Mechanism of Potential-Dependent CO₂ Reductionand H₂ Evolution during Electrocatalytic CO₂ Process

Abstract

Developing effective strategies to suppress the hydrogen evolution reaction (HER) under high potentials is pivotal for industrializing the electrocatalytic CO₂ reduction reaction (CO₂RR). However, progress remains constrained by an insufficient mechanistic understanding of the potential-dependent competition between CO₂RR and HER. Motivated by previous experimental endeavors, we perform a systematic theoretical probing into the mechanism of HER and CO₂RR under varying potentials over Cu as the prototype and find that potential-modulated interfacial K⁺ concentrations govern the HER/CO₂RR selectivity transition. Specifically, the distinct K⁺ distribution state induced by different potentials can impose a distinguished effect on the free energy barriers of the rate-determining step (RDS) of HER and CO₂RR, making HER or CO₂RR the dominant reaction under different situations. The proposed innovative insights into reaction mechanisms can well unveil the experimentally observed potential-dependent HER/CO₂RR antagonism and inspire us to propose a feasible strategy to inhibit HER over Cu-based catalysts, i.e., maintaining a CO₂RR-favored cation concentration near the reaction interface under high potentials.