Conversion of Lignin into Porous Carbons for High-Performance Supercapacitors via Spray Drying and KOH Activation: Structure-Properties Relationship and Reaction Mechanism

Lignin-derived porous carbons have emerged as promising electrode materials for supercapacitors.However,the challenge remains in designing and controlling their structure to achieve ideal electrochemical performance due to the complex molecular structure of lignin and its intricate chemical reactions during the activation process.In this study,three porous carbons were synthesized from lignin by spray drying and chemical activation with vary-ing KOH ratios.The specific surface area and structural order of the prepared porous carbon continued to increase with the increase of the KOH ratio.Thermogravimetric-mass spectrometry(TG-MS)was employed to track the molecular fragments generated during the pyrolysis of KOH-activated lignin,and the mechanism of the thermochemical conversion was investigated.During the thermochemical conversion of lignin,KOH facili-tated the removal of H2 and CO,leading to the formation of not only more micropores and mesopores,but also more ordered carbon structures.The pore structure exhibited a greater impact than the carbon structure on the electrochemical performance of porous carbon.The optimized porous carbon exhibited a capacitance of 256 F g-1 at a current density of 0.2 A g-1,making it an ideal electrode material for high-performance supercapacitors.

Activated carbon prepared from waste tire pyrolysis carbon black via CO_(2)/KOH activation used as supercapacitor electrode

As the quantity of waste tires increases,more pyrolysis carbon black(CBp),a type of low value-added carbon black,is being produced.However,the application of CBp has been limited.Therefore,it is necessary to identify and expand applications of CBp.This work focuses on the preparation of activated carbon(AC)from CBp using the physicochemical activation of carbon dioxide(CO_(2))and potassium hydroxide(KOH).Thereafter,AC is applied to the electrode of the electrical double-layer capacitor(EDLC).The AC prepared by CO_(2)/KOH activation exhibited a hierarchical pore structure.The specific surface area increased from 415 to 733 m^(2)g^(−1),and in combination with low ash content of 1.51%,ensured abundant ion diffusion channels and active sites to store charge.The EDLC comprising the AC(AC-2)electrode prepared by excitation of CO_(2)(300 sccm)and KOH had a reasonable gravimetric specific capacitance of 192 F g^(−1)at 0.5 A g^(−1),and exhibited a good rate capability of 73%at 50 A g^(−1)in a three-electrode system.Moreover,the EDLC device comprising the AC-2 electrode delivered excellent cycling stability(capacitance retention of 106%after 10000 cycles at 2 A g^(−1)in a two-electrode system).Furthermore,a symmetric supercapacitor based on an AC electrode that exhibits a supreme energy density of 4.7 Wh kg^(−1)and a maximum power density of 6362.6 W kg^(−1)is demonstrated.

Activated Carbon from Rice Husk with One-Step KOH Mechanical Mixing Activation as Adsorbent for Treating Phenolic Wastewater

This study investigates how large-surface-area biocarbons with high phenolic adsorption capacities can be obtained from cheap and abundant rice husk(RH).The RH is directly mixed with potassium hydroxide(KOH)and activated in a flowing N_(2) atmosphere,and the effects of the pyrolysis temperature and KOH to RH ratio on the structure of the obtained activated carbon adsorbents and their adsorption of p-nitrophenol and phenol are studied.The results show that the optimum pyrolysis temperature of RH is 750℃,whereby the highest surface area of 2047 m^(2)/g and best adsorption performance are obtained with a KOH to RH ratio of 3:1.Moreover,the obtained biocarbons achieve a maximum adsorption capacity of 175 mg/g for phenol and 430 mg/g for p-nitrophenol,which are higher than most previously reported data.

Effects of thermal activation conditions on the microstructure regulation of corncob-derived activated carbon for hydrogen storage

Activated carbons derived from corncob （CACs） were prepared by pyrolysis carbonization and KOH activation. Through modifying activation conditions, samples with large pore volume and ultrahigh BET specific surface area could be obtained. The sample achieved the highest hydrogen uptake capacity of 5.80 wt% at 40 bar and -196℃ The as-obtained samples were characterized by N2-sorption, transmission electron microscopy （TEM） and scanning electron microscopy （SEM）. Besides, thermogravimetric analysis was also employed to investigate the activation behavior of CACs. Detailed investigation on the activation parameters reveals that moderate activation temperature and heating rate are favorable for preparing CACs with high surface area, large pore volume and optimal pore size distribution. Meanwhile, the micropore volume between 0.65 nm and 0.85 nm along with BET surface area and total pore volume has great effects on hydrogen uptake capacities. The present results indicate that CACs are the most promising materials for hydrogen storage application.

Metal-organic framework-derived porous carbon for the advanced aqueous zinc-ion hybrid capacitor

Aqueous zinc ion hybrid capacitors(ZIHCs)are considered one of the most promising electrochemical energy storage systems due to their high safety,environmental friendliness,low cost,and high power density.However,the low energy density and the lack of sustainable design strategies for the cathodes hinder the practical application of ZIHCs.Herein,we design the N and O co-doped porous carbon cathode by annealing metal-organic framework(ZIF-8).ZIF-8 retains the original dodecahedral structure with a high specific surface(2814.67 m^(2)/g)and I_(G)/I_(D) ratio of 1.0 during carbonization and achieves self-doping of N and O heteroatoms.Abundant defect sites are introduced into the porous carbon to provide additional active sites for ion adsorption after the activation of carbonized ZIF-8 by KOH treatment.The ZIHCs assembled with modified ZIF-8 as the cathode and commercial zinc foil as the anode show an energy density of 125 W∙h/kg and a power density of 79 W/kg.In addition,this ZIHCs device achieves capacity retention of 77.8%after 9000 electrochemical cycles,which is attributed to the diverse pore structure and plentiful defect sites of ZIF-8-800(KOH).The proposed strategy may be useful in developing high-performance metal-ion hybrid capacitors for large-scale energy storage.

Preparation and Electrochemical Performance Study of Catalytic Cracking Oil Slurry-based Porous Carbon Materials

Catalytic cracking oil slurry is a by-product of catalytic cracking projects,and the efficient conversion and sustainable utilization of this material are issues of continuous concern in the petroleum refining industry.In this study,oxygen-enriched activated carbon is prepared using a one-step KOH activation method with catalytic cracking oil slurry as the raw material.The as-prepared oil slurry-based activated carbon exhibits a high specific surface area of 2102 m^(2)/g,welldefined micropores with an average diameter of 2 nm,and a rich oxygen doping content of 32.97%.The electrochemical performance of the nitrogen-doped porous carbon is tested in a three-electrode system using a 6 mol/L KOH solution as the electrolyte.It achieves a specific capacitance of up to 230 F/g at a current density of 1 A/g.Moreover,the capacitance retention rate exceeds 89%after 10000 charge and discharge cycles,demonstrating excellent cycle stability.This method not only improves the utilization efficiency of industrial fuel waste but also reduces the production cost of supercapacitor electrode materials,thereby providing a simple and effective strategy for the resource utilization of catalytic cracking oil slurries.

Synthesis of one-dimensional carbon nanostructures and their application as anode materials in lithium ion batteries

An efficient synthesis of carbon nanofibers by pyrolysis of as-prepared polypyrrole nanowires was reported. Under the subsequent KOH activation, a significant morphology variation was detected and the obtained sample took on a ribbon-like structure. The morphology and structure of the carbon nanofibers and carbon nanoribbons were characterized. When the as-prepared one-dimensional carbon nanostructures were used as anode materials in lithium ion batteries, both of them exhibited superior cyclical stability and good rate properties. After 50 cycles, the reversible capacity of carbon nanofibers electrode maintained 530 mA·h/g. Concerning carbon nanoribbons, the reversible capacity is always larger than 850 mA·h/g and the reversible capacity retention after 23 cycles is 86%.

Two-Step Preparation of Hierarchical Porous Carbon Materials Derived from Tannin for Use as an Electrode Material for Supercapacitors

The development and utilization of biomass and agroforestry processing byproducts for high-value applications have been an important topic in the field of renewable materials research.Based on this,a two-step microwave hydrothermal pre-carbonization and KOH activation method was proposed to synthesize tannin-based activated carbons with a high specific surface area,hierarchical pore structure,and good electrochemical performance.The microstructure,texture properties,and physicochemical characteristics were investigated.The results show that the prepared tannin-based activated carbons presented a hierarchical pore structure(micro-and mesopores)with a specific surface area as high as 997.46 m^(3) g^(−1).The electrochemical analysis shows that the tannin-based activated carbons have good wettability and charge transfer rates.Under the three-electrode system with 6 M KOH as the electrolyte,the active material TAC_(600-4) had a maximum specific capacitance of 171 F g^(−1)at 0.5 A g^(−1).As the current density increases to 10 A g^(−1),the specific capacitance can still be maintained at 149 F g^(−1),indicating a good rate capability.Therefore,the specific surface area and pore size of tannin-based activated carbons can be effectively adjusted by the alkali/carbon ratio,making it a promising supercapacitor electrode material and providing a new method for the high-value development of tannins in the field of electrochemical energy storage.

The Influence of Dry or Wet Activating Process to the Electrochemical Features of Biowaste Carbon

The utilization of biowaste to the activated carbon(AC)as electrode material is conducive to alleviating the energy crisis and promoting the high value-added.The popular KOH activation has been applied for years,but rare report clarified the difference of dry and wet activation,with which the batch producing technique could be different.Here nitrogen doped hierarchical AC was derived from wood chip by a wet or dry KOH activation.The surface area,framework structure and surface feature were characterized to reveal the effect of wet and dry activation.1.44 at%of nitrogen doped AC was made by dry KOH activation,which was higher than the AC derived from wet KOH activation with 1.36 at%of nitrogen.Their electrochemical properties were investigated in 6 mol L^(-1)of KOH,the capacitance of wAC was 401 F g^(-1)at 0.5 A g^(-1),but dAC possessed a capacitance of 215 F g^(-1).These indicated that AC obtained by using wet KOH activation displayed a potential application in energy field.

2-Steps Preparation Activated Carbon from Solidago Canadensis:Carbonized by Electrial heating and Activated by Microwave Radiation

The activated carbon(AC)was prepared from Solidago Canadensis(SC),an alien invasive plant.The plant was firstly carbonized under nitrogen at 400 ℃ for 90 min in an electrical furnace,and then the carbonized product was activated with KOH through microwave radiation.Effects of KOH/C ratio,microwave power,microwave radiation time on the adsorption capacities and yield of AC were evaluated.It indicated that the optimum conditions were KOH/C ratio 2 g/g,microwave power 700 W,and microwave radiation time 6 min.The carbonation process of SC was analyzed by thermogravimetry(TG).The pore structural parameters and surface functional groups of the AC were characterized by nitrogen adsorption-desorption and Fourier Transformed Infrared Spectroscopy(FTIR),respectively.The activation yield,the surface area,the average pore size,and the average micropore size of AC prepared from optimum conditions were 53.75%,1 888 m2/g,0.567 nm,and 0.488 nm,respectively.The adsorption amounts of AC were 302.4 mg/g for methylene blue and 1 470.27 mg/g for iodine.

Synthesis,characterization and life cycle assessment of electrochemically exfoliated KOH-activated holey graphene

Graphene materials have drawn tremendous attention in recent years.The formation of holes and pores on graphene sheets can provide transfer channels and facilitate the ion/electron transport kinetics.In this study,graphene nanosheets were prepared electrochemically,and then,they were used as the starting material for the preparation of holey graphene(HG)through the KOH activation process.The weight ratio of initial electrochemically exfoliated graphene(EEG)to KOH was optimized according to the morphological features,BET surface area examination,graphene number of layers calculated from XRD patterns,and the ID/IG ratio obtained from Raman analysis.Results showed that increasing the KOH amount led to the achievement of higher values of ID/IG and surface area and less re-stacking of graphene sheets which occurs because of the heat treatment process.The environmental burdens of the production routes for the preparation of EEG and HG were investigated by cradle-to-gate life cycle assessment(LCA).The LCA results of EEG production indicated that electricity with the contributions of 94%,91%,82%,and 75%of the total impact in four environmental categories,including fossil fuel depletion,ozone depletion,global warming,and smog was the main environmental weakness.In the pore generation process,KOH was recognized as the biggest contributor(about 51%to 83%of the total impact)in six impact categories,including ozone depletion,non-carcinogenics,smog,global warming,carcinogenics,and eutrophication which could be attributed to its high consumption amount(21.9 kg).This work offers environmental considerations for the development of sustainable graphene materials.

Superior CO2 uptake on nitrogen doped carbonaceous adsorbents from commercial phenolic resin

In this study,N-doped porous carbons were produced with commercial phenolic resin as the raw material,urea as the nitrogen source and KOH as the activation agent.Different from conventional carbonization-nitriding-activation three-step method,a facile two-step process was explored to produce N-incorporated porous carbons.The as-obtained adsorbents hold superior CO2 uptake,i.e.5.01 and 7.47 mmol/g at 25℃and 0℃under 1 bar,respectively.The synergistic effects of N species on the surface and narrow micropores of the adsorbents decide their CO2 uptake under 25℃and atmospheric pressure.These phenolic resin-derived adsorbents also possess many extremely promising CO2 adsorption features like good recyclability,quick adsorption kinetics,modest heat of adsorption,great selectivity of CO2 over N2 and outstanding dynamic adsorption capacity.Cheap precursor,easy preparation strategy and excellent CO2 adsorption properties make these phenolic resin-derived N-doped carbonaceous adsorbents highly promising in CO2 capture.

Effect of surface area and heteroatom of porous carbon materials on electrochemical capacitance in aqueous and organic electrolytes

A series of porous carbon materials with wide range of specific surface areas and different heteroatom contents had been prepared using polyaniline as carbon precursor and KOH as an activating agent. Effect of surface area and heteroatom of porous carbon materials on specific capacitance was investigated thoroughly in two typical aqueous KOH and organic 1-butyl-3- methylimidazolium tetrafluoroborate/acetonitirle electrolytes. The different trends of capacitance performance were observed in these two electrolytes. Electrochemical analyses suggested that the presence of faradaic interactions on heteroatom-enriched carbon materials in organic environment is less significant than that observed in aqueous electrolytes. Thus, in aqueous electrolyte, a balance between surface area and heteroatom content of activated porous carbon would be found to develop a supercapacitor with high energy density. In organic electrolyte, the capacitance performance of porous carbon is strongly dependent on the surface area. The results may be useful for the design of porous carbon-based supercapacitor with the desired capacitive performance in aqueous and organic electrolytes.

Activated carbon produced from paulownia sawdust for high-performance CO_2 sorbents

In this paper, activated carbons （ACs） with high specific surface areas were successfully synthesized by simple one-step carbonization-activation from paulownia sawdust biomass, and the effects of the synthetic conditions on their CO2 capture capacity were investigated as well. The results show that, when the mass ratio between activator and biomass is 4, the activation temperature is 700℃ and the activation time is 1 h, as-made AC provides the most micropores for CO2 adsorption. As a consequence, the maximum CO2 uptake of 8.0 mmol/g is obtained at 0 ℃ and 1 bar.

Hierarchical porous carbon derived from coal-based carbon foam for high-performance supercapacitors

Hierarchical porous carbon(HPC)from bituminous coal was designed and synthesized through pyrolysis foaming and KOH activation.The obtained HPC(NCF-KOH)were characterized by a high specific surface area(S_(BET))of 3472.41 m^(2)/g,appropriate mesopores with V_(mes)/V_(total)of 57%,and a proper amount of surface oxygen content(10.03%).This NCF-KOH exhibited a high specific capacitance of 487 F/g at 1.0 A/g and a rate capability of 400 F/g at 50 A/g based on the three-electrode configuration.As an electrode for a symmetric capacitor,a specific capacitance of 299 F/g at 0.5 A/g was exhibited,and the specific capacitance retained 96%of the initial capacity at 5 A/g after 10,000 cycles.Furthermore,under the power density of 249.6 W/kg in 6 mol/L KOH,a high energy density of 10.34 Wh/kg was obtained.The excellent charge storage capability benefited from its interconnected hierarchical pore structure with high accessible surface area and the suitable amount of oxygen-containing functional groups.Thus,an effective strategy to synthesize HPC for high-performance supercapacitors serves as a promising way of converting coal into advanced carbon materials.

Preparation and performance evaluation of resin-derived carbon spheres for desulfurization of fuels

A polystyrene-based ion-exchange resin was employed as the precursor for preparation of resin-derived carbon spheres （RCSs） through KOH activation with various impregnation ratios. Pore structure, yield and hardness, surface functional groups of the samples and their adsorption performance towards dibenzothiophene （DBT） were investigated. The RCSs with large surface areas （up to 2696 m2/g） and total pore volumes （up to 1.46 cm3/g） exhibited larger adsorption capacities than a commercial ac- tivated carbon, F400. Polanyi-Dubinin-Mane （PDM） model was applied to fit the adsorption data, which proved that micropore filling was involved during the adsorption process. Moreover, a good linear relationship was observed between the ex- tra-micropore volume and adsorption capacity. Intra-particle diffusion （IPD） model was used to describe the kinetic data of DBT onto the adsorbents. The adsorption processes were divided into three stages according to the different diffusion parame- ter. The selective adsorption towards DBT in the presence of competing compounds was also investigated and the high selec- tivity of the RSCs towards DBT may be attributed to the large quantity of acidic oxygen-containing groups.

Efficient nitrogen doped porous carbonaceous CO_(2) adsorbents based on lotus leaf

In this work, the waste biomass lotus leaf was converted into N-doped porous carbonaceous CO_(2) adsorbents. The synthesis process includes carbonization of lotus leaf, melamine post-treatment and KOH activation. For the resultant sorbents, high nitrogen content can be contained due to the melamine modification and advanced porous structure were formed by KOH etching. These samples were carefully characterized by different techniques and their CO_(2) adsorption properties were investigated in detail. These sorbents hold good CO_(2) adsorption abilities, up to 3.87 and 5.89 mmol/g at 25 and 0 °C under 1 bar, respectively. By thorough investigation, the combined interplay of N content and narrow microporous volume was found to be responsible for the CO_(2) uptake for this series of sorbents. Together with the high CO_(2) adsorption abilities, these carbons also display excellent reversibility, high CO_(2)/N 2 selectivity, applicable heat of adsorption, fast CO_(2) adsorption kinetics and good dynamic CO_(2) adsorption capacity. This study reveals a universal method of obtaining N-doped porous carbonaceous sorbents from leaves. The low cost of raw materials accompanied by easy synthesis procedure disclose the enormous potential of leaves-based carbons in CO_(2) capture as well as many other applications.

Synthesis of porous carbon spheres derived from lignin through a facile method for high performance supercapacitors

Porous carbon spheres（PCS） derived from lignin have been prepared through a facile method and fabricated as electrodes for electric double-layer capacitors. Spherical shaped mixtures of lignosulfonate and crystalized KOH are formed by spray drying of a solution of lignosulfonate and KOH. Activation by KOH is performed at high temperatures along with lignosulfonate carbonization. With an appropriate pore structure, the obtained PCS have a specific surface area of 1372.87 m^2 g^-1 and show a capacitance of 340 F g^-1 in 3 M KOH at a current density of 0.5 A g^-1. Moreover, a symmetric supercapacitor fabricated using the PCS as electrodes show a maximum capacitance of 68.5 F g^-1, and an energy density of 9.7 W h kg^-1 at a power density of 250 W kg^-1. The capacity retention is more than 94.5% after 5000 galvanostatic chargedischarge cycles. The excellent characteristics seem to be ascribed to the pore structures of PCS that have a large specific surface area and a low electrical resistance.

Nitrogen-doped porous carbons from polyacrylonitrile fiber as effective CO_(2) adsorbents

In this report, nitrogen-doped porous carbons were synthesized from polyacrylonitrile fiber by a facile two-step synthesis process i.e. carbonization followed by KOH activation. Activation temperature and KOH/carbon ratio are two parameters to tune the porosity and surface chemical properties of sorbents. The as-obtained sorbents were carefully characterized.Special attention was paid concerning the change of sorbents’ morphology with respect to synthesis conditions. Under the activation temperatures of this study, the sorbents can still retain their fibrous structure when the KOH/carbon mass ratio is 1. Further increasing the KOH amount will destroy the original morphology of polyacrylonitrile fiber. CO_(2)adsorption performance tests show that a sorbent retaining the fibrous shape possesses the highest CO_(2)uptake of 3.95 mmol/g at 25℃and 1 bar. Comprehensive investigation found that the mutual effect of narrow microporosity and doped N content govern the CO_(2)adsorption capacity of these adsorbents. Furthermore, these polyacrylonitrile fiber-derived carbons present multiple outstanding CO_(2)capture properties such as excellent recyclability, high CO_(2)/N_(2)selectivity, fast adsorption kinetics, suitable heat of adsorption, and good dynamic adsorption capacity. Hence, nitrogen-doped porous carbons with fibrous structure are promising in CO_(2)capture.

Fabrication of coconut shell-derived porous carbons for CO_(2) adsorption application

Biomass-derived porous carbons have been considered as the most potential candidate for effective CO_(2) adsorbent thanks to being widely-available precursor and having highly porous structure and stable chemical/physical features.However,the biomass-derived porous carbons still suffer from the poor optimization process in terms of the synthesis conditions.Herein,we have successfully fabricated coconut shell-derived porous carbon by a simple one-step synthesis process.The as-prepared carbon exhibits advanced textual activity together with well-designed micropore morphology and possesses oxygen-containing functional groups(reached 18.81 wt%)within the carbon matrix.Depending on the different activating temperatures(from 700 to 800℃)and KOH/biomass mass ratios(from 0.3 to 1),the 750℃ and 0.5 mass ratio were found to be enabling the highest CO_(2) capture performance.The optimal adsorbent was achieved a high CO_(2) uptake capacity of 5.92 and 4.15 mmol·g^(−1) at 0 and 25℃(1 bar),respectively.More importantly,as-prepared carbon adsorbent exhibited moderate isosteric heat of adsorption and high CO_(2)/N_(2) selectivity.The results were revealed not only the textural feature but also the surface functional groups critically determine the CO_(2) capture performance,indicating coconut shell-derived porous carbon has a considerable potential as a solid-state adsorbent for the CO_(2) capture.