The crucial role of electrolyte cations in CO2 electroreduction has received intensive attention. One prevailing theory is that through electrostatic interactions or direct coordination, larger cations such as Cs+ can better stabilize the key intermediate species for CO and multicarbon (C2+) product generation, for example, on silver and copper. Herein, we show that smaller, acidic alkali metal cations greatly enhance CO2-to-methanol conversion kinetics (Li+ > Na+ > K+ > Cs+) on an immobilized molecular cobalt catalyst unlike the trend for CO and C2+. Through kinetic isotope effect studies and electrokinetic analyses, we found that hydration shell of a cation serves as a proton donor in the rate-determining protonation step of adsorbed CHO where acidic cations promote the proton-coupled electron transfer. This study reveals the promotional effect of cation solvation environment on CO2 electroreduction beyond the widely acknowledged stabilizing effect of cations.
Materials and Methods, Supplementary Text and Figures