The effects of water addition to an oxidant on the cathodic overpotential of La-doped BaCoO 3 and Sm 0.5Sr 0.5CoO 3 cathodes were investigated in this study. It was found that the overpotential of La-doped BaCoO 3 decreased by the addition of H 2O to oxygen. In particular, the decrease in the overpotential by addition of H 2O was greater with the decreasing operating temperature of the cell. Therefore, it becomes clear that the maximum power density increased by the addition of H 2O to the oxidant. Positive effects of water on the cathodic overpotential are also observed on Sm 0.5Sr 0.5CoO 3. Therefore, the positive effects of water on cathodic reaction are not limited to La-doped BaCoO 3, but are also expected on general oxide cathodes. The positive effects of a humidified oxidant were sustained stably over 50 h, and X-ray diffraction measurement suggests that there is no change in the crystal structure of an La-doped BaCoO 3 cathode or an LaGaO 3-based oxide electrolyte. The improved cathodic activity by addition of H 2O was studied further by using 18O surface exchange measurement. Although the diffusion coefficient was independent of the coexisting water, the surface exchange coefficient was greatly increased by the addition of water. Therefore, water existing in a cathode seems to assist the dissociation of oxygen into an oxide ion. Therefore, it is considered that a humidified oxidant is one of the effective methods to suppress the cathodic overpotential at decreased temperature.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Renewable Energy, Sustainability and the Environment
- Surfaces, Coatings and Films
- Materials Chemistry