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

Abstract

Al3+ -doped SnnormalP2normalO7 proton conductors were prepared by controlling the initial composition of the reactants [ SnnormalO2 , Al(OH)3 , and normalH3PnormalO4 ]. normalSn1−xnormalAlxnormalPynormalOz with y<2 displayed conductivities approximately two orders of magnitude lower than normalSn1−xnormalAlxnormalP2normalO7 , while those of normalSn1−xnormalAlxnormalPynormalOz with y2 exhibited conductivities at a maximum of 1.99 times higher. However, because the conductivity values of normalSn1−xnormalAlxnormalPynormalOz with y2 were not stable, the optimal value of y in normalSn1−xnormalAlxnormalPynormalOz was determined to be 2. Partial substitution of Al3+ for Sn4+ in normalSn1−xnormalAlxnormalP2normalO7 led to an increase in the conductivity up until x=0.05 . As a result, the conductivity reached 0.045Scm−1 at 100°C , 0.15Scm−1 at 200°C , and 0.19Scm−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.

Niobium phosphates as an intermediate temperature proton conducting electrolyte for fuel cells

“…29 showed a conductivity of several orders of magnitude lower. It was suggested that the excess phosphoric acid in the preparation promoted the formation of a secondary amorphous phase in grain boundaries, which was considered to provide additional pathways for proton transport, 30 and therefore significantly enhance the conductivity.…”

“…It can be seen from the figure that the obtained EMF was very close to the theoretical values calculated from the Nernst equation. The ratio of the measured EMF to the theoretical value was assumed to be the proton transference number 30,34 and was found to be between 0.97 and 0.98. This indicated the protonic nature of the ionic conductivity of the niobium phosphates.…”

A Sb‐doped SnP2O7 Solid Proton Conductor for Intermediate Temperature Fuel Cells

“…In recent years, considerable effort has been made to develop novel solid proton conductors for fuel cells, based on pyrophosphates of tetravalent metals [7][8][9][10][11] that operate at 200-300°C. Various MP 2 O 7 (M = Si, Zr, Ti, etc.)…”

Intermediate-temperature proton conductors and their applications to energy and environmental devices

“…13) Interestingly, the proton conductivity of SnP 2 O 7 could be increased to ³10 ¹1 S cm ¹1 by the substitution of low valency cations, including In 3+ , 18) Al 3+ , 19) Mg 2+ , 20) Sb 3+ , 21) Sc 3+ , 22) and Ga 3+ 23) for part of the Sn 4+ cations. This conductivity value is sufficiently high for good performance of electrochemical devices.…”