Enhanced protonic and oxygen-ionic conductivity in Ga-doped Nd2Ce2O7 electrolytes for intermediate-temperature solid oxide fuel cell

Abstract

Developing mixed oxygen-ion and proton conductors with high ionic conductivity is crucial for advancing intermediate temperature-solid oxide fuel cell (IT-SOFC). In this study, a novel Nd2-xGaxCe2O7 (NGCO, x = 0, 0.05, 0.075, 0.10 and 0.15) ceramic is synthesized by the citric acid-nitrate sol-gel combustion process. The influence of Ga doping on crystal structure, oxygen vacancy, morphology, proton transport characteristic and electrochemical performance of this materials is systematically investigated. It is found that the NGCO exhibits the fluorite-type structure and belongs to space group Fm3¯m. NGCO shows remarkable chemical stability, resisting harmful effects from CO2, water, and wet hydrogen exposure. Adding a small amount of Ga results in high-density ceramics with enlarged grain size and reduced grain boundary density. Nd1.925Ga0.075Ce2O7 (7.5NGCO) displays outstanding conductivities, exceeding Nd2Ce2O7 (NCO) by 271.4% and 248.6% in dry air and wet hydrogen conditions. Further, an anode-supported structure fuel cell with 7.5NGCO electrolyte is constructed and evaluated. The peak power density (PPD) at 700 °C reaches 702 mW/cm2, a 96% enhancement over the fuel cells with NCO electrolyte. These findings indicate that Ga-doped NCO electrolyte holds promise as a proton-conducting electrolyte suitable for IT-SOFC.