Effects of iron addition on material characteristics and pseudo-capacitive Behavior of mn-oxide electrodes

Iron addition was attempted in this study to improve the pseudo-capacitive property of Mn oxides. The oxides were prepared on graphite substrates by anodic deposition. The deposition solutions were 0.25 M manganese acetate [Mn(CH3COO)(2)] aqueous solutions with various amount of FeCl3 (up to 0.15 M ). Crystal structure and surface morphology of the deposited oxides were examined by X-ray diffraction and scanning electron microscopy, while their chemical state was analyzed by X-ray photoelectron spectroscopy and X-ray absorption near edge structure. Moreover, specific capacitances of the oxide electrodes were determined by cyclic voltammetry in 2 M KCl electrolyte. Experimental results indicated that the incorporated iron presented as divalent and trivalent forms in the binary oxides. Although iron addition did not change the nanocrystalline structure of the deposited Mn oxide, it caused the chemical state and surface morphology variations of the oxide electrodes. Consequently, their pseudo-capacitive performances were modified. The optimum specific capacitance of 212 F g(-1) was found for the oxide deposited in the solution containing 0.05 M FeCl3. The value was 21% higher than that of the plain Mn oxide. Capacitance-retained ratio of the oxide after 1000 charge-discharge cycles was also improved from 70 to 85% because of iron addition. (C) 2007 The Electrochemical Society.