Photocatalysts For Water Splitting Research Articles

Two-dimensional ferroelastic semiconductors InXY (X = S, Se; Y = Cl, Br, I): Promising candidates for photocatalytic water splitting with tunable electronic anisotropy

We have identified a class of two-dimensional ferroelastic monolayers, denoted as InXY (where X = S, Se; Y = Cl, Br, I), through first-principles calculations. The dynamic, thermal, and mechanical stabilities of these InXY monolayers are validated by phonon dispersion spectra, AIMD calculations, and elastic constants, respectively. These monolayers exhibit semiconducting behavior with bandgaps ranging from 1.94 to 2.85 eV and possess excellent ferroelasticity with strong ferroelastic signals and moderate ferroelastic switching barriers. Notably, the band edge positions of InSBr and InSI monolayers are observed to stride the water redox potentials at pH = 0, indicating their potential as photocatalysts for water splitting in acidic environments. We also explored the effects of biaxial strain on the band edge alignments and photocatalytic performance of these monolayers. Moreover, the InXY monolayers exhibit excellent anisotropic optical absorption across the visible to ultraviolet regions, along with high anisotropic carrier transport. The coupling of ferroelastic and anisotropic properties in these monolayers offers promising opportunities for designing controllable electronic devices, thereby expanding their potential applications in multifunctional materials. Our findings reveal that the InXY monolayers are promising candidates for efficient photocatalytic water splitting and controllable optoelectronic applications.

Mechanism of Anodic Dissolution of Tungsten in Sulfate–Fluoride Solutions

Thin passive films on tungsten play an important role during the surface levelling of the metal for various applications and during the initial stages of electrochemical synthesis of thick, nanoporous layers that perform well as photo-absorbers and photo-catalysts for light-assisted water splitting. In the present work, the passivation of tungsten featuring metal dissolution and thin oxide film formation is studied by a combination of in situ electrochemical (voltammetry and impedance spectroscopy) and spectro-electrochemical methods coupled with ex situ surface oxide characterization by XPS. Voltametric and impedance data are successfully reproduced by a kinetic model featuring oxide growth and dissolution coupled with the recombination of point defects, as well as a multistep tungsten dissolution reaction at the oxide/electrolyte interface. The model is in good agreement with the spectro-electrochemical data on soluble oxidation products and the surface chemical composition of the passive oxide.

Direct Z-scheme GeC/GaSe heterojunction by first-principles study for photocatalytic water splitting

In this study, we constructed the direct Z-scheme heterojunction by vertically stacking monolayers of GeC and GaSe. And systematically explored its stability, electronic structure, optical absorption characteristics and photocatalytic mechanism with first principles calculations. Our results show that the GeC/GaSe heterojunction possesses an indirect-gap of 1.88 eV and exhibits a staggered energy-band structure. In comparison to the individual monolayers of GeC and GaSe, the GeC/GaSe heterojunction has more excellent absorption of far-ultraviolet and visible light. And the electrons and holes in the GeC/GaSe heterojunction have a transmission path resembling the letter Z. There is also an internal electric field from GeC to GaSe in the heterojunction, which accelerates the photoelectrons and holes along the Z direction when the heterojunction receives light. Furthermore, further studies suggest that the GeC/GaSe heterojunction can be utilized as a photocatalytic material for water splitting under pH = 0–14. Besides, the bandwidth and optical absorption properties of the GeC/GaSe heterojunction can be adjusted by biaxial strains. Moreover, Gibbs free energy calculations during water splitting demonstrate that the GeC/GaSe heterojunction exhibits a highly driven force for both OER and HER. Thus, direct Z-scheme GeC/GaSe heterojunction has the capability to be a promising photocatalyst for water splitting.

Optical response of Zr[formula omitted]CO[formula omitted]/MoS[formula omitted] van der Waals heterostructures calculated using first-principles calculations

In the field of material science, the search for a material with an optimal bandgap of approximately 1.40 eV that can act as an efficient photocatalyst for water splitting using solar spectrum irradiation is a noble mission. In this article, we explore the structural, electronic structure, optical and photocatalytic properties of Zr2CO2/MoS2 vdW heterostructures. Our results demonstrates that the Zr2CO2/MoS2 vdW heterostructure can be reliably synthesized. This is due to a minimal lattice mismatch of less than 3%, a negative adhesion energy of -4.23 meV/Å 2, and inherent dynamic stability. The electronic band structure calculations indicate that the Zr2CO2/MoS2 vdW heterostructure is an indirect bandgap semiconductor. We found that the conduction band minimum (CBM) and valance band maximum (VBM) of the heterostructure are located in different monolayers. Furthermore, under −2% biaxial strain a transition from type-I to type-II (staggered) band alignment occurred. Stacking 2D MoS2 on the Zr2CO2 monolayer results in a vdW heterostructure, and as a result, the HSE calculated bandgap of the Zr2CO2/MoS2 vdW heterostructure in most stable configuration lying in the ideal range for photocatalytic applications. We also studied the heterostructure’s optical properties to understand its response to incident photons with energies up to 14 eV. Based on our findings, Zr2CO2/MoS2 heterostructures are desirable for optoelectronic device applications operated in visible range. Our research offers fresh recommendations for developing novel, highly effective photocatalytic compounds with numerous optical device applications.

Janus NbOBrI monolayer for efficient photocatalytic overall water splitting

Due to the presence of a built-in electric field, two-dimensional Janus materials can effectively reduce photogenerated carrier recombination while promoting carrier separation. In this work, the viability of Janus NbOBrI monolayer as a high-efficiency photocatalyst for water splitting was examined using first-principles calculations. The results demonstrate that the Janus NbOBrI monolayer exhibits appropriate band-edge potentials, significant visible light absorptions, high carrier separation efficiency and high enough carrier mobility along the Peierls distortion direction. Moreover, we have determined the variations in the Gibbs free energy for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) at various pHs, and found that the OER can occur spontaneously in the light environment. Applying -1.5 % uniaxial strain in the a(b) direction of the NbOBrI monolayer helps to increase the reduction potential and provide sufficient power for the HER, resulting in a solar-to-hydrogen (STH) efficiency of 8.9 % (9.3 %).

(Invited) Photocatalysis of Mg-Doped SrTiO3 for Conversion of CO2 with H2O

Photocatalysis has been highly attracting the world-wide attentions among many approaches to convert CO2 into value-added products such as CO, HCOOH, CH3OH and CH4, because photocatalytic conversion of CO2 can be a solution for global warming in terms of its renewability, harmlessness, relatively low cost, and stability. Large number of photocatalysts reported in the research field of the photocatalytic conversion of CO2 require the photoirradiation with deep UV light < 300 nm. Recently, our research group found that Al-doped SrTiO3 photocatalyst (Al-STO), which has been previously reported as a superior photocatalyst for overall water splitting[1], also showed the photocatalytic activity for the conversion of CO2 into CO[2]. In this study, the effect of metal dopant in SrTiO3 on the photocatalytic conversion of CO2 was investigated, and it was found that Mg-doped SrTiO3 showed excellent photocatalytic activity for the conversion of CO2 into CO in the presence of AgCo dual cocatalyst[3].Mg-doped SrTiO3 (Mg-STO) was synthesized by a flux method; the mixture of SrTiO3, MgO, and SrCl2 flux was calcined at 1418 K for 15 h. Ag and Co dual cocatalyst was loaded by a chemical reduction method. An aqueous solution of NaH2PO2 reductant was added to the suspension containing Mg-STO, AgNO3, and Co(NO3)2, and it was kept at 353 K for 90 min with vigorous stirring. Photocatalytic conversion of CO2 with H2O was carried out using an external-irradiation-type reaction vessel. AgCo/Mg-STO was dispersed in an aqueous solution of 0.1 M NaHCO3, and high purity CO2 gas was bubbled into the suspension at a flow rate of 30 mL min−1. The monochromatic UV LED lamp (365 nm) was used as a light source. The gaseous products were analyzed by TCD-GC (H2, O2) and FID-GC equipped with a methanizer (CO).AgCo/Mg-STO exhibited much higher photocatalytic activity for the conversion of CO2 into CO than AgCo/STO and AgCo/Al-STO, which were previously reported. CO was produced at a formation rate of 20 μmol h−1, which was 2.3 times larger than that for Al-STO, and the selectivity toward CO evolution was almost 100 %. H2 formation was completely suppressed in this case. Moreover, the stoichiometric amount of O2 was evolved, indicating that H2O should contribute to the photocatalytic conversion of CO2 as an electron donor. The isotope-labeling experiments using 13CO2 gas as a substrate revealed that the carbon source of CO evolved in this photocatalytic reaction CO2 gas bubbled into the suspension. Therefore, we concluded that CO2 surely split into CO and O2 by the photocatalysis of AgCo/Mg-STO. According to SEM images of undoped STO and Mg-STO, particle shape was obviously changed by Mg doping from pure cubes to irregular edge-shaved cubes. {110} facets were observed in Mg-STO accompanied with {100} facets. Moreover, Ag and Co species were selectively located on the {100} facets and the {110} edge-shaved facets, respectively, after the photoirradiation. The photogenerated electrons and holes were considered to be transferred to {100} and {110} facets separately, and the anisotropic charge transfer should result in the high photocatalytic activity of Mg-STO for the conversion of CO2 with H2O.[1] T. Takata et al., Nature, 2020, 581, 411-414.[2] S. Wang et al., Chem. Sci., 2021, 12, 4940-4948.[3] T. Nakamoto et al., Catal. Sci. Technol., 2023, 13, 4534-4541.

SiC/PtSe2 van der Waals heterostructure: A high-efficiency direct Z-scheme photocatalyst for overall water splitting predicted from first-principles study

The discovery of effective photocatalytic substances is crucial in reducing energy shortages and ecological contamination. This research involves creating SiC/PtSe2 van der Waals heterostructure with both SiC and PtSe2 monolayers, employing first-principles calculations for comprehensive theoretical analysis of their structural stability, electronic characteristics, optical features, Bader charge, and solar-to-hydrogen (STH) efficiency. Findings indicate that the SiC/PtSe2 heterostructure is a semiconductor with an indirect bandgap of 1.52 eV and a direct Z-scheme charge transfer path, facilitating more efficient segregation of photogenerated electron-hole pairs. The Bader charge indicates that the SiC layer accumulates positive charges and the PtSe2 layer accumulates negative charges, constituting a built-in electric field pointing from the SiC side to the PtSe2 side at the interface region, which can impede the complexation of the photogenerated electron-hole pairs. Furthermore, the SiC/PtSe2 heterostructure exhibits excellent optical absorption properties across both the ultraviolet and visible spectra, coupled with an exceptionally high STH efficiency of 34.7 %, significantly enhancing solar energy utilization. Ultimately, the Gibbs free energy calculations reveal the significant catalytic efficiency of the SiC/PtSe2 heterostructure for redox reactions. Based on these results, the SiC/PtSe2 heterostructure is a direct Z-scheme photocatalyst for overall water splitting.

Achieving near-infrared photocatalytic overall water splitting with singular crystalline C3N4 from semi-molten-salt treatment

Developing singular semiconductor photocatalyst for overall water splitting (OWS) is of significance for commercialization of solar-fuel-production technologies but is critically challenging due to the rigorous requirements for band structure and charge-utilization capability, especially under long-wavelength light. Herein, we report the development of a highly crystalline C3N4 photocatalyst for efficient OWS under near-infrared (NIR) irradiation (λ >700 nm). An effective semi-molten-salt approach with solid/liquid medium was used to treat the oxygen-containing precursor and to minimize undesired nitrogen defects that the traditional strategies always suffer from. The fully condensed structure with high crystallinity was therefore achieved for oxygen-incorporated C3N4 with NIR absorption. Benefiting from simultaneous realization of high crystallinity for efficient charge separation/migration and narrowed bandgap for broad light harvesting, synthesized singular C3N4 presented unprecedented OWS performances with hydrogen/oxygen evolution amount of 1.2/0.6 μmol over 30 h under NIR irradiation. This work provides a conceptual strategy for the design of advanced OWS-active photocatalysts.

Heteroepitaxial MOF-on-MOF Photocatalyst for Solar-Driven Water Splitting.

Assembly of different metal-organic frameworks (MOFs) into hybrid MOF-on-MOF heterostructures has been established as a promising approach to develop synergistic performances for a variety of applications. Here, we explore the performance of a MOF-on-MOF heterostructure by epitaxial growth of MIL-88B(Fe) onto UiO-66(Zr)-NH2 nanoparticles. The face-selective design and appropriate energy band structure alignment of the selected MOF constituents have permitted its application as an active heterogeneous photocatalyst for solar-driven water splitting. The composite achieves apparent quantum yields for photocatalytic overall water splitting at 400 and 450 nm of about 0.9%, values that compare much favorably with previous analogous reports. Understanding of this high activity has been gained by spectroscopic and electrochemical characterization together with scanning transmission and transmission electron microscopy (STEM, TEM) measurements. This study exemplifies the possibility of developing a MOF-on-MOF heterostructure that operates under a Z-scheme mechanism and exhibits outstanding activity toward photocatalytic water splitting under solar light.

Small dataset machine-learning approach for efficient design space exploration: engineering ZnTe-based high-entropy alloys for water splitting

Aiming toward a sustainable energy era, the design of efficient photocatalysts for water splitting by engineering their band properties has been actively studied. One promising avenue for the band engineering of active photocatalysts is the use of solid-solution alloying. However, the enormous possible configurations of multicomponent alloys hinders the experimental screening of this multidimensional material space, providing an opportunity for machine learning (ML) approaches to help accelerate the discovery of new multicomponent alloy materials. A conventional prerequisite for ML approaches is a large database of accurate material properties, which may require exhaustive computational and/or experimental resources. This study demonstrates that the screening of solid-solution alloys (up to hexanary systems) can be performed using a small database to minimize (and optimize) the number of high-level computational calculations. Specifically, we use ZnTe-based alloys as a prototypical example and employ a secure independent screening and sparsifing operator with the recently developed agreement method (α-method). Furthermore, we discuss and propose design routes to determine the optimal solid-solution ZnTe-based alloys for photoassisted water-splitting reactions.

First-principles study on the electronic structure and photocatalytic properties of novel two-dimensional Janus CrXCN4 (X = Si, Ge)

Abundant studies demonstrate the significant role of Janus-structured two dimensional semiconductors as photocatalytic materials, highlighting their substantial advantages and importance in photocatalysis. In this work, CrXCN4 (X = Si, Ge) Janus monolayers were constructed based on CrC2N4, and the thermal stability, thermodynamic stability, mechanical stability, electronic properties, and optical properties of the monolayers were systematically investigated. Furthermore, an investigation was conducted to examine the impact of biaxial strain on their electronic and light absorption properties. The findings reveal that both monolayers exhibit direct band gap characteristics, with high absorption coefficients for visible light owing to their appropriate band gaps (1.44 eV for CrSiCN4 and 1.15 eV for CrGeCN4, respectively). At compressive strains exceeding 3%, the CrSiCN4 monolayer demonstrates an optimal band edge position, suggesting its potential as a photocatalyst for overall water splitting. Furthermore, as the compressive strain increases, the absorption spectra have blue-shifted and the absorption coefficient becomes higher, exceeding 2 × 105 cm−1 under a −3% compressive strain. Our study highlights the potential applications of CrXCN4 monolayers in the field of optoelectronic device, particularly emphasizing the promising candidacy of CrSiCN4 as an efficient photocatalyst.

First-Principles Computational Screening of Two-Dimensional Polar Materials for Photocatalytic Water Splitting.

The band gap constraint of the photocatalyst for overall water splitting limits the utilization of solar energy. A strategy to broaden the range of light absorption is employing a two-dimensional (2D) polar material as photocatalyst, benefiting from the deflection of the energy level due to their intrinsic internal electric field. Here, by using first-principles computational screening, we search for 2D polar semiconductors for photocatalytic water splitting from both ground- and excited-state perspectives. Applying a unique electronic structure model of polar materials, there are 13 photocatalyst candidates for the hydrogen evolution reaction (HER) and 8 candidates for the oxygen evolution reaction (OER) without barrier energies from the perspective of the ground-state free energy variation calculation. In particular, Cu2As4Cl2S3 and Cu2As4Br2S3 can catalyze HER and OER simultaneously, becoming promising photocatalysts for overall water splitting. Furthermore, by combining ground-state band structure calculations with excited-state charge distribution and transfer calculated by linear-response time-dependent density functional theory (LR-TDDFT) and time-dependent ab initio nonadiabatic molecular dynamics (NAMD), respectively, the rationality of the 2D polar material model has been manifested. The intrinsic built-in electric field promotes the separation of charge carriers while suppressing their recombination. Therefore, our computational work provides a high-throughput method to design high-performance photocatalysts for water splitting.

Janus SnXY monolayers (X= P, As, Sb; Y[dbnd]H, CH3): A new class of two-dimensional photocatalysts for water splitting

Following the successful synthesis of NaSnAs in 2021, in the present study, a series of two-dimensional SnXY monolayers with X = P, As, Sb, and Y = H, CH3 are theoretically predicted. First principle calculations are performed to investigate the structural, electronic, mechanical, and optical properties of these materials. The results predict desirable dynamical and thermal stabilities with high mechanical strength for considered systems. It is found that all SnXY monolayers are semiconductors with a direct band-gap lying in the visible region. The values of band-gap decrease as the size of the X atom increases which indicates the dominant contribution of the X atom in the band edge positions. Employing biaxial strain leads to narrowing the electronic band-gaps and suggests a strain-tuneable band-gap character in these structures. The results also highlight high carrier mobilities along the SnXY monolayers. By virtue of possessing suitably large band gaps, well-matched band offsets, robust optical absorption within the visible spectrum, high carrier mobility, and moderate exciton binding energies, these systems are poised as prospective candidates for applications in photocatalysis. Accordingly, we have also explored the photocatalytic activity of SnPH and SnAsH monolayers toward oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The calculated reaction free energy profiles demonstrate the exceptional performance of these systems in facilitating overall water splitting. This study provides a comprehensive vision of novel 2D SnXY monolayers and a new outlook for designing superior photocatalysts for water splitting.

High-performance photocatalytic hydrogen evolution in a Zn0.5Cd0.5S/MoS2 p–n heterojunction

With respect to solid-solution photocatalysts for water splitting, researchers have focused on improving the loading and stability of catalysts, which have been major concerns and research interests. Herein, the fabrication of Zn0.5Cd0.5S/MoS2 nanocomposites involved a two-step method that encompassed hydrothermal synthesis and physical mixing. Experimental results confirmed that the Zn0.5Cd0.5S/MoS2 nanocomposites exhibited outstanding photocatalytic performance. In particular, they exhibited a notable hydrogen precipitation rate of 19.41 mmol/(g*h). The hydrogen production performance of Zn0.5Cd0.5S/MoS2 was approximately nine times greater than that of pure Zn0.5Cd0.5S, indicating a considerable increase. The observed enhancement in photocatalytic efficiency can be attributed to the formation of a p–n heterojunction between Zn0.5Cd0.5S and MoS2. This particular junction helped in separating and migrating photoinduced charge carriers, ultimately improving the photocatalytic performance. Furthermore, the addition of excess thiourea in MoS2 preparation produced Mo–O defects and increased the layer spacing of the involved material, improving the electron transfer and visible-light utilization of the material. The inhibition of carrier recombination was beneficial for synthesizing efficient and long-lasting photocatalysts.

Facile Synthesis of Organic–Inorganic Hybrid Heterojunctions of Glycolated Conjugated Polymer‐TiO2−X for Efficient Photocatalytic Hydrogen Evolution

AbstractThe utilization of the organic–inorganic hybrid photocatalysts for water splitting has gained significant attention due to their ability to combine the advantages of both materials and generate synergistic effects. However, they are still far from practical application due to the limited understanding of the interactions between these two components and the complexity of their preparation process. Herein, a facial approach by combining a glycolated conjugated polymer with a TiO2−X mesoporous sphere to prepare high‐efficiency hybrid photocatalysts is presented. The functionalization of conjugated polymers with hydrophilic oligo (ethylene glycol) side chains can not only facilitate the dispersion of conjugated polymers in water but also promote the interaction with TiO2−X forming stable heterojunction nanoparticles. An apparent quantum yield of 53.3% at 365 nm and a hydrogen evolution rate of 35.7 mmol h−1 g−1 is achieved by the photocatalyst in the presence of Pt co‐catalyst. Advanced photophysical studies based on femtosecond transient absorption spectroscopy and in situ, XPS analyses reveal the charge transfer mechanism at type II heterojunction interfaces. This work shows the promising prospect of glycolated polymers in the construction of hybrid heterojunctions for photocatalytic hydrogen production and offers a deep understanding of high photocatalytic performance by such heterojunction photocatalysts.

Study on electronic, optical and photocatalytic properties of vdW heterostructures based on SnS2 and Janus PtSSe monolayers

Based on the SnS2 and Janus-PtSSe monolayers, we designed six new vdW heterostructures (HS). By investigating their structural stability, we selected out the structure most likely to be synthesized in the experiment, AA-stacking SnS2/SPtSe HS. Then we further explored its electronic, optical and photocatalytic properties, and found that this HS has a suitable band gap and considerable optical absorption coefficient. In addition, the HS possesses a typical type-II band structure and build-in electric field from SnS2 to SPtSe at the interfaces, which is benefit to separate the carries into different spaces to enhance its catalytic properties. At the end of this work, photocatalytic properties of this HS for water splitting were studied. Appropriate band edges for SnS2/SPtSe HS make it as potential photocatalyst for water splitting in acid environment.

First principles study on the type-II g-C6N6/PtSSe heterojunction: A potential photocatalyst for overall water splitting

Constructing suitable van der Waals heterojunction is considered to be an efficient way to develop and design new multifunctional devices. In this work, DFT calculations have been preformed to investigate the stacking structures, electronic, optical as well as catalytic properties of vertical heterojunctions (g-C6N6/PtSSe) constructed from graphene-like C6N6 layer and PtSSe monolayer. It is predicted that Se-side contacted heterojunction (CN/SePtS) is a typical type-II semiconductor with band edges satisfying the conditions of overall water splitting, thus can be a potential photocatalyst. In addition, CN/SePtS also possesses good absorption ranging from ultraviolet to visible light regions. It is also found that strain engineering can further tune the electronic and optical properties of the heterojunction and even improve its visible light absorption. By considering the effect of optical driving force, CN/SePtS heterojunction with 4 % biaxial tensile strain is recommended to be a good candidate for overall water splitting photocatalyst. Our research can provide a guidance for designing new optoelectronic devices and photocatalysts based on g-C6N6/PtSSe vdW heterojunctions.

Efficient visible-light-driven photocatalytic hydrogen evolution in novel type-II SnS2/Al2S2 van der Waals heterostructures

With the exacerbation of environmental pollution and the energy crisis, the development and design of environmentally friendly and efficient photocatalytic catalysts for water splitting with visible light have become particularly imperative. This study delves into the detailed investigation of the novel type-II van der Waals heterostructure of SnS2/Al2S2 utilizing first-principles calculation methods. By leveraging the advantages of indirect type-II band alignment and high carrier mobility, the efficient separation of electron-hole pairs is achieved, thereby facilitating enhanced participation of electrons and holes in photocatalytic reactions. Furthermore, the heterostructure manifests a peak optical absorption coefficient value of approximately 5.34×104 cm−1 in the visible light spectrum, accompanied by the occurrence of red-shifting, which fosters efficient absorption of visible light. It is noteworthy that under conditions of pH = 0–3.7, the heterojunction surpasses the redox potential of water splitting, concurrently displaying a substantial hydrogen evolution reaction (HER) and a high efficiency of converting sunlight to hydrogen (22.31 %). These results underscore the promising potential of the SnS2/Al2S2 heterostructure as a photocatalyst for water splitting, offering crucial theoretical support and practical guidance for the further advancement of hydrogen production via water splitting technology.

Water Structure in the First Layers on TiO2: A Key Factor for Boosting Solar-Driven Water-Splitting Performances.

The water hydrogen-bonded network is strongly perturbed in the first layers in contact with the semiconductor surface. Even though this aspect influences the outer-sphere electron transfer, it was not recognized that it is a crucial factor impacting the solar-driven water-splitting performances. To fill this gap, we have selected two TiO2 anatase samples (with and without B-doping), and by extensive experimental and computational investigations, we have demonstrated that the remarkable 5-fold increase in water-splitting photoactivity of the B-doped sample cannot be ascribed to effects typically associated to enhanced photocatalytic properties, such as band gap, heterojunctions, crystal facets, and other aspects. Studying these samples by combining FTIR measurements under controlled humidity with first-principles simulations sheds light on the role and nature of the first-layer water structure in contact with the photocatalyst surfaces. It turns out that the doping hampers the percolation of tetrahedrally coordinated water molecules while enhancing the population of topological H-bond defects forming approximately linear H-bonded chains. This work unveils how doping the semiconductor surface affects the local electric field, determining the water splitting rate by influencing the H-bond topologies in the first water layers. This evidence opens new prospects for designing efficient photocatalysts for water splitting.

Two-Dimensional GeC/MXY (M = Zr, Hf; X, Y = S, Se) Heterojunctions Used as Highly Efficient Overall Water-Splitting Photocatalysts.

Hydrogen generation by photocatalytic water-splitting holds great promise for addressing the serious global energy and environmental crises, and has recently received significant attention from researchers. In this work, a method of assembling GeC/MXY (M = Zr, Hf; X, Y = S, Se) heterojunctions (HJs) by combining GeC and MXY monolayers (MLs) to construct direct Z-scheme photocatalytic systems is proposed. Based on first-principles calculations, we found that all the GeC/MXY HJs are stable van der Waals (vdW) HJs with indirect bandgaps. These HJs possess small bandgaps and exhibit strong light-absorption ability across a wide range. Furthermore, the built-in electric field (BIEF) around the heterointerface can accelerate photoinduced carrier separation. More interestingly, the suitable band edges of GeC/MXY HJs ensure sufficient kinetic potential to spontaneously accomplish water redox reactions under light irradiation. Overall, the strong light-harvesting ability, wide light-absorption range, small bandgaps, large heterointerfacial BIEFs, suitable band alignments, and carrier migration paths render GeC/MXY HJs highly efficient photocatalysts for overall water decomposition.