Co₃O₄/MnO₂ Core/Shell-Nanostructured Pseudocapacitor Electrode

Experimental

For Co3O4 deposition, a piece of bare CFP (SGL Technologies, 1 cm × 5 cm) was soaked in a 100 mL, Teflon-lined, stainless steel autoclave that was filled with a solution containing cobalt nitrate hexahydrate (0.2 M) and 0.1 M ammonium nitrate dissolved in ammonium hydroxide solution (9 wt %). The autoclave was heated to 90 °C for 8 h, and was then naturally cooled. To deposit MnO2, the blackcolored CFP was thoroughly washed with deionized water, dipped again in the autoclave filled with an aqueous solution (40 mL) containing 71.2 mM KMnO4 and HCl (1 mL), and heated at 140 °C for 30 min. The amounts of Co3O4 and MnO2 deposited on CFP were 2.0 and 2.3 mg/cm2, respectively.

Co3O4 and MnO2 were identified using an X-ray diffractometer (Rigaku D/Max-2500/PC) and a Renishaw 2000 confocal Raman microscope. The Brunauer–Emmett–Teller (BET) surface area was determined from the nitrogen adsorption/ desorption isotherm measured using a BELSORP MINI II (BEL JAPAN). A scanning electron microscope (SEM, Hitachi S-4800 FESEM) was employed to examine the surface morphology of the electrodes. The electrochemical performance of the electrodes was investigated via a threeelectrode system with an Ag/AgCl reference electrode and Pt counter electrode in 0.5 M NaSO4 electrolyte. CA and Cm were determined via cyclic voltammetry (CV) performed at various scan rates using the following equation: CA = ∫I·dt/ (ΔV × S) and Cm = ∫I·dt/(ΔV × M), where I is the oxidation/ reduction current, dt is the time differential, ΔV is the potential window, S is the geometrical area of the electrode, and M is the mass of the active material.

Supporting Information. XRD pattern of MnO2 deposited on CFP; CVs and Cm and CA of MnO2 electrode at different scan rates.