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Conversion of carbon-containing biomass into useful carbon products is highly demanded. A rising understanding of environmental problems explains the growing focus on evaluating bioproducts and wastes in numerous applications. Herein, the wheat husks derived activated carbon (WHAC) was employed as electrode material for supercapacitors' energy storage. Three samples of activated carbon were made using wheat husks, which were activated at different temperatures. The prepared electrodes were characterized and electrochemically tested using Fourier-transform infrared spectroscopy, X-ray powder diffraction, scanning electron microscope, cyclic voltammetry, galvanostatic charge-discharge, and electrical impedance spectroscopy. The maximum capacitance (271.5 F g−1 at a current density of 0.5 A g−1) was observed for AC-800, activated at 800 °C. The electrochemical impedance showed low resistance (3.659 Ω) and low-frequency response (6.84 s). The AC-800 electrode exhibited the capacitance retention of 82% after 5000 cycles. The excellent electrochemical properties reveal the utilization of biomass waste as a potential electrode material for supercapacitors. The process used is simple, environmentally friendly, and could significantly reduce the county's biomass wastes from wheat husks. The approach can not only reduce environmental pollution but develop porous carbon electrodes for energy storage devices. Image 1 • The wheat husks derived activated carbon was prepared on Ni foam substrate. • The activated carbon was chemically activated by impregnating KOH. • The optimum activation temperature was found to be 800 °C. • The electrode showed a high specific capacitance of 271.5 F/g. • The electrode exhibited high energy, power density and cyclic stability. [ABSTRACT FROM AUTHOR]

Achieving a net-zero target via a circular economy approach necessitates maximizing the recycling of waste into higher-value materials. In the present study, spent coffee grounds (SCG) from industrial food processing biomass waste are converted into a high-performance anode material used in lithium-ion batteries via one-step carbonization of ZnCl 2 at 550 °C. The hybrid composites (HCs) are collected after the process contained C- and Zn-based mixed oxides, such as zinc silicate (Zn 2 SiO 4) and zinc ferrate (ZnFe 2 O 4). The content of Zn-based mixed oxides in HCs increases with the initial ZnCl 2 :SCG mass ratio and reaches its maximum at a ratio of 2:1 wt/wt (HCs_2). The electrochemical performance of the HC-based anodes is proportional to the loaded Zn content when the ZnCl 2 :SCG mass ratio increases from 0 to 2. The optimized anode (HCs_2) exhibits a charge capacity of 692 mAh g−1 and capacity retention of 86 % at the 100th cycle, whereas the corresponding values for HCs_0 anode (without ZnCl 2 treatment) are 311 mAh g−1 and 73.3 %. The superior electrochemical performance of the optimized anode is attributed to the nanosized Zn 2 SiO 4 and ZnFe 2 O 4 , stabilization effect of activated carbon matrices, and a strategy that increases the proportions of high-capacity components. [Display omitted] • ZnCl 2 activation converts spent coffee grounds to valuable hybrid composites (HCs). • The HCs consisting of C-based and Zn-based oxides is prepared via a simple pyrolysis. • Carbon matrices and nanosized Zn-based oxides support to improve electrochemical performance. • HCs_2 electrode exhibits stable cyclability, delivers a capacity of 692 mAh g−1 after 100 cycles. • The HCs are suggested as a low-cost and green anode for advanced lithium-ion batteries. [ABSTRACT FROM AUTHOR]

Conversion of bio-waste into activated carbon is an environmentally friendly approach that reduces the pressure on biowaste disposal. Here we describe the preparation of activated carbon from the biowaste of the lemon peel by carbonization at 400 °C followed by chemical activation employing KOH. The activation parameters like temperature and mass ratio of precursor and KOH are optimized to obtain carbon material of better capacitive performance. The mass ratio and temperature of activation are optimized as 1:1 and 600 °C (ALP-600) respectively by systematic analysis of the capacitive performance of carbon materials in acidic (0.5 M H 2 SO 4) and alkaline (2 M KOH) electrolytes. The superior performance of ALP-600 despite its lower surface area (744.78 m2 g-1) is attributed to its hierarchical porosity as the mesopores improve the capacitive performance by providing connectivity between the pores. ALP-600 delivers a higher specific capacitance of 152.14 Fg-1 and better power rate capability evident from the quasi-rectangular shape of cyclic voltammogram even at a higher scan rate of 100 mVs−1 in the acidic electrolyte. The high energy density of 4.67 Whkg−1 and a high-power density of 8113 Wkg-1 is achieved with the symmetric capacitor. The symmetric capacitor of configuration ALP-600 || 0.5 M H 2 SO 4 || ALP-600 exhibits excellent cycling stability over 10,000 cycles with 99.5% coulombic efficiency and insignificant capacitance loss. • Carbon electrodes are derived from the biowaste of lemon peel by chemical activation employing KOH. • Activation temperature and the mass ratio of precursor and KOH are optimized to achieve hierarchical porosity. • Carbon obtained at the activation condition of 1:1 mass ratio and 600 °C (ALP-600) exhibits excellent capacitive performance. • ALP-600 shows high specific capacitance of 152.14 Fg-1 in 0.5 M H 2 SO 4. • The symmetric capacitor employing ALP-600 retains 99.5% of coulombic efficiency over 10,000 cycles. [ABSTRACT FROM AUTHOR]