JP6572416B1 - Conductive nanofiber member, fuel cell member, fuel cell, and method of manufacturing conductive nanofiber member - Google Patents

Abstract

Disclosed is a conductive nanofiber member capable of ensuring conductivity, improving catalyst supporting ability, and suppressing cracks, and a method for producing the same. The present invention includes a carbon nanofiber member 2 composed of a plurality of fibrous carbon nanofibers 21. The carbon nanofiber member 2 has a plurality of pores 21a and is analyzed by a BJH method. The resulting pore volume is 4 cm or more and 8 nm or less, and the pore volume is 0.2 cm 3 / g or more. In the present invention, at least one of the catalyst layer 421 of the anode electrode 42 and the catalyst layer 431 of the cathode electrode 43 is composed of the conductive nanofiber member 1. [Selection] Figure 2

Description

  The present invention relates to a conductive nanofiber member, a fuel cell member, a fuel cell, and a method for producing a conductive nanofiber member.

  The conductive nanofiber member is an aggregate (for example, a sheet-like member) of carbon nanofibers having conductivity. The conductive nanofiber member can be used, for example, as a fuel cell member. For example, JP 2012-188790 A describes a method for producing carbon nanofibers using an electrospinning method.

JP 2012-188790 A

  Here, in the case where the conductive nanofiber member is used as a practical member such as a battery, it is preferable that the conductive nanofiber member has a conductivity and easily supports the catalyst. That is, the conductive nanofiber member is required to at least ensure conductivity and improve the performance as a carrier (catalyst support ability). In other words, it is desired that the conductive nanofiber member has a configuration and performance suitable as a practical member such as a battery component. Further, the conventional catalyst layer (electrode element of the fuel cell) is easily cracked, and there is room for improvement in terms of durability.

  The present invention has been made in view of such circumstances, and provides a conductive nanofiber member capable of ensuring conductivity, improving catalyst supporting ability, and suppressing cracks, and a method for manufacturing the same. Objective. It is another object of the present invention to provide a fuel cell member and a fuel cell using these conductive nanofiber members.

The conductive nanofiber member according to the first aspect of the present invention includes a carbon nanofiber member composed of a plurality of fibrous carbon nanofibers, the carbon nanofiber member having a plurality of pores, and a BJH method. The pore volume having a pore diameter of 4 nm or more and 8 nm or less obtained by analysis according to the above is configured to be 0.2 cm ³ / g or more, and the pores having a pore diameter of 4 nm or more and 8 nm or less are formed on the surface of the carbon nanofiber member. And a plurality of pores located inside the carbon nanofiber member and communicating with the outside via pores located on the surface.

A method for producing a conductive nanofiber member according to Aspect 3 of the present invention is a method for producing a conductive nanofiber member that is an aggregate of carbon nanofibers, and is composed of an organic material that can be electrospun and an inorganic material. A solution preparation step of preparing a mixed solution containing an inorganic template that is a mold, a deposition layer formation step of forming a sheet-like deposition layer composed of fibrous materials from the mixture solution by electrospinning, and the deposition A primary firing step in which a firing process including primary firing is performed on the layer, and a pore forming step in which the inorganic template is removed from the deposited layer after the primary firing step to form a plurality of pores in the deposited layer And a secondary firing step of subjecting the deposited layer after the pore formation step to a secondary firing at a higher temperature than the primary firing, and the inorganic template has an average particle size of 4 nm to 8 nm. Inorganic materials that are Wherein, said deposition layer after the secondary sintering step, in a state in which the catalyst is not supported, 8 nm or less of the pore volume of pore diameter 4nm or more obtained by the analysis by the BJH method, with 0.2 cm 3 / ^g or more It is characterized by being configured.

  Moreover, the manufacturing method of the electroconductive nanofiber member which concerns on aspect 4 of this invention is a manufacturing method of the electroconductive nanofiber member which is an aggregate | assembly of carbon nanofiber, Comprising: The organic material which can be electrospun, and an inorganic material A solution preparation step of preparing a mixed solution containing an inorganic template that is a configured template, a deposition layer forming step of forming a sheet-like deposition layer composed of fibrous materials from the mixture solution by electrospinning, A primary firing step for performing a firing process including primary firing on the deposited layer, and pores for removing the inorganic template from the deposited layer after the primary firing step to form a plurality of pores in the deposited layer And a secondary firing step of subjecting the deposited layer after the pore formation step to secondary firing at a higher temperature than the primary firing, wherein the inorganic template has a different average particle size Consists of multiple inorganic materials And wherein the are.

  According to aspects 1 and 3 of the present invention, since the conductive nanofiber member is composed of fibrous carbon nanofibers, the conductivity of one conductor (carbon) is higher than the aggregate composed of particulate carbon. The distance is long, the electric resistance is small, and good conductivity is ensured. Moreover, since the pore volume with a pore diameter of 4 to 8 nm is large, a configuration suitable for supporting a catalyst having a small average particle diameter is realized. In addition, since the carbon nanofiber member is an aggregate of carbon nanofibers having a length, even when baked at the time of manufacture, cracks are less likely to occur than the aggregate of particulate carbon. As described above, according to the first and third aspects of the present invention, in the conductive nanofiber member, it is possible to ensure conductivity, improve the catalyst supporting ability, and suppress cracking.

Further, according to the state-like 4 of the present invention, it is possible to carbon nanofibers member, by function pore size to have multiple types of pores are different. For this reason, it is possible to secure conductivity and improve the catalyst carrying capacity, and it is possible to realize a configuration suitable for a practical member such as a fuel cell. In other words, it is possible to form pores corresponding to the catalyst on which the pores are to be supported, and to simultaneously form pores for improving the mobility of electrons and fluids.

It is a conceptual diagram which shows the electroconductive nanofiber member of this embodiment. It is a conceptual diagram which shows the carbon nanofiber and catalyst of this embodiment. It is a flowchart for demonstrating the manufacturing method of the electroconductive nanofiber member of this embodiment. It is a conceptual diagram which shows the structure of the fuel cell of this embodiment. 2 is a scanning electron micrograph of a high specific surface area carbon nanofiber sheet in Example 1. FIG. 2 is a transmission electron micrograph of a high specific surface area carbon nanofiber sheet carrying a platinum catalyst in Example 1. FIG. 2 is a transmission electron micrograph of a high specific surface area carbon nanofiber sheet carrying a platinum catalyst in Example 1. FIG. It is a figure which shows pore volume distribution of Example 1,2. It is a figure which shows the pore volume distribution of Examples 3-5. It is a reference figure for demonstrating a peak.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1, FIG. 2, and FIG. 4 are conceptual diagrams for explanation, and some of the shape notations and symbols are omitted for a large number of portions (carbon nanofibers and pores).
As shown in FIG.1 and FIG.2, the electroconductive nanofiber member 1 of this embodiment is an aggregate | assembly of the carbon nanofiber 21, and is formed in the sheet form. It can be said that the conductive nanofiber member 1 is a non-woven fabric or a sheet member having conductivity. Specifically, the conductive nanofiber member 1 includes a sheet-like carbon nanofiber member 2 composed of a plurality of fibrous carbon nanofibers 21 and a catalyst 3 supported on the carbon nanofibers 21. .

The carbon nanofiber member 2 has a plurality of pores 21a, and is configured such that the pore volume having a pore diameter of 4 to 8 nm obtained by analysis by the BJH method is 0.2 cm ³ / g or more. The carbon nanofiber member 2 has a total pore volume of 0.6 cm ³ / g or more and is configured to have at least one peak of pore volume between pore diameters of 4 to 30 nm.

A peak is a portion (curve) that appears in a convex shape in a pore volume distribution (pore distribution curve) in which the vertical axis represents differential pore volume (cm ³ / g / nm) and the horizontal axis represents pore diameter (nm). And the peak apex (maximum value) is 0.04 cm ³ / g / nm or more. Furthermore, as shown in FIG. 10, in the pore volume distribution, the first base point r1 is a point where the vertical axis value first becomes 0 or the minimum value from the peak apex P1 toward the side where the horizontal axis value becomes smaller, and is the same. A point where the vertical axis value first becomes 0 or a minimum value from the peak apex P1 toward the side where the horizontal axis value increases is defined as a second base point r2. In this case, the larger one of the first base point r1 and the second base point r2 is defined as the reference point (here, the second reference point r2), and the vertical value at the reference point and the vertical value of the peak vertex P1. The difference between this and the difference is 0.008 (cm ³ / g / nm) or more as “peak”.
Moreover, in this specification, a particle size, a fiber diameter, and a pore diameter mean the diameter of each object. In the present specification, the description “numerical value Z1 to numerical value Z2” or “numerical value Z1 to numerical value Z2” means “numerical value Z1 or more and numerical value Z2 or less”.

The carbon nanofiber member 2 is configured such that the D3 / G ratio obtained by Raman spectroscopic measurement is 1.0 or less. The carbon nanofibers 21 are configured so that the average fiber diameter is 50 nm to 150 nm. The carbon nanofibers 21 are configured so that the average aspect ratio is 5 or more. In the present embodiment, a fiber having an average aspect ratio of 5 or more that is clearly not particulate is referred to as a fiber. The carbon nanofiber member 2 is configured such that the BET specific surface area is 300 m ² / g or more. The above-mentioned various numerical values are for the carbon nanofiber member 2 or the carbon nanofiber 21 and are for the case where the catalyst 3 is not supported.

  The catalyst 3 is supported on the surface of the carbon nanofiber 21 and the pores 21a. The catalyst 3 is configured such that the average particle diameter measured with a transmission electron microscope is 5 nm or less when the loading ratio is 30 wt% or more. The average particle diameter of the catalyst 3 is preferably small from the viewpoint of surface area expansion, and is preferably not too small from the viewpoint of non-dissolution, and is preferably 2 nm or more and 5 nm or less. The catalyst is a transition metal catalyst, and preferably contains at least one metal selected from the group consisting of titanium, cobalt, iron, nickel, copper, zirconia and platinum.

(Production method)
Here, a manufacturing method of the conductive nanofiber member 1 will be described. Each process is performed by an operator using various devices. As shown in FIG. 3, first, a mixed solution containing an organic material that can be electrospun and an inorganic template that is a template made of an inorganic material is prepared (S101). The inorganic template is selected according to the pore diameter to be applied. In this embodiment, as the inorganic template, a plurality of types of templates, that is, a first inorganic template having an average particle size of 4 to 8 nm, and a second inorganic template having an average particle size (for example, 10 to 24 nm) larger than the first inorganic template, Is used. And the sheet-like deposition layer comprised with the fibrous material is produced by the electrospinning method (electrospinning method) using the said mixed solution (S102).

  Subsequently, a firing process including primary firing is performed on the deposited layer (S103). Specifically, the firing treatment includes firing as a flameproofing / infusibilizing treatment and primary firing as a carbonization treatment. The primary firing is performed at 1000 ° C. or less, for example. Then, the inorganic template is removed with an acid or alkaline solution from the fired deposited layer (S104). Thus, a plurality of pores 21a are formed in the carbon nanofiber 21, and a carbon nanofiber sheet that is a porous body is obtained.

  And the secondary baking as a graphitization process (high crystallization process) is performed with respect to the said carbon nanofiber sheet (S105). Thereby, the sheet-like carbon nanofiber member 2 is formed. Secondary baking is performed, for example in the range of 1200-2800 degreeC, and can improve durability and electroconductivity of the carbon nanofiber member 2. FIG. Conductive nanofiber member 1 (carbon nanofiber member 2) having a D3 / G ratio of 1.0 or less is produced by secondary firing. Here, for example, when the secondary firing was performed on a porous body made of particulate carbon as in the prior art, the volume became about 1/4 or less, and most of the pores disappeared. However, according to the said manufacturing method, a pore is maintained even after secondary baking. Finally, the catalyst 3 is supported on the carbon nanofiber member 2 (S106). Thereby, the conductive nanofiber member 1 is manufactured.

  In summary, the manufacturing method of the conductive nanofiber member 1 includes a solution preparation step of preparing a mixed solution including an organic material that can be electrospun and an inorganic template that is a template made of an inorganic material, and an electrospinning method. A deposition layer forming step for forming a sheet-like deposition layer composed of fibrous materials from the mixed solution, a primary firing step for performing a firing process including primary firing on the deposited layer, and a deposited layer after the primary firing step Pore forming step of removing inorganic template from the substrate and forming a plurality of pores in the deposited layer, and secondary firing step of performing secondary firing at a higher temperature than the primary firing on the deposited layer after the pore forming step The inorganic template includes an inorganic material having an average particle diameter of 4 to 8 nm. The inorganic mold is composed of a plurality of inorganic materials having different average particle diameters. Furthermore, the manufacturing method includes a catalyst supporting step of supporting a catalyst that can be supported on the pores of the deposited layer after the secondary firing step. Note that FIG. 1 can be referred to for the outer shape of the deposited layer (1).

(Fuel cell components)
The conductive nanofiber member 1 is preferably used as a fuel cell member. A fuel cell is a power generator that reacts supplied hydrogen and oxygen to convert chemical reaction energy into electrical energy. As shown in FIG. 4, the fuel cell 9 of the present embodiment is a polymer electrolyte fuel cell, and includes a fuel cell member 4 and separators 5 and 6 disposed so as to sandwich the fuel cell member 4. It is equipped with. The fuel cell member 4 is a membrane / electrode assembly (MEA), and is disposed on the electrolyte layer 41, the anode electrode 42 disposed on one side of the electrolyte layer 41, and the other side of the electrolyte layer 41. Cathode electrode 43. The electrolyte layer 41 is a polymer electrolyte membrane (PEM).

  The anode electrode 42 is a fuel electrode into which hydrogen is fed, and includes a catalyst layer 421 and a gas diffusion layer 422. The catalyst layer 421 is a layer that serves as a reaction field for battery reaction, and is joined to the electrolyte layer 41. The catalyst layer 421 is disposed between the electrolyte layer 41 and the gas diffusion layer 422. The gas diffusion layer (GDL) 422 is porous and has conductivity, and is a layer for uniformly distributing hydrogen to the catalyst layer 421.

  The cathode electrode 43 is an air electrode into which air (oxygen) is sent, and includes a catalyst layer 431 and a gas diffusion layer 432. The catalyst layer 431 is a layer that serves as a reaction field for battery reaction, and is joined to the electrolyte layer 41 so as to face the anode electrode 42 with the electrolyte layer 41 interposed therebetween. The catalyst layer 431 is disposed between the electrolyte layer 41 and the gas diffusion layer 432. The gas diffusion layer (GDL) 432 is porous and conductive, and is a layer for uniformly distributing air to the catalyst layer 431.

  In the present embodiment, at least one of the catalyst layer 421 of the anode electrode 42 and the catalyst layer 431 of the cathode electrode 43 is composed of the conductive nanofiber member 1. Each of the electrodes 42 and 43 may include a water repellent layer between the catalyst layers 421 and 431 and the gas diffusion layers 422 and 432. The separators 5 and 6 are conductive members that form a gas flow path. For example, a plurality of grooves are formed on the surface. The separator 5 is disposed on the anode electrode 42 side, and the separator 6 is disposed on the cathode electrode 43 side.

(effect)
According to the present embodiment, since the conductive nanofiber member 1 is composed of the fibrous carbon nanofibers 21 as a whole, it has one conductor (carbon) rather than the conductive member composed of particulate carbon. The conductive distance is long, the electric resistance is small, and good conductivity is ensured. Moreover, since the pore volume with a pore diameter of 4 to 8 nm is large, it is suitable for supporting a catalyst having a small average particle diameter. Since the surface area of the catalyst as a whole can be increased by reducing the average particle diameter of the catalyst, the average particle diameter is preferably small to some extent from the viewpoint of the catalyst function. The present embodiment is suitable for supporting such a suitable catalyst (for example, an average particle diameter of 2 to 5 nm). It is preferable that the catalyst is supported in pores larger than its own particle diameter and supported in pores somewhat larger than itself from the viewpoint of activity. In addition, since the carbon nanofiber member 2 is an aggregate of carbon nanofibers 21 having a length, even when baked at the time of manufacture, cracks are less likely to occur than the aggregate of particulate carbon. As described above, according to this embodiment, it is possible to ensure conductivity, improve the catalyst supporting ability, and suppress cracking. In addition, a catalyst having a small particle size is easily supported with high durability in 4 to 8 nm pores. Therefore, according to this embodiment, the activity and durability of the catalyst can also be improved.

Further, since the carbon nanofiber member 2 has a total pore volume of 0.6 cm ³ / g or more and a structure having at least one pore volume peak in the range of the pore diameter of 4 nm to 30 nm, the catalyst Not only the carrying ability but also the mobility of gas and water through the pores is improved. When the conductive nanofiber member 1 is used as a fuel cell member, the permeability of the reaction gas is improved, and the water generated by the reaction is discharged better.

  The carbon nanofiber member 2 is configured such that the D3 / G ratio obtained by Raman spectroscopy is 1.0 or less. For this reason, chemical durability is high and the fall of the catalyst activity in a cycle test can be suppressed.

  Moreover, since the average fiber diameter of the carbon nanofiber 21 is 50 nm or more and 150 nm or less, the generation of a catalyst that enters the central portion of the carbon nanofiber 21 and hardly functions effectively is suppressed, and the catalyst efficiency can be increased. In addition, as a member for a fuel cell, a space (gap between fibers) increases due to a large fiber diameter, and it is suppressed that electrons do not flow easily. It is suppressed that it becomes difficult to flow. That is, the conductive nanofiber member 1 is more suitable for the fuel cell member.

  In addition, since the average aspect ratio of the carbon nanofibers 21 is 5 or more, the carbon nanofibers 21 are clearly not in the form of particles but in a more directional shape. However, the volume is hardly reduced and the pores are easily maintained. Furthermore, durability and electrical conductivity are improved by secondary firing. Thus, according to the present embodiment, it is easy to create a large number of pores with a targeted diameter, and accordingly, even if the volume of the carbon nanofiber member 2 is small, effective performance can be exhibited, and durability and The conductivity can be improved.

In addition, since the carbon nanofiber member 2 has a BET specific surface area of 300 m ² / g or more, the present embodiment easily supports the catalyst, and is suitable as a practical part such as a fuel cell member. In addition, since the average particle size of the supported catalyst is 5 nm or less in a high concentration loading with a loading rate of 30 wt% or more, high catalytic activity can be realized. Moreover, according to the member 4 for fuel cells, the electroconductive nanofiber member 1 having the above characteristics can provide a small and high-performance fuel cell having excellent power generation characteristics.

  In addition, since a plurality of types of pores having different pore diameters can be formed, the conductive nanofiber member 1 can have pores suitable for supporting a catalyst and pores suitable for movement of gas and water (relative diameters). A plurality of types of pores according to the aimed function. That is, according to the present embodiment, it is possible to create a configuration suitable for the device (fuel cell or the like) to be applied. In addition, according to the manufacturing method of the present embodiment, a conductive nanofiber member particularly suitable for a fuel cell is created. The conductive nanofiber member is applied to a device other than a fuel cell (for example, a secondary battery). May be.

  The conductive nanofiber member 1 on which the catalyst 3 is not supported, that is, the carbon nanofiber member 2 can also be said to be a member that can ensure conductivity and improve the catalyst support capability. In addition, since the carbon nanofiber member 2 has pores 21a and conductivity, and also has durability by secondary firing, it can be made as it is or finely and other members of the fuel cell (for example, gas diffusion layer or water repellent layer) ).

Hereinafter, the conductive nanofiber member 1 and the fuel cell member 4 will be described in more detail. In the description, the “high specific surface area carbon nanofiber sheet” corresponds to the carbon nanofiber member 2.
A high specific surface area carbon nanofiber sheet with high chemical durability is produced by spraying an organic material or a solution containing an organic / inorganic mixed material onto a collector plate or a rotating drum collector by electrospinning. A high specific surface area nanofiber sheet obtained by forming a deposited layer of a product, firing the fibrous deposited layer at 1000 ° C. or less, and then activating it with water vapor or removing an inorganic template with an acid or alkali solution And a step of producing a high specific surface area carbon nanofiber sheet having high chemical durability by firing the high specific surface area nanofiber sheet at a high temperature of 1000 ° C. or higher.

  The organic material that can be electrospun is not particularly limited, and specific examples thereof include polyacrylonitrile resin, polyimide resin, pitch, and polyethylene glycol. These may be used alone or in combination of two or more. May be used. The solvent for dissolving the organic material is selected according to the type of the organic material, and examples thereof include N, N-dimethylformamide, dioxane, acetone, tetrahydrofuran, and alcohols such as methanol and ethanol.

  The inorganic material that can be added is not particularly limited, and specific examples include silicon dioxide dispersion, cerium dioxide dispersion, zinc oxide dispersion, and the like. These may be used alone or in combination of two or more. Also good. Examples of the inorganic material dispersion solution include N, N-dimethylformamide, dioxane, acetone, tetrahydrofuran, and alcohols such as methanol and ethanol.

  The carbon nanofiber sheet is an aggregate of carbon nanofibers, but has an average fiber diameter of 150 nm or less. Thereby, it is possible to obtain a carbon nanofiber sheet having a high specific surface area and a high density of the catalyst layer, and a high catalyst carrying capacity and conductivity.

  In the electrospinning method, when a high voltage of 15 kV or higher is applied to a nozzle from which an organic material-containing solution is jetted, the organic material-containing solution is discharged toward the collector, becomes nanofibers in the electric field, and is deposited on the collector.

  In the electrospinning method, the nanofiber is formed by keeping the applied voltage and the distance between the nozzle and the collector appropriate. Further, nanofibers having a desired average diameter can be obtained depending on the difference in organic material components, the concentration of the organic material solution, the rotational speed of the rotating drum collector, and the presence or absence of additives.

  The concentration of the organic material-containing solution is not particularly limited and varies depending on the composition of the organic material, but is preferably in the range of 3 to 10% by mass. If the concentration of the organic material in the solution is less than 3% by mass, the fiber is often not formed, and if it exceeds 10% by mass, the fiber diameter becomes too thick.

  The concentration of the inorganic template to be added is not particularly limited and varies depending on the composition of the organic material, but is preferably 0.1 to 15% by mass of the spinning solution. When the amount is less than 0.1% by mass, the effect of the added inorganic material is thin.

  In addition, the inorganic template is not particularly limited, but is preferably nano-dispersed in a solvent similar to the solvent used for the organic material. When an inorganic mold is used from a solid, it is difficult to disperse aggregates, it is difficult to impart satisfactory pores to the fiber, and the fiber strength may be reduced. Further, in order to give pores having a pore diameter of 4 to 8 nm, those having an average particle diameter of 4 to 8 nm are preferable, and in order to give pores having a pore diameter of 10 nm or more, those having an average particle diameter of 10 nm or more. Is preferably used. That is, an inorganic template having an average particle size corresponding to the target pore diameter is selected.

  Subsequently, the obtained nanofiber sheet is subjected to flame resistance / infusibilization treatment and primary firing treatment to obtain a carbon nanofiber sheet. The flame resistance / infusibilization treatment is performed by raising the temperature from room temperature to 250 to 300 ° C. in an oxygen-containing atmosphere, and then maintaining the same temperature for 30 minutes to 3 hours. In the primary firing treatment, after flameproofing and infusibilization treatment, the temperature is gradually raised to a temperature in the range of 500 to 1000 ° C. in an inert gas atmosphere such as nitrogen or argon gas, and then at that temperature for about 0 to 60 minutes. It is done by holding.

  Then, it is set as a porous body by processing the obtained primary baking carbon nanofiber sheet. The method is not particularly limited, but is performed by steam activation treatment or removal of the inorganic template. The steam activation treatment is desirably performed at a temperature of 700 to 900 ° C. and a water amount of 10 mL to 1 L in a range of 1 minute to 1 hour. When the temperature falls below 700 ° C., the treatment time falls below 10 minutes, or the amount of water falls below 10 mL, the treatment effect is lowered. On the other hand, if the temperature exceeds 900 ° C., the processing time exceeds 1 hour, or the amount of moisture exceeds 1 L, the processing time increases or the processing becomes excessive and the cost becomes too high. The inorganic template can be removed using an acid or alkaline aqueous solution.

  Subsequently, by subjecting the obtained primary fired carbon nanofiber sheet having a high specific surface area to secondary firing, a high specific surface area carbon nanofiber sheet having high chemical durability and conductivity can be obtained. The secondary firing temperature range is not particularly limited, but is performed in the range of 1200 to 2800 ° C. When the temperature is lower than 1200 ° C., durability and conductivity are lowered, and when the temperature is higher than 2800 ° C., pores are lost and the specific surface area is reduced.

The high specific surface area carbon nanofiber sheet thus obtained has a fiber diameter of about 50 to 150 nm, a high specific surface area of 300 m ² / g or more, and has an excellent metal catalyst supporting ability. Show. The above-mentioned high specific surface area carbon nanofiber sheet can be used as it is or as a carbon rod having an aspect ratio of 5 or more after being pulverized by a pulverizer.

  Examples of the fuel cell catalyst supported on the high specific surface area carbon nanofiber sheet include metal catalysts including metal oxides and alloys, carbon alloy catalysts, and the like. In the present invention, metal catalysts are suitable. Specific examples of the metal catalyst include transition metals such as platinum, gold, silver, palladium, ruthenium, cobalt, nickel, and chromium, and alloys thereof, among which platinum and platinum alloys are preferable.

  The method for supporting the catalyst is not particularly limited, and a conventionally known method can be adopted. In this embodiment, it is preferable to use a precipitation method. In addition, it is preferable to subject the high specific surface area carbon nanofiber sheet to a surface treatment with an inorganic acid such as sulfuric acid or nitric acid alone or a mixed acid or ozone obtained by mixing as a pretreatment for supporting. Thereby, in catalyst loading by the solution reduction method, it is possible to improve the catalyst loading ratio on the high specific surface area carbon nanofiber sheet and to highly disperse the catalyst.

  The membrane / electrode assembly (membrane electrode assembly) of the present embodiment uses the above-described fuel cell member for at least one of an anode electrode and a cathode electrode arranged on both sides of the electrolyte layer. In general, a polymer electrolyte membrane is used for an electrolyte layer (electrolyte membrane) which is one component of the membrane-electrode assembly. Examples of the polymer electrolyte membrane include a perfluorosulfonic acid membrane and a hydrocarbon electrolyte membrane having a sulfonic acid group.

  The method for producing the membrane / electrode assembly is not particularly limited, but a method of integrating the electrode, the polymer electrolyte membrane, and the gas diffusion layer by general thermal pressing or the like can be employed. For example, after a proton conducting polymer solution such as Nafion (registered trademark) is applied to a high specific surface area carbon nanofiber sheet, the proton conducting polymer solution is interposed between a gas diffusion layer such as carbon paper and a polymer electrolyte membrane. Are sandwiched between carbon nanofiber sheets having a high specific surface area and integrated by thermal pressing or the like.

  Thus, according to the present embodiment, the catalyst layer is excellent in conductivity, material permeability, and durability using a carbon nanofiber sheet having many pores and a high specific surface area. It is possible to provide a fuel cell catalyst member (electrode, carrier) that does not crack during production. According to the present embodiment, by using the conductive nanofiber member 1 as an electrode for a fuel cell, a membrane / electrode assembly having excellent power generation characteristics, a small size, a high performance and a high durability, and a fuel cell including the same Can be provided.

  As a result of earnest research, the present inventors have carbonized and fired nanofibers obtained by an electrospinning method as a carbon material constituting an electrode for a fuel cell, and catalysts such as transition metals on the outer and inner surfaces of the carbon nanofiber. The inventors have found that the above-described configuration can be realized by providing a large number of pores having excellent supporting ability, and further controlling the pore distribution in the nanofiber, and the present invention has been completed.

The fuel cell member 4 of the present embodiment is a fuel cell electrode made of carbon nanofibers having an average fiber diameter of 50 nm to 150 nm and an average aspect ratio of 5 or more that can be adjusted by a pulverizer or the like. The carbon nanofiber 21 has a pore volume of 4 nm to 8 nm obtained by BJH analysis of 0.2 cm ³ / g or more and a BET specific surface area of 300 m ² / g or more. The catalyst is supported on the surface.

(Description of Examples)
(1) Observation of morphology of high specific surface area carbon nanofiber sheet and measurement of average fiber diameter of carbon nanofiber High specific surface area carbon using scanning electron microscope (JEOL Ltd., JSM-6010 PLUS / LA) 100 spots were selected at random from an electron micrograph of the nanofiber sheet, the fiber diameter was measured from the side of the carbon nanofiber, and the average value of all the measurement results was taken as the average fiber diameter.

(2) Observation of morphology of a high specific surface area carbon nanofiber sheet carrying a metal catalyst using a transmission electron microscope The observation of the morphology of a high specific surface area carbon nanofiber sheet carrying a metal catalyst was conducted using a field emission transmission electron microscope (JEOL Ltd.) JEM-2100F) manufactured by company was used.

(3) Measurement of platinum carrying amount The platinum carrying amount of the high specific surface area carbon nanofiber sheet carrying a metal catalyst was measured using a differential thermal balance (manufactured by Rigaku Corporation, Thermo plus TG8120).

(4) Measurement of BET specific surface area The specific surface area of the carbon nanofiber sheet or carbon black is measured by an automatic specific surface area / pore distribution measuring device (BELSORP-mini II, manufactured by Microtrack Bell Co., Ltd.), and nitrogen gas is adsorbed. It was performed using.

[Example 1]
(1) Preparation of electrospinning solution Polyacrylonitrile (manufactured by Sigma Aldrich Japan Co., Ltd.) 6.5, nano silica (prepared from Snowtex XS, manufactured by Nissan Chemical Industries, Ltd.) 3.5, N, N-dimethylformamide (Kishida Chemical Co., Ltd.) (Manufactured by company) was mixed at a mass ratio of 90.0 to prepare an electrospinning solution. The nanosilica functions as an inorganic template and contributes to the creation of pores having a pore diameter of about 4 to 6 nm.

(2) Electrospinning The electrospinning solution obtained above was electrospun using a rotating drum collector using an electrospinning apparatus.

(3) Flame resistance / infusibilization treatment The nanofiber sheet obtained as described above was heated from room temperature to 230 ° C. in an oxygen-existing atmosphere in 3 hours, and then heated to 300 ° C. in 3 hours. Flame resistance and infusibilization treatment was carried out by maintaining the time.

(4) Primary firing treatment The nanofiber sheet after the flameproofing / infusibilization treatment was subjected to a primary firing treatment to obtain a primary firing carbon nanofiber sheet. The temperature raising condition was that the temperature was raised from room temperature to 600 ° C. and held at 600 ° C. for 1 hour. Firing was performed under a nitrogen gas stream.

(5) Template removal treatment The obtained primary calcined carbon nanofiber sheet was immersed in an aqueous sodium hydroxide solution for treatment. After the alkali treatment, the residue was separated, and the residue was washed with a sodium hydroxide aqueous solution, pure water, acetic acid aqueous solution and pure water in this order. Thereafter, the residue was dried to obtain a primary baked carbon nanofiber sheet from which the mold was removed.

(6) Secondary firing treatment The primary firing carbon nanofiber sheet from which the obtained mold has been removed is subjected to a secondary firing treatment at 1800 ° C. for 1 hour in an inert gas stream in a degreasing furnace to obtain a high specific surface area. A carbon nanofiber sheet was obtained.
The obtained high specific surface area carbon nanofiber sheet was observed with a scanning electron microscope. FIG. 5 shows a scanning electron micrograph of the high specific surface area carbon nanofiber sheet (carbon nanofiber member 2). The average fiber diameter was 132 nm. Moreover, it was 440 m < ² > / g when the BET specific surface area was measured. Further, the pore volume of 4 to 8 nm obtained by BJH analysis was 0.31 m ³ / g, and the total pore volume was 0.67 m ³ / g. The volume resistivity was 0.1 Ω · cm. The D3 / G ratio measured by Raman spectroscopy was 0.4.

(7) Platinum catalyst support by precipitation method The high specific surface area carbon nanofibers were crushed in advance by a wet method until each flake piece was about several tens of μm and provided for support. Into a mixed solution of 495 mL of ultrapure water and 5 mL of ethanol, 100 mg of high specific surface area carbon nanofiber flakes formed into flakes by the above method was added, and subjected to ultrasonic treatment for 30 minutes, and uniformly dispersed in the solution. To the dispersion, 500 μL of a hexahydroxoplatinum (IV) acid ethanolamine solution (platinum concentration: 100 g / L) was added and stirred with heating. After the liquid temperature reached 80 ° C., a 1.75 mol / L acetic acid aqueous solution was divided into 24 times and a total of 960 μL was added. After acetic acid addition, the liquid temperature was kept at 80 ° C. and reacted for 2 hours. After completion of the reaction, the solution was subjected to suction filtration, and the treated high specific surface area carbon nanofibers were dried at 80 ° C. for 1 hour. After the treatment, the carbon nanofibers with a high specific surface area are re-dispersed in a solution of 495 mL of water and 5 mL of ethanol, this dispersion is heated to 50 ° C., and 1.2 mL of formic acid is added with stirring and reacted as it is for 2 hours. Went. Thereafter, the sample was again filtered by suction filtration, washed with water, and dried at 80 ° C. for 1 hour to obtain a high specific surface area carbon nanofiber sheet carrying a platinum catalyst. The platinum content of the obtained high specific surface area carbon nanofiber sheet carrying the platinum catalyst was 33 ± 1%, and almost all of the charged platinum was carried.

  The result of having observed the obtained high specific surface area carbon nanofiber sheet which carried the platinum catalyst with the transmission electron microscope is shown in FIG.6 and FIG.7. As shown in FIGS. 6 and 7, it was confirmed that the platinum catalyst was supported on the nanofibers with high density and high dispersion.

(8) Production of membrane / electrode assembly A high specific surface area carbon nanofiber sheet carrying a platinum catalyst and a Nafion (registered trademark) solution were mixed, and a catalyst ink for cathode was prepared by stirring using zirconia beads. The obtained cathode catalyst ink was applied to the surface of the transfer substrate so that the amount of platinum was 0.1 g / cm ² and dried to prepare a cathode catalyst layer transfer sheet. At this time, no cracks were observed in the catalyst layer.

Also, platinum-supported carbon (commercially available 30% platinum-supported carbon) and a Nafion (registered trademark) solution were mixed, and an anode catalyst ink was prepared by stirring using zirconia beads. The obtained anode catalyst ink was applied to the surface of the transfer substrate so that the amount of platinum was 0.05 g / cm ² and dried to prepare an anode catalyst layer transfer sheet.

  Using the cathode catalyst layer transfer sheet and anode catalyst layer transfer sheet prepared by the above method, the cathode catalyst layer is heated on one side of the polymer electrolyte membrane and the anode catalyst layer is heated on the other side. The film was transferred by pressure and sandwiched between two pieces of carbon paper to produce a membrane / electrode assembly.

(9) Evaluation of power generation characteristics A single cell was prepared using the membrane-electrode assembly prepared by the above method, and the current-voltage characteristics of the fuel cell were measured. As a result, cathode platinum at a power density at a voltage of 0.8 V was obtained. The amount used was 1.06 g / kW. In addition, when the current-voltage characteristics after 10,000 potential cycle tests with 1.0 V hold for 3 seconds and 0.6 V hold for 3 seconds were measured 10,000 times, the output density at a voltage of 0.8 V was obtained. The amount of cathode platinum used was 3.14 g / kW. The conditions are: single cell: 1 cm ² cell (manufactured by FC Development Co., Ltd., ND-1), cell temperature: 80 ° C., evaluation apparatus: FC evaluation test apparatus (manufactured by Toyo Corporation, AutoPEM), anode: hydrogen 0.5 L / min, humidity 100% RH, cathode: air 1.0 L / min, humidity 100% RH.

[Example 2]
Before the (6) secondary firing treatment of Example 1, steam activation treatment was performed as follows, and the others were performed in the same manner as in Example 1.
(Water vapor activation treatment)
The primary-fired carbon nanofiber sheet from which the mold was removed was laid on a mesh-like carbon plate and subjected to a steam activation treatment at 850 ° C. for 60 minutes to obtain a steam activation carbon nanofiber sheet. The treatment was carried out under a nitrogen stream under the condition of 50 mL of water.

As a result, the average fiber diameter of the obtained high specific surface area carbon nanofiber sheet was 103 nm. Moreover, it was 1058 m < ² > / g when the BET specific surface area was measured. Furthermore, the pore volume of 4 to 8 nm obtained by BJH analysis was 0.60 m ³ / g, and the total pore volume was 1.48 m ³ / g. The volume resistivity was 0.1 Ω · cm. The D3 / G ratio measured by Raman spectroscopy was 0.4. In addition, when the cathode electrode was produced using a high specific surface area carbon nanofiber sheet carrying a platinum catalyst, no cracks were observed, and when power generation characteristics were evaluated, cathode platinum was used at a power density of 0.8V. The amount was 1.43 g / kW. In addition, when the current-voltage characteristics after 10,000 potential cycle tests with 1.0 V hold for 3 seconds and 0.6 V hold for 3 seconds were measured 10,000 times, the output density at a voltage of 0.8 V was obtained. The amount of cathode platinum used was 2.81 g / kW.

[Example 3]
In the preparation of the electrospinning solution of Example 1 (1), the electrospinning solution was prepared at the following mass ratio.
Polyacrylonitrile (Sigma Aldrich Japan Co., Ltd.) 6.0
Nano silica (prepared from Snowtex XS, manufactured by Nissan Chemical Industries, Ltd.) 3.0
Nanosilica (prepared from Nissan Chemical Industries, Ltd. organosilica sol MA-ST-M) 1.0
N, N-dimethylformamide (Kishida Chemical Co., Ltd.) 90.0
Except for this, the same processing as in Example 1 was performed. The latter nano silica also functions as an inorganic template and contributes to the creation of pores having a pore diameter of about 20 to 25 nm.
Next, the power generation characteristics of the fuel cell were evaluated in the same manner as in Example 1.
As a result, the average fiber diameter of the obtained high specific surface area carbon nanofiber sheet was 112 nm. Moreover, it was 503 m < ² > / g when the BET specific surface area was measured. Furthermore, the pore volume of 4 to 8 nm obtained by BJH analysis was 0.33 m ³ / g, and the total pore volume was 1.04 m ³ / g. The volume resistivity was 0.11 Ω · cm. The D3 / G ratio measured by Raman spectroscopy was 0.5. In addition, when the cathode electrode was produced using a high specific surface area carbon nanofiber sheet carrying a platinum catalyst, no cracks were observed, and when power generation characteristics were evaluated, cathode platinum was used at a power density of 0.8V. The amount was 2.98 g / kW. In addition, when the current-voltage characteristics after 10,000 potential cycle tests with 1.0 V hold for 3 seconds and 0.6 V hold for 3 seconds were measured 10,000 times, the output density at a voltage of 0.8 V was obtained. The amount of cathode platinum used was 9.75 g / kW.

[Example 4]
In the preparation of the electrospinning solution of Example 1 (1), the electrospinning solution was prepared at the following mass ratio.
Polyacrylonitrile (Sigma Aldrich Japan Co., Ltd.) 6.0
Nano silica (prepared from Snowtex XS, manufactured by Nissan Chemical Industries, Ltd.) 2.0
Nanosilica (prepared from Nissan Chemical Industries, Ltd. organosilica sol MA-ST-M) 2.0
N, N-dimethylformamide (Kishida Chemical Co., Ltd.) 90.0
Except for this, the same processing as in Example 1 was performed. The latter nano silica also functions as an inorganic template and contributes to the creation of pores having a pore diameter of about 20 to 25 nm.
Next, the power generation characteristics of the fuel cell were evaluated in the same manner as in Example 1.
As a result, the average fiber diameter of the obtained high specific surface area carbon nanofiber sheet was 107 nm. Moreover, it was 394 m < ² > / g when the BET specific surface area was measured. Further 8nm pore volume from 4 obtained in BJH analysis is 0.20 m ³ / g, total pore volume was 1.00 m ³ / g. The volume resistivity was 0.10 Ω · cm. The D3 / G ratio measured by Raman spectroscopy was 0.7. In addition, when the cathode electrode was produced using a high specific surface area carbon nanofiber sheet carrying a platinum catalyst, no cracks were observed, and when power generation characteristics were evaluated, cathode platinum was used at a power density of 0.8V. The amount was 2.22 g / kW. In addition, when the current-voltage characteristics after 10,000 potential cycle tests with 1.0 V hold for 3 seconds and 0.6 V hold for 3 seconds were measured 10,000 times, the output density at a voltage of 0.8 V was obtained. The amount of cathode platinum used was 9.55 g / kW.

[Example 5]
In the preparation of the electrospinning solution of Example 1 (1), the electrospinning solution was prepared at the following mass ratio.
Polyacrylonitrile (Sigma Aldrich Japan Co., Ltd.) 6.0
Nano silica (prepared from Snowtex XS, manufactured by Nissan Chemical Industries, Ltd.) 2.0
Nanosilica (prepared from Nissan Chemical Industries' organosilica sol TOL-ST) 4.0
N, N-dimethylformamide (manufactured by Kishida Chemical Co., Ltd.) 88.0
Except for this, the same processing as in Example 1 was performed. The latter nanosilica also functions as an inorganic template and contributes to the creation of pores having a pore diameter of approximately 10 to 15 nm.
Next, the power generation characteristics of the fuel cell were evaluated in the same manner as in Example 1.
As a result, the average fiber diameter of the obtained high specific surface area carbon nanofiber sheet was 114 nm. Moreover, it was 490 m < ² > / g when the BET specific surface area was measured. Further 8nm pore volume from 4 obtained in BJH analysis is 0.20 m ³ / g, total pore volume was 1.35 m ³ / g. The volume resistivity was 0.12 Ω · cm. The D3 / G ratio measured by Raman spectroscopy was 0.7. In addition, when the cathode electrode was produced using a high specific surface area carbon nanofiber sheet carrying a platinum catalyst, no cracks were observed, and when power generation characteristics were evaluated, cathode platinum was used at a power density of 0.8V. The amount was 1.67 g / kW. In addition, when the current-voltage characteristics after 10,000 potential cycle tests with 1.0 V hold for 3 seconds and 0.6 V hold for 3 seconds were measured 10,000 times, the output density at a voltage of 0.8 V was obtained. The amount of cathode platinum used was 7.07 g / kW.

[Comparative Example 1]
In the preparation of the electrospinning solution of Example 1 (1), the electrospinning solution was prepared at the following mass ratio.
Polyacrylonitrile (Sigma Aldrich Japan Co., Ltd.) 7.0
N, N-dimethylformamide (Kishida Chemical Co., Ltd.) 93.0
Moreover, in (4) primary baking process of Example 1, it heated up from room temperature to 800 degreeC, and hold | maintained at 800 degreeC for 1 hour. In addition, (5) template removal treatment of Example 1 was not performed. Except for these, the same processing as in Example 2 was performed.

Next, the power generation characteristics of the fuel cell were evaluated in the same manner as in Example 1. As a result, the average fiber diameter of the obtained high specific surface area carbon nanofiber sheet was 49 nm. Moreover, it was 194 m < ² > / g when the BET specific surface area was measured. Furthermore, the pore volume of 4 to 8 nm obtained by BJH analysis was 0.04 m ³ / g, and the total pore volume was 0.35 m ³ / g. The volume resistivity was 0.2 Ω · cm. The D3 / G ratio measured by Raman spectroscopy was 0.3. In addition, when the cathode electrode was produced using a high specific surface area carbon nanofiber sheet carrying a platinum catalyst, no cracks were observed, and when power generation characteristics were evaluated, cathode platinum was used at a power density of 0.8V. The amount was 3.51 g / kW. In addition, when the current-voltage characteristics after 10,000 potential cycle tests with 1.0 V hold for 3 seconds and 0.6 V hold for 3 seconds were measured 10,000 times, the output density at a voltage of 0.8 V was obtained. The amount of cathode platinum used was 17.0 g / kW, which was inferior to Examples 1 to 5, and sufficient characteristics could not be obtained.

[Comparative Example 2]
In the preparation of the electrospinning solution of Example 1 (1), the electrospinning solution was prepared at the following mass ratio.
Polyacrylonitrile (Sigma Aldrich Japan Co., Ltd.) 6.0
Nanosilica (prepared from Nissan Chemical Industries, Ltd. organosilica sol TOL-ST) 3.5
N, N-dimethylformamide (Kishida Chemical Co., Ltd.) 90.5
Except for this, the same processing as in Example 1 was performed.

Next, the power generation characteristics of the fuel cell were evaluated in the same manner as in Example 1. As a result, the average fiber diameter of the obtained high specific surface area carbon nanofiber sheet was 125 nm. Moreover, it was 383 m < ² > / g when the BET specific surface area was measured. Further, the pore volume of 4 to 8 nm obtained by BJH analysis was 0.09 m ³ / g, and the total pore volume was 1.17 m ³ / g. The volume resistivity was 0.10 Ω · cm. The D3 / G ratio measured by Raman spectroscopy was 0.5. In addition, when the cathode electrode was produced using a high specific surface area carbon nanofiber sheet carrying a platinum catalyst, no cracks were observed, and when power generation characteristics were evaluated, cathode platinum was used at a power density of 0.8V. The amount was 3.51 g / kW. In addition, when the current-voltage characteristics after 10,000 potential cycle tests with 1.0 V hold for 3 seconds and 0.6 V hold for 3 seconds were measured 10,000 times, the output density at a voltage of 0.8 V was obtained. The amount of cathode platinum used was 17.0 g / kW, which was inferior to Examples 1 to 5, and sufficient characteristics could not be obtained.

[Comparative Example 3]
In the preparation of the electrospinning solution of Example 1 (1), the electrospinning solution was prepared at the following mass ratio.
Polyacrylonitrile (Sigma Aldrich Japan Co., Ltd.) 6.0
Nanosilica (prepared from Nissan Chemical Industries, Ltd. organosilica sol MA-ST-M) 3.5
N, N-dimethylformamide (Kishida Chemical Co., Ltd.) 90.5
Except for this, the same processing as in Example 1 was performed.

Next, the power generation characteristics of the fuel cell were evaluated in the same manner as in Example 1. As a result, the average fiber diameter of the obtained high specific surface area carbon nanofiber sheet was 110 nm. Moreover, it was 219 m < ² > / g when the BET specific surface area was measured. Furthermore, the pore volume of 4 to 8 nm obtained by BJH analysis was 0.04 m ³ / g, and the total pore volume was 1.00 m ³ / g. The volume resistivity was 0.10 Ω · cm. The D3 / G ratio measured by Raman spectroscopy was 0.7. In addition, when the cathode electrode was produced using a high specific surface area carbon nanofiber sheet carrying a platinum catalyst, no cracks were observed, and when power generation characteristics were evaluated, cathode platinum was used at a power density of 0.8V. The amount was 3.12 g / kW. In addition, when the current-voltage characteristics after 10,000 potential cycle tests with 1.0 V hold for 3 seconds and 0.6 V hold for 3 seconds were measured 10,000 times, the output density at a voltage of 0.8 V was obtained. The amount of cathode platinum used was 22.3 g / kW, which was inferior to Examples 1 to 5, and sufficient characteristics could not be obtained.

[Comparative Example 4]
In the preparation of the electrospinning solution of Example 1 (1), the electrospinning solution was prepared at the following mass ratio.
Polyacrylonitrile (Sigma Aldrich Japan Co., Ltd.) 6.0
Nanosilica (prepared from Snowtex XS manufactured by Nissan Chemical Industries, Ltd.) 1.0
N, N-dimethylformamide (Kishida Chemical Co., Ltd.) 93.0
Except for this, the same processing as in Example 1 was performed.

Next, the power generation characteristics of the fuel cell were evaluated in the same manner as in Example 1. As a result, the average fiber diameter of the obtained high specific surface area carbon nanofiber sheet was 75 nm. Moreover, it was 170 m < ² > / g when the BET specific surface area was measured. Furthermore, the pore volume of 4 to 8 nm obtained by BJH analysis was 0.13 m ³ / g, and the total pore volume was 0.34 m ³ / g. The volume resistivity was 0.07 Ω · cm. The D3 / G ratio measured by Raman spectroscopy was 0.8. In addition, when the cathode electrode was produced using a high specific surface area carbon nanofiber sheet carrying a platinum catalyst, no cracks were observed, and when power generation characteristics were evaluated, cathode platinum was used at a power density of 0.8V. The amount was 2.88 g / kW. In addition, when the current-voltage characteristics after 10,000 potential cycle tests with 1.0 V hold for 3 seconds and 0.6 V hold for 3 seconds were measured 10,000 times, the output density at a voltage of 0.8 V was obtained. The amount of cathode platinum used was 21.0 g / kW, which was inferior to Examples 1 to 5, and sufficient characteristics could not be obtained.

[Comparative Example 5]
In preparation of the catalyst ink for the cathode (see (8) of Example 1), platinum was supported on the ketjen black EC300J, which is a commercially available carbon black, for the cathode according to (7) the platinum catalyst supported by the precipitation precipitation method of Example 1. Using the platinum-supported carbon black, a membrane / electrode assembly was produced.

Next, the power generation characteristics of the fuel cell were evaluated in the same manner as in Example 1. As a result, the BET specific surface area was measured and found to be 795 m ² / g. Furthermore, the pore volume of 4 to 8 nm obtained by BJH analysis was 0.11 m ³ / g, and the total pore volume was 1.11 m ³ / g. The volume resistivity was 0.3 Ω · cm. The D3 / G ratio measured by Raman spectroscopy was 1.3. Cracks were observed when the cathode electrode was produced. Further, when the power generation characteristics were evaluated, the amount of cathode platinum used at a power density at a voltage of 0.8 V was 1.87 g / kW. As for this initial cathode platinum usage fee, Comparative Example 5 has a value superior to that of Examples 3 and 4, but Comparative Example 5 is cracked, and there is a problem in terms of durability. In addition, when the current-voltage characteristics after 10,000 potential cycle tests with 1.0 V hold for 3 seconds and 0.6 V hold for 3 seconds were measured 10,000 times, the output density at a voltage of 0.8 V was obtained. The amount of cathode platinum used was 15.0 g / kW, which was inferior to Examples 1 to 5, and sufficient characteristics could not be obtained.

[Comparative Example 6]
Comparative Example 6 differs from Comparative Example 5 in that Ketjen Black EC300J, a commercially available carbon black, was subjected to heat treatment at 1800 ° C. for 1 hour in a nitrogen atmosphere for the cathode. A membrane / electrode assembly was prepared using platinum-supported carbon black supporting platinum by precipitation precipitation.

Next, the power generation characteristics of the fuel cell were evaluated in the same manner as in Example 1. As a result, the BET specific surface area was measured and found to be 153 m ² / g. Further 8nm pore volume from 4 obtained in BJH analysis is 0.04 m ³ / g, total pore volume was 1.01m ³ / g. The volume resistivity was 0.5 Ω · cm. The D3 / G ratio measured by Raman spectroscopy was 1.1. Cracks were observed when the cathode electrode was produced. When the power generation characteristics were evaluated, the amount of cathode platinum used at a power density at a voltage of 0.8 V was 2.57 g / kW. In addition, when the current-voltage characteristics after 10,000 potential cycle tests with 1.0 V hold for 3 seconds and 0.6 V hold for 3 seconds were measured 10,000 times, the output density at a voltage of 0.8 V was obtained. The amount of cathode platinum used was 30 g / kW or more, which was inferior to Examples 1 to 5, and sufficient characteristics could not be obtained.

[Comparative Example 7]
In preparation of cathode catalyst ink (see (8) in Example 1), platinum was supported on the commercial carbon black Vulcan XC-72R according to (7) platinum catalyst support in Example 1 by precipitation precipitation method. Using the platinum-supported carbon black, a membrane / electrode assembly was produced.

Next, the power generation characteristics of the fuel cell were evaluated in the same manner as in Example 1. As a result, the BET specific surface area was measured and found to be 221 m ² / g. Furthermore, the pore volume of 4 to 8 nm obtained by BJH analysis was 0.03 m ³ / g, and the total pore volume was 0.55 m ³ / g. The volume resistivity was 0.7 Ω · cm. The D3 / G ratio measured by Raman spectroscopy was 2.2. Cracks were observed when the cathode electrode was produced. Further, when the power generation characteristics were evaluated, the amount of cathode platinum used at the output density at a voltage of 0.8 V was 2.74 g / kW. In addition, when the current-voltage characteristics after 10,000 potential cycle tests with 1.0 V hold for 3 seconds and 0.6 V hold for 3 seconds were measured 10,000 times, the output density at a voltage of 0.8 V was obtained. The amount of cathode platinum used was 30 g / kW or more, which was inferior to Examples 1 to 5, and sufficient characteristics could not be obtained.

A summary of the evaluation results of Examples 1 to 5 and Comparative Examples 1 to 7 is shown in Table 1. The BET specific surface area is preferably 300 m ² / g or more, more preferably 350 m ² / g or more, and even more preferably 390 m ² / g or more. As shown in FIG. 8, Example 1 (solid line) and Example 2 (broken line) are configured to have one pore volume peak in the pore diameter range of 4 nm to 30 nm. Moreover, as shown in FIG. 9, Example 3 (dashed line), Example 4 (solid line), and Example 5 (broken line) have a plurality of pore volume peaks in the range of the pore diameter of 4 nm to 30 nm. It is configured as follows. Examples 3 and 4 have two peaks, and Example 5 has four peaks (Example 5 can be said to have two large peaks when viewed largely). According to Examples 1-5, the outstanding platinum usage-amount was implement | achieved and the improvement of the catalyst carrying | support ability has been confirmed. Moreover, in Examples 1-5 and Comparative Examples 1-4, the aggregate | assembly of the fibrous carbon nanofiber by an electrospinning method is used as a cathode electrode, and it is rather than particulate carbon black (Comparative Examples 5-7). Good conductivity was ensured. In Examples 1 to 5, in the preparation of the electrospinning solution (solution preparation step), the mass ratio of the inorganic template (nanosilica) that contributes to the creation of pores with a pore diameter of 4 to 6 nm is 2.0 or more. Yes. The mass ratio of the inorganic template contributing to the pore diameter of 4 to 6 nm is preferably 2 or more and 10 or less from the viewpoint of ensuring the strength. Moreover, in Examples 1-5 and Comparative Examples 1-4, the crack did not generate | occur | produce.

  The present invention is not limited to the above embodiment.

DESCRIPTION OF SYMBOLS 1 ... Conductive nanofiber member, 2 ... Carbon nanofiber member (conductive nanofiber member), 21 ... Carbon nanofiber, 21a ... Fine pore, 3 ... Catalyst, 4 ... Fuel cell member, 41 ... Electrolyte layer, 42 ... Anode electrode, 421 ... Catalyst layer, 422 ... Gas diffusion layer, 43 ... Cathode electrode, 431 ... Catalyst layer, 432 ... Gas diffusion layer, 5, 6 ... Separator, 9 ... Fuel cell

Claims (19)

Comprising a carbon nanofiber member composed of a plurality of fibrous carbon nanofibers;
The carbon nanofiber member has a plurality of pores, and a pore volume having a pore diameter of 4 nm or more and 8 nm or less obtained by analysis by a BJH method is configured to be 0.2 cm ³ / g or more ,
The pores having a pore diameter of 4 nm or more and 8 nm or less are a plurality of pores located on the surface of the carbon nanofiber and a plurality of pores located inside the carbon nanofiber and communicated to the outside via the pores located on the surface. And a conductive nanofiber member. The carbon nanofiber member has a total pore volume of 0.6 cm ³ / g or more and a pore volume peak of at least 1 in the pore diameter range of 4 nm to 30 nm in the results obtained by analysis by the BJH method. The conductive nanofiber member according to claim 1, which is configured to have one.   The conductive nanofiber member according to claim 1 or 2, wherein the carbon nanofiber member is configured so that a D3 / G ratio obtained by Raman spectroscopic measurement is 1.0 or less.   The conductive nanofiber member according to any one of claims 1 to 3, wherein the carbon nanofiber is configured to have an average fiber diameter of 50 nm or more and 150 nm or less.   The conductive nanofiber member according to any one of claims 1 to 4, wherein the carbon nanofiber is configured to have an average aspect ratio of 5 or more. The conductive nanofiber member according to claim 1, wherein the carbon nanofiber member is configured to have a BET specific surface area of 300 m ² / g or more.   The conductive nanofiber member according to claim 1, further comprising a catalyst supported on a surface of the carbon nanofiber and the pores.   The conductive nanofiber member according to claim 7, wherein the catalyst is configured such that an average particle diameter measured by a transmission electron microscope is 5 nm or less at a loading rate of 30 wt% or more.   The conductive nanofiber member according to claim 7 or 8, wherein the catalyst is a transition metal catalyst.   The conductive nanofiber member according to claim 9, wherein the transition metal catalyst includes at least one metal selected from the group consisting of titanium, cobalt, iron, nickel, copper, zirconia, and platinum. The carbon nanofiber member has a total pore volume of 0.6 cm ³ / g or more and a plurality of pore volume peaks in the pore diameter range of 4 nm to 30 nm in the results obtained by the analysis by the BJH method. The conductive nanofiber member according to any one of claims 1 to 10, which is configured as described above. A fuel cell member comprising: an electrolyte layer; an anode electrode disposed on one side of the electrolyte layer; and a cathode electrode disposed on the other side of the electrolyte layer,
The member for fuel cells, wherein at least one of the catalyst layer of the anode electrode and the catalyst layer of the cathode electrode is composed of the conductive nanofiber member according to any one of claims 7 to 11 . A fuel cell comprising the fuel cell member according to claim 12 . A method for producing a conductive nanofiber member that is an aggregate of carbon nanofibers,
A solution creating step of creating a mixed solution including an organic material that can be electrospun and an inorganic template that is a template composed of an inorganic material;
A deposition layer forming step of forming a sheet-like deposition layer composed of fibrous materials from the mixed solution by electrospinning;
A primary firing step of performing a firing treatment including primary firing on the deposited layer;
Removing the inorganic template from the deposited layer after the primary firing step and forming a plurality of pores in the deposited layer; and
A secondary firing step of performing secondary firing at a temperature higher than the primary firing for the deposited layer after the pore forming step;
Including
The inorganic mold manufacturing method of the average particle size of the inorganic material including conductive nano fibers member is 4nm or more 8nm or less.   The deposited layer after the secondary firing step has a pore volume of 0.2 cm or more and a pore diameter of 4 nm or more and 8 nm or less obtained by analysis by the BJH method in a state where no catalyst is supported. ³ The method for producing a conductive nanofiber member according to claim 14, wherein the method is configured to be not less than / g. The method for producing a conductive nanofiber member according to claim 14 or 15, wherein the inorganic template is composed of a plurality of inorganic materials having different average particle diameters. A method for producing a conductive nanofiber member that is an aggregate of carbon nanofibers,
A solution creating step of creating a mixed solution including an organic material that can be electrospun and an inorganic template that is a template composed of an inorganic material;
A deposition layer forming step of forming a sheet-like deposition layer composed of fibrous materials from the mixed solution by electrospinning;
A primary firing step of performing a firing treatment including primary firing on the deposited layer;
Removing the inorganic template from the deposited layer after the primary firing step and forming a plurality of pores in the deposited layer; and
A secondary firing step of performing secondary firing at a temperature higher than the primary firing for the deposited layer after the pore forming step;
Including
The said inorganic mold is a manufacturing method of the electroconductive nanofiber member comprised with the some inorganic material from which average particle diameter differs. The method for producing a conductive nanofiber member according to any one of claims 14 to 17, wherein a firing temperature of the secondary firing is 1200 ° C or higher and 2800 ° C or lower. The method for producing a conductive nanofiber member according to any one of claims 14 to 18, further comprising a catalyst supporting step of supporting a catalyst on the surface of the deposited layer and the pores after the secondary firing step.