Tailoring oxygen vacancies and hydration kinetics in perovskite oxygen electrodes through potassium doping for high-performance reversible protonic ceramic cells

The development of reversible protonic ceramic cells (R-PCCs) is limited by the sluggish reaction kinetics of oxygen electrode. Herein, we propose that introducing potassium (K) into Ba(Co 0.7 Fe 0.3 ) 0.85 Ta 0.15 O 3-δ (BCFT) not only promotes the oxygen vacancy formation and proton uptake, but also enhances oxygen exchange and oxygen dissociation capability, thereby leading to enhanced catalytic activity. R-PCCs with the obtained Ba 0.9 K 0.1 (Co 0.7 Fe 0.3 ) 0.85 Ta 0.15 O 3-δ (BKCFT10) oxygen electrode exhibit good performance in both fuel cell mode (1.21W cm −2 at 650 °C) and electrolysis mode (−1.76 A cm −2 at 1.4 V and 650 °C) compared to pristine BCFT (1.06W cm −2 in fuel cell mode and −1.63 A cm −2 at 1.4 V in electrolysis mode, respectively). Additionally, the R-PCCs show excellent stability in fuel cell (200 h), electrolysis (200 h) modes, and reversible cycling measurement (15 cycles for 30 h). The systematic experiments and theoretical calculations convincingly demonstrate that potassium substitution is an effective method for developing novel oxygen electrode materials for R-PCCs.