Sweet-Lime-Peels-Derived Activated-Carbon-Based Electrode for Highly Efficient Supercapacitor and Flow-Through Water Desalination

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 morphological 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 H2SO4 and 1 M NaCI) and ionic liquid electrolytes (EMIMBF4). SLP-AC based electrodes showed high electrochemical charge storage capacity 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.