Steering CO2 electrolysis selectivity by modulating the local reaction environment: An online DEMS approach for Cu electrodes

Electrochemical CO₂ reduction is a typical surface-mediated reaction, with its reaction kinetics and product distributions largely dependent on the dynamic evolution of reactive species at the cathode–catholyte interface and on the resultant mass transport within the hydrodynamic boundary layer in the vicinity of the cathode. To resolve the complex local reaction environment of branching CO₂ reduction pathways, we here present a differential electrochemical mass spectroscopic (DEMS) approach for Cu electrodes to investigate CO₂ mass transport, the local concentration gradients of buffering anions, and the Cu surface topology effects on CO₂ electrolysis selectivity at a temporal resolution of ∼400 ​ms. As a proof of concept, these tuning knobs were validated on an anion exchange membrane electrolyzer, which delivered a Faradaic efficiency of up to 40.4% and a partial current density of 121 ​mA ​cm⁻² for CO₂-to-C₂H₄ valorization. This methodology, which bridges the study of fundamental surface electrochemistry and the upgrading of practical electrolyzer performance, could be of general interest in helping to achieve a sustainable circular carbon economy.