Flash transition as a possible origin for low open circuit voltage in thin film solid oxide fuel cells

The open circuit voltage of solid oxide fuel cells (SOFCs), made with thin film electrolytes of yttria-stabilized cubic zirconia, often lies below the Nernstian value, which has been prescribed to processing defects. The effect persists in films fabricated by different methods and even when their thickness ranges from nanometers to micrometers, which is well beyond the electron direct tunneling length scale. Here we explain this phenomenon in terms of an alternative mechanism, a flash transition, where yttria stabilized zirconia can partially transition into an electronic state; the transition depends on (i) the resistance of the electrolyte, (ii) the electric field and (iii) the temperature. The variability in the open circuit voltage is subscribed to processing-related variability in the resistivity of the films, which has a strong influence on the flash transition.