Enhancement in CO2 Electroreduction upon Pr Infiltration of Ceria Electrodes

Mixed electronic and ionic conducting (MIEC) CeOx electrodes are well known for CO2 electrolysis at high temperatures (800oC). Pr infiltration of CeOx/YSZ resulted in significant enhancement in CO yield in CO2 (+H2) environments. This study provides a first account of electrochemical and thermochemical (reverse water gas shift) reactions proceeding simultaneously on a solid oxide electrode and describes the effect of reactant concentrations and applied bias on product formation. The electrode resistance was found to reduce with increasing bias due to its MIEC character. These electrodes performed even under extreme currents (~ 2A/cm2) without significant overpotential penalty. Reaction was evaluated under various CO2 and H2 concentrations. Operando Raman spectroscopy and online mass spectroscopy (MS) were used to track structure property relationships. CO2 production correlated with the reduction of Ce4+ centers to Ce3+ with progressive application of bias. Upto 5% concentration of CO2, no coking was observed even under extremely high currents ~ 2A/cm2. At higher concentrations of CO2, strong bias resulted in coke formation without affecting the general activity of the catalyst. Raman bands of coke formation strongly correlated with complete disappearance of 450 cm-1 band, associated with Ce4+ sites and the disappearance of metal carbonyl band in this material. A “Ce3+-- CO” site mediated coking mechanism is proposed. The catalyst could be quickly regenerated using thermochemical and electrochemical techniques.