Vertically aligned iron (III) oxyhydroxide/oxide nanosheets grown on iron substrates for electrochemical charge storage

• γ-FeOOH and γ-Fe2O3 nanosheets were grown on iron substrates as electrodes.
• Electrochemical capacitance studies were performed in KOH, Na2SO4 and Na2SO3.
• The electrode exhibited high areal capacitance (0.3–0.4 F/cm2) in Na2SO3.
• γ-FeOOH was found to be not stable in Na2SO4, undergoing dissolution with repeated cycles.

Large area self-standing nanosheets of mixed iron (III) oxyhydroxide/oxide (lepidocrocite, γ-FeOOH and maghemite, γ-Fe2O3) were grown directly from an iron foil based on a simple chemical oxidation route. The γ-FeOOH and γ-Fe2O3 nanosheets on a conductive substrate can be used directly as an electrode, eliminating additional electrode fabrication procedures. The electrode exhibited high areal capacitance (0.3–0.4 F/cm2) and good cycling stability in Na2SO3 electrolyte. Additionally, cycling studies in Na2SO4 disclosed that iron (III) oxyhydroxide/oxide are not stable in Na2SO4, undergoing reductive dissolution with repeated cycling in negative potential window.