1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 z Energy Technology & Environmental Science Sweet-Lime-Peels-Derived Activated-Carbon-Based Electrode for Highly Efficient Supercapacitor and Flow-Through Water Desalination Dinesh J. Ahirrao, [a] Sneha Tambat, [b] A. B. Pandit, [b] and Neetu Jha* [a] In the present work, highly porous activated carbon with an excellent surface area has been successfully synthesized from the agricultural waste product; sweet lime peels (Citrus limetta) using a facile chemical approach. The structural and morpho- logical properties of sweet lime peels derived activated carbon (SLP-AC) were studied using X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Brunauer-Emmett-Teller (BET) surface area and pore structure were studied using nitrogen adsorption-desorption isotherms. Electrochemical characterizations were performed in two and three electrode cell configurations using techniques like cyclic voltammetry (CV), Galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS) in aqueous (1 M H 2 SO 4 and 1 M NaCl) and ionic liquid electrolytes (EMIMBF 4 ). SLP-AC based electrodes showed high electrochemical charge storage ca- pacity of 421.67 F/g (at 1 A/g) along with outstanding cyclic stability up to 10000 GCD cycles. Fabricated supercapacitor device demonstrated high energy density of 45.53 Wh/kg in the ionic liquid electrolyte. SLP-AC was also used to prepare the porous sponge electrodes to study their applicability in flow-through electrode capacitive deionization (CDI), where it achieved the maximum electrosorption capacity of 22.8 mg/g. The electrosorption results fitted well with the Langmuir isotherm and the kinetics study indicates a pseudo-first-order kinetic model for the electrosorption of salt ions onto the electrodes surface. This confirms the outstanding performance of SLP-AC as a highly stable and low-cost electrode material for supercapacitors and water desalination applications. Introduction Waste management is a global issue, which needs immediate attention to evade further consequences. In India, per capita waste generation, in cities is in the range of 200 to 600 grams per day. With the alarming increase in population growth, this rate of waste production will continue to increase. According to the report provided by the ministry of environment and forest, in the year 2016, India alone is responsible for the production of 62 million tons of waste per annum. Out of this, only 75–80% of the waste gets collected and 22–28% of it is recycled in an environmentally friendly way and rest is allowed to lie in the landfills and forests. The ministry estimated that by the year 2030, waste generation will increase from 62 million tons to about 165 million tons per year. It is an inevitable desire of humankind to get rid of the waste but practically it is very difficult to completely dispose of such a tremendous amount of waste. This is one of the most serious threats to mankind, which needs to be resolved at priority. Majority of waste that is being generated can possibly be the potential precursor for the production of carbon. [1] However, the sum of waste accrues only from the sweet lime is worth noticing, because its production is about 15% per year of a total fruit market and it is one of the most cultivated fruit worldwide. [2] Citrus fruits waste is considered unsafe and has the potential to cause soil pollution if directly deposed into the soil because it releases phenol compounds which decreases the soil fertility. [3] The sweet lime peels are composed of cellulose, hemicelluloses, and pectin. These are well known and excellent natural precursors for the production of carbon. [4] Hence, to avoid its unwanted effects on soil, it is better to process it for the production of high surface area activated carbon for its various promising carbon-based applications like energy storage and desalination. Energy storage devices like supercapacitors (SCs) have gained huge attention in recent times due to their fascinating features like high power density, excellent cycling stability, and high durability. [5] Supercapacitors can be used in the wide range of applications where short-term energy burst is required such as; electric vehicles, power tools, hybrid cars, trains, and buses for the regenerative braking system. Supercapacitors are categorised into two types based on their charge storage mechanisms; pseudocapacitors and electric double layer capacitors (EDLCs). In pseudocapacitors, electrodes are fabri- cated using a metal oxide or conducting polymer, which stores the charges by means of redox reactions (faradically). Unfortu- nately, the practical use of pseudocapacitors is restricted owing [a] D. J. Ahirrao, Dr. N. Jha Department of physics, Department of chemical engineering, Institute Of Chemical Technology, Mumbai-400019, India E-mail: nr.jha@ictmumbai.edu.in [b] S. Tambat, Prof. A. B. Pandit Department of chemical engineering, Institute Of Chemical Technology, Mumbai-400019, India E-mail: nr.jha@ictmumbai.edu.in Supporting information for this article is available on the WWW under https://doi.org/10.1002/slct.201803417 Full Papers DOI: 10.1002/slct.201803417 2610 ChemistrySelect 2019, 4, 2610 – 2625 © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim