The BaCe0.16Y0.04Fe0.8O3-d nanocomposite: A new high-performance cobalt-free triple-conducting cathode for protonic ceramic fuel cells operating at reduced temperatures

Compared with conventional oxygen-ion-conducting solid oxide fuel cells (O-SOFCs), proton ceramic fuel cells (PCFCs) are more attractive for low-temperature operation due to their smaller activation energy and higher ionic conductivity at reduced temperatures. However, most of the PCFCs still exhibit lower power outputs than O-SOFCs until now due to the lack of suitable and high-performance cathode materials. Cobalt (Co)-based perovskite oxides have been widely employed as cathodes for PCFCs, and suffer from poor thermo-mechanical compatibility with the electrolyte and inferior structural stability. Herein, Co-free triple-conducting perovskite-based nanocomposites are reported as highly active and stable cathodes for PCFCs. By tailoring the Ce/Y co-doping amounts in BaFeO3-δ, Ba(Ce0.8Y0.2)xFe1-xO3-δ (x = 0.1, 0.2 and 0.3) perovskites experience a phase transformation from a single-phase (x = 0.1, O^2-/e^-conducting) into a composite (x = 0.2 and 0.3, O^2-/e^-and H⁺/e^-conducting) to achieve triple-conducting capability. The optimized BaCe0.16Y0.04Fe0.8O3-δ nanocomposite cathode displays superior activity for the oxygen reduction reaction (ORR) with low area-specific resistances of 0.27 and 1.49 ω cm²at 600 and 500 °C, respectively, surpassing most of the reported Co-free PCFC cathodes. The BaCe0.16Y0.04Fe0.8O3-δ cathode also exhibits superior thermo-mechanical compatibility with BaZr0.1Ce0.7Y0.1Yb0.1O3-δ electrolyte and improved CO2 tolerance due to the strong interaction between O^2-/e^-and H⁺/e^-conducting phases and the optimized dual-phase composition. Consequently, an anode-supported single cell with the BaCe0.16Y0.04Fe0.8O3-δ cathode delivers a high peak power density of 829 mW cm^-2at 650 °C and a durable operation for ∼450 h at 550 °C. This work provides a highly promising Co-free cathode for PCFCs, which may accelerate the commercialization of this technology.