Studies On Electrocatalytic Properties Of Two-dimensional Transition Metal Compounds

The solution to the energy crisis problem has become a research hotpot on efficient and low-cost sustainable energy conversion systems by scholars at home and abroad in recent years.In order to solve the problems of limited reserves and serious pollution of traditional fossil energy sources,it is imperative to conduct research on green and efficient electrocatalytic hydrogen production,in which electrochemical Hydrogen Evolution Reaction（HER）,Oxygen Reduction Reaction（ORR）and oxygen Evolution Reaction（OER）play a central role i.Understanding the influence of the composition and structure of catalysts on their electrocatalytic performance is an effective strategy to develop high-performance electrocatalysts.Further research on the influence of adjustment strategies based on composition,surface structure,phase interface and other aspects on the geometric and electronic structure of catalysts,adsorption of reaction species and reaction mechanism can not only screen out catalysts with better performance,but also provide theoretical basis for rational design and development of high-performance catalysts.In this paper,based on density functional theory,the HER properties of Os N₂/Re N₂and Zn CS₃,and the electrocatalytic performance of Mn B₂C₂ in ORR and OER were systematically studied.The internal mechanism of action was discussed by means on calculation of electronic structure and thermodynamic analysis.The research content of this paper mainly includes:（1）Theoretical prediction on HER properties of two-dimensional layered Os N₂/Re N₂.The stability of predicted materials were proved by the global optimization algorithm of structure and molecular dynamics simulation.The metallic properties and high Fermi velocity of the material were demonstrated by the calculation of the electronic band structure,and the good conductivity and high electron exchange efficiency of the material were speculated.It is found that the Gibbs free energy for hydrogen adsorption（ΔG_H）is low by calculating the overpotential required for the reaction,indicating that this kind of material is suitable to act as HER catalyst.In order to further reduce their HER overpotentials,tiny biaxial strains were applied which makeΔG_H of Os N₂and Re N₂ approach.In addition to strain,the coverage of hydrogen also has a significant effect on HER performance of Os N₂/Re N₂:Re N₂ has a better catalytic effect under high hydrogen coverage,while Os N₂ is more suitable for hydrogen production under low hydrogen coverage.Interestingly,we found a synergistic effect between strain and coverage in the modulation of HER catalytic activity of Os N₂/Re N₂.（2）Theoretical study on HER properties of the two-dimensional transition metal sulfide Zn CS₃.The Zn CS₃ monolayer presents a typical sandwich structure with good stability and electrical conductivity.The calculational results show that the exposed S atom acts as the active site for HER,and it is the p orbital of S atom that makes the major contribution to hydrogen adsorption.The metallic characteristics remain unchanged before and after the adsorption of H atom.It has been found that the hydrogen adsorption strength of Zn CS₃ is the most moderate under the condition of low hydrogen atom coverage.The result of the p band center as a function of strain shows that the catalytic activity of Zn CS₃ is closely related to the center of p band of S.Therefore,the catalytic activity of Zn CS₃ can be effectively modulated by regulating the p band center of S.（3）Theoretical study on OER/ORR bifunctional catalytic performance of two-dimensional Mn B₂C₂ materials.The predicted two-dimensional material Mn B₂C₂has a stable structure at room temperature,with good OER/ORR bifunctional catalyst without additional doping and modification.We further studied the origin of its high catalytic activity,and found that it is mainly related to the high-spin state of Mn²⁺,for Mn²⁺can effectively neutralize the adsorption strength of the intermediate state of the reaction,and thus reduce the reaction energy barrier.The study on Mn²⁺and the p band center location of B and C could further proved the above conclusion.In conclusion,all these interesting theoretical findings at the atomic level can provide important references for experimentally controlled synthesis of high efficiency catalysts such as transition metal compounds.