Biowaste-based porous carbon for supercapacitor: The influence of preparation processes on structure and performance

Upcycling biowaste into advanced carbon materials via low-temperature plasma hybrid system: applications, mechanisms, strategies and future prospects

This review focuses on the recent advances in the sustainable conversion of biowaste to valuable carbonaceous materials. This study summarizes the significant progress in biowaste-derived carbon materials (BCMs) via a plasma hybrid system. This includes systematic studies like AI-based multi-coupling systems, promising synthesis strategies from an economic point of view, and their potential applications towards energy, environment, and biomedicine. Plasma modified BCM has a new transition lattice phase and exhibits high resilience, while fabrication and formation mechanisms of BCMs are reviewed in plasma hybrid system. A unique 2D structure can be designed and formulated from the biowaste with fascinating physicochemical properties like high surface area, unique defect sites, and excellent conductivity. The structure of BCMs offers various activated sites for element doping and it shows satisfactory adsorption capability, and dynamic performance in the field of electrochemistry. In recent years, many studies have been reported on the biowaste conversion into valuable materials for various applications. Synthesis methods are an indispensable factor that directly affects the structure and properties of BCMs. Therefore, it is imperative to review the facile synthesis methods and the mechanisms behind the formation of BCMs derived from the low-temperature plasma hybrid system, which is the necessity to obtain BCMs having desirable structure and properties by choosing a suitable synthesis process. Advanced carbon-neutral materials could be widely synthesized as catalysts for application in environmental remediation, energy conversion and storage, and biotechnology.

In Situ, Nitrogen-Doped Porous Carbon Derived from Mixed Biomass as Ultra-High-Performance Supercapacitor

How to address the destruction of the porous structure caused by elemental doping in biochar derived from biomass is still challenging. In this work, the in-situ nitrogen-doped porous carbons (ABPCs) were synthesized for supercapacitor electrode applications through pre-carbonization and activation processes using nitrogen-rich pigskin and broccoli. Detailed characterization of ABPCs revealed that the best simple ABPC-4 exhibited a super high specific surface area (3030.2-3147.0 m2 g-1) and plentiful nitrogen (1.35-2.38 wt%) and oxygen content (10.08-15.35 wt%), which provided more active sites and improved the conductivity and electrochemical activity of the material. Remarkably, ABPC-4 showed an outstanding specific capacitance of 473.03 F g-1 at 1 A g-1. After 10,000 cycles, its capacitance retention decreased by only 4.92% at a current density of 10 A g-1 in 6 M KOH. The assembled symmetric supercapacitor ABPC-4//ABPC-4 achieved a power density of 161.85 W kg-1 at the maximum energy density of 17.51 Wh kg-1 and maintained an energy density of 6.71 Wh kg-1 when the power density increased to 3221.13 W kg-1. This study provides a mixed doping approach to achieve multi-element doping, offering a promising way to apply supercapacitors using mixed biomass.

Nitrogen-Doped Porous Carbons Derived from Peanut Shells as Efficient Electrodes for High-Performance Supercapacitors

The doping of porous carbon materials with nitrogen is an effective approach to enhance the electrochemical performance of electrode materials. In this study, nitrogen-doped porous carbon derived from peanut shells was prepared as an electrode for supercapacitors. Melamine, urea, urea phosphate, and ammonium dihydrogen phosphate were employed as different nitrogen dopants. The optimized electrode material PA-1-1 prepared by peanut shells, with ammonium dihydrogen phosphate as a nitrogen dopant, exhibited a N content of 3.11% and a specific surface area of 602.7 m2/g. In 6 M KOH, the PA-1-1 electrode delivered a high specific capacitance of 208.3 F/g at a current density of 1 A/g. Furthermore, the PA-1-1 electrode demonstrated an excellent rate performance with a specific capacitance of 170.0 F/g (retention rate of 81.6%) maintained at 20 A/g. It delivered a capacitance of PA-1-1 with a specific capacitance retention of 98.8% at 20 A/g after 5000 cycles, indicating excellent cycling stability. The PA-1-1//PA-1-1 symmetric supercapacitor exhibited an energy density of 17.7 Wh/kg at a power density of 2467.0 W/kg. This work not only presents attractive N-doped porous carbon materials for supercapacitors but also offers a novel insight into the rational design of biochar carbon derived from waste peelings.

Low-cost pyrolysis of biomass-derived nitrogen-doped porous carbon: Chlorella vulgaris replaces melamine as a nitrogen source

Porous carbon generated from biomass has a rich pore structure, is inexpensive, and has a lot of promise for use as a carbon material for energy storage devices. In this work, nitrogen-doped porous carbon was prepared by co-pyrolysis using bagasse as the precursor and chlorella as the nitrogen source. ZnCl2 acts as both an activator and a nitrogen fixer during activation to generate pores and reduce nitrogen loss. The thermal weight loss experiments showed that the pyrolysis temperatures of bagasse and chlorella overlap, which created the possibility for the synthesis of nitrogen-rich biochar. The optimum sample (ZBC@C-5) possessed a surface area of 1508 m2g-1 with abundant nitrogen-containing functional groups. ZBC@C-5 in the three-electrode system exhibited 244.1F/g at 0.5A/g, which was extremely close to ZBC@M made with melamine as the nitrogen source. This provides new opportunities for the use of low-cost nitrogen sources. Furthermore, the devices exhibit better voltage retention (39%) and capacitance retention (96.3%). The goal of this research is to find a low cost, and effective method for creating nitrogen-doped porous carbon materials with better electrochemical performance for highly valuable applications using bagasse and chlorella.

Soluble starch-derived porous carbon microspheres with interconnected and hierarchical structure by a low dosage KOH activation for ultrahigh rate supercapacitors

The developed porous structure and high density are essential to enhance the bulk performance of carbon-based supercapacitors. Nevertheless, it remains a significant challenge to optimize the balance between the porous structure and the density of carbon materials to realize superior gravimetric and areal electrochemical performance. The soluble starch-derived interconnected hierarchical porous carbon microspheres were prepared through a simple hydrothermal treatment succeeded by chemical activation with a low dosage of KOH. Due to the formation of interconnected spherical morphology, hierarchical porous structure, reasonable mesopore volume (0.33 cm3 g-1) and specific surface area (1162 m2 g-1), the prepared carbon microsphere has an ultrahigh capacitance of 394 F g-1 @ 1 A g-1 and a high capacitance retention of 62.7 % @ 80 A g-1. The assembled two-electrode device displays good cycle stability after 20,000 cycles and an ultra-high energy density of 11.6 Wh kg-1 @ 250 W kg-1. Moreover, the sample still exhibits a specific capacitance of 165 F g-1 @ 1 A g-1 at a high mass loading of 10 mg cm-2, resulting in a high areal capacitance of 1.65 F cm-2. The strategy proposed in this study, via a low-dose KOH activation process, provides the way for the synthesis of high-performance porous carbon materials.

Top-Down Thickness Reduction Synthesis of Biomass-Derived Carbon Nanosheets with Hierarchical Pore Structure for High-Performance Supercapacitors

Carbon electrode materials with superior rate performance are highly demanded in application scenarios of high power output/input, especially when paired with organic electrolyte for extended voltage window and high energy storage. By extracting thin sheets of entangled cellulose fibers from cell wall structures, porous carbon nanosheets as templated from the cellulose sheets are synthesized. Evident thickness reduction effect has been demonstrated with thickness reduced from several micrometers to several nanometers of the obtained thickness-reduced activated carbon nanosheets (TRAC), which endow the material with a large surface area and high pore volume. The obtained TRAC exhibits significantly enhanced ion diffusion kinetics and superior rate capability thanks to the shortened diffusion pathway and suitable pore size distribution. Effects of sonication time have also been investigated, showing a trade-off between ion diffusion kinetics and pseudocapacitive contribution. This thickness-reduction method is extendable to many other biomass sources as cellulose sheets are widely existed in nature, offering a practical and easy-to-implement strategy of fabricating porous carbon nanostructures for efficient energy storage and utilization.

Mesoporous graphitic carbon electrodes derived from boat-fruited shells of Sterculia Foetida for symmetric supercapacitors for energy storage applications

In recent years, intensive research efforts have focused on translating biomass waste into value-added carbon materials broadcasted for their significant role in energy and environmental applications. For the first time, high-performance carbonaceous materials for energy storage applications were developed from the multi-void structure of the boat-fruited shells of Sterculia Foetida (SF). In that view, synthesized mesoporous graphitic activated carbon (g-AC) via the combination of carbonization at various elevating temperatures of 700, 800, and 900 °C, respectively, and alkali activation by KOH, with a high specific surface area of 1040.5 m2 g-1 and a mesopore volume of 0.295 cm3 g-1. In a three-electrode configuration, the improved electrode (SF-K900) exhibited excellent electrochemical behavior, which was observed in an aqueous electrolyte (1 M H2SO4) with a high specific capacitance of 308.6 F/g at a current density of 1 A/g, owing to the interconnected mesopore structures and high surface area of SF-K900. The symmetric supercapacitor (SSC) delivered the specific capacitance of 138 F/g at 1 A/g with a high energy density (ED) of 13.4 Wh/kg at the power density (PD) of 24.12 kW/kg with remarkable cycle stability and supercapacitive retention of 93% over 5000 cycles. Based on the findings, it is possible to develop low-cost active electrode materials for high-rate performance SSC using mesoporous g-AC derived from SF boat-fruited shells.

In Situ N, O Co-Doped Nanoporous Carbon Derived from Mixed Egg and Rice Waste as Green Supercapacitor

The conversion of nitrogen-oxygen-rich biomass wastes into heteroatomic co-doped nanostructured carbons used as energy storage materials has received widespread attention. In this study, an in situ nitrogen-oxygen co-doped porous carbon was prepared for supercapacitor applications via a two-step method of pre-carbonization and pyrolytic activation using mixed egg yolk/white and rice waste. The optimal sample (YPAC-1) was found to have a 3D honeycomb structure composed of abundant micropores and mesopores with a high specific surface area of 1572.1 m2 g-1, which provided abundant storage space and a wide transport path for electrolyte ions. Notably, the specific capacitance of the constructed three-electrode system was as high as 446.22 F g-1 at a current density of 1 A g-1 and remained above 50% at 10 A g-1. The capacitance retention was 82.26% after up to 10,000 cycles. The symmetrical capacitor based on YPAC-1 with a two-electrode structure exhibited an energy density of 8.3 Wh kg-1 when the power density was 136 W kg-1. These results indicate that porous carbon materials prepared from mixed protein and carbohydrate waste have promising applications in the field of supercapacitors.

N/O Co-doped hierarchical nanoporous biochar derived from waste polypropylene nonwoven for high-performance supercapacitors

How to efficiently treat municipal solid waste (MSW) has become one of the critical solutions in response to the call for "carbon neutrality". Here, the waste polypropylene nonwoven fabric of waste diapers was converted into hierarchical nanoporous biochar (HPBC) through pre-carbonization and activation processes as an ideal precursor for supercapacitors (SCs) with excellent performance. The prepared HPBC-750-4 with an ultrahigh specific surface area (3838.04 m2 g-1) and abundant heteroatomic oxygen (13.25%) and nitrogen (1.16%) codoped porous biochar structure. Given its structural advantages, HPBC-750-4 achieved a specific capacitance of 340.9 F g-1 at a current density of 1 A g-1 in a three-electrode system. Its capacitance retention rate was above 99.2% after 10 000 cycles at a current density of 10 A g-1, which indicated an excellent rate capability and long-term cycling stability. Furthermore, the HPBC-750-4//HPBC-750-4 symmetric SC exhibited a superb energy density of 10.02 W h kg-1 with a power density of 96.15 W kg-1 in a 6 M KOH electrolyte. This work not only demonstrates the enormous potential of waste polypropylene nonwoven fabric in the SC industry but also provides an economically feasible means of managing MSW.

In Situ N, O-Dually Doped Nanoporous Biochar Derived from Waste Eutrophic Spirulina for High-Performance Supercapacitors

Sustainable and high-performance energy storage materials are crucial to address global energy and environmental challenges. In this study, Spirulina platensis was used as the carbon and nitrogen source, and Spirulina-based nanoporous biochar (SNPB) was synthesized through chemical activation using KOH as the activating agent in N2 atmosphere. SNPB-800-4 was characterized by N2 adsorption-desorption and XPS, showing a high specific surface area (2923.7 m2 g-1) and abundant heteroatomic oxygen (13.78%) and nitrogen (2.55%). SNPB-800-4 demonstrated an exceptional capacitance of 348 F g-1 at a current density of 1 A g-1 and a remarkable capacitance retention of 94.14% after 10,000 cycles at a current density of 10 A g-1 in 6 M KOH. Notably, symmetric supercapacitors SNPB-800-4//SNPB-800-4 achieved the maximum energy and power densities of 17.99 Wh kg-1 and 162.48 W kg-1, respectively, at a current density of 0.5 A g-1, and still maintained 2.66 Wh kg-1 when the power density was increased to 9685.08 W kg-1 at a current density of 30 A g-1. This work provides an easily scalable and straightforward way to convert waste algae biomass into in situ N, O-dually doped biochar for ultra-high-power supercapacitors.

Magnetically Guided Synthesis of Anisotropic Porous Carbons toward Efficient CO2 Capture and Magnetic Separation of Oil

Conventional synthetic strategies do not allow one to impart structural anisotropy into porous carbons, thus leading to limited control over their textural properties. While structural anisotropy alters the mechanical properties of materials, it also introduces an additional degree of directionality to increase the pore connectivity and thus the flux in the designed direction. Accordingly, in this work the structure of porous carbons prepared from resorcinol-formaldehyde gels has been rendered anisotropic by integrating superparamagnetic colloids to the sol-gel precursor solution and by applying a uniform magnetic field during the sol-gel transition, which enables the self-assembly of magnetic colloids into chainlike structures to template the growth of the gel phase. Notably, the anisotropic pore structure is maintained upon pyrolysis of the gel, leading to hierarchically porous carbon monoliths with tunable structure and porosities. With an advantage granted to anisotropic materials, these porous carbons showed higher porosity, a higher CO₂ uptake capacity of 3.45 mmol g^-1 at 273 K at 1.1 bar, and faster adsorption kinetics compared to the ones synthesized in the absence of magnetic field. Moreover, these materials were also used as magnetic sorbents with fast adsorption kinetics for efficient oil-spill cleanup and retrieved easily by using an external magnetic field.

Hierarchical hollow tubular fibrous brucite-templated carbons obtained by KOH activation for supercapacitors

Hierarchical hollow tubular porous carbons have been widely used in applications of supercapacitors, batteries, CO₂ capture and catalysis due to their hollow tubular morphology, large aspect ratio, abundant pore structure and superior conductivity. Herein, hierarchical hollow tubular fibrous brucite-templated carbons (AHTFBC_s) were prepared using natural mineral fiber brucite as the template and KOH as the chemical activator. The effects of different KOH additions on the pore structure and capacitive performance of AHTFBC_s were systematically studied. The specific surface area and micropore content of AHTFBC_s after KOH activation were higher than those of HTFBC. The specific surface area of the HTFBC is 400 m² g^-1, while the activated AHTFBC₅ has a specific surface area of up to 625 m² g^-1. In particular, compared with HTFBC (6.1%), a series of AHTFBC_s (22.1% for AHTFBC₂, 23.9% for AHTFBC₃, 26.8% for AHTFBC₄ and 22.9% for AHTFBC₅) with significantly increased micropore content were prepared by controlling the amount of KOH added. The AHTFBC₄ electrode displays a high capacitance of 197 F g^-1 at 1 A g^-1 and the capacitance retention of 100% after 10 000 cycles at 5 A g^-1 in the three-electrode system. And an AHTFBC₄//AHTFBC₄ symmetric supercapacitor exhibits the capacitance of 109 F g^-1 at 1 A g^-1 in 6 M KOH and an energy density of 5.8 W h kg^-1 at 199.0 W kg^-1 in 1 M Na₂SO₄ electrolyte. In addition, the capacity retention of AHTFBC₄ in the symmetric supercapacitor was maintained at 92% after 5000 cycles in both 6 M KOH and 1 M Na₂SO₄ electrolytes.

Preparation and Electrochemical Performance of Bio-Oil-Derived Hydrochar as a Supercapacitor Electrode Material

The rapid consumption of fossil energy and the urgent demand for sustainable development have significantly promoted worldwide efforts to explore new technology for energy conversion and storage. Carbon-based supercapacitors have received increasing attention. The use of biomass and waste as a carbon precursor is environmentally friendly and economical. In this study, hydrothermal pretreatment was used to synthetize coke from bio-oil, which can create a honeycomb-like structure that is advantageous for electrolyte transport. Furthermore, hydrothermal pretreatment, which is low in temperature, can create a low graphitization degree which can make heteroatom introduction and activation easier. Then, urea and KOH were used for doping and activation, which can improve conductivity and capacitance. Compared with no heteroatom and activation hydrothermal char (HC) (58.3 F/g at 1 A/g), the prepared carbon material nitrogen doping activated hydrothermal carbon (NAHC1) had a good electrochemical performance of 225.4 F/g at 1 A/g. The specific capacitance of the prepared NAHC1 was improved by 3.8 times compared with that of HC.

Momordica Grosvenori Shell-Derived Porous Carbon Materials for High-Efficiency Symmetric Supercapacitors

Porous carbon materials derived from waste biomass have received broad interest in supercapacitor research due to their high specific surface area, good electrical conductivity, and excellent electrochemical performance. In this work, Momordica grosvenori shell-derived porous carbons (MGCs) were synthesized by high-temperature carbonization and subsequent activation by potassium hydroxide (KOH). As a supercapacitor electrode, the optimized MGCs-2 sample exhibits superior electrochemical performance. For example, a high specific capacitance of 367 F∙g^-1 is achieved at 0.5 A∙g^-1. Even at 20 A∙g^-1, more than 260 F∙g^-1 can be retained. Moreover, it also reveals favorable cycling stability (more than 96% of capacitance retention after 10,000 cycles at 5 A∙g^-1). These results demonstrate that porous carbon materials derived from Momordica grosvenori shells are one of the most promising electrode candidate materials for practical use in the fields of electrochemical energy storage and conversion.

Facile Synthesis of Sustainable Activated Biochars with Different Pore Structures as Efficient Additive-Carbon-Free Anodes for Lithium- and Sodium-Ion Batteries

The present work elucidates facile one-pot synthesis from biomass forestry waste (Norway spruce bark) and its chemical activation yielding high specific surface area (S _BET) biochars as efficient lithium- and sodium-ion storage anodes. The chemically activated biochar using ZnCl₂ (Biochar-1) produced a highly mesoporous carbon containing 96.1% mesopores in its structure as compared to only 56.1% mesoporosity from KOH-activated biochars (Biochar-2). The latter exhibited a lower degree of graphitization with disordered and defective carbon structures, while the former presented more formation of ordered graphite sheets in its structure as analyzed from Raman spectra. In addition, both biochars presented a high degree of functionalities on their surfaces but Biochar-1 presented a pyridinic-nitrogen group, which helps improve its electrochemical response. When tested electrochemically, Biochar-1 showed an excellent rate capability and the longest capacity retentions of 370 mA h g^-1 at 100 mA g^-1 (100 cycles), 332.4 mA h g^-1 at 500 mA g^-1 (1000 cycles), and 319 mA h g^-1 at 1000 mA g^-1 after 5000 cycles, rendering as an alternative biomass anode for lithium-ion batteries (LIBs). Moreover, as a negative electrode in sodium-ion batteries, Biochar-1 delivered discharge capacities of 147.7 mA h g^-1 at 50 mA g^-1 (140 cycles) and 126 mA h g^-1 at 100 mA g^-1 after 440 cycles.

Multifunctional Loblolly Pine-Derived Superactivated Hydrochar: Effect of Hydrothermal Carbonization on Hydrogen and Electron Storage with Carbon Dioxide and Dye Removal

Pore modulation via hydrothermal carbonization (HTC) needs investigation due to its crucial effect on surface that influences its multirole utilization of such ultraporous sorbents in applications of energy storage- hydrogen and capacitive- as well as for pollutant abatement- carbon capture and dye removal. Hence, loblolly pine was hydrothermally carbonized followed by KOH activation to synthesize superactivated hydrochars (SAH). The resulting SAHs had specific surface area (SSA) 1462-1703 m²/g, total pore (TPV) and micropore volume (MPV) of 0.62-0.78 cm³/g and 0.33-0.49 cm³/g, respectively. The SAHs exhibit excellent multifunctional performance with remarkably high atmospheric CO₂ capture of 145.2 mg/g and high pressure cryogenic H₂ storage of 54.9 mg/g. The fabricated supercapacitor displayed substantial specific capacitance value of maximum 47.2 Fg^-1 at 1 A g^-1 in 6 M KOH and highest MB dye removal of 719.4 mg/g. Higher HTC temperature resulted in increased surface porosity as higher SSA, TPV benefitted H₂ storage and MB dye removal while superior MPV favored CO₂ capture. Moderate HTC temperature ensured higher mesopore-to-macropore volume ratio favoring electrochemical performance. Isotherm modelling of the adsorbates was compared using models: Langmuir, Freundlich, Langmuir- Freundlich and Temkin.

Cedar Wood-Based Biochar: Properties, Characterization, and Applications as Anodes in Microbial Fuel Cell

In this study, the relationship between pyrolysis temperature of woody biomass and physicochemical properties of derived biochar was investigated for microbial fuel cell (MFC) application. Physical and chemical properties of biochar were characterized for different pyrolysis temperatures. Results showed that biochar obtained at 400 °C was not conductor, while biochars prepared at 600 °C, 700 °C, and 900 °C exhibited decreased electrical resistivity of (7 ± 6) × 10³ Ω.m, (1.8 ± 0.2) Ω.m, and (16 ± 3) × 10^-3 Ω.m, respectively. Rising pyrolysis temperature from 400 to 700 °C exhibited honeycomb-like macroporous structures of biochar with an increase in the specific surface area from 310 to 484 m².g^-1. However, the production of biochar at 900 °C reduced its specific surface area to 136 m².g^-1 and caused the loss of the ordered honeycomb structure. MFCs using anodes based on biochar prepared at 900 °C produced maximum power densities ((9.9 ± 0.6) mW.m^-2) higher than that obtained with biochar pyrolyzed at 700 °C ((5.8 ± 0.1) mW.m^-2) and with conventional carbon felt anodes ((1.9 ± 0.2) mW.m^-2). SEM images of biochar-based anodes indicated the clogging of macropores in honeycomb structure of biochar prepared at 700 °C by growth of electroactive biofilms, which might impede the supply of substrate and the removal of metabolites from the inside of the electrode. These findings highlight that electrical conductivity of biochar is the major parameter for ensuring efficient anodes in microbial fuel cell application. Schematic representation of cedar wood-based biochar and its application as anode in MFC.

Ulothrix-Derived Sulfur-Doped Porous Carbon for High-Performance Symmetric Supercapacitors

With the demand for carbon dioxide emission reduction, the sustainable conversion of useless biomass into high-value energy storage devices has received excellent scientific and technological attention. The high synthesis cost and low specific capacitance limited the supercapacitor application. Therefore, biomass-derived sulfur-doping porous carbon (SPC) has been synthesized from ulothrix using simple pyrolysis and chemical activation methods. The unique activated carbon material exhibits a high specific surface area (2490 m² g^-1), and the effect of the activator addition ratio was systematically investigated. The optimized SPC-2 displayed a high specific capacitance (324 F g^-1 at 1 A g^-1) and excellent cycling stability (90.6% retention after 50 000 cycles). Furthermore, a symmetric supercapacitor (SSC) based on SPC-2 demonstrated a high energy density (12.9 Wh kg^-1) at an 800 W kg^-1 power density. This work offers a simple, economical, and ecofriendly synthetic strategy of converting widespread, useless biomass waste into high-performance supercapacitor applications.

A sustainable one-step strategy for highly graphitized capacitive carbons with hierarchical micro-meso-macro porosity

Large micropore surface area, superior electrical conductivity and suitable pore size are simultaneously desired characteristics for high-performance capacitive carbons. However, these desired features tend to be mutually competing, and are generally difficult to integrate into a single carbon. Considering this challenge, we developed a sustainable, less time-demanding, pollution-free strategy to construct highly graphitized porous carbon (GPC) by one-step heat-treatment. This approach achieves the need of the abovementioned characteristics for capacitive carbons, wherein potassium ferrate works as both an activating agent and graphitization catalyst to achieve synchronous hierarchical porosity and graphitization of wasted natural wood, and the resultant carbon materials possess a large micropore surface area of 870.4 m2 g-1, a highly graphitic carbon skeleton and a well-interconnected micro-meso-macropore structure. The assembled GPC-based symmetrical capacitors exhibited a satisfactory capacitive performance in different aqueous electrolytes (H2SO4, KOH and Na2SO4), including high specific capacitance, prominent rate capability, satisfactory energy density and good cycle stability. Meanwhile, we compared the contributions of porosity and the graphitized structure to capacitive performance, and porosity was dominant in determining capacitance and the graphitized skeleton had a positive effect in enhancing the capacitive performance. In addition, we established the relationship between the structure of GPC and electrochemical capacitive performance in different aqueous electrolytes, providing a valuable reference for GPC-based supercapacitors in different practical applications. More importantly, this strategy holds great promise to sustainably convert biowaste to high-added-value capacitive carbons for advanced energy storage applications in the future.

Hierarchically porous activated carbons prepared via a dissipative process: a high-capacity cathode for Li-ion capacitors

Activated carbons with high specific surface area (SSA) and well-modulated pore structure are highly desirable for achieving high-performance capacitive energy storage. Herein, hierarchically porous activated carbons (PACs) are synthesized by a tableting-activation method. The quick release of high-pressure gaseous products from the inside of the tablets can be regarded as a dissipative process, which leads to the formation of well-ordered high density meso- or macropores in the resulting material. The porous structure of the PACs has been modulated by adjusting the dissipative process parameters, such as the tableting pressure and tablet thickness. As a result, the optimal PAC (PAC-10) possesses an ultrahigh SSA (up to 3211 m² g^-1) and a well-developed hierarchical porous structure, which leads to an excellent capacitive energy-storage performance both in an aqueous electrolyte supercapacitor system and a Li ion capacitor (LIC) system. In particular, as a cathode for LICs, PAC-10 exhibits an extremely high specific capacity of 251 mA h g^-1 at 0.5 A g^-1 and still retains 158 mA h g^-1 at a high rate of 15 A g^-1.

Boosting the Electrochemical Performance of Polyaniline by One-Step Electrochemical Deposition on Nickel Foam for High-Performance Asymmetric Supercapacitor

Energy generation can be clean and sustainable if it is dependent on renewable resources and it can be prominently utilized if stored efficiently. Recently, biomass-derived carbon and polymers have been focused on developing less hazardous eco-friendly electrodes for energy storage devices. We have focused on boosting the supercapacitor's energy storage ability by engineering efficient electrodes in this context. The well-known conductive polymer, polyaniline (PANI), deposited on nickel foam (NF) is used as a positive electrode, while the activated carbon derived from jute sticks (JAC) deposited on NF is used as a negative electrode. The asymmetric supercapacitor (ASC) is fabricated for the electrochemical studies and found that the device has exhibited an energy density of 24 µWh/cm² at a power density of 3571 µW/cm². Furthermore, the ASC PANI/NF//KOH//JAC/NF has exhibited good stability with ~86% capacitance retention even after 1000 cycles. Thus, the enhanced electrochemical performances of ASC are congregated by depositing PANI on NF that boosts the electrode's conductivity. Such deposition patterns are assured by faster ions diffusion, higher surface area, and ample electroactive sites for better electrolyte interaction. Besides advancing technology, such work also encourages sustainability.

Redox molecule Alizarin red S anchored on biomass-derived porous carbon for enhanced supercapacitive performance

Biomass-derived porous carbon as a conductive framework in which the redox molecule Alizarin red S is anchored by strong interactions.

Flute-type porous carbon derived from soybean shells for high-performance all-solid-state symmetric supercapacitors

Flute-type porous carbon was successfully prepared from soybean shells through convenient methods. The influence of mass ratio on the structure and electrochemical performance of porous carbon obtained from soybean shells was investigated in detail. The obtained porous carbon exhibited a micro-tube morphology structure with a specific surface area of 2802 m² g⁻¹, pore volume of 1.36 cm³ g⁻¹, and appropriate pore size distribution. The porous carbon showed good electrochemical properties as an electrode material for supercapacitors. The optimal porous carbon SSAC4 exhibited high specific capacitance of 465 F g⁻¹ (1 A g⁻¹) and 287 F g⁻¹ (20 A g⁻¹) in a three-electrode system with 6 M KOH electrolyte. In addition, the as-assembled SSAC4-based all-solid-state supercapacitors delivered a high specific capacitance of 294 F g⁻¹ at 0.1 A g⁻¹ and excellent cycling stability of 86.2% after 10 000 cycles at 5 A g⁻¹.

Flute type porous carbon is successfully derived from soybean shell through a convenient method. The porous carbon shows good electrochemical properties as an electrode material for supercapacitors.

Hierarchical flower-like architecture of nickel phosphide anchored with nitrogen-doped carbon quantum dots and cobalt oxide for advanced hybrid supercapacitors

The exploitation of hybrid supercapacitors with excellent electrochemical properties is of great significance for energy storage systems. Herein, a three-dimensional hierarchical flower-like architecture of nickel phosphide (Ni₂P) decorated with nitrogen-doped carbon quantum dots (N-CQDs) and cobalt oxide (Co₃O₄) is constructed by an effective two-step hydrothermal strategy followed by in situ phosphorization process. Introducing N-CQDs with superior electrochemical characteristics can not only induce the formation of N-CQDs deposited nickel hydroxide (Ni(OH)₂) flower-like architecture but also significantly enhance the electrochemical features of Ni(OH)₂ nanosheets. After combination with Co₃O₄ nanoparticles and phosphorization treatment, an advanced cathode of Ni₂P/Co₃O₄/N-CQDs with enriched surface phosphate ions is obtained, which possesses an ultra-high capacity of 1044 C g^-1 (2088 F g^-1) at 1 A g^-1 with a splendid rate capacity of 876 C g^-1 (1752 F g^-1) at 20 A g^-1. Moreover, a device assembled by Ni₂P/Co₃O₄/N-CQDs hierarchical flower-like architecture and p-phenylenediamine functionalized reduced graphene oxide (PPD/rGO) nanosheets depicts a commendable energy density of 53.5 Wh kg^-1 at 772.9 W kg^-1. This work provides a novel hierarchical multi-component electrode material with decent electrochemical capacities for hybrid supercapacitors, which has a broad prospect in energy storage devices.

Three-dimensional porous carbon derived from different organic acid salts for application in electrochemical sensing

Three-dimensional porous carbon materials were synthesized by the one-step pyrolysis of organic salts with different numbers of hydroxyl groups on the side chain (sodium tartrate, sodium malate and sodium succinate). Further, the formation of these porous carbon materials was explored. And then, three kinds of carbon materials were used for constructing electrochemical sensors for nitrite detection, respectively. Porous carbon derived from sodium tartrate (PCST) showed the highest electrocatalytic ability for nitrite oxidation among all three materials. The PCST-based sensors allow for rapid detection of nitrite in a wide linear range of 0.1-100 μM with a low detection limit of 0.043 μM. The sensor was applied to detect nitrite in meat samples and the results tested by the developed sensor were consistent with the results obtained by HPLC. We envision that PCST-based electrochemical sensor is promising as an alternative choice for the development of electrochemical analysis.

Combined effect of nitrogen-doped functional groups and porosity of porous carbons on electrochemical performance of supercapacitors

In this work, nitrogen-doped porous carbons obtained from chitosan, gelatine, and green algae were investigated in their role as supercapacitor electrodes. The effects of three factors on electrochemical performance have been studied-of the specific surface area, functional groups, and a porous structure. Varying nitrogen contents (from 5.46 to 10.08 wt.%) and specific surface areas (from 532 to 1095 m2 g-1) were obtained by modifying the carbon precursor and the carbonization temperature. Doping nitrogen into carbon at a level of 5.74-7.09 wt.% appears to be the optimum for obtaining high electrochemical capacitance. The obtained carbons exhibited high capacitance (231 F g-1 at 0.1 A g-1) and cycle durability in a 0.2 mol L-1 K2SO4 electrolyte. Capacitance retention was equal to 91% at 5 A g-1 after 10,000 chronopotentiometry cycles. An analysis of electrochemical behaviour reveals the influence that nitrogen functional groups have on pseudocapacitance. While quaternary-N and pyrrolic-N nitrogen groups have an enhancing effect, due to the presence of a positive charge and thus improved electron transfer at high current loads, the most important functional group affecting energy storage performance is graphite-N/quaternary-N. The study points out that the search for the most favourable organic precursors is as important as the process of converting precursors to carbon-based electrode materials.

Promising activated carbon derived from sugarcane tip as electrode material for high-performance supercapacitors

We present a simple, low-cost method for producing activated-carbon materials from sugarcane tips (ST) via two-step pre-carbonization and KOH activation treatment. After optimizing the amount of KOH, the resulting ST-derived activated carbon prepared with a KOH to PC-ST mass ratio of 2 (ACST-2) contained 17.04 wt% oxygen and had a large surface area of 1206.85 m² g^-1, which could be attributed to the large number of micropores in ACST-2. In a three-electrode system, the ACST-2 electrode exhibited a high specific capacitance of 259 F g^-1 at 0.5 A g^-1 and good rate capability with 82.66% retention from 0.5 to 10 A g^-1. In addition, it displayed a high capacitance retention of 89.6% after 5000 cycles at a current density of 3 A g^-1, demonstrating excellent cycling stability. Furthermore, the ACST-2//ACST-2 symmetric supercapacitor could realize a high specific energy density of 7.93 W h kg^-1 at a specific power density of 100 W kg^-1 in 6 M KOH electrolyte. These results demonstrate that sugarcane tips, which are inexpensive and easily accessible agricultural waste, can be used to create a novel biomass precursor for the production of low-cost activated carbon materials for high-performance supercapacitors.

Electrochemical performance of the homologous molybdenum(vi) redox-active gel polymer electrolyte system

PVA–H₃PO₄–Na₂MoO₄ and PVA–H₃PO₄–PMo₁₂ are assembled into a single solid-state supercapacitor to improve the specific capacitance. Homologous molybdenum (vi) of PMo₁₂ and Na₂MoO₄ provides synergistic effect to improve faradaic capacitance performance.

Sustainable biomass-based hierarchical porous carbon for energy storage: A novel route to maintain electrochemically attractive natural structure of precursor

The development of sustainable and renewable energy storage devices with low cost and environment friendly features is an extremely urgent issue that needs to be solved. Herein, low-cost and sustainable biomass chitin, possessing natural fibrous, O/N-enriched and porous structure, was employed as a porous carbon (PC) precursor. However, a huge challenge in PC preparation is to maintain the natural electrochemically attractive structure of chitin while obtaining highly porous structure. In this study, by utilizing the molten protecting effect and micropore-creating ability of CuCl₂ 2H₂O, the obtained PCs maintain the natural structure, achieve high yield (46%), and simultaneously develop hierarchical pores with a specific surface area range of 1635-2381 m² g^-1, a tunable micropore volume ratio range of 63.5-96.8%, and high surface O/N contents (N: 3.1-9.0 wt% and O: 10.5-12.8 wt%). Benefiting from these excellent properties, optimized PC achieves a high specific capacitance of 286 F g^-1 at 0.5 A g^-1 and a remarkably high rate capability of 88% at 10 A g^-1; moreover, it even exhibits a rate capability of 80% at an ultrahigh current density of 50 A g^-1. The optimized PC-based supercapacitor assembled in Na₂SO₄ electrolyte shows a high energy density of 15.41 W h kg^-1 at 0.19 kW kg^-1 and achieves 76% energy density retention when the power density increased tenfold. Thus, this study presents a new way to fully utilize biomass, especially with electrochemically attractive natural structure, for developing advanced energy storage devices.

One-step production of N-O-P-S co-doped porous carbon from bean worms for supercapacitors with high performance

In recent years, multi-heteroatom-doped hierarchical porous carbons (HPCs) derived from natural potential precursors and synthesized in a simple, efficient and environmentally friendly manner have received extensive attention in many critical technology applications. Herein, bean worms (BWs), a pest in bean fields, were innovatively employed as a precursor via a one-step method to prepare N-O-P-S co-doped porous carbon materials. The pore structure and surface elemental composition of carbon can be modified by adjusting KOH dosage, exhibiting a high surface area (S _BET) of 1967.1 m² g^-1 together with many surface functional groups. The BW-based electrodes for supercapacitors were shown to have a good capacitance of up to 371.8 F g^-1 in 6 M KOH electrolyte at 0.1 A g^-1, and good rate properties with 190 F g^-1 at a high current density of 10 A g^-1. Furthermore, a symmetric supercapacitor based on the optimal carbon material (BWPC_1/3) was also assembled with a wide voltage window of 2.0 V, demonstrating satisfactory energy density (27.5 W h kg^-1 at 200 W kg^-1) and electrochemical cycling stability (97.1% retention at 10 A g^-1 over 10 000 charge/discharge cycles). The facile strategy proposed in this work provides an attractive way to achieve high-efficiency and scalable production of biomass-derived HPCs for energy storage.