Proton Conduction in In3 + -Doped SnP2O7 at Intermediate Temperatures

SnP 2 O 7 -based proton conductors were characterized by Fourier transform infrared spectroscopy (FTIR), temperature-programmed desorption (TPD), X-ray diffraction (XRD), and electrochemical techniques. Undoped SnP 2 O 7 showed overall conductivities greater than 10 -2 S cm -1 in the temperature range of 75-300°C. The proton transport numbers of this material at 250°C under various conditions were estimated, based on the ratio of the electromotive force of the galvanic cells to the theoretical values, to be 0.97-0.99 in humidified H 2 and 0.89-0.92 under fuel cell conditions. Partial substitution of In 3+ for Sn 4+ led to an increase in the proton conductivity (from 5.56 X 10 -2 to 1.95 X 10 -1 S cm -1 at 250°C, for example). FTIR and TPD measurements revealed that the effects of doping on the proton conductivity could be attributed to an increase in the proton concentration in the bulk Sn 1-x In x P 2 O 7 . The deficiency of P 2 O 2 ions in the Sn 1-x In x P 2 O 7 bulk decreased the proton conductivity by several orders of magnitude, which was explained as due to a decrease in the proton mobility rather than the proton concentration. The mechanism of proton incorporation and conduction is examined and discussed in detail.

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