Oxygen exchange and bulk diffusivity of BaCo_0.4Fe_0.4Zr_0.1Y_0.1O_3-δ Quantitative assessment of active cathode material for protonic ceramic fuel cells

The oxygen surface exchange and bulk diffusivity of BaCo0.4Fe0.4Zr0.1Y0.1O3-delta 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 degrees 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-delta is a good oxygen conductor. k was found to vary with pO(2) and surface area while the chemical diffusion coefficient D remained invariant with pO(2) and surface coating. The fitted kinetic parameters obtained from ECR with reduction process (high to low pO(2)) were compared with that of the oxidation process (low to high pO(2)). 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-delta cathode and an anode prepared by phase inversion tape casting in a configuration of 40 wt% BCZYSm13 + 60 wt% NiO | BCZYSm13 | BCFZY(0.1) exhibited a power density of similar to 200 mW/cm(2) at 600 degrees C.