Cation-induced changes in the inner- and outer-sphere mechanisms of electrocatalytic CO reduction.

The underlying mechanism of cation effects on CORR remains debated. Herein, we study cation effects by simulating both outer-sphere electron transfer (OS-ET) and inner-sphere electron transfer (IS-ET) pathways during CORR via constrained density functional theory molecular dynamics (cDFT-MD) and slow-growth DFT-MD (SG-DFT-MD), respectively. Our results show without any cations, only OS-ET is feasible with a barrier of 1.21 eV. In the presence of K (Li), OS-ET shows a very high barrier of 2.93 eV (4.15 eV) thus being prohibited. However, cations promote CO activation through IS-ET with the barrier of only 0.61 eV (K) and 0.91 eV (Li), generating the key intermediate (adsorbed CO[Formula: see text]). Without cations, CO-to-COFormula: see text conversion cannot proceed. Our findings reveal cation effects arise from short-range Coulomb interactions with reaction intermediates. These results disclose that cations modulate the inner- and outer-sphere pathways of CORR, offering substantial insights on the cation specificity in the initial CORR steps.