Understanding the oxygen reduction reaction of one-dimensional Ca3Co2O6 cathodes for SOFC

Abstract

Understanding the processes of different cathode materials is part of the journey toward the development of intermediate-temperature solid oxide fuel cells. In this work, the one-dimensional Ca3Co2O6 (C326) electrode and its composite with Ce0.9Gd0.1O2-δ (CGO) are systematically investigated as a function of sintering temperature using a symmetrical cell test. For both batches of samples, the optimum sintering temperature is 1000 °C. Interpretation of the impedance spectra reveals that this optimization is associated with improvements in the processes of surface diffusion and interfacial charge transfer due to the higher effective reaction area for ionic transfer at the electrode/electrolyte interface and better connectivity between the electrode grains. The temperature dependence of the individual processes indicates that the addition of CGO significantly improves the steps of dissociative oxygen adsorption and diffusion, which should occur first on its surface, with the charge transfer of oxygen species at the CGO/C326 boundary being the rate-limiting step.