Molecular level insights on the pulsed electrochemical CO2 reduction

Abstract Electrochemical CO2 reduction reaction (CO2RR) occurring at the electrode/electrolyte interface is sensitive to both the potential and concentration polarization. Compared to static electrolysis at a fixed potential, pulsed electrolysis with alternating anodic and cathodic potentials is an intriguing approach that not only reconstructs the surface structure, but also regulates the local pH and mass transport from the electrolyte side in the immediate vicinity of the cathode. Herein, via a combined online mass spectrometry investigation with sub-second temporal resolution and 1-dimensional diffusion profile simulations, we reveal that heightened surface CO2 concentration promotes CO2RR over H2 evolution for both polycrystalline Ag and Cu electrodes after anodic pulses. Moreover, mild oxidative pulses generate a roughened surface topology with under-coordinated Ag or Cu sites, delivering the best CO2-to-CO and CO2-to-C2+ performance, respectively. Surface-enhanced infrared absorption spectroscopy elucidates the potential dependence of *CO and *OCHO species on Ag as well as the gradually improved *CO consumption rate over under-coordinated Cu after oxidative pulses, directly correlating apparent CO2RR selectivity with dynamic interfacial chemistry at the molecular level.