Surface Area Of Carbon Fibers Research Articles

Highly porous and conductive functional carbon fibers from electrospun phosphorus-containing lignin fibers

Functional carbon fibers were prepared by carbonization of thermostabilized electrospun lignin-fibers at 500–900 °C followed by a high temperature thermal treatment at 1200–1600 °C. The effect of the preparation temperature on their surface chemistry, structural order, textural properties and electrochemical behavior has been stablished. Maximum porosity development is obtained at 900 °C. The addition of phosphoric acid in the electrospinning lignin solution shortens the stabilization time of the fibers, increases the carbonization yield, generates phosphorus functional groups (P content as high as 3% wt.) and increases the BET surface area of carbon fibers from 840 to 1143 m 2 g −1 . Interestingly, when phosphorus-containing carbon fibers are treated even at very high temperature, 1600 °C, most of the porosity is preserved (A BET = 822 m 2 g −1 ). XPS depth profile reveals the presence of reduced phosphorus in the core of carbonized fibers. XRD and TEM analysis make evident that the presence of phosphorus induces curvature of the graphitic layers, which seems to hinder the stacking of the graphene layers, explaining the preservation of microporosity after the thermal treatment at high temperature. However, Raman and XRD analyses point out that the presence of phosphorus does not affect the lateral growing of the crystallites. Thus, phosphorus preserves the porosity and allows the development of the electrical conductivity after the thermal treatments. Gravimetric capacitances of 79 F g −1 and capacitance retention of 63% at 68 A g −1 have been determined for phosphorus-containing carbon fibers prepared at 1200 °C. • Electrospinning of H 3 PO 4 lignin solution produced P-containing carbon fibers. • Experimental evidence about curvature of graphitic layers induced by P is reported. • P impedes the stacking of graphene layers while allowing their lateral growing. • P in carbon fibers core prevents from porosity shrinkage after heat treatment at 1600 °C. • Electrical conductivity and capacitance retention is promoted after heat treatment.

Graphene aerogel modified carbon fiber reinforced composite structural supercapacitors

This paper reports the design of a structural supercapacitor using a continuous network of graphene aerogel (GA) impregnated on carbon fiber (CF) fabrics to prepare CF reinforced composite. The GA is synthesized by hydrothermal process of Graphene oxide precursor that enabled the thermal reduction and self-assembly of GA onto the CF fabrics. Composite supercapacitor is prepared by resin infusion technique using GA-modified CF, dielectric electrospun veil separator and an ionic liquid modified epoxy electrolyte. The modification of CFs with highly interconnected and porous GA has provided a significant improvement in the surface area of CFs, resulting in excellent electron transport properties. CF fabrics with 28% GA loading exhibited a capacitance of 92.5 F g−1 at 1 mVs−1, which is 550 times higher than the capacitance of neat CFs and provides an excellent capacitance retention of 98% after 10000 charge-discharge cycles. GA-modified CF reinforced composites yield the highest capacitance of 56 mF g−1. This study provides a practical method for multifunctional, light weight, CF reinforced composites for energy storage applications.

Accessible Surface Area in Porous Carbon Electrodes and Its Impact on Redox Flow Battery Performance

Carbon-fiber electrodes exhibit many desirable material properties including conductivity, porosity, and chemical stability, and, accordingly, are employed in a range of electrochemical technologies.1 Such electrodes are particularly important in redox flow battery (RFB) systems, as they serve multiple critical functions including providing surface area for electrochemical reactions, distributing liquid electrolytes, and conducting electrons and heat. While commercially available materials possess suitable permeability and conductivity, the performance of pristine substrates is limited, thus oxidative treatment prior to use is common practice.2,3 Partial oxidation of the electrode surface has been shown to add a range of oxygen functional groups, which improve hydrophilicity and, in some cases, catalyze redox reactions, as well as to increase available surface area for the electrochemical reactions.4,5 Both effects are posited to improve electrode performance but their relative importance and effectiveness remains unclear.6 Here, we critically assess the nature of the surface area generated by thermal pretreatment in air and its role on RFB electrode performance. Using binder-free Freundenberg H23 as a model substrate, we systematically vary pretreatment time and temperature to create different surface morphologies and develop structure-function relations. First, we use Brauner Emmanuel Teller gas adsorption (e.g., N2, Kr, Ar/CO2) and mercury porosimetry to estimate physical surface area and pore size distribution. In parallel, we use voltammetry and impedance spectroscopy to determine electrochemically active surface area with different electrolyte compositions. In general, we find that only a fraction of the physical surface area is accessible for electrochemical redox reactions due, in large part, to the nanoscopic dimensions of the added surface area. Second, we develop a simple mathematical model to assess the effectiveness of the available surface area of carbon fibers for Faradaic reactions. We find that, under typical RFB operating conditions, external mass transfer limitations govern performance, limiting the utilization of recessed areas generated during pretreatment. Ultimately, these results highlight the potential limits of performance improvement strategies based on increasing surface area of fibrous substrates and motivate new approaches for electrode development. Acknowledgements The authors acknowledge the financial support of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the United States Department of Energy. K.V.G acknowledges additional funding from the National Science Foundation Graduate Research Fellowship. The authors acknowledge the Center for Nanoscale Systems and the NSF’s National Nanotechnology Infrastructure Network (NNIN) for the use of Nanoscale Analysis facility for electrode property characterization. References M. H. Chakrabarti et al., Journal of Power Sources, 253, 150–166 (2014).T. J. Rabbow, M. Trampert, P. Pokorny, P. Binder, and A. H. Whitehead, Electrochimica Acta, 173, 17–23 (2015).N. Pour et al., The Journal of Physical Chemistry C, 119, 5311–5318 (2015).B. Sun and M. Skyllas-Kazacos, Electrochim. Acta, 37, 8 (1992).T. J. Rabbow and A. H. Whitehead, Carbon, 111, 782–788 (2017).K. V. Greco, A. Forner-Cuenca, A. Mularczyk, J. Eller, and F. R. Brushett, ACS Applied Materials & Interfaces, 10, 44430–44442 (2018).

Fabrication of poly-sulfosalicylic acid film decorated pure carbon fiber as electrochemical sensing platform for detection of theophylline

In this work, we integrated the superiority of good conductivity, large surface area of carbon fibers and the catalytic property, good biocompatibility of polymer sulfosalicylic acid to construct a novel electrochemical sensor to detect theophylline in drug analysis. The morphology of nanocomposite was characterized by scanning electron microscopy (SEM). The polymerization between monomers was observed by Fourier transform infrared spectroscopy (FTIR). The composite between carbon material and polymer was verified by Raman spectrum. Under the optimal experimental conditions, the concentration of theophylline (0.6∼137 μM) and the peak current value revealed a good linear relationship and the limit of detection as low as 0.2 μM. In addition, the proposed sensor exhibits repeatability, stability and ease of selectivity.

Fabrication of Poly-Sulfosalicylic Acid Film Decorated Pure Carbon Fiber As Electrochemical Sensing Platform for Detection of Theophylline

Theophylline (1,3-dimethylxanthine, TP) is a xanthine alkaloid that stimulates breathing system. It is widely used as a bronchodilator drug for the treatment of various asthma diseases. Determining the concentration of theophylline is important in medical affairs through simple, rapid, accurate and inexpensive methods. Electrochemical technology has got development due to its high sensitivity, stability, simplicity, low cost, ease of use, and in-situ analysis.In this work, we combined the advantage of good conductivity, large surface area of carbon fibers and the catalytic property, good biocompatibility of polymer sulfosalicylic acid to construct a novel electrochemical sensor to detect theophylline in drug analysis. The morphology of nanocomposite was characterized by electron microscopy (SEM). The polymerization between monomers was observed by Fourier transform infrared spectroscopy (FTIR). The composite between carbon material and polymer was verified by Raman spectrum. Under the optimal experimental conditions, the concentration of theophylline (0.6 ~ 137μM) and the peak current value showed a good linear relationship and the limit of detection as low as 0.2μM. In addition, the proposed sensor exhibits repeatability, stability and ease of selectivity.

Flexible Microsensor Made of Boron-Doped Graphene Quantum Dots/ZnO Nanorod for Voltammetric Sensing of Hydroquinone

The micro size and mechanical properties of carbon fiber make it an ideal electrode material, but the low surface area of carbon fiber promotes a poor electrochemical response. The combination of graphene quantum dots and metal oxide may modulate their chemical and electrochemical properties, resulting in synergistic signal amplification effect. In this study, a new robust nano-hybrid microelectrode was designed by modifying carbon fiber with boron-doped graphene quantum dots/ZnO nanorod for the electrocatalytic analysis of hydroquinone (HQ). Remarkably, high specific surface area of vertically-aligned ZnO nanorod promoted loading of high-density boron-doped graphene quantum dots. Electrochemical results showed that these modifications promoted a larger active surface area and electron transfer of the carbon fiber microelectrode, as well as enhancement of the electrocatalytic activity toward HQ. Under optimal conditions, the linear response range of the proposed microelectrode to HQ was 0.1 to 100 μM, and the limit of detection was 0.03 μM. The proposed microelectrodes show good repeatability, reproducibility and electrode stability. Furthermore, the proposed microelectrode was successfully applied to environmental water samples analysis of HQ, providing a new method for the efficient detection of HQ.

Coconut-based activated carbon fibers for efficient adsorption of various organic dyes.

In this study, using coconut fibers as raw material, activated carbon fibers were prepared via carbonization and KOH activation processes. The morphology, composition, specific surface area, pore structure and thermal stability of the resulting activated carbon fibers were systematically characterized. It was found that the activation process increases the specific surface area of carbon fibers to a greater extent via formation of a large number of micropores (0.7–1.8 nm) and a certain amount of slit-shaped mesopores (2–9 nm). The specific surface area and the pore volume of the activated carbon fibers reach 1556 m2 g−1 and 0.72 cm3 g−1, respectively. The activation process can also decompose the tar deposits formed after the carbonization process by pyrolysis, making the surface of the activated carbon fibers smoother. To study the adsorption properties of the as-prepared activated carbon fibers, the adsorption capacities and adsorption kinetics of various organic dyes including methylene blue, Congo red and neutral red were investigated. The adsorption capacities of the dyes increased with the increasing initial dye concentrations, and varied greatly with the pH value of the system. In methylene blue and neutral red systems, the adsorption capacities reach the maximum at pH 9, and in the Congo red system, it reaches the maximum at pH 3. The adsorption capacities of the activated carbon fibers in methylene blue, Congo red and neutral red systems reached equilibrium at 150, 120, and 120 min, and the maximum adsorption capacities were 21.3, 22.1, and 20.7 mg g−1, respectively. The kinetics of the adsorption process was investigated using three models including pseudo-first-order, pseudo-second-order and intraparticle diffusion models. The results indicated that the dynamic adsorption processes of coconut-based activated carbon fibers to methylene blue, Congo red and neutral red were all in accordance with the second-order kinetic model, and the equations are as follows: t/Qt = 0.1028 + t/21.3220, t/Qt = 0.1128 + t/21.5982 and t/Qt = 0.0210 + t/20.6612.

Abatement of p-Nitrophenol from Aqueous Solutions Using Oxidized Carbon Fiber

Two oxidized carbon fibers (o-CF and o-CF-400) with microporous structure and surface area as high as ~ 1500-1130 m2/g were prepared from commercial carbon fiber felt to be used as good carbon adsorbents for removing highly toxic organic pollutant. The obtained oxidized CF samples were characterized by SEM, N2 adsorption isotherms at -196oC as well as Boehm's titration and FTIR techniques. Removal of p-nitrophenol (p-NP), as a probe organic pollutant existed in wastewater of various industries, was studied in a batch mode. Kinetic and equilibrium adsorption studies were investigated and found that the adsorption data of p-NP molecules were well-fitted with pseudo-second-order model and Langmuir isotherm. Based on the porosity developed in oxidized CFs, PNP molecules are mostly accommodated onto micropores. An oxidized carbon fiber, o-CF showed the higher removal of p-NP than that obtained using o-CF-400 due to its high micropore surface area (1450 m2/g). It was clearly observed that the adsorption of p-NP depended remarkably on the surface area of carbon fibers. It was found that values of monolayer adsorption capacity obtained by application of Langmuir equation were 258 and 155 mg/g using o-CF and o-CF-400 adsorbents, respectively, at 25oC and pH 4. Finally, it can be concluded that the both oxidized carbon fibers can be emerged as effective adsorbents because they exhibited a great adsorption capability in removing organic pollutants from wastewater.

Microporous carbon fibers prepared from cellulose as efficient sorbents for removal of chlorinated phenols

Cellulose-based microporous carbon fibers (CFs) were evaluated for the adsorption of 2-Chlorophenol (CP), 2,4-Dichlorophenol (DCP), and 2,4,6-Trichlorophenol (TCP), which are persistent organic pollutants in wastewater. CFs with different surface area values were prepared by using ZnCl2 as a chemical activator, and the samples were characterized by BET, FTIR, SEM, PALS, Zeta potential, and pH titration analysis. The point of zero charge values for CF-1, CF-2, and CF-3 were found as 8.14, 6.79, and 7.01, respectively. The surface area of CFs were determined as 454 m2/g (CF-1), 760 m2/g (CF-2), and 1217 m2/g (CF-3), and PALS measurements at ambient temperature and vacuum indicated the effective pore diameter of about 0.6 nm for all samples. The adsorption of chlorophenols was examined at different solution pH, temperature, and contact time. At the optimum pH of 6.0, the DCP adsorption capacities of CFs, namely, CF-1, CF-2, and CF-3 were calculated as 29.27, 229.81, and 244.09 mg/g, respectively. The adsorption capacity of the CF-3 sample was found to be an ideal adsorbent for CPs removal from aqueous solutions. A comparison of the adsorption kinetic data was best described by the pseudo second-order and particle diffusion models. For the CF-2 sample, the initial sorption rates of CP, DCP, and TCP were found in the increasing order as 2.084, 32.23, and 43.63 mg/g min. Similar order of the sorption rates were also observed for CF-1 and CF-3 samples. The obtained results demonstrated the fact that among the CP homologues, TCP showed both a higher affinity and a higher diffusion rate for all CFs. The adsorption process was found to be exothermic, and the entropy values were positive, depicting that CPs were randomly distributed at the solid/solution interface.

Nanowire modified carbon fibers for enhanced electrical energy storage

The study of electrochemical super-capacitors has become one of the most attractive topics in both academia and industry as energy storage devices because of their high power density, long life cycles, and high charge/discharge efficiency. Recently, there has been increasing interest in the development of multifunctional structural energy storage devices such as structural super-capacitors for applications in aerospace, automobiles, and portable electronics. These multifunctional structural super-capacitors provide structures combining energy storage and load bearing functionalities, leading to material systems with reduced volume and/or weight. Due to their superior materials properties, carbon fiber composites have been widely used in structural applications for aerospace and automotive industries. Besides, carbon fiber has good electrical conductivity which will provide lower equivalent series resistance; therefore, it can be an excellent candidate for structural energy storage applications. Hence, this paper is focused on performing a pilot study for using nanowire/carbon fiber hybrids as building materials for structural energy storage materials; aiming at enhancing the charge/discharge rate and energy density. This hybrid material combines the high specific surface area of carbon fiber and pseudo-capacitive effect of metal oxide nanowires, which were grown hydrothermally in an aligned fashion on carbon fibers. The aligned nanowire array could provide a higher specific surface area that leads to high electrode-electrolyte contact area thus fast ion diffusion rates. Scanning Electron Microscopy and X-Ray Diffraction measurements are used for the initial characterization of this nanowire/carbon fiber hybrid material system. Electrochemical testing is performed using a potentio-galvanostat. The results show that gold sputtered nanowire carbon fiber hybrid provides 65.9% higher energy density than bare carbon fiber cloth as super-capacitor.

Fabrication and Characterization of Porous Non-Woven Carbon Based Highly Sensitive Gas Sensors Derived by Magnesium Oxide

Nanoporous non-woven carbon fibers for a gas sensor were prepared from a pitch/polyacrylonitrile (PAN) mixed solution through an electrospinning process and their gas-sensing properties were investigated. In order to create nanoscale pores, magnesium oxide (MgO) powders were added as a pore-forming agent during the mixing of these carbon precursors. The prepared nanoporous carbon fibers derived from the MgO pore-forming agent were characterized by scanning electron microscopy (SEM), <TEX>$N_2$</TEX>-adsorption isotherms, and a gas-sensing analysis. The SEM images showed that the MgO powders affected the viscosity of the pitch/PAN solution, which led to the production of beaded fibers. The specific surface area of carbon fibers increased from 2.0 to <TEX>$763.2m^2/g$</TEX> when using this method. The template method therefore improved the porous structure, which allows for more efficient gas adsorption. The sensing ability and the response time for the NO gas adsorption were improved by the increased surface area and micropore fraction. In conclusion, the carbon fibers with high micropore fractions created through the use of MgO as a pore-forming agent exhibited improved NO gas sensitivity.

Properties of differently shaped activated carbon fibers

Differently shaped carbon fibers (R-, I-, C-, Y-, and X-type) were prepared from melt-spinning of reformed naphtha cracking bottom oil precursors through various shaped spinnerets. These carbon fibers were activated by steam and activation properties were compared. The decrease of hydraulic radius resulted in the extending of the external surface area of carbon fibers. Activation energy and rate of differently shaped carbon fibers were affected by external surface area. Especially, the activation rate of tetralobal carbon fibers (X-type) appeared much larger than other shaped carbon fibers due to the smallest hydraulic radius. Adsorption capacity of tetralobal activated carbon fibers was also larger than other shaped activated carbon fibers.

Physical activation and characterization of multi-walled carbon nanotubes catalytically synthesized from methane

A series of treatment processes were employed to purify and then physically activate the multi-walled carbon nanotubes obtained using catalytic decomposition of methane. In order to characterize and compare the activation effect, the carbon fibers were also treated by the same activation processes. The results showed that the normal physical activation by CO 2 or steam has not too much effect on the surface area of purified multi-walled carbon nanotubes, in particular, the carbon nanotubes were burned when using the poignant activation conditions. However, the surface area of carbon fibers availably etched in the same activation processes is much increased. In addition, the mechanisms of physical activation on multi-walled carbon nanotubes and carbon fibers have been investigated.

Relationship between the Carbon Fiber Strands Assembly and the Amount of Attached Microorganism.

Relation between the form of assembly of carbon fiber strands and the amount of attached microorganism was studied by using an artificial waterway set up at the side of the pond AZAMI. A variety of rectangular sail-type carbon samples were prepared by arranging a definite number of the strands (N) in parallel to each other in width of A cm and in length of B cm. These samples were placed on a setting frame with a length of L0, and then immersed in the circulating water pumped up continuously from the pond during the period of each four months in winter and summer. The amount of microorganism attached and proliferated in carbon fiber entanglement network was evaluated by weight increase(Winc). It was found that Winc depends on the relative length, B/L0 and the value of N/A, namely, compactness of the strand consisting of 12, 000 monofilaments. The former value was closely related to easy separation of the strand into monofilaments that gives rise to an increase in effective surface area of carbon fibers for initial attachment of microorganism, while the latter was a function of an effective volume of network in water for proliferation of microorganism. A suggestion obtained was, further, that aerobe microorganism was preferential species within the carbon fiber network perturbed by water flow which leads to an increase in the rate of exchange of water in the network and this probably be related to the high bending modulus of carbon fiber filament. A most preferable result for proliferation of microorganism was obtained at the condition of B/L0=1.4 and N/A=2.7, and the average distance between neighboring carbon monofilaments entrapped in the aggregates of microorganism reached to about 750μm corresponding to ca. 100-folds of the diameter of carbon monofilaments.

Influence of tension during oxidative stabilization on SO 2 adsorption characteristics of polyacrylonitrile (PAN) based activated carbon fibers

PAN-based carbon fibers were stabilized under various tensions in the presence of air at 230 °C and sequentially activated at 950 °C following carbonization. The prepared carbon fibers were tested for their SO 2 adsorption capacity using a thermogravimeter. The magnitude of tension during stabilization and gas environment were varied to study their effects on SO 2 adsorption capacity. It was found that the tension during the stabilization and the gas atmosphere during activation affect the carbon fiber properties, which are closely related to the SO 2 adsorption capacity. The influence of stabilization tension and activation atmosphere on the SO 2 adsorption capacity appear to arise from their effects on the amount of oxygen functional groups and the surface area of carbon fiber. The highest SO 2 adsorption capacity and improved mechanical strength were observed when PAN fibers were activated under steam.

Structure and active surface area of carbon fibers

The surface characteristics and oxidation rates of two carbon fibers, T-300 (PAN) and VSB-32 (pitch), before and after graphitization at 2973 K, are reported. The as-received (AR) and graphitized (GR) fibers have insignificant open porosity, small BET areas (<0.7 m 2/g), and small concentrations of alkali metals. Attempts have been made to measure values of apparent active surface areas (AASA) using oxygen chemisorption techniques at 573 K. For the T-300 AR fiber, AASA increases as the measurements are repeated on the same sample, and the value finally approaches the initial BET area because carbon gasification occurs during the measurements. Extrapolation of AASA values to zero-level gasification yields the true active surface area (TASA), 0.075 m 2/g. A similar trend has been observed with the T-300 GR fiber, and the TASA, obtained by extrapolation, at a starting oxygen pressure below 2.67 K Pa, is 0.024 m 2/g. However, at higher pressures, a second group of active sites, whose area is 0.067 m 2/g, is observed. With the VSB-32 AR and GR fibers, the extent of gasification below 0.67 K Pa is insignificant, and the TASA and AASA are similar; they amount to 0.029 and 0.019 m 2/g respectively. Furthermore, there is no indication of a second group of active site at higher chem-isorption pressures.