Preparation and electrochemical properties of ultra-fine Mn–Ni–Cu oxides for supercapacitors

Ultra-fine Mn–Ni–Cu oxides (MNCO) are obtained by calcining a solid-state coordination derived oxalate Mn0.68Ni0.22Cu0.10C2O4·nH2O at 250–450 °C. The obtained MNCO present micron-sized agglomerates composed of primary particles with a size of ∼200 nm. The 250 °C- and 350 °C-obtained MNCO are poorly crystallized with a structure of α-MnO2, while the 450 °C-obtained MNCO contain multiphase oxides with structures of α-MnO2, γ-MnO2 and Mn2O3. Electrochemical properties are investigated by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy in 6 mol L−1 KOH electrolyte. The MNCO electrodes exhibit good supercapacitive performance, superior to that of powder-based MnO2 electrodes. At a scan rate of 2 mV s−1, the 250 °C-, 350 °C-, and 450 °C-obtained MNCO electrodes deliver capacitance values of 490, 293 and 205 F g−1, respectively. At a current density of 1000 mA g−1, the 250 °C-, 350 °C-, and 450 °C-obtained MNCO symmetrical capacitors exhibit capacitance values of 368, 286, and 135 F g−1, respectively, retaining about 75, 81 and 87% of their initial capacitance values after 500 cycles, respectively.