Novel proton-conducting hexagonal perovskites Ba7In6–xYxAl2O19 for solid oxide fuel cells

Abstract

The solid solution Ba7In6–xYxAl2O19 (0≤x≤0.25) with a hexagonal perovskite-like structure was prepared by the solid-state route. The introduction of yttrium was accompanied by an increase in lattice parameters. The total conductivity as a function of pO2 and T was measured at different humidity. The partial conductivities were found by transport number measurements and were fitted based on the defect formation model. Oxygen-ion and proton conductivities were found to increase with Y3+ content as a result of an increase in cell volume and free volume, which was accompanied by a decrease in the activation energy of both oxygen-ion and proton conductivity. Oxygen-ion conductivity and proton conductivity dominated below 500 °C in dry (pH2O=3.5×10−5 atm) and in wet (pH2O=1.92×10−2 atm) conditions, respectively. Doping makes it possible to increase proton conductivity by an order of magnitude (500 °C) and significantly increase the proton transport numbers.The prepared phases exhibited excellent chemical stability during thermal treatment in carbon dioxide (pCO2=1 atm).