Water uptake kinetics and electrical transport in BaCe0.6Zr0.2Y0.1M0.1O3−δ (M = Tb, Pr, Fe) protonic conductors

Abstract

BaCe0.6Zr0.2Y0.1M0.1O3−δ (M = Fe, Pr, Tb) is a mixed conducting oxide in which three mobile charge carriers - oxygen ion, electron/hole, and protonic defects - are present. These types of materials have gained much interest as electrode materials for protonic ceramic fuel cells (PCFCs) and protonic ceramic electrolysis cells (PCECs). In this study, the water uptake and oxygen transport properties of different BaCe0.6Zr0.2Y0.1M0.1O3−δ samples were investigated at different pH2O using Thermogravimetry (TG) and Electrical Conductivity Relaxation (ECR) methods at various temperatures. TG results showed that in all samples the mass increases during the switch from dry to wet atmospheres, which indicates proton incorporation into the materials. The kinetics of the water uptake process differed depending on the type of substituent used. The studies of pO2 dependence of total conductivity allowed for the determination of partial conductivities in BaCe0.6Zr0.2Y0.1Tb0.1O3−δ (BCZYTb), which shows a predominant p-type conduction mechanism above 600 °C. The electrical conductivity relaxation (ECR) studies performed for a chosen BCZYTb sample have shown that the hydration/dehydration processes were asymmetric two-fold, whereas the oxidation/reduction processes had typical single-fold kinetics. Furthermore, a significant influence of pH2O on the oxidation and reduction kinetics was observed.