Exploration of Co-Fe alloy precipitation and electrochemical behavior hysteresis using Lanthanum and Cobalt co-substituted SrFeO3-δ SOFC anode

The in-situ precipitated nano metal particles from perovskites have shown broad interest and wide applications in solid oxide fuel cells (SOFCs) as well as in batteries and catalysts. However, the correlations between the precipitation and SOFC anode performance evolution are still unclear. Herein, equal proportion of La/Sr (A-site) and Co/Fe (B-site) co-substituted La0.5Sr0.5Co0.45Fe0.45Nb0.1O3-δ (LSCFN) perovskite oxide is designed and prepared to investigate the Co-Fe alloy precipitation process and the corresponding electrochemical behavior evolution. After annealing in 3% H2O - 97% H2 at temperature of 750-850 °C the A2B2O5 brownmillerite structure is detected as emerging phase from initial ABO3 perovskite, accompanied with the exsolution of Co1-xFex alloy nano particles. Both the brownmillerite structure in oxide substrate and the Iron content in exsolved Co1-xFex particles show an increase with increasing of reducing temperature and time length. As a result the anode performance hysteresis is observed, showing distinct reduction temperature-dependent and reduction time-dependent electrochemical behaviors. The DC conductivity of the porous LSCFN anode layer shows continuous decrease at 750 °C while both the ohmic and polarization resistances show an increase, suggesting a tight correlation to the anode structure and composition evolution. The proposed strategy to pre-reduce the anode at elevated temperature (800 °C) and then decrease to lower operation temperature (750 °C) is demonstrated to effectively mitigate the Co-Fe nano particles coarsening and could presumably slow down the anode polarization resistance degradation.