Modification of Misfit-Layered Cathode Materials for Improving Electrocatalyic Activity in Reversible Protonic Ceramic Cells

In reversible protonic ceramic cells (RPCCs), due to their fast oxygen reaction kinetics, perovskite-structured cathode materials have been in the spotlight up to this point. However, such materials have some drawbacks such as low phase stability in humid atmospheres, high thermal expansion coefficient, and relatively low proton conductivity despite high electrocatalytic activities when used as steam-air electrodes. Hence, we suggest that novel misfit-layered structure Ca 3 Co 4 O 9+δ (CCO)-based materials be used to overcome these technical issues with superior performance in RPCCs. Although CCO is a cobaltite-material, CCO has a similar thermal expansion coefficient as BZCYYb electrolyte’s (10‒12×10 -6 K -1 ). Moreover, the plate-like morphology of the CCO-based materials are favorable for the introduction or emission of steam. Further, with alkali metal doping in Ca-site, CCO generates extra charge carrier species with the modified Co oxidation state, which results in high proton uptake and diffusion mechanism. Altogether, 5 mol% potassium-doped CCO-cells show great potential as a cathode material.