Abstract
Two hydrothermal techniques under microwave irradiation were used to synthesize γ-MnO2 from 90°C to 150°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)2S2O8. The structures and morphologies of the samples were analyzed using X-ray diffraction, scanning electron microscopy, and N2 physisorption measurements. The electrochemical properties were evaluated through cyclic voltammetry and electrochemical impedance spectroscopy. The γ-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 µm; 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°C and 10 min has the highest specific surface area of up to 59.08 m2 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.Graphic abstract
Highlights
In recent years, MnO2-based materials have attracted keen interest as electrochemical capacitors, as their specific capacitances are several times greater than that of Extended author information available on the last page of the article conventional capacitors
This study focused on the influence of the morphology and size of γ-MnO2 obtained by two microwave-assisted hydrothermal techniques on the specific capacitance
A series of M nO2 nanostructures were synthesized by microwave-assisted hydrothermal techniques, following two procedures: qualitative chemical analysis of samples obtained were determined with the scanning electron microscopy (SEM) JEOL JSM 6701F and with
Summary
In recent years, MnO2-based materials have attracted keen interest as electrochemical capacitors, as their specific capacitances are several times greater than that of. This study focused on the influence of the morphology and size of γ-MnO2 obtained by two microwave-assisted hydrothermal techniques on the specific capacitance. The first hydrothermal method produces γ-MnO2 through the reduction of permanganate solution, with Mn (II), according to the following reaction:[20]. The dissolved reactants for Methods A and B were transferred to a microwave-assisted hydrothermal reactor model Flexi-Wave from Milestone. The specific surface area was estimated by N 2 adsorption–desorption tests and the electrochemical properties of the γ-MnO2, synthesized by the two microwave-assisted hydrothermal methods, were investigated by the cyclic voltammetry and electrochemical impedance spectroscopy techniques. A series of M nO2 nanostructures were synthesized by microwave-assisted hydrothermal techniques, following two procedures: qualitative chemical analysis of samples obtained were determined with the SEM JEOL JSM 6701F and with
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