Single-atom metal-nitrogen-graphene (M-N-Gra) catalysts are promising materials for electrocatalytic CO2 reduction reaction (CO2RR).However,theoretical explorations on such systems were greatly hindered because of the complexity in modeling solid/liquid interface and electrochemical environment.In the current work,we investigated two crucial processes in CO2RR,i.e.adsorption and desorption of CO2 and CO at Fe-N4 center,with an explicit aqueous model.We used the ab initio molecular dynamics simulations associated with free energy sampling methods and electrode potential analysis to estimate the energetics under electrochemical environment,and found significant difference in aqueous solution compared with the same process in vacuum.The effect of applied electrode potential on the adsorption structures,charge transfer and free energies of both CO2 and CO on Fe-N-Gra was thoroughly discussed.These findings bring insights in fundamental understandings of the CO2RR process under realistic conditions,and facilitate future design of efficient M-N-Gra-based CO2RR catalysts.