Summary Porous carbon 2D nanosheets (CNSs) with micro‐mesopores interconnected are indispensable for energy conversion systems and storage applications. Herein, we synthesize free‐template highly micro‐mesoporous carbon nanosheet as electrode material for boosting supercapacitor performances. The activated carbon nanosheets derived from bio‐waste were prepared by chemical impregnation followed by high‐temperature pyrolysis without hard/soft/salt template‐assisted and free‐binder adhesives. Garlic skin wastes were selected as a precursor. Furthermore, activated carbon was designed in pellet/coin solids without the addition of binder materials. The porous carbon pellets exhibit a thin 2D nanosheet structure of 15 nm followed by unique wooden labyrinth‐like and rod‐like structures. The result showed that the impregnation of different chemical concentrations increases the surface area to 273% as high as 1002.920 m2 g−1 with a total volume of 1.3270 cm3 g−1. Moreover, the mesoporosity dominated 66.4%, followed by sub‐ultra‐micropores. In the symmetric supercapacitor, the carbon nanosheet boosted the specific capacitance almost 3‐fold to 320.95 F g−1 in the aqueous electrolyte of 1 M H2SO4. The supercapacitor cell has a high energy density of 43.12 Wh kg−1 and power density of 161.99 W kg−1 at a constant current density of 1.0 A g−1. This work proposes a more effective, green, efficient, and controlled approach to obtain bio‐waste‐based porous carbon 2D nanosheet with a controlled pore structure for energy conversion and storage systems. Novelty Statement The novelty of this study is a green synthesis has possessed highly micro‐mesopores nanosheet bio‐waste. 2D nanosheet was prepared free‐template and free‐binder. Sub‐ultra‐micropores were confirmed with dominated mesoporosity of 66.8%. Carbon nanosheet boosted specific capacitance almost 3‐fold to 320.95 F g−1.

An environmental approach is needed in the production of activated carbon as electrode material in supercapacitor applications. Activated carbon provides high specific surface area and well-developed pore structures. These circumstances compromise high electrochemical performance for supercapacitor. Therefore, this research focusses on fabricating the activated carbon derived from garlic peels through the chemical activation of potassium hydroxide under various concentrations, combined with 1-integrated stage pyrolysis. The morphology of activated carbon was observed using scanning electron microscopy (SEM), embedded in energy dispersive X-ray (EDS) for analyzing the elemental status. The crystalline degree of the activated carbon was observed using X-ray diffraction (XRD). The electrochemical performances of cell supercapacitor-based-ACM electrodes were evaluated with cyclic voltammetry (CV) and galvanostatic charging-discharging (GDC). The activated carbon was prepared in monolithic form without binder materials and shows a sponge liked-porous structure with high electrochemical performance, including specific capacitance of 204 F g−1, with energy and power of 28.58, 71.16 W kg−1 under current densities 1 A g−1, in the 2-electrode system of 1 M H2SO4 electrolyte. The results showed that using an environmental approach in the production of activated carbon monolithic derived from garlic peels has high electrochemical performance. HIGHLIGHTS Activated carbon was performed in monolithic form Activated carbon monolithic was prepared in low chemically activated ACM was produced without binder material ACM exhibits high specific capacitance of 204 F g-1 GRAPHICAL ABSTRACT

Abstrak. Karbon aktif yang berasal dari biomassa telah menjadi bahan material dasar yang sudah digunakan secara luas untuk berbagai aplikasi eperti penyerapan, absorben, elektroda, penyimpan energi, dan aplikasi lainnya. Oleh karena itu perlu untuk pengoptimalkan sumber mentah karbon aktif berbiaya rendah dan memiliki porositas yang tinggi.  Biomassa kulit bawang putih sebagai bahan dasar pembuatan karbon aktif melalui proses pra-karbonisasi, aktivasi kimia dengan aktivator KOH dan ZnCl2 dengan masing-masing kosentrasi sebesar 0,25 M, 0,5 M, dan 0,75 M dan tanpa aktivator kimia. Proses karbonisasi dengan suhu 600°C dialiri gas nitrogen dan diaktivasi fisika dengan suhu 850°C. Penyusutan massa karbon sebesar 29,4%. Nilai densitas dari elektroda karbon untuk aktivator KOH dengan kosentrasi 0,5M yaitu 0,64 g.cm-3dan untuk aktivator ZnCl2 dengan kosentrasi 0,5M yaitu 0,71 g.cm-3. Gugus fungsi yang dimiliki elektroda kulit bawang putih diidentifikasi sebagai C-C, C C (alkuna), C-H (alkana), dan (O-H) yaitu pada bilangan gelombang 1600 cm-1, 1500 cm-1, 2950 cm-1 dan 2900-3600 cm-1. Hasil penelitian menunjukkan bahwa pada aktivator KOH dan ZnCl2 dengan kosentrasi 0,5 M kondisi terbaik untuk variasi guna menunjang pengoptimalkan sumber mentah karbon aktif dan bisa digunakan dalam berbagai apliasi yang lebih luas. Abstract. Activated carbon derived from biomass has become a basic material that has been used widely for various applications such as absorption, absorbent, electrodes, energy storage, and other applications. Therefore, it is necessary to optimize the raw source of activated carbon which is low cost and has high porosity. Garlic skin biomass as a basic material for making activated carbon through a pre-carbonization process, chemical activation with KOH and ZnCl2 activators with concentrations of 0,25 M, 0,5 M, and 0,75 M respectively and without chemical activators. The carbonization process with a temperature of 600°C is flowed with nitrogen gas and is physically activated at a temperature of 850°C. Shrinkage of carbon by 29.4%. The density value of the carbon electrode for the KOH activator with a concentration of 0.5M is 0.64 g.cm-3 and for the ZnCl2 activator with a concentration of 0,5M is 0,71 g.cm-3. The functional groups possessed by the garlic skin electrode were identified as C-C, C = C (alkynes), C-H (alkanes), and (O-H), namely at the wave numbers 1600 cm-1, 1500 cm-1, 2950 cm-1 and 2900-3600 cm-1. The results showed that the KOH and ZnCl2 activators with a concentration of 0.5 M were the best conditions for variation in order to optimize the raw source of activated carbon and could be used in a wider variety of applications.