Macro- and microporous carbon monoliths with high surface areas pyrolyzed from poly(divinylbenzene) networks

Carbon monoliths with well-defined macropores and high surface areas were prepared by carbonization of macroporous poly(divinylbenzene) (PDVB) monoliths. The carbonization reactions of PDVB networks are studied by thermal analysis and FT-IR measurements. According to the measurement results, the PDVB networks are mostly pyrolyzed at 430 °C and their structures dynamically change to graphite-like structure between 600 and 700 °C. The macropore structure retained while the mesopores disappeared after carbonization. In addition, the surface area of the obtained carbons dramatically increased over 900 °C. The typical carbon monolith carbonized at 1000 °C for 2 h had a surface area of 1500 m² g^?1 and uniform macropores with a diameter of 1 μm.     

Kinetic and equilibrium adsorption of methylene blue and remazol dyes onto steam-activated carbons developed from date pits

Steam-activated carbons DS2 and DS5 were prepared by gasifying 600 °C-date pits carbonization products with steam at 950 °C to burn-off = 20 and 50%, respectively. The textural properties of these carbons were determined from the nitrogen adsorption at ?196 °C. The chemistry of the carbon surface was determined from the surface pH and from neutralization of the surface carbon–oxygen groups of basic and acidic type. The kinetic and equilibrium adsorption of MB and RY on DS2 and DS5 was determined at 27 and 37 °C and at initial sorption solution pH 3–7.DS2 and DS5 have expanded surface area, large total pore volume and contain both micro and mesoporosity. They have on their surface basic and acidic groups of different strength and functionality. This enhanced the sorption of the cationic dye (MB) and of the anionic dye (RY). The adsorption of MB and RY on DS2 and DS5 involves intraparticle diffusion and followed pseudo-second order kinetics. The adsorption isotherms were applicable to the Langmuir isotherm and high monolayer capacities for MB and RY dyes were evaluated indicating the high efficiencies of the carbons for dye adsorption.     

Effects of pyrolysis conditions on the physical characteristics of oil-palm-shell activated carbons used in aqueous phase phenol adsorption

Oil-palm shells, a biomass by-product from palm-oil mills, were converted into activated carbons by vacuum or nitrogen pyrolysis, followed by steam activation. The effects of pyrolysis environment, temperature and hold time on the physical characteristics of the activated carbons were studied. The optimum pyrolysis conditions for preparing activated carbons for obtaining high pore surface area are vacuum pyrolysis at a pyrolysis temperature of 675 °C and 2 h hold time. The activation conditions were fixed at a temperature of 900 °C and 1 h hold time. The activated carbons thus obtained possessed well-developed porosities, predominantly microporosities. For the pyrolysis atmosphere, it was found that significant improvement in the surface characteristics of the activated carbons was obtained for those pyrolysed under vacuum. Adsorption capacities of activated carbons were determined using phenol solution. For the activated carbons pyrolysed under optimum vacuum conditions, a maximum phenol adsorption capacity of 166 mg/g of carbon was obtained. A linear relationship between the BET surface area and the adsorptive capacity was shown.     

Enhanced electrochemical capacitance of nitrogen-doped carbon gels synthesized by microwave-assisted polymerization of resorcinol and formaldehyde

Nitrogen-doped carbon gels were synthesized by ammonia-assisted carbonization of resorcinol–formaldehyde (RF) polymers obtained under microwave irradiation without any basic catalyst. Compared with the RF polymer synthesized by the conventional hydrothermal method, microwave polymerization produced spherical beads with a higher surface area (1710 m²/g vs. 1080 m²/g), and smaller (∼700 nm vs. ∼5 μm) but more uniform bead sizes. The majority of their pores were micropores. As a result, the electrochemical capacitance of microwave-assisted nitrogen-doped carbons was significantly higher than that of materials prepared by the conventional hydrothermal method. Thus microwave-assisted polymerization followed by ammonia-assisted carbonization is a useful method to synthesize nitrogen-doped carbon gels for electrochemical double layer capacitors.     

Reticular Sn nanoparticle-dispersed PAN-based carbon nanofibers for anode material in rechargeable lithium-ion batteries

Reticular tin nanoparticle-dispersed carbon (Sn/C) nanofibers were fabricated by stabilization of electrospun SnCl₄/PAN composite fibers and subsequent carbonization at different temperatures. These Sn/C composite nanofibers used as anode materials for rechargeable lithium-ion batteries (LIBs) show that the Sn/C nanofibers at 700 and 850 °C present much higher charge (785.8 and 811 mA h g^?1) and discharge (1211.7 and 993 mA h g^?1) capacities than those at 550 and 1000 °C and the as-received CNFs at 850 °C, corresponding to coulombic efficiencies of 64.9% and 81.7%, respectively. The superior electrochemical properties of the intriguing Sn/C nanofibers indicate a promising application in high performance Li-ion batteries.     

Preparation of activated carbon from Turbinaria turbinata seaweeds and its use as supercapacitor electrode materials

Turbinaria turbinata brown seaweeds were tested as carbon electrode material in symmetric, electrochemical supercapacitors. The electrochemical properties of the carbon materials were characterised for their application as supercapacitors using cyclic voltammetry, galvanostatic charge/discharge method and electrochemical impedance spectroscopic analyses. Our initial results showed that the optimal behaviour was obtained for the sample prepared by pyrolysis at 800 °C. The average surface area of the carbon was 812 m²/g. Electrochemical tests with an organic electrolyte gave the following interesting results: a capacitance of 74.5 F/g, a specific series resistance of 0.5 Ω cm² and an ionic resistivity of 1.3 Ω cm². These results show the promising capacitive properties of carbon derived from seaweeds and their application in electrochemical supercapacitors.     

Treatment and characterization of gas diffusion layers by sucrose carbonization for PEMFC applications

In this article, a new treatment of gas diffusion layers (GDLs) was proposed by sucrose carbonization in order to obtain high hydrophobicity with low PTFE loading. Carbon was coated both on the cross position and stem of carbon fiber, resulting in the enhancement of carbon paper roughness, which improved the hydrophobicity of carbon paper with low PTFE loading. The water contact angle of carbonized carbon paper with 10 wt.% PTFE loading was measured as 137 ± 1° at 25 °C, which was higher than 125 ± 1° for non-carbonized carbon paper with the same PTFE loading. The performances of MEAs prepared by carbonized carbon paper were higher than those of MEAs prepared by non-carbonized carbon paper. The MEA prepared by carbonized carbon paper with 10 wt.% PTFE loading showed excellent performance compared to the other MEAs.     

Effects of potassium distributions in carbonizations of bituminous coal

The carbonization of coal/KOH mixtures were investigated to identify the influence of potassium distributions on characteristics of the final products. The products were characterized using TGA, BET, TEM and adsorption of lead from its aqueous solutions with initial concentrations of 10–100 ppm. For the activated carbon obtained at 600 °C, the potassium distribution affected both the BET surface areas (661–1994 m²/g) and the meso- and micro-pore volumes ratios (0.48–0.91). There were also evolutions of nanostructures of both straight and curved tubular morphologies as evidenced by TEM micrograph. The samples exhibited different adsorptive capacities when tested in adsorption of lead from aqueous solutions. The adsorption followed second order kinetics and the equilibrium data were better described by empirical Freudlich isotherm model. The amount of lead adsorbed ranges from 4.3 to 47.3 mg/g. Thus, different degrees of potassium effects led to activated carbons with different surface and adsorptive properties.     

Effects of H3PO4 and KOH in carbonization of lignocellulosic material

Samples of lignocellulosic material, stem of date palm (Phoenix dactylifera), were carbonized at different temperatures (400–600 °C) to investigate the effects of their impregnation with aqueous solution of either phosphoric acid (85 wt%) or potassium hydroxide (3 wt%). The products were characterized using BET nitrogen adsorption, helium pycnometry, Scanning Electron Microscopy (SEM) and oil adsorption from oil–water emulsion (oil viscosity, 60 mPa s at 25 °C). True densities of the products generally increased with increase in carbonization temperature. Impregnated samples (acid/base) showed wider differences in densities at 400 (1.978/1.375 g/cm³) than at 600 °C (1.955/2.010 g/cm³). Without impregnation, the sample carbonized at 600 °C showed higher density of 2.190 g/cm³. This sample has impervious surface with BET surface area of 124 m²/g. Acid-impregnated sample carbonized at 500 °C has the highest surface area of 1100 m²/g and most regular pores as evidenced by SEM micrographs. The amounts of oil adsorbed decreased with increase in carbonization temperature. Without impregnation, sample carbonized at 400 °C exhibited equilibrium adsorption of 4 g/g which decreases to about a half for sample carbonized at 600 °C. Impregnation led to different adsorptive capacities. There are respective increase (48 wt%) and decrease (5 wt%) by the acid- or base-impregnated samples carbonized at 600 °C. This suggests higher occurrence of oil adsorption-enhancing surface functional groups such as carbonyl, carboxyl and phenolic in the former sample.     

Impact of reforming catalyst on the anodic polarisation resistance in single-chamber SOFC fed by methane

This paper emphasises the electrochemical and catalytic properties of a Ni–10% GDC (10% gadolinium-doped ceria) cermet anode of a single-chamber solid oxide fuel cell (SC-SOFC). Innovative coupling of electrochemical impedance spectroscopy with gas chromatography measurements was carried out to characterise the anode material using an operando approach. The experiments were conducted in a symmetric anode/electrolyte/anode cell prepared by slurry coating resulting in 100 μm-thick anode layers. The electrochemical performance was assessed using a two-electrode arrangement between 400 °C and 650 °C, in a methane-rich atmosphere containing CH₄, O₂ and H₂O in a 14:2:6 volumetric ratio. The insertion of a Pt–CeO₂ based catalyst with high specific surface area inside the cermet layer was found to promote hydrogen production from the Water Gas Shift reaction and consequently to improve the electrochemical performances. Indeed, a promising polarisation resistance value of 12 Ω cm² was achieved at 600 °C with a catalytic loading of only 15 wt.%.     

Adsorption kinetics of various gases in carbon molecular sieves (CMS) produced from palm shell

Carbon molecular sieves (CMS) have been prepared from locally available palm shell of Tenera type by a thermal treatment technique involving carbonization followed by steam activation and benzene deposition technique. Carbonization of the dried palm shells was done at 900 °C for duration of 1 h followed by steam activation at 830 °C for 30–420 min to achieve activated carbons with different degree of burn-offs. The highest micropore volume of activated carbon obtained at 53.2% burn-off was found suitable to be used as a precursor for CMS production. Subsequent benzene deposition onto activated samples at temperature range from 600 to 900 °C for various benzene concentrations have resulted in a series of CMS with different kinetic selectivities. The molecular sieving behaviour of the CMS products was assessed by kinetic adsorption isotherms of O₂, N₂, CO₂ and CH₄ at room temperature.     

Impact of synthesis conditions on surface chemistry and structure of carbide-derived carbons

Carbide-derived carbons produced by chlorination of titanium carbide at 600, 800, or 1100 °C were subjected to a post-treatment at 600 °C in Ar, H₂, or NH₃ atmosphere. Experimental results suggest that the chlorination temperature influences the ordering of carbon in a manner that impacts specific surface area and porosity. Higher chlorination temperatures lead to higher total pore volume and increased ordering, but lower microporosity. The effect of post-treatments on surface chemistry is pronounced only for samples chlorinated at 600 °C; post-treatments in Ar are shown to be less effective for chlorine removal than those performed in H₂ or NH₃. Post-treatments in Ar result in a lower total pore volume compared to the ones in H₂ or NH₃ for the same chlorination temperature. Samples chlorinated at higher temperatures contained less oxygen functionalities than samples chlorinated at 600 °C, and showed correspondingly less desorption of H₂O, possibly due to diminished uptake of ambient water.     

Polyimide-derived carbon nanofiber membranes as anodes for high-performance flexible lithium ion batteries

Heteroatoms-doped carbon nanofiber membranes with flexible features were prepared by electrospinning with heterocyclic polyimide (PI) structures containing biphenyl and pyrimidine rings. The products with optimized treatment could achieve 695 mAh/g at 0.1 A/g and retain 245 mAh/g at 1.5 A/g after 300 cycles when used as anode for Li-ion batteries.     

Pyrolysis of wood impregnated with phosphoric acid for the production of activated carbon: Kinetics and porosity development studies

The pyrolysis of impregnated wood for the production of activated carbon is investigated. Laboratory experiments are performed in a TG for heating rates of 10 °C/min and 20 °C/min and a mathematical model for the kinetics of the pyrolysis process is developed and validated. The effect of the temperature and of the time duration of the pyrolysis process on the specific surface of the activated carbon is examined on the basis of experiments conducted in a crossed bed reactor. Results indicate that the temperature and the residence time in the pyrolysis reactor may be optimised. Indeed, it is found that the maximum specific surface of the end product is obtained for pyrolysis processes conducted at a temperature of 400 °C for a time period of 1 h.     

Highly porous electrodes from novel corn grains-based activated carbons for electrical double layer capacitors

In this study, novel corn grains-based activated carbons (CG-ACs) were prepared and their use as electrodes in the electrical double layer capacitor (EDLC) performed successfully. The structural properties, energetic heterogeneities and surface functional groups of CG-ACs were characterized using different techniques like nitrogen sorption data, adsorption energy distribution (AED) and X-ray photoelectric spectroscopy (XPS). The electrochemical properties of various CG-ACs were evaluated by using cyclic voltammetry. The maximum specific capacitance value as 257 F g⁻¹ was obtained in 6 M KOH electrolyte solution. The effects of various properties of the porous carbon materials on the EDLC performance were discussed.     

Ultrathin free-standing electrospun carbon nanofibers web as the electrode of the vanadium flow batteries

Ultrathin free-standing electrospun carbon nanofiber web(ECNFW) used for the electrodes of the vanadium flow battery(VFB) has been fabricated by the electrospinning technique followed by the carbonization process in this study to reduce the ohmic polarization of the VFB. The microstructure, surface chemistry and electrochemical performance of ECNFW carbonized at various temperatures from 800 to 1400 °C have been investigated. The results show that ECNFW carbonized at 1100 °C exhibits the highest electrocatalytic activity toward the V~(2+)/V~(3+)redox reaction, and its electrocatalytic activity decreases along with the increase of carbonization temperature due to the drooping of the surface functional groups.While for the VO~(2+)/VO_2~+redox couple, the electrocatalytic activity of ECNFW carbonized above 1100 °C barely changes as the carbonization temperature rises. It indicates that the surface functional groups could function as the reaction sites for the V~(2+)/V~(3+)redox couple, but have not any catalytic effect for the VO~(2+)/VO_2~+redox couple. And the single cell test result suggests that ECNFW carbonized at 1100 °C is a promising material as the VFB electrode and the VFB with ECNFW electrodes obtains a super low internal resistance of 250 mΩ cm~2.     

Effects of feedstock pre-drying on carbonization of KOH-mixed bituminous coal in preparation of activated carbon

Activated carbon samples of different porosities and other characteristic features have been prepared using bituminous coal–KOH feedstocks of different degrees of pre-drying. The feedstocks were subjected to thermogravimetric analysis from 30 to 1000 °C. Different weight loss profiles and carbon burnt-off were obtained. This was associated with different level of potassium intercalations in the coal matrix and concomitant different extent of reactions with carbon. Another set of feedstocks was carbonized at 600 or 800 °C to obtain samples of activated carbon. The activated carbons were characterized using BET surface area, SEM, FTIR and XRD. These reflected the effects of pre-drying on the products. The surface area and V_meso/V_micro ratio increase with increase in duration of pre-drying. XRD profiles indicated lower proportion of aromatic stacking in the sample with highest surface area (1994 m²/g) and V_meso/V_micro ratio (0.91) than in the other samples. The pre-drying could be used as a key variable for obtaining activated carbons of different porosities.     

Generation of carbon nanostructures with diverse morphologies by the catalytic aerosol-assisted vapor-phase synthesis method

The Fe catalyst-supported aerosol-assisted synthesis method was used to prepare carbon products of diverse morphologies from toluene. Aerosol mist generation was accomplished with an ultrasonic device. An open-ended quartz boat for powder collection was placed in the maximum temperature zone of the tube reactor (850 °C or 1000 °C). The morphology of the products was studied by SEM and TEM microscopy. Structural characterization was provided by powder XRD, whereas Raman spectroscopy was used to determine the structural quality/homogeneity of the products. The hydrogen gas sorption capacity of the product prepared at 850 °C was relatively high despite its rather moderate BET specific surface area.     

Formation and characterization of magnetic barium ferrite hollow fibers with high specific surface area via sol–gel process

The magnetic barium ferrite (BaFe₁₂O₁₉) hollow fibers with a high specific surface area about 22–38 m² g^?1, diameters around 1 μm and a ratio of the hollow diameter to the fiber diameter estimated about 1/2–2/3 have been prepared by the gel-precursor transformation process. The precursor and resulting ferrite hollow fibers were analyzed by thermo-gravimetric and differential scanning calorimetry, infrared spectroscopy, scanning electron microscopy and X-ray diffraction. The specific surface area was measured by the Brunauer–Emmett–Teller method. The gel formed at pH 5.5 has a good spinnability. A pure barium ferrite phase is formed after calcined at 750 °C for 2 h and fabricated of nanograins about 38 nm with a hexagonal plate-like morphology, which are increased to about 72 nm with the calcination temperature increased up to 1050 °C. The barium ferrite hollow fibers obtained at 750 °C for 2 h have a specific surface area 38.1 m² g^?1 and average pore size 6.5 nm and then the specific surface area and average pore size show a reduction tendency with the calcination temperature increasing from 750 to 1050 °C owing to the particle growth and fiber densification. These barium ferrite hollow fibers exhibit typical hard-magnetic materials characteristics and the formation mechanism for hollow structures is discussed.     

High performance nanostructured IT-SOFC cathodes prepared by novel chemical method

The electrochemical performance of La_0.4Sr_0.6Co_0.8Fe_0.2O_3−δ (LSCF) cathodes with different nano/microstructures is compared using the area specific resistance (ASR). Cathodes are prepared using two chemical routes, including a novel method to obtain nanosized LSCF oxide. The results clearly point that the intermediate temperature solid oxide fuel cells (IT-SOFC) cathode performance strongly depends on microstructure and that ASR can vary more than two orders of magnitude for identical composition and different morphologies, reaching values as low as 0.05 Ω cm² at 600 °C and 0.4 Ω cm² at 450 °C using the novel chemical route, which are even lower than the best known cathodes for IT-SOFC.