Protonic Electroceramics for Fuel Cells

Whereas the conventional solid oxide fuel cell uses an oxygen‐ion conducting electroceramic, materials also exist which, at least over a restricted temperature range, perform as hydrogen ion, or proton, conductors. In principle, solid oxide fuel cells based on these materials are possible. With increasing temperature some degree of oxygen ion mobility is also observed, so that these materials are then mixed ionic conductors. The electrochemical characteristics observed may be influenced strongly by the choice and structure of the contacting electrode material. The open‐circuit voltage for example may be significantly less than that indicated by thermodynamics. In addition the external faradaic efficiency of ionic devices based on mixed conductivity electroceramics may also be reduced. The effects relate to the selectivity of the interface for charge exchange by the diverse carriers. Some results on perovskite cathodic materials contacting cerate protonic conductors are presented.