Synthesis and characterization of porous carbon derived from activated banana peels with hierarchical porosity for improved electrochemical performance

Synthesis of mesoporous carbon from banana peels with silica gel 60 as the hard templates

The synthesis of mesoporous carbon was successfully performed through solid-solid phase reaction employing banana peel powder as the carbon source and silica gel 60 (SG-60) as the hard template. The synthesis was initiated by hydrothermal heating to introduce the banana powder to SG-60 surface, followed by the carbonization process to form the mesoporous carbon. FTIR, Raman, XRF, and XRD characterization confirmed the success of the carbonization step, while N2 physisorption and TEM characterization confirmed the mesoporous structure formation of the synthesized carbon with the template. At an optimum carbon-to-silica precursor ratio of 3 : 1, the synthesized carbon with SG-60 templates proceeds to a specific surface area of 476.97 m2 g-1, which is around 55-fold higher than the one synthesized without any template. Furthermore, evaluation of the capacitance performances was done by creating composite electrodes with nickel foam as the support and polyvinylidene difluoride as the binder. The evaluation was carried out using cyclic voltammetry in 3.0 M KOH, galvanic charge-discharge, and electrochemical impedance spectroscopy confirming a high correlation between the specific surface area and the specific capacitance. The banana peels-derived mesoporous carbon demonstrates a specific capacitance value of 23.1 F g-1, measured using the cyclic voltammetry method. Good stability of the prepared electrode over 2500 voltammetric cycles was also demonstrated, indicating that the use of SG-60 as the hard template is suitable for synthesizing carbon with mesoporous structure from biomass.

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.

From Waste to Power: Developing Structural Supercapacitors with Red Mud and Jute Stick

Developing effective, cost-efficient, and eco-friendly energy storage solutions is crucial for sustainable building structures. Red mud, a waste material, was used as the electrolyte and separator in supercapacitors, alongside activated carbon derived from jute sticks coated on steel mesh electrodes. Tests on RM-enhanced supercapacitors showed that 20 % by weight of RM was the best amount. This increased the modulus of elasticity by 33 %, the tensile strength by 3 %, and the compressive strength by 10 %. Durability was largely unaffected, with minimal additional water absorption and slight shrinkage variation. The supercapacitor cell had an extended cell potential of 1.5 V and a maximum specific capacitance of 62.3 F g-1 at 0.4 A g-1, as shown by electrochemical tests. This improved energy density to 19.5 Wh kg-1, with a power density of 301.8 W kg-1 at 0.4 A g-1 and a maximum power density of 605.8 W kg-1 at 0.8 A g-1. The cell retained 77 % of its initial capacitance after 450 continuous GCD cycles, demonstrating notable stability. This stability is due to the solid electrolyte and the synergy between JC and RM, indicating promising advancements for future energy storage devices.

Activated Carbon Derived from Cucumber Peel for Use as a Supercapacitor Electrode Material

Biowaste conversion into activated carbon is a sustainable and inexpensive approach that relieves the pressure on its disposal. Here, we prepared micro-mesoporous activated carbons (ACs) from cucumber peels through carbonization at 600 °C followed by thermal activation at different temperatures. The ACs were tested as supercapacitors for the first time. The carbon activated at 800 °C (ACP-800) showed a high specific capacitance value of 300 F/g at a scan rate of 5 mV/s in the cyclic voltammetry and 331 F/g at the current density of 0.1 A/g in the galvanostatic charge-discharge analysis. At the current density of 1 A/g, the specific discharge capacitance was 286 F/g and retained 100% capacity after 2000 cycles. Their properties were analyzed by scanning electron microscopy, energy-dispersive X-ray analysis, porosity, thermal analysis, and Fourier-transform infrared spectroscopy. The specific surface area of this sample was calculated to be 2333 m2 g-1 using the Brunauer-Emmett-Teller method. The excellent performance of ACP-800 is mainly attributed to its hierarchical porosity, as the mesopores provide connectivity between the micropores and improve the capacitive performance. These electrochemical properties enable this carbon material prepared from cucumber peels to be a potential source for supercapacitor materials.

Efficient integration of electrocoagulation treatment with the spray-pyrolyzed activated carbon coating on stainless steel electrodes for textile effluent-bath reuse with ease

In this study, the electrocoagulation (EC) treatment was used to minimize and separate pollutants from textile industrial wastewater (TIWW), including high color, chemical oxygen demand (COD), total organic carbon (TOC), and total dissolved solids (TDS). To enhance the EC treatment efficiency, a novel strategy has been followed in the study that involves thin-film coating on 316 stainless steel (SS) electrodes with banana peel-derived activated carbon (BPAC) by dip coating, spin coating, or spray coating. Among the different types of coating, thickness and contact angle measurements have elucidated that the spray coating of BPAC on SS electrode is the best tool with minimum thickness and contact angle. In this study, a bare SS electrode was used as the anode and a thin-film spray-coated BPAC on the SS electrode was used as the cathode. Moreover, optimization plays a key role in EC treatment process, where operating conditions such as a current density of 10 mA/cm2 , contact time of 15 min, and a pH of 7 were fixed. As a result, the findings indicate comparatively high color removal of 98%, COD removal of 91%, TOC removal of 89.6%, and TDS removal of 68% are achieved with ease. Accordingly, in comparison with plain SS electrodes or dip- or spin-coated BPAC on SS electrodes, spray-coated BPAC on SS electrodes in EC treatment outperforms in removing high color, TOC, COD, and TDS. Overall, the study highlights the potential of EC treatment integrated with adsorption procedures for TIWW treatment. Particularly, the use of thin-film spray-coated BPAC on SS electrodes in the EC treatment process led to an effective and sustainable tool for treating and reuse of TIWW. It is due to its low operation and maintenance cost and studied in a short interval of time. Finally, the ultimate goal was firmly achieved in pilot-scale studies by the safe discharge into the environment or reuse of treated textile wastewater. Thus, it is a promising alternative with an environmentally friendly footprint that could be easily implemented in any textile industry premises. PRACTITIONER POINTS: Heavy metals, oils, facts, suspended solids, and other pollutants can be removed from industrial effluent by using electrocoagulation. The process is both cost-effective and energy-efficient, and it is easily integrated with other water treatment technologies. According to the findings of this study, minimum current density should be applied to BPAC-SS-coated electrodes by DC power supplies to treat textile industry effluents at low operating costs. When compared with a plain SS electrode, the spray-coated BPAC on SS electrode provides better performance in effluent treatment.

Synthesis of Activated Porous Carbon from Red Dragon Fruit Peel Waste for Highly Active Catalytic Reduction in Toxic Organic Dyes

In this study, an alternative precursor for production of biomass-derived activated carbon was introduced using dragon fruit (Hylocereus costaricensis) peels. Chemical activators such as FeCl3, MgCl2, ZnCl2 were used in the thermal carbonization process to convert carbon into porous carbon (PC). However, heteroatom-doped PC catalysts including N-, B-, and P-doped carbon catalysts in the field of dye removal is highly desirable. Several approaches (XRD, FE-SEM/TEM, XPS, FT-IR, EDS, and elemental mapping) were employed to examine the surface morphology, surface properties, and elemental composition of the PC catalyst. The catalytic activity of metal-free PC catalyst was demonstrated for methylene blue (MB), crystal violet (CV), and Nile blue (NB) in a mild environment The corresponding rate constant (kapp) values were estimated as 0.2473, 0.3248, and 0.3056 min−1, respectively, for MB, CV, and NB, which were significantly greater than those of numerous reports. It exhibited the best catalytic activity and recyclability. Moreover, the approach proposed here could create new opportunities for the remediation of organic dyes in lakes and industrial wastewater.

Valorization of Banana Peel Using Carbonization: Potential Use in the Sustainable Manufacturing of Flexible Supercapacitors

Sustainable and environmentally friendly activated carbon from biomass materials is proposed to produce supercapacitors from banana peels and has the potential to replace the non-sustainable and hazardous process from either graphite or/and fossil fuels. In order to determine the potential of using banana peel for supercapacitor application, raw banana peel, a bio-waste, was activated both mechanically and chemically to observe the real differences. The sample was activated at 700 °C and chemically activated using KOH. Characterization of activated banana peel was performed using FTIR, DLS, TGA and XRD analytical equipment. FTIR analysis revised the presence of hydroxyl, carbonyl and aromatic compounds on a banana peel cellulose-based carbon. The TGA results proved that 700 °C could be sufficient to totally carbonize banana peel. DLS clearly showed a strong difference between the carbonized and KOH-activated material in particle size distribution. Meanwhile, surface area analysis using BET displayed an increase from 553.862 m²/g to 565.024 m²/g BET in surface area (SBET) when carbon was activated using KOH with a nitrogen isotherm at 77.350 K. Specific capacitance was increased from 0.3997 Fg^-1 to 0.821 Fg^-1, suggesting more than a 100% increase in the specific capacity due to KOH activation, as proved by the cyclic voltammetry (CV) curve. The X-ray diffraction results revealed the patterns of activated carbon. The findings demonstrated the feasibility of using banana peel waste as a low-cost and sustainable material for the preparation of flexible supercapacitor batteries.

Recent Advanced Supercapacitor: A Review of Storage Mechanisms, Electrode Materials, Modification, and Perspectives

In recent years, the development of energy storage devices has received much attention due to the increasing demand for renewable energy. Supercapacitors (SCs) have attracted considerable attention among various energy storage devices due to their high specific capacity, high power density, long cycle life, economic efficiency, environmental friendliness, high safety, and fast charge/discharge rates. SCs are devices that can store large amounts of electrical energy and release it quickly, making them ideal for use in a wide range of applications. They are often used in conjunction with batteries to provide a power boost when needed and can also be used as a standalone power source. They can be used in various potential applications, such as portable equipment, smart electronic systems, electric vehicles, and grid energy storage systems. There are a variety of materials that have been studied for use as SC electrodes, each with its advantages and limitations. The electrode material must have a high surface area to volume ratio to enable high energy storage densities. Additionally, the electrode material must be highly conductive to enable efficient charge transfer. Over the past several years, several novel materials have been developed which can be used to improve the capacitance of the SCs. This article reviews three types of SCs: electrochemical double-layer capacitors (EDLCs), pseudocapacitors, and hybrid supercapacitors, their respective development, energy storage mechanisms, and the latest research progress in material preparation and modification. In addition, it proposes potentially feasible solutions to the problems encountered during the development of supercapacitors and looks forward to the future development direction of SCs.

Electrochemical Performance of Chemically Activated Carbons from Sawdust as Supercapacitor Electrodes

Activated carbons (ACs) have been the most widespread carbon materials used in supercapacitors (SCs) due to their easy processing methods, good electrical conductivity, and abundant porosity. For the manufacture of electrodes, the obtained activated carbon based on sawdust (karagash and pine) was mixed with conductive carbon and polyvinylidene fluoride as a binder, in ratios of 75% activated carbon, 10% conductive carbon black, and 15% polyvinylidene fluoride (PVDF) in an N-methyl pyrrolidinone solution, to form a slurry and applied to a titanium foil. The total mass of each electrode was limited to vary from 2.0 to 4.0 mg. After that, the electrodes fitted with the separator and electrolyte solution were symmetrically assembled into sandwich-type cell construction. The carbon's electrochemical properties were evaluated using cyclic voltammetry (CV) and galvanostatic charge-discharge (CGD) studies in a two-electrode cell in 6M KOH. The CV and CGD measurements were realized at different scan rates (5-160 mV s^-1) and current densities (0.1-2.0 A g^-1) in the potential window of 1 V. ACs from KOH activation showed a high specific capacitance of 202 F g^-1 for karagash sawdust and 161 F g^-1 for pine sawdust at low mass loading of 1.15 mg cm^-2 and scan rate of 5 mV s^-1 in cyclic voltammetry test and 193 and 159 F g^-1 at a gravimetric current density of 0.1 A g^-1 in the galvanostatic charge-discharge test. The specific discharge capacitance is 177 and 131 F g^-1 at a current density of 2 A g^-1. Even at a relatively high scan rate of 160 mV s^-1, a decent specific capacitance of 147 F g^-1 and 114 F g^-1 was obtained, leading to high energy densities of 26.0 and 22.1 W h kg^-1 based on averaged electrode mass. Surface properties and the porous structure of the ACs were studied by scanning electron microscopy, energy-dispersive X-ray analysis, Raman spectroscopy, and the Brunauer-Emmett-Teller method.

Banana Peel and Conductive Polymers-Based Flexible Supercapacitors for Energy Harvesting and Storage

Flexible supercapacitors are highly demanding due to their wearability, washability, lightweight property and rollability. In this paper, a comprehensive review on flexible supercapacitors based on conductive polymers such as polypyrrole (PPy), polyaniline (PANI) and poly(3,4-ethylenedioxtthiophne)-polystyrene sulfonate (PEDOT:PSS). Methods of enhancing the conductivity of PEDOT:PSS polymer using various composites and chemical solutions have been reviewed in detail. Furthermore, supercapacitors based on carbonized banana peels and methods of activation have been discussed in point. This review covers the up-to-date progress achieved in conductive polymer-based materials for supercapacitor electrodes. The effect of various composites with PEDOT:PSS have been discussed. The review result indicated that flexible, stretchable, lightweight, washable, and disposable wearable electronics based on banana peel and conductive polymers are highly demanding.

Boosting capacitive performance of manganese oxide nanorods by decorating with three-dimensional crushed graphene

This work reports the rational design of MnOx nanorods on 3D crushed reduced graphene oxide (MnOx/C-rGO) by chemical reduction of Ni-incorporated graphene oxide (GO) followed by chemical etching to remove Ni. The resulting MnOx/C-rGO composite synergistically integrates the electronic properties and geometry structure of MnOx and 3D C-rGO. As a result, MnOx/C-rGO shows a significantly higher specific capacitance (Csp) of 863 F g-1 than MnOx/2D graphene sheets (MnOx/S-rGO) (373 F g-1) and MnOx (200 F g-1) at a current density of 0.2 A g-1. Furthermore, when assembled into symmetric supercapacitors, the MnOx/C-rGO-based device delivers a higher Csp (288 F g-1) than MnOx/S-rGO-based device (75 F g-1) at a current density of 0.3 A g-1. The superior capacitive performance of the MnOx/C-rGO-based symmetric device is attributed to the enlarged accessible surface, reduced lamellar stacking of graphene, and improved ionic transport provided by the 3D architecture of MnOx/C-rGO. In addition, the MnOx/C-rGO-based device exhibits an energy density of 23 Wh kg-1 at a power density of 113 Wkg-1, and long-term cycling stability, demonstrating its promising potential for practical application.

Electrochemical properties of an activated carbon xerogel monolith from resorcinol-formaldehyde for supercapacitor electrode applications

Activated carbon xerogel monoliths were prepared from resorcinol and formaldehyde via a catalyst-free and template-free hydrothermal polycondensation reaction, followed by pyrolysis and activation. The ratio of resorcinol (R) to distilled water (W) was varied to afford an interconnected pore structure with controlled pore size, while the pyrolysis temperature was optimized to give high specific surface area. Activation was carried out at 700 °C after soaking the samples in 6 M KOH aqueous solution. The same process, called "heat treatment", was also carried out without soaking in KOH for comparison. The weight loss upon pyrolysis, activation and heat treatment and the weight gain via KOH soaking were measured. Field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA) and an N2 sorption instrument were utilized for characterization. Additionally, electrochemical properties were evaluated using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS) with a 3-electrode system, while a 2-electrode system was also employed for selected samples. The highest specific capacitance of 323 F g-1 via GCD at 1 A g-1 was obtained at the R/W ratio of 45 and with 500 °C pyrolysis. In addition, this sample also exhibited 89.4% retention at 20 A g-1 in the current density variation and 100% retention in 5000 cycling tests.

Electrochemical energy storage electrodes from fruit biochar

This review investigates the electrochemical energy storage electrode (EESE) as the most important part of the electrochemical energy storage devices (EES) prepared from fruit-derived carbon. The EES devices include batteries, supercapacitors, and hybrid devices that have various regular and advanced applications. The preparation of EESE from fruit wastes not only reduce the price of the electrode but also lead to enhance the electrochemical properties of the electrode. The astonishing results of fruits biochar at electrochemical analyses guarantee the performance of these electrodes as EESE. Also, using fruit waste as the precursor of the EESE due to protect the environment and reduce environmental pollutions.

Ex-situ nitrogen-doped porous carbons as electrode materials for high performance supercapacitor

Nitrogen (N) doping of porous carbon materials is an effective strategy for enhancing the electrochemical performance of electrode materials. Herein, we report on ex-situ (post) nitrogen-doped porous carbons prepared using a biomass waste, peanut shell (PS) as a carbon source and melamine as the nitrogen source. The synthesis method involved a two-step mechanism, initial chemical activation of the PS using KOH and post N-doping of the activated carbon. The effect of the activating agent/precursor ratio and the ex-situ N-doping on the structural, textural, electrochemical properties of the porous carbons was studied. The ex-situ N-doped porous carbon with an optimum amount of KOH to PS exhibited the best capacitance performance with a specific surface area (SSA) of 1442 m² g^-1 and an enriched nitrogen content (3.2 at %). The fabricated symmetric device exhibited a 251.2 F g^-1 specific capacitance per electrode at a gravimetric current of 1 A g^-1 in aqueous electrolyte (2.5 M KNO₃) at a wide cell voltage of 2.0 V. A specific energy of 35 Wh kg^-1 with a corresponding specific power of 1 kW kg^-1 at 1 A g^-1 was delivered with the device still retaining up to 22 Wh kg^-1 and a 20 kW kg^-1 specific power even at 20 A g^-1. Moreover, long term device stability was exhibited with an 83.2% capacity retention over 20 000 charge/discharge cycles and also a good rate capability after 180 h of floating at 5 A g^-1. This great performance of the symmetric supercapacitor can be correlated to the surface porosity and post nitrogen-doping effect which increased the electrochemically-active sites resulting in a remarkable charge storage capability.

Onion-derived activated carbons with enhanced surface area for improved hydrogen storage and electrochemical energy application

High surface area activated carbons (ACs) were prepared from a hydrochar derived from waste onion peels. The resulting ACs had a unique graphene-like nanosheet morphology. The presence of N (0.7%) and O content (8.1%) in the OPAC-800 °C was indicative of in situ incorporation of nitrogen groups from the onion peels. The specific surface area and pore volume of the best OPAC sample was found to be 3150 m² g⁻¹ and 1.64 cm³ g⁻¹, respectively. The hydrogen uptake of all the OPAC samples was established to be above 3 wt% (at 77 K and 1 bar) with the highest being 3.67 wt% (800 °C). Additionally, the OPAC-800 °C achieved a specific capacitance of 169 F g⁻¹ at a specific current of 0.5 A g⁻¹ and retained a capacitance of 149 F g⁻¹ at 5 A g⁻¹ in a three electrode system using 3 M KNO₃. A symmetric supercapacitor based on the OPAC-800 °C//OPAC-800 °C electrode provided a capacitance of 158 F g⁻¹ at 0.5 A g⁻¹. The maximum specific energy and power was found to be 14 W h kg⁻¹ and 400 W kg⁻¹, respectively. Moreover, the device exhibited a high coulombic efficiency of 99.85% at 5 A g⁻¹ after 10 000 cycles. The results suggested that the high surface area graphene-like carbon nanostructures are excellent materials for enhanced hydrogen storage and supercapacitor applications.

Graphene-like activated carbons (ACs), with excellent properties for enhanced hydrogen storage and supercapacitor applications, were prepared from waste onion peels.

Effect of porosity enhancing agents on the electrochemical performance of high-energy ultracapacitor electrodes derived from peanut shell waste

In this study, the synthesis of porous activated carbon nanostructures from peanut (Arachis hypogea) shell waste (PSW) was described using different porosity enhancing agents (PEA) at various mass concentrations via a two-step process. The textural properties obtained were depicted with relatively high specific surface area values of 1457 m² g⁻¹, 1625 m² g⁻¹ and 2547 m² g⁻¹ for KHCO_3, K₂CO₃ and KOH respectively at a mass concentration of 1 to 4 which were complemented by the presence of a blend of micropores, mesopores and macropores. The structural analyses confirmed the successful transformation of the carbon-containing waste into an amorphous and disordered carbonaceous material. The electrochemical performance of the material electrodes was tested in a 2.5 M KNO₃ aqueous electrolyte depicted its ability to operate reversibly in both negative and positive potential ranges of 0.90 V. The activated carbon obtained from the carbonized CPSW:PEA with a mass ratio of 1:4 yielded the best electrode performance for all featured PEAs. The porous carbons obtained using KOH activation displayed a higher specific capacitance and the lower equivalent series resistance as compared to others. The remarkable performance further corroborated the findings linked to the textural and structural properties of the material. The assembled device operated in a neutral electrolyte (2.5 M KNO₃) at a cell potential of 1.80 V, yielded a ca. 224.3 F g⁻¹ specific capacitance at a specific current of 1 A g⁻¹ with a corresponding specific energy of 25.2 Wh kg⁻¹ and 0.9 kW kg⁻¹ of specific power. This device energy was retained at 17.7 Wh kg⁻¹ when the specific current was quadrupled signifying an excellent supercapacitive retention with a corresponding specific power of 3.6 kW kg⁻¹. These results suggested that peanut shell waste derived activated carbons are promising candidates for high-performance supercapacitors.