Morphological changes and electrochemical response of mixed nickel manganese oxides as charge storage electrodes

Nickel manganese (Ni-Mn) oxide films were prepared by potentiostatic electrodeposition over stainless steel and post-thermal annealing at 250 degrees C. Morphological and structural changes were observed depending on the Ni to Mn ratio in the electrolyte. Single-phase Ni1-xMnxO oxide was formed at low Mn content, whereas two phases composed of Ni1-xMnxO and NixMn(3-x)O(4) were formed at high Mn content. Electrochemical studies revealed an increase of the specific capacitance of the mixed Ni-Mn oxide electrodes compared to the single metal oxides, thus pin-pointing a synergistic effect. The Ni-Mn oxide film displayed a specific capacitance of about 300 F g(-1) in a potential window of 0.5 V at an applied current density of 1 A g(-1). The rate capability of the oxides was 58% when the applied current was increased from 1 A g(-1) to 10 A g(-1). The Ni-Mn oxide film exhibits excellent cycling stability with 100% capacitance retention after 1500 cycles.