Revealing the Joint Contribution of Potential and Water Molecules to the High CO₂RR Activity of a Single Nickel Atom Catalyst

Nitrogen-doped graphene-supported single-atom catalysts (SACs) with maximum atom utilization have high catalytic activity for CO 2 reduction reaction (CO 2 RR). Nevertheless, theoretical exploration of these systems remains immensely insufficient due to the complexity of a realistic microenvironment in CO 2 RR. This work, taking the NiN 4 SAC as a probe, systematically investigates the synergistic effect of applied potential and water molecules on CO 2 RR performance. Results show that only under relatively higher applied potentials and the H 2 O molecule could jointly contribute to chemisorption and activation of CO 2 . Two possible proton sources during the CO 2 RR process are considered. Under relatively high potentials, H 2 O-containing H is the proton source for the initial CO 2 activation. The reaction energies and energy barriers for both *CO 2 → *COOH and *COOH → *CO steps are linearly correlated to applied potentials. This can be attributed to the enhanced spin state enabling stronger interaction of the Ni metal center and *COOH intermediate, which is conducive to facilitating the CO 2 RR process. This work not only explains a long-standing puzzle for an important catalyst but also highlights the joint contribution of the applied potential and water molecules, which can guide more rational elucidation of other electrocatalytic mechanisms and more effective catalyst design.