Recent advances in synthesis and analysis of Fe(VI) cathodes: solution phase and solid-state Fe(VI) syntheses,reversible thin-film Fe(VI) synthesis,coating-stabilized Fe(VI) synthesis,and Fe(VI) analytical methodologies

Fe(VI) batteries based on unusual ferrate cathodic charge storage have been studied for quite a few years. So far, a class of Fe(VI) compounds have been successfully synthesized and studied as the cathodic materials in both alkaline and nonaqueous battery systems. This paper provides a summary of the syntheses of a range of Fe(VI) cathodes including the alkali Fe(VI) salts Li₂FeO₄, K _x Na_(2?x)FeO₄, K₂FeO₄, Rb₂FeO₄, Cs₂FeO₄, as well as alkali earth Fe(VI) salts CaFeO₄, SrFeO₄, BaFeO₄, and a transition metal Fe(VI) salt Ag₂FeO₄. Two synthesis routes summarized in this paper are the solution phase synthesis and the solid-state synthesis. Preparation of coating-stabilized (coated with KMnO₄, SiO₂, TiO₂, or ZrO₂) Fe(VI) cathodes and preparation of thin-film reversible Fe(VI/III) cathodes are also presented. Fe(VI) analytical methodologies summarized in this paper include Fourier transform infrared spectrometry, titrimetric (chromite), ultraviolet-visible spectroscopy, X-ray diffraction, inductively coupled plasma spectroscopy, Mössbauer spectrometry, potentiometric, galvanostatic, and cyclic voltammetry. Cathodic charge transfer of Fe(VI) is also briefly presented.