JP5302137B2 - Gas diffusion layer material for polymer electrolyte fuel cells - Google Patents

Description

  The present invention relates to a gas diffusion layer material used for a polymer electrolyte fuel cell.

  A fuel cell is one in which fuel (hydrogen, etc.) and air (oxygen) are continuously supplied to different electrodes, and they are electrochemically reacted using a catalyst contained in the electrodes. A system that generates electrical energy. In addition, depending on the type of electrolyte used in the fuel cell, the alkaline electrolyte type, phosphoric acid type and solid polymer type having a relatively low operating temperature, and the molten carbonate type and solid oxide electrolyte type having a high operating temperature are used. It is divided roughly into. Among these various fuel cells, in particular, in a fuel cell using a solid polymer electrolyte (solid polymer fuel cell), the operating temperature is close to room temperature, and the size, thickness and weight are reduced. Therefore, it is expected to be applied to portable devices and fuel cell vehicles.

  Here, the polymer electrolyte fuel cell has a structure in which a polymer electrolyte / electrode assembly is sandwiched between separators engraved with a reaction gas supply channel as a basic unit (single cell). It is configured by stacking single cells and connecting them in series. In addition, a solid polymer electrolyte / electrode assembly in such a single cell has a gas diffusion electrode in which a gas diffusion layer is supported on a catalyst layer on both sides of a diaphragm made of a solid polymer electrolyte. They are joined together so as to be on the side of the diaphragm (solid polymer electrolyte). In the single cell, hydrogen or the like as a fuel is stored in the chamber (fuel chamber) on the side where one gas diffusion electrode is present, and oxygen is stored in the chamber (oxidant chamber) on the side where the other gas diffusion electrode is present. By supplying oxygen-containing gas such as air or air and connecting an external load circuit between both gas diffusion electrodes, the generated electrical energy is utilized.

  In the polymer electrolyte fuel cell having the structure as described above, the gas diffusion layer is used for sufficiently diffusing the fuel gas (hydrogen, etc.) or oxygen supplied to each unit cell in the unit cell. Since the fuel gas is sufficiently diffused by the gas diffusion layer, the fuel gas is efficiently supplied to the diaphragm (solid polymer electrolyte) having the catalyst layer bonded to the surface. is there.

  Such a gas diffusion layer is required to have gas diffusibility, conductivity, and corrosion resistance (acid resistance). In conventional polymer electrolyte fuel cells, conductive porous materials such as carbon paper and carbon cloth are used. A gas diffusion layer made of a conductive material or a material obtained by subjecting a conductive porous material to a water repellent treatment has been widely used. Further, in Patent Document 1 (Japanese Patent No. 3954793), it is formed from a mesh sheet made of ceramics and the like, and a mixture of a conductive powder and a water-repellent filler filling the voids of the mesh sheet. A fuel cell gas diffusion layer characterized by the above has been proposed.

  However, the conventional gas diffusion layer has a problem that the price of the gas diffusion layer is high due to its expensive material and high manufacturing cost. However, since the mechanical strength is not sufficient, there is a problem that the thickness of the gas diffusion layer must be increased when using them.

  In order to promote the use of polymer electrolyte fuel cells, first of all, it is required to reduce the price, and among the components constituting the polymer electrolyte fuel cell, the proportion of the fuel cell price in particular There is a demand for lower gas diffusion layer prices. Secondly, thinning of the polymer electrolyte fuel cell is required, and research and development regarding the thinning of each constituent member has been actively conducted.

Japanese Patent No. 3954793

  Here, the present invention has been made in the background of such circumstances, and the problem to be solved is that it has excellent gas diffusibility, conductivity and acid resistance, and is low in cost. It is another object of the present invention to provide a gas diffusion layer material for a polymer electrolyte fuel cell that can greatly contribute to the thinning of the fuel cell.

  And in order to solve such a problem advantageously, this invention has the 1st coating layer which has copper as a main component in the whole surface of the exposed part in a resin net-like sheet | seat, and this 1st coating layer The gas diffusion layer material of a polymer electrolyte fuel cell having a second coating layer mainly composed of chromium on the outside of the substrate is the gist thereof.

In the gas diffusion layer material of the polymer electrolyte fuel cell according to the present invention, the preferred embodiments are as follows.
1) The first coating layer is a copper plating layer.
2) The second coating layer is formed according to a sputtering method or an ion plating method.
3) The surface treatment for imparting hydrophilicity is performed on the entire exposed portion of the resin net-like sheet before the first coating layer is formed.
4) A surface treatment for imparting hydrophilicity is performed on the surface of the first coating layer before the second coating layer is formed.
5) The surface treatment for imparting hydrophilicity is low-pressure plasma treatment or atmospheric pressure plasma treatment.
6) The resin net-like sheet is made of polyester.
7) The resin net-like sheet is subjected to calender roll processing.
8) The resin mesh sheet is a woven sheet.
9) In the above aspect 8), the resin wire constituting the woven fabric sheet has a diameter of 30 μm to 90 μm.
10) In the above aspect 8) or 9), the mesh number of the woven fabric sheet is 100 to 400 mesh.

  Thus, in the gas diffusion layer material of the polymer electrolyte fuel cell according to the present invention, the entire surface of the exposed portion of the resin net-like sheet has the first coating layer containing copper as a main component. A second coating layer mainly composed of chromium is provided outside the first coating layer. By adopting such a configuration, even if the gas diffusion layer material of the present invention is thin, it has excellent gas diffusibility, conductivity and acid resistance, and is a machine required for the gas diffusion layer. It is possible to reduce the thickness of a single cell in a polymer electrolyte fuel cell because it sufficiently satisfies the mechanical strength, etc., and as a result, a solid structure with a stack structure in which such single cells are stacked and connected in series. The molecular fuel cell can be advantageously reduced in thickness (downsized).

  Further, the gas diffusion layer material of the present invention has a resin net-like sheet as a base material, which is very inexpensive as compared with conventional carbon paper and the like, and is excellent in flexibility (flexibility). . Therefore, the gas diffusion layer material of the present invention can be continuously produced by a roll-to-roll method or the like, and coupled with the fact that the base material (resin mesh sheet) is inexpensive, keeps the price low. In other words, it can greatly contribute to the cost reduction of the polymer electrolyte fuel cell.

  By the way, when manufacturing the gas diffusion layer material of the polymer electrolyte fuel cell according to the present invention, first, a resin net-like sheet as a base material is prepared. Here, examples of the resin constituting the resin net-like sheet include synthetic fibers such as polyester, polyethylene, polypropylene, nylon, and acrylic. In the present invention, particularly polyester (particularly polyethylene terephthalate) is used. Adopted advantageously because of its excellent heat resistance.

  Further, the form of the reticulated sheet made of these resins is not particularly limited, and is a plain weave, knitted cloth, mesh, or a reticulated web or perforated sheet having many holes (such as a punching sheet) ) Can also be used. In the present invention, a woven sheet is particularly advantageously used.

  In the present invention, when a sheet made of a heat-welding resin wire (resin yarn) is used as the resin net-like sheet, the conductivity in the surface direction and the thickness direction in the gas diffusion layer material is stabilized, and the resin In order to improve the coverage of the first coating layer on the net-like sheet, and further the coverage of the second coating layer on the first coating layer, the resin net-like sheet may be subjected to calender roll processing. desirable. This is because such a calender roll process advantageously facilitates smoothing and thinning of the resin net-like sheet.

  In the present invention, when a woven sheet is used as the resin sheet, the resin wire (resin yarn) constituting the woven sheet preferably has a wire diameter of 30 μm to 90 μm. When the wire diameter of the resin wire (resin yarn) is less than 30 μm, since the wire diameter is thin, handling as a resin yarn is difficult, and it is difficult to produce a woven sheet. On the other hand, if the wire diameter exceeds 90 μm, the thickness of the entangled portion of the warp and weft exceeds 180 μm, which is not preferable in terms of thinning. When the number of meshes is less than 100 mesh, the diameter of the opening is too large. Therefore, when the finally obtained gas diffusion layer is used for a polymer electrolyte fuel cell, the catalyst layer located immediately below the opening Insufficient supply of electrons to the battery may reduce the output and energy efficiency of the fuel cell. On the other hand, when the number of meshes exceeds 400 meshes, since the diameter of the opening is too small, the diffusibility of the reaction gas or water generated by the reaction is lowered, and the output may be reduced. For these reasons, a woven sheet having a mesh number of 100 to 400 mesh is advantageously used in the present invention. The number of meshes represents the number of resin wires (resin yarns) in the warp direction per inch.

  In the present invention, a resin net-like sheet having a thickness of about 60 μm to 180 μm is generally used.

  Further, when manufacturing the gas diffusion layer material according to the present invention, before forming the first coating layer to be described later, a surface treatment for imparting hydrophilicity to the entire exposed portion of the resin net-like sheet is performed. It is preferable to apply. By applying such a surface treatment, the adhesion between the resin net-like sheet and the first coating layer is more advantageously improved, and greatly contributes to the improvement of the durability of the gas diffusion layer finally obtained. obtain. Examples of the surface treatment for imparting hydrophilicity include low-pressure plasma treatment, atmospheric pressure plasma treatment, UV treatment, and the like. Various conditions for performing these treatments are the resins constituting the resin net-like sheet. It will be determined appropriately according to the type of the item.

  After the resin net-like sheet as described above is subjected to calender roll processing and / or surface treatment for imparting hydrophilicity as necessary, copper is mainly applied to the entire exposed portion of the resin net-like sheet. A first coating layer as a component is formed. By providing such a first coating layer, conductivity is imparted to the resin net-like sheet.

Here, when forming the first coating layer mainly composed of copper, a wet plating method (hereinafter referred to as a plating method) such as an electroless plating method or an electrolytic plating method is advantageously employed, and roll-to- It is desirable to carry out continuously by a roll method or the like. Further, preferably, as the amount of deposition of copper per unit area of the resin net-like sheets is ^{50μg / cm 2 ~10000μg / cm 2} , the first cover layer is formed. However, when the copper adhesion amount is 50 μg / cm ² , there is a risk that sufficient conductivity cannot be obtained in the gas diffusion layer material. On the other hand, when the copper adhesion amount exceeds 10,000 μg / cm ² , This is because the productivity is sufficient, but the productivity may deteriorate. Note that both the amount of copper and the amount of chromium to be described later are measured according to the fluorescent X-ray method.

  For the first coating layer mainly composed of copper thus formed, preferably, a surface treatment for imparting hydrophilicity is performed before the second coating layer described later is formed. Applied. Such surface treatment can more advantageously improve the adhesion between the first coating layer and the second coating layer, and can greatly contribute to the improvement of the durability of the gas diffusion layer finally obtained. It is. In addition, as the surface treatment for imparting hydrophilicity, it is possible to adopt the same method as described above as the surface treatment for the resin net sheet.

  And if the said surface treatment is given with respect to a 1st coating layer as needed, the 2nd coating layer which has chromium as a main component is formed in the outer side of this 1st coating layer. Thus, by providing the second coating layer, the gas diffusion layer material of the present invention exhibits excellent acid resistance.

The second coating layer containing chromium as a main component must cover the outside of the first coating layer containing copper as a main component, that is, the entire exposed portion of the first coating layer. It is. Therefore, it is preferable to first coat one surface of the resin mesh sheet provided with the first coating layer, and then cover the other surface. The so provided, the second coating layer mainly composed of chromium, it is preferable adhesion amount of chromium is ^{40μg / cm 2 ~200μg / cm 2} . When the adhesion amount is less than 40 μg / cm ² , there is a possibility that sufficient acid resistance is not obtained in the gas diffusion layer material. On the other hand, when the adhesion amount exceeds 200 μg / cm ² , the acid resistance is sufficient. However, productivity may be deteriorated.

  In forming the second coating layer mainly composed of chromium, a vapor deposition method such as a sputtering method, an ion plating method, a vacuum evaporation method, or a plasma CVD method can be used. From the viewpoint of obtaining a dense second coating layer, a sputtering method or an ion plating method is particularly advantageously employed.

  As the sputtering method, a direct current magnetron sputtering method, a high frequency magnetron sputtering method, an ion beam sputtering method, or the like can be used. Sputtering can be performed by a general magnetron sputtering method using a DC power source, but by sputtering using an AC power source or a pulse power source, sputtering can be stabilized over a long period of time and a high output can be applied. It becomes. The second coating layer in the present invention can also be formed by C-MAG of BOC in the United States, Leibold of Germany, or Twin Mag (dual mug) of Ardennes.

  As the ion plating method, a known ion plating method such as a pressure gradient discharge method, a hollow cathode discharge method, an arc discharge method, or the like can be employed.

  The second coating layer using the vapor deposition method can be formed by either a batch method or a roll-to-roll method. However, the productivity is excellent and the manufacturing cost can be kept low. A roll-to-roll system is advantageously employed.

  The gas diffusion layer material obtained as described above exhibits excellent gas diffusibility, conductivity, and acid resistance, and has a significantly reduced cost compared to the conventional one. is there. By employing such a gas diffusion layer material, it is possible to greatly contribute to the cost reduction of the polymer electrolyte fuel cell. In addition, the gas diffusion layer material of the present invention has sufficient gas strength, electrical conductivity and acid resistance while sufficiently satisfying the mechanical strength required for the gas diffusion layer even if it is thin. Therefore, it is possible to reduce the thickness of a single cell in a polymer electrolyte fuel cell, and thus reduce the thickness of a polymer electrolyte fuel cell having a stack structure in which such single cells are stacked and connected in series ( It is possible to advantageously reduce the size).

  Some examples of the present invention will be shown below to clarify the present invention more specifically. However, the present invention is not limited by the description of such examples. Needless to say. In addition to the following examples, the present invention includes various modifications based on the knowledge of those skilled in the art without departing from the spirit of the present invention, in addition to the above-described specific description. It should be understood that modifications, improvements, etc. can be made.

  First, a 20 denier (45 μm) polyethylene terephthalate monofilament is used as the warp, and a 20 denier (45 μm) polyethylene terephthalate monofilament is used as the weft. A plain fabric sheet having a thickness of 90 μm and 150 mesh was prepared. The plain woven fabric sheet was calendered to obtain a resin sheet having a thickness of 70 μm. Such calender roll processing uses a two-roll calender roll machine to set a plain fabric sheet on a metal roll (lower roll) heated to 150 ° C., and with a paper roll (upper roll) at a predetermined pressure. Was carried out by applying pressure.

  A gas diffusion layer material was prepared using the obtained resin sheet.

-Invention Example 1-
The resin sheet was immersed in a weak alkaline degreasing solution at 65 ° C. for 5 minutes for degreasing treatment, and then the resin sheet was washed with water. Next, the resin-made sheet was immersed in a palladium-tin mixed catalyst solution at 25 ° C. for 5 minutes to adsorb the palladium-tin compound on the surface of the resin-made sheet, and then the sheet was washed with water. Thereafter, the resin sheet was immersed in hydrochloric acid at 40 ° C. for 5 minutes to remove tin, and after metallized palladium was formed on the sheet surface using the catalyst core as a catalyst core, the sheet was washed with water. Then, the resin sheet is immersed in the copper plating solution, and the surface of the resin sheet is plated for a predetermined time at 30 ° C. while suppressing the self-decomposition of the copper plating solution by air stirring. By washing with water and air drying, a first coating layer containing copper as a main component was formed on the sheet surface. In addition, in the 1st coating layer formed in the exposed part of the resin-made sheet | seats, the adhesion amount of copper was 7610 microgram / cm < ² >.

The resin sheet provided with the first coating layer was subjected to a peel test using an adhesive tape to evaluate the adhesion of the first coating layer, and evaluated according to the following criteria. The evaluation results are also shown in Table 1 below.
○: Adhesion of copper is not observed on the adhesive tape used in the peel test.
(Triangle | delta): Adhesion of copper is recognized partially on the adhesive tape used for the peeling test.
X: Adhesion of copper is recognized on the whole surface of the adhesive tape used for the peeling test.

The resin sheet provided with the first coating layer was set in a sealed chamber of the sputtering apparatus, and the inside of the chamber was once evacuated to a vacuum degree of 7 × 10 ⁻³ Pa. Next, after introducing argon gas into the chamber and setting the argon gas pressure to 2.0 Pa, direct current power (450 W) is applied, and direct current sputtering is performed on the resin sheet for 1 minute. Chromium was deposited on one side of the first coating layer of the sheet. A gas diffusion layer material (Invention Example 1) was obtained by attaching chromium to the other surface of the first coating layer of the resin sheet according to the same method. The second coating layer in the gas diffusion layer material thus obtained (Invention Example 1) had a chromium adhesion of 107 μg / cm ² .

  For the obtained gas diffusion layer material (Invention Example 1), in order to evaluate the adhesion between the second coating layer and the first coating layer, a peel test was performed according to the same method as described above, and the same Evaluation was made according to criteria. The evaluation results are also shown in Table 2 below.

-Invention Example 2-
Low-pressure plasma treatment was performed on the resin sheet before forming the first coating layer and on the first coating layer in the resin sheet before forming the second coating layer, respectively. Except for the above, a gas diffusion layer material (Invention Example 2) was produced in the same manner as in Invention 1. Specifically, the low-pressure plasma treatment was performed according to the following method. That is, a resin sheet (thickness: 70 μm, 150 mesh) was set in a vacuum chamber, and the inside of the chamber was once evacuated to a degree of vacuum of 7 × 10 ⁻³ Pa. Next, 28 sccm of argon gas was introduced into the chamber, and the argon gas pressure was set to 2.0 Pa. Then, 13.56 MHz high frequency power: 120 W was applied for 1 minute.

  The electric resistance of the two types of gas diffusion layer materials (Invention Examples 1 and 2) obtained as described above was measured. The electric resistance in the surface direction of the obtained gas diffusion layer material was measured by a four-terminal method using a surface resistance meter (trade name: Loresta-EP MCP-T360) manufactured by MITSUBISHI CHEMICAL ANALYTECH. Moreover, the electrical resistance in the thickness direction was measured by the following method. A sample of the gas diffusion layer material cut to 10 mm square is placed on the aluminum plate used as the back electrode, and the upper electrode is placed thereon and fixed. Each probe connected to each electrode is manufactured by ADCMT Co., Ltd. Connected to Digital Multimeter (type 7461A). Next, a current of 10 mA was passed through the upper electrode and the back electrode to determine the voltage between both electrodes, and the electrical resistance (Ω) in the thickness direction was measured. The electrical resistance thus measured is shown in Table 1 below. In Table 1 below, measurement results of Invention Example 3 described later are also shown.

  As is apparent from the results in Table 1, when the gas diffusion layer material according to the present invention is manufactured, the resin sheet before the first coating layer is formed and the second coating layer are formed. Adhesion between the resin sheet and the first coating layer in the gas diffusion layer material obtained by applying a surface treatment (low pressure plasma treatment) to impart hydrophilicity to the previous first coating layer It was confirmed that both the properties and the adhesion between the first coating layer and the second coating layer were improved.

  A gas diffusion layer was produced by cutting out a predetermined size (22 mm square) using the gas diffusion layer material (Invention Example 2) obtained according to the above-described method. The following measurement and evaluation were performed on the obtained gas diffusion layer.

-Evaluation of acid resistance-
After measuring the electrical resistance in the surface direction in advance, the gas diffusion layer was immersed in an aqueous sulfuric acid solution (pH: 4) at 80 ° C. for 60 hours. After such immersion, the electric resistance in the surface direction of the gas diffusion layer was measured again. The measurement results are shown in Table 2 below. Further, as a comparative example, a commercially available carbon paper or a SUS mesh was used to cut out to the same size to produce a gas diffusion layer, and the same experiment was performed. The measurement results of these comparative examples are also shown in Table 2 below.

  As is clear from the results in Table 2, it was recognized that the gas diffusion layer according to the present invention exhibited high conductivity and excellent acid resistance.

-Performance evaluation of solid polymer electrolyte fuel cell-
First, for the purpose of reducing contact resistance with the catalyst layer and imparting water repellency to the two gas diffusion layers of the present invention (obtained from the material of Invention Example 2), the conductivity The paste was applied and allowed to air dry for 30 minutes. Next, one diffusion layer was set on the anode separator of the fuel cell and fixed with a gasket having a thickness of 100 μm. Then, set the solid polymer electrolyte membrane / electrode assembly, set another gas diffusion layer and gasket with a thickness of 100 μm in this order, and sandwich them with the cathode separator, and then fix them with screws. Thus, a single cell was produced. As the solid polymer electrolyte membrane / electrode assembly, a perfluorosulfonic acid membrane (trade name: Nafion, registered trademark, manufactured by DuPont) formed on both sides of the catalyst layer was used.

The obtained single cell was incorporated into a current-voltage power generation evaluation apparatus (type FC5100 series) manufactured by Chino Corporation. Water is heated to 80 ° C. and the solid electrolyte membrane is moistened with the water vapor for 30 minutes. Then, 1 L of humidified hydrogen gas (humidity: 95%) at 80 ° C. is introduced into the anode side, while the cathode side is introduced. Then, humidified air at 80 ° C. (humidity: 95%) was introduced at 2.5 L / min, and the resulting current and voltage were measured. As a result, the battery output of this single cell is 750 mV when measured at a current density of 0.4 A / cm ² , and has the same battery output as a single cell using a gas diffusion layer made of conventional carbon paper. However, it was recognized.

-Invention Example 3-
A gas diffusion layer material was produced in the same manner as in Example 2 except that the second coating layer was formed according to the ion plating method. The formation of the second coating layer by the ion plating method was specifically performed as follows.

Cr (chromium) pellets for coating were placed in the hearth of a pressure gradient discharge ion plating apparatus. Next, a first coating layer is formed, and a resin sheet subjected to low-pressure plasma treatment on the surface of the first coating layer is set in a sealed chamber of the ion plating apparatus, and the inside of the chamber is once, Vacuum degree: Evacuated to 7 × 10 ⁻⁴ Pa. Next, after introducing argon gas into the chamber and setting the argon gas pressure to 0.1 Pa, plasma is generated by applying ion beam power: 3 kW, the shutter is opened, and chromium is applied to one side of the sheet. Was attached. Further, chromium was similarly deposited on the other side of the sheet. As a result, a gas diffusion layer material having a ^second coating layer mainly composed of chromium (amount of chromium adhesion: 110 μg / cm ² ) outside the first coating layer was obtained (see Table 1 above). . It was confirmed that the electric resistance and acid resistance of the obtained gas diffusion layer material were comparable to those of Example 2 of the present invention in which the second coating layer was formed by the sputtering method.

Claims (11)

  The entire surface of the exposed portion of the resin net-like sheet has a first coating layer mainly composed of copper, and has a second coating layer mainly composed of chromium outside the first coating layer. Gas diffusion layer material for polymer electrolyte fuel cells.   The gas diffusion layer material for a polymer electrolyte fuel cell according to claim 1, wherein the first coating layer is a copper plating layer.   The gas diffusion layer material for a polymer electrolyte fuel cell according to claim 1 or 2, wherein the second coating layer is formed according to a sputtering method or an ion plating method.   4. The surface treatment for imparting hydrophilicity is performed on the entire exposed portion of the resin net-like sheet before the first coating layer is formed. 5. The gas diffusion layer material of the polymer electrolyte fuel cell described.   5. The surface treatment according to claim 1, wherein a surface treatment for imparting hydrophilicity is performed on a surface of the first coating layer before the second coating layer is formed. Gas diffusion layer material for polymer electrolyte fuel cells.   6. The gas diffusion layer material for a polymer electrolyte fuel cell according to claim 4, wherein the surface treatment for imparting hydrophilicity is low-pressure plasma treatment or atmospheric pressure plasma treatment.   The gas diffusion layer material for a polymer electrolyte fuel cell according to any one of claims 1 to 6, wherein the resin mesh sheet is made of polyester.   The gas diffusion layer material for a polymer electrolyte fuel cell according to any one of claims 1 to 7, wherein the resin net-like sheet is subjected to calender roll processing.   The gas diffusion layer material for a polymer electrolyte fuel cell according to any one of claims 1 to 8, wherein the resin net-like sheet is a woven fabric sheet.   10. The gas diffusion layer material for a polymer electrolyte fuel cell according to claim 9, wherein a diameter of a resin wire constituting the fabric sheet is 30 μm to 90 μm. The gas diffusion layer material for a polymer electrolyte fuel cell according to claim 9 or 10, wherein the mesh number of the woven fabric sheet is 100 to 400 mesh.