From Trash to Treasure: Direct Transformation of Onion Husks into Three-Dimensional Interconnected Porous Carbon Frameworks for High-Performance Supercapacitors in Organic Electrolyte

Porous Carbon Electrode Made of Biomass DNAs for High-Efficiency Quasi-Solid-State Supercapacitor

Since companies have declared their commitment to operating with 100% renewable energy, developing electrical storage systems using natural eco-friendly resources is in full swing. Efforts to replace existing materials in core electrode materials are accelerating, but the use of toxic chemicals in the complex production process is decreasing its value. This study presents a unique porous carbon electrode made of pure biomass DNA wastes synthesized simply via a single step of hydrogelation-calcination without activation through carbonization. Electrochemical analysis of the electrodes revealed energy storage performance with an outstanding specific capacitance of 563.34 F g-1 at 1 A g-1. The QSSC exhibited an energy density of 13.05 Wh kg-1 and a power density of 486.67 W kg-1. It was connected to a solar panel for renewable energy storage and successfully powered a digital clock and LEDs (Light Emitting Diode), demonstrating the potential of advanced sustainable and cost-effective energy storage solutions.

Crafting the architecture of biomass-derived activated carbon via electrochemical insights for supercapacitors: a review

Escalating energy demands have often ignited ground-breaking innovations in the current era of electrochemical energy storage systems. Supercapacitors (SCs) have emerged as frontrunners in this regard owing to their exclusive features such ultra-high cyclic stability, power density, and ability to be derived from sustainable sources. Despite their promising attributes, they typically fail in terms of energy density, which poses a significant hindrance to their widespread commercialization. Hence, researchers have been exploring different cutting-edge technologies to address these challenges. This review focuses on biomass-derived activated carbon (BDAC) as a promising material for SCs. Initially, the methodology and key factors involved in synthesising BDAC, including crafting the building blocks of SCs, is detailed. Further, various conventional and novel material characterization techniques are examined, highlighting important insights from different biomass sources. This comprehensive investigation seeks to deepen our understanding of the properties of materials and their significance in various applications. Next, the architectural concepts of SCs, including their construction and energy storage mechanisms, are highlighted. Finally, the translation of the unravelled BDAC metrics into promising SCs is reviewed with comprehensive device-level visualisations and quantifications of the electrochemical performance of SCs using various techniques, including cyclic voltammetry (CV), galvanostatic charge-discharge test (GCD), electrochemical impedance spectroscopy (EIS), cyclic tests (CT), voltage holding tests (VHT) and self-discharge tests (SDT). The review is concluded with a discussion that overviews peanut-shell-derived activated carbon as it is a common and promising source in our geographical setting. Overall, the review explores the current and futuristic pivotal roles of BDAC in the broad field of energy storage, especially in SC construction and commercialisation.

Potential Development of Porous Carbon Composites Generated from the Biomass for Energy Storage Applications

Creating an innovative and environmentally friendly energy storage system is of vital importance due to the growing number of environmental problems and the fast exhaustion of fossil fuels. Energy storage using porous carbon composites generated from biomass has attracted a lot of attention in the research community. This is primarily due to the environmentally friendly nature, abundant availability in nature, accessibility, affordability, and long-term viability of macro/meso/microporous carbon sourced from a variety of biological materials. Extensive information on the design and the building of an energy storage device that uses supercapacitors was a part of this research. This study examines both porous carbon electrodes (ranging from 44 to 1050 F/g) and biomasses with a large surface area (between 215 and 3532 m2/g). Supposedly, these electrodes have a capacitive retention performance of about 99.7 percent after 1000 cycles. The energy density of symmetric supercapacitors is also considered, with values between 5.1 and 138.4 Wh/kg. In this review, we look at the basic structures of biomass and how they affect porous carbon synthesis. It also discusses the effects of different structured porous carbon materials on electrochemical performance and analyzes them. In recent developments, significant steps have been made across various fields including fuel cells, carbon capture, and the utilization of biomass-derived carbonaceous nanoparticles. Notably, our study delves into the innovative energy conversion and storage potentials inherent in these materials. This comprehensive investigation seeks to lay the foundation for forthcoming energy storage research endeavors by delineating the current advancements and anticipating potential challenges in fabricating porous carbon composites sourced from biomass.

Asymmetric Supercapacitors Based on ZnCo2O4 Nanohexagons and Orange Peel Derived Activated Carbon Electrodes

Herein, the performance of asymmetric supercapacitors (ASC) fabricated using ZnCo2O4 (ZCO) nano-hexagons and orange peel-derived activated carbon (OPAC) as electrodes was studied. ZCO was prepared by a double hydroxide method and OPAC was prepared from orange peel followed by KOH activation. For ZCO, the calcination temperature was determined using TGA analysis. The XRD showed the presence of a cubic spinel structure. The chemical structure was analyzed using XPS, FTIR, and Raman spectroscopy respectively. For OPAC, the presence of an amorphous nature was inferred; FTIR and Raman studies indicate the presence of functional groups and defect structure in the material. The presence of ZCO nano-hexagons was observed from SEM and TEM respectively. For OPAC, an interconnected pore structure was observed from the SEM image. The specific capacitance for ZCO and OPAC was found to be 194 F.g-1 and 159 F.g-1 at a current density of 0.25 A.g-1. Further, an ASC was fabricated using ZCO as a positive and OPAC as a negative electrode in 2M KOH-soaked separator. A cell voltage of 1.2 V was achieved and the specific capacitance was calculated to be 64 F.g-1 at 0.25 A.g-1. Further, the cyclic stability and the changes at the electrode/electrolyte interface were studied.

Structural and Electrochemical Evolution of Water Hyacinth-Derived Activated Carbon with Gamma Pretreatment for Supercapacitor Applications

This study introduces a gamma pretreatment of water hyacinth powder for activated carbon (AC) production with improved electrochemical properties for supercapacitor applications. The structural and morphological changes of post-irradiation were meticulously analyzed using scanning electron microscopy (SEM), Raman spectroscopy, Fourier-transform infrared spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET) analysis, and X-ray photoelectron spectroscopy (XPS). The pretreatment significantly modifies the pore structure and reduces the particle size of the resulting activated carbon (WHAC). Nitrogen adsorption-desorption isotherms indicated a substantial increase in micropore volume with escalating doses of gamma irradiation. Electrochemically, the activated carbon produced from pretreated WH at 100 kGy exhibited a marked increase in specific capacitance, reaching 257.82 F g-1, a notable improvement over the 95.35 F g-1 of its untreated counterpart, while maintaining 99.40% capacitance after 7000 cycles. These findings suggest that gamma-pretreated biomasses are promising precursors for fabricating high-performance supercapacitor electrodes, offering a viable and environmentally friendly alternative for energy storage technology development.

Enhancement of CO2 adsorption on activated carbons produced from avocado seeds by combined solvothermal carbonization and thermal KOH activation

A new strategy for ultramicroporous activated carbons production from avocado seeds was developed. Combined solvothermal carbonization and thermal KOH activation were conducted. Solvothermal carbonizations were performed in a stainless-steel autoclave lined with Teflon at the temperature of 180 °C for 12 h in three different liquids (water, methanol, isopropyl alcohol). Chars were activated by KOH. The carbonization combined with activation took place in the oven at 850 °C for 1 h. All the samples were very good CO2 sorbents. The highest CO2 adsorption at a pressure of 1 bar was achieved for activated carbon produced using isopropanol. The best carbon dioxide adsorption was equal to 6.47 mmol/g at 0 °C and 4.35 mmol/g at 20 °C.

Investigation of CO2 Adsorption on Avocado Stone-Derived Activated Carbon Obtained through NaOH Treatment

Activated carbons were prepared from avocado stone through NaOH activation and subsequent carbonization. The following textural parameters were achieved: specific surface area: 817-1172 m²/g, total pore volume: 0.538-0.691 cm³/g, micropore volume 0.259-0.375 cm³/g. The well-developed microporosity resulted in a good CO₂ adsorption value of 5.9 mmol/g at a temperature of 0 °C and 1 bar and selectivity over nitrogen for flue gas simulation. The activated carbons were investigated using nitrogen sorption at -196 °C, CO₂ sorption, X-ray diffraction, and SEM. It was found that the adsorption data were more in line with the Sips model. The isosteric heat of adsorption for the best sorbent was calculated. It was found that the isosteric heat of adsorption changed in the range of 25 to 40 kJ/mol depending on the surface coverage. The novelty of the work is the production of highly microporous activated carbons from avocado stones with high CO₂ adsorption. Before now, the activation of avocado stones using NaOH had never been described.

Review on upgrading organic waste to value-added carbon materials for energy and environmental applications

Value-added materials such as biochar and activated carbon that are produced using thermo-chemical conversion of organic waste have gained an emerging interest for the application in the fields of energy and environment because of their low cost and unique physico-chemical properties. Organic waste-derived materials have multifunctional abilities in the field of environment for capturing greenhouse gases and remediation of contaminated soil and water as well as in the field of energy storage and conversion. This review critically evaluates and discusses the current thermo-chemical approaches for upgrading organic waste to value-added carbon materials, performance enhancement of these materials via activation and/or surface modification, and recent research findings related to energy and environmental applications. Moreover, this review provides detailed guidelines for preparing high-performance organic waste-derived materials and insights for their potential applications. Key challenges associated with the sustainable management of organic waste for ecological and socio-economic benefits and potential solutions are also discussed.

Sustainable recycling of waste polystyrene into hierarchical porous carbon nanosheets with potential applications in supercapacitors

Herein, polystyrene waste was carbonized into mesoporous carbon nanosheets (CNS) using the template method. The pore structure of the obtained CNS was further tuned by KOH activation, resulting in the formation of hierarchical porous carbon sheets with a specific surface area of 2650 m² g^-1 and a pore volume of 2.43 cm³ g^-1. Benefiting from these unique properties, in a three electrode system, the hierarchical porous carbon sheets displayed a specific capacitance of 323 F g^-1 at 0.5 A g^-1 in a 6 M KOH electrolyte, good rate capability (222 F g^-1 at 20 A g^-1) and cycle stability (92.6% of capacitance retention after 10 000 cycles). More importantly, an energy density of 44.1 Wh kg^-1 was also displayed with a power density of 757.1 W kg^-1 in an organic electrolyte. In this regard, the present strategy demonstrates a facile approach for recycling plastic waste into high value-added products, which will potentially pave the way for the treatment of plastic waste in the future.

An ionic liquid-modified reduced graphene oxide electrode material with favourable electrochemical properties

The supercapacitor assembled by a RGO–IL material showed an outstanding energy density (50.19 W h kg⁻¹) and could light an LED for 30 s.

Hydrothermal carbonization of various lignocellulosics: Fuel characteristics of hydrochars and surface characteristics of activated hydrochars

In the present study, various lignocellulosic biowastes (wood sawdust, olive pomace, walnut shell, apricot seed, tea stalk, hazelnut husk) were hydrothermally carbonized at 220 °C for 90 min. Since the hydrochars have several end-uses, this study particularly investigates their end-use as solid fuels and precursors of activated carbon after chemical activation. Activated hydrochars were obtained from the hydrochars of wood sawdust, olive pomace, walnut shell, apricot seed, tea stalk, hazelnut husk by chemical activation with KOH at 600 °C. As fuels, all hydrochars had higher fixed carbon content, lower volatile matter content and higher ignition temperatures compared to their original biomass samples. Olive pomace hydrochar, which has high heating value (25.56 MJ/kg) and low ash content (5.5%), has the best fuel properties among hydrochars investigated. Activated hydrochars demonstrated BET surface areas of 308.9-666.7 m²/g (activated hydrochar of wood sawdust and tea stalk), and total pore volumes of 0.25-0.73 cm³/g (activated hydrochar of olive pomace and wood sawdust). The average pore size distribution of the activated hydrochars ranged between 1.05 nm (olive pomace)- 4.74 nm (wood sawdust). All agricultural-based activated hydrochars had similar average pore size distribution of 1.05-1.25 nm, which fell in the range of super-microporous structure. With the average pore size of 4.74 nm, activated hydrochar of wood sawdust could be classified under mesoporous structure. This study clearly points out that biomass type definitely affected fuel properties of hydrochars and the porous structure of the activated hydrochars.

High performance hierarchical porous carbon derived from distinctive plant tissue for supercapacitor

It is generally acknowledged that the activation method and component of the precursor are of great importance for making porous carbon. In this study, four plant materials belong to one genus were selected as optimized plant material to produce hierarchical porous carbon for supercapacitors, the influence of initial structure was discussed. All the produced porous carbons have large specific surface area (higher than 2342 m² g⁻¹), high microporosity (more than 57%), and high pore volume (larger than 1.32 cm³ g⁻¹). All the samples show characteristic of electrical double layer capacitance, and the onion-based porous carbon obtain highest specific capacitance of 568 F g⁻¹ at the current density of 0.1 A g⁻¹. With the current density rising from 1 A g⁻¹ to 50 A g⁻¹, the specific capacitance only decreases for 20%. After 5000 cycles, all the samples show relatively high capacitance retention (up to 97%). Two-step acid pickling has washed most impurities and directly lead to small equivalent series resistance (lower than 0.2 Ω). The samples show high power density and energy density (71 W h kg⁻¹@180 W kg⁻¹, 210 kW kg⁻¹@33 W h kg⁻¹). This study open an avenue to create high-performance hierarchical porous carbon based on plant architecture.

Nitrogen self-doped activated carbons via the direct activation of Samanea saman leaves for high energy density supercapacitors

In this study, nitrogen self-doped activated carbons (ACs) obtained via the direct activation of Samanea saman green leaves (SSLs) for high energy density supercapacitors were investigated. The SSL-derived direct-activated carbons (hereinafter referred to SD-ACs) were synthesized by impregnating sodium hydroxide as an activating agent and heating up to 720 °C without a hydrothermal carbonization or pyrolysis step. The optimum condition was investigated by varying the weight ratio of raw SSLs to NaOH. Surpassing the ACs derived from the two-step convention method, SD-ACs showed superior properties, including a higher surface area (2930 m2 g-1), total pore volume (1.37 cm3 g-1) and nitrogen content (4.6 at%). Moreover, SD-ACs exhibited enhanced electrochemical properties with specific gravimetric and volumetric capacitances of 179 F g-1 and 88 F cm-3 in an organic electrolyte, respectively, a high capacitance retention of approximately 87% at a current density of 0.5 A g-1 and excellent cycling stability of 97.5% after 3000 cycles at a current density of 5 A g-1. Moreover, the potential window of the supercapacitor cell was extended to 3.5 V with a significantly enhanced energy density of up to 79 W h kg-1. These results demonstrate that the direct activation of nitrogen-enriched SSLs offers advantages in terms of simplicity, low-cost and sustainable synthetic route to achieve nitrogen self-doped ACs for high energy density supercapacitors, which exhibit superior properties to that of ACs prepared via the conventional method.

Facile synthesis of high-surface-area nanoporous carbon from biomass resources and its application in supercapacitors

It is critical for nanoporous carbons to have a large surface area, and low cost and be readily available for challenging energy and environmental issues. The pursuit of all three characteristics, particularly large surface area, is a formidable challenge because traditional methods to produce porous carbon materials with a high surface area are complicated and expensive, frequently resulting in pollution (commonly from the activation process). Here we report a facile method to synthesize nanoporous carbon materials with a high surface area of up to 1234 m² g⁻¹ and an average pore diameter of 0.88 nm through a simple carbonization procedure with carefully selected carbon precursors (biomass material) and carbonization conditions. It is the high surface area that leads to a high capacitance (up to 213 F g⁻¹ at 0.1 A g⁻¹) and a stable cycle performance (6.6% loss over 12 000 cycles) as shown in a three-electrode cell. Furthermore, the high capacitance (107 F g⁻¹ at 0.1 A g⁻¹) can be obtained in a supercapacitor device. This facile approach may open a door for the preparation of high surface area porous carbons for energy storage.

High-surface-area nanoporous carbon is obtained by direct pyrolysis of biomass resources without an activation process. An electrochemical test shows high capacitance.

Symmetric Supercapacitor Electrodes from KOH Activation of Pristine, Carbonized, and Hydrothermally Treated Melia azedarach Stones

Waste biomass-derived activated carbons (ACs) are promising materials for supercapacitor electrodes due to their abundance and low cost. In this study, we investigated the potential use of Melia azedarach (MA) stones to prepare ACs for supercapacitors. The ash content was considerably lower in MA stones (0.7% ash) than that found in other lignocellulosic wastes. ACs were prepared by KOH activation of pristine, carbonized, and hydrothermally-treated MA stones. The morphology, composition, surface area, porosity, and surface chemistry of the ACs were determined. Electrochemical measurements were carried out in three- and two-electrode cells, 3EC and 2EC, respectively, using 1 M H₂SO₄ as the electrolyte. The highest capacitance from galvanostatic charge-discharge (GCD) in 2EC ranged between 232 and 240 F·g⁻¹ at 1 A·g⁻¹. The maximum energy density reached was 27.4 Wh·kg⁻¹ at a power density of 110 W·kg⁻¹. Electrochemical impedance spectroscopy (EIS) revealed an increase in equivalent series resistance (ESR) and charge transfer resistance (R_CT) with greater ash content. Electrochemical performance of MA stone-derived ACs was compared with that of other ACs described in the recent literature that were prepared from different biomass wastes and results showed that they are among the best ACs for supercapacitor applications.