A Highly Efficient and Robust Bifunctional Perovskite-Type Air Electrode with Triple-Conducting Behavior for Low-Temperature Solid Oxide Fuel Cells

Cobalt-rich materials have generally been recognized as the prevailing candidates of cathodes for low-temperature solid oxide fuel cells (LT-SOFCs, 400–600 °C). Regrettably, their instability and high cost are the major concerns for future commercialization. In response to these drawbacks, here, an A-site-deficient low-cobalt-containing perovskite-type oxide, Ba_0.95Fe_0.7Co_0.2Sc_0.1O_3-δ (BFCS0.95), as an efficient bifunctional electrode with triple-conducting (H⁺|O²⁻|e⁻) nature for oxygen-ion conducting SOFCs (O-SOFCs) and proton conducting SOFCs (H-SOFCs) is proposed. BFCS0.95 electrode exhibits impressive versatility in catalyzing oxygen reduction reaction, i.e., ultralow area-specific resistances (0.072 Ω cm² for O-SOFCs and 0.4 Ω cm² for H-SOFCs at 550 °C, respectively), extraordinarily high power outputs (1092 mW cm⁻² for O-SOFCs and 419 mW cm⁻² for H-SOFCs at 550 °C, respectively), excellent long-term durability (>100 h for O-SOFCs and H-SOFCs at 600 °C), remarkable reversibility between pure air and CO₂-containing air, and superior resistance against temperature fluctuations. The combined experimental and computational studies elucidate the roles of A-site deficient state and triple-conducting behavior, both of which are essential to overall electrochemical performance. Low-cobalt-containing feature also makes BFCS0.95 cathode economically competitive among all cobalt-containing analogues. Overall, the finding paves a highly efficient route to develop bifunctional electrodes for LT-SOFCs toward a sustainable energy future.