Lowering the operating temperature is a universal R&D challenge for the development of low-temperature (<600 °C) solid oxide fuel cells (SOFCs) that meet the demands of commercialization. Regarding the traditional electrolyte materials of SOFCs, bulk diffusion is the main ionic conduction mechanism, which is primarily affected by the bulk density and operating temperatures. In this study, we report a new mechanism for the Ce0.9Gd0.1O2-δ (GDC) electrolyte based on a nanocrystalline structure with surface or grain boundary conduction, exhibiting an extremely high ionic conductivity of 0.37 S·cm-1 at 550 °C. The fuel cell with the nanocrystalline structure GDC electrolyte (0.5 mm in thickness) can deliver a remarkable peak power density of 591.8 mW·cm-2 at 550 °C, which is approximately 3.5 times higher than that for the cell with the GDC electrolyte densified at 1550 °C. An amorphous layer enriched by oxygen vacancies was found at the surface of the nano-GDC particles in the fuel cell test atmosphere, which was attributed to the ion conduction channel of the grain boundary diffusion. The ionic conduction at the interfaces between the particles was discovered to be the dominant conduction mechanism of the nanocrystalline structure GDC electrolyte. Oxygen ions and protons were determined to be the charge carriers in this interfacial conduction phenomenon, and the conduction of oxygen ions was dominant.
Keywords: Gd0.1Ce0.9O2; electrolyte; interfacial conduction; nanocrystalline; solid oxide fuel cell; transference number.