Absence of CO2 electroreduction on copper, gold and silver electrodes without metal cations in solution

The electrocatalytic reduction of carbon dioxide is widely studied for the sustainable production of fuels and chemicals. Metal ions in the electrolyte influence the reaction performance, although their main role is under discussion. Here we studied CO2 reduction on gold electrodes through cyclic voltammetry and showed that, without a metal cation, the reaction does not take place in a pure 1 mM H2SO4 electrolyte. We further investigated the CO2 reduction with and without metal cations in solution using scanning electrochemical microscopy in the surface-generation tip-collection mode with a platinum ultramicroelectrode as a CO and H-2 sensor. CO is only produced on gold, silver or copper if a metal cation is added to the electrolyte. Density functional theory simulations confirmed that partially desolvated metal cations stabilize the CO2- intermediate via a short-range electrostatic interaction, which enables its reduction. Overall, our results redefine the reaction mechanism and provide definitive evidence that positively charged species from the electrolyte are key to stabilize the crucial reaction intermediate.