CO2-to-methanol electroconversion on a molecular cobalt catalyst facilitated by acidic cations

Abstract

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, respectively. Here we show that smaller, more acidic alkali metal cations greatly enhance CO2-to-methanol conversion kinetics (Li+ > Na+ > K+ > Cs+) on an immobilized molecular cobalt catalyst, unlike the trend observed for CO and C2+. Through electrokinetic analyses and kinetic isotope effect studies along with computational investigations, we show that the 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. The non-innocence of electrolyte cations in the activity of CO2 reduction has been widely acknowledged, although these complex effects are not fully understood. Here, opposite to the trend observed with Cu and Ag surfaces, smaller alkali cations greatly enhance CO2-to-methanol conversion on a cobalt molecular electrocatalyst.