Intermediate-Temperature Proton Conduction in Al[sup 3+]-Doped SnP[sub 2]O[sub 7]

Abstract

Al3+ -doped Sn P2 O7 proton conductors were prepared by controlling the initial composition of the reactants [Sn O2, Al (OH)3, and H3 P O4]. Sn1-x Alx Py Oz with y<2 displayed conductivities approximately two orders of magnitude lower than Sn1-x Alx P2 O7, while those of Sn1-x Alx Py Oz with y>2 exhibited conductivities at a maximum of 1.99 times higher. However, because the conductivity values of Sn1-x Alx Py Oz with y>2 were not stable, the optimal value of y in Sn1-x Alx Py Oz was determined to be 2. Partial substitution of Al3+ for Sn4+ in Sn1-x Alx P2 O7 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°C, 0.15 S cm-1 at 200°C, and 0.19 S cm-1 at 300°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 ∼1, and a fuel cell using this material demonstrated that the dc conductivity was comparable to the ac conductivity. © 2007 The Electrochemical Society.