Two-dimensional TeX/Y(X=C,Si,Ge;Y=P,As,Sb,Bi) Heterostructures Of Photocatalytic Water Splitting For Hydrogen Evolusion Reaction: A First-principles Study

Finding environmentally friendly,low-cost,clean and renewable energy is an effective solution to achieve the goals of “emission peak” and “carbon neutrality”.As a high-quality clean energy source,hydrogen has a high strategic value in our country’s energy transformation.Using solar photocatalytic water splitting as an ideal solution for hydrogen production is expected to become the main method for future hydrogen energy supply systems.Whether a semiconductor photocatalyst can efficiently utilize sunlight is the decisive factor to improve the efficiency of photocatalytic water splitting for hydrogen production.Therefore,exploring new semiconductor photocatalysts has become a frontier hotspot in physics,chemistry,and energy disciplines in recent years.In the field of photocatalysis,two-dimensional semiconductor materials have advantages,especially the new two-dimensional materials with different vacuum levels(VL),which can break through the limit of band gap and meet the conditions of photocatalytic water splitting to improve the solar to hydrogen(STH)conversion efficiency,which provides a possibility for the further development of high-efficiency photocatalysts.Therefore,in this paper,TeX(X = C,Si,Ge)monolayer and TeX/Y(X = C,Si,Ge;Y = P,As,Sb,Bi)vertical heterostructures geometries are designed.And based on the first principles,the photocatalytic mechanism of these new two-dimensional materials and the performance of water splitting for hydrogen evolution driven by sunlight were studied,so as to provide theoretical guidance for the experimental preparation of high efficiency photocatalysts.Specifically,the following studies were included:1.The geometry of TeX(X = C,Si,Ge)monolayer with only two atomic layers and an asymmetric configuration in the z-direction was constructed.And the dynamics and thermodynamic stabilities were confirmed by phonon dispersion curves and ab initio molecular dynamics simulations,respectively.The band structure,density of state,band edge position,VL,and light absorption were calculated by using the HSE06 hybrid functional method.The differential charge density,and Bader charge analysis confirmed the intrinsic electric field of the structure.And the photocatalytic water splitting to hydrogen production scheme was determined based on the VLs of the two surfaces and the positions of the band edges.At the same time,the optimal scheme is further determined by combining the charge density distribution of the valence band maximum(VBM)and the conduction band minimum(CBM),and the photocatalytic performance of the structure is evaluated by calculating the corresponding STH conversion efficiency.The results show that the Te C monolayer with an indirect bandgap of 2.01 e V,meets the band edge position requirements for overall water splitting under the optimal photocatalytic water splitting to hydrogen production scheme.Since the two surfaces of the monolayer with different VLs,the redox levels of each surface are changed,and large overpotential is obtained with a small band gap to achieve higher STH conversion efficiency.Since the TeSi and Te Ge monolayers’ VBMs fail to meet the conditions for the oxygen evolution reaction,the effects of strain engineering are further considered on the optimal photocatalytic hydrogen evolution scheme of the three structures.Tensile strains exceeding 2% and 1%,respectively,can make the TeSi and Te Ge monolayers meet the requirements of overall water splitting.The band gap can also be reduced by improving strain engineering.TheSTH conversion efficiency reaches 32.74% at 8% tensile strain for Te C and 22.09% for TeSi at 20% tensile strain,both of which exceed the theoretical limit of 17.51% for conventional single VL monolayers.The calculated Gibbs free energy changes of the TeX monolayer are 0.7619-1.4802 e V,which are within the range of the hydrogen evolution reaction that have been confirmed by experiments.These computational results suggest that the newly discovered TeX monolayer,especially Te C,is a good candidate for the development of photocatalytic hydrogen evolution photocatalysts with high STH conversion efficiency.2.The mechanism and performance of photocatalytic water splitting to hydrogen production of TeX/Y(X = C,Si,Ge;Y = P,As,Sb,Bi)van der Waals heterostructures constructed by TeX(X = C,Si,Ge)monolayers and group-Ⅴ elements P,As,Sb,and Bi monolayers were investigated using HSE06 hybrid density functional calculations.A total of 36 stacking configurations was considered when designing the geometric configuration of the TeX/Y heterostructures.Screening and research of 36 heterostructures based on criteria such as lattice optimization and energy stability,type II band alignment,and suitable band edge positions.And the energy stability of the heterostructures was determined by calculating the formation energy,the electronic structure was calculated to determine the band alignment type of the heterostructures,the direction of the built-in electric field of the heterostructures was determined by Bader charge analysis and differential charge density,the band edge position of the hydrogen and oxygen evolution reaction was determined based on the direct Z-scheme photocatalytic water splitting to hydrogen production and electronic structure of the heterostructures,and STH efficiencies were calculated for eight heterostructures that meet the requirements for the band edge of overall water splitting.The TeSi/P-Ι and TeSi/As-II heterostructures with the highest STH efficiency were selected for detailed and comprehensive analysis and further study.The thermodynamic stability of the TeSi/P-Ι and TeSi/As-II heterostructures was confirmed by ab initio molecular dynamics simulations.The light absorption of each monolayer isolated from the TeSi/P-Ι and TeSi/As-II heterostructures has enhanced light absorption compared to the original monolayers in the visible region.Meanwhile,the Gibbs free energy changes of hydrogen evolution reactions for TeSi/P-Ι and TeSi/As-II heterostructures are 0.18 and 1.48 e V,respectively,which are favorable for the realization of hydrogen evolution reactions in the experiments.Combined with the higher STH conversion efficiencies of 16.84% and 27.76% for the TeSi/P-Ι and TeSi/As-II heterostructures,respectively,which are both higher than the 13.38% of the Te C monolayer in the previous study(the TeSi monolayer does not meet the photocatalytic water splitting for hydrogen evolution condition),indicating that the construction of heterostructures can indeed enhance the photocatalytic performance.It is shown that both TeSi/P-Ι and TeSi/As-II heterostructures are promising candidates for photocatalysts.