LAUSR

Cation effects have been shown in numerous experiments to play significant role in electrocatalysis. To understand these effects at molecular level, we systematically investigate the structures and capacitances of electric double layers (EDLs) with a variety of cations as counter charges at Pt(111)-COad/water interfaces with ab initio molecular dynamics (AIMD). It is encouraging to find that the computed Helmholtz capacitances for different cations are in quantitative agreement with experiment, and the trend of cation effects on capacitances shows clear correlation with the structures of cations at interfaces, which are closely related to their sizes and hydration energies. More importantly, we demonstrate the Helmholtz capacitances as the key descriptor for measuring the activity of CO-CO dimerization, the rate-determining step for C2 + formation in electroreduction of CO and CO2. Our work provides atomistic insights into cation effects on electric double layers and electrocatalysis that are crucial for optimizing electrode and electrolyte materials.