Synthesis and characterization of mesoporous Mn–Ni oxides for supercapacitors

Mesoporous Mn–Ni oxides with the chemical compositions of Mn1-xNixOδ (x = 0, 0.2, and 0.4) were prepared by a solid-state reaction route, using manganese sulfate, nickel chloride, and potassium hydroxide as starting materials. The obtained Mn–Ni oxides, mainly consisting of the phases of α- and γ-MnO2, presented irregular mesoporous agglomerates built from ultra-fine particles. Specific surface area of Mn1–xNixOδ was 42.8, 59.6, and 84.5 m2 g−1 for x = 0, 0.2, and 0.4, respectively. Electrochemical properties were investigated by cyclic voltammetry and galvanostatic charge/discharge in 6 mol L−1 KOH electrolyte. Specific capacitances of Mn1-xNixOδ were 343, 528, and 411 F g−1 at a scan rate of 2 mV s−1 for x = 0, 0.2, and 0.4, respectively, and decreased to 157, 183, and 130 F g−1 with increasing scan rate to 100 mV s−1, respectively. After 500 cycles at a current density of 1.24 A g−1, the symmetrical Mn1–xNixOδ capacitors delivered specific capacitances of 160, 250, and 132 F g−1 for x = 0, 0.2, and 0.4, respectively, retaining about 82%, 89%, and 75% of their respective initial capacitances. The Mn0.8Ni0.2Oδ material showed better supercapacitive performance, which was promising for supercapacitor applications.