Conductivity studies of dense yttrium-doped BaZrO 3 sintered at 1325 °C

Abstract

High-temperature proton conductors have wide applications in the areas of fuel cells, electrolysis and hydrogen separation. Barium zirconate-based materials are of interest due to their good stability and high protonic conductivity. The reported conductivity of these ceramic materials is generally less than 10 −2 S/cm, even at high temperatures. This is not high enough for an electrolyte-supported device to achieve an ASR of less than 0.2 Ω cm 2 therefore thin film electrolytes are required for successful application. As BaZrO 3-based materials have to be sintered at temperatures as high as 1700 °C, this makes it difficult to find a suitable supporting electrode which will not undergo significant chemical reaction with the BaZrO 3-based electrolyte during fabrication of the required electrode supported electrolyte. In this paper, proton-conducting BaZr 0.8Y 0.2O 2.9 was successfully sintered at 1325 °C with a relative density of 96% via addition of 1 wt% ZnO. Fabrication of electrochemical cells using proton-conducting BaZr 0.8Y 0.2O 2.9 as the electrolyte thus becomes possible. The formula of the 1 wt% ZnO added sample is Ba 0.97Zr 0.77Y 0.19Zn 0.04O 3− δ which exhibits a tetragonal structure with space group P4/ mbm (127); a=5.9787(1) Å, c=4.2345(1) Å, V=151.36(1) Å 3. It was found that a solid solution was formed for a limited range of Zn doping. Conductivity has been studied as a function of atmosphere (air, dry and wet 5% H 2/Ar) with the changes in bulk and grain boundary on changing atmosphere being monitored as a function of time. The total conductivity of Ba 0.97Zr 0.77Y 0.19Zn 0.04O 3– δ is 1.0×10 −3 S/cm above 600 °C therefore it may be used as a proton-conducting thin film electrolyte for efficient electrochemical devices at such temperatures. The grain boundary resistance is insignificant at high temperature for the well-sintered sample.