Protonic ceramic electrochemical cells (PCECs) are promising solid-state energy conversion devices which enable the conversion of energy between electricity and hydrogen at intermediate temperatures. Rapid conversion between chemical and electrical energy via PCEC technology will assist in overcoming grand challenges in energy storage. To achieve highly efficient reversible operation between hydrogen production and electricity generation, boosting water-oxidation and oxygen reduction activities of the oxygen electrode while maintaining the durable operation is one of the early-stage technical opportunities. In this study, an A-site deficient layered perovskite (PrBa_0.8Ca_0.2)_0.95Co₂O_6−δ has been developed as an oxygen electrode for a PCEC which presents superior electrochemical performances. The electrolysis current density reached as high as −0.72 A cm⁻² at 1.3 V, and a peak power density of 0.540 W cm⁻² was obtained at 600 °C in electrolysis and fuel cell mode, respectively. The PCEC with the new electrode shows good durability under practical operating conditions for 160 hours in both operating modes with no observable degradation. The reversibility between the electrolysis and fuel cell mode is also successfully demonstrated.

Proton conducting ceramics show promise in fuel cells, electrolyzers, permeation membranes, sensor applications, and membrane reactors. Among several types of materials that exhibit proton conduction, perovskite oxides show high proton conductivity at intermediate temperatures, presenting potential benefits for long-term use and lower costs for energy applications. Doped barium zirconate, BaZrO₃, is a material that has shown high proton conductivity with encouraging chemical stability. Therefore, it is considered a promising material especially for proton-conducting solid oxide electrochemical cells. Although the proton conduction of doped BaZrO₃ has been extensively characterized, the specific phenomena behind its proton conduction are not fully understood. Only recently have specialized techniques and computational tools begun to elucidate the phenomena that determine the conduction properties of the material. In this mini review, an evaluation of the factors affecting the proton conductivity of doped BaZrO₃ perovskites and the phenomena governing variations in proton concentration and mobility are presented. Special attention is given to proton interactions with dopants and their resulting effect on hydration and transport properties. Technical strategies are provided to give some guidance on the development of protonic ceramics in energy conversion applications.