**1. Introduction**

Over the century, the evolution of electronic devices has been rehabilitated rapidly and day by day. The transistor incorporation led to reducing the feature size of any realistic instruments, and besides that, the efficacy has to be ameliorated for that purpose. The continual advancement of the fabrication methodologies of printed circuit boards makes the transistors significantly small, permitting the huge number of transistors in one plate and lessen the consumption of electric power of the integrated circuit. In the present day, many electronic devices are used in miniature sizes and too much power for any operation. Subsequently, energy

storage devices are required in the same formation used in those new small devices, batteries, and capacitors, which are hindrances to their improvement. The batteries are analysed, which are lower of flexibility, higher weight, and mainly possess huge space in the particular equipment. Generally, the capacitors with low storage capacity with low energy occupy a huge space, mainly electrolytic capacitors, restrained by shape. Moreover, the capacitors need to solder directly to the integrated circuit; their electrical polarity cannot be reversed in electrolytic capacitors. In this scenario, this chapter explores a probable elucidation to the above-said context based on IPMC (ionic polymer-metal composite) systems. These attain capacitive features after dipping in the ionic solution; then, the membrane becomes flexible and lightweight with stored potential, a new kind of flexible capacitor. Furthermore, the flexible IPMC membrane capacitor is malleable and easily used in polarity reversal based on needs. In most cases, the analysis and application of the IPMC polymer matrix entirely focused on the actuator's application [1–5]. This chapter focused on another part of IPMC, i.e., the energy storage application. The different fabrication procedures and corresponding attributes of the polymer system are discussed thoroughly here. Prominent displacements analyse IPMCs within lower density forces. In the mechanical energy harvesting system, IPMCs are investigated using the generated lower electric power values, but irrespective of using significant mechanical pressures, the reverse function is happened as with the piezoelectric type materials [6, 7]. Present-day, electric double-layer capacitors (EDLCs) and lithium-ion batteries are the maxima used energy storage devices on the scale of important commercial use. Every device exhibits definite attribution and applications that need high energy density (Whkg�<sup>1</sup> ) for lithium batteries and high power density (Wkg�<sup>1</sup> ) of EDLC system [8–11]. Furthermore, few polymers depict several characteristics changes and some benefits in the potential application field in the presence of electrical stimulation; those are called electro-active polymers or EAPs. Those materials are showing response in size and shape by the variation of electrical stimulation. This material is categorised into two depending on the activation mechanism, i.e., ionic and electronic or field-activated [12, 13]. Generally, the electronic grade exhibits a higher energy density of mechanical energy; in comparison, ionic systems potentially employed ion diffusion or transportation consist of the electrolyte-electrode interface. Conductive polymers, ionic polymer gels, and composites of ionic polymer-metal are examples of some ionic EAPs. The electromechanical response of the membrane, showing huge strain at electrical stimulation, is very similar to the biological tissues. The Ionic polymers are introduced in fuel cells application in the 1960s; the features of EAP and the connexion of electromechanical ion-transportation of metal-ionic polymer composites (IPMC) were invented in 1992 by researchers in the United States and Japan [14, 15]. In general, IPMC comprises a membrane of polyelectrolyte, normally Flemion or Nafion covered on all sides with a conductive metal. After that, the counter-ions are neutralised, stabilising the electrical anionic charge of the covalently stable to the pillar of the membrane. The hydrated cations transportation between an IPMC polymer matrix is kept within the voltage applied, and corresponding electrostatic interactions enhance the bending. IPMCs are the working actuator that delineates lower impedance. Moreover, the water-based IPMCs generally dissociate with solvent content when it is subjected to 1.23 Volts higher. IPMCs are corroborated as the smartest prominence materials for larger bending deformation and lighter weight within significantly less applied voltages [16–18]. However, To fabricate chemically coated IPMC membrane, electrodes of metal ions gold, platinum, etc., are distributed through the hydrophilic sections of the polymer matrix and generally decrease the consistent metal atoms of zero-valence. Paddison et al. [19] researched the measurement of hydrated Nafion's permittivity in the

range of broadband frequency. Their outcomes denote that the dielectric constant enhances with incrementing the water content, reduced with frequency increase.
