Proton Pumping Boosts Energy Conversion in Hydrogen-Permeable Metal-Supported Protonic Fuel Cells

Protonic ceramic fuel cells (PCFCs) have limited application below 500 °C owing to their high ohmic and polarization resistances. Hence, efforts are ongoing to develop advanced fuel cells based on semiconductor device science as well as material interfacial engineering. Here, we demonstrate that hydrogen-permeable metal-supported fuel cells (HMFCs) exhibit improved energy conversion efficiency at relatively lower temperatures due to the retardation of secondary conduction (that of the oxide ions) at the oxide/metal heterointerface. The electrolyte membrane in HMFCs is forced to gain extra protons to compensate for the charge from the oxide ions accumulating via blocking, resulting in extremely high proton conductivity. Simultaneously, the heavily hydrated membrane pumps protons out of the cathode side during cell operation. This significantly promotes interfacial proton diffusion for cathode reactions. Hence, HMFCs can operate at high efficiency even at temperatures lower than the operational temperature of PCFCs and will help improve the power generation performance of protonic oxide fuel cells at temperatures lower than 500 °C.