Oxygen exchange and bulk diffusivity of BaCo0.4Fe0.4Zr0.1Y0.1O3-δ: Quantitative assessment of active cathode material for protonic ceramic fuel cells

Abstract

The oxygen surface exchange and bulk diffusivity of BaCo0.4Fe0.4Zr0.1Y0.1O3-δ were determined by electrical conductivity relaxation (ECR) in order to quantitively assess cathode performance for protonic ceramic fuel cells (PCFCs). The measurements were performed at 600 °C, following pO2-step changes between 80 ppm to pure oxygen. The apparent value of surface exchange coefficient (k) and diffusion coefficient D, indicates BaCo0.4Fe0.4Zr0.1Y0.1O3-δ is a good oxygen conductor. k was found to vary with pO2 and surface area while the chemical diffusion coefficient D remained invariant with pO2 and surface coating. The fitted kinetic parameters obtained from ECR with reduction process (high to low pO2) were compared with that of the oxidation process (low to high pO2). In the presence of H2O, oxygen exchange kinetics was suppressed because of the competitive adsorption relationship between oxygen and H2O. Single cell measurements employing single phase BaCo0.4Fe0.4Zr0.1Y0.1O3-δ cathode and an anode prepared by phase inversion tape casting in a configuration of 40 wt% BCZYSm13 + 60 wt% NiO | BCZYSm13 | BCFZY0.1 exhibited a power density of ~200 mW/cm2 at 600 °C.