High-performing and stable non-doped ceria electrolyte with amorphous carbonate coating layer for low-temperature solid oxide fuel cells

ABSTRACT Recent studies have realized fast ionic transport in pure ceria (CeO2) via surface conduction without using conventional structural doping, indicating a promising strategy to develop electrolytes for low-temperature solid oxide fuel cells (LT-SOFCs). In this work, to further develop the potential of non-doped ceria, a new CeO2 electrolyte (CeO2#1) is synthesized through precipitation method by using Na2CO3 as precipitant for surface modification, and compared with two other CeO2 samples (CeO2#2 and CeO2#3) prepared by NH4HCO3 and KOH precipitants. The CeO2#1 is found to be composed of ceria and slight amorphous Na2CO3, while CeO2#2 and CeO2#3 contain simplex ceria. When applied in SOFCs, the CeO2#1 electrolyte achieves attractive fuel cell performance (706 mW cm−2 at 550 °C) with good stability, demonstrably superior to those of CeO2#2 and CeO2#3 electrolytes. Further impedance spectra analysis manifests the high proton conductivity of CeO2#1, and suggests that the electrochemical performance superiority of CeO2#1 should be ascribed to its micro-structural feature. Subsequent TEM characterization confirms the existence of Na2CO3 in CeO2#1 as an ultra-thin coating layer, benefiting from which, the CeO2 can be protected from being reduced by H2 and enable high ionic conductivity by virtue of ceria/carbonate interface. This work thus points out a new type of non-doped ceria electrolytes with different working mechanism from previous studies and indicates a feasible approach to develop high-performing and stable electrolytes for LT-SOFCs.