Effects of Al2O3 doping in BaCeO3 on chemical stability and electrical conductivity of proton conducting oxides

BaCeO3 doped with trivalent ions have high proton conductivity but poor chemical stability against CO2. Al-doped BaCeO3 (Ba(Ce1−xAlx)O3−δ) was fabricated via conventional solid oxide reactions, and their chemical stabilities against CO2 and electrical conductivities were compared with those of Y-doped BaCeO3, which is a promising proton conducting oxide. The chemical stabilities against CO2 were enhanced by doping with Al; however, the electrical conductivities decreased. However, an abnormal increase in the electrical conductivity at temperatures ranging from 400 to 470 °C occurred when the Al content was above 15 mol%. In order to explain such an abnormal increase in electrical conductivity, thermogravimetric and X-ray diffraction analyses were performed at high temperatures, and the abnormal increase in electrical conductivity was correlated with water incorporation reactions and a transformation of the crystal structures with changes in temperature. •Al-doped BaCeO3 (Ba(Ce,Al)O3) was fabricated instead of rare-earth doped BaCeO3.•Ba(Ce,Al)O3 showed better chemical stability than rare-earth doped BaCeO3.•Ba(Ce,Al)O3 showed the abnormal increase of conductivity during cooling at 460 °C.•Proton conductivity of Ba(Ce,Al)O3 was comparable to that of Ba(Ce,Y)O3 at 450 °C.