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 Mn(0.68) Ni(0.22)CU(0.10)C(2)O(4)center dot nH(2)O at 250-450 degrees C. The obtained MNCO present micron-sized agglomerates composed of primary particles with a size of similar to 200 nm. The 250 degrees C- and 350 degrees C-obtained MNCO are poorly crystallized with a structure of alpha-MnO(2), while the 450 degrees C-obtained MNCO contain multiphase oxides with structures of alpha-MnO(2), gamma-MnO(2) and Mn(2)O(3). 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 MnO(2) electrodes. At a scan rate of 2 mV s(-1), the 250 degrees C-, 350 degrees C-, and 450 degrees C-obtained MNCO electrodes deliver capacitance values of 490, 293 and 205 Fg(-1) respectively. At a current density of 1000 mAg(-1), the 250 degrees C-, 350 degrees C-, and 450 degrees C-obtained MNCO symmetrical capacitors exhibit capacitance values of 368, 286, and 135 Fg(-1), respectively, retaining about 75, 81 and 87% of their initial capacitance values after 500 cycles, respectively. 2011 (C) Elsevier B.V. All rights reserved.