Cation effects on CO₂ reduction catalyzed by single-crystal and polycrystalline gold under well-defined mass transport conditions.

Abstract

The presence of alkali metal cations in the electrolyte substantially affects the reactivity and selectivity of electrochemical carbon dioxide (CO₂) reduction (CO₂R). This study examines the role of cations in CO₂R on single-crystal and polycrystalline Au under controlled mass-transport conditions. It establishes that CO₂ adsorption is the rate-determining step regardless of cation type or surface structure. Density functional theory calculations show that electron transfer occurs to a solvated CO₂-cation complex. A more positive potential of zero charge enhances CO₂R activity only on Au with similar surface coordination. The symmetry factor (β) of the rate-determining step varies with surface structure and cation identity, with density functional theory calculations indicating β's sensitivity to surface and double-layer structures. These findings emphasize the importance of both surface and double-layer structures in understanding cation effects on CO₂R.