Three-dimensional ZnO@TiO2 core-shell nanostructures decorated with plasmonic Au nanoparticles for promoting photoelectrochemical water splitting

A novel three-dimensional (3D) core-shell nanostructure decorated with plasmonic Au nanoparticles (NPs) was prepared for photoelectrochemical water splitting. In the new nanostructure, ZnO nanorods (NRs) are perpendicular to ZnO nanosheets (NSs), and the ZnO NSs-NRs are coated with a thin TiO₂ shell formed by liquid phase deposition. The plasmonic Au NPs were formed in situ on the surface of ZnO NSs-NRs@TiO₂ by thermal reduction. A thin TiO₂ shell and uniformly distributed Au NPs were successfully obtained. The photoconversion efficiency and photocurrent density of the 3D ZnO NSs-NRs@TiO₂-Au nanostructure respectively reached 0.48% and 1.73 mA cm⁻² at 1.23 V vs. reversible hydrogen electrode, 4.80 and 4.33 times higher than those of ZnO NSs, respectively. The thin TiO₂ shell effectively promoted charge separation, while the surface plasmon resonance effects of the Au NPs improved the photocurrent density. The findings suggest that the 3D ZnO NSs-NRs@TiO₂-Au nanostructure is a promising photoanode for photoelectrochemical water splitting.     

An efficient tandem photoelectrochemical cell composed of FeOOH/TiO2/BiVO4 and Cu2O for self-driven solar water splitting

An integrated solar water splitting tandem cell without external bias was designed using a FeOOH modified TiO₂/BiVO₄ photoanode as a photoanode and p-Cu₂O as a photocathode in this study. An apparent photocurrent (0.37 mA/cm² at operating voltage of +0.36 V_RHE) for the tandem cell without applied bias was measured, which is corresponding to a photoconversion efficiency of 0.46%. Besides, the photocurrent of FeOOH modified TiO₂/BiVO₄–Cu₂O is much higher than the operating point given by pure BiVO₄ and Cu₂O photocathode (∼0.07 mA/cm² at +0.42 V_RHE). Then we established a FeOOH modified TiO₂/BiVO₄–Cu₂O two-electrode system and measured the current density-voltage curves under AM 1.5G illumination. The unassisted photocurrent density is 0.12 mA/cm⁻² and the corresponding amounts of hydrogen and oxygen evolved by the tandem PEC cell without bias are 2.36 μmol/cm² and 1.09 μmol/cm² after testing for 2.5 h. The photoelectrochemical (PEC) properties of the FeOOH modified TiO₂/BiVO₄ photoanode were further studied to demonstrate the electrons transport process of solar water splitting. This aspect provides a fundamental challenge to establish an unbiased and stabilized photoelectrochemical (PEC) solar water splitting tandem cell with higher solar-to-hydrogen efficiency.     

Ultrathin hematite films deposited layer-by-layer on a TiO2 underlayer for efficient water splitting under visible light

Ultrathin hematite (α-Fe₂O₃) film deposited on a TiO₂ underlayer as a photoanode for photoelectrochemical water splitting was described. The TiO₂ underlayer was coated on conductive fluorine-doped tin oxide (FTO) glass by spin coating. The hematite films were formed layer-by-layer by repeating the separated two-phase hydrolysis-solvothermal reaction of iron(III) acetylacetonate and aqueous ammonia. A photocurrent density of 0.683 mA cm⁻² at +1.5 V vs. RHE (reversible hydrogen electrode) was obtained under visible light (>420 nm, 100 mW cm⁻²) illumination. The TiO₂ underlayer plays an important role in the formation of hematite film, acting as an intermediary to alleviate the dead layer effect and as a support of large surface areas to coat greater amounts of Fe₂O₃. The as-prepared photoanodes are notably stable and highly efficient for photoelectrochemical water splitting under visible light. This study provides a facile synthesis process for the controlled production of highly active ultrathin hematite film and a simple route for photocurrent enhancement using several photoanodes in tandem.     

In2O3:Sn/TiO2/CdS heterojunction nanowire array photoanode in photoelectrochemical cells

The design of photoanode with highly efficient light harvesting and charge collection properties is important in photoelectrochemical (PEC) cell performance for hydrogen production. Here, we report the hierarchical In₂O₃:Sn/TiO₂/CdS heterojunction nanowire array photoanode (ITO/TiO₂/CdS-nanowire array photoanode) as it provides a short travel distance for charge carrier and long light absorption pathway by scattering effect. In addition, optical properties and device performance of the ITO/TiO₂/CdS-nanowire array photoanode were compared with the TiO₂ nanoparticle/CdS photoanode. The photocatalytic properties for water splitting were measured in the presence of sacrificial agent such as SO₃²⁻ and S²⁻ ions. Under illumination (AM 1.5G, 100 mW/cm²), ITO/TiO₂/CdS-nanowire array photoanode exhibits a photocurrent density of 8.36 mA/cm² at 0 V versus Ag/AgCl, which is four times higher than the TiO₂ nanoparticle/CdS photoanode. The maximum applied bias photon-to-current efficiency for the ITO/TiO₂/CdS-nanowire array and the TiO₂ nanoparticle/CdS photoanode were 3.33% and 2.09%, respectively. The improved light harvesting and the charge collection properties due to the increased light absorption pathway and reduced electron travel distance by ITO nanowire lead to enhancement of PEC performance.     

The co-decorated TiO2 nanorod array photoanodes by CdS/CdSe to promote photoelectrochemical water splitting

A cascade structure of TiO₂/CdS/CdSe semiconductor heterojunction is synthesized using a three-step technique of facile hydrothermal growth for the enhancement of the photoelectrochemical performances. The optical and photoelectrochemical properties controlled by the deposition processing parameters have been investigated. It is shown that the patterns of semiconductor heterojunction enlarge the absorption range of solar spectra, and improve the properties of the photogenerated charge carriers describing separation and transportation, and reduce the interface resistance between the photoelectrode and electrolyte comparing with the pure TiO₂ and CdS-decorated TiO₂ nanorod array photoanodes. The higher photocurrent density and photoconversion efficiency are up to 4.23 mA cm⁻² and 4.2%, which are the 4.1 and 25.3 times superior than that of the pure TiO₂ photoanode. The hydrothermal growth time increment of CdSe yields greater photoelectrochemical water splitting performances. The underlying physics mechanisms have been discussed based on forming a type-Ⅱ energy band alignment structure.     

Simultaneously efficient light absorption and charge transport of CdS/TiO2 nanotube array toward improved photoelectrochemical performance

CdS has been widely used to modify TiO₂-based photoanodes for photoelectrochemical (PEC) water splitting. Due to the poor interface contact between chalcogenides and oxides, however, such CdS modified TiO₂ materials usually exhibit inefficient separation and transport of charges, leading to an unsatisfactory efficiency during the PEC water splitting process. Addressing this issue, we herein report a CdS/TiO₂ nanotube array (CdS/TNA) photoanode that was fabricated through a successive ion layer absorption and reaction (SILAR) method with an additional subsequent annealing. This post-annealing process is essential to enhance the interface contact between the CdS and the TNAs, resulting in an accelerated transfer of photogenerated electrons from the CdS to the TNAs. In addition, the post-annealing also improves the light absorption capability of the CdS/TNA photoanode. The simultaneous enhancement of charge transport and light absorption provided by the post-annealing is essential for improving the PEC performance of the CdS/TNA photoanode. The CdS/TNA photoanode obtained by this strategy exhibits a much enhanced PEC performance in water splitting, and its photocurrent density and solar-to-hydrogen conversion efficiency could reach 4.56 mA cm⁻² at 1.23 V vs. reversible hydrogen electrode and 5.61%, respectively. This simple but effective route can provide a general strategy for obtaining high-performance oxide-based photoelectrodes.     

Efficient suppression of surface charge recombination by CoP-Modified nanoporous BiVO4 for photoelectrochemical water splitting

BiVO₄ is a promising photoanode material for water splitting due to its substantial absorption of solar light as well as favorable band edge positions. However, the poor water oxidation kinetics of BiVO₄ results in its insufficient photocurrent density. Herein, we demonstrate the use of CoP nanoparticles for facile surface modification of nanoporous BiVO₄ photoanode in potassium borate buffer solution (pH 9.0), which can generate a tremendous cathodic shift of ~430 mV in the onset potential for photoelectrochemical water oxidation. In addition, a remarkable photocurrent density of 4.1 mA cm^?2 is achieved at 1.23 V vs. RHE under AM 1.5G illumination. The photoelectrochemical measurement using sodium sulfite as a hole scavenger clearly shows that the greatly improved performances are attributed to the efficient suppression of interfacial charge recombination through loading of CoP catalyst. Moreover, the maximum surface charge injection yield can reach >81% at 1.23 V vs. RHE and the maximum IPCE of CoP/BiVO₄ can reach 75.8% at 420 nm, suggesting the potential application of CoP-modified BiVO₄ photoanode for overall solar water splitting in cost-effective tandem photoelectrochemical cells.     

New method for improving the bulk charge separation of hematite with enhanced water splitting

Due to its poor bulk charge separation efficiency, the photoelectrochemical (PEC) performance of pristine hematite prepared directly from an electrodeposited Fe film is limited. Au-modification of hematite via a simple immersion method improves the PEC performance two-fold to 0.31 mA cm⁻². The Au nanoparticles deposited from HAuCl₄ act as plasmonic photosensitizers and electron collectors to improve the light absorption and bulk charge separation efficiency of the photoanode. In addition, the increase in the (110) plane and specific surface area induced by HAuCl₄ enhances the bulk charge separation efficiency. After further modification with Ti, the photocurrent response of the resulting Ti/Au/α-Fe₂O₃ photoanode improves to 0.51 mA cm⁻²; this increase is attributed to its increased light absorption, bulk charge separation efficiency (η_bulk), and surface charge injection efficiency (η_surface). In this work, the effect of Au and Ti on the crystalline structure, morphology and PEC performance of the novel electrodeposited hematite photoanode are investigated by systematical characterization.     

TiO2-rutile/anatase homojunction with enhanced charge separation for photoelectrochemical water splitting

The mismatched interfaces of heterojunction usually have lots of defects, deriving in recombination of generated electron-hole pairs. On the other hand, homojunction interfaces are considered to be beneficial to the separation of charge carriers due to the similar characteristics in two sides of homojunction. TiO₂ have rutile and anatase two typical photoactive phases in nature. In this work, TiO₂-rutile/anatase (TiO₂-R/A) homojunction photoanode is fabricated by in situ growth of anatase TiO₂ on TiO₂-R surface. By contrast with TiO₂-rutile/rutile (TiO₂-R/R) photoanode, TiO₂-R/A displays higher photocurrent density (1.70 mA cm^?2 at 0.6 V vs. SCE). Deep insight into the mechanism suggests that TiO₂-R/A homojunction has intense band bending and enhanced surface area, which facilitate the charge separation and transmission. This study offers some novel insights to design and fabricate semiconductors photoanodes for highly efficient photocatalytic reactions.     

2D/3D WO3/BiVO4 heterostructures for efficient photoelectrocatalytic water splitting

Developing novel photoanodes with high efficiency for photoelectrochemical (PEC) water splitting has become the key to solar energy conversion and storage realm. Herein, 3D worm-like bismuth vanadate (BiVO₄) is grafted on 2D thin tungsten trioxide (WO₃) underlayer by electrodeposition to form mixed–dimensional structured photoanode, resulting in significant improvement of the photocatalytic performance and the charge separation efficiency. Characterization results prove that the mixed–dimensional structured can boost the photocatalytic activity by suppressing back reaction and charge recombination of the bulk BiVO₄. Simultaneously, the electrical conductivity of photoanode can be increased by W⁶⁺ doping. Furthermore, a robust catalyst NiCo₂O_x is coated onto the surface of WO₃/BiVO₄ photoanode, exhibiting a desirable photocurrent of 3.85 mA cm^?2 at 1.23 V vs. RHE and an excellent stability over 3 h. Both the excellent photocurrent density and great operational stability of this 2D/3D WO₃/BiVO₄ photoanode make it a promising material for practical applications.     

CdS and CdSe nanoparticles activated 1D TiO2 heterostructure nanoarray photoelectrodes for enhanced photoelectrocatalytic water splitting

Herein, we report the fabrication of nanocrystals activated 1D TiO₂ nanorods heterostructure photoanode with top-open vertical photoanode structure by hydrothermal and SILAR method. The vertical nanorod heterostructure could effectively manifest the interface with electrolyte and photoanode for dynamic water oxidation. Furthermore, thermodynamically stable TiO₂ nanorod and its conduction band alignment with CdS and CdSe nanocrystals uphold the charge separation and culminate the photocurrent density to 2.01 mA cm^?2 at 1.23 V RHE. The decoration of CdS and CdSe co-crystals on TiO₂ exhibited a significantly enhanced photoresponse and clear evidence of the negative shift of onset-potential with a five-fold increment of solar to hydrogen generation.     

Enhanced photoelectrochemical performance of 2D core-shell WO3/CuWO4 uniform heterojunction via in situ synthesis and modification of Co-Pi co-catalyst

In order to enhance the photoelectrochemical (PEC) performance of tungsten oxide (WO₃), it is critical to overcome the problems of narrow visible light absorption range and low carrier separation efficiency. In this work, we firstly prepared the 2D plate-like WO₃/CuWO₄ uniform core-shell heterojunction through in-situ synthesis method. After modification with the amorphous Co-Pi co-catalyst, the ternary uniform core-shell structure photoanode achieved a photocurrent of 1.4 mA/cm² at 1.23 V vs. RHE, which was about 6.67 and 1.75 times higher than that of pristine WO₃ and 2D uniform core-shell heterojunction, respectively. Furthermore, the onset potential of 2D WO₃/CuWO₄/Co-Pi core-shell heterojunction occurred a negatively shifts of about 20 mV. Experiments illuminated that the enhanced PEC performance of WO₃/CuWO₄/Co-Pi photoanode was attributed to the broader light absorption, reduced carrier transfer barrier and increased carrier separation efficiency. The work provides a strategy of maximizing the advantages of core-shell heterojunction and co-catalyst to achieve effective PEC performance.     

3D cross-linked BiOI decorated ZnO/CdS nanorod arrays: A cost-effective hydrogen evolution photoanode with high photoelectrocatalytic activity

ZnO/CdS photoanode with an excellent photoelectrochemical (PEC) performance for water splitting to produce hydrogen, but its practical application is seriously hindered owing to the photocorrosion induced by photoholes on the surface of CdS. Herein, a 3D cross-linked heterostructure ZnO/CdS/BiOI nanorod arrays (NRAs) has been prepared by a simple solvothermal strategy. Under visible light illumination (λ > 420 nm), the ZnO/CdS/BiOI NRAs photoanode shows an excellent PEC activity and generates a photocurrent density of 9.12 mA cm⁻² at 1.1 V vs. RHE, which is 1.8 times higher than that of the ZnO/CdS NRAs photoanode in the alkaline electrolyte. Furthermore, the photoanode achieves a high photo conversion efficiency of 3.49% and a long-time stability over 6000 s. It is proposed that the BiOI nanosheets not only serve as protecting layer to restrain the photocorrosion of CdS, but also facilitate the charge separation in CdS by the virtue of the p-n junction formed between CdS and BiOI.     

Bi2S3 entrenched BiVO4/WO3 multidimensional triadic photoanode for enhanced photoelectrochemical hydrogen evolution applications

The catalytic reactivity and photoactivity of WO₃ and BiVO₄ oxide semiconductors have general obstacles as electrodes in emergent photo-electrochemical (PEC) hydrogen evolution applications. The present work comprises the integration of photocatalyst with wide visible photon absorption material which is vital for hydrogen evolution in photo-electrocatalytic water splitting. Herein, the 1D WO₃ NWs have been integrated with stable water oxidation photocatalysts of BiVO₄ and Bi₂S₃ as a photoanode (Bi₂S₃/BiVO₄/WO₃) for photoelectrochemical hydrogen evolution reactions. The morphological variations in the Bi₂S₃/BiVO₄/WO₃ heterostructure manifest catalytic activity and rapid charge transfer characteristics owing to band alignment and a wide range of visible photon absorption. The optimized Bi₂S₃/BiVO₄/WO₃ multidimensional photoanode accomplishes a superior photocurrent density of 1.52 mA/cm², a seven-fold higher than pristine WO₃ photoanode counterpart (0.2 mA/cm²) at 1 V vs. RHE. A prodigious lowest onset potential of ?0.01 V vs. RHE) has been achieved which enables very high solar to hydrogen conversion. The photoelectrode with entangled morphology such as nanosheets, nanocrystals and nanorods expanded their surface to volume ratio having enhanced catalytic performance. The hybrid photoanodes have demonstrated the lowest charge transfer resistance of 360 Ohm/cm² with a 7-fold rise in hydrogen evolution performance. The resultant triadic Bi₂S₃/BiVO₄/WO₃ heterostructure appeared to be an emerging stable photo-electro catalyst for hydrogen evolution applications.     

Optimized photoactive coatings prepared with functionalized TiO2

Functionalization of TiO₂ nanoparticles with silane coupling agents was investigated aimed at low-temperature photoelectrode manufacturing for solar driven water splitting application. Different silanes were grafted on the surface of TiO₂ in toluene solvent under mild condition. The electrodes were prepared with spin coating by dispersing functionalized particles in DMAc onto FTO glass and dried under vacuum atmosphere at low temperature. UV–Vis spectroscopy of TiO₂ powder and its electrodes was studied, and it was found that the spectrum of the modified TiO₂ slightly shifted to higher wavelengths. The electrode prepared with functionalized TiO₂ showed photocurrent density of up to 0.14 mA cm⁻² compared to 0.04 mAcm⁻² for pristine TiO₂ at 1.23 V, in the water oxidation reaction. The increase in photocurrent density was due to better binding of the TiO₂ particles to the substrate resulting in better charge collection observed under SEM. To enhance the photoelectrochemical efficiency, heat treatment was performed and 300 °C was found to be the best heat treatment temperature. The incident photon to current efficiency measurement exhibited an external quantum efficiency up to 4.9% for this heat-treated electrode. Mott-Schottky was plotted to examine the flat band potential. The result showed that the modification resulted in a decrease in the flat band potential suggesting that the charge recombination loss is lower compared to neat TiO₂ electrode.     

Investigation of the annealing treatment on the performance of TiO2 photoanode

Developing low-cost semiconductor photoanode toward efficient and stable oxygen evolution reaction (OER) is highly desirable for photoelectrochemical (PEC) water splitting. Herein, nanoparticulate titanium dioxide (TiO₂) electrodes were prepared using Degussa P25 powders by spin-coating method. The effects of annealing conditions on the PEC performance of the nanoparticulate TiO₂ photoanode was systematically investigated including temperature, annealing time and atmosphere. The results demonstrate that the TiO₂/fluorine-doped tin oxide substrates (FTO/TiO₂) electrode annealed at argon (Ar) atmosphere under 450 °C shows the highest PEC performance. The photocurrent density of FTO/TiO₂ annealed in Ar for only 0.5 h reached to 120 μA/cm² at 0.3 V vs. Hg/HgO which is about 10 times higher than that of the unannealed one. The X-ray photoelectron spectroscopy (XPS) results show the thermal treatment can produce oxygen vacancies on the surface of TiO₂ which reduce the recombination of photogenerated electron-hole pairs and expanding the visible light absorption by introducing defective energy levels. The electrochemical impedance spectroscopy (EIS) approves that appropriate annealing treatment can effectively enhance the electron conductivity resulting in low charge transfer resistance. All these factors contribute to improving the PEC activity of TiO₂ photoanode.     

Bi2S3 anchored ZnS/ZnO nanorod arrays photoanode for enhanced visible light driven photo electrochemical properties

We report on the enhanced photoelectrochemical water splitting of hybrid ZnS/ZnO core-shell nanorod arrays functionalized with Bi₂S₃ nanosheets as photoanode. The ZnO nanorod arrays were prepared by a facile hydrothermal approach and sulphurized to form ZnS shell. Subsequently porous Bi₂S₃ nanosheets were arbitrarily decorated on the nanorod arrays by ionic adsorption and reaction method. Substantial enhancement in photocurrents with twofold increment is observed for hybrid photoanode compared to pristine counterparts. The structural and morphological properties of nano hybrid Bi₂S₃/ZnS/ZnO samples were analyzed by field emission scanning electron microscopy and X-ray diffraction. The higher wavelength shift in the absorption edge of Bi₂S_3/ZnS/ZnO photocatalyst was observed in diffuse reflectance UV–Visible spectra. The low temperature photoluminescence and impedance spectra of Bi₂S₃/ZnS/ZnO photoanode confirm that Bi₂S₃ functionalization reduces the recombination of electron–hole pair and facilitates barrier free charge transfer. The Bi₂S₃/ZnS/ZnO photoanode device exhibits photocurrent density of 220 μA/cm² at 0.2 V vs. Ag/AgCl under the electrolyte solution at pH ~10.8. The resultant hybrid photoanode withhold good stability and maintain the facile charge carrier generation and separation. Bi₂S₃ topological nanosheets are responsible for the absorption of complete visible photons while ZnS/Bi₂S₃ inter-junction provides the robust electron-hole pair separation at their interface due to infiltration pathway. The photoactive hybridization of Bi₂S₃/ZnS/ZnO provokes the enhanced donor charge density for efficient hydrogen evolution reaction.     

TiO2/CeO2 core/shell heterojunction nanoarrays for highly efficient photoelectrochemical water splitting

In this paper, novel TiO₂/CeO₂ core/shell heterojunction nanorod (NR) arrays were synthesized as photoanode for photoelectrochemical (PEC) water splitting via a simple and facial two-step hydrothermal approach. This synthesis route can obtain different amount of CeO₂ nanoparticles by controlling the hydrothermal time and eventually achieve uniform TiO₂/CeO₂ core/shell nanostructures. The uniform TiO₂/CeO₂ core/shell heterojunction nanoarrays exhibit a markedly enhanced photocurrent density of 5.30 mA·cm^?2 compared to that of pristine TiO₂ NR 1.79 mA·cm^?2 at 1.23 V vs. RHE in 1 M KOH solution. The superior PEC performance of the TiO₂/CeO₂ core/shell heterojunction is primarily due to much enhanced visible light absorption and appropriate gradient energy gap structure. This work not only offers the synthesis route for the novel TiO₂/CeO₂ core/shell heterojunction, but also suggests that this new core/shell heterojunction has a great potential application for efficient PEC water splitting devices.     

First demonstration of photoelectrochemical water splitting by commercial W–Cu powder metallurgy parts converted to highly porous 3D WO3/W skeletons

Hydrogen evolution through photoelectrochemical (PEC) water splitting by tungsten oxide-based photoanodes, as a stable and environmental-friendly material with moderate band gap, has attracted significant interest in recent years. The performance of WO₃ photoanode could be hindered by its poor oxygen evolution reaction kinetics and high charge carrier recombination rate. Additionally, scalable and cost-effective commercial procedure to prepare nanostructured electrodes is still challenging. We present, for the first time, a novel and scalable method to fabricate highly efficient self-supported WO₃/W nanostructured photoanodes from commercial W–Cu powder metallurgy (P/M) parts for water splitting. The electrodes were prepared by electrochemical etching of Cu networks followed by hydrothermal growth of WO₃ nanoflakes. Interconnected channels of W skeleton provided high active surface area for the growth of WO₃ nanoflakes with a thickness of ~40 nm and lateral dimension of ~250 nm. The optimized photoelectrode having 35% interconnected porosity exhibited an impressive current density of 4.36 mA cm⁻² comprising a remarkable photocurrent of 1.71 mA cm⁻² at 1.23 V vs. RHE under 100 mW cm⁻² simulated sunlight. This achievement is amongst the highest reported photocurrents for WO₃ photoelectrodes with tungsten substrate reported so far. Impedance and Mott-Schottky analyses evidenced fast charge transfer, low recombination rate, and accelerated O₂ detachment provided by optimum 3D porous WO₃/W electrode. Due to the nature of the commercial P/M parts and low-temperature hydrothermal processing, the procedure is cost-effective and scalable which can pave a new route for the fabrication of highly porous and efficient water splitting electrodes.     

Construction of g-C3N4/BCN two-dimensional heterojunction photoanode for enhanced photoelectrochemical water splitting

Two-dimensional heterojunction g-C₃N₄/BCN was constructed via thermal polymerization process. The formed two-dimensional heterostructure could enhance the interfacial contact area between BCN and porous g-C₃N₄ as well as shorten the photogenerated charge carriers transfer time and distance. The two-dimensional g-C₃N₄/BCN heterojunction photoanode shows enhanced photoelectrochemical (PEC) performance for water splitting under visible-light irradiation, which primarily originates from the improved charge transfer and separation, and prolonged lifetime of electrons. Under the visible light irradiation, the g-C₃N₄/BCN heterojunction sample yields a photocurrent density of ∼0.62 mA cm⁻² at 1.23 V vs. RHE, which is about eight times as many as that of CN (0.08 mA cm⁻²) electrode at the same conditions. In addition, the possible electron transfer model and mechanism of PEC water splitting for H₂ evolution have been discussed.