Electrochemical investigation of MnO2 electrode material for supercapacitors

MnO₂ electrode material is synthesized by low temperature solid state reaction between KMnO₄ and MnCl₂. Effects of the KMnO₄:MnCl₂ molar ratio on the structure, morphology and electrochemical properties of the as-prepared sample were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical tests. Results showed that the obtained MnO₂ is α-MnO₂, the average diameter is about 0.5-1.5 μm, which are constituted of nanoparticles of 20 nm. Under 100 mA g⁻¹, the specific capacitances of the prepared sample is 258.7, 219.6, 215.3, 198.5 and 209.5 F g⁻¹ at the KMnO₄/MnCl₂ molar ratio of 3:2, 2:1, 1:1, 1:2 and 2:3, respectively. And the MnO₂ sample with a KMnO₄/MnCl₂ molar ratio of 3:2 exhibits the best discharge capacitance and cycle performance. When the charge/discharge rate increases to 300 mA g⁻¹, the sample still remains initial discharge capacitance of 165.3 F g⁻¹, and the discharge capacitance is 145.9 F g⁻¹ after 200 cycles, the capacitance retention rate is 102.4% during the 20-200th cycles. Therefore, the MnO₂ sample is an excellent material for use in supercapacitors because of its large specific capacitance and good cycle performance.