Structural and electrochemical properties of newly synthesized Fe-substituted MnO2 samples

Mn1-xFexO2 samples, synthesized by a low-temperature process, were characterized for their structural, physical, and electrochemical properties. From X-ray data and EDX analysis in both SEM and HRTEM modes, combined with Fe-57 Mossbauer spectroscopy, we gave direct evidence for the first time for a true Fe substitution for Mn up to x = 0.3. Beyond such value, the samples are multiphase. The presence of iron was found to affect the electrochemical behavior, with namely the appearance of a second plateau at -0.8 V (vs Hg/HgO) with increasing the iron content at the expense of the one occurring at -0.45 V in the pure MnO2 phase. We will present evidence, as deduced from both HREM and Mossbauer measurements on reduced samples, that the origin of the -0.8 V plateau could be nested in the electrochemical activity of the FeMn2O4 phase toward proton in aqueous media.