Candidate For Photocatalytic Water Splitting Research Articles

A DFT investigation of Li substitution in CsCaY3 (Y[dbnd]F, Cl, Br) having admirable optoelectronic characteristics as a viable candidate for photocatalytic water splitting

In this study we investigated pristine and Li substituted Cs1-xLixCaY3 (YF, Cl, Br) lead free halide perovskite with different concentrations x = 0, 0.11, 0.33, 0.55, 0.77, and 1 using CASTEP under Density functional theory (DFT) has been employed under Perdew Burke Ernzerhof generalized gradient approximation (GGA-PBE) and Ultrasoft pseudo potential (USSP) approaches. Understudy pristine materials have a cubic phase Pm3 m space group. At the same time, doped compositions show a tetragonal phase structure except those in which Li completely swaps out Cs, so both end materials own a cubic nature. Li introduced at the Cs site is more effective than Ca because additional gamma points formed, influencing the electronic formation of pristine CsCaF3, CsCaCl3, and CsCaBr3 minimized band gap from 6.299 to 4.152 eV, 5.261–3.613 eV and 4.338–2.752 eV respectively. All compositions are thermodynamically stable, as suggested by the negative values of the formation energy. For all compositions, the Fermi level resides near the valence band which confirms the p-type behavior of the semiconductors. All of the materials retain the indirect bandgap. The total/partial/elemental density of states calculated has been approximated to provide a full picture of the band structure. Although elastic constants for all compounds, whether cubic or tetragonal, are used to predict mechanical parameters such as bulk modulus, shear modulus, young modulus, Poisson ratio, and Pugh's ratio, materials were first developed to support born stability criteria. From all of the compositions Cs1-xLixCaF3 for x = (0.11, 0.55, 0.77, and 1) and Cs0.23Li0.77CaCl3 are found to be mechanically unstable. All other combinations are stable, whether cubic or tetragonal. We evaluated and contrasted many optical properties like absorption spectra, refractive index, dielectric function, reflectivity, and energy loss function of pristine CsCaY3 (YF, Cl, Br) in comparison with Li substitution concentrations. For both pristine and Li substituted CsCaY3 (YF, Cl, Br) the overall water splitting was explored. All the compositions can be used for hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and overall water splitting reactions but Cs0.23Li0.77CaBr3 is a good catalyst among all. It is proposed that the aforementioned materials have a bandgap range suitable for solar cell applications in addition to being lead-free for environmentally conscious applications in photocatalytic activity.

Two-dimensional Janus SnS/MoSi2N4 structure for high-efficiency photocatalytic splitting

Energy consumption and environmental pollution need us to explore new and sustainable energy sources. Photocatalytic water splitting for hydrogen production offers one of the most effective solutions to this problem. Identifying an advanced photocatalyst is essential to achieve high-efficiency photocatalytic water splitting. We observed that the SnS/MoSi2N4 van der Waals heterostructure (vdWH) is a viable candidate for photocatalytic water splitting using density functional theory (DFT). Our investigation has revealed that the SnS/MoSi2N4 vdWH exhibits type-II band alignment, which is highly advantageous for spatially separating photoexcited electron-hole pairs. Remarkably, this type-II band arrangement remains stable across different stacking forms of the vdWH. Meanwhile, SnS/MoSi2N4 vdWH exhibits high light absorption ability. After considering the Janus effect, we have ascertained that SnS/MoSi2N4 vdWH likely possesses appropriate band edge positions for facilitating water splitting. Moreover, we revealed that bandgap and light absorption of SnS/MoSi2N4 vdWH could be further improved by applying the strain while SnS/MoSi2N4 vdWH still maintains the appropriate band edge positions. The results suggest that SnS/MoSi2N4 vdWH is an ideal photocatalyst for water splitting.

Synthesis and photocatalytic activity of LaTiO2N using titanium oxide nanosheet/La3+ hybrids as a precursor

LaTiO2N, which has attracted attention as a promising candidate for photocatalytic water splitting, was synthesized through a method that utilized a titania nanosheet/La3+/La(OH)3 hybrid system as a precursor.

GaSe/YAlS3: A type-II van der Waals heterostructure with ultrahigh solar-to-hydrogen efficiency for photocatalytic water splitting

Photocatalytic water splitting, a process aimed at hydrogen production, is considered a pivotal clean energy sources to achieve environmental friendliness and high energy efficiency in the future. The crux of achieving this objective lies in the design of stable and efficient catalysts. Herein, we proposed a novel type-II band alignment GaSe/YAlS3 van der Waals heterostructure with robust stability for photocatalytic water splitting. The intrinsic electric field of YAlS3 monolayer can break the requirement of band gap (>1.23 eV) in traditional photocatalytic water splitting theory and significantly enhancing the utilization of solar energy. Encouragingly, compared to individual monolayers GaSe or YAlS3, the optical absorption coefficients of the GaSe/YAlS3 heterostructure are significantly improved and the corrected solar-to-hydrogen (STH) efficiency is improved by 406% and 132%, respectively, reaching an impressive 29.73% efficiency. Furthermore, the heterostructure demonstrates exceptional overall water splitting performance across a broad pH range and maintains a consistently high STH efficiency (25.41%∼34.71%) under a wide range biaxial strain (−6%–5%). In addition, the designed GaSe/YAlS3 heterostructure showcases enhanced absorption of visible as well as partial absorption of infrared light for photocatalytic water splitting. These compelling findings unequivocally establish GaSe/YAlS3 heterostructure as an excellent and promising candidate for photocatalytic water splitting.

Doped MoS2 Polymorph for an Improved Hydrogen Evolution Reaction.

Green hydrogen produced from solar energy could be one of the solutions to the growing energy shortage as non-renewable energy sources are phased out. However, the current catalyst materials used for photocatalytic water splitting (PWS) cannot compete with other renewable technologies when it comes to efficiency and production cost. Transition-metal dichalcogenides, such as molybdenum disulfides (MoS2), have previously proven to have electronic and optical properties that could tackle these challenges. In this work, optical properties, the d-band center, and Gibbs free energy are calculated for seven MoS2 polymorphs using first-principles calculations and density functional theory (DFT) to show that they could be suitable as photocatalysts for PWS. Out of the seven, the two polymorphs 3Ha and 2R1 were shown to have d-band center values closest to the optimal value, while the Gibbs free energy for all seven polymorphs was within 5% of each other. In a previous study, we found that 3Hb had the highest electron mobility among all seven polymorphs and an optimal bandgap for photocatalytic reactions. The 3Hb polymorphs were therefore selected for further study. An in-depth analysis of the enhancement of the electronic properties and the Gibbs free energy through substitutional doping with Al, Co, N, and Ni was carried out. For the very first time, substitutional doping of MoS2 was attempted. We found that replacing one Mo atom with Al, Co, I, N, and Ni lowered the Gibbs free energy by a factor of 10, which would increase the hydrogen evolution reaction of the catalyst. Our study further shows that 3Hb with one S atom replaced with Al, Co, I, N, or Ni is dynamically and mechanically stable, while for 3Hb, replacing one Mo atom with Al and Ni makes the structure stable. Based on the low Gibbs free energy, stability, and electronic bandgap 3Hb, MoS2 doped with Al for one Mo atom emerges as a promising candidate for photocatalytic water splitting.

Forecasting the unrevealed surface-controlled photocatalytic water splitting in two-dimensional Ag2Se with ultrafast carrier mobility: a first-principles study

It has been hypothesized that a thermodynamically feasible Ag2Se monolayer could be a potential candidate for photocatalytic water splitting.

Two-dimensional AlN/TMO van der Waals heterojunction as a promising photocatalyst for water splitting driven by visible light.

In this study, the photocatalytic properties of AlN/TMO heterojunctions formed by coupling MoO2 and WO2 of transition metal oxides with AlN are studied in detail using first-principles calculations with the aim of finding efficient and low-cost photocatalysts for water splitting to produce hydrogen to reduce environmental pollution. The AIMD, phonon spectrum, and elastic constants demonstrated the thermodynamic, kinetic, and mechanical stabilities of the AlN/TMO heterojunction. The results showed that the AlN/MoO2 (1.55 eV) and AlN/WO2 (1.99 eV) heterojunctions have typical type-II energy band arrangements, which can effectively promote the separation of photogenerated electrons and hole pairs. Meanwhile, the AlN/MoO2 heterojunction showed excellent carrier mobilities (electron, 250.05 cm2 V-1 S-1 and hole, 45 467.07 cm2 V-1 S-1), which greatly exceeded those of each component. The AlN/WO2 heterojunction showed an excellent HER (-0.07 eV) performance, which was close to the expected value. For the AlN/WO2 heterojunction, a suitable band gap value, excellent HER, and other properties indicated that it has the potential to become a new candidate for photocatalytic water splitting. Our study enriches the theoretical research of transition metal oxide materials and wide-band gap materials by providing a reference direction for the design of reasonably high-quality photocatalysts.

Strain-induced ultrahigh power conversion efficiency in BP-MoSe2 vdW heterostructure

Photocatalytic water splitting is a promising method for hydrogen production, and the search for efficient photocatalysts has received extensive attention. Two-dimensional van der Waals (vdW) heterostructures have recently been considered excellent candidates for photocatalytic water splitting. In this work, a BP-MoSe2 vdW heterostructure composed of a blue phosphorus (BP) and MoSe2 monolayer was studied as a potential photocatalyst for water splitting using first-principles calculations. The results show that the heterostructure has a type-II band structure, and the band edges straddle water redox potentials under biaxial strains from −3% to 2%, satisfying the requirements for photocatalytic water splitting. In addition, the heterostructure has excellent power conversion efficiency (PCE) and strong optical absorption in both visible light and near-ultraviolet region, indicating that it is a very promising candidate for photocatalytic water splitting. Specifically, the PCE was enhanced to ∼20.2% under a tensile strain of 2%. The Gibbs free energy profiles indicate that BP-MoSe2 vdW heterostructure exhibits good catalytic performance in hydrogen and oxygen evolution reactions. In particular, high carrier mobility implies that the transfer of carriers to reactive sites is easy, and the recombination probability of photogenerated electron–hole pairs is reduced.

Type-II CuFe2O4/Graphitic Carbon Nitride Heterojunctions for High-Efficiency Photocatalytic and Electrocatalytic Hydrogen Generation.

Solar water splitting has emerged as an urgent imperative as hydrogen emerges as an increasingly important form of energy storage. g-C3N4 is an ideal candidate for photocatalytic water splitting as a result of the excellent alignment of its band edges with water redox potentials. To mitigate electron-hole recombination that has limited the performance of g-C3N4, we have developed a semiconductor heterostructure of g-C3N4 with CuFe2O4 nanoparticles (NPs) as a highly efficient photocatalyst. Visible-light-driven photocatalytic properties of CuFe2O4/g-C3N4 heterostructures with different CuFe2O4 loadings have been examined with two sacrificial agents. An up to 2.5-fold enhancement in catalytic efficiency is observed for CuFe2O4/g-C3N4 heterostructures over g-C3N4 nanosheets alone with the apparent quantum yield of H2 production approaching 25%. The improved photocatalytic activity of the heterostructures suggests that introducing CuFe2O4 NPs provides more active sites and reduces electron-hole recombination. The g-C3N4/CuFe2O4 heterostructures furthermore show enhanced electrocatalytic HER activity as compared to the individual components as a result of which by making heterostructures g-C3N4 with CuFe2O4 increased the active catalytic surface for the electrocatalytic water splitting reaction. The enhanced faradaic efficiency of the prepared heterostructures makes it a potential candidate for efficient hydrogen generation. Nevertheless, the designed heterostructure materials exhibited significant photo- and electrocatalytic activity toward the HER, which demonstrates a method for methodically enhancing catalytic performance by creating heterostructures with the best energetic offsets.

Cadmium Sulfide 3D Photonic Crystal with Hierarchically Ordered Macropores for Highly Efficient Photocatalytic Hydrogen Generation.

Cadmium sulfide is a potential candidate for photocatalytic water splitting. However, CdS nanoparticles have a high recombination rate of photoinduced carriers induced by aggregation. Therefore, decreasing the recombination rate and increasing the migration rate of photogenerated carriers are essential to drive the development and application of CdS in hydrogen production. In this study, we design CdS with a three-dimensional ordered macroporous (3DOM) structure using polymethylmethacrylate as a template. It not only retains the excellent visible light response of CdS but also improves the easy recombination of photogenerated carriers in CdS nanoparticles by taking advantage of the unique ability of mass transfer, charge separation, and migration in the 3DOM structure. Meanwhile, the highly ordered periodic structure of 3DOM CdS can produce a slow photon effect of photonic crystals to obtain more photoinduced carriers. In particular, we found that a suitable stop-band position is beneficial to maximize the utilization of the slow photon effect. The photocatalytic hydrogen evolution rate of Pt-CdS is considerably improved after constructing the 3DOM structure. This study provides a new design strategy of ordered macroporous sulfide catalysts to achieve high photocatalytic activity.

Intrinsic direct bandgap semiconductor with high stability, strong anisotropy and controllable edge position in BrHfN monolayer

Based on first-principles calculations, the BrHfN monolayer has a direct band gap of 3.19 eV, and the edge position can be adjusted by applying pressure. The BrHfN monolayer meets the energy band structure requirements of photocatalytic water splitting. In addition, the calculation of cohesive energy shows the feasibility of the experiment. Ab initio molecular dynamics simulations at room temperature and phonon dispersion curves show the stability of the structure. Young's modulus can be as high as 158 N m−1, and Poisson's ratio shows high anisotropy. High absorption coefficients, appropriate band edge positions and strong ability for carrier separation and transfer make it a promising candidate for photocatalytic water splitting. Additionally, the band structure and optical absorption of monolayer BrHfN can be effectively tuned by strain effect. Our research provides valuable insight for finding more potential functional two-dimensional semiconductors applied in optoelectronics, solar energy conversion, and photocatalytic water splitting.

Internal and external electric field tunable electronic structures for photocatalytic water splitting: Janus transition-metal chalcogenides/C3N4 van der Waals heterojunctions

Structural symmetry-breaking plays a crucial role in determining the electronic structures of two-dimensional (2D) materials. Janus transition-metal dichalcogenides (TMDs) break the out-of-plane mirror symmetry of TMD and induce a built-in electric field in the 2D Janus TMD to present rather exotic properties with applications. There forms a coupled electric field by the intra-layer and inter-layer of Janus TMDs with the stacking van der Waals (vdW) heterojunctions, which can effectively change the intrinsic property and reconstruct the band structure. Here, vdW heterojunction composed of Janus WXY (X/Y = S, Se and Te; X ≠ Y) and C3N4 is explored by using the first-principles calculation method. The results show that all the vdW heterojunctions, except WSTe/C3N4, can meet the band gap and band-edge position requirements of photocatalytic water splitting when they are modulated by a limited external electric field. The detailed electronic analysis shows that the external electric field will affect the band-edge position and further change the band gap of the type-II vdW heterojunction. Finally, only WSeTe/C3N4 vdW heterojunction possessing high optical absorption strength and broad spectrum width is the best candidate for photocatalytic water splitting. This work provides a new understanding and stimulates more studies for photocatalytic water splitting in Janus based vdW heterojunctions.

NbS2Cl2 monolayer: A promising 2D semiconductor for photocatalytic water splitting

Hydrogen production from photocatalytic water splitting is one of the most effective means to solve the existing energy and environmental problems, and photocatalysts that can efficiently capture sunlight have been pursued for a long time. In this work, on the basis of density functional theory (DFT) computations, we proposed a novel two-dimensional material, namely NbS2Cl2 monolayer, as a promising candidate for photocatalytic water splitting. According to our results, NbS2Cl2 monolayer is kinetically and thermodynamically stable, and can be separated from its layered bulk structure easily due to the small cleavage energy of 0.25 J/m2. Remarkably, NbS2Cl2 monolayer is a semiconductor with a direct band gap of 2.71 eV, and the positions of its valence and conduction edges are suitable for water redox reactions. Moreover, NbS2Cl2 monolayer also has considerable optical absorption that covers the solar spectrum from ultraviolet to visible regions. These superior performances make 2D NbS2Cl2 a promising catalyst for photocatalytic water splitting.

Toward photocatalytic hydrogen generation over BiVO4 by controlling particle size

Owing to excellent light absorption and high activity for oxygen evolution, monoclinic bismuth vanadate (BiVO4) is regarded as an ideal candidate for photocatalytic water splitting. However, its application is limited by the large particle size in micrometer scale, as well as the slightly positive conduction band. In this work, we successfully synthesized nano-BiVO4 with particle size ranged from 27 nm to 57 nm by wet chemical method based on electrostatic spinning method. Unlike bulk BiVO4, the nano-sized BiVO4 possesses the ability to generate hydrogen by water splitting, and the activity could reach up to 1.66 μmol h−1 g−1 with the assistance of Pt. The enhanced activity is mainly attributed to the improvements resulted from reduced particle size, which includes elevated conduction band, enlarged specific surface area and promoted charge separation. This work provides a simple method for synthesizing photocatalyst with small particle size and high yield.

GeC/GaN vdW Heterojunctions: A Promising Photocatalyst for Overall Water Splitting and Solar Energy Conversion.

Two-dimensional van der Waals (vdW) heterojunctions have been regarded as promising candidates for photocatalytic water splitting and solar energy conversion. Here, we propose a two-dimensional GeC/GaN vdW heterostructure, where the GaN monolayer and the GeC monolayer are stacked. The binding energy, phonon spectrum, and elastic constants demonstrate this material's high dynamic and mechanical stability. Most notably, the GW band structure, GW + Bethe-Salpeter equation (BSE) optical absorption spectrum, and the band alignment of the density functional theory (DFT) scheme and empirical formula reveal that the GeC/GaN vdW heterostructures have a dramatically high optical absorption coefficient (∼105 cm-1) in the visible region and a suitable band edge with sufficiently large kinetic overpotentials of the hydrogen evolution reaction (ΔEc ≥ 1.945 eV) and the oxygen evolution reaction (ΔEv ≥ 1.244 eV). Photogenerated electrons and holes aggregate on the GeC monolayer and GaN monolayer surfaces, respectively, which could make this heterojunction a promising candidate for photocatalytic water splitting and solar energy conversion.

Theoretical Investigation of Monolayer RhTeCl Semiconductors as Photocatalysts for Water Splitting

Photocatalytic water splitting, an environmentally friendly approach for producing hydrogen, is a feasible and efficient solution for the environmental and energy crisis. A major challenge for photocatalytic water splitting is searching for catalysts with suitable band gap and band alignment with promising electronic and optical properties. Herein, we predict a novel two-dimensional material, monolayer RhTeCl, which is potentially exfoliable from its bulk counterparts with a small cleavage energy (~0.39 J/m2). Dynamical, thermal, and mechanical stabilities, as well as suitable direct band gap (2.49 eV) and band edge positions qualify monolayer RhTeCl as a promising candidate for photocatalytic water splitting. High electron mobility and exciton binding energy further suppress the electron-hole recombination, and good light harvesting ability is presented with pronounced optical absorbance in the visible light and ultraviolet regions. In addition, the Gibbs free energy diagram shows that water splitting on...

Effect of Bulk Hydrogen on the Photocatalytic Activity of Semiconducting Ta3N5: A Hybrid-DFT Viewpoint

Ta3N5 is a promising candidate for photocatalytic water splitting. Hydrogen impurities are always introduced into the Ta3N5 lattice during ammonolysis of TaOx precursors. Limited attention has been...

Rational modulation of p-n homojunction in P-doped g-C3N4 decorated with Ti3C2 for photocatalytic overall water splitting

As a metal-free polymeric semiconductor, graphitic carbon nitride (g-C3N4) is a promising candidate for photocatalytic water splitting but suffers from the insufficient optical absorption and sluggish utilization of photocarriers. Herein, based on the energy band engineering theory, a new design philosophy of tunable p-n homojunction is proposed and realized in a novel P-doped g-C3N4 (PCN) material. Through regulating the tendency of transformation in p-n homojunction, a strong internal electric field is built and integrated with two secondary internal electric fields by further decorating with Ti3C2, leading to the formation of a triple-internal electric field system. Thus the spatial separation efficiency of photocarriers is improved and their lifetime is prolonged. The specific photocatalyst exhibits excellent overall water splitting performance in pure water with a notable quantum yield. This work presents a peculiar concept of adjustable p-n homojunction and holds great significance for the rational design of advanced photocatalyst in water splitting.

Few-Layer P4O2: A Promising Photocatalyst for Water Splitting.

Photocatalytic water splitting by a two-dimensional material is a promising technology for producing clean and renewable energy. Development of this field requires candidate materials with desirable optoelectronic properties. Here, we present a detailed theoretical investigation of the atomic and electronic structure of few-layer P4O2 systems to predict their optoelectronic properties. We predict that the three-layer P4O2 with normal packing (α-3), ingeniously combining all desired optoelectronic features, is an ideal candidate for photocatalytic water splitting. It fascinatingly bears nearly a direct band gap (1.40 eV), appropriate band edge position, high solar-to-hydrogen efficiency (17.15%), high sunlight absorption efficiency, and ultrahigh carrier mobility (21 460 cm2 V-1 s-1) at room temperature. These results make three-layer P4O2 a promising candidate for photocatalytic water splitting.

Stacking effect on electronic, photocatalytic and optical properties: A comparison between bilayer and monolayer SnS

In this work, the stacking-dependent optoelectronic performances of a bilayer SnS were explored based on density functional theory (DFT). The results demonstrated that an AB-stacking induces an indirect-to-direct transition, a feature that is capable of vanquishing electron transition impediment from an intrinsic indirect monolayer SnS. An anisotropic and small carrier effective mass exists in all the stacking models, among which the AB-stacking with the lowest value favors high carrier mobility. Calculated band alignments are indicative of acceptable and adjustable photocatalytic activity for all the stacking models, unlike the monolayer SnS. The AB-stacking configuration possesses the strongest redox power, which facilitates it to be a potential candidate for photocatalytic water splitting. Additionally, the AB-stacking does effectively improve optoelectronic properties. The study demonstrated that layer-stacking is an availably adjustable method in the fields of sunlight-driven photocatalysis for nano-optoelectronic devices.