Inclination to exploit renewable energy and their potential storage by facile, cost-effective, and above all in a green way are exactly what the current alternative energy research is looking for. The high-performance supercapacitor devices made up with the electrode materials synthesized in a simple and ecofriendly way are in utmost demand and the ultimate goal for widespread commercialization. Keeping these points in view, one pot green synthesis of active electrode material rGO-Au composite is achieved which not only performs as a very good supercapacitor in three-electrode configuration but also demonstrates extremely well as a coin cell device, ready to use. Ascorbic acid, which is commonly found in citrus fruits, plays an important role to reduce graphene oxide into rGO and simultaneously gold salt into gold nanoparticles, resulting in rGO-Au composite. The maximum recorded specific capacitance by CV measurement is 303.02 Fg⁻¹at a scan rate of 5 mVs⁻¹. Hindrance in the commercialization is caused by the differences in the supercapacitor performances between three electrode configurations and finally the proposed device. Here the proposed coin cell device exhibits maximum areal and mass specific capacitance of 62.43 mFcm⁻²and 56.09 Fg⁻¹, respectively, that is very high among all reported graphene based composite devices benefitted over with commercially viable high capacity retention up to 80% even after 10,000 cycles. The proposed device demonstrates high energy density (∼ E_D= 7.79 Wh/Kg) comparable to batteries and an optimum power density (∼ P_D= 2512.9 W/Kg) close to supercapacitor insinuating it is an effective green supercapacitor for commercialization.

New electrode materials for supercapacitor devices are the primary focus of current research into energy-storage devices. Besides, exact control of the proportions of these new materials while forming electrodes for coin cell supercapacitor devices is very important for the large-scale manufacturing or at industrial scale. Here we report a facile synthesis of CrOOH with ascorbic acid and explore an exact composition with reduced graphene oxide to achieve a highly efficient electrode material for supercapacitor devices. The rGO is synthesized by modified Hummer's method followed by reduction with ascorbic acid, whereas ultrasmall CrOOH nanoparticles result via hydrothermal treatment of the reactants Cr(NO₃)₃, NaOH, and ascorbic acid at 120 °C for 12 h. The ultrasmall CrOOH nanoparticles show an amorphous phase with particle size range 3-10 nm and a calculated band gap of 3.28 eV. Six different composites are prepared by varying the proportion of CrOOH and rGO materials and further utilized as active electrode materials for fabrication of the coin cell supercapacitor devices. We report the highest specific capacitance for the 70% CrOOH and 30% rGO composite that exhibits a capacitance of 199.8 mF cm^-2 with a long cyclic stability up to the tested 10,000 charge/discharge cycles. The proposed supercapacitor device exhibits a high energy and power density of 8.26 Wh kg^-1 and 3756.9 W kg^-1, respectively, at Ragone Plot, showing the commercial viability of the device.

Metal–organic frameworks (MOFs) are hybrid materials that are being explored as active electrode materials in energy storage devices, such as rechargeable batteries and supercapacitors (SCs), due to their high surface area, controllable chemical composition, and periodic ordering. However, the facile and controlled synthesis of a pure MOF phase without impurities or without going through a complicated purification process (that also reduces the yield) are challenges that must be resolved for their potential industrial applications. Moreover, various oxide formations of the Ni during Ni-MOF synthesis also represent an issue that affects the purity and performance. To resolve these issues, we report the controlled synthesis of nickel-based metal–organic frameworks (NiMOFs) by optimizing different growth parameters during hydrothermal synthesis and by utilizing nickel chloride as metal salt and H₂bdt as the organic ligand, in a ratio of 1:1 at 150 °C. Furthermore, the synthesis was optimized by introducing a magnetic stirring stage, and the reaction temperature varied across 100, 150, and 200 °C to achieve the optimized growth of the NiMOFs crystal. The rarely used H₂bdt ligand for Ni-MOF synthesis and the introduction of the ultrasonication stage before putting it in the furnace led to the formation of a pure phase without impurities and oxide formation. The synthesized materials were further characterized by powder X-ray diffraction (XRD) technique, scanning electron microscopy (SEM), and UV–vis spectroscopy. The SEM images exhibited the formation of nano NiMOFs having a rectangular prism shape. The average size was 126.25 nm, 176.0 nm, and 268.4 nm for the samples (1:1)s synthesized at 100 °C, 150 °C, and 200 °C, respectively. The electrochemical performances were examined in a three-electrode configuration, in a wide potential window from −0.4 V to 0.55 V, and an electrolyte concentration of 2M KOH was maintained for each measurement. The charge–discharge galvanostatic measurement results in specific capacitances of 606.62 F/g, 307.33 F/g, and 287.42 F/g at a current density of 1 A/g for the synthesized materials at 100 °C, 150 °C, and 200 °C, respectively.