Construction of Sheet-on-Hollow Cube Cu2-xS/ZnIn2S4 p-n Heterojunction for Enhanced Visible-Light-Driven Photocatalytic Hydrogen Production

Construction of Sheet-on-Hollow Cube Cu2-xS/ZnIn2S4 p-n Heterojunction for Enhanced Visible-Light-Driven Photocatalytic Hydrogen Production | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL Energy & Environmental Materials This is a preprint and has not been peer reviewed. Data may be preliminary. 8 August 2025 V1 Latest version Share on Construction of Sheet-on-Hollow Cube Cu2-xS/ZnIn2S4 p-n Heterojunction for Enhanced Visible-Light-Driven Photocatalytic Hydrogen Production Authors : Yuan Liu , Jian Yu , Hangang Qiao , Yuhan Zhao , Dongtao Zhang , Xiaojing Chu , Chuanqi Li , and Chen Zhu 0009-0005-4668-9354 [email protected] Authors Info & Affiliations https://doi.org/10.22541/au.175469404.44194621/v1 Published ENERGY & ENVIRONMENTAL MATERIALS Version of record Peer review timeline 245 views 256 downloads Contents Abstract Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract The photocatalytic performance is governed by three critical kinetic processes: photon absorption efficiency, charge carrier separation dynamics, and interfacial reaction kinetics. Strategic engineering through morphological design, elemental doping, heterojunction construction, and vacancy engineering has emerged as effective approaches to enhance these interrelated processes. Herein, we demonstrate a p-n junction photocatalyst via in-situ growth of n-type ZnIn2S4 nanosheets on p-type Cu2‒xS hollow nanocubes. This hierarchical architecture enables synergistic enhancement of charge separation through built-in electric field effects, achieving most suppression of electron-hole recombination compared to pristine ZnIn2S4. The optimized Cu2‒xS/ZnIn2S4 composite exhibits exceptional visible-light-driven hydrogen evolution activity, delivering a production rate of 5.7 mmol h⁻¹ g⁻¹ under broad-spectrum irradiation (λ ≥ 420 nm), 9.5-fold higher than bare ZnIn2S4 (0.6 mmol h⁻¹ g⁻¹). Notably, an apparent quantum efficiency of 11.4% was achieved at 420 nm monochromatic light, accompanied by remarkable stability over long-term cyclic tests. Combined X-ray photoelectron spectroscopy analysis and density functional theory (DFT) calculations reveal dual enhancement mechanisms: the redistribution of interface charges helps to increase the density of photogenerated electrons and photogenerated holes as well as facilitate efficient carrier migration, while the p-n junction’s band alignment promotes redox reaction kinetics. This work provides fundamental insights into heterojunction engineering for developing cost-effective photocatalytic systems. Article category: Full Paper Subcategory: Photocatalysis Construction of Sheet-on-Hollow Cube Cu 2-x S/ZnIn 2 S 4 p-n Heterojunction for Enhanced Visible-Light-Driven Photocatalytic Hydrogen Production Yuan Liu a , Jian Yu a , Hangang Qiao b , Yuhan Zhao c , Dontao Zhang a , Xiaojing Chu a , Chuanqi Li a, *, and Chen Zhu a, * Prof. Yuan Liu, Jian Yu, Dontao Zhang, Xiaojing Chu, Dr. Chuanqi Li, and Dr. Chen Zhu a College of Chemistry and Chemical Engineering, Henan University of Technology, Zhengzhou, Henan, 450001, China E-mail: [email protected] ; [email protected] Hangang Qiao b Xinmi Industrial Development Promotion Center, Xinmi, Henan, 452370, China Yuhan Zhao c Henan Graphene New Material Technology Company Limited, Zhengzhou, Henan, 450001, China KEYWORDS photocatalytic H 2 generation, p-n junction, Cu 2‒x S/ZnIn 2 S 4 ABSTRACT The photocatalytic performance is governed by three critical kinetic processes: photon absorption efficiency, charge carrier separation dynamics, and interfacial reaction kinetics. Strategic engineering through morphological design, elemental doping, heterojunction construction, and vacancy engineering has emerged as effective approaches to enhance these interrelated processes. Herein, we demonstrate a p-n junction photocatalyst via in-situ growth of n-type ZnIn 2 S 4 nanosheets on p-type Cu 2‒x S hollow nanocubes. This hierarchical architecture enables synergistic enhancement of charge separation through built-in electric field effects, achieving most suppression of electron-hole recombination compared to pristine ZnIn 2 S 4 . The optimized Cu 2‒x S/ZnIn 2 S 4 composite exhibits exceptional visible-light-driven hydrogen evolution activity, delivering a production rate of 5.7 mmol h⁻¹ g⁻¹ under broad-spectrum irradiation (λ ≥ 420 nm), 9.5-fold higher than bare ZnIn 2 S 4 (0.6 mmol h⁻¹ g⁻¹). Notably, an apparent quantum efficiency of 11.4% was achieved at 420 nm monochromatic light, accompanied by remarkable stability over long-term cyclic tests. Combined X-ray photoelectron spectroscopy analysis and density functional theory (DFT) calculations reveal dual enhancement mechanisms: the redistribution of interface charges helps to increase the density of photogenerated electrons and photogenerated holes as well as facilitate efficient carrier migration, while the p-n junction’s band alignment promotes redox reaction kinetics. This work provides fundamental insights into heterojunction engineering for developing cost-effective photocatalytic systems. 1. Introduction Amidst the dual pressures of continuous depletion of global fossil fuel reserves and carbon emissions triggering the climate crisis, breakthroughs in renewable energy technologies have emerged as a pivotal pathway toward achieving sustainable development goals. [1-3] Light-driven water decomposition has become a pivotal approach in renewable energy systems, integrating solar-to-chemical conversion processes with the generation of clean hydrogen fuels. [4-6] This third-generation clean energy solution leverages semiconductor heterojunctions to enhance photogenerated carrier separation, improving solar-to-hydrogen (STH) efficiencies in state-of-the-art systems. [7,8] The technology has a triple environmental benefit: zero carbon emissions throughout the reaction; high hydrogen calorific value; low energy consumption. [9,10] At present, the energy conversion efficiency of the photocatalytic hydrogen evolution system is restricted by the synergy of multi-level kinetic processes, designing and developing efficient catalysts remains a difficult problem. [11-13] The unique mechanism of p-n junctions grants them extensive applications in the field of photocatalysis. Strategic interface modification between p-n semiconductors generates an intrinsic electric field at the heterointerface, significantly improving photoinduced carrier separation and reducing electron-hole pair recombination rates, ultimately boosting catalytic performance. The unidirectional charge transfer pathway inherent in this configuration streamlines catalyst selection criteria. Through strategic band alignment engineering, synergistic spectral utilization is achieved, effectively broadening the light absorption range of the catalyst. Furthermore, the space charge region of the p-n junction concurrently mitigates photo-corrosion effects, substantially improving the operational stability and prolonging the service lifetime of the catalytic system. [14-16] Localized Surface Plasmon Resonance (LSPR) is a unique phenomenon arising from the collective oscillation of conductive electrons in metals (such as gold, [17] silver, [18] copper [19] ), highly doped semiconductor nanostructures and non-chemically balanced compounds (such as Cu 2‒ x S, [20] WO 3- x [21] ). Its fundamental nature lies in the coupled resonance between confined electromagnetic fields and the dynamic modulation of electron clouds. This mechanism enables significant near-field enhancement and hot carrier generation. [22] This material exhibits unique capabilities for effective light-matter interactions, profoundly influencing its optical properties. By confining electromagnetic radiation to sub-wavelength dimensions, the localized surface plasmon resonance effect amplifies local electromagnetic fields. This enhancement mechanism directly improves solar energy harvesting efficiency and boosts photocatalytic activity. [23,24] This effect enhances photocatalytic performance through three synergistic mechanisms: 1) Localized electromagnetic field enhancement extends the optical absorption cross-section into the visible-near infrared spectrum (400-1200 nm), 2) hot electron injection elevates charge carrier separation efficiency, and 3) non-radiative decay-induced localized thermal effects accelerate surface hydrolysis kinetics. These plasmonic phenomena collectively enable broadband solar energy utilization while maintaining thermodynamic stability. [25,26] LSPR materials present a groundbreaking approach to transcend the intrinsic bandgap limitations of semiconductors, demonstrating exceptional enhancement in photocatalytic hydrogen evolution efficiency through mechanisms such as localized electromagnetic field amplification and hot carrier injection in water splitting systems. [27] ZnIn 2 S 4 (ZIS), an n-type ternary sulfide semiconductor with a bandgap of 2.2-2.5 eV, features an appropriately positioned conduction band (CB) edge and demonstrates excellent stability, rendering it widely applicable in photocatalytic systems. [28] However, due to its low charge separation efficiency, short lifetime of photogenerated electrons and photo-corrosion, its efficiency in photocatalytic hydrogen production is not ideal. [29] Therefore, the development of heterojunction materials combined with ZIS to improve hydrogen production efficiency has been widely studied in recent years. Cu 2‒ x S, a prototypical non-stoichiometric chalcogenide semiconductor, demonstrates tunable optoelectronic properties governed by its copper vacancy-dominated defect structure. Precise control of the stoichiometric parameter x (0 < x ≤ 1) enables continuous bandgap engineering from 1.2 to 2.1 eV [30] (This is exemplified by specific compositions: Cu 1.96 S exhibits a bandgap of 1.35 eV, while Cu 1.8 S shows 1.71 eV [31] ). The plasmonic resonance characteristics of the material system are derived from the change of free carrier concentration induced by copper vacancy. By constructing Cu 2‒ x S/g-C 3 N 4 heterojunction, the light absorption band of g-C 3 N 4 is improved from 450 nm to 1900 nm by more than 4 times compared with g-C 3 N 4 , which is more than Ag/g-C 3 N 4 , Au/g-C 3 N 4 absorption band is even longer. [32] This study developed a hierarchical Cu 2‒ x S/ZIS heterostructure through a two-step synthesis strategy, where ZIS nanosheets were epitaxially grown on hollow Cu 2‒ x S cubic substrates. The engineered p-n junction configuration facilitates directional carrier migration via its intrinsic band alignment, synergistically enhancing charge separation kinetics and photocatalytic hydrogen evolution activity. The enhanced photocatalytic activity arises from four mutually reinforcing factors: Cu 2‒ x S’s architecturally engineered hollow cubic framework demonstrates significantly augmented surface-to-volume ratios, creating abundant exposed catalytic sites. Moreover, this structure can enhance the absorption and scattering capabilities of light, and more effectively utilize light energy, copper vacancy-mediated LSPR effects, atomic-level charge transfer pathways at heterointerfaces, and effective photo-corrosion suppression through hole-trapping processes. The heterostructure demonstrates enhanced hydrogen evolution activity under visible-light illumination (λ ≥ 420 nm), with both experimental characterizations and computational simulations verifying its p-n junction configuration. This work establishes a new paradigm for developing sunlight-driven photocatalytic systems through rational integration of plasmonic effects and junction engineering. 2. Experimental Section 2.1 Synthesis of Cu 2-x S hollow cube Initially, 80 mL of deionized water was mixed with 374.5 mg of CuSO 4 ·5H 2 O and 147.1 mg of sodium citrate under constant magnetic stirring for 15 minutes, resulting in a uniform blue solution. Subsequently, 25 mL of NaOH solution (1.25 M) was gradually added to the mixture under agitation, followed by additional stirring for 15 min to yield a blue suspension. The resulting suspension was then treated with 55 mL of ascorbic acid solution (0.03 M), stirred for 5 min, and allowed to stand for 1 h. The precipitate was subsequently collected by centrifugation, washed three times with deionized water, and dried in a vacuum oven at 60℃ for 12 h to obtain red Cu 2 O powder. The synthesized Cu 2 O particles underwent ultrasonic dispersion in 30 mL of absolute methanol with high-speed magnetic agitation (500 rpm) for 3 min to achieve homogeneous suspension. Subsequently, 3 mL of 0.05 M Na 2 S·9H 2 O aqueous solution was introduced dropwise into the reaction system. After 3 min of continuous stirring, the mixture was subjected to centrifugation (5 min) to collect the intermediate product. The precipitation was dispersed in 30 mL methanol, 5 mL HCl (1 M) was added, stirred for 1 min. The resultant material was collected via centrifugation (5 min), subjected to sequential purification using deionized water and ethanol, then desiccated under vacuum at 60°C for 12 h, ultimately producing brown Cu 2‒ x S powder. 2.2 Synthesis of Cu 2‒x S/ZnIn 2 S 4 and ZnIn 2 S 4 In a typical synthesis, 0.272 g of ZnCl 2 , 1.17 g of InCl 3 ·4H 2 O, and 0.3 g of thioacetamide (TAA) were dissolved in 80 mL of HCl solution (pH = 2.5) under magnetic stirring. The homogeneous solution was then doped with 4 mg Cu 2‒ x S nanoparticles, followed by 30 min sonication treatment to achieve colloidal stability before introducing 20 mL deionized water. The resultant suspension was hydrothermally treated at 80°C for 2 h in a temperature-controlled water bath. Post-cooling, solid products were isolated by centrifugal separation, subjected to triple washing cycles with deionized water and anhydrous ethanol, and ultimately vacuum-desiccated at 60°C for 12 h to acquire the Cu 2‒ x S/ZIS heterostructure. By maintaining identical synthetic conditions while systematically varying the Cu 2‒ x S loading (2, 8, 16, and 25 mg), a series of comparative samples including pristine ZIS and Cu 2‒ x S/ZIS hybrids were fabricated. The resulting powders were designated as Cu 2‒ x S/ZIS- y , where y = 1-5 corresponds to incremental Cu 2‒ x S concentrations. 2.3. DFT Calculations In this study, all DFT calculations were carried out using the Vienna Ab-initio Simulation Package (VASP) with the frozen-core all-electron projector-augment-wave (PAW) method. [33-35] The exchange and correlation energies for all systems were treated under the generalized gradient approximation (GGA) proposed by Perdew-Burke-Ernzerhof (PBE). [36] A plane-wave basis set with a kinetic energy cutoff of 500 eV was implemented. Empirical dispersion corrections via the DFT-D3 scheme were incorporated to account for van der Waals interactions. [37] Convergence criteria of 10⁻ 5 eV for electronic self-consistency and 0.03 eV/Å for ionic relaxation forces were enforced. A four-layer Cu 2 S (220) supercell with 2×3 periodicity was constructed, where the bottom two atomic layers remained fixed during structural optimization while permitting relaxation of surface layers. Surface defects were introduced through selective removal of two copper atoms from the top layer. For ZIS simulations, a (001) oriented supercell with lattice parameters of a = b = 15.73 Å and c = 30 Å was modeled. Vacuum spacing exceeding 15 Å was maintained perpendicular to all surfaces to eliminate spurious interactions. The Brillouin zone integration employed a Γ-centered 2×2×1 k-point sampling grid. Structural visualization and analysis were conducted using the VESTA software package. [38] 3. Results and discussion 3.1. Characterization of morphology and structure Figure 1a schematically illustrates the three-stage synthesis process of the Cu 2‒ x S/ZIS heterostructure photocatalyst. Firstly, Cu 2 O nanocubes were synthesized via a chemical reduction method. In the second step, the surface of Cu 2 O was sulphated into Cu 2‒ x S using Na 2 S·9H 2 O, and then Cu 2 O was removed with HCl to obtain Cu 2‒ x S hollow nanocubes. Finally, ZIS nanosheets were in-situ grown on the surface of Cu 2‒ x S by hydrothermal growth method to yield the hierarchical Cu 2- x S/ZIS photocatalyst. The microstructural characteristics of the specimens were characterized through scanning electron microscopy (SEM) and transmission electron microscopy (TEM) imaging techniques. As shown in Figure 1b and 1c, we synthesized Cu 2‒ x S (Figure 1c) hollow nanocubes from Cu 2 O (Figure 1b) and grew ZIS nanosheets on the surface of Cu 2‒ x S hollow nanocubes by in-situ growth method, eventually forming Cu 2‒ x S/ZIS nanostructures (Figure 1d). Figure 1e shows the hollow cube structure of Cu 2‒ x S, and the dimensions are consistent. Figure S1. shows the transmission image of nano-sheet-like ZIS. Figure 1f shows Cu 2‒ x S coated with ZIS, the (103) crystal plane of ZIS and the (220) crystal plane of Cu 2‒ x S are measured by HRTEM diagram (Figure 1g), preliminarily confirming that we have successfully prepared the Cu 2‒ x S/ZIS nanostructure of Cu 2‒ x S coated with ZIS. To further verify the structural characterization of the material, HAADF-STEM-EDX was used to draw the element distribution diagram (Figure 1h). The results show that the distributions of Cu, Zn, In, and S are consistent with the previous TEM analysis results, confirming that Cu 2‒ x S is successfully encapsulated by ZIS. From the elemental composition of the Cu 2‒ x S/ZIS-2 samples in the EDX spectra (Table S1), it can be seen that the atomic mass fractions of Cu and S account for approximately 12%, indicating that Cu 2‒ x S accounts for 12% of the total mass of the composite samples. Figure 1. (a) Schematic diagram of the synthesis process of Cu 2‒ x S/ZIS. FESEM images of (b) Cu 2 O, (c) Cu 2‒ x S and (d) Cu 2‒ x S/ZIS-2. TEM images of (e) Cu 2‒ x S and (f) Cu 2‒ x S/ZIS-2. (g) HRTEM image of Cu 2‒ x S/ZIS-2. (h) EDX elemental mappings of Cu, Zn, In and S elements in Cu 2‒ x S/ZIS-2. The crystallographic evolution during material synthesis was characterized by X-ray diffraction analysis, as depicted in Figure 2a. The diffraction pattern of the Cu 2‒ x S phase shows prominent peaks at 2θ = 27.4° and 31.7°, which index to the (110) and (200) crystallographic planes of cubic Cu 2 S (JCPDS 84-1770). Notably, a systematic rightward shift was observed for the (220) and (311) planes, attributed to lattice contraction induced by copper vacancies as verified by Rietveld structural refinement. This conclusively demonstrates the successful synthesis of vacancy-engineered Cu 2‒ x S. The ZIS phase displayed characteristic reflections at 21.5°, 27.6°, 47.1°, and 52.4°, corresponding to the (006), (102), (110), and (116) crystallographic orientations, respectively, in agreement with the standard pattern (JCPDS 72-0773), indicating high phase purity. In the Cu 2‒ x S/ZIS composite (Figure 2c), the coexistence of distinct diffraction signatures from both phases with negligible peak broadening verifies effective heterojunction formation without structural degradation. Figure S2 shows the XRD patterns of Cu 2‒ x S/ZIS before and after the reaction. X-ray diffraction analysis of the post-reaction composite catalyst demonstrates excellent structural stability, with maintained peak positions and intensities confirming minimal structural degradation. The electron paramagnetic resonance profiles in Figure 2b reveal distinct electronic configurations: Cu 2‒ x S exhibits a characteristic resonance at g = 2.002, directly evidencing S vacancy defects. This is because the Cu vacancy causes the adjacent S 2‒ to be oxidized to S ‒ , resulting in unpaired electrons in S. The signal appeared at the g factor of 2.002, further proving the successful preparation of Cu 2 S with Cu vacancies. [39,40] The EPR signal also appeared at the same position for Cu 2‒ x S/ZIS, indicating that during the preparation process of Cu 2‒ x S/ZIS, no change in the structure of Cu 2‒ x S was caused. It indicates that the Cu vacancies of Cu 2‒ x S exist stably. The specific surface area and pore structure of the catalyst were determined by the Brunauer-Enmet-Teller (BET) method (Figure S3 and Figure S4). Both ZIS and Cu 2‒ x S/ZIS exhibited typical Type IV isotherms with obvious hysteresis loops, revealing their mesoporous characteristics. The results show that the specific surface areas of ZIS and Cu 2‒ x S/ZIS are 153.13 and 138.6 m 2 g ‒1 , respectively. The specific surface area of Cu 2‒ x S/ZIS is smaller than that of ZIS, which may be caused by the tight coating of Cu 2‒ x S by ZIS. The elemental composition of the prepared photocatalysts were analyzed using XPS. The elemental composition analysis via XPS survey scans verified the coexistence of Cu, Zn, In, and S in all specimens (Figure S5). Element-specific chemical states were investigated through high-resolution XPS spectral deconvolution. As depicted in Figure 2c, the S 2p core-level spectra for all three materials exhibit characteristic doublet peaks corresponding to S 2p 1/2 and S 2p 3/2 spin-orbit components. It can be found that in the XPS high-resolution spectrum of S 2p of Cu 2‒ x S, the shape of the overall peak has changed. This might be due to the existence of Cu vacancies causing the change of S, and this result corresponds to the EPR result. The interfacial charge transfer dynamics in the Cu 2‒ x S/ZIS heterojunction were elucidated through high-resolution XPS analysis (Figure 2d-f). The In 3d spectrum (Figure 2d) exhibited characteristic spin-orbit splitting with 3d 5/2 and 3d 3/2 peaks at 445.13 eV and 452.67 eV in pristine ZIS, demonstrating a systematic +0.04 eV positive shift in the composite (445.17 eV/452.72 eV). This binding energy evolution (ΔBE = +0.04 eV) indicates electron depletion at In 3+ sites. Concurrently, Zn 2p 3/2 peaks shifted +0.13 eV (ZIS: 1022.25 eV and composite: 1022.38 eV, Figure 2e), confirming charge transfer from Zn 2+ centers. Contrastingly, Cu 2p 3/2 binding energies decreased by 0.03 eV (932.46 eV to 932.43 eV, Figure 2f) with enhanced satellite intensity, signaling electron accumulation at Cu + sites. These opposite chemical shift directions (In/Zn: +ΔBE; Cu: -ΔBE) collectively indicate the role of electron transfer from ZIS to Cu 2‒ x S., establishing a built-in electric field of Cu 2‒ x S/ZIS is from ZIS to Cu 2‒ x S. Figure 2. (a) XRD patterns of Cu 2‒ x S, ZIS and Cu 2‒ x S/ZIS. (b) EPR spectra of Cu 2‒ x S, ZIS and Cu 2‒ x S/ZIS. (c) S 2p XPS spectra of Cu 2‒ x S, ZIS and Cu 2‒ x S/ZIS. (d) In 3d and (e) Zn 2p XPS spectra of ZIS and Cu 2‒ x S/ZIS. (f) Cu 2p XPS spectra of Cu 2‒ x S and Cu 2‒ x S/ZIS. 3.2. Photocatalytic hydrogen production performance The hydrogen production performance was evaluated through visible-light-driven photocatalysis (λ ≥ 420 nm) with triethanolamine (TEOA) serving as the sacrificial agent. As shown in Figure 3a, pristine Cu 2‒ x S exhibited no detectable H 2 production activity, while pure ZIS showed a modest generation rate of 0.6 mmol g⁻¹ h⁻¹. It is notable that the H 2 production rate of the Cu 2‒ x S/ZIS composite increases significantly and shows a typical volcanic trend. The hydrogen production rate of the Cu 2‒ x S/ZIS-2 catalyst reached the highest level, which was 5.7 mmol g ‒1 h ‒1 . Compared with ZIS alone, the hydrogen production rate increased by 9.5 times. Figure 3b shows the hydrogen production of Cu 2‒ x S, ZIS, and Cu 2‒ x S/ZIS within 4 hours under visible light irradiation. It can be seen that by introducing Cu 2‒ x S into ZIS, the hydrogen production has been greatly increased. Meanwhile, the AQE of Cu 2‒ x S/ZIS-2 reached 11.4% (Figure 3c). Under similar reaction conditions, it surpassed the vast majority of representative photocatalysts ( Table S2 ). During the 16-hour intermittent visible light irradiation period(Figure 3d), the stability of the photocatalyst was evaluated, and no significant reduction in the activity of the photocatalyst was found, indicating that Cu 2‒ x S/ZIS-2 has good stability in long-term photocatalytic applications. Figure 3. (a) The H 2 generation rate of Cu 2‒ x S/ZIS photocatalysts with different Cu 2‒ x S contents under light exposure. (b) The amount of H 2 generated by the catalytic hydrolysis of Cu 2‒ x S, ZIS, and Cu 2‒ x S/ZIS within four hours under visible light irradiation (λ ≥ 420 nm). (c) Uv-vis and wavelength-related AQE for hydrogen production by photocatalysis with Cu 2‒ x S/ZIS-2. (d) Recovery experiment of hydrogen produced by photocatalysis with Cu 2‒ x S/ZIS-2. 3.3. The photoelectric physicochemical properties of the catalysts As shown in Figure 4a, through the ultraviolet-visible diffuse reflection test of the catalyst, it can be observed that the absorption band edge of ZIS is about 500 nm. Due to the plasmon effect of Cu 2‒ x S, Cu 2‒ x S/ZIS has excellent light absorption performance throughout the visible light region. By using the Kubelka-Munk method and through extrapolation ( α h ν ) 2 and photon energy (h ν ), the bandgap energies (E g ) of Cu 2‒ x S and ZIS were determined to be 1.52 and 2.35 eV (Figure 4b). The Mott-Schottky (M-S) analysis confirmed the semiconductor type and flat band potential of the catalyst. Mott-Schottky analyses under dark conditions (Figure 4c-d) demonstrate frequency-dependent capacitive behavior for both materials when measured at 1, 2, and 3 kHz. The characteristic negative slope in Cu 2‒ x S’s potential-capacitance relationship conclusively identifies its p-type semiconducting nature. The characteristic positive slope observed in ZIS’s Mott-Schottky plot conclusively demonstrates n-type semiconductor behavior. Thus, it is further confirmed that the prepared Cu 2‒ x S/ZIS photocatalytic material belongs to the p-n junction. The measured values of the flat band potentials of Cu 2‒ x S and ZIS were 1.43 V and ‒1.21 V vs . Ag/AgCl, respectively. Since the difference between the standard hydrogen electrode and Ag/AgCl was approximately 0.2 V, the converted flat band potentials were 1.63 V and ‒1.01 V vs . NHE, respectively. Because the valence band of p-type semiconductors is usually located approximately 0.2 V below the flat band potential, and the conduction band of n-type semiconductors is located approximately 0.2 V above the flat band potential, [41] the conduction band potential of Cu 2‒ x S is ‒0.09 V vs . NHE, and the valence band potential is 1.43 V vs . NHE. The conduction band potential of ZIS is ‒1.21 V vs. NHE, and the valence band potential is 1.14 V vs . NHE (Table S3). Figure 4e is the band structure diagrams of ZIS and Cu 2‒ x S drawn based on the test results of UV-Vis and M-S, the positions of their conduction bands can be utilized to ascertain hydrogen production capability. It can be found that the test results are consistent with the hydrogen production performance results of the two pure-phase catalysts previously described. Figure 4f Shows the photoluminescence (PL) emission spectrum of the sample. Its characterization revealed pronounced quenching effects in Cu 2‒ x S/ZIS compared to ZIS and Cu 2‒ x S, demonstrating that heterojunction formation effectively inhibits carrier recombination while enhancing charge carrier mobility through optimized band alignment. Figure 4g shows the normalized OCP attenuation plot of the sample. It can be found that after the termination of illumination, the attenuation rate of Cu 2‒ x S/ZIS is slower than that of Cu 2‒ x S and ZIS, indicating that the photogenerated charges on Cu 2‒ x S/ZIS have been effectively transferred and the recombination of photogenerated electrons and holes has been suppressed. It further explains that the recombination of photogenerated electron-hole pairs is effectively suppressed by the p-n heterojunction, while the charge transport efficiency is simultaneously enhanced. The transfer efficiency of photogenerated carriers is revealed through electrochemical impedance diagrams. It can be seen from Figure 4h that the semi-circular radius of Cu 2‒ x S/ZIS is smaller than that of Cu 2‒ x S and ZIS, indicating that its charge transfer resistance is smaller and the charge transfer efficiency is higher. The separation efficiency of photogenerated carriers was revealed through the transient current-time (i-t) curve, as shown in Figure 4i, it can be observed that Cu 2‒ x S/ZIS shows a higher photocurrent response than Cu 2‒ x S and ZIS, indicating that Cu 2‒ x S/ZIS achieves more effective separation. Figure 4. (a) UV-Vis DRS of Cu 2‒ x S, ZIS, Cu 2‒ x S/ZIS. (b) Plots of ( a h ν ) 2 versus photon energy of Cu 2‒ x S, and ZIS. M-S graphs of (c) Cu 2‒ x S and (d) ZIS. (e) The semiconductor band structure diagrams of ZIS and Cu 2‒ x S, (f) PL emission spectrum, (g) The normalized OCP plots, (h) EIS Nyquist plots, (i) Transient i−t curves. 3.4. DFT Calculations To elucidate the interfacial electron transfer dynamics between ZIS and Cu 2‒ x S, the work functions (W f ) of both semiconductors were systematically calculated. As illustrated in Figure 5a and 5b, the determined W f values for ZIS and Cu 2‒ x S are 4.07 eV and 5.1 eV, respectively, revealing a lower Fermi level position in Cu 2‒ x S relative to ZIS. This W f disparity drives spontaneous electron migration across the contact interface from ZIS to Cu 2‒ x S until Fermi level equilibration, consequently inducing band bending and establishing a built-in electric field at the Cu 2‒ x S/ZIS heterojunction. Based on comprehensive experimental and DFT analyses, the underlying photocatalytic mechanism was elucidated through structural, charge separation, and carrier transport perspectives, as schematically illustrated in Figure 5c and 5d. UV-vis DRS combined with M-S analysis verifies a staggered band alignment between ZIS and Cu 2‒ x S. The synergistic application of XPS analysis and DFT modeling demonstrated interfacial charge reorganization, where ZIS conduction band electrons transfer to Cu 2‒ x S’s CB, concomitant with hole migration from Cu 2‒ x S’s valence band to ZIS’s VB, thereby inducing an interfacial built-in potential (Figure 5c). This charge transfer mechanism facilitated the construction of a p-n junction photocatalyst (Figure 5d), where under visible-light irradiation (λ ≥ 420 nm), photoexcited electrons in the CB of Cu 2‒ x S diffuse to the CB of ZIS, preserving the more negative reduction potential of ZIS while increasing available electrons for water reduction. Concurrently, holes accumulated in the VB of Cu 2‒ x S are efficiently scavenged by TEOA, effectively suppressing charge recombination. Morphologically, the multi-level hierarchical hollow cubic structure (Figure 5e) enhances light absorption through multiple utilization of light reflection. Meanwhile, the large surface-to-volume ratio facilitates exposure of multiple catalytic centers, significantly promoting hydrogen evolution reactions. Moreover, the hierarchical integration and ultra-thin characteristics of hollow Cu 2‒ x S cubes and ZIS nanosheets shorten the charge transfer pathway to the catalytic surface, enabling the timely transfer of photogenerated electrons and holes and effectively promote the separation of photogenerated electron-hole pairs. Collectively, these synergistic mechanisms lead to marked enhancement in hydrogen evolution efficiency through optimized photocatalytic water splitting. The calculated work functions of ZIS. (b) The calculated work functions of Cu 2‒ x S. (c) The band structure diagram of the Cu 2- x S/ZIS p-n junction. (d) The band structure of the Cu 2- x S/ZIS p-n junction under illumination. (e) Schematic illustration of some advantages of the hierarchical hollow cube-in-cube structure for photocatalytic reaction. 4. Conclusions In conclusion, we developed a plasmon-enhanced p-n junction photocatalyst through controlled integration of p-type Cu 2‒ x S hollow cubes and n-type ZnIn 2 S 4 (ZIS) nanosheets via an in-situ hydrothermal growth protocol. The optimized heterostructure with 12 wt% Cu 2‒ x S loading demonstrates exceptional H 2 evolution reaction (HER) activity under visible light irradiation, achieving a record HER rate of 5.7 mmol·g⁻¹·h⁻¹ with apparent quantum efficiency of 11.4% at 420 nm. Through combined photoelectrochemistry tests, optical characterization and DFT calculations, we elucidate three synergistic enhancement mechanisms: 1) built-in electric field effects in p-n junctions promots the separation of photogenerated electron-hole pairs, accelerates their transfer and prolongs their lifetime, 2) LSPR excited hot-carrier increases carrier density and enhances the range of light absorption; 3) The multi-level hollow cubic structure utilizes light reflection to enhance light absorption, the large specific surface area provides abundant active sites, the hierarchical integration of hollow Cu 2‒ x S cubes and ZIS nanosheets, along with their ultrathin characteristics, shortens the charge transfer path to the catalytic surface, enabling timely transfer of photogenerated electrons and holes. This work establishes a new paradigm for photocatalytic H 2 generation through rational integration of interfacial engineering and plasmonic effects. Conflict of Interest The authors declare no conflict of interest. Acknowledgements This work was financially supported by the National Natural Science Foundation of China (No. 22205058), Natural Science Foundation of Henan Province (252300421709), Foundation of Henan University of Technology (No. 31401584, 2023BS051, 2023BS064, 2021BS024, 21421250) and Cultivation Project of Tuoxin Team in Henan University of Technology, China (No. 2024TXTD11). References [1] Photocatalytic chemoselective transfer hydrogenation of quinolines to tetrahydroquinolines on hierarchical NiO/In 2 O 3 –CdS microspheres. Y. Zhang, W. W. Yu, S. Cao, Z. Sun, X. W. Nie, Y. F. Liu, and Z. K. Zhao, ACS Catal. 2021 , 11 , 13408-13415 [2] Advances in Atomically Dispersed Catalysts for Water Splitting. Y. Q. Li, Y. B. Liu, M. Y. Guo, M. Y. Li, H. Hao, C. Y. Wang, L. X. Jin, C. B. Zhao, X. Z. Shao, and X. H. Yu, Adv. Funct. Mater. 2025 , 2425056. 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Collection Energy & Environmental Materials Keywords cu2‒xs/znin2s4 p-n junction photocatalytic h2 generation Authors Affiliations Yuan Liu Henan University of Technology View all articles by this author Jian Yu Henan University of Technology View all articles by this author Hangang Qiao Xinmi Industrial Development Promotion Center View all articles by this author Yuhan Zhao Henan Graphene New Material Technology Company Limited View all articles by this author Dongtao Zhang Henan University of Technology View all articles by this author Xiaojing Chu Zhengzhou University of Technology View all articles by this author Chuanqi Li Henan University of Technology View all articles by this author Chen Zhu 0009-0005-4668-9354 [email protected] Henan University of Technology View all articles by this author Metrics & Citations Metrics Article Usage 245 views 256 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Yuan Liu, Jian Yu, Hangang Qiao, et al. Construction of Sheet-on-Hollow Cube Cu2-xS/ZnIn2S4 p-n Heterojunction for Enhanced Visible-Light-Driven Photocatalytic Hydrogen Production. Authorea . 08 August 2025. DOI: https://doi.org/10.22541/au.175469404.44194621/v1 If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download. For more information or tips please see 'Downloading to a citation manager' in the Help menu . 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