Multidimensional Nanomaterials for Supercapacitors: Next Generation Energy Storage

The “next-generation materials” are those materials that have high efficiency, high-performance structural stability, easy manufacturability, and multifunctional capabilities. These new materials can be classified based on dimension, shape, composition, and nanostructure like 0D, 1D, 2D, and 3D. These materials have unique enhanced properties viz. electronic, optical, mechanical, magnetic, optoelectronics, vitrification, thermal properties, etc. Due to these outstanding features, these smart materials could be a game changer for prospects. Tuning the properties of such advanced materials provides a wide variety of fascinating opportunities. This chapter aims to provide a comprehensive overview of materials used to fabricate supercapacitor point of view and several other latest applications. The nanomaterials, discussed in this chapter along with their properties are Graphene, nanotubes, nanocomposites, microwave-absorbing materials, nanoparticles, biomaterials, and selfhealing polymers. It also discusses future directions for the development of advanced materials that perform well to anticipate future trends and highlight their relevance in real-world contexts. This chapter could become the torchbearer for new researchers working in the field of multifunctional advanced materials.

Over the past few years, supercapacitors have been spotlighted because of the challenges faced by other energy storage systems. The supercapacitor possesses excellent power density and long-term durability with an eco-friendly nature. Due to their wide range of advantages, supercapacitors are applicable especially in electric vehicles, heavy-duty vehicles, telecommunication, electric aircraft, and consumer electronic products. As per the charge storage mechanism, supercapacitors are divided into three categories based on their charge-storing method: electric double-layer capacitors (EDLCs), pseudocapacitors, and hybrid capacitors. The electrode materials such as graphene, activated carbon, metal oxides, conducting polymers, etc., were widely applied, for better performance. The electrolyte is a crucial component in the mechanism of the supercapacitor to run the system at a higher voltage and thus there are various electrolytes such as solid, inorganic, and organic based on the application of the materials, and the electrolytes are chosen. However, the supercapacitors suffer from low energy density. Currently, research is more focused on advanced materials and various synthesis methods to overcome the drawbacks. This chapter provides a detailed understanding of supercapacitors with redox and non-redox reactions -the broad classification of the supercapacitor -their charge storage mechanism -various electrode materials -electrolytes (aqueous, non-aqueous, and solid) and current collectors, etc. Finally, the parameters that help in estimating the performance of supercapacitors are (specific capacitance, energy density, and power density) included.

Graphene has attracted a lot of attention in recent years since its discovery because of its unique structural, mechanical, optical, electric, and thermal properties, making it a viable candidate for a wide range of applications. Graphene, a 2- dimensional network of carbon atoms with high conductivity and surface area is a potential material for high-performance applications. For conceivably ground-breaking uses in lithium-ion batteries, solar cells, sensing, and photocatalytic applications, graphene is being used as a filler or composite material with polymers, metals, and metal oxides. Graphene's primary derivatives are graphene oxide (GO) and reducedgraphene oxide (rGO). Graphite can be oxidised to produce GO, and it can be reduced to produce rGO. There is a lot of interest in the application of energy storage in different industries because of the fascinating features of graphene and its derivatives. In the last decade, there has been a lot of interest in the energy storage applications of nanomaterials based on graphene, and numerous groups have started working in this area all over the world. Graphene is perfect for the manufacture of energy storage devices due to its exceptional compatibility, solubility, and selectivity. It is possible to do this, especially if they have been exposed to metal oxide, which causes only minor sheet restacking. The high conductivity of the interconnected networks of graphene is another factor influencing it as a material for energy storage applications.

Currently, Quantum dot nanomaterials have received a lot of attention due to their intriguing features. Most intriguing is how they can be used as electrodes to create safe chemical-free supercapacitor parts and produce clean energy. Due to their high charge storage capacity and stability, quantum dot electrodes are increasingly in demand for high-tech hybrid supercapacitors. This chapter covers the electrochemical performance, physiochemical characteristics, and synthesis of numerous quantum dots. They are also provided with information about the electrochemical characteristics of various supercapacitors. To show readers the potential of this field of study, the best operational factors are highlighted.

The scarcity of natural stocks of fossil fuels and the rising pollutant ions evolved from the burning of carbon-containing fuels, has triggered the necessity for clean, renewable, and sustainable energies to be generated and its subsequent storage in portable form to meet the on-demand consumption. However, the performances of storage materials are still limited for extensive real-world applications due to their sluggish ion diffusion kinetics, lack of efficiency in extreme weather conditions, poor chemical stability, and many more. Therefore, it is highly requisite to discuss the development and assess the performances of new advanced energy storage materials. In this chapter, we are specifically keen to discuss the design, synthesis, chemistry, and properties of various MOFs based electrode materials for energy storage devices like batteries and supercapacitors, which can necessarily store electrical energies by implementing the use of suitable electrode and electrolyte materials through an upright fabrication technique. Generally, MOFs contain both inorganic metal ions and organic ligands/linkers which enable great control over their structural and compositional modifications to optimize the properties like porosity, stability, surface area, redox activity, and electrical conductivity and show great promise to generate high energy storage performances, in the recent past. However, despite the current success, MOFs based electrode materials have faced a lot of challenges in terms of the choice of suitable metals and organic ligand moieties, rich host-guest interactions, preparation of composites with desired morphology and properties, control over composite composition, scalability of the process and many more which needs to be addressed for its full-proof use in the real-world application as energy storage materials and thusly, this chapter is important to discuss.

The growing interest and demand for energy storage applications have significantly encouraged the development of a broad range of functional 2D materials. Owing to the extraordinary properties including 2D lamellar structure, larger interlayer space, mechanical strength, high thermal and electrical conductivity, and negative zetapotential, carbides/nitrides/carbonitrides of transition metal, usually known as MXenes have received the interest of researchers in the development of environmentally friendly materials for storage and conversion of energy. In this chapter, we focused on the MXene, their methods of preparation, the progress of development of various MXenes, and their modification for the storage of energy. Here, we have discussed the various storage devices for energy including batteries and superconductors. This chapter offers scientific inspiration and literature for the rational design and synthesis of high-capacity MXenes and their composites that can fulfill the increased demand for next-generation energy storage devices.

The development of new materials and technologies that can efficiently store energy while delivering power quickly has been the subject of numerous investigations. In an electrochemical supercapacitor (E-SC), the electric charge is stored in a doublelayer formed at the electrode/electrolyte interface (EEI), which is based on the surface area as well as pore size availability. The high surface area provided by the micropores (pore diameter: 2 nm) is essential for charging the E-SCs and calculating the capacitance values. Mesopores (2 nm < pore diameter < 50 nm) allow good electrolyte penetration and offer a high-power density (2 nm pore diameter 50 nm). However, because a lot of non-carbonaceous materials are used to make E-SC electrodes, more in-situ analytical characterisation tools along with electrochemical techniques are needed. It is crucial to have at least a brief understanding of the electrochemical processes occurring at the EEI of E-SC electrodes (or devices). Variations in electrochemical, morphological and surface, and crystallographic properties will be used to categorise the data gathered by the state-of-the-art characterisation techniques. This chapter also provides a resource for researchers by outlining the methods to learn more about E-SCs and opportunities to achieve additional functionalities beyond those related to energy storage.

In this chapter, the types of electrolytes and the alteration in capacitance with pore size, their power density, and energy density along with the interaction of electrolytes with current collectors are discussed. The electrolytes’ electrochemical stability broadly estimates the working cell voltage provided that the electrodes are stable under operating cell voltage. The electrolytes are divided into various categories such as liquid electrolyte, solid-state, and redox-active electrolyte. The liquid electrolytes are further categorized into aqueous and non-aqueous electrolytes. The critical performance parameters such as stability, lifetime, operating temperature, operating voltage, etc. are believed to be affected by electrolytes. Moreover, the electrolytes are believed to interact with the current collectors, additives, binders, separators, and electrode material to affect the practical performance of supercapacitors. However, the capacitance of the electrolyte depends upon the ion size and the matching between the electrode pore size and electrolyte ion size. The power density and energy density depend upon the potential window, ionic conductivity, and electrochemical stability along with concentration, respectively. Further, the ionelectrode interaction is supposed to affect the cycle life and power density as well. The thermal stability of electrolytes depends upon their boiling points, freezing points, and salt solubility and the equivalent series resistance depends upon ion conductivity, mobility, and viscosity.

Energy storage devices are essential because of ever-worsening fossil fuel depletion, increasing energy demand, and increasing environmental pollution. Maxwell Technologies, NessCap, Ashai Glass, and Panasonic commercialize carbon-based conventional supercapacitor devices. Carbon materials like graphene, carbon nanotubes, and activated carbon, are considered favourable materials for bendable and wearable electronic devices. The graphene, because of its high conductivity (thermal ~5 × 103 W m-1 K-1, electrical ~102 to 108 S m-1), extraordinary surface area (theoretically ~2630 m2 g-1), outstanding electrochemical performance (100 to 200 F g -1), less weight compared to transition metal oxides (because of less molecular weight of the carbon), outperform every other carbon material [1, 2]. The fiber-shaped supercapacitors are considered a potential future candidate for electrochemical energy storage systems and have gained considerable attention from the energy storage research community. This chapter discusses the importance of fiber-shaped supercapacitors, their evolution, various forms of their device structures, and electrolytes used for fiber-shaped supercapacitors. Further, the wet-spinning technique for synthesizing graphene fibers and their composites with pseudo-capacitive materials are also discussed.

Recently, Quantum dot nanomaterials have been explored to a great extent for their exciting properties. Their application as electrodes to produce clean energy and hazardous chemical-free components of supercapacitors is the most interesting. The quantum dot electrodes are found to offer high charge storage capacity as well as stability that ultimately boosts their demand in advanced hybrid supercapacitors. This chapter discusses the synthesis, physiochemical features, properties, and electrochemical performance of various quantum dots. Additionally, insights into their electrochemical properties in different supercapacitors are illustrated. The best operational parameters are highlighted to provide readers with the future scope of this research area.

In the last two decades, nanomaterials with enhanced active sites and better surface kinetics as compared to their bulk counterpart, have been significantly studied for supercapacitor electrode materials. Contemporarily, Metal-organic frameworks (MOFs) by virtue of versatile structure, charge conduction, high porosity, and redoxactive functionality have also emerged as the most potential materials for nextgeneration energy storage technologies. Despite these excellent features, the bulk phase inorganic-MOFs have some chemical and physical limitations that hinder cell performance and thus novel materials are required. Recently, MOFs-based nanomaterials(nMOF) got due attention leading to the discovery of a variety of properties not observed or relevant in bulk systems, such as well-defined 3D structures, permanent porosity, and accelerated adsorption/desorption kinetics. That's why nMOFs are considered an emerging class of modular nanomaterials. However, understanding of nMOFs is still in its infancy, film uniformity along with the unstable structure in a highly corrosive electrolyte is still a bottleneck problem. In this chapter, the recent developments of pristine MOF and MOF-derived porous nanocomposites for the nextgeneration supercapacitor applications will be discussed.

Technological advances in recent decades have augmented the demand for durable and inexpensive energy storage devices with higher charge capacity. Owing to their unique charge storage and surface capability, a recent class of two-dimensional (2D) materials known as MXenes has been widely used in energy storage devices. MXenes are the layered transition metal carbides, nitrides, and/or carbonitrides produced via selective etching of interleaved “A” layers from parent MAX phases. Unlike other 2D materials, MXenes earned great attention because of their intrinsic surface functional groups, hydrophilicity, unique electrochemical nature, high conductivity, and superior charge storage capacity. Such features render MXenes as the ultimate material from the 2D family, thus inspiring researchers to delve further into experimental and theoretical realms. Numerous attempts have been made to elucidate synthesis strategies to produce MXene and its fundamental characteristics. The current chapter emphasizes the recent advancements in MXene-based electrochemical energy storage applications using supercapacitors which are recognized as a dominant source. The effect of MXene's morphology and electrode growth on the charge-storage mechanism has also been highlighted in subsequent sections. In addition, this chapter outlines the current state-of-the-art on the supercapacitors compromised of the MXenebased composites. A discussion of relevant challenges associated with such materials for energy storage applications is also presented, and future perspectives provide additional insight into their practical aspects.

Energy storage is one of the crucial requirements for today’s life to store energy for later use. Energy storage critically reduces the dependence on backup power supplies. In recent times, fascinatingly, energy storage systems have been developed in compactable sizes and shapes with sustainable and appreciable backup power. However, due to some challenges in conventional storage systems, supercapacitors are gaining a huge interest which satisfies the increasing demands of energy storage devices. Supercapacitors are well-recognized for their long cycle life, high power density, and the ability for less charge and discharge time. Accordingly, in supercapacitor electrodes, activated carbon is extensively used as a base material. Current research documented that the amorphous mixed metal oxides and nanostructured oxides are also used in supercapacitor devices to exhibit high performance. Keeping this in view, this chapter is reviewed to provide information on the different types of recent developments in supercapacitors and their performance. In addition, recent developments in green approaches to supercapacitor applications in MnO2 -based electrodes and composites, supercapacitors performance, power capability, and cycle life are also discussed.

Supercapacitors are gaining prominence in the realm of energy storage devices due to their high power density, extended cycle stability, and fast charge/discharge rates. Supercapacitors are widely used in industries such as service grids, transportation, consumer electronics, wearable and flexible systems, energy harvesting, etc. Due to their remarkable high-power performance, high reliability, and extended lifetime, they are a key electrochemical device for energy storage; as a result, the worldwide supercapacitor market is rapidly developing. Supercapacitors have a straightforward basic construction, but different products for various applications require cells in various configurations. The application of supercapacitors from the perspective of the industry is the subject of this chapter.

The contemporary research environment calls for developing nextgeneration devices using cutting-edge technologies for energy storage applications. Supercapacitors are becoming burgeoning contenders in the energy sector due to their increased durability and quicker charge storage capacity. In contrast to batteries and fuel cells, supercapacitors are a less realistic solution for practical applications. Additionally, there is a pressing need for fabrication techniques that must be addressed to deliver an appropriate supercapacitor electrode. The book chapter will better describe the difficulties encountered during various supercapacitor research, development, and commercial application phases. Finally, a conclusive prognosis has been given on how the discussion above will deliver essential insights and create chances to expand the possible application of new-generation supercapacitors.