Synthesis, Characterization, and Ionic Conductivity Studies of Simultaneously Substituted K- and Ga-Doped BaZrO₃

Ceramic fuel cells possess tremendous advantages over PMFCs due to their fuel flexibility and requirement of low-purity hydrogen. Despite high conversion efficiency, the high cost of ultra high-purity hydrogen required for the operation limits the application of PMFCs. Although ceramic fuel cells operate at elevated temperature, high performance coupled with multifuel flexibility makes ceramic fuel cells a superior option as a static power source to generate electricity compared to thermal coal-fired power plants. BaZr_1- Y O_3- based protonic conductors get a high degree of interest due to their superior structural stability, but their poor conductivity at higher temperature limits the performance of ceramic fuel cells. To overcome the low ionic conductivity issues of BaZrO₃ based materials at elevated temperature, the simultaneous doping of smaller Ga on the Zr site and K on the Ba site was employed here to create higher concentration of oxide-ion vacancies for the realization of superior conductivities. The simultaneous substitution of K and Ga created the oxygen vacancy-type point defects resulting in higher ionic conductivity ∼10^-2 S/cm above 650 °C. The conductivity represented here for the Ba_0.8K_0.2Zr_0.8Ga_0.2O_2.8 sample is superior or equivalent to the conductivity obtained for yttria-stabilized zirconia, a well-known ceramic oxide-ion electrolyte.