Multiscale insights of interfacial transport and kinetics in acidic CO2 electroreduction.

Acidic electrochemical CO2 reduction (CO2RR) mitigates CO2 loss and energy inefficiencies but suffers from limited selectivity. Insufficient understanding of the interfacial microenvironment and cation specificity hinders the development of efficient interfacial design methods. Here, we integrate ab initio-derived reaction kinetics with mass transfer modeling into a multiscale framework that reproduces the bell-shaped Faradaic efficiency profile inaccessible to the Butler-Volmer equations. Our results emphasize the role of hydrogen bonding in CO2 activation and reveal a potential-dependent shift in the rate-determining steps. We also demonstrate that cations inhibit competing hydrogen evolution by strengthening the interfacial electric field and disrupting the hydrogen-bond network. However, their accumulation near the outer Helmholtz plane induces strong steric effects, impeding CO2 supply. Furthermore, the parametric analysis highlights the critical role of strategies such as pressurization and pore-confined electrolyte control in overcoming interfacial CO2 transport limitations, enhancing selectivity, and broadening the operating potential window. This work advances a multiscale perspective on interfacial mass transfer and cation effects, establishing a unified framework for reaction interface design in acidic CO2RR.