Advances and challenges in developing protonic ceramic cells

Unlike solid oxide cells (SOCs), which use oxygen ions as charge carriers, protonic ceramic cells (PCCs) utilize protons as primary charge carriers. As a result, PCCs have a unique conduction mechanism that shows higher ionic conductivity with lower activation energy than those of SOCs. Moreover, PCCs have additional critical advantages for commercialization, such as easy gas separation and no fuel dilution at the fuel electrode. At present, PCCs are receiving significant research attention, primarily motivated by their higher performance, superior stability at lower operating temperatures, and greater system simplicity than SOCs. However, despite these advantages and the overall potential of PCCs, their electrochemical performance and stability have not yet significantly exceeded those of SOCs. This review discusses three pathways toward solving the problems currently impacting the PCC development: (1) proton conducting ceramic materials, including proton conducting mechanisms, defects in materials that impact the overall conductivity, and rational design and engineering strategies for enhancing proton conductivity; (2) manufacturing process for fabricating the desired PCC electrolyte layer with large grain size and preserved stoichiometry; (3) improving the interfacial reaction, including enhancing the surface reactivity by controlling the charge-transfer reactant concentrations and increasing the electrolyte/electrode contact area.