Estimating Degradations of La0.57Sr0.38Co0.2Fe0.8O3-δ Oxygen Diffusion and Surface Exchange Coefficients by Effective Reaction Thickness

Abstract

The degradation of La0.57Sr0.38Co0.2Fe0.8O3-δ (LSCF) cathode is investigated by focusing on the change in effective reaction thickness. The durability tests showed severe degradation for the thinner electrodes, which suggests that the degradation in surface exchange coefficient (k) is the dominant degradation factor rather than the bulk diffusion coefficient (D). For the quantitative evaluation of k and D, the electrochemical impedance spectroscopy analyses demonstrated that the degradation rate of k was larger than that of D, and both degraded larger for thinner electrodes. The changes in effective reaction thickness are estimated by numerical simulation with the obtained degradation rates of D and k. The effective reaction thickness elongated in thinner electrodes due to the excessive decrease in k. This implies that the degradation is accelerated in thinner electrodes where effective reaction thickness exceeds physical electrode thickness and larger local overpotential is imposed.