Cation effect on the elementary steps of the electrochemical CO reduction reaction on Cu

The nature of the cations in an electrolyte has a substantial impact on the performance of the electrochemical CO2 and CO reduction reaction (CO(2)RR), however, its mechanism at the molecular level remains the subject of debate. Major gaps in our understanding include how cations affect key physicochemical variables at electrochemical interfaces and the elementary steps of the CO(2)RR. In this work, we have quantitatively determined the impact of cations on the enthalpy and entropy of CO adsorption on Cu under electrochemical conditions. CO adsorption becomes increasingly unfavourable in the sequence Li+ > Na+ > K+ > Cs+ with a substantial enthalpy–entropy compensation effect. Importantly, cations affect the stability of the initial and transition states of the CORR in opposite directions. Our results provide insights into the effect of cations on individual elementary steps in the CORR and demonstrate that the ability to stabilize the transition state in the conversion of adsorbed CO is a decisive factor. The mechanism of electrocatalytic CO/CO2 reduction on Cu surfaces is complex and its various mechanisms remain under debate, including the important role of cations in the electrolyte. Here the authors quantitatively determine the impact of alkali cations on the thermodynamics of CO adsorption under electrochemical conditions and the activation parameters of the rate-determining step.