JP2019046570A - Membrane electrode assembly, fuel cell and electrolyte membrane for membrane electrode assembly - Google Patents

Abstract

The present invention provides a membrane electrode assembly which can be thinned while suppressing deterioration and variation of the performance of a fuel cell.
A membrane electrode assembly 100 in which an anode electrode 10 is joined to one surface of an electrolyte membrane 20 and a cathode electrode 30 is joined to the other surface, wherein the anode electrode 10 and the cathode electrode 30 are connected to the electrolyte membrane 20. A gas flow path formed in at least a partial region of the overlapping surface and connecting the porous catalyst layer 12, 32 to the opposite surface of the overlapping surface of the porous catalyst layers 12, 32 carrying the catalyst and the electrolyte membrane 20 14 and 34, wherein the electrolyte membrane 20 has a convex portion 22 that fits into the concave portions 16 and 36 when the porous catalyst layers 12 and 32 have concave portions 16 and 36.
[Selected figure] Figure 1B

Description

  The present invention relates to a membrane electrode assembly, a fuel cell, and an electrolyte membrane for a membrane electrode assembly, and more particularly to a membrane electrode assembly suitably used for a fuel cell having an integral thin structure.

  In recent years, with the portability, miniaturization, and high performance of various electric devices, there is an increasing demand for improvement in performance of small batteries serving as the power source. Further, along with these developments, further thinning of the battery is required.

  As a battery suitable for downsizing, for example, a polymer electrolyte fuel cell is used, and various research and development have been advanced. A conventional polymer fuel cell generally has a seven-layer structure of a fuel flow channel (separator), a diffusion layer, a catalyst layer, a polymer electrolyte membrane, a catalyst layer, a diffusion layer, and a fuel flow channel (separator) There are many things. Further, in a conventional polymer fuel cell, a powdery catalyst in which fine platinum particles are supported on the surface of carbon powder is used as a catalyst layer.

  However, in a fuel cell of this type of conventional structure, a fuel cell held by a pair of separators for the purpose of reducing the electrical contact resistance between components such as a catalyst powder-electrolyte membrane manufactured in a separate step Need to be tightened with a strong force. For this reason, it is said that there is an inherent limit to thinning the conventional polymer type battery from the viewpoint of securing the strength of the fuel flow channel.

  On the other hand, a fuel cell electrode structure using metal-supporting porous silicon has been proposed as a structure used for a fuel cell that can be thinned and can also increase the output (see Patent Document 1). ).

Unexamined-Japanese-Patent No. 2007-119897 JP, 2008-98070, A

Kuriyama, Nariaki, et al. "Design and fabrication of MEMS-based monolithic fuel cells." Sensors and Actuators A: Physical 145 (2008): p. 354-362. Esquivel, JP, et al. "Fabrication and characterization of a passive silicon-based direct methanol fuel cell." Microsystem technologies 14.4-5 (2008): p.535-541. Esquivel, J. P., et al. "Towards a compact SU-8 micro-direct methanol fuel cell." Journal of Power Sources 195.24 (2010): p. 8110-8115.

  The electrode structure for a fuel cell using the metal-supporting porous silicon described in Patent Document 1 described above immerses a silicon substrate having a porous layer on one surface in a plating solution, and a metal is used in the porous layer of the silicon substrate. It is deposited to form a catalyst layer. According to this electrode assembly, it is possible to construct a fuel cell having a thickness of 300 μm or less by sandwiching a polymer electrolyte membrane with the electrode assembly.

  A MEMS (Micro Electro Mechanical Systems) technology can be used to manufacture this metal-supported porous silicon. The MEMS technology refers to a technology for manufacturing a microstructure having both a mechanical function and an electrical function by using a semiconductor manufacturing process or a microfabrication process used for a semiconductor integrated circuit or the like.

  On the other hand, the membrane electrode assembly described in Patent Document 2 has an electrolyte membrane in which an electrolyte polymer is filled in pores of a porous membrane, and an anode electrode is bonded on one side and a cathode electrode is bonded on the other side. At least one of the electrodes is formed using MEMS technology.

  Here, in order to manufacture a fuel cell using the electrode structures described in Patent Document 1 and Patent Document 2, it is necessary to bond and bond a polymer electrolyte membrane and an electrode structure, but the above-described polymer In the membrane electrode assembly which consists of an electrolyte membrane and an electrode structure, it turned out that the following novel subjects exist.

  That is, when forming a porous catalyst layer by immersing a silicon substrate having a porous layer in a plating solution, at least a part of the formed porous catalyst layer portion may be recessed by several μm from the surface of the silicon substrate I understood. And, as the porous catalyst layer portion is depressed, a void is easily generated between the polymer electrolyte membrane and the electrode structure, and as a result, the adhesion between these members is lowered to inhibit proton conduction, which is high. In order to increase the area for obtaining the output, it has been found that the deterioration and the variation of the performance of the fuel cell are caused.

  On the other hand, when the catalyst layer is formed by the deposition technique etc., the catalyst layer may rise from the surface of the silicon substrate (see, for example, non-patent documents 1 to 3). It has also been found that in the portion of (3), a void is easily generated between the polymer electrolyte membrane and the above, or there is a problem that the raised portion is damaged as described above.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a membrane electrode assembly, a fuel cell, and a membrane electrode assembly which can be thinned while suppressing deterioration and variation of the performance of the fuel cell. An object of the present invention is to provide an electrolyte membrane.

  As a result of intensive studies, the present inventors have adopted the above-described problem by employing an electrolyte membrane having a convex portion or a concave portion, which is fitted to the concave portion or the convex portion present in the porous catalyst layer in the electrode structure. It has been found that it can be solved, and the present invention has been completed.

That is, a membrane electrode assembly according to the present invention is a membrane electrode assembly in which an anode electrode is bonded to one surface of an electrolyte membrane and a cathode electrode is bonded to the other surface,
At least one of the anode electrode and the cathode electrode is formed in at least a partial region of the overlapping surface with the electrolyte membrane, and the opposite of the overlapping surface with the porous catalyst layer supporting the catalyst and the electrolyte membrane A gas flow path communicating the surface with the porous catalyst layer,
The electrolyte membrane has a convex portion that fits into the concave portion when the porous catalyst layer has a concave portion, and has a concave portion that fits into the convex portion when the porous catalyst layer has a convex portion. It is characterized by

  In a preferred embodiment of the above-mentioned membrane electrode assembly, the electrolyte membrane is characterized in that the inside of the pores of the porous polymer membrane is filled with the electrolyte polymer.

  A fuel cell according to the present invention is characterized by using the above-mentioned membrane electrode assembly.

  The electrolyte membrane for a membrane electrode assembly according to the present invention is an electrolyte membrane used for the above membrane electrode assembly, and the electrolyte membrane fits in the recess when the porous catalyst layer has a recess. It has a convex part, and when the said porous catalyst layer has a convex part, it is characterized by having a concave part which adapts to the said convex part.

  In a preferred embodiment of the above electrolyte membrane for membrane electrode assembly, the electrolyte membrane is characterized in that the inside of the pores of the porous polymer membrane is filled with the electrolyte polymer.

  The method of producing an electrolyte membrane for a membrane electrode assembly according to the present invention is the method of producing an electrolyte membrane for a membrane electrode assembly as described above, wherein the concave portion or the convex portion is formed in the porous polymer membrane by plasma etching. And a step of filling the porous polymer membrane in which the concave portion or the convex portion is formed with an electrolyte polymer.

  In a preferred embodiment of the method of manufacturing an electrolyte membrane for a membrane electrode assembly, the etching is performed at a temperature of less than 110 ° C. as a temperature at which the plasma etching is performed.

  The method for producing a membrane electrode assembly according to the present invention comprises the steps of producing an electrolyte membrane using the above method for producing an electrolyte membrane for membrane electrode assembly, the obtained electrolyte membrane as the anode electrode and the cathode electrode. And a step of sandwiching and hot pressing.

  According to the present invention, it is possible to achieve a large area for obtaining high output by adopting an electrolyte membrane having a convex portion or a concave portion adapted to a concave portion or a convex portion present in the porous catalyst layer in the electrode structure. Accordingly, it is possible to provide a membrane electrode assembly, a fuel cell, and an electrolyte membrane for a membrane electrode assembly which can be thinned while suppressing deterioration and variation of the performance of the fuel cell.

FIG. 1A is an end view of a membrane electrode assembly according to an embodiment of the present invention. FIG. 1B is a perspective view of a membrane electrode assembly according to an embodiment of the present invention. FIG. 2A is a top view of a porous electrolyte membrane having a convex portion produced in an example. FIG. 2B is a front view of a porous electrolyte membrane having a convex portion produced in an example. FIG. 3 is a graph showing cell voltage, current density and power density characteristics in the fuel cell according to the example. FIG. 4 is a graph showing cell voltage, current density and power density characteristics in a fuel cell according to a comparative example.

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

<Basic configuration of membrane electrode assembly>
FIG. 1A is an end view of a membrane electrode assembly according to an embodiment of the present invention, and FIG. 1B is a perspective view thereof. The membrane electrode assembly 100 according to the present embodiment is configured by bonding the anode electrode 10 to one surface of the electrolyte membrane 20 and the cathode electrode 30 to the other surface. The anode electrode 10 and the cathode electrode 30 each have a porous catalyst layer 12, 32 in which a catalyst is supported on at least a partial region of the overlapping surface with the electrolyte membrane 20. In addition, the anode electrode 10 and the cathode electrode 30 are gas flows that are through holes that connect the porous catalyst layers 12 and 32 to the opposite surface of the overlapping surface with the electrolyte membrane 20 to become a flow path for fuel or oxidant. Each has a passage 14, 34.

  Further, on the opposite side of the anode electrode 10 and the cathode electrode 30 on the side opposite to the surface on which the electrolyte film 20 is overlapped, an anode side current collection layer 18 and a cathode side current collection layer 38 for collecting electricity generated are respectively Have. Furthermore, in order to ensure the continuity between the porous catalyst layers 12 and 32 and the anode electrode 10 or the cathode electrode 30, a porous catalyst layer is formed on the side where the anode electrode 10 and the cathode electrode 30 overlap with the electrolyte membrane 20. Current collector layers 19 and 39 are formed to be in contact with 12 and 32, respectively.

The operation of a fuel cell using the above membrane electrode assembly will be described. When the hydrogen-containing fuel is supplied to the gas flow channel 14 provided in the anode electrode 10, the hydrogen-containing fuel moves to the porous catalyst layer 12. By catalytic action of platinum or the like supported on the porous catalyst layer 12, hydrogen molecules in the hydrogen-containing fuel are decomposed into electrons and hydrogen ions (H ⁺ ). The electrons pass from the porous catalyst layer 12 through the current collector layer 19, the anode electrode 10, and the anode side current collection layer 18, and through the external conducting wire (not shown), the cathode side current collection layer 38, the cathode electrode 30, the current flows through the current collector layer 39 and the porous catalyst layer 32.

On the other hand, hydrogen ions (H ⁺ ) generated in the porous catalyst layer 12 move to the porous catalyst layer 32 via the electrolyte membrane 20. The hydrogen ions (H ⁺ ) generated in the porous catalyst layer 12 are supplied from the gas flow path 34 provided in the cathode electrode 30 and are transferred to the porous catalyst layer 32 with oxygen in an oxidant such as air, and the like. Water (H ₂ O) is generated in combination with the electrons moving through the conducting wire.

  By the way, the above-mentioned electrode structure (anode electrode 10 or cathode electrode 30) to which MEMS technology is applied integrates a separator, a gas diffusion layer, and a catalyst layer which are configured as separate parts in a conventional fuel cell on one silicon substrate. It is formed. As a result, there is no process for fastening in order to secure the electrical conduction between the layers, and the thinning is realized. In addition, since the fuel flow path is formed on the silicon substrate and platinum or the like used for the catalyst layer has a porous shape, it also plays a role of a gas diffusion layer.

  Although details will be described later, in order to manufacture this integrated electrode structure, it is necessary to form a porous catalyst layer on a silicon substrate. At this time, the porous silicon layer is formed by anodizing the silicon substrate in a hydrofluoric acid solution. Thereafter, the porous silicon layer is immersed in a platinum plating solution to which hydrofluoric acid has been added to reform it into a porous platinum layer.

  In the formation of the porous catalyst layer, the inventors of the present invention shrink the porous shape by substituting silicon for platinum, and at least a part of the formed porous catalyst layer is larger than the silicon substrate surface. I found that it was depressed several micrometers.

  In addition, when the reaction area is expanded to increase the output for practical use of the fuel cell using the integrated electrode structure, the output density is greatly dispersed as the reaction area is expanded, and the performance is It turned out that it is on the decline tendency. The inventors of the present invention tend to form voids between the porous catalyst layer in which the depressions are formed and the polymer electrolyte membrane as a cause of the reduction in performance, and as a result, the adhesion between these members is reduced to cause proton conduction. Was considered to be inhibited.

  So, in the membrane electrode assembly 100 concerning this embodiment, the electrolyte membrane 20 which has the convex part 22 of the form adapted to the recessed parts 16 and 36 which exist in the porous catalyst layers 12 and 32 in an electrode structure is employ | adopted.

  As a result, even if a recess is formed in a part of the porous catalyst layers 12 and 32, the projections 22 of the electrolyte membrane 20 adhere to the recesses 16 and 36 of the porous catalyst layers 12 and 32, respectively. It is possible to reduce the space between the porous catalyst layers 12 and 32 and the electrolyte membrane 20 as much as possible. As a result, the proton conductivity is improved, and the performance deterioration and variation of the fuel cell can be improved.

  The above “conforming” means that the concave portions 16 and 36 of the porous catalyst layers 12 and 32 and the convex portions 22 of the electrolyte membrane 20 can be superimposed on each other with as little space as possible. It is shown that the surface shape of the convex portion 22 follows the surface shape of the concave portions 16 and 36 of the porous catalyst layers 12 and 32. On the other hand, when the porous catalyst layers 12 and 32 have a convex portion, it means that the surface shape of the recess of the electrolyte membrane 20 follows the surface shape of the recess of the porous catalyst layers 12 and 32.

<Details of membrane electrode assembly>
Next, each component in the membrane electrode assembly 100 configured as described above will be described in detail.

(electrode)
The anode electrode 10 and the cathode electrode 30 (which may be collectively referred to as “electrode” or “electrode assembly” in the present specification) of the membrane electrode assembly 100 according to the present embodiment overlap with the electrolyte membrane 20. The opposite surface of the overlapping surface of the porous catalyst layers 12 and 32 on which the catalyst is supported, which is formed in at least a partial area of the surface, and the flow path of the fuel or oxidant, and the porous surface Each of the gas flow paths 14 and 34 which are through holes communicating the catalyst layers 12 and 32 is provided. And the anode electrode 10 and the cathode electrode 30 are formed using the said MEMS technique.

  So far, the electrode has a two-layer structure in which a catalyst layer and a diffusion layer are stacked, and has a separator that has a flow path for supplying fuel or an oxidant, a current collector that collects generated electricity, etc. It was mainstream to be considered as a separate member.

  However, by using the above-described MEMS technology, it is possible to make an extremely minute structure. For this reason, the necessity of producing each member as a separate member like a conventional electrode, a separator, a current collector, etc. is also becoming smaller. That is, it is possible to manufacture an electrode as an integral member in a form incorporating not only the catalyst function and the diffusion function but also the supply function of the fuel and the oxidant and the current collection function.

  In addition, the porous catalyst layers 12 and 32 in the above electrode not only fulfill the function as a conventional gas diffusion layer by having a porous structure, but are composed of a catalyst such as platinum and so on as a conventional catalyst layer. Perform both functions and functions. That is, the porous catalyst layers 12 and 32 function as a gas diffusion layer / catalyst layer.

  Here, the porous catalyst layers 12 and 32 have many through holes penetrating from the surface in contact with the gas flow channels 14 and 34 to the surface in contact with the electrolyte membrane 20. In the porous layer, non-penetrating holes may be present as long as at least a part has the penetrating portion.

  In this case, the through holes may penetrate substantially perpendicularly to the surface of the porous layer, or may penetrate at an angle of less than 90 ° with respect to the membrane surface. Moreover, it may penetrate at random, such as meandering and a zigzag shape.

  The cross-sectional shape of the through hole is not particularly limited. As a cross-sectional shape of the through hole, a circular shape, an elliptical shape, a polygonal shape, a shape in which these are connected, a combination of these, and the like can be exemplified.

  The upper limit of the porosity of the porous catalyst layers 12 and 32 is preferably 90% or less, more preferably 80% or less, from the viewpoint of securing high mechanical strength and keeping the electric resistance of the catalyst layer low. , 75% or less is more preferable. On the other hand, the lower limit of the porosity of the porous catalyst layers 12 and 32 is preferably 20% or more, more preferably 30% or more, and 50% or more from the viewpoint of supply of fuel etc., catalyst layer formation process, etc. More preferable.

  In the case where the raw material of the porous catalyst layers 12 and 32 (the material before being reformed by platinum etc.) is porous silicon, the above-mentioned porosity is the weight measurement before and after the porosification by anodic oxidation, and the cross-sectional observation It can be determined from volumetric measurement of the porous layer by

  The upper limit of the pore diameter of the porous catalyst layers 12 and 32 is preferably 100 μm or less, more preferably 10 μm or less, from the viewpoint of fuel permeability and the like. On the other hand, the lower limit of the pore diameter of the porous catalyst layers 12 and 32 is preferably 10 nm or more, more preferably 50 nm or more, from the viewpoint of the catalyst layer forming process and the like.

  In addition, the said hole diameter can be calculated | required by electron microscope observation.

  In the above electrode configuration, the catalyst is supported on the surface of the pores of the porous catalyst layers 12 and 32. Alternatively, the catalyst metal itself forms the porous catalyst layers 12, 32.

  The catalyst is preferably supported on the surface of the pore by plating, from the viewpoint that a relatively inexpensive plating technique can be used, and the catalyst is less likely to come off the pore.

  The catalyst may be distributed over the entire area of the porous catalyst layers 12 and 32, or the surface of the porous catalyst layers 12 and 32 on the electrolyte membrane 20 side may be porous toward the gas flow channels 14 and 34. It may be distributed over a distance less than the thickness of the quality catalyst layers 12 and 32, or the like.

As an upper limit of catalyst content, 10 mg / cm < ² > or less is preferable and 5 mg / cm < ² > or less is more preferable. When the catalyst content is too high, the particle size of the catalyst such as platinum becomes large, and the utilization efficiency per weight of the catalyst tends to decrease. On the other hand, when the particle size is kept small, the catalyst layer must be thickened, and the catalyst utilization rate at a location far from the electrolyte membrane tends to decrease. On the other hand, the lower limit of the catalyst content, in terms of maintaining performance, preferably 0.001 mg / cm ² or more, more preferably 0.01 mg / cm ^2.

  In the above electrode configuration, the current collector layers 19 and 39 are formed on the surface on which the porous catalyst layers 12 and 32 are formed. Since the conduction between the porous catalyst layers 12 and 32 and the silicon substrate (anode electrode 10 and cathode electrode 30) is uncertain only by forming the porous catalyst layers 12 and 32 on the electrodes, electrons generated during power generation There is a possibility that it can not be taken out enough. Therefore, it is an object to ensure conduction by forming a conductive thin film such as gold.

At this time, if the porous catalyst layers 12 and 32 are all covered with a thin film such as gold, there is a possibility that hydrogen ions (H ⁺ ) may become an obstacle when moving from the anode to the cathode at the time of fuel supply. Therefore, a thin film is formed on at least a part of the porous catalyst layers 12 and 32.

  As a material of the electrode according to the present embodiment, for example, conductor materials such as titanium, nickel, alloys thereof, silicon, germanium, selenium single substance doped with ions, GaAs, GaP, InP, CdTe, ZnSe, SiC A semiconductor material such as one obtained by ion doping a compound semiconductor such as, etc. can be used as a suitable one. Preferably, a semiconductor material can be used suitably.

  Among semiconductor materials, silicon can be most preferably used from the viewpoint that semiconductor processing technology can be applied, from the viewpoint of easy processing, and from the viewpoint of compound semiconductors that are easily broken.

  As the silicon, for example, n-type silicon having a relatively high etching rate can be suitably used. From the viewpoint of reducing the loss of electrical energy, etc., highly doped n-type silicon having a resistivity of preferably 0.01 Ω or less, more preferably 0.005 Ω or less can be most preferably used.

  Examples of the catalyst material include noble metals such as platinum, platinum-ruthenium alloy, palladium, platinum-cobalt alloy and platinum-iron alloy, and noble metal alloys. These may be used alone or in combination of two or more.

  In addition, platinum etc. can be used suitably as a catalyst for cathode electrodes. Moreover, as a catalyst for an anode electrode, platinum-ruthenium alloy etc. which are easy to reduce poisoning of the catalyst by carbon monoxide can be used suitably.

  Examples of materials for the current collector layers 19 and 39 include copper, silver, gold, platinum, palladium, alloys thereof, stainless steel, and the like. These may be used alone or in combination of two or more.

  The thickness of the electrode is not particularly limited, and can be appropriately set in consideration of weight reduction, electric resistance, and the like. The upper limit of the thickness of the electrode is preferably 1 mm or less from the viewpoint of being advantageous for weight reduction, size reduction, and the like. On the other hand, the lower limit of the thickness of the electrode is preferably 0.05 mm or more from the viewpoint of difficulty in securing a flow path for fuel or the like when it is excessively thin, and poor handling in the MEMS process.

  The upper limit of the thickness of the porous catalyst layers 12 and 32 is preferably 100 μm or less, more preferably 50 μm or less, and still more preferably 20 μm or less from the viewpoint of large resistance and large battery performance if the layer is too thick. On the other hand, the lower limit of the thickness of the porous catalyst layers 12 and 32 is preferably 1 μm or more, more preferably 2 μm or more, and still more preferably 5 μm or more from the viewpoint that when it is too thin, the strength is not maintained and the catalyst is easily collapsed.

  The upper limit of the thickness of the current collector layers 19 and 39 is preferably 10 μm or less, more preferably 1 μm or less, from the viewpoint of being easily damaged by plating stress if the layer is too thick. On the other hand, the lower limit of the thickness of the current collector layer is preferably 10 nm or more, more preferably 100 nm or more, from the viewpoint that resistance is generated when the thickness is too thin.

  The shape of the flow path of the gas flow path 14 serving as the flow path of the fuel and the flow path of the gas flow path 34 serving as the flow path of the oxidant in the electrode are particularly limited as long as the fuel or the oxidant can be supplied. It is not a thing. Other than the flow channel shape as shown in FIGS. 1A and 1B, it may be a serpentine shape (single serpentine, multi serpentine shape, etc.) often used for a fuel cell separator, or a gas flow path formed in a spiral shape. .

(Electrolyte membrane)
The electrolyte membrane 20 which concerns on this embodiment has the convex part 22 of the form adapted to the recessed part 16 and 36 which exist in the porous catalyst layers 12 and 32 in an electrode. As shown in FIGS. 1A and 1B, in the present embodiment, circular convexes 22 are formed on the upper and lower surfaces of the electrolyte membrane 20 at the center in the in-plane direction of the electrolyte membrane 20, respectively.

  The shape of the convex portion is not limited as long as the convex portion 22 is simply formed on the surface of the electrolyte membrane 20, and the concave portions 16 and 36 formed in the porous catalyst layers 12 and 32 of the electrodes to be overlapped and joined. It is important to have a compatible shape. In addition, by providing minute unevenness on the surface of the electrolyte membrane 20, the technical idea is different from that in which the contact area with the opposing electrode is increased. By having this configuration, as described above, the space between the porous catalyst layers 12 and 32 and the electrolyte membrane 20 can be reduced as much as possible, and as a result, the proton conductivity becomes good, and the performance of the fuel cell decreases. Variation can be improved.

  In the present embodiment, although the porous catalyst layers 12 and 32 have the concave portions 16 and 36 and the electrolyte membrane has the convex portions 22 formed, the porous catalyst layers 12 and 32 are described. When a protrusion is present in the porous catalyst layers 12 and 32 due to a part of the protrusion rising, the electrolyte membrane 20 is provided with a recess adapted to the protrusion.

  The electrolyte membrane 20 may be made of a single electrolyte membrane such as Nafion (registered trademark: manufactured by DuPont), as long as it has the above-described convex portion 22. However, the Nafion membrane or a fluorine-based electrolyte membrane equivalent to this has the property that it absorbs alcohol and water and swells, and its surface area tends to increase. For this reason, in the case where the electrolyte membrane 20 is provided with the convex portion 22 having a shape adapted to the concave portions 16 and 36 of the porous catalyst layers 12 and 32, the electrolyte membrane 20 swells and dries due to repetition of power generation and stop of the fuel cell. Due to the effect of the surface area change of the electrolyte membrane 20 being alternately exposed to the state, a gap may be generated between the porous catalyst layers 12 and 32 and the electrolyte membrane 20 during long-term operation of the fuel cell . In addition, there is a possibility that the electrode formed by the MEMS technology may be broken (deteriorated).

  Therefore, as the electrolyte membrane 20 used for the membrane electrode assembly 100 of the present embodiment, it is preferable that the inside of the pores of the porous polymer membrane having the convex portion 22 be filled with the electrolyte polymer. According to the electrolyte membrane 20 in which the electrolyte polymer is filled in the porous base matrix having the heat resistance and the chemical stability, the porous base maintains the strength of the electrolyte membrane 20, and the electrolyte polymer filled in the inside makes hydrogen It can exhibit ion conductivity. Then, since the pores are filled with an electrolyte of several tens to several hundreds of nm or less, the swelling of the electrolyte membrane 20 at the time of water absorption is largely suppressed. For this reason, if the electrolyte polymer 20 is filled with the electrolyte polymer in the pores of the porous polymer film, the electrolyte film 20 is used as the electrolyte film 20 having the convex part 22 in a form adapted to the concave parts of the porous catalyst layers 12 and 32. The swelling of the porous catalyst layers 12 and 32 can be suppressed as a result, and the adhesion between the concave portions 16 and 36 of the porous catalyst layers 12 and 32 and the convex portions 22 of the electrolyte membrane 20 is not impaired. As a result, longer-term operation of the fuel cell is possible.

[Porous polymer membrane]
As the porous polymer membrane, a polyolefin-based membrane having a large number of microspaces (voids) inside thereof and in which the microspaces communicate with one surface and the other surface in the thickness direction is suitably used. The porous polymer membrane having the projections 22 can be manufactured, for example, by plasma etching in the method of manufacturing an electrolyte membrane described later. The projections 22 are formed by the porous catalyst layers 12 and 32 of the electrodes. Since it is necessary to perform proton conduction opposite to the above, at least a part of the surface of the convex portion 22 needs to communicate the fine space with one surface and the other surface in the thickness direction.

  As polyolefin which comprises a polyolefin type porous membrane, polyethylene, a polypropylene, polyethylene-polypropylene copolymer, and these mixtures are mentioned, for example. The polyolefin-based porous membrane preferably includes, from the viewpoint of durability, a polyethylene-based porous membrane containing polyethylene as a main component.

  The polyolefin-based porous membrane may be a stretched porous membrane obtained by stretching a polyolefin-based membrane to make it porous, or it may be an unstretched porous membrane obtained by forming a polyolefin-based membrane in a non-stretched state. Good. Preferably, in terms of mechanical strength, an expanded porous membrane is mentioned. Examples of the stretched porous membrane include uniaxially stretched porous membranes stretched in uniaxial directions, and biaxially stretched porous membranes stretched in biaxial directions orthogonal to each other. Preferably, from the balance of strength, a biaxially stretched porous membrane can be mentioned.

  The polyolefin-based porous membrane may be composed of a single layer polyolefin-based porous membrane. Alternatively, it may be a multilayer porous membrane having a plurality of polyolefin porous membranes, or a multilayer porous membrane having at least one polyolefin porous membrane and another porous membrane. Alternatively, a porous membrane obtained by blending a plurality of polyolefins, or a porous membrane obtained by blending an inorganic substance and a heat resistant resin with polyolefin may be used.

The porosity of the polyolefin-based porous membrane is, for example, 10% or more, preferably 20% or more, and for example, 80% or less, preferably 70% or less. Porosity, providing a sample of the polyolefin porous membrane of 10 cm × 10 cm, and measuring the sample volume (cm ³⁾ and mass (g), "porosity (%) = (1- Weight / It can calculate using the formula of (resin density x sample volume) x 100 ".

  The air permeability (Gurley value) of the polyolefin-based porous membrane is, for example, 1000 seconds / 100 cc or less, preferably 500 seconds / 100 cc or less, and for example, 10 seconds / 100 cc or more, preferably 50 seconds / 100 cc. It is above. Air permeability can be measured by a method in accordance with JIS-P8117.

  The thickness of the polyolefin-based porous membrane is, for example, 1 μm or more, preferably 5 μm or more, and for example, 100 μm or less, preferably 50 μm or less.

[Electrolyte polymer]
Preferred examples of the electrolyte polymer include polymers having one or more electrolyte groups in the main chain and / or side chains, polymers containing an electrolyte such as an acid or a normal temperature molten salt, and the like. One or more of these polymers may be contained. In addition, these polymers may be crosslinked as necessary.

  In addition, the electrolyte polymer may be present as a polymer before being filled into the pores, or after the polymer precursor capable of forming the electrolyte polymer is filled into the pores, polymerization, crosslinking, etc. may occur. It may be used as an electrolyte polymer. The specific filling method of the electrolyte polymer will be described in the manufacturing method of the electrolyte membrane described later.

  As an electrolyte group contained in an electrolyte polymer, acidic groups, such as a sulfonic acid group, a sulfone imide group, a phosphonic acid group, a phosphonous acid group, a carboxylic acid group, are illustrated. One or more of these may be contained. Among these, from the viewpoint of easily obtaining high proton conductivity, a sulfonic acid group can be suitably used.

  As the electrolyte polymer, a perfluorocarbon sulfonic acid based polymer such as Nafion (registered trademark), a perfluorocarbon phosphonic acid based polymer, a trifluorostyrene sulfonic acid based polymer, etc., a fluorine based polymer in which all or part of the polymer skeleton is fluorinated A polysulfone sulfonic acid, a polyaryl ether ketone sulfonic acid, a polybenzimidazole alkyl sulfonic acid, a polybenzimidazole alkyl phosphonic acid, and the like; A group having a group; a monomer having an electrolyte group, a monomer having a functional group that can be converted to an electrolyte group, a monomer having a site capable of introducing an electrolyte group before and after polymerization, an electrolyte comprising a combination thereof Such as a polymer having Nomar as monomer units are exemplified. One or more of these may be contained.

  As a monomer having an electrolyte group, 2- (meth) acrylamido-2-methylpropanesulfonic acid, 2- (meth) acrylamido-2-methylpropanephosphonic acid, styrene sulfonic acid, (meth) allyl sulfonic acid, vinyl sulfonic acid And isoprene sulfonic acid, (meth) acrylic acid, maleic acid, crotonic acid, vinylphosphonic acid, acidic phosphoric acid group-containing (meth) acrylate and the like. In addition, "(meth) acrylic" means "acrylic and / or methacrylic", "(meth) allyl" means "allyl and / or methallyl", and "(meth) acrylate" means "acrylate and / or methacrylate" Do.

  As a monomer which has a functional group which can be converted into an electrolyte group before and after the said superposition | polymerization, the salt of the said compound, an anhydride, ester, etc. are illustrated. When the acid residue of the monomer to be used is a derivative such as a salt, an anhydride, or an ester, proton conductivity can be imparted by converting it to a protonic acid type after polymerization.

  As a monomer which has a site | part which can introduce | transduce an electrolyte group before and behind the said superposition | polymerization, the monomer which has benzene rings, such as styrene, (alpha)-methylstyrene, chloromethylstyrene, t- butylstyrene, is illustrated. In addition, as a method of introduce | transducing electrolyte group into these, the method of sulfonation with sulfonation agents, such as chlorosulfonic acid, concentrated sulfuric acid, sulfur trioxide, etc. are mentioned.

  As these electrolyte monomers, vinyl compounds having a sulfonic acid group, vinyl compounds having a phosphoric acid group, and the like are preferable from the viewpoint of excellent proton conductivity and the like, and more preferably, from the viewpoint of having high polymerizability -(Meth) acrylamido -2- methyl propane sulfonic acid etc.

  From the viewpoint of obtaining high ion conductivity, it is preferable that substantially all of the pores of the porous membrane be filled with the electrolyte polymer. However, not all pores of the porous membrane must be filled with the electrolyte polymer, but if the ion conductivity, fuel permeability and the like are not adversely affected, the electrolyte polymer is filled. Uneven holes may be partially present.

<Method of manufacturing membrane electrode assembly>
Then, the manufacturing method of the membrane electrode assembly 100 of the said structure is demonstrated in detail.

(Method of manufacturing electrode)
The above-described MEMS technology is used to manufacture the electrodes. Specifically, a process of forming the gas flow channels 14, 34 by etching so as not to penetrate one surface of a substrate having a predetermined thickness such as a silicon wafer, and the bottom of the gas flow channels 14, 34 There is a method including the steps of forming the porous silicon layer up to the opposite surface of the substrate to form a porous silicon layer, and supporting a catalyst such as platinum inside the pores of the porous silicon layer.

  The etching in the above electrode forming method may be wet etching or dry etching such as plasma etching. It can be selected appropriately in consideration of the electrode material, the flow path shape and the like.

  When silicon is used as the electrode material, a method of making part of the substrate porous can include an anodic oxidation method and the like. The pore diameter, shape, layer thickness, etc. of the porous silicon layer may be appropriately determined according to the resistivity of the silicon single crystal used, the current density at anodic oxidation, the anodic oxidation time, the composition of the anodic oxidation solution, the concentration, the temperature, etc. It is possible to control by adjusting.

The upper limit of the current density during the anodization, and less likely to occur electropolishing, from the viewpoint of easy to promote pore formation, preferably 10000 A / ^{m 2} or less, more preferably 5000A / ^{m 2} or less, 2000A / ^{m 2} The following is more preferable. On the other hand, the lower limit of the current density in anodic oxidation is preferably 1 A / m ² or more, more preferably 10 A / m ² or more, from the viewpoint that the porosity is not too small.

As the anodizing solution, for example, one or two or more compounds capable of forming a fluorine ion by dissolving in water, alcohol, etc., such as hydrofluoric acid, sodium fluoride, ammonium fluoride, etc., suitable as water, alcohol etc. A solution dissolved in a solvent can be mentioned. The concentration of fluorine ions in the anodizing liquid, typically ^may be a 0.5mol / dm ³ ~25mol / dm 3 approximately.

  The upper limit of the solution temperature of the anodized solution is preferably 25 ° C. or less, more preferably 20 ° C. or less, from the viewpoint of the uniformity of the reaction and the like. On the other hand, the lower limit of the solution temperature of the anodized solution is preferably 0 ° C. or more, more preferably 10 ° C. or more, from the viewpoint of the reaction rate.

  Subsequently, as a method of supporting the catalyst in the pores of the porous layer, plating methods such as electroless plating and electrolytic plating, sputtering method, adsorption of metal colloid and the like can be mentioned. Among these methods, the plating method is preferably used from the viewpoint of being easy to hold the catalyst in the pores, relatively easy to control, and inexpensive as the catalyst supporting method.

  The plating solution used in the plating method can be prepared by dissolving, for example, one or two or more soluble salts containing a catalytic metal to be supported as a constituent element in a suitable solvent such as water. At this time, when silicon is used as the porous layer material, it is preferable to contain fluorine ions in the plating solution using hydrofluoric acid or the like when performing electroless plating.

  A catalyst metal such as platinum having a smaller ionization tendency than silicon receives electrons emitted from silicon, is reduced and spontaneously precipitates, and plating proceeds. However, with the progress of plating, it is conceivable that an insulating film (silicon oxide film) serving as a barrier to the progress of plating is formed on the surface of the hole. Therefore, the formation of the insulating film is suppressed by the presence of the fluorine ions, which facilitates the progress of the plating.

  The upper limit of the solution temperature of the plating solution is preferably 25 ° C. or less, more preferably 20 ° C. or less, from the viewpoint of nuclear growth and the like. On the other hand, the lower limit of the solution temperature of the plating solution is preferably 0 ° C. or more, more preferably 5 ° C. or more, from the viewpoint of the reaction rate.

  Next, a specific example of the method of manufacturing the electrode will be described.

  As a method of manufacturing an electrode according to the present embodiment, for example, (1) patterning of fuel flow channel, (2) formation of porous silicon layer, (3) formation of porous platinum layer, (4) current collector (collector An electrode can be manufactured by the flow of formation of (electrolytic film), (5) formation of a fuel flow path.

As a more specific example, an electrode can be produced by the following procedure.
1. A chip having a predetermined shape is cut out from the silicon wafer with an oxide film by dicing.
2. The cut-out silicon chip is immersed in hydrofluoric acid to remove the oxide film on the surface.
3. A Cu thin film is formed on one side of the silicon chip by vacuum evaporation.
4. A positive photoresist is spin-coated on the deposited Cu thin film and then baked for a predetermined time.
5. A photo mask is placed on the chip, and ultraviolet light is applied from above to perform photolithography. Thereafter, a developer is dropped onto the chip and development is performed for a predetermined time.
6. The Cu in the portion patterned by Fe ₂ Cl ₃ (II) is removed.
7. Remove the photoresist with acetone.
8. The back surface of the surface on which the fuel flow path is patterned is immersed in a hydrofluoric acid solution (water, ethanol, HF mixed solution), and an anodic oxidation is performed by applying a current. Thereby, a porous silicon layer is formed.
9. The porous silicon portion is immersed in a hydrofluoric acid-added platinum plating solution to reform it into porous platinum.
10. An I-type mask is covered on the surface on the catalyst layer side, and Au (current collector layer) is deposited by sputtering.
11. A fuel flow path is formed by plasma etching using Cu as an etching mask. At this time, the porous platinum layer plays a role as an etching stop layer.

(Manufacturing method of electrolyte membrane)
As a method of manufacturing an electrolyte membrane according to the present embodiment, an example of manufacturing a porous polymer membrane filled with an electrolyte polymer will be described. In addition, the electrolyte membrane which concerns on this invention does not necessarily need to have a porous polymer membrane, for example, the case where it forms with electrolyte polymer single-piece is also contained.

[Preparation of porous polymer membrane]
As a method for obtaining a porous membrane, although it varies depending on the material, a method by drawing, a solution or a melt of a membrane material in which a pore forming material is dispersed is coated in a film form, and the solvent is removed by evaporation, A method of forming a film by cooling the film material in a molten state and removing the pore-forming material to form pores, punching, drilling, laser, chemical and physical processes on the film material formed into a film. Method of forming a hole using processing means such as selective etching, After pouring a melt of a film material such as a polymer into a mold capable of transferring the hole, the hole is removed by peeling it off And the like.

  When the material of the porous membrane is a polymer, the most common method is a method by stretching. That is, in this method, a film material such as a polymer and a liquid or solid pore former are mixed by a method such as melt mixing, the pore former is once finely dispersed, and this is extruded from a T die or the like. The pore forming material is removed by a method such as stretching and washing to obtain a porous membrane.

  As a stretching method, there are methods such as uniaxial stretching and biaxial stretching. The shape and the like of the hole can be determined depending on the ratio of stretching, the ratio and type of the pore forming material, the blending amount, the type of the membrane material, and the like.

  When the porous membrane is formed of a hydrophobic polymer material, at least one surface of the surface of the porous membrane may be subjected to a hydrophilic treatment. In the case of impregnating the porous portion with a highly hydrophilic electrolyte material, if the porous film is rendered hydrophilic in advance, the impregnatability into the porous portion is improved, and the productivity of the membrane electrode assembly can be improved. It is from.

  Specifically as a method of the above-mentioned hydrophilic treatment, surfactant treatment, corona treatment, sulfonation treatment, graft treatment of hydrophilic polymer etc. can be illustrated, for example. One or more of these treatments may be used in combination.

[Processing of porous polymer membrane by plasma etching]
The porous polymer membrane is processed so that the porous polymer membrane prepared above is adapted to the recess of the porous catalyst layer formed on the electrode.

  As a processing method of the porous polymer film, for example, various methods such as a method of heat-pressing a portion other than the place where the convex portion is to be formed, a method of performing plasma etching, chemical etching, and sand blast can be considered.

  Here, the projections or depressions of the electrolyte membrane that are compatible with the depressions or projections present in the porous catalyst layer face the porous catalyst layer of the electrode as described in the above [porous polymer membrane]. Since it is necessary to conduct proton conduction, it is required that the fine space be in communication with one surface in the thickness direction and in many directions.

  For this reason, when the convex portion is provided on the surface facing the porous catalyst layer in the electrolyte membrane, the pores on the surface of the convex portion are maintained even if the portion other than the portion where the convex portion is formed is heat-pressed. There is no particular problem. On the other hand, in the case where the concave portion is provided on the surface facing the porous catalyst layer in the electrolyte membrane, when heat pressing is performed on the portion where the concave portion is provided at high temperature and high pressure, the pores on the concave surface are crushed, resulting in proton conduction. There is a limit to the recess formation that can be applied, as it may interfere. In this case, it is preferable to perform plasma etching in which the pores on the surface are easily retained even after the treatment.

  Plasma etching is classified as dry etching. In dry etching, in addition to chemical reactions, ions having high energy collide toward the surface of the sample, and physical forces such as a sputtering effect to repel the workpiece also act. Plasma etching is also called reactive ion etching (RIE).

  When forming a convex part or a concave part in a porous polymer film by plasma etching, a mask of Cu or the like is provided on a part to form the convex part, a part not covered with a mask of Cu or the like is etched, Form.

  As a temperature at the time of performing the said plasma etching, it is preferable to etch at the temperature of less than 110 degreeC. When the temperature is 110 ° C. or more, the porous polymer membrane may be deformed or discolored due to the temperature rise of the porous polymer membrane.

  Further, when etching is performed at a temperature of less than 110 ° C., although it depends on the apparatus, for example, it is preferable to set the etching time per one time to less than 4 minutes as the time for performing plasma etching at 100 W output. Furthermore, it is preferable to carry out processing while cooling the porous electrolyte membrane, for example, by passing cooling water through the inside of a table on which the porous electrolyte membrane is to be installed. Furthermore, in order to enhance the cooling effect between the porous polymer membrane and the table, it is also preferable to interpose an adhesive tape, a low vapor pressure oil or the like between the porous polymer membrane and the table.

[Packing of electrolyte polymer]
The method for filling the electrolyte polymer in the pores of the porous polymer membrane is not particularly limited. A method of impregnating a solution or dispersion of an electrolyte polymer or a molten electrolyte polymer in a pore, a solution or a dispersion of a polymer precursor of an electrolyte polymer, or a molten polymer precursor in a pore, and then And polymer functional groups that can be converted to electrolyte groups after polymerization, and the like, to form an electrolyte polymer.

  As the impregnation method, a method of immersing the porous polymer membrane in the solution or the like, various coating methods (die coating method, comma coating method, gravure coating method, roll, etc.) to the porous polymer membrane Coating methods, such as a coating method, a bar coating method, a reverse coating method, etc. can be mentioned. These may be used alone or in combination of two or more.

  At the time of the above impregnation, if necessary, one or more of a crosslinking agent, a polymerization initiator (photopolymerization initiator, thermal initiator, redox initiator polymerization initiator, etc.), a curing agent, a surfactant, etc. You may add.

  When the polymer precursor is used, the polymer precursor contains at least one or more of the above-described electrolyte monomers. Furthermore, you may contain a crosslinking agent as needed.

  In this case, since a crosslinking point can be formed at the time of formation of the electrolyte polymer, it becomes easy to form a crosslinked body of the electrolyte polymer. Therefore, the insolubility and infusibility of the electrolyte polymer filled in the pores of the electrolyte membrane are improved, and it becomes difficult to drop out of the pores.

  Examples of the crosslinking agent include a compound having two or more polymerizable functional groups in one molecule, and a compound having a polymerizable double bond and another functional group capable of crosslinking reaction in one molecule. it can. One or more of these may be contained.

  Examples of the compound having two or more polymerizable functional groups in one molecule include N, N′-methylenebis (meth) acrylamide, N, N′-ethylenebis (meth) acrylamide, N, N′-propylenebis ( Meta) acrylamide, N, N'- butylene bis (meth) acrylamide, polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, trimethylol propane diallyl ether, pentaerythritol triallyl ether, divinyl benzene, bisphenol di (meth) Crosslinkable monomers such as acrylates, isocyanuric acid di (meth) acrylate, tetraallyloxyethane, triallylamine, diallyloxyacetate and the like can be mentioned.

  Examples of the compound having a polymerizable double bond and another functional group capable of crosslinking reaction in one molecule include crosslinking monomers such as N-methylol acrylamide, N-methoxymethyl acrylamide, N-butoxymethyl acrylamide and the like. be able to. These can be crosslinked by radical polymerization of the polymerizable double bond followed by heating to cause a condensation reaction or the like, or heating can be performed simultaneously with radical polymerization to cause a similar crosslinking reaction.

  The crosslinking agent is not limited to a compound having a carbon-carbon double bond, and although the polymerization reaction rate is somewhat small, a compound having a bifunctional or higher epoxy compound, a phenyl group having a hydroxymethyl group, etc. is also used. It can also be done. When using the said epoxy compound, a crosslinking point is formed by reacting with acids, such as a carboxyl group contained in a polymer.

  The above-mentioned polymer precursor may contain the above-mentioned electrolyte monomer and the above-mentioned crosslinking agent and monomers copolymerized alone or in combination, if necessary. Examples of this type of monomer include (meth) acrylic esters, (meth) acrylamides, maleimides, styrenes, vinyl organic acids, allyl compounds and methallyl compounds. One or more of these may be contained.

  The method of polymerizing the electrolyte monomer contained in the above-mentioned polymer precursor is not particularly limited, and any generally known method can be used. As such a polymerization method, thermal initiators such as peroxides and azo compounds, thermal polymerization using a redox type polymerization initiator, light using a photopolymerization initiator capable of generating radicals by irradiation of light such as ultraviolet rays Examples thereof include polymerization, polymerization by an electron beam, radiation and the like. These may be used alone or in combination of two or more.

  When the electrolyte membrane is produced, the electrolyte polymer and the polymer precursor can be impregnated into the pores of the porous polymer membrane as they are when they themselves are liquid and have a low viscosity. In this case, the preferable viscosity is about 1 to 10000 mPa · s at 25 ° C.

  On the other hand, when it is difficult to impregnate the pores of the porous polymer membrane as it is, a solution in which at least one of an electrolyte polymer and a polymer precursor is dissolved in a suitable solvent, or a suitable dispersion medium It is preferable to use a dispersion dispersed in water. In this case, the preferable viscosity is about 1 to 10000 mPa · s at 25 ° C. The viscosity is a value measured by a B-type viscometer.

  As the solvent and the dispersion medium, aromatic organic solvents such as toluene, xylene and benzene, aliphatic organic solvents such as hexane and heptane, chlorinated solvents such as chloroform and dichloroethane, ethers such as diethyl ether, methyl ethyl ketone, Ketones such as cyclohexanone, esters such as ethyl acetate and butyl acetate, cyclic ethers such as 1,4-dioxane and tetrahydrofuran, amide solvents such as dimethylformamide, dimethylacetamide and N-methyl-2-pyrrolidone, water, Alcohol etc. can be mentioned. One or more of these may be contained. Among these, it is preferable to mainly contain water because it is excellent in handleability, economic efficiency and the like.

  The upper limit of the concentration of the solution or dispersion is preferably 100% by mass or less, more preferably 90% by mass or less, and still more preferably 80% by mass or less from the viewpoint that the higher the concentration, the better the performance. On the other hand, as the lower limit of the concentration of the above solution or dispersion, if the concentration is too low, filling will be insufficient, and if it is not repeated many times, filling will be difficult and productivity will deteriorate, etc. 10 mass% or more is preferable, 20 mass% or more is further more preferable.

  When the electrolyte polymer layer is formed on the surface of the porous polymer membrane when the electrolyte membrane is manufactured, as a method of removing the electrolyte polymer layer, it is made of resin fiber or the like, rubbed with a brush or the like, scraper or the like The method of scraping off etc. can be mentioned. The above method may be performed after being moistened with water or the like, or while washing. These methods may be used alone or in combination of two or more.

(Junction of electrolyte membrane and electrode)
Subsequently, a method of forming a membrane electrode assembly by bonding an electrolyte membrane and an electrode (anode electrode, cathode electrode) will be described. As a method of joining the electrode to the electrolyte membrane, the electrolyte material is not necessarily essential, but is applied to at least one of the surface of the electrolyte membrane and the surface of the porous layer of the electrode, and then the electrolyte membrane A method of sandwiching by an anode electrode and a cathode electrode and heating and pressing by a hot press etc. can be mentioned.

  Examples of the electrolyte material include fluorine-based electrolyte polymers such as Nafion (registered trademark), and ionomers comprising hydrocarbon-based polymers such as polystyrene sulfonic acid, ethylene styrene styrene sulfonate copolymer, and sulfonated polyether sulfone. . These may be used alone or in combination of two or more.

  The heating temperature and pressurizing force at the time of the heating and pressurizing may be appropriately selected in consideration of the material of the porous polymer film, the type of the electrolyte material to be dissolved in the solvent, and the like.

  In general, when the heating temperature or the pressure is excessively high, the porous polymer membrane tends to be deformed or the electrode is likely to be broken. On the other hand, when the heating temperature or the pressing force is excessively low, the adhesiveness tends to be lowered. Therefore, it is preferable to keep these in mind when bonding the electrolyte membrane and the electrode.

<Fuel cell>
The fuel cell according to the present embodiment is manufactured using the membrane electrode assembly described above. In the fuel cell according to the present embodiment, one or two or more of the membrane electrode assemblies may be stacked. As a fuel supplied to the fuel cell according to the present embodiment, hydrogen, alcohols such as methanol, ethanol, propanol, butanol and the like can be appropriately used. On the other hand, oxygen, air or the like can be used as the oxidizing agent supplied to the fuel cell according to the present embodiment.

  EXAMPLES The present invention will be more specifically described below with reference to examples and comparative examples, but the present invention is not limited to these examples.

1. Preparation of Electrolyte Membrane (Example: Electrolyte Membrane Having Convex Portions)
Using Toray Industries, Ltd. polyethylene microporous membrane (SETELA (registered trademark) F30CT1: film thickness 30 μm, Gurley air permeability 300 seconds / 100 cc, porosity 47%, puncture strength 540 gf) as a porous polymer film An electrolyte membrane having a convex portion was produced. First, on one surface of the porous polymer film, a Cu disk with a diameter of 7.5 mm is used as a mask to cover a predetermined position, and oxygen is used as an etching gas (flow rate: 10 sccm). Made by: RIE-10N), plasma etching was performed for 6 minutes and 40 seconds as an accumulated time divided into two times so that the etching time per time was less than 4 minutes, and the output time was 100 W. After completion of the first etching, the etching gas was stopped and cooling for 5 minutes was performed, and then a second etching was performed.

  In addition, it is known that the maximum depth of the hollow portion of the porous catalyst layer is about 4 μm as an electrode to be used in the present embodiment by preliminary examination, and the porous height used in the present embodiment In order to reduce the thickness of the molecular film by about 4 μm by plasma etching, it has been found that about 6 minutes and 40 seconds is appropriate as the cumulative time for etching.

  In the porous polymer film plasma-etched under the above conditions, no dimensional deformation or deterioration (opaque) was observed. Further, it was confirmed by the micrometer that the film thickness of the outer side of the diameter 7.5 mm masked by the Cu disk was reduced to a depth of 4 μm.

  Subsequently, plasma etching was performed on the other surface of the porous polymer film in the same manner to have a convex portion with a diameter of 7.5 mm and to reduce the film thickness around it to 4 μm. The top view of the porous polymer membrane (the modified porous polymer membrane) having the convex portion obtained as described above is shown in FIG. 2A and the front view is shown in FIG. 2B. From the above, a convex porous membrane having a diameter of 7 and 5 mm was formed on both sides of the porous polymer membrane at the in-plane central portion of the porous polymer membrane, and a modified porous membrane was produced with the periphery reduced by 8 μm thickness on both sides.

  Subsequently, the prepared modified porous membrane is subjected to a hydrophilization treatment with an aqueous solution of SDS (Sodium Dodecyl benzenesulfonate), and then a crosslinking agent (N, N) is used as an aqueous solution of AMPS (2-Acrylamido-2-methylpropan Sulfonic Acid) and SDS. -Low temperature immersion in a solution to which an aqueous solution of -Methylenebis acrylamide) and AAAPH (2,2'-Azobis (2-methylpropionamidine) dihydrochloride) is added, followed by standing at 60 ° C for 16 hours, washing with water and then immersion in 1 M sulfuric acid As a proton-type variant electrolyte membrane.

Comparative Example: Flat Electrolyte Membrane Having No Convex Portions
A flat proton electrolyte membrane was prepared in the same manner as in the example except that the above-mentioned porous polymer membrane was not subjected to plasma etching.

2. Preparation of Electrode As a sample, an n-type silicon wafer with an oxide film was prepared which had a thickness of 110 ± 10 μm, a resistivity of 0.001 to 0.003 Ωcm, and a (100) surface mirror-polished on both sides. Note that a silicon electrode having a low resistivity is used to have a function as a current collector.

  First, a 15 mm × 15 mm chip was cut out from a silicon wafer with an oxide film by dicing. The cut-out silicon chip was immersed in 46% HF for 90 seconds to remove the oxide film on the surface.

  A Cu thin film (thickness: about 100 μm) was formed on one side of the silicon chip by vacuum evaporation. Next, a photoresist (“OFPR-800 LB” manufactured by Tokyo Ohka Kogyo Co., Ltd.) was applied to the surface of the Cu thin film to form a resist film (thickness: 50 μm).

  Next, a photomask with a linear flow path pattern with 100 μm and 200 μm pitches for the mask width and the opening width (flow path spacing is 100 μm for the convex and concave portions, respectively) in a 1 mm × 4 mm area at the center of the wafer. The resist pattern was placed, exposed to ultraviolet light to expose the flow path pattern, and then developed to form a resist pattern.

  Furthermore, after removing Cu along the above resist pattern using a 42 ° Bome (about 48% by weight) ferric chloride solution, the above resist pattern was removed using acetone. Thus, a Cu mask pattern was formed on the surface of the silicon wafer.

Subsequently, the back side of the silicon wafer having a Cu mask pattern formed on the surface is brought into contact with a mixed solution of ultrapure water, hydrofluoric acid (purity 46 mass%) and ethanol mixed at a mass ratio of 5: 3: 2. The Then, anodization was performed by applying a current at a liquid temperature of 10 ° C. and a current density of 70 mA / m ² for 390 seconds with the silicon wafer as an anode. Thereby, a porous layer was formed in a range of about 10 μm in depth from the back surface of the silicon wafer.

Next, the porous layer was treated with a plating solution (1.0 MH ₂ SO ₄ + 20 mM) at a solution temperature of 20 ° C.
The substrate was immersed in H ₂ PtCl ₄ +300 mM HF), the plating solution was slowly stirred, and electroless plating was performed for 15 minutes. Thus, the platinum catalyst was supported in the pores of the porous layer. The cross section of the silicon wafer after formation of the platinum catalyst was observed by SEM.
It was deposited in layers throughout the porous layer. Also, the platinum catalyst was mainly deposited in the range of about 7 μm in depth from the back surface of the silicon wafer.

  Then, an I-type mask was covered on the surface of the formed porous catalyst layer, and Au was deposited by sputtering to form a current collector layer.

Finally, using the above-mentioned Cu mask pattern, plasma etching silicon along this pattern to form a reaction area (a porous platinum layer and a current collector layer on the back of the surface on which the porous platinum layer of the catalyst layer is formed). The gas flow path to reach it was formed. The etching conditions were: etching time: about 100 minutes, gas flow rate: SF6: 12 sccm, O ₂ : 5 sccm, RF power: 50 W, vacuum value: 2.2 to 2.8 Pa. Thereby, the gas flow path in which each flow path bottom part was in contact with the porous layer was formed.

  Thus, the porous catalyst layer on which the platinum catalyst is supported, the current collector layer formed so as to overlap a portion of the porous catalyst layer, the opposite surface of the porous catalyst layer surface side and the porous catalyst layer A plate-like silicon electrode having a communicating gas flow path was obtained.

3. Production of Membrane-Electrode Assembly The electrodes produced above were joined to both sides of the variant electrolyte membrane having the convex portion produced above. First, the porous catalyst layer surface of the electrode prepared above was immersed in isopropanol, and Nafion solution (5% Nafion solution: isopropanol = 1: 6) was applied to the surface of the porous catalyst layer. Subsequently, the modified electrolyte membrane prepared above was dipped in the above-mentioned Nafion solution, and then this electrolyte membrane was sandwiched between two electrodes and hot pressed at 100 ° C. for 30 minutes under a pressure of 0.24 MPa. Thus, a membrane electrode assembly according to the example having a thickness of 230 μm was produced.

  Further, a membrane electrode assembly according to a comparative example was produced in the same manner for the flat electrolyte membrane produced above.

4. Power generation test Each fuel cell using each of the membrane electrode assembly according to the example and the membrane electrode assembly according to the comparative example, in an aluminum jig in which a channel for supplying hydrogen and oxygen serving as fuel is dug The spring pressure was applied to ensure electrical continuity. In addition, since the fuel cell needs to insulate the anode side from the cathode side, the metal contact portion is insulated using a masking tape. After this fuel cell was set in a constant temperature bath, air was flowed through the flow path layer of the cathode electrode and hydrogen was flowed through the flow path layer of the anode electrode to conduct a power generation test. The operating conditions were a hydrogen flow rate of 10.0 sccm, an air flow rate of 5.0 sccm, and a temperature in the thermostatic chamber of 40 ° C.

FIG. 3 is a graph showing cell voltage, current density and power density characteristics in the fuel cell according to the example, and FIG. 4 is a graph showing cell voltage, current density and power density characteristics in the fuel cell according to the comparative example Indicates In the fuel cell according to the example, as shown in the result of FIG. 3, the maximum power density of 1050 mW / cm ² could be obtained. On the other hand, in the fuel cell according to the comparative example, as shown in the result of FIG. 4, the maximum power density was 180 mW / cm ² .

DESCRIPTION OF SYMBOLS 10 anode electrode 12, 32 porous catalyst layer 14, 34 gas flow path 16, 36 recessed part 18 anode side current collection layer 19, 39 current collector layer 20 electrolyte film 22 convex part 30 cathode electrode 38 cathode side current collection layer 100 film Electrode assembly

Claims (8)

A membrane electrode assembly in which an anode electrode is bonded to one surface of an electrolyte membrane and a cathode electrode is bonded to the other surface,
At least one of the anode electrode and the cathode electrode is formed in at least a partial region of the overlapping surface with the electrolyte membrane, and the opposite of the overlapping surface with the porous catalyst layer supporting the catalyst and the electrolyte membrane A gas flow path communicating the surface with the porous catalyst layer,
The electrolyte membrane has a convex portion that fits into the concave portion when the porous catalyst layer has a concave portion, and has a concave portion that fits into the convex portion when the porous catalyst layer has a convex portion. A membrane electrode assembly characterized in that.   The membrane / electrode assembly according to claim 1, wherein the electrolyte membrane is one in which pores of a porous polymer membrane are filled with an electrolyte polymer.   A fuel cell using the membrane electrode assembly according to claim 1 or 2. It is an electrolyte membrane used for the membrane electrode assembly of Claim 1 or 2, Comprising:
The electrolyte membrane has a convex portion that fits into the concave portion when the porous catalyst layer has a concave portion, and has a concave portion that fits into the convex portion when the porous catalyst layer has a convex portion. An electrolyte membrane for membrane electrode assembly characterized by the above.   5. The electrolyte membrane for membrane electrode assembly according to claim 4, wherein the electrolyte membrane is one in which pores of a porous polymer membrane are filled with an electrolyte polymer. It is a manufacturing method of the electrolyte membrane for membrane electrode assemblies according to claim 5,
Forming the recess or the protrusion in the porous polymer film by plasma etching;
Filling the electrolyte polymer in the porous polymer membrane in which the concave portion or the convex portion is formed, and a method of manufacturing an electrolyte membrane for a membrane electrode assembly.   7. The method for producing an electrolyte membrane for a membrane electrode assembly according to claim 6, wherein the etching is performed at a temperature of less than 110 ° C. as a temperature at which the plasma etching is performed. A process of producing an electrolyte membrane using the method of producing an electrolyte membrane for membrane electrode assembly according to claim 6 or 7;
And D. sandwiching the obtained electrolyte membrane between the anode electrode and the cathode electrode and hot-pressing the obtained electrolyte membrane.

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