In Situ Engineering of a Cobalt‐free Perovskite Air Electrode Enabling Efficient Reversible Oxygen Reduction/evolution Reactions

Abstract Reversible protonic ceramic electrochemical cells (R‐PCECs) have received increasing focus for their good capability of converting and storing energy. However, the widely used cobalt‐based air electrodes are less thermomechanically compatible with the electrolyte and lack stability, which largely limits the development of R‐PCECs. Herein, a cobalt‐free perovskite with a nominal composition of PrBa 0.8 Ca 0.2 Fe 1.8 Ce 0.2 O 6 δ (PBCFC) is reported, which is in–situ engineered to a (Ba, Ce) deficient‐PBCFC phase, a BaCeO 3 , and a CeO 2 phase under typical operating conditions, delivering a low area–specific resistance of 0.10 Ωcm 2 at 700 o C. The generated BaCeO 3 and CeO 2 particles increase the conduction/transfer of protons and oxygen ions, thus providing extra active sites for the oxygen reactions. When utilized as an air electrode on a single cell, it achieves encouraging performance at 700 °C: a peak power density of 1.78 Wcm −2 and a current density of 5.00 Acm −2 at 1.3 V in the dual mode of the fuel cell (FC) and electrolysis (EL) mode with reasonable Faradaic efficiencies. In addition, the cells exhibit favorable operational durability of 65 h (FC mode), 95 h (EL mode), and promising cycling stability of 200 h.