Theoretical Understanding of Potential-Dependent Electrocatalytic CO2RR and Competition with HER upon Cobalt Single Atom Supported by Phthalocyanine Monolayer

Cobalt-doped phthalocyanine monolayer (Co-Pc) catalyst has shown promising performance in electrochemical CO2 reduction experimentally. However, most theoretic investigations based on computational hydrogen electrode (CHE) model inaccurately predict catalytic behaviors and exhibit contradictive mechanistic pathways. In this work, grand canonical density functional theory (GC-DFT) combined CANDLE continuum solvation model was used to more precisely simulate CO2RR upon Co-Pc. The calculation results reasonably explained the activation of CO2 and HER (hydrogen evolution reaction) competition and also predicted potential determined step and onset potential, which all are excellently consistent with experimental values. The potential-dependent competition among physical and chemical adsorption of CO2 and H formation and the reason for high CO2RR selectivity at a specific potential range were well explained: the charge of the reaction intermediate is the key to potential-dependent behaviors; larger electron transfer in H adsorption than CO2 adsorption is the primary reason for HER suppression of CO2RR at high potential. This is a general phenomenon seen in various heterogeneous catalysts, hindering practical electrochemical CO2RR.