Impact of Pulsed CO2 Electrolysis on Surface Structures and Product Distribution for Oxide-Derived Cu

Using potential pulses in Cu-catalyzed CO2 electroreduction (CO2RR) has recently shown great promise in steering product selectivity. However, the effect of these pulses on the catalyst structure and, therefore, the formation of C1 and C2 products remain unclear. Herein, we altered the applied potential of the anodic pulse and varied the duration of the cathodic CO2RR pulse to investigate the effect of both the oxidation state and restructuring of an oxide-derived Cu nanoparticle catalyst on the CO2RR. Shorter cathodic pulses and a higher anodic pulse potential led to a higher ethanol-to-ethylene Faradaic efficiency (FE) ratio, an increase in the C1 FE, and a suppression of the hydrogen evolution reaction (HER). We tracked the structural evolution of the CuO catalyst by in situ X-ray absorption spectroscopy (XAS) during the (pulsed) CO2RR. The CuO catalyst was fully reduced under potentiostatic conditions, whereas residual CuOx was detected during pulsed CO2 electrolysis. Quasi-in situ X-ray photoelectron spectroscopy (XPS) further emphasized that the surface of the Cu catalyst was significantly impacted by the application of potential pulses, whereby a higher fraction of CuOx was observed with the application of shorter cathodic pulses and higher anodic pulse potentials. Moreover, X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed that sintering and defect formation took place during pulsed CO2RR, resulting in an irreversible morphological change, which was associated with the enhanced formation of C1 products.