EP3246436A1

EP3246436A1 - Process for the preparation of highly porous carbon fibers by fast carbonization of carbon precursor fibers

Info

Publication number: EP3246436A1
Application number: EP16001137.5A
Authority: EP
Inventors: Martin Möller; Alexander Kühne; Helga Thomas; Dennis Go; Jochen Stollenwerk; Philipp Lott
Original assignee: Dwi - Leibniz-Institut fur Interaktive Mat E V; Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV; DWI Leibniz Institut fuer Interaktive Materialien eV
Current assignee: Dwi - Leibniz-Institut fur Interaktive Mat E V; Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV; DWI Leibniz Institut fuer Interaktive Materialien eV
Priority date: 2016-05-19
Filing date: 2016-05-19
Publication date: 2017-11-22

Abstract

The present invention is related to highly porous carbon fibers, to a process of manufacturing such highly porous carbon fibers based on fast carbonization of carbon precursor fibers, and to the use of such highly porous carbon fibers. The process of manufacturing highly porous carbon fibers according to the present invention comprises a stabilization step, wherein carbon precursor fibers are heated in an oxidizing or non-oxidizing atmosphere at temperatures in the range of from 200 to 500°C, and a pyrolysis step, wherein the such treated carbon precursor fibers are heated in a non-oxidizing atmosphere at temperatures above those of the stabilization step via laser induced heating, microwave heating, or assisted plasma heating, wherein the heating rate in the pyrolysis step is from 5 to 500 K/s, respectively. The obtained highly porous carbon fibers have a surface area in the range of from 100 to 2500 m²/g, and a pore diameter in the range of from 0.1 to 10 nm. The highly porous carbon fibers according to the present invention are ideally suited as a composite material, as an electrode material and/or an electrode coating, as an adsorbent, as a filtration medium, as a catalyst support. Moreover, the highly porous carbon fibers according to the present invention are particularly applicable in charge storage, gas storage, filtration and adsorption devices.

Description

The present invention relates to highly porous carbon fibers with nanometer sized pore diameters and high surface areas, to a process of manufacturing such highly porous carbon fibers based on fast carbonization of carbon precursor fibers, and to the use of such highly porous carbon fibers.
Carbon fibers find broad applications within many technical fields. For example, they are applied as composite materials due to their high mechanical stability and their facile processability to produce textiles and cloths for reinforced materials. Furthermore, their electrical conductivity makes carbon fibers ideally suited for applications such as electrodes or electrode coatings, when prepared as non-woven materials in batteries, capacitors, transistors ( EP 0 698 935 A1 ) and fuel cells ( EP 1 813 701 A1 ).
Carbon fibers can be prepared from a variety of precursors. Suitable carbon precursor fibers are, for example, synthetic viscose, polyacrylonitrile, aromatic polyamides, 1,2-polybutadiene as well as natural materials such as cellulose, lignin, pitch etc.
In general, there are two main steps involved in the carbonization process to form carbon fibers from carbon precursor fibers. The first step is the stabilization which converts the precursor polymer into an infusible structure in an oxidizing or non-oxidizing atmosphere at temperatures usually between 200 and 500°C. The second step is the pyrolysis in an inert, non-oxidizing atmosphere which yields the desired graphitic structure at temperatures between 700 and 4000°C.
Alternatively, carbon fibers can be prepared from stabilized polyacrylonitrile or aromatic polyamide fibers by treatment with laser irradiation. For example, graphitization is accomplished by combining conventional heating (1200 to 3600°C) with the irradiation of a laser beam generated by a CO₂ gas laser in a time of more than 100 ms in a non-oxidizing atmosphere ( US 3,699,210 ).
In another process based on laser irradiation, carbon fibers are obtained by using a CO₂ gas laser at a power of at least 5.0 kWsg^-1 in the presence of air, with the laser beam inducing high temperatures in the stabilized carbon fibers, resulting in carbonization (between 700 and 1200°C) and graphitization (between 1200 and 3600°C) of the carbon fiber ( DE 100 57 867 C1 ).
Further processes for carbonization and graphitization of carbon precursor fibers other than thermal treatments are microwave heating and microwave assisted plasma treatment. Microwave heating is, for example, conducted for 1 to 30 min at frequencies of from 300 to 30000 MHz and power densities between 0.1 and 300 kW/m² ( US 2011/0158895 A1 ). Microwave assisted plasma treatment can be conducted in a plasma chamber to produce carbon fibers ( US 2011/0079505 A1 ).
However, none of the above-described processes allows to produce carbon fibers which are highly porous and which have a high surface area.
Up to now, such high surface areas can only be obtained by applying a pore-providing template to the carbon precursor fibers, or by adding catalytic compounds which degrade the fiber surface during heating. Following this approach, activated carbon particles are incorporated into the carbon fibers. By tuning the size of the activated carbon particles, some of the porosity is available on the surface of the carbon fiber matrix ( US 2012/0189877 A1 ).
Furthermore, porous carbon fibers can be produced by graphitization of fibers made from halogenated polymers with a metal catalyst, producing gas during the graphitization, which leads to pore sizes between 1 and 3000 nm ( US 2007/0134151 A1 ).
Alternatively, porous carbon fibers can be prepared from polyacrylonitrile with gas forming additives. As such additives, starch ( US 2010/0081351 A1 )and metal containing polymers ( EP 1 375 707 A1 ) can be applied, which disintegrate at high temperatures, thus producing a high surface area by forming pores, and releasing the degradation compounds from the carbon fiber.
Such an evaporation of the additive at high temperatures induces high porosity on the surface of the resulting carbon fibers ( US 2007/0142225 A1 ). In a similar approach, porous hollow carbon fibers can be prepared by coaxially spinning of a solution of an oxygen containing polymer in the core and a polyacrylonitrile precursor with an additive in the sheath. The core polymer disintegrates upon heating, while the evaporating additive induces porosity in the resulting hollow carbon fiber ( CN 102691136 A ).
Moreover, catalytic metal nanoparticles can be added to induce local degradation of the carbon precursor fibers during conversion into carbon fibers at high temperatures. The catalytic metal nanoparticles partially convert the carbon precursor fibers into gases (containing mainly CO₂), which induces porosity on the surface of the resulting carbon fibers ( CA 2 619 829 A1 ).
Similar to activated carbon, carbon fibers can also be made porous by chemically etching the carbon fiber after carbonization, thus increasing the surface area. Said etching can be conducted in solutions containing ammonium salts ( US 5,521,008 ) or alkali metal compounds ( EP 0 927 778 A1 ).
As can be taken from the above-described processes, an additional treatment step and/or the presence of additives are/is required to induce porosity in the carbon fibers, leading to increased production times and costs and/or to the presence of undesired components.
Therefore, the technical problem underlying the present invention is to provide a process of manufacturing highly porous carbon fibers, wherein the porosity of the carbon fibers is already induced during carbonization and graphitization, i.e. during the pyrolysis step, without the need of any additional treatment step as well as without the need of any additives.
This problem is solved by providing the embodiments characterized in the claims.
In particular, there is provided a process of manufacturing highly porous carbon fibers by fast carbonization of carbon precursor fibers, comprising:

a stabilization step, wherein carbon precursor fibers are heated in an oxidizing or non-oxidizing atmosphere at temperatures in the range of from 200 to 500°C; and
a pyrolysis step, wherein the such treated carbon precursor fibers are heated in a non-oxidizing atmosphere at temperatures above those of the stabilization step via laser induced heating, microwave heating, or assisted plasma heating, wherein the heating rate in the pyrolysis step is from 5 to 500 K/s, respectively.

The process of manufacturing highly porous carbon fibers according to the present invention allows to produce highly porous carbon fibers having a high surface area and small pore diameters.
The carbon fibers obtained by the process according to the present invention have a surface area in the range of from 100 to 2500 m²/g, and a pore diameter in the range of from 0.1 to 10 nm.
In this context, the surface area and the pore diameter of the carbon fibers can be measured by any appropriate method known in the art. For example, the surface area and the pore diameter can be determined by Brunauer-Hugh Emmett-Teller (BET) gas adsorption isothermal analysis and by scanning electron microscopy. In addition, scanning electron microscopy and Fourier transform infrared spectroscopy can be performed to analyze the progress of the carbonization and graphitization, i.e. the conversion of the carbon precursor fibers into graphitic carbon.

Fig. 1 shows Fourier transform infrared absorption spectra of pristine polyacrylonitrile (blue squares), stabilized polyacrylonitrile at 270°C (red triangles), thermally carbonized polyacrylonitrile at 1100°C (black circles), and fast carbonized polyacrylonitrile using infrared laser emission and a heating rate of 50 K/s (gray diamonds).
Fig. 2 shows a scanning electron micrograph of a carbon fiber non-woven after thermal carbonization, exhibiting a smooth fiber surface.
Fig. 3 shows a scanning electron micrograph of a carbon fiber non-woven after fast carbonization (laser), exhibiting a highly porous fiber surface.
Fig.4 shows a scanning electron micrograph of a carbon fiber non-woven after thermal carbonization, followed by chemical activation with KOH. The fiber surface exhibits large pores.
Figs. 5 and 6 show scanning electron micrographs of a carbon fiber non-woven after fast carbonization (by a single plasma jet), revealing a three-dimensional carbon fiber network exhibiting a high porosity.
Fig. 7 shows the Transmission spectra of PAN and a PAN with 0.1% of Epolight 1117 as a molecular absorber dye.

As found out by the inventors, highly porous carbon fibers having a high surface area can be obtained by fast carbonization when conducting fast non-thermal heating within the pyrolysis step via laser induced heating, microwave heating, or assisted plasma heating. By applying a heating rate of from 5 to 500 K/s in the pyrolysis step, the present invention has been accomplished.
According to the present invention, no additional treatment step other than the stabilization step and the pyrolysis step, for example a chemical activation step conducted after carbonization, is required to achieve both a high porosity and a high surface area in the resulting carbon fibers. Both properties are obtained by said fast carbonization in the pyrolysis step. Besides, no additional compound and/or catalyst to induce porosity in the carbon fibers have/has to be added before or during carbonization, either, to obtain carbon fibers having a surface area in the range of from 100 to 2500 m²/g, and a pore diameter in the range of from 0.1 to 10 nm. Therefore, the highly porous carbon fibers according to the present invention are produced economically, thus saving time, costs, and resources.
Besides these beneficial effects which relate to the process of manufacturing itself, the highly porous carbon fibers obtained therefrom are free from any undesired components. Compared to the porous carbon fibers known in the art, the highly porous carbon fibers according to the present invention thus exhibit an increased purity, i.e. carbon content, which is required in applications such as filtration and adsorption for gas, water and solvent purifications as well as in electronic applications.
According to the present invention, the stabilized carbon precursor fibers are exposed to fast heating in the pyrolysis step, which is selected from the group consisting of laser induced heating, microwave heating, and assisted plasma heating. In each case, such fast carbonization is conducted at a heating rate of from 5 to 500 K/s, leading to an explosive expulsion of gases, thereby producing fine pores on the surface of the resulting carbon fibers.
During the carbonization and graphitization of carbon precursor fibers such as pitch, cellulosics, lignin, Kevlar coated with polyimide, nylon, poly(phenyleneoxadiazole), poly(methyl vinyl ketone), polyacetylene, polyacetylene copolymer blends, polyarylacetylene, polybenzimidazole, polybutadiene, polyethylene, polyimide, polymerizable naphthalene derivatives, polystyrene and pitch blends, Rayon, syndiotactic 1,2-polybutadiene and polyacrylonitrile in particular, gases such as hydrogen, carbon dioxide, water, hydrogen cyanide, ammonia, nitrogen, carbon monoxide, and methane are produced in low amounts.
In the processes known in the art for producing carbon fibers, the above-mentioned gases are generated over time, and slowly diffuse out of the fiber, thus resulting in a smooth carbon fiber surface.
To the contrary, in the present invention, due to fast carbonization via heating by laser, microwave, or plasma treatment, the above-mentioned gases are instantaneously formed, and are explosively expelled from the fiber, thus leaving a porous surface behind. Surprisingly, due to the fast heating conducted in the pyrolysis step according to the present invention, extremely large and porous surface areas are obtained in combination with small pore diameters.
When fast carbonization is conducted via laser induced heating in the pyrolysis step, its duration is preferably 1 fs to 30 min. In a preferred embodiment, the irradiation of continuous wave lasers with emission wavelengths of from 200 to 11000 nm is used. In an alternative embodiment, the irradiation of pulsed lasers with emission wavelengths of from 200 to 11000 nm and pulse durations in the millisecond, microsecond, nanosecond, picosecond, or femtosecond range is used. Laser induced heating based on the above-mentioned technically relevant wavelengths is less time-consuming as well as less energy-consuming compared to existing methods.
In case that fast carbonization is conducted via microwave heating in the pyrolysis step, its duration is preferably 1 s to 10 min. In addition, it is preferred to use microwave frequencies in the range of from 1 to 13 GHz, preferably at a power of from 500 to 1000 W.
Fast carbonization can also be conducted via assisted plasma heating in the pyrolysis step. Preferably, its duration is then 1 ms to 10 min. Moreover, it is preferred that argon, nitrogen, or mixtures thereof are used as a gas source, preferably at a gas flow rate of from 100 to 2500 sccm (standard cubic centimeters per minute) to prevent oxidation during pyrolysis. Preferred plasma initiation frequencies are in the range of from 10 kHz to 3 MHz, preferably at a power of from 20 to 60 W. Preferably, the plasma jet treatment is performed with a single plasma jet or with an array of several plasma jets. In addition, it is preferred that the plasma jet or the plasma jet array is guided in a linear, meandering, or rotating fashion. Furthermore, it is preferred that the distance between the plasma jet or the plasma jet array and the material is in the range of from 1 to 10 mm.
According to the present invention, polyacrylonitrile or a copolymer based on polyacrylonitrile is preferably used as a constituent material of the carbon precursor fibers. In case that a copolymer based on polyacrylonitrile is used, at least 50 mol% of acrylonitrile are contained therein. In this case, it is particularly preferable that acrylonitrile is copolymerized with at least one selected from the group consisting of a (C₂-C₆) monoolefin, a vinylaromatic, a vinylaminoaromatic, a vinyl halide, a (C₁-C₆) alkyl (meth)acrylate, a (meth)acrylamide, a vinyl pyrrolidone, a vinyl pyridine, a (C₁-C₆) hydroxyalkyl (meth)acrylate, a (meth)acrylic acid, an itaconic acid, an acrylamidomethylpropylsulfonic acid, sodium methallyl sulfonate, and an N-hydroxy-containing (C₁-C₆) alkyl(meth)acrylamide.
A further preferable embodiment of the present invention is the use of polyamide containing at least 50 mol% of amide monomers as a constituent material of the carbon precursor fibers, wherein the carbon precursor fibers contain at least 50 wt% of said polyamide.
In an alternative embodiment, cellulose, lignin, or pitch can also be preferably used as a constituent material of the carbon precursor fibers, containing at least 50 wt% of cellulose, lignin, or pitch.
According to the present invention, the process of manufacturing highly porous carbon fibers is also suitable for composites comprising carbon precursor fibers as well as a non-reactive and non-volatile filler material. In this respect, it is preferred that the carbon precursor fibers contain up to 20 wt% of such a non-reactive and non-volatile filler material.
Principally, any non-reactive and non-volatile filler material such as metal- and semiconductor nanoparticles and carbon based nanofillers (graphene, few layer graphene, graphene nanoplatelets, carbon nanotubes and pigments, polymeric or molecular dyes) can be admixed to the carbon precursor fibers.
In a preferred embodiment, the non-reactive and non-volatile filler material is at least one selected from the group consisting of metal salts, metal based nanoparticles, graphitic carbon, graphene nanoplatelets, exfoliated graphene, carbon nanotubes, asphaltenes or molecular IR absorbing dyes.
According to the present invention, carbon fibers having a high porosity, a high surface area, and small pore diameters can be obtained regardless of whether or not one or more of the above-mentioned non-reactive and non-volatile filler material(s) is/are contained therein. Since said filler materials do not degrade during the carbonization step, they do not actively increase the porosity of the carbon fibers beyond their own, i.e. the slight increase of the surface area of the carbon fibers with increasing content of the filler material occurs due to the inherent porosity of the latter.
The carbon precursor fibers can be provided to the stabilization step in any appropriate form. However, it is preferable that the carbon precursor fibers are either electrospun or forcespun (rotational spinning) from a solution in advance, preferably at a concentration of from 1 to 60 wt%. In another preferred embodiment, the carbon precursor fibers are spun in a melt blow setup, optionally from a solution at a preferable concentration of from 1 to 60 wt%, before being provided to the stabilization step. Alternatively, the carbon precursor fibers can be spun by wet spinning, dry spinning, gel-spinning, or drawing. Irrespective of the above processing, fast carbonization can be conducted for any of such processed carbon precursor fibers.
In a further aspect, the present invention relates to the use of the above-described highly porous carbon fibers as a composite material, as an electrode material and/or an electrode coating, as an adsorbent, as a filtration medium and as a catalyst support.
In addition, the highly porous carbon fibers according to the present invention are applicable in charge storage, gas storage, filtration and adsorption devices.
The following Examples are intended to further illustrate the present invention. The claims are not to be construed as being limited thereto.

Example 1

Non-wovens made of polyacrylonitrile were obtained by electrospinning from solution, resulting in fiber diameters in the range of several hundreds of nanometers. These non-wovens were then stabilized at 270°C in an oven under atmospheric conditions (air).
Subsequently, the such stabilized non-wovens were carbonized using irradiation of an infrared diode laser with simultaneous emission at wavelengths of 968 and 998 nm in a non-oxidizing atmosphere. Fast heating was conducted at a heating rate of 50 K/s up to a final temperature of 1200°C, and held there for 60 s.
As a Comparative Example, another batch of the stabilized non-wovens was thermally carbonized in an oven at a temperature of from 1100 to 1200°C in a non-oxidizing atmosphere.
Fourier transform infrared spectroscopy revealed identical spectral features of the thermally carbonized fibers and the laser carbonized fibers, i.e. the fast carbonized fibers, indicating full conversion of the polyacrylonitrile precursor fibers into graphitic carbon (cf. Fig. 1).
The surface area of the carbon fiber non-wovens was determined using BET gas adsorption isotherms and scanning electron microscopy. The fast carbonized fibers obtained via laser induced heating were at least 40 times larger in surface area than the correspondingly thermally carbonized fibers (cf. Table 1, Figs. 2 and 3).

In addition, for further comparison, chemical activation using KOH was conducted, which increased the surface area of the thermally carbonized fibers by a factor of about 10. However, the porosity and the surface area were not as high as for the fast carbonized fibers (cf. Table 1, and Fig. 4).

Table 1

	carbonization		carbonization + chemical activation
	surface area (m²/g)	pore diameter (nm)	surface area (m²/g)	pore diameter (nm)
thermal carbonization	11.6	8.4	139.7	4.9
fast carbonization (laser)	492.5	3.9	143.3	1.8

By contrast, chemical activation of the fast carbonized fibers led to a reduction of the surface area to the extent of the thermally carbonized and activated fibers.

Example 2

Non-wovens made of polyacrylonitrile were obtained by forcespinning (rotational spinning) from solution, resulting in slightly larger diameters (500 nm into the micron scale).
Stabilization and pyrolysis conditions were the same as in Example 1. The such obtained thermally carbonized and fast carbonized fibers were analyzed correspondingly. In accordance with Example 1, the fast carbonized fibers exhibited much smaller pore diameters than the thermally carbonized fibers (cf. Table 2). Table 2

pore diameter (nm)

thermal carbonization 9.2

fast carbonization (laser) 3.3

Example 3

A non-reactive and non-volatile filler material was added to the carbon precursor fibers to obtain highly porous composite carbon fibers.
Graphene nanoplatelets were exfoliated in the same solvent as the polyacrylonitrile precursor fibers. Exfoliation of the graphene nanoplatelets was accomplished using ultrasonication, and large aggregates were removed from the exfoliated graphene sheets using centrifugation. The dissolved graphene sheets were added to the polyacrylonitrile solution, and then electrospun into corresponding non-wovens.

Stabilization and pyrolysis conditions were the same as in Example 1. The such obtained thermally carbonized and fast carbonized fibers were analyzed correspondingly (cf. Table 3).

Table 3

	0.1% GNP		1.0% GNP		1.5% GNP
	surface area (m²/g)	pore diameter (nm)	surface area (m²/g)	pore diameter (nm)	surface area (m²/g)	pore diameter (nm)
thermal carbonization	13.1	7.9	21.5	7.5	48.9	5.9
fast carbonization (laser)	125	2.4	143.9	3.6	148.3	2.2

GNP = graphene nanoplatelet exfoliated into few layer graphene sheets

The GNP filler material may obstruct fast gas diffusion, i.e. the microsized graphene sheets inhibited the fast expulsion of the gases generated during carbonization from the fibers, which led to lower surface areas compared to carbon fibers without any non-reactive and non-volatile filler material(s) contained therein. As can be taken from Table 3, the fast carbonization process resulted in much larger surface areas and smaller pore diameters compared to the thermal carbonization process.

Example 4

Non-wovens were prepared and stabilized under the same conditions as in Example 1, and were then exposed to a single plasma jet. The surface area of the such obtained carbon fibers was analyzed using scanning electron microscopy. As can be taken from Figs. 5 and 6, a three-dimensional carbon fiber network exhibiting a high porosity was obtained.

Example 5

Non-wovens were under the same conditions as in Example 3; however, with an IR absorbing dye Epolight 1117 admixed instead of GNP. The resulting mixture has an increased absorption in the IR spectrum, suitable for irradiation with the diode laser used in Example 1.

Claims

A process of manufacturing highly porous carbon fibers by fast carbonization of carbon precursor fibers, comprising:
a stabilization step, wherein carbon precursor fibers are heated in an oxidizing or non-oxidizing atmosphere at temperatures in the range of from 200 to 500°C; and

a pyrolysis step, wherein the such treated carbon precursor fibers are heated in a non-oxidizing atmosphere at temperatures above those of the stabilization step via laser induced heating, microwave heating, or assisted plasma heating, wherein the heating rate in the pyrolysis step is from 5 to 500 K/s, respectively.
The process according to claim 1, wherein the pyrolysis step is conducted for 1 fs to 30 min via laser induced heating either using the irradiation of continuous wave lasers with emission wavelengths of from 200 to 11000 nm, or using the irradiation of pulsed lasers with emission wavelengths of from 200 to 11000 nm and pulse durations in the millisecond, microsecond, nanosecond, picosecond, or femtosecond range.
The process according to claim 1, wherein the pyrolysis step is conducted for 1 s to 10 min via microwave heating using microwave frequencies in the range of from 1 to 13 GHz at a power of from 500 to 1000 W.
The process according to claim 1, wherein the pyrolysis step is conducted for 1 ms to 10 min via assisted plasma heating using argon, nitrogen, or mixtures thereof as a gas source at a gas flow rate of from 100 to 2500 sccm, and using plasma initiation frequencies in the range of from 10 kHz to 3 MHz at a power of from 20 to 60 W, with the plasma jet or the plasma jet array being guided in a linear, meandering, or rotating fashion, and with the distance between the plasma jet or the plasma jet array and the material being in the range of from 1 to 10 mm.
The process according to any one of claims 1 to 4, wherein polyacrylonitrile or a copolymer based on polyacrylonitrile which contains at least 50 mol% of acrylonitrile is used as a constituent material of the carbon precursor fibers.
The process according to claim 5, wherein the copolymer based on polyacrylonitrile contains acrylonitrile copolymerized with at least one selected from the group consisting of a (C₂-C₆) monoolefin, a vinylaromatic, a vinylaminoaromatic, a vinyl halide, a (C₁-C₆) alkyl (meth)acrylate, a (meth)acrylamide, a vinyl pyrrolidone, a vinyl pyridine, a (C₁-C₆) hydroxyalkyl (meth)acrylate, a (meth)acrylic acid, an itaconic acid, an acrylamidomethylpropylsulfonic acid, sodium methallyl sulfonate, and an N-hydroxy-containing (C₁-C₆) alkyl(meth)acrylamide.
The process according to any one of claims 1 to 4, wherein polyamide containing at least 50 mol% of amide monomers is used as a constituent material of the carbon precursor fibers, wherein the carbon precursor fibers contain at least 50 wt% of said polyamide.
The process according to any one of claims 1 to 4, wherein cellulose, lignin, or pitch is used as a constituent material of the carbon precursor fibers, containing at least 50 wt% of cellulose, lignin, or pitch.
The process according to any one of claims 1 to 8, wherein the carbon precursor fibers contain up to 20 wt% of a non-reactive and non-volatile filler material.
The process according to claim 9, wherein the non-reactive and non-volatile filler material is at least one selected from the group consisting of metal salts, metal based nanoparticles, graphitic carbon, graphene nanoplatelets, exfoliated graphene, carbon nanotubes, asphaltenes or molecular IR absorbing dyes.
The process according to any one of claims 1 to 10, wherein the carbon precursor fibers are either electrospun or forcespun from a solution at a concentration of from 1 to 60 wt% before being provided to the stabilization step.
The process according to any one of claims 1 to 10, wherein the carbon precursor fibers are spun in a melt blow setup, optionally from a solution at a concentration of from 1 to 60 wt%, before being provided to the stabilization step.
The process according to any one of claims 1 to 10, wherein the carbon precursor fibers are spun by wet spinning, dry spinning, gel-spinning, or drawing before being provided to the stabilization step.
Highly porous carbon fibers obtained by the process according to any one of claims 1 to 13, wherein the highly porous carbon fibers have a surface area in the range of from 100 to 2500 m²/g, and a pore diameter in the range of from 0.1 to 10 nm.
Use of the highly porous carbon fibers according to claim 14 as a composite material, as an electrode material and/or an electrode coating, as an adsorbent, as a filtration medium, as a catalyst support as well as in charge storage, gas storage, filtration and adsorption devices.