Microwave-Assisted Synthesis and Characterization of γ-MnO2 for High-Performance Supercapacitors

Two hydrothermal techniques under microwave irradiation were used to synthesize gamma-MnO2 from 90 degrees C to 150 degrees C in 10-30 min. The first technique is based on reducing KMnO4 with MnSO4, and the second one involves liquid-phase oxidation between MnSO4 and (NH4)(2)S2O8. The structures and morphologies of the samples were analyzed using X-ray diffraction, scanning electron microscopy, and N-2 physisorption measurements. The electrochemical properties were evaluated through cyclic voltammetry and electrochemical impedance spectroscopy. The gamma-MnO2 materials obtained by the first technique mainly exhibited nanorods with diameters of 40-60 nm, and the samples obtained by the second technique showed flower-like microspheres with diameters of 1-2 mu m; each flower was composed of nanosheets with a thickness of 10-20 nm. The processing time directly depends on the size of the nanorods. The sample synthesized by the first technique at 150 degrees C and 10 min has the highest specific surface area of up to 59.08 m(2) g(-1) and mean pore diameter of 34.11 nm. Furthermore, this sample exhibits a near-rectangular cyclic voltammetry curves and high specific capacitance of 331.3 F g(-1) in 0.1 M Na2SO4 solution at 5 mV s(-1) scan rate.

Automated summary

Two hydrothermal techniques under microwave irradiation were used to synthesize gamma-MnO2 with different morphologies. The nanorods obtained by the first technique exhibit a high specific surface area, while the flower-like microspheres obtained by the second technique show promising electrochemical performance.