Rational structuring engineering of a hydrogenation-dominated air electrode with Ag exsolution for reversible protonic ceramic cells

Triple conductive oxide provides the advantage of simultaneously conducting H⁺/O²⁻/e⁻, making it an ideal choice for protonic ceramic cells (PCCs) air electrodes. However, it is imperative to comprehend the competitive relationship between its proton uptake, hydration and hydrogenation processes for informing future designs for air electrodes. Here, we designed Ba_0.95Ag_0.05Co_0.8Sc_0.1Nb_0.1O_3-δ (BACSN) electrode materials co-doped with Nb⁵⁺ to optimize oxygen vacancy concentration and enhance proton transport capacity through high-valent Sc³⁺. It turns out to be hydrogenation-dominant proved by electrical conductivity relaxation and thermogravimetric characterization. As hydrogenation process machanism enables to reduce cations, 5% Ag was incorporated at the A site and in-situ exsolution of Ag nanoparticle onto the surface is observed after water treatment. Computational and experimental results demonstrate that the BACSN@Ag exhibits outstanding proton uptake ability and electrochemical performance. More importantly, a self-optimization ability in fuel cell mode is demonstrated due to water generation. This work provides new insights for improving the design of PCCs air electrodes with regard to oxygen vacancy regulation and proton uptake capabilities.