Rapid microwave-assisted solid-state obtention of Mn 3 O 4 and its electrochemical characterization for application as supercapacitor electrodes

A rapid and facile microwave-assisted method coupled with a mild mechanical treatment is proposed to obtain Mn 3 O 4 with good properties to be used as a supercapacitor material. Mn 3 O 4 was produced by thermal decomposition of ε-MnO 2 using microwave irradiation in a practical setup and a domestic microwave oven. XRD results, supported by other physical characterizations such as TG/DTA and FTIR and Raman spectroscopy analyses, attested that Mn 3 O 4 was obtained as a single phase after only 5 min of microwave heating. After submitting an oxide sample to a mild mechanical treatment in an adapted ball-mill setup for 30 min, SEM micrographs and BET analyses revealed a particle size in the range of 200–600 nm and a fivefold increase of the specific surface area. The pseudocapacitive behavior of electrodes prepared with the thus obtained Mn 3 O 4 was analyzed by cyclic voltammetry in a 0.1 mol L –1 Na 2 SO 4 aqueous solution. Galvanostatic charge and discharge tests of these electrodes were performed in the 1.0 to 5.0 A g –1 range in the same electrolyte; at 1.0 A g –1 , they presented an initial specific capacitance of about 160 F g –1 and good electrochemical stability up to 5000 cycles.