A self-breathing electrode enabled by interface regulation and gradient wettability engineering for industrial H_2O_2 electrosynthesis

Domain: chemistry
Published: 2026-01-15
Editorial outcome: major_revision

Abstract
High-performance gas diffusion electrodes (GDEs) are essential for electrochemical H2O2 production, yet conventional catalyst layers (CLs) suffer from PTFE-fused encapsulation and disordered pores that create mass-transport bottlenecks and suppress three-phase interface (TPI) formation. Here, we introduce a non-fused particulate-packed catalyst/binder interface and elucidate the mechanisms governing TPI formation through 3D reconstruction and mesoscale LBM analyses. Guided by these insights, we construct a hierarchical gradient CL with ordered porosity and tunable wettability contrast, and multiscale simulations together with in-situ breakthrough and microfluidic experiments confirm capillarity-driven electrolyte displacement and directional self-transport of H2O2, enabling stable Faraday efficiencies > 85% at 300 mA cm–2 for 300 h. We further develop a 400 cm2 four-unit self-breathing flow-through stack integrating thermal, fluidic, and electronic systems for continuous, oxygen-free, low-cost H2O2 generation. This work offers a fundamental design framework for advanced GDEs and demonstrates a milestone integrated self-breathing H2O2 electrosynthesis system with commercial viability.

Introduction
Hydrogen peroxide (H2O2) is a green oxidant widely used in sustainable chemical synthesis and pollutant treatment, serving as a cornerstone of modern green chemistry1,2. Currently, over 95% of H2O2 is produced via the anthraquinone process—a complex route that generates substantial hazardous by-products with high energy consumption and cost3. As a sustainable alternative, the electrochemical two-electron oxygen reduction reaction (2e− ORR) enables economical, on-site H2O2 production using only air, water, and renewable electricity. This decentralized approach supports the chemical industry’s green transition and aligns with carbon neutrality goals4–6.

Gas diffusion electrodes (GDEs) represent the most promising electrode architecture for 2e− ORR, as they physically separate gas and liquid phases and help overcome oxygen solubility limitation7. Despite decades of catalyst-focused research, GDEs continue to suffer from well-known “flooding” under high current densities—a key bottleneck to industrial deployment8–10. Strategies such as increasing polytetrafluoroethylene (PTFE) content or incorporating electrospun hydrophobic layers can mitigate flooding but often compromise conductivity due to a trade-off between hydrophobicity and electron transport11–13. Even recent strategies like crack engineering that facilitate gas access fail to fully prevent flooding in catalyst regions beyond the cracks14. These results expose a critical paradox: while catalyst innovation has flourished, GDE structural limitations continue to impede industrial adoption. This persistent challenge highlights a critical knowledge gap in electrode engineering—the lack of established design principles for three-phase interface (TPI) construction has confined structural optimization to empirical trial-and-error approaches.

Traditionally, catalyst layers (CLs) are fabricated by depositing a slurry of catalyst particles, PTFE, and alcohol-based solvents onto a gas diffusion layer (GDL)12,15. To ensure the hydrophobicity of the PTFE, calcination is typically required to remove residual surfactants11,16. However, this fabrication route conceals three critical limitations. (1) Slurry dispersion issue. PTFE tends to aggregate and separate from catalysts in alcohol media, especially at high loadings17,18. (2) Covered and segregated interface structure. Upon calcination, PTFE melts non-uniformly: some coats catalyst surfaces, forming an insulating armor that increases resistance, while the rest forms isolated hydrophobic islands detached from the catalyst12,16,19,20. This dual structure imposes a PTFE content threshold—representing the root of the long-standing trade-off between hydrophobicity and electron transport in GDEs. (3) The emergence of spatial disorder: the coexistence of coated and segregated PTFE domains results in randomly distributed wettability and pore structures, creating a mass transport maze that disrupts capillary-driven convection and obstructs removal of in situ generated H2O2. These findings highlight that ambiguous catalyst-binder interfaces and disordered CL structures fundamentally limit GDE performance. Rather than incremental improvements within this constrained paradigm, transformative advances require a complete architectural redesign of the CL.

Bridging this gap in interface engineering demands a systematic understanding of the pore architecture arising from catalyst–binder interactions and its role in TPI formation within the CL21. However, conventional tools—scanning electron microscopy (SEM), contact angle (CA) measurements, and N2 adsorption/desorption—fail to resolve true 3D microstructures. SEM provides only 2D projections; CA is affected by surface roughness and binder exposure6,22; and N2 adsorption/desorption offers only statistical pore data, lacking spatial context. To date, the actual spatial arrangement of catalyst/binder components and their resulting pore structures in CLs remain poorly understood. Equally unclear is how the triple-phase microenvironment controls 2e– ORR mass transport, creates active zones, and accelerates reaction kinetics.

Here, a non-fused particulate-packed catalyst/binder interface (Fig. 1) is introduced, in which discrete PTFE is embedded within the catalyst matrix to form a packed-contact, pore-percolated structure that exposes active sites and supports dense TPIs. Using focused ion beam-scanning electron microscopy (FIB-SEM) 3D reconstruction, the Lattice Boltzmann Method (LBM), and the Quartet Structure Generation Set (QSGS), electrolyte intrusion was quantitatively revealed to be governed by the coupling of wettability and pore geometry, uncovering the structural origin of TPI formation. Guided by these findings, an ordered CL with controlled wettability gradients and hierarchical pores was subsequently developed, and multiscale simulations together with microfluidic experiments validated that Laplace pressure-driven directional H2O2 transport occurs through the CL. The optimized electrodes were operated stably for over 500, 300, and 50 h at 15, 300, and 400 mA cm−2, respectively, maintaining FE above 80%. Finally, we scaled up the design to a 400 cm2 five-cell modular flow-through cell stack, integrating electronic, thermal, and fluidic subsystems into a commercially viable in situ H2O2 synthesis platform. This fully assembled platform enables in situ H2O2 production using only air, water, and electricity, achieving a cost as low as $0.381 kg−1—marking a key step toward decentralized, cost-effective and low-carbon manufacturing of H2O2.

Results
Non-fused particulate-packed interface structure
To investigate the effect of the catalyst/binder interface structure on electrochemical H2O2 production, two GDEs were fabricated using PTFE as the binder: one with a conventional fused–segregated interface (FSE), and another with a non-fused particulate-packed interface (PPE), prepared via different deposition methods (Supplementary Fig. 1; Methods). In the FSE electrode, a significant portion of CB is covered by fused PTFE, while in localized regions, PTFE coalesces into large patches (Fig. 2a), forming hydrophobic islands—a phenomenon previously reported6,12,22. In contrast, PPE exhibits discrete PTFE particles co-packed with CB in a stacked arrangement (Fig. 2a). To isolate the effect of microscale interface structure, key deposition variables were controlled to yield comparable CL thicknesses—a factor known to influence performance23. Cross-sectional SEM (Fig. 2b) shows only a minor difference in thickness between FSE (110.2 μm) and PPE (119.8 μm), likely due to hot-press-induced densification. PTFE content was also adjusted to match initial wettability (CA = 150°, Fig. 2c), and both used identical hydrophobic carbon paper as the gas diffusion layer (Supplementary Fig. 2). These controls ensured that microscale interface architecture was the sole performance variable. Electrolysis was conducted in a divided, self-breathing cell open to ambient air (Supplementary Fig. 3). At 15 mA cm–2, both electrodes showed similar FE (80–90%) (Fig. 2d), consistent with prior work13,24,25. However, at 300 mA cm–2, FSE dropped below 1% FE within 5 h, while PPE maintained >80% (Fig. 2e). These findings clearly demonstrate that, while both electrodes share similar macroscopic characteristics, the microscopic interface structure introduces a profound performance gulf.

To elucidate the performance disparity between the two GDEs, their physicochemical properties and O2/electrolyte mass transport behavior were systematically investigated. In the diffusion-limited open-air system used here, efficient O2 delivery to active sites is essential for sustaining the 2e– ORR. Stepwise chronoamperometry (25 mA cm–2 per step) was employed to monitor FE and steady-state potential under increasing current, thereby quantifying oxygen transport limitations. As shown in Fig. 2f, PPE exhibited stable potential shifts within 300 mV and consistent FE, suggesting that the reaction remained under kinetic and ohmic control without significant mass transport limitations. In contrast, FSE exhibited rising overpotentials and declining FE, signaling concentration polarization and the onset of parasitic 4e− ORR or hydrogen evolution reaction (HER). Interestingly, post-electrolysis CA was higher for FSE than PPE (Fig. 2c)—contrary to the expectation that higher hydrophobicity promotes gas diffusion. Given their identical catalyst, initial wettability, and macroscale structure, this counterintuitive result highlights a key insight: the observed difference in oxygen transport capability likely arises from variations in microscopic interface architecture. Multiscale SEM imaging revealed that PPE features a discrete particulate network, with PTFE embedded between CB domains to form a porous structure (Supplementary Fig. 4a–c), while FSE exhibits melted PTFE coverage and isolated hydrophobic domains (Supplementary Fig. 4d–f). This fused-driven restructuring significantly reduced microporosity and yielded a denser catalyst layer (Supplementary Fig. 4d). Mercury intrusion porosimetry quantitatively confirmed these structural differences, revealing that PPE exhibited higher macro-/mesopore content, greater pore volume, and lower tortuosity (Supplementary Fig. 5), consistent with a more efficient mass transport regime across the CL. These findings collectively suggest that the microscopic interface structure governs the porosity, gas access, and mass transport regime of the CL, ultimately dictating whether efficient 2e– ORR can be sustained under demanding conditions.

To clarify how microscale pore structures influence species transport, mesoscale simulations of gas-liquid-solid interactions within the CLs of FSE and PPE were performed. CL architectures were reconstructed using the QSGS method by tuning the PTFE nucleation probability (P) and phase occupation ratio (Rp), mimicking PTFE melting and CB encapsulation while maintaining the same packing density as PPE, thereby isolating the influence of densification caused by hot pressing. As shown in Supplementary Fig. 8, PPE-cal exhibited partial PTFE fusion but lacked the compact morphology of FSE. Electrochemical H2O2 synthesis revealed a clear performance hierarchy of PPE > PPE-cal > FSE, indicating that both molten encapsulation and reduced porosity contribute to the degraded performance of conventional electrodes (Supplementary Fig. 9). Similar binder-induced encapsulation effects have also been observed in ionomer-based catalyst layers (e.g., Nafion coatings on Pt/C), where excessive polymer coverage hinders gas diffusion, highlighting the broader relevance of this interfacial limitation30. These findings indicate that the microscopic interface architecture plays an important role in shaping pore morphology and mass-transport pathways, which in turn influence electrode performance at high current densities. (see detailed analysis below).

CL optimization based on non-fused particulate interface architecture
Having identified the optimal interface architecture, we systematically varied the PTFE–to–CB mass ratio (P/C = 0–1.5, with fixed catalyst loading) to tune the abundance and spatial distribution of non-fused particulate-packed interfaces. Electrolysis tests were conducted across 15–400 mA cm–2 (Fig. 3a and Supplementary Fig. 10). Due to the fabrication method, even the PTFE-free electrode (P/C = 0) exhibited 80% and 60% FE at 15 and 100 mA cm–2, respectively—demonstrating performance that remains competitive with certain PTFE-containing systems reported in the literature13,31,32. However, CB oxidation in H2O2-rich environments gradually increases hydrophilicity, restricting O2 access at higher currents31,33. Stepwise chronoamperometry confirmed this: P/C-0 showed large voltage deviation and rapid FE decline beyond 200 mA cm–2, indicating severe oxygen transport limitations and parasitic hydrogen evolution (Fig. 3b, c), consistent with the FE trend in Fig. 3a. In contrast, PTFE-containing GDEs maintained >80% FE and stable voltages up to 250 mA cm–2 (Fig. 3a). This consistent performance contrasts with previous studies, which reported significant performance divergence even below 100 mA cm–2 and within 1 h of operation6,11,12,34. These results reaffirm that particulate-packed interfaces promote full exposure of catalytic active sites, delivering consistent performance under low oxygen demand. At higher current densities, greater oxygen demand requires more PTFE to sustain hydrophobicity and gas transport, shifting optimal FE toward higher P/C ratios (Fig. 3a). LSV confirmed this trend: at low potentials, all electrodes responded similarly, with P/C-0 slightly higher due to enhanced ionic transport from its more hydrophilic surface. As potential increased, P/C-0 exhibited a clear deviation from linearity, with current growth slowing due to oxygen transport limitation, while P/C-0.9 maintained a linear response, reflecting improved O2 access and overall performance (Fig. 3d).

Unexpectedly, the FE of P/C-1.2 and P/C-1.5 sharply declined to 69 and 41%, respectively, at 400 mA cm–2 (Fig. 3a). We hypothesized that excessive hydrophobicity might hinder proton transport. To test this, Nafion was added to the ink to enhance proton conductivity; however, performance did not recover, ruling out proton transport as the limiting factor (Fig. 3a). In contrast, supplying external oxygen to the GDL side restored the performance of P/C-1.5 to P/C-0.9 levels, confirming oxygen transport as the primary bottleneck. Paradoxically, P/C-1.5 would theoretically be expected to offer enhanced oxygen retention compared to P/C-0.9. This counterintuitive result suggests the presence of microscale limitations within the CL that override the bulk material properties. SEM images revealed clear spatial separation between PTFE and CB in P/C-1.5 (Fig. 3e). Such inhomogeneous distribution causes electrolyte to preferentially migrate toward CB-rich zones under surface tension, undermining the formation of effective triple-phase interfaces (Fig. 3f). Thus, oxygen transport and TPI stability are governed not merely by the amount of hydrophobic binder, but by its spatial localization within the CL.

To further investigate the origin of PTFE/CB separation at high P/C ratios, ink formulations were analyzed using a laser particle size analyzer35,36. As shown in Fig. 3e, increasing the P/C ratio shifted the particle size distribution toward larger diameters, with elevated D50 and D90 values (Supplementary Table 1). This indicates that higher PTFE content led to increased precipitation in the ink, which likely contributed to large PTFE agglomerates during CL fabrication17,37. While the impact of ink dispersion on fuel cell electrodes is well established38,39, such effects remain underexplored in H2O2 electrosynthesis. In alcohol-based media, PTFE readily flocculates due to low surface energy and poor dispersion stability17. We found that elevated temperature, rapid PTFE addition, and high P/C ratios exacerbated flocculation, driven by strong interparticle attraction and bridging effects in neutral, nonionic solvents (Supplementary Fig. 11 and Supplementary Table 2)18,40. These results suggest that although particulate-packed structures benefit from increased PTFE content in theory, poor dispersion imposes a practical upper limit—one that may require advanced dispersion strategies to overcome.

Mechanism of gas-liquid transport and TPI in CLs
To clarify how catalyst and binder co-assembly shapes internal pores and governs gas-liquid interactions, we combined 3D FIB-SEM reconstruction with mesoscale simulations to visualize and quantify internal fluid behavior. The real 3D structure of the CL was reconstructed via FIB-SEM (Supplementary Fig. 12), with two pretreatment protocols validated beforehand (Supplementary Note 1; Supplementary Figs. 13 and 14) to ensure structural integrity41,42. The reconstructed CL (Fig. 4a) reveals PTFE and CB as interspersed particulate aggregates, forming a packed granular network. PTFE appears as spheres or loose flocculates (10–100 nm, Supplementary Fig. 15). These 3D images confirm that PTFE and CB are interspersed as particulate ensembles, forming a packed granular architecture (Fig. 4b). Quantitative voxel-based analysis revealed the particle size, porosity, and pore size distribution of each component. The CL exhibited a bimodal solid-phase size distribution: CB was primarily found in the 0–50 nm range, consistent with its intrinsic size (~30 nm; Supplementary Fig. 16)43. The overall porosity (~0.73) aligned well with mercury intrusion data (Supplementary Fig. 17, and Fig. 2g). While micropores (<10 nm) dominated the pore population, as widely reported16, our CLs contained a significantly higher fraction of meso- and macropores, which are more favorable for O2 and H2O2 transport.

After obtaining the 3D structure of the real CL, we simulated gas–liquid–solid three-phase flow using the LBM29,44. In these simulations, the electrolyte was treated as an ideal, incompressible, charge-neutral fluid. Although this simplification neglects ionic strength and electrostatic effects, it captures the capillary-driven intrusion dominated by pore geometry and wettability at the mesoscale. Similar assumptions are widely used in multiphase-flow models of porous electrodes for fuel cells, validating its suitability for describing gas-liquid dynamics in GDEs29. To avoid the non-physical interfacial film artifacts commonly encountered in traditional pseudopotential models near solid surfaces, we adopted a recently developed phase-field model and implemented it on a GPU-accelerated CUDA platform (simulation parameters in Supplementary Table 3)45,46. The physical model and boundary conditions are shown in Supplementary Fig. 15. Figure 4c presents a YZ cross-section at x=110 (Supplementary Fig. 18). The visualization clearly reveals that isolated hydrophilic CB domains are rapidly infiltrated by the electrolyte. In contrast, regions where PTFE and CB coexist support the formation of TPI, underscoring that sharp wettability contrast is a prerequisite for TPI formation. Additionally, some CB-only pores resist flooding, suggesting geometry and wettability co-govern TPIs development. 3D renderings (Supplementary Fig. 19) further show that intrusion occurs through finger-like pathways rather than uniform fronts, characteristic of capillary-driven flow47. Local wettability gradients at CB/PTFE interfaces trap air pockets of various sizes, fostering stable TPIs. Figure 4d shows that as intrusion proceeds, gas-liquid interfaces proliferate and interconnected air channels form, enabling efficient O2 transport. Notably, even after the electrolyte exits the domain at timestep 170,000, gas pockets persist through timestep 200,000 (see Supplementary Movie 1). We quantified this behavior by tracking time-resolved liquid saturation (Supplementary Fig. 20), confirming that part of the pore volume remains consistently gas-filled at steady state48. These findings capture the ways in which electrolyte transport can be guided by pore geometry and wettability gradients rather than being entirely random. This directional control marks a paradigm shift—from blocked to guided transport—and provides a theoretically sound route for constructing durable and efficient triple-phase interfaces.

To assess the feasibility of guiding electrolyte transport through structural regulation, the QSGS algorithm was used to generate CL structures by tuning nucleation probability (P) and phase occupation ratio (Rp), and gas-liquid behavior was quantified via LBM. Structures 1–3 shared similar PTFE dispersion but progressively increased PTFE content and decreased porosity by raising Rp. Structures 2, 4, and 5 maintained constant PTFE content while increasing spatial uniformity through higher P (Supplementary Fig. 21; Supplementary Tables 4 and 5). LBM simulations showed that increasing PTFE content (structures 1–3) reduced electrolyte saturation—suggesting that lower porosity can effectively impede water intrusion (Fig. 4e, f). However, increased PTFE content failed to alleviate CB flooding or enhance TPI formation—a finding that rationalizes why excessive PTFE loading in prior studies failed to improve electrode performance. In structure 3, PTFE aggregation and segregation further accelerated catalyst flooding, further explaining performance decline at high PTFE loadings (Supplementary Figs. 22 and 23). In contrast, improving PTFE dispersion at constant content (structures 2, 4, and 5) significantly increased the spatial density of gas-liquid-solid interfaces (Fig. 4g and Supplementary Fig. 24) and formed more dense and continuous gas networks (Supplementary Fig. 25), underscoring ink dispersion quality as a key performance factor. Notably, liquid saturation remained largely unchanged across these, suggesting porosity and PTFE content are the dominant factor governing electrolyte penetration (Fig. 4h). To clarify the mechanism of TPI formation, we modeled pores with varied wettability and geometry (Supplementary Fig. 26). As shown in Supplementary Fig. 27, phase separation occurred mainly in pores bordered by contrasting wettability, whereas symmetrical capillary forces drove water to hydrophilic regions, stabilizing gas in hydrophobic domains—thereby stabilizing TPIs. Furthermore, pore size played a decisive role: small hydrophobic pores significantly delayed water invasion, consistent with our earlier saturation–porosity analysis, while smaller hydrophilic pores accelerated it. Together, these findings indicate that gas-liquid dynamics are jointly governed by pore morphology and wettability—offering critical guidance for rational TPI design.

Hierarchical gradient CL for liquid repellence and guided product transport
Building on previous findings, a hierarchically structured CL with porosity and wettability gradients was designed to guide electrolyte transport. To systematically assess the influence of gradient design, we fabricated electrodes with dual-layer (PPE-D) and triple-layer (PPE-T) gradient architectures in addition to a single-layer reference (PPE). For PPE-D, a PTFE-rich ink was first coated onto the gas diffusion layer (GDL) and sintered to form a dense, highly hydrophobic layer with fine pores, serving as the first CL49. A second catalyst layer composed of non-fused particulate packing was then deposited on top, yielding a dual-gradient structure (PPE-D) with controlled PTFE content (1.8–3.6 mg cm–2) (Supplementary Fig. 28). Cross-sectional EDS mapping (Fig. 5a) qualitatively confirmed that the bottom layer is denser and richer in fused PTFE, establishing a clear porosity gradient. Mercury intrusion porosimetry (Supplementary Fig. 29) quantitatively confirmed a porosity gradient, with a marked decrease in pore volume toward the PTFE-rich bottom layer, consistent with densification and partial pore blockage from sintering. Because contact-angle measurements are unreliable for rough porous surfaces, PTFE loading was used as a quantitative indicator of hydrophobicity. The higher PTFE content in the bottom layer indicates stronger electrolyte repellence, confirming coupled porosity–wettability gradients across the CL.

For PPE-T, while adding another low-PTFE catalyst layer could further steepen the gradient, such multilayer assembly would complicate fabrication and hinder scalability. Instead, oxygen plasma etching provides a rapid, controllable, and catalyst-independent approach to tune surface hydrophilicity without additional coating or structural damage50. We therefore applied plasma etching to PPE-D, enabling a simple and scalable enhancement of surface wettability. The treatment introduces oxygenated groups (–OH, C=O, C–O–C) that raise surface energy and reduce the top-layer contact angle from 158° to 30° (Supplementary Fig. 30). XPS and EDS analyses verified the incorporation of these oxygenated groups, and the plasma parameters were optimized to preserve catalyst activity and pore morphology (Supplementary Fig. 31–33). The resulting electrode, PPE-T, thus exhibits a continuous porosity–wettability gradient throughout the CL.

We next compared the performance of PPE, PPE-D, and PPE-T to evaluate the effect of gradient steepness. The dual-gradient design (PPE-D1.8) maintained 83% FE after 5 h—43% higher than PPE (Fig. 5b and Supplementary Fig. 34). The same performance hierarchy of FSE < PPE < PPE-D was maintained under both acidic and alkaline electrolytes, confirming that the structural design principles are generally applicable across different pH environments (Supplementary Fig. 35). The introduction of a surface-modified hydrophilic layer further amplified this effect: PPE-T outperformed both PPE and PPE-D, maintaining nearly 100% FE during the first 3 h (Fig. 5b). Across 0–500 mA cm–2, PPE-T exhibited a near-linear increase in H₂O₂ production rate, consistent with reduced oxygen-transport limitations (Supplementary Fig. 36). These results demonstrate that introducing multi-layered wettability gradients via scalable surface modification strategies can substantially enhance GDE performance under practical operating conditions.

To elucidate the origin of the performance enhancement, LBM simulations were combined with in situ experiments to assess electrolyte breakthrough behavior. Gradient and non-gradient structures were generated using a modified QSGS algorithm (Supplementary Fig. 37). The simulations showed that, at the same timestep, PPE-D restricted electrolyte intrusion to localized gas-liquid regions, preserving oxygen pathways, whereas PPE was completely flooded (Supplementary Fig. 38). These trends were further verified by in situ breakthrough pressure tests (Supplementary Fig. 39). Under constant mechanical load and applied potential, the time required for peroxide test paper on the GDL to show discoloration was recorded (Supplementary Fig. 40). Multiplying the applied pressure by breakthrough time yielded the resistance impulse (RI), a quantitative indicator of intrinsic flooding resistance. The RI values of all electrodes were compared to evaluate their flooding resistance (Supplementary Fig. 41). Both PPE-D and PPE-T exhibited significantly higher RI than PPE, confirming their resistance to electrolyte intrusion under electrowetting and explaining their improved performance. Further analysis of the relationship between FE and RI (Fig. 5c) revealed two distinct regimes: in the low-RI range, FE rose steeply with increasing RI (slope = 0.054), reflecting the positive contribution of enhanced hydrophobicity; beyond a critical RI, the increase plateaued (slope = 0.0025), suggesting that the barrier effect alone had approached its limit. Notably, PPE-T deviated from this linear correlation—its RI decreased, yet its FE increased significantly. This deviation suggests that, in addition to passive flooding resistance, an extra transport behavior may have emerged, potentially associated with the steeper wettability gradient. To further separate these effects, additional electrolysis experiments were performed by floating PPE and PPE-T horizontally on the electrolyte surface without any applied hydrostatic pressure, thereby minimizing the influence of breakthrough pressure. Even under pressure-free conditions, PPE-T maintained a higher FE than PPE (Supplementary Fig. 42), confirming that observed performance enhancement cannot be solely attributed to passive barrier protection. Instead, it likely results from a synergistic interplay between passive anti-flooding resistance and additional gradient-induced mass transport.

To further elucidate this behavior, LBM and molecular dynamics (MD) simulations were subsequently conducted to analyze the in situ diffusion of H2O2 within the CL at mesoscale and molecular scales, respectively. The LBM simulations revealed that H2O2 spontaneously migrates toward regions with larger pores and lower PTFE content, thereby preserving dry domains that maintain access to oxygen (Supplementary Fig. 43 and Supplementary Movie 2). To quantify this effect, MD simulations were conducted to calculate mass-transfer coefficients (Supplementary Fig. 44 and Fig. 5d)23. Despite identical PTFE content, the gradient CL exhibited directional H2O2 diffusion with a transport coefficient of 2.05 × 10–5 cm2 s–1, 37.6% higher than the bidirectional diffusion observed in the non-gradient system (1.49 × 10–5 cm2 s–1, Fig. 5e, f). Simultaneously, the removal of H2O2 facilitated O2 diffusion into the CL, increasing its mass-transfer coefficient from 1.26 × 10–4 to 1.61 × 10–4 cm2 s–1 (a 27.8% improvement). These enhancements suppress local H2O2 accumulation and promote O2 replenishment at the TPI. While the LBM and MD simulations capture the qualitative influence of pore architecture and wettability on electrolyte intrusion and product transport, they do not fully reproduce the complexity of real electrochemical interfaces, including reaction kinetics, ion transport, and surface heterogeneity. The simulation results should therefore be interpreted as mechanistic insights rather than quantitative predictions. Since real-time nanoscale electrochemical imaging remains challenging, we developed a custom PDMS-based microfluidic visualization platform (2×2 cm) incorporating QSGS-derived gradient pore structures with fluorosilane-treated frameworks mimicking PTFE hydrophobicity (Fig. 5g)51. A potassium titanyl oxalate solution containing H2O2 was injected into the chip center to simulate in situ product generation. Visualization experiments (Supplementary Movie 3 and 4) showed that, in the hydrophobic gradient chip, H2O2 consistently migrated toward the large-pore region, leaving the small-pore side dry. Convex menisci at narrow throats indicated capillary barriers generating a net Laplace force that drove fluid directionally. In contrast, the hydrophilic gradient chip displayed symmetric diffusion and rapid flooding. These results highlight the critical role of wettability and pore gradients in directing mass transport and maintaining TPI integrity. Taken together, these findings reveal two synergistic yet distinct mechanisms that jointly govern electrode stability and efficiency: the dense hydrophobic sub-layer serves as a passive barrier that resists electrolyte intrusion, while the wettability gradient actively drives directional product evacuation and sustains TPIs under dynamic operation.

Milestone demonstration of a commercial-scale self-breathing electrosynthesis platform
Electrode durability under harsh conditions remains a key barrier to industrial translation. The long-term stability of PPE-T without external aeration was evaluated across various current densities. To avoid thermal artifacts (Supplementary Fig. 45), the electrolyte was periodically replaced—every 4 h at low current and every 1 h at high current—without any electrode cleaning or hydrophobic regeneration, preserving realistic operational conditions. PPE-T maintained 90% FE over 500 h at 15 mA cm–2, producing 0.4 wt% H2O2 per cycle. At 300 mA cm–2, it stably delivered 3 wt% H2O2 h–1 for 300 h at 85% FE—meeting the requirements of most industrial water treatment applications. Even at the extreme current density of 400 mA cm–2, PPE-T sustained 80% FE for 50 h (Fig. 6a, where the slight FE drop after 45 h likely arises from partial flooding in the catalytic layer, which could be mitigated by further optimizing the pore gradient and PTFE distribution). A benchmarking analysis against recent literature is provided in Supplementary Table 6, showing that our electrode delivers performance competitive with H2O2 electrosynthesis systems reported over the past decade under similar operating conditions10–13,15,22,31,32,49,52. To enhance scalability, we transitioned from lab-scale batch cells to a modular, oxygen-fed flow-through electrolyzer (Supplementary Fig. 46), incorporating a dual-membrane solid-state electrolyte. This system enabled continuous production of high-purity H2O2 (9000–19,000 mg L–1) across 80–240 mA cm–2 at 4–10 V (Supplementary Fig. 47). The production cost was as low as $1.1 kg–1, with a single-stack capital cost of $81.2. This low capital requirement stands in stark contrast to the substantial investments needed for conventional anthraquinone facilities, making this approach especially promising for distributed and scalable deployment (Supplementary Note 2).

Building on the demonstrated durability of PPE-T, we developed a pilot-scale self-breathing H2O2 electrosynthesis platform (Fig. 6b). A modular stack comprising four serially connected electrolyzers (100 cm2 GDE each) was integrated with electronic, fluidic, and thermal management subsystems, forming a commercially viable in situ H2O2 platform (Fig. 6c and Fig. 6d). Operating under alkaline conditions, the system maintained 85–95% FE at 100 mA cm–2 for over 100 h (Fig. 6e). Notably, this stability was achieved despite electrolyte pumping-induced dynamic pressure, which typically accelerates flooding in open, non-pressurized systems—a challenge widely acknowledged in recent literature53. Under these demanding conditions, the sustained efficiency underscores the reliable performance and operational stability of our electrode design. Crucially, eliminating the need for pure oxygen supply simplifies system integration and reduces both capital and spatial demands. With a production cost of $0.381 kg−1 and an installation footprint under 4 m2, the system achieves competitive economic and spatial performance compared with recently reported values (e.g., $0.398 kg–1)8. This work presents an integrated self-breathing GDE-based H2O2 electrosynthesis system operated at pilot scale, demonstrating the feasibility of translating laboratory concepts into practical operation. The platform highlights the potential of decentralized and sustainable peroxide production for future industrial implementation.

Methods
Chemicals and materials
Carbon black (Vulcan XC-72R) was obtained from Cabot Corporation. A 60 wt% PTFE dispersion was provided by Guangdong Canrd New Energy Technology Co., Ltd. Carbon paper (TGP-H-060), a cation exchange membrane (Fumasep FKB-PK-130, 50×50 mm×130 µm), and 5 wt% Nafion solution (D520) were purchased from Suzhou Sinero Technology Co., Ltd. Ti/IrO2-Ta2O5 plates were supplied by Suzhou Shuertai Industrial Technology Co., Ltd. Sodium sulfate (Na2SO4, ≥99.0%, AR), sulfuric acid (H2SO4, 98%, AR), isopropanol (≥99.7%, AR), and sodium hydroxide (NaOH, ≥96%, AR) were purchased from China National Pharmaceutical Group Co., Ltd. Potassium titanium (IV) oxalate (KTiO(C2O4)2, ≥98%) was also obtained from Macklin. Unless otherwise stated, all reagents were of analytical grade. The cation exchange membrane was used to separate the catholyte and anolyte. Before use, the membrane was soaked in 0.5 mol L–1 NaCl at 25 °C for 24 h and rinsed with deionized water. All electrolytes were prepared freshly before each experiment and used immediately without further purification.

Fabrication of different cathodes
Fused-coated electrode with segregated interface (FSE): To prepare the FSE electrode with a conventional fused PTFE/CB interface, 150 mg of CB was dispersed in isopropanol/deionized water and sonicated for 5 min. PTFE emulsion (PTFE/CB=0.9) was added dropwise under continuous sonication. The mixture was sonicated at 70 °C until a paste formed and coated onto carbon paper (CP), which served as both the current collector and gas diffusion layer. The electrode was hot-pressed at 10 MPa and 60 °C for 5 min, then annealed at 340 °C for 1 h.

Particulate-packed electrode (PPE): For the non-fused particulate-packed interface structure, 150 mg of CB was dispersed in 10 ml isopropanol and sonicated for 5 min at 10 °C. A specified amount of 60 wt% PTFE emulsion (PTFE/CB=0.3–1.5) was separately mixed with 4 mL deionized water and added dropwise to the CB dispersion during 1 h sonication. The resulting ink was spray-coated onto CP using a Catalyst Coating Membrane spray-coating device (CCM, HEPHAS Energy, China) under vacuum (substrate temperature: 60 °C; ink pressure: 0.25 MPa; atomization: 3.5 MPa; width: 1.0 MPa). Multiple layers were applied with 5 min intervals for drying. After spraying, electrodes were dried at 60 °C for 12 h. During the spray-coating and high-temperature drying steps, rapid solvent evaporation removed the surface-active agents in the PTFE emulsion. As these surfactants are soluble in the solvent phase, they volatilized together with the solvent. EDS analysis of the as-prepared PPE electrodes (Supplementary Fig. 48) showed no oxygen signal from residual surfactants, confirming that the PTFE maintained its hydrophobicity without sintering.

Calcined particulate-packed electrode (PPE-cal): PPE electrodes were calcined at 340 °C for 1 h without hot pressing to induce partial PTFE melting while preserving the same macroscopic density as PPE.

Dual-layer porous/wettability electrode (PPE-D): The PPE-D electrode was prepared similarly to PPE, but with PTFE/CB ratios of 1.8–3.6. A dense base layer was first deposited (2 mL ink) and calcined at 340 °C for 1 h. A second layer was then spray-coated atop the first using the same method as PPE.

Three-layer wettability gradient electrode (PPE-T): PPE-D electrodes were subjected to oxygen plasma etching (100 W, 600 s) to create a top layer with enhanced hydrophilicity, yielding a triple-wettability CL.

For all electrodes, the catalyst mass was held constant, with PTFE content adjusted to control the binder/catalyst ratio. Electrode dimensions were 5 cm×5 cm (total) and 3 cm×3 cm (active area). The catalyst loading of the PPE and FSE electrodes was fixed at 6 mg cm–2, while PPE-D and PPE-T electrodes were prepared with a loading of 8 mg cm–2. The loading was controlled by the dispensed volume of catalyst ink during spray coating. The final mass loading was determined by weighing the coated electrode after drying, subtracting the mass of the pristine carbon paper, and dividing the net mass by the coated geometric area.

Electrochemical H2O2 production
Electrosynthesis of H2O2 was conducted in a custom two-compartment cell (Supplementary Fig. 3) separated by a cation exchange membrane (CEM, Fumasep Fkb-pk-130), Na2SO4 as the supporting electrolyte. Initially, the anode and cathode chambers contained 120 mL and 70 mL of electrolyte solution, respectively. The GDE (mass loading of 6 mg cm–2) cathode and a Ti/IrO2–Ta2O5 anode (40×40×1 mm, Ir:Ta=8:2, mass loading of 1 mg cm–2) were positioned 30 mm apart. The cathode GDL was exposed to ambient air without external aeration. Electrolysis was performed under magnetic stirring (500 rpm) and constant current conditions (15–400 mA cm–2), powered by a DC supply (0–20 A, 0–30 V). All measurements were conducted at room temperature (20 °C). At predetermined time intervals, 1 mL of catholyte was withdrawn using a micropipette for H2O2 quantification. The remaining catholyte volume was measured simultaneously and used for Faradaic efficiency calculations.

Two testing modes were adopted. At low current densities (15, 100 mA cm–2), electrolysis was performed for 4 h in 0.1 mol L–1 Na2SO4 (pH=5.84±0.01), with H2O2 concentrations sampled every 40 min. At high current densities (200–400 mA cm–2), 1 mol L–1 Na2SO4 (pH=6.92±0.06) was used, and periodic electrolyte replacement was employed to mitigate thermal decomposition. Each electrode was tested over five 1-h cycles, with H2O2 yield and Faradaic efficiency calculated from collected samples. Error bars represent standard deviation from triplicate tests (n=15).

Electrolysis under different pH conditions. To evaluate the generality of the structural design, electrochemical tests were conducted under acidic (1 mol L–1 H2SO4, pH=0.56±0.03) and alkaline conditions (1 mol L–1 NaOH, pH=13.45±0.02). The experiments were performed using the same self-breathing two-compartment cell (Supplementary Fig. 3) as described above. Constant-current electrolysis was carried out at a current density of 400 mA cm–2, and the hydrogen peroxide concentration after each cycle was determined by the potassium titanium oxalate method. Error bars represent standard deviation from tests (n=3).

The floating gas diffusion electrode (GDE) performance under zero hydrostatic pressure was evaluated in a conventional single-compartment, membrane-free electrochemical cell (Supplementary Fig. 42) containing 300 mL of 1 mol L–1 Na2SO4 (pH=6.92±0.06). The GDE was gently placed on the electrolyte surface to float freely without external pressure, and a platinum foil was used as the counter electrode. Chronoamperometric measurements were performed at a constant current density of 300 mA cm–2. PPE and PPE-T electrodes with mass loadings of 6 and 8 mg cm–2, respectively, were tested under identical conditions. After 30 min of electrolysis, the electrolyte was sampled for H2O2 quantification to determine the Faradaic efficiency (FE). All measurements were conducted in triplicate (n=3), and results are reported as mean values with standard deviations.

Commercial-scale self-breathing electrosynthesis experiments. Commercial-scale electrolysis experiments were carried out on a custom-built self-breathing electrosynthesis platform equipped with independent anodic and cathodic circulation systems, separated by a cation exchange membrane (Nafion 117, 110×110 mm×183 µm). The electrolyzer operated under ambient pressure with natural air supply to the cathode side. The applied current density was 100 mA cm–2, and the system was operated in continuous circulation mode. The anolyte consisted of 5 mol L–1 NaOH (pH=14±0.02) solution, which was periodically replenished with 32 wt% NaOH to maintain alkalinity. The catholyte was deionized water, recirculated in a closed loop. Temperature regulation was achieved through a built-in water-jacket heat exchanger integrated into both electrolyte tanks. A total of 1 L catholyte was used in each run and replaced every 2 h of recirculation. The system was operated for 10 h per day, followed by flushing with deionized water.

GDE resistance pulse testing
H2O2 test strips preparation. Qualitative filter paper was soaked in a solution of 5 mol L–1 H2SO4 and 0.1 mol L–1 potassium titanium oxalate, then dried at 60 °C and cut to match the observation window size, yielding peroxide-sensitive test strips.

Resistance pulse test. An in situ breakthrough test was conducted to quantify the GDE’s resistance to electrolyte intrusion. The GDE was mounted in a custom vertical setup in which 1 mol L–1 Na2SO4 was supplied through a scaled glass tube. The CL surface of the GDE was positioned at the 0 cm reference mark, and the hydrostatic pressure was controlled by adjusting the liquid height (h) above this level. A Pt electrode served as the counter electrode, while the GDE functioned as the cathode for H2O2 generation under a constant applied voltage. During operation, the combined effects of hydrostatic pressure and electrowetting caused electrolyte to progressively intrude into the CL. Breakthrough was detected using a hydrogen peroxide indicator strip placed at the GDL side of the GDE; the appearance of a localized yellow discoloration marked the breakthrough point. The breakthrough time (t) corresponding to each preset liquid height (h) was recorded. The product of h·t was used to quantify flooding resistance.

The resistance impulse of the GDE is expressed as:
I=F·t (1)
F=ρ·g·h·S (2)
Where I is the resistance impulse of the GDE (Ns). F is the force exerted on the GDE by the electrolyte pressure (N). t is the time (s). ρ is the density of the electrolyte (kg m–3). g is the gravitational acceleration (m s–2). h is the height of the electrolyte in the glass tube (m). S is the area of the GDE in contact with the electrolyte (m2).

Electrode characterization
The morphology and elemental composition of the GDEs were characterized using field-emission scanning electron microscopy (FE-SEM, HITACHI SU8010) equipped with an energy-dispersive X-ray spectrometer (EDS, Oxford X-Max). Surface chemical states were analyzed by X-ray photoelectron spectroscopy (XPS, PHI 5000 VersaProbe III). Static contact angles were measured using a goniometer (Krüss DSA25 Basic).

Linear sweep voltammetry (LSV) curves were collected at a scan rate of 20 mV s–1 over a potential window of 0 to −4 V vs. SCE in 1 mol L–1 Na2SO4 solution (pH=6.92±0.06), using a Ti/IrO2–Ta2O5 counter electrode. Electrochemical impedance spectroscopy (EIS) was conducted at open-circuit potential (−0.158 V) in the same electrolyte, with a frequency range of 105 to 10−1 Hz and an amplitude of 5 mV. EIS spectra were fitted using ZView software with an appropriate equivalent circuit.

Catalyst intrinsic activity and selectivity were evaluated using a rotating ring–disk electrode (RRDE, Pine Instruments) in O2-saturated 0.1 mol L–1 KOH (pH=13±0.05). Measurements were performed using a glassy carbon disk (0.2475 cm2) and Pt ring (0.1866 cm2, N=0.37) at 1600 rpm with a scan rate of 10 mV s–1. Hydrophilic surface modification via plasma etching was performed using a CPC-Fplus plasma cleaner.

Stepwise chronoamperometry was conducted in 1 mol L–1 Na2SO4 solution (pH=6.92±0.06) to evaluate oxygen mass transfer under self-breathing conditions. The setup was identical to that used for H2O2 electrosynthesis but operated in a three-electrode mode, with the GDE as the working electrode, SCE as the reference, and a Ti/IrO2–Ta2O5 mesh as the counter electrode. A current density of 25 mA cm–2 was applied initially, followed by 25 mA cm–2 increments every 3 min up to 250 mA cm–2. H2O2 concentrations were measured at the end of each step, and the net H2O2 formed in each interval was used to calculate the Faradaic efficiency at steady state.

All electrochemical measurements were performed using a potentiostat/galvanostat (DongHua DH7000, China). All electrochemical potentials were measured against a saturated calomel electrode (SCE, +0.241 V vs. NHE at 25 °C, China). The reference electrode was calibrated prior to each set of experiments using a standard hydrogen electrode (SHE) in 0.1 mol L–1 H2SO4. Potentials were converted to the reversible hydrogen electrode (RHE) scale using:
ERHE = ESCE + 0.242 + 0.059 × pH
where 0.242 V is the standard potential of SCE versus NHE at 25 °C. All potentials reported in this work are presented without iR compensation unless otherwise stated. The solution resistance (Rs) was measured by high-frequency EIS for each electrolyte, with typical values of 4.55±0.6 Ω in 1 mol L–1 Na2SO4 (LSV measurements) and 37.7±0.6 Ω in 0.1 mol L–1 KOH (RRDE measurements).

Pore structure parameters including size distribution, permeability, and tortuosity were obtained by mercury intrusion porosimetry (Micromeritics AutoPore IV 9500, 0.5–33,000 psi). 3D CL morphology was reconstructed using FIB-SEM (FEI Helios Nanolab G3 UC). Catalyst ink particle size distribution was measured with a laser diffraction analyzer (Bettersize 2600).

H2O2 product quantification
The concentration of the produced H2O2 was determined using a UV–Vis spectrophotometer (Agilent Technologies, Inc., USA) and the potassium titanium (IV) oxalate method at λ=400 nm14. Potassium titanium (IV) oxalate can react with H2O2 to form a stable yellow-orange titanium (IV)-peroxide complex, with its color depth being proportional to the H2O2 concentration. Different dilution factors were chosen based on the current density, and samples were diluted before measurement. The standard curve for H2O2 quantification was shown in Supplementary Fig. 49. No additional liquid- or gas-phase products were detected. This is consistent with the inert Na2SO4 electrolyte, where dissolved O2 is the only reducible species. Faradaic efficiency (FE) was calculated using the following formula, based on the measured concentration and the volume of electrolyte in the cathode compartment at each sampling time:
FE(%) = nFCV / It × 100% (3)
where n is the number of electrons transferred for O2 reduction to H2O2 (n=2), F is the Faraday constant (96486 C mol–1), C is the concentration of H2O2 (mol L–1), V is the volume of electrolyte (L), I is the current (A), and t is the electrolysis time (s). All FE values reported in this study were obtained under galvanostatic operation at the specified current densities.

PTFE-based ink preparation/dispersion optimization
Nine PTFE-containing mixed solutions were prepared using various sequences, solvent compositions, and ultrasonication conditions. Each formulation consisted of 4 mL (or 2 mL) deionized water, 5 mL isopropanol, and 0.15 mL of 5 wt% PTFE emulsion. The mixtures were ultrasonicated at either 10 °C or 40 °C. Nine different mixing methods were as follows (Supplementary Fig. 11):
1. PTFE emulsion was directly added to isopropanol, followed by water. Ultrasonication was performed at 10 °C.
2. PTFE emulsion was first diluted with water, then added all at once to isopropanol. Ultrasonication was performed at 10 °C.
3. PTFE emulsion was first diluted with water, then slowly added dropwise into isopropanol. Ultrasonication was performed at 10 °C.
4. PTFE emulsion was directly added to isopropanol, followed by water. Ultrasonication was performed at 40 °C.
5. PTFE emulsion was first diluted with water, then added all at once to isopropanol. Ultrasonication was performed at 40 °C.
6. PTFE emulsion was first diluted with water, then slowly added dropwise into isopropanol. Ultrasonication was performed at 40 °C.
7. Using 2 mL water instead of 4 mL, PTFE emulsion was directly added to isopropanol, followed by water. Ultrasonication was performed at 40 °C.
8. Using 2 mL water, PTFE emulsion was first diluted with water, then added all at once to isopropanol. Ultrasonication was performed at 40 °C.
9. Using 2 mL water, PTFE emulsion was first diluted with water, then slowly added dropwise into isopropanol. Ultrasonication was performed at 40 °C.

FIB-SEM 3D reconstruction method
Electrodes were cut into 5 mm×5 mm pieces, washed with ethanol, and vacuum-impregnated with epoxy resin for 12 h before curing at 65 °C. After hardening, samples were mounted in the FIB-SEM (FEI Helios Nanolab G3 UC) and sequentially imaged at 5 nm slicing intervals, yielding 600 images (3×2.5 µm2). Two sample-preparation approaches were evaluated prior to FIB-SEM imaging: (i) epoxy embedding, which provided mechanical stability and was therefore used for all analyses presented in the main text, and (ii) direct cutting and loading of unembedded electrodes, which was examined only for comparison. A detailed discussion of the differences between these approaches is provided in Supplementary Note 1.

3D reconstruction was performed using Avizo. Image stacks were auto-aligned, and noise and curtaining artifacts were removed using FFT filtering, mean filtering, non-local means (NLM), and anisotropic diffusion. Solid and pore phases were segmented using Otsu’s thresholding, followed by gray-level-based segmentation to distinguish carbon black (CB) and PTFE. Boolean operations were then used to isolate CB and pore domains, and voxel interpolation was applied to generate the final 3D structure (Fig. S12).

Quartet structure generation set method
The 3D catalyst layer (CL) structure was generated using the Quartet Structure Generation Set (QSGS) method proposed by Wang et al.54. This stochasticalgorithm controls phase morphology via four parameters: nucleation probability (Pc), directional growth probability (Pi), inter-phase attachment probability (Pnm), and target phase volume fraction (Rp). Pc determines the initial spatial distribution of nucleation sites; lower values promote localized aggregation. Pi governs anisotropic phase growth along 26 discrete directions (cube vertices, edges, and faces), with direction-specific probabilities listed in Supplementary Table 4. Given the anisotropic, particulate morphology observed in FIB-SEM images, PTFE and CB phases were modeled with non-uniform Pi values. Pnm defines the interaction between phases, such as CB attachment to PTFE. Growth proceeds iteratively until each phase reaches the predefined volume fraction Rp.

Three-dimensional CL structures of the FSE and PPE electrodes were reconstructed using the QSGS method (Fig. S7). In addition to these, five representative QSGS-generated structures were produced to systematically examine the effects of PTFE loading and dispersion (Fig. S21). Structures (1), (2), and (3) share the same PTFE nucleation probability (Pc) but exhibit increasing PTFE volume fractions (Rp), mimicking CLs prepared from inks with identical dispersion conditions but different PTFE loadings. Structures (2), (4), and (5) maintain a constant Rp while varying P, corresponding to identical ink compositions subjected to different dispersion qualities. Increasing Pc results in more uniform PTFE/CB mixing with fewer aggregated PTFE domains. In addition, multiple QSGS reconstructions were performed to obtain the three-dimensional structure of the gradient-engineered PPE-T catalyst layer.

Lattice Boltzmann method
To accurately simulate two-phase flow within the CL, we used the phase-field lattice Boltzmann equation developed by Long et al., which is capable of predicting the wetting behavior of fluid pairs with large density ratios. In this model, the liquid-solid free energy is treated as part of the chemical potential rather than as a boundary condition, simplifying the implementation of wetting boundary conditions. Additionally, the AC equation is solved using a well-balanced LBE model, which further improves numerical stability and ensures accurate prediction of two-phase flow and wetting behavior with large density ratios. The LBM program was implemented in C++ and parallelized using the CUDA platform and GPU for efficient computation45,46.

The conservative Allen–Cahn equation can be expressed by
∂ϕ/∂t +∇·(ϕu)=∇·[M(∇ϕ−λn)] (4)
where M is the mobility, n is the unit vector normal to the interface. λ is a function of ϕ. ϕ taking 1 and 0 represent the liquid and gas phase fluids. The fluid velocity u in Eq.(S2) is governed by the following Navier–Stokes equations with the force,
∇·u=0 (5)
∂(ρu)/∂t +∇·(ρuu)= −∇p+∇·[μ(∇u+∇uT)] +Fs +G (6)
where ρ is the fluid density, p is the hydrodynamic pressure, μ is the dynamic viscosity by μ=ρν, ν is the kinematic viscosity, Fs is the surface tension force, and G is the possible body force.

The LB evolution equation with the BGK collision operator for the conservative Allen–Cahn equation can be written as
fi(x+ciδt, t+δt) − fi(x,t)= −1/τf [fi(x,t)−feq(x,t)] + δt Fi(x,t) (7)
feq = ωiϕ [1 + (ci·u)/cs2] (8)
where fi(x,t) is the particle distribution function, τf is the non-dimensional relaxation time related to the mobility, Fi(x,t) is the source term, and a simple form of the feq(x,t) is equilibrium distribution function, cs is the sound speed, ci are the discrete velocities, and ωi are the weighting coefficients.

The order parameter in the present model can be computed by
ϕ= ∑ fi (9)

The distribution of fluid density in a two-phase system physically is consistent with that of the order parameter. To satisfy this physical property, the fluid density should take the linear interpolation,
ρ=ϕ ρl + (1−ϕ)ρg (10)
where ρl and ρg represent the densities of the liquid and gas phases.

This version clarifies that additional details regarding wetting boundary optimization can be found in the cited references.

Electrolyte invasion model. Electrolyte intrusion into the catalyst layer was simulated using a multiphase lattice Boltzmann model. The liquid phase was injected from one side of the catalyst layer with a constant inlet velocity, while the opposite side was defined as an outlet boundary condition with non-gradient constraints for pressure and velocity. The remaining four faces of the domain were treated as periodic boundaries to mimic an infinitely extended porous medium. The physical size of the simulated subvolume was 2×2×3 µm3, consistent with the FIB-SEM reconstructed catalyst layer used in Fig. S18.

Self-transport of in situ generated H2O2. To mimic the in situ electrogeneration and subsequent transport of H2O2 inside the catalyst layer, a second lattice Boltzmann model was constructed in which a local water source term was imposed at the center of the reconstructed catalyst layer domain to represent H2O2 formation at active sites. Both through-plane ends of the catalyst layer were specified as outlet boundaries with non-gradient conditions for velocity and scalar fields, allowing the generated H2O2 solution to leave the domain from either side. The remaining four faces were defined as constant-velocity inlet boundaries to maintain a steady convective flow of electrolyte through the porous structure. The detailed boundary configuration for this model is shown in Fig. S43.

Saturation
The saturation of each phase is calculated as follows:
SL = εL/ε, SA = εA/ε (11)
where εL and εA are the porosity of liquid and air, which denote the amount of space occupied by the liquid and air, respectively. Therefore, saturation is defined as the ratio of each phase to the porosity of the porous media55.

Molecular dynamics
Atomistic molecular dynamic simulations have been performed in the GROMACS56 (version 2022.6) simulation package using the CHARMM36 force field57 and the water molecules were modeled using the TIP3P water model. PTFE molecules were first placed on both sides of a slice of C54 carbon sheets filled with 300 H2O molecules. The first system has 40 chains on top and 10 on the bottom, and the other system has 25 chains on both sides. For both systems, the upper layer was filled with 500 O2 molecules and 2000 water molecules, the lower layer was filled with around 4000 water molecules, resulting in a system size of 5×5×12 nm. On both sides of the simulation box, implicit walls were placed to prevent molecules moving to the other side through the periodic boundary. After thousands of steps of energy minimization, the system was equilibrated for 500 ps followed by 4000 ps production molecular dynamics process under the canonic ensemble. An integration time-step of 1 fs was used and the temperature was coupled to 298 K using the Nose-Hoover method and a cutoff scheme of 1.2 nm was used for the non-bonded interactions, and the Particle Mesh Ewald method58 with a fourier spacing of 0.1 nm was applied for the long range electrostatic interactions. All covalent bonds with hydrogen atoms were constraint using the LINCS algorithm59. The mean squared displacements (MSD) of O2 and H2O2 molecules in different systems were calculated to quantify their mass-transfer behavior. The MSD is calculated as follows:
MSD = 1/N ∑ <|Δ~r(t)|2> (12)

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "This manuscript by Tian et al. presents a highly significant advancement in the design of gas diffusion electrodes (GDEs) for electrochemical H₂O₂ production. The authors introduce a novel \"non-fused particulate-packed interface\" architecture that fundamentally overcomes the long-standing trade-off between hydrophobicity and catalyst site accessibility in conventional GDEs. The work is exceptionally thorough, combining rational electrode design, advanced 3D characterization, multiscale simulations (from molecular to mesoscale), and a compelling demonstration of a pilot-scale, commercially viable system. The narrative is clear, logical, and powerfully supported by a wealth of high-quality data. The insights into the role of the catalyst-binder interface in governing three-phase interface formation are of broad importance to the fields of electrocatalysis, fuel cells, and CO₂ reduction. While the work is of outstanding quality and impact, I believe it could be further strengthened by addressing a key alternative hypothesis and slightly refining the narrative logic concerning the final electrode optimization. Therefore, I recommend Major Revision.\n\n1.The performance enhancement of the gradient electrodes (PPE-D and PPE-T) is primarily attributed to Laplace pressure-driven \"directional H₂O₂ transport\". While the microfluidic experiments and simulations provide compelling evidence for this phenomenon, a plausible alternative hypothesis exists: the performance gain might be predominantly due to the dense, highly hydrophobic bottom layer acting as a superior physical barrier, which simply increases the breakthrough pressure and passively prevents flooding, rather than actively guiding product away. The current narrative strongly emphasizes the more sophisticated \"directional transport\" mechanism. To strengthen the conclusion, I would ask the authors to:\nExplicitly discuss this alternative hypothesis in the main text.\nProvide a more direct analysis to decouple these two effects. Could the Resistance Impulse (RI) data be used more quantitatively to estimate the contribution of the barrier effect versus the directional transport? A more balanced discussion acknowledging the synergistic role of both mechanisms would make the claims even more robust.\n2. The transition from the rationally-designed, dual-layer PPE-D to the plasma-treated PPE-T feels somewhat abrupt from a narrative standpoint. While the performance of PPE-T is superior, the intellectual leap is not as well-justified as previous steps in the story. Please add a brief transitional discussion before introducing PPE-T, explaining why a steeper wettability gradient was hypothesized to be beneficial based on the findings from PPE-D, and why oxygen plasma etching was chosen as a scalable and effective strategy to achieve this. This would better integrate the PPE-T development into the main logical flow of designing electrodes based on fundamental understanding.", "reviewer_2": "This manuscript reports a rationally designed gas diffusion electrode (GDE) architecture combining a non-fused particulate-packed catalyst–binder interface and a hierarchical wettability/pore gradient, which enables self-breathing hydrogen peroxide (H2O2) electrosynthesis under ambient air without external oxygen supply. The authors convincingly demonstrate that this structure not only enhances three-phase interface (TPI) formation but also resolves flooding issues at high current densities. Moreover, the study integrates advanced three-dimensional structure reconstruction and high-resolution Lattice Boltzmann simulations to elucidate gas-liquid-solid distribution at the mesoscale, thereby offering mechanistic insights into interface evolution. Particularly impressive is the engineering of a modular 400 cm2 flow-through stack incorporating electronic, thermal, and fluidic systems, achieving industrially relevant performance and cost metrics.\nTo the best of my knowledge, this is the first report to bridge fundamental interface engineering with large-scale implementation for electrochemical H2O2 production. The work presents a significant advance toward practical and decentralized oxidant manufacturing. While the manuscript is well-structured and the data convincing, I believe the authors should address the following points to further solidify the claims and improve reproducibility. With these minor but important clarifications and additions, I believe the manuscript could be suitable for publication in Nature Communications.\n1. The authors emphasize that the non-fused particulate-packed interface plays a central role in enhancing electrosynthesis performance, and attribute the reduced performance of conventional electrodes to molten interface structures caused by hot pressing or sintering. However, it is not clearly distinguished whether the observed differences arise primarily from the interface morphology (i.e., molten encapsulation) or from reduced porosity due to densification during hot pressing. Since the structural change involves both factors, it is recommended that the authors supplement with experimental or comparative discussion to decouple and clarify the independent effect of the molten interface.\n2. In lines 57–58, the authors state that sintering is typically used to remove surfactants from PTFE and maintain its hydrophobicity. Yet, to avoid molten interfaces, sintering was intentionally skipped in this work. The authors should explain how the PTFE’s hydrophobicity was retained in the absence of sintering and whether any pretreatment or washing was used to remove residual surfactants. This clarification is critical for reproducibility.\n3. While the authors attribute performance suppression to molten encapsulation by PTFE, it is unclear whether this phenomenon is specific to PTFE or generally applies to other binder systems. A brief discussion (or reference to comparative experiments, e.g., with Nafion or other binders) would help establish the generality of this observation.\n4. In Fig. 6d, it is observed that the PPE-T electrode shows a noticeable decline in Faradaic efficiency starting around the 45th hour under a current density of 400 mA cm⁻². Although the overall durability and performance are impressive, the authors should provide a brief explanation of this trend—e.g., whether it may arise from flooding, oxygen depletion, catalyst degradation, or structural changes—and discuss whether further optimization of the interface structure or gradient parameters could mitigate this behavior in future iterations. Addressing this point would enhance the completeness of the discussion without diminishing the study’s overall impact.\n5. In Fig. 6c, the benchmarking table is informative and positions the work well among prior studies. However, recent advances in 2025 are underrepresented. The authors are encouraged to update the comparison with the latest publications to ensure comprehensive context and highlight the distinctiveness of this study.\n6. In Fig. 6, c and d may have been mistakenly swapped. The figure captions and data shown do not seem to correspond to their labels. The authors should double-check and revise the labels accordingly to avoid confusion for readers.\n7. in the experimental section, why different concentration of Na2SO4 solutions were used under different current densities? Please give the explanation.\n8. section “Chemicals and materials”, in contrast to other researches which used XC-72R, I have notices that the carbon black you used is XC-72. Could you explain to me that the reason you use this type of carbon black?\nIn addition, the following format issues should not be ignored.\n9.Please check through the manuscript and reduce the use of “we introduce”, “we identify”, “we construct” “we then developed”……\n10.Please check the tenses throughout the manuscript.", "reviewer_3": "This manuscript reports a rationally designed gas diffusion electrode (GDE) architecture that combines a non-fused particulate-packed catalyst-binder interface with a hierarchical wettability and pore gradient. This configuration enables self-breathing H2O2 electrosynthesis under ambient air without external oxygen supply. The study further integrates three-dimensional structural reconstruction and high-resolution Lattice Boltzmann simulations to visualize gas-liquid-solid distributions at the mesoscale, providing mechanistic insights into interfacial transport phenomena. Of particular note is the engineering of a modular 400 cm² flow-through stack that incorporates electronic, thermal, and fluidic subsystems. This platform achieves industrially relevant performance and cost benchmarks, underscoring the translational potential of the proposed design. The work represents a notable step forward toward decentralized and sustainable oxidant manufacturing. Overall, this manuscript is well-organized with robust performance and systematic mechanism elucidation. As such, I recommend the publication of this manuscript in Nature Communications after addressing the following issues.\n1. Quantitative Validation of the QSGS-Reconstructed Structures. The QSGS method is employed in Figures 2g and 4e/g to generate representative 3D catalyst layer morphologies for simulation. However, the manuscript does not provide sufficient quantitative validation of how well these synthetic structures reflect the true morphology obtained via FIB-SEM reconstruction. To enhance the credibility and generalizability of the simulation results, the authors are encouraged to compare key structural parameters between the real and simulated structures. Providing such a comparison in the form of a figure or table would strengthen the justification for using the QSGS model and support the relevance of the simulation conclusions.\n2. Applicability and Limitations of LBM Fluid Assumptions. The LBM simulations assume an ideal, incompressible fluid to model electrolyte intrusion and gas-liquid interface dynamics. However, in real electrochemical environments, factors such as H2O2 accumulation, ionic strength variation, and charge transport may influence capillary behavior and wettability. While simplifications are necessary for computational feasibility, the authors should briefly discuss whether these assumptions might affect the validity or scope of the conclusions derived from the model.\n3. Clarification of the Inverted Performance Trend in PPE-D with Increasing PTFE Content.\nIn Figure 5b, the authors examine the effect of varying PTFE content in the first layer of the PPE-D electrode. Although the introduction of a gradient structure is expected to improve electrode performance, the observed Faradaic efficiency does not increase with higher PTFE loading. Instead, enhancing the gradient appears to diminish performance. This counterintuitive trend has not been sufficiently discussed. The authors are encouraged to provide a more detailed explanation of the underlying mechanism, which would help strengthen the theoretical foundation of the gradient optimization strategy.\n4. Quantitative Characterization of the Gradient Structure. The manuscript introduces a gradient wettability and porosity design in the CL (e.g., Figure 5a), which is central to the proposed directional transport mechanism. However, the current evidence provided is primarily qualitative. It is recommended that the authors include more quantitative characterization of the gradient structure, such as spatially resolved measurements of contact angle, PTFE content distribution, or porosity variation. These data would help to validate the existence and effectiveness of the proposed gradient and support the conclusions drawn from it.\n5. Inclusion of the Most Recent Studies. In Figure 6c, the authors benchmark the performance of their electrode against representative studies published over the past decade. While this comparison is valuable, the dataset would benefit from the inclusion of more recent studies—particularly those published in 2025—that address similar challenges such as high-current-density operation, ambient-air electrosynthesis, or long-term stability. Incorporating these up-to-date references would better contextualize the novelty and competitiveness of the present work within the current state of the field.", "reviewer_4": "This work presents a novel design of gas diffusion electrodes for electrochemical H₂O₂ production. A comprehensive investigation employing advanced characterization and simulation was conducted to delineate the influence of the electrode structure. The findings hold significant promise for industrial applications. Specific comments are provided below:\n1. Most of the electrochemical data are collected in neutral Na₂SO₄ electrolytes. Yet many industrial processes (e.g., disinfection, chemical synthesis) also require acidic media. The authors should either provide representative acidic/alkaline data or discuss the generalizability of their design principles across different electrolytes.\n2. The electrocatalytic performance of commercial carbon black appears limited. Have the authors considered exploring alternative carbon-based materials with enhanced activity, such as oxidized carbon black or other modified carbons, to further improve electrode performance?\n3. The experimental details of commercial-scale self-breathing electrosynthesis platform should be provided.\n4. For the scale-up system, the authors utilized alkaline electrolyte and solid-state electrolyte. It remains unclear whether the conclusions drawn from experiments in neutral electrolyte are applicable under these conditions.\n5. The LBM and MD simulations form the basis of many mechanistic conclusions (e.g., directional H₂O₂ transport, wettability-governed TPI formation). While trends are consistent with experiments, the link between simulated parameters and measurable electrode properties could be further reinforced.", "reviewer_5": "I co-reviewed this manuscript with one of the reviewers who provided the listed reports. This is part of the Nature Communications initiative to facilitate training in peer review and to provide appropriate recognition for Early Career Researchers who co-review manuscripts."}, "author_response": "Response to reviewers’comments and changes made in the manuscript\nManuscript ID: NCOMMS-25-53419\nA Self-Breathing Electrode Enabled by Interface Regulation and Gradient Wettability\nEngineering for Industrial H O Electrosynthesis\n2 2\nREVIEWER 1\nGeneral Comment: This manuscript by Tian et al. presents a highly significant advancement in the\ndesign of gas diffusion electrodes (GDEs) for electrochemical H O production. The authors\n2 2\nintroduce a novel \"non-fused particulate-packed interface\" architecture that fundamentally\novercomes the long-standing trade-off between hydrophobicity and catalyst site accessibility in\nconventional GDEs. The work is exceptionally thorough, combining rational electrode design,\nadvanced 3D characterization, multiscale simulations (from molecular to mesoscale), and a\ncompelling demonstration of a pilot-scale, commercially viable system. The narrative is clear,\nlogical, and powerfully supported by a wealth of high-quality data. The insights into the role of the\ncatalyst-binder interface in governing three-phase interface formation are of broad importance to\nthe fields of electrocatalysis, fuel cells, and CO reduction. While the work is of outstanding quality\n2\nand impact, I believe it could be further strengthened by addressing a key alternative hypothesis and\nslightly refining the narrative logic concerning the final electrode optimization. Therefore, I\nrecommend Major Revision.\nResponse: We sincerely thank the reviewer for the very positive and encouraging assessment of our\nwork. We deeply appreciate the recognition of the significance, completeness, and potential impact\nof this study, as well as the thoughtful and constructive suggestions aimed at further strengthening\nthe manuscript.\nThe reviewer’s insightful comments have helped us refine both the scientific interpretation and the\nnarrative structure of the paper. In particular, the suggested improvements motivated us to (i) clarify\nthe key aspects of our design rationale and mechanistic understanding, (ii) restructure the subsection\non gradient electrodes to achieve smoother logical flow, and (iii) include new analyses and\nexperiments to test alternative hypotheses and ensure the robustness of our conclusions. These\nrevisions have substantially enhanced the rigor, comprehensiveness, and clarity of the manuscript.\nWe are deeply grateful for the reviewer’s time, expertise, and constructive feedback, which have\nbeen invaluable in improving the quality and impact of this work. Detailed point-by-point responses\nare provided below.\nComment 1: The performance enhancement of the gradient electrodes (PPE-D and PPE-T) is\nprimarily attributed to Laplace pressure-driven \"directional H O transport\". While the microfluidic\n2 2\nexperiments and simulations provide compelling evidence for this phenomenon, a plausible\nalternative hypothesis exists: the performance gain might be predominantly due to the dense, highly\nhydrophobic bottom layer acting as a superior physical barrier, which simply increases the\nbreakthrough pressure and passively prevents flooding, rather than actively guiding product away.\nThe current narrative strongly emphasizes the more sophisticated \"directional transport\" mechanism.\nTo strengthen the conclusion, I would ask the authors to:\nExplicitly discuss this alternative hypothesis in the main text.\nProvide a more direct analysis to decouple these two effects. Could the Resistance Impulse (RI) data\nbe used more quantitatively to estimate the contribution of the barrier effect versus the directional\ntransport? A more balanced discussion acknowledging the synergistic role of both mechanisms\nwould make the claims even more robust.\nResponse: We sincerely appreciate the reviewer’s insightful and constructive comments. We fully\nagree that a plausible alternative hypothesis indeed exists: the performance enhancement of the\ngradient electrodes (PPE-D and PPE-T) could primarily originate from the dense, highly\nhydrophobic bottom layer acting as a superior physical barrier that increases breakthrough pressure\nand passively prevents flooding, rather than from an active, Laplace–pressure–driven directional\ntransport mechanism. We completely understand the reviewer’s concern regarding the need to\ndistinguish these two effects, and we have therefore conducted additional experiments and analyses\nto decouple their respective contributions, aiming to make our mechanistic interpretation clearer\nand more rigorous. Specifically, we have (i) incorporated new quantitative RI-FE correlation\nanalysis to examine the extent to which the flooding resistance (barrier effect) contributes to\nperformance improvement, and (ii) designed zero–hydrostatic–pressure experiments to directly\neliminate the barrier contribution and verify whether the gradient-induced self-transport remains\nactive under pressure-free conditions.\nFirst, we explicitly acknowledge that both PPE-D and PPE-T exhibit higher resistance impulses (RI)\nthan PPE, indicating that their enhanced flooding resistance indeed contributes to performance\nimprovement. To quantify this relationship, we plotted Faradaic efficiency (FE) as a function of RI\nand observed a two-stage linear correlation (Fig.R1): in the low-RI regime, FE increased rapidly\nwith RI (slope = 0.054), confirming the positive effect of hydrophobic binder content; however,\nbeyond a certain RI threshold, the FE increase plateaued, suggesting that the barrier effect alone had\nreached its optimization limit. Notably, PPE-D falls on this FE-RI trend, implying that its\nperformance gain is largely captured by increased breakthrough pressure; this does not preclude\ngradient-assisted transport in PPE-D, but indicates it is not rate-limiting under our conditions.\nIntriguingly, PPE-T deviates from this trend—it displays a slightly lower RI than PPE-D yet a\nsignificantly higher FE. This counter-intuitive result suggests an additional contribution beyond\npassive flooding resistance.\nFig. R1. Correlation between Faradaic efficiency (FE) and the resistance to intrusion (RI).\nSecond, to further decouple these two effects, we performed additional electrolysis experiments\nwith the PPE and PPE-T positioned horizontally, allowing them to float on the electrolyte surface\nwithout any applied hydrostatic pressure. Under these zero-head conditions, the PPE-T still\nachieved significantly higher Faradaic efficiency (Fig. R2). This result confirms that an additional\nmechanism—namely, the gradient-induced self-transport of products—plays a critical role in\nsustaining efficient electrosynthesis. Together, these complementary experiments allow us to\ndisentangle the respective contributions of passive barrier reinforcement and active self-transport,\nclarifying their synergistic roles in governing overall electrode performance. Furthermore, we have\nadded a dedicated paragraph discussing the cooperative relationship between these two mechanisms,\nproviding a more balanced and comprehensive interpretation that, as the reviewer suggested, makes\nour claims even more robust.\nFig. R2. Performance Comparison of Floating Gas Diffusion Electrodes under Zero\nHydrostatic Pressure. a Photograph of the electrolysis setup with the Gas Diffusion Electrode\n(GDE) floating on the surface of the electrolyte (300 mL). A platinum foil counter electrode was\nused, and the current density was maintained at 300 mA cm-2. b Faradaic efficiency (FE) of PPE\nand PPE-T electrodes after 30 minutes of operation. The PPE-T electrode achieved a higher FE\n(54.78%) compared to the PPE electrode (40.18%), confirming the contribution of a Laplace–\npressure–driven, gradient-induced self-transport mechanism. The overall lower FE values, relative\nto standard configurations, are attributed to the absence of a cation-exchange membrane in this setup,\nwhich permits H O decomposition at the anode under high electron flux—a factor independent of\n2 2\nthe mechanistic focus of this study.\nIn the revised manuscript, the original Fig. 6a has been integrated into Fig. 5b. The previous Fig. 5b\nand Fig. 6b have been moved to the Supplementary Information as Supplementary Figs. 34 and 36,\nrespectively. Fig. R1 has been included as Fig. 5c in the revised version, and Fig. R2 has been moved\nto the Supplementary Information as Supplementary Fig. 42. The complete revised Fig. 5 and Fig.\n6 are provided below for your reference.\n“Fig. 5 | Gradient wettability and structural hierarchy promote directional transport and enhance electrode\nperformance. a Cross-sectional EDS mapping results of PPE-D featuring a dense hydrophobic bottom layer and a\nparticulate-packed top layer, forming a structural and wettability gradient. b H2O2 yield and corresponding FE for\ndifferent GDEs. c Correlation between Faradaic efficiency (FE) and the resistance to intrusion (RI). d Molecular\ndynamics rendering of H2O2 diffusion trajectories within gradient versus non-gradient CLs. e Time-resolved spatial\ndensity distributions of H2O2 molecules, showing preferential migration toward regions with larger pores and lower\nPTFE content in the gradient structure. f Mean square displacement (MSD) of H2O2 and O2 molecules in gradient\nand non-gradient CLs, indicating enhanced directional transport in the presence of wettability gradients. g Schematic\nof the microfluidic device designed to visualize directional H2O2 flow in biomimetic CL channels. h Experimental\nvisualization of H2O2 transport in microfluidic chips with hydrophobic and hydrophilic gradients. The H2O2 solution\n(mixed with potassium titanyl oxalate) appears pink and is injected from the central region. Pores are shown in blue\nand the solid skeleton in white. The observed capillary-driven directional transport is consistent with the CL gradient\ndesign (See Supplementary Videos 3 and 4 for experimental details.).”\n“Figure 6 | Industrial validation and scale-up of self-breathing electrodes under demanding conditions. a\nLong-term stability of PPE-T at 15, 300, and 400 mA cm-2. b Benchmarking PPE-T against state–of–the–art systems\nfrom the past decade in terms of current density, operation duration, and FE (See Supplementary Table S3 for full\ndata and references)10-13,15,22,31,32,48,52. c Photograph of a fully integrated, pilot-scale electrolyzer system with four\nserially connected cells, incorporating electronic, fluidic, and thermal subsystems. d Exploded schematic of the four-\ncell modular stack. Key components include: 1/17, end plates; 2/5/9/11/16, silicone gaskets; 3, multifunctional\nbipolar plate enabling both self-breathing and structural support; 4, self-breathing GDE; 6, cathode flow plate;\n7, proton-exchange membrane; 8, anode; 10, anode flow plate; 12-14, serially connected electrochemical cells, each\nassembled from components 3-11; 16, anode current collector. e Long-term stability of the scaled system.”\nThe related description has been included and highlighted in red in the revised version of the\nmanuscript, which is also shown below for your reference.\n“Both PPE-D and PPE-T exhibited significantly higher RI than PPE, confirming their superior\nresistance to electrolyte intrusion under electrowetting and explaining their improved performance.\nFurther analysis of the relationship between FE and RI (Fig. 5c) revealed two distinct regimes: in\nthe low-RI range, FE rose steeply with increasing RI (slope = 0.054), reflecting the positive\ncontribution of enhanced hydrophobicity; beyond a critical RI, the increase plateaued (slope =\n0.0025), suggesting that the barrier effect alone had approached its limit. Notably, PPE-T deviated\nfrom this linear correlation—its RI decreased, yet its FE increased significantly. This deviation\nsuggests that, in addition to passive flooding resistance, an extra transport behavior may have\nemerged, potentially associated with the steeper wettability gradient. To further separate these\neffects, additional electrolysis experiments were performed by floating PPE and PPE-T horizontally\non the electrolyte surface without any applied hydrostatic pressure, thereby minimizing the\ninfluence of breakthrough pressure. Even under pressure-free conditions, PPE-T maintained a\nhigher FE than PPE (Fig. S42), confirming that its superior performance cannot be solely attributed\nto passive barrier protection. Instead, it likely results from a synergistic interplay between passive\nanti-flooding resistance and additional gradient-induced mass transport.” (Page 12–13, Lines 325–\n337)\n“In contrast, the hydrophilic gradient chip displayed symmetric diffusion and rapid flooding. These\nresults highlight the critical role of wettability and pore gradients in directing mass transport and\nmaintaining TPI integrity. Taken together, these findings reveal two synergistic yet distinct\nmechanisms that jointly govern electrode stability and efficiency: the dense hydrophobic sublayer\nserves as a passive barrier that resists electrolyte intrusion, while the wettability gradient actively\ndrives directional product evacuation and sustains TPIs under dynamic operation.” (Page 13, Lines\n353–358)\nComment 2: The transition from the rationally-designed, dual-layer PPE-D to the plasma-treated\nPPE-T feels somewhat abrupt from a narrative standpoint. While the performance of PPE-T is\nsuperior, the intellectual leap is not as well-justified as previous steps in the story. Please add a brief\ntransitional discussion before introducing PPE-T, explaining why a steeper wettability gradient was\nhypothesized to be beneficial based on the findings from PPE-D, and why oxygen plasma etching\nwas chosen as a scalable and effective strategy to achieve this. This would better integrate the PPE-\nT development into the main logical flow of designing electrodes based on fundamental\nunderstanding.\nResponse: We sincerely appreciate the reviewer’s thoughtful comments on the narrative structure\nand logical flow of this section. We also highly value a concise and coherent presentation, as a\nrigorous and logically organized narrative greatly improves the readability and scientific clarity of\nthe work. This comment is closely related to Comment 1, and we have comprehensively revised the\ncorresponding subsection to enhance continuity and conceptual depth.\nFirst, as detailed in our response to Comment 1, we no longer present PPE-T as a separate design\nstep. Instead, PPE, PPE-D, and PPE-T are now discussed together within an integrated framework,\nenabling a natural comparison of their flooding resistance and product-transport behaviors. This\nrestructuring eliminates the previously abrupt transition between PPE-D and PPE-T and provides a\nsmoother and more logical progression from electrode design to mechanistic interpretation.\nSecond, we have further clarified why oxygen plasma etching was chosen as a scalable and effective\napproach to achieve a steeper wettability gradient. While adding an additional catalyst layer with\nlower PTFE content could in principle generate a more pronounced gradient, such multilayer\nassembly would significantly complicate fabrication and hinder scalability. In contrast, oxygen\nplasma etching offers a rapid, controllable, and catalyst-agnostic surface-modification route that can\ntailor surface hydrophilicity without additional loading steps or structural damage to the existing\nCL. This technique therefore provides a convenient and practical means to construct a third\nwettability gradient layer. These revisions have strengthened both the narrative coherence and the\nscientific justification for introducing PPE-T.\nThe related description has been included and highlighted in red in the revised version of the\nmanuscript, which is also shown below for your reference.\n“Hierarchical Gradient CL for Liquid Repellence and Guided Product Transport\nBuilding on previous findings, a hierarchically structured CL with porosity and wettability gradients\nwas designed to guide electrolyte transport. To systematically assess the influence of gradient design,\nwe fabricated electrodes with dual-layer (PPE-D) and triple-layer (PPE-T) gradient architectures in\naddition to a single-layer reference (PPE). For PPE-D, a PTFE-rich ink was first coated onto the gas\ndiffusion layer (GDL) and sintered to form a dense, highly hydrophobic layer with fine pores,\nserving as the first CL49. A second catalyst layer composed of non-fused particulate packing was\nthen deposited on top, yielding a dual-gradient structure (PPE-D) with controlled PTFE content\n(1.8-3.6 mg cm-2) (Fig. S28). Cross-sectional EDS mapping (Fig. 5a) qualitatively confirmed that\nthe bottom layer is denser and richer in fused PTFE, establishing a clear porosity gradient. Mercury\nintrusion porosimetry (Fig. S29) quantitatively confirmed a porosity gradient, with a marked\ndecrease in pore volume toward the PTFE-rich bottom layer, consistent with densification and\npartial pore blockage from sintering. Because contact-angle measurements are unreliable for rough\nporous surfaces, PTFE loading was used as a quantitative indicator of hydrophobicity. The higher\nPTFE content in the bottom layer indicates stronger electrolyte repellence, confirming coupled\nporosity–wettability gradients across the CL.\nFor PPE-T, while adding another low-PTFE catalyst layer could further steepen the gradient, such\nmultilayer assembly would complicate fabrication and hinder scalability. Instead, oxygen plasma\netching provides a rapid, controllable, and catalyst-independent approach to tune surface\nhydrophilicity without additional coating or structural damage50. We therefore applied plasma\netching to PPE-D, enabling a simple and scalable enhancement of surface wettability. The treatment\nintroduces oxygenated groups (–OH, C=O, C–O–C) that raise surface energy and reduce the top-\nlayer contact angle from 158° to 30° (Fig. S30). XPS and EDS analyses verified the incorporation\nof these oxygenated groups, and the plasma parameters were optimized to preserve catalyst activity\nand pore morphology (Fig. S31- S33). The resulting electrode, PPE-T, thus exhibits a continuous\nporosity–wettability gradient throughout the CL.\nWe next compared the performance of PPE, PPE-D, and PPE-T to evaluate the effect of gradient\nsteepness. The dual-gradient design (PPE-D1.8) maintained 83% FE after 5 h—43% higher than\nPPE (Fig. 5b and Fig. S34). The same performance hierarchy of FSE < PPE < PPE-D was\nmaintained under both acidic and alkaline electrolytes, confirming that the structural design\nprinciples are generally applicable across different pH environments (Fig. S35). The introduction of\na surface-modified hydrophilic layer further amplified this effect: PPE-T outperformed both PPE\nand PPE-D, maintaining nearly 100% FE during the first 3 h (Fig. 5b). Across 0-500 mA cm-2, PPE-\nT exhibited a near-linear increase in H O production rate, indicating that oxygen-transport\n2 2\nlimitations were fully resolved (Fig. S36). These results demonstrate that introducing multi-layered\nwettability gradients via scalable surface modification strategies can substantially enhance GDE\nperformance under practical operating conditions.\nTo elucidate the origin of the performance enhancement, LBM simulations were combined with in-\nsitu experiments to assess electrolyte breakthrough behavior. Gradient and non-gradient structures\nwere generated using a modified QSGS algorithm (Fig. S37). The simulations showed that, at the\nsame timestep, PPE-D restricted electrolyte intrusion to localized gas-liquid regions, preserving\noxygen pathways, whereas PPE was completely flooded (Fig. S38). These trends were further\nverified by in-situ breakthrough pressure tests (Fig. S39). Under constant mechanical load and\napplied potential, the time required for peroxide test paper on the GDL to show discoloration was\nrecorded (Fig. S40). Multiplying the applied pressure by breakthrough time yielded the resistance\nimpulse (RI), a quantitative indicator of intrinsic flooding resistance. The RI values of all electrodes\nwere compared to evaluate their flooding resistance (Fig. S41). Both PPE-D and PPE-T exhibited\nsignificantly higher RI than PPE, confirming their superior resistance to electrolyte intrusion under\nelectrowetting and explaining their improved performance. Further analysis of the relationship\nbetween FE and RI (Fig. 5c) revealed two distinct regimes: in the low-RI range, FE rose steeply\nwith increasing RI (slope = 0.054), reflecting the positive contribution of enhanced hydrophobicity;\nbeyond a critical RI, the increase plateaued (slope = 0.0025), suggesting that the barrier effect alone\nhad approached its limit. Notably, PPE-T deviated from this linear correlation—its RI decreased,\nyet its FE increased significantly. This deviation suggests that, in addition to passive flooding\nresistance, an extra transport behavior may have emerged, potentially associated with the steeper\nwettability gradient. To further separate these effects, additional electrolysis experiments were\nperformed by floating PPE and PPE-T horizontally on the electrolyte surface without any applied\nhydrostatic pressure, thereby minimizing the influence of breakthrough pressure. Even under\npressure-free conditions, PPE-T maintained a higher FE than PPE (Fig. S42), confirming that its\nsuperior performance cannot be solely attributed to passive barrier protection. Instead, it likely\nresults from a synergistic interplay between passive anti-flooding resistance and additional gradient-\ninduced mass transport.\nTo further elucidate this behavior, LBM and molecular dynamics (MD) simulations were\nsubsequently conducted to analyze the in-situ diffusion of H O within the CL at mesoscale and\n2 2\nmolecular scales, respectively. The LBM simulations revealed that H O spontaneously migrates\n2 2\ntoward regions with larger pores and lower PTFE content, thereby preserving dry domains that\nmaintain access to oxygen (Fig. S43 and Video 2). To quantify this effect, MD simulations were\nconducted to calculate mass-transfer coefficients (Fig. S44 and Fig. 5d) 23. Despite identical PTFE\ncontent, the gradient CL exhibited directional H O diffusion with a transport coefficient of 2.05 ×\n2 2\n10-5 cm2/s, 37.6% higher than the bidirectional diffusion observed in the non-gradient system (1.49\n× 10-5 cm2/s, Fig. 5e and Fig. 5f). Simultaneously, the removal of H O facilitated O diffusion into\n2 2 2\nthe CL, increasing its mass-transfer coefficient from 1.26 × 10-4 to 1.61 × 10-4 cm2/s (a 27.8%\nimprovement). These enhancements suppress local H O accumulation and promote O\n2 2 2\nreplenishment at the TPI. Since real-time nanoscale electrochemical imaging remains challenging,\nwe developed a custom PDMS-based microfluidic visualization platform (2 × 2 cm) incorporating\nQSGS-derived gradient pore structures with fluorosilane-treated frameworks mimicking PTFE\nhydrophobicity (Fig. 5g) 51. A potassium titanyl oxalate solution containing H O was injected into\n2 2\nthe chip center to simulate in-situ product generation. Visualization experiments (Supplementary\nVideos 3–4) showed that, in the hydrophobic gradient chip, H O consistently migrated toward the\n2 2\nlarge-pore region, leaving the small-pore side dry. Convex menisci at narrow throats indicated\ncapillary barriers generating a net Laplace force that drove fluid directionally. In contrast, the\nhydrophilic gradient chip displayed symmetric diffusion and rapid flooding. These results highlight\nthe critical role of wettability and pore gradients in directing mass transport and maintaining TPI\nintegrity. Taken together, these findings reveal two synergistic yet distinct mechanisms that jointly\ngovern electrode stability and efficiency: the dense hydrophobic sublayer serves as a passive barrier\nthat resists electrolyte intrusion, while the wettability gradient actively drives directional product\nevacuation and sustains TPIs under dynamic operation.” (Page 12–13, Lines 285–358)\n“For PPE-T, while adding another low-PTFE catalyst layer could further steepen the gradient, such\nmultilayer assembly would complicate fabrication and hinder scalability. Instead, oxygen plasma\netching provides a rapid, controllable, and catalyst-independent approach to tune surface\nhydrophilicity without additional coating or structural damage50. We therefore applied plasma\netching to PPE-D, enabling a simple and scalable enhancement of surface wettability.” (Page 12,\nLines 299–307)\nREVIEWER 2\nGeneral Comment: This manuscript reports a rationally designed gas diffusion electrode (GDE)\narchitecture combining a non-fused particulate-packed catalyst–binder interface and a hierarchical\nwettability/pore gradient, which enables self-breathing hydrogen peroxide (H O ) electrosynthesis\n2 2\nunder ambient air without external oxygen supply. The authors convincingly demonstrate that this\nstructure not only enhances three-phase interface (TPI) formation but also resolves flooding issues\nat high current densities. Moreover, the study integrates advanced three-dimensional structure\nreconstruction and high-resolution Lattice Boltzmann simulations to elucidate gas-liquid-solid\ndistribution at the mesoscale, thereby offering mechanistic insights into interface evolution.\nParticularly impressive is the engineering of a modular 400 cm2 flow-through stack incorporating\nelectronic, thermal, and fluidic systems, achieving industrially relevant performance and cost\nmetrics.\nTo the best of my knowledge, this is the first report to bridge fundamental interface engineering\nwith large-scale implementation for electrochemical H O production. The work presents a\n2 2\nsignificant advance toward practical and decentralized oxidant manufacturing. While the manuscript\nis well-structured and the data convincing, I believe the authors should address the following points\nto further solidify the claims and improve reproducibility. With these minor but important\nclarifications and additions, I believe the manuscript could be suitable for publication in Nature\nCommunications.\nResponse: We sincerely thank the reviewer for the careful reading of our manuscript and for the\nprofessional and insightful comments. We deeply appreciate the reviewer’s recognition of our work\nand the constructive suggestions provided, which reflect a sharp understanding of both the technical\nand methodological aspects of this study.\nIn response, we have thoroughly revised the manuscript to:\n(1) clarify the respective roles of molten encapsulation and densification in determining the catalyst–\nbinder interface structure and performance;\n(2) explain how the hydrophobicity of PTFE was maintained in the absence of sintering and verify\nthe removal of residual surfactants;\n(3) expand the discussion on the applicability of the observed interface effect to other binder systems;\n(4) address the Faradaic efficiency decline at high current density and discuss possible structural or\noperational causes;\n(5) update the benchmarking data with the most recent publications from 2025;\n(6) correct the labeling issue identified in Figure 6;\n(7) provide further clarification regarding the Na SO concentration and the selection of carbon\n2 4\nblack (XC-72); and\n(8) refine the writing style and tense consistency throughout the text.\nWe truly appreciate the reviewer’s valuable insights, which have helped us to further enhance the\nrigor, clarity, and overall quality of the revised manuscript.\nComment 1: The authors emphasize that the non-fused particulate-packed interface plays a central\nrole in enhancing electrosynthesis performance, and attribute the reduced performance of\nconventional electrodes to molten interface structures caused by hot pressing or sintering. However,\nit is not clearly distinguished whether the observed differences arise primarily from the interface\nmorphology (i.e., molten encapsulation) or from reduced porosity due to densification during hot\npressing. Since the structural change involves both factors, it is recommended that the authors\nsupplement with experimental or comparative discussion to decouple and clarify the independent\neffect of the molten interface.\nResponse: We sincerely thank the reviewer for this professional and insightful comment. We fully\nagree that, in the previous version, the effects of PTFE fusion and structural densification induced\nby hot pressing were not explicitly decoupled. To clarify this point, we conducted an additional\ncomparative experiment to isolate the morphological effect of PTFE fusion from the compaction\neffect.\nSpecifically, we fabricated a calcined particulate-packed electrode (PPE-cal) by calcining the spray-\ncoated PPE electrode at 340 °C for 1 h without hot pressing. This process induced partial PTFE\nmelting and encapsulation of carbon particles while maintaining the same macroscopic density as\nthe original PPE electrode, thereby eliminating the influence of densification. As shown in Fig. R3,\nPPE-cal exhibited partial fusion of PTFE but lacked the compact morphology observed in the hot-\npressed FSE electrode. Electrochemical H O synthesis tests revealed that PPE-cal exhibited a lower\n2 2\nFaradaic efficiency than PPE but remained markedly superior to FSE (Fig. R4). This performance\nhierarchy (PPE > PPE-cal > FSE) demonstrates that both molten encapsulation and pore-structure\nvariation contribute to the performance degradation of conventional electrodes, with microstructural\npore changes playing the dominant role.\nFig. R3. Morphological comparisons of PPE and PPE-cal. SEM images of PPE (a -a ) and\n1 3\nPPE -cal (b -b ).\n1 3\nFig. R4. H O yield and corresponding FE of FSE. a PPE-cal and PPE at 15 mA cm-2 and b\n2 2\n300 mA cm-2.\nThe related revisions have been incorporated into both the main manuscript and the Supplementary\nInformation, highlighted in red for your convenience. The updated sections are also shown below\nfor reference. Specifically, Fig. R3 and R4 have been included as Supplementary Fig. 8 and 9,\nrespectively, in the revised Supplementary Information, and the preparation method of PPE-cal has\nbeen added to the Methods section of the revised manuscript.\n“It should be noted that the above analysis mainly attributes the inferior performance of FSE to pore\ndensification, while the intrinsic limitation associated with PTFE encapsulation of carbon particles\nhas not been fully clarified. To decouple these two effects, a comparison electrode (PPE-cal) was\nprepared by calcining the spray-coated PPE at 340 ℃ without hot pressing. This treatment induced\npartial PTFE melting and CB encapsulation while maintaining the same packing density as PPE,\nthereby isolating the influence of densification caused by hot pressing. As shown in Fig. S8, PPE-\ncal exhibited partial PTFE fusion but lacked the compact morphology of FSE. Electrochemical H O\n2 2\nsynthesis revealed a clear performance hierarchy of PPE > PPE-cal > FSE, indicating that both\nmolten encapsulation and reduced porosity contribute to the degraded performance of conventional\nelectrodes (Fig.S9). Similar binder-induced encapsulation effects have also been observed in\nionomer-based catalyst layers (e.g., Nafion coatings on Pt/C), where excessive polymer coverage\nhinders gas diffusion, highlighting the broader relevance of this interfacial limitation.” (Page 7,\nLines 158–167)\n“Calcined particulate-packed electrode (PPE-cal): PPE electrodes were calcined at 340 °C for 1 h\nwithout hot pressing to induce partial PTFE melting while preserving the same macroscopic density\nas PPE.” (Page 17, Lines 451–452)\nComment 2: In lines 57–58, the authors state that sintering is typically used to remove surfactants\nfrom PTFE and maintain its hydrophobicity. Yet, to avoid molten interfaces, sintering was\nintentionally skipped in this work. The authors should explain how the PTFE’s hydrophobicity was\nretained in the absence of sintering and whether any pretreatment or washing was used to remove\nresidual surfactants. This clarification is critical for reproducibility.\nResponse: We sincerely thank the reviewer for this sharp and constructive comment, which greatly\nhelps to improve the clarity and reproducibility of our work. In the fabrication of PPE electrodes,\nthe layer–by–layer spray-coating combined with sequential high-temperature drying effectively\npromotes solvent evaporation. Because the surface-active agents in the PTFE emulsion are soluble\nin the solvent phase, they are volatilized together with the solvent during this process. As a result,\nthe PTFE retains its intrinsic hydrophobicity even without sintering.\nTo verify this, we performed energy-dispersive X-ray spectroscopy (EDS) on the as-prepared PPE\nelectrodes. The EDS spectrum (Fig. R5) shows no oxygen signal attributable to surfactant residues\nin the catalyst layer, confirming that the surfactant was completely removed during spraying and\ndrying.\nFig. R5. EDS elemental mapping and corresponding composition analysis of the catalyst layer\nsurface.\nFig. R5 has been included as Supplementary Fig. 49 in the revised Supplementary Information. In\naddition, the corresponding descriptions have been incorporated into the revised manuscript\n(Methods section) and the Supplementary Information, highlighted in red for clarity, as shown\nbelow for your reference.\n“During the spray-coating and high-temperature drying steps, rapid solvent evaporation removed\nthe surface-active agents in the PTFE emulsion. As these surfactants are soluble in the solvent phase,\nthey volatilized together with the solvent. EDS analysis of the as-prepared PPE electrodes\n(Supplementary Fig. S48) showed no oxygen signal from residual surfactants, confirming that the\nPTFE maintained its hydrophobicity without sintering.” (Page 17, Lines 446–450)\nComment 3: While the authors attribute performance suppression to molten encapsulation by PTFE,\nit is unclear whether this phenomenon is specific to PTFE or generally applies to other binder\nsystems. A brief discussion (or reference to comparative experiments, e.g., with Nafion or other\nbinders) would help establish the generality of this observation.\nResponse: We thank the reviewer for this perceptive question. Indeed, the issue of binder\nencapsulation of catalyst particles is not unique to PTFE — analogous challenges have been\nreported in various electrocatalytic systems employing ionomer binders. Below, we provide a brief\ncontextual discussion with literature support.\n1. In fuel-cell catalyst layers, Chen et al. demonstrated that a “covered-type” catalyst/ionomer\ninterfacial structure severely limits oxygen transport, as O molecules must diffuse through the\n2\nionomer film and internal microchannels to reach Pt/C surfaces. They deliberately designed a “non-\ncovered” interface to mitigate this limitation1.\n2.More generally, Li et al. reported that high ionomer loading or overly conformal ionomer films\ncan significantly impair gas (particularly oxygen) transport in the catalyst layer2.\n3. Huang et al. also revealed that when ionomer films tightly cover carbon or catalyst surfaces,\nwater\nclustering, anisotropic transport, and hindered reactant diffusion occur within the confined\nmicroenvironment3.\nThese studies collectively suggest that binder-induced encapsulation limiting gas accessibility is a\ngeneral challenge, not exclusive to PTFE, especially when binder films become overly conformal\nor excessive. However, since the current work focuses on PTFE-based gas diffusion electrodes and\nthe specific thermally-induced morphological transitions of PTFE, we did not perform comparative\nexperiments with other binders (e.g., Nafion) in this study. To address this point, we have added a\nbrief discussion in the Discussion section, acknowledging that similar encapsulation effects may\nalso arise in other binder systems.\nThe related description has been included and highlighted in red in the revised version of the\nmanuscript, which is also shown below for your reference.\n“Similar binder-induced encapsulation effects have also been observed in ionomer-based catalyst\nlayers (e.g., Nafion coatings on Pt/C), where excessive polymer coverage hinders gas diffusion,\nhighlighting the broader relevance of this interfacial limitation” (Page 7, Lines 165–167)\nComment 4: In Fig. 6d, it is observed that the PPE-T electrode shows a noticeable decline in\nFaradaic efficiency starting around the 45th hour under a current density of 400 mA cm-2. Although\nthe overall durability and performance are impressive, the authors should provide a brief explanation\nof this trend—e.g., whether it may arise from flooding, oxygen depletion, catalyst degradation, or\nstructural changes—and discuss whether further optimization of the interface structure or gradient\nparameters could mitigate this behavior in future iterations. Addressing this point would enhance\nthe completeness of the discussion without diminishing the study’s overall impact.\nResponse: We thank the reviewer for this constructive comment. The gradual decline in Faradaic\nefficiency after approximately 45 h at 400 mA cm-2 primarily arises from intensified electrowetting\nunder high current density, which significantly promotes electrolyte infiltration. The electric field-\ninduced alteration of local wettability triggers capillary forces that exceed the accommodation\ncapacity of the existing gradient structure, leading to partial flooding of the catalytic layer. This,\nin turn, disturbs oxygen transport within the self-breathing configuration and causes a local imbalance\nin the gas-liquid distribution. This phenomenon becomes evident only under the most aggressive\noperating condition (400 mA cm-2, continuous electrolysis for 50 h), whereas the electrode remains\nhighly stable at ≤ 300 mA cm-2 for more than 300 h.\nThis issue can be mitigated by further optimizing the pore-size gradient and the spatial distribution\nof PTFE to better tolerate more aggressive current densities. Importantly, this observation does not\ncompromise the validity of our design strategy but instead highlights valuable opportunities for\nstructural refinement in future iterations.\nTo clarify this point, we have added a brief explanation in the Results and Discussion section, stating\nthat the slight decline in FE after 45 h at 400 mA cm-2 likely results from intensified electrowetting–\ninduced electrolyte intrusion that exceeds the tolerance of the current gradient structure, leading to\npartial flooding in the catalytic layer. This effect can be further mitigated by optimizing the pore-\nsize gradient and spatial PTFE distribution. The related description has been included and\nhighlighted in red in the revised version of the manuscript, which is also shown below for your reference.\n“(Fig. 6a, where the slight decline in FE after 45 h at 400 mA cm-2 is attributed to electrowetting-\ninduced partial flooding within the catalytic layer, which can be mitigated by further optimizing the\npore-size gradient and spatial PTFE distribution)” (Page 15, Lines 380-382)\nComment 5: In Fig. 6c, the benchmarking table is informative and positions the work well among\nprior studies. However, recent advances in 2025 are underrepresented. The authors are encouraged\nto update the comparison with the latest publications to ensure comprehensive context and highlight\nthe distinctiveness of this study.\nResponse: We sincerely thank the reviewer for this valuable suggestion. We have carefully updated\nthe benchmarking table (Supplementary Table 6) and the corresponding discussion (Fig. 6b and\nrelated text) to include the most recent publications from 2025 (Fig.R6). This update provides a\nmore comprehensive comparison and further emphasizes the distinctiveness and advancement of\nour work relative to the latest studies.\n[Figure Redacted]\nFig. R6. Benchmarking PPE-T against state-of-the-art systems from the past decade in terms of\ncurrent density, operation duration, and FE (See Supplementary Table S6 for full data and references)\nFurthermore, the 2025 data newly added in Supplementary Table S6 are also presented below for\nyour convenience and reference.\nTable S6. Performance comparison of electrodes prepared using different strategies (Newly added\nperformance data for 2025).\nReaction Total\nElectrode Current Electrolytconcentra\nElectrolyzer Cathode Anode Electrolyt time per reaction\nNo. Date O2 source Binder area density e volum tion FE Ref.\nstructure catalyst catalyst es cycle time\n(cm2) (mA/cm2) e(ml) (mg/L)\n（h） (h)\nHSO 500 / 30 / / 0.9\n2 4\nadditional F-in/out-\n41 2025 divided Nafion Pt 4 (0.05mol 43\noxygen CNTs 200 / 50 / / 0.93\n/L)\nadditional AlO/Al KOH\n2 3\n42 2025 divided Nafion RuO/Ti 1 250 / 100 / / 0.9 44\n2\noxygen –O-C (1mol/L)\n1\nadditional Commer AEM\n43 2025 divided IrO 100 DI water 100 / 500 / 17000 0.8 45\n2\noxygen cial CB ionomer\nadditional FeO@\n3 4\n44 2025 divided Nafion Pt 4 DI water 50 / 60 / / 0.91 46\noxygen TNC-AE\nKOH\nadditional D20- glassy\n45 2025 divided Nafion / (0.1mol/ 200 / 400 3000 15600 0.9. 47\noxygen vulcan carbon\nL)\nKOH\nadditional B-meso-\n46 2025 divided Nafion Ru-Ir-Ti 4 (0.1mol/ 100 / 100 / / 0.9 48\noxygen PC\nL)\nadditional glassy KOH\n47 2025 divided Ni-C Nafion / 250 / 100 / 24660 0.9 49\noxygen carbon (1mol/L)\nadditional NiFeW\n48 2025 divided Nafion RuIr@Ti 4 DI water 50 / 140 / 10000 0.75 50\noxygen LDH\nComment 6: In Fig. 6, c and d may have been mistakenly swapped. The figure captions and data\nshown do not seem to correspond to their labels. The authors should double-check and revise the\nlabels accordingly to avoid confusion for readers.\nResponse: We thank the reviewer for carefully pointing out this oversight. We have double-checked\nthe figures and corrected the labels of Fig. 6c and Fig. 6d to ensure full consistency between the\ncaptions and the corresponding data. The revised version has been carefully verified to avoid any\nfurther confusion for readers.\nComment 7: In the experimental section, why different concentration of Na SO solutions were\n2 4\nused under different current densities? Please give the explanation.\nResponse: We thank the reviewer for this relevant question. Different concentrations of Na SO\n2 4\nelectrolyte were used to maintain appropriate ionic conductivity and minimize system heat\ngeneration at varying current densities. Excessive heat accumulation can accelerate the self-\ndecomposition of H O , as demonstrated in Fig. S45. Therefore, using higher electrolyte\n2 2\nconcentrations at elevated current densities effectively reduced internal resistance and thermal\nbuildup, ensuring consistent electrochemical conditions across all tests. This adjustment does not\naffect the validity of the comparative results.\nTo clarify this point, the related description has been included and highlighted in red in the revised\nversion of the manuscript (Methods section), which is also shown below for your reference.\n“At high current densities (200–400 mA cm-2), 1 M Na SO was used, and periodic electrolyte\n2 4\nreplacement was employed to mitigate thermal decomposition.” (Page 17–18, lines 468–469)\nComment 8: Section “Chemicals and materials”, in contrast to other researches which used XC-\n72R, I have notices that the carbon black you used is XC-72. Could you explain to me that the reason\nyou use this type of carbon black?\nResponse: We thank the reviewer for carefully noticing this detail. The carbon black used in this\nwork was indeed XC-72R, and the appearance of “XC-72” in the Chemicals and Materials section\nwas a typographical error. We have corrected it to “XC-72R” in the revised manuscript to accurately\nreflect the material used in all experiments.\nComment 9: Please check through the manuscript and reduce the use of “we introduce”, “we\nidentify”, “we construct” “we then developed”……\nResponse: We thank the reviewer for this valuable stylistic suggestion. Following the comment, we\nhave carefully reviewed the entire manuscript and reduced repetitive use of first-person expressions,\nparticularly in the Methods and Results sections where procedural and descriptive sentences have\nbeen revised into passive or impersonal forms.\nAt the same time, a moderate number of first-person statements were intentionally retained to\nmaintain sentence variety and preserve the emphasis and narrative strength of key conclusions. This\nbalanced revision improves readability while ensuring a formal and coherent tone throughout the\nmanuscript.\nTo clarify this point, the related description has been included and highlighted in red in the revised\nversion of the manuscript, which is also shown below for your reference.\n“Here, a non-fused particulate-packed catalyst/binder interface (Fig. 1) is introduced, in which\ndiscrete PTFE is embedded within the catalyst matrix to form a “packed-contact, pore-percolated”\nstructure that exposes active sites and supports dense TPIs.” (Page 3, Lines 78–80)\n“Using focused ion beam-scanning electron microscopy (FIB-SEM) 3D reconstruction, the Lattice\nBoltzmann Method (LBM), and the Quartet Structure Generation Set (QSGS), electrolyte intrusion\nwas quantitatively revealed to be governed by the coupling of wettability and pore geometry,\nuncovering the structural origin of TPI formation. Guided by these findings, an ordered CL with\ncontrolled wettability gradients and hierarchical pores was subsequently developed, and multiscale\nsimulations together with microfluidic experiments validated that Laplace pressure-driven\ndirectional H O transport occurs through the CL.” (Page 3, Lines 80–85)\n2 2\n“To investigate the effect of the catalyst/binder interface structure on electrochemical H O\n2 2\nproduction, two GDEs were fabricated using PTFE as the binder.” (Page 4, Lines 101–102)\n“To elucidate the performance disparity between the two GDEs, their physicochemical properties\nand O /electrolyte mass transport behavior were systematically investigated.” (Page 5, Lines 117–\n2\n118)\n“To clarify how microscale pore structures influence species transport, mesoscale simulations of\ngas-liquid-solid interactions within the CLs of FSE and PPE were performed.” (Page 7, Lines 147–\n148)\n“To further investigate the origin of PTFE/CB separation at high P/C ratios, ink formulations were\nanalyzed using a laser particle size analyzer.” (Page 9, Lines 208–209)\n“To assess the feasibility of guiding electrolyte transport through structural regulation, the QSGS\nalgorithm was used to generate CL structures by tuning nucleation probability (P ) and phase\nc\noccupation ratio (R ), and gas-liquid behavior was quantified via LBM.” (Page 11, Lines 264–266)\np\n“Building on previous findings, a hierarchically structured CL with porosity and wettability\ngradients was designed to guide electrolyte transport.” (Page 12, Lines 286–287)\n“To elucidate the origin of the performance enhancement, LBM simulations were combined with\nin-situ experiments to assess electrolyte breakthrough behavior.” (Page 12, Lines 317–318)\n“The long-term stability of PPE-T without external aeration was evaluated across various current\ndensities.” (Page 15, Lines 374–375)\nComment 10: Please check the tenses throughout the manuscript.\nResponse: We thank the reviewer for this helpful reminder. The manuscript has been carefully\nrechecked to ensure consistent and appropriate use of verb tenses. Specifically, past tense is now\nconsistently applied to describe experimental procedures and observations, while present tense is\nused for general statements, conclusions, and mechanistic interpretations. These revisions improve\ngrammatical consistency and align the manuscript with the Nature Communications style\nconventions.\nREVIEWER 3\nGeneral Comment: This manuscript reports a rationally designed gas diffusion electrode (GDE)\narchitecture that combines a non-fused particulate-packed catalyst-binder interface with a\nhierarchical wettability and pore gradient. This configuration enables self-breathing H O\n2 2\nelectrosynthesis under ambient air without external oxygen supply. The study further integrates\nthree-dimensional structural reconstruction and high-resolution Lattice Boltzmann simulations to\nvisualize gas-liquid-solid distributions at the mesoscale, providing mechanistic insights into\ninterfacial transport phenomena. Of particular note is the engineering of a modular 400 cm2 flow-\nthrough stack that incorporates electronic, thermal, and fluidic subsystems. This platform achieves\nindustrially relevant performance and cost benchmarks, underscoring the translational potential of\nthe proposed design. The work represents a notable step forward toward decentralized and\nsustainable oxidant manufacturing. Overall, this manuscript is well-organized with robust\nperformance and systematic mechanism elucidation. As such, I recommend the publication of this\nmanuscript in Nature Communications after addressing the following issues.\nResponse: We sincerely appreciate the reviewer’s positive assessment of our work and strong\nsupport for its publication, as well as the constructive suggestions that have significantly improved\nthe quality of the manuscript. These suggestions have prompted us to further refine our analyses and\nclarify key aspects of the design rationale, thereby making our study more rigorous, comprehensive,\nand precise.\nIn the revised version, we have carefully addressed all the raised points by:\n(1) quantitatively validating the QSGS-reconstructed structures through comparison with real FIB-\nSEM data;\n(2) discussing the applicability and limitations of the LBM model assumptions;\n(3) clarifying the mechanism behind the inverted trend observed in PPE-D electrodes with\nincreasing PTFE content;\n(4) providing additional quantitative characterization of the gradient structure to substantiate\ndirectional transport; and\n(5) updating the benchmarking dataset with the latest studies (2025) to better position our work in\nthe current research landscape.\nThese revisions have significantly enhanced the technical completeness and contextual depth of the\nmanuscript. We are deeply grateful for the reviewer’s constructive suggestions and strong support\nfor the publication of our work in Nature Communications.\nComment 1: Quantitative Validation of the QSGS-Reconstructed Structures\nThe QSGS method is employed in Figures 2g and 4e/g to generate representative 3D catalyst layer\nmorphologies for simulation. However, the manuscript does not provide sufficient quantitative\nvalidation of how well these synthetic structures reflect the true morphology obtained via FIB-SEM\nreconstruction. To enhance the credibility and generalizability of the simulation results, the authors\nare encouraged to compare key structural parameters between the real and simulated structures.\nProviding such a comparison in the form of a figure or table would strengthen the justification for\nusing the QSGS model and support the relevance of the simulation conclusions.\nResponse: We thank the reviewer for raising this important point. We agree that validating the\naccuracy of the QSGS-based structure generation is crucial to establishing the relevance and\ngeneralizability of the simulation results. In the revised manuscript, we have added both\nmethodological justification and quantitative validation for the QSGS-reconstructed structures to\nstrengthen the credibility of our simulations.\nFirst, we note that the QSGS method has been widely adopted for stochastic reconstruction of\nporous electrodes in recent high-impact studies of catalyst layers for fuel cells, water electrolysis,\nand electrochemical energy systems4-6. These works have demonstrated that QSGS effectively\nreproduces realistic pore connectivity and phase distribution, providing a reliable framework for\ninvestigating transport phenomena in multiphase electrode media.\nSecond, to quantitatively assess the representativeness of our generated structures, we compared\ntwo key parameters between the FIB-SEM reconstructed catalyst layer and the QSGS model:\nporosity (0.73 vs 0.65) and CB/PTFE volume ratio (1.09 vs 1.33). The modest deviations confirm\nthat the synthetic geometries capture the essential morphological characteristics of the real structure.\nA new bar-chart comparison (Fig. R7) has been added to the Supplementary Information to visualize\nthese results.\nFig. R7. Quantitative validation of Quartet Structure Generation Set (QSGS)-generated structures\nagainst FIB-SEM reconstruction. Comparison of porosity and CB/PTFE volume ratio between the\nQSGS-generated and FIB-SEM-reconstructed catalyst layers. The FIB-SEM structure exhibits a\nporosity of 0.73 and a CB/PTFE volume ratio of 1.09, while the corresponding QSGS-generated\nstructure shows 0.65 and 1.33, respectively. Although slight differences exist, they remain within an\nacceptable range. The purpose of employing QSGS in this study was to intentionally construct\nmorphologies with tunable gradients to examine how different pore and phase distributions\ninfluence multiphase transport and triple-phase-interface formation. Therefore, these minor\ndiscrepancies do not compromise the mechanistic insights or the generality of the conclusions. The\noverall good agreement validates the reliability of the QSGS reconstruction method used in this\nwork.\nThird, we acknowledge that certain differences remain between the real and simulated structures.\nHowever, our goal in employing QSGS was not to exactly replicate the experimental morphology\nbut rather to intentionally construct a set of random structures with controlled gradients in structural\nparameters, enabling a systematic investigation of how different porosity and phase distributions\naffect multiphase flow and triple–phase–interface formation. Therefore, these minor differences do\nnot compromise the mechanistic insights or the generality of the conclusions drawn from the\nsimulations. We again thank the reviewer for this careful and valuable suggestion, which has helped\nus clarify the rationale and strengthen the credibility of our modelling approach.\nThe related description has been included and highlighted in red in the revised versions of the\nmanuscript and the Supplementary Information, where Fig. R7 has been incorporated as\nSupplementary Fig. 6. The updated content is also shown below for your reference.\n“The reliability of the QSGS-generated structures was quantitatively validated by comparing their\nporosity and CB/PTFE volume ratio with those of the FIB-SEM reconstructed catalyst layer,\nshowing good consistency (Fig. S6).” (Page 7, Lines 150–152)\nComment 2: Applicability and Limitations of LBM Fluid Assumptions\nThe LBM simulations assume an ideal, incompressible fluid to model electrolyte intrusion and gas-\nliquid interface dynamics. However, in real electrochemical environments, factors such as H O\n2 2\naccumulation, ionic strength variation, and charge transport may influence capillary behavior and\nwettability. While simplifications are necessary for computational feasibility, the authors should\nbriefly discuss whether these assumptions might affect the validity or scope of the conclusions\nderived from the model.\nResponse: We thank the reviewer for raising this important point. It is true that our LBM simulations\nsimplify the electrolyte as an ideal, incompressible, and charge-neutral fluid, and therefore do not\nexplicitly account for variations in H O concentration, ionic strength, or electric double-layer\n2 2\ninteractions during electrochemical operation. These effects could, in principle, influence capillarity,\nlocal wettability, and interfacial tension at the nanoscale.\nHowever, our focus is on mesoscale multiphase transport phenomena—specifically, the liquid\ninvasion patterns, gas-liquid interface distribution, and three-phase interface (TPI) formation\nbehavior—within the porous catalyst layer. At this scale, transport dynamics are predominantly\ngoverned by pore structure, wettability gradients, and geometrical confinement rather than by\nelectrostatic or ion-specific interactions. The assumptions of an ideal fluid allow us to isolate and\nsystematically evaluate the influence of structural parameters on capillary-driven electrolyte\nintrusion, which is the core scope of our investigation.\nThis modeling strategy is consistent with mainstream approaches widely adopted in porous media\nsimulations for gas diffusion electrodes (GDEs), particularly in fields such as CO electroreduction\n2\nand PEM fuel cells. In these studies, the liquid phase is typically modeled as an incompressible,\ncharge-neutral fluid, and capillarity and wettability are treated as the primary drivers of multiphase\ntransport at the mesoscale. Although this approach simplifies electrostatic interactions and ionic\neffects, it remains well-suited for capturing the dominant mechanisms governing gas–liquid\ndistribution and electrolyte intrusion in structurally complex porous electrodes. Therefore, we\nbelieve the assumptions used in our LBM framework are reasonable and appropriate for the scope\nand scale of this study7,8.\nWe believe that the omission of electrokinetic factors, while acknowledged, does not compromise\nthe validity of our qualitative conclusions. Rather, it enhances computational tractability and\nhighlights the structural determinants of TPI formation. Future extensions may incorporate multi-\nphysics coupling to explore electrochemical feedbacks, but this lies beyond the scope of the current\nstudy.\nTo address this concern, we have added the clarification to the “Mechanism of Gas-Liquid Transport\nand TPI in CLs” section. The related description has been included and highlighted in red in the\nrevised version of the manuscript, which is also shown below for your reference.\n“In these simulations, the electrolyte was treated as an ideal, incompressible, charge-neutral fluid.\nAlthough this simplification neglects ionic strength and electrostatic effects, it captures the\ncapillary-driven intrusion dominated by pore geometry and wettability at the mesoscale. Similar\nassumptions are widely used in multiphase-flow models of porous electrodes for fuel cells,\nvalidating its suitability for describing gas-liquid dynamics in GDEs.” (Page 11, Lines 244–247)\nComment 3: Clarification of the Inverted Performance Trend in PPE-D with Increasing PTFE\nContent\nIn Figure 5b, the authors examine the effect of varying PTFE content in the first layer of the PPE-D electrode. Although the introduction of a gradient structure is expected to improve electrode performance, the observed Faradaic efficiency does not increase with higher PTFE loading. Instead, enhancing the gradient appears to diminish performance. This counterintuitive trend has not been sufficiently discussed. The authors are encouraged to provide a more detailed explanation of the underlying mechanism, which would help strengthen the theoretical foundation of the gradient optimization strategy.\nResponse: We sincerely thank the reviewer for raising this important and insightful point. Indeed,\nas shown originally in Figure 5b (which has now been moved to Supplementary Figure S34 in the\nrevised manuscript, following suggestions from other reviewers), the Faradaic efficiency of the\nPPE-D electrodes does not increase monotonically with higher PTFE content in the first layer—a\ntrend that appears counterintuitive given the expected benefit of a more pronounced wettability\ngradient.\nWe attribute this non-monotonic behavior primarily to the dispersion limitations of slurries with\nhigh PTFE loadings. As discussed in the section \"CL Optimization Based on Non-Fused Particulate\nInterface Architecture,\" elevated PTFE content leads to poor dispersion and local agglomeration.\nThis issue is further exacerbated during sintering, where PTFE tends to form continuous, film-like\ndomains rather than remaining finely dispersed. Such morphological inhomogeneity disrupts the\nintended wettability gradient and, in some regions, even produces an inverse gradient, thereby\ncompromising the formation of a well-defined gas-liquid-solid interface and ultimately impairing\nelectrode performance.\nThus, the observed decline in Faradaic efficiency at higher PTFE levels does not refute the\ntheoretical merits of gradient structures, but rather reflects fabrication-related limitations under the\ncurrent processing conditions.\nIt should be noted that the subsection \"Hierarchical Gradient CL for Liquid Repellence and Guided\nProduct Transport\" has been substantially reorganized in light of the input from one reviewer.\nAs a result, the data from the original Figure 5b are now located in Supplementary Figure S34.\nWe attach great importance to your observation and have taken care to incorporate the detailed\ndiscussion and clarification regarding this mechanism into the caption of Supplementary Figure S34.\nAll pertinent modifications have been highlighted in red within the revised manuscript.\nThe related description has been included and highlighted in red in the revised version of the\nmanuscript and supplementary information (Fig.S34), which is also shown below for your reference.\n“Further increasing PTFE loading led to a performance decline, attributed to inhomogeneous PTFE\ndispersion and aggregation at high loadings. Moreover, excessive sintering promotes the\ncoalescence of PTFE into continuous hydrophobic domains, which disrupts the intended gradient\nand even induces local reverse gradients. This limitation stems from current fabrication constraints\nrather than from the concept of gradient design itself.” (Supplementary information, Page 39, Lines\n298–302)\nComment 4: Quantitative Characterization of the Gradient Structure\nThe manuscript introduces a gradient wettability and porosity design in the CL (e.g., Figure 5a),\nwhich is central to the proposed directional transport mechanism. However, the current evidence\nprovided is primarily qualitative. It is recommended that the authors include more quantitative\ncharacterization of the gradient structure, such as spatially resolved measurements of contact angle,\nPTFE content distribution, or porosity variation. These data would help to validate the existence and\neffectiveness of the proposed gradient and support the conclusions drawn from it.\nResponse: We sincerely thank the reviewer for this thoughtful and rigorous suggestion. We agree\nthat the existence and effectiveness of the wettability and porosity gradient in the CL should be\nsupported by more quantitative evidence.\nIt is well-established that higher PTFE content can reduce pore volume due to pore blockage or\nagglomeration during electrode fabrication and heat treatment9,10. To verify the porosity gradient in\nour system, we conducted mercury intrusion porosimetry to independently quantify the porosity of\nthe first and second layers. The results, now included in Figure R8, clearly show a lower porosity\nin the PTFE-rich first layer, confirming the presence of a structural gradient across the CL.\nFig. R8. Porosity of different PTFE/CB catalytic layers\nRegarding wettability, although contact angle measurement is a widely used method for quantifying\nsurface hydrophobicity, it can be significantly affected by surface roughness, especially in porous\nelectrodes. For CLs with moderate to high PTFE content, the difference in contact angle between\nlayers is often within a narrow range, making it difficult to distinguish gradient strength by this\nmethod alone. As an alternative, we used PTFE content in each layer as a proxy for wettability.\nSince PTFE is inherently hydrophobic, layers with higher PTFE loading exhibit stronger electrolyte\nrepellence in the pore network. This interpretation is consistent with previous studies demonstrating\nthat increasing PTFE content enhances water resistance in gas diffusion layers.\nThe related description has been included and highlighted in red in the revised versions of the\nmanuscript and the Supplementary Information, where Fig. R8 has been incorporated as\nSupplementary Fig. 29. The updated content is also shown below for your reference.\n“Mercury intrusion porosimetry (Fig. S29) quantitatively confirmed a porosity gradient, with a\nmarked decrease in pore volume toward the PTFE-rich bottom layer, consistent with densification and\npartial pore blockage from sintering. Because contact-angle measurements are unreliable for\nrough porous surfaces, PTFE loading was used as a quantitative indicator of hydrophobicity. The\nhigher PTFE content in the bottom layer indicates stronger electrolyte repellence, confirming\ncoupled porosity–wettability gradients across the CL.” (Page 12, Lines 293–298)\nComment 5: Inclusion of the Most Recent Studies\nIn Figure 6c, the authors benchmark the performance of their electrode against representative studies\npublished over the past decade. While this comparison is valuable, the dataset would benefit from\nthe inclusion of more recent studies—particularly those published in 2025—that address similar\nchallenges such as high-current-density operation, ambient-air electrosynthesis, or long-term\nstability. Incorporating these up-to-date references would better contextualize the novelty and\ncompetitiveness of the present work within the current state of the field.\nResponse: We sincerely thank the reviewer for this valuable suggestion. We have carefully updated\nthe benchmarking table (Supplementary Table 6) and the corresponding discussion (Fig. 6b and\nrelated text) to include the most recent publications from 2025 (Fig.R9). This update provides a\nmore comprehensive comparison and further emphasizes the distinctiveness and advancement of\nour work relative to the latest studies.\n[Figure Redacted]\nFig. R9. Benchmarking PPE-T against state-of-the-art systems from the past decade in terms of\ncurrent density, operation duration, and FE (See Supplementary Table S6 for full data and references)\nFurthermore, the 2025 data newly added in Supplementary Table S6 are also presented below for\nyour convenience and reference.\nTable S6. Performance comparison of electrodes prepared using different strategies (Newly added\nperformance data for 2025).\nReaction Total\nElectrode Current Electrolytconcentra\nElectrolyzer Cathode Anode Electrolyt time per reaction\nNo. Date O2 source Binder area density e volum tion FE Ref.\nstructure catalyst catalyst es cycle time\n(cm2) (mA/cm2) e(ml) (mg/L)\n（h） (h)\nHSO 500 / 30 / / 0.9\n2 4\nadditional F-in/out-\n41 2025 divided Nafion Pt 4 (0.05mol 43\noxygen CNTs 200 / 50 / / 0.93\n/L)\nadditional AlO/Al KOH\n2 3\n42 2025 divided Nafion RuO/Ti 1 250 / 100 / / 0.9 44\n2\noxygen –O-C (1mol/L)\n1\nadditional Commer AEM\n43 2025 divided IrO 100 DI water 100 / 500 / 17000 0.8 45\n2\noxygen cial CB ionomer\nadditional FeO@\n3 4\n44 2025 divided Nafion Pt 4 DI water 50 / 60 / / 0.91 46\noxygen TNC-AE\nKOH\nadditional D20- glassy\n45 2025 divided Nafion / (0.1mol/ 200 / 400 3000 15600 0.9. 47\noxygen vulcan carbon\nL)\nKOH\nadditional B-meso-\n46 2025 divided Nafion Ru-Ir-Ti 4 (0.1mol/ 100 / 100 / / 0.9 48\noxygen PC\nL)\nadditional glassy KOH\n47 2025 divided Ni-C Nafion / 250 / 100 / 24660 0.9 49\noxygen carbon (1mol/L)\nadditional NiFeW\n48 2025 divided Nafion RuIr@Ti 4 DI water 50 / 140 / 10000 0.75 50\noxygen LDH\nREVIEWER 4\nGeneral Comment: This work presents a novel design of gas diffusion electrodes for\nelectrochemical H O production. A comprehensive investigation employing advanced\n2 2\ncharacterization and simulation was conducted to delineate the influence of the electrode structure.\nThe findings hold significant promise for industrial applications. Specific comments are provided\nbelow:\nResponse: We sincerely thank the reviewer for the positive and encouraging evaluation of our work.\nWe are grateful that the reviewer recognizes the novelty of our electrode design, the comprehensive\ncombination of experimental characterization and multiscale simulations, and the industrial\nrelevance of our findings. We have carefully addressed all specific comments point by point, and\nthe manuscript has been substantially revised to clarify the universality of the design principles,\nprovide more details on the scale-up system, and strengthen the connection between simulations\nand experimental observables. We believe that these revisions have further improved the rigor,\nclarity, and overall impact of the manuscript.\nComment 1: Most of the electrochemical data are collected in neutral Na SO electrolytes. Yet\n2 4\nmany industrial processes (e.g., disinfection, chemical synthesis) also require acidic media. The\nauthors should either provide representative acidic/alkaline data or discuss the generalizability of\ntheir design principles across different electrolytes.\nResponse: We sincerely thank the reviewer for this valuable suggestion. To further verify the\ngeneral applicability of our structural design, we conducted additional electrolysis experiments\nunder both acidic (1 mol L-1 H SO ) and alkaline (1 mol L-1 NaOH) conditions, while maintaining\n2 4\nthe same self-breathing configuration and current density (400 mA cm-2). The results demonstrate\nthat the performance hierarchy of the electrodes remains consistent across all pH environments—\nFSE < PPE < PPE-D—highlighting the robustness of the pore–wettability–coupled regulation\nmechanism. Specifically, in acidic media, the average Faradaic efficiencies (FE) of FSE, PPE, and\nPPE-D were 12.88%, 54.45%, and 60.45%, respectively; whereas in alkaline media, the\ncorresponding values were 20.41%, 84.23%, and 94.13% (Fig.R10).\nFig. R10. Faradaic Efficiency of FSE, PPE, and PPE-D Electrodes in 1 mol L-1 H SO and 1\n2 4\nmol L-1 NaOH Electrolytes. To assess the general applicability of our electrode design, we\nevaluated the performance of FSE, PPE, and PPE-D electrodes in both acidic and alkaline\nelectrolytes. The consistent performance hierarchy (FSE < PPE < PPE-D) across these distinct pH\nenvironments underscores the robustness of our pore-wettability-coupled design. While the absolute\nFaradaic efficiency is influenced by the electrolyte-dependent intrinsic kinetics of the two-electron\nORR, the maintained performance order confirms that the capillarity-dominated infiltration\ndynamics, governed by the electrode's porous architecture and wettability distribution, play a\ndecisive role in determining the overall performance.\nThe absolute variation in FE with pH is expected and arises from the known influence of electrolyte\nacidity on the two-electron selectivity of carbon-based catalysts. Acidic environments generally\nsuppress the two-electron ORR selectivity of carbon materials, while neutral and alkaline media\ncreate locally alkaline interfaces and anion-induced H O repulsion, which together enhance\n2 2\nselectivity and yield11. Nevertheless, despite these intrinsic kinetic differences, the observed\nelectrode order (FSE < PPE < PPE-D) remains unchanged, confirming that our structural design\nprinciples are independent of electrolyte pH.\nMechanistically, although acidic electrolytes improve ionic conductivity and alkaline electrolytes\nintensify interfacial electrowetting due to the formation of a compact electric double layer, these\nfactors do not override the capillarity-dominated infiltration dynamics governed by pore geometry,\nwettability distribution, and contact-line pinning. The non-fused particulate-packed catalyst/binder\ninterface (PPE) already redistributes local capillary pressures and facilitates gas accessibility\ncompared with the conventional fused–segregated structure (FSE). The hierarchical and gradient\nCL architecture (PPE-D) further amplifies these effects by inducing directional liquid displacement\nand stabilizing continuous gas pathways, thereby sustaining selective two-electron ORR pathways\nfor H O generation.\n2 2\nOverall, while ionic mobility and electrolyte composition influence charge transfer and reaction\nkinetics, the mesoscale liquid infiltration behavior within the catalyst layer is more strongly\ngoverned by capillary effects associated with the porous architecture. In such porous media, two-\nphase transport is largely dictated by capillary forces determined by pore structure (size, shape, and\nconnectivity) and the pinning of the solid-liquid-gas contact line. This capillarity-governed yet\nstructurally engineered mechanism provides a robust basis for the pH-independent applicability of\nboth the particulate-packed and gradient electrode designs proposed in this work.\nThe related description has been included and highlighted in red in the revised versions of the\nmanuscript and the Supplementary Information, where Fig. R10 has been incorporated as\nSupplementary Fig. 35. The updated content is also shown below for your reference.\n“The same performance hierarchy of FSE < PPE < PPE-D was maintained under both acidic and\nalkaline electrolytes, confirming that the structural design principles are generally applicable across\ndifferent pH environments (Fig. S35).” (Page 12, Lines 309–311)\n“Electrolysis under different pH conditions. To evaluate the generality of the structural design,\nelectrochemical tests were conducted under acidic and alkaline conditions (1mol L-1 H SO or 1\n2 4\nmol L-1 NaOH). The experiments were performed using the same self-breathing two-compartment\ncell as described above. Constant-current electrolysis was carried out at a current density of 400 mA\ncm-2, and the hydrogen peroxide concentration after each cycle was determined by the potassium\ntitanium oxalate method.” (Page 18, Lines 472–476)\nComment 2: The electrocatalytic performance of commercial carbon black appears limited. Have\nthe authors considered exploring alternative carbon-based materials with enhanced activity, such as\noxidized carbon black or other modified carbons, to further improve electrode performance?\nResponse: We sincerely thank the reviewer for this insightful suggestion. We agree that coupling\nsurface-chemistry engineering (e.g., oxidized or heteroatom-doped carbons) with catalyst-layer (CL)\narchitecture represents a valuable route to enhance intrinsic 2e⁻-ORR activity and H O selectivity.\n2 2\nIn the present work, however, we intentionally employed commercial carbon black as a chemically\nuniform baseline so that the observed performance enhancement could be unambiguously attributed\nto the interface architecture—namely, the non-fused particulate-packed interface and the\nhierarchical wettability gradient—rather than to variations in catalyst composition. Below, we\nclarify (i) why our design principles are expected to be broadly valid regardless of the carbon type,\nand (ii) why we did not include additional experiments with modified carbons in this study.\n(i) Universality of the design principles at the mesoscale\nAt the mesoscale relevant to gas-diffusion electrodes, two-phase transport behavior is primarily\ngoverned by capillary effects and contact-line pinning, which are controlled by pore geometry,\nconnectivity, and the wettability contrast between the carbon matrix and the hydrophobic binder\n(PTFE). These parameters dictate the formation and stability of triple-phase interfaces (TPIs), as\nwell as oxygen percolation and electrolyte intrusion. Replacing the carbon with an oxidized or doped\nvariant may slightly modify the intrinsic surface wettability of the carbon phase, but it does not alter\nthe hydrophobicity of PTFE, the particulate-packed network, or the hierarchical pore connectivity.\nConsequently, the pore–wettability-coupled regulation of electrolyte intrusion and TPI formation\nremains applicable across different carbon chemistries. In this framework, the macroscopic gas–\nliquid transport remains capillarity-dominated, while the microscopic chemical differences mainly\ninfluence local reaction kinetics rather than the overall mass-transport regime.\n(ii) Rationale for not including surface-modified carbons in this work\nWe fully acknowledge that exploring surface-modified carbons is a scientifically meaningful\ndirection for future research. However, incorporating such materials would introduce multiple\ncoupled factors that extend beyond the scope of the current study. First, surface oxidation or\nheteroatom doping inevitably changes surface energy and contact angles, which may weaken\ncontact-line pinning and increase electrolyte uptake, thereby altering the capillary landscape and\npartially counteracting the structural advantages of the particulate-packed or gradient CL. Second,\nmodifications to surface polarity and acid-base character also affect ionomer-carbon interactions\nand ink rheology, influencing PTFE dispersion, film formation, and mesoscale pore connectivity.\nThese intertwined effects make it difficult to decouple intrinsic catalytic improvements from\nstructural and transport phenomena without a comprehensive parametric study.\nTherefore, to maintain a clear mechanistic focus, we deliberately confined this work to a single,\nwell-defined catalyst chemistry. This allows us to isolate and reveal how non-fused particulate-\npacked interfaces and hierarchical wettability gradients govern capillary-driven gas-liquid transport\nand electrode performance. Nevertheless, we fully agree with the reviewer that this represents an\nexciting and forward-looking direction for future research that integrates surface-chemistry\nengineering with hierarchical and gradient CL design.\nComment 3: The experimental details of commercial-scale self-breathing electrosynthesis platform\nshould be provided.\nResponse: We thank the reviewer for this constructive suggestion. In response, we have\nsupplemented detailed information on the commercial-scale self-breathing electrosynthesis\nplatform in the revised manuscript. Specifically, Fig. R11 now provides photographs and schematic\ndescriptions of the system configuration, including the fluid circulation and thermal management\nsubsystems. The fluid system consists of anodic and cathodic reservoirs equipped with pumps to\nensure continuous electrolyte recirculation, while the thermal management system employs an\ninternal water-jacket heat exchanger embedded within the electrolyte tanks to stabilize operating\ntemperature.\nFig. R11. Photographs and schematic of the commercial-scale self-breathing electrosynthesis\nplatform. The fluid system consists of two electrolyte reservoirs connected to peristaltic pumps for\ncontinuous recirculation. The anodic loop contains a 5 mol L-1 NaOH solution, with 32 wt% liquid\nalkali periodically added to maintain alkalinity, while the cathodic loop contains deionized water.\nEach of the two circulatory loops is instrumented with check valves, flow meters, and pressure\ntransducers to regulate the flow rate. The anolyte reservoir is equipped with a level sensor for\ninitiating automated alkali replenishment via the control system, and a pH transducer is integrated\ninto the fluid path. The thermal management system employs a built-in water-jacket heat exchanger\ninside each tank to maintain stable electrolyte temperature during prolonged electrolysis. The power\nsupply is mounted atop the unit as a separate module (not shown in the figure). Electrolysis was\nperformed at a current density of 100 mA cm-2 under self-breathing operation at ambient pressure.\nThe system configuration ensures stable electrolyte circulation, effective heat removal, and uniform\ngas-liquid distribution across the electrode area, demonstrating the scalability of the self-breathing\nH O electrosynthesis technology.\n2 2\nIn addition, the Methods section has been updated to include the operating parameters:\nCurrent density: 100 mA cm-2;\nAnolyte: 5 mol L-1 NaOH solution, continuously recirculated with periodic addition of 32 wt%\nNaOH to maintain alkalinity;\nCatholyte: deionized water, recirculated in a closed loop;\nOperation mode: continuous electrolysis under ambient pressure and self-breathing conditions.\nThese additions ensure transparency and reproducibility of the large-scale operation and highlight\nthe scalability of the proposed electrode design.\nThe related description has been included and highlighted in red in the revised versions of the\nmanuscript and the Supplementary Information, where Fig. R11 has been incorporated as\nSupplementary Fig. 48. The updated content is also shown below for your reference.\n“Commercial-scale self-breathing electrosynthesis experiments. Commercial-scale electrolysis\nexperiments were conducted using a custom-built self-breathing electrosynthesis platform equipped\nwith independent anodic and cathodic circulation systems. The electrolyzer operated under ambient\npressure with natural air supply to the cathode side. The applied current density was 100 mA cm-2,\nand the system was operated in continuous circulation mode. The anolyte consisted of 5 mol L-1\nNaOH solution, which was periodically replenished with 32 wt% NaOH to maintain alkalinity. The\ncatholyte was deionized water, recirculated in a closed loop. Temperature regulation was achieved\nthrough a built-in water-jacket heat exchanger integrated into both electrolyte tanks. The catholyte\nwas replaced every 2 h during operation; runs lasted 10 h per day, after which the system was flushed\nwith deionized water.” (Page 18, Line 477–484)\nComment 4: For the scale-up system, the authors utilized alkaline electrolyte and solid-state\nelectrolyte. It remains unclear whether the conclusions drawn from experiments in neutral\nelectrolyte are applicable under these conditions.\nResponse: We sincerely thank the reviewer for this thoughtful and important comment. We fully\nunderstand the reviewer’s concern regarding the applicability of the conclusions obtained under\nneutral conditions to the alkaline and solid-state configurations used in the scale-up system. While\nno additional experiments were performed specifically for the scaled platform, we have carefully\nexamined the physicochemical evolution of the electrolyte environment to ensure consistency\nbetween laboratory and pilot scales. In the two-compartment cell used for laboratory-scale tests, the\ninitially neutral Na SO electrolyte gradually becomes alkaline during electrolysis because OH⁻ ions\n2 4\nare continuously generated by the 2e⁻-ORR and cations migrate through the membrane. In the scale-\nup system, the anolyte is alkaline and the cathode is initially supplied with pure water; during\noperation, the cathode environment similarly evolves from neutral to alkaline. Therefore, in terms\nof pH evolution, the scale-up configuration and the neutral-electrolyte system undergo essentially\nthe same process.\nAs demonstrated in the additional experiments performed under acidic, neutral, and alkaline\nconditions (Fig. S35), the Faradaic–efficiency–potential trends and the performance hierarchy\n(PPE-D > PPE > FSE) were well preserved across all pH environments. These findings confirm that\ncapillary-force-dominated electrolyte infiltration provides a general, pH-independent framework for\nengineering stable self-breathing electrodes for H O production. Consequently, the conclusions\n2 2\ndrawn from the neutral-electrolyte experiments are fully applicable to the alkaline and solid-state\nconfigurations used in the scale-up system.\nComment 5: The LBM and MD simulations form the basis of many mechanistic conclusions (e.g.,\ndirectional H O transport, wettability-governed TPI formation). While trends are consistent with\n2 2\nexperiments, the link between simulated parameters and measurable electrode properties could be\nfurther reinforced.\nResponse: We sincerely appreciate the reviewer’s insightful comment. We fully agree that clarifying\nthe connection between simulation parameters and experimentally measurable electrode properties\nis crucial for validating the mechanistic conclusions. It is worth emphasizing that the primary goal\nof our modelling is not to numerically fit experimental data, but to reveal mesoscale and molecular-\nlevel mechanisms using parameters that are directly comparable to measurable structural and\nphysicochemical quantities. This approach allows the simulations to establish a physically\ninterpretable correspondence with experiments, rather than a purely empirical one.\n(i) LBM Simulations: Mesoscale Validation and Mechanism Elucidation\nThe lattice Boltzmann simulations were constructed on 3D structures derived from FIB-SEM\nreconstruction and QSGS-generated analogues, which quantitatively reproduce the experimental\nporosity and CB/PTFE volume ratio (0.73 vs 0.65 and 1.09 vs 1.33, respectively; Fig. R11).\nIn addition, key physical parameters were set to reflect realistic conditions: the gas-liquid density\nratio was 1:800 and the viscosity ratio 1:15 (Supplementary Table 3), consistent with the actual\nproperty ratios of O and aqueous electrolyte systems. The simulated capillary-pressure thresholds\n2\nand liquid-phase saturation trends therefore reflect experimentally relevant fluid properties. These\nresults reproduce the experimentally measured Resistance Impulse (RI) hierarchy, validating that\nthe simulated liquid-invasion dynamics capture the same capillary physics that govern flooding\nresistance in real electrodes.\nFig. R11. Quantitative validation of Quartet Structure Generation Set (QSGS)-generated structures\nagainst FIB-SEM reconstruction. Comparison of porosity and CB/PTFE volume ratio between the\nQSGS-generated and FIB-SEM-reconstructed catalyst layers. The FIB-SEM structure exhibits a\nporosity of 0.73 and a CB/PTFE volume ratio of 1.09, while the corresponding QSGS-generated\nstructure shows 0.65 and 1.33, respectively. Although slight differences exist, they remain within an\nacceptable range. The purpose of employing QSGS in this study was to intentionally construct\nmorphologies with tunable gradients to examine how different pore and phase distributions\ninfluence multiphase transport and triple-phase-interface formation. Therefore, these minor\ndiscrepancies do not compromise the mechanistic insights or the generality of the conclusions. The\noverall good agreement validates the reliability of the QSGS reconstruction method used in this\nwork.\n(ii) MD simulations: Mesoscale Validation and Mechanism Elucidation\nAt the nanoscale, the molecular dynamics simulations were parameterized using experimentally\nrelevant interfacial energies and atomic compositions of carbon and PTFE, capturing the realistic\npolarity and wetting asymmetry within confined pores. The model consisted of a C carbon slab\n54\ncoated with PTFE chains of varying densities on both sides, forming nanoscale channels (5 × 5 ×\n12 nm) filled with H O , O , and H O molecules. Two representative configurations were\n2 2 2 2\nconstructed: one with an asymmetric PTFE distribution (40 chains on one side and 10 on the other)\nand another with a symmetric distribution (25 chains on each side). The diffusion behaviors of O ,\n2 2 2\ninfluences molecular transport. The simulated directional migration of H O in the asymmetric\n2 2\nsystem is consistent with the experimentally observed Faradaic-efficiency enhancement from PPE\nto PPE-D/T, indicating that local interfacial asymmetry facilitates preferential product removal.\nThus, the MD results establish a clear link between nanoscale diffusion behavior and the\nmacroscopic selectivity and mass-transport performance of the electrodes.\n(iii) Interpretation and generality\nTaken together, the LBM and MD simulations were designed to reflect experimentally accessible\nstructural and wetting parameters, providing a consistent physical mapping between model inputs\nand measurable electrode features. While minor differences inevitably exist between simulated and\nactual morphologies, our goal was to intentionally construct controlled structures and wettability\ngradients to elucidate how porosity and phase distribution govern multiphase flow and TPI\nformation. Therefore, these simulations reinforce mechanistic understanding rather than serve as\ndirect numerical reproduction. We again thank the reviewer for this constructive comment, which\nprompted us to clarify the rationale and strengthen the credibility of our multiscale modelling\nframework.\nAchieve High-Performing Membrane Electrode Assembly. J. Am. Chem. Soc. 146, 30388-\n30396 (2024).\nperformance proton exchange membrane fuel cells. Chem. Soc. Rev. 54, 8555-8581 (2025).\ncomponent transport in the cathode catalyst layer of PEM fuel cells: A molecular dynamics\nstudy. Journal of Chemical Physics 160, 044910 (2024).\ntransport in lithium-ion battery porous electrodes using the lattice Boltzmann method. Applied\nEnergy 194, 530-539 (2017).\nvia stochastic reconstruction method. Energy and Ai 13, 100245 (2023).\nnanoporous medium based on pore-scale numerical simulations with lattice Boltzmann method.\nPhys. Rev. E 104, 065304 (2021).\nfuel cell with deep learning. Nat. Commun. 14, 15 (2023).\nTransfer for Efficient Electroreduction of CO . Adv. Funct. Mater. 13, 2302007 (2023).\n2\nbreathing PEMFC. J. Electroanal. Chem. 952, 117963 (2024).\n2 2\ndual membrane electrode assembly solid electrolyte electrolyzer. Chem. Eng. J. 486, 150246\n(2024).\nH2O2 electrosynthesis. Nat. Commun. 15, 10632 (2024)."}, {"round": 2, "reviewer_comments": {"reviewer_1": "I found that the authors have done an excellent job addressing the issues raised previously.", "reviewer_2": "after carefully reviewing, I am Ok with this version of the manuscript, accept as it is", "reviewer_3": "The authors have well addressed the concerns raised, thus I would like to suggest the acceptance of the work.", "reviewer_4": "The authors have well addressed most of the questions/concerns from reviewers, and the manuscript has been improved.\nAlthough some of the suggested additional investigations were not taken into consideration, the overall quality of this work\nmeets the standards and expectations."}, "author_response": ""}]

Decision letter