Carbon film and method for producing the same

Abstract

Provided is a carbon film including: a plurality of fibrous carbon nanostructures; and a conductive carbon, wherein the plurality of fibrous carbon nanostructures has a BET specific surface area of 500 m.sup.2/g or more. Also provided is a method of producing a carbon film, the method including mixing a conductive carbon into a fibrous carbon nanostructure dispersion liquid containing a plurality of fibrous carbon nanostructures having a BET specific surface area of 500 m.sup.2/g or more, a dispersant, and a solvent, and subsequently removing the solvent to form a carbon film.

Claims

1. A carbon film, comprising: a plurality of fibrous carbon nanostructures; and a conductive carbon, wherein the plurality of fibrous carbon nanostructures has a BET specific surface area of 500 m.sup.2/g or more, and the plurality of fibrous carbon nanostructures and the conductive carbon are in contact and are not physically fused.

2. The carbon film according to claim 1, wherein a content ratio by mass of the plurality of fibrous carbon nanostructures to the conductive carbon (fibrous carbon nanostructures/conductive carbon) is from 95/5 to 35/65.

3. The carbon film according to claim 1, wherein the plurality of fibrous carbon nanostructures includes one or more carbon nanotubes.

4. A method of producing a carbon film, the method comprising: mixing conductive carbon into a fibrous carbon nanostructure dispersion liquid containing a plurality of fibrous carbon nanostructures having a BET specific surface area of 500 m.sup.2/g or more, a dispersant, and a solvent; and subsequently removing the solvent to form a carbon film, wherein the carbon film comprises the plurality of fibrous carbon nanostructures and the conductive carbon which are in contact and are not physically fused.

5. The method according to claim 4, the method further comprising: preparing the fibrous carbon nanostructure dispersion liquid by subjecting a coarse dispersion liquid containing the plurality of fibrous carbon nanostructures, the dispersant, and the solvent to dispersion treatment that brings about a cavitation effect or a crushing effect in order to disperse the fibrous carbon nanostructures.

6. The method according to claim 4, wherein a content ratio by mass of the plurality of fibrous carbon nanostructures to the conductive carbon (fibrous carbon nanostructures/conductive carbon) in the fibrous carbon nanostructure dispersion liquid is from 95/5 to 35/65.

7. The method according to claim 4, wherein the plurality of fibrous carbon nanostructures includes one or more carbon nanotubes.

Description

EXAMPLES

(1) Hereinafter, the present disclosure will be described in detail with reference to Examples. However, the present disclosure is not limited to these Examples.

(2) <Synthesis of Fibrous Carbon Nanostructures>

(3) Fibrous carbon nanostructures were synthesized according to the following procedure.

(4) A coating liquid A for catalyst supporting layer formation was prepared by dissolving 1.9 g of aluminum tri-sec-butoxide, used as an aluminum compound, in 100 mL of 2-propanol, used as an organic solvent, and further adding and dissolving 0.9 g of triisopropanolamine, used as a stabilizer.

(5) Additionally, a coating liquid B for catalyst layer formation was prepared by dissolving 174 mg of iron acetate, used as an iron compound, in 100 mL of 2-propanol, used as an organic solvent, and further adding and dissolving 190 mg of triisopropanolamine, used as a stabilizer.

(6) The coating liquid A described above was applied onto the surface of an FeCr alloy SUS430 base plate (available from JFE Steel Corporation, 40 mm100 mm, thickness 0.3 mm, Cr 18%, arithmetic average roughness Ra approximately 0.59 m), used as a substrate, by dip coating under ambient conditions of a room temperature of 25 C. and a relative humidity of 50%. In detail, the substrate was immersed in the coating liquid A and was held in the coating liquid A for 20 s before being pulled up with a pulling-up speed of 10 mm/s. Thereafter, air drying was performed for 5 minutes, heating at a temperature of 300 C. in an air environment was performed for 30 minutes, and cooling was performed to room temperature to form an alumina thin film (catalyst supporting layer) of 40 nm in thickness on the substrate.

(7) Next, the coating liquid B described above was applied onto the alumina thin film on the substrate by dip coating under ambient conditions of a room temperature of 25 C. and a relative humidity of 50%. In detail, the substrate having the alumina thin film thereon was immersed in the coating liquid B and was held in the coating liquid B for 20 s before being pulled up with a pulling-up speed of 3 mm/s. Thereafter, air drying (drying temperature 45 C.) was performed for 5 minutes to form an iron thin film (catalyst layer) of 3 nm in thickness.

(8) In this manner, a catalyst substrate 1, which had the alumina thin film and the iron thin film on the substrate in this order, was obtained.

(9) The prepared catalyst substrate 1 was loaded into a reaction furnace of a CVD device maintained at a furnace internal temperature of 750 C. and a furnace internal pressure of 1.0210.sup.5 Pa, and a mixed gas of 100 sccm of He and 800 sccm of H.sub.2 was introduced into the reaction furnace for 10 minutes (formation step). Next, a mixed gas of 850 sccm of He, 100 sccm of ethylene, and 50 sccm of H.sub.2O-containing He (relative humidity 23%) was supplied into the reaction furnace for 8 minutes (growth step), while the furnace internal temperature of 750 C. and the furnace internal pressure of 1.0210.sup.5 Pa were maintained.

(10) Thereafter, 1,000 sccm of He was supplied into the reaction furnace in order to purge residual feedstock gas and catalyst activating material. By the above processes, an aligned fibrous carbon nanostructure aggregate 1 was obtained. The aligned fibrous carbon nanostructure aggregate 1 that was obtained had a yield of 1.8 mg/cm.sup.2, a G/D ratio of 3.7, a density of 0.03 g/cm.sup.3, a BET specific surface area of 1,060 m.sup.2/g, and a carbon purity of 99.9%. The aligned fibrous carbon nanostructure aggregate 1 that had been prepared was peeled from the catalyst substrate 1 to obtain fibrous carbon nanostructures.

(11) <Preparation of Fibrous Carbon Nanostructure Dispersion Liquid 1>

(12) The previously described fibrous carbon nanostructures were added in an amount of 1.0 g to 500 mL of 2 mass % sodium deoxycholate (DOC) aqueous solution, used as a dispersant-containing solvent, to obtain a coarse dispersion liquid containing DOC as a dispersant. The coarse dispersion liquid containing the fibrous carbon nanostructures was loaded into a high-pressure homogenizer (trade name BERYU SYSTEM PRO, available from Beryu Corp.) having a multi-step pressure control device (multi-step pressure reducer) configured to apply back pressure during dispersion, and the coarse dispersion liquid was subjected to dispersion treatment at a pressure of 100 MPa. In detail, the fibrous carbon nanostructures were dispersed by imparting shear force on the coarse dispersion liquid while applying back pressure and, as a result, a fibrous carbon nanostructure dispersion liquid 1 was obtained as the fibrous carbon nanostructure dispersion liquid. Additionally, in the dispersion treatment, dispersion liquid flowing out from the high-pressure homogenizer was returned to the high-pressure homogenizer, and dispersion treatment was carried out in this manner for 10 minutes.

(13) <Preparation of Fibrous Carbon Nanostructure Dispersion Liquid 2>

(14) A fibrous carbon nanostructure dispersion liquid 2 was obtained by the same procedure with the exception that the fibrous carbon nanostructures used in the fibrous carbon nanostructure dispersion liquid 1 were replaced by JC142 (BET specific surface area 650 m.sup.2/g, G/D ratio 0.6, carbon purity 99.1%) available from JEIO Co., Ltd.

Preparation of Comparative Example Dispersion Liquid

(15) A comparative example dispersion liquid was obtained by the same procedure with the exception that the fibrous carbon nanostructures used in the fibrous carbon nanostructure dispersion liquid 1 were replaced by NC7000 (BET specific surface area 270 m.sup.2/g, G/D ratio 0.3, carbon purity 89.1%) available from Nanocyl.

Example 1

(16) Into a 200 mL beaker, 100 g the prepared fibrous carbon nanostructure dispersion liquid 1 and 0.022 g of expanded graphite (trade name EC500, available from Ito Graphite Co., Ltd.) were placed. Then, filtration was performed at 0.09 MPa by using a vacuum filtration device equipped with a membrane filter. After the end of filtration, isopropyl alcohol and water were passed through the vacuum filtration device to wash a carbon film formed on the membrane filter, and then air was passed through the vacuum filtration device for 15 minutes. After that, the prepared carbon film/membrane filter were immersed in ethanol, and the carbon film was peeled from the membrane filter to obtain a carbon film 1.

(17) The film density of the obtained carbon film 1 was measured to be 0.75 g/cm.sup.3. The glossiness of the produced CNT film 1 was measured at 60 using a gloss meter (Gloss Checker available from Horiba, Ltd., wavelength 890 nm). The measured glossiness was 25. Surface resistivity of the produced carbon film 1 was measured by the four-terminal four-probe method using a conductivity meter Loresta GP (Loresta is a registered trademark in Japan, other countries, or both), available from Mitsubishi Chemical Corporation. The measured surface resistance was 2.3 /sq.

(18) The carbon film 1 had a circular shape having a diameter of 50 mm, an area of approximately 20 cm.sup.2, and a thickness of 20 m, which correspond to the dimension of the membrane filter. The carbon film 1 had excellent film-forming properties, maintained the film form even after being peeled from the filter, and also had excellent free-standing properties.

Example 2

(19) A carbon film 2 was formed by the same procedure as in Example 1 with the exception that the amount of expanded graphite (trade name EC500, available from Ito Graphite Co., Ltd.) used in Example 1 was changed to 0.050 g. The film density of the obtained carbon film 2 was measured to be 0.68 g/cm.sup.3. Furthermore, for the produced carbon film 2, the glossiness at 60 was measured to be 18, and the surface resistivity was measured to be 2.4 /sq.

(20) Similarly to the carbon film 1, the obtained carbon film 2 had substantially the same dimension as the membrane filter, had excellent film-forming properties, maintained the film form even after being peeled from the filter, and also had excellent free-standing properties.

Example 3

(21) A carbon film 3 was formed by the same procedure as in Example 1 with the exception that the amount of expanded graphite (trade name EC500, available from Ito Graphite Co., Ltd.) used in Example 1 was changed to 0.133 g. The film density of the obtained carbon film 3 was measured to be 0.62 g/cm.sup.3. Furthermore, for the produced carbon film 3, the glossiness at 60 was measured to be 8, and the surface resistivity was measured to be 3.3 /sq.

(22) Similarly to the carbon film 1, the obtained carbon film 3 had substantially the same dimension as the membrane filter, had excellent film-forming properties, maintained the film form even after being peeled from the filter, and also had excellent free-standing properties.

Example 4

(23) A carbon film 4 was formed by the same procedure as in Example 1 with the exception that expanded graphite (trade name EC500, available from Ito Graphite Co., Ltd.) was replaced by carbon black (trade name TOKABLACK #4300, available from Tokai Carbon Co., Ltd.) and the blended amount was also changed to 0.300 g. The film density of the obtained carbon film 4 was measured to be 0.78 g/cm.sup.3. Furthermore, for the produced carbon film 4, the glossiness at 60 was measured to be 12, and the surface resistivity was measured to be 2.8 /sq.

(24) Similarly to the carbon film 1, the obtained carbon film 4 had substantially the same dimension as the membrane filter, had excellent film-forming properties, maintained the film form even after being peeled from the filter, and also had excellent free-standing properties.

Example 5

(25) A carbon film 5 was formed by the same procedure as in Example 1 with the exception that the fibrous carbon nanostructure dispersion liquid 1 (also referred to as CNT dispersion liquid 1), which was used in Example 1, was replaced by the fibrous carbon nanostructure dispersion liquid 2 (also referred to as CNT dispersion liquid 2). The film density of the obtained carbon film 5 was measured to be 0.64 g/cm.sup.3. Furthermore, for the produced carbon film 5, the glossiness at 60 was measured to be 12, and the surface resistivity was measured to be 3.4 /sq.

(26) Similarly to the carbon film 1, the obtained carbon film 5 had substantially the same dimension as the membrane filter, had excellent film-forming properties, maintained the film form even after being peeled from the filter, and also had excellent free-standing properties.

Example 6

(27) A carbon film 6 was formed by the same procedure as in Example 1 with the exception that the amount of expanded graphite (trade name EC500, available from Ito Graphite Co., Ltd.) used in Example 1 was changed to 0.467 g. The film density of the obtained carbon film 6 was measured to be 0.42 g/cm.sup.3. Furthermore, for the produced carbon film 6, the glossiness at 60 was measured to be 3, and the surface resistivity was measured to be 4.0 /sq.

(28) Although the obtained carbon film 6 maintained the film form even after being peeled from the filter and also had excellent free-standing properties, film contraction was observed.

Comparative Example 1

(29) A comparative example carbon film 1 was formed by the same procedure with the exception that the fibrous carbon nanostructure dispersion liquid 1, which was used in Example 1, was replaced by the comparative example dispersion liquid.

(30) In the obtained comparative example carbon film 1, significant film contraction was observed, and significant cracking was observed in the film formed on the membrane filter, and free-standing properties were not observed. It was impossible to evaluate the comparative example carbon film 1.

(31) Table 1 below depicts results of Examples and Comparative Example described above. Regarding film-forming properties of each of the obtained carbon films, after the carbon film was peeled from the membrane filter, when the carbon film maintained the film form having substantially the same dimension as the membrane filter, the film-forming properties were evaluated as A (excellent), when more or less contraction to a practically harmless degree was confirmed, the film-forming properties were evaluated as B (good), and when cracking was confirmed, the film-forming properties were evaluated as C (failure). Free-standing properties of each of the obtained carbon films were evaluated as A (good) when free-standing properties were confirmed and were evaluated as B (failure) when free-standing properties were not confirmed. Additionally, evaluation and measurement were not possible for some categories, which are indicated by - (hyphens).

(32) TABLE-US-00001 TABLE 1 Example Example Example Example Example Example Comparative 1 2 3 4 5 6 Example 1 Fibrous Blended amount [g] 0.2 0.2 0.2 0.2 0.2 0.2 0.2 carbon BET specific 1060 1060 1060 1060 650 1060 270 nanostructures surface area [m.sup.2/g] Conductive Type Expanded Expanded Expanded Carbon Expanded Expanded Expanded carbon graphite graphite graphite black graphite graphite graphite Blended amount [g] 0.022 0.050 0.133 0.300 0.022 0.467 0.022 Fibrous carbon nanostructures/ 90/10 80/20 60/40 40/60 90/10 30/70 90/10 Conductive carbon [mass ratio] Carbon film Film-forming A A A A A B C characteristics properties Free-standing A A A A A A B properties Surface resistivity 2.3 2.4 3.3 2.8 3.4 4.0 [/sq.] Glossiness 25 18 8 12 12 3 Film density 0.75 0.68 0.62 0.78 0.64 0.42 [g/cm.sup.3]

(33) As seen from Table 1, the carbon films according to Examples, which include other components than fibrous nanostructures such as CNTs, have excellent free-standing properties and electrical conductivity.

INDUSTRIAL APPLICABILITY

(34) The present disclosure provides a carbon film that has excellent free-standing properties and electrical conductivity and a method of producing the same.