In the emerging arena of renewable energy technologies, one of the highly faced challenges is the development of efficient and sustainable energy storage devices. Supercapacitor being one such potential device, widely used to tap the gap between energy and power densities of batteries and capacitors. Supercapacitors with their forefront characteristics like minimum maintenance requirement, relative energy storage along with moderate cycle life, possess high power density making them a superior storage device till date. Based on energy storage mechanisms, they are classified into two categories namely electrochemical double-layer capacitors (EDLCs) and pseudocapacitors (PCs), which are non-Faradaic and Faradaic with redox mechanisms, respectively. Hence, different electrode materials are required for different storage mechanisms. Nevertheless, performance of supercapacitor also relies on factors such as electrolyte and voltage range of electrochemical system. Materials used for EDLCs typically possess high surface area, whereas PC materials rely on charge transfer mechanism. In this chapter, we are focusing to provide an insight into different electrode materials such as carbon-based materials, conducting polymers, and metal oxide used in supercapacitors.

Supercapacitors are the most advanced, promising, and emerging energy storing devices in the future energy technology. In recent times, rapid progress is made in the development of fundamental and applied aspects related to supercapacitors. Supercapacitors also tender exceptional power density and durability. As such supercapacitors are highly explored for large number of emerging energy storing technologies including mobile devices to address energy storage and harvesting. The testing techniques for supercapacitors due to high specific capacitance require constraints like time constants and as such require suitable adaptations and modifications of the conventional techniques and instrumentation to yield desired estimations. Consequently, the prime importance is paved in terms of developing the testing techniques to determine electrochemical characteristics of novel supercapacitor materials. In this contrast, various state-of-the-art techniques are developed to estimate electrical, thermal, charging/discharging behavior of supercapacitors. This chapter encapsulates the electrochemical techniques dedicated for parameter estimation pertaining to supercapacitors.

The need for energy-storage devices to manage an ever-increasing energy crisis in the industrial world is well recognized. Various technologies are used to meet energy-saving needs. Supercapacitors are of particular interest in a growing number of mobile devices. There are various approaches available to increase the performance of supercapacitors and to find new materials possessing higher energy and power density. At the same time, the inherent characteristics of the new materials for high power generation/storage/discharge with regard to life-cycle also need to be improved. Carbon-based nanocomposites are heavily used in emerging supercapacitors. This review mainly focuses on the recent developments on unzipped multiwalled carbon nanotube (UzMWCNT) via various routes and Mxenes towards energy storage applications.

Electrochemical capacitors (supercapacitors) play a key role in the development of new technologies for energy storage applications. However, their energy density must be increased to enable their use in a wider range of applications. One of the main strategies focuses on the improvement of the performance of carbon electrodes. These materials display excellent properties such as well-developed porosity, adequate pore size distribution, and tunable surface chemistry. Nevertheless, their degradation under high voltage conditions is one of the main drawbacks of the production of devices with an enhanced response. Different approaches have been proposed for designing carbon materials with improved properties for electrochemical applications. In this review, we propose different methodologies for the synthesis of carbon materials with enhanced electrochemical properties from two different points of view: carbon morphology and surface chemistry. These methodologies and their effect on the electrochemical performance are thoroughly discussed from a fundamental point of view as well as a practical technological application.

Hybrid supercapacitors (HSCs) are made by the combination of electric double-layer capacitor (EDLC) materials, various types of pseudocapacitive, and battery-type materials. The progress made on the improvement of energy density without sacrificing the power density attracted the researchers to move toward HSC. The specific capacitance of the HSC showed a superior value than the EDLC or pseudocapacitance-based supercapacitors. Numerous advancements have been made on the HSCs with the development in preparation of electrode materials, electrolyte, formation of component, device structure, and the new mechanisms for the improvement of electrochemical characteristics. This chapter specifically emphasis the new development made on the HSCs based on the layered double hydroxides, metal–organic frameworks (MOFs), MOF-derived materials and their composites. The specific characteristics requirement of the electrode material, electrolyte, the substrate in support of electrode materials, and the progress made on them for smart supercapacitors are discussed.

Supercapacitors are the modern-day state-of-the-art energy storing devices based on the electrochemical conversion principles. The supercapacitors are portrayed as energy-storing devices analogous to batteries and fuel cells. The supercapacitors, however, differ in the characteristics and hence are dedicated for diverse applications. The supercapacitors comprise five components in its configuration, namely, electrode, electrolyte, separator, current collector, and sealants. The two main characteristic components of the supercapacitor on which most of the properties are determined to include electrode and electrolytes. The electrode and electrolyte perform the fundamental operations in supercapacitors. This chapter is dedicated toward the electrolytes that are essential for supercapacitors in terms of operating potential and their applicability. The supercapacitor fundamentals along with different types of electrolytes are discussed along with their properties.

Supercapacitors are energy storage devices that are designed on the mechanism of ion adsorption from an electrolyte due to its greater surface area of the electrode materials. Supercapacitor performance has significantly improved over last decade as electrode materials have been tailored at the nanometer scale and electrolytes have achieved a significant interest, supporting more effective storage mechanisms. Desolvation of the ions effects in remarkably high capacitances in carbon-based materials with nanopores. The pseudo-capacitive effect is caused by surface redox reactions in oxide materials. Understanding the storage mechanisms underlying charge storage in these materials is important for sustainable development of supercapacitors in the future. We summarize current progress in understanding the charge storage mechanism in carbon- and oxide-based supercapacitors, and also challenges that still need to be overcome in order to build better supercapacitors.

Electrical sensors, flexible displays, and health monitors are examples of wearable electronic gadgets that have recently received high impact and have moved continuously in the direction of progress. Wearable supercapacitors have piqued attention because of their high steadiness, cheap cost, rapid charging/discharging, and high efficiency, all of which make them perfect for producing completely flexible electronics. This concept focuses on the potential performance of yarn-shaped and planar supercapacitors, as well as recent advances and triumphs in flexible and wearable supercapacitors. The working mechanisms of electrode materials such as carbon-based materials, different types of metal oxide-based materials, and conductive polymers are discussed, with a focus on performance improvement. A summary of the most recent representative techniques and active materials of freshly created high-performance supercapacitors is presented. Furthermore, the electrically conductive supporting materials for 1D and 2D electrode designs are investigated.

Modern electronic devices and electrical transportation systems are powered by batteries, solar cells, and supercapacitor-based energy devices. The current trend is to employ smart-hybrid supercapacitors that are engineered to store and deliver sustainable and renewable energy to meet the energy needs of electric transportation and wearable gadgets. Smart-hybrid supercapacitors are found to have potential in developing superior energy devices (with increased specific capacitance, energy-storing capability, and high durability). Currently, electronic devices are inevitable in the digital world to be employed for multitasking toward betterment of life. The electric vehicle market is growing in order to provide a sustainable and renewable way of energy-efficient transportation. To improve the performance of these electrical vehicles, functionalized smart-hybrid supercapacitors are employed. In recent years, intense research work is carried out on smart-hybrid supercapacitors to provide extended service lifetime, proficient energy storage as well as pollution-free, and sustainable technology for energy storage and other related devices. A plethora of research works has been reported on engineering supercapacitors and their utilization in the construction of electronic devices and electric vehicles. This chapter discusses in detail about the working mechanism, fabrication techniques, optimization of configuration, electrode technology, and application of smart-hybrid supercapacitors in modern electronic systems with an emphasis on transportation technology. Further, characteristics like self-charging, self-healing, self-protection, stretchability, shape memory, sensing, electrochromism, photo-switching, and photodetection are also reviewed. An outlook of the existing technological challenges in the development of smart-hybrid supercapacitors is also elucidated.