wavelength range of 2.5 to 20 μm. Each\ncomplete heating/cooling cycle lasted for ~60 s.\nWe have added these new results into the revised manuscript and included Figure R18 as\nFigure S71 in the supplementary information.\nIt was worth noting that the HEAs/LIG heater showed excellent stability during the rapid on/off\ncycling test (Supplementary Fig. 71). The outstanding cycling stability comes from the robust\ninterface between the HEA-NPs and the LIG substrate, as well as the intrinsic high-temperature\nstability and anti-oxidation properties of the graphene shell-encapsulated HEA-NPs\ncomposition. (Page 15, Manuscript)\nREVIEWER #2\nReviewer’s Comments\nThis manuscript presents the synthesis of high-entropy alloy nanoparticles (HEA-NPs) on\nlaser-induced graphene (LIG) using femtosecond (fs) laser irradiation, aiming to demonstrate\nenhanced Joule heating performance. However, this reviewer finds several fundamental\nconcerns that undermine the validity and significance of the reported results.\nOur Response\nWe are grateful to the reviewer for their careful feedback on our manuscript. Your comments\nare very insightful and helpful to improve our manuscript.Below are our detailed responses to\neach raised concern and suggestion.\nReviewer’s Comments\n1. The justification for using a femtosecond laser is insufficient. While the authors claim a\nthermal mechanism for HEA nanoparticle formation, femtosecond lasers are typically\nassociated with non-thermal, \"cold\" ablation processes. The manuscript does not demonstrate\nclear advantages of fs lasers over more accessible alternatives like nanosecond or CW lasers,\nraising concerns about the method’s practicality and relevance.\nOur Response\nWe sincerely thank the reviewer for this valuable comment regarding the practicality and\nrelevance of femtosecond laser synthesis HEA-NPs. Here is our point-to-point response.\nThe initial interaction of a single femtosecond laser pulse with a material is often non-\nthermal, dominated by direct field ionization and Coulomb explosion. This \"cold\"\nablation process is indeed beneficial for high-precision machining. It should be noted that this process\noften usually occurs at the low repetition rate regime, where thermal accumulation can be\nusually negligible. The surface peak temperature decreases to the initial degree before the next\nlaser pulse arrives. These features minimize the thermal collateral damage and heat affected\nzone. In this regime, the repetition rate is usually a few kHz. However, the fabrication\nefficiency is also limited by the low pulse repetition rate [Laser Photonics Rev., 2021, 15,\n2000455]. When the repetition rate of femtosecond laser pulse reaches several hundred kHz\n(typically above 100 kHz), the time interval between consecutive laser pulses becomes shorter\nthan the duration required for the absorbed energy to diffuse out of the focal volume. This will\nlead to significant local thermal accumulation effects. While this conclusion was originally\ndrawn from studies on femtosecond laser processing of glass substrates, in our work, we\nutilized the LIG, which exhibits ultrahigh light absorptivity, as the substrate and selected a high\nfemtosecond laser repetition rate of 400 kHz. This configuration offers distinct advantages for\nthe synthesis of HEA-NPs. The thermal formation mechanism of HEA-NPs has been validated\nby many research [Science, 2022, 376, eabn3103; Adv. Mater., 2025, 37, 2412337]. Following\nthe ultrafast heating induced the simultaneous decomposion of all metal salts, the molten\ndroplet undergoes an ultrafast quenching process. This extreme quenching rate is an important\nfactor that kinetically traps the multiple immiscible metallic elements into a single-phase HEA\nsolid solution, suppressing the phase separation and nucleation of intermetallic compounds that\nwould occur under slower cooling. Therefore, the femtosecond laser creates a unique ultrafast\nthermal cycle that is perfectly suited for HEA formation. These advantages of the femtosecond\nlaser are reflected in the synthesized HEA-NPs.\nBased on our experimental findings and supporting literature, the femtosecond laser\ndemonstrates obvious advantages over nanosecond and continuous wave (CW) lasers for the\nsynthesis of HEA-NPs. Femtosecond laser synthesis enables the formation of significantly\nsmaller HEA-NPs compared to those typically obtained with CW laser [J. Mater. Chem. A,\n2024, 12, 21744-21757]. This is a direct consequence of the ultrahigh heating and cooling\nrates, which rapidly freeze the nucleated liquid droplets, effectively suppressing coalescence\nthat lead to coarse and irregular particles under the slower thermal cycles of CW laser. A key\npractical advantage is the ability to synthesize HEA-NPs directly in ambient atmosphere without\nrequiring liquid environments or chemical reductants.Many nanosecond laser methods or other\ntechniques for producing non-oxide HEA-NPs necessitate such controlled conditions [Adv.\nMater., 2025, 37, 2504099; Light Sci. Appl., 2024, 13, 270; Energy Environ. Sci., 2024, 17,\n8670-8682;Adv. Funct. Mater., 2023, 33, 2211279;Nat. Synth., 2022, 1, 138-146; Adv. Funct.\nMater., 2022, 32, 2110645]. The femtosecond laser achieves this through ultrafast and non-\nequilibrium energy deposition, while the extremely short interaction time minimizes oxidation\nof HEA-NPs despite being performed in air. Furthermore, the femtosecond laser induced multi-\nlayer graphene-encapsulated HEA-NPs structures contribute to enhancing the durability of the\nelectrothermal device and effectively prevents subsequent oxidation of the HEA-NPs, as\nverified by experiments [Adv. Mater., 2024, 36, 2402391].\nTo improve the practicality and relevance of femtosecond laser synthesis HEA-NPs, we have\nadded and corrected this crucial discussion about the advantages of femtosecond laser in the\nrevised manuscript and supplementary information:\nThe femtosecond laser demonstrates obvious advantages over nanosecond and continuous\nwave (CW) lasers for the synthesis of HEA-NPs (Supplementary Table 6). Femtosecond laser\nsynthesis enables the formation of significantly smaller HEA-NPs compared to those typically\nobtained with CW laser40. This is a direct consequence of the ultrahigh heating and cooling\nrates, which rapidly freeze the nucleated liquid droplets, effectively suppressing coalescence\nthat leads to coarse and irregular particles under the slower thermal cycles of CW laser. A key\npractical advantage is the ability to synthesize HEA-NPs directly in ambient atmosphere\nwithout requiring liquid environments or chemical reductants. Many nanosecond laser methods\nor other techniques for producing non-oxide HEA-NPs necessitate such controlled\nconditions32,41–46. The femtosecond laser achieves this through ultrafast and non-equilibrium\nenergy deposition, while the extremely short interaction time minimizes oxidation of HEA-\nNPs despite being performed in air. (Page 4, manuscript)\nSupplementary Table 6. Comparative analysis of laser synthesis methods for HEAs.\nLaser source Supporter Atmosphere Reductant Production Ref.\nFemtosecond Our\nLIG Air None HEA-NPs\nlaser work\nNanosecond\nNone Liquid None Au-based HEA-NPs 35\nlaser\nNanosecond\nMXene Ar None HEA-NPs 21\nlaser\nNanosecond\nLIG Ar None HEA-NPs 22\nlaser\nCW laser CP Air Sodium citrate HEA-NPs 20\nCW laser None Liquid None HEAs 36\nCW laser CNTs N None HEA-NPs 19\nVarious Liquid None HEA-NPs 37\nlaser\nNanosecond\nMWCNTs N None HEA-NPs 38\n2\nlaser\nReviewer’s Comments\n2. The thermal simulation based on the classical heat diffusion equation is also problematic. It\nfails to capture ultrafast non-equilibrium dynamics occurring in the first few picoseconds after\nfs-laser exposure, leading to questionable predictions such as a ~3000 K peak temperature and\na cooling rate of ~5.6 × 10^11 K/s. Figures 1b–d rely heavily on this model, without addressing\nmaterial phase stability or the validity of such extreme thermal conditions. Key physical effects\nsuch as laser ablation, evident in Fig. S13, and heat accumulation from pulse overlap are\nneglected in the simulation. These omissions limit the credibility of the thermal analysis and\nthe claimed mechanism of HEA nanoparticle formation.\nOur Response\nWe sincerely thank the reviewer for these insightful and critical comments regarding our\nthermal simulation. Below are our point-to-point response.\nWe agree with the reviewer that the classical thermal diffusion model has limitations,\nparticularly in its inability to capture the ultrafast non-equilibrium dynamics between electrons\nand the lattice within the first few picoseconds following femtosecond laser exposure. A more\nrigorous approach for describing such ultrafast phenomena is indeed the two-temperature\nmodel (TTM), which has been extensively validated for confirmed metal or semiconductor\nrelated systems and can effectively simulate the temporal evolution of both electron and lattice\ntemperatures [Adv. Mater., 2025, e12727; Nano-Micro Lett., 2025, 17, 179; Adv. Funct. Mater.,\n2025, 35, 2424526]. However, theapplication of the TTM requires a set of precise parameters,\nsuch as the electron-phonon coupling factor, electronic heat capacity, and electron thermal\nconductivity. In our study, the irradiated material is a complex composite of pyrolytic porous\ngraphene and high-entropy metallic precursors. For our specific composite system, the key\nparameters required for TTM are not well-defined and established at this stage. Considering\nthis constraint, we therefore adopted the classical heat diffusion model as a simplified but\ntractable alternative to provide qualitative insights into the thermal profiles. While we\nrecognize that this classical heat diffusion model is coarse and ignores some nuances of\nultrafast dynamics, it has been effectively employed in prior femtosecond laser studies on\ncarbon-based materials to explain rapid thermal cycles [ACS Nano, 2023, 17, 18893-18904;\nAdv. Funct. Mater., 2023, 33, 2213514; Adv. Opt. Mater., 2021, 9, 2100793]. It effectively\nprovides a qualitative understanding for the trend of ultrahigh heating and cooling rates, such\nas the peak temperature of ~3000 K and cooling rate of ~5.6 × 1011 K s−1 . The ultrahigh peak\ntemperature is indicative of a regime where the absorbed energy is sufficient to cause\nprecursors to decompose simultaneously, which is a necessary condition for the formation of\nHEA-NPs. The ultrahigh cooling rate is a fundamental and well-established principle for\nsuppressing phase segregation and promoting the stabilization of a single solid-solution phase.\nThus, while the exact numerical value is determined by the model, the phenomenon of ultrafast\nheating/cooling and its consequence is physically reasonable, which is supported by many\nexisting research [Science, 2022, 376, eabn3103; Nat. Synth., 2022, 1, 138-146; Nat. Commun.,\n2025, 16, 3403; Light Sci. Appl., 2024, 13, 270; Adv. Mater., 2025, 37, 2412337]. These\nextreme thermal conditions are essential for HEA-NPs formation. The high entropy stabilizes\nthe solid-solution at high temperatures, and the rapid cooling kinetically \"freezes\" this state.\nThe experimental characterizations of the resulting particles also support the FeCoNiCrMnRu\nHEA-NPs formation. Therefore, the predicted extreme thermal conditions are not only\nplausible but are the driver for the observed HEA nanoparticle formation (Figure R19).\nWe agree that our model simplifies some important physical effects such as neglecting laser\nablation and heat accumulation from pulse overlap. The heat accumulation from pulse overlap\nis also a critical factor for the overall processing outcome. In this initial study, our simulation\nwas focused on the thermal response induced by a single femtosecond laser pulse to understand\nthe fundamental thermal formation mechanism of HEA-NPs from the precursor material.\nAdditionally, the high heat dissipation efficiency of the graphene substrate helps minimize\npotential damage to the substrate caused by heat accumulation effects under high repetition\nrate femtosecond laser. The simplification is an effective approach to decouple the complex\nmulti-pulse effects. We fully know that the model can be refined, and we are actively working\non developing multi-pulse models, which can fully describe the macroscopic morphology.\nWe appreciate the professional advice provided by the reviewers. We will clarify the\nlimitations and the qualitative nature of our thermal analysis in the revised manuscript. Further\nrefinement of the thermal model and potentially through experimental determination of the\nnecessary parameters for this model will be a key focus of our future work.\nFigure R19. HAADF-STEM images and the corresponding EDS elemental mappings for\nHEA-NPs (Fe, Co, Ni, Cr, Mn, and Ru).\nWe have revised the manuscript to include a more explicit discussion of these model limitations\nand the interpretive nature of the absolute values, ensuring a balanced presentation of our\nthermal analysis:\nThe highly localized femtosecond laser pulse could facilitate rapid cooling and help preserve\nthe single-phase random atomic configuration to promote the formation of uniform HEA solid\nsolutions3,9,10. (Page 4, manuscript)\nIt is noted that the classical heat diffusion model employed here provides an estimate of the\nextreme thermal cycle but does not capture the initial electron-lattice non-equilibrium. The\npredicted temperatures and heating/cooling rates should be interpreted as the qualitative\nconditions of the extreme conditions that facilitate rapid melting and solidification, consistent\nwith the formation of HEA-NPs. While the exact numerical value is determined by the model,\nthe phenomenon of ultrafast heating/cooling and its consequence is physically reasonable.\n(Page 4, manuscript)\nReviewer’s Comments\n3. Lastly, the metric of “electrothermal efficiency” appears equivalent to area-normalized\nthermal resistance, which may overstate performance for thinner films. The comparison in Fig.\n4g seems not fair, as many cited devices were designed for multifunctionality, not optimized\nheating.\nOur Response\nWe thank the reviewer for this astute observation and raising these important points regarding\nthe electrothermal performance metrics and comparison. We fully agree with the reviewer that\na fair comparison is crucial. As for the electric heater, upon reaching a steady temperature, a\npower balance is established between the input power and the power losses due to thermal\nradiation and convection:\n2\n𝑈0 4 4\nwhere U\n0\nis the applied voltage, R= isℎ t𝑐h𝐴e( r𝑇e𝑠si−sta𝑇n0c)e+, hℎc 𝑅is𝐴 t(h𝑇e𝑠 co−nv𝑇e0c)tive heat transfer coefficient,\n𝑅\nA is the working surface area, T is the stable temperature, T is the ambient temperature, h is\nS 0 R\nthe convective heat transfer coefficient, respectively. In fact, our defined electrothermal\nefficiency (E ), which is the slope of the fitted line from input power density to saturated\nT\ntemperature), is the inverse of the total heat transfer coefficient:\n1\nwhen the E is higher, less power d𝐸en 𝑇 s=ity is required for reaching the same saturated\nT ℎ𝑐 +ℎ𝑅\ntemperature. E quantifies how efficiently electrical power is converted into a temperature\nT\nincrease against environmental heat losses. We deliberately chose this normalized parameter\n(°C cm2 W−1) to enable a cross-comparison of different electrothermal materials on a relative\nperformance basis, as it effectively eliminates the influence of the heated area. This\nelectrothermal efficiency metric is somewhat different from the area-normalized thermal\nresistance, which also takes into account radiative heat dissipation. The E is governed by\nT\nconvection and radiation to the ambient, which is insensitive to the film thickness.\nThe comparison in Figure R20 aims to situate our work within the broader field of the thin-\nfilm heaters and flexible thermal management platforms. We agree that some of the cited\ndevices were designed with additional functionalities. However, a primary function highlighted\nand evaluated in all these cited works is their performance as electrothermal heaters. The\ncomparison is made against their reported heating capabilities that used the same or similar\nmetrics. All devices included in the comparison are thin film heaters, ensuring a relevant and\nfair comparison of their fundamental electrothermal properties. From another perspective, our\nprepared HEAs/LIG is also a multifunctional platform. In our work, the HEAs/LIG composite\nis designed for Joule heating, but it might also possess significant potential for electrocatalysis,\nsensing, and other applications [Light Sci. Appl., 2024, 13, 270]. The excellent electrothermal\nperformance reported here is a valuable functionality achieved on this versatile platform.\nFinally, the reviewer raises an excellent point about multifunctionality. Indeed, while the\nprimary focus of our work currently focuses on ultrafast‑laser synthesis of HEA-NPs on LIG\nas a high-efficiency Joule heater, we are actively investigating broader functionalities of\nHEAs/LIG.\nFigure R20. Comparison of electrothermal conversion efficiency between the HEAs/LIG and\nvarious heaters.\nWe have also added corresponding discussion about the multifunctionality of Figure 4g in the\nrevised manuscript:\nThis comparison was intended to provide a performance standard for our prepared HEAs/LIG\nwithin the landscape of reported advanced film and flexible electrothermal devices. It was\nacknowledged that some of the compared devices were developed for multifunctional\napplications. (Page 12, Manuscript)\nREVIEWER #3\nReviewer’s Comments\nIn this manuscript, they achieved the successful fabrication of FeCoNiCrMnRu HEA-NPs on\nLIG by using femtosecond laser ultrafast solid-phase synthesis. It is a novel research. Some\nparts should be revised. It can be accepted after revisions.\nOur Response\nWe appreciate the reviewer’s valuable comments and your recognition of the novelty and\nscientific merits of this manuscript. Below are our detailed responses to each raised concern\nand suggestion.\nReviewer’s Comments\n1. Pristine LIG (P-LIG) was prepared using femtosecond laser direct writing technology. How\nmuch of the yield of the nanoparticles should be menthened? How many grams did you\nprepared?\nOur Response\nWe sincerely thank the reviewer for this insightful question. The FeCoNiCrMnRu HEA-NPs\nin this work were synthesized in situ and are strongly anchored to the fibrillar network of the\nP-LIG substrate and used as the Joule heater. They are not collected as a free-standing powder.\nTherefore, the metrics of yield and grams prepared are not directly applicable to our laser\nsynthesis process. However, based on the concentration of the FeCoNiCrMnRu precursor\nsolution (0.1 M), the used volume (160 μL) and the coated area (20 mm × 20 mm), we can\nestimate the mass loading of the FeCoNiCrMnRu HEA-NPs on the LIG to be ~1.5 mg cm⁻2.\nAs the HEA-NPs are not independent, a precise mass in grams cannot be provided.\nHowever, we can describe the scale of our preparation. In a typical experiment, we prepared a\nHEAs/LIG sample with a geometric area of 20 mm × 20 mm covered with the HEA-NPs\ncomposites. Using the mass loading value above for a typical sample, the total mass of HEA-\nNPs synthesized per sample was ~6.0 mg. This entire preparation process took less than 20\nminutes and exhibited high efficiency.\nReviewer’s Comments\n2. How to control the particle size to make it uniform by so fast laser processing. A TEM image\nof the nano HEA particles should be added.\nOur Response\nWe sincerely thank the appreciate for this insightful comment regarding the control and\nuniformity of the HEA-NPs size. We have conducted additional experiments to investigate the\neffect of laser scanning speeds. Specifically, we have now included STEM images and\ncorresponding particle size distribution analyses of the synthesized HEA-NPs fabricated at\ndifferent laser scanning speeds (50, 70, and 90 mms⁻1) (Figure R21). Our results consistently\ndemonstrate that increasing the laser scanning speed leads to a decrease in the average\nnanoparticle size [Light Sci. Appl., 2024, 13, 270]. This trend can be attributed to the reduced\ninteraction time and effective growth time for the nanoparticles at higher scanning speeds,\nwhich limits the coalescence. While a general trend is established, the current STEM images\nshow some larger nanoparticles within the distribution. We attribute this primarily to the\ninherent temperature gradient generated by the Gaussian profile of the femtosecond laser beam.\nThis profile creates a non-uniform thermal field where the center of the laser spot reaches a\nhigher temperature, potentially leading to increased coalescence and the formation of a\nminority of larger nanoparticles. To address this and achieve superior size control with a more\nuniform distribution in future work, we plan to employ laser beam shaping techniques to create\na more uniform energy distribution across the processing area. This is expected to minimize\nlocalized hot spots and yield nanoparticles with a more uniform size distribution.\nFigure R21. STEM images and particle size distribution analysis of HEAs/LIG with laser\nscanning speeds of (a) 50, (b) 70, and (c) 90 mm s−1.\nwe have also added the above Figure R21 as Figure S36 in the supplementary information\nand discussion about the particle size in the revised manuscript:\nFurthermore, the particle size of the FeCoNiCrMnRu HEA-NPs was found to decrease with\nincreasing laser scanning speed (Supplementary Fig. 36). This trend can be attributed to the\nreduced interaction time and effective growth time for the nanoparticles at higher scanning\nspeeds, which limits the coalescence. (Page 8, Manuscript)\nReviewer’s Comments\n3. How can you find it for high-performance Joule heating applications? occasionally?\nOur Response\nWe thank the reviewer for this insightful question regarding the high-performance Joule\nheating applications of HEAs/LIG. Our research originally focused on the electrical\nconductivity and electrothermal conversion performance of LIG. During these research, we\nrecognized that while the LIG holds great promise, there was an need in this field to further\nenhance its electrical and thermal properties for more demanding applications. This directed\nour attention to the emerging field of HEAs.\nTraditionally, there existed performance tradeoffs where high-conductivity metals possess\nlow emissivity, while the metal oxides with high emissivity often had poor electrical\nconductivity. To overcome this, we devised a synergistic design strategy (Figure R22). From\nthe perspective of electrical conductivity, the HEA-NPs acted as the conductive bridges within\nthe porous network of LIG. This effectively lowered the overall sheet resistance of the\ncomposite film (from 90.7 to 51.8 Ω sq−1). From the perspective of infrared emissivity, we\nleveraged the intrinsic 3D porous and interconnected structure of LIG, which is highly effective\nat trapping and emitting infrared radiation. This design ensures that the composite still\nmaintained a high broadband infrared emissivity of ~0.98 across a broad wavelength range of\n2.5–20 μm despite the incorporation of HEA-NPs, which might exhibit lower emissivity.\nThe key to realizing this design was our ultrafast femtosecond laser synthesis method. We\ndiscovered that this method could directly synthesize HEA-NPs on the LIG in ambient air. This\none-step, in-situ fabrication method proved to be highly effective, which created ideal non-\nequilibrium conditions for HEA-NPs formation. Consequently, the resulting HEAs-decorated\nLIG composites demonstrated a significant enhancement in Joule heating, alongside\noutstanding electrothermal conversion efficiency (~285.4 °C cm2 W−1) and cycle stability.\nThe overall performance surpassed that of most previously reported materials, as presented in the\nmanuscript.\nFigure R22. Schematic illustration of the design of high-performance Joule heating materials\nenabled by HEA-NPs and LIG.\nReviewer’s Comments\n4. Why did you choose FeCoNiCrMnRu? Ru is very expensive? Why must you add Ru?\nHow about the property without Ru?\nOur Response\nWe greatly appreciate the reviewer’s valuable questions. The element selection, cost-\neffectiveness of Ru, and its necessity are crucial for the material design strategy. We have\nconducted further experiments and refined our discussion to provide a more comprehensive\nand accurate explanation. Our selection of FeCoNiCrMn was primarily based on literature\nsurvey and considerations of configurational entropy (Figure R23), because it represents a\nwell-established, foundational HEA system with proven phase stability [Nat. Commun., 2022,\n113, 2662; Adv. Sci., 2023, 10, 2300426; Energy Environ. Sci., 2024, 17, 8670-8682]. Building\nupon this, we further investigated the possibility of enhancing the configurational entropy by\nincorporating Ru to form FeCoNiCrMnRu. This approach has been experimentally verified as\nfeasible, and the resulting slight increase in configurational entropy is expected to be beneficial\nfor electrothermal conversion performance.\nWe agree that the Ru is relatively expensive and its supply can be constrained. In our initial\ndesign, Ru was selected primarily to modestly increase configurational entropy rather than to\nleverage any Ru-specific noble-metal functionality. However, our femtosecond laser process\nforms HEA-NPs directly on the LIG, the areal loading of every element (Fe, Co, Ni, Cr, Mn,\nand Ru) is very low, with an expected total loading density of ~1.5 mg cm⁻2. Therefore, even\nif Ru was used, its contribution to device-level cost is limited. Indeed, Ru is not indispensable.\nIt was included as one option to lift configurational entropy with a chemically robust element.\nOther metals (e.g., Cu, Mo, Zn, Sn) can substitute this role in future iterations with similar\ndesign logic for preparing single-phase HEAs while avoiding cost and supply risk.\nTo verify the significance of Ru and configurational entropy (ΔS ), we fabricated and\nconf\ntested three HEAs/LIG composites: FeCoNiCrMnRu (with Ru and high ΔS ), FeCoNiCrRu\nconf\n(low ΔS ), and FeCoNiCrMn (no Ru) (Figure R24). The comprehensive results were\nconf\npresented in Figure R25 (sheet resistance), Figure R26 (Joule heating performance), Figure\nR27 (infrared camera images),and Figure R28 (infrared emissivity). The senary\nFeCoNiCrMnRu sample (~51.8 Ω sq−1) also showed a slightly lower sheet resistance compared\nto both quinary FeCoNiCrRu (~60.2 Ω sq−1) and FeCoNiCrMn (~59.9 Ω sq−1). Furthermore,\nthe FeCoNiCrMnRu showed a performance improvement in equilibrium temperatures at the\n8V voltage compared to both FeCoNiCrRu and FeCoNiCrMn. Specifically, the equilibrium\ntemperatures of FeCoNiCrMnRu, FeCoNiCrRu, and FeCoNiCrMn were ~204.1 °C, ~183.4°C,\nand ~185.3°C, respectively. The infrared emissivity was consistently high across all three\nsamples, indicating that this property is predominantly governed by the LIG carrier rather than\nthe specific HEA composition. These results suggested that the metallic elements in this system\ncontributed in a largely equivalent manner to the electrical and thermal properties. The slight\nperformance advantage of the senary FeCoNiCrMnRu was more accurately attributed to its\nhigher configurational entropy rather than to the specific chemical identity of Ru.\nFigure R23. HAADF-STEM images and the corresponding EDS elemental mappings for\nHEA-NPs (Fe, Co, Ni, Cr, and Mn).\nFigure R24. Optical photos of (a) FeCoNiCrMnRu HEAs/LIG, (b) FeCoNiCrRu HEAs/LIG,\nand (c) FeCoNiCrMn HEAs/LIG surfaces.\nFigure R25. Sheet resistance of FeCoNiCrMn the HEAs/LIG, FeCoNiCrRu HEAs/LIG, and\nFeCoNiCrMnRuHEAs/LIG.\nFigure R26. Temperature-time curves of the FeCoNiCrMn HEAs/LIG, FeCoNiCrRu\nHEAs/LIG, and FeCoNiCrMnRu HEAs/LIG at the voltages of 8 V.\nFigure R27. Corresponding infrared camera images of the FeCoNiCrMn HEAs/LIG,\nFeCoNiCrRuHEAs/LIG, and FeCoNiCrMnRuHEAs/LIG at the voltages of 8 V.\nFigure R28. Infrared emissivity of the FeCoNiCrMn HEAs/LIG, FeCoNiCrRu HEAs/LIG,\nand FeCoNiCrMnRuHEAs/LIG in the wavelength range of 2.5 to 20 μm.\nWe have revised the manuscript to incorporate this new data and the refined discussion .We\nalso included Figure R24 as Figure S37, Figure R25 as Figure S38, Figure R26 as Figure\nS50, Figure R27 as Figure S51, and Figure R28 as Figure S56 in the supplementary\ninformation.\nBased on the concentration of the FeCoNiCrMnRu precursor solution (0.1 M), the used volume\n(160 μL) and the coated area (20 mm × 20 mm), we can estimate the mass loading of the\nFeCoNiCrMnRu HEA-NPs on the LIG to be ~1.5 mg cm⁻2. Therefore, even if Ru was used\nwith considering its cost and supply, its contribution to device-level cost is limited. However,\nit is also desirable to investigate a wider range of low-cost and abundant elements, such as Cu,\nZn, Mo, and Sn, to either replace Ru or further increase the configurational entropy, which is\nanticipated to correspondingly enhance the electrothermal performance of the HEAs/LIG\ncomposite. (Page 5, Manuscript)\nThe senary FeCoNiCrMnRu sample also showed a slightly lower sheet resistance compared to\nboth quinary FeCoNiCrRu (~60.2 Ω sq−1) and FeCoNiCrMn (~59.9 Ω sq−1) (Supplementary\nFigs. 37 and 38). (Page 9, Manuscript)\nAs for the high entropy samples, the FeCoNiCrMnRu showed a performance improvement in\nequilibrium temperatures at the 8V voltage compared to both FeCoNiCrRu and FeCoNiCrMn.\nSpecifically, the equilibrium temperatures of the FeCoNiCrMnRu, FeCoNiCrRu, and\nFeCoNiCrMn were ~204.1 °C, ~183.4°C, and ~185.3°C, respectively (Supplementary Figs. 50\nand 51). (Page 12, Manuscript)\nThe infrared emissivity was consistently high across all the FeCoNiCrMnRu, FeCoNiCrRu,\nand FeCoNiCrMn samples, further indicating that this property is predominantly governed by\nthe LIG carrier rather than the specific HEA composition. (Supplementary Fig. 56). (Page 13,\nManuscript)\nReviewer’s Comments\n5. High-performance Joule heating applications of the FeCoNiCrMnRu HEA-NPs should\nconsider the oxidation problems of the particles. It will be oxided quickly in air.\nOur Response\nWe sincerely appreciate the reviewer for raising the point regarding the oxidation stability of\nthe FeCoNiCrMnRu HEA-NPs for Joule heating applications, which is indeed a common and\nsignificant concern for metallic nanoparticles. We fully agree with the reviewer that the\noxidation of metallic NPs in air and during heating cycles can severely degrade their\nperformance. The emissivity of mid-infrared band (2.5−20 μm) was measured by a Fourier\ntransform infrared spectrometer with a gold integrating sphere (PIKE). To address this concern,\nwe have conducted a thorough post-analysis of samples that were synthesized approximately\nsix months ago and have since been exposed to ambient air (including periods of high humidity)\nand multiple Joule heating/cooling cycles. The performance of these aged HEAs/LIG samples\nremained remarkably stable, with negligible changes in both electrical resistance and\nemissivity (Figure R29). We further performed detailed TEM and EDS analysis on these aged\nsamples. The results clearly demonstrate that the HEA-NPs maintained their metallic character\nwithout significant oxidation (Figure R30). The EDS analysis show an oxygen signal\nassociated with the HEA-NPs (Figure R31). We attribute this exceptional oxidation resistance\nto the unique core-shell structure formed during our femtosecond laser processing. The HEA-\nNPs are predominantly encapsulated by a few layers of graphene. The graphene shell can serve\nas a protective layer, preventing the oxidation of the underlying metallic HEA cores during\nprolonged operation, thereby enhancing the long-term stability of the heater [Adv. Mater., 2024,\n36, 2402391]. Our work demonstrates that this strategy is equally effective for stabilizing\ncomplex HEA systems in oxidizing atmospheres and under thermal conditions, which is a key\nadvantage for the practical application of our material in durable, high-performance heating\nelements.\nFigure R29. (a) Sheet resistance and (b) infrared emissivity of the HEAs/LIG in the\nwavelength range of 2.5 to 20 μm before and after stability test. A sample stored for eight\nmonths under ambient conditions with the temperature 20–25 °C and relative humidity of\n~70%, while the other subjected to extensive Joule heating-cooling cycles after 100 cycles.\nFigure R30. HRTEM images of HEA-NPs after stability test, showing the multilayer graphene\nencapsulating the HEA-NPs.\nFigure R31. HAADF-STEM images and the corresponding EDS elemental mappings for\nHEA-NPs (Fe, Co, Ni, Cr, Mn, Ru, and O) after stability test.\nWe have also added corresponding discussion about the stability of HEA-NPs in the revised\nmanuscript. We also included Figure R29 as Figure S60, Figure R30 as Figure S61, and\nFigure R31 as Figure S62 in the supplementary information, as follows:\nFurthermore, the HEAs/LIG samples also showed excellent durability and stability during the\nair exposure, high humidity, and repeated heating/cooling test. The sheet resistance and surface\nemissivity of both tested samples almost remained unchanged after stability test\n(Supplementary Fig. 60). This exceptional oxidation resistance was attributed to the unique\ncore-shell structure formed during our femtosecond laser processing (Supplementary Fig. 61).\nThe formed graphene shell encapsulating the HEA-NPs provides an excellent barrier against\noxidation and moisture (Supplementary Fig. 62). The porous and robust LIG substrate firmly\nanchors the HEA-NPs, preventing their migration and agglomeration under repeated thermal\ntreatment. (Page 13, Manuscript)\nA List of changes in the main text of the revised manuscript\n1. Added Figs. S60, S61, S62 and some discussions about the oxidation stability of the HEA-\nNPs in the main text (Page 13), according to Reviewers #1 and #3.\n2. Added some discussions about the influence of the HEOs on the emissivity and conductivity\nin the main text (Page 8 and 10), according to Reviewer #1.\n3. Modified the blackbody radiation curves in Fig. 4h, Figs. S54, and S58, according to\nReviewer #1.\n4. Added some uncertainty discussions and clear disclosure of material constants and boundary\nconditions in the supplementary information (Note S2 and S8), according to Reviewer #1.\n5. Added Figs. S12, S13, S14 and some discussions about the large-area uniformity, batch-to-\nbatch reproducibility, and practical throughput considerations of femtosecond direct writing in\nthe main text (Page 5), according to Reviewer #1.\n6. Added Fig. S53 and some discussions about the bending durability of HEAs/LIG in the main\ntext (Page 12), according to Reviewer #1.\n7. Added the detailed assumptions, parameters, and calculation approach in the supplementary\ninformation (Note S9), according to Reviewer #1.\n8. Added some discussions about the material criticality and potential substitutions in the main\ntext (Page 5), according to Reviewers #1 and #3.\n9. Added Figs. S37, S38, S50, S51, S56 and some discussions in the main text (Page 9, 12, and\n13) to show the role of Ru and configurational entropy, according to Reviewers #1 and #3.\n10. Added Fig. S71 and some discussions in the main text (Page 15) to show the rapid on/off\ncycling stability of HEAs/LIG, according to Reviewer #1.\n11. Added some discussions in the main text (Page 4) and modified the analysis in the\nsupplementary information (Table S6) to show the practicality of using femtosecond laser for\npreparing HEA-NPs, according to Reviewer #2.\n12. Added some discussions about the thermal simulation limitations in the main text (Page 4),\naccording to Reviewer #2.\n13. Added some discussions about the multifunctionality in the main text (Page 12), according\nto Reviewer #2.\n14. Added Fig. S36 and some discussions in the main text (Page 8) to show the particle size of\nHEAs/LIG, according to Reviewer #3."}, {"round": 2, "reviewer_comments": {"reviewer_1": "The authors have addressed all concerns satisfactorily. Recommend acceptance for publication.", "reviewer_2": "The authors’ revised discussion on femtosecond laser processing adopts a more conservative tone and demonstrates an acceptable academic depth compared with similar recent reports.\nThe authors’ response helps understand the rationale behind employing E_T = 1/(h_c + h_r) as a normalized and comparative parameter for electrothermal performance. However, the terminology “energy-use efficiency” or “electrothermal conversion efficiency” used in the manuscript is then conceptually ambiguous. As Joule heating intrinsically converts electrical energy into heat with nearly 100% efficiency, E_T cannot be regarded as an energy-conversion efficiency in the thermodynamic sense.\nRegarding this point, the “energy saving” demonstration in Fig. 5(g–i) requires further clarification. Given that Joule heating converts electricity into heat at nearly 100% efficiency regardless of heater type, the generated heat should be transferred to the surroundings through radiation and convection. As acknowledged by the authors, E_T corresponds to the inverse of the effective heat-transfer coefficient. Thus, the local ΔT/P ratio merely indicates that the film has reduced heat loss to its immediate surroundings. In this study, however, the stated purpose of the heater is to warm the environment by transferring heat outward. Consequently, a heater with a high E_Tvalue acts as a good thermal insulator, not necessarily as an effective space heater.\nIt is therefore essential to clarify whether the temperature reported in Fig. 5h represents the surface temperature of the heater or the air temperature inside the house model. Furthermore, while the study claims high emissivity for the HEA heater, high emissivity would increase h_r and consequently lower E_T. This consideration appears inconsistent with the high “electrothermal conversion efficiency” for the HEA heater.\nIf the authors are unable to provide a convincing rebuttal to the above concerns, it indicates that the original novelty and conceptual foundation of the work are not sufficiently persuasive.", "reviewer_3": "I am satisfied with the revision. It can be accepted now."}, "author_response": "The Response to the Reviewer’s Comments\nManuscript Number: NCOMMS-25-66444A\nTitle: Ultrafast achieving multiscale high-entropy alloys/graphene for high-performance Joule\nheating\nAuthors: Lingxiao Wang, Kai Yin, Jianqiang Xiao, Xinghao Song, Jiaqing Pei, Jun He, Ji-An\nDuan\nNature Communications\nWe are indebted to the reviewers for their time and effort in reviewing our paper. The\ndetailed comments from the referees are very impressive and greatly valued. We are happy to\nhave such excellent advice for improving the paper’s quality. With our best efforts and best\nknowledge, we have made changes by following the referees’ comments. This report\nsummarizes our understanding of the recommendations and the changes we have made in\nresponse. The reviewers’ comments are reproduced following by the corresponding\nmodifications to the manuscript.\nIn this report, some reference numbers, equations, and figures are marked by an R, for\nexample, Figure R1, to distinguish them from those numbers for Figures in our original paper,\nfor examples, Figure 1 and Figure S1. Different descriptions are also marked with different\ncolors: Reviewer’s comments are black; Our response is marked with blue and red; The part\ninvolved the revised manuscript in our response is red.\nREVIEWER #1\nReviewer’s Comments\nThe authors have addressed all concerns satisfactorily. Recommend acceptance for\npublication.\nOur Response\nThank you for reviewing this work and supporting its publication in Nature Communications.\nREVIEWER #2\nReviewer’s Comments\nThe authors’ revised discussion on femtosecond laser processing adopts a more conservative\ntone and demonstrates an acceptable academic depth compared with similar recent reports.\nOur Response\nWe sincerely thank the reviewer for this positive assessment of the revised discussion on\nfemtosecond laser processing and for recognizing the academic depth of our work.\nReviewer’s Comments\n1. The authors’ response helps understand the rationale behind employing E_T = 1/(h_c + h_r)\nas a normalized and comparative parameter for electrothermal performance. However, the\nterminology “energy-use efficiency” or “electrothermal conversion efficiency” used in the\nmanuscript is then conceptually ambiguous. As Joule heating intrinsically converts electrical\nenergy into heat with nearly 100% efficiency, E_T cannot be regarded as an energy-conversion\nefficiency in the thermodynamic sense.\nOur Response\nWe sincerely thank the reviewer for this critical comment regarding the terminology “energy-\nuse efficiency” or “electrothermal conversion efficiency”. We agree that the Joule heating does\nindeed convert electrical energy to heat with nearly 100% efficiency. In our study, E was\nT\nintroduced as a performance index that reflects how effectively the generated heat is retained\nby the heater material under given convection and radiation conditions, rather than as a\nthermodynamic efficiency. In fact, many literature have also used this index to compare the\nheating efficiency of electric heaters [ACS Appl. Mater. Interfaces, 2012, 4, 2338-2342; Mater.\nDes., 2015, 86, 72-79; Carbon, 2019, 144, 116-126; Small, 2022, 18, 2202906]. To avoid\nconceptual ambiguity, we will revise the terminology throughout the manuscript. Accordingly,\nthe abbreviation of E (electrothermal conversion efficiency) has been changed to HEE (heater\nT\nenergy efficiency) in the following response.\nIn the revised manuscript, we have replaced the terminology “electrothermal conversion\nefficiency” with “heater energy efficiency” where appropriate, as follows:\nNotably, the multiscale composite material (HEAs/LIG) can serve as Joule heating material,\nachieving a heater energy efficiency of ~285.4 °C cm2 W−1. (Page 2, Manuscript)\nWe further established the relationship between equilibrium temperature and input power\ndensity, and summarized the heater energy efficiency of other advanced electrothermal\nmaterials. (Page 12, Manuscript)\nAs for the HEAs/LIG, the fitting calculation showed a heater energy efficiency of up to\n~285.4 °C cm2 W−1, indicating superior performance that surpassed most electrothermal\nmaterials (Fig. 4g and Supplementary Table 7)49–51. (Page 12, Manuscript)\nRemarkably, the resulting HEAs/LIG functions as an outstanding Joule heater, delivering a\nheater energy efficiency of ~285.4 °C cm2 W−1 and average infrared emissivity of ~0.98 across\na wide wavelength range of 2.5–20 μm. (Page 17, Manuscript)\nReviewer’s Comments\n2. Regarding this point, the “energy saving” demonstration in Fig. 5(g–i) requires further\nclarification. Given that Joule heating converts electricity into heat at nearly 100% efficiency\nregardless of heater type, the generated heat should be transferred to the surroundings through\nradiation and convection. As acknowledged by the authors, E_T corresponds to the inverse of\nthe effective heat-transfer coefficient. Thus, the local ΔT/P ratio merely indicates that the film\nhas reduced heat loss to its immediate surroundings. In this study, however, the stated purpose\nof the heater is to warm the environment by transferring heat outward. Consequently, a heater\nwith a high E_T value acts as a good thermal insulator, not necessarily as an effective space\nheater.\nOur Response\nWe sincerely appreciate this important conceptual point. As for the Joule heating, the electrical\nenergy is converted into heat with nearly 100% efficiency for any resistive heater. In this sense,\nthere is no fundamental thermodynamic conversion efficiency difference between our\nHEAs/LIG heater and a conventional one. In Fig. 5(g–i), the temperature we track is the surface\ntemperature of a titanium sheet placed inside the house model (Fig. 5h), which acts as a heated\nobject. The “energy saving” specifically refers to the ability to reach a given target temperature\nof a representative heated object inside the house model using lower electrical power, under\nidentical external boundary conditions. That is, we compare how much electrical power is\nrequired for different heaters to bring the same object to the same temperature.As the reviewer\nnotes, a larger HEE indicates a larger temperature rise for a given input power and can be\nviewed as a higher effective thermal resistance between the heater and its surroundings. At the\nsame time, the HEAs/LIG heater exhibits high infrared emissivity, which enhances radiative\nheat transfer toward the interior of the house model, where the titanium sheet is located. It\nindicates that, for a given input power, more of the heat from the HEAs/LIG heater is\neffectively directed toward the intended target, thereby exhibiting better energy efficiency ratio.\nFurthermore, we contend that high HEE and high infrared emissivity are not fundamentally\ncontradictory. Theoretically, an exceptionally high infrared emissivity may reduce HEE due to\nincreased radiative heat loss. However, our HEAs/LIG heater simultaneously exhibits both\nhigh HEE and infrared emissivity, demonstrating its exceptional energy utilization efficiency\nand radiative heating capability.\nReviewer’s Comments\n3. It is therefore essential to clarify whether the temperature reported in Fig. 5h represents the\nsurface temperature of the heater or the air temperature inside the house model. Furthermore,\nwhile the study claims high emissivity for the HEA heater, high emissivity would increase h_r\nand consequently lower E_T. This consideration appears inconsistent with the high\n“electrothermal conversion efficiency” for the HEA heater.\nOur Response\nWe thank the reviewer for pointing out this missing clarification. In Fig. 5h, the plotted\ntemperature corresponds to the upper surface temperature of the heated Ti sheet placed inside\nthe house model, rather than the bulk air temperature. The design of the experiment device is\nsimilar to Fig. 5a. The Ti sheet was mounted at the center of the interior space and directly\nexposed to the radiative heating from the HEAs/LIG heater. Its upper surface temperature was\nmonitored by a temperature sensor attached to the sheet, and the recorded value is demonstrated\nin Fig. 5h.\nWe agree with reviewer that this is a valid point. From a fundamental heat-transfer\nperspective, an increase in infrared emissivity directly leads to a higher radiative heat-transfer\ncoefficient (h). All else being equal, this would result in a larger total heat-transfer coefficient\nr\nand therefore a lower value of HEE. This relationship is correctly noted. However, h is not the\nr\nsole determinant of HEE. The calculated HEE value reflects the combined effect of both\nradiative and convective heat-loss pathways from the heater surface. The prepared HEAs/LIG\ncomposite features a complex and porous micro/nano-structured surface. Previous literature\nsuggests that this morphology can be effective at suppressing air convection near the\nHEAs/LIG surface through stabilizing the air boundary layer and reducing effective air flow\n[Int. J. Heat Mass Tran., 2024, 220, 124941; Ceram. Int., 2024, 50, 36792-36799; Interceram.-\nInt. Ceram. Rev., 2021, 70, 38-45]. Thus, there is no fundamental contradiction. The high\nemissivity ensures efficient radiative output once the heater is heated, while the surface\nmorphology minimizes convective losses. This synergy allows the heater to achieve a high\nsteady-state temperature with low input power and then to release that heat primarily as useful\ninfrared radiation.\nIn the revised manuscript, we have corrected the corresponding illustration to clarify the\nmeasurement:\nAt 5 V voltage, the HEAs/LIG heater could lift the upper surface temperature of the heated\nobject from ~−7.5 °C to a human-comfortable level of ~24.0 °C, while CEH failed under the\nsame conditions (Fig. 5h and Supplementary Fig. 73). (Page 15, Manuscript)\nFig. 5h, Temperature changes of the upper surface of heated object inside the house when\nradiated by HEAs/LIG, P-LIG, and CEH, respectively. (Page 16, Manuscript)\nThe laser-treated Ti substrate was used as the heated object in the radiative thermal transfer\nexperiment (Fig. 5b and 5h). (Page 17, Manuscript)\nReviewer’s Comments\n4. If the authors are unable to provide a convincing rebuttal to the above concerns, it indicates\nthat the original novelty and conceptual foundation of the work are not sufficiently persuasive.\nOur Response\nWe sincerely thank the reviewer for this critical comment. The novelty and conceptual\nfoundation of our work do not solely depend on the interpretation of the heater energy\nefficiency HEE. While the clarification regarding HEE is an important technical point, the core\ninnovations of this study are multifaceted and robust.\nIn our work, we demonstrate the ultrafast femtosecond laser solid-phase synthesis of\nFeCoNiCrMnRu HEA-NPs on the LIG for the first time. Utilizing super-black LIG substrates\nand the ultrashort femtosecond laser pulse, this approach enables ultrafast heating and cooling\nrates. This facilitates the successful synthesis of disordered HEA-NPs.\nFurthermore, we found that the HEA precursors significantly reduced the electrical\nresistance and enhanced the electrothermal conversion performance of LIG. Density functional\ntheory calculations revealed that the resistance reduction originates from the deoxygenation\nand renovation of LIG induced by HEA-NPs, coupled with an increased density of states owing\nto HEA-NPs loading. The HEAs/LIG demonstrates excellent heater energy efficiency\n(~285.4 °C cm2 W−1), superior to most reported electrothermal materials.\nPrevious studies indicate that HEA-NPs usually exhibit high visible-light absorption,\nwhereas high-entropy oxides demonstrate high infrared emissivity. Our designed HEAs/LIG\ncomposite overcomes the limitation of HEA-NPs by loading them onto the LIG surface,\nachieving ultrahigh broadband infrared emissivity. Meanwhile, the femtosecond laser\nreconstruction of LIG surface can generate rougher hierarchical micro/nanostructures with\nfeature sizes exceeding infrared wavelength, enhancing the interaction between infrared light\nand substrates for further improving the infrared emissivity. Consequently, the fabricated\nHEAs/LIG achieves an average infrared emissivity of ~0.98 across the 2.5–20 μm, which\noutperforms most high emissivity materials.\nFinally, we demonstrate a series of applications utilizing the HEAs/LIG as a Joule heater,\nincluding radiative thermal transfer, electric warming, and rapid ice melting. For heating\napplications in cold winter environments, our HEAs/LIG heater achieves a ~49.1% energy\nsaving compared to conventional electric heater (CEH), highlighting its significant potential\nfor energy-efficient thermal management.\nREVIEWER #3\nReviewer’s Comments\nI am satisfied with the revision. It can be accepted now.\nOur Response\nThank you for reviewing this work and supporting its publication in Nature Communications.\nA List of changes in the main text of the revised manuscript\n1. Changed the terminology “electrothermal conversion efficiency” with “heater energy\nefficiency” in the main text (Page 2, 12 and 17), according to Reviewer #2.\n2. Added illustration about the recorded temperature of the heated object in the main text (Page\n15, 16 and 17), according to Reviewer #2."}, {"round": 3, "reviewer_comments": {"reviewer_1": "After carefully reviewing the latest comments from Reviewer #2 together with the authors’ rebuttal, I am inclined to support acceptance of the manuscript, provided that the conclusions are interpreted within clearly defined boundaries. In my assessment, the remaining disagreement is primarily related to the scope and wording of the interpretation rather than to the validity of the experimental data or the scientific soundness of the work. The study convincingly demonstrates a novel femtosecond-laser enabled route for fabricating high-entropy alloy nanoparticles on LIG and establishes their ultrahigh emissivity and effective radiative heat delivery to a nearby target object. When “heater energy efficiency (HEE)” is understood as a comparative performance metric, namely, the electrical power required to achieve a specified heating outcome under identical conditions, there is no fundamental physical inconsistency between ultrahigh emissivity and the reported heating performance. Indeed, the “heater energy efficiency” metric is a widely recognized and commonly adopted parameter for comparing the energy utilization efficiency of various electro‑thermal conversion devices, such as Adv. Funct. Mater. 2023, 33, 2213357, Adv. Eng. Mater. 2022, 24, 2200368, and Small, 2022, 18, 2202906. The method for calculating the “heater energy efficiency” adopted in the manuscript is also consistent with those reported in other literature.\nRegarding the “energy saving” and heat-transfer interpretation, I agree that the manuscript should not be read as demonstrating improved general space-heating efficiency. However, the experimental data robustly support a more focused and well-defined conclusion: the proposed radiative heating approach achieves measurable reductions in electrical power consumption required to reach the same target-object temperature, within the specific geometric and enclosed conditions tested. The authors have explicitly confined the “energy saving” claim to the aforementioned conditions. The energy-saving performance of the HEAs/LIG composites has been experimentally verified, and its significant energy-saving potential has further been validated through simulations. Additionally, the authors reasonably suggest that the LIG morphology contributes to suppressing convection, thereby maintaining excellent “heater energy efficiency” even under conditions of high infrared emissivity, which should be regarded as a plausible contributing factor. Considering the above points collectively, I believe the manuscript is scientifically robust. With such restrained interpretation and minor textual refinement, the work makes a meaningful contribution to radiative heating materials and can be suitable for publication.", "reviewer_2": "This reviewer appreciates the multidisciplinary nature of the study and its contributions to femtosecond-laser synthesis of high-entropy alloy nanoparticles and broadband emissivity control. However, the claimed coexistence of ultrahigh emissivity and high heater energy efficiency (HEE) remains supported only qualitatively, and the demonstrated “energy saving” should be interpreted strictly in the context of radiative heating of a target object rather than as an improvement in general space-heating efficiency.\nIn particular, the assertion that the LIG surface morphology suppresses convection sufficiently to compensate for increased radiative losses is not convincingly validated. This is a nontrivial heat-transfer argument, and the cited literature is not directly related to this problem. Moreover, within a small “house model” enclosure, buoyancy-driven natural convection is difficult to suppress in practice. As such, the concept of an LIG-based space heater remains scientifically fragile and open to further debate."}, "author_response": "The Response to the Reviewer’s Comments\nManuscript Number: NCOMMS-25-66444B\nTitle: Femtosecond laser synthesis of multiscale high-entropy alloys/graphene composites for\nhigh-performance Joule heating\nAuthors: Lingxiao Wang, Kai Yin, Jianqiang Xiao, Xinghao Song, Jiaqing Pei, Jun He, Ji-An\nDuan\nNature Communications\nWe are indebted to the reviewers for their time and effort in reviewing our paper. The\ndetailed comments from the referees are very impressive and greatly valued. We are happy to\nhave such excellent advice for improving the paper’s quality. With our best efforts and best\nknowledge, we have made changes by following the referees’ comments. This report\nsummarizes our understanding of the recommendations and the changes we have made in\nresponse. The reviewers’ comments are reproduced following by the corresponding\nmodifications to the manuscript.\nIn this report, some reference numbers, equations, and figures are marked by an R, for\nexample, Figure R1, to distinguish them from those numbers for Figures in our original paper,\nfor examples, Figure 1 and Figure S1. Different descriptions are also marked with different\ncolors: Reviewer’s comments are black; Our response is marked with blue and red; The part\ninvolved the revised manuscript in our response is red.\nREVIEWER #1\nReviewer’s Comments\nAfter carefully reviewing the latest comments from Reviewer #2 together with the authors’\nrebuttal, I am inclined to support acceptance of the manuscript, provided that the conclusions\nare interpreted within clearly defined boundaries. In my assessment, the remaining\ndisagreement is primarily related to the scope and wording of the interpretation rather than to\nthe validity of the experimental data or the scientific soundness of the work. The study\nconvincingly demonstrates a novel femtosecond-laser enabled route for fabricating high-\nentropy alloy nanoparticles on LIG and establishes their ultrahigh emissivity and effective\nradiative heat delivery to a nearby target object. When “heater energy efficiency (HEE)” is\nunderstood as a comparative performance metric, namely, the electrical power required to\nachieve a specified heating outcome under identical conditions, there is no fundamental\nphysical inconsistency between ultrahigh emissivity and the reported heating performance.\nIndeed, the “heater energy efficiency” metric is a widely recognized and commonly adopted\nparameter for comparing the energy utilization efficiency of various electro‑thermal\nconversion devices, such as Adv. Funct. Mater. 2023, 33, 2213357, Adv. Eng. Mater. 2022, 24,\n2200368, and Small, 2022, 18, 2202906. The method for calculating the “heater energy\nefficiency” adopted in the manuscript is also consistent with those reported in other literature.\nRegarding the “energy saving” and heat-transfer interpretation, I agree that the\nmanuscript should not be read as demonstrating improved general space-heating efficiency.\nHowever, the experimental data robustly support a more focused and well-defined conclusion:\nthe proposed radiative heating approach achieves measurable reductions in electrical power\nconsumption required to reach the same target-object temperature, within the specific\ngeometric and enclosed conditions tested. The authors have explicitly confined the “energy\nsaving” claim to the aforementioned conditions. The energy-saving performance of the\nHEAs/LIG composites has been experimentally verified, and its significant energy-saving\npotential has further been validated through simulations. Additionally, the authors reasonably\nsuggest that the LIG morphology contributes to suppressing convection, thereby maintaining\nexcellent “heater energy efficiency” even under conditions of high infrared emissivity, which\nshould be regarded as a plausible contributing factor. Considering the above points\ncollectively, I believe the manuscript is scientifically robust. With such restrained\ninterpretation and minor textual refinement, the work makes a meaningful contribution to\nradiative heating materials and can be suitable for publication.\nOur Response\nThank you for reviewing this work and supporting its publication in Nature Communications.\nWe sincerely thank Reviewer #1 for the thorough assessment and strong support for publication.\nWe have carefully addressed the recommendation for \"minor textual refinement\" and ensured\nour conclusions are \"interpreted within clearly defined boundaries.\"\nThe specific revisions made in the manuscript are as follows:\nHeater energy efficiency can be interpreted as a comparative performance metric, representing\nthe electrical power density required to achieve a specified surface temperature under identical\ninput conditions. (Page 10, Manuscript)\nThe high heater efficiency of HEAs/LIG represents an objective outcome derived after\naccounting for both infrared radiation and convective heat transfer.The higher heater efficiency\nof HEAs/LIG may also be plausibly attributed to the disruption of air convection by their\nsurface structural morphology. (Page 10, Manuscript)\nDue to the high heater energy efficiency and infrared emissivity, the HEAs/LIG could achieve\na higher surface temperature under the same electrical power input. This elevated temperature,\ncoupled with the high emissivity, enables efficient radiative heating of objects. (Page 12,\nManuscript)\nUnder the tested specific geometric and enclosed conditions (housing model), HEAs/LIG\nheaters achieved a measurable reduction in the electrical energy consumption required to reach\nthe same target object temperature, thereby demonstrating an energy-saving effect. (Page 12,\nManuscript)\nREVIEWER #2\nReviewer’s Comments\nThis reviewer appreciates the multidisciplinary nature of the study and its contributions to\nfemtosecond-laser synthesis of high-entropy alloy nanoparticles and broadband emissivity\ncontrol. However, the claimed coexistence of ultrahigh emissivity and high heater energy\nefficiency (HEE) remains supported only qualitatively, and the demonstrated “energy saving”\nshould be interpreted strictly in the context of radiative heating of a target object rather than\nas an improvement in general space-heating efficiency.\nIn particular, the assertion that the LIG surface morphology suppresses convection\nsufficiently to compensate for increased radiative losses is not convincingly validated. This is\na nontrivial heat-transfer argument, and the cited literature is not directly related to this\nproblem. Moreover, within a small “house model” enclosure, buoyancy-driven natural\nconvection is difficult to suppress in practice. As such, the concept of an LIG-based space\nheater remains scientifically fragile and open to further debate.\nOur Response\nWe sincerely thank Reviewer #2 for the continued engagement and acknowledgment of our\ncontributions to femtosecond-laser synthesis and emissivity control. We have clarified that the\n\"energy-saving effect\" discussed in the paper specifically refers to the reduction in electrical\nenergy consumption in the context of heating of a target object. This clarification has been\nconsistently incorporated in the main text. In addition, a discussion has been incorporated\nregarding the possibility that the surface morphology enhances heater efficiency by disrupting\nthermal convection.\nThe specific revisions made in the manuscript are as follows:\nHeater energy efficiency can be interpreted as a comparative performance metric, representing\nthe electrical power density required to achieve a specified surface temperature under identical\ninput conditions. (Page 10, Manuscript)\nThe high heater efficiency of HEAs/LIG represents an objective outcome derived after\naccounting for both infrared radiation and convective heat transfer.The higher heater efficiency\nof HEAs/LIG may also be plausibly attributed to the disruption of air convection by their\nsurface structural morphology. (Page 10, Manuscript)\nDue to the high heater energy efficiency and infrared emissivity, the HEAs/LIG could achieve\na higher surface temperature under the same electrical power input. This elevated temperature,\ncoupled with the high emissivity, enables efficient radiative heating of objects. (Page 12,\nManuscript)\nUnder the tested specific geometric and enclosed conditions (housing model), HEAs/LIG\nheaters achieved a measurable reduction in the electrical energy consumption required to reach\nthe same target object temperature, thereby demonstrating an energy-saving effect. (Page 12,\nManuscript)\nA List of changes in the main text of the revised manuscript\n1. Tempered and clarified the claims related to LIG morphology, heater energy efficiency, and\nenergy saving in the main text (Page 10 and 12), according to Reviewers #1 and #2."}]

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