In Situ Electrochemical Recovery: Sediment Transformation under Chromium Poisoning in Reversible Solid Oxide Cells with La_0.6Sr_0.4Co_0.2Fe_0.8O_3−σ-Based Oxygen Electrodes

Reversible solid oxide cells (RSOCs) are an all-solid-state electrochemical device, which can convert H₂ into electricity in the fuel cell (SOFC) mode and electrolyze H₂O into fuel gas in the electrolytic cell (SOEC) mode, exhibiting good application prospect in the development of carbon neutrality. However, the degradation of the air electrode caused by Cr-containing steel interconnects is a major obstacle that limits the broader application of RSOCs. Herein, the Cr poisoning effect on La_0.6Sr_0.4Co_0.2Fe_0.8O_3-σ (LSCF)-based oxygen electrodes under the electrolysis mode was systematically investigated. The phase transition of the sediment during the chromium poisoning process was captured and monitored. When tested under the presence of Fe-Cr interconnects at 800 °C for 40 h, SrCrO₄ on the surface of LSCF was clearly identified through XRD and Raman analysis as the main deposition, and with the prolonged operating time, LaCrO₃ slowly emerged. Due to the much higher electrical conductivity of LaCrO₃ compared to SrCrO₄, the negative effect induced by Cr poisoning was offset along with test progressing due to the deposition transition phenomenon. Inspired by the interesting discoveries, transition from SrCrO₄ to LaCrO₃ can be artificially facilitated by switching the operating mode to the SOEC mode, which can partially recover the dramatic degradation caused by the Cr poisoning effect under the SOFC mode. The feasibility of the in situ electrochemical recovery method was also verified by the experimental results. The peak power density of the cells decreased from 0.829 to 0.505 W/cm² when operating under the SOFC mode with an Fe-Cr metal connector, and after in situ electrochemical recovery in the SOEC mode, the peak power density recovered to 0.630 W/cm². This study provides a new strategy for achieving high performance and stability of RSOCs.