Fabrication of hierarchical Mn-Co-P nanospheres as positive electrode material for ultra-stable asymmetric supercapacitor

Herein, the novel Mn-Co-P nano-spheres and acacia wood-derived activated carbon (ACWC) as positive and negative electrodes, respectively, were used to develop an ultra-stable asymmetric supercapacitor. The Mn-Co-P nano sphere was synthesized by a hydrothermal method to give distinct characterization morphology and electrochemical performance. Detail with regard to its physical and chemical properties of the active material coated on the nickel substrate are studied by X-ray diffraction, field-emission scanning electron microscopy, field-emission transmission electron microscopy, high-resolution X-ray photoelectron spectroscopy analyses, thermogravimetric analysis (TGA), and N2 adsorption-desorption isotherms. The electrochemical properties of the prepared materials were tested in electrolyte by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS). Results show that the Mn-Co-P electrode has a high specific capacity of 119.34 mAh g−1 at 0.5 A g−1 current density. The ACWC active carbon was prepared from acacia wood to give a high surface area of 1210 m2g−1, with a high specific capacitance of 225 F g−1 at 0.5 A g−1. Asymmetric supercapacitor devices based on the electrodes exhibit a high energy density of 36.2 Wh kg−1 at 850.00 W kg−1. In addition, outstanding cycling number stability of 93.3 % capacitance retention over 10,000 cycles was achieved using sodium sulphate (0.5 M) as an electrolyte.