Effect of pore formers characteristics and melt infiltration parameters on microstructure and electrical properties of BaCe0.7Zr0.1Y0.2O3−δ-carbonate composite electrolyte

In the present work, Ba Zr0.1Ce0.7Y0.2O3−δ (BZCY7)-(Li/Na)2CO3 composite electrolytes fabricated by infiltration of molten carbonate phase into porous based BZCY7 electrolytes, prepared by using different types of pore formers including graphite, active carbon and starch. The effect of pore formers sizes, morphologies and their amounts, was investigated on the volume fraction of porosities, which can be created during sintering of BZCY7 electrolytes and on the morphologies of the formed porosities. The effect of created pores morphologies, sizes, their volume fractions and also infiltration's temperature and time on the degree of infiltration and electrical conductivity of the fabricated composite electrolytes were also studied. The results proved that by using 20 wt% of each type of the used pore formers, same amount of porosities in the range of 40-45 vol.% would be created during sintering of BZCY7 compound at 1400 °C for 5 h. By using pore formers more than 20 wt%, the amount of created porosities did not change or just increased a little and soon after it nearly became saturated. Optimum temperature and time for infiltration of melt carbonate phase was determined in the range of 530-570 °C for 2 h. Based on the four probe electrical conductivity measurements as a function of temperature, it was shown that for the composite electrolytes the Arrhenius conductivity curves is divided, at the melting point of carbonate phase, to two regions with two different slopes. The results also proved that at temperatures higher and lower than the melting point of carbonate phase, electrical conductivity of the composite electrolytes were higher and lower than what determined for dense BZCY7 based electrolyte, respectively. It was also shown that, the increase in electrical conductivity by increasing volume fraction of the carbonate phase from 10 to 20 vol percent was significant. Using carbonate phase more than 20 vol percent, although electrical conductivity increased but the rate of increasing in electrical conductivity decreased. The results also proved that electrical conductivity of the composite fabricated by using active carbon, as pore former, was highest.