Intermediate-temperature proton conduction in Al3+-doped SnP2O7

Al3+-doped SnP2O7 proton conductors were prepared by controlling the initial composition of the reactants [SnO2, Al (OH)(3), and H3PO4]. Sn1-xAlxPyOz with y < 2 displayed conductivities approximately two orders of magnitude lower than Sn1-xAlxP2O7, while those of Sn1-xAlxPyOz with y > 2 exhibited conductivities at a maximum of 1.99 times higher. However, because the conductivity values of Sn1-xAlxPyOz with y > 2 were not stable, the optimal value of y in Sn1-xAlxPyOz was determined to be 2. Partial substitution of Al3+ for Sn4+ in Sn1-xAlxP2O7 led to an increase in the conductivity up until x = 0.05. As a result, the conductivity reached 0.045 S cm(-1) at 100 degrees C, 0.15 S cm(-1) at 200 degrees C, and 0.19 S cm(-1) at 300 degrees C when the x and y values were 0.05 and 2, respectively. A hydrogen concentration cell with this material demonstrated that the ionic transport number was similar to 1, and a fuel cell using this material demonstrated that the dc conductivity was comparable to the ac conductivity. (c) 2007 The Electrochemical Society.