Photocatalyst For Overall Water Splitting Research Articles

The SnC/WS2 vdW heterojunction: A prospective direct Z-scheme photocatalyst for overall water decomposition with high STH efficiency and catalytic activity

Searching for an advanced photocatalyst is a solution to the global energy scarcity and environmental problem. In this paper, we construct a SnC/WS2 heterojunction and its structural, electronic, optical and photocatalytic properties have been investigated by first-principles calculations. The SnC/WS2 heterojunction exhibits thermodynamic stability, with a type II (staggered) energy band structure and an indirect bandgap of 1.393 eV. A built-in electrical field with direction from SnC layer to WS2 layer is formed together with a band bending in interface region. The SnC/WS2 heterojunction is a direct Z-scheme photocatalyst supporting overall water decomposition, allowing a reductive reaction to take place in the conduction band of the SnC layer to produce H2 and an oxidative reaction in the valence band of the WS2 layer to produce O2. Meanwhile, the light absorption of the SnC/WS2 heterojunction is superior to that of the two single layer materials, with the highest absorption peak 5.3 × 105 in visible light region and a solar-to-hydrogen efficiency of 42 %. Furthermore, the Gibbs free energy calculations demonstrate the high catalytic activity of the SnC/WS2 heterojunction for redox reactions. The findings reveal that the SnC/WS2 heterojunction is a super-efficient direct Z-scheme photocatalyst for overall water splitting.

Cu doping enhanced ZnIn2S4/TiO2(VO) Z-scheme heterojunction for efficient photocatalytic overall water splitting

The design and synthesis of efficient photocatalysts for overall water splitting is a promising research topic. By reasonable modification, the hydrogen evolution photocatalyst can have the ability for overall water splitting. Both ZnIn2S4 and TiO2 have shown great potential in the field of photocatalytic hydrogen evolution, but their use for efficient overall water splitting is challenging. In this work, a Z-scheme heterojunction material of Cu-doped ZnIn2S4 composite TiO2 with rich oxygen vacancies was synthesized. Cu doping enhanced the light absorption, reduced the bandgap, and improved photocatalytic activity. In addition, the oxygen vacancies in TiO2 were conducive to the separation and migration of electron-hole pairs, and the construction of a Z-scheme heterojunction between ZnIn2S4 and TiO2 can also effectively promote the separation and migration of carriers. Therefore, the photocatalytic activity of this material was significantly improved and exhibited excellent overall water splitting activity without any sacrificial agents and co-catalysts. The optimized hydrogen and oxygen evolution rates were 589.64 μmol/g/h and 292.75 μmol/g/h, respectively. This work provided favorable evidence for metal element doping to promote the photocatalytic activity of composite heterojunction materials and provided a new strategy for the development of heterojunction photocatalysts for overall water splitting.

An efficient particulate photocatalyst for overall water splitting based on scandium and magnesium co-doped strontium titanate

A high photocatalytic performance for overall water splitting was demonstrated over a photocatalyst based on a magnesium and scandium co-doped strontium titanate particle composed of a cubic shape having a nanosized step structure on the edge of the particle.

Computational Screening of 2D All‐Inorganic Lead‐Free Halide Perovskites A3B2X9 for Photovoltaic and Photocatalytic Applications

AbstractExploration of low‐dimensional Pb‐free halide perovskites with high stability and outstanding properties is still a pursuing target for developing integrated optoelectronic devices. Herein, comprehensive computational screening of a new class of two‐dimensional (2D) all‐inorganic Pb‐free A3B2X9 perovskites is performed based on the first‐principles calculations. The results indicate that the structural and electronic properties of 2D A3B2X9 structures strongly depend on the B‐X bonding interactions, which makes that their thermodynamic stability follows the trend of A3Bi2X9≈A3Sb2X9>A3In2X9>A3Ga2X9 and their interlayer interactions show a reversal trend. Owing to the lack of lone‐pair electron effect, A3In2X9 indicate direct bandgap characteristics and present the relatively smaller bandgaps and higher electron mobilities than A3Sb2X9 and A3Bi2X9. Benefit from optimal bandgaps (0.8–2.1 eV) and large absorption coefficients (104–105 cm−1) in the visible region, A3B2I9 (B = In, Sb, Bi) exhibit high power conversion efficiency up to 18.2%. Moreover, A3B2I9 (B = Sb, Bi) is verified as efficient photocatalysts for overall water splitting. The theoretical solar‐to‐hydrogen efficiency of Rb3Bi2I9 and Cs3Bi2I9 are >16%. This work suggests huge potential of 2D A3B2X9 perovskites for photovoltaic and photocatalytic applications.

Understanding Photocatalytic Overall Water Splitting of β-Ketoamine COFs through the N-C Site Synergistic Mechanism.

Overcoming the sluggish reaction kinetics of the oxygen evolution reaction (OER) is a determining factor for the practical application of photocatalysts for overall water splitting. Two-dimensional covalent organic frameworks (2D-COFs) offer an ideal platform for catalyst design in the field of overall water splitting for their exceptional chemical tunability and high efficiency of light capture. In this work, four β-ketoamine 2D-COFs, consisting of 1,3,5-triformylphloroglucinol (Tp) groups and different linkers with pyridine segments, were constructed and optimized. By means of first-principles calculations, the band structures, free energy changes of photocatalytic hydrogen evolution reaction (HER) and OER, and charge density distributions were calculated and investigated systemically to discuss the visible-light response, overall water splitting activities on active sites, and the characteristic of charge transfer and separation. The protonated pyridine N derived from the double-H2O closed-ring H-bond adsorption model could efficiently induce N-C sites' synergistic effect between pyridine N and its ortho-position C to minimize the OER energy barrier and to enhance the charge transfer and separation. A N-C site synergistic mechanism has been proposed to provide a comprehensive explanation for the experimental results and a new strategy to design novel 2D-COF photocatalysts for overall water splitting.

High carrier mobility ZrSSe/SnX (X=S, Se, S2, Se2) vdW heterostructures for photocatalytic overall water splitting: A first-principles study

Recently, the assembly of novel two-dimensional materials via van der Waals (vdW) interactions to form heterostructures is considered an effective strategy for producing materials with enhanced photocatalytic activities. This study systematically explored the optoelectronic and photocatalytic properties and carrier mobilities of novel ZrSSe/SnX (X = S, Se, S2, Se2) vdW heterostructures using density functional theory. The formation energies, elastic constants, phonon dispersions, and results of ab-initio molecular dynamic simulations indicate structural, mechanical, dynamic, and thermal stability. The electronic band structure and optical properties are calculated using hybrid functional HSE06 for accurate calculations. The results of calculations using the bandgap center technique based on density functional theory show that ZrSSe/SnSe, ZrSSe/SnS2, and ZrSSe/SnSe2 heterostructures possess suitable band edges for photocatalytic overall water splitting. The optical absorption spectrum covers a broad range from 104 in the visible region and increases to 105 in the UV region. Furthermore, the ZrSSe/SnX (X = S, Se, S2, Se2) heterostructures have high carrier mobilities of the order of 105. High mobilities help carriers to move quickly and reduce the recombination rate of holes and electrons. The findings indicate that ZrSSe/SnX (X = S, Se, S2, Se2) heterostructures are potentially efficient visible-light photocatalysts for overall water splitting.

Robust hybrid bismuth perovskites as potential photocatalysts for overall water splitting

Robust hybrid bismuth perovskites as potential photocatalysts for overall water splitting

The Isoelectronic Dopant in the Z-Scheme SnS2/β-As Heterostructure Enhancing Photocatalytic Overall Water Splitting.

The catalytic field aims to decrease reaction barriers, accelerate reaction processes, and enhance the selectivity toward a target product. This study uses first-principles calculations to design a modified direct Z-scheme SnS2/β-As heterostructure as a potential photocatalyst for overall water splitting. Our previous investigations have demonstrated that the SnS2/β-As heterostructure can realize a hydrogen evolution reaction (HER) under light, while the oxygen evolution reaction (OER) follows a pathway involving the intermediate HOOH*. Interestingly, by substituting an S atom of SnS2 with a Se or Te atom, the rate-determining step of the OER is significantly reduced from 3.76 eV to 2.56 or 2.22 eV. Moreover, the OER can occur directly without the transition via HOOH*. Isoelectronic doping effectively trades off the adsorption strength of OER intermediates and promotes the OER process. This work highlights the dual benefits of isoelectronic doping, namely lowering the reaction barrier of the rate-determining step and promoting the selectivity of end products. These findings provide insights into the rational design of high-efficiency photocatalysts for water splitting.

Two-dimensional MoSe2/PtSe2 van der Waals type-II heterostructure: Promising visible light photocatalyst for overall water splitting

The development of simple and efficient visible light photocatalytic catalysts for hydrogen production from water is an important development direction in the field of photocatalysis, and composite two-dimensional materials are found to be promising candidates. This paper constructs a novel two-dimensional MoSe2/PtSe2 type-II heterojunction and systematically studies its geometric structure, electronic structure, and optical properties by first-principles calculation. It is evident that the heterojunction has good thermodynamic, kinetic, and mechanical stability, as well as excellent hole carrier mobility, which is conducive to the separation of photogenerated electrons and holes. The optical properties show that MoSe2/PtSe2 heterojunction has the best optical absorption efficiency for visible light and has the ability to cross the water-cracking oxidation-reduction potential at pH = 4. More importantly, the MoSe2/PtSe2 heterojunction shows great hydrogen absorption reaction performance, indicating that it is a potential photocatalyst for overall water splitting of visible light, and has broad application prospects in the field of photocatalysis and optoelectronics.

Electronic and optical properties of two-dimensional III2-VI3 materials with the FE-WZ′ structure

Based on the first-principles calculations, we have investigated the mechanical, phonon, electronic and optical properties of two-dimensional (2D) In2Te3 (FE-WZ′ phase) family. The Y(θ) value for all M2X3 materials exceeds 67 N/m, with Al2S3 exhibiting the best mechanical strength, surpassing to that of MoS2 (∼124.3 N/m in the x and y directions). Phonon calculations reveal that the acoustic branch with the lowest frequency is mainly dominated by out-of-plane vibrations of the metal atoms and non-metallic atoms. Ga2Te3 exhibits dynamic instability due to the softening of the optical phonon branch. Incorporating spin–orbit coupling (SOC) in In2Se3 and In2Te3 converts them into direct semiconductors. These materials possess an electrostatic potential difference ranging from 0.73 to 2.11 eV, which effectively reduces the band gap required for water splitting in the infrared region. Moreover, the M2X3 monolayers with intrinsic electric fields are great coveted photocatalysts for overall water splitting. Remarkably, In2Se3 displays a solar-to-hydrogen efficiency of 28.6%, which is significant for commercial applications.

Enhanced performance of Janus XMSiY2 (X=S, Se; M=Mo, W; and Y=N, P) monolayers for photocatalytic water splitting via strain engineering

In this article, using first-principles calculations, we propose XMSiY2 (X = S, Se; M = Mo, W; and Y=N, P) monolayers as a Janus form of MA2Z4 family and investigate their electronic, spintronic, and photocatalytic properties. The obtained band structures show that XMSiY2 monolayers are semiconductors with bandgaps ranging from 1.21 eV to 2.98 eV. Considering spin-orbit coupling, we observe that broken out-of-plane symmetry in the XMSiY2 structures leads to Rashba spin-splitting at the Γ point and lack of inversion symmetry results in Zeeman spin-splitting at the K point of the valence bands. The monolayers with W atom exhibit larger Zeeman spin-splitting (up to 0.479 eV for SeWSiP2) which indicates that XWSiY2 monolayers are promising materials for spintronic and valleytronic applications. Assisted by the large work function difference (Δ&varphi) between two surfaces of the Janus XMSiY2 monolayers, all the proposed structures satisfy the band alignment requirement for overall water splitting. Benefiting from strong solar absorption, large carrier mobility (up to 104 cm2 V−1 s−1) and huge difference between electron and hole mobilities, XMSiY2 monolayers are predicted to be high performance photocatalysts. Lastly, the effect of biaxial strain on the photocatalytic properties of the proposed monolayers is comprehensively investigated and it is found that compressive strain helps XMSiY2 structures to act as great photocatalysts for overall water splitting in an expanded range of pH. In addition, tensile strain can broaden and intensify the solar light absorption spectrum of XMSiY2 monolayers to achieve high performance photocatalysts.

WS2/MoSe2 van der Waals heterojunctions applied to photocatalysts for overall water splitting

Addressing the energy crisis and environmental pollution necessitates efficient photocatalysts for hydrogen production via water hydrolysis. This study uncovers the potential of a novel photocatalyst - two-dimensional transition metal dichalcogenides (TMDs) heterojunction. Using density functional theory (DFT), we examined the photocatalytic performance of the two-dimensional WS2/MoSe2 heterojunctions for water splitting. Our findings reveal a direct band gap of 1.65 eV and a type II band structure in the heterojunction. This structure facilitates the separation of electrons and holes in the WS2 and MoSe2 monolayers, thereby significantly inhibiting electron-hole recombination. Furthermore, high optical absorption coefficient (105 cm − 1), small effective mass of electron(hole), low interlayer barrier, and adjustable band-edge stress in the heterostructure collectively enhance photocatalytic efficiency.

Two-dimensional CrSe2/GaN heterostructures for visible-light photocatalysis with high utilization of solar energy

Nowadays, designing a two-dimensional (2D) van der Waals heterostructure (vdWH) is one of the most promising methods for improving photocatalytic performance and harvesting solar energy. Here, we proposed a novel CrSe2/GaN vdWH as an efficient photocatalyst for overall water splitting. The elastic constants, phonon dispersion, and ab-initio molecular dynamics simulation show high mechanical and thermodynamic stability. The HSE06 functional reveals that CrSe2/GaN vdWHs possess a direct bandgap. The DFT scheme suggests that the current vdWH belongs to the type-II band alignment and has enough kinetic redox potentials for overall photocatalytic water splitting. The intrinsic electric-field accelerates the photogenerated carrier separation. The carrier mobility of the CrSe2/GaN vdWH is observed to be enhanced as compared to the mobility of the CrSe2 monolayer. Additionally, the optical absorption of the vdWH is found to be high in the visible and ultraviolet regions. The CrSe2/GaN vdWH has a high efficiency of solar-to-hydrogen energy conversion (33.41%). The Gibbs free energy shows that the redox reactions (HER & OER) could be sustained under the action of an external electric-field. Finally, the external strain can tune the band edge and optical absorption of the CrSe2/GaN vdWH for desired applications. Therefore, the CrSe2/GaN vdW heterostructure could be an excellent photocatalyst for water splitting with high solar energy conversion.

Vacancy-induced spontaneous H2 evolution by overall water splitting on MoTe2/Ti2CO2: A two-dimensional direct Z scheme heterostructure

Photocatalysts with direct Z-scheme heterostructures hold great potential for hydrogen production by solar-driven overall water splitting. However, building highly efficient direct Z-scheme heterostructures is still a challenge. This work develops a novel MoTe2/Ti2CO2 heterostructure as a potential direct Z-scheme photocatalyst for overall water splitting. First-principles computations utilizing density functional theory (DFT) have been used in this study to carefully study several aspects of the heterostructure, including vdW binding energy, formation of the internal electric field, electronic structure, optical properties, and thermodynamic feasibility of water splitting. According to these calculations, the superior interlayer interaction in MoTe2/Ti2CO2 results in a substantial built-in electric field suitable for carrier separation. These findings indicate that the suggested vdW heterostructure is a direct Z-scheme water-splitting photocatalyst with suitable band alignments and a broad light absorption range. This enhanced interaction resulted in a significant increase of photocurrent compared to both the monolayers. Additionally, it is envisaged that the heterojunction will serve as photocatalyst for the oxygen evolution process (OER) and the hydrogen evolution process (HER). The results demonstrate that MoTe2/Ti2CO2 heterostructure with Te vacancy has a low Gibbs free energy of the HER, favoring spontaneous hydrogen evolution in both acidic and neutral conditions. The suggested heterostructure exhibits a commendable solar-to-hydrogen efficiency of 15.25%, making it a viable option for commercial implementation. This research offers a theoretical foundation for designing novel, two-dimensional overall water-splitting photocatalysts in an effort to produce clean energy.

Two-dimensional g-GeC/PtSe2 van der Waals heterostructure: a visible light-driven direct Z-scheme photocatalyst for overall water splitting

The vertical stacking of different two-dimensional materials to construct van der Waals heterostructures (vdWHs) opens up a promising platform for designing high-efficiency photocatalysts. Direct Z-scheme heterostructures for photocatalytic dissociation have received much attention in recent years, in which charge carriers migrate directly between two semiconductors without redox mediators. Here, the electronic and optical properties as well as the solar-to-hydrogen conversion efficiency of g-GeC/ PtSe2 vdWHs are systematically investigated, especially for their high-efficiency visible-light water splitting catalyst features. Calculations show that the g-GeC/ PtSe2 vdWH is a semiconductor with an indirect band gap of 1.356 eV, featuring a type-II band alignment. The built-in electric field E int and band bending at the interface lead to a direct Z-scheme photocatalytic structure, and photocatalytic water splitting can be realized in the pH range of 0–14. In particular, with biaxial tensile strain ϵ= 4% applied, the g-GeC/PtSe2 vdWH possesses a smaller band gap, wider visible light response range and very high STH conversion efficiency (η STH) up to 49.07%, entirely satisfying the optimal photocatalytic water splitting conditions. This work provides a new perspective for designing promising direct Z-scheme visible light water splitting catalysts with a high-efficiency solar energy conversion, beneficially to the development of clean energy.

2D/2D Janus BiTeCl/GeSe vdW heterostructure as a robust high-performance S-scheme photocatalyst for water splitting

Two-dimensional (2D) S-scheme van der Waals (vdW) heterostructures (HSs) have aroused much interest as advanced photocatalysts due to their strong redox ability and light utilization. In this work, we have proposed a 2D/2D vdW HS composed of Janus BiTeCl monolayer (ML) and GeSe ML, and systematically investigated its photocatalytic performance using first-principles calculations. Our results show that the HS exhibits an appropriate electronic band in which the existence of intrinsic built-in electric field from GeSe ML to BiTeCl ML enhances the separation of photo-induced electron-hole pairs and certifies a S-scheme mechanism in the HS. Furthermore, the optical and electronic properties of the HS are nearly independent of either biaxial or uniaxial strain, showing robustness of the HS applied in an ever-changing environment. Notably, the HS can achieve spontaneously solar-driven water splitting and exhibits an enhanced solar-to-hydrogen (STH) efficiency up to 19.27 % owing to its S-scheme mechanism and wide range of light absorption with high absorption coefficient. Our results give insights to the structure, electronic and photocatalytic properties of 2D/2D Janus BiTeCl/GeSe vdW HS and may provide a promising S-scheme photocatalyst for overall water splitting.

2D/2D Cu-tetrahydroxyquinone MOF/N-doped graphene heterojunction as photocatalyst for overall water splitting

2D/2D Cu-tetrahydroxyquinone MOF/N-doped graphene heterojunction as photocatalyst for overall water splitting

Exploration of Photocatalytic Overall Water Splitting Mechanisms in the Z-Scheme SnS2/β-As Heterostructure

The Z-scheme heterostructure photocatalysts have irreplaceable advantages over other heterostructures due to their ability to separate the spatial carriers and retain strong redox ability. In this study, we explored the SnS2/β-As (β-arsenene) van der Waals heterostructure with Z-scheme properties and suitable band edge positions as a potential photocatalyst for overall water splitting. Under appropriate conditions, the hydrogen evolution reaction (HER) barrier is much closer to 0. Based on the oxidation product criteria, the SnS2/β-As heterostructure photocatalyst may generate multiple end products, including •OH, H2O2, and O2. Moreover, we screen the optimal and most possible reaction pathway OER-III under irradiation among three underlying oxygen evolution reaction (OER) mechanisms, in which the intermediate species HOOH* acts as a bridge for subsequent reactions. The solar-to-hydrogen conversion efficiency of the heterostructure can reach 17.18%. This work provides new insights into designing superior photocatalysts for overall water splitting and recognizing the OER mechanism.

Rh-doped ultrathin NiFeLDH nanosheets drive efficient photocatalytic water splitting

NiFeLDH (Layered double hydroxide) semiconductors are promising for harnessing light energy. The development of transition metal-based photocatalysts consisting of rhodium building blocks is not only beneficial for the separation and transfer of photo-generated carriers in photocatalytic reactions but also an effective means of widening the optical window of light absorption. In this report, a facile hydrothermal approach is employed in modulating NiFeLDH nanosheets arrays with optimal molar ratio of Rhodium (Rh) in LDH to engineer a robust hierarchical NiFeLDH-Rh photocatalytic system towords efficient hydrogen evolution reaction (HER) under visible light. In a systematic investigation, the NiFeLDH is grown on nickel foam and controlled doping of Rhodium led to fine-tuning of their electronic structure and efficient visible light-driven proton reduction system due to its multiple accessible active sites boosting the photocatalytic performance. Furthermore, the 2D hierarchical nanosheet arrays can speed up electron diffusion and assure fast electron/mass transfer while maintaining high photocatalytic stability. The NiFeLDH-Rh composite demonstrated an enhanced hydrogen generation rate of 2.09 mmolg−1h−1 (AQY = 6.1%). The photocurrent density and transient photocurrent curve show rapid charge transfer as well as the unique electron transfer paths through the contact surface, resulting in efficient charge separation. Moreover DFT and photoelectrochemical studies reveal higher HER activity due to the augmented electric field between Rh and NiFeLDH complex. This research offers a novel strategy and new insights into the investigation of highly active photocatalysts for overall water splitting.

Z-Scheme Modulated Charge Transfer on InVO4 @ZnIn2 S4 for Durable Overall Water Splitting.

The charge transfer within heterojunction is crucial for the efficiency and stability of photocatalyst for overall water splitting (OWS). Herein, InVO4 nanosheets have been employed as a support for the lateral epitaxial growth of ZnIn2 S4 nanosheets to produce hierarchical InVO4 @ZnIn2 S4 (InVZ) heterojunctions. The distinct branching heterostructure facilitates active site exposure and mass transfer, further boosting the participation of ZnIn2 S4 and InVO4 for proton reduction and water oxidation, respectively. The unique Z-scheme modulated charge transfer, visualized by simulation and in situ analysis, has been proved to promote the spatial separation of photoexcited charges and strengthen the anti-photocorrosion capability of InVZ. The optimized InVZ heterojunction presents improved OWS (153.3µmolh-1 g-1 for H2 and 76.9µmolh-1 g-1 for O2 ) and competitive H2 production (21090µmolh-1 g-1 ). Even after 20 times (100h) of cycle experiment, it still holds more than 88% OWS activity and a complete structure.