Acceleration of electrocatalytic CO₂reduction by adding proton-coupled electron transfer inducing compounds

The induction of the concerted proton-coupled electron transfer (PCET) during electrochemical carbon dioxide (CO2) reduction was examined by introducing proton-donating compounds (acetic acid, malic acid, maleic acid, and pyridine derivatives) into an electrolyte. In the presence of proton-donating compounds, a copper (Cu) foil electrode showed enhanced CO2 reduction activity as well as the occurrence of the deuterium kinetic isotope effect, indicating that the concerted PCET promoted the reduction reaction. When a tin (Sn) foil was also subjected to electrocatalysis in an electrolyte containing a proton donor, enhanced activity was similarly observed, although the pKa range where the enhancement occurred was different from that observed for a Cu electrode. This discrepancy in the pKa range reflects a difference in the form of the intermediate species generated on Cu and Sn electrodes. Notably, these results demonstrate that the method presented here can be employed to induce the concerted PCET on a metal electrode irrespective of the reaction mechanism for CO2 reduction.