JP2013133262A - Carbon nanofiber structure, carbon nanofiber electrode, and method for manufacturing the carbon nanofiber structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon nanofiber structure which enables formation of a carbon nanofiber electrode capable of imparting excellent electrochemical performance to an electrochemical element, a carbon nanofiber electrode, and a method for manufacturing the carbon nanofiber structure.SOLUTION: The carbon nanofiber structure 100 comprises a substrate 10 and a carbon nanofiber assembly layer 50 disposed on one surface 10a side of the substrate 10 and formed by assembling a plurality of carbon nanofibers 51 oriented along a direction away from the one surface 10a. Holes 52 having a hole diameter of 0.3-7 μm are formed in the carbon nanofiber assembly layer 50 by the plurality of carbon nanofibers 51, and the total area of the holes 52 is 1 to <40% of the apparent area of an end face 50a of the carbon nanofiber assembly layer 50 on the side opposite to the substrate 10.

Description

  The present invention relates to a carbon nanofiber structure, a carbon nanofiber electrode, and a method for producing a carbon nanofiber structure.

  Carbon nanotube electrodes have attracted attention because they have excellent conductivity as electrodes and wires for dye-sensitized solar cells, lithium ion secondary batteries, lithium ion capacitors, electric double layer capacitors, fuel cells and the like.

  In particular, in a dye-sensitized solar cell, the carbon nanotube electrode has been expected to exhibit performance comparable to that of a platinum electrode.

  As such a carbon nanotube electrode, for example, the one described in Patent Document 1 is known. Patent Document 1 discloses a carbon nanotube bulk structure obtained by patterning a metal catalyst in a plurality of regions on a substrate and chemical vapor deposition of the plurality of carbon nanotubes on the metal catalyst.

International Publication No. 2006/011655

  However, the carbon nanotube bulk structure described in Patent Document 1 has the following problems.

  That is, a layer formed by collecting a plurality of carbon nanotubes in the carbon nanotube bulk structure described in Patent Document 1 (hereinafter referred to as “carbon nanotube assembly layer”) is applied to an electrode of an electrochemical element. It was not always possible to impart excellent electrochemical performance to the electrochemical element.

  The present invention has been made in view of the above circumstances, a carbon nanofiber structure capable of forming a carbon nanofiber electrode capable of imparting excellent electrochemical performance to an electrochemical element, a carbon nanofiber electrode, and It aims at providing the manufacturing method of a carbon nanofiber structure.

  As a result of intensive studies to solve the above problems, the inventor of the present invention has excellent electrochemical performance with respect to electrochemical devices in the carbon nanotube aggregate layer constituting the carbon nanotube bulk structure described in Patent Document 1. Regarding the reason why a carbon nanofiber electrode capable of imparting a carbon atom cannot be formed, the carbon nanotube aggregate layer described in Patent Document 1 considered that the electrolyte was not sufficiently transported inside. Therefore, the present inventor has considered to form holes in the carbon nanotube assembly layer described in Patent Document 1 along the orientation direction of the carbon nanotubes. However, it was not always possible to impart excellent electrochemical performance to the electrochemical element simply by forming the holes. For example, if a large hole is formed, the electrolyte is considered to be sufficiently transported to the inside. However, in fact, when a large hole is formed, the internal diffusion of the electrolyte is rather deteriorated. Therefore, as a result of further earnest research, the present inventor found that the above problem can be solved by forming holes having a specific hole diameter in the carbon nanofiber assembly layer with a specific area ratio, and completed the present invention. It came to do.

  That is, the present invention comprises a base material, and a carbon nanofiber assembly layer formed by assembling a plurality of carbon nanofibers provided on one surface side of the base material and oriented along a direction away from the one surface, A hole having a hole diameter of 0.3 to 7 μm is formed by being surrounded by a plurality of carbon nanofibers, and in the carbon nanofiber assembly layer, the total area of the holes is within the carbon nanofiber assembly layer. It is a carbon nanofiber structure which is 1% or more and less than 40% with respect to the apparent area of the end surface opposite to the substrate.

  According to this carbon nanofiber structure, in the carbon nanofiber assembly layer provided on the one surface side of the base material, a hole having a hole diameter of 0.3 to 7 μm is surrounded by a plurality of carbon nanofibers. Is formed. For this reason, for example, when an electrode of an electrochemical element including an electrolyte is formed from the carbon nanofiber structure, the electrolyte can be easily and effectively transported into the carbon nanofiber assembly layer through the holes. Become. Therefore, the carbon nanofiber structure of the present invention can form a carbon nanofiber electrode capable of imparting excellent electrochemical performance to the electrochemical element. Further, the carbon nanofiber structure of the present invention has a carbon nanofiber assembly layer formed by aggregating a plurality of carbon nanofibers on one surface side of the substrate, and the carbon nanofiber assembly layer includes a plurality of carbon nanofibers. A hole is formed by being surrounded by the fiber. That is, this hole does not separate the carbon nanofiber assembly layer. For this reason, a longer carbon yarn can be obtained by extracting a carbon yarn formed by continuously bonding a plurality of carbon nanofibers from the carbon nanofiber assembly layer.

  The carbon nanofiber structure is useful when the length of the carbon nanofiber is larger than the maximum value of the hole diameter of the hole.

  This is because, as the length along the orientation direction of the carbon nanofiber is larger than the maximum value of the pore diameter, the electrolyte is moved to the inside of the carbon nanofiber assembly layer in order to improve the electrochemical performance of the electrochemical device. This is because the need for transportation increases.

  In the carbon nanofiber structure, the hole is preferably a through hole. In this case, when the carbon nanofiber structure of the present invention is applied to an electrode of an electrochemical device, the electrolyte can be transported more sufficiently to the inside of the carbon nanofiber assembly layer than when the hole is not a through hole. It becomes possible. As a result, it is possible to impart more excellent electrochemical performance to the electrochemical element.

  Moreover, this invention is a carbon nanofiber electrode provided with the carbon nanofiber structure mentioned above.

  The present invention may also be a carbon nanofiber electrode obtained by transferring the carbon nanofiber assembly layer of the carbon nanofiber structure described above onto a conductive substrate.

  According to these carbon nanofiber electrodes, when the carbon nanofiber electrode is used as an electrode of an electrochemical element including an electrolyte, the electrolyte is easily and effectively transported to the inside of the carbon nanofiber assembly layer through the holes. It becomes possible to make it. Therefore, when the carbon nanofiber electrode of the present invention is applied to an electrode of an electrochemical element, it is possible to impart excellent electrochemical performance to the electrochemical element.

  Furthermore, the present invention provides a preparatory step of preparing a structure for forming a carbon nanofiber formed by providing a metal catalyst on one surface of a substrate, and a chemical vapor phase on the metal catalyst of the structure for forming carbon nanofiber. By supplying a source gas containing carbon to the metal catalyst by a growth method, orienting a plurality of carbon nanofibers along a direction away from one surface of the substrate, and assembling the plurality of carbon nanofibers. A carbon nanofiber growth process for forming a carbon nanofiber structure having a carbon nanofiber assembly layer, wherein the hole is formed on the metal catalyst side of the carbon nanofiber formation structure, and has a diameter of 0.3 to 7 μm. A carbon nanofiber structure in which the total area of the holes having a diameter is 1% or more and less than 40% with respect to the area of the catalyst supporting surface provided with the metal catalyst It is a manufacturing method.

  According to this manufacturing method, when carbon nanofibers are grown by chemical vapor deposition (hereinafter sometimes referred to as “CVD method”) in the carbon nanofiber growth step, the raw material gas containing carbon is used as a metal catalyst. Supplied. At this time, the raw material gas diffuses into the metal catalyst, and carbon nanofibers are deposited from the catalyst surface. While the activity of the catalyst is maintained, this diffusion and precipitation occur continuously, and carbon nanofibers grow. At this time, generally, as the carbon nanotubes grow, the carbon nanofibers grown on one surface of the substrate inhibit gas diffusion, making it difficult to supply the gas to the metal catalyst. As a result, there is a difference in the supply amount of the raw material gas between the exposed portion of the metal catalyst exposed to the raw material gas and the coated portion covered with the carbon nanofibers. That is, nonuniformity occurs in terms of the amount of gas supplied to the metal catalyst. For this reason, a difference occurs in the growth rate of the carbon nanofibers between the exposed portion and the coated portion. This becomes remarkable as the volume of the carbon nanofiber assembly layer increases.

  In that respect, in the production method of the present invention, the total area of the holes formed on the metal catalyst side of the carbon nanofiber forming structure and having a hole diameter of 0.3 to 7 μm is the catalyst supporting surface provided with the metal catalyst. The area ratio is 1% or more and less than 40%. As a result, the following effects are exhibited.

  That is, first, carbon nanofibers grow on the metal catalyst in a direction away from one surface of the substrate. In other words, the carbon nanofibers grow in a direction away from one surface of the substrate on a region other than the region where the metal catalyst is not formed on one surface of the substrate. Thus, a carbon nanofiber assembly layer is formed by assembling a plurality of growing carbon nanofibers. At this time, by being surrounded by a plurality of carbon nanofibers, holes having a pore diameter of 0.3 to 7 μm have the same area ratio as the area ratio of the holes formed on the metal catalyst side in the carbon nanofiber forming structure. It is formed. That is, the total area of pores having a pore diameter of 0.3 to 7 μm in the carbon nanofiber aggregate layer is 1% or more and less than 40% with respect to the apparent area of the end surface on the opposite side of the carbon nanofiber aggregate layer. Formed with. The source gas can diffuse into the carbon nanofiber assembly layer through the holes, and can easily reach the metal catalyst. As a result, in the metal catalyst, it is possible to reduce the difference in the supply amount of the raw material gas between the exposed portion and the coated portion, and it is possible to reduce the difference in the growth rate of the carbon nanofibers in both portions.

  When the carbon nanofibers are grown in this way, even if the carbon nanofibers are elongated, it is possible to sufficiently suppress the carbon nanofibers from being bent. In addition, since the growth of the plurality of carbon nanofibers is sufficiently suppressed from inhibiting each other's growth, the productivity of the carbon nanofibers can be sufficiently improved.

  Furthermore, in the carbon nanofiber structure obtained by the production method of the present invention, the carbon nanofiber assembly layer provided on one surface side of the substrate has a plurality of holes having a hole diameter of 0.3 to 7 μm. It is formed moderately by being surrounded. For this reason, for example, when an electrode of an electrochemical element including an electrolyte is formed from the carbon nanofiber structure, the electrolyte can be easily and effectively transported into the carbon nanofiber assembly layer through the holes. Become. Therefore, the carbon nanofiber structure obtained by the production method of the present invention can form a carbon nanofiber electrode capable of imparting excellent electrochemical performance to the electrochemical element.

  Furthermore, the carbon nanofiber structure obtained by the production method of the present invention has a carbon nanofiber assembly layer formed by aggregating a plurality of carbon nanofibers on one surface side of the base material. In this carbon nanofiber assembly layer, A hole is formed by being surrounded by a plurality of carbon nanofibers. That is, this hole does not separate the carbon nanofiber assembly layer. For this reason, a longer carbon yarn can be obtained by extracting a carbon yarn formed by continuously bonding a plurality of carbon nanofibers from the carbon nanofiber assembly layer.

  In the said manufacturing method, it is preferable that the said base material is an oxygen ion conductive substrate.

When carbon nanofibers are grown on the metal catalyst of the structure for forming carbon nanofibers by a CVD method, a raw material gas containing carbon is supplied to the metal catalyst. At this time, since the base material is an oxygen ion conductive substrate, oxygen ions in the base material are conducted through the base material and reach the metal catalyst. For this reason, even if carburization occurs in the metal catalyst due to the raw material gas containing carbon or carbon material is deposited on the surface of the metal catalyst due to a secondary reaction product of the raw material gas, oxygen ions that have reached the metal catalyst Reacts with these carbons to become CO ₂ or the like, so that carburization and deposition of carbon materials can be sufficiently suppressed. Accordingly, it is possible to sufficiently suppress the decrease in the catalyst supporting function of the metal catalyst, and it is possible to grow the carbon nanofibers more sufficiently.

  In the manufacturing method, the carbon nanofiber-forming structure further includes a metal oxide layer provided between the substrate and the metal catalyst, and the thickness of the metal oxide layer is 0.5 to 10 nm. It is preferable that

  In this case, compared with the case where the thickness of a metal oxide layer remove | deviates from the said range, when growing a carbon nanofiber, a carbon nanofiber can be grown more effectively.

  In the manufacturing method, in the structure for forming carbon nanofibers, the hole forms an opening in the one surface of the base material, and the region on the surface of the base material excluding the opening portion has the hole. It may be obtained by forming a metal catalyst.

  In the present invention, “carbon nanofiber” refers to a hollow or solid fibrous body made of carbon and having a thickness of 50 nm or less.

Further, in the present invention, “hole diameter” or “hole diameter” refers to the area S of a two-dimensional image when a hole or hole is observed with a scanning electron microscope (SEM), and the area S is equal to the area of a circle. From the area, the following formula:
R = 2 × (S / π) ^1/2
The value of R calculated based on

  ADVANTAGE OF THE INVENTION According to this invention, the carbon nanofiber structure which can form the carbon nanofiber electrode which can provide the electrochemical performance outstanding with respect to the electrochemical element, the carbon nanofiber electrode, and the manufacturing method of a carbon nanofiber structure Is provided.

It is a cut surface end elevation showing one embodiment of a carbon nanofiber structure concerning the present invention. It is a fragmentary top view which shows the carbon nanofiber structure of FIG. It is a cut surface end view which shows the structure for carbon nanofiber formation of FIG. It is a cut surface end view which shows the base material used when manufacturing the carbon nanofiber structure of FIG. It is a cut surface end view which shows the state by which the mask particle is arrange | positioned on one surface of the base material of FIG. FIG. 5 is a cross-sectional end view showing a state where mask particles and a metal catalyst film are formed on one surface of the base material in FIG. 4. It is a cut surface end view which shows other embodiment of the carbon nanofiber structure based on this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[First Embodiment]
FIG. 1 is a sectional end view showing a first embodiment of the carbon nanofiber structure of the present invention, and FIG. 2 is a partial plan view showing the carbon nanofiber structure of FIG. As shown in FIG. 1, the carbon nanofiber structure 100 includes a carbon nanofiber forming structure 40 and a carbon nanofiber assembly layer 50 provided on the carbon nanofiber forming structure 40. The carbon nanofiber assembly layer 50 is formed by assembling a plurality of carbon nanofibers 51.

  The carbon nanofiber forming structure 40 includes a base material 10 and a granular metal catalyst 30 supported on one surface 10a of the base material 10 and acting as a catalyst when the carbon nanofiber 51 is formed. The carbon nanofiber forming structure 40 has holes 11 formed between the granular metal catalysts 30.

  In the carbon nanofiber assembly layer 50, the carbon nanofibers 51 are oriented along the direction away from the base material 10 from the metal catalyst 30. The carbon nanofiber 51 may be a single-layer carbon nanofiber or a multilayer carbon nanofiber.

  As shown in FIG. 2, the carbon nanofiber assembly layer 50 has a hole 52, and the hole 52 is formed by being surrounded by a plurality of carbon nanofibers 51. In the carbon nanofiber assembly layer 50, the hole 52 is a through hole and communicates with the hole 11 formed between the granular metal catalysts 30. The hole 52 has a hole diameter of 0.3 to 7 μm. In the carbon nanofiber assembly layer 50, the total area of the holes 52 is an end surface of the carbon nanofiber assembly layer 50 on the side opposite to the base material 10 (hereinafter referred to as “hole”). , Referred to as “upper end surface”), which is 1% or more and less than 40% with respect to the apparent area of 50a. Here, the total area of the holes 52 is calculated by observing the holes 52 of the carbon nanofiber assembly layer 50 from the direction orthogonal to the one surface 10a of the substrate 10. The apparent area of the upper end surface 50a is calculated by observing the upper end surface 50a of the carbon nanofiber assembly layer 50 from the direction orthogonal to the one surface 10a of the base material 10. The apparent area means an area including not only the hole 52 but also a part other than the hole 52.

  According to the carbon nanofiber structure 100, in the carbon nanofiber assembly layer 50 provided on the one surface 10 a side of the substrate 10, the holes 52 having a hole diameter of 0.3 to 7 μm are surrounded by the plurality of carbon nanofibers 51. Is formed appropriately. For this reason, for example, when an electrode of an electrochemical element including an electrolyte is formed from the carbon nanofiber structure 100, the electrolyte is easily and effectively transported into the carbon nanofiber assembly layer 50 through the holes 52. Is possible. Therefore, the carbon nanofiber structure 100 can form a carbon nanofiber electrode capable of imparting excellent electrochemical performance to the electrochemical element. Further, the carbon nanofiber structure 100 has a carbon nanofiber assembly layer 50 formed by aggregating a plurality of carbon nanofibers 51 on the one surface 10a side of the base material 10, and in the carbon nanofiber assembly layer 50, holes 52 Is formed by being surrounded by a plurality of carbon nanofibers 51. That is, the holes 52 do not separate the carbon nanofiber assembly layer 50. For this reason, when a carbon yarn formed by continuously bonding a plurality of carbon nanofibers 51 is drawn out from the carbon nanofiber assembly layer 50, a longer carbon yarn can be obtained.

  Moreover, in this embodiment, since the hole 52 is a through-hole, when the carbon nanofiber structure 100 is applied to an electrode of an electrochemical element, the electrolyte is more sufficiently used than when the hole 52 is not a through-hole. It is possible to transport to the inside of the carbon nanofiber assembly layer 50. As a result, it is possible to impart more excellent electrochemical performance to the electrochemical element.

  Here, the carbon nanofiber assembly layer 50 will be described in detail.

  In the carbon nanofiber assembly layer 50, the hole 52 may have a hole diameter of 0.3 to 7 μm, preferably 0.3 to 6 μm, and more preferably 0.3 to 5 μm.

  The total area of the holes 52 may be 1% or more and less than 40% with respect to the apparent area of the upper end surface 50a of the carbon nanofiber assembly layer 50, but is preferably 1% or more and less than 30%, more preferably. Is 1% or more and less than 20%.

  The length along the orientation direction of the carbon nanofiber 51 may be equal to or smaller than the maximum value of the hole diameter of the hole 52 or may be larger than the maximum value of the hole diameter. This is useful when the length along the orientation direction of the fiber 51 is larger than the maximum value of the hole diameter of the hole 52. This is because as the length along the orientation direction of the carbon nanofiber 51 is larger than the maximum value of the hole diameter of the hole 52, the electrolyte is added to the carbon nanofiber assembly layer 50 in order to improve the electrochemical performance of the electrochemical element. This is because the need for transportation increases. Specifically, the carbon nanofiber structure 100 is particularly useful when the length along the orientation direction of the carbon nanofiber 51 is 10 to 100 times the maximum value of the hole diameter of the hole 52.

  Next, a method for manufacturing the carbon nanofiber structure 100 will be described.

<Preparation process>
First, a carbon nanofiber forming structure 40 is prepared in which a metal catalyst 30 is provided on one surface 10a of the substrate 10 (see FIG. 3). The carbon nanofiber forming structure 40 is formed as follows, for example.

  First, as shown in FIG. 4, the base material 10 is prepared. As the base material 10, for example, a metal such as alumina, silicon, or titanium is used.

  The thickness of the base material 10 is usually 100 to 10,000 μm, but preferably 500 to 5000 μm. In this case, the base material 10 is provided with sufficient strength as compared with the case where it is out of the range of 500 to 5000 μm.

  Next, as shown in FIG. 5, for example, mask particles 20 serving as a mask such as alumina particles are arranged on one surface 10 a of the substrate 10. At this time, the average particle diameter of the mask particles 20 is appropriately adjusted according to the hole diameter of the hole 11 to be formed. For example, when the hole 11 having a hole diameter of 0.3 to 7 μm is to be formed, the particle diameter of the mask particles 20 is, for example, about 1 μm, and the mask particles 20 may be disposed at a concentration that moderately aggregates.

(Catalyst loading process)
Next, as shown in FIG. 6, the metal catalyst film 30 </ b> A is supported on the one surface 10 a that is the catalyst supporting surface of the base material 10.

  As the metal catalyst constituting the metal catalyst film 30A, a known metal catalyst used for growing carbon nanofibers can be used. Examples of such metal catalysts include V, Mo, Fe, Co, Ni, Pd, Pt, Rh, Ru, W, Al, Au, and Ti. These can be used alone or in combination of two or more. Among these, V, Mo, Fe, Co, Ni, Pd, Pt, Rh, Ru, and W are preferable because carbon nanofibers can be more effectively grown.

  The thickness of the metal catalyst film 30A may be, for example, 0.5 to 10 nm.

  Next, the mask particles 20 are removed. The removal of the mask particles 20 can be performed by supplying alcohol, for example.

  Then, the particulate metal catalyst 30 is formed by heating the metal catalyst film 30A in a reducing atmosphere.

  The average particle diameter of the particulate metal catalyst 30 is usually 1 to 50 nm, but preferably 2 to 25 nm. In this case, it is possible to grow the carbon nanofiber 51 more effectively than when the range of 2 to 25 nm is exceeded.

  In this way, the carbon nanofiber forming structure 40 in which the hole 11 is formed on one surface of the metal catalyst 30 side is obtained.

  Here, although the hole diameter of the hole 11 should just be 0.3-7 micrometers, Preferably it is 0.3-6 micrometers, More preferably, it is 0.3-5 micrometers.

  Further, the total area of the holes 11 may be 1% or more and less than 40%, preferably 1% or more and less than 30%, with respect to the area of the one surface 10a that is the catalyst supporting surface provided with the metal catalyst 30. Preferably it is 1% or more and less than 20%.

<Carbon nanofiber growth process>
Next, a raw material gas containing carbon is supplied to the metal catalyst 30 by CVD, and the carbon nanofibers 51 are grown on the metal catalyst 30 of the carbon nanofiber forming structure 40.

  Here, the raw material gas containing carbon may be any material as long as it generates the carbon nanofiber 51 in the presence of a suitable catalyst, for example, a saturated hydrocarbon compound such as methane, ethane, propane, Examples thereof include unsaturated hydrocarbon compounds such as ethylene, propylene and acetylene, and aromatic hydrocarbon compounds such as benzene and toluene. Of these, methane, ethylene, propylene, and acetylene are preferable. As a form of introducing the carbon-containing compound, it may be introduced in a gaseous state, mixed with an inert gas such as argon, or mixed with hydrogen gas and introduced. Alternatively, it may be introduced as a saturated vapor in an inert gas.

At this time, an oxygen-containing gas containing oxygen may be mixed into the source gas. In this case, when the carbon nanofiber 51 is formed, the metal catalyst 30 is carburized by the raw material gas containing carbon, or a carbon substance is deposited on the surface of the metal catalyst 30 by a secondary reaction product of the raw material gas. Even when trying to do so, the oxygen-containing gas supplied to the metal catalyst 30 reacts with these carbons to become CO ₂ or the like, so that carburization and deposition of carbon substances can be suppressed.

  Here, the oxygen-containing gas containing oxygen may be any gas that can supply oxygen to the metal catalyst 30 at an appropriate temperature. Examples of such oxygen-containing gas include pure oxygen gas, atmospheric air, and the like. And oxygen molecule-containing gas. Alternatively, as the oxygen-containing gas, an oxygen molecule-free gas composed of water, carbon monoxide, an oxygen-containing hydrocarbon compound such as methanol, ethanol, or acetone can be used. Of these, the oxygen-containing hydrocarbon compound can also serve as the source gas.

  The oxygen-containing gas may be supplied by itself, mixed with an inert gas such as argon, or supplied as a saturated vapor in the inert gas. Also good. The oxygen concentration in the atmosphere supplied with the oxygen-containing gas when forming the carbon nanofiber 51 is preferably 0.003 to 0.03% by volume in terms of oxygen molecule concentration. When the oxygen molecular concentration is within the above range, the carbon nanofibers 51 can be grown more effectively than when the oxygen molecule concentration is outside the above range.

  In the CVD method, heat or plasma is used as an energy source.

  At this time, the pressure at which the carbon nanofibers 51 are grown is usually 100 to 150,000 Pa, preferably 1000 to 122000 Pa. Moreover, the temperature at the time of growing the carbon nanofiber 51 is 500-900 degreeC normally, Preferably it is 550-800 degreeC.

  Thus, holes 52 having a hole diameter of 0.3 to 7 μm are formed, and the total area of the holes 52 is 1% or more and less than 40% with respect to the apparent area of the upper end surface 50a of the carbon nanofiber assembly layer 50. The carbon nanofiber structure 100 provided with the nanofiber assembly layer 50 is obtained (FIG. 1).

  When the carbon nanofiber structure 100 is manufactured as described above, a raw material gas containing carbon is supplied to the metal catalyst 30 when the carbon nanofiber 51 is grown by the CVD method in the carbon nanofiber growth step. At this time, the raw material gas diffuses into the metal catalyst 30 and the carbon nanofibers 51 are deposited from the surface of the metal catalyst 30. While the activity of the metal catalyst 30 is maintained, this diffusion and precipitation occur continuously, and the carbon nanofibers 51 grow. At this time, generally, as the carbon nanotubes 51 grow, the carbon nanofibers 51 grown on the one surface 10a of the base material 10 inhibit gas diffusion, making it difficult to supply the gas to the metal catalyst 30. As a result, a difference occurs in the supply amount of the raw material gas between the exposed portion of the metal catalyst 30 exposed to the raw material gas and the covered portion covered with the carbon nanofibers 51. That is, nonuniformity occurs in terms of the amount of gas supplied to the metal catalyst 30. For this reason, a difference occurs in the growth rate of the carbon nanofiber 51 between the exposed portion and the coated portion. This becomes remarkable as the surface area of the carbon nanofiber assembly layer 50 increases.

  In that respect, in the method of manufacturing the carbon nanofiber structure 100 described above, the total area of the holes formed on the metal catalyst 30 side of the carbon nanofiber forming structure 40 and having a hole diameter of 0.3 to 7 μm is metal. It is formed in an area ratio of 1% or more and less than 40% with respect to the area of the one surface 10a which is the catalyst supporting surface on which the catalyst 30 is provided. As a result, the following effects are exhibited.

  That is, first, the carbon nanofibers 51 grow on the metal catalyst 30 in a direction away from the one surface 10a of the substrate 10. In other words, the carbon nanofibers 51 grow in a direction away from the one surface 10a of the substrate 10 on a region other than the region where the metal catalyst 30 is not formed on the one surface 10a of the substrate 10. Then, a carbon nanofiber assembly layer 50 is formed by assembling a plurality of growing carbon nanofibers 51. At this time, the holes 52 having a hole diameter of 0.03 to 7 μm by the plurality of carbon nanofibers 51 have the same area ratio as the area ratio of the holes 11 formed on the metal catalyst 30 side of the carbon nanofiber forming structure 40. Formed with. That is, the total area of the holes 52 having a hole diameter of 0.3 to 7 μm in the carbon nanofiber assembly layer 50 is 1% or more and less than 40% with respect to the apparent area of the upper end surface 50a of the carbon nanofiber assembly layer 50. Formed as follows. The source gas can diffuse into the carbon nanofiber assembly layer 50 through the holes 52 and can easily reach the metal catalyst 30. As a result, in the metal catalyst 30, it is possible to reduce the difference in the supply amount of the raw material gas between the exposed portion and the covered portion, and it is possible to reduce the difference in the growth rate of the carbon nanofiber 51 in both portions. Become.

  For this reason, even if the carbon nanofiber 51 grows long, it becomes possible to sufficiently suppress the carbon nanofiber 51 from being bent. In addition, since the growth of the plurality of carbon nanofibers 51 is sufficiently suppressed from inhibiting each other's growth, the productivity of the carbon nanofibers 51 can be sufficiently improved.

  Further, in the obtained carbon nanofiber structure 100, in the carbon nanofiber assembly layer 50 provided on the one surface 10a side of the base material 10, a plurality of holes 52 having a hole diameter of 0.3 to 7 μm are formed in the plurality of carbon nanofibers 51. It is formed moderately by being surrounded. For this reason, for example, when an electrode of an electrochemical element including an electrolyte is formed from the carbon nanofiber structure 100, the electrolyte is easily and effectively transported into the carbon nanofiber assembly layer 50 through the holes 52. Is possible. Therefore, the carbon nanofiber structure 100 obtained as described above can form a carbon nanofiber electrode capable of imparting excellent electrochemical performance to the electrochemical element.

  Further, the carbon nanofiber structure 100 obtained as described above has a carbon nanofiber assembly layer 50 formed by aggregating a plurality of carbon nanofibers 51 on the one surface 10a side of the base material 10, and this carbon nanofiber. In the aggregate layer 50, the holes 52 are formed by being surrounded by a plurality of carbon nanofibers 51. That is, the holes 52 do not separate the carbon nanofiber assembly layer 50. For this reason, when a carbon yarn formed by continuously bonding a plurality of carbon nanofibers 51 is drawn out from the carbon nanofiber assembly layer 50, a longer carbon yarn can be obtained.

  When a carbon nanofiber electrode is formed using the carbon nanofiber structure 100 formed in this manner, the carbon nanofiber electrode is formed by applying the carbon nanofiber assembly layer 50 of the carbon nanofiber structure 100 to a conductive substrate for the electrode. It can be formed by transferring. The carbon nanofiber assembly layer 50 may be transferred to the electrode conductive substrate by, for example, pressing the conductive adhesive film between the electrode conductive substrate and the conductive substrate. Examples of the conductive substrate for the electrode include a titanium substrate. When a conductive material is used as the base material 10, a carbon nanofiber electrode is formed as it is by the carbon nanofiber structure 100.

[Second Embodiment]
Next, 2nd Embodiment of the carbon nanofiber structure of this invention is described using FIG. FIG. 7 is a cross-sectional end view showing a second embodiment of the carbon nanofiber structure of the present invention. As shown in FIG. 7, the carbon nanofiber structure 200 of the present embodiment further includes a metal oxide layer 220 between the one surface 10a of the base material 10 and the metal catalyst 30, and the metal oxide layer 220 is 0. . Different from the carbon nanofiber structure 100 of the first embodiment in that it has a thickness of 5 to 10 nm.

  According to the carbon nanofiber structure 200 of the present embodiment, when the carbon nanofibers 51 are grown on the metal catalyst 30 of the carbon nanofiber formation structure 210 by the CVD method, the carbon nanofibers are formed on the metal oxide layer 220. The fiber 51 can be grown sufficiently.

  The metal oxide layer 220 is made of a metal oxide. The metal oxide may be a metal oxide, but is preferably a Group II or Group III metal oxide from the viewpoint of thermodynamic stability in a reducing atmosphere. Among these, a Group III metal oxide is more preferable from the viewpoint of the catalyst supporting function. Examples of Group III metal oxides include aluminum oxide, magnesium aluminate, and cerium oxide, with aluminum oxide being most preferred. In this case, the carbon nanofibers 51 can be grown more sufficiently than when the metal oxide is a metal oxide other than aluminum oxide.

  In the present embodiment, the thickness of the metal oxide layer 220 is preferably 1 to 8 nm. In this case, the carbon nanofibers 51 can be grown more effectively than when the thickness of the metal oxide layer 220 is outside the range of 1 to 8 nm.

  The metal oxide layer 220 can be formed by, for example, a sputtering method. At this time, the target may be either a single metal or a metal oxide, but it is necessary to supply an oxygen gas having an appropriate concentration depending on the type of the target. At this time, the temperature of the base material 10 is preferably set to 20 to 300 ° C. for the purpose of improving the adhesion with the metal oxide layer 220.

The present invention is not limited to the first and second embodiments described above. For example, in the first and second embodiments, a metal such as alumina, silicon, or titanium is used as the base material 10, but an oxygen ion conductive oxide can also be used as the base material 10. In this case, when the carbon nanofibers 51 are grown on the metal catalyst 30 of the carbon nanofiber forming structure 40 by the CVD method, the base material 10 is heated to such an extent that oxygen ions can move. Oxygen ions are conducted through the substrate 10 and reach the metal catalyst 30 or the metal oxide layer 220. For this reason, carburization occurs in the metal catalyst 30 or the metal oxide layer 220 by the raw material gas containing carbon, or a carbon substance is formed on the surface of the metal catalyst 30 or the metal oxide layer 220 by a secondary reaction product of the raw material gas. Even if it is to be deposited, oxygen ions that have reached the metal catalyst 30 or the metal oxide layer 220 react with these carbons to become CO ₂ or the like, thereby suppressing carburization and deposition of carbon substances. . Furthermore, by supplying the oxygen-containing gas from the surface 10a side of the base material 10, it becomes possible to more effectively suppress carburization and carbon material deposition.

  Although the said oxygen ion conductive oxide should just be an oxide which can conduct oxygen ion, the base material 10 shall be 500 degreeC or more high temperature by CVD method. For this reason, the oxygen ion conductive oxide is preferably a high temperature oxygen ion conductive oxide capable of conducting oxygen ions at a high temperature of 500 ° C. or higher. As the high-temperature oxygen ion conductive oxide, for example, stabilized zirconia obtained by stabilizing zirconia with an oxide can be used. Examples of the oxide that stabilizes all or part of the high-temperature oxygen ion conductive oxide such as zirconia include scandia, yttria, lanthania, ceria, calcia, and magnesia, and these oxides include high-temperature oxygen ions. The conductive oxide is preferably contained at a concentration in the range of 2 to 13 mol%. Further, as the high temperature oxygen ion conductive oxide, a perovskite oxide having oxygen defects can be used. Examples of the perovskite oxide include strontium titanate and calcium ferrate.

  In the first embodiment, as a method for forming the hole 11 in the one surface 10a on the metal catalyst 30 side of the carbon nanofiber forming structure 40, the mask particles 20 are arranged on the one surface 10a of the base material 10, and the metal catalyst is formed. Although the hole 11 is formed by removing the mask particle 20 after forming the film 30A, the hole 11 can also be formed by other methods. That is, after forming a mask on one surface 10a of the base material 10 by lithography and supporting the metal catalyst 30, a method of removing the mask, and removing the part of the supported metal catalyst 30 with a laser to remove the holes 11 , A method of removing a part of the supported metal catalyst 30 by ultrasonic cavitation, an opening is formed on one surface 10a of the substrate 10, and the opening is removed from the one surface 10a of the substrate 10. A method of forming the hole 11 by forming the metal catalyst 30 on the region, and after forming the recess by polishing the surface of the sintered body, the metal catalyst 30 is supported on the region where the recess is not formed. The method of forming the hole 11 by this is mentioned.

  Further, in the first and second embodiments, the hole 52 is a through hole in the carbon nanofiber assembly layer 50, but the hole 52 does not necessarily have to be a through hole in the carbon nanofiber assembly layer 50.

  Hereinafter, the content of the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

Example 1
An alumina substrate having a thickness of 1000 μm serving as a base material was prepared. Then, alumina fine particles having a diameter of 1 μm were dispersed on the surface of the alumina substrate. Then, a 2 nm thick iron thin film serving as a catalyst was formed on the surface of the alumina substrate using a sputtering method. Thereafter, the alumina fine particles were removed with alcohol, and the alumina substrate was dried. Thus, a laminate composed of the alumina substrate and the iron thin film was obtained. At this time, holes having a hole diameter distribution of 0.7 to 5 μm were dispersed and formed in the iron thin film.

  Next, this laminated body was accommodated in the electric furnace set to the temperature of 800 degreeC. At this time, argon gas at atmospheric pressure was supplied to the electric furnace at a flow rate of 500 sccm.

  Then, after the temperature of the alumina substrate is stabilized, hydrogen gas is mixed in the argon gas so as to be 2.5% by volume, the iron thin film is reduced, and catalyst particles having an average particle diameter of 5 nm are formed on the surface of the alumina substrate. Formed. Thus, a carbon nanofiber forming structure was obtained. At this time, the ratio of the catalyst supporting area based on the catalyst supporting area of Comparative Example 1 was 0.92.

  Next, acetylene gas was supplied so that it might become 2.5 volume% in argon gas supplied in an electric furnace.

  In this way, the carbon nanofibers were grown for 10 minutes in the direction away from the catalyst particles to form a carbon nanofiber assembly layer. Thus, a carbon nanofiber structure was obtained. In the obtained carbon nanofiber structure, pores having a pore diameter distribution of 0.7 to 5 μm are dispersed and formed in the carbon nanofiber assembly layer. At this time, the total area of the pores is the carbon nanofiber structure. It was 8% of the apparent area of the upper end of the body (hereinafter referred to as “apparent upper area”). The length of the carbon nanofiber (CNF) was 200 μm.

(Example 2)
Alumina fine particles having a diameter of 1 μm are dispersed on the surface of the alumina substrate, holes having a hole diameter distribution of 0.7 to 3 μm are dispersed in the iron thin film, and the catalyst supporting area of Comparative Example 1 is used as a reference. A carbon nanofiber structure was obtained in the same manner as in Example 1, except that the ratio of the supported catalyst area was as shown in Table 1. In the obtained carbon nanofiber structure, pores having a pore size distribution of 0.7 to 3 μm are dispersed and formed in the carbon nanofiber assembly layer. At this time, the total area of the pores is the carbon nanofiber structure. It was 1% of the apparent upper end area of the body. The length of the carbon nanofiber was 120 μm.

(Example 3)
Alumina fine particles having a diameter of 1 μm are dispersed on the surface of the alumina substrate, holes having a distribution of hole diameters of 2 to 7 μm are dispersed in the iron thin film, and a catalyst based on the catalyst supporting area of Comparative Example 1 A carbon nanofiber structure was obtained in the same manner as in Example 1 except that the ratio of the supported areas was as shown in Table 1. In the obtained carbon nanofiber structure, pores having a pore diameter distribution of 2 to 7 μm are dispersed in the carbon nanofiber assembly layer. At this time, the total area of the pores is the same as that of the carbon nanofiber structure. It was 39% of the apparent upper end area. The length of the carbon nanofiber was 200 μm.

Example 4
A carbon nanofiber structure was obtained in the same manner as in Example 1 except that the carbon nanofiber was grown for 5 minutes. In the obtained carbon nanofiber structure, pores having a pore diameter distribution of 0.7 to 5 μm are dispersed and formed in the carbon nanofiber assembly layer. At this time, the total area of the pores is the carbon nanofiber structure. It was 8% of the apparent upper end area of the body. The length of the carbon nanofiber was 100 μm.

(Example 5)
A carbon nanofiber structure was obtained in the same manner as in Example 2 except that the carbon nanofibers were grown for 8 minutes. In the obtained carbon nanofiber structure, pores having a pore size distribution of 0.7 to 3 μm are dispersed and formed in the carbon nanofiber assembly layer. At this time, the total area of the pores is the carbon nanofiber structure. It was 1% of the apparent upper end area of the body. The length of the carbon nanofiber was 100 μm.

(Example 6)
A carbon nanofiber structure was obtained in the same manner as in Example 3 except that the carbon nanofiber was grown for 5 minutes. In the obtained carbon nanofiber structure, pores having a pore diameter distribution of 3 to 7 μm are dispersed and formed in the carbon nanofiber assembly layer. At this time, the total area of the pores is the same as that of the carbon nanofiber structure. It was 39% of the apparent upper end area. The length of the carbon nanofiber was 100 μm.

(Example 7)
A carbon nanofiber structure was obtained in the same manner as in Example 2 except that a plate-like yttria-stabilized zirconia base material (containing 10 mol% of yttria) having a thickness of 1000 μm was prepared. In the obtained carbon nanofiber structure, pores having a pore size distribution of 0.7 to 3 μm are dispersed and formed in the carbon nanofiber assembly layer. At this time, the total area of the pores is the carbon nanofiber structure. It was 1% of the apparent upper end area of the body. The length of the carbon nanofiber was 110 μm.

(Example 8)
A plate-like yttria-stabilized zirconia base material (containing 10 mol% of yttria) having a thickness of 1000 μm was prepared. Then, after forming a recess having a distribution of hole diameter 0.3~4μm by polishing the substrate surface to form an aluminum oxide layer having a thickness of 2nm by sputtering (AlO _X). At this time, the target was aluminum oxide (99.99%) alone, and sputtering was performed at a pressure of 0.007 Torr while supplying argon at a flow rate of 19 sccm and oxygen at 1 sccm.

  Next, an iron thin film having a thickness of 2 nm serving as a catalyst was formed on the surface of the aluminum oxide layer by sputtering. Thus, holes having a distribution of hole diameters of 0.3 to 4 μm were dispersed and formed in the laminate composed of the base material, the aluminum oxide layer and the iron thin film, and the catalyst supporting area of Comparative Example 1 was used as a reference. A carbon nanofiber structure was obtained in the same manner as in Example 1 except that the ratio of the catalyst supporting area was as shown in Table 1. In the obtained carbon nanofiber structure, pores having a pore size distribution of 0.3 to 4 μm are dispersed in the carbon nanofiber assembly layer. At this time, the total area of the pores is the carbon nanofiber structure. It was 10% of the apparent upper end area of the body. The length of the carbon nanofiber was 300 μm.

Example 9
The aluminum oxide layer was formed to have a thickness of 4 nm, and the ratio of the catalyst supporting area based on the catalyst supporting area of Comparative Example 1 was set as shown in Table 1, and the same as in Example 8. Thus, a carbon nanofiber structure was obtained. In the obtained carbon nanofiber structure, pores having a pore size distribution of 0.3 to 4 μm are dispersed in the carbon nanofiber assembly layer. At this time, the total area of the pores is the carbon nanofiber structure. It was 12% of the apparent upper end area of the body. The length of the carbon nanofiber was 250 μm.

(Example 10)
The aluminum oxide layer was formed so as to have a thickness of 8 nm, and the ratio of the catalyst supporting area based on the catalyst supporting area of Comparative Example 1 was set as shown in Table 1 in the same manner as in Example 8. Thus, a carbon nanofiber structure was obtained. In the obtained carbon nanofiber structure, pores having a pore size distribution of 0.3 to 4 μm are dispersed in the carbon nanofiber assembly layer. At this time, the total area of the pores is the carbon nanofiber structure. It was 11% of the apparent upper end area of the body. The length of the carbon nanofiber was 150 μm.

(Example 11)
The aluminum oxide layer was formed so as to have a thickness of 12 nm, and the ratio of the catalyst supporting area based on the catalyst supporting area of Comparative Example 1 was set as shown in Table 1 in the same manner as in Example 8. Thus, a carbon nanofiber structure was obtained. In the obtained carbon nanofiber structure, pores having a pore size distribution of 0.3 to 4 μm are dispersed in the carbon nanofiber assembly layer. At this time, the total area of the pores is the carbon nanofiber structure. It was 10% of the apparent upper end area of the body. The length of the carbon nanofiber was 110 μm.

(Example 12)
The aluminum oxide layer was formed so as to have a thickness of 0.3 nm, and the ratio of the catalyst supporting area based on the catalyst supporting area of Comparative Example 1 was as shown in Table 1 except for that shown in Table 1. Similarly, a carbon nanofiber structure was obtained. In the obtained carbon nanofiber structure, pores having a pore size distribution of 0.3 to 4 μm are dispersed in the carbon nanofiber assembly layer. At this time, the total area of the pores is the carbon nanofiber structure. It was 10% of the apparent upper end area of the body. The length of the carbon nanofiber was 110 μm.

(Comparative Example 1)
A carbon nanofiber structure was obtained in the same manner as in Example 1 except that the aluminum fine particles were not dispersed on the surface of the alumina substrate and an iron thin film was formed by sputtering. In the obtained carbon nanofiber structure, no holes were formed in the carbon nanofiber assembly layer. The length of the carbon nanofiber was 100 μm.

(Comparative Example 2)
Alumina fine particles having a diameter of 1 μm are dispersed on the surface of the alumina substrate, holes having a hole diameter distribution of 5 to 12 μm are dispersed in the iron thin film, and a catalyst based on the catalyst carrying area of Comparative Example 1 is used as a reference. A carbon nanofiber structure was obtained in the same manner as in Example 1 except that the ratio of the supported areas was as shown in Table 1. In the obtained carbon nanofiber structure, pores having a pore diameter distribution of 5 to 12 μm are dispersed in the carbon nanofiber assembly layer. At this time, the total area of the pores is the same as that of the carbon nanofiber structure. It was 55% of the apparent upper end area. The length of the carbon nanofiber was 200 μm.

(Comparative Example 3)
A carbon nanofiber structure was produced in the same manner as in Comparative Example 2 except that carbon nanofibers were grown for 5 minutes and the ratio of the catalyst carrying area based on the catalyst carrying area of Comparative Example 1 was as shown in Table 1. Got. In the obtained carbon nanofiber structure, pores having a pore diameter distribution of 5 to 12 μm are dispersed in the carbon nanofiber assembly layer. At this time, the total area of the pores is the same as that of the carbon nanofiber structure. It was 55% of the apparent upper end area. The length of the carbon nanofiber was 100 μm.

[Evaluation]
(Electrochemical characteristics 1-Reduction characteristics)
For electrochemical property measurement using the carbon nanotube structures of Examples 1 to 12 and Comparative Examples 1 to 3 as a working electrode sandwiched between titanium meshes, a platinum wire as a counter electrode, and a silver / silver nitrate pair in acetonitrile as a reference electrode A cell was produced. Also, 5mM 1,2-dimethyl-3-n-propylimidazolium iodide, 2mM iodine, 100mM tetra-n-butylammonium tetrafluoroborate dissolved in 3-methoxypropionitrile as the electrolyte Was prepared, and this electrolytic solution was filled in the cell. And about the said electrochemical characteristic measurement cell, the cyclic voltammetry measurement of the iodide ion was performed under room temperature atmospheric conditions, and the reduction | restoration characteristic was evaluated. Specifically, the amount of iodide ion reduction peak current was measured. The results are shown in Table 1. In Table 1, the iodide ion reduction peak current amount per weight of carbon nanofiber (CNF) is displayed as a relative value with the iodide ion reduction peak current amount per weight of CNF in Comparative Example 1 being 1. did.

(Electrochemical characteristics 2-capacitance)
A separator is sandwiched between two carbon nanotube structures of Examples 1 to 12 and Comparative Examples 1 to 3, and a laminate sandwiched between titanium meshes is sandwiched between two glass plates and fixed. A bipolar cell for measuring electric double layer capacity was prepared. And this cell is a 1 mol / L dehydrating electrolytic solution (trade name: Capasolve-CPG-00005, Kida Chemical Co., Ltd.) obtained by dissolving tetraethylammonium tetrafluoroborate (Et ₄ NBF ₄ ) in propylene carbonate (PC). And the capacitance was measured. The results are shown in Table 1. In Table 1, the capacitance per weight of the carbon nanofiber (CNF) is displayed as a relative value with the capacitance per weight of the CNF of Comparative Example 1 being 1.

  From the results shown in Table 1, although the electrochemical property measurement cells according to Examples 1 to 12 showed no significant change in the reduction potential as compared with the electrochemical property measurement cells according to Comparative Examples 1 to 3. It was found that the reduction peak current amount per weight of the carbon nanofiber used was sufficiently increased.

  This is because the transport of electrolyte to the inside of the carbon nanofiber assembly layer has been improved by appropriately forming pores in the carbon nanofiber assembly layer, so that not only the surface layer but also the inside of the carbon nanofiber assembly layer has a reduction reaction. This is probably because the reduction peak current has improved. In addition, when the hole which has a big hole diameter was formed like the comparative example 2, the amount of reduction | restoration peak electric current per weight of carbon nanofiber became low, and the result that internal diffusion of electrolyte solution became worse on the contrary was obtained. This is presumably because the density of the carbon nanofibers decreased, the strength of the carbon nanofiber assembly layer became insufficient, and the carbon nanofibers were crushed.

  Moreover, the bipolar cell for electric double layer capacity | capacitance measurement which concerns on Examples 1-12 is compared with the bipolar cell for electric double layer capacity | capacitance measurement which concerns on Comparative Examples 1-3 per weight of a carbon nanofiber. It was found that the capacitance was sufficiently large.

  This is because the transport of electrolyte to the inside of the carbon nanofiber assembly layer has been improved by appropriately forming holes in the carbon nanofiber assembly layer, so that not only the outermost layer of the carbon nanofiber assembly layer but also the inside can be used effectively. It is thought that it was because it became.

  From the above, according to the carbon nanofiber structure of the present invention, it was confirmed that a carbon nanofiber electrode capable of imparting excellent electrochemical performance to an electrochemical element can be formed.

10 ... Base material 10a ... One side (catalyst carrying surface)
DESCRIPTION OF SYMBOLS 11 ... Hole 30 ... Metal catalyst 40 ... Carbon nanofiber formation structure 50 ... Carbon nanofiber assembly layer 50a ... End face 51 ... Carbon nanofiber 52 ... Hole 100,200 ... Carbon nanofiber structure 220 ... Metal oxide layer

Claims (9)

A substrate;
A carbon nanofiber assembly layer formed by assembling a plurality of carbon nanofibers provided on one side of the base material and oriented along a direction away from the one surface;
A hole having a hole diameter of 0.3 to 7 μm is formed by being surrounded by the plurality of carbon nanofibers,
In the carbon nanofiber assembly layer, the total area of the pores is 1% or more and less than 40% with respect to the apparent area of the end surface opposite to the substrate in the carbon nanofiber assembly layer Structure.   The carbon nanofiber structure according to claim 1, wherein a length of the carbon nanofiber is larger than a maximum value of the hole diameter of the hole.   The carbon nanofiber structure according to claim 1 or 2, wherein the hole is a through hole.   A carbon nanofiber electrode comprising the carbon nanofiber structure according to claim 1.   A carbon nanofiber electrode obtained by transferring the carbon nanofiber assembly layer of the carbon nanofiber structure according to any one of claims 1 to 3 to a conductive substrate. A preparation step of preparing a carbon nanofiber forming structure in which a metal catalyst is provided on one surface of a substrate;
A source gas containing carbon is supplied to the metal catalyst by chemical vapor deposition on the metal catalyst of the structure for forming the carbon nanofiber, and a plurality of gas is provided along a direction away from one surface of the substrate. A carbon nanofiber growth step of orienting carbon nanofibers to form a carbon nanofiber structure having a carbon nanofiber assembly layer formed by assembling the plurality of carbon nanofibers,
The total area of holes formed on the metal catalyst side of the carbon nanofiber forming structure and having a hole diameter of 0.3 to 7 μm is 1% with respect to the area of the catalyst support surface on which the metal catalyst is provided. It is formed with less than 40%,
A method for producing a carbon nanofiber structure.   The method for producing a carbon nanofiber structure according to claim 6, wherein the base material is an oxygen ion conductive substrate.   The carbon nanofiber forming structure further includes a metal oxide layer provided between the base material and the metal catalyst, and the metal oxide layer has a thickness of 0.5 to 10 nm. The manufacturing method of the carbon nanofiber structure of Claim 6 or 7.   In the carbon nanofiber forming structure, the hole forms an opening in the one surface of the base material, and forms the metal catalyst on a region of the one surface of the base material excluding the opening portion. The manufacturing method of the carbon nanofiber structure as described in any one of Claims 6-8 obtained by these.

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