Milan Jana

Non-covalent functionalization of reduced graphene oxide using sulfanilic acid azocromotrop and its application as a supercapacitor electrode material

Sulfanilic acid azocromotrop (SAC) modified reduced graphene oxide (SAC-RGO) was prepared by simple non-covalent functionalization of graphene oxide (GO) followed by post reduction using hydrazine monohydrate. Spectral analysis (Fourier transform infrared, Raman and X-ray photoelectron spectroscopy) revealed that successful modification had occurred of GO with SAC through π–π interaction. The electrical conductivity of SAC-RGO was found to be ∼551 S m−1. The capacitive performance of SAC-RGO was recorded using a three electrode set up with 1 (M) aqueous H2SO4 as the electrolyte. The –SO3H functionalities of SAC contributed pseudocapacitance as evidenced from the redox peaks (at ∼0.43 and 0.27 V) present in the cyclic voltammetric (CV) curves measured for SAC-RGO. The contribution of electrical double layer capacitance was evidenced from the near rectangular shaped CV curves and resulted in a high specific capacitance of 366 F g−1 at a current density of 1.2 A g−1 for SAC-RGO electrode. An asymmetric device (SAC-RGO//RGO) was designed with SAC-RGO as the positive electrode and RGO as the negative electrode. The device showed an energy density of ∼25.8 W h kg−1 at a power density of ∼980 W kg−1. The asymmetric device showed retention in specific capacitance of ∼72% after 5000 charge–discharge cycles. The Nyquist data of the device was fitted with Z-view and different components (solution resistance, charge-transfer resistance and Warburg elements) were calculated from the fitted curves.

Band Gap Engineering of Boron Nitride by Graphene and Its Application as Positive Electrode Material in Asymmetric Supercapacitor Device

Nanostructured hexagonal boron nitride (h-BN)/reduced graphene oxide (RGO) composite is prepared by insertion of h-BN into the graphene oxide through hydrothermal reaction. Formation of the super lattice is confirmed by the existence of two separate UV-visible absorption edges corresponding to two different band gaps. The composite materials show enhanced electrical conductivity as compared to the bulk h-BN. A high specific capacitance of ∼824 F g(-1) is achieved at a current density of 4 A g(-1) for the composite in three-electrode electrochemical measurement. The potential window of the composite electrode lies in the range from -0.1 to 0.5 V in 6 M aqueous KOH electrolyte. The operating voltage is increased to 1.4 V in asymmetric supercapacitor (ASC) device where the thermally reduced graphene oxide is used as the negative electrode and the h-BN/RGO composite as the positive electrode. The ASC exhibits a specific capacitance of 145.7 F g(-1) at a current density of 6 A g(-1) and high energy density of 39.6 W h kg(-1) corresponding to a large power density of ∼4200 W kg(-1). Therefore, a facile hydrothermal route is demonstrated for the first time to utilize h-BN-based composite materials as energy storage electrode materials for supercapacitor applications.

Growth of Ni–Co binary hydroxide on a reduced graphene oxide surface by a successive ionic layer adsorption and reaction (SILAR) method for high performance asymmetric supercapacitor electrodes

A simple, additive-free, cost-effective and scalable successive ionic layer adsorption and reaction (SILAR) method is reported to prepare nickel–cobalt binary hydroxide (Ni–Co–BH) on a reduced graphene oxide (RGO) directing template over a macro-porous conductive nickel foam substrate. This green technique is not only considered as fundamental research interest, but also describes the commercial applications of supercapacitors to reduce the electrode fabrication cost. Three different Ni–Co–BH–G (Ni–Co–BH/RGO) composites are synthesised by tailoring the nickel–cobalt ratios. The flower-like 3D framework of Ni–Co–BH–G provides a porous nano-structure to facilitate the charge transfer and ion diffusion. The cathodic peak current density vs. square root of the scan rate slope values of cyclic voltammetry are consistent with specific capacitance (SC) retention (vs. current density) from charge–discharge curves and the diffusion time constant of the Nyquist plot of the Ni–Co–BH–G composites. Taking the advantage of 3D conductive mesoporous open framework, the Ni–Co–BH–G has provided an excellent SC of 2130 F g−1 at 2 A g−1. An asymmetric supercapacitor device is designed with the optimized Ni–Co–BH–G as the positive electrode and concentrated HNO3 treated conducting carbon cloth (CCN) as the negative electrode. An excellent energy density of ∼92 W h kg−1 and a high power density of ∼7.0 kW kg−1 with lifetime stability up to 10000 charge–discharge cycles (capacitance retention ∼ 80%) are provided by the asymmetric device. Four asymmetric devices have been assembled in series, which provided ∼5.6 V charge–discharge potential. The assembled system has powered a 5 V light-emitting diode (LED) successfully.

Development of high energy density supercapacitor through hydrothermal synthesis of RGO/nano-structured cobalt sulphide composites.

Co9S8/reduced graphene oxide (RGO) composites were prepared on nickel foam substrate through hydrothermal reaction and used directly as supercapacitor electrode. The field emission scanning electron microscopy analysis of the composites showed the formation of Co9S8 nano-rods on the RGO surfaces. The average crystal size of the Co9S8 nano rods grown on the RGO sheets were ∼25-36 nm as calculated from x-ray diffraction analysis. The reduction of graphene oxide (GO) was confirmed by Raman and x-ray photoelectron spectroscopy analysis. The electrical conductivity of the Co9S8/RGO composite was recorded as 1690 S m(-1) at room temperature, which is much higher than that of pure GO further confirming the hydrothermal reduction of GO. Cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy were investigated to check the electrochemical performances of the Co9S8/RGO composites. The Co9S8/RGO composites supported on nickel foam showed very high specific capacitance (Sc)(1349 F g(-1) at a current density of 2.2 A g(-1)), energy density (68.6 W h kg(-1)) and power density (1319 W kg(-1)) in 6 M KOH electrolyte. The retention in Sc of the composite electrode was found to be ∼96% after 1000 charge-discharge cycles.

Morphology controlled synthesis of MnCO3–RGO materials and their supercapacitor applications

MnCO3-reduced graphene oxide (MnCO3–RGO) was grown on nickel foam by a facile successive ionic layer adsorption and reaction (SILAR) method and used as a supercapacitor electrode. The morphology of the MnCO3 functionalities was tuned from lotus to flake to spherical shape using different chelating agents during synthesis. The length and width of the individual petals of the lotus structure MnCO3 were found to be ∼200–300 and 50–100 nm, respectively. The reduction of graphene oxide (GO) in MnCO3–RGO composites was confirmed by Raman spectroscopy and electrical conductivity data analysis. The lotus shaped MnCO3 grown on RGO sheets provided a high surface area and electrical conductivity as compared to the developed electrode materials. The cyclic voltammetry, galvanostatic charge–discharge (GCD) and electrochemical impedance spectroscopy analyses showed that the lotus shaped MnCO3 grown on RGO sheets provided higher current response, large specific capacitance (SC) and low solution, charge-transfer and Warburg resistance as compared to the flake and spherically shaped MnCO3 grown on RGO sheets. A fabricated asymmetric supercapacitor (ASC) device with MnCO3 (lotus) – RGO as the positive electrode and sonochemically reduced GO as the negative electrode – exhibited a working potential of ∼0–1.6 V, SC of ∼ 335 F g−1 at ∼2 A g−1 (∼468 mF cm−2 at ∼2.8 mA cm−2), an energy density of ∼120 W h kg−1 (∼0.16 mW h cm−2) and a power density of ∼16 kW kg−1 (∼22 mW cm−2) with a GCD stability of ∼73% after 10 000 cycles.

One Pot Synthesis of Cu2O-RGO Composite Using Mango Bark Extract for Supercapacitor Application

A facile and green approach is demonstrated for the simultaneous reduction of graphene oxide (GO) and copper acetate to prepare Cu2O-reduced graphene oxide (Cu2O-RGO) composite using mango bark extract. Reduction of GO and formation of Cu2O-RGO has been confirmed by FT-IR spectroscopy. The morphology of Cu2O is found to be spherical (~10 nm) shape from TEM and FE-SEM image studies. The CV profile of Cu2O-RGO composite exhibits a working potential of −0.1 to 0.7 V with a pair of anodic and cathodic peaks at ~0.15 and 0.38 V, respectively at a scan rate of ~10 mV s−1. The high electrochemical performance is attributed to the synergistic contribution of redox like Cu2O and electrochemical double layer capacitance of RGO. The specific capacitance is found to be ~470 F g−1 at a current density of 2 A g−1.