JP2006228501A - Polymer electrolyte fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polymer electrolyte fuel cell suppressing flooding caused by water in a cathode and continuously stably generating electric power. <P>SOLUTION: The polymer electrolyte fuel cell has a solid polymer electrolyte membrane, an anode arranged on one surface of the solid polymer electrolyte membrane, and the cathode arranged on the other surface of the solid polymer electrolyte membrane, and a water repellent-hydrophilic pattern comprising a water repellent part and a hydrophilic part is installed in the cathode. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a polymer electrolyte fuel cell.

  Solid polymer fuel cells are actively studied as next-generation energy devices. Among them, direct methanol fuel cells (hereinafter referred to as DMFC) are expected to be used as power sources for portable equipment because they can take out hydrogen ions directly from the fuel and do not require a reformer or hydrogen cylinder. Yes.

  In the DMFC, water is generated at the oxygen electrode due to a reaction accompanying power generation, and proton conduction is performed through the water. Therefore, water supplied to the fuel electrode side passes through the proton exchange membrane together with hydrogen ions and passes through the proton exchange membrane. Reach the pole side. One feature of the DMFC is that it can be operated at a low temperature of 80 ° C. or lower. For this reason, the water generated at the oxygen electrode or the water that arrives from the fuel electrode, which is called flooding, is condensed on the oxygen electrode to the oxygen electrode. A phenomenon that hinders the supply of oxygen occurs. The decrease in output due to insufficient oxygen supply due to flooding is particularly noticeable during continuous operation and high output operation.

  In order to solve this problem, there is a method in which a hydrophilic portion is provided on the entire surface of the oxygen electrode and an absorbent of an aqueous solution is disposed on the outer periphery thereof (Japanese Patent Application Laid-Open No. 2004-296175: Patent Document 1), or water from the oxygen electrode to the outside. A method of disposing a water-absorbent sheet in a cell as a discharge member (Japanese Patent Laid-Open No. 2004-165002: Patent Document 2) has been proposed.

However, as described in Patent Document 1, when the hydrophilic part is provided on the entire surface of the oxygen electrode, the gas channel is blocked by the hydrophilic part itself, or when the hydrophilic part is covered with water, the gas channel is blocked by the water. Therefore, there is a possibility that oxygen supply to the oxygen electrode is delayed. Furthermore, when an absorbent is used, it is difficult for water to evaporate from the absorbent when used at room temperature. Therefore, in order to use it continuously, an apparatus for regenerating the absorbent such as a heater is necessary. Disadvantageous. Moreover, since such an absorbent produces a large volume change with moisture absorption, there is a possibility that the gas flow path is blocked or the cell is destroyed. In addition, as described in Patent Document 2, when a water-absorbent sheet is disposed as a drainage member in a cell, the structure of the electrode becomes complicated, and productivity becomes a problem.
JP 2004-296175 A JP 2004-165002 A

  In view of the above problems, an object of the present invention is to provide a polymer electrolyte fuel cell that has a simple structure and that can suppress flooding due to water in the cathode and can continuously generate power stably.

  The present invention relates to a solid polymer fuel having a solid polymer electrolyte membrane, an anode provided on one surface of the solid polymer electrolyte membrane, and a cathode provided on the other surface of the solid polymer electrolyte membrane. The present invention relates to a solid polymer fuel cell, wherein the cathode is provided with a water repellent-hydrophilic pattern comprising a water repellent part and a hydrophilic part.

  According to the present invention, it is possible to provide a polymer electrolyte fuel cell that has a simple structure and is capable of suppressing flooding due to water in the cathode and continuously generating power stably.

  The main features of the present invention are a solid polymer electrolyte membrane, an anode (fuel electrode) provided on one surface of the solid polymer electrolyte membrane, and the other surface of the solid polymer electrolyte membrane. In a fuel cell structure having a cathode (oxygen electrode), the cathode has a water repellent-hydrophilic pattern composed of a water repellent part and a hydrophilic part.

  This water-repellent-hydrophilic pattern is formed on the surface of the cathode opposite to the electrolyte membrane side, that is, on the outermost surface of the cathode on the outside air side (oxidant gas supply side) from the viewpoint of sufficiently suppressing flooding at the cathode. Preferably it is.

  Thus, by providing the cathode with a water-repellent-hydrophilic pattern comprising a water-repellent part and a hydrophilic part, water generated at the cathode (oxygen electrode) or water that reaches the cathode from the anode (fuel electrode) Since the water repellent part does not stay in the water repellent part, it is difficult for the water to cover the entire surface of the cathode. Therefore, a sufficient gas flow path is ensured, and the oxidant gas can be sufficiently supplied to the cathode.

  It is preferable that the hydrophilic portion of the water repellent / hydrophilic pattern is continuously provided to the cathode end portion in a certain direction. For example, it is preferable to use a pattern in which a plurality of linear hydrophilic portions continuous from one end portion to the other end portion of the cathode in a certain direction and a water repellent portion is disposed in a space between these hydrophilic portions. it can.

  Since this hydrophilic portion can be continuously arranged in the gas flow direction and the gravity direction, the water collected in the hydrophilic portion is the cathode end portion according to the formation region of the hydrophilic portion, for example, a line-shaped hydrophilic pattern portion. It is easy to be released to the outside.

  In a structure in which the cathode has a catalyst layer containing a catalyst provided on the solid electrolyte membrane side and a gas-permeable current collector layer (diffusion layer) provided on the catalyst layer, the current collector layer It is preferable to provide a water repellent-hydrophilic pattern. Since the oxidant gas supplied to the cathode mainly diffuses from the water repellent part into the current collector layer, even if the entire hydrophilic part is covered with water, the oxidant gas is sufficiently supplied to the catalyst layer. Can be supplied.

The water repellent and the hydrophilic agent for forming the water repellent-hydrophilic pattern in the present invention are not particularly limited, and various conventionally known materials can be used. Examples of water repellents include fluorine-based polymers such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride, fluorine-based silane coupling agents such as fluoroalkylsilane, trimethylchlorosilane, methyltriethoxysilane, and vinyltriethoxysilane. And organic silane coupling agents such as polyethylene and polypropylene, and organic polymers having no hydrophilic functional group. Examples of the hydrophilic agent include inorganic oxides such as SiO ₂ , TiO ₂ , Al ₂ O ₃ , ZrO ₂ , and ZnO, and hydrophilic polymers such as polyvinyl alcohol, and one or a mixture of these is used. be able to. The water repellent and hydrophilic agent are applied only to the electrode surface and do not hinder the diffusion of the oxidizing gas into the cathode.

  The water repellent-hydrophilic pattern in the present invention is not particularly limited as long as it is a shape capable of guiding water to the cathode end according to the gas flow direction or the gravity direction. The hydrophilic portion is preferably provided continuously to the cathode end portion in a certain direction, and such a pattern shape can effectively induce water to the cathode end portion. For example, as a water repellent-hydrophilic pattern, there are a plurality of line-shaped hydrophilic portions continuous from one end to the other end of the cathode in a certain direction, and the water repellent portions are arranged in the space between these hydrophilic portions. Patterns. Such a pattern is preferable in that it has excellent water drainage and is easy to form. Specifically, an alternating pattern in which line-shaped hydrophilic pattern portions and line-shaped hydrophobic pattern portions are alternately arranged can be formed on the outermost surface on the outside air side of the cathode. Further, a water repellent portion may be formed on the entire outside air side outermost surface of the cathode, and a hydrophilic pattern portion may be formed on the water repellent portion. In addition, as a hydrophilic pattern part, a taper-like pattern in which the width increases from any part on the cathode toward the end part, for example, toward the end part, and from a plurality of arbitrary parts on the cathode to a central line-like pattern For example, a vein-shaped pattern that merges toward the surface.

  The water repellent / hydrophilic pattern is preferably formed on the outermost surface of the cathode on the outside air side (oxidant gas supply side). When the cathode has the above-described catalyst layer and current collector layer, the cathode is preferably formed on the outermost side of the current collector layer. This water-repellent-hydrophilic pattern only needs to have a water-repellent region and a hydrophilic region having a specific pattern shape in the vicinity of a contact plane with the outside air (air or oxygen) of the cathode.

  The formation of the water repellent part and the hydrophilic part of the water repellent-hydrophilic pattern can be performed, for example, by coating, that is, after applying one member, the other member can be applied to an unapplied region. Alternatively, after applying the water repellent member, the hydrophilic member may be partially applied on the application region. In the formation of the water repellent part and the hydrophilic part, it is desirable that the coating amount be such as not to prevent the diffusion of the oxidant gas into the cathode. From the viewpoint of obtaining sufficient water repellency and hydrophilicity, the thickness of the coating film can be set in the range of, for example, 10 nm to 0.1 mm, preferably 100 nm to 0.01 mm.

  The polymer electrolyte fuel cell described above can be provided with a drainage means at the end of the hydrophilic portion of the water repellent / hydrophilic pattern. As this drainage means, a drainage member that is in contact with the end of the hydrophilic portion and extends so as to be exposed to the outside of the fuel cell can be provided. Such drainage means can absorb the moisture collected in the hydrophilic portion and discharge the moisture to the outside by transpiration. Thereby, it becomes possible to discharge the moisture on the cathode more efficiently.

  The drainage member is not particularly limited as long as it has water permeability, and conventionally known water-absorbing members and porous members can be used. For example, a water-absorbing nonwoven fabric or a porous film that can suck up liquid by capillary force can be suitably used.

  The solid electrolyte membrane in the present invention has a role of electrically separating the anode and the cathode and moving protons (hydrogen ions) between the two. For this reason, the solid electrolyte membrane is preferably a membrane having high proton conductivity. Further, it is preferably chemically stable with respect to the fuel and oxidant used and has high mechanical strength. As a material constituting such a solid electrolyte membrane, for example, a polymer having a proton acid group such as a sulfonic acid group, a sulfoalkyl group, a phosphoric acid group, a phosphone group, a phosphine group, a carboxyl group, or a sulfonimide group is used. be able to. Especially, the organic polymer which has a sulfonic acid group as an ion exchange group can be used suitably.

  As the anode and the cathode, an electrode structure employed in a conventional polymer electrolyte fuel cell can be used. For example, a laminated structure of a gas permeable current collector layer (diffusion layer) and a catalyst layer can be employed.

  The catalyst layer can be formed, for example, by applying a solution mixed with a catalyst and a proton conductive material, and if necessary, a water repellent such as polytetrafluoroethylene, and a conductivity imparting agent such as carbon, on the current collector layer. it can.

  As the anode and cathode catalyst, platinum or an alloy containing platinum as a main component (hereinafter, “platinum-based alloy”) such as platinum-ruthenium alloy can be preferably used. Examples of other platinum alloys include alloys with rhenium, rhodium, palladium, iridium, ruthenium, gold, silver and the like. The anode and cathode catalysts may be the same or different. As this catalyst, catalyst particles supported on a carbon material such as carbon black can be suitably used.

  The proton conductive material is not particularly limited as long as it has water resistance and protons are rapidly conducted in the catalyst layer, and the polymer used as the above-mentioned solid electrolyte membrane can be used.

  As the current collector layer (diffusion layer), a conductive porous substrate such as carbon paper, carbon molded body, carbon sintered body, sintered metal, and foam metal can be used. These current collector layers can be appropriately subjected to water repellency or hydrophilic treatment or conductivity imparting treatment.

  Examples of the fuel include alcohols such as methanol, ethers such as dimethyl ether, hydrogen gas, and hydrocarbon reformed gas. Among these, alcohols such as methanol, particularly aqueous alcohol solutions can be preferably used. On the other hand, air or oxygen can be used as the oxidant gas.

  Examples The present invention will be described in detail by examples, but the present invention is not limited to these examples.

[Example 1]
FIG. 1 shows a schematic cross-sectional structure of a direct methanol fuel cell (single cell) in this example. In the figure, 101 is an electrolyte membrane, 102 is an oxygen electrode (cathode), 103 is a fuel electrode (anode), 104 is a current collector, 105 is a water repellent-hydrophilic pattern, 106 is an air flow path, 107 is a fuel flow path, Reference numeral 111 denotes an insulating member.

First, conditions for producing a membrane electrode assembly (MEA) used in the fuel cell will be described. Carbon carrying Pt 30 wt% and Ru 20 wt% was dispersed with a Nafion solution (manufactured by DuPont) to prepare a slurry, and this slurry was applied to a stainless steel porous mat serving as a current collector 104 and dried. 103 (anode). On the other hand, carbon carrying Pt 40 wt% is dispersed in a Nafion solution (manufactured by DuPont) to prepare a slurry, which is applied to a stainless steel porous mat serving as a current collector 104 and dried, and this is dried with an oxygen electrode 102 ( Cathode). The coating amount, the fuel electrode Pt is 8-10 mg / cm ^2, oxygen electrode was adjusted to Pt becomes 10 to 15 mg / cm ^2.

Next, the water repellent / hydrophilic pattern 105 shown in FIG. 2 was formed on the non-catalyst-coated surface (surface opposite to the catalyst-coated surface) of the stainless steel mat on the oxygen electrode side. The water repellent-hydrophilic pattern 105 was formed by alternately applying a water repellent member and a hydrophilic member so that the water repellent pattern portion 108 had a width of 5 mm and the hydrophilic pattern portion 109 had a width of 2 mm. A PTFE dispersion was used for the water repellent pattern portion 108, and a TiO ₂ dispersion containing 10 wt% polyvinyl alcohol as a binder was used for the hydrophilic pattern portion 109. The water repellent / hydrophilic pattern 105 is provided so that the longitudinal direction of the pattern is arranged along the air flow direction indicated by an arrow as shown in FIG.

  The fuel electrode 103 and the oxygen electrode 102 sandwiched an electrolyte membrane 101 (trade name: Nafion 117, manufactured by DuPont) with a thickness of 180 μm and pressed at 10 MPa, 130 ° C. for 1 minute to obtain an MEA.

  Using this MEA, a direct methanol fuel cell (DMFC) shown in FIG. 1 was produced.

[Example 2]
FIG. 3 shows a schematic cross-sectional structure of the DMFC (single cell) of this example. It was produced in the same manner as in Example 1 except that a cellulose nonwoven fabric was disposed as the drainage member 110 at one end of the water repellent / hydrophilic pattern 105 in the cell.

[Comparative Example]
FIG. 5 shows a schematic cross-sectional structure of a DMFC (single cell) of this comparative example. It was produced in the same manner as in Example 1 except that the water repellent / hydrophilic pattern was not provided on the catalyst-uncoated surface of the stainless steel mat on the oxygen electrode (cathode) side.

A constant current power generation test was performed on the single cells produced in Examples 1 and 2 and the comparative example. The fuel electrode (anode) is 8 vol. A% methanol aqueous solution was circulated, and air was supplied to the oxygen electrode (cathode) with a fan. The current density was 62.5 mA / cm ² . The result is shown in FIG.

  From this result, in the comparative example, flooding occurred due to the generated water, and the output was greatly reduced because oxygen was cut off, but in Example 1 where the water repellent-hydrophilic pattern was formed in the electrode part, it occurred. It has been clarified that the voltage drop is sufficiently suppressed because water moves from the water repellent pattern portion to the hydrophilic pattern portion and is discharged to the outside. Moreover, in Example 2 provided with the drainage member, since the water moved from the water repellent pattern portion to the hydrophilic pattern portion is more efficiently discharged to the outside by the drainage member, there is almost no voltage drop. It became clear.

  Thus, by forming a water-repellent-hydrophilic pattern on the oxygen electrode (cathode), water generated at the oxygen electrode or water reaching the oxygen from the fuel electrode does not cover the entire surface of the oxygen electrode. Since they are collected from the portion into the hydrophilic pattern portion and discharged to the outside through the hydrophilic pattern portion, flooding does not occur and stable power generation can be performed continuously. Even if the hydrophilic pattern portion is covered with water, the gas diffuses from the water repellent pattern portion into the current collector, and the gas flow path is not blocked. Moreover, by providing a drainage member on the end face of the hydrophilic pattern portion, the generated water can be discharged to the outside more efficiently.

Schematic sectional view showing a polymer electrolyte fuel cell of Example 1 in the present invention The figure which shows the water-repellent-hydrophilic pattern on the oxygen pole in this invention Typical sectional drawing which shows the polymer electrolyte fuel cell of Example 2 in this invention Diagram showing results of constant current power generation test of fuel cell Schematic sectional view showing a polymer electrolyte fuel cell of a comparative example according to the prior art

Explanation of symbols

101: Electrolyte membrane 102: Oxygen electrode (cathode)
103: Fuel electrode (anode)
104: current collector 105: water repellent-hydrophilic pattern 106: air flow path 107: fuel flow path 108: water repellent pattern part 109: hydrophilic pattern part 110: drainage means 111: insulating member

Claims (6)

  In the solid polymer electrolyte fuel cell having a solid polymer electrolyte membrane, an anode provided on one surface of the solid polymer electrolyte membrane, and a cathode provided on the other surface of the solid polymer electrolyte membrane, A solid polymer fuel cell, wherein a water repellent-hydrophilic pattern comprising a water repellent part and a hydrophilic part is provided on a cathode.   2. The polymer electrolyte fuel cell according to claim 1, wherein the hydrophilic portion of the water-repellent-hydrophilic pattern is continuously provided to a cathode end portion in a certain direction.   The water repellent-hydrophilic pattern has a plurality of line-shaped hydrophilic portions that are continuous from one end portion to the other end portion of the cathode in a certain direction, and the water repellent portions are arranged in a space between these hydrophilic portions. Item 8. The polymer electrolyte fuel cell according to Item 1.   The cathode has a catalyst layer containing a catalyst provided on the solid electrolyte membrane side and a gas-permeable current collector layer provided on the catalyst layer. 4. The polymer electrolyte fuel cell according to claim 1, wherein the water repellent / hydrophilic pattern is provided on an outer surface.   The polymer electrolyte fuel cell according to any one of claims 1 to 4, wherein a drainage means is provided at an end of the hydrophilic portion of the water repellent-hydrophilic pattern.   The polymer electrolyte fuel cell according to claim 5, wherein the drainage means has a drainage member that contacts an end of the hydrophilic portion and extends to the outside of the fuel cell.

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