Electrochemically Reduced Graphene Oxide Deposited on Nickel-Nickel Oxide Foam for Supercapacitor Applications: Toward High Specific Capacitance

Electrochemical supercapacitors are known as the next-generation energy storage device due to their high capacitive capacities, high cycle stability and fast recharging. Types of supercapacitors include electrical double-layer capacitors (EDLCs) and pseudocapacitors. Various types of materials include transition metal oxides and conductive polymers as applications. Several studies have been conducted to the surface area of electro-active materials to create a high specific capacitance. Also, the use of high conductivity materials such as carbon nanotubes and graphene can also increase the conductivity of metal oxide electrodes. Meanwhile, graphene is an excellent choice for the growth of metal oxides due to its high conductivity, electrochemical stability, high surface and excellent mechanical properties. This paper introduced a new two-step method for generating a highly nanoporous nickel and nickel oxide (Ni-NiO) foam/Electrochemically reduced graphene oxide (ERGO) electrode with an exceptional specific capacitance for supercapacitor applications. This method first involved a drop cast of graphene oxide on Ni-NiO foam, and in the next step, graphene oxide was reduced in a constant current method at a current density of -0.6 mA cm-2 to -20 mA cm-2 in a 1 M KOH electrolyte. The Raman spectra for GO and ERGO at a density of -1.2, -3.0, -5.0 and -10 mA cm-2 were shown in Fig. 1(a). The ID/IG intensity ratio was 0.89, 0.93, 0.95, 1.0 and 1.11, respectively. As a result, the major oxygen functional groups which were intercalated into the interlayer spacing of graphite was eliminated. The XPS spectrum for GO 14th Annual Electrochemistry Seminar of Iran Materials and Energy Research Center (MERC), 12- 13 Dec, 2018 216 sheets and Ni-NiO-foam/ERGO composite at a current density of -10 mA cm-2 showed a significant decrease in the oxygen-containing functional groups, especially peak C (epoxy)/C-OH. These results indicated that functional groups have been significantly eliminated (Fig. 1(b,c)). According to the galvanostatic charge-discharge (GCD) curve for the Ni-NiO foam/electrochemically reduced graphene oxide, a specific capacitance of 1995 F g-1 was obtained at a current density of 1 A g-1 (Fig. 1(d,e)). Also, after 6000 cycles at a current density of 20 A g- 1, 95.1% of the initial specific capacitance was maintained (Fig. 1(f)).