Microstructural evolution of cobalt-doped barium cerate–zirconate at elevated temperatures under moist reducing conditions

Barium cerates doped with rare earth and transition metal ions are attractive candidate materials for clean-energy applications owing to their catalytic activity combined with mixed ionic–electronic conductivity for electrochemical hydrogen separation. However, the stability of these materials at elevated temperatures in the presence of moisture and CO2 is not completely understood. In the present work, Co-doped barium cerate–zirconate pellets (BaCe0.25Zr0.47Co0.13O3−δ) were exposed to a moist reducing environment at 600 °C and 927 °C for 24 h. The as-sintered and reduced pellets were sectioned using FIB and characterized using conventional TEM, STEM and XEDS. The evolution of the microstructure of the material at each step has been reported. The as-sintered material showed a tendency toward Co ex-solution resulting in the formation of a BaO–CoO phase at the grain boundaries. At elevated temperatures, reduction appeared to play a role in the transformation of the material chemistry and microstructure.