Charge storage mechanism of copper hexacyanoferrate nanocubes for supercapacitors

The widely accepted theory concerning the electrochemical energy storage mechanism of copper hexacyanoferrate (CuHCF) for supercapacitors is that CuHCF stores charge by the reversible redox processes of Fe3+/Fe2+ couple and Cu cations are electrochemically inactive. In this work, CuHCF nanocubes (CuHCF-NC) were synthesized in the presence of potassium citrate and its electrochemical properties were tentatively studied in 1 mol/L Na2SO4 aqueous electrolyte. Good supercapacitive performance was exhibited. The combined analyses of cyclic voltammogram (CV) and X-ray photoelectron spectroscopy (XPS) disclosed that the CuHCF nanocubes underwent the redox reactions of Fe3+/Fe2+ and Cu2+/Cu+ couples to store charges. The Cu2+/Cu+ redox couple was activated due to the strong coordination interaction between the carboxylate groups of citrate ions and surface Cu cations.