GRAPHENE AND METAL OXIDE BASED MATERIALS FOR SUPERCAPACITOR APPLICATION

Abstract

Storage of energy has always been a critical matter; especially when it has been generated from renewable sources. Battery, Supercapacitor, or Ultracapacitor, Fuel Cells are considered as different types of storage devices used in the current century. Supercapacitor is a kind of electrochemical capacitor, which is a reliable supplement in the power sources aspect due to their remarkable advantages like, quick charge/discharge process, excellent cycling properties and highpower densities in conjugation with simple design and construction. The low energy density of these electrochemical capacitors is primarily a major roadblock for the rapid development of ultracapacitors. In general, supercapacitor electrode materials require a sufficiently large active surface area, high electrical conductivity, appropriate pore size distribution, and thinner dielectrics for better performance. To increase the energy density a number of approaches have been employed to design and fabricate the electrode materials with different types of porous nanostructures including graphene and their functionalized derivatives, activated carbon-based materials, conductive nanocarbons, fullerenes, conductive polymers metal oxides and their composites are conducive to improve specific capacitances, rate capability and stability of the electrode material. In this regard, two-dimensional sp2-bonded graphene nanosheets can be an excellent choice owing to their excellent conductivity, large surface area, and remarkably high mechanical stiffness. However, strong agglomeration tendency and difficulty in dispersion limit the active surface area and charge storage capacity of pristine graphene. The surface modification through covalent functionalization can amicably solve agglomeration and dispersion problems enhancing processability to boost the electrochemical performance. Researchers are working for the development of low-cost materials for supercapacitor electrodes. From this concept, the research was motivated to synthesize or use different materials or combination of materials that will be abundantly available and does not harm the environment. In order to ascertain the role and effect of various electrolytes on the electrochemical performances, a comprehensive electrochemical study using large varieties of electrolyte was carried out by employing aminated graphene as electrode materials. The aminated graphenes have been synthesised through chemical functionalization of graphene oxide usinlong-chainin amines [octylamine (OA) and octadecylamine (ODA)] covalently bonded to graphene oxide and subsequent in-situ reduction produced more stable reduced aminated graphene oxides. The octylamine modified reduced graphene oxide (rGO-OA) produces promising galvanic charge discharge supercapacitance value of 678.7 F/g with energy density 455.99 Wh/kg and power density 107.99 W/kg in zinc chloride (ZnCl2) electrolyte. On the other hand, rGO-OA in oxalic acid electrolyte shows the charge-discharge supercapacitance value of 336.08 F/g at 0.05 A/g current density and also produces an energy density of 241.98 Wh/kg and moderate power density of 221.85 W/kg. Similar trends can be observed with octadecyl amine-modified reduced graphene oxide (rGO-ODA). Thus, the best capacitance values of 248 F/g and 110 F/g in ZnCl2 and oxalic acid electrolytes respectively were recorded for rGO-ODA. The EIS measurement using Nyquist and Bode plots also divulged the better capacitive and charge transfer behavior of rGO-OA in ZnCl2 and Oxalic acid electrolytes. The effect of partially reduced fullerenol-graphene oxide (rFGO) nanofiller on supercapacitance properties of binary nanocomposites containing phenylene-alt-thiophene fluorescence conducting polymer (FCP) was investigated. Nanocomposites were prepared by solution mixing, which allows uniform nanofiller distribution into the polymer matrix. Microscopic analyses of nanocomposites display homogeneous dispersion of nanofiller into the polymer matrix. Supercapacitance properties of binary nanocomposites in three different electrolytes (acid, neutral, and alkaline) were investigated and the best galvanic charge-discharge result of 173 F/g at 2 A/g current density was obtained at 2 wt % loading up to 500th cycle for rFGO in acid electrolyte only. Specially prepared rayon-based activated carbon fibre/fabric (ACF) has been explored as a potential alternative for the conventional carbonaceous materials (like, graphene, carbon nanotube, activated carbon) to be used as composite electrodes with metal oxide. Herein, the composite material of cobalt ferrite (CoFe2O4, Cof) and activated carbon fabric/fiber is examined as potential electrode materials for ultracapacitor applications. The composite material produces electrochemical capacitances as high as 1287 F/g and 788 F/g at a scan rate of 2 mV/s in 0.5 M phosphoric acid and 0.5 M sulfuric acid electrolytes, respectively. The ACF is derived from rayonbased carbon fabric through activation and carbonization processes in a tubular furnace. The ACF, cobalt ferrite, and electrode material derived thereof are analyzed by FTIR, XPS, BET surface area analyzer, FESEM, and XRD methods. The electrochemical behavior of the cobalt ferrite decorated ACF electrode material exhibits a slightly higher energy density (176.98 Wh/kg) in H3PO4 than in H2SO4 (150.79 Wh/kg) electrolyte. The stability (~ 74%) of electrode materials is retained even after 3500 cycles of charge-discharge in acid electrolytes. Thus, Cof-ACF could be used as a costeffective, compact, and light-weight electrode material with enhanced stability and improved performance for ultracapacitor and energy storage device applications.Toward the goal of green and sustainable energy conversion and storage, double perovskite oxide materials are always prone to display not only exciting properties but also act as advanced electroactive material in various energy-related practical applications though such double perovskite oxides are highly desirable. To understand the role of 3d-4d metal ions in double perovskite towards energy storage applications, three ruthenium-based disordered double perovskites namely Ca2MnRuO6 (CMRO), Ca2Mn1.25Ru0.75O6 (CMRO-1) and Ca2Mn0.75Ru1.25O6 (CMRO-2) have been synthesized and supercapacitor performances have been accomplished by prepared of the oxide-rGO composite electrodes. The electrochemical measurement reveals that the as-fabricated CMRO-2 oxide-rGO composite electrode possesses a much higher capacitance of 598.8 F g−1 at a scan rate of 2 mV s-1 (386.3 at 2 A g−1) in 0.5 M H3PO4 electrolyte solution with maximum capacitance drop of 30 % after 3000 charge-discharge cycles compared to 0.5 M H2SO4 electrolyte medium. Remarkably, the CMRO-2 oxide-rGO composite electrode exhibited a maximum energy density of 431.1 Wh kg– 1 at a power density of 14.4 W kg–1 in 0.5 M H3PO4 electrolyte. Notably, the slight variation in Mn/Ru concentration during synthetic conditions in title double perovskite structures commendably electrochemical performances and able to produce exciting results.