Operando Studies on Solid Oxide Ceria Electrodes during CO2 Electroreduction

Abstract: CeOx-YSZ electrode performed well for CO2 electro-reduction in both pure CO2 and CO2 (+H2) feeds.. In pure CO2, 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 (~5%) resulted in reverse Water Gas Shift reaction and an additional Raman band at 480 cm-1 (φ). The CO formation was more facile in presence of H2 at a lower bias compared to the pure CO2 stream. The electronic conductivity showed a slight dip at low biases (5% H2) due to the reoxidation of Ce3+ sites to Ce4+-H- (hydridic) sites. Both H2 and CO2 concentrations positively correlated with CO formation and supressed H2O electrolysis. First principles-based calculations indicate that adsorption of H into bulk makes it easier to create oxygen defect in CeO2 making the creation of Ce3+ sites easier. When adsorbed around oxygen defects the H acquires a hydridic (H-) nature. The φ band is likely to be associated with phonon modes containing H adsorbed around undefective sites. No coking was observed in both pure CO2 and CO2 (+H2) feed streams.