Investigation on Capacitance Mechanisms of Fe[sub 3]O[sub 4] Electrochemical Capacitors

The capacitance mechanisms of magnetite electrochemical capacitor in , , and KOH aqueous solutions have been investigated by electrochemical quartz-crystal microbalance analysis, along with cyclic voltammetry and X-ray photoelectron spectroscopy. The oxide thin-film electrode was prepared by an electroplating method, and exhibits a capacitance of , 25, and in , , and , respectively. Strong specific adsorption of the anion species was evidenced in all solutions. Experimental results indicate that, in , the capacitive current of magnetite electrode originates from the combination of electric double-layer capacitance (EDLC) and the pseudocapacitance that involves successive reduction of the specifically adsorbed sulfite anions, from through, e.g., , and vice versa. In , the current is due entirely to EDLC. Furthermore, due to the specific adsorption behavior, magnetite exhibits high EDLC, , in both and solutions. The lowest capacitance of magnetite was observed in KOH, which is attributed to the formation of an insulating layer on the magnetite surface.