Electrochemical Growth of Iron Oxide Thin Films with Nanorods and Nanosheets for Capacitors

Porous iron oxide films with nanorods and nanosheets were anodically deposited onto the nickel substrates by a plating bath of Fe(NH4)(2)(SO4)(2)center dot 6H(2)O, sodium acetate, and sodium sulfate at room temperature. Nucleation and growth mechanism of the iron oxide film was found to be an instantaneous nucleation and growth of two-dimensional cylindrical iron oxide. X-ray diffraction patterns show that the as-deposited iron oxide is orthorhombic alpha-FeOOH, which converts into rhombohedral Fe2O3 after annealing at temperature above 300 degrees C. Annealing temperatures influences both the chemical composition and grain size of the film, and consequently determines the capacitive behavior of the film investigated by cyclic voltammetry in 1 M Li2SO4 aqueous solution. An optimal annealing temperature of 300 degrees C is obtained in terms of the film's specific capacitance. Morphology of the film deposited at a current density higher than 0.125 mA cm(-2) shows nanosheets, while the film deposited at a current density lower than 0.125 mA cm(-2) shows nanorods. Specific capacitance of a film with nanosheets is higher than that of a film with nanorods.