Nanostructures and Capacitive Characteristics of Hydrous Manganese Oxide Prepared by Electrochemical Deposition

Abstract

Amorphous manganese oxide deposits with nanostructures (denoted as a­MnOx⋅nH2O)a­MnOx⋅nH2O) were electrochemically deposited onto graphite substrates from 0.16 M MnSO4⋅5H2OMnSO4⋅5H2O with pH 5.6 by means of the potentiostatic, galvanostatic, and potentiodynamic techniques. The maximum specific capacitance of a­MnOx⋅nH2Oa­MnOx⋅nH2O deposits plated in different modes, measured from cyclic voltammetry at 25 mV s⁻¹, is about 230 F g⁻¹ in a potential window of 1.0 V. The high electrochemical reversibility, high-power characteristics, good stability, and improved frequency responses in 0.1 M Na2SO4Na2SO4 for these nanostructured a­MnOx⋅nH2Oa­MnOx⋅nH2O deposits prepared by electrochemical methods demonstrate their promising potential in the application to electrochemical supercapacitors. The nanostructure of a­MnOx⋅nH2O,a­MnOx⋅nH2O, clearly observed by means of a scanning electron microscope, was found to depend strongly on the deposition mode. The similar capacitive performance of all deposits prepared in different modes was attributable to their nonstoichiometric nature with a very similar oxidation state, demonstrated by XPS spectra. © 2003 The Electrochemical Society. All rights reserved.