On the Role of Bimetal-Doped BaCoO_3−δ Perovskites as Highly Active Oxygen Electrodes of Protonic Ceramic Electrochemical Cells

Protonic ceramic electrochemical cells (PCECs) hold great promise as an energy conversion and storage technology at lower temperatures (400–650 °C). However, the sluggish reaction kinetics at the oxygen electrode hinder the electrochemical activity of PCECs. Herein, a series of bifunctional oxygen electrodes based on bimetal-doped BaCoO_3-δ (BCO) are reported. Doping hampers hexagonal perovskite formation and transforms BCO into cubic perovskite, improving water uptake and hydration abilities. Density functional theory calculations highlight the effects of phase transformation on the proton transport properties of oxygen electrodes. Notably, PCECs incorporating the bimetal-doped electrodes exhibit maximum power densities of 3.15 W cm⁻² (650 °C) and 2.25 W cm⁻² (600 °C) in fuel cell mode, as well as a current density of 4.21 A cm⁻² at 1.3 V (650 °C) in electrolysis cell mode, setting record-high values. The findings provide insights into the rational design of bifunctional oxygen electrodes for high-performance PCECs.