Enhancing LSCF-based air electrode durability: Insights into sulfur poisoning and air purification

Abstract

The electrochemical performance of perovskite-type air electrodes in solid oxide cells is strongly affected by a trace amount of SO2 as the air impurity. The present work aims to study air purification efficiency in suppressing the degradation rate for the LSCF-GDC air electrode while operating under different SO2 concentrations. For this purpose, the electrochemical performance of symmetrical cells was evaluated using impedance spectra measured over 320 h and compared with intrinsic electrode degradation in synthetic air. Accordingly, the intrinsic degradation rate was measured at 0.05 mΩ cm2 h−1 while exposing the cell to synthetic air containing 10 and 100 ppb SO2, causing a severe increase to 0.17 and 0.30 mΩ cm2 h−1, respectively. Nevertheless, the calculated degradation rate under purified air containing 100 ppb SO2 was similar to the LSCF-GDC intrinsic degradation rate, representing the high practicality of filter material to adsorb SO2 species. Interpreting the impedance spectra using a distribution of relaxation times (DRT) and a complex nonlinear least squares fit (CNLS) revealed that the intrinsic degradation mechanisms were the limitation of dissociative surface adsorption of oxygen and charge transfer to the adsorbed oxygen. At the same time, inhibition of the O2 adsorption caused by the deposition of SrO, SO32−, and SrSO4 phases and increasing surface diffusion resistance for the adsorbed oxygen atoms were the rate-determining steps in SO2-containing synthetic air. Lastly, the effective suppression of degradation rate by gas purification indicates an extensive use of filter material to extend the lifespan of SOCs.