Study On Catalytic Performance Of Monolayer Cr₂O₃ Based On First Principles Calculation

Energy is closely related to people’s lives.The non-renewability of fossil fuels and the environmental problems caused by fossil fuels have prompted the exploration of new energy sources.Using solar energy to produce hydrogen has become a research hotspot.At the same time,the traditional industrial ammonia synthesis process also has the disadvantages of high energy consumption and high pollution.Electrocatalytic ammonia production can greatly improve this situation.Designing or synthesizing an excellent catalyst is the primary issue for both photocatalytic hydrogen production and electrocatalytic nitrogen fixation.And it is a goal that researchers are constantly pursuing.Cr₂O₃monolayer（Cr₂O₃ML）is a promising catalyst material and has many advantages such as low cost,large specific surface area,abundant reserves and strong designability et al.This article takes Cr₂O₃monolayer as the object and uses density functional theory（DFT）calculations to explore its catalytic mechanism in hydrogen evolution reaction（HER）,oxygen evolution reaction（OER）and nitrogen reduction reaction（NRR）.The improvement of the catalytic activity of Cr₂O₃ML has been explored.The main content of this article includes the catalysis of these three reactions.Aiming at the HER reaction characteristics of Cr₂O₃monolayer,three feasible strategies are carried out to activate the catalytic activity of Cr₂O₃ML through biaxial strain,transition metal（TM）atom doping and introducing vacancies.The results of DFT calculation show that the Gibbs free energy of HER gradually decreases with the increase of strain.In response to this phenomenon,we explain how strain changes the energy barrier of HER from the perspective of changes in the bonding strength between hydrogen atoms and catalytically active site atoms.The Cr atoms on the surface of Cr₂O₃ML are doped with TM atoms.And the HER catalytic activity at different sites on the surface was calculated.The changes of HER catalytic performance when Cr vacancies or O vacancies exist on the surface of Cr₂O₃ML are also studied.The band structure under vacancy defects is given in this paper.Aiming at the OER characteristics of Cr₂O₃monolayer,the OER catalytic activity of the intrinsic Cr₂O₃ML catalyst is studied.The Cr₂O₃ML was doped with TM atoms,and it is found that Pt,Ni,Fe,and Zn doped systems can all improve the OER catalytic performance of the catalyst.Then biaxial strain is applied to the Pt and Fe doped systems to explore the changes in the catalytic performance of Cr₂O₃ML.By studying the catalytic performance of OER when there are Cr vacancies or O vacancies on the surface of Cr₂O₃ML,it is found that there is a linear relationship between the energy difference between O*and OOH*intermediates and the overpotential,which provides guidance for the design of Cr₂O₃ML catalyst.Aiming at the NRR characteristics of Cr₂O₃monolayer,the NRR catalytic activity of the intrinsic Cr₂O₃ML catalyst is studied.After Cr₂O₃ML is doped with TM atoms,the activation effect of the TM atoms on N₂is studied.And their tendency to preferentially undergo NRR or their competitive reaction HER is judged.Through the calculation of the free energy of each elementary reaction of the doped system,the intermediate state that affects the reaction energy barrier is found.Finally,the NRR catalytic performance calculations were carried out for the case where there are O vacancies on the Cr₂O₃ML surface.The results show that the O vacancies have a significant effect on the reduction of the reaction energy barrier and can improve the catalytic activity.