Ionic Conduction in In3＋-doped ZrP2O7 at Intermediate Temperatures

A new series of Zr1-xInxP2O7 （x=0.03, 0.06, 0.09, 0.12） samples were prepared by a solid state reaction method. XRD patterns indicated that the samples of x=0.03–0.09 exhibited a single cubic phase structure, and the doping limit of In3＋ in ZrP2O7 was x=0.09. The conduction behavior was investigated in wet hydrogen using various electrochemical methods including AC impedance spectroscopy, isotope effect, gas concentration cells at intermediate temperatures （373–573 K）. The conductivities were affected by the doping levels, and increased in the order： σ （x=0.03）〈σ （x=0.12）〈σ （x=0.06）〈σ （x=0.09）. The highest conductivity was observed for the sample Zr0.91In0.09P2O7 to be 1.59×10-2 S·cm-1 in wet hydrogen at 573 K. The isotope effect also confirmed the proton conduction of the sample under water vapor-containing atmosphere. It was found that in wet hydrogen atmosphere Zr0.91In0.09P2O7 was almost pure ionic conductor, the ionic conduction was contributed mainly to proton and partially to oxide ionic. The H2/air fuel cell using x=0.09 sample as electrolyte （thickness： 1.73 mm） generated a maximum power density of 13.5 mW·cm？2 at 423 K and 16.9 mW·cm？2 at 448 K, respectively.