The crystal structure and proton conductivity of cerium pyrophosphate are investigated to explore its potential electrolyte applications for intermediate temperature fuel cell. Among the CeP2O7 thin plates, which are sintered at 300-900 degrees C, the 450 degrees C CeP2O7 sample exhibits superior proton conductivity under humidified conditions. Its conductivity, measured with impedance spectroscopy, is higher than 10(-2)S cm(-1) in the intermediate temperature range, with a maximum value 3.0 x 10(-2)S cm(-1) at 180 degrees C. When 10 mol% Mg is doped on the Ce site of CeP2O7, the maximum conductivity is raised to 4.0 x 10(-2)S cm(-1) at 200 degrees C. The Mg doping not only raises the conductivity, but also shifts and widens its temperature window for electrolyte applications. Ce0.9Mg0.1 P2O7 is considered a more appropriate composition, with conductivity > 10(-2)S cm(-1) between 160 and 280 degrees C. Accordingly, a hydrogen-air cell is built with the Ce0.9Mg0.1 P2O7 electrolyte and its performance is measured. The fuel cell generates electricity up to 122 mA cm(-2) at 0.33 V using 50% H-2 at 240 degrees C. (C) 2011 Elsevier Ltd. All rights reserved.