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

Novel proton-conductive electrolytes (NH4)xK1-xPO3 were developed for use in intermediate-temperature fuel cells. (NH4)0.20K0.80PO3 exhibited a high stability at 300°C and showed a high proton conductivity of 4.57×10-3 S cm-1 in dry Ar, and of 3.14×10-3 S cm-1 in Ar humidified at 80°C. Even at 400°C, the electrolyte was stable, and its conductivity reached 8.04×10-3 S cm-1 in dry Ar, and 7.47×10-3 S cm-1 in Ar humidified at R.T. The results of thermogravimetry showed a 2.8% loss of the mass after being kept at 300℃ for 100 h, which suggested that NH3 (and other unknown components) were volatilized during heating. SEM observation revealed that the electrolyte separated into two phases: crystalline KPO3 and an amorphous phase (HPO3) when heated at 300°C. The former acted as a matrix, and the latter worked as a proton conductor