Gadolinium-Doped Ceria-NaCoO₂ Heterogeneous Semiconductor Ionic Materials for Solid Oxide Fuel Cell Application

Solid oxide fuel cells (SOFCs) possess the merits of high power density, high energy conversion efficiency, and low emissions with diverse fuels and have attracted wide attention in the energy fields. However, the excessively high operating temperature limits its commercialization from aspects of cost and durability. It is urgent to find other ceramic membrane materials with superionic conductivity at low and intermediate temperatures to reduce the temperature of SOFCs. Semiconductor ionic composites based on oxide semiconductors can be used as heterogeneous functional membrane materials to develop low-temperature SOFCs. Herein we report a heterostructure material formed by gadolinium-doped ceria (GDC) and NaCoO₂ (NCO) as a functional membrane. The fuel cell with the optimized functional composite membrane achieved a peak power density of 1097 mW·cm^-2 at 550 °C, in which an ionic conductivity of 0.33 S·cm^-1 at 550 °C was obtained for the heterostructure composite. Proton conduction in the heterostructure composite was confirmed by X-ray photoelectron spectroscopy, Raman spectroscopy, and electrochemical impedance spectroscopy. Interfacial proton-transport and bulk oxygen-ion conduction mechanisms are proposed and discussed.