Operando studies on solid oxide ceria electrodes during CO2 electroreduction

CeOx-YSZ electrode performed well for CO2 electro-reduction in both CO2 and CO2 (+H2) feeds. The electrochemical interface which is dependent on environmental conditions and bias, was imaged using operando Raman spectroscopy and optical microscopy. In CO2 (without H2), operando Raman and online mass spectroscopy studies revealed that, upon application of the bias, CO production correlated with the reduction of Ce4+ sites to Ce3+ sites as evidenced by decay in the intensity of the Raman band at 450 cm−1 (α). The electronic conductivity increased with applied bias due to an increase in Ce3+ sites. The addition of H2 resulted in reverse Water Gas Shift (RWGS) reaction and H2O electrolysis besides CO2 reduction. The CO formation was more facile in the presence of H2 compared to the one without it. Both H2 and CO2 concentrations positively correlated with CO formation and suppressed H2O electrolysis. Transient studies indicated that the amount of Ce3+ sites directly correlated with thermochemical CO production. In particular, Ce3+ sites influenced CO2 reduction without affecting the overall RWGS reaction. First principles-based calculations shed light on the formation of hydride-type species upon hydrogen incorporation within CeOx. H incorporation promoted oxygen defect formation, facilitating both reactive oxygen removal and augmented CO production. © 2024