Exceptional characteristics of ceria for energy technologies

Perhaps the greatest challenge facing our planet is sustainable energy. Ceria, both doped and undoped, plays a prominent role in a range of energy technologies as a result of its high ionic conductivity, moderate electronic conductivity, chemical stability, mechanical robustness and exceptional chemical and electrochemical activity. Areas of application of ceria include fuel cells, as both electrolyte and anode component, catalytic converters, and, most recently, thermochemical solar fuel production. We present here an overview of the thermodynamic and kinetic factors that render ceria useful in these devices, focusing particularly on hydrogen electro-oxidation as occurs in fuel cell anodes. Studies employing patterned metal current collectors on epitaxial ceria thin films reveal the relative activities of the ceria surface and the triple-phase boundary between metal, oxide and gas. Remarkably, the activity of the oxide surface overwhelms the contribution of the metal at all but the highest number-density of triple-phase boundaries.