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 CuO _x 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 CuO _x 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.