Dipole synergy enables fast directional charge transport for solar hydrogen and benzaldehyde coproduction

Domain: physics
Published: 2025-12-11
Editorial outcome: major_revision

Abstract
Artificial photosynthesis for hydrogen evolution coupled with benzyl alcohol photoreforming faces efficiency challenges due to insufficient charge directional transfer. Here, we report a synergistic strategy integrating the polarization electric field from asymmetric Zn3In4S9 and the interface dipole field induced by MoS2 to drive fast charge dynamics. The optimized 6%-MoS2/Zn3In4S9 exhibits notable photocatalytic performance, generating 41.19 mmol g-1 h-1 of hydrogen and 43.33 mmol g-1 h-1 of benzaldehyde, which is 11.8 to 12.2 times higher than that of Zn3In4S9. Notably, apparent quantum yields reach 36.6% ± 0.7% for hydrogen and 40.0% ± 0.3% for benzaldehyde (3 times), while retaining 93.8% and 87% of initial activity after 30 hours, demonstrating high stability. In this work, we reveal that the intrinsic dipole of Zn3In4S9 generates a polarization electric field, suppressing bulk charge recombination. Concurrently, the MoS2-induced interface dipole field creates a fast electron transport pathway from Zn3In4S9 to MoS2.

Introduction
Hydrogen energy, recognized as the most promising clean energy carrier of the 21st century, combines the advantages of zero carbon emissions and high energy density, positioning it as a crucial option for future energy solutions1. Photocatalytic technology has the potential to convert abundant solar energy into hydrogen energy2. However, traditional water-splitting methods face limitations due to the bottleneck of the oxidation half-reaction. Although sacrificial agents such as triethanolamine, lactic acid, and Na2S/Na2SO3 can enhance hydrogen production efficiency, their use results in energy waste of holes (h+) in the valence band (VB) of the catalyst, increases costs, emits CO2, and exhibit slow oxidation kinetics3,4. These factors significantly constrain the scalability of the technology. To address this issue, we achieved the dual objectives of electron-driven hydrogen production and hole-mediated organic conversion. Studies utilizing benzyl alcohol (BA) as a medium demonstrate that its hydroxyl group can effectively capture h+ and facilitate proton-driven hydrogen production through a dehydrogenation reaction. Concurrently, BA is selectively oxidized to benzaldehyde (BAD), which serves as a fundamental raw material in both the pharmaceutical and spice industries, thereby establishing an economic cycle model5.

The core of photocatalytic technology lies in the development of high-performance photocatalytic materials. Currently, sulfides6, metal and nonmetal oxides7,8, and nitrogen-carbon compounds represent the mainstream materials in photocatalysis9. The two-dimensional hexagonal crystal system ZnIn2S4 has demonstrated significant potential for photocatalytic hydrogen production10. This structure possesses -SH surface active sites, demonstrating excellent physicochemical stability and an appropriate band structure. These characteristics enable the selective activation of C-H bonds and the dehydrogenation of organic substrates, which hold significant application value11. However, the photocatalytic performance of ZnIn2S4 is constrained by the rapid recombination of electron-hole (e⁻-h⁺) pairs within the bulk phase. To mitigate this challenge, researchers have explored various strategies, including the introduction of cocatalysts12, heterojunction engineering13, morphology control14, and elemental doping15, all aimed at enhancing the photocatalytic activity of ZnIn2S4. While these efforts have effectively alleviated the e⁻-h⁺ complexation on the material surface, the e⁻-h⁺ complexation in the bulk phase remains a significant challenge that requires urgent attention16. When the crystal structure symmetry of the photocatalyst is disturbed, the positive and negative charge centers within it are displaced, resulting in the formation of a dipole moment. This phenomenon subsequently induces a polarization electric field (PEF) within the bulk phase17. This finding introduces a novel strategy to enhance charge separation efficiency in the bulk phase of photocatalysts, which is anticipated to overcome existing technical bottlenecks and facilitate the further advancement of photocatalytic technology.

In this work, we address the challenge of insufficient bulk phase charge separation efficiency by leveraging the PEF induced by the intrinsic dipole moment in asymmetric Zn3In4S9. Furthermore, we introduce an economically efficient co-catalyst, MoS2, at the Zn3In4S9 interface, which induces the formation of an interface dipole field (IDF) to establish a pathway for fast electron directional transfer. Experimental results indicate that the synergistic effect of PEF and IDF, induced by dipole-field engineering, significantly enhances the fast directional transfer of electrons from the conduction band (CB) of Zn3In4S9 to MoS2. The photocatalytic generation rates of H2 and BAD for the 6%-MoS2/Zn3In4S9 composite reached notable values of 41.19 mmol g−1 h−1 and 43.33 mmol g−1 h−1, respectively. These rates are 11.8 and 12.2 times higher than those observed for Zn3In4S9. The apparent quantum yield (AQY) of H2 and BAD reached 36.6% ± 0.7% (n=3 independent experiments) and 40.0% ± 0.3% (n=3), respectively, when subjected to monochromatic light irradiation at a wavelength of 420 nm. The 6%-MoS2/Zn3In4S9 material demonstrates high long-term stability in photocatalytic H2 and BAD production, retaining 93.8% and 87% of its initial productivity rates after 30 h. These results are competitive with those reported in previous studies. The synergistic effect of PEF and IDF facilitates the formation of fast electron transport channels. This insight provides a novel perspective on the directional movement of photo-generated charge carriers, clarifying the mechanism behind efficient synergistic photocatalytic H2 production and the selective oxidation of BA to BAD.

Results
Photocatalyst characterization
The MoS2 nanospheres formed a distinctive “balls-on-ball” structure on the surface of Zn3In4S9 microspheres through the solvothermal method. (Fig. 1a). Initially, Zn2+ and In3+ ions, characterized by their high charge density and small ionic radius, preferentially adsorb onto the surface of MoS2 nanospheres, demonstrating strong adsorption properties. Subsequently, S2- ions participate by forming ligand bonds with the adsorbed ions, which initiates the nucleation of Zn3In4S9. As the reaction progresses, additional ions are attracted to the nuclei, leading to the expansion of the clusters. This process culminates in the formation of Zn3In4S9 nanoparticles, representing crystal growth. As these particles mature, Zn3In4S9 microspheres coalesce into larger structures, ultimately arranging into a compact “balls-on-ball” configuration. To thoroughly investigate the surface morphology and structural characteristics of the catalysts, we employed a series of microscopy techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and atomic force microscopy (AFM). The results indicate that Zn3In4S9 and MoS2 display distinct nanosphere morphologies, with a notable size difference: ~3.5 μm for Zn3In4S9 and around 500 nm for MoS2 (Supplementary Fig. 1a–d, and Supplementary Fig. 2a, c). The SEM images of the 6%-MoS2/Zn3In4S9 reveal that the MoS2 nanospheres are firmly adhered to the surface of the Zn3In4S9 microspheres (Fig. 1b, and Supplementary Fig. 1e, f). The lattice spacings of Zn3In4S9 (0.32 nm) and MoS2 (0.62 nm), corresponding to the (102) and (002) crystal planes, respectively, were further elucidated in the HRTEM images of the 6%-MoS2/Zn3In4S9 (Fig. 1c, and Supplementary Fig. 2b, d)18,19. High-angle annular dark field (HAADF) and energy dispersive X-ray spectroscopy (EDS) analyses revealed a uniform distribution of Zn, In, Mo, and S elements within the 6%-MoS2/Zn3In4S9 (Fig. 1d–g, and Supplementary Fig. 3). The AFM measurements indicated that the height fluctuation of Zn3In4S9 microspheres ranged from 10 nm to −11.4 nm, while the height variation of the composite material introducing with 6% MoS2 expanded to ±20 nm (Fig. 1h, i). Within a specific observation area, the maximum thickness of Zn3In4S9 was measured at 7.4 nm, whereas the maximum thickness of the 6%-MoS2/Zn3In4S9 increased to 19.2 nm (Fig. 1j). These changes demonstrate that MoS2 nanospheres are firmly adhered to the surface of Zn3In4S9 microspheres, resulting in an overall increase in thickness, which aligns with the observations from SEM. Overall, these findings confirm the robust construction of the 6%-MoS2/Zn3In4S9 heterojunction interface, suggesting that the interactions at the interface may contribute to the establishment of fast electron transport channels20.

To systematically investigate the crystal structure, chemical bonding characteristics, and surface electronic states of the materials, this study employed a multi-scale characterization approach that integrates X-ray diffraction (XRD), Raman spectroscopy, in situ X-ray photoelectron spectroscopy (in situ XPS), X-ray absorption near-edge structure (XANES), and extended X-ray absorption fine structure (EXAFS). XRD analysis (Fig. 2a, and Supplementary Fig. 4a) revealed that MoS2 exhibited distinct diffraction peaks at 13.7° (002), 33.3° (100), 39.4° (103), and 58.8° (110) (PDF#00-037-1492)19. The Zn3In4S9 and y-MoS2/Zn3In4S9 composite exhibited characteristic peaks at 21.3° (006), 27.6° (102), 30.0° (104), 39.4° (108), 47.1° (110), 52.2° (116), and 55.6° (202) (PDF#04-009-4784)21. Notably, only the diffraction signals of Zn3In4S9 were observed in the y-MoS2/Zn3In4S9 composite, with no detectable peaks corresponding to MoS2. This phenomenon is likely attributed to the low loading of MoS2 and the physical shielding effect caused by the larger Zn3In4S9 microspheres enveloping the smaller MoS2 nanospheres. Raman spectra further verified the lattice vibrational properties of the composites (Supplementary Fig. 4b). The Raman peaks observed at 244, 300, and 354 cm−1 correspond to the LO, LO longitudinal optical vibrations, and A1g vibrational modes of the crystal structure of Zn3In4S9 22. The FT-IR analysis revealed that MoS2 exhibits three prominent absorption peaks at 1608 cm−1, 1400 cm−1, and 1135 cm−1 23,24. Meanwhile, Zn3In4S9 displays four distinct absorption peaks at 1605 cm−1, 1400 cm−1, 1043 cm−1, and 637 cm−1 25–27. Additionally, the absorption peak at 3555 cm−1 is attributed to the elongation oscillation of O-H bonds in water (Supplementary Fig. 5)28. In situ XPS analysis revealed the presence of Zn, In, Mo, and S on the surface of 6%-MoS2/Zn3In4S9, with calibration set at C 1s 284.8 eV (Supplementary Fig. 6). The binding energy of 6%-MoS2/Zn3In4S9-dark indicated that the Zn 2p level was observed at 1022.0 eV, In 3d at 445.1 eV, Mo 3d at 229.3 eV, and S 2p at 161.9 eV, corresponding to the +2, +3, +4, and −2 valence states, respectively (Supplementary Fig. 7)29,30. It is noteworthy that the binding energies of Zn 2p and In 3d are elevated in the 6%-MoS2/Zn3In4S9-dark composite compared to Zn3In4S9 (Supplementary Fig. 9). In contrast, the binding energies of Mo 3d and S 2p are reduced, indicating the transfer of interfacial electrons from Zn3In4S9 to MoS2 31. To verify the reproducibility of the binding energy shift trend, we conducted two independent in situ XPS measurements on 6%-MoS2/Zn3In4S9, ensuring strict calibration of the C 1s reference peak at 284.8 eV. The results indicated a significant change in binding energy under light conditions. The Zn 2p3/2 binding energy increased from 1022.0 eV in the dark to 1022.2 eV under light, while the In 3d5/2 binding energy rose from 445.1 eV to 445.3 eV. In contrast, the Mo 3d5/2 binding energy decreased from 229.3 eV to 229.1 eV, and the S 2p3/2 binding energy also decreased from 161.9 eV to 161.8 eV (Supplementary Fig. 7). This reproducible pattern of binding energy shifts confirms the stable electron transfer from Zn3In4S9 to MoS2 (Supplementary Fig. 8)32. XANES and EXAFS techniques were employed to investigate the local structure of the materials. The variation in the photon energy of the MoS2 absorption edge, relative to the Mo foil, indicates changes in its local coordination environment (Fig. 2b)33. Additionally, the raw oscillatory signals in k-space from Mo foil, MoS2, and 6%-MoS2/Zn3In4S9 are processed and Fourier transformed into R-space (Fig. 2c). In the R space EXAFS analysis, the following bond length changes were observed: the Mo-Mo bond length of Mo foil was 2.45 Å, while the Mo-S bond length of MoS2 was 1.88 Å. In the 6%-MoS2/Zn3In4S9 composite material, the Mo-Mo bond length increases to 2.61 Å, and the Mo-S bond length decreases to 1.86 Å (Fig. 2d). Bond length variations arise mainly from electron redistribution driven by IDF34. Fig. 2e compares the Zn K-edge XANES spectra for Zn foil, Zn3In4S9, and 6%-MoS2/Zn3In4S9. Compared to Zn foil, the absorption edge of Zn3In4S9 slightly shifts towards the high-energy region. This shift indicates that Zn predominantly exists in the +2 valence state. This observation is consistent with the conclusions drawn from XPS regarding its valence state 17,18. It is noteworthy that, compared to Zn3In4S9, the white line peak intensity of the 6%-MoS2/Zn3In4S9 composite material has decreased. This decrease can be attributed to the introduction of MoS2, which results in a reduction of the coordination number of Zn sites and weakens the density of empty states35. The EXAFS fitting analysis in both K-space and R-space reveals that the 6%-MoS2/Zn3In4S9 exhibits a distinct Zn-S coordination peak at 1.85 Å, which is significantly more pronounced than the Zn-Zn metallic bond peak observed at 2.26 Å in the Zn foils (Fig. 2f, g). This observation suggests the formation of stronger covalent interactions between the Zn and S atoms. (Supplementary Table 1). Compared to Zn3In4S9, the reduced Zn-S bond length in 6%-MoS2/Zn3In4S9 suggests a higher Zn-S bond energy and enhanced chemical stability of the material35. Further analysis of the Zn and Mo K-edge EXAFS signals through wavelet transform (WT) reveals that the WT contour plots of 6%-MoS2/Zn3In4S9 exhibit significant differences compared to those of MoS2 and Zn3In4S9 (Fig. 2h, i, and Supplementary Fig. 10). This significant change indicates the formation process of the IDF, characterized by the directional migration of electrons from Zn3In4S9 to MoS2 35. The redistribution of interface charges not only optimizes the local coordination environment of the material but also establishes a channel for the transport of fast charge carriers during photocatalytic reactions 35. To further investigate the band structure of photocatalysts, we conducted analyses using ultraviolet-visible (UV-vis) diffuse reflectance spectroscopy, Mott Schottky (MS) testing, and XPS-VB spectroscopy measurement. In comparison to Zn3In4S9, the 6%-MoS2/Zn3In4S9 demonstrates improved performance in visible light absorption. This enhancement is characterized by a slight red shift of the absorption edge and an increased capacity to absorb a broader spectrum of visible wavelengths (Supplementary Fig. 11). The flat-band potential of Zn3In4S9, measured at −0.92 V, was evaluated using MS spectroscopy (Supplementary Fig. 12). This value was then converted to a reversible hydrogen electrode (RHE) potential through the application of the Nernst equation (ERHE = EAg/Cl + 0.05916pH + E0Ag/Cl)23. The CB potential of Zn3In4S9 RHE was calculated to be −0.3 eV. The VB potential was determined using the energy band formula (EVB = ECB + Eg), yielding a value of 2.27 eV, which is consistent with the findings from XPS-VB spectroscopy (Supplementary Fig. 13a)36. The work function of 6%-MoS2/Zn3In4S9 (Φ=2.09 eV) is lower than that of Zn3In4S9 (Φ=2.31 eV), indicating that the interfacial modification with 6% MoS2 effectively reduces the energy barrier and facilitates the formation of fast electron transport channels (Supplementary Fig. 13b, d)37. This observation confirms the establishment of an IDF. The same methodology was employed to calculate the energy band structures of the other photocatalysts, culminating in the generation of the energy band diagrams for each photocatalyst. (Supplementary Fig. 14, Supplementary Table 2). To evaluate the physical properties of the materials, we examined the specific surface area and pore size distribution of the samples (Supplementary Fig. 15, Supplementary Table 3). All the photocatalysts demonstrated type IV isotherms, while Zn3In4S9 and 6%-MoS2/Zn3In4S9 showed H4 hysteresis loops as well as mesoporous structures. Significantly, 6%-MoS2/Zn3In4S9 revealed a greater specific surface area, offering additional active sites for the photocatalytic processes.

Dipole-synergistic driving of charge dynamics
We employed density functional theory (DFT) on idealized structural models to investigate the possible formation mechanism of the PEF in the bulk phase of Zn3In4S9. Additionally, we explored the IDF generated at the Zn3In4S9 interface modified with MoS2, with calculations suggesting a potential fast electron transport pathway established by this synergistic effect. The electrostatic potential (V) of Zn3In4S9 along the [001] polarity axis exhibits a potential difference (ΔV) of 2.51 eV and a dipole moment (μ) of 2.95 eÅ (Fig. 3a, and Supplementary Table 4). This represents a significant enhancement compared to ZnIn2S4, which shows a ΔV of 2.21 eV and a μ of 2.61 eÅ. This indicates that the bulk-phase asymmetry of the Zn3In4S9 crystal exceeds that of ZnIn2S4 (Supplementary Figs. 16–17). Consequently, the bulk-phase environment of Zn3In4S9 is more conducive to suppressing the ineffective complexation of photogenerated e⁻-h⁺ pairs. The significant abrupt change in electrostatic potential at the interface between the [In-S] and [Zn-S] layers indicates active charge transfer between the two layers22. This asymmetric structure leads to spontaneous polarization within the bulk of Zn3In4S9, forming a PEF. The PEF drives electrons across the interface from the [Zn-S] layer into the [In-S] layer, effectively suppressing the ineffective recombination of e⁻-h⁺ pairs within the Zn3In4S9 bulk phase. It is noteworthy that the [Mo-S] and [In-S] interfaces of MoS2/Zn3In4S9 exhibit a significant potential difference (ΔV = 9.63 eV). This observation suggests the presence of substantial charge transfer between the [Mo-S] and [In-S] interfaces (Fig. 3b). Furthermore, it indicates that the MoS2-modified Zn3In4S9 interface generates an IDF, which provides a foundation for the establishment of fast electron directional transport channels. To verify the direction of electron transfer at the MoS2 and Zn3In4S9 interface, we conducted charge density difference calculations. The color distribution visually illustrates the regions of electron enrichment (yellow) and depletion (green) at the MoS2/Zn3In4S9 interface (Fig. 3c). Electrons are enriched on the MoS2 side, while electron depletion is evident on the Zn3In4S9 side, thereby confirming the transfer of electrons from Zn3In4S9 to MoS2. To accurately quantify the electron gain and loss between each atom, we employed the Bader charge analysis method (Fig. 3d, e). The results indicate that the Bader charges of Zn, In, and S atoms in Zn3In4S9 are −0.017 eV, −0.174 eV, and −0.095 eV, respectively, all demonstrating characteristics of electron loss. In contrast, the Bader charges of Mo and S atoms in MoS2 are 0.073 eV and 0.373 eV, respectively, which signifies a strong electron capture capability. Based on these findings, we have designed a schematic diagram that illustrates the mechanism of fast electron directional transport (Fig. 3f). The asymmetric structure of Zn3In4S9 initially establishes a PEF, which facilitates the transfer of electrons from the [Zn-S] layer to the [In-S] layer. Subsequently, the IDF generated at the interface between MoS2 and Zn3In4S9 further accelerates the migration of electrons towards MoS2. In summary, these observational results provide robust support for our proposed synergistic strategy. integrating the PEF of Zn3In4S9 with the IDF induced by MoS2 to achieve fast charge dynamics. Piezoresponse Force Microscopy (PFM) has emerged as a significant experimental tool for probing the existence of PEF, owing to its reversible linear relationship between electric field and mechanical deformation38. The PFM results demonstrate that ZnIn2S4, Zn3In4S9, and the 6%-MoS2/Zn3In4S9 composite exhibit typical piezoelectric behavior, characterized by distinct butterfly-shaped amplitude loops and well-defined positively and negatively polarized regions (Fig. 3g, h, Supplementary Fig. 18). This observation confirms the presence of internal PEF in these materials. Additionally, the slope of the amplitude loop serves as an indicator of the strength of piezoelectric polarization16. Zn3In4S9 (1.61 mV/V) exhibits stronger spontaneous polarization compared to ZnIn2S4 (1.21 mV/V). Compared to Zn3In4S9, the 6%-MoS2/Zn3In4S9 demonstrates a polarization strength that is 3.52 times greater than that of Zn3In4S9 (Fig. 3i).

To fundamentally investigate the mechanism of constructing electron highways through IDF engineering, we systematically characterized the materials using ultraviolet-assisted Kelvin probe force microscopy (KPFM) under 365 nm illumination. The analysis of the contact potential difference (CPD) for Zn3In4S9 under both dark and illuminated conditions revealed a substantial increase in CPD, rising from 4.5 mV in the dark to 414.6 mV in the light (Fig. 4a, b). The significant enhancement of CPD indicates that, under light excitation, the intrinsic dipole moment in the asymmetric structure of the Zn3In4S9 bulk phase spontaneously generates a PEF. This phenomenon greatly accelerates the effective migration of photo-generated h+ from the bulk phase of Zn3In4S9 to its surface39. The efficiency of charge carrier separation can be quantitatively assessed by calculating the CPD difference between light and dark conditions (ΔCPD = CPDlight - CPDdark)22,40. Comparative analysis revealed that the 6%-MoS2/Zn3In4S9 exhibited a ΔCPD value of 451.6 mV, which is significantly higher than that of Zn3In4S9, recorded at 410.1 mV (Fig. 4c–f). The optimal loading of MoS2 at 6% on Zn3In4S9 leads to the formation of an IDF that effectively suppresses interfacial e⁻-h⁺ recombination, while simultaneously establishing an fast unidirectional charge transmission channel. The surface potentials of Zn3In4S9 and 6%-MoS2/Zn3In4S9 under dark conditions are 3 mV and 12 mV, respectively (Supplementary Fig. 19). Based on these surface potential values, we can utilize specific calculation formulas (detailed formulas are provided in the Supplementary Information) to compute their surface charge densities (ρ) and PEF intensities41. Furthermore, when calculations are performed using the Zeta potential in conjunction with the Gouy-Chapman equation, we find that the surface charge densities of Zn3In4S9 and 6%-MoS2/Zn3In4S9 are 28.5 mC m-2 and 41.1 mC m-2, respectively (Supplementary Fig. 20a). Therefore, the PEF intensity of 6%-MoS2/Zn3In4S9 is 2.41 times that of Zn3In4S9 (Supplementary Fig. 20b). KPFM analysis reveals that charge dynamics are driven by the synergistic action of the PEF from the intrinsic dipole moment in asymmetric Zn3In4S9 and the IDF induced by MoS2. The carrier kinetic behaviors of Zn3In4S9 and 6%-MoS2/Zn3In4S9 were systematically investigated using femtosecond transient absorption spectroscopy (fs-TAS) under pump light excitation at 340 nm. As shown in Fig. 4g, h, Zn3In4S9 and 6%-MoS2/Zn3In4S9 exhibit significant negative ground state bleaching (GSB) signals in the 450-510 nm range. This phenomenon originates from the energy dissipation associated with the compounding process of photoexcited e--h⁺ pairs42. After laser excitation, the ΔA signal peaks rapidly within 1 ps and subsequently decays gradually, reflecting the relaxation process of the excited state43. This dynamic evolution encompasses the migration of localized carriers to the excited state, which ultimately transforms into free carriers. The pseudo-color mapping further validated the time-domain evolution characteristics of the fs-TAS (Fig. 4i, j). The carrier lifetimes of Zn3In4S9 and 6%-MoS2/Zn3In4S9 were determined to exhibit both fast and slow components, respectively, by fitting the decay curves at 475 nm using a double-exponential function. The fast decay lifetime (τ1) is associated with the rapid recombination of excited state electrons and h+ within the bulk phase of Zn3In4S9, while the slow decay lifetime (τ2) is attributed to the trans-interfacial transfer of electrons from the CB of Zn3In4S9 to MoS2 44. The τ1 (526.9 ps and 677.02 ps) and the τ2 (11940.2 ps and 18191.69 ps) for Zn3In4S9 and 6%-MoS2/Zn3In4S9 (Fig. 4k, l, and Supplementary Table 5), respectively. It is worth noting that the average decay lifetime (τave) of 6%-MoS2/Zn3In4S9 (τave = 10674.63 ps) is significantly prolonged compared to Zn3In4S9 (τave = 7374.87 ps). The fluorescence lifetime range of 6%-MoS2/Zn3In4S9, spanning from 694 to 1021 ps, is the broadest when compared to that of Zn3In4S9 (686 to 739 ps) and 18%-MoS2/Zn3In4S9 (539 to 927 ps). Notably, the maximum value exceeds 1000 ps (Supplementary Fig. 21). fs-TAS and fluorescence lifetime testing demonstrated that an optimal loading of MoS2 (6%) induces an IDF at the Zn3In4S9 interface, effectively suppressing e⁻-h⁺ recombination at this interface and establishing an fast directional transport channel for charges to MoS2. Consequently, this significantly prolongs the lifetime of photogenerated charge carriers. To investigate the migration efficiency of interfacial photogenerated carriers in gradient-MoS2 decorated asymmetric Zn3In4S9 structures, we conducted a series of tests including electrochemical impedance spectroscopy (EIS), surface photocurrent (SPC), linear scanning voltammetry (LSV), photoluminescence spectroscopy (PL), time-resolved photoluminescence spectroscopy (TRPL), and cyclic voltammetry (CV). Compared to ZnIn2S4, Zn3In4S9 exhibits a smaller EIS semicircle radius, indicating a reduced interfacial charge transfer resistance. Furthermore, Zn3In4S9 demonstrates a significantly enhanced photocurrent response, suggesting improved efficiency in photogenerated carrier generation and separation, which facilitates rapid charge migration (Supplementary Fig. 22a, b). The EIS results indicate that the semicircle radius of the 6%-MoS2/Zn3In4S9 in the low-frequency region is significantly reduced compared to that of Zn3In4S9 and y-MoS2/Zn3In4S9 (Supplementary Fig. 22a, Supplementary Fig. 23a). This findings suggests that an appropriate amount of MoS2 loading can greatly reduce the interface resistance of Zn3In4S9, thereby accelerating the transfer of electrons from the Zn3In4S9 interface to MoS2 45. The 6%-MoS2/Zn3In4S9 composite demonstrates the highest photocurrent density, attributed to the formation of an IDF induced by the optimal amount of (6%) MoS2 (Supplementary Fig. 22b, and Supplementary Fig. 23b). This IDF significantly enhances the separation and transport of photogenerated carriers46. The LSV results demonstrated that at a photocurrent density of 20 mA/cm², the hydrogen precipitation overpotential of 6%-MoS2/Zn3In4S9 was −1.63 V. This value represents the lowest hydrogen precipitation overpotential among Zn3In4S9 and other composite photocatalysts, indicating a more rapid hydrogen evolution reaction (HER) rate. (Supplementary Fig. 22c, and Supplementary Fig. 23c)47. To investigate the e--h⁺ coupling and lifetime mechanism in greater depth, we conducted PL and TRPL tests using an excitation wavelength of 525 nm. The 6%-MoS2/Zn3In4S9 composite exhibited the lowest fluorescence signal intensity (Supplementary Fig. 22d, and Supplementary Fig. 24a) and the longest e--h⁺ pair lifetime (5.47 ns) compared to the other samples: Zn3In4S9 (1.51 ns), 9%-MoS2/Zn3In4S9 (3.30 ns), and 18%-MoS2/Zn3In4S9 (2.82 ns) (Supplementary Fig. 22e, and Supplementary Fig. 24b). The IDF induced by the optimal amount of MoS2 (6%) in the Zn3In4S9 interface establishes a highway for electron transport, significantly reducing the recombination of e--h⁺ pairs at the Zn3In4S9 interface and consequently extending their lifetime (Supplementary Table 6)13,48. The CV evaluation revealed that the 6%-MoS2/Zn3In4S9 exhibited the highest electrochemically active surface area, measuring 0.31 μF (Supplementary Fig. 22f, Supplementary Fig. 23d), in comparison to other samples: Zn3In4S9 (0.11 μF), 3%-MoS2/Zn3In4S9 (0.254 μF), 9%-MoS2/Zn3In4S9 (0.250 μF), and 18%-MoS2/Zn3In4S9 (0.22 μF). This observation was recorded at scanning rates ranging from 20 to 90 mV/s (Supplementary Fig. 25), indicating that the 6%-MoS2/Zn3In4S9 composite possesses a greater number of active sites and enhanced photocatalytic activity.

Solar hydrogen coupled with alcohol photoreforming
To thoroughly investigate the photocatalytic activity, we assessed the performance of various photocatalysts in the dehydrogenation reaction and the synergistic conversion of BA to BAD. The H2 and BAD production rates of Zn3In4S9 were measured at 3.49 mmol g−1 h−1 and 3.55 mmol g−1 h−1, which are 2.3 and 1.5 times higher than those of ZnIn2S4, respectively. (Fig. 5a, d). In contrast, the 6%-MoS2/Zn3In4S9 composite, modified with 6% MoS2, exhibited significantly enhanced photocatalytic activity, with H2 and BAD production rates elevated to 41.19 mmol g−1 h−1 and 43.33 mmol g−1 h−1, representing increases of 11.8 and 12.2 times compared to those of Zn3In4S9, respectively. (Supplementary Table 7). This is attributed to the introduction of a moderate amount (6%) of MoS2, which induces an IDF at the Zn3In4S9 interface. This IDF establishes an fast electron transmission channel from the Zn3In4S9 interface to MoS2, significantly suppressing the ineffective recombination of e--h⁺ pairs at the Zn3In4S9 interface. The performance is competitive with that of many reported photocatalysts in photocatalytic BA dehydrogenation systems (Supplementary Fig. 26, and Supplementary Table 8). To elucidate the synergistic mechanism of PEF-IDF, we constructed a 6%-MoS2/ZnIn2S4 control system, with structural integrity confirmed through XRD and XPS characterization (Supplementary Fig. 27). The catalytic activity of this system, measured in terms of H2 production (5.24 mmol g−1 h−1) and BAD yield (6.71 mmol g−1 h−1), was found to be only 12.6%–15.5% of that observed for 6%-MoS2/Zn3In4S9 (Supplementary Fig. 28). The complete inactivity of pure MoS2 conclusively demonstrates the dominant role of the bulk photoelectrochemical functionality of Zn3In4S9. Notably, the physically mixed 6%-MoS2/ZnIn2S4 exhibited a 96% reduction in hydrogen production activity (1.67 mmol g−1 h−1) compared to the sample synthesized via solvothermal methods. This significant order-of-magnitude difference provides compelling evidence for the necessity of IDF formation, ultimately elucidating the fundamental mechanism underlying the synergy between PEF and IDF in catalytic enhancement. To validate the advantages of MoS2, we prepared a control sample of 6%-Co9S8/Zn3In4S9. XRD and XPS characterizations confirmed its successful preparation (Supplementary Figs. 29, 30). However, its photocatalytic performance was significantly inferior to that of the 6%-MoS2/Zn3In4S9. Specifically, the H2 yield (5.12 mmol g−1 h−1), BAD yield (3.28 mmol g−1 h−1), and BAD selectivity (53.7%) were all much lower (Supplementary Fig. 31). This difference is primarily attributed to weaker interfacial dipole effects and an insufficient ability for proton reduction, which underscore the irreplaceable role of MoS2 in interface engineering and catalytic activity. We extracted 100 μL from the 6%-MoS2/Zn3In4S9 solution at 30-min intervals during the reaction process for liquid chromatography analysis. The results indicated a significant decrease in the BA concentration over time, while the BAD concentration continuously increased (Supplementary Fig. 32). The infrared thermal imaging of 6%-MoS2/Zn3In4S9 over time under 300 W xenon lamp irradiation (Supplementary Fig. 33). The cooling system of the photoreactor ensures a uniform heat distribution throughout the solution, resulting in minimal temperature variation. Consequently, the 6%-MoS2/Zn3In4S9 does not exhibit significant heat accumulation, and the reaction process is devoid of any photothermal effects. The experimental results indicated that the hydrogen production rate remained relatively constant across varying temperatures, suggesting that temperature is not a critical factor influencing catalytic performance. To investigate the key active species involved in the selective oxidation of BA to BAD, we conducted control experiments under an argon atmosphere and utilized free radical scavengers to eliminate specific active species (Fig. 5b, Supplementary Table 9). The experimental results indicated that the incorporation of triethanolamine (TEOA) effectively eliminated h+ and significantly decreased the rates of H2 production and BAD synthesis49. This suggests that h+ plays a critical role in the process. In contrast, the introduction of K2S2O8 (KPS) effectively removed electrons and significantly inhibited H2 production50. This observation confirms the critical role of photogenerated electrons in the reduction of H+ protons to H2. The introduction of benzoquinone (BQ) and tert-butanol (t-BuOH) effectively eliminates •O2− and •OH, respectively, while having minimal impact on hydrogen production and BAD synthesis50,51. This observation suggests that h+ and electrons serve as the primary active species within the reaction system. To evaluate the photocatalytic activity of the 6%-MoS2/Zn3In4S9 photocatalysts with greater accuracy and comprehensiveness, we designed a series of controlled-variable experiments utilizing band-pass filters at various wavelengths (λ = 350, 380, 420, 450, 475, and 500 nm). The results indicated that the production of both H2 and BAD reached their peaks at 1126.76 μmol and 1240.10 μmol, respectively, under 420 nm irradiation. Meanwhile, the apparent quantum yields (AQY) were determined to be 36.6 ± 0.7% for H2 and 40.0 ± 0.3% for BAD (n=3). (Fig. 5c, Supplementary Table 10). It is noteworthy that in three independently repeated AQY experiments, the AQY values for H2 and BAD production exhibited notable stability, further corroborating the high activity of 6%-MoS2/Zn3In4S9 (Supplementary Fig. 34). We fully recognize the potential impact of temperature on the kinetics of the photocatalytic reaction under strictly controlled conditions (λ > 420 nm illumination, 6%-MoS2/Zn3In4S9). We assessed the H2 production rate at temperature intervals of 4°C, 8°C, 12°C, 16°C, 20°C, and 24°C (Fig. 5e). To highlight the advantages of BA, we evaluated the H2 production rate of the 6%-MoS2/Zn3In4S9 photocatalyst under identical conditions in sacrificial systems (Fig. 5f), including pure water cracking, Na2S/Na2SO3, TEOA, and lactic acid52. The results indicated that the H2 production rate of the reaction system utilizing BA was optimal, with its H2 production performance improved by factors of 27.66, 6.88, 5.92, and 4.7, respectively, when compared to the other systems. This finding suggests that BA, as a specialized h+ transport medium, can significantly enhance the utilization efficiency of photogenerated h+. The 6%-MoS2/Zn3In4S9 demonstrates broad applicability for the oxidative dehydrogenation of various aromatic alcohols, facilitating the efficient production of corresponding aromatic aldehydes alongside H2 evolution (Supplementary Fig. 35, and Supplementary Table 11). Additionally, we assessed the stability of the 6%-MoS2/Zn3In4S9. The photocatalytic system demonstrated excellent stability, maintaining 93.8% and 87% of its initial H2 and BAD production rates, respectively, after 10 cycles (Fig. 5g). We analyzed the 6%-MoS2/Zn3In4S9 after the 10th cycle using XRD, Raman, and XPS (Supplementary Figs. 36–38). The results indicated that the position and intensity of the peaks remained consistent before and after the reaction. This study further confirm the high efficiency and stability of the 6%-MoS2/Zn3In4S9 photocatalyst.

Cascaded C-H activation pathway
To elucidate the mechanistic insights into synergistic photocatalytic H2 evolution coupled with cascaded C-H activation during BA to BAD conversion, we conducted an in situ electron paramagnetic resonance (in situ EPR) test to monitor the fluctuations in the concentrations of reactive electron (e-), h+, and α-hydroxybenzoyl (Cα) radical intermediates throughout the reaction course. We selected TEMPO as an efficient spin-trapping agent to capture and measure the photogenerated e- and h+ under varying conditions. In the absence of light, TEMPO displays a distinct EPR signal characterized by a typical triplet state spectral ratio of 1:1:153,54. Upon introducing light into an aqueous system containing the catalyst with BA, we observed that the decay of the EPR signal was most pronounced in the experimental group utilizing 6%-MoS2/Zn3In4S9 (Fig. 6a). This observation suggests that this 6%-MoS2/Zn3In4S9 is capable of generating the highest concentration of reactive e- under light excitation, which subsequently reduce TEMPO to TEMPOH. Furthermore, the photogenerated h+ exhibited the capacity to oxidize TEMPO to TEMPO+55. Notably, the 6%-MoS2/Zn3In4S9 demonstrated the most pronounced reduction in EPR signals, thereby further confirming its high efficiency in generating reactive h+ under light conditions (Fig. 6b). To verify the key intermediate in the selective oxidation of BA to generate BAD, we introduced DMPO as an additional spin-trapping agent. This approach successfully captured the EPR signals of the α-hydroxyphenyl radical (•CH(OH)Ph). Six characteristic peaks were observed in the EPR spectra, coinciding with those of the DMPO-Cα radical adduct56. This not only confirms the generation of the -CH(OH)Ph radical but also highlight the central role of direct oxidation of BA by the h+ in this reaction pathway. Under light conditions, the 6%-MoS2/Zn3In4S9 exhibited a significantly stronger DMPO-Cα radical signal (Fig. 6c), thereby demonstrating its high efficacy in facilitating the selective oxidation of BA to BAD. We conducted an in-depth analysis of the free energy changes of intermediate species and transition states between Zn3In4S9 and MoS2/Zn3In4S9 using DFT calculations (Fig. 6d). The adsorption energy of Zn3In4S9 modified with MoS2 for BA molecules decreased from −1.55 eV to −0.94 eV (Supplementary Table 12), which significantly diminishes the adsorption effect. This alteration facilitates the reduction of the energy barrier (ΔG) in the rate-determining step of the BA oxidation reaction, thereby accelerating the overall catalytic reaction rate. A deuterium labeling experiment has been meticulously designed to investigate the source of hydrogen during the photocatalytic dehydrogenation reaction of BA. The primary innovation of this experiment lies in the utilization of D2O (deuterated water) as the reaction medium, replacing conventional H2O (pure water), to effectively trace the migration trajectories of hydrogen and deuterium atoms. The gas generated under these conditions served as a hydrogen source and participated in the hydrogenation reduction reaction of 1-vinylnaphthalene (C10H7CH=CH2). Upon completion of the experiment, we conducted a gas chromatography-mass spectrometry (GC-MS) analysis of the solution in reactor 2 (Fig. 6e, Supplementary Fig. 39). The analytical results indicated the formation of four distinct products during the hydrogenation of 1-vinylnaphthalene (C10H7CHCH2) to 1-ethylnaphthalene: C10H7CH2CH3 (I, m/z=156), C10H7CH2CH2D (II, m/z=157), C10H7CHDCH3 (III, m/z=157), and C10H7CHDCH2D (IV, m/z=158)22. Products I and II yield C10H7CH2+ (m/z=141) following the removal of alkyl groups (-CH3 and -CH2D), whereas products III and IV generate C10H7CHD+ (m/z=142) after the corresponding alkyl groups are removed. These products provide direct verification of the effective integration of hydrogen atoms released during the oxidation of BA and deuterium atoms supplied by D2O in the hydrogenation reaction, offering conclusive evidence for the multiple sources of hydrogen. Finally, we conducted liquid chromatography analysis on the solution in reactor 1, as well as on the BA and BAD standard samples, to confirm the peak times of each component (Supplementary Fig. 40). The results indicated that the peak times of BA and BAD in the solution from reactor 1 were highly consistent with those of the standard samples, and a significant quantity of BAD was detected in the solution from reactor 1. Through an in-depth analysis of theoretical calculations and experimental results, this study effectively elucidates the mechanism of fast charge transfer driven by the synergistic effects of PEF and IDF in photocatalytic hydrogen production and the photoreforming of aromatic alcohols (Fig. 6f). The intrinsic dipole of asymmetric Zn3In4S9 generates a PEF that effectively suppresses bulk-phase charge recombination. Following photoexcitation, the PEF facilitates the rapid migration of electrons to the Zn3In4S9 interface. Pure Zn3In4S9 exhibits limited photocatalytic activity due to insufficient charge separation solely driven by its bulk PEF, coupled with sluggish surface reaction kinetics for both water and BA oxidation. Notably, MoS2 induces an IDF at the Zn3In4S9 interface, creating an fast directional electron transport channel that allows for the efficient injection of electrons into MoS2 while retaining h+ in the VB of Zn3In4S9. The spatially separated h+ exhibit strong oxidizing properties, which enable them to cleave the α-C-H bond in BA, generating the •CH(OH)Ph radical and a proton (H). Following this, the O-H bond experiences hole-induced oxidation, resulting in its cleavage and the release of another proton (H), ultimately yielding BAD through a double-hole oxidation process. The enriched electrons on MoS2 can synergistically reduce protons released from BA oxidation and those generated from water dissociation, thereby achieving efficient simultaneous hydrogen production. This bifunctional charge utilization mechanism, which integrates directed fast charge transport and cascading redox reactions, establishes a paradigm for the development of high-performance artificial photosynthetic systems.

Methods
Synthesis of photocatalysts
Synthesis of y-MoS2/Zn3In4S9. In a 60 mL water-ethanol solution, 3 mmol of ZnCl2 (Sinopharm Chemical Reagent Co., Ltd., ≥98.0%) and 4 mmol of InCl3·4H2O (Beijing InnoChem Science & Technology Co., Ltd., 99.9%) were dissolved with vigorous stirring for 20 min. Subsequently, 9 mmol of thioacetamide (C2H5NS, Beijing InnoChem Science & Technology Co., Ltd., 98.0%) was added, and stirring was continued for an additional 20 min. Subsequently, varying amounts of flower-like MoS2 (4.8, 9.6, 14.4, 19.2, 24, and 28.8 mg) were added to the mixture and stirred for an additional 30 min. The mixture was reacted at 160°C for 12 h. The resulting product was then successively washed with ethanol and distilled water, followed by drying for subsequent use. The resulting product was designated as y-MoS2/Zn3In4S9, where y represents the molar ratio of MoS2 to Zn3In4S9 at 3%, 6%, 9%, 12%, 15%, and 18%, respectively. For detailed preparation procedures of additional catalysts, please refer to the supplementary information.

Photocatalytic activity measurements
The production of solar hydrogen synergizes effectively with organic synthesis. In this experiment, 20 mg of the photocatalyst was uniformly dispersed in a three-necked glass reaction flask containing 50 mL of H2O and 3 mL of BA (Sinopharm Chemical Reagent Co., Ltd., ≥99.0%) solution. Subsequently, the mixed system was subjected to sonication for 20 min. Prior to sealing the reactor, argon gas was employed to effectively eliminate air and dissolved oxygen from both the reactor and the solution. Following this, the circulating water system was activated to maintain the reactor temperature at 4oC. Subsequently, a xenon lamp (CEL-HXF300-T3) emitting wavelengths (λ > 420 nm) was activated to irradiate the solution for a duration of up to three hours. During this interval, hydrogen (H2) was collected from the reactor every 30 min, and its concentration was analyzed using a gas chromatography system (GC-7920, Beijing, China). After 3 h, 5 mL of the solution was extracted, filtered by centrifugation, and passed through a 0.22 μm pore size filter. The concentrations of BA and BAD were then determined using liquid chromatography (Agilent 1260 Infinity II, inert Sustain C18). The yields of H2, BA, and BAD were quantified using the external standard method, with the relevant standard curves presented in Supplementary Fig. 41. For further details regarding characterization methods, parameter settings, and catalyst activity testing, please refer to the supplementary information. The reaction selectivity is calculated using the following formula (1):

Selectivity (%) = (C2 / (C0 - C1)) × 100% (1)

In the photocatalytic system, the concentrations of BA and its derivative, BAD, after the reaction are denoted as C1 and C2, respectively. C0 represents the initial concentration of BA.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "The authors reports a Zn₃In₄S₉/MoS₂ balls-on-ball heterostructure in which an intrinsic polarization-electric-field (PEF) in asymmetric Zn₃In₄S₉ is coupled with an interface-dipole-field (IDF) generated by MoS₂. At 6 wt % MoS₂ loading, the composite achieves impressive rates of H₂ formation and benzaldehyde oxidation under λ > 420 nm illumination with record AQYs and great stability . A combination of a wide range of techniques including for instance DFT, KPFM, fs-TAS and PFM is used to argue that the synergistic dipole fields suppress bulk recombination and create an ultrafast, directional electron pathway from Zn₃In₄S₉ to MoS₂, enabling simultaneous hydrogen evolution and selective benzyl-alcohol oxidation.\nThe study addresses an important bottleneck in photocatalysis, directional carrier extraction across both the bulk and the interface, and proposes an dipole-engineering strategy. The catalytic figures-of-merit are among the highest reported for non-noble-metal systems using alcohol reforming as the oxidation half-reaction, and the PEF and IDF effects are supported by a broad experimental toolkit. The work will be of interest to the photocatalysis, materials-chemistry and artificial-photosynthesis communities. However, several points require clarification or additional evidence before the manuscript can be recommended for publication:\n1-My major concern is if the improvement in the catalytic activity is unequivocally associated with the PEF and IDF effects. The authors argue that BA adsorption is affected by the presence of MoS2, resulting in lower barriers for its oxidation. This suggest that the catalytic enhancement might be, at least partially, attributed to substrate-catalyst interactions promoted by MoS2. Is the MoS2 the site for BA adsorption and activation? Why MoS2 modifies BA adsorption considering the mechanistic proposal where bulk Zn₃In₄S₉ is the oxidizing site? Do the ZnIn2S4 or Zn3In4S9 (in the absence of MoS2) oxidize BA efficiently in the presence of a suitable electron acceptor? That would support the Zn3In4S9 as the main oxidation site. In addition, the fact that other electron donors result in much lower H2 production rates suggest that substrate interaction might have a major impact.\n2-The authors propose a synergistic effect involving PEF and IDF exerted by the combination of Zn₃In₄S₉ and MoS₂. However, it remains unclear whether the simple effect of MoS2 incorporation would be enough to promote the observed changes in the photodynamics and photocatalysis. To elucidate this, exploring the equivalent material formed by ZnIn2S4 with MoS2, where no bulk PEF is present, would demonstrate the role of the synergistic effect. A control using Zn3In4S9 and independent MoS2 for catalysis seems also an appropriate control experiment.\n3-I was wondering why superficial MoS2 causes larger PEF as inferred from the hystheresis slopes and PEF intensities considering that PEF is associated to the lower symmetry in the bulk material.\n4- While the optimal MoS2 loading of 6% is clear, I failed at understanding the nature of this observation, and why higher percentages of MoS2 (considering still low ratio) fail at improving the charge separation and charge carrier dynamic, and in turns, photocatalysis.\n5-In Fig. 4 j, what is the peak at 550 aprox. at longer delay times?\n6- It remains unclear why oxidation of BA is significantly more efficient than other potential electron donors, considering the unfavorable thermodynamics (the redox potential for BA oxidation is relatively high). Why the TEOA decreases the H2 production if it efficiently eliminated h+?\n7-Why does the mOD in the TAS experiments not come back to 0? That suggest the influence of different intermediates?\n8-The photocatalytic reactions are performed at 4ºC, but I understand the photodynamic characterization is done at room temperature. The authors suggest there is no photothermal effect due to heat accumulation by the catalyst, but I wonder whether there is a temperature effect due to the lower temperature of the reaction set-up. Also careful comparison with other systems might considering temperatures employed.", "reviewer_2": "This paper reports a synergistic strategy integrating the polarization electric field (PEF) from asymmetric Zn3In4S9 and the interface dipole field (IDF) induced by MoS2 to drive ultrafast charge dynamics. The systematic study combining DFT calculations, KPFM analysis, and fs-TAS demonstrates the spontaneous polarization of dipole moments in the asymmetric structure of Zn3In4S9 generates a PEF, which significantly suppresses the ineffective recombination of e- and h+. The MoS2/Zn3In4S9 interface induces the formation of IDF, which facilitates the construction of ultrafast charge transfer channels directed towards MoS2. The optimized 6%-MoS2/Zn3In4S9 exhibits high photocatalytic performance for the production of H2 and benzaldehyde (BAD) under 420 nm light. This manuscript may be acceptable for publication after addressing the following concerns.\n(1) In this work, “the MoS2 microspheres formed a distinctive “balls-to-ball” structure on the surface of Zn3In4S9 nanospheres through the solvothermal method”. Firstly, this description is incorrect. As shown in Fig. 1, the sizes of Zn3In4S9 spheres are much larger than those of MoS2 spheres. It should be stated that the MoS2 nanospheres formed a distinctive “balls-to-ball” structure on the surface of Zn3In4S9 microspheres. In addition, such “balls-to-ball” structure is not conducive to the formation of a closely integrated interface. As shown in Fig 1b, numerous MoS2 nanospheres are scattered rather than being loaded on Zn3In4S9 microspheres. This structure is not conducive to the formation of interface dipole field (IDF).\n(2) The authors claim that the changes in Mo-Mo and Mo-S bond lengths are attributed to the transition of MoS2 from the 2H phase to the metallic 1T phase. Please provide further evidence.\n(3) DFT calculation (Fig. 3c) indicates that “Electrons are enriched on the MoS2 side, while electron depletion is evident on the Zn3In4S9 side, thereby confirming the transfer of electrons from Zn3In4S9 to MoS2”. On the other hand, in situ XPS analysis demonstrates the transfer of interfacial electrons from Zn3In4S9 to MoS2 under light irradiation. These results seem contradictory to each other.\n(4) If MoS2 is replaced by other metals or semiconductors to form a heterostructure with Zn3In4S9, will the IDF still be formed? What are the advantages of MoS2?\n(5) There are some clerical errors in the text. Please carefully check and correct them.", "reviewer_3": "This manuscript presents a highly innovative and rigorous study on the synergistic effects of polarization electric fields (PEF) and interface dipole fields (IDF) in enhancing photocatalytic performance for hydrogen evolution coupled with benzyl alcohol oxidation. The work is well-executed, with comprehensive experimental and theoretical analyses supporting the proposed mechanism. The results are significant and could have broad implications for artificial photosynthesis. I recommend minor revisions to clarify certain aspects and strengthen the manuscript, making it suitable for publication in Nature Communications after some comments are well addressed to improve the quality further.\n1. The introduction is informative, with a clear and progressive series from the importance of hydrogen energy to the limitations of the existing technology to the solution of this study. Discussing the limitations of ZnIn2S4 and its improvement strategy provides sufficient theoretical support for the research motivation. However, when referring to “ZnIn2S4”, it is suggested to add a brief description of its structural features, for example, \"The two-dimensional hexagonal crystal system of ZnIn2S4 is characterized by its unique SH surface active sites and suitable energy band structure, which shows remarkable potential in photocatalytic hydrogen production.\n2. The origin of the optimal 6% MoS2 loading. (e.g., why higher loadings reduce performance) should be briefly addressed in the main text.\n3. The photocatalytic stability test (Fig. 5g) shows excellent retention (93.8% for H2), but the slight decline in BAD yield (87%) warrants a brief discussion. Are there potential side reactions or intermediate accumulations affecting selectivity?\n4. The authors should provide a reasonable explanation in Supplementary Figure 7c and Supplementary Figure 30d, or conduct additional testing, to clarify why the Mo signal peaks are weak.\n5. It is suggested that the authors add some comparisons of photoelectric performance tests of ZnIn2S4 and Zn3In4S9 to highlight the advantages of Zn3In4S9 over ZnIn2S4.\n6. The abstract clearly outlines the core of the study, including the background, methodology, main findings and implications, in a well-structured and logical manner. In particular, a “dipole synergy” mechanism is proposed for the polarization study, which is a novel and promising concept. The materials were analyzed in detail using various characterization tools (e.g., SEM, TEM, XPS, XRD, etc.), and the data are sufficient and supportive of the conclusions. However, it is suggested that the generalizability of this mechanism to other catalytic systems and the possible challenges for industrial applications be further elaborated in the discussion section.", "reviewer_4": "This manuscript reports a MoS2/Zn3In4S9 photocatalyst that synergistically performs hydrogen evolution and benzyl alcohol oxidation with high efficiency and selectivity under visible light irradiation. The photocatalytic activity obtained by the authors is impressive, which was attributed to the improved charge separation due to the polarization electric field from asymmetric Zn3In4S9 and the interface dipole field induced by MoS2. Though the results are promising, some crucial issues need to be concerned.\n1. The apparent quantum yield (AQY) under 420 nm illumination appears remarkably high in this study. Could you please provide a detailed description of the experimental procedure for AQY measurement? Specifically, does the testing methodology and experimental setup follow standard protocols for conventional photocatalytic evaluation?\n2. A notable dimensional inconsistency is observed between the AFM-measured sizes of Zn₃In₄S₉ and MoS₂ (on the order of tens of nanometers) and the corresponding SEM/TEM-reported dimensions (3.5 μm and 500 nm, respectively). Could you please provide a detailed explanation for:\n(a) The potential causes underlying this size discrepancy.\n(b) Which set of measurements more accurately represents the true particle dimensions in the photocatalytic system.\n3. Despite the high MoS₂ loading content (18 wt%) in the MoS₂/Zn₃In₄S₉ composite catalyst, no characteristic peaks of MoS₂ were detected across multiple characterization techniques (XRD, FTIR, Raman, and XPS survey scan). Please describe the reasons for the absence of MoS₂ features in each analytical technique.\n4. The observed decrease in Zn 2p/In 3d binding energies during in situ XPS under illumination appears contradictory to conventional photoelectron spectroscopy principles. Specifically, the interpretation that \"the accumulation of h⁺ leads to a relative reduction in the local electron density of Zn 2p and In 3d, thereby exhibiting an overall decrease in binding energy\" warrants careful examination because: According to fundamental XPS theory, hole accumulation (h⁺) typically increases binding energies. Please clarify:\n(a) If the direction of BE changes is reproducible across multiple measurements\n(b) How this observation aligns with your proposed charge transfer mechanism\n5. The comparative XPS analysis presented in Supplementary Fig. 8 between MoS₂/Zn₃In₄S₉ and ZnIn₂S₄ appears problematic since these are fundamentally different materials (Zn₃In₄S₉ vs. ZnIn₂S₄). How can such comparison provide meaningful insights when the baseline materials differ?\n6. Regarding the XPS analysis, two critical issues require clarification:\n(a) Absence of Mo 3d Binding Energy Values for MoS₂\n(b) Ambiguity in S 2p Peak Assignment:\nThe observed S 2p binding energy decrease in MoS₂/Zn₃In₄S₉-dark (vs. Zn₃In₄S₉) raises questions about sulfur speciation because: Both components contain S: Zn₃In₄S₉ (S²⁻) and MoS₂ (S₂²⁻) have distinct sulfur coordinations. How to determine the attribution of the S 2p peak at this location?\n7. The paper mentions that \"The photon energy at the absorption edge of MoS2 exceeds that of Mo foil, suggesting that Mo (+4) atoms in MoS2 are present in a higher oxidation state (Fig. 2b).\" Explain why the photon energy at the absorption edge of the composite catalyst is even higher than that of MoS2. Analyze the oxidation state of Mo in the composite catalyst—if its oxidation state is higher than +4, does this contradict the electron transfer from Zn3In4S9 to MoS2 (as XPS analysis shows a decrease in the binding energy of Mo 3d in the composite catalyst)?\n8. In Figure 2d, Mo-Mo bonds appear in 6%-MoS2/Zn3In4S9. Are these bonds reflected in the XPS Mo 3d spectrum? Please explain with the peak fitting of Mo 3d.\n9. Regarding the determination of the conduction band potential from the flat-band potential, could you please clarify the specific calculation methodology employed, and the potential error range of this approach as validated by complementary characterization techniques?\n10. Regarding the bandgap determination in Supplementary Fig. 10, the following inconsistencies require clarification:The bandgap calculated from the UV-Vis absorption edge (Eg(eV) = hc/λg = 1240/λg(nm)) differs from that obtained via Tauc plot analysis. What is the fundamental reason for this discrepancy? Please experimentally validate the more reliable method for bandgap determination.\n11. Regarding the role of MoS2 in the composite system, please clarify whether it functions solely as a cocatalyst or exhibits dual functionality (both light absorption and catalytic activity).\n12. In the femtosecond transient absorption spectroscopy analysis, the biexponential fitting of the decay kinetics yields two characteristic lifetimes (τ1 and τ2) for Zn3In4S9. Since no interfa-cial electron transfer occurs in the pure Zn3In4S9 system, please clarify the physical origins of these two distinct lifetimes.\n13. Regarding the 450 nm dynamics in the femtosecond transient absorption (fs-TA) spectra, several critical observations require clarification:\n(a) The positive signal at 450 nm contradicts the expected negative ground-state bleach (GSB) signal. What physical process could generate this positive ΔOD?\n(b) Why does 450 nm exhibit detectable kinetics despite lacking prominent features in the 2D spectra?\n(c) Provide raw ΔOD spectra at key delay times to confirm the 450 nm feature’s spectral shape.\n14. The time-resolved fluorescence curves in Figures S20e and S22b exhibit a gradual rise prior to the decay phase. Could you please explain the underlying mechanism for this initial rising feature?\n15. The photocatalytic experiments were conducted at 4℃. Could you please discuss how different reaction temperatures might affect the catalytic performance, based on your experimental observations?\n16. Minor revisions required:\n(a) Correct unit formatting from \"mmol·g-1·h-1\" to \"mmol g-1 h-1\".\n(b) \"The flat-band potential of Zn3In4S9, measured at 0.92 V\". \"0.92 V\"should be corrected to \"-0.92 V\"."}, "author_response": "I think the authors have clarified some aspects about the mechanism that were unclear and raised my previous concern, so I recommend publication."}]

Decision letter