Electrochemical impact of the carbonate in ceria-carbonate composite for low temperature solid oxide fuel cell

Ceria-carbonate composite has been suggested as a promising electrolyte for solid oxide fuel cells operating at low temperatures. However, the roles of carbonate in the enhancement of the superionic conductivity and fuel cell performance of ceria-carbonate composite electrolytes are not yet confirmed. In this work, we look into the chemical and ionic state, transmission and segregation of carbonate and alkali cations under normal and electrochemical conditions. The XRD measurement confirms that there are not any carbonate crystals in the sample electrolyte. It is interesting to see that part of the carbonate and alkali ions are not formed into the stoichiometric carbonate in sample materials under the typical electrical field condition from the EDS and XPS analysis. Instead, carbonate (CO32−) and alkali ions accumulate in the cathode side, which we believe, was caused by the electrochemical “catalyst” of CO2 and alkali ions that accelerated the electrochemical oxygen reduction reaction, while the CO32− ions as one of the charge carriers which diffuse from fuel cell cathode to anode are on account of the concentration gradient. Those together contribute to the excellent electrochemical performances of ceria-carbonate composite electrolyte for low temperature solid oxide fuel cell.