Reaction mechanism and kinetics for CO(2) 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 CO(2) to CO, but the nature of the Ni sites (Ni-N(2)C(2), Ni-N(3)C(1), 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 10 mA cm(−2)) U(onset) = −0.84 V (vs. RHE) for Ni-N(2)C(2) site and U(onset) = −0.92 V for Ni-N(3)C(1) site in agreement with experiments, and U(onset) = −1.03 V for Ni-N(4). We predict that the highest current is for Ni-N(4), leading to 700 mA cm(−2) at U = −1.12 V. To help determine the actual sites in the experiments, we predict the XPS binding energy shift and CO vibrational frequency for each site.