The activated carbon electrode made from acacia leaves (Acacia mangium wild) has been developed successfully. The preparation of the electrodes used a combination of chemical and physical activation with temperature variations at 800 °C, 850 °C, 900 °C, and 950 °C. Highest specific capacitance of activated carbon was 113 F g −1 in the two electrode system and showed excellent electrochemical performances. Additionally, activated carbon exhibits 95.73% purity with a specific surface area of 714.492 m 2 g −1 . These excellent results show great potential in developing energy storage devices with high specific capacitance for supercapacitor applications.

BACKGROUND Agro‐industrial co‐products rich in lignocellulose, for example cassava petiole (CP) waste, have high potential as sources of porous carbon materials, alongside other impressive advantages, including ease of acquisition, abundance and availability, renewability and low cost. This work shows the successful treatment of mesoporous carbon with rod‐like structure derived from agro‐industrial CP waste carbonized and physically activated by direct one‐stage integrated pyrolysis using a zinc chloride (ZnCl2) activator agent, in the production of a supercapacitor electrode for energy storage. The ZnCl2 was tested at varying concentrations, including 0.5, 0.7 and 0.9 mol L–1. The surface morphology, chemical content, surface area and porous size distribution were evaluated to determine the physical properties of activated carbon, and a cyclic voltammetry method was used to assess the electrochemical characteristics using a two‐electrode system in 1 mol L–1 H2SO4 as an electrolyte. RESULTS The porous carbon obtained displayed a rod‐like morphology structure, featuring numerous hierarchical tuneable and well‐confirmed micropores and mesopores. This monolithic material contained predominantly C (87.85%), demonstrating a maximum surface area of 759.816 m2 g−1 at 0.9 mol L–1 concentration. Furthermore, the highest specific capacitance reached was 193 F g−1 at 0.7 mol L–1, with maximum energy and power densities of 26.90 Wh kg−1 and 96.94 W kg−1, respectively. CONCLUSION The novel rod‐like mesoporous carbon derived from CP waste produced using a facile, cost‐effective and sustainable method, without metal–organic framework or templates, shows great potential as an electrode material for enhanced supercapacitor performance. © 2020 Society of Chemical Industry (SCI)

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Carbonization and activation have been exploited as an economic and efficient approach toward the production of porous activated carbon monolith derived from green stem of cassava (GSC). In addition, ZnCl 2 was used as a chemical activator agent at various concentrations, therefore serving as a key factor in the development of porous carbon. The carbonization process (N 2) was integrated with physical activation (CO 2), and then N 2 sorption, scanning electron microscopy, X-ray diffraction, energy dispersive X-ray were examined to evaluate the specific surface area, pore structure characteristic, morphology structure, crystallinity, and the surface element, respectively. Furthermore, cyclic voltammetry was used to measure the electrochemical performance, through a two-electrode system in 1M H 2 SO 4. Therefore, the synthesized porous activated carbon exhibits a micropores-mesopores combination, and the optimized sample demonstrated nanosheet and nanofiber structures. The results show a high electrochemical behavior in 1M H 2 SO 4 electrolytes, by the electrodes, with specific capacitance, energy, and power densities of 164.58 F g −1 , 22.86 Wh kg −1 , and 82.38 W kg −1 , respectively. This route confirms the opportunity of using novel GSC in the production of porous carbon monolith with nanosheet/nanofiber structure for supercapacitor applications. K E Y W O R D S activated carbon, carbon porous, green stem of cassava, monolith, supercapacitor 1 | INTRODUCTION Green, renewable, and sustainable sources of energy systems are obtainable through the conversion of wind, water, and solar energy, 1 hence proper capture and storage is required for environmental friendly and economic application. 2 Meanwhile, supercapacitors possessing high power density, high charge-discharge rate, long cycle life, have the ability to store energy in the form of electric charges, 3 by providing a performance between capacitors and batteries. Conversely, the difference between both is that capacitors store and deliver energy incredibly quickly, while batteries have an ability to store high energy densities and also high voltages. 4 However, the main challenge of supercapacitor is related to the energy density entry through the narrow gap of batteries. Several electrode materials have been developed and suggested to improve energy density, power density, and cycle life of supercapacitor, 5 and three types were identified. These were then classified into carbonaceous

A three-dimensional pore structure on activated carbon derived from hierarchically bamboo stem was synthesized in the monolithic form for increased applicability as a supercapacitor electrode. The preparation involved two step carbonizations, using a chemical activation at different concentrations. Subsequently, the morphology, chemical content, specific surface area and pore size distribution, as well as crystalline degree were evaluated with scanning electron microscopy, energy X-ray (EDX), N2 sorption and X-ray diffraction, respectively. Therefore, cyclic voltammetry (CV) was used to assess the electrochemical performance, in a two electrode system. The result shows the significant impact of the three-dimensional structure on electrochemical performance, and the optimized sample exhibited specific capacitance of 168.8 F g-1, energy density of 23.44 Wh kg-1, and power density of 84.46 W kg-1.

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Various eggs shell membranes (ESMs) have been used as a separator for supercapacitor application. The separator was prepared from different membranes such as chicken eggs shell membrane (CESM), duck eggs shell membrane (DESM) and goose eggs shell membrane (GESM). The ESMs were tested as a separator in a two-electrode system, the sandwich-type supercapacitor cell consists of two activated carbon monoliths as electrodes, two stainless steel as current collectors and 1 M H2SO4 solution as an electrolyte. The electrochemical performance of the ESMs was characterized by an electrochemical impedance spectroscopy, a cyclic voltammetry and a galvanostatic charge-discharge. The results of this study exhibit all of the ESMs as a good candidate for supercapacitor separator. However, the CESM was shown excellence electrochemical properties, such as low resistance, high energy density and power density. The scanning electron microscope (SEM) micrograph and X-ray diffraction analysis were also proved that the ESMs are a promising low-cost separator for supercapacitor application.