One-pot synthesis of composite NiO/graphitic carbon flakes with contact glow discharge electrolysis for electrochemical supercapacitors

Thanks to their high power density and degree of reversibility, supercapacitors are electrochemical devices that narrow the gap between secondary batteries and traditional dielectric capacitors in the traditional Ragone plot. However, their use is still hindered by their capability to achieve higher energy density. In this work, we present a one-pot synthesis procedure of composite graphitic carbon flake-supported NiO for electrochemical energy storage application. We used cathodic contact glow discharge electrolysis by applying 120Vdc terminal voltage between a thin Pt wire, slightly submerged in an aqueous solution of NiSO4(H2O)(6)+Na2SO4, and a large surface area carbon graphite anode. Strong active species generated within the micro-plasma volume locally reduce the nickel precursors to form NiO materials, while at the anodically polarized graphite rod, the forces holding the graphene layers together are weakened by ion/solvent intercalation producing micrometer-sized graphitic carbon flakes. The morphological characterization is carried out by electron microscopy, energy dispersive X-ray spectroscopy, powder X-ray diffraction, and micro-Raman spectroscopy. Cyclic voltammetry, constant-current charge/discharge, and electrochemical impedance spectroscopy in 5moll(-1) KOH solution are carried out to evaluate the electrochemical energy storage performance of the material. We show that carbon flake-supported NiO exhibits the dual combination of electric double-layer capacitance with faradic behavior, giving 495Fg(-1) specific capacitance at 2Ag(-1) current density. Copyright (c) 2015 John Wiley & Sons, Ltd.