Eco‐Friendly and High Performance Supercapacitors for Elevated Temperature Applications Using Recycled Tea Leaves

Abstract

energy supply are required. Hence, an efficient local energy storage/production system plays a vital role for such applications. [1] The supercapacitor is one of the efficient energy storage systems which can store energy via electric double layer and faradic reactions. [2,3] The electric double layer capacitor (EDLC) stores the charge over the active surface area of the material and shows very durable performance over long period. [3,4] Thus, creating carbon with a high surface area could be one of the ways to improve the performance of EDLC-based supercapacitor devices. There are several publications documenting the utilization of waste-derived carbon source such as seeds, seed shells, leaves, bagasse, waste paper, and tyre. [5][6][7][8][9][10][11][12] Waste tea is an additional exciting source for carbon. [13] Most of the time, an activation step is required to achieve the high surface area to enhance the performance of the carbon. Activation of waste-derived carbon can be done using various methods including chemical, steam, and CO 2 -based activation. [14][15][16][17] For example, steam activated carbon from fir wood showed an activated surface area of 1131 m 2 g −1 while, CO 2 activated empty fruit bunches of palm showed a surface area of 1704 m 2 g −1 . [12,13] KOH activation is the most popular way to create high surface area and Used tea leaves are utilized for preparation of carbon with high surface area and electrochemical properties. Surface area and pore size of tea leaves derived carbon are controlled by varying the amount of KOH as activating agent. The maximum surface area of 2532 m 2 g −1 is observed, which is much higher than unactivated tea leaves (3.6 m 2 g −1 ). It is observed that the size of the electrolyte ions has a profound effect on the energy storage capacity. The maximum specific capacitance of 292 F g −1 is observed in 3 m KOH electrolyte with outstanding cyclic stability, while the lowest specific capacitance of 246 F g −1 is obtained in 3 m LiOH electrolyte at 2 mV s −1 . The tea leaves derived electrode shows almost 100% capacitance retention up to 5000 cycles of study. The symmetrical supercapacitor device shows a maximum specific capacitance of 0.64 F cm −2 at 1 mA cm −2 and about 95% of specific capacitance is retained after increasing current density to 12 mA cm −2 , confirming the high rate stability of the device. An improvement over 35% in the charge storage capacity is seen when increasing device temperature from 10 to 80 °C. The study suggests that used tea leaves can be used for the fabrication of environment friendly high performance supercapacitor devices at a low cost.

Waste Coffee Management: Deriving High-Performance Supercapacitors Using Nitrogen-Doped Coffee-Derived Carbon

“…This could be due to increased nitrogen content within the carbon resulting in improved graphitic structure even after activation, as observed in previous reports [11,26]. The graphitization ratio of CP-NA was much higher than that of previously reported N, P co-doped activated coffee and ZnCl 2 activated coffee shell samples [9,10].…”

“…Phosphorous and nitrogen co-doped activated carbon from spent coffee grounds was synthesized using ammonium polyphosphate via microwave-assisted synthesis [10]. In our previous studies, we have reported facile production of bio-waste-derived activated carbons using KOH activation, for supercapacitor applications [11][12][13][14][15][16]. Utilizing the KOH activation technique, we have demonstrated varied pore size distribution, control over the surface area of activated carbons and a resulting promising charge storage performance of the device.…”

Electrodeposited Nanostructured CoFe2O4 for Overall Water Splitting and Supercapacitor Applications

“…Higher specific capacitance values were observed with decreasing scan rates. A similar behavior was observed in other reports of energy storage systems [28,[42][43][44]. The CV curves of CoFe 2 O 4 ED@NF in 3M KOH electrolyte at various scan rates are given in Figure S7a.…”

“…This could be the result of sufficient time provided for redox reactions at low current densities. Redox reactions promoted at low current densities lead to better charge storage compared with other non-faradic systems [43][44][45][46]. At a current density of 0.5 A/g, a high specific capacitance of 768 F/g was observed.…”

Highly flame‐retardant polyurethane foam based on reactive phosphorus polyol and limonene‐based polyol

“…Comparison of Raman spectra for foams with 0%, 1%, and 2% phosphorus can be observed from Figure . Phosphorus‐containing burnt foams showed two peaks around 1350 and 1560 cm −1 representing diamond and graphitic phase of carbon, respectively . Ratio of intensities of diamond ( I d ) and graphitic phase ( I g ) determines the structure of char.…”