Sn–Dy–Cu Triply Doped BaZr0.1Ce0.7Y0.2O3−δ: A Chemically Stable and Highly Proton-Conductive Electrolyte for Low-Temperature Solid Oxide Fuel Cells

BaCeO3-based proton conductors have comparatively high-proton conductivity, but the low chemical stability and high sintering temperature seriously hinder their practical applications in protonic ceramic fuel cells. Herein, we demonstrate that this limitation can be conciliated by using a triple-doping strategy in a BaZr0.1Ce0.7Y0.2O3−δ (BZCY) electrolyte, where the triply doped BaCe0.7Sn0.1Dy0.15Cu0.05O3−δ (BCSDCu) exhibits better chemical stability and conductivity and lower sintering temperature compared with the pristine BZCY. The phase-pure BCSDCu can be obtained at the sintering temperature of 1100 °C prepared by solid-state reaction. The dense BCSDCu (>95%) is achieved at 1350 °C, which is significantly lower than the 1550 °C of BZCY. The BCSDCu presents competitive proton conductivity of 13.6 mS cm–1 under a moist H2 atmosphere at 600 °C. The anode-supported single cell with the BCSDCu (≈40 μm) as the electrolyte reaches the highest power density of 390 mW cm–2 at 600 °C. On the basis of the distribution of relaxation time analysis, we not only distinguish the contribution of grain and grain-boundary conductivities but also identify the rate-determining step of the single-cell performance. The protonic conductivities, mechanical properties, and impurity clean parts induced by grain size effects are discussed for the BCSDCu proton conductor.