JP2007335251A - Electrode for fuel cell, membrane electrode assembly, and cell for fuel battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode for a fuel cell or the like, capable of enhancing power generation performance and reducing a catalyst content compatibly. <P>SOLUTION: This electrode 13 for the fuel cell of the present invention has a catalyst layer 1 abutting to an electrolyte membrane 11a. The catalyst layer 1 comprises a stripe type carbon nano wall 3 with respective graphene sheets 31 arranged substantially orthogonally with respect to a surface of the electrolyte membrane 11a, and extended only one-dimensionally along a direction parallel to the surface of the electrolyte membrane 11a. Pt 41 and an ion conductive layer 6 comprising an electrolyte are provided on the each graphene sheet 31 of the carbon nano wall 3. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell electrode, a membrane electrode assembly, and a fuel cell.

  The fuel cell stack is formed by stacking a plurality of cells 10 as shown in FIG. Each cell 10 includes a membrane electrode assembly (MEA) 11 and a separator 12, and adjacent cells 10 share a separator 12.

  Each membrane electrode assembly 11 includes an electrolyte membrane 11a made of a solid polymer membrane such as Nafion (registered trademark, Nafion (manufactured by Dupon)), and a cathode electrode joined to one surface of the electrolyte membrane 11a and supplied with air. 11b and an anode 11c joined to the other surface of the electrolyte membrane 11a and supplied with fuel.

  Each separator 12 is laminated with each membrane electrode assembly 11 sandwiched therebetween, and each separator forms an air chamber 12b on each cathode electrode 11b side and a fuel chamber 12c on each anode electrode 11c side. ing. The air supplied to the fuel cell stack flows through all the air chambers 12b of each cell 10, and the fuel supplied to the fuel cell stack flows through all the fuel chambers 12c of each cell 10. It is like that.

  As shown in FIG. 7, a general cathode electrode 11b is located on the electrolyte membrane 11a side, and has a catalyst layer 1b having a catalyst-carrying carbon in which a catalyst is supported on carbon particles and an electrolyte, and the opposite side of the electrolyte membrane 11a. And a diffusion layer 2b for supplying electrons to the catalyst layer 1b and diffusing air. The anode 11c is located on the electrolyte membrane 11a side and is located on the non-electrolyte side of the catalyst layer 1c having the catalyst-supporting carbon and the electrolyte, and collects electrons generated by an electrochemical reaction in the catalyst layer 1c. And a diffusion layer 2c for diffusing the fuel gas.

  In the catalyst layer 1b of the cathode electrode 11b, protons are conducted from the electrolyte membrane 11a through the electrolyte. Further, electrons are conducted from the diffusion layer 2b through the carbon particles, and oxygen is supplied through the electrolyte. These protons, electrons, and oxygen react electrochemically to produce water. The generated water is drained to the diffusion layer 2b through the electrolyte.

  In the catalyst layer 1c of the anode 11c, hydrogen is supplied from the diffusion layer 2c through the electrolyte. This hydrogen is decomposed into protons and electrons by an electrochemical reaction. Protons are conducted to the electrolyte membrane 11a through the electrolyte. The electrons are conducted to the diffusion layer 2c through the carbon particles.

  The membrane electrode assembly 11 is manufactured as follows (for example, Patent Document 1). First, a base material, a diffusion layer paste, a cathode electrode paste, and an anode electrode paste are prepared. The base material is a conductor having pores such as carbon cloth. The diffusion paste is a mixture of conductive particles such as carbon particles and PTFE particles as water repellent particles. The cathode electrode paste is a mixture of Pt-supported carbon in which Pt as a catalyst is previously supported on conductive particles such as carbon particles, and an electrolyte such as Nafion (registered trademark). The anode electrode paste is a mixture of a Pt-supported carbon catalyst and an electrolyte such as Nafion (registered trademark).

  Next, the diffusion layer paste is applied to both surfaces of the substrate and dried to form the diffusion layer 2b. Thereafter, the cathode electrode paste is applied to one surface of the diffusion layer 2b and dried to form the catalyst layer 1b. Thus, the cathode electrode 11b is obtained. On the other hand, the anode electrode paste is applied to one surface of the diffusion layer 2c of another substrate and dried to form the catalyst layer 1c. Thus, the anode 11c is obtained.

  And it arrange | positions so that the electrolyte layer 11a which consists of Nafion (trademark) etc. may be pinched | interposed between the cathode electrode 11b and the anode electrode 11c, and the thermocompression bonding by a hot press is performed. In this way, the membrane electrode assembly 11 can be obtained.

JP-A-2005-174768

  However, the catalyst layers 1b and 1c of the electrode for a fuel cell which is the cathode electrode 11b or the anode electrode 11c of Patent Document 1 above are electrolytes between carbon cloth fibers or carbon particles which are electron conduction paths through which electrons are conducted. Therefore, electronic resistance is large. Further, since the electron conduction path is formed by the contact of the carbon particles, the electronic resistance due to these contact resistances is also large. Further, the catalyst layers 1b and 1c of the fuel cell electrode have a large ionic resistance because conductive particles such as carbon particles are interposed in an electrolyte which is an ion conduction path through which ions are conducted. Therefore, the electrochemical reaction is difficult to be performed efficiently, and there is a limitation on the power generation performance.

  Further, in this fuel cell electrode, water such as generated water is easily impregnated between the pores and carbon particles of the base material such as carbon cloth, and the drainage is insufficient, and the remaining water supplies hydrogen and oxygen. The nature is also insufficient. For this reason, the fuel cell electrode still has limitations on power generation performance.

  Further, in this fuel cell electrode, since the catalyst is dispersed throughout the catalyst layers 1b and 1c, only a part of the catalyst is in contact with hydrogen or oxygen, making it difficult to perform an electrochemical reaction. It can be wasted.

  Further, in the conventional fuel cell electrode, since an electrolyte is present in the electron conduction path, a good current distribution cannot be obtained in the catalyst layers 1b and 1c, and electrons are uniformly supplied to the catalyst layer 1b of the cathode electrode 11b. Or diffusion layers 2b and 2c for efficiently collecting electrons generated in the catalyst layer 1c of the anode 11c. In this case, the electronic resistance increases by the amount of the diffusion layers 2b and 2c, and there is a limitation on the power generation performance. In addition, the diffusion layers 2b and 2c may complicate the electrode structure.

  The present invention has been made in view of the above-described conventional situation, and it is a problem to be solved to provide a fuel cell electrode capable of achieving improvement in power generation performance, reduction in catalyst content, and simplification of the structure. It is said. And this invention makes it the subject which should be solved to provide the membrane electrode assembly and cell for fuel cells using the electrode for fuel cells.

The fuel cell electrode of the present invention is a fuel cell electrode having a catalyst layer in contact with an electrolyte membrane.
The catalyst layer has carbon nanowalls in which graphene sheets are arranged substantially at right angles to the surface of the electrolyte membrane, and each graphene sheet extends only one-dimensionally in a direction parallel to the surface of the electrolyte membrane,
A catalyst and an ion conductive layer made of an electrolyte are provided on the surface of each graphene sheet of the carbon nanowall.

  In the fuel cell electrode of the present invention, the graphene sheet of carbon nanowall is disposed substantially perpendicular to the surface of the electrolyte membrane, and the graphene sheet itself does not contain an electrolyte. This shortens the electron conduction path in a direction substantially perpendicular to the electrolyte membrane surface in the catalyst layer. Further, since the graphene sheet itself is an integral structure of carbon, the electron conduction path is formed larger than that in which the electron conduction path is formed by contact of the carbon particles. That is, the electronic resistance is reduced. In this fuel cell electrode, an electrolyte of an ion conductive layer is provided on the surface of each graphene sheet. Thereby, the ion conduction path in the direction perpendicular to the electrolyte membrane surface in the catalyst layer is shortened. That is, the ionic resistance is reduced. Therefore, the electrochemical reaction is easily performed efficiently.

  Also, in this fuel cell electrode, each graphene sheet is a carbon nanowall that extends only one dimension in a direction parallel to the surface of the electrolyte membrane, so that a continuous space that continues in one direction from one side of the catalyst layer Is formed. This continuous space can be larger than the pores between the carbon particles. For this reason, the produced | generated water etc. are suitably drained through this continuous space, and the supply property of hydrogen and oxygen improves. In particular, if oxygen is supplied from one side by a blower, the generated water is suitably drained along the flow to the other side, and the oxygen supply performance is reliably improved. Therefore, the electrochemical reaction is easily performed efficiently.

  In this fuel cell electrode, a catalyst is provided on the surface of each graphene sheet, and hydrogen and oxygen come into contact with the surface of each graphene sheet through a space between the graphene sheets, and almost all the catalysts undergo an electrochemical reaction. The catalyst content is reduced.

  Further, in this fuel cell electrode, since there is no electrolyte in the graphene sheet, which is an electron conduction path, the supply of electrons at the cathode electrode and the collection of electrons at the anode electrode can be performed without providing a diffusion layer. Done well. Therefore, the diffusion layer can be omitted, the electronic resistance can be further reduced by the amount of the diffusion layer, and the power generation performance is further improved. If the diffusion layer is omitted, the structure of the electrode can be simplified.

  Therefore, according to the fuel cell electrode of the present invention, it is possible to improve the power generation performance, reduce the catalyst content, and simplify the structure.

  Carbon nanofibers and carbon nanotubes are also known as materials that can realize an electron conduction path in which no electrolyte is present (for example, JP-A-2005-203332). Moreover, it is considered that a space can be secured between them. However, it is difficult to arrange the electron conduction path substantially at right angles to the surface of the electrolyte membrane, and it is considered that the practical use is difficult. Moreover, the space which can be ensured between these tends to be the same or smaller than the pores between the fibers of the carbon cloth and between the carbon particles. On the other hand, since it is difficult to arrange these in contact with each other, the contact resistance between the carbon nanofibers and the like increases. That is, the electronic resistance increases. Furthermore, it is difficult to form the space so as to be continuous in one direction. In contrast, carbon nanowalls are disclosed in “Oriented growth of carbon nanowalls by RF plasma CVD” (Journal of Plasma and Fusion Research Vol.81, No.9 September 2005 P.669-673). It is possible to dispose the graphene sheet substantially perpendicular to the surface of the substrate. Moreover, it is also possible to provide a relatively large and continuous space in one direction between the graphene sheets. Therefore, it is easy to arrange the electron conduction path at a right angle to the surface of the electrolyte membrane by attaching the grown carbon nanowall to the electrolyte membrane or using the electrolyte membrane as the base material. Is possible. In addition, it is possible to improve drainage properties and supply capability of hydrogen and oxygen.

  In the fuel cell electrode of the present invention, the surface of the graphene sheet is preferably provided with catalyst-supporting conductive particles in which a catalyst is supported on the conductive particles. Thereby, the reaction area in which an electrochemical reaction is performed in a catalyst layer increases. Therefore, the power generation performance of the fuel cell can be improved.

  The membrane electrode assembly of the present invention comprises the electrolyte membrane and a pair of fuel cell electrodes that sandwich the electrolyte membrane and the catalyst layer has the carbon nanowalls.

  According to this membrane electrode assembly, it is possible to obtain a fuel cell and a fuel cell stack that can achieve improved power generation performance, reduced catalyst content, and simplified structure.

  The cell for a fuel cell according to the present invention includes the membrane electrode assembly and the membrane electrode assembly so that an air chamber is formed on one catalyst layer side and a fuel chamber is formed on the other catalyst layer side. And a separator made of a conductive material forming a pair for sandwiching the body.

  According to this fuel cell, a fuel cell stack that can achieve improved power generation performance, reduced catalyst content, and simplified structure can be obtained.

  The fuel-electric stack is obtained by combining a large number of the membrane electrode assemblies or the cells.

  The fuel cell system to which the fuel cell stack is applied exhibits high power generation performance for the reasons described above.

  Embodiments will be described below with reference to the drawings.

  As shown in FIGS. 1 and 2, in the fuel cell electrode 13 of the example, the catalyst layer 1 has carbon nanowalls 3.

  As shown in FIG. 3, the carbon nanowall 3 is of a stripe type in which each graphene sheet 31 extends only one-dimensionally. Each graphene sheet 31 extends from several nanometers to several tens of nanometers, and this length is the thickness of the plate-like carbon nanowall 3. In the carbon nanowall 3, a graphene sheet 31 is disposed at a substantially right angle with respect to the surface of the electrolyte membrane 11 a, and a continuous space 5 that is continuous in one direction from one side surface of the catalyst layer 1 between the graphene sheets 31. Is present.

  As shown in FIG. 4, both surfaces of each graphene sheet 31 carry Pt 41 and are coated with an ion conductive layer 6 made of an electrolyte.

  In this fuel cell electrode 13, a diffusion layer 2 made of a known carbon cloth or the like is formed on the surface opposite to the electrolyte membrane 11a.

  The fuel cell electrode 13 configured as described above is a membrane electrode assembly 11 as shown in FIG. The membrane electrode assembly 11 includes an electrolyte membrane 11a, and a cathode electrode 11b and an anode electrode 11c in which the catalyst layer 1 is made of carbon nanowalls 3 or the like.

  And this membrane electrode assembly 11 is made into the cell 10 for fuel cells similarly to the past. The fuel cell 10 includes a membrane electrode assembly 11 and an air chamber 12b on one catalyst layer 1 side and a membrane electrode assembly 11 so that a fuel chamber 12c is formed on the other catalyst layer 1 side. And a separator 12 made of a conductive material forming a pair for sandwiching. A number of fuel cell cells 10 are stacked to obtain a fuel cell stack.

  This fuel cell stack constitutes a fuel cell system together with a motor, a blower, a hydrogen cylinder, a controller and the like. Air is supplied to each air chamber 12b by a blower, and hydrogen in a hydrogen cylinder is supplied to the fuel chamber 12c. Thereby, an electromotive force is generated between the cathode electrode 11b and the anode electrode 11c by an electrochemical reaction between the air supplied to the catalyst layer 1 and hydrogen.

  At this time, hydrogen is supplied to the catalyst layer 1 through the diffusion layer 2 at the anode 11 c. In the catalyst layer 1, hydrogen fills the continuous space 5 existing between the graphene sheets 31, and is oxidized into protons and electrons by Pt 42 provided on the surface of each graphene sheet 31. The generated protons are supplied to the electrolyte membrane 11a through the ion conductive layer 6 having a low ionic resistance, and reach the catalyst layer 1 of the cathode electrode 11b through the electrolyte membrane 11a. Further, the generated electrons are collected to the diffusion layer 2 through the graphene sheet 31 having a low electronic resistance.

  On the other hand, at the cathode electrode 11 b, oxygen and electrons are supplied to the catalyst layer 1 through the diffusion layer 2. Protons are supplied to the catalyst layer 1 through the electrolyte membrane 11a. In the catalyst layer 1 on the cathode electrode side, oxygen fills the continuous space 5 existing between the graphene sheets 31, and electrons pass through the graphene sheet 31 having a low electronic resistance without containing an electrolyte. Go across the whole. Protons spread throughout the catalyst layer 1 through the ion conductive layer 6 having a low ion resistance. For this reason, an electrochemical reaction by oxygen, electrons, and protons occurs on almost the entire surface of the graphene sheet 31 of the catalyst layer 1. The water generated by the reaction is suitably drained from the continuous space 5 to the diffusion layer 2, so that the supply of hydrogen and oxygen is improved. Therefore, an electrochemical reaction is efficiently performed and power generation performance is improved.

  Further, in this fuel cell stack, as shown in FIG. 1, when the electrode 13 is the cathode electrode 11b, air is supplied from one side surface of the catalyst layer 1 in one direction (direction indicated by an arrow). The When the electrode 13 is the anode 11c, hydrogen is supplied from one side surface of the catalyst layer 1 in one direction (direction indicated by an arrow). In that case, the diffusion layer 2 does not need a function of diffusing air or the like, and only needs to have a function of conducting electrons, and thus can be a dense body. In the cathode electrode 11b, water is generated by an electrochemical reaction in the catalyst layer 1, and the generated water is suitably drained out of the catalyst layer 1b by using this air flow. , Oxygen supply is improved. Therefore, the electrochemical reaction is performed efficiently and the power generation performance is improved.

  Further, in the fuel cell stack of this embodiment, in the fuel cell electrode 13 constituting the fuel cell stack, Pt 41 is not disposed in the entire catalyst layer 1 but is disposed on the surface of the graphene sheet 31. Therefore, Pt41 that does not participate in the electrochemical reaction is not wasted, and almost all Pt41 is involved in the electrochemical reaction, so that the Pt content is reduced.

  Therefore, the fuel cell stack of the embodiment can achieve improved power generation performance, reduced catalyst content, and simplified structure.

  In the above embodiment, Pt41 is supported on both surfaces of the graphene sheet 31, but Pt-supporting carbon 4 may be provided on both surfaces of each graphene sheet 31, as shown in FIG. The Pt-supported carbon 4 is a known one in which Pt 41 is supported on the carbon particles 42. In this case, the reaction area where the electrochemical reaction is performed is increased, and the power generation performance is improved.

  Further, in the fuel cell stack of the above embodiment, the diffusion layer 2 of the membrane electrode assembly 11 is formed on the surface of the catalyst layer 1 opposite to the electrolyte membrane 11a. Is possible. Even in this case, the supply of electrons at the cathode electrode 11b and the collection of electrons at the anode electrode 11c are favorably performed. Therefore, even if the diffusion layer 2 is omitted, the electric resistance is eliminated by the amount corresponding to the diffusion layer 2, so that the power generation performance is further improved. If the diffusion layer 2 is omitted, the structure can be simplified, for example, the electrode 13, the membrane electrode assembly 11, the cell 10, and eventually the fuel cell stack can be made thinner.

  While the present invention has been described with reference to the embodiments, it is needless to say that the present invention is not limited to the above-described embodiments and can be appropriately modified and applied without departing from the spirit thereof.

  INDUSTRIAL APPLICABILITY The present invention can be used for a fuel cell system such as a moving power source for an electric vehicle, an outdoor stationary power source, and a portable power source.

It is a perspective view which shows a part of membrane electrode assembly of an Example. It is a schematic cross section which shows a part of membrane electrode assembly of an Example. It is a perspective view which shows a part of carbon nanowall of an Example. It is sectional drawing which shows a part of catalyst layer of an Example. It is a partial cross section figure showing other examples of a catalyst layer. It is a schematic cross section which shows a part of stack for fuel cells. It is a schematic cross section showing a general membrane electrode assembly.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Catalyst layer 11a ... Electrolyte membrane 3 ... Carbon nanowall 31 ... Graphene sheet 4 ... Pt carrying | support carbon 5 ... Continuous space 6 ... Ion conduction layer

Claims (4)

In the fuel cell electrode having a catalyst layer in contact with the electrolyte membrane,
The catalyst layer has carbon nanowalls in which graphene sheets are arranged substantially at right angles to the surface of the electrolyte membrane, and each graphene sheet extends only one-dimensionally in a direction parallel to the surface of the electrolyte membrane,
An electrode for a fuel cell, characterized in that a catalyst and an ion conductive layer made of an electrolyte are provided on the surface of each graphene sheet of the carbon nanowall.   2. The fuel cell electrode according to claim 1, wherein catalyst-supporting conductive particles in which the catalyst is supported on conductive particles are provided on the surface of each graphene sheet.   3. A membrane electrode assembly comprising: the electrolyte membrane; and the pair of fuel cell electrodes according to claim 1 or 2, wherein the catalyst layer has the carbon nanowall sandwiching the electrolyte membrane.   A membrane electrode assembly according to claim 3 and a pair of sandwiching the membrane electrode assembly so that an air chamber is formed on one catalyst layer side and a fuel chamber is formed on the other catalyst layer side. A fuel cell comprising a separator made of a conductive material.

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