CA1281784C - Flexible, electrically conductive composites, process for their manufacture, and their use - Google Patents

Abstract

Abstract Flexible, electrically conductive composites, process for their manufacture, and their use The invention relates to an electrically conductive com-posite comprising a carbon-fiber carrier having a speci-fic surface of less than 100 m2/g and an electrically conductive polymer, the form of the composite being flex-ible and that of the carbon-fiber carrier being felt-like.
The subject of the invention is furthermore a process for the manufacture of said composite and its use.

In addition to its flexibility, the novel composite is notable for a considerable specific conductance and an increased specific surface.

Description

~4 HOECHST AKTIENGESELLSCHAFT HOE 86/F 064 Dr.DA/DE

Flexible, electrically conductive composites, process for their manufacture, and their use It is known that heteroaromatics can be polymerized dur-ing anodic oxidation under suitable conditions and in doing so form electrically conducting polymers which are of interest for electrical engineering, in semiconductor components, sw;tches, screening materials, solar cells and as electrode materials in electrochemical syntheses and in reversible charge storage devices (cf., for ex-ample, I~M J. Res. Develop. 27, 330 (1983)).

However, a considerable disadvantage of most of the pro-ducts described is that they are produced as brittle films or powders and as a consequence of their insolu-bility and lack of thermal plasticity, cannot be conver-ted to a processable form (cf., for example, J. Phys.
Chem. 1983, 2289~. An exception is formed by polypyr-role, which under suitable conditions is produced as a solid, to some extent flexible film (cf., for example, German Offenlegungsschrift 3,226,278). Nevertheless, even for this material, the subsequent shape is already approximately determined during synthesis by the elec-trode shape. In addition, it has virtually no internal surface so that only the geometrical surface is avail-able for the abovement;oned applications. The tensile strength can be increased by incorporating carbon fibers or fabrics made of carbon fibers in polypyrroles ~cf.
Japanese Offenlegungsschrift 83-89,639 The composites obtained as a result have, however, little flexibility and, ;n add;tion, have only a relatively low specif;c surface. For applicat;ons of electr;cally conduct;ng polymers, for example, as electrodes ;n electrochem;cal processes or ;n storage cells, in addit;on to the mecha-n;cal stabil;ty, the rapid charge transport and mass transfer capab;lit;es, ;n part;cular, play an ;mportant part. In th;s connect;on, a dec;s;ve cr;terion for rapid exchange reactions is the spec;fic surface avai lable.

The ob ject of the present invention ~as therefore to provide an electrically conductive composite comprising carbon-fiber carriers and an electrically conducting polymer, and also a process for the manufacture thereof.
Said composite should be sufficiently flexible and have an increased specific surface, but the specific surface of the carrier material itself should be within the 10 usual range.

To achieve said object the invention proposes an electri-cally conductive composite comprising a carbon-fiber carrier having a specific surface of Less than 100 m2/g and an electically conductive Polymer, the specific sur-face of the composite being greater than that of the electrically conducting polymer, ~herein the form of the composite is flexible and that of the carbon-fiber car-rier is felt-like.
The invention also relates to a process for manufactur-;ng said composites by applying an electrically conduc-tive polymer to a carbon-fiber carrier having a specific surface of less than 100 m2/g, ~herein a felt-like carbon-fiber carrier is used.

The carrier material of the novel composite comprises carbon, including graphite and should have a felt-like structu~e. In this case this should be understood to mean an arrangement of fiber-like constituents ~hich presents as uniform a space filling as possible in all three directions so that neither marked cavities nor regions ~ith a build-up of fiber bundles are produced.

As examples of such carrier materials mention may be made of carbon felts, in particular soft carbon felts, graphite felts and carbon felts reinforced by carbon-fiber fabrics.

. ~4 An arrangement oriented in two dimensions having many contact points and fibers arranged in parallel to form bundles, such as is encountered in carbon-fiber fabrics, results in uneven deposition of the conducting polymer and also in the formation of sol;d blocks and, conse-quently, in a reduction of the specific surface. In addition, the flexibility is substantially lost under these circumstances.

The felt-like carbon carrier material of the novel com-posite has a specific surface of less than 100 m2/g, pre-ferably of 0.01 to 10 m2/g and in particular, of 0.1 to 5 m2/g, determined by the BET method (for >0.5 m2/g) or calculated using the formula specified further below.
As electrically conducting polymers, according to the invention in principle all the products known for this purpose are suitable, such as those described in IBM J.
Res. Develop. 27, 330 ff (1983) and in the IBM Research Report (Electrochemical Synthesis of Conducting Polymers;
A.F. Diaz and J. Bargon, 23.11.1983). They should have a spec;fic conductance at room temperature of at least 10 5 ohm 1 cm 1, preferably at least 1û 3 ohm 1 cm 1 and should be solid at room temperature. Preferably, Z5 however, said polymers co0prise structural units which are derived from the monomers of the general formulae (I) and/or (II) specified further below. As examples of such electrically conducting polymers mention may be made here of: poly(pyrrole), poly(3-methylpyrrole), poly(3,4-dimethylpyrrole), poly(N-methylpyrrole)~ poly-(3-chloropyrrole), poly(thiophene), poly(3-methylthio-phene), poly(3,4-dimethylthiophene), poly(thienothio-phene), poly(thienoPyrrole), poly(carbazole), poly(1,2-di(2-thienyl)ethene), poly(1,2-di(3-methylthien-2-yl)-ethene), poly(1,2-di(2-furyl)ethene), poly(1-~2-furanyL)-2-(2-thienyl)ethene), poly(1-(2-pyrrolyl)-2-(2-thienyl)ethene), poly(1,4-di(2-thienyl)buta-1,3-diene), poly(1,4-di(2-furyl)buta-1,3-diene), poly(1,4-di(2-thienyl)benzene), poly(terthienyl(2,5-di(2-thienyl)thio-.

-- 4 --phene)), poly(2,5-d;(2-th;enyl)pyrrole) and poly(2,2'-d;th;ophene).

Depending on the structure of the matrix material and the density of the electrically conducting polymer, the quantity of electrically conducting polymer which is combined with the carbon-felt carrier is, as a rule, be-tween 5% and 80%, in particular between 10% and 50%, based on the total composite.
The Layer th;ckness of the electr;cally conducting poly-mer on the carbon-felt carr;er ;s usually between 0.1 and 25 ~m, preferably between 1 and 6 ~m. In th;s man-ner, a large geometrical surface of the composite is produced when the novel carrier material ;s used, s;nce the average d;stance between the individual fibers of the felt is suff;ciently large and coalescence through the polymer with the above Layer thicknesses does not take place or does not take place to a substantial ex-tent. On the contrary, ;n the nove~ compos;te, thepolymer coating on the carbon-felt fibers is fairly uni-form.

~he novel comPOsite has an improved flexibility compared with conventional composites comprising carbon fibers and a conducting polymer. This is revealed by the fact that ;t survives the bend test described further below without fracture.

In addit;on, the specific surface of the novel composite is in general a factor of 2 to 200 greater, preferably 5 to 100 greater and in particuLar, 10 to 50 greater than the specific surface of the respective pure poly-mer having the same surface area, so that a Larger part of the conducting polymer is available when used as an electrode in electrochemical syntheses and in storage cells. Said specific surface is determined by calcula-tion using the formula specified further below.

Moreo~er, the nove~ compos;tes are notable for high sta-bil;ty even when electrically conducting polymers are used which under usual deposition conditions are produ-ced only as powders or brittle films, and they have, in addition, a fairly low specific resistance since an op-timum charge transport can take place through the inter-calated carbon skeleton in conjunction with the intimate contact with the conducting polymer. The sPecific re-sistance is usually therefore in the range from 0.1 to 100 ohm cm, preferabLy 1 to 10 ohm cm, and the specific conductance is correspondingly 0 01 to 10 ohm 1 cm 1, pre-ferably 0.1 to 1 ohm 1 cm 1.

The combination of these special properties, as a result of which the novel composite differs from the kno~n com-posites based on carbon fibers, makes it possible to use said composite for applications which require, in addi-tion to rapid charge transport and mass transfer, an un-usual geometry (for example, extremely flat) with the possibility of matching to specified structures. In addition, however, they can be used also in all the fields in which the eLectrically conducting polymers hitherto known are of interest, for example as catalysts, electrical switches, semiconductor components, screening materials, solar cells, large-area heating conductors, and aLso, in particular, as electrodes for electrosyn-theses and in reversible charge storage devices ~batter-ies).

The method of manufacturing the novel composite is to app~y the electrically conducting polymer to the felt-like carrier material using knoun polymerization methods.
Preferably, this is done by electrochemical polymeriza-tion, in particular anodic oxidation of corresponding ~ 35 monomers, the felt-like carrier material acting as an ;~ anode, under conditions known per se for this purpose.

The electrochemical polymeri2ation of the monomers or of the comonomer mixtures is accordingly performed in ' ~28~784 one of the usual electrolyte solvent systems which is sta~le under the conditions of the electrochemical poly-merizat;on and wh;ch must have an adequate solubility for the monomer and the conducting salt. Dipolar apro-S t;c solvents such as acetonitrile, propylene carbonate,dimethylformamide, dimethyl sulfoxide and nitromethane, are preferably used. Ho~ever, other solvents, such as methylene chloride or tetrahydrofuran may also be used.
An addition of 1 to 5% water is beneficial in some cases.
In the case of monomers having a low oxidation potentia~, such as, for example, pyrrole, it is even possible to polymerize from aqueous dispersions, if necessary, with dispersants added.

As a rule, the monomer concentration is 0.û01 to 5 mol, preferably 0.01 to 1 mol of monomer per liter of electro-lyte solvent.

As conducting salts, which serve, in particular, to transport current during the electrochemical polymeriza-tion, but which are also contained in the polymer pro-duced and affect the properties thereof, use is made of the usual conducting salts such as, are mentioned, for example, in the German Offenlegungsschrift 3,2Z6,278.
Here mention may be made as examples of tetrafluorobor-ates, hexafluoroarsenates, hexafLuoroantimonates, hexa-fluorophosphates, hexachloroantimonates, perchlorates, hydrogensulfates and sulfates. Aromatic and aliphatic alkyl and arylsulfonates and perfluorinated alkylsulfon-ates are also suitable. In addition to the alkalineearth metal cations and H(+~, in particular the alkali metal cations are suitable as cations for the conducting salts. Cations of the type R4N( ) or R4Pt ), in ~hich the radicals R in each case denote, independently of each other, hydrogen and/or lower alkyl radicals, cyclo-al;phatic or aromatic radicals, prove to be particularly beneficial. In some cases a mixture of R4N( ) and Ht+) proves to be especially beneficial for the uniformity and peel strength of the polymer deposit. The quantity of conducting salt ;s ;n general ;n the range from 0.001 to 1 mol, preferably 0.01 to 0.5 mol per liter of solvent.

An improvement in the uniformity and peel strength of the polymer deposit can be achieved by adding acid to the electrolyte This holds true, in particular, if monomers according to the formula (II) below are used.
The acids on which the conducting salts described above are based, in particular, perchloric acid, tetrafluoro-boric acid, hexafLuorophosphoric acid, trifluoromethane-sulfonic acid, toluenesulfonic acid and benzenesulfonic acid are, for examPle, suitable.

The electrochemical polymerization may be Performed in the usual cells or electrolysis apparatuses. Simple electrolysis apparatuses comprising an undivided cell, two or more electrodes and an external current source, are, for example, quite suitable. However, it is also possible to use divided cells with diaphragms or ion exchange membranes or those having reference electrodes for determining the potential precisely. Measurement of the quantity of electricity is expedient, since the quantity of polymer deposited and, for the same carrier material, also the layer thickness is proportional thereto. In this manner it is possible to contro~ the thickness of the coating on the carbon fibers. An electrolysis apparatus in which the cathode is of flat construction at the bottom and the anode is passed through the electrolyte in the form of a tape with a constant rate of advance, makes it possible to conduct the process continuously.

Under these circumstances, use is made~ as mentioned, of the felt-like materials made of carbon, which act as a carrier in the novel composite, as the anode. Carbon felts, soft carbon felts or graphite felts of differing flexibility which are obtainabLe commercially, eg.
(R) Sigratherm KFA, KFB, GFD or PF types, are, for example, suitable for this Purpose~ Said anode material ;: ' :

can be used in any desired shape, preferably, however, a flat arrangement aligned parallel to the cathode is chosen in order to achieve as uniform a sheathing of the carbon fibers as possible. For this purpose the anode material is clamped in a nonconducting frame which pre-ferably comprises a plastic material which is inert to-wards the electrolyte. The carbon-felt anode can be gripped in the frame and/or screwed in using plastic-material screws. The frame must ensure un;mpeded access of the electro~yte to the anode and should therefore only box in the anode or have a reticular structure.
Contact is made to the anode by one or more metal clips which are either disposed outside the electrolyte or are insu~ated excePt for the contacting surface.
The type and design of the cathode is not critical, it being possible to use one or more cathodes. The cathode comprises one of the usual electrode materials, such as, for example, graphite, preferably, however, stainless steel or platinum. It is generally arranged parallel to the anode; if two cathodes are used, these are situ-ated at the same distance in front of and behind the anode. This parallel arrangement of two cathodes favors the uniformity of the polymer deposit. If only one cathode is used, repeatedly turning the anode has the same effect.

The process is normally performed at room temperature, but the temperature may also vary uithin a wide range, uhich is limited in the downward direction by the solidi-fication temperature and in the upper direction by the boiling point of the electrolyte/solvent system, and is usually between -50 and 8ûC, preferably -10 and 4ûC.

Any DC source which supplies a sufficiently high electri-cal vo~tage is suitable as a current source for operat-ing the electrolytic ce~l in which the process is per-formed. Usually the electrochemical polymerization is conducted ~ith a voltage of 0.1 to 100 V, preferably in ;:::
:
: `
. ,: .: .. . .

.'784 the range from 1.5 to 30 V. Values for the current den-sity in the range from 0.01 to 100 mA/cm2, in particular in the range from 0.1 to 10 mA/cm2, have proved benefi-cial and advantageous.

The duration of electrolysis depends, inter alia, on the electrolyte system used, the particular electrolysis conditions, and also, in particular, on the desired coating thickness. Usually the duration of electrolysis is 1 to 12 hours, preferably 2 to 8 hours To remove adhering conducting salt, the co~posite obtained in the electrolysis is washed with solvents, preferably with the electrolyte solvent, and dried at temperatures in the range 20 - 150C, optionally under vacuum. Electrically conducting polymer which only loosly adheres to the composite can be removed mechanically, for example by carefully brushing off, by blowing off, for example, with compressed air, or by treatment with ultra-sound in an inert liquid.

As monomers of the conducting po~ymers to be deposited on the carrier material, the aromatics and heteroaroma-tics known for this purpose are suitable. Preferably, howeYer, compounds of the general formula (I) R2 R~

~y ~ (I) are suitable for this purpose. Here the radicals R2 and R3 are in each case, independently of each other, hydro-gen, halogen, (C1-C4)-alkyl, aryl, preferably phenyl or thienyl, or form an aromatic ring uith each other, preferably a benzene, thiophene or pyrrole ring. The radicals R1 and R4 are in each case, independently of each other, either hydrogen or form with R2 or R3 an aro-matic ring, preferab(y a benzene, thiophene or pyr~ole ring. X corresponds to 0, S, NH, N-alkyl, preferably ~:
....

'784 N-(C1-C4)alkyl, or N-aryl, preferably N-phenyl. In parti-cular, pyrrole, 3-chloropyrrole, 3-methylpyrrole, 3,4-dimethylpyrrole, N-methylpyrrole, thiophene, 3-methyl-thiophene, 3,4-dimethylthiophene, thienothiophene, thieno-pyrrole and carbazole are suitable.

Compounds of the general formula (II) R5 ,R R ,R
H~}K~H (II) can also be used as monomers. The radicals R5, R6, R7 and R8 are in each case, independently of each other, hydrogen, (C1-C4)alkyl or aryl, preferably phenyl or thienyl. Y and Z correspond, independently of each other, to 0, S, NH, N-alkyl, preferably N-(C1-C4)alkyl, or N-aryl, preferably N-phenyl. K represents aryl, pre-ferably phenyl, heteroaryl, preferably thienyl, furanyl, pyrrolyl or a conjugated system of the formula (III) ~CH = CH~n (III) with n = 0 to 3.
In particular, 1,2-di(2-thienyl)ethene, 1,2-di(3-methyl-thien-2-yl)ethene, 1,2-di(2-furyl)ethene, 1-(2-furyl)-2-(2-thienyl)ethene, 1-(2-pyrrolyl)-2-(2-thienyl)ethene, 1,4-di(2-thienyl)buta-1,3-diene, 1,4-di(2-furyl)buta-1,3-diene, 1,4-di(2-thienyl)benzene, terthienyl(2,5-di(2-thienyl)thiophene), 2,5-di(2-thienyl)pyrrole and 2,2'-dithiophene are suitable.

Mixtures of the monomers may also be used, in particular also mixtures of monomers of the formula (I) with those of the formula (II), and also, if necessary, also mix-tures with other compounds copolymerizable therewith.

The invention is explained in more detail by the following examples. The parts and percentages specified ;n the examples are based, unless otherw;se noted, on the weight.
The m;nimum specific surface was calculated using the following formula, the quantities R, D and Z being de-termined from SEM photographs:
A = 2 ~( R+D ~ Z
G
A: specific surface ~m2/g], R: radius of a carbon fiber [m], D: mean thickness of the Polymer layer [m], Z: mean number of fibers in the composite, G: weight of the composite Cg].

The specific conductance of the composites was determined by means of four-point measurement at various points so that, as a result of chance variations in the microsco-pic structure at the particular test point, a range of conductances was obtained. The flexibility was deter-mined from a bend test ;n which the composite was rolledround a cylinder of a certain diameter and examined for any fracture. The flexibility criterion is cons;dered to be fulfilled if the quotient obtained by d;viding the thickness of the composite by the diameter of the cylin-der around which the composite can be rolled withoutfracture is equal to or greater than 10 2, preferably equal to or greater than 5 x 10 2 This was the case for the composites of the novel Examples 1 to 9.

Example 1 3.7 parts of tri(n-butyl)amine, 7.6 parts of p-toluene-sulfonic acid hydrate, 1.34 parts of pyrrole and 200 parts of acetonitriLe were introduced into an undivided electrolysis celL. The cathode comprised optionally platinum or V2A steel. As anode, a carbon felt (specific surface (BET) = approx. 0.5 m2/g, Sigratherm KFB 2, made by Sigri Elektrographit GmbH) was mounted parallel to the cathode using a spacer. With an anodic current dens;ty 28~.'78~

of 0 8 mA/cm2 (anode surface on both s;des) and a cell voltage of 2.5 V a flex;ble compos;te having a specific surface of approx. 0.18 m2/g and a specif;c conductance of 0.2 - 1 ohm 1 cm 1 and comprising 66 parts of carbon S and 34 parts of polypyrrole was obtained after an electroly-sis period of 4 hours. The thickness of the polypyrro~e coating was 2 - 4 ~m.

Example 2 4.34 parts of tetraethylammonium tetrafluoroborate, 1.34 parts of pyrrole and 30û parts of acetonitrile were in-troduced into an undivided electrolysis cell. Under the electrolysis conditions as in Example 1, a flexible com-posite having a specific surface of approx. 0.18 m2/gand a specific conductance of 0.2 - 1 ohm 1 cm 1 and com-prising 69 parts of carbon and 31 parts of polypyr-role was obtained after an electrolysis period of 4 hours. The thickness of the polypyrrole coating was 2 -4 ~m.

Example 3 4.34 parts of tetraethylammonium tetrafluoroborate, 1.34 parts of pyrrole and 350 parts of acetonitrile ~ere in-troduced into an undivided electrolysis cell. A carbon felt (specific surface (BET) = 0.3 - 0.4 m2/g) ("Sigra-therm 6FD") was used as anode. One V2A cathode in each case was arranged on both sides of the anode at the same distance. ~ith an anodic current density of 0.5 mA/cm2 (anode surface on both sides) and a cell voltage of 25 V, a flexible composite having a specific surface of approx.
0.21 mZ/g and a specific conductance of 0.2 - 1 ohm 1 cm 1 and comprising 57 parts of carbon and 43 parts of polypyrrole was obtained after an electrolysis period ot 4 hours and subsequent cleaning. The polypyrrole "
coating was 4 - 6 ~m thick.

~:

:

:
, -' ' ` '- ~
.

~2~784 Example 4 4.34 parts of tetraethylammonium tetrafluoroborate, 0.98 parts of 3-methylthiophene and 200 parts of acetonitrile were electroly2ed in an und;vided cell under the condi-tions as in Example 1. A flexible composite, which com-prised 75X carbon and 25% poly(3-methylthiophene), was obtained. Its specific surface was approx. 0.16 m2/g and its specific conductance was 0.2 - 1 ohm 1 cm 1. The polymer coating was 1 - 2 ~m thick.

Example 5 4.34 parts of tetraethylammonium tetrafluoroborate, 1.76 parts of 50X aqueous tetrafluoroboric acid, 1.67 parts of carbazole and 200 parts of acetonitrile were electro-lyzed in an undivided cell as in Example 1. With an anodic current density of û.3 mA/cm2 (anode surface on both sides) and a cell voltage of 25 V, a flexible com-posite having a specific surface of approx. 0.18 m2/g anda specific conductance of 0.2 - 1 ohm 1 cm 1 and compri-sing 60 parts of carbon and 40 parts of polycarbazole was obtained after an electrolysis period of 8 hours.
The thickness of the polycarbazole coating vas 2 - 5 ~m.
Example 6 4.34 parts of tetraethylammonium tetrafluoroborate, 0.88 parts of SOX a~ueous tetrafluoroboric acid, 0.96 parts of ~E)-1,2-di(2-thienyl)ethene and 200 parts of aceto-nitrile uere electrolyzed as in Example 5. A flexible composite having a specific surface of approx. 0.15 m2/g and a specific conductance of 0.2 - 1 ohm 1 cm 1 compri-sing 64 parts of carbon and 36 parts of poly~1,2-di(2-, thienyl)ethene) ~as obtained after an electrolysis peri-od of 6 hours. The coating of conducting polymer under these circumstances uas 1 - 3 ~m thick.

~; ~'',' ,~. .~."

'-`` ` 12 Examp~e 7 -4.34 parts of tetraethylammonium tetrafluoroborate, 0.88 parts of 50% aqueous tetrafluoroboric acid, 0.80 parts of (E)-1,2-di(2-furyl)ethene and 200 parts of aceto-nitrile were electrolyzed as in Example 5. A composite comprising 68 parts of carbon and 32 parts of poly(1,2-di(2-furyl)ethene) was obtained after an electrolysis period of 7 hours. The flexible composite had a speci-fic surface of 0.13 m2/g and a specific conductance of0.2 - 1 ohm 1 cm 1 for a polymer layer thickness of 1 -2 ~m.

Example 8 4.34 parts of tetraethylammonium tetrafluoroborate, 0.88 parts of 50% aqueous tetrafluoroboric acid, 0.85 parts of (E,E)-1,4-di(2-thienyl~buta-1,3-diene and 200 parts of acetonitrile ~ere electrolyzed as in Example 5. A
composite comprising 77 parts of carbon and 23 parts of poly(1,4-di(2-thienyl)butadiene) was obtained after an electroLysis period of S hours. The f~exible composite had a specific surface of approx. 0.10 m2/g and a sPecific conductance of 0.2 - 1 ohm 1 cm 1 for a polymer layer thickness of 1 - 2 ~m.

Example 9 4.34 parts of tetraethylammonium tetrafluoroborate, 0.88 parts of 50~ aqueous tetrafluoroboric acid, 0.96 parts of 1,4-di(2-thienyl)benzene and 200 parts of acetonit-rile were electrolyzed as in Example S. A flexible com-posite comPrising 66 parts of carbon and 34 parts of poly(1,4-di(2-thienyl)benzene) was obtained after an electro~ysis period of 7 hours. The composite had a specific surface of approx. 0.15 m2~g and a specitic con-ductance of 0.2 - 1 ohm 1 c- 1 for a polymer layer thick-~;~ ness of 2 - 4 ~m.

: ~ :
', ' :
- , -~4 Comparison experiment ~ 3.01 parts of tetraethylammonium p-toluenesulfonate, 0.97 parts of N-methylpyrrole, 1 part of water and 200 parts of acetonitrile were ;ntroduced ;nto an und;vided electrolysis cell A platinum sheet was used as cathode, and a cloth-like flat fabric comprising carbon fibers (7 - 8 ,um diameter) having a length of 25 mm and a width of 20 mm was used as anode. The electropolymerization was carried out at a current density of 4 mA and a cell voltage of 2 - 2.5 V. A composite comprising 80 parts of carbon and 20 parts of poly(N-methylpyrrole) was ob-tained after 6 hours. The polymer layer thickness on detached carbon fibers was 1 - 2 um and the spec;f;c conductance 0.2 - 1 ohm 1 cm 1 Despite a coat;ng th;ckness of 2 ,um maximum, it was not poss;ble to calculate the spec;fic surface of the compo-site obtained using the above formula since large re-gions of the fiber bundles had coalesced.

The flexibility of the composite was insufficient topass the bend test described further above.

Claims (10)

1. An electrically conductive composite comprising a carbon-fiber carrier having a specific surface of less than 100 m2/g and an electrically conductive polymer, the speci-fic surface of the composite being greater than that of the electrically conductive polymer, wherein the form of the composite is flexible and that of the carbon-fiber carrier is felt-like.

2. An electrically conductive composite as claimed in claim 1, wherein the specific surface of the composite is 2 to 200 times greater than that of the electrically conductive polymer of the same surface area.

3. An electrically conductive composite as claimed in claim 1, wherein the layer thickness of the electrically con-ductive polymer on the carbon fibers is 0.1 - 25 µm.

4. An electrically conductive composite as claimed in claim 1, wherein the electrically conductive polymer contains substantially structural units which are derived from at least one monomer of the formula (I) below (I) in which R2 and R3 denote in each case, independently of each other, hydrogen, halogen, (C1-C4)alkyl, or aryl, or form an aromatic ring with each other, and R1 and R4, independently of each other, are either hydrogen or form an aromatic ring with R2 or R3, and X represents 0, S, NH, N-alkyl, or N-aryl.

5. An electrically conductive composite as claimed in claim 1, wherein the electrically conductive polymer contains substantially structural units which are derived from at least one polymer of the formula (II) below (II) in which R5, R6, R7 and R8 are in each case, independent-ly of each other hydrogen, alkyl, aryl, and Y and also Z
represent, independently of each other, 0, S, NH, N-alkyl or N-aryl, and K is aryl, heteroaryl or a conjugated system of the formula (Ill) ? CH = CH ?n (III) with n = 0 to 3.

6. A process for manufacturing electrically conductive com-posites as claimed in claim 1 by applying an electrically conductive polymer to a carbon-fiber carrier with a spe-cific surface of less than 100 m2/g, wherein a felt-like carbon-fiber carrier is used.

7. The process as claimed in claim 6, wherein the applica-tion of the electrically conductive polymer is carried out by electrochemical polymerization of corresponding monomers, the felt-like carbon-fiber carrier being con-nected as anode.

8. The process as claimed in claim 5, wherein as monomer, those of one or both of formulae (I) and (II) are used.

9. The process as claimed in claim 6, wherein the electro-chemical polymerization is carried out in the presence of a conducting salt and an acid.

10. The use of the electrically conductive composites as claimed in claim 1 as catalysts, electrical switches, semiconductor components, screening materials or as elec-trodes in reversible charge storage devices and in elec-trochemical syntheses.