Elucidating the Electrocatalytic CO₂ Reduction Reaction over a Model Single-Atom Nickel Catalyst

Designing effective electrocatalysts for the carbon dioxide reduction reaction (CO₂RR) is an appealing approach to tackling the challenges posed by rising CO₂ levels and realizing a closed carbon cycle. However, fundamental understanding of the complicated CO₂RR mechanism in CO₂ electrocatalysis is still lacking because model systems are limited. We have designed a model nickel single-atom catalyst (Ni SAC) with a uniform structure and well-defined Ni-N₄ moiety on a conductive carbon support with which to explore the electrochemical CO₂RR. Operando X-ray absorption near-edge structure spectroscopy, Raman spectroscopy, and near-ambient X-ray photoelectron spectroscopy, revealed that Ni⁺ in the Ni SAC was highly active for CO₂ activation, and functioned as an authentic catalytically active site for the CO₂RR. Furthermore, through combination with a kinetics study, the rate-determining step of the CO₂RR was determined to be *CO₂ ⁻+H⁺→*COOH. This study tackles the four challenges faced by the CO₂RR; namely, activity, selectivity, stability, and dynamics.