Proton conductivity of potassium doped barium zirconates

Potassium doped barium zirconates have been synthesized by solid state reactions. It was found that the solubility limit of potassium on A-sites is between 5% and 10%. Introducing extra potassium leads to the formation of second phase or YSZ impurities. The water uptake of barium zirconates was increased even with 5% doping of potassium at the A-site. The sintering conditions and conductivity can be improved significantly by adding 1 wt% ZnO during material synthesis. The maximum solubility for yttrium at B-sites is around 15 at% after introducing 1 wt% zinc. The conductivity of Ba0.95K0.05Zr0.85 Y0.11Zn0.04O3-delta at 600 degrees C is 2.2 x 10(-3) S/cm in wet 5% H-2. The activation energies for bulk and grain boundary are 0.29(2), 0.79(2)eV in wet 5% H-2 and 0.31(1), 0.74(3)eV in dry 5% H-2. A power density of 7.7 mW/cm(2) at 718 degrees C was observed when a 1 mm thick Ba0.95K0.05Zr0.85Y0.11Zn0.04O3-delta pellet was used as electrolyte and platinum electrodes.