Operando Interfacial Dynamics Govern Cation Effects in Electrochemical CO2RR

Electrolyte cations profoundly influence electrocatalytic reactions, such as the electrochemical CO 2 reduction. How cation identity controls operando interfacial dynamics and selectivity remains unresolved, not least due to a lack of methods capable of resolving such dynamics. Here we show that understanding cation effects requires a time-domain perspective, by combining Dynamic Response Spectroscopy with operando ATR-SEIRAS and sequence-learning neural networks trained on over 10 5 time-resolved spectra. We resolve cation-specific (Li + , Na + , K + , and Cs + ) differences in charge-discharge reversibility and temporal coupling between solvent, ions, and adsorbates. Supported by AIMD simulations, we reveal that the double layer evolves through smooth relaxation and intermittent collective reorganizations, dependent on cation identity. Catalysis depends on whether interfacial reorganizations are dynamically coupled to adsorbate stabilization and electricfield buildup. These results identify time-domain descriptors of interfacial adaptability as key activity and selectivity determinants, opening pathways toward dynamic catalytic operation that leverages interfacial reorganization for enhanced performance.