Introduction

Supercapacitors (SCs), which have high density, high operating temperatures, cyclic stability, and low costs, are employed as energy storage devices. Traditional aqueous SCs, such as electric double-layer capacitors, have a poor energy density, which does not match the commercial needs of electronic devices. Supercapacitors, the most recent generation of clean chemical power sources, have received a lot of attention due to their high power density, strong cycle stability, rapid charge and discharge, low weight, and small size. It has been used extensively in a variety of gadgets, including solar panels, electric cars, trains, and electronic devices. Electrodes, electrolytes, current collectors, separators, and related auxiliary devices make up the bulk of a supercapacitor. Electrode materials play a vital role in determining the characteristics of supercapacitors. Electric double-layer supercapacitors (EDLCs) are frequently made from carbon-based materials, primarily activated carbon, carbon fibers, carbon nanotubes, and graphene. The carbon material can suit the energy storage needs of EDLCs and also has the benefits of superior wettability, a large surface area, high conductivity, and a wide electrochemical window. A brand-new type of carbon material called carbide-derived carbon (CDC) offers exceptional chemical resistance and excellent electrical conductivity. In order to create an electrical double layer, the charge is separated at the electrode interface in electrical double-layer capacitors (EDLCs). A wide number of potential applications are made possible by the reversible nature of this energy storage mechanism and the storage capacity of EDLCs to send high power density and long cycle life. They can, for instance, be used to supply beginning power for start-stop systems in cars, backup power sources for computers, grid regulators for wind and solar energy systems, and open airplanes. However, electric vehicles are the most practical use for EDLCs. Greater control over the arrangement of electrode materials during electrode production and drying is made possible by the approach, which has been demonstrated to significantly increase performance and give additional functionality for lithium-based energy storage applications. In order to find stable Zn anode electrode materials for Zn-ion batteries with extended cycles, several studies have been conducted. The 3D porous copper skeleton's inherent superior electrical conductivity and open structure guaranteed consistent Zn deposition and stripping. Compounding using pseudo capacitive material solves the issue. Such as metal oxides, noble metals, and conducting polymers, which have high specific capacitance.

Materials and Methods

3. Experimental process -

3.1. Preparation of Activated carbon –

Three key factors, namely the impregnation ratio (IR) (mass of ZnCl2/mass of raw material), holding time (HT), and carbonization temperature, are crucial in the preparation of activated carbon from the precursor (CT). A sample weighing around 10 g was impregnated with ZnCl2 during the process, with a chemical ratio ranging from 0.5 to 1. [7]

3.2. Preparation of carbon nanotube-

Through the use of a template co-assembly technique, N-doped porous carbon nanotubes (NCTs) with a micro-/meso-structure and crumpled surface were created. The 3-aminophenol-formaldehyde resin (AM) was employed as a carbon and nitrogen precursor, tetraethyl orthosilicate (TEOS) was used as a pore-forming agent, and cheap and easily accessible halloysite (HNT) served as a hard template to create a tubular structure. The obtained NCTs exhibit variable wall thickness, a distinctive crumpled surface, and homogeneous tubular morphology. The high SSA, plentiful pore structure, optimal ion diffusion channels, and low migration resistances of the improved NCTs allow for superior rate performance and cycling stability in supercapacitors. [8]

3.3. Preparation of Graphene -

Natural graphite was used to create graphene oxide (GO) using a modified Hummers method [26]. 200 mg of KMnO4 was added to 54 mL of distilled water to create a homogeneous solution, which was then dropped into 46 mL of GO suspension (1.533 mg mL1) while being vigorously stirred for two hours. The mixture was then heated for 8 minutes in a standard household microwave oven (Galanz, P70D20N1P-G5(W0), 700 W), and cooled to room temperature. The materials were acquired, cleaned with distilled water, and freeze-dried. [9]

3.4. Preparation of RGO/NiCo2S4 aerogel-

In a typical experiment, 15 mL of DI water and 45 mg of GO were mixed to form a homogenous dispersion (3 mg/ml), which was then sonicated in an ultrasound bath for 30 minutes. After that, the solution was agitated for another 30 minutes while 0.20 mmol of Ni(NO3)2.6H2O and 0.40 mmol of Co(NO3)2.6H2O were dissolved in it. After stirring the mixture for 30 minutes, 1.20 mmol of thiourea was added. A 20 mL hydrothermal stainless steel reactor lined with PTFE and heated to 180 o C for 5 hours with the produced solution was used to create a hydrogel composite. Journal 4 1 Pre-proof In order to get rid of the byproducts and unreacted components 2, the product was lastly submerged in DI water for a week. They were the RGO/NiCo2S4 aerogels acquired through the freeze-drying process. The same technique was used to create bare RGO aerogels for comparison but without the addition of nickel precursors of cobalt sulfide.[10]

3.5. Preparation of carbon foam –

A unique technique for creating lightweight, free-standing carbon foam (CF)-decorated cobalt oxide (Co 3 O 4) nanostructures has been published. The polyurethane (PU) foam replica method with phenolic resin was used to create the freestanding CF first. This was followed by oxidation stabilization and carbonization at 1000 0C in an inert environment. The in-situ hydrothermal technique was then used to decorate free-standing CF with various Co 3 O 4 nanoparticle (NP) contents. [11]

3.6. Preparation of carbide-derived carbon –

First, to create SiOC powder, 6 g of silicone resin powder was sintered at 1000 °C for 4 hours in an argon environment. With a mass ratio of 1:3, the resulting SiOC powder was combined with NaOH powder. The combined powders were then heated to 800°C and held there for one hour in an atmosphere of argon. The CDC was collected after being dried in a vacuum oven and cleaned with deionized water. Solvothermal precipitation was used to create the composite materials of TiO2/CDC. In order to create a homogeneous solution, 0.1 g of CDC and 0.02 g of titanium sulfate were first dispersed concurrently in 60 ml of 100% ethanol. The mixes were then put into a 100 mL Teflon-lined stainless steel reactor sealed and kept at 75 °C for 4 hours in the oven. The residual precipitate was repeatedly rinsed with deionized water, dried in a vacuum for an entire night, and then the supernatant liquid was separated to produce the TiO2/CDC composite material. Without altering the other conditions, the mass of the additional titanium sulfate was changed to 0.04 g and 0.06 g for comparison. TiO2/CDC1 (0.02 g), TiO2/CDC2 (0.04 g), and TiO2/CDC3 are the names of the TiO2/CDC composites that were created using various quantities of titanium sulfate (0.06 g). [12]

Conclusion

In this review article, one of the key types of supercapacitors is the electrical double layer capacitor. Additionally, we are studying the primary varieties of carbon, including carbon nanotubes, graphene, carbon aerogels, carbon foam, and carbon generated from carbides. From these articles, it is clear that EDLCs are excellent electrode materials for supercapacitors and are also useful for expanding their surface area. The effects of various electrode thicknesses, porous structures, and starting electrolyte concentrations on the EDLC capacitance, energy, and power were studied. The specific capacitance per gramme of the EDLC increases when thicker electrodes are used at low current densities; at high current densities, thicker electrodes still produce better results. In this study, graphene served as a protective layer on the surface of a Zn foil, and it had the role of inhibiting the growth of Zn dendrites and enhancing cyclic stability. In comparison to Zn foil, graphene (Zn) displayed 200 times superior electrochemical performances and a longer cycle life. Using a solvothermal technique, TiO2/CDC composites with porous structures were created. On the surface of the CDC material, uniformly sized spherical TiO2 particles grew. It has been proven that the ideal capacitance results in remarkable rate performance and long-term cycle behaviour. Saccharum spontaneum is a promising material for active carbon. Additionally, it has excellent carbonization and holding temperatures. Using a hydrothermal technique, a highly porous 3D RGO/NiCo2S4 aerogel composite was successfully created. The composite material that was obtained has a high current density. Additionally, one-step, quick-synthesis aerogel nanocomposites.