Cation-Dependent Impact of CO2 on Cu-Catalyzed Electrochemical CO Reduction Reaction

The electrochemical CO 2 reduction reaction (CO 2 RR) on Cu occurs via two tandem steps, i.e., the CO 2 -to-CO conversion and the electrochemical CO reduction reaction (CORR). Thus, Cu-catalyzed CO 2 RR on Cu is, in fact, coelectrolysis of CO 2 and CO, which makes the impact of interfacial CO 2 on the CORR a relevant factor in determining the overall CO 2 RR performance. In this work, we report the surprising observation that the effect of interfacial CO 2 on the formation rate of C 2+ products depends on the nature of cations in the electrolyte, i.e., beneficial with K + and Cs + while inhibitory with Li + and Na + . Density functional theory calculations indicate that interfacial CO 2 δ− affects electrode-mediated reactions in two distinct modes with opposite effects, i.e., a general inhibitory effect of CO 2 δ− as an interfacial negatively charged species and a cation-specific promoting effect via direct CO 2 -cation interactions. The relative contributions of these two competing effects determine the overall impact of CO 2 on the CORR. Furthermore, analysis of isotopologue distributions of products in the coelectrolysis of mixtures of 13 CO/ 12 CO 2 reveals the influence of cations on the multiple steps of the CO 2 RR.