## 3 Applications of IL-Based Gels
### Supercapacitors  
Electrochemical capacitors, commonly referred to as supercapacitors (SCs), are considered as promising energy storage devices that store electrical energy at the interface between the electrode and electrolyte. Recently, SCs have attracted increasing attention because of their high power density (\(\sim\)10 kW kg\({}^{-1}\)), outstanding cyclic stability (\(\sim\)1,000,000 cycles), fast charge-discharge rate, and superior safety while keeping a reasonable energy density [104]. Micro-supercapacitors (MSCs) offering high-energy and power performance are known as a class of supercapacitors with a miniaturized configuration. SCs and MSCs are emerging as high-performance electrochemical energy storage and clean renewable energy generation devices that supply power for various electronic devices, including hybrid vehicles, portable electronics, military devices, space equipment, next-generation electric cars, microdevices, and internet of things. Based on the energy storage principle, SCs can be classified into two types, i.e., electric double layer capacitor (EDLC), where charge is stored through fast ion adsorption at the electrode/electrolyte interface, and pseudocapacitor, which stores electrical energy by reversible redox reactions at the surface of the electrodes. Traditionally, liquid electrolytes have been used in SCs, which is often associated with several drawbacks such as narrow potential window, limited cycle stability, and possibility of leakage. IL-based gel electrolytes exhibiting a wide potential window, less volatility, high conductivity, and good mechanical strength are considered an advantageous alternative to typical liquid electrolytes [105]. To date, efforts have been made towards the fabrication and design of highly efficient SCs and MSCs with IL-based gel electrolytes [106; 107; 108]. Among the various SCs, lithium ion capacitors (LICs) are reported to be a promising energy storage device that combines the high energy density of batteries and high power density of SCs [109]. Recently, carbon-based materials such as carbon black, activated carbon (AC) CNTs, graphene, and reduced graphene oxide (rGO) have also been used intensively as electrodes in SCs due to their high specific area and remarkable conductivity [110]. In 2015, [PERSON] and coworkers fabricated an SC using modified rGO electrodes with IL-based gel electrolyte consisting of EMIMBF\({}_{4}\) IL and P(VDF-HFP). The SCs showed a high specific capacitance (Csp) of 242 F g\({}^{-1}\) at 5 mV s\({}^{-1}\) and a charge/discharge stability up to 12,000 cycles [111]. By using a BMPTFSI/PMMA electrolyte and graphene electrode, [PERSON] et al. assembled a high-performance SC possessing a specific capacitance, energy density, and power density of 83 F g\({}^{-1}\), 25.7 Wh Kg\({}^{-1}\), and 35.2 kW kg\({}^{-1}\), respectively. [112]. Similarly, [PERSON] and colleagues reported the construction of SCs using P(VDF-HFP)/EMIMTFSI electrolyte and polydimethylsiloxane/CNT electrodes, which exhibited a superior capacitance retention of 96.6% for up to 3000 cycles [113]. In 2018, [PERSON] et al. introduced a (1.4-di(vinylimidazolium)butane bisbro-mide) (DVIMBr) and 2-hydroxyethylmethacrylate (HEMA)-based IL-based gel electrolyte in 1-butyl-3 methylimidazolium hexafluorophosphate (BMIMPF\({}_{6}\)) IL solvent for EDLC application [105]. The supercapacitor with IL-based gel electrolytes showed promising performance with a specific capacitance of 1.5-3 mF cm\({}^{-2}\), as revealed from electrochemical tests. In the same year, [PERSON] et al. reported an aligned IL-based gel prepared by UV-copolymerization of N,N-dimethylacrylamide (DMAA) and BMIMBF\({}_{4}\) IL for high-temperature SCs with a specific capacitance of 176 F g\({}^{-1}\) at 25\({}^{\circ}\)C using carbon nanocage electrode materials [114]. Meanwhile, [PERSON] et al.