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Review

Zinc Indium Sulfide Materials for Photocatalytic Hydrogen Production via Water Splitting: A Short Review

by
Lang Yao
1,†,
Shice Zeng
1,†,
Shuxiang Yang
2,
Honghua Zhang
1,
Yue Ma
3,
Guangying Zhou
1,4,5,* and
Jianzhang Fang
1,4,5,*
1
School of Environment, South China Normal University, Guangzhou 510006, China
2
School of Information and Optoelectronic Science and Engineering, South China Normal University, Guangzhou 510006, China
3
School of Chemistry, South China Normal University, Guangzhou 510006, China
4
Guangdong Provincial Key Laboratory of Chemical Pollution and Environmental Safety, South China Normal University, Guangzhou 510006, China
5
MOE Key Laboratory of Theoretical Chemistry of Environment, South China Normal University, Guangzhou 510006, China
*
Authors to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Catalysts 2025, 15(3), 271; https://doi.org/10.3390/catal15030271
Submission received: 30 January 2025 / Revised: 3 March 2025 / Accepted: 10 March 2025 / Published: 13 March 2025
(This article belongs to the Special Issue Recent Advances in Photo/Electrocatalytic Water Splitting)
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Abstract

:
Photocatalytic water splitting for hydrogen production is seen as a promising solution to energy problems due to its eco-friendly and sustainable properties, which have attracted considerable interest. Despite progress, the efficiency and selectivity of solar-driven photocatalytic hydrogen generation are still below optimal levels, making it a major challenge to effectively harness solar energy for hydrogen production through photocatalytic water splitting. Advancing high-performance semiconductor photocatalysts is seen as key to tackling this issue. Zinc indium sulfide (ZnIn2S4) has gained attention in recent years as a promising semiconductor material for photocatalytic hydrogen production, thanks to its advantageous properties. Studies in photocatalysis are shifting toward the continuous development and modification of materials, with the goal of enhancing efficiency and extending their applications in environmental and energy fields. With proper development, the material may eventually be suitable for large-scale commercial use. Recent studies have aimed at boosting the photocatalytic hydrogen evolution (PHE) efficiency of ZnIn2S4-based photocatalysts through a range of experimental techniques, including surface modifications, forming semiconductor heterojunctions, doping with metals and nonmetals, defect engineering, and particle size analysis. The purpose of this review is to explain the design strategies for ZnIn2S4-based photocatalysts through these approaches and to provide a thorough summary of the latest developments in their role as catalysts for hydrogen production.

1. Introduction

The Industrial Revolution’s emergence and the rapid development of science and technology have played a major role in making life more convenient for humans. This developmental path has, at the same time, contributed to and intensified energy shortages. With the rise of the Industrial Revolution and the swift pace of scientific and technological progress, energy consumption has become a critical concern, posing serious challenges to both the sustainable development of nations and the stability of societies [1,2,3]. Additionally, as the global population continues to grow, the increased demand has led to the overuse of traditional fossil fuels like natural gas and oil, making the energy shortage issue even more pressing [4,5,6]. With its endless supply, environmental benefits, and impressive efficiency, hydrogen energy is considered a leading contender among alternative energy sources to fulfill future energy needs. However, the majority of hydrogen production today relies on natural gas, coal, crude oil, or water electrolysis, all of which need substantial heat and electricity. Therefore, harnessing solar energy for photocatalytic hydrogen production is regarded as an attractive and practical method for tackling the worldwide energy crisis, offering a sustainable and eco-friendly option [7].
Water photolysis for hydrogen production is thermodynamically defined as a reaction that results in a rise in Gibbs free energy, requiring the overcoming of a notable energy barrier of approximately 273.13 kJ/mol [8]. It is widely accepted that for a photocatalyst to be effective in photocatalytic hydrogen production, the bottom of its conduction band must be more negative than the reduction potential of H+/H2 (0 V vs. NHE, pH = 0). At the same time, the top of the valence band should be more positive than the potential needed for the oxidation of H2O to produce O2 (1.23 V vs. NHE, pH = 0) [9]. These conditions ensure that the photocatalyst is capable of driving the essential redox reactions needed for efficient water splitting. Therefore, selecting catalytic materials that have the proper band gaps is essential for the efficiency of the photocatalytic hydrogen production process. From a kinetic viewpoint, after light at a specific wavelength is absorbed, photogenerated carriers migrate from the bulk of the semiconductor material to the surface, a process that spans different time scales and spatial dimensions. A key area of research is aimed at reducing the recombination of photogenerated carriers during this process to improve the quantum efficiency of photocatalysts. To overcome these issues, it is important to implement different modification techniques designed to increase visible light absorption, lower the recombination rate of photogenerated carriers, and decrease the potential barrier for the hydrogen evolution reaction [10,11,12,13,14]. Implementing these strategies is key to enhancing the performance of photocatalysts in hydrogen production and improving the performance of photocatalysts in hydrogen generation. Ternary metal sulfides have gained significant attention in recent years for their efficient photocatalytic hydrogen production under visible light, driven by their advantageous energy band structures and extensive surface areas [15,16,17]. ZnIn2S4, which fits the general formula AB2×4, displays a direct bandgap of approximately 2.5 eV among these materials. Moreover, ZnIn2S4 shows semiconductor characteristics, featuring a strong absorption coefficient and excellent photostability [18,19,20]. ZnIn2S4, an exciting ternary sulfide compound, offers significant economic advantages and environmental sustainability for a wide range of applications. The Earth’s crust contains large amounts of zinc, indium, and sulfur, which makes mining them relatively inexpensive. In contrast to costly precious metal catalysts, these elements are much more affordable, making them an attractive choice for a range of industrial applications. The role it plays in photocatalytic hydrogen production and the removal of pollutants underscores its sustainable potential [21]. Affordable modification methods and composite construction can improve its performance, positioning ZnIn2S4 as a promising option for advancing sustainable technologies to tackle environmental issues. While cadmium sulfide has been extensively studied, ZnIn2S4 stands out, consisting of eco-friendly elements and providing better physicochemical stability, enhanced durability, and a broader scope of potential applications in PHE. The unique properties of ZnIn2S4 position it as a highly promising material for the future of photocatalytic hydrogen production. Recently, there has been a noticeable shortage of comprehensive studies on ZnIn2S4-based photocatalyst systems for water splitting, highlighting an important gap in the development of these materials. The review begins by carefully exploring the intrinsic semiconductor characteristics of ZnIn2S4, with particular attention given to its polymorphic crystallographic structures and electronic band arrangements. Following this, a detailed review of ZnIn2S4-based photocatalytic systems for hydrogen evolution is presented, addressing key aspects including morphology, structural adjustments, doping techniques, vacancy introduction, heterojunction formation, and particle size optimization. In conclusion, the review examines the ongoing challenges and potential future directions while proposing possible solutions.

2. Fundamental Properties of ZnIn2S4

Density functional theory (DFT) calculations were conducted to gain insight into the electronic structures of the hexagonal and cubic ZnIn2S4. As observed in Figure 1a,b, the valence band of both phases is primarily influenced by the contributions of the Zn 3d and In 5s5p orbitals, with a minor contribution from the S 3p orbitals. The conduction band was primarily composed of In 5s and 5p orbitals, along with a marginal contribution from Zn 4s and 4p orbitals. The band structures presented in Figure 1c,d suggest that both materials are typical direct-band-gap semiconductors, a finding that aligns with the analysis of the UV–visible absorption spectra. The band gaps of hexagonal and cubic ZnIn2S4 were determined to be 0.28 eV and 1.36 eV, respectively, whereas the experimental values were 2.34 eV and 2.41 eV. In general, ZnIn2S4 is a semiconductor characterized by a layered structure, capable of crystallizing into three distinct polymorphic forms, namely, cubic, hexagonal, and rhombohedral lattices, as illustrated in Figure 1e–g [22]. The atomic arrangement within its layers follows a specific stacking sequence of S-Zn-S-In-S-In-S. The hexagonal polymorph of ZnIn2S4 can display various polytypes, characterized by either ABCA or ABAB stacking patterns for sulfur (S) atoms. Each crystal unit encompasses all constituent elements—zinc (Zn), indium (In), and sulfur (S). Within each unit, Zn atoms are tetrahedrally coordinated with S atoms, while In atoms are octahedrally coordinated with S atoms. The stacking of these structural units often leads to the formation of sulfur vacancies within the layers due to the relatively weak bonding between adjacent sulfur layers. Consequently, several polytypes are observed, including those with one packet, three packets, and twenty-four packets per unit cell, referred to as 1H, 3R, and 24R, respectively [23,24]. The cubic phase of ZnIn2S4, which adopts a spinel structure, features a typical ABC stacking of S atoms, with Zn atoms occupying tetrahedral interstices and In atoms exclusively located at octahedral interstices within the structure.

3. The Principles of H2 Generation via Water Splitting

Figure 2 illustrates the band gap and band edge positions of diverse semiconductor photocatalysts [25]. Among these, materials such as ZnS, Fe2O3, and WO3 have been extensively investigated for their applications in solar hydrogen production [26,27,28]. Nevertheless, despite certain exceptions observed in specific semiconductor photocatalysts, the majority exhibit limited efficiency under visible-light irradiation. Consequently, the development of photocatalysts capable of effectively harnessing solar energy remains a significant scientific challenge.
The ZnIn2S4 semiconductor photocatalyst exhibits an optimal crystal and band structure, which facilitates the achievement of efficient photocatalytic hydrogen evolution (PHE). A comprehensive understanding of the mechanistic details underlying the entire photocatalytic process, particularly PHE, is crucial for attaining high hydrogen production rates [29,30].

4. Hydrogen Generation of ZnIn2S4-Based Photocatalysts

4.1. Modification of ZnIn2S4

Morphology and structure engineering have been demonstrated to significantly enhance the photocatalytic performance of nanostructured photocatalysts [31]. This improvement can be attributed to several key factors: (1) an increase in specific surface area; (2) enhanced exposure of surface active sites for photocatalytic reactions [32,33]; (3) improved mass transportation and light absorption; and (4) accelerated charge carrier migration and suppression of charge recombination.
In their study, Shen et al. [34] synthesized ZnIn2S4 photocatalysts with distinct morphologies, namely self-organized nanospheres and rose-like microclusters, using a hydrothermal method. Specifically, ZnSO4·7H2O and In(NO3)3·4H2O, along with a double excess of thioacetamide (TAA), were dissolved in distilled water. The resulting mixed solution was transferred into a Teflon-lined autoclave and maintained at 160 °C for 24 h. After cooling to room temperature, a yellow precipitate was obtained, which was subsequently washed with ethanol and distilled water. The sample was then dried under vacuum at 80 °C to yield the final ZnIn2S4 product.
The morphology of ZnIn2S4 synthesized under aqueous-, methanol-, and ethylene glycol (EG)-mediated conditions was characterized using field-emission scanning electron microscopy (FESEM). As shown in Figure 3, the ZnIn2S4 prepared in aqueous conditions (ZIS-H2O) exhibited a flowering cherry, sphere-like structure composed of numerous petal-like ZnIn2S4 nanosheets. The observed growth tendency of lamellar structures is likely associated with the inherent layered characteristics of hexagonal ZnIn2S4. Aqueous-mediated ZnIn2S4 showed the highest crystallinity (micro-structure) among the three products, resulting in the most efficient photocatalytic hydrogen evolution under visible-light irradiation.

4.2. Heterojunctions of Photocatalysis

For single-component semiconductor photocatalysts, bulk and surface recombination are prevalent during the photocatalytic hydrogen evolution (PHE) process, as illustrated in the accompanying figure. Furthermore, the strong Coulombic interaction between photogenerated electron–hole pairs often causes electrons in the conduction band to recombine with holes in the valence band, resulting in significant charge recombination, as depicted in the figure. Consequently, the PHE performance of single semiconductor photocatalysts is typically limited by their low charge separation efficiency. To address these challenges, heterojunction photocatalysts, which integrate two or more semiconductors, have emerged as a promising strategy [35,36,37]. These systems not only broaden the light absorption range but also effectively suppress charge recombination, thereby enhancing PHE performance. In the case of ZnIn2S4-based photocatalysts, five primary types of heterojunctions have been identified based on their band structure alignment (as shown in Figure 4 [38]): type-I, type-II, p–n junctions, Z-scheme, and S-scheme heterojunctions. Each of these configurations offers unique mechanisms for optimizing charge separation and improving photocatalytic efficiency.

4.2.1. Type-I Heterojunction

The type-I heterojunction, composed of two semiconductors, is characterized by a straddling bandgap alignment. In this configuration, both the conduction band (CB) and valence band (VB) of semiconductor 1 are positioned at higher energy levels compared to those of semiconductor 2. Under light irradiation, photogenerated electrons and holes migrate from semiconductor 1 to semiconductor 2, accumulating on the latter. This charge accumulation enhances the density of photogenerated electrons, which can improve hydrogen evolution reaction (HER) performance [39,40]. However, a significant limitation of type-I heterojunctions is the ineffective separation of electron–hole pairs, as both electrons and holes accumulate on the same semiconductor. Additionally, the redox capability of type-I heterojunction photocatalysts is generally limited because redox reactions occur on the semiconductor with relatively lower redox potential. Consequently, although type-I heterojunctions facilitate charge separation, they are often unsuitable for achieving efficient photocatalytic hydrogen evolution (PHE) via water splitting.
For instance, Fan et al. synthesized a type-I FeIn2S4/ZnIn2S4 heterojunction photocatalyst, achieving a PHE rate of 4.21 mmol·g−1·h−1, which is nearly six times higher than that of pure ZnIn2S4 [41]. As presented in Figure 5, the enhanced PHE performance of the FeIn2S4/ZnIn2S4 heterojunction is attributed to the giant interfacial electric field (IEF) generated by the Fermi level difference between ZnIn2S4 (ZIS) and FeIn2S4 (FIS). This IEF promotes efficient charge separation and transfer at the type-I interface. Furthermore, the electrons separated on FIS provide numerous surface reaction active sites, facilitating effective electron injection into the aqueous solution and significantly boosting photocatalytic hydrogen generation activity.

4.2.2. Type-II Heterojunction

In type-II heterojunctions, a staggered bandgap alignment is established between the two constituent semiconductors, which is highly advantageous for facilitating efficient charge transfer. During the photocatalytic hydrogen evolution (PHE) process, photogenerated electrons in the conduction band (CB) of semiconductor 1 migrate to the conduction band of semiconductor 2, while photogenerated holes in the valence band (VB) of semiconductor 2 transfer to the valence band of semiconductor 1. This “double transfer route” of charge carriers significantly enhances the separation efficiency of photogenerated electron–hole pairs [42,43]. Additionally, the presence of an internal electric field within the type-II heterojunction substantially prolongs the lifetime of photogenerated electrons, further improving the overall photocatalytic performance.
Ye et al. synthesized a type-II heterojunction In2S3/ZnIn2S4 photocatalyst, achieving a photocatalytic hydrogen evolution (PHE) rate of 5690 μmol·g−1·h−1, which is 8.4 times higher than that of pure ZnIn2S41 [44]. As demonstrated in Figure 6, the enhanced PHE performance of the In2S3/ZnIn2S4 heterojunction is attributed to the formation of a type-II band alignment between In2S3 (INS) and ZnIn2S4 (ZIS). This configuration significantly improves the efficiency of photogenerated carrier separation and extends the range of visible light absorption, thereby enhancing the overall photocatalytic activity.

4.2.3. p–n Junction

The combination of p-type and n-type semiconductors to form a p–n junction creates an additional built-in electric field, which facilitates the efficient transfer of electron–hole pairs and enhances photocatalytic hydrogen evolution (PHE) performance. In p-type semiconductors, the Fermi level (EF) is located near the valence band (VB), while, in n-type semiconductors, it is positioned close to the conduction band (CB). Upon the formation of a p–n junction, electrons diffuse from the p-type semiconductor to the n-type semiconductor, resulting in the accumulation of negative charge species in the p-type region. Simultaneously, holes migrate from the n-type semiconductor to the p-type semiconductor, leading to the accumulation of positive charge species in the n-type region. When the Fermi level system reaches equilibrium, the diffusion of electron–hole pairs ceases, and a stable inner electric field is established at the interface between the n-type and p-type semiconductors [45,46].
Compared to type-II heterojunctions, p–n junctions are more effective in achieving the separation of photogenerated electron–hole pairs due to the presence of this inner electric field. This enhanced charge separation capability makes p–n junctions a promising strategy for improving the efficiency of photocatalytic systems. Guo et al. designed and prepared an efficient ZnIn2S4@CuInS2 microfluidic core–shell, p–n heterojunction using a two-step hydrothermal method [47]. As presented in Figure 7, The results show that the marigold-like microspheres of the ZnIn2S4@CuInS2 heterojunction consist of thin nanosheets with high lattice matching and a large interfacial contact area, which promotes charge separation and transfer for solar hydrogen production. In addition, the close interfacial contact between n-type ZnIn2S4 and p-type CuInS2 forms a unique p–n heterojunction, which further promotes charge separation due to the built-in electric field. As a result, among all the prepared photocatalysts, the ZnIn2S4@CuInS2 photocatalyst containing 5 atomic % CuInS2 showed the highest hydrogen yield for H2 evolution (1168 μmol−1g−1), which is nearly four times higher than that of the pristine ZnIn2S4.

4.2.4. S-Scheme Heterojunction Photocatalysts

Xie et al. synthesized a S-scheme heterojunction ZnIn2S4/ZnO photocatalyst using a one-step solvothermal method, achieving a photocatalytic hydrogen evolution (PHE) rate of 3036 μmol·g−1·h−1, which is five times higher than that of pure ZnIn2S4 [48]. In this system, electrons are transferred from ZnIn2S4 to ZnO through hybridization, resulting in the formation of an interfacial electric field (IEF) directed from ZnIn2S4 to ZnO. The enhanced PHE performance of the ZnIn2S4/SnS2 heterojunction is attributed to the formation of a step-scheme (S-scheme) heterojunction at the interface of ZnIn2S4 and SnS2. Figure 8a illustrates a significant enhancement in the photocurrent of the 2ZnIn2S4/ZnO heterojunction, demonstrating a strong photocurrent response. Meanwhile, it can be shown from Figure 8b that, among all photocatalysts, the EIS Nyquist diagram of the 2ZnIn2S4/ZnO heterojunction photocatalyst has minimum arc radius, manifesting that better current migration occurs at the 2ZnIn2S4/ZnO heterojunction interface. As shown in Figure 8c,d, the photocatalytic properties of bare ZnO and ZnIn2S4 are relatively limited. The hydrogen evolution rates of pure ZnO and ZnIn2S4 are 29 and 3528 μmol⋅g−1h−1, respectively, when ethanol is used as the sacrificial reagent, and approximately 0 and 603 μmol⋅g−1h−1 in water. However, when ZnO and ZnIn2S4 are combined to form heterostructures, their photocatalytic performance improves significantly. The photocatalytic hydrogen evolution (PHE) activity of the 2ZnIn2S4/ZnO heterostructure is optimal, with an average PHE rate of 13,638 and 3036 μmol⋅g−1h−1, with or without the sacrificial reagent. This performance is approximately 470 and 3036 times higher than that of pure ZnO and about four and five times greater than that of ZnIn2S4, respectively. Moreover, as demonstrated in Figure 8e, the amount of H2 evolution for the 2ZnIn2S4/ZnO heterojunction composite material remains largely unaffected, with no substantial decrease in photocatalytic activity after four cycles. Furthermore, the wavelength-dependent apparent quantum efficiencies (AQEs) of the 2ZnIn2S4/ZnO heterojunction photocatalyst were evaluated (Figure 8f). The variation in AQEs for 2ZnIn2S4/ZnO corresponds closely with the trends observed in the optical absorption spectrum. The AQE values of 2ZnIn2S4/ZnO are 39.32% at 365 nm, 5.85% at 420 nm, 0.80% at 450 nm, 1.11% at 500 nm, and 0.33% at 550 nm, respectively. Experimental findings revealed that after hybridization, ZnIn2S4 undergoes a bend in its energy band due to electron depletion, while ZnO experiences a bending of its energy band, attributed to electron accumulation. As presented in Figure 8g–i, this results in the formation of an IEF that extends from ZnIn2S4 to ZnO. Additionally, under the influence of light and excitation, the electrons of the conduction band of ZnO migrate to the VB of ZnIn2S4 under the action of the IEF, which complexes with the hole; moreover, the VB of ZnO retains the strongly oxidizing hole, and the CB of ZnIn2S4 retains the strongly reducing electron. The oxygen generation occurs in the valence band of ZnO, while hydrogen production occurs in the conduction band of ZnIn2S4, enabling the spatial isolation of these processes. These results demonstrate that 2ZnIn2S4/ZnO exhibits excellent light absorption and utilization capabilities. Above all, this S-scheme configuration significantly promotes the separation of electron–hole (e−–h+) pairs, thereby improving the overall photocatalytic efficiency.

4.2.5. Z-Scheme Heterojunction Photocatalysts

In 2021, Zuo et al. reported the in situ synthesis of a TiO2-ZnIn2S4 heterostructure [49]. Ultrathin TiO2 nanosheets (NSs) were synthesized using a modified hydrothermal method. To prepare the composite, varying amounts of TiO2 NSs were dispersed into a glycerol aqueous solution (60 mL, 20 v%, pH = 2). Subsequently, InCl3·4H2O (1.2 mmol), ZnCl2 (1.2 mmol), and thioacetamide (3.2 mmol) were sequentially added to the solution under continuous stirring. The reaction mixture was then heated in an oil bath at 80 °C for 2 h. After cooling, the solid product was washed three times with deionized water and ethanol and dried under vacuum at 60 °C. The synthesized materials were labeled as TNZIS-Y, where Y represents the amount of TiO2 NSs added (10, 30, 50, 80, and 120 mg). As illustrated in Figure 9a–j, High-resolution transmission electron microscopy (HRTEM) analysis of a series of prepared catalysts revealed three distinct crystal lattices corresponding to TiO2 (101), ZnIn2S4 (102), and ZnIn2S4 (108). The coexistence of these lattices and the clear heterojunction interface confirm the formation of a tightly integrated heterojunction between TiO2 and ZnIn2S4 in TNZIS-50. The photocatalytic hydrogen generation (PHG) activity of the prepared materials was evaluated in a mixed solution of water and triethanolamine under UV–vis light irradiation without the use of any cocatalyst. TNZIS-50 exhibited exceptional PHG efficiency, achieving a rate of 18,077.2 μmol·g−1·h−1.
Based on theoretical predictions and experimental data, a direct Z-scheme heterojunction (DZH) mechanism was proposed for the TiO2-ZnIn2S4 system. As demonstrated in Figure 9k, When TiO2 and ZnIn2S4 are combined, the difference in their work functions (Φ) and Fermi levels (EF) induces the formation of an interfacial electric field (IEF) and energy band bending. Under photoexcitation, electrons in both TiO2 and ZnIn2S4 are excited to their respective conduction bands (CB). Due to the interfacial IEF and band bending, the photoexcited electrons in the CB of TiO2 spontaneously transfer to the valence band (VB) of ZnIn2S4, where they recombine with the residual holes. This DZH mechanism not only avoids charge recombination at the electron mediator but also ensures efficient separation of photogenerated electron–hole pairs, thereby enhancing redox properties. These improvements contribute to the superior photocatalytic activity of the heterostructure in various applications.

4.3. Metal and Non-Metal-Doped ZnIn2S4

Among the various strategies employed to enhance the photocatalytic hydrogen production capability of ZnIn2S4, doping with metallic and non-metallic elements has proven to be an effective approach. Metal doping, in particular, can modulate the electronic structure of ZnIn2S4, improve surface dynamics, accelerate the transfer of photogenerated electrons, and provide additional active sites, thereby enhancing photocatalytic hydrogen production [50,51]. Furthermore, the spatial distribution and particle size of the doped metal can be precisely controlled to maximize light absorption and provide sufficient active sites for catalytic reactions. In 2022, Sun et al. reported the development of Pd-doped ZnIn2S4 as a visible light-activated photocatalyst for water splitting [52]. Under visible light irradiation, two-dimensional (2D) hexagonal ZnIn2S4 (ZIS) modified with Pd single atoms (Pd0.03/ZIS) demonstrated the ability to split pure water without the need for a sacrificial agent, simultaneously generating H2 and H2O2. The incorporation of Pd single atoms facilitated the transfer of photogenerated electrons, enhancing the separation of electron–hole pairs and significantly improving photocatalytic performance for pure water splitting (Figure 10a–f). Meanwhile, as shown in Figure 10g–i, the Pd0.03/ZIS photocatalyst achieved remarkable H2 and H2O2 yields of 1037.9 and 1021.4 μmol·g−1·h−1, respectively, surpassing the performance of most known photocatalytic water-splitting catalysts. In contrast, pristine ZIS exhibited a H2 yield of only 50.3 μmol·g−1·h−1. The H2 yield of Pd0.03/ZIS was approximately 20 times higher than that of ZIS, highlighting the significant role of Pd single atoms in promoting photocatalytic pure water decomposition. This study provides a novel approach for designing efficient catalysts for overall water splitting, offering new insights into the development of advanced photocatalytic systems. Non-metallic doping is a highly effective strategy for modifying the electronic structure of ZnIn2S4 and enhancing its photocatalytic performance by optimizing the reaction surface. When ZnIn2S4 is doped with non-metallic elements, the photocatalyst is significantly improved by reducing the rate of charge recombination induced by light absorption and accelerating charge mobility, thereby increasing hydrogen (H2) production efficiency. In addition, theoretical calculations play an important role in revealing the mechanism of the materials in photocatalytic hydrogen production applications. In 2022, Wei-Kean Chong et al. reported the doping of ZnIn2S4 with non-metallic phosphorus (P) [53]. Through their DFT study, they showed in detail that substituting phosphorus for sulfur (S) atoms in the ZnIn2S4 structure resulted in the most stable P-ZnIn2S4 configuration. This doping led to a reduction in bandgap energy, an upward shift of the valence band maximum (VBM), an increase in electron density near the VBM, and a decrease in the H+ adsorption–desorption barrier. These changes were critical for enhancing the hydrogen evolution reaction (HER). In 2025, Zeng et al. explored the synergistic enhancement of photocatalytic hydrogen production using nitrogen (N)-doped ZnIn2S4 (N-ZIS) in combination with tungstophosphoric acid (TPA) [54]. Although N-ZIS formed a heterojunction structure with TPA, the N doping itself significantly boosted the catalytic effect. The photocatalytic hydrogen production rate of 1N-ZIS reached 5940.08 μmol·g−1·h−1, which is 2.75 times higher than that of pristine ZIS (2159.22 μmol·g−1·h−1). Upon forming the composite, W6+ in TPA was partially reduced to W4+, resulting in the coexistence of W6+ and W4+. This confirmed the interfacial electron transfer from N-ZIS to TPA, facilitated by the W6+/W4+ redox pair. The close contact between N-ZIS and TPA, along with the built-in electric field, enabled highly efficient charge transfer and separation. The photocatalytic hydrogen production rate of the N-ZIS/TPA-15 composite reached an impressive 17,345.53 μmol·g−1·h−1. This rate was 2.92 times higher than that of N-ZIS (5940.08 μmol·g−1·h−1) and 8.03 times higher than that of pristine ZIS (2159.22 μmol·g−1·h−1) under the same test conditions. These findings provide new insights into the design of efficient photocatalysts for hydrogen production and overall water splitting, highlighting the potential of non-metallic doping and heterojunction engineering in advancing photocatalytic technologies.

4.4. Vacancy Introducing

In the year 2024, Zhang et al. documented the synthesis of untreated ZIS microspheres, denoted as ZIS, employing a self-templated strategy [55]. The creation of (InS)v was subsequently achieved through treatments with hydrazine hydrate. By meticulously regulating the volume of hydrazine hydrate, the concentrations of (InS)v within the treated specimens, labeled as ZIS-x (where x = 5, 10, 15, indicating the milliliters of hydrazine hydrate utilized), were systematically varied. A distinct EPR signal at 2.004, associated with S vacancies, was detected in each ZIS sample. It is well-established that three critical factors influence the photocatalytic performance of semiconductors: light absorption capacity, charge separation efficiency, and surface redox reactivity. As shown in Figure 11A, the ZIS-10 exhibits the highest current and onset potential among all the samples, suggesting that it possesses the greatest hydrogen evolution activity, likely due to the extensive exposure of [In-S]6 octahedra. This finding implies that the [In-S]6 octahedra may serve as the active sites for hydrogen evolution. As can be seen from Figure 11B–D, density functional theory (DFT) calculations were performed to further elucidate the mechanism behind the enhanced hydrogen evolution activity. The free energy (ΔGH*) for hydrogen adsorption was calculated, which is widely recognized as a key descriptor for HER catalysts. The HER process is generally understood to involve three main steps: (i) the adsorption of a proton (H+) and its combination with an electron (e−), (ii) the formation of the active intermediate H*, and (iii) the release of molecular hydrogen. It is commonly accepted that when the optimal value of ΔGH* is close to thermoneutral, i.e., ΔGH* ≈ 0, the catalyst is generally considered ideal for HER. The ΔGH* of pristine ZIS is as high as 1.13 eV (corresponding to the structure of H* adsorbed on the S atom of the [In-S]4 tetrahedron), indicating an unfavorable and weak adsorption of H*. In contrast, the exposed In and S atoms in defective ZIS may act as active sites for HER. DFT calculations revealed that the ΔGH* sharply decreases to −0.26 eV when the In atom is exposed following tetrahedral vacancy formation as the active site. Additionally, a nearly zero ΔGH* ~0.05 eV was calculated for the S atom on the [In-S]6 octahedron as the active site. The DFT calculation results clearly demonstrate that reaction sites with higher activity can be created with (InS)v by optimizing ΔGH*.

4.5. Size Dependent ZnIn2S4

Understanding quantum-confined electronic properties and interfacial charge transfer in nanostructured systems is crucial for developing functional materials, enhancing energy conversion technologies, and paving the way for next-generation sustainable energy solutions that address global energy challenges. In 2024, Andreou et al. conducted extensive investigations into the size-dependent electronic and catalytic properties of these frameworks [56]. They explored how variations in nanocrystal size influence band edge positions and charge-transfer kinetics, employing both spectroscopic and electrochemical methods (Figure 8a–g). The findings highlight the critical role that nanocrystal size plays in tailoring the materials’ functionality, paving the way for optimized applications in fields such as photocatalysis and energy conversion. This work not only contributes to the understanding of nanocrystal behavior but also opens new avenues for the design of advanced materials with enhanced performance characteristics. The 1/CSC2−E plots show that ZIS samples exhibit n-type semiconductor behavior, confirmed by their positive slopes during analysis (Figure 12a). Figure 12b effectively illustrates the key concept discussed, namely, the systematic variation of band edges, EFB and EVB, with a nanocrystal size that reveals that shifts in band-edge positions stem from the limited number of electron wave functions. This reduction significantly impacts the density of states in conduction and valence bands, highlighting the influence of particle size reduction on electronic properties. The discretization of energy levels within electronic states in the band structure significantly widens the bandgap, influencing the behavior of semiconductors. In ZIS nanocrystals, size reduction further enhances interfacial charge-transfer kinetics and charge separation rates. This improvement is crucial for the efficiency of photogenerated carriers, facilitating their roles in water-splitting reactions. Consequently, optimizing these factors can lead to advancements in sustainable energy technologies and enhanced photocatalytic performance (Figure 12c–f). The UV−vis spectra in Figure 12g reveal that as the diameter of nanoparticles decreases from 12 nm to 4 nm, the bandgap absorption significantly increases from approximately 2.66 eV to 2.80 eV, indicating enhanced optical absorption properties. The energy gap shift in semiconductor systems arises from size-induced quantum confinement transitions, similar to those observed in individual quantum dots and clusters, highlighting unique nanoscale properties. The study of ultrasmall nanocrystals reveals that surface sulfur vacancies significantly affect charge transfer and separation rates. These vacancies lead to increased carrier recombination losses, resulting in reduced photocurrent and diminished photocatalytic activity, ultimately impacting their efficiency in applications. Mesoporous ensembles composed of 6 nm-sized ZIS nanocrystals (NCs) demonstrate remarkable photocatalytic hydrogen evolution performance. This efficiency stems from their short diffusion path for charge carriers, high donor density, and minimized charge recombination. Achieving a rate of 7.8 mmol h−1 gcat−1 H2, these ensembles maintain consistent performance without significant decay over 15 h of operation (Figure 12h,i).

5. Summary and Perspectives

Photocatalysis is emerging as a crucial technology, with substantial potential for combating environmental pollution and enabling the sustainable generation of hydrogen through water splitting. Photocatalytic reactions have garnered considerable attention in recent years as an effective solution to hydrogen production, with extensive studies focusing on ZnIn2S4-based photocatalysts across various areas of science. A key challenge impeding the efficiency of ZnIn2S4-based photocatalysis is the rapid recombination of electron–hole pairs generated by light, which slows down the overall rate of hydrogen production. Several approaches have been explored to resolve this issue, including structural modifications, the creation of heterojunctions, and doping with either metals or non-metals. Table 1 provides an overview of the literature on photocatalytic hydrogen generation using ZnIn2S4-based materials. This review examines the strategic design of photocatalysts aimed at enhancing hydrogen production through various approaches.
This review focuses on the strategic design of photocatalysts intended to improve hydrogen production efficiency using various methods. Moreover, progress in ZnIn2S4-based photocatalysts is anticipated to lead to considerable enhancements in their performance. In this report, we highlight the recent advancements in ZnIn2S4-based materials for hydrogen production, focusing on their improved photocatalytic activity, performance evaluation, and overall importance. We hope this work will serve as a useful resource to inspire and guide future research in the development of advanced photocatalytic systems.

Author Contributions

Conceptualization, G.Z. and J.F.; methodology, S.Z., L.Y., and H.Z.; validation, S.Z. and H.Z.; investigation; resources, S.Y. and Y.M.; data curation, S.Z. and S.Y.; writing—original draft preparation, S.Z., H.Z., and L.Y.; writing—review and editing, S.Z., L.Y., and S.Y.; visualization, H.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

Data sharing is not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. The DOS of (a) hexagonal ZnIn2S4 and (b) cubic ZnIn2S4. The calculated band structures of (c) hexagonal ZnIn2S4 and (d) cubic ZnIn2S4. Crystal structures of (e) hexagonal; (f) cubic and (g) rhombohedral ZnIn2S4. Reprinted with permission from ref [22]. Copyright (2011), Elsevier.
Figure 1. The DOS of (a) hexagonal ZnIn2S4 and (b) cubic ZnIn2S4. The calculated band structures of (c) hexagonal ZnIn2S4 and (d) cubic ZnIn2S4. Crystal structures of (e) hexagonal; (f) cubic and (g) rhombohedral ZnIn2S4. Reprinted with permission from ref [22]. Copyright (2011), Elsevier.
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Figure 2. An illustration showing the band-gap energies of several representative semiconductor photocatalysts. Reprinted with permission from ref [25]. Copyright (2022), Wiley.
Figure 2. An illustration showing the band-gap energies of several representative semiconductor photocatalysts. Reprinted with permission from ref [25]. Copyright (2022), Wiley.
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Figure 3. FESEM images of ZnIn2S4 prepared in (a,b) aqueous-, (c,d) methanol-, and (e,f) ethylene glycol-mediated conditions. Reprinted with permission from ref. [34] Copyright (2008), Elsevier.
Figure 3. FESEM images of ZnIn2S4 prepared in (a,b) aqueous-, (c,d) methanol-, and (e,f) ethylene glycol-mediated conditions. Reprinted with permission from ref. [34] Copyright (2008), Elsevier.
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Figure 4. Schematic illustration of electron–hole pairs transfer in (A) type-I, (B) type-II, (C) Z-scheme, (D) p–n, (E) S-scheme (RP: reduction photocatalyst; OP: oxidation photocatalyst) and (F) co-catalyst deposition-based heterojunctions. PC 1 and PC 2 represent photocatalyst 1 and photocatalyst 2, respectively. Reprinted with permission from ref. [38] Copyright (2011), Elsevier.
Figure 4. Schematic illustration of electron–hole pairs transfer in (A) type-I, (B) type-II, (C) Z-scheme, (D) p–n, (E) S-scheme (RP: reduction photocatalyst; OP: oxidation photocatalyst) and (F) co-catalyst deposition-based heterojunctions. PC 1 and PC 2 represent photocatalyst 1 and photocatalyst 2, respectively. Reprinted with permission from ref. [38] Copyright (2011), Elsevier.
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Figure 5. The formation of FIS@ZIS heterojunction photocatalyst and the proposed charge transfer mechanism. Reprinted with permission from ref. [41] Copyright (2024), Elsevier.
Figure 5. The formation of FIS@ZIS heterojunction photocatalyst and the proposed charge transfer mechanism. Reprinted with permission from ref. [41] Copyright (2024), Elsevier.
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Figure 6. Photocatalytic reaction mechanism diagram. Reprinted with permission from ref. [44] Copyright (2024), Elsevier.
Figure 6. Photocatalytic reaction mechanism diagram. Reprinted with permission from ref. [44] Copyright (2024), Elsevier.
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Figure 7. Schematic diagrams of formation of p–n junction and proposed charge separation process in the ZIS@CIS core–shell photocatalysts under visible-light irradiation [47]. Reprinted with permission from ref. Copyright (2020), American Chemical Society.
Figure 7. Schematic diagrams of formation of p–n junction and proposed charge separation process in the ZIS@CIS core–shell photocatalysts under visible-light irradiation [47]. Reprinted with permission from ref. Copyright (2020), American Chemical Society.
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Figure 8. Transient photocurrent responses (a) and EIS spectra (b) of ZnO, ZnIn2S4, and 2ZnIn2S4/ZnO samples. PHE performances of the photocatalysts (c) ZnO, ZnIn2S4, and the heterojuctions; (d) PHE rates of ZnIn2S4, ZnO, and the heterojunctions; (e) cyclic stability test of 2ZnIn2S4/ZnO under Xenon lamp irradiation; (f) AQE diagram of 2ZnIn2S4/ZnO at different wavelengths; (g–i) schematic diagram of IEF-induced S-scheme mechanism of ZnIn2S4/ZnO heterojunction for PHE under full-light irradiation. Reprinted with permission from ref. [48] Copyright (2023), Elsevier.
Figure 8. Transient photocurrent responses (a) and EIS spectra (b) of ZnO, ZnIn2S4, and 2ZnIn2S4/ZnO samples. PHE performances of the photocatalysts (c) ZnO, ZnIn2S4, and the heterojuctions; (d) PHE rates of ZnIn2S4, ZnO, and the heterojunctions; (e) cyclic stability test of 2ZnIn2S4/ZnO under Xenon lamp irradiation; (f) AQE diagram of 2ZnIn2S4/ZnO at different wavelengths; (g–i) schematic diagram of IEF-induced S-scheme mechanism of ZnIn2S4/ZnO heterojunction for PHE under full-light irradiation. Reprinted with permission from ref. [48] Copyright (2023), Elsevier.
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Figure 9. FESEM images of (a) TNZIS-10, (b) TNZIS-30, (c,f) TNZIS-50, (d) TNZIS-80, and (e) TNZIS-120. (g–i) TEM images of TNZIS-50. (j) SEM EDX element (Ti, O, Zn, In, and S) mappings of TNZIS-50. (k) Schematic illustration for the reaction mechanism of PWS over direct Z-scheme TNZIS heterojunction. Reprinted with permission from ref. [49] Copyright (2021), Elsevier.
Figure 9. FESEM images of (a) TNZIS-10, (b) TNZIS-30, (c,f) TNZIS-50, (d) TNZIS-80, and (e) TNZIS-120. (g–i) TEM images of TNZIS-50. (j) SEM EDX element (Ti, O, Zn, In, and S) mappings of TNZIS-50. (k) Schematic illustration for the reaction mechanism of PWS over direct Z-scheme TNZIS heterojunction. Reprinted with permission from ref. [49] Copyright (2021), Elsevier.
Catalysts 15 00271 g009
Catalysts 15 00271 g010
Figure 10. (a) UV–vis diffuse reflectance spectra for ZIS and Pd0.03/ZIS. Insets are the real pictures of ZIS (left) and Pd0.03/ZIS (right). (b) Schematic illustration of the band structures of ZIS and Pd0.03/ZIS. (c) PL spectra of ZIS and Pd0.03/ZIS (excited at 363 nm). (d) Transient photocurrent responses of ZIS and Pd0.03/ZIS with and without light irradiation. (e) EIS curves of ZIS and Pd0.03/ZIS with and without light irradiation. Inset is the corresponding equivalent circuit. (f) TRPL decay spectra of ZIS and Pd0.03/ZIS. (g) Photocatalytic H2 evolution activities of ZIS, Pd0.03/ZIS and Pd NP/ZIS under simulated sunlight irradiation (AM 1.5G). (h) Photocatalytic pure water splitting over Pd0.03/ZIS under simulated sunlight irradiation (300 W Xenon lamp, AM 1.5G) in 3 h. (i) Photocatalytic pure water splitting over ZIS and Pd0.03/ZIS under simulated sunlight irradiation (300 W Xenon lamp, AM 1.5G) and visible light irradiation (300 W Xenon lamp, λ > 420 nm). Reprinted with permission from ref. [52] Copyright (2023), Springer.
Figure 10. (a) UV–vis diffuse reflectance spectra for ZIS and Pd0.03/ZIS. Insets are the real pictures of ZIS (left) and Pd0.03/ZIS (right). (b) Schematic illustration of the band structures of ZIS and Pd0.03/ZIS. (c) PL spectra of ZIS and Pd0.03/ZIS (excited at 363 nm). (d) Transient photocurrent responses of ZIS and Pd0.03/ZIS with and without light irradiation. (e) EIS curves of ZIS and Pd0.03/ZIS with and without light irradiation. Inset is the corresponding equivalent circuit. (f) TRPL decay spectra of ZIS and Pd0.03/ZIS. (g) Photocatalytic H2 evolution activities of ZIS, Pd0.03/ZIS and Pd NP/ZIS under simulated sunlight irradiation (AM 1.5G). (h) Photocatalytic pure water splitting over Pd0.03/ZIS under simulated sunlight irradiation (300 W Xenon lamp, AM 1.5G) in 3 h. (i) Photocatalytic pure water splitting over ZIS and Pd0.03/ZIS under simulated sunlight irradiation (300 W Xenon lamp, AM 1.5G) and visible light irradiation (300 W Xenon lamp, λ > 420 nm). Reprinted with permission from ref. [52] Copyright (2023), Springer.
Catalysts 15 00271 g010
Catalysts 15 00271 g011
Figure 11. (A) LSV of ZIS, ZIS-5, ZIS-10, and ZIS-15, respectively. The optimized structures of (B) original ZIS and (C) defective ZIS. (D) Hydrogen adsorption free energy of original ZIS and defective ZIS samples. Reprinted with permission from ref. [55] Copyright (2024), Elsevier.
Figure 11. (A) LSV of ZIS, ZIS-5, ZIS-10, and ZIS-15, respectively. The optimized structures of (B) original ZIS and (C) defective ZIS. (D) Hydrogen adsorption free energy of original ZIS and defective ZIS samples. Reprinted with permission from ref. [55] Copyright (2024), Elsevier.
Catalysts 15 00271 g011
Catalysts 15 00271 g012
Figure 12. (a) Mott−Schottky plots and (b) energy band diagrams (ECB: conduction band energy, EVB: valence band energy, EF: Fermi level, H+/H2redox potential) of different ZIS catalysts. (c) Open circuit potential versus elapsed time for mesoporous n-ZIS NCFs under switching on/off AM1.5G illumination (10 s light on). The inset shows the change of the VOC at the catalyst/liquid interface under chopped illumination; when the light is switched on, a charge accumulation occurs at the interface of ZIS NCs, mitigating the surface band bending. (d) EIS Nyquist plots (Inset: equivalent Randles circuit model), (e) time-resolved PL decay spectra under 375 nm laser pulse excitation (Inset: magnified view of the PL decayspectra), and (f) transient photocurrent spectra under the applied bias of −1 V (100 W visible-light-emitting diode) of the mesoporous n-ZIS NCFs and polycrystalline bulk ZIS catalysts. In panels (a,d,e), the red lines are fit to the experimental data. (g) UV−vis absorption spectra and (inset) the corresponding Tauc. (h) Photocatalytic H2 generation rates of different ZIS catalysts under nonoptimized conditions (1 mg mL−1 catalyst in 0.35 M Na2S/0.25M Na2SO3 aqueous solution; λ ≥ 380 nm light irradiation; 20 ± 2 °C). (i) Time-dependent hydrogen evolutions (lines) and average H2-production rates (column) at the course of the photocatalytic stability studies over 6-ZIS NCF catalyst. Reprinted with permission from ref. [56] Copyright (2024), American Chemical Society.
Figure 12. (a) Mott−Schottky plots and (b) energy band diagrams (ECB: conduction band energy, EVB: valence band energy, EF: Fermi level, H+/H2redox potential) of different ZIS catalysts. (c) Open circuit potential versus elapsed time for mesoporous n-ZIS NCFs under switching on/off AM1.5G illumination (10 s light on). The inset shows the change of the VOC at the catalyst/liquid interface under chopped illumination; when the light is switched on, a charge accumulation occurs at the interface of ZIS NCs, mitigating the surface band bending. (d) EIS Nyquist plots (Inset: equivalent Randles circuit model), (e) time-resolved PL decay spectra under 375 nm laser pulse excitation (Inset: magnified view of the PL decayspectra), and (f) transient photocurrent spectra under the applied bias of −1 V (100 W visible-light-emitting diode) of the mesoporous n-ZIS NCFs and polycrystalline bulk ZIS catalysts. In panels (a,d,e), the red lines are fit to the experimental data. (g) UV−vis absorption spectra and (inset) the corresponding Tauc. (h) Photocatalytic H2 generation rates of different ZIS catalysts under nonoptimized conditions (1 mg mL−1 catalyst in 0.35 M Na2S/0.25M Na2SO3 aqueous solution; λ ≥ 380 nm light irradiation; 20 ± 2 °C). (i) Time-dependent hydrogen evolutions (lines) and average H2-production rates (column) at the course of the photocatalytic stability studies over 6-ZIS NCF catalyst. Reprinted with permission from ref. [56] Copyright (2024), American Chemical Society.
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Table 1. Photocatalytic H2 generation of ZnIn2S4-based materials.
Table 1. Photocatalytic H2 generation of ZnIn2S4-based materials.
EntryTypeMass of PhotocatalystSacrificial AgentLight SourceH2 Generation RateReference
1Aqueous-mediated ZnIn2S4200 mgNa2SO3/Na2S300 W Xenon lamp27.3 μmol h−1 [33]
2FIS@ZIS25 mgNa2S/Na2SO3300 W Xenon lamp4.21 mmol h−1 g−1[41]
3In2S3/ZnIn2S410 mg10 vol% TEOA300 W Xe lamp, λ > 420 nm5.69 mmol h−1 g−1[44]
4ZnIn2S4@CuInS250 mgNa2S/Na2SO3300 W Xenon lamp1168 μmol·g−1[47]
52ZnIn2S4/ZnO20 mgNone 300 W Xe lamp3.036 mmol h−1 g−1[48]
6TiO2-ZnIn2S420 mgNone300 W Xe lamp214.9 μmol h−1 g−1[49]
7Pd0.03/ZIS20 mgNone300 W Xenon lamp, AM 1.5 G1037.9 μmol h−1 g−1[52]
8N-ZIS/TPA10 mg0.1 M
ascorbic acid		300 W Xe lamp, λ > 420 nm17,345.53 μmol h−1 g−1[54]
9ZIS-105 mg0.05 M ascorbic acid300 W Xe lamp (λ > 420 nm)10.7 mmol h−1 g−1[55]
106-ZIS NCF30 mg10% v/v TEA300 W Xe lamp 7.8 mmol h−1 g−1[56]
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Yao, L.; Zeng, S.; Yang, S.; Zhang, H.; Ma, Y.; Zhou, G.; Fang, J. Zinc Indium Sulfide Materials for Photocatalytic Hydrogen Production via Water Splitting: A Short Review. Catalysts 2025, 15, 271. https://doi.org/10.3390/catal15030271

AMA Style

Yao L, Zeng S, Yang S, Zhang H, Ma Y, Zhou G, Fang J. Zinc Indium Sulfide Materials for Photocatalytic Hydrogen Production via Water Splitting: A Short Review. Catalysts. 2025; 15(3):271. https://doi.org/10.3390/catal15030271

Chicago/Turabian Style

Yao, Lang, Shice Zeng, Shuxiang Yang, Honghua Zhang, Yue Ma, Guangying Zhou, and Jianzhang Fang. 2025. "Zinc Indium Sulfide Materials for Photocatalytic Hydrogen Production via Water Splitting: A Short Review" Catalysts 15, no. 3: 271. https://doi.org/10.3390/catal15030271

APA Style

Yao, L., Zeng, S., Yang, S., Zhang, H., Ma, Y., Zhou, G., & Fang, J. (2025). Zinc Indium Sulfide Materials for Photocatalytic Hydrogen Production via Water Splitting: A Short Review. Catalysts, 15(3), 271. https://doi.org/10.3390/catal15030271

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