Highly conductive and stable Er_xCe_0.05Bi_0.95-xO_1.5+δ solid electrolytes for low-temperature solid-oxide fuel cells

Low-temperature solid oxide fuel cells (LT-SOFCs) are key to meeting China's dual-carbon goal, but existing solid electrolytes suffer from low conductivity. Here, a highly conductive Er/Ce co-doped bismuth oxide (ErxCe5SB, x = mol%) electrolyte is reported. Synthesis is achieved by reverse coprecipitation, and ErxCe5SB has a cubic fluorite structure with a uniform particle size of 100–200 nm, although Er5Ce5SB and Er10CeSB contain a minor rhombohedral phase. Dense pellets (relative density: 93 %) are formed after sintering at 800 °C for 6 h, and the lattice constants decrease with the increase in erbium dopant concentration. Er20Ce5SB had an impressive ionic conductivity of 0.016 S cm-1 at 450 °C. Notably, after being annealed at 600 °C for 4032 h, Er20Ce5SB showcased a commendable stability in conductivity, measuring approximately 0.09 S cm⁻¹, with only a minor drop in its conductivity value. Even after such extended annealing, Er20Ce5SB retained its pure cubic phase structure, devoid of any impurities. Oxygen-ion ordering yields a superstructure, as observed by HR-TEM. Because of its high conductivity and long-term stability, Er20Ce5SB is a promising LT-SOFC electrolyte material.