Is Fluorine Incorporation in the La0.6Sr0.4Co0.2Fe0.8O3-δ Improving Its Electrochemical Behavior for Solid Oxide Cells Applications?

F-doped La0.6Sr0.4Co0.2Fe0.8O3-x-delta Fx (LSCFFx, x = 0.05, 0.10, and 0.20) materials are evaluated as oxygen electrodes for solid oxide fuel and electrolyser cell application. Materials have been prepared via low-temperature topotactic route by fluorination of the parent oxide with polyvinylidene fluorine (PVDF). A decrease in the polarisation resistance (R-p) is observed for the "LSCFFx" symmetric cells. However, the improved electrochemical behavior for the symmetric cells cannot be explained by the presence of fluorine, as post mortem chemical analysis shows that fluorine is absent from the materials after the calcination treatment, contradicting previous results from the literature and calling for deeper understanding. The presence of fluorine is proved to result in a sluggish surface exchange rate compared with the LSCF oxide via pulsed isotopic exchange technique. Despite the absence of fluorine in the fabricated symmetric cell, annealing with PVDF at low temperatures prior to the electrode fabrication is proven to be a beneficial step to improve the electrochemical performance of LSCF material with applications for solid oxide cells. Studies with room temperature X-ray diffraction, X-ray photoelectron spectroscopy, and M & ouml;ssbauer spectroscopy suggest that increased oxygen vacancy concentration, structural disorder and changes in the cobalt/iron valence state distribution are potential explanations for the reduced R-p.