Reaction mechanism and kinetics for CO2 reduction on nickel single atom catalysts from quantum mechanics
A recently developed quantum mechanical grand canonical potential kinetics method is applied to predict reaction mechanisms and rates for CO2 reduction at different sites of graphene-supported Ni-SACs to determine faradic efficiency, turn over frequency, and Tafel slope for CO and H2 production for all three sites.
Abstract
<jats:title>Abstract</jats:title><jats:p>Experiments have shown that graphene-supported Ni-single atom catalysts (Ni-SACs) provide a promising strategy for the electrochemical reduction of CO<jats:sub>2</jats:sub> to CO, but the nature of the Ni sites (Ni-N<jats:sub>2</jats:sub>C<jats:sub>2</jats:sub>, Ni-N<jats:sub>3</jats:sub>C<jats:sub>1</jats:sub>, Ni-N<jats:sub>4</jats:sub>) 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<jats:sub>2</jats:sub> production for all three sites. We predict an onset potential (at 10 mA cm<jats:sup>−2</jats:sup>) U<jats:sub>onset</jats:sub> = −0.84 V (vs. RHE) for Ni-N<jats:sub>2</jats:sub>C<jats:sub>2</jats:sub> site and U<jats:sub>onset</jats:sub> = −0.92 V for Ni-N<jats:sub>3</jats:sub>C<jats:sub>1</jats:sub> site in agreement with experiments, and U<jats:sub>onset</jats:sub> = −1.03 V for Ni-N<jats:sub>4</jats:sub>. We predict that the highest current is for Ni-N<jats:sub>4</jats:sub>, leading to 700 mA cm<jats:sup>−2</jats:sup> 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.</jats:p>