Transport properties of highly dense proton-conducting BaCe0.8–xZrxDy0.2O3–δ materials in low- and high-temperature ranges

Abstract

Proton-conducting materials constitute a class of oxide compounds possessing the required properties for application as electrolytes for low- and intermediate temperature solid oxide cells. In the present investigation, new highly dense BaCe0.8−xZrxDy0.2O3−δ ceramic materials (x = 0.2 … 0.6, Δx = 0.1) are successfully prepared and their electrochemical properties are thoroughly characterised. The separation of total conductivity in bulk and grain boundary components along with ionic and electronic contributions is performed using 2-probe AC and 4-probe DC conductivity measurements. The obtained results reveal that the bulk region determines the transport properties of the materials, starting from ∼190 °C for x = 0.2 and 470 °C for x = 0.6, whereas at lower temperatures the total conductivity is controlled by the grain boundaries. According to high-temperature measurements performed in air and hydrogen atmospheres with a wide water vapour partial pressure variation, the Zr-enriched samples (in comparison with the Ce-enriched ones) exhibit a higher contribution of electronic conductivity in oxidising atmospheres and a lower contribution of proton conductivity in reducing atmospheres. The negative effects of Zr for Ce substitution on the transport properties are compensated by their higher chemical stability, motivating the optimal composition exploration required for the specified electrochemical devices.