JP2007242407A - Solid polymer electrolyte membrane type cell, and its component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a component being a component constituting a solid polymer electrolyte membrane type cell, that is, a fuel cell or a water electrolysis-fuel cell reversible cell, facilitating assembly work of a cell stack by forming, into an integrated component, a reaction gas/water diffusing body and a separator/bipolar plate, and capable of preventing increase of contact resistance between the components. <P>SOLUTION: This component of the cell is composed by stacking the reaction gas/water diffusing body on the separator/bipolar plate and integrating them with each other by diffusion joining. It is preferable that a nonconductor coating film of a metal oxide is formed on surfaces of the reaction gas/water diffusing body and the separator/bipolar plate by executing at least one kind of treatment within an electrolysis anode treatment, a chemical treatment, and a heat treatment in an air or oxygen atmosphere after the diffusion joining. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a component of a solid polymer electrolyte membrane type (hereinafter abbreviated as “solid polymer type”) cell, which is a reaction gas / water diffuser (hereinafter simply referred to as “diffuser”) and a separator / bipolar. The present invention relates to improvement of a laminate with a plate (hereinafter simply referred to as “separator”), and also relates to a polymer electrolyte fuel cell assembled using this component.

As shown in FIG. 1, a solid polymer type cell, typically a fuel cell, basically has one MEA (Membrane Electrode Assembly), two separators / bipolar plates, Consists of two reaction gas / reaction liquid diffusers, two power supply plates, two insulating plates and two end plates, or one MEA, two separators / bipolar plates It consists of one reactant gas / reaction liquid diffuser, one metal insoluble electrode, two power supply / current collector plates, two insulating plates, and two end plates.

By stacking one MEA, two separators / bipolar plates and two reaction gas / reaction liquid diffusers using the above components, or one MEA, two separators For example, a single cell of a fuel cell is formed by stacking a bipolar plate, a reactant gas / reaction liquid diffuser, and a metal insoluble electrode. A plurality of single cells are stacked to form a cell stack. A power supply / current collector plate, an insulating plate, and an end plate are arranged at both ends of the cell stack, and the bolts provided on the end plate are tightened to form the shape. The fuel cell is configured in the manner of maintaining.

In the cell configuration, an example in which an MEA and a diffuser are integrated can be seen (Patent Document 1). However, this type of cell including a fuel cell basically has a threshold of MEA or electrolyte membrane. An electrochemical reaction apparatus having two isolated reaction chambers between two separators / bipolar plates, with two electrodes so that the reactant / product can be handled in the case of gas A structure in which at least one of them is a gas diffusion electrode is more general.

In addition to various fuel cells, solid polymer type cells having such a structure include water electrolysis cells, reversible cells (integrated fuel cells and water electrolysis cells, “integrated renewable fuel cells” URFCS and Cell) for dehumidification, cell for oxygen concentration in air, cell for soda electrolysis with oxygen cathode, cell for on-site ozone or hydrogen peroxide production, and nitrous acid gas, Freon gas, carbon dioxide It is an electrochemical cell that is expected to have a wide variety of uses, such as an electrochemical cell for processing.

In these polymer electrolyte cells, if the scale of the cell is increased by increasing the size of the single cell, the restriction on the processing accuracy associated with the increase in the size of the component will increase, and the components will be uniform when tightened. We encounter problems such as difficulty in obtaining contact. Scale-up by increasing the size of a single cell also increases the electrolysis current and power generation current for each single cell. As a result, the efficiency of the entire system decreases due to an increase in voltage drop and a decrease in rectification efficiency of the power supply. There is also the problem of doing. Therefore, as shown in FIG. 1, it is usual to scale up with a cell stack in which a plurality of single cells are stacked.

The formation of transport paths for reactants and products / by-products in single cells and stacks of such polymer electrolyte cells is an “external manifold system” in which an external introduction path is provided for each cell. Or a space formed by stacking openings provided in the constituent members is used as a main line of the header pipe structure, and a mechanism for branching out of each single cell from there is provided in the cell. According to one of "method". Usually, an internal manifold system is selected which is advantageous in terms of cost reduction and space saving due to simplification of the structure.

In the internal manifold system, the reactants supplied from the outside first flow into the cell chambers from the flow dividing mechanism provided in each cell through the internal manifold, and pass through the flow path provided on the separator. Since the reactant fluid flows out to the diffuser side and permeates there to reach the electrode surface, two or more kinds of reaction fluids are formed in the two isolated reaction chambers formed in the cell as described above. When supplying different reactants, it is necessary to provide an internal manifold for each chamber. Basically, a total of four openings are provided for the entrance and exit of the reaction gas A and the entrance and exit of the reaction gas B. However, when the reaction system is exothermic and the introduction of coolant is necessary, When the number of cells reaches several tens to several hundreds, it is necessary to additionally provide an internal manifold for the cooling system entrance / exit.

When stacking dozens to several hundreds of such solid polymer cells, it is important to stabilize quality by simplifying the stacking work and improving the reliability of the work, For this purpose, it is basically an advantageous measure to reduce the number of parts of the cell component as much as possible.

In the scale-up of polymer electrolyte cells by stacking, if the number of cells to be stacked is increased, the required quantity of separator / bipolar plate and reaction water / reaction gas diffuser, which are basic components of the cell, Naturally it will increase. Therefore, in order to reduce the cost of the solid polymer cell, it is important to reduce the manufacturing cost of each separator / bipolar plate and reaction water / reaction gas diffuser.

In general, a separator of a polymer electrolyte cell is provided with an opening (a) for forming an internal manifold and a plurality of concave and convex portions (b) shown in FIG. Of these, the concave portion is usually called a “channel” and functions as a flow path that promotes a uniform flow of the reaction gas / reaction water flowing from the internal manifold to the entire electrode surface. Usually formed by a channel. On the other hand, the convex portion is responsible for electronic conduction and thermal conduction between the separator and the diffuser, and functions as an energization and heat transfer surface. In the following description, this convex portion is referred to as a “contact portion”.

Such flow paths and electrical contact parts can be selected from known processing techniques such as mechanical cutting, cold pressing and superplastic pressing, sand blasting and chemical etching, electrolytic polishing, resin molding, etc. Can be formed.

In order to fully perform the functions of the flow path and the electric contact portion provided on the separator, first, the reactant is uniformly distributed to each channel with respect to the flow path, and the product and by-products are discharged. Therefore, there is a demand for a structure that can smoothly perform the above. For this purpose, design of dimensions such as the shape, depth, and width of the flow path is appropriate, and high processing accuracy for realizing it is required. The simplest as to the shape of the flow path is a parallel channel type in which the respective channels are arranged in parallel as shown in FIG. 2, but a device for further improving the function has been proposed (Patent Documents 2 and 3). ), A number of techniques for realizing complicated processing with high accuracy and low cost have been disclosed (Patent Documents 4 to 6).

The separator also needs to have a threshold value so that the gas as a reactant and the water as a reaction product are not mixed between adjacent cells constituting the stack. If a metal plate is used as a separator, or if a metal thin film layer is formed on the separator surface, there will be no problem because sufficient threshold is secured by itself, but resin molded products and graphite materials are used. In this case, a gas impermeability treatment is necessary particularly for the purpose of reducing the gas permeation amount. Although the technology is also disclosed (Patent Document 7), it is generally more preferable to use a metal material or a material coated with a metal thin film than a graphite-based material. Threshold can be easily provided.

On the other hand, the separator has a property in which the solid polymer electrolyte membrane itself exhibits weak acidity or strong acidity, or weak alkalinity or strong alkalinity during operation or stoppage, or a reactant supplied into the cell, Corrosion, pitting, and elution may occur due to exposure to impurities, reaction products and by-products, and supplied water vapor. Also, one of the two separators constituting each cell (one side when the separator is applied as a bipolar plate) is polarized to the anode potential during or before operation. In such an environment, if a separator made of an inappropriate material is used, metal ions and metal oxoacid ions are eluted from the separator and are captured by the electrolyte membrane, or are formed from metal oxides and water formed from the metal ions. Oxide adheres to the electrolyte membrane to increase the resistance of the electrolyte membrane, which greatly reduces the performance of the solid polymer cell. Ultimately, the separator itself corrodes and collapses, or stress corrosion cracking occurs due to the cell clamping force, so that the solid polymer cell itself becomes unusable.

In order to cope with this problem, the separator material is required to have acid resistance or alkali resistance, corrosion resistance, and anode resistance at the same time. If the anode potential is 0.8 to 1.0 V (vs. NHE) or less, graphite, valve metals other than Ti and Ti, Ti alloys and oxides, nitrides, silicides and carbides, Al and Al alloys, Al oxide, stainless steel, Ni-based alloy, etc. may be used, but separator materials that can be used in an environment exceeding 1.0 V (vs. NHE) are Ti and other valve metals in an acidic environment, Almost limited to Ti alloys, Ti oxides, nitrides, silicides and carbides, and Al oxides. Even in an alkaline environment, Ni and Ni-based alloys can be used in addition to the materials that can be used in the acidic environment.

In the contact portion on the separator, it is important to ensure electronic conductivity as described above. In order to ensure electronic conductivity, in addition to using metal moldings and graphite, the use of resin molding materials impregnated with conductive powder (Patent Document 8), the resin molding matrix proposed by the applicant There is also one in which a conductive material is coated thereon by electroless plating or sputtering (Patent Document 9). The electrical resistance of the separator itself depends on the specific resistance of the metal used, and sufficient electronic conductivity is ensured in the separator having a thickness of usually 1 cm or less. The place where the electronic conductivity of the separator is determined is the contact portion between the separator and the diffuser shown in FIG. 3, and the contact resistance between the two is a problem.

The contact surface is also placed in the environment described above. If the electron conducting medium of both the separator and the diffuser is a graphite-based material, the non-conductive film is not formed, so the contact resistance of the contact portion does not increase over time, but the contact portion of the separator, or When one or both surfaces of the diffuser are made of metal, a non-conductive film is formed over time, and the contact resistance increases with the growth. In valve metals such as Ti and their alloys, their oxides are semiconducting, so when they are arranged on the anode side, they finally show insulation properties, and when Al is used, the oxides Since it is an insulator, it exhibits insulating properties when it is arranged on either the anode side or the cathode side, and the progress of the electrochemical reaction in the cell is hindered.

Thus, when a metal is selected as the material for the solid polymer type separator, the acid resistance, alkali resistance, corrosion resistance, and anode resistance are improved, and at the same time, the gap between the diffuser due to the growth of the nonconductive film is improved. It is necessary to suppress an increase in contact resistance. From this point of view, a noble metal such as Au, Pt, Ir, Ru, Ag, an alloy thereof, or an oxide thin film layer is formed by electroless plating, electroplating, or sputtering on the flow path portion, contact portion, or the entire surface of the separator. Or a method of forming a conductive coating such as graphite or Ti-based powder material has been devised (Patent Documents 10 to 12).

Among the above methods, the formation of the noble metal thin film layer is a technique that has been practiced for a long time in the formation of contact parts of electronic components and electrode thin films of alkaline electrolysis devices. Although it can be said that it is a very effective technique for improving the property and ensuring the electronic conductivity, the problem is an increase in cost due to the use of an expensive noble metal on the separator. As a countermeasure, there is a technique for reducing the cost by making the noble metal thin film layer thinner and reducing the amount of noble metal used (Patent Documents 13 and 14).
Japanese Patent Application No. 2002-295311 USP 5454666 JP2004-158379 JP 2000-236881 JP2003-242994 JP 2004-119346 A JP 2001-85032 A JP 2002-289217 A JP 2003-36867 A JP2000-21419 JP 2004-31166 A JP 2004-235091 A JP 2001-297777 A JP 2004-265695 A

When forming a conductive coating film with a conductive powder material, if noble metals such as Au and Ag are used for the conductive carrier, the use of noble metals increases the cost. Compared with sputtering and plating, the use of noble metals is reduced. Since it is difficult to reduce the amount, graphite-based materials, which are other non-noble metal materials with relatively high acid resistance, alkali resistance, corrosion resistance, and anode resistance, and powder materials of Ti-based alloys are used as conductive carriers. Ingenuity to use is made.

However, polymer electrolyte fuel cells have been developed for distributed vehicles and homes, and if this type of fuel cell comes to market, even if recycling is taken into consideration, The number of separators required in the global market will be enormous, exceeding several hundred million. Applying precious metal coating, which is a precious resource, to the separator that is considered to require the largest area of the solid polymer cell component, it is possible to increase the price of precious metal and deplete resources in the future. It is clear that it is inevitable and unwise. In addition, it is difficult to achieve a pinhole-less coating when forming a noble metal thin film. If a pinhole occurs, the corrosion of the substrate is caused by water vapor, air, oxygen, etc. reaching the substrate metal plate from there. There is also a concern that the growth of the non-conductive film progresses and the noble metal coating layer eventually peels off.

On the other hand, the formation of a coating film using a graphite-based material or a Ti-based alloy powder material as a conductive carrier is an advantageous technique in that no precious metal is used, but the coating film is a porous film formed by a collection of powders. Therefore, the presence of pinholes is unavoidable, and there is also a concern that non-conductive film growth of the substrate may occur and the covering layer may fall off, and since the conductive support is not a noble metal, noble metal coating was applied. As compared with the separator, a problem remains in anode durability in an environment of a high anode polarization voltage exceeding 1.0 V (vs. NHE).

In general, the object of the present invention is to reduce the number of cell components in order to simplify the stacking work in a polymer electrolyte cell in which dozens to hundreds of single cells are stacked. An object of the present invention is to provide a component of a solid polymer type cell. More specifically, the object of the present invention is excellent in acid resistance or alkali resistance, corrosion resistance, and anode resistance, and can prevent an increase in the contact resistance between the separator and the diffuser caused by the growth of the nonconductive film, In addition, it is possible to significantly reduce the amount of noble metal used, and in particular, an inexpensive separator / solid polymer cell that does not require coating of a noble metal or a conductive coating on the separator. It is to provide a laminated integrated part of a diffuser.

The separator / diffusion body laminate of the present invention that achieves the above object comprises a reaction gas / water diffusion body, which is a constituent member of a solid polymer electrolyte membrane cell, and a separator / bipolar plate, and diffusion. It is the component of the cell obtained by integrating by joining.

As is well known, diffusion bonding is the contact of members while supplying energy to the surface of the member by applying heat, ultrasonic waves, high frequency or vibration in a state where two components are in contact with each other. This is a processing method in which both members are mixed by diffusion at the joining portion by applying pressure to the surface, and an integrated structure is formed and joined, thereby realizing joining below the melting point of the constituent members. For this reason, a joined part that is welded at a low temperature is obtained, and in the surface layer part of the joined metal part, free electron clouds are overlapped between the constituent members, thereby ensuring electronic conductivity. Therefore, it is possible to conduct electrons between the separator and the diffuser in the metal bulk of the joint, and it is difficult to be affected by the growth of the non-conductive film that is likely to occur in the metal surface layer portion, and has a stable electron conductivity. And a diffuser stack can be obtained.

A cell component produced by stacking and integrating a separator and a diffuser manufactured according to the present invention is excellent in acid resistance, alkali resistance, corrosion resistance, and anode resistance, and does not increase contact resistance even when used for a long time. Since no precious metal is used or even if it is used, the amount of the precious metal is small, the manufacturing cost is low, and there is no problem of resources. If a solid polymer cell is assembled using these components, the separator and diffuser are already integrated, so the number of components can be reduced and the production cost of the solid polymer cell can be reduced. It can be kept low.

In a preferred embodiment to be described later, in the cross section of the separator part, the diffuser part, and the contact part of the component, the material having the base material layer, the protective layer by the nonconductive film, and the electron conduction functional band shown in FIG. The structure can be realized, and the acid resistance, alkali resistance, corrosion resistance, and anode resistance are further improved, and the increase in the contact resistance between the separator and the diffusion layer caused by the growth of the nonconductive film can be prevented.

Conductivity is imparted to the surface on the side opposite to the joint to the diffuser after joining or before joining the cell component in which the separator and diffuser of the present invention are laminated and integrated. If the processing is performed, high electronic conductivity between the separator and the MEA can be ensured even when the solid polymer cell having the structure shown in FIG. 1 is formed.

By applying at least one treatment of electrolytic anodic treatment, chemical solution treatment, water vapor atmosphere treatment, and heat treatment in air or oxygen atmosphere to the component obtained by the above-described process for imparting conductivity, the diffuser and By forming a non-conductive oxide film on the separator surface where no electrical conductivity is required and using this as a protective layer, it is possible to make the laminate have acid and alkali resistance, corrosion resistance, and anode resistance. is there. In this case, although a non-conductive film is formed on the surface layer of the junction between the separator and the diffuser, the electron conduction between the separator and the diffuser is performed within the metal bulk of the junction, Electronic conductivity is not hindered.

In accordance with the present invention, the process of manufacturing the component part in which the separator and the diffuser are laminated and integrated is as shown in the upper to middle stages of FIG. To manufacture a laminate, first select a metal material available on the market, such as valve metals such as Ti, Ta, and Nb, alloys thereof, Al and alloys thereof, stainless steel, or Ni-based sulfuric acid-resistant steel. A separator member having a flow path, a contact portion, and a manifold opening having the above-described shape is prepared by mechanical cutting, cold pressing and superplastic pressing, sand blasting, chemical etching, and electrolytic polishing.

For such a separator material, a metal is easy to use, but even if it is not a metal, a coating of a conductive metal material by electroless plating or sputtering on the resin molded base material according to the applicant's proposal, Any material can be used as long as it is applied to the contact surface of the separator corresponding to the junction with the diffuser. Similarly, when a graphite material is used as a separator material, a conductive metal material coating by electroless plating or sputtering is applied to at least the contact surface of the separator that contacts the diffuser. If it is, it can be used.

On the other hand, as a diffuser which is another member of this component, a metal fiber manufactured from valve metals such as Ti, Ta, Nb, alloys thereof, Al and alloys thereof, stainless steel, nickel-based sulfuric acid-resistant steel, etc. A non-woven fabric, a sintered metal powder, expanded metal, or micromesh, and a porous body obtained by combining and joining two or more of them can be used.

By using a porous material such as commercially available carbon paper or carbon cloth as a base material, and by coating the conductive metal material described above on one side of the base material by a method such as electroless plating, electroplating, sputtering, A diffuser that can be used by being joined to a separator is obtained.

Similarly, a polymer porous material such as a filter material for a filter made of foamed polyurethane, polyethylene, or polypropylene, or a material obtained by laminating and welding them is used as a base material, and it is electroless. Plating, electroplating, sputtering, etc., so that the conductive metal material described above exists on both surfaces of the base material and the entire surface in the hole, should also be used for joining to the separator. Can do.

Finally, one or two separators prepared as described above and one or two diffusers are laminated and applied with appropriate pressure in air or, if necessary, vacuum or N ₂ or Ar In such an inert gas atmosphere, by integrating by diffusion bonding using any one of heat, ultrasonic waves, high frequency or vibration as an energy source, the cell component of the present invention can be obtained.

In practicing the present invention, it is desirable that the combination of the separator, the diffuser, and the metal material covering the surface thereof is basically the same material from the viewpoint of enabling the joining process to be performed easily and reliably. When alloy materials are used for one or both, it is desirable that at least their main components match. It is preferable that both materials have a coefficient of thermal expansion as close as possible, but if the difference is within 10%, it is possible to avoid voids in the joint portion or distortion due to temperature rise and fall, Good bonding can be obtained.

In the case where the properties of the material of the separator and the diffuser cannot be substantially matched, and thus there is a risk of causing poor bonding, either the separator or the diffuser is made of a metal having the same main component, Alternatively, the bonding state can be effectively improved by coating with a metal that has a difference in thermal expansion coefficient within 10% and bonding after forming a thin film layer having a thickness of 0.5 to 2 μm.

As a material of the separator and the diffuser, when performing the present invention using a valve metal such as Ti, Ta, Nb, Al and its alloys, or stainless steel, when a bonding failure occurs, the cause is as follows: It is conceivable that a strong non-conductive film is formed on one or both of the separator and the diffusion member before the bonding treatment. In order to ensure the bonding process using the above materials, it is effective to perform pretreatment such as sandblasting, chemical etching, electrolytic polishing, electrolytic degreasing on one or both of the separator and the diffuser Is.

When the components of the cell obtained by diffusion bonding are to have better acid and alkali resistance, corrosion resistance, and anode resistance, Ti, as a material for the separator, the diffusion body itself, and its coating layer, in particular, Valve metal such as Nb, Ta or Al or its alloy is selected, and the obtained joined body is subjected to treatment such as electrolytic anodic treatment, oxidant chemical treatment, steam atmosphere treatment, heat treatment in air or oxygen atmosphere, etc. It is recommended that a dense and strong non-conductive oxide film be formed on the surface of the material by performing any one or a combination thereof. The pattern is as shown from the middle to the bottom of FIG.

The step of imparting electron conductivity to the surface layer of the diffuser portion on the side opposite to the bonded portion of the obtained laminate can be performed without any problem as long as it is performed by any of the following methods. One of them is Pt, on the surface opposite to the bonding surface with respect to the diffusion body before the bonding process, in which a metal thin film is formed on a metal porous body, a carbon porous body, or a plastic porous body. That is, a precious metal such as Ir, Ru, Au, Ag, or a material made of Ni and an alloy thereof is coated in advance using a technique such as electroless plating, electrolytic plating, or sputtering.

The other is that the components obtained as described above, or those subjected to further non-conductive oxide film formation treatment, are sandblasted, electrolyzed on the surface opposite to the junction of the diffuser. After polishing, chemical etching, etc., according to a known technique, a precious metal such as Pt, Ir, Ru, Au, Ag or Ni and its alloy is coated by electroless plating, electrolytic plating, sputtering. . However, when a partial conductive treatment is performed on the surface of the diffuser after the bonding treatment, it is necessary to mask a portion unnecessary for the treatment with a tape or to perform a strict masking using a photoresist. Therefore, it is a good idea to conduct conductive treatment on one side of the diffuser in advance before joining.

In addition to the above-described method, the surface of the diffuser may be treated by using Ti nitride, silicide, carbide or boride as the diffuser material, or these Ti compounds may be used in commercially available Ti materials. It is possible to use a material in which a porous body made of a material is bonded, or a method in which the surface layer of a porous material made of Ti is previously formed as a nitride, silicide, carbide or boride by a reactive sputtering method. It is.

The cross section of the contact part of the cell component obtained according to the present invention and the flow of electrons there are as shown in the upper part of FIG. On the other hand, the cross section of the cell stack and the flow of electrons in the cell stack when the diffusion bonding according to the present invention is not performed are as shown in the lower part of FIG. It can be seen from this figure that a non-conductive coating can occur and contact resistance can increase.

The typical expanded view which shows the typical structure of a solid polymer electrolyte membrane type cell. The perspective view which shows the shape of the separator / bipolar plate used for the cell of FIG. 1, and the enlarged view of a part of cross section. The perspective view and the enlarged view of the one part cross section which show the location where contact resistance arises between a separator / bipolar plate and a reaction gas / water diffuser in a cell. Process drawing explaining the process of carrying out the process of manufacturing the component of a cell by laminating | stacking and integrating a separator / bipolar plate and a reactive gas / water diffuser, and the process of making a non-conductor. It is a figure explaining the mechanism in which the effect of this invention arises, Comprising: The upper stage shows the case where this invention is implemented, and the lower stage does not implement, respectively.

Claims (4)

A component of the cell obtained by laminating a reaction gas / water diffuser of a solid polymer electrolyte membrane cell and a separator / bipolar plate and integrating them by diffusion bonding. The component of the cell according to claim 1, wherein the surface of the reaction gas / water diffuser is coated with a noble metal or a conductive paste to ensure conductivity on the surface side of the reaction gas / water diffuser. After integrating by diffusion bonding, reactive gas / water diffuser and separator / bipolar plate are obtained by performing at least one of electrolytic anodic treatment, chemical treatment, steam atmosphere treatment, and heat treatment in air or oxygen atmosphere. 3. A cell component according to claim 1 or 2, wherein a non-conductive film of metal oxide is formed on the surface of said metal oxide. A solid polymer electrolyte membrane cell configured using the cell component according to claim 1.

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