Proton conductive solid electrolytes for high-efficiency intermediate temperature solid oxide fuel cells

Proton conductive electrolytes of (NH4)xM1−xPO3 (M = K, Rb, and Cs) solid solutions were prepared for the intermediate temperature fuel cells. The alkaline metal ions in the solid solutions worked to improve the thermal stability of electrolyte at 300ºC. The ionic conductivities of (NH4)xM1−xPO3 (M = Rb, Cs) electrolytes were about 7 Í10−3 S cm−1 at 300ºC and maintained the conductivity for 200 h in dry Ar, which was brought about by proton formed by decomposition of the electrolytes. The conductivity depended mostly on the content of NH4+ ion in the electrolyte, and the effect of alkaline cation was minor. Consequently, it is important to increase NH4+ content without a decrease in thermal stability to improve the proton conductivity