Electrochemical supercapacitor performance of MnO2 nanorods via precursor ratio and hydrothermal temperature variation

In this work, we detail a hydrothermal synthesis of MnO₂ nanorods at a temperature of 120 °C, employing different ratios of precursors. The precursors used include manganese chloride tetrahydrate and potassium permanganate with molar ratios of 1:3, 1:1, and 3:1. Thermal analysis indicated that the 1:3 precursor ratio exhibited the lowest activation energy of 40 kJ/mol, making it suitable for MnO₂ synthesis. Analysis through X-ray diffraction confirmed the presence of β-MnO₂ in all ratios studied, with the smallest crystals, measuring 7 nm, identified specifically in the 1:3 ratio. X-ray photoelectron spectroscopy analysis demonstrated that manganese in MnO₂ exists in an oxidation state of + 4. Moreover, we synthesized MnO₂ employing a 1:3 precursor ratio at hydrothermal temperatures of 150, 180, and 210 °C, and assessed the influence of the synthesis temperature on the electrochemical features. The cyclic voltammetry (CV) analysis demonstrated that the MnO₂ synthesized at 120 °C reached a specific capacitance of 452 F/g at a scan rate of 2 mV/s. In addition, the galvanostatic charge–discharge (GCD) analysis provided evidence of an energy density of 35 Wh/kg and a power density of 495 W/kg at a current density of 5 A/g, suggesting its substantial potential as a superior electrode material for the fabrication of supercapacitors.