Photocatalytic Hydrogen Generation Research Articles

Charge self-regulation over in-plane two-dimensional/two-dimensional hetero-cocatalyst for robust photocatalytic hydrogen generation

The rationally designing and constructing atomic-level heterointerface of two-dimensional (2D) chalcogenides is highly desirable to overcome the sluggish H2O-activation process toward efficient solar-driven hydrogen evolution. Herein, a novel in-plane 2D/2D molybdenum disulfide-rhenium disulfide (ReS2-MoS2) heterostructure is well-designed to induce the charge self-regulation of active site by forming electron-enriched Re(4−δ)+ and electron-deficient S(2−δ)− sites, thus collectively facilitating the activation of adsorbed H2O molecules and its subsequent H2 evolution. Furthermore, the obtained in-plane heterogenous ReS2-MoS2 nanosheet can powerfully transfer photoexcited electrons to inhibit photocarrier recombination as observed by advanced Kelvin probe measurement (KPFM), in-situ X-ray photoelectron spectroscopy (XPS) and femtosecond transient absorption spectroscopy (fs-TAS). As expected, the obtained ReS2-MoS2/TiO2 photocatalyst achieves an outperformed H2-generation rate of 6878.3 μmol h−1 g−1 with visualizing H2 bubbles in alkaline/neutral conditions. This work about in-plane 2D/2D heterostructure with strong free-electron interaction provides a promising strategy for designing novel and efficient catalysts for various applications.

A S-scheme 0D/2D heterojunction formed by decorating Cd0.5Zn0.5S nanoparticles on Cu2MoS4 plates for efficient photocatalytic hydrogen generation

Rationally designing a Step-scheme (S-scheme) hetero-structured photocatalyst with high redox capability and separation efficiency of photoinduced carriers is considered as an attractive approach to address the shortcomings of single component and traditional hetero-structured photocatalyst. Herein, enlightened by the predictions of density functional theory (DFT), a unique S-scheme heterojunction photocatalyst was successfully fabricated by incorporating zero-dimensional (0D) Cd0.5Zn0.5S (CZS) on two-dimensional (2D) lamellar Cu2MoS4 (CMS) plates via a facile coprecipitation method, which substantially enhances the photocatalytic activity for hydrogen (H2) generation. CZS nanoparticles deposited on the surface of CMS nanoplates play a crucial role in creating highly intimate heterojunction interfaces and abundant exposed reaction sites, laying the foundation for improved photocatalytic performance. Furthermore, the significant difference in Fermi levels and band structures between CZS and CMS result in the formation of the internal electric field (IEF) and energy band bending at the interface of the heterojunction. This S-scheme charge transfer path enables 0D/2D CZS/CMS heterojunction possesses an exceptional capacity to maintain the robust redox potential and boosts the separation efficiency of light-induced carriers, as verified by DFT calculations and energy band structure analyses. As expected, the optimal heterojunction exhibits a satisfactory H2 generation rate of 13.1 mmol·g-1·h−1, which is nearly 7.7-fold higher than that of individual CZS. This study is expected to inspire the design of morphology-controlled hetero-structured photocatalyst with S-scheme charge transfer route for photocatalytic H2 generation.

Synergistic approach: Photocatalytic hydrogen generation for curcumin hydrogenation

Sn1-xFexO2 (x = 0, 0.1, 0.2 & 0.3) nanomaterials were successfully synthesized by co-precipitation technique and characterized by XRD, FTIR, SEM-EDAX, TG/DSC, etc. XPS revealed the presence of Fe+3 & Sn+4 ions in the SnO2 crystal lattice. Insertion of Fe shifts the absorption of SnO2 to the visible region. These synthesized nanomaterials show efficiency for hydrogen generation and degradation of organic dyes in the presence of visible light. The water splitting was performed under different conditions. A maximum hydrogen production rate of 12.8 mmol g−1h−1 was observed for Sn0.8Fe0.2O2 with glucose as a sacrificial agent. The photogenerated H2 finds application in hydrogenation of curcumin to tetrahydrocurcumin.

Broad Light Absorption and Multichannel Charge Transfer Mediated by Topological Surface State in CdS/ZnS/Bi2Se3 Nanotubes for Improved Photocatalytic Hydrogen Production

AbstractSemiconductor heterojunctions have garnered extensive interest in photocatalytic hydrogen generation, yet the limited light absorption and charge transfer efficiencies still restrict the photocatalytic performance. The topological insulator has unique surface states and high‐mobility electrons, demonstrating the significant potential for enhancing photocatalysis. Herein, a ternary photocatalyst based on a topological insulator, in which CdS and ZnS nanoparticles are grown on Bi2Se3 nanotube, is prepared for efficient photocatalysis driven by topological surface state for the first time. Under simulated solar light irradiation, the CdS/ZnS/Bi2Se3 nanotubes display a robust photocatalytic hydrogen production rate of 7.13 mmol h−1 g−1, which is 69.2 times of CdS and comparable to many CdS‐based photocatalysts. The unique hollow structure, topological surface state of Bi2Se3, and cooperative bandgap excitations of the three components endow the hybrids with wide light response to harvest solar energy. Meanwhile, the multichannel charge transfer facilitated by topological surface state and internal electric fields within the hybrids effectively suppresses the recombination of the photogenerated charge carriers. This mechanism maintains a high concentration of stable electrons on Bi2Se3, resulting in highly efficient hydrogen production. This work provides a new inspiration for designing heterojunction photocatalysts based on topological insulators for high‐efficiency solar‐driven energy conversion.

Constructing multifunctional novel noble-metal free NiS/ZnS/g-C3N4 ternary nanocomposites for highly active superior photocatalytic water splitting

Ultrasound-assisted wet-impregnation approach and cation-exchange hydrothermal method are employed effectively to develop the ternary nanocomposites NiS/ZnS/g-C3N4 (NZ-CN) with promising photocatalytic hydrogen (H2) generation activity. Several analytical techniques are utilized to characterize the as-synthesized NiS/ZnS/g-C3N4 nanocomposites to study their physical and chemical characteristics. The H2 production activity of the synthesized photocatalysts was tested using a 250 W halogen lamp with Na2S (0.25 M) and Na2SO3 (0.35 M) as sacrificial reagents. The optimized NZ-CN7.5% (3% NiS/ZnS/7.5% g-C3N4) catalyst displayed an exceptional H₂ generation rate of 8624 μmol h⁻1 g⁻1, exceeding both, pristine g-C3N4 (by 22.1 times) and 3% NiS/ZnS (by 3 times). This represents the highest reported rate of H₂ evolution for a graphitic carbon nitride (g-C3N4) based ternary nanocomposite under simulated solar radiation. By reusing the used NZ-CN7.5% (3% NiS/ZnS/7.5% g-C3N4) photocatalyst in four consecutive runs, the stability of the catalyst was investigated, and their individual activity in the H2 production activity was assessed. This study provides valuable insights for designing efficient noble metal-free g–C3N4–based photocatalysts, which can significantly contribute to the transition to solar-driven hydrogen generation. Further, we proposed a plausible mechanism for the photocatalytic H2 generation process over the NiS/ZnS/g-C3N4 photocatalyst.

Interface-engineering derived WS2/S-g-C3N4 nanosheet Z-scheme heterostructures towards enhanced photocatalytic redox and H2O2 generation

The growth of WS2 on S-doped graphic carbon nitrides (g-C3N4) was controlled to utilize horizontal implanting and get fine interfacial characteristic. Superior thin S-doped g-C3N4 nanosheets were fabricated via a two-step thermal polymerization at high temperature. Subsequent solvothermal procedure was used to create WS2/S-g-C3N4 (WS2/SCN) photocatalytic heterojunctions with optimized component ratios, in which doped S components in g-C3N4 play an important role for the horizontal growth and homogeneous distribution of WS2 nanosheets. Z-scheme charge transfer mechanism was proposed according to various characterizations. Photocatalytic rhodamine B (Rh B) degradation test indicated that WS2/SCN 15 % (sample WS2/SCN-3) revealed the best performance, in which Rh B of 92.8 % was photocatalytic oxidated with 20 min. Photocatalytic hydrogen generation experiments indicated that sample WS2/SCN-3 exhibited a H2 generation rate of 1380 μmol·g−1∙h−1, which was 3.7 times of that of S-g-C3N4 nanosheets. These WS2/S-g-C3N4 heterojunctions also exhibited excellent performance for photocatalytic H2O2 evolution. Sample WS2/SCN-3 exhibited a H2O2 generation rate of 5216 μmol·g−1·h−1 which was 6.4 times that of S-g-C3N4 sample. This excellent photocatalytic activity is scribed to WS2/S-g-C3N4 layered heterojunctions with well-developed interface characteristic. The result supplied an efficient approach for the preparation of photocatalysts.

Synthesis of carbon-metal interface ilmenite type nanostructures using ultrasonication-assisted sol-gel process for visible-light-driven hydrogen production from methanol and antibiotic wastewater removal

In this study, a new carbon-metal (C-Ti) interface was synthesized by chemically connecting perovskite ilmenite-type (FeTiO) nanostructures with carbon produced from biowaste (BC) using a simple sol-gel process assisted by ultrasonication. This interface can use visible light to produce hydrogen from hydrocarbons (methanol solution) and remove the antibiotic ciprofloxacin (CIF) from wastewater. Following optimization, BC15@FeTiO nanostructures displayed the highest visible light active photocatalytic hydrogen generation rate of 415.43 μmol·h−1·g−1. Furthermore, these nanostructures removed the CIF rate at 91.09 % for 120 minutes. The efficient electron transfer between BC and FeTiO via the chemically connected C-Ti interface promotes the formation of visible-light active photocatalytic hydrogen generation from methanol and the removal of antibiotic CIF into innocuous byproducts. This study also offers a new, low-cost carbon material made chemically from biowaste.

Bi & Mo co-doped In2S3 nano-foam blocks for boosted photocatalytic hydrogen generation

The design and construction of dual modifications on photocatalysts is a promising strategy to improve the photocatalytic properties. Herein, we fabricated the In2S3 nano-foam blocks with dual modifications of Bi & Mo co-doping and structure construction via a simple hydrothermal method to achieve an enhanced photocatalytic hydrogen generation. The results reveal that Bi & Mo co-doped In2S3 nano-foam blocks exhibit a high hydrogen generation rate of 5.45 mmol/g/h, which is 27 times that of bulk In2S3. Owing to the structural advantages, the enhanced specific surface area of the as-prepared nano-foam blocks improve the light harvesting efficiency of photocatalytic system. More importantly, the doped Bi and Mo atoms boost the improvement in the transfer and separation of photogenerated electrons and holes by introducing the impurity energy level. This work provides a reliable strategy for the design and fabrication of high-efficiency photocatalytic reaction system.

Monolayer BiOI doped with nonmetals (B, C, N, Si, P, S) to enhance photocatalytic hydrogen precipitation performance

Efficient photocatalysts play a crucial role in producing green and clean hydrogen energy. BiOI is a good material for photocatalytic hydrogen generation. However, the low position of the conduction band also affects its redox ability. We studied the electronic structure and hydrogen evolution reaction (HER) catalytic performance of six nonmetals doped BiOI based on the first principles calculation. The relationship between doping elements and catalytic performance was explained. We used the DFT + U method to find that the band gap values of X-BiOI (X = B, C, N, Si, P, S) are 1.99 eV, 1.23 eV, 1.73 eV, 2.08 eV, 1.40 eV and 1.77 eV, respectively. After nonmetal doping, the bottom position of the conduction band of BiOI rises, which enhances the reduction ability. Specifically, the impurity energy levels generated in the band gap of B and Si doped BiOI reduce the recombination rate of photogenerated carriers, and lower the work function to 5.62 eV and 5.45 eV, respectively. Studies on hydrogen production performance show that B-doped BiOI has the strongest reduction ability and the best catalytic effect, with the lowest ΔGH* (1.57 eV). This research provides some ideas for understanding nonmetal doped materials for the photocatalytic hydrogen evolution system.

Application of Quantum Dots for Photocatalytic Hydrogen Evolution Reaction

There is increased interest in the conversion of solar energy into green chemical energy because of the depletion of fossil fuels and their unpleasant environmental effect. Photocatalytic hydrogen generation from water involves the direct conversion of solar energy into H2 fuels, which exhibits significant advantages and immense promise. Nevertheless, photocatalytic efficiency is considerably lower than the standard range of industrial applications. Low light absorption efficiency, the rapid recombination of photogenerated electrons and holes, slow surface redox reaction kinetics and low photostability are well known to be key factors negatively affecting photocatalytic hydrogen production. Therefore, to construct highly efficient and stable photocatalysts is important and necessary for the development of photocatalytic hydrogen generation technology. In this review, quantum dots (QDs)-based photocatalysts have emerged with representative achievements. Due to their excellent light-harvesting ability, low recombination efficiency of photogenerated electrons and holes, and abundant surface active sites, QDs have attracted remarkable interest as photocatalysts and/or cocatalyst for developing highly efficient photocatalysts. In this review, the application of QDs for photocatalytic H2 production is emphatically introduced. First, the special photophysical properties of QDs are briefly described. Then, recent progress into the research on QDs in photocatalytic H2 production is introduced, in three types: semiconductor QDs (e.g., CdS, CdMnS, and InP QDs), metal QDs (e.g., Au, Pt and Ag QDs), and MXene QDs and carbon QDs (CDQs). Finally, the challenges and prospects of photocatalytic H2 evolution with QDs in the future are discussed.

TiO2 Films with Macroscopic Chiral Nematic-Like Structure Stabilized by Copper Promoting Light-Harvesting Capability for Hydrogen Generation.

Cellulose nanocrystals (CNCs) have inspired the synthesis of various advanced nanomaterials, opening opportunities for different applications. However, a simple and robust approach for transferring the long-range chiral nematic nanostructures into TiO2 photocatalyst is still fancy. Herein, a successful fabrication of freestanding TiO2 films maintaining their macroscopic chiral nematic structures after removing the CNCs biotemplate is reported. It is demonstrated that including copper acetate in the sol avoids the epitaxial growth of the lamellar-like structure of TiO2 and stabilizes the chiral nematic structure instead. The experimental results and optical simulation demonstrate an enhancement at the blue and red edges of the Fabry-Pérot reflectance peak located in the visible range. This enhancement arises from the light scattering effect induced by the formation of the chiral nematic structure. The nanostructured films showed 5.3 times higher performance in the photocatalytic hydrogen generation, compared to lamellar TiO2, and benefited from the presence of copper species for charge carriers' separation. This work is therefore anticipated to provide a simple approach for the design of chiral nematic photocatalysts and also offers insights into the electron transfer mechanisms on TiO2/CuxO with variable oxidation states for photocatalytic hydrogen generation.

Materials Advances in Photocatalytic Solar Hydrogen Production: Integrating Systems and Economics for a Sustainable Future.

Photocatalytic solar hydrogen generation, encompassing both overall water splitting and organic reforming, presents a promising avenue for green hydrogen production. This technology holds the potential for reduced capital costs in comparison to competing methods like photovoltaic-electrocatalysis and photoelectrocatalysis, owing to its simplicity and fewer auxiliary components. However, the current solar-to-hydrogen efficiency of photocatalytic solar hydrogen production has predominantly remained low at ≈1-2% or lower, mainly due to curtailed access to the entire solar spectrum, thus impeding practical application of photocatalytic solar hydrogen production. This review offers an integrated, multidisciplinary perspective on photocatalytic solar hydrogen production. Specifically, the review presents the existing approaches in photocatalyst and system designs aimed at significantly boosting the solar-to-hydrogen efficiency, while also considering factors of cost and scalability of each approach. In-depth discussions extending beyond the efficacy of material and system design strategies are particularly vital to identify potential hurdles in translating photocatalysis research to large-scale applications. Ultimately, this review aims to provide understanding and perspective of feasible pathways for commercializing photocatalytic solar hydrogen production technology, considering both engineering and economic standpoints.

Interconnected Periodic Macroporous NaNbO3 for High-Efficiency Solar-Driven Photocatalytic Hydrogen Evolution.

Highly ordered periodic macroporous structures have been extensively utilized to significantly enhance the photocatalytic activity. However, constructing 3D interconnected ordered porous ternary nanostructures with highly crystalline frameworks remains a formidable challenge. Here, we introduce the design and fabrication of 3D interconnected periodic macroporous NaNbO3 (PM NaNbO3) to effectively increase the density of surface-active sites and optimize the photogenerated carrier-transfer efficiency. By incorporating Pt as a cocatalyst, PM NaNbO3 exhibits an exceptional photocatalytic hydrogen generation rate of 10.04 mmol h-1 g-1, which is approximately six and five times higher than those of calcined NaNbO3 (C-NaNbO3) and hydrothermal NaNbO3 (H-NaNbO3), respectively. This outstanding performance can be attributed to the synergistic effects arising from its well-interconnected pore architecture, large surface area, enhanced light absorption capability, and improved charge carrier separation and transport efficiency. The findings presented in this study demonstrate an innovative approach toward designing hierarchically periodic macroporous materials for solar-driven hydrogen production.

Strong hetero-interface interaction in 2D/2D WSe2/ZnIn2S4 heterostructures for highly-efficient photocatalytic hydrogen generation

Green hydrogen is urgently required for sustainable development of human beings and rational construction of heterostructures holds great promising for photocatalytic hydrogen generation. Herein, 2D/2D WSe2/ZnIn2S4 heterostructures with strong hetero-interface interaction and abundant contact were constructed via an impregnation-annealing strategy. Efficient charge transfer from ZnIn2S4 to WSe2 was evidenced by transient absorption spectroscopy in crafted heterostructures owing to the tight and 2D face-to-face contact. As a result, the prepared WSe2/ZnIn2S4 heterostructures exhibited boosted photocatalytic performance and a highest hydrogen evolution rate of 3.377 mmol/(g h) was achieved with an apparent quantum yield of 45.7% at 420 nm. The work not only provides new strategies to achieve efficient 2D/2D heterostructures but also paves the way for the development of green hydrogen in the future.

Synergy of oxygen doping and nitrogen vacancy for promoting photocatalytic hydrogen generation of g-C3N4

Photocatalytic hydrogen (H2) generation is a promising and renewable solution to address the energy crisis, but is currently hindered by the limited carrier separation and deficient active sites of photocatalysts. In this study, oxygen (O) doping and nitrogen (N) vacancy co-modified hollow tubular g-C3N4 (O-CN-NV) is successfully prepared to enhance the photocatalytic H2 production. The incorporation of O doping facilitates the separation of photogenerated carriers within the tubular CN, while the N vacancy acts as the surface active site for capturing the photoinduced electrons. As a result, the photocatalytic H2 generation over O–CN–NV reaches 339.4 μmol g−1 h−1 under visible light irradiation, which is 6.1 times higher than that of bulk g-C3N4 (CN). This unique design holds great promise for the development of high-performance photocatalysts to produce renewable fuels.

Impact of Anchoring Groups on the Photocatalytic Performance of Iridium(III) Complexes and Their Toxicological Analysis.

Three different iridium(III) complexes, labelled as Ir1-Ir3, each bearing a unique anchoring moiety (diethyl [2,2'-bipyridine]-4,4'-dicarboxylate, tetraethyl [2,2'-bipyridine]-4,4'-diylbis(phosphonate), or [2,2'-biquinoline]-4,4'-dicarboxylic acid), were synthesized to serve as photosensitizers. Their electrochemical and photophysical characteristics were systematically investigated. ERP measurements were employed to elucidate the impact of the anchoring groups on the photocatalytic hydrogen generation performance of the complexes. The novel iridium(III) complexes were integrated with platinized TiO2 (Pt-TiO2) nanoparticles and tested for their ability to catalyze hydrogen production under visible light. A H2 turnover number (TON) of up to 3670 was obtained upon irradiation for 120 h. The complexes with tetraethyl [2,2'-bipyridine]-4,4'-diylbis(phosphonate) anchoring groups were found to outperform those bearing other moieties, which may be one of the important steps in the development of high-efficiency iridium(III) photosensitizers for hydrogen generation by water splitting. Additionally, toxicological analyses found no significant difference in the toxicity to luminescent bacteria of any of the present iridium(III) complexes compared with that of TiO2, which implies that the complexes investigated in this study do not pose a high risk to the aquatic environment compared to TiO2.

Enhanced photocatalytic hydrogen generation efficiency through molybdenum-sulfur dual sites synergistic catalysis

Photocatalysis has gained significant attention in recent years for water splitting, with graphitic carbon nitride (g-C3N4) emerging as a promising candidate. However, the low carrier mobility and the lack of active sites for hydrogen evolution limit photocatalytic hydrogen evolution performance. Herein, this work presents a facile approach to achieve single Mo sites with a unique local coordination structure featuring one Mo atom coordinated with two nitrogen atoms and one sulfur atom. Among the prepared photocatalysts, 6 wt% Mo/SCN exhibits the highest photocatalytic hydrogen evolution activity with a yield rate of 4.05 mmol g-1 h-1, which is 13 times higher than that of pure g-C3N4 and superior to most of the g-C3N4 series photocatalysts. Experimental results and density functional theory calculations confirm that the Mo single-atom and S atom have synergistic catalysis under the co-modification, and the formed Mo-S bonds will enhance the ability of the substrate to anchor the Mo single-atom to enhance the stability of the photocatalyst. This work offers insights into transition metal single-atom and synergistic catalysis design for photocatalytic hydrogen evolution.

Edge-Rich 3D Structuring of Metal Chalcogenide/Graphene with Vertical Nanosheets for Efficient Photocatalytic Hydrogen Production.

Constructing pertinent nanoarchitecture with abundant exposed active sites is a valid strategy for boosting photocatalytic hydrogen generation. However, the controllable approach of an ideal architecture comprising vertically standing transition metal chalcogenides (TMDs) nanosheets on a 3D graphene network remains challenging despite the potential for efficient photocatalytic hydrogen production. In this study, we fabricated edge-rich 3D structuring photocatalysts involving vertically grown TMDs nanosheets on a 3D porous graphene framework (referred to as 3D Gr). 2D TMDs (MoS2 and WS2)/3D Gr heterostructures were produced by location-specific photon-pen writing and metal-organic chemical vapor deposition for maximum edge site exposure enabling efficient photocatalytic reactivity. Vertically aligned 2D Mo(W)S2/3D Gr heterostructures exhibited distinctly boosted hydrogen production because of the 3D Gr caused by synergetic impacts associated with the large specific surface area and improved density of exposed active sites in vertically standing Mo(W)S2. The heterostructure involving graphene and TMDs corroborates an optimum charge transport pathway to rapidly separate the photogenerated electron-hole pairs, allowing more electrons to contribute to the photocatalytic hydrogen generation reaction. Consequently, the size-tailored heterostructure showed a superior hydrogen generation rate of 6.51 mmol g-1 h-1 for MoS2/3D graphene and 7.26 mmol g-1 h-1 for WS2/3D graphene, respectively, which were 3.59 and 3.76 times greater than that of MoS2 and WS2 samples. This study offers a promising path for the potential of 3D structuring of vertical TMDs/graphene heterostructure with edge-rich nanosheets for photocatalytic applications.

Recent Advances in Graphene-Based Single-Atom Photocatalysts for CO2 Reduction and H2 Production

The extensive use of single-atom catalysts (SACs) has appeared as a significant area of investigation in contemporary study. The single-atom catalyst, characterized by its maximum atomic proficiency and great discernment of the transition-metal center, has a unique combination of benefits from both heterogeneous and homogeneous catalysts. Consequently, it effectively bridges the gap between these two types of catalysts, leveraging their distinctive features. The utilization of SACs immobilized on graphene substrates has garnered considerable interest, primarily because of their capacity to facilitate selective and efficient photocatalytic processes. This review aims to comprehensively summarize the progress and potential uses of SACs made from graphene in photocatalytic carbon dioxide (CO2) reduction and hydrogen (H2) generation. The focus is on their contribution to converting solar energy into chemical energy. The present study represents the various preparation methods and characterization approaches of graphene-based single-atom photocatalyst This review investigates the detailed mechanisms underlying these photocatalytic processes and discusses recent studies that have demonstrated remarkable H2 production rates through various graphene-based single-atom photocatalysts. Additionally, the pivotal roleof theoretical simulations, likedensity functional theory (DFT), to understand the structural functional relationships of these SACs are discussed. The potential of graphene-based SACs to revolutionize solar-to-chemical energy conversion through photocatalytic CO2 reduction and H2 production is underscored, along with addressing challenges and outlining future directions for this developing area of study. By shedding light on the progress and potential of these catalysts, this review contributes to the collective pursuit of sustainable and efficient energy conversion strategies to mitigate the global climate crisis.

The nature of photocatalytic hydrogen generation on silicon nanowires prepared by MAWC

Highly n-doped silicon nanowires (SiNWs) exhibit excellent hydrogen generation. Our results indicate three hydrogen generation possibilities, i.e. SiNWs oxidation, photocatalysis and the cleavage of dangling H bonds, are jointly responsible for the efficient hydrogen generation. Oxidation accounts for about 80% of total hydrogen, photocatalysis contributes less than 20% of total hydrogen, and about 0.1% of total hydrogen is from cleavage of dangling H bonds. SiNWs were oxidized in water and form SiOx (0 < X < 2) thin layer. Furthermore, the ratio of photo-generated hydrogen to photo-generated oxygen is about 2.4:1. It suggests that photocatalysis appears to be a process of water splitting. This study is significant to reveal the mechanism of hydrogen production on SiNWs prepared by Metal-Assisted Wet Chemical Etching (MAWC).