Preparation and characterization of Ce- and La-doped Ba2In2O5 as candidates for intermediate temperature (100–500 °C) solid proton conductors

Five different compositions of brownmillerite materials, Ce- and La-doped, and undoped Ba2In2O5 were synthesized via the solid-state reaction and the glycine-nitrate combustion process. Properties of the materials were characterized using XRD, HR-TEM, and TGA/DSC techniques. Conductivity measurements by AC impedance spectroscopy, performed in air and hydrogen-containing atmospheres, in the temperature range from 100 °C to 500 °C, were correlated to the properties of the materials and revealed the effects of dopant, microstructure, temperature and atmosphere on the total electrical conductivity of the materials. All compositions showed low conductivity in air. In hydrogen-containing atmospheres, while Ce- and La-doped Ba2In2O5 showed low conductivity (4 × 10−6–3 × 10−6 S cm−1 at 500 °C), undoped Ba2In2O5 demonstrated a surprisingly high conductivity (between 0.02 S cm−1 and 0.7 S cm−1 in the temperature range from 300 °C to 500 °C), especially samples produced by the glycine-nitrate process. This finding creates potential opportunity for using Ba2In2O5 as a proton-conductive material in intermediate temperature fuel cells.

► Potential for intermediate temperature proton conductors.
► Focus on relationship between the materials bulk properties and the conductivity.
► Improved understanding of the conduction mechanisms in proton conductive ceramics.
► Ba2In2O5 demonstrated a surprisingly high conductivity in hydrogen.