Tailoring conductivity properties of chemically stable BaIn1 − x − yTixZryO2.5 + (x + y)/2 − n(OH)2n electrolytes for proton conducting fuel cells

Eight proton conducting oxygen-deficient perovskites BaIn1 − x − yTixZryO2.5 + (x + y)/2 − n(OH)2n with 0.2 ≤ x + y ≤ 0.5; 0 ≤ n ≤ 0.4 compounds were prepared by solid state reaction at 1350 °C in air and studied by TGA, thermodiffraction, SEM and EIS. At low temperature, below 180 °C, all compounds react with water vapor to incorporate protons. Hydration is associated with highly negative thermodynamic parameters. All the compounds present a disordered cubic symmetry except for the hydrated phases with the highest In content (x + y = 0.2) which present a cubic to tetragonal transformation below 250 °C. Phases are chemically stable towards moisture and 3% CO2 atmosphere in temperature and present thermal expansion properties compatible with standard fuel cell materials. At high temperature the conductivity is mainly anionic (σO2– ≈ 0.01 S cm− 1 at 700 °C) and below 600 °C proton conductivity is observed. The best level of H+ conductivity was found for BaIn0.8Ti0.05Zr0.15O2.6 (at 400 °C, σH + = 2 × 10− 3 S cm− 1). For this family of compounds, it is shown that the proton conductivity level at 400 °C is correlated to the basicity and that good protonic conductors at low temperature are also good anionic conductors at high temperature.