Reaction mechanism and kinetics for CO2 reduction on nickel single atom catalysts from quantum mechanics

Experiments have shown that graphene-supported Ni-single atom catalysts (Ni-SACs) provide a promising strategy for the electrochemical reduction of CO2 to CO, but the nature of the Ni sites (Ni-N2C2, Ni-N3C1, Ni-N-4) in Ni-SACs has not been determined experimentally. Here, we apply the recently developed grand canonical potential kinetics (GCP-K) formulation of quantum mechanics to predict the kinetics as a function of applied potential (U) to determine faradic efficiency, turn over frequency, and Tafel slope for CO and H-2 production for all three sites. We predict an onset potential (at 10mAcm(-2)) U-onset=-0.84V (vs. RHE) for Ni-N2C2 site and U-onset=-0.92V for Ni-N3C1 site in agreement with experiments, and U-onset=-1.03V for Ni-N-4. We predict that the highest current is for Ni-N-4, leading to 700mAcm(-2) at U=-1.12V. To help determine the actual sites in the experiments, we predict the XPS binding energy shift and CO vibrational frequency for each site. Single atom catalysts (SACs) are promising in electrocatalysis but challenging to characterize. Here, the authors apply a recently developed quantum mechanical grand canonical potential kinetics method to predict reaction mechanisms and rates for CO2 reduction at different sites of graphene-supported Ni-SACs.