Content area
Full text
Introduction
Clean energy and environmental protection are considered two critical components of environmental sustainability. However, the rise in global energy demand, decline of fossil fuels, climate change, and air pollution entails greater use of renewable and sustainable energy sources, necessitating the development of reliable energy storage systems with high ability [1, 2, 3, 4, 5–6]. Also, the massive rise of portable electronic devices and electric vehicles has created a compelling need for high-energy–density storage systems [7]. In the present scenario, there is a pressing need to move focus away from fossil fuels and look toward biomass-derived materials for energy storage and conversion [8].
Electrochemical energy storage devices such as supercapacitors [9, 10], lithium-ion batteries [11, 12, 13, 14–15], and fuel cells [16] are reliable candidates for next-generation energy systems. Among these devices, supercapacitors with higher power density, fast charge–discharge rate, good cycling life, simple means of operation, and greater coulombic efficiency bridge the gap between capacitors and batteries [17, 18]. Supercapacitors find numerous applications in many areas of use, such as electric cars, portable electronic devices, and smart electrical grids [17]. On the basis of charge storage mechanism, a supercapacitor can be grouped into two, namely pseudo capacitor and electric double-layer capacitor (EDLC). In a pseudo capacitor, the charge storage is based on the faradaically collected charge at the surface of the electrode occurring due to the redox reactions [19]. For this purpose, the commonly used electrode materials are metal oxide [20], metal hydroxide [21], metal sulfides [22], and conducting polymers [23]. Whereas for EDLC, the charge is stored on the electrode/electrolyte interface by creating a double layer [24, 25]. This type of charge storage mechanism is found in carbon materials due to their high surface area and conductivity [26].
Carbon is one of the most intensively investigated electrode materials because of its low price, excellent micro to nanopore structure, high surface area, outstanding electrical conductivity, better thermal stability, and corrosion-less properties [27, 28]. The ability of porous carbon materials to shorten the ion diffusion path and buffer charge/discharge volume charge has been well demonstrated for its application towards supercapacitors and batteries [1, 28, 29]. Among several precursors of carbon, biomass is the most potential carbon precursor for producing low-cost porous carbon products like mesoporous...