Mechanism Of Copper-based Single-atom Alloy Catalysts For Electrochemical CO₂ Reduction

Since the industrial revolution,the massive emission of carbon dioxide（CO₂）and other greenhouse gases have caused a series of environmental problems,including global warming,melting of glaciers and ocean acidification.Therefore,reducing CO₂ into high value-added product fuels is currently a hot spot in the international community.Compared with thermal catalysis and photocatalysis,electrocatalysis is widely adopted in CO₂ reduction reaction（CO₂RR）due to its advantage of low cost and high electron transfer efficiency,and the product that can be regulated by changing the applied voltage.However,electrochemical CO₂RR still needs to overcome a high reaction energy barrier,as same as compete with hydrogen evolution reaction（HER）.The copper（Cu）catalyst not only inhibit HER,but also has moderate CO adsorption energy.Therefore,Cu-based catalysts can efficiently catalyze the generation hydrocarbons.In addition,various chemical modification methods such as alloying doping have been used to further improve the selectivity of hydrocarbon generation.This work systematically studies the mechanism of electrocatalytic CO₂RR on 3d transition metal single atom doped Cu-based catalysts（TM₁/Cu（111）,where M=Sc,Ti,V,Cr,Mn,Fe,Co,Ni and Zn）by means of first-principles density functional theory（DFT）.The effect of transition metal doping Cu（111）on the pathway and selectivity of CO₂RR have also been researched,which provide comprehensive design strategy and research direction for high-efficiency electrocatalysts.This work systematically studied the reaction mechanism and sources of catalytic activity of nine transition metal single-atom-doped Cu（111）-based catalysts for the electrocatalysis of CO₂RR to CH₄ and CH₃OH,mainly by studying the adsorption behavior of 20 reaction intermediates on the catalyst surface.First,the structural stability of the catalyst was judged by studying the geometry of the catalyst and the binding energy of TM to the Cu（111）substrate.The calculation results show that,except Zn/Cu（111）,TM can be stably adsorbed on Cu（111）.Second,the capture and activation of CO₂ by TM₁/Cu（111）was investigated,and it was found that Sc/Cu（111）,Ti/Cu（111）and V/Cu（111）could be effective compared to pure Cu（111）.Cr/Cu（111）,Mn/Cu（111）,Fe/Cu（111）and Co/Cu（111）showed weaker CO₂ adsorption,but could still activate CO₂,while Ni/Cu（111）and Cu（111）performed less than ideally.Therefore,alloying can activate the inert molecule CO₂ efficiently to some extent,and it is further found that the bond angle of CO₂ adsorbed on the catalyst surface can be used as a descriptor to describe the degree of catalyst activation of CO₂.In addition,based on the DFT calculation results,it was found that TM₁/Cu（111）as a catalyst can effectively inhibit HER,improve the activity and selectivity of CO₂ initial reduction,and ensure that^*CO can be stably adsorbed on the surface instead of forming HCOOH and CO.Finally,the CORR of the catalyst surface was investigated,and it was found that the energy on the surface of pure Cu（111）was more favorable for the generation of HCHO,while TM₁/Cu（111）showed high selectivity for the generation of CH₄.It is worth noting that the binding energy of^*OH on the catalyst surface can be used as a descriptor to describe the catalytic activity of TM₁/Cu（111）.Based on the above analysis,it was found that V/Cu（111）showed the best catalytic activity and selectivity as a catalyst for electrocatalytic CO₂ reduction.