Self-assembled amorphous manganese oxide/hydroxide spheres via multi-phase electrochemical interactions in reverse micelle electrolytes and their capacitive behavior

Abstract

Amorphous matrices of three-dimensionally interconnected MnO_x/MnOOH nano-spheres were electrochemically assembled onto a carbon substrate by a pulse galvanostatic method (PGM) in a nonionic reverse micelle electrolyte. The synthesized material showed a unique morphology which was attributed to a synergistic effect between the amphiphilic molecule based interface membrane as a soft template and the PGM approach. The transfer of the reactant was remarkably special because of the elusive thermodynamic and kinetic parameters of the interactions at the interface between the two different phases such as the polar phase–interface membrane, interface membrane–nonpolar phase and polar phase–electrode interactions. Further work involved investigations into the potential application of the assembled MnO_x/MnOOH films as high performance supercapacitor electrode materials. The capacitive performance of the assembled MnO_x/MnOOH was tested in a solution of 0.5 M Na₂SO₄. The highest specific discharge capacitance of 1659 F g⁻¹ was achieved at a current density of 2 A g⁻¹, and remained as high as 782 F g⁻¹ even at a very large current density of 10 A g⁻¹. The outstanding capacitance properties were ascribed to the ternary oxide composites forming highly porous nanostructures which guaranteed a large specific surface, full utilization of Mn oxides and a small amount of degradation of amorphous MnO₂. The results indicate the feasibility of electrochemically synthesizing Mn oxides in unconventional micelle electrolytes, and their successful application in supercapacitors.