Thermal efficiency of solid electrolyte fuel cells with mixed conduction

The effect of mixed anionic and n-type electronic conduction in solid electrolytes on the thermal efficiency of a fuel cell system was analyzed quantitatively. The mixed conduction observed when electrolytes based on ceria are used in H₂/air fuel cell applications lowers the maximum attainable cell thermal efficiency to below 40%. Neither the zirconia nor the ceria based solid oxide electrolytes studied to date can be used in a low temperature (700 °C) system that meets simultaneously the requirements of power density and thermal efficiency for electric utility power plants. The material properties required for an advanced fuel cell power plant solid electrolyte were derived in terms of the ionic conductivity and the Schmalzried parameters P⊕ and P? : σ_ion > 0.033 (ω-cm)^?1, P⊕ > 10³ atm., P? < 10^?23 atm. at 700 °C.