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-sitedeficient low-cobalt-containing perovskite-type oxide, Ba 0.95 Fe 0.7 Co 0.2 Sc 0.1 O 3-δ (BFCS0.95), as an efficient bifunctional electrode with triple-conducting (H + |O 2− |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 cm 2 for O-SOFCs and 0.4 Ω cm 2 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 CO 2 -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.

Figure 6. a) Optimized structure and b) charge density map of BSFP perovskite.

Developing high-performance and cost-effective cathodes is ever-increasingly vital for the advancement of intermediate-temperature solid oxide fuel cells (IT-SOFCs). To facilitate the popularization of nonprecious metallic and cobalt-free oxygen reduction electrodes, herein, we propose a novel perovskite-based BaFeO3−δ (BF) matrix, Ba0.75Sr0.25Fe0.875Y0.125O3−δ (BSFY), as a highly active cathode for IT-SOFCs. To our satisfaction, the BSFY electrode showcases a low area-specific resistance of 0.063 Ω cm2, as well as a high peak power density of 1288 mW cm–2 at 600 °C, yielding a more than threefold improvement compared to that of its BF counterpart (371 mW cm–2). The long-term durability test highlights its practicability under the IT operating condition. When tested in 10 vol % CO2-containing air, the BSFY electrode exhibits impressive resistance against contaminants within 50 h (<0.4 Ω cm2 with a deterioration rate of ∼0.00011 Ω cm2 min–1). Coupled with its reversible response between pure air and the contaminant, the BSFY cathode is expected to be a promising cobalt-free alternative with high CO2 resistance for IT-SOFCs.

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