JP2007123197A - Gas diffusion electrode for fuel cell and method of manufacturing the same, and polymer electrolyte fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas diffusion electrode for a fuel cell which is improved in water drainage, and also to provide a polymer electrolyte fuel cell. <P>SOLUTION: The gas diffusion electrode 12 for the fuel cell comprises a catalyst layer 3, and a conductive and porous gas diffusion layer 7. The surface of the gas diffusion layer 7 being contacting with the catalyst layer 3 has at least one groove 14 for making fluid circulate or store therein, and the groove has a convex-concave structure on the bottom in parallel to the longitudinal direction of the groove and is opened to the outside at least one end. The polymer electrolyte fuel cell uses the gas diffusion electrode for the fuel cell. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a gas diffusion electrode for a fuel cell, a production method thereof, and a polymer electrolyte fuel cell.

  The polymer electrolyte fuel cell is expected as a future energy generation device because of its high energy conversion efficiency, cleanliness, and quietness. In particular, in recent years, not only for applications such as automobiles and household generators, but also because of its high energy density and low operating temperature, it can be installed in small electrical devices such as mobile phones, laptop computers, and digital cameras. It has the potential to be driven for a longer time than conventional secondary batteries, and is attracting attention.

  However, although the polymer electrolyte fuel cell can be driven even at an operating temperature of 100 ° C. or lower, there is a problem that the voltage gradually decreases with the lapse of the power generation time and the power generation stops at the end. This is due to the so-called “flooding” in which the power generation reaction is stopped by blocking the supply of the fuel gas, which is a reactant, because the water generated by the reaction stays in the gap that becomes the fuel gas ventilation hole. is there. In particular, flooding is likely to occur in the catalyst layer on the cathode side where water is generated.

  Further, for practical use as a fuel cell for a small electric device, it is essential to make the entire system compact. In particular, when a fuel cell is mounted on a small electrical device, it is necessary to downsize the battery itself, and a method of supplying air from the vent hole to the air electrode by natural diffusion without using a pump or a blower (air breathing) : Air Breathing). In such a case, since generated water can be discharged out of the fuel cell only by natural evaporation, flooding often occurs.

  In general, a separator of a fuel cell is provided with a fluid circulation groove for preventing flooding, and this groove is used as a gas diffusion path and a drainage flow path of generated water. Furthermore, in order to smoothly discharge water, a water repellent such as polytetrafluoroethylene (PTFE) is applied to the groove surface of the separator as necessary, and the separator material, groove processing method, groove shape, etc. are devised. Or Further, in the air-breathing type fuel cell, the porosity of the gas supply / exhaust part is increased to 90% or more by using a porous conductor such as foam metal instead of the grooved separator, and the generated water Some have been devised to promote natural diffusion of water and to use voids as drainage for generated water.

  However, when the fuel cell is driven at a high current density for a long time, the voltage drop of the fuel cell occurs. This is because water vapor generated by power generation is condensed in the holes of the gas diffusion electrode composed of the gas diffusion layer and the catalyst layer, and flooding occurs in the gas diffusion electrode.

  Further, in a fuel cell of a type in which a membrane-electrode assembly (MEA) is sandwiched by a separator having a gas flow groove or a stacked fuel cell, the diffusion distance of reaction gas and water vapor from the outside of the cell depending on the position in the electrode surface Therefore, the water vapor partial pressure distribution is generated in the plane of the gas diffusion electrode. In this case, when the fuel cell is driven at a high load for a long time, the difference in the water vapor partial pressure distribution becomes large and locally approaches the saturated water vapor pressure. As a result, the generated water vapor locally condenses inside the vacancies inside the gas diffusion electrode, closes the vacancies, and causes local flooding.

In order to prevent such flooding in the gas diffusion electrode, it is necessary to improve the drainage of the gas diffusion electrode.
For this purpose, the inside of the pores of the gas diffusion layer and the catalyst layer is often provided with water repellency by a water repellent such as PTFE.

  As a specific material for the gas diffusion layer, carbon cloth or carbon paper made of a mixture of carbon fibers or carbon fine particles having a diameter of several μm and a hydrophobic polymer such as PTFE is used.

  The catalyst layer is also provided with water repellency by mixing fine particles of hydrophobic polymer such as PTFE. However, since PTFE fine particles are non-conductive and have no catalytic activity, if a large amount of PTFE fine particles are added to increase the hydrophobicity of the catalyst layer, the catalyst activity and the catalyst utilization rate are lowered.

  As described above, the gas diffusion layer and the catalyst layer are provided with water repellency, but the water repellency of both is often adjusted so that catalyst layer> gas diffusion layer. This is to move the condensed water from the catalyst layer to the gas diffusion layer and to prevent back flow of water from the gas diffusion layer to the catalyst layer.

  However, soaking water into a porous body imparted with hydrophobicity has a large resistance in principle, so the penetration rate of water into the gas diffusion layer is slow, and when the fuel cell is driven at a high load, the catalyst layer The amount of generated water generated by condensation exceeds the permeation rate into the gas diffusion layer, and the condensed water stays at the gas diffusion layer / catalyst layer interface.

  On the contrary, the produced water may condense in the gas diffusion layer. In this case, the produced water is pushed out to the surface of the gas diffusion layer, but a part of the condensed water is deposited at the gas diffusion layer / catalyst layer interface. . And since both a catalyst layer and a gas diffusion layer are hydrophobic, as a result of being hard to permeate into both pores, condensed water that stays at the interface is generated.

  When the power density of the fuel cell is low, all the generated water diffuses with water vapor, so that the above-mentioned problem does not occur. However, when the fuel cell is driven at a high current density for a long time, as described above, due to the difference in the water vapor diffusion rate distribution, the portion of the water vapor partial pressure locally increases in the vicinity of the saturated water vapor pressure in the gas diffusion electrode. Therefore, the amount of product water condensed in the gas diffusion layer or the catalyst layer increases with the driving time. In such a case, the condensed water staying at the gas diffusion layer / catalyst layer interface increases as described above.

  When the generated water stays at the gas diffusion layer / catalyst layer interface, even if a small amount of water is formed, a wide area water film is formed, so that the supply area of the reaction gas to the catalyst layer is greatly reduced. As a result, the fuel cell The voltage will drop significantly or power generation will stop.

  As described above, in the method of imparting water repellency to the gas diffusion layer and the catalyst layer, when the fuel cell is driven at a high load for a long time, there is a problem that condensed water stays at the gas diffusion layer / catalyst layer interface. In other words, the drainage performance of the gas diffusion electrode could not be improved efficiently.

  In order to solve such a problem, a method (Patent Document 1) is proposed in which a filler composed of two kinds of fine particles having different hydrophobicity is mixed in the gas diffusion layer to separate the drainage path and the reaction gas diffusion path. Yes.

Furthermore, a method of providing a drainage groove on the surface of the catalyst layer in contact with the gas diffusion layer (Patent Documents 2 and 3), a method of providing a through hole in the gas diffusion layer (Patent Document 4), and a hydrophobic through hole in the gas diffusion layer And a method of providing a hydrophilic through hole (Patent Document 5) has also been proposed.
JP-A-10-289723 JP 2004-327358 A JP 2005-38780 A JP 2005-85517 A JP 2003-151585 A

However, the conventional method as described above has the following problems.
First, in the case of the configuration described in Patent Document 1, since the drainage path and the reaction gas diffusion path in the gas diffusion layer are expected to be formed by chance, the structure of each path is not controlled. The path and the reaction gas diffusion path may be longer than necessary. Alternatively, there is a problem in that both paths are connected in the middle, and the drainage may stop in the middle and block the gas diffusion path.

  Further, in the case of the structure described in Patent Documents 2 and 3, in which the groove for drainage is provided on the surface of the catalyst layer in contact with the gas diffusion layer, the catalyst loading amount is reduced by an amount corresponding to the groove volume, so that the reaction of the catalyst. There is a problem that the area is reduced and the output density of the fuel cell is lowered.

  Moreover, in the structure which provides a through-hole in the gas diffusion layer of patent document 4, distribution of a through-hole is optimally arrange | positioned according to the water vapor partial pressure distribution in an electrode surface. However, since there is no connection between the distributions of the through holes, the desired effect cannot be obtained if the current density distribution in the electrode surface, that is, the variation of the water vapor partial pressure distribution varies from the design value. was there. Since the water vapor partial pressure distribution in the electrode surface fluctuates easily and greatly depending on the air supply flow direction, there is a problem that the effect cannot be obtained in a fuel cell of a type in which the air supply flow direction is not constant. It was.

  In addition, the water vapor partial pressure distribution varies greatly depending on the fuel cell operating conditions, such as immediately after starting the fuel cell, during long-time driving, and immediately after stopping and restarting after long-time driving, as well as fuel cell load fluctuations Depending on the situation. Therefore, the above-described configuration is effective for a fuel cell that has almost no load fluctuation, such as a stationary fuel cell, and that has a low frequency of starting and stopping mainly in continuous operation. However, in a fuel cell for small electrical equipment that is frequently started and stopped and is capable of following a certain amount of load fluctuation, there is a problem that the flooding suppression effect by the above configuration can be obtained only in a limited manner.

  Moreover, in the structure which provided the through-hole in the gas diffusion layer described in patent document 5, and the through-hole was completely isolate | separated into the gas diffusion path and the water diffusion path, as described in Example 2, as the diffusion layer base material Non-porous material such as metal is used. In this case, it is difficult for the fuel gas to reach the catalyst in contact with the base material and the reaction area of the catalyst is reduced. As a result, although flooding can be suppressed, the limiting current density is reduced due to the reaction gas supply rate limiting. It was.

  Furthermore, since the through hole is completely separated from the gas diffusion path and the water diffusion path, in the case of an air-breathing type fuel cell that uses a porous conductor such as foam metal instead of the separator, the above structure is used. There is a problem that the flooding suppression effect can be obtained only in a limited manner.

  This is because the pores in the conductive porous body usually have a continuous pore structure, so the inside of the pores can only be controlled to be either hydrophobic or hydrophilic, and the gas diffusion layer can be used for gas diffusion. This is because no matter how much the through hole and the water diffusion through hole are separated, both paths intersect in the conductive porous body.

The conventional technique has the above-described problems, and a technique for efficiently improving the drainage of the gas diffusion electrode has been demanded.
The present invention has been made in view of the above circumstances, and a gas diffusion electrode for a fuel cell with improved drainage by providing a groove for circulating or accumulating fluid on the surface of the gas diffusion layer in contact with the catalyst layer. And a manufacturing method thereof.

  The present invention also provides a polymer electrolyte fuel cell having stable power generation characteristics using the gas diffusion electrode described above at low cost.

The present invention has been made through extensive studies to solve the above-described problems, and has the following configuration.
A gas diffusion electrode for a fuel cell that solves the above-described problems is a gas diffusion electrode for a fuel cell that includes a catalyst layer and a conductive porous gas diffusion layer. It is characterized in that at least one groove for circulating or accumulating is provided.

It is preferable that the bottom of the groove has irregularities parallel to the length direction of the groove.
At least one end of the groove is preferably open to the outside of the gas diffusion layer.
It is preferable that the width of the groove is reduced from the central portion toward the outer peripheral portion.

The width of the groove is preferably 1 μm or more and 1000 μm or less.
The interval between the grooves is preferably 5 μm or more and 1000 μm or less.
It is preferable that the pores of the gas diffusion layer are hydrophobic, and the surface of the groove is hydrophilic.

It is preferable that the pores of the gas diffusion layer are hydrophilic and the surface of the groove is hydrophobic.
The surface of the gas diffusion layer in contact with the catalyst layer is preferably composed of one or more selected from the group consisting of carbon fine particles, carbon fiber, foam metal, foam alloy and metal fiber.

The gas diffusion electrode is preferably a cathode.
In addition, a method for manufacturing a gas diffusion electrode for a fuel cell that solves the above-described problem is a method for manufacturing a gas diffusion electrode for a fuel cell that includes a catalyst layer and a conductive porous gas diffusion layer. And a step of forming a groove for circulating or accumulating a fluid by irradiating a surface in contact with the catalyst layer with a laser.

Further, a polymer electrolyte fuel cell that solves the above-described problems is characterized by using the fuel cell gas diffusion electrode.
The present invention also provides a polymer electrolyte fuel cell having stable power generation characteristics at a low cost by using the gas diffusion electrode with improved drainage.

  According to the present invention, water stays at the interface between the gas diffusion layer and the catalyst layer, and flooding that hinders the supply of the reaction gas can be reduced. Therefore, the fuel cell can be stably driven for a long time with a high load. it can.

ADVANTAGE OF THE INVENTION According to this invention, the gas diffusion electrode for fuel cells which improved the drainage property can be provided by providing the groove | channel which distribute | circulates or stores a fluid in the surface which contact | connects the catalyst layer of a gas diffusion layer.
In addition, the present invention can provide a polymer electrolyte fuel cell using the above gas diffusion electrode and having stable power generation characteristics at low cost.

Exemplary embodiments of a gas diffusion electrode of a polymer electrolyte fuel cell of the present invention will be described below in detail with reference to the drawings.
However, the materials, dimensions, shapes, relative arrangements, and the like of the constituent members described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. Absent. Similarly, the manufacturing method described below is not the only one.

  A preferred embodiment is a fuel cell gas comprising a catalyst layer and a conductive porous gas diffusion layer, wherein at least one groove for circulating or storing fluid is provided on a surface of the gas diffusion layer in contact with the catalyst layer. It is a diffusion electrode (hereinafter referred to as “grooved GDE, Gas Diffusion Electrode”).

  FIG. 1 is a schematic diagram showing an example of a cross-sectional configuration of a single polymer electrolyte fuel cell unit cell produced using the grooved GDE of the present invention. In FIG. 1, 1 is a solid polymer electrolyte membrane, and a pair of catalyst layers, that is, a catalyst layer 2 on the anode side and a catalyst layer 3 on the cathode side are arranged with this sandwiched therebetween.

  In the present embodiment, an example in which the grooved GDE of the present invention is arranged only on the cathode (air electrode) side is shown, but the arrangement configuration is not limited thereto. For example, it includes the case where the grooved GDE of the present invention is disposed on both poles, or the case where the grooved GDE of the present invention is disposed only on the anode side, and various configurations can be preferably selected.

  The cathode side catalyst layer 3 includes a catalyst 4 and a catalyst carrier 5 that supports the catalyst 4. An anode side gas diffusion layer 6 and an anode side electrode (fuel electrode) 8 are arranged outside the catalyst layer 2 on the anode side. A cathode-side gas diffusion layer 7, a porous conductor 13, and a cathode-side electrode (air electrode) 9 are disposed outside the catalyst layer 3 on the cathode side. Reference numeral 14 denotes a groove provided in the cathode-side gas diffusion layer 7.

  The solid polymer electrolyte membrane 1 is formed of a polymer material such as a perfluorocarbon polymer having a sulfonic acid group or a non-fluorine polymer. For example, a sulfonic acid type perfluorocarbon polymer, a polysulfone resin, a phosphonic acid group or a carboxyl group is used. A perfluorocarbon polymer having an acid group can be preferably used. An example of a perfluorosulfonic acid polymer is Nafion (manufactured by DuPont) 112. Examples of the non-fluorine polymer include sulfonated square structure polyether ketone and polysulfone.

When proton H ⁺ moves in the electrolyte membrane toward the cathode side, the electrolyte membrane also has a function of holding water molecules because the hydrophilic portion in the electrolyte moves using water molecules as a medium. Is preferred. Therefore, the function of the solid polymer electrolyte membrane is to transmit proton H ⁺ generated on the anode side to the cathode side and not to pass unreacted reaction gases (hydrogen and oxygen) and to have a predetermined water retention function. is necessary. Any one satisfying this condition can be selected and used.

  The catalyst layer 4 is a porous layer composed of an electron conductor having hydrogen reducing ability or oxygen oxidizing ability and a proton conducting electrolyte. Any catalyst layer can be selected and used as long as it has catalytic ability (hydrogen reduction ability or oxygen oxidation ability) for fuel cell reaction, proton conductivity, electron conductivity, and gas diffusibility.

  Specifically, fine particles comprising platinum group metals such as platinum, rhodium, ruthenium, iridium, palladium, osmium, and alloys thereof can be used as the catalyst. As the catalyst layer, a porous layer in which catalyst fine particles are mixed with a proton conductive electrolyte and processed into a layer shape, or a catalyst in which the catalyst fine particles are dispersed and supported on a carrier such as carbon fine particles is mixed with a proton conductive electrolyte. A porous layer processed into a layer shape can be preferably used. It is more preferable to mix a water repellent with the catalyst layer.

  The role of the catalyst carrier 5 is to improve the catalytic activity as a co-catalyst, to maintain the shape of the hydrophobic catalyst 4, to secure the electron conduction channel, to increase the specific surface area, etc. For example, carbon black, platinum fine particle layer or gold fine particle film layer It can be preferably used. Note that the catalyst carrier 5 is not necessarily used.

  The gas diffusion layers 6 and 7 supply the fuel gas or air uniformly and sufficiently in the plane to the electrode reaction region in the catalyst layer of the fuel electrode or the air electrode in order to efficiently perform the fuel cell reaction, The charge generated by the anode electrode reaction is released to the outside of the single cell, and the reaction product water and unreacted gas are efficiently discharged to the outside of the single cell.

  The gas diffusion layer may be a conductive porous material, and preferably has a hydrophobic property. Specifically, those made of at least one material selected from the group consisting of hydrophobic resin, carbon fine particles, carbon fiber, foam metal, foam alloy and metal fiber are preferable. For example, carbon cloth or carbon paper can be preferably used.

  Next, FIG. 2 is a scanning electron micrograph (magnification 100 times) showing the groove cross-sectional structure of the thin film of the gas diffusion layer used in the grooved GDE of the example of the present invention. FIG. 3 is a scanning electron micrograph (magnification 500 times) showing the groove cross-sectional structure of the same gas diffusion layer as FIG.

  As shown in FIGS. 2 and 3, for example, the grooved GDE of the present invention is a catalyst for the gas diffusion layer in a gas diffusion electrode for a fuel cell composed of a catalyst layer and a conductive porous gas diffusion layer. The surface contacting the layer side is provided with a fluid circulation groove or a groove acting as a fluid reservoir. By doing so, even if the generated water stays at the interface between the catalyst layer and the gas diffusion layer, the generated water is guided into the groove, so that the water stays at the interface and does not stretch a thin wide film. Thus, it is possible to prevent a significant decrease in the area of gas supply to the catalyst layer.

  4A and 4B are schematic views showing a part of a gas diffusion layer used in the grooved GDE of the present invention. FIG. 4A is a plan view, and FIG. 4B is a cross-sectional view taken along the line AA ′. In FIG. 4, at least one groove 14 is provided on the surface of the gas diffusion layer 7 in contact with the catalyst layer side. The bottom 15 of the groove 14 is preferably provided with irregularities having a concave portion 16 and a convex portion 17 parallel to the length direction of the groove. Moreover, it is preferable that at least one end of the groove is open to the outer side 18 of the gas diffusion layer 7.

  Since at least one end of the groove of the grooved GDE is open to the outside of the gas diffusion layer surface, water accumulated in the groove is easily discharged from the end surface of the gas diffusion layer. Further, in cases other than the high-power operation where water discharge is a problem, the groove is not filled with water, so that the groove can be used as a diffusion path for the reaction gas and water vapor.

  The groove provided on the surface of the gas diffusion layer in contact with the catalyst layer has a groove width W of 1 μm to 1000 μm, preferably 10 μm to 100 μm. If it is less than 1 μm, the width of the groove becomes too small and the viscosity force in the groove of condensed water increases, so that the water flow resistance increases and the drainage capacity decreases. If the thickness exceeds 1000 μm, the width of the groove becomes too large. Therefore, when the gas diffusion layer is laminated on the MEA, the MEA or the gas diffusion layer may be deformed and the groove may be crushed.

  Further, the depth D of the groove provided in the gas diffusion layer is 1 μm or more, preferably 5 μm or more. If the depth is less than 1 μm, the depth of the groove is small, so that the viscous force in the groove of condensed water increases, so that the water transfer resistance increases and the drainage capacity decreases. The upper limit of the groove depth D is not strictly limited, but is preferably about half the thickness of the gas diffusion layer. If the depth D of the groove becomes too large with respect to the thickness of the gas diffusion layer, the mechanical strength of the gas diffusion layer itself is weakened, which is not preferable because the gas diffusion layer is easily broken when the fuel cell is assembled. .

  Further, one or a plurality of grooves are provided on the surface of the gas diffusion layer in contact with the catalyst layer, but it is preferable to provide a plurality of grooves. When a plurality of grooves are provided, the distance between the grooves is preferably 5 μm or more and 1000 μm or less, and more preferably 10 μm or more and 100 μm or less. If the thickness is less than 5 μm, the groove interval becomes too small, and the flange between the grooves tends to peel off. On the other hand, if it is 1000 μm or more, the groove interval becomes too large, and the distance until the condensed water generated between the grooves reaches the groove part becomes too long, so that the drainage is deteriorated.

When the surface of the groove is made hydrophilic, the inside of the pores of the gas diffusion layer is preferably made hydrophobic.
In this way, the groove can be made independent as a drainage path and the pores of the gas diffusion layer can be made independent as a gas diffusion path. It is possible to efficiently supply to the layer.

  On the contrary, when the surface of the groove is made hydrophobic, it is preferable that the pores of the gas diffusion layer are made hydrophilic. In this way, the groove can be made independent as a gas diffusion path and the pores of the gas diffusion layer as drainage paths, so that the gas diffusibility is less likely to be hindered by water and the reaction gas can be catalyzed. It is possible to efficiently supply to the layer.

  The width of the groove is preferably reduced from a high water vapor partial pressure portion toward a low water vapor partial pressure portion. Water vapor generated by power generation tends to agglomerate in the portion where the water vapor partial pressure is high, but by forming the groove width as described above, the condensed water is reduced to the portion where the water vapor partial pressure is low due to the capillary force and Knudsen effect. Since it can be guided or dispersed, local flooding can be made difficult to occur. For example, the width of the groove is preferably reduced from the central portion toward the outer peripheral portion.

  The surface of the gas diffusion layer in contact with the catalyst layer is a conductive porous material made of at least one material selected from the group consisting of carbon fine particles, carbon fiber, foam metal, foam alloy and metal fiber. It is preferable that

  The gas diffusion electrode is preferably a cathode. In the polymer electrolyte fuel cell, generated water is generated in the catalyst layer on the cathode side, so that flooding is likely to occur at the cathode, and the effect of the present invention is great.

  Next, the manufacturing method of the gas diffusion electrode for fuel cells of this invention is demonstrated. The method for producing a gas diffusion electrode for a fuel cell according to the present invention includes a step of forming a groove for circulating or storing a fluid by irradiating a surface of the gas diffusion layer in contact with the catalyst layer with a laser.

  As a method of providing a groove on the surface of the gas diffusion layer in contact with the catalyst layer, it is preferable to use a laser. By machining with a laser, the groove can be machined accurately and at low cost. When carbon cloth is used as the gas diffusion layer, the groove shape is preferably processed on the carbon fine particle layer side. Normally, carbon cloth has a surface made of carbon fiber woven fabric and a surface made of carbon fine particle layer on the front and back, but since the surface made of carbon cloth is woven fabric, it is difficult to accurately process the groove shape. It is.

  As the kind of laser for processing the groove, any laser can be used as long as it can cut the carbon fine particle layer. However, if an excessively high power laser is irradiated, the gas diffusion layer itself is cut in a short time, resulting in poor workability.

In addition, when the inside of the groove is made hydrophilic, it is preferable to make the hydrophobic resin on the groove surface hydrophilic at the same time as the groove processing because the number of steps can be reduced and the manufacturing cost can be reduced.
For example, when the hydrophobic resin that is a water repellent in the gas diffusion layer is made of a fluorocarbon polymer, an excimer laser such as ArF or KrF is irradiated to the gas diffusion layer in an atmosphere of water vapor or hydrazine. This is preferable because the defluorination reaction proceeds from the C—F group in the fluorocarbon polymer, and the groove surface is hydrophilized simultaneously with the formation of the groove.

  Various methods can be used as a method for producing a single fuel cell using the grooved GDE of the present invention. The following is an example of the configuration shown in FIG. In addition, this invention is not limited to the following manufacturing method at all.

(1) A catalyst layer is prepared.
A platinum-supporting carbon catalyst layer or a platinum black catalyst layer is formed on the PTFE sheet using a doctor blade. The thickness of the catalyst layer is preferably in the range of 20 to 40 μm. The catalyst slurry used in this example is a mixture of platinum-supported carbon (manufactured by Johnson Matthey, HiSPEC 4000) or platinum black (manufactured by Johnson Matthey, HiSPEC 1000), Nafion, PTFE, IPA (isopropyl alcohol), and water.

(2) Create an MEA.
The solid polymer electrolyte membrane (manufactured by Dupont, Nafion 112) is sandwiched between the pair of catalyst layers produced as described above so that the PTFE sheet is on the outside, and hot pressing is performed. Furthermore, by peeling the PTFE sheet, the pair of catalyst layers are transferred to the solid polymer electrolyte membrane, and the electrolyte membrane and the pair of catalyst layers are joined to obtain a membrane-electrode assembly (MEA).

(3) A grooved gas diffusion layer is prepared.
Using a carbon cloth (LT1400-W manufactured by E-TEK) as a gas diffusion layer, a desired groove shape is processed with a laser on the carbon fine particle layer side. The laser output, beam size, pulse width, scanning speed, etc. are adjusted so as to obtain a desired groove shape.

(4) Create a single cell.
The MEA prepared in (2) is sandwiched between the grooved gas diffusion layer prepared in (3), the fuel electrode, and the air electrode as shown in FIG.

  The present invention is not limited to the polymer electrolyte fuel cell having a single cell configuration, and can also be applied to a polymer electrolyte fuel cell having a configuration in which a plurality of single cells are stacked.

Next, specific examples will be shown to describe the present invention in detail.
Example 1
In this example, a polymer electrolyte fuel cell having the configuration shown in FIG. 1 in the embodiment was produced.

Hereinafter, the manufacturing process of the polymer electrolyte fuel cell according to the present embodiment will be described in detail.
(Process 1)
A platinum black catalyst layer having a thickness of about 20 μm was formed on a PTFE sheet as a transfer layer to the polymer electrolyte membrane by a doctor blade method. The catalyst slurry used here is a kneaded mixture of 1 part by mass of platinum black (manufactured by Johnson Matthey, HiSPEC 1000), 0.07 parts by mass of Nafion, 1 part by mass of IPA, and 0.4 parts by mass of water. At this time, the amount of Pt supported was 5.3 mg / cm ² .

(Process 2)
Two catalyst layers prepared in Step 1 were cut out in accordance with the electrode dimensions, sandwiched between solid polymer electrolyte membranes (manufactured by Dupont, Nafion 112), and hot pressed under press conditions of 8 MPa, 150 ° C., and 1 min. Thereafter, the PTFE sheet was peeled off to transfer the pair of catalyst layers to the polymer electrolyte membrane, thereby joining the electrolyte membrane and the pair of catalyst layers.

(Process 3)
A carbon cloth (LT1400-W manufactured by E-TEK) was used as the gas diffusion layer, and the surface of the carbon cloth made of carbon fine particles was irradiated with a YAG laser to process the groove shape. The laser output was 8 W, the beam size was 50 μm, the pulse width was 3 μm / Pulse, and the scanning speed was 25 mm / second. To make the groove width 80 μm, the laser is irradiated twice per groove, the first irradiation is the groove width 50 μm, and the second irradiation is shifted in the groove width direction by 30 μm from the first irradiation. I went.

  Scanning electron micrographs of the groove shape after processing are shown in FIG. 2 (magnification 100 times) and FIG. 3 (magnification 500 times). As can be seen from these figures, a groove having a width of about 80 μm and a depth of about 25 μm is formed in the carbon fine particle layer.

  The above operation was repeated to obtain a gas diffusion layer in which grooves having a width of 80 μm were arranged on the entire surface of the carbon fine particle layer at intervals of 80 μm. Thereafter, the gas diffusion layer was cut out according to the electrode dimensions, and all the groove end portions were opened at the side surfaces of the gas diffusion layer.

(Process 4)
The grooved gas diffusion layer obtained in step 3 is disposed on the cathode side of the MEA obtained in step 2, and the gas diffusion layer not grooved is disposed on the anode side, and further, a fuel electrode plate and an air electrode plate A single cell was formed by sandwiching a foam metal (Sumitomo Electric, Celmet 2 mm thickness, stainless steel), which is a kind of porous conductor, as shown in FIG. Here, a slit was provided in the fuel electrode plate so that hydrogen gas could flow.

  On the other hand, the air electrode plate was not provided with a slit. In this configuration, air and generated water can flow from the surface of the foam metal and the side surface of the gas diffusion layer. In addition, since the groove provided in the cathode side gas diffusion layer is open on the side of the gas diffusion layer, air and generated water can flow more smoothly than when a gas diffusion layer without a groove is used. .

  With respect to the single cell manufactured through the above steps, the characteristics were evaluated using the evaluation apparatus having the configuration shown in FIG. When the anode electrode side was filled with hydrogen gas at the dead end, the cathode electrode side was opened to the atmosphere, and a discharge test was performed at a battery temperature of 80 ° C., current-voltage characteristics as shown in FIG. 6 were obtained. .

As Comparative Example 1, FIG. 6 shows an example in which a single cell prepared in the same manner except that the gas diffusion layer LT-1400W that has not been grooved is used as the cathode is used.
Since the effect of the grooved GDE of the present invention is a reduction in diffusion polarization, in the low current density region where diffusion polarization is small in principle, the difference between the example and the comparative example was not so much seen. However, the difference began to be observed in the vicinity of 300 mA / cm ² , and the effect of the grooved GDE of the present invention became more remarkable as the region became a high current density region, that is, a diffusion polarization controlling region. When the voltage at 600 mA / cm ² , which is the diffusion polarization limiting region, is compared, the single cell of this example can take a voltage of 0.42 V or more, whereas the comparative example has a voltage of about 0.17 V, which is only about 40%. It was not obtained. That is, in the grooved GDE layer of this example, deterioration of battery characteristics due to diffusion polarization was significantly suppressed as compared with the GDE layer of the comparative example. This indicates that the grooved GDE layer of the present invention is superior in drainage to the comparative GDE layer.

Next, FIG. 7 shows the time variation of the voltage when the single cell of Example 1 is continuously generated at a current density of 470 mA / cm ² together with the result of the single cell of Comparative Example 1.
The single cell using the grooved GDE of this example was maintained at a voltage of 0.6 V or more even after 90 minutes, and the voltage increased with the passage of time. In the single cell, the voltage was about 0.05 V lower than that at the start of power generation, and the voltage suddenly became 0 V 82 minutes after the start of power generation, and power generation stopped. In this case, the produced water condensed in the gas diffusion electrode stayed and accumulated at the gas diffusion layer / catalyst layer interface. As a result, the water droplets of the staying water are connected to each other at a certain point in time, forming a thin and wide water film covering the entire gas diffusion layer / catalyst layer interface, so that the supply of oxygen to the catalyst layer is momentarily interrupted. It is thought that the power generation was stopped because of this.

  On the other hand, in the single cell of this example, even if the generated water is condensed in the gas diffusion electrode, the condensed water stays in the groove provided in the gas diffusion layer, so that the oxygen supply to the catalyst layer is blocked. There is no power and power generation continues. Furthermore, the condensed water staying in the groove has the effect of humidifying the electrolyte in the electrolyte membrane and the catalyst layer, so that the proton conductivity of the MEA is improved, the voltage rises with the lapse of power generation time, and on the contrary, the power generation stops. It is thought that the power density of the battery has been improved.

  This is because the grooved GDE layer of this example has better drainage than the GDE layer of the comparative example, and the moisture state at the gas diffusion layer / catalyst interface is autonomously and optimally controlled. It shows that the battery performance stability and power density were improved at the same time.

  The gas diffusion electrode of the present invention can improve drainage from the catalyst layer and the gas diffusion layer by providing a groove at the interface between the gas diffusion layer and the catalyst layer. Can be driven for hours.

  The polymer electrolyte fuel cell provided with the gas diffusion electrode of the present invention can be used as a fuel cell for small electric devices such as a mobile phone, a notebook computer, and a digital camera.

It is a schematic diagram showing an example of a section composition of a polymer electrolyte fuel cell single cell produced using GDE with a groove of the present invention. It is a scanning electron micrograph (100-times multiplication factor) which shows the groove | channel cross-sectional structure of the thin film of the gas diffusion layer used for GDE with a groove | channel of the Example of this invention. It is a scanning electron micrograph (500-times multiplication factor) which shows the groove | channel cross-section structure of the thin film of the gas diffusion layer used for GDE with a groove | channel of the Example of this invention. It is the schematic which shows a part of gas diffusion layer used for GDE with a groove | channel of this invention. It is a schematic diagram of the evaluation apparatus of a polymer electrolyte fuel cell. It is a figure which shows the characteristic of the voltage-current density of the polymer electrolyte fuel cell of Example 1 and Comparative Example 1 of this invention. It is a figure which shows the time change of the voltage in the output current density of 470 mA / cm < ² > of the polymer electrolyte fuel cell of Example 1 and Comparative Example 1 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Solid polymer electrolyte membrane 2 Anode side catalyst layer 3 Cathode side catalyst layer 4 Catalyst 5 Catalyst support 6 Anode side gas diffusion layer 7 Cathode side gas diffusion layer 8 Anode side electrode (fuel electrode)
9 Cathode side electrode (air electrode)
DESCRIPTION OF SYMBOLS 10 Membrane-electrode assembly 11 Anode-side gas diffusion electrode 12 Cathode-side gas diffusion electrode 13 Porous conductor 14 Groove 15 Groove bottom 16 Recess 17 Projection 18 Outside of gas diffusion layer

Claims (12)

  In a gas diffusion electrode for a fuel cell composed of a catalyst layer and a conductive porous gas diffusion layer, at least one groove for circulating or accumulating fluid is provided on a surface of the gas diffusion layer in contact with the catalyst layer. A gas diffusion electrode for a fuel cell.   The gas diffusion electrode for a fuel cell according to claim 1, wherein the bottom of the groove has irregularities parallel to the length direction of the groove.   The gas diffusion electrode for a fuel cell according to claim 1 or 2, wherein at least one end of the groove is open to the outside of the gas diffusion layer.   The gas diffusion electrode for a fuel cell according to any one of claims 1 to 3, wherein a width of the groove is reduced from a central portion toward an outer peripheral portion.   The gas diffusion electrode for a fuel cell according to any one of claims 1 to 4, wherein the groove has a width of 1 µm or more and 1000 µm or less.   The gas diffusion electrode for a fuel cell according to any one of claims 1 to 5, wherein an interval between the grooves is 5 µm or more and 1000 µm or less.   The gas diffusion electrode for a fuel cell according to any one of claims 1 to 6, wherein the pores of the gas diffusion layer are hydrophobic, and the surface of the groove is hydrophilic.   The gas diffusion electrode for a fuel cell according to any one of claims 1 to 7, wherein the inside of the pores of the gas diffusion layer is hydrophilic, and the surface of the groove is hydrophobic.   The surface of the gas diffusion layer in contact with the catalyst layer is made of at least one selected from the group consisting of carbon fine particles, carbon fiber, foam metal, foam alloy and metal fiber. A gas diffusion electrode for a fuel cell according to any one of the above items.   The gas diffusion electrode for a fuel cell according to any one of claims 1 to 9, wherein the gas diffusion electrode is a cathode.   In a method for producing a gas diffusion electrode for a fuel cell comprising a catalyst layer and a conductive porous gas diffusion layer, a fluid is circulated or accumulated by irradiating a surface of the gas diffusion layer in contact with the catalyst layer with a laser. The manufacturing method of the gas diffusion electrode for fuel cells characterized by including the process of forming a groove | channel.   A polymer electrolyte fuel cell using the gas diffusion electrode for a fuel cell according to any one of claims 1 to 10.