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

Abstract

Abstract Eight proton conducting oxygen-deficient perovskites BaIn 1 − x − y Ti x Zr y O 2.5 + (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% CO 2 atmosphere in temperature and present thermal expansion properties compatible with standard fuel cell materials. At high temperature the conductivity is mainly anionic (σ O2– ≈ 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 BaIn 0.8 Ti 0.05 Zr 0.15 O 2.6 (at 400 °C, σ H + = 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.