JP2013045563A - Fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress occurrence of short-cut of a reaction fluid by employing a structure which can be manufactured easily and is simple as compared with conventional arts.SOLUTION: A fuel cell includes: a membrane electrode assembly including a solid polymer electrolyte membrane on each of both faces of which a catalyst electrode layer is formed; a diffusion layer arranged on each of both faces of the membrane electrode assembly; and separators holding the membrane electrode assembly and the diffusion layers. In the fuel cell, a reaction fluid passage is provided at least between one separator and one diffusion layer, and at least a part of a rib constituting a wall surface of the reaction fluid passage comprises a water repellent member.

Description

  The present invention relates to a fuel cell.

A fuel cell is a power generator that extracts electrical energy by an electrochemical reaction between hydrogen (H ₂ ) as a fuel gas and oxygen (O ₂ ) as an oxidizing gas. In the following description, the fuel gas and the oxidizing gas may be simply referred to as “reaction gas” or “reaction fluid” without particular distinction. This fuel cell is constituted by a fuel cell (also simply referred to as “cell”) in which a membrane-electrode assembly (MEA) is sandwiched between separators. The membrane electrode assembly has a structure in which a catalyst electrode layer is formed on both surfaces of a solid polymer electrolyte membrane having proton (H ⁺ ) conductivity (hereinafter also simply referred to as “electrolyte membrane” or “electrolyte layer”). doing. The separator has a structure in which a groove as a flow path of a reaction gas (reaction fluid) is formed on the surface on the membrane electrode assembly side.

  A diffusion layer is usually provided between the membrane electrode assembly and the separator to improve the diffusibility of the reaction gas supplied to the catalyst electrode layer of the membrane electrode assembly via the reaction gas flow path. Yes. As the structure of the diffusion layer, further improvement in diffusibility is being promoted. For this reason, it should be supplied to a certain region of the membrane electrode assembly via the reaction gas flow path, but it is supplied via the diffusion layer without passing through the reaction gas flow path. It was found that a so-called shortcut occurred and the power generation performance deteriorated.

  In Patent Document 1, the density of the second region of the diffusion layer in contact with the rib portion sandwiched between the reaction fluid channels is set higher than the first region of the diffusion layer in contact with the reaction fluid channel formed in the separator. A technique for increasing the water repellency or increasing the water repellency is described. This suppresses the occurrence of the shortcut by using the second region as a weir and using the first region as a channel along the reaction fluid channel.

JP 2005-293966 A JP 2008-287924 A JP 2010-232062 A

  However, in the above prior art, the second region having a higher density or water repellency than the first region must be formed or processed in the diffusion layer so as to correspond to the rib portion sandwiched between the reaction fluid flow paths. There is a problem. There is also a problem that the assembly accuracy between the diffusion layer and the separator is required. Therefore, it is desired to suppress the occurrence of a shortcut of the reaction fluid with a structure that is easier to manufacture and simpler than the prior art.

  An object of the present invention is to provide a technique capable of suppressing the occurrence of a shortcut of a reaction fluid with a simpler structure that is easier to manufacture than the prior art.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

[Application Example 1]
A membrane electrode assembly in which a catalyst electrode layer is formed on each side of a solid polymer electrolyte membrane; a diffusion layer disposed on each side of the membrane electrode assembly; and the membrane electrode assembly and the diffusion layer A separator sandwiched between the at least one separator and the diffusion layer, a groove-like reaction fluid channel is provided between the separator and the wall of the reaction fluid channel. A fuel cell characterized in that at least a part of the rib portion is made of a water-repellent member.
In the above fuel cell, liquid water stays in a weir shape without draining into the reaction fluid flow path in the diffusion layer portion that contacts the rib portion constituted by the water repellent member. Since the diffusion is inhibited and the reaction fluid flows along the rib portion formed of the water repellent member, it is possible to suppress the occurrence of a shortcut of the reaction fluid.

[Application Example 2]
The fuel cell according to Application Example 1, wherein the rib portion of the reaction fluid channel includes a segment channel rib unit that divides the reaction fluid channel into a plurality of segment channels, and the plurality of segment channels. A fuel cell, wherein the flow channel rib is formed of the water repellent member.
In this case, since the divided flow channel rib portion that divides the reaction fluid flow channel into a plurality of divided flow channels is not formed of a water-repellent member, drainage from the diffusion layer portion that is in contact is enabled and conductivity is improved. Since the channel rib portion that divides the reaction fluid channel into a plurality of segment channels is formed of a water-repellent member, a plurality of segment channels and a plurality of segment channels adjacent thereto can be obtained. It is possible to suppress the occurrence of a reaction fluid shortcut between the two.

[Application Example 3]
The fuel cell according to Application Example 2, wherein the reaction fluid flow path includes a flow direction changing unit that changes a flow direction of the reaction fluid flowing inside, and the flow separating the outside of the flow direction changing unit. A fuel cell characterized in that a road rib portion is constituted by the water repellent member.
In this case, it becomes easy to drain liquid water that tends to accumulate outside the flow direction changing portion.

  The present invention can be realized in various forms, for example, in the form of a fuel cell, a membrane / electrode / diffusion layer assembly, or the like.

It is a schematic perspective view which shows the structure of the fuel cell to which this invention is applied. It is a schematic sectional drawing in the AA of FIG. It is a schematic perspective view which expands and shows area | region RCa shown in FIG. It is explanatory drawing which shows the modification of the water repellent part which comprises the fuel cell of this invention. It is explanatory drawing which shows the modification of the membrane electrode assembly diffusion layer and water-repellent part which comprise the fuel cell of this invention.

  FIG. 1 is a schematic perspective view showing the configuration of a fuel cell to which the present invention is applied. FIG. 2 is a schematic cross-sectional view taken along line AA in FIG. As shown in FIGS. 1 and 2, in the fuel cell 100, a diffusion layer 12C and a water repellent portion 30C are sequentially laminated on the cathode side surface of the membrane electrode assembly 10, and the diffusion layer 12A is formed on the anode side surface. And the water repellent part 30A are sequentially laminated, and are sandwiched by applying pressure from both sides between the cathode side separator 20C and the anode side separator 20A.

  The membrane electrode assembly (MEA) 10 has a structure in which catalyst electrode layers (catalyst layers) are formed on both surfaces of an electrolyte membrane (solid polymer electrolyte membrane), respectively. The membrane electrode assembly 10 can be produced, for example, by forming a catalyst electrode layer by applying a paste-like catalyst electrode material on both surfaces of the electrolyte membrane and subjecting it to a heat drying treatment.

  The electrolyte membrane is a proton conductive ion exchange membrane formed of a solid polymer material such as a fluorine resin, and exhibits good proton conductivity in a wet state. As this electrolyte membrane, for example, a Nafion membrane (manufactured by DuPont) is used. The catalyst electrode layer includes a catalyst metal that promotes an electrochemical reaction, an electrolyte having proton conductivity, and carbon particles having electron conductivity. As the catalyst metal, for example, platinum (Pt) or an alloy composed of Pt and another metal (for example, a Pt alloy in which cobalt or nickel is mixed) can be used. As the electrolyte, a fluorine-based resin that conducts hydrated protons via a sulfonic acid group, for example, a Nafion solution, is used as in the electrolyte membrane. The catalyst metal is supported on carbon particles, and in each catalyst electrode, carbon particles (catalyst particles) supporting the catalyst metal and an electrolyte are mixed. Carbon particles for supporting a catalytic metal (hereinafter referred to as “supporting carbon particles”) are generally made of carbon particles (carbon powder) that are commercially available, and have their water repellency improved by heat treatment. Hydrated carbon particles are used. The catalyst electrode material is obtained by kneading a mixed aqueous solution of the catalyst particle electrolyte into a paste.

  The diffusion layers 12C and 12A are made of a gas permeable conductive member, for example, a carbon porous body such as carbon cloth or carbon paper, or a metal porous body such as a metal mesh or foam metal.

The water repellent portions 30C and 30A are made of a water repellent member, for example, a water repellent resin material such as a fluororesin. As shown in FIGS. 1 and 2, the cathode-side water-repellent portion 30C is provided between the cathode-side separator 20C and the diffusion layer 12C, with a serpentine-type channel space GFC (GFC1, GFC1-2, GFC2, GFC2). −3, GFC3) function as rib portions on both sides (hereinafter also referred to as “flow channel rib portions”). This flow path space GFC becomes an oxidizing gas flow path (corresponding to a reaction fluid flow path) through which air containing oxygen (O ₂ ) that is an oxidizing gas as a reaction gas (corresponding to the reaction fluid) passes. Similarly, the anode-side water-repellent part 30A has a fuel gas flow path (reaction fluid flow) through which hydrogen (H ₂ ) as a reaction gas passes between the anode-side separator 20A and the diffusion layer 12A. It functions as a flow channel rib on both sides constituting a flow channel space.

  The separators 20C and 20A can be formed of a gas-impermeable conductive member, for example, dense carbon that is compressed by gas and impermeable to gas, or a press-molded metal plate. On the surface of the cathode-side separator 20C on the diffusion layer 12C side, as shown in FIGS. 1 and 2, a convex rib portion (hereinafter referred to as “section flow”) that divides the oxidizing gas flow path GFC into a plurality of section flow paths FPC. RPC) (also referred to as “road rib portion”) is formed so as to be in contact with the diffusion layer 12C. Similarly, on the surface of the anode-side separator 20A on the diffusion layer 12A side, a convex rib portion (segmented channel rib portion) RPA that divides the fuel gas channel GFA into a plurality of segmented channels FPA is formed. .

  In addition, although illustration is abbreviate | omitted, the refrigerant | coolant flow path is provided in the outer surface side of separator 20C, 20A. Further, on the outer peripheral side of the fuel cell 100, a manifold connected to the reaction gas flow path and the refrigerant flow path is provided.

  Here, as shown in FIG. 2, the oxidant gas flow paths GFC1, GFC2, and GFC3 adjacent to each other are separated by flow path rib portions 30C that are water repellent portions. The oxidizing gas flow paths GFC1, GFC2, and GFC3 are divided into a plurality of divided flow paths FPC by the divided flow path rib portions RPC. The liquid water present in the portion of the diffusion layer 12C in contact with the divided flow channel rib portion RPC and the divided flow channel FPC passes through the wall surface of the divided flow channel rib portion RPA or by the flow of oxidizing gas in the divided flow channel FPC. It is sucked up and discharged. For this reason, the oxidant gas can be diffused through the portion of the diffusion layer 12C in contact with the divided flow path rib portion RPC.

  On the other hand, since the contact surface of the diffusion layer 12C that is in contact with the flow path rib portion 30C has water repellency, liquid water is sucked into the divided flow path FPC through the wall surface of the flow path rib portion 30C. It becomes difficult. For this reason, since the dam-like staying liquid water part Lw is formed in the part of the diffusion layer 12C in contact with the flow path rib part 30C, the diffusion of the oxidizing gas through this part is inhibited. As a result, the oxidizing gas flows along the oxidizing gas flow path GFC (GFC1, GFC1-2, GFC2, GFC2-3, GFC3) divided by the flow path rib portion 30C. For example, the oxidizing gas flowing through the oxidizing gas flow path GFC1 can be prevented from diffusing through the diffusion layer 12C and flowing to the region corresponding to the oxidizing gas flow path GFC2. Note that if the weir-like staying liquid water portion Lw is equal to or smaller than a certain width (about 3 mm), it can be said that gas can be supplied by gas diffusion in the catalyst electrode layer, and there is no influence on power generation. Therefore, the width of the flow path rib portion 30C may be set so that the weir-like staying liquid water portion Lw has a certain width (about 3 mm) or less.

  In the above description, the oxidizing gas passage on the cathode side has been described, but the same applies to the fuel gas passage on the anode side.

  As described above, in the fuel cell of the present embodiment, the dam-like staying liquid water portion is formed in the diffusion layer in contact with the flow channel rib portion formed of the water repellent member, and the reaction gas is formed in the flow channel rib portion. Since it flows along, the generation | occurrence | production of the shortcut of a reactive gas can be suppressed. In addition, since the flow path rib part composed of the water repellent member is sandwiched between the separator and the diffusion layer, the water repellent coating is applied, for example, when the rib part contacting the diffusion layer is water repellent coated. Does not peel off and has excellent durability.

  FIG. 3 is a schematic perspective view showing the region RCa shown in FIG. 1 in an enlarged manner. This region RCa is a region where the flow of the oxidizing gas that has flowed through the oxidizing gas channel GFC1-2 changes in the direction of the oxidizing gas channel GFC2 (also referred to as “flow direction changing unit”).

  In the outer peripheral side portion of the flow direction changing portion RCa (the corner portion of the flow path rib portion 30C in the example shown in the figure), the liquid water pool Wp is usually easily formed. Temporarily, the wall surface of the outer peripheral side portion of the flow direction changing portion RCa is not the flow channel rib portion 30C formed of the water repellent member as in the embodiment, but the divided flow channel rib portion RPC formed on the surface of the separator 20C. Assume a similar structure. In this case, once the liquid water pool Wp is formed, the formed liquid water pool Wp is likely to be in close contact with the wall surface, so that the oxidizing gas is difficult to separate between the liquid water pool Wp and the wall surface, and drainage is difficult. Become. For this reason, the supply of oxidizing gas is deficient with respect to the region of the membrane electrode assembly corresponding to the flow path where the liquid water pool Wp exists, and the power generation performance in this region is lowered, resulting in the power generation performance of the entire fuel cell. Will drop.

  On the other hand, in the case of the present embodiment, the wall surface of the outer peripheral side portion of the flow changing portion RCa is the wall surface of the channel rib portion 30C formed of the water repellent member, so that the adhesion of liquid water is low. Even if the water pool Wp is formed, the oxidizing gas easily enters between the liquid water pool Wp and the wall surface, and is easily drained.

  Although FIG. 3 has been described with respect to the region RCa in FIG. 1, the same applies to the other regions RCb, RCc, and RCd. However, when the oxidizing gas channel GFC is arranged along the vertical plane, and the oxidizing gas channel GFC1 is arranged on the upper side and the oxidizing gas channel GFC3 is arranged on the lower side, it is effective in the regions RCa and RCb. is there. Further, when the oxidizing gas flow path GFC is arranged along the vertical plane, and the oxidizing gas flow path GFC3 is on the upper side and the oxidizing gas flow path GFC1 is on the lower side, it is effective in the regions RCc and RCd. is there.

  Although the above description has been given of the flow direction changing portion of the oxidation gas flow path on the cathode side, the same applies to the fuel gas flow path on the anode side.

  FIG. 4 is an explanatory view showing a modified example of the water repellent part constituting the fuel cell of the present invention. Instead of the water repellent portions 30C and 30A shown in FIG. 1, water repellent portions 30Ca and 30Aa having shape stabilizing portions 32Ca and 32Aa may be used as shown in FIG. In this case, since it becomes easy to keep the shape of the water repellent part in a stable state, the water repellent part is easy to handle, and the positioning of the water repellent part during assembly of the fuel cell is facilitated.

  FIG. 5 is an explanatory view showing a modified example of the membrane electrode assembly, the diffusion layer, and the water repellent part constituting the fuel cell of the present invention. The fuel cell 100 of the embodiment shown in FIG. 1 has a configuration in which diffusion layers 12C and 12A and water repellent portions 30C and 30A are sequentially stacked on a membrane electrode assembly 10 and sandwiched between separators 20C and 20A. However, as shown in FIG. 5, on a membrane electrode diffusion layer assembly (MEGA) 14 in which diffusion layers 12 </ b> C and 12 </ b> A are integrally formed on the catalyst electrode layer of the membrane electrode assembly 10. The membrane electrode diffusion layer assembly 16 in which the water repellent portions 30C and 30A are thermocompression bonded at a temperature equal to or higher than the melting point of the water repellent member may be used. Since this membrane electrode diffusion layer assembly 16 has the membrane electrode diffusion layer assembly 14 sandwiched between the water repellent portions 30C and 30A from both sides, a frame for improving the handling of the membrane electrode diffusion layer assembly 14 which is a thin film. Also serves as a function. Thereby, the frame for handling a membrane electrode assembly and a diffusion layer can be reduced at the time of assembly of a fuel cell. In the case of the configuration of the fuel cell 100 shown in FIG. 1, it is difficult to position the water repellent portions 30C and 30A and the separators 20C and 20A during assembly. However, if the membrane electrode diffusion layer assembly 16 shown in FIG. 5 is used, positioning can be easily performed. Further, since the water repellent portions 30A and 30C are thermocompression bonded to the diffusion layers 12C and 12A, the diffusion layers 12C and 12A of the water repellent portions 30C and 30A are compared with the case of the configuration of the fuel cell 100 shown in FIG. It is possible to enhance the adhesion to the gas and to enhance the shortcut effect of the reactive gas.

  In addition, this invention is not restricted to said Example and embodiment, In the range which does not deviate from the summary, it is possible to implement in various aspects.

  In the above embodiment, the case of the serpentine type reaction gas channel has been described as an example. However, in the parallel type reaction gas channel, the composite type reaction channel, etc. It is possible to provide flow path rib portions formed of water members. Also, in the reaction gas flow channel using a porous material channel made of a porous material such as foam metal or an expanded metal, the rib portion constituting the wall surface that partitions between adjacent porous material channels (corresponding to the above-mentioned channel rib portion) Can be a rib portion made of a water-repellent member. Even in the case of a reaction gas flow path using a porous body flow path, it is configured to have a divided flow path rib section that is divided into a plurality of divided flow paths and a flow path rib section that is divided into a plurality of divided flow paths. You can also. As described above, in various reaction gas flow paths, at least a part of the rib portions constituting the wall surface of the reaction gas flow path can be formed of a water repellent member.

  In the above-described embodiment, the case where the channel rib portions of both the oxidizing gas channel and the fuel gas channel are configured by the water repellent member is shown. However, the channel rib portion of either one of the reaction gas channels is water repellent. You may make it comprise with a member.

DESCRIPTION OF SYMBOLS 100 ... Fuel cell 10 ... Membrane electrode assembly 12A, 12C ... Diffusion layer 14 ... Membrane electrode diffusion layer assembly 16 ... Membrane electrode diffusion layer assembly 20A, 20C ... Separator 30A, 30Aa, 30C, 30Ca ... Water repellent part (flow) Road rib part)
32Ca ... shape stabilizing part GFC1 ... oxidizing gas channel GFC2 ... oxidizing gas channel GFC1-2 ... oxidizing gas channel GFC3 ... oxidizing gas channel Lw ... stagnant liquid water part GFA ... channel space (fuel gas channel)
GFC: Channel space (oxidizing gas channel)
FPA ... Sectional flow path RPA ... Sectional flow path rib part FPC ... Sectional flow path RPC ... Sectional flow path rib part RCa, RCb, RCc ... Area (flow direction changing part)
Wp ... Puddle of liquid water

Claims (4)

A membrane electrode assembly in which a catalyst electrode layer is formed on each side of a solid polymer electrolyte membrane; a diffusion layer disposed on each side of the membrane electrode assembly; and the membrane electrode assembly and the diffusion layer A fuel cell comprising a sandwiching separator,
A reaction fluid flow path is provided between at least one of the separator and the diffusion layer,
At least a part of the rib portions constituting the wall surface of the reaction fluid flow path is formed of a water repellent member. The fuel cell according to claim 1,
The rib portion of the reaction fluid channel includes: a segment channel rib unit that divides the reaction fluid channel into a plurality of segment channels; and a channel rib unit that segments each segment channel. Including
The fuel cell, wherein the flow path rib portion is formed of the water repellent member. The fuel cell according to claim 2, wherein
The reaction fluid flow path has a flow direction changing portion for changing the flow direction of the reaction fluid flowing inside,
The fuel cell, wherein the flow path rib portion separating the outer peripheral side of the flow direction changing portion is formed of the water repellent member. A membrane electrode diffusion layer assembly in which a catalyst electrode layer and a diffusion layer are sequentially formed on both sides of a solid polymer electrolyte membrane, sandwiched between separators in a fuel cell,
In the fuel cell, a reaction fluid flow path is provided between at least one of the separators and the diffusion layer,
At least a part of the rib portion constituting the wall surface of the reaction fluid channel is formed of a water repellent member,
The membrane / electrode diffusion layer assembly is characterized in that the water repellent member is formed on the diffusion layer.

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