A first-principles investigation of Janus MoSSe as a catalyst for photocatalytic water-splitting
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Photocatalytic water splitting
Photocatalytic water splitting has been widely studied as a means of converting solar energy into hydrogen as an ideal energy carrier in the future. Systems for photocatalytic water splitting can be divided into one-step excitation and two-step excitation processes. The former uses a single photocatalyst while the latter uses a pair of photocatalysts to separately generate hydrogen and oxygen. Significant progress has been made in each type of photocatalytic water splitting system in recent years, although improving the solar-to-hydrogen energy conversion efficiency and constructing practical technologies remain important tasks. This perspective summarizes recent advances in the field of photocatalytic overall water splitting, with a focus on the design of photocatalysts, co-catalysts and reaction systems. The associated challenges and potential approaches to practical solar hydrogen production via photocatalytic water splitting are also presented.
Photocatalytic water splitting
Energy transformation
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Hydrogen production via solar light-driven water dissociation has been regarded as an artificial and effective process to overcome the environmental problem as well as solving the current energy crisis. In this regard, numerous works have mainly been devoted to developing the appropriate photocatalyst which satisfies the conditions for water splitting and understanding the photocatalysis process. In this study, we propose for the first time the potential application of the two-dimensional Janus aluminum oxysulfide Al2OS as an efficient photocatalyst material for hydrogen-production H2 through the first-principles calculations. Janus Al2OS monolayer has been designed from the parental binary aluminum sulfide AlS by substituting one sub-layer of sulfide atoms (S) to oxygen atoms (O). The electronic properties of the pristine AlS and the derived Janus Al2OS were computed using GGA-PBE and HSE06 functionals. According to the band structure, AlS monolayer shows a semiconductor behavior with an indirect bandgap of 2.14 eV whereas, the Janus Al2OS exhibits a direct bandgap of 1.579 eV. Motivated by the desirable bandgap of the Janus Al2OS, the absorption-coefficient of Janus Al2OS shows strong visible light harvesting compared to the parental AlS. Furthermore, the photocatalytic performance of Al2OS has been investigated. Our calculations demonstrate that the band edge position of Al2OS is suitable for the hydrogen evolution reaction (HER). More importantly, based on the reaction coordinate, it was found that the Gibbs free-energy ΔGH∗ of Al2OS is 0.97 eV which is smaller than of the two-dimensional Janus Ga2 XY (X, Y = S, Se, Te with X ≠ Y) reported recently. Moreover, this value decreases from 0.97 eV to 0.69 eV under 0.5 V/Å of an external electrical field. Our results indicate that Janus Al2OS fulfills the fundamental requirements for efficient photo-catalyst under visible light and provides new guidance for hydrogen-production via water splitting.
Photocatalytic water splitting
Acceptor
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Recently, a new family of the Janus NbSeTe monolayer has exciting development prospects for two-dimensional (2D) asymmetric layered materials that demonstrate outstanding properties for high-performance nanoelectronics and optoelectronics applications. Motivated by the fascinating properties of the Janus monolayer, we have studied the gas sensing properties of the Janus NbSeTe monolayer for CO, CO2, NO, NO2, H2S, and SO2 gas molecules using first-principles calculations that will have eminent application in the field of personal security, protection of the environment, and various other industries. We have calculated the adsorption energies and sensing height from the Janus NbSeTe monolayer surface to the gas molecules to detect the binding strength for these considered toxic gases. In addition, considerable charge transfer between Janus monolayer and gas molecules were calculated to confirm the detection of toxic gases. Due to the presence of asymmetric structures of the Janus NbSeTe monolayer, the projected density of states, charge transfer, binding strength, and transport properties displayed distinct behavior when these toxic gases absorbed at Se- and Te-sites of the Janus monolayer. Based on the ultra-low recovery time in the order of μs for NO and NO2 and ps for CO, CO2, H2S, and SO2 gas molecules in the visible region at room temperature suggest that the Janus monolayer as a better candidate for reusable sensors for gas sensing materials. From the transport properties, it can be observed that there is a significant variation of I−V characteristics and sensitivity of the Janus NbSeTe monolayer before and after adsorbing gas molecules demonstrates the feasibility of NbSeTe material that makes it an ideal material for a high-sensitivity gas sensor.
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Photocatalytic overall water splitting into H2 and O2 is expected to be a promising method for the efficient utilization of solar energy. The design of optimal photocatalyst structures is a key to efficient overall water splitting, and the development of photocatalysts which can efficiently convert large portion of visible light spectrum has been required. Recently, a series of complex perovskite type transition metal oxynitrides, LaMgxT 1-xO1+3xN2-3x, was developed as photocatalysts for direct water splitting operable at wide wavelength of visible light. In addition two-step excitation water splitting via a novel photocatalytic device termed as photocatalyst sheet was developed. This consists of two types of semiconductors (hydrogen evolution photocatalyst and oxygen evolution photocatalyst) particles embedded in a conductive layer, and showed high efficiency for overall water splitting. These recent advances in photocatalytic water splitting were introduced.
Photocatalytic water splitting
Visible spectrum
Oxygen evolution
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Photocatalytic water splitting
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Abstract Inspired by superior gas sensing properties of PtSe 2 monolayer and tunable gas sensing properties of Janus MoSSe monolayer, we study the gas sensing properties of the Janus PtSSe monolayer for CO, CO 2 , H 2 O, NH 3 , NO and NO 2 gas molecules using first-principles density functional calculations. We calculate adsorption height and adsorption energies of the gas molecules to assess the adsorption strength of the gas molecules. Then the charge transfer from PtSSe to gas molecules is evaluated. We also investigate the effects of strain and external electric field on the gas sensing properties of Janus PtSSe monolayer. We finally reveal the origin of the superior gas sensing properties from projected density of states analysis. Our results suggest that the Janus PtSSe monolayer is a promising gas sensor with superior and tunable sensing properties.
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With a view to the particularity of overall water splitting,the preparation of photocatalytic materials and their performance for hydrogen and oxygen production from overall water splitting are reviewed in relation to the design of structure and energy band of photocatalytic materials as well as their surface modification.The principle of two step reaction(Z system) for overall water splitting and several currently available Z systems are introduced.Furthermore,existing problems of photocatalytic overall water splitting are also briefed.
Photocatalytic water splitting
Oxygen evolution
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Photocatalytic water splitting
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Photocatalytic water splitting can realize a direct conversion from solar energy into green hydrogen energy, which is conducive to effectively mitigate energy crisis and environmental issues. Single‐atom catalysts (SACs) have shown great potential in photocatalytic hydrogen evolution, with unique geometric and electronic structures that help to boost mass and charge transfer during photocatalytic processes. Herein, recent advances of SACs in photocatalytic water splitting are focused upon. To decrease aggregation and realize sufficient utilization of metal atoms, different synthesis strategies for SACs are documented. For photocatalytic hydrogen evolution, the catalytic performances, active sites, and structure–property relationships of SACs including Al, Co, Ni, Pd, Ag, and Pt single sites are highlighted. The existing challenges and future directions of SACs in photocatalytic water splitting are provided.
Photocatalytic water splitting
Hydrogen atom
Solar energy conversion
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Monolayer transition metal dichalcogenides (TMDs) have been regarded as the most promising low-cost alternatives to noble metals as catalysts for the hydrogen evolution reaction (HER). However, their limited catalytically active sites for the HER hinder their practical application. In this paper, the catalytic performances of the edge sites of Janus monolayer MoXY (X/Y = S, Se and Te) were investigated using density functional theory. The results show that both the Mo-edge and chalcogen atomic edges of Janus monolayer MoXY are catalytically active for the HER; thus Janus monolayer MoXY exhibits better catalytic performance than monolayer MoS2. These results are useful for the improvement of the catalytic performance of TMDs by the formation of the Janus monolayer MoXY.
Chalcogen
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