Porous Activated Carbon Research Articles

Hydrothermal Synthesis of CoMoO4/Co9S8 Nanorod Arrays on Nickel Foam for High-Performance Asymmetric Supercapacitors with High Energy Density

CoMoO4/Co9S8 nanorod arrays supported on nickel foam are successfully assembled via a facile two-step hydrothermal route. Due to the unique nanorod array structure, the CoMoO4/Co9S8, as the electrode, possesses a high capacity 1.54mA h·cm−2 (343.21mA h·g−1) and a large capacitance 9.17Fcm−2 (2059.26Fg−1) at a current density of 20 mA·cm−2 (4.44 A·g−1), and an excellent cycling stability (8.6% degradation after 3000 cycles). The asymmetric supercapacitor based on the CoMoO4/Co9S8 nanorod arrays as a positive electrode and porous active carbon as a negative electrode in an alkaline KOH aqueous electrolyte is fabricated. Owing to the synergetic effect between CoMoO4/Co9S8 and active carbon, CoMoO4/Co9S8//active carbon asymmetric supercapacitor exhibits an outstanding energy density of 42 Wh·kg−1 and an excellent cycling stability with 89.5% specific capacitance retained after 5000 cycles in an operating voltage of 1.6V. The facile synthesis route and remarkable supercapacitive performance of the CoMoO4/Co9S8 nanorod arrays is promising as a positive electrode materials for high-performance asymmetric supercapacitors.

Synthesis of MnO Nano-Particle@Flourine Doped Carbon and Its Application in Hybrid Supercapacitor

In order to meet the increasing demand for the high energy and high power in the same time, while neither secondary batteries nor double-layer supercapacitors cannot satisfy, a new energy storage device, hybrid supercapacitor, attracked lots of attentions in recent days. The new device hybrid the double layer capacitor electrode, which provides the high power density, with the secondary battery electrode, which supplys the high energy density. Various of lithium ion batteries(LIBs) electrodes are introduced into this hybrid system. As the alternative materials to the carbonaceous anode in commercial LIBs, numerous of transition metals have been studied as the anode of LIBs due to their high theoretical capacity, high safety and environmental benignity. Here, a transition metal MnO, a promising material used as anode in LIBs, worked with porous carbon materials to form a new lithium ion hybrid supercapacitor. In this device, MnO is used as negative electrode. Meantime the porous active carbon electrode serves as positive electrode. Similar with other transition metal materials, the intrinsic high resistance, large volume variation during the charge and discharge will still impede the MnO involving into the hybrid system. Especially the late one will cause the pulverization of the MnO materials and then the loosing contact between active materials and current collector. This will cause a significantly capacity fading and bad cycling stability. Since the high energy capacity, excellent cycle-ability and good rate performance are the major merits of hybrid supercapacitor, therefore those problems of MnO should be solved first. To solve those problems, covering nano-sized MnO materials with conductive carbon layer is a proper approach. Furthermore, It is widely recognized that doping hetero-atom onto the carbon can change their electronic configuration and then improve the electrochemical performances of the carbon materials. Therefore, in this study, a fluorine-doped carbon encapsulated MnO nano-particle (MnONP@FC) was fabricated through a novel process. In this synthesis process, Nafion ionomers was used as the fluorine doped carbon precursor. As shown in Scheme 1, Mn ions are first self-assembly trapped within the Nafion matrix through the electrostatic interaction between positive charged Mn ion and negative charged sulfonate end groups in Nafion ionomer. Then after pyrolysis under nitrogen atmosphere, the Nafion ionomers was transformed into carbon frameworks and MnO nano-particles was formed and highly dispersed within them. The formed MnONP@FC was characterized through SEM, TEM and XPS and the electrochemical performances of the hybrid device, which composited MnONP@FC with the porous carbon materials, were also investigated. The results exhibited that this new hybrid supercapacitor showed a high energy density up to 40 mAh g-1, long cycle stability and good rate performance. Figure 1

Protic ionic liquids with N-chloroalkyl functionalized cations as electrolytes for carbon-based electrochemical capacitors

This study reports on the implementation of protic ionic liquids (PILs) with N‐chloroalkyl functionalized cations and [TFSI]− anion as electrolytes for activated carbon (AC) based electrochemical capacitors (ECs). The electrochemical stability of PILs themselves and risk of corrosive behavior in contact with stainless steel (SSt) and aluminum (Al), as prospective current collectors materials, were investigated. Similar negative stability limits were proven for both materials, yet advantageous passivation of Al under anodic polarization was evidenced. Afterwards, the electrochemical stability was evaluated on porous AC electrodes by potential window opening measurements. For all PILs, it evidenced almost identical performance and stability on AC-electrode under positive polarization owing to the common [TFSI]− anion. Under negative polarization, depending on the electron withdrawing effect of the N-chloroalkyl group on the N-H bond, two types of PIL behavior followed the region of EDL charging: hydrogen chemisorption onto AC or direct electrolyte decomposition. In the former case, the reduction potential of the protonated amine during cathodic sweep, as well as the desorption peak location during the anodic one were proven to be dependent on pKa of the protonated amine. The stability data were used to interpret the voltage limits of symmetric two-electrode cells implementing electrodes made from the same carbon. Finally, the performance of ECs based on the PILs with N-chloroalkyl functionalized cations was determined.

Walnut shell – Derived activated carbon: Synthesis and its application in the sulfur cathode for lithium–sulfur batteries

Biomass walnut shell was used to prepare activated carbon (AC) through a carbonization treatment and an activation procedure with potassium hydroxide (KOH). AC showed hierarchical pores: 0.6 nm micropores, 2.7 nm mesopores and macropores with average diameter of 50 nm, providing a large specific surface area of 2318 m2 g−1. This highly porous AC was tested as a host material to encapsulate sulfur via a vapor phase infusion process. The developed AC-S electrode showed a high initial specific capacity of 1350 mAh g−1 and good capacity retention over 100 cycles at 0.1 C for lithium–sulfur battery.

Effect of acid and hydrothermal treatments on the dye adsorption properties of biomass-derived activated carbon

Different types of acid pretreatment are known to influence the removal of certain components from pine wood sawdust, due to differences in the acid hydrolysis, which also predetermine the final formation and adsorptive properties of the produced activated carbon (AC) through subsequent potassium hydroxide activation. AC made by using phosphorous acid as an acid pretreatment had the largest absorption capacity of methylene blue (MB) dye due to its highest acidity. Subsequently, the effects on the adsorption variables for this AC such as initial pH, MB concentration, contact time and temperature were investigated. The resulting adsorption process was classified as pseudo-second-order kinetic model, and the Langmuir isotherm model better described the equilibrium data in comparison with the Freundlich isotherm model. The outcome showed that a lower temperature had an increased adsorption capacity of sawdust-derived AC pretreated with phosphorous acid, which allowed maximum adsorption capacities of 303.03 mg/g at 30 °C, implying that the adsorption was an endothermic process. Phosphorous acid pretreatment and activation processes proved to be an effective strategy to prepare highly porous AC from sawdust, with high potential to cationic dye removal from liquid phases.

High-surface-area tofu based activated porous carbon for electrical double-layer capacitors

Activated porous carbon (APC), which is used as the electrode material in electrical double layer capacitors (EDLCs), is constantly being developed to enhance its electrochemical performance with low cost. Nevertheless, APC still encounters important challenges due to the limited amount of raw material resources. Herein, we propose a novel and simple approach to synthesize APC from tofu using a simple synthesis process involving carbonization with KOH activation. To obtain the optimized APC, three types of APCs are prepared using different weight ratios of 1:3, 1:4, and 1:5 (WTofu/WKOH) during the carbonization. The optimized APC electrode shows an outstanding specific capacitance of 207 F g−1 at a current density of 0.1 A g−1, a remarkable high-rate performance, an impressive energy density of 25.7–19.9 W h kg−1, and an excellent cycling stability for up to 2000 cycles. Therefore, this unique approach to obtain APC using tofu yield a material with some useful qualities in terms of an increased number of electroactive sites based on a high surface area, and an improved wettability based on the oxygen-containing functional groups on the surface of the APC. Accordingly, tofu-based APC is a promising alternative to conventional APC.

Porous Active Carbon Layer Modified Graphene for High-performance Supercapacitor

Carbon-based nanostructures have drawn special attention for use in supercapacitive applications due to their high specific surface area and stability. Balancing the conflict between activity and the conductivity of carbon based electrode materials would contribute to comprehensive energy storage performance for practical application. In this work, an activated carbon layer covered graphene (ACG) with adjustable thickness has been fabricated by hydrothermal treatment of graphene oxide with glucose and further activation with a KOH agent. The electrochemical performance of ACG is related to the thickness of the active layer on the surface of the ACG. The ACG with a suitable thickness of 1–2nm exhibits a high specific capacitance of 248.4Fg−1 at 1Ag−1 and perfect rate performance with a high capacitance of 187.5Fg−1 at a large current density of 100Ag−1 owing to both high activity and conductivity. Particularly, the synergetic effect of the active porous carbon and conductive graphene results in considerable energy properties of the ACG based symmetric devices.

Elimination of methane in exhaust gas from biogas upgrading process by immobilized methane-oxidizing bacteria

Biogas upgrading is essential for the comprehensive utilization of biogas as substitute of natural gas. However, the methane in the biogas can be fully recovered during the upgrading process of biogas, and the exhaust gas produced during biogas upgrading may contain a very low concentration of methane. If the exhaust gas with low concentration methane releases to atmosphere, it will be harmful to environment. In addition, the utilization of large amounts of digestate produced from biogas plant is another important issue for the development of biogas industry. In this study, solid digestate was used to produce active carbon, which was subsequently used as immobilized material for methane-oxidizing bacteria (MOB) in biofilter. Biofilter with MOB immobilized on active carbon was used to eliminate the methane in exhaust gas from biogas upgrading process. Results showed porous active carbon was successfully made from solid digestate. The final methane elimination capacity of immobilized MOB reached about 13molh−1m−3, which was more 4 times higher than that of MOB without immobilization.

Nitrogen-doped porous activated carbon derived from cocoon silk as a highly efficient metal-free electrocatalyst for the oxygen reduction reaction

Nitrogen-doped porous activated carbon (PAC) has been fabricated via a facile heat-treatment and chemical activation of cocoon silk. The prepared PAC exhibits excellent ORR catalytic activity.

Response surface methodology approach for optimization of Cu2+, Ni2+ and Pb2+ adsorption using KOH-activated carbon from banana peel

This study aims at optimizing the adsorption of heavy metal ions onto banana peel derived activated carbon (AC) using response surface methodology (RSM) involving central composite design (CCD). The cheap, non-toxic and locally available banana peel was subjected to carbonization and subsequently KOH-activation to produce the porous AC, which was then characterized by SEM and FTIR analyses. In RSM study, the individual and interactive effects of three critical variables including heavy metal ion concentration, pH of solution and AC dosage on the adsorption capacity were optimized. The maximum adsorption capacity appeared to follow the order: Cu2+ (14.3mg/g)<Ni2+ (27.4mg/g)<Pb2+ (34.5mg/g) that agreed well with the verification experiments, revealing the reliability and suitability of the optimization approach. In addition, the results of isotherm study show that the Langmuir model can be used to best describe the adsorption behavior of Cu2+ and Ni2+ onto the banana peel derived activated carbon.

Three-dimensional flexible carbon electrode for symmetrical supercapacitors

Three-dimensional (3D) porous active carbon (AC) is fabricated by pyrolysis, pre-carbonization, and alkali activation of the biomass of pomelo peels (PP). The PP-derived AC has abundant micro/meso/macropores boosting a large specific surface area of 1665m2g−1 and facilitating incorporation of the carbon nanotubes (CNTs) and reduced graphene oxide (rGO) into the materials. After mixing with CNTs and rGO, the hybrid carbon film with 80wt% AC (AC/rGO/CNT) exhibits a large capacitance of 214Fg−1 at 1Ag−1, good rate capability, as well as excellent mechanical properties. The specific capacitance of the assembled symmetrical capacitor comprising the hybrid carbon film is 101.5Fg−1 at 1Ag−1 and in conjunction with the superior cycling stability, the high-performance flexible carbon-based supercapacitors (SCs) have large commercial potential.

Biobased Nano Porous Active Carbon Fibers for High-Performance Supercapacitors.

Activated carbon fibers (ACFs) with different pore structure have been prepared from wood sawdust using the KOH activation method. A study was conducted to examine the influence of the activation parameters (temperature, alkali/carbon ratio, and time) on the morphology and structure of the as-prepared ACFs developed in the process of pore generation and evolution. Activation temperature was very essential for the formation of utramicropores (<0.6 nm), which greatly contributed to the electric double layer capacitance. The significance of metallic potassium vapor evolved when the temperature was above 800 °C, since the generation of 0.8- and 1.1 nm micropores cannot be ignored. When the the KOH/fiber ratio was increased and the activation time was prolonged, to some extent, the micropores were enlarged to small mesopores within 2-5 nm. The sample with the optimal condition exhibited the highest specific capacitance (225 F g(-1) at a current density of 0.5 A g(-1)). Its ability to retain capacitance corresponding to 10 A g(-1) and 6 M KOH was 85.3%, demonstrating a good rate capability. With 10 000 charge-discharge cycles at 3 A g(-1), the supercapacitor kept 94.2% capacity, showing outstanding electrochemical performance as promising electrode material.

Simultaneously obtaining fluorescent carbon dots and porous active carbon for supercapacitors from biomass

We present a facile and green approach to simultaneously synthesize fluorescent carbon dots and porous active carbon for supercapacitors via a two-step carbonization process from a widely available protein-rich biomass precursor – soybeans.

Hierarchical porous active carbon from fallen leaves by synergy of K2CO3 and their supercapacitor performance

The active carbon materials (ACs) derived from fallen leaves (FLs) are prepared by the activations of mixed KOH and K2CO3. Characterizations reveal that the use of single activator KOH creates the most of micropores in three dimensional and K2CO3 produces the mesopores/macropores mostly in shallow. When combining KOH with K2CO3, the pore size of ACs is enlarged. The surface areas and hierarchical pore structures are related to the mass ratio of two activators. The electrochemical properties are monitored with the cyclic voltametry, charging-discharging and electrical impedance spectra. The prepared sample displays high specific capacitance of up to 242 F g−1 (0.3 A g−1, 6 M KOH) in a two-electrode system. Their good cycling stability with nearly no capacitance decrease is obtained after 2000 cycles.

Preparation and Characterization of Green Porous Palm Shell Based Activated Carbon by Two Step Chemical Activation Using KOH

The large quantity of agricultural waste materials that poses disposal challenge to our environment could be converted into useful products such as activated carbon (AC). Palm oil shell based porous AC was prepared by two step process using KOH as the chemical activant. Palm oil shell was carbonized at 800°C for 2 hours and activated using CO2 at same temperature for 1 hour which yield 23.27% fixed carbon. The AC was characterized by Langmuir surface area, BET surface area and pore volume of 410.7 m2/g, 350 m2/g and 0.2 cm3/g respectively, the FTIR analysis identified the presence of alkanes, carbonyls and hydroxyls as the main functional groups in the AC. Scanning electron microscopy images illustrates the gradual formation of pores from the precursor to the produced AC due to elimination of volatiles and contaminants in the material. However, the AC produced showed basic properties suitable for the removal of hydrophobic organic contaminants in water and wastewater.

Enhanced supercapacitive performance on TiO2@C coaxial nano-rod array through a bio-inspired approach

A coaxial core–shell structured TiO2@carbon nano-rod arrays (TiO2@C NRAs) was constructed and tested as a supercapacitor electrode in this study. Dopamine was self-assembled into a polydopamine nano-rod arrays within the TiO2 nano-tube arrays (TiO2 NTAs) and was used as a precursor for the carbon nano-rod generation. Electrochemical measurements showed that the electrodes made with coaxial TiO2@C NRAs exhibited substantially higher electrochemical performances such as larger areal capacitance and faster charge/discharge capability than those of the pristine TiO2 NTA electrode and porous active carbon materials. Benefiting from the enhanced electrical conductivity and increased surface area of the coaxial nano-rod structure, the prepared coaxial TiO2@C NRAs electrode achieved a remarkable areal capacitance of 40.75mFcm−2 at a current density of 0.2mAcm−2, which was significantly higher than that of the pristine TiO2 NTAs (0.31mFcm−2).

Mesoporous and adsorptive properties of palm date seed activated carbon prepared via sequential hydrothermal carbonization and sodium hydroxide activation

Mesoporous activated carbon (AC) was prepared via sodium hydroxide (NaOH) activation of hydrochar from the hydrothermal carbonization (HTC) of palm date seed (PDS). The textural, morphological, and chemical properties of the produced hydrochar AC were investigated. NaOH activation enhanced the porosity and surface functionality of the hydrochar. Batch equilibration methods were performed to explore the process parameters that affected the adsorption of the prepared AC on methylene blue (MB), including initial concentration, contact time, solution pH and temperature. The Freundlich isotherm model better depicted the equilibrium data compared with the Langmuir isotherm model. Temperature was found to negatively affect the adsorption capacity of the prepared AC, which exhibited 612.1, 464.3 and 410.0mg/g maximum MB adsorption capacities at 30, 40 and 50°C, respectively. The pseudo-second order kinetic model best described the kinetic data. HTC and NaOH activation was proven to be an effective method in preparing highly porous AC from PDS, with good potential for cationic dye removal from liquid phase.

Hierarchical porous carbon derived from recycled waste filter paper as high-performance supercapacitor electrodes

Hierarchical activated porous carbon (APC) was synthesized through convenient chemical activation with ZnCl2 using recycled waste filter paper as the carbon precursor.

Fluorescent carbon quantum dots, capacitance and catalysis active porous carbon microspheres from beer

Fluorescent nitrogen containing carbon quantum dots (NCQDs) and porous carbon microspheres (PCMs) were simultaneously synthesized by a facile hydrothermal method using beer as precursor.

Hydrogen ion supercapacitor: a new hybrid configuration of highly dispersed MnO₂ in porous carbon coupled with nitrogen-doped highly ordered mesoporous carbon with enhanced H-insertion.

A new configuration of hydrogen ion supercapacitors was reported. A positive electrode composed of pseudocapacitive MnO2, highly dispersed into active porous carbon through an impregnation method, was combined with a nitrogen-doped highly ordered mesoporous carbon with enhanced electrochemical hydrogen insertion capacity as a negative electrode. During the operation, hydrogen ion shuttled between MnO2 and carbon electrodes. The MnO2 was formed on the surface of nanostructured carbon through a spontaneous redox reaction. Operating in an aqueous neutral solution, the hybrid device demonstrated an extended working voltage to ∼2.1 V with good cycle life.