JP2012119169A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the durability of an electrolyte membrane having high proton conductivity.SOLUTION: In a cell 15, a membrane electrode assembly (MEA) comprising an anode 21 and a cathode 22 on both sides of an electrolyte membrane 20, is held between gas diffusion layers 23 and 24 and gas separators 25 and 26. Via the separators, an in-cell fuel gas passage 47 and an in-cell oxidant gas passage 48 with a groove width L face the electrolyte membrane 20. The electrolyte membrane 20 has properties satisfying that a swelling pressure in the membrane caused by swelling, is lower than a buckling load of the electrolyte membrane caused by membrane deformation due to swelling and causing the electrolyte membrane 20 to buckle into the gas passages with the groove width L.

Description

  The present invention relates to a fuel cell in which a membrane electrode assembly in which both anode and cathode electrodes are joined to both membrane surfaces of an electrolyte membrane is sandwiched between a gas diffusion layer and a flow path member.

  A fuel cell generates electricity by an electrochemical reaction between fuel and its oxidant, for example, hydrogen and oxygen. In such a fuel cell, both anode and cathode electrodes are formed on both membrane surfaces of a proton-conducting electrolyte membrane (for example, a solid polymer membrane), and a fuel gas and an oxidizing gas are passed through the gas diffusion layer on both electrodes. For example, hydrogen gas and air are supplied.

  The power generation of the fuel cell depends on the progress of the electrochemical reaction through the electrolyte membrane, and the proton conductivity of the electrolyte membrane is suitable when the membrane is in an appropriate wet state. For this reason, measures such as supplying a humidified gas at the time of drying are usually taken so as to prevent the electrolyte membrane from being dried as much as possible. However, even under such circumstances, the electrolyte membrane repeats drying and wetting. Drying and wetting of the electrolyte membrane causes contraction and expansion of the membrane, so that the electrolyte membrane is likely to be wrinkled or broken. Such wrinkles and breaks can cause cross leaks due to breakage of the electrolyte membrane. Therefore, various proposals have been made to improve the durability of the electrolyte membrane (for example, Patent Document 1 below).

JP 2007-165077 A

  In the technique proposed in the above-mentioned patent document, the dimensional change in the surface direction of the electrolyte membrane that occurs during the transition of the wet and dry state of the membrane is made smaller than the maximum elastic deformation amount in the surface direction of the electrolyte membrane in the dry state. The durability against cross leaks is enhanced by suppressing the formation of folds. By the way, although it is possible to cope with repeated drying and wetting of the electrolyte membrane, there are various usage environments and operating conditions of the fuel cell. For example, the fuel cell operation is often performed with a low-humidified electrolyte membrane. . When the electrolyte membrane is low humidified, the proton conductivity is lowered. As a countermeasure, it is effective to increase the ion exchange capacity of the electrolyte membrane and increase the proton conductivity at the time of low humidification. However, when the ion exchange capacity is increased, the swelling rate of the electrolyte membrane is generally increased, and the deformation of the membrane accompanying the swelling also increases. Therefore, the electrolyte membrane is likely to be wrinkled or broken due to factors other than repeated drying and wetting of the membrane. It is feared to become.

  The present invention has been made to solve at least a part of the above-described conventional problems, and an object of the present invention is to improve the durability of an electrolyte membrane while improving proton conductivity.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the following configuration is adopted.

[Application 1: Fuel cell]
A membrane electrode assembly in which both anode and cathode electrodes are joined to both membrane surfaces of an electrolyte membrane is sandwiched between gas diffusion layers, and a gas flow path is provided for gas supply / discharge to the gas diffusion layer. A fuel cell in which the membrane electrode assembly and the gas diffusion layer are sandwiched by a gas flow path member,
The electrolyte membrane has a swelling pressure generated in the membrane as it swells, and a seat on the electrolyte membrane when the deformed electrolyte membrane buckles due to deformation of the electrolyte membrane due to swelling. The gist is that the swelling pressure has a property smaller than the buckling load in relation to the bending load.

  In the fuel cell having the above-described configuration, in the electrolyte membrane, a swelling pressure is generated in the membrane as it swells, and deformation occurs in association with the swelling. Although the electrolyte membrane is sandwiched and restrained by the gas diffusion layer and the gas flow path member as a membrane electrode assembly in which both electrodes are joined to both membrane surfaces, the electrolyte membrane is located at a location facing the gas flow path of the gas flow path member. The restraint is loosened. Therefore, there is room for buckling so that the electrolyte membrane enters the gas flow path due to deformation accompanying swelling, and the swelling pressure acts on the buckled portion.

  In the fuel cell having the above-described configuration, the swelling pressure does not exceed the buckling load because the swelling pressure is smaller than the buckling load in the relationship between the swelling pressure of the electrolyte membrane and the buckling load. As a result, according to the fuel cell having the above-described configuration, the swelling pressure exceeding the buckling load does not act on the electrolyte membrane at the buckled portion facing the gas flow path, so that damage caused by wrinkles or breakage of the electrolyte membrane is not caused. It can be suppressed and durability can be improved. In addition, since the swelling pressure has a relationship that increases as the ion exchange capacity (IEC) of the electrolyte membrane increases, the ion exchange capacity is increased within a range that does not exceed the buckling load, and proton conductivity is improved. Can also be achieved. The ion exchange capacity at this time can be increased even in the case of low humidification regardless of the humidified state of the electrolyte membrane. Therefore, according to the fuel cell having the above-described configuration, the power generation capacity under low humidification conditions is improved. It can also be maintained or improved.

  The fuel cell described above can be configured as follows. For example, a protective film that covers the electrolyte membrane at the periphery of the electrolyte membrane and a seal member that seals the periphery of the membrane electrode assembly with the protective film interposed between the protective film and the gas diffusion layer At the same time, it is sandwiched between the gas flow path members. In this way, after sealing at the periphery, the electrolyte membrane has an elastic modulus of the membrane in a wet condition causing swelling, and the swelling pressure accompanying the swelling is higher than the elastic modulus of the protective film. It may have a property smaller than the buckling load of the protective film. This has the following advantages.

  First, the situation that may occur when the periphery of the membrane electrode assembly is sealed with the protective film will be described first. In the coating | coated location (henceforth a film coating location) with a protective film, an electrolyte membrane receives restrictions by a protective film, and if the separation | spacing leaves | separates from a film coating location to the electrode side, the restrictions will loosen. Therefore, in the vicinity of the film-covered portion on the electrode side, the electrolyte membrane is susceptible to deformation due to swelling. If the ion exchange capacity of the electrolyte membrane is increased, the membrane deformation due to swelling also increases as described above, so that the electrolyte membrane is likely to be wrinkled or broken in the vicinity of the film coating portion on the electrode side. Is concerned. In the fuel cell of the above aspect, from such a viewpoint, the electrolyte membrane has a modulus of elasticity in a wet state causing swelling, which is larger than the modulus of elasticity of the protective film, and the swelling pressure associated with swelling is The film had properties smaller than the buckling load of the film.

  In the fuel cell of this aspect, for the electrolyte membrane and the protective film sandwiching the electrolyte membrane, the elastic modulus of the electrolyte membrane in a wet state causing swelling is greater than that of the protective film. Therefore, the electrolyte membrane is constrained at the film coating location by the protective film, and when the electrode coating is separated from the film coating location, the constraint is loosened, but the deformation of the electrolyte membrane due to swelling near the film coating location is Since the film can be deformed along with the film deformation, the film is not strongly regulated by the protective film. Moreover, in the fuel cell of the above aspect, since the swelling pressure generated in the electrolyte membrane with the swelling is smaller than the buckling load of the protective film, the swelling pressure of the electrolyte membrane should not exceed the buckling load of the protective film. become. As a result, according to the fuel cell of the above aspect, since the swelling pressure exceeding the buckling load does not act on the protective film at the film covering portion by the protective film, the protective film and the electrolyte membrane sandwiched between the protective film and the electrolyte film In this case, damage due to wrinkles and breakage can be suppressed, and durability can be improved.

  In addition to this, since the swelling pressure of the electrolyte membrane has a relationship that increases as the ion exchange capacity (IEC) of the electrolyte membrane increases, the ion exchange capacity is set within a range that does not exceed the buckling load of the protective film. The proton conductivity can be improved by increasing the proton conductivity. Since the ion exchange capacity at this time can be increased even in the case of low humidification regardless of the humidified state of the electrolyte membrane, according to the fuel cell of the above aspect, the power generation capacity under low humidification conditions is improved. It can also be maintained or improved. And this aspect is one aspect of the fuel cell of application 1 of the above configuration having the property that the swelling pressure of the electrolyte membrane is smaller than the buckling load of the electrolyte membrane itself. The above effect can be further enhanced.

It is explanatory drawing which shows roughly the cross section of the single cell 15 which comprises the fuel cell 10 of a present Example. It is a graph showing the function y (= {-ln (Em / IEC * ρ)}) when the swelling rate V _m is a variable x. It is explanatory drawing which shows distinction of an electrode area | region and a peripheral area | region by planarly viewing MEA which the single cell 15 has. It is explanatory drawing which shows schematically the structure of each member in the periphery of the electrolyte membrane 20 used as the premise of a modified example by cross-sectional view.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory view schematically showing a single cell 15 constituting the fuel cell 10 of the present embodiment in a cross-sectional view. The fuel cell 10 of this embodiment is a polymer electrolyte fuel cell having a stack structure in which a plurality of single cells 15 having the configuration shown in FIG. 1 are stacked.

  The single cell 15 includes both electrodes of an anode 21 and a cathode 22 on both sides of the electrolyte membrane 20. The anode 21 and the cathode 22 are formed on both membrane surfaces of the electrolyte membrane 20 and form a membrane electrode assembly (MEA) together with the electrolyte membrane 20. In addition, the single cell 15 includes an anode-side gas diffusion layer 23, a cathode-side gas diffusion layer 24, and gas separators 25 and 26 that sandwich the electrode-formed electrolyte membrane 20 from both sides, and both gas diffusion layers correspond to each other. It is joined to the electrode.

  The electrolyte membrane 20 is a proton conductive ion exchange membrane formed of a solid polymer material (electrolyte resin), and exhibits proton conductivity based on its ion exchange capacity (IEC). In this embodiment, the electrolyte membrane 20 is a proton-conductive ion exchange membrane (hereinafter referred to as a fluorine ion exchange membrane for convenience) formed of a fluorine polymer electrolyte resin, or a hydrocarbon polymer electrolyte. One of proton-conductive ion exchange membranes (hereinafter, referred to as a hydrocarbon ion exchange membrane for convenience) formed of a resin. In this case, the fluorine-based ion exchange membrane is an ion-exchange membrane formed of a fluorine-based polymer electrolyte resin in which the main chain and side chain hydrogen represented by the perfluorocarbon sulfonic acid resin membrane are all substituted with fluorine. Hydrocarbon ion-exchange membrane is a hydrocarbon having a polymer main chain composed of carbon and hydrogen after having an ion exchange group such as a sulfonic acid group, a carboxylic acid group, a boronic acid group, a phosphonic acid group, and a hydroxyl group. Ion exchange membranes formed of a polymer electrolyte resin, including those partially substituted with fluorine and those containing hetero atoms other than fluorine.

  The anode 21 and the cathode 22 include a catalyst (for example, platinum or a platinum alloy), and are formed by supporting these catalysts on a conductive carrier (for example, carbon particles). The anode side gas diffusion layer 23 and the cathode side gas diffusion layer 24 are formed of a conductive member having gas permeability, for example, carbon paper or carbon cloth.

  The gas separator 25 is provided with an in-cell fuel gas flow channel 47 for flowing a fuel gas containing hydrogen on the anode side gas diffusion layer 23 side. The gas separator 26 is provided with an in-cell oxidizing gas flow path 48 through which an oxidizing gas containing oxygen (air in this embodiment) flows, on the cathode side gas diffusion layer 24 side. Both the gas flow paths in these separators are formed on the electrode surface with a groove width L as shown in FIG. 1, and are involved in the supply and discharge of gas to and from the respective gas diffusion layers. Although not shown in the figure, an inter-cell refrigerant flow path through which a refrigerant flows can be formed between adjacent single cells 15, for example. These gas separators 25 and 26 are made of a gas-impermeable conductive member, for example, a dense carbon made by compressing carbon and impermeable to gas, baked carbon, or a metal material such as stainless steel.

  Although not shown in FIG. 1, a plurality of holes are formed at predetermined positions near the outer peripheries of the gas separators 25 and 26. The plurality of holes overlap each other when the gas separators 25 and 26 are laminated together with other members and the fuel cell 10 is assembled, thereby forming a flow path that penetrates the fuel cell 10 in the lamination direction. That is, a manifold for supplying and discharging fuel gas, oxidizing gas, or refrigerant is formed with respect to the in-cell fuel gas channel 47, the in-cell oxidizing gas channel 48, or the inter-cell refrigerant channel.

  The fuel cell 10 of this embodiment supplies the hydrogen gas from the in-cell fuel gas flow channel 47 of the gas separator 25 to the anode 21 while diffusing in the anode side gas diffusion layer 23. As for air, the air from the in-cell oxidizing gas flow channel 48 of the gas separator 26 is supplied to the cathode 22 while being diffused by the cathode side gas diffusion layer 24.

  Next, the relationship between the electrolyte membrane 20 used in the fuel cell 10 of this embodiment and the in-cell fuel gas channel 47 and the in-cell oxidizing gas channel 48 involved in gas supply / discharge will be described. In this embodiment, the swelling pressure generated in the membrane of the electrolyte membrane 20 with the swelling and the electrolyte membrane 20 deformed with the swelling are the in-cell fuel gas channel 47 or the in-cell oxidizing gas channel having the groove width L. The buckling load that is applied to the electrolyte membrane 20 when buckling by entering 48 is satisfied.

In the formula 1, the left side shows the swelling pressure for the electrolyte membrane 20, and the swelling pressure is an elastic modulus E _m [MPa] of the electrolyte membrane 20 in a wet state causing swelling and a wet situation causing swelling. It is calculated from the swelling rate V _m [%] of the electrolyte membrane 20 and the film thickness d _m [m] of the electrolyte membrane 20. Right side shows the above-mentioned buckling load for the electrolyte membrane 20, the buckling load, the elastic modulus E _m of the electrolyte membrane 20 [MPa] and the thickness d _m [m], and cell fuel gas flow path 47 And the groove width L [m] of the oxidizing gas channel 48 in the cell.

Rearranging this formula 1, the formula 2 to the left and swelling ratio V _m.

The swelling rate V _{m on the} left side in Equation 2 is the ion exchange capacity IEC [meq / g] of the electrolyte membrane 20, the elastic modulus E _m [MPa] of the electrolyte membrane 20, and the membrane dry density ρ [g] of the electrolyte membrane 20. / Cm ³ ], it can be represented by the following Equation 3 empirically.

In Equation 3, characters A and B are constants determined experimentally or empirically. Formula 3 is a linear function with the swelling rate V _m as a variable x, where y is {−ln (E _m / IEC · ρ)}. FIG. 2 is a graph showing a function y (= {− ln (E _m / IEC · ρ)}) when the swelling rate V _m is a variable x. FIG. 2 shows that the relationship of Equation 3 holds whether the electrolyte membrane 20 is a fluorine ion exchange membrane or a hydrocarbon ion exchange membrane. Further, Equation 3 indicates that when the ion exchange capacity IEC of the electrolyte membrane 20 increases, the swelling rate V _m of the electrolyte membrane 20 also increases. Therefore, the above relationship between both the ion exchange capacity IEC and the swelling rate V _m. This holds true whether the electrolyte membrane 20 is a fluorine ion exchange membrane or a hydrocarbon ion exchange membrane.

Substituting the swelling ratio V _m of Equation 3 into Equation 2, the following Equation 4 is obtained.

In the fuel cell 10 of the present embodiment, the groove width L of the in-cell fuel gas flow channel 47 and the in-cell oxidizing gas flow channel 48, the ion exchange capacity IEC and the elastic modulus E _{m of the} electrolyte membrane 20 are satisfied so as to satisfy Formula 4. Determined. In this case, Equation 4 is equivalent to Equation 1 because it is obtained by the modification of Equation 1 described above. Therefore, to satisfy this formula 4, the groove width L of the cell fuel gas flow path 47 and the cell oxidizing gas channel 48, a formula 1 by determining the ion-exchange capacity IEC and modulus E _m of the electrolyte membrane 20 As a result, the electrolyte membrane 20 has a property that the swelling pressure, which is the left side of Equation 1, is smaller than the buckling load on the right side.

As satisfying Equation 4 as described above, the groove width L of the cell fuel gas flow path 47 and the cell oxidizing gas channel 48, and the ion exchange capacity IEC of the electrolyte membrane 20, the elastic modulus E _m and the thickness d _m First, the groove width L is set to a practical groove width. On top of that, for the ion-exchange capacity IEC and modulus E _m of the electrolyte membrane 20, for example, in the case of a fluorine-based ion-exchange membrane as the electrolyte membrane 20 is an ion-exchange capacity IEC and elasticity determined as satisfying Equation 4 Adjusting the ion exchange equivalent and adjusting the molecular weight by adjusting the blending of the sulfone resin having a sulfonic acid group that is an ion exchange group (polar group) in the production process using the fluororesin so that the rate E _m can be obtained. Alternatively, blending adjustment of a crosslinking agent involved in resin polymerization is performed.

  Next, the fuel cell 10 of the example product having the electrolyte membrane 20 that satisfies the relationship between the swelling pressure and the buckling load expressed in the above-described Equation 1, that is, the electrolyte membrane 20 that satisfies Equation 4 equivalent to Equation 1 is shown. The performance evaluation will be described. The comparative example product to be evaluated is a fuel cell in which the relationship between the swelling pressure and the buckling load is contrary to Equation 1. In addition to the electrode area of the single cell 15, the size of the electrolyte membrane, etc., the in-cell fuel gas channel 47, The groove width L of the in-cell oxidizing gas channel 48 is the same as that of the example product. And about the Example goods and the comparative example goods, the single cell 15 of the fuel cell of each comparative example and the Example was subjected to the dry and wet cycle test, and performance evaluation was performed.

  In this dry / wet cycle test, the cell temperature was set to 80 ° C., and the gas supply / power generation at a relative humidity of 100% for 8 minutes and the gas supply / power generation in a dry state for 2 minutes were defined as one cycle. It was decided to repeat. Regarding this dry and wet cycle test, the comparison results of the performance evaluation of the fuel cell 10 of this example and the comparative example fuel cell are shown in the following table. As shown in this table, a comparative example product and an example product are prepared for each type of electrolyte membrane 20, that is, for each of a fluorine-based ion exchange membrane (F-based electrolyte membrane) and a hydrocarbon-based ion exchange membrane (HC-based electrolyte membrane). And contrasted. In the table, the right-side value is the same because the groove width L is the same for the comparative example product and the example product (see Formula 4).

  The example product satisfies Formula 4 (Formula 1) in the electrolyte membrane 20 of the fluorine ion exchange membrane and the hydrocarbon ion exchange membrane, and the comparative product does not satisfy this. After the 1200 cycles of the wet and dry cycle test, the single cell was disassembled and examined for the presence or absence of membrane wrinkles in the electrolyte membrane 20. Specifically, the electrolyte membrane 20 and both electrodes of the anode 21 and the cathode 22 on both sides thereof were connected. When the presence or absence of film wrinkles in the MEA including (see FIG. 1) was examined, none of the examples satisfying Equation 4 (Equation 1) was observed with respect to Equation 4 (Equation 1). Films wrinkles were observed in all of the comparative products that were not satisfied. In this case, the MEA is sandwiched between the gas separator 25 and the gas separator 26 with the anode side gas diffusion layer 23 and the cathode side gas diffusion layer 24 interposed therebetween, as shown in FIG. An internal fuel gas channel 47 or an in-cell oxidizing gas channel 48 is provided. Therefore, the movement of the MEA and the electrolyte membrane 20 is restricted in the rib between the flow paths, and the restriction is loosened in the range facing both the gas flow paths. For these reasons, the trace portion of the film wrinkle observed in the comparative example product almost coincides with the range facing the gas flow path.

Membrane wrinkles generated in the MEA (electrolyte membrane 20) can cause cross leakage due to breakage of the electrolyte membrane 20 and the MEA including the membrane. Therefore, it can be said that each of the above-described examples has high durability. In other words, the properties of the electrolyte membrane 20 are defined so that the swelling pressure of the electrolyte membrane 20 satisfies Equation 4 equivalent to Equation 1 indicating a relationship smaller than the buckling load of the electrolyte membrane 20 (specifically, the gas flow path). by defining the ion-exchange capacity IEC and modulus E _m of groove width L and the electrolyte membrane 20) of great significance is that the electrolyte membrane 20 that swelling pressure is to have a buckling load smaller properties Yes, it was confirmed that the durability of the electrolyte membrane 20 can be improved by defining in this way.

The difference in the durability of the electrolyte membrane 20 between the comparative example product and the example product can be explained as follows. First, as described above, to satisfy the formula 4, by defining the ion-exchange capacity IEC and modulus E _m of groove width L and the electrolyte membrane 20 of the gas flow path in the unit cell 15, the electrolyte along with the swelling The electrolyte membrane 20 whose swelling pressure (the left side of Formula 1) generated in the membrane 20 is deformed with the swelling enters the in-cell fuel gas channel 47 or the in-cell oxidizing gas channel 48 having the groove width L and is seated. When buckling, the buckling load (right side of Formula 1) applied to the electrolyte membrane 20 can be prevented from exceeding. For this reason, in the fuel cell 10 of the example product of this embodiment, even if the electrolyte membrane 20 enters the in-cell fuel gas channel 47 and the in-cell oxidizing gas channel 48 due to deformation due to swelling, Since the swelling pressure acting on the buckling point does not exceed the buckling load, in the example product, the shrinkage and expansion are repeated in each cycle of the wet and dry cycle test, and the film wrinkle is not removed after the dry and wet cycle test. It can be inferred that it will not remain. As a result, according to the fuel cell 10 of the present embodiment, it is possible to suppress damage caused by wrinkles or breakage of the electrolyte membrane 20 and improve durability.

Additionally, the swelling pressure of the electrolyte membrane 20 is obtained by multiplying the elastic modulus E _m and the thickness d _m in swelling ratio V _m of the film, the swelling ratio V _m, i.e. swelling pressure from equation 3, The ion exchange capacity IEC of the electrolyte membrane 20 increases due to an increase. For this reason, the proton conductivity can be improved by increasing the ion exchange capacity IEC within a range where the swelling pressure does not exceed the buckling load. Since the ion exchange capacity IEC at this time can be increased regardless of the humidification state of the electrolyte membrane 20, the fuel cell 10 of the present embodiment can be used under a low humidification condition. The power generation capacity of the fuel cell 10 can be maintained or improved. Moreover, as the value of the right side approximates the value of the left side after satisfying Expression 4, it is possible to improve both durability and power generation performance.

  Next, a modified example will be described. In this modification, the durability of the periphery of the electrolyte membrane 20 is also improved. FIG. 3 is an explanatory diagram showing the distinction between the electrode region and the peripheral region in plan view of the MEA of the single cell 15, and FIG. 4 is a cross-sectional view of the configuration of each member at the peripheral edge of the electrolyte membrane 20 which is a premise of the modification. It is explanatory drawing shown roughly.

  As shown in FIG. 3, the MEA has a rectangular shape in a plan view, and a central region following the rectangular shape is an electrode surface region 100 occupied by the anode 21 and the cathode 22, and a frame shape surrounding the region on the outside. Let the region be the peripheral region 110. FIG. 3 shows a plan view of one side of the MEA, for example, the anode 21 side, but the same applies to the cathode 22 side which is the other side. As shown in FIG. 4, when the electrode surface region 100 and the peripheral region 110 are continuous, that is, when the vertical peripheral edge or the horizontal peripheral edge in FIG. 3 is viewed in cross section, the electrolyte membrane 20 constituting the MEA in the single cell 15 is A range corresponding to the electrode surface region 100 is defined as an electrode surface region 20s, and a range corresponding to the peripheral region 110 is defined as a peripheral region 20e. The peripheral region 20e extends from the electrode surface region 20s to the peripheral side. The MEA is provided with the anode 21 and the cathode 22 joined to both film surfaces of the electrode surface region 20s of the electrolyte membrane 20, and the peripheral region 20e corresponding to the peripheral region 110 is covered with the protective film 30 on the front and back. In this embodiment, the protective film 30 is covered on both sides to secure gas sealing on the anode side and the cathode side, but the protective film 30 may be one of the anode and the cathode.

  The protective film 30 serves as a key to protect the peripheral area 20e of the peripheral area 110 in the MEA, specifically, the electrolyte membrane 20. In FIG. 4, the protective film 30 covers the peripheral edges of both the anode 21 and the cathode 22, but the electrolyte membrane 20 may be covered so as not to include the peripheral edges of both electrodes. The protective film 30 is formed of a resin film such as polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polypropylene (PP), polyethylene (PE), and is formed on the peripheral region 110 on the surface of the peripheral region 20e. It is joined over. In this case, the elastic modulus and buckling load as physical properties of the protective film 30 are defined in relation to the physical properties of the electrolyte membrane 20 as will be described later.

  As described above, the single cell 15 is formed by overlapping the anode side gas diffusion layer 23 and the cathode side gas diffusion layer 24 on the MEA to which the protective film 30 has been bonded, and by using the resin sealing material 32 having a sealing function, the peripheral region It seals including the peripheral edge part of the part 20e, the protective film 30 of the front and back, and both said gas diffusion layers. In addition, the single cell 15 sandwiches the MEA together with both the gas diffusion layers and the sealing material 32 with the gas separator 25 and the gas separator 26. As a result, as described in FIG. 1, the hydrogen gas that has flowed from the in-cell fuel gas flow path 47 (see FIG. 1) of the gas separator 25 is supplied to the anode 21 through the anode-side gas diffusion layer 23, and the gas Air that has flowed in from the in-cell oxidizing gas flow path 48 (see FIG. 1) of the separator 26 is supplied to the cathode 22 via the cathode-side gas diffusion layer 24, and an electrochemical reaction proceeds in the electrolyte membrane 20. The gas supply described above is continued in a state of being sealed at the periphery of the MEA by the sealing material 32.

  Next, the relationship between the electrolyte membrane 20 and the protective film 30 when the peripheral edge of the electrolyte membrane 20 is covered with the protective film 30 as shown in FIG. In this case, the peripheral region 110 of the electrolyte membrane 20 covered with the protective film 30 is a non-power generation region in which gas is not supplied or discharged by the in-cell fuel gas channel 47 or the in-cell oxidizing gas channel 48. The relationship described below between the protective film 30 and the protective film 30 can be individually defined as the relationship between the swelling pressure and the buckling load of the electrolyte membrane 20 of Formula 1 described above. Can do.

  When the sealing structure shown in FIG. 4 is adopted, the swelling pressure of the electrolyte membrane 20 and the electrolyte membrane 20 elastic modulus and the elastic modulus of the protective film 30 which are the premise of the modified example are set so as to satisfy the relationship of the following formula 5. About the buckling load of the protective film 30, it was made to satisfy | fill the relationship of following Numerical formula 6.

Equation 5 above shows the elastic modulus E _m of the electrolyte membrane 20 [MPa] in the wet conditions that cause swelling at the left-hand, the elastic modulus E _m of the electrolyte membrane 20, the elastic modulus of the right side of the protective film 30 It becomes larger than E _f [MPa]. In Equation 6, the left side indicates the swelling pressure for the electrolyte membrane 20, and the swelling pressure indicates the elastic modulus E _m [MPa] of the electrolyte membrane 20 and the swelling rate V of the electrolyte membrane 20 in a wet condition causing swelling. It is calculated from _m [%] and the film thickness d _m [m] of the electrolyte membrane 20. The right side shows the buckling load when the protective film 30 is bent, and this buckling load is shown in FIG. 4 with the elastic modulus E _f [MPa] and the film thickness d _f [m] of the protective film 30. It is calculated from the sandwiching width L _f [m] of the electrolyte membrane 20 by the protective film 30. The buckling load when the protective film 30 on the right side of Equation 6 is bent is calculated from the attached Equations 7-8.

Formula 7 is a formula of Euler's buckling load, and the film buckling load P _f is the film length L, the film elastic modulus E, and the cross section of the film shown in Formula 8 (cross-sectional area: film width bx film thickness d). It is obtained by the secondary moment I. In this case, the protective film 30 nipped width L _f by the next L in Equation 7, the film thickness d _f, the d in Equation 8.

In applying the protection by the protective film 30 shown in FIGS. 3 to 4 to the fuel cell 10 of the above-described embodiment, on the premise, the electrolyte membrane 20 elastic modulus _Em and the protective film 30 are set so as to satisfy the above-described numerical formula 5. The elastic modulus _Em was determined, and the swelling pressure of the electrolyte membrane 20 and the buckling load of the protective film 30 were determined so as to satisfy Equation 6 above. Then, by determining the electrolyte membrane 20 modulus of elasticity E _m and the protective film 30 E _m, and the buckling load of the swelling pressure and the protective film 30 for the electrolyte membrane 20 so as to satisfy the equation 5 Equation 6, the electrolyte membrane 20, the elastic modulus E _m is greater than the elastic modulus elastic modulus E _m of the protective film 30, and, becomes the swelling pressure of the electrolyte membrane 20 has a buckling load is less than the properties of the protective film 30.

In this case, the swelling rate V _m of the electrolyte membrane 20 is expressed by the ion exchange capacity IEC [meq / g] of the electrolyte membrane 20 and the elastic modulus E _m [MPa] of the electrolyte membrane 20 as shown in Equation 3 above. And Equation 3 can be substituted into Equation 6 because the membrane dry density ρ [g / cm ³ ] of the electrolyte membrane 20 is obtained. This way, the left-hand side of equation 6 is obtained by the ion-exchange capacity IEC and the elastic modulus E _m and the membrane dry density ρ and thickness d _m of the electrolyte membrane 20. Therefore, to satisfy Equation 6, and the ion exchange capacity IEC and the elastic modulus E _m and the membrane dry density ρ and thickness d _m of the electrolyte membrane 20, the elastic modulus of the right side of the protective film 30 E _f and the film thickness d it may be determined and _f and the clamping width L _f. Of these, the film thickness d _m and the film thickness d _f and clamping width L _f, since it can be pre-defined as to the circumstances as a single cell 15, as in effect, satisfying Equation 6, the electrolyte membrane The ion exchange capacity IEC, the elastic modulus _Em and the membrane dry density ρ of 20, and the elastic modulus E _f of the protective film 30 may be determined. The ion-exchange capacity IEC and modulus E _m of the electrolyte membrane 20 may be performed blending adjustment of sulfonic resin in the manufacturing process such as described above, the elastic modulus E _f of the protective film 30, above It is only necessary to select a resin material having an elastic modulus in a range that satisfies the above mathematical formula.

Next, the relationship (elastic modulus relationship) between the elastic modulus E _{m of} the electrolyte membrane 20 and the elastic modulus E _f of the protective film 30 expressed by the above-described mathematical formulas 5 to 6, and the swelling pressure of the electrolytic membrane 20 and the seat of the protective film 30 The performance evaluation of the fuel cell 10 of the example product having the electrolyte membrane 20 that satisfies the relationship with the bending load (swelling pressure relationship) will be described. The comparative example product to be evaluated is a fuel cell in which both the elastic modulus relationship and the swelling pressure relationship are contrary to Equations 5 to 6, and the protective film 30 in addition to the electrode area of the single cell 15, the size of the electrolyte membrane, and the like. The sandwiching width L _f of the electrolyte membrane 20 is the same as that of the example product. And about the Example goods and the comparative example goods, the single cell 15 of the fuel cell of each comparative example and an Example was subjected to the above-mentioned dry and wet cycle test, and performance evaluation was performed. If the electrolyte membrane 20 is damaged in the vicinity of the location where the protective film 30 is covered, gas leakage from the damaged location may occur. Therefore, for the fuel cell 10 of this example and the comparative example fuel cell, the relationship between the number of cycles of the wet and dry cycle test and the amount of gas leak was examined, and the comparison results of the performance evaluation are shown in the following table. In addition, the electrolyte membrane type | mold in a table | surface shows that it is the same kind with an Example product and a comparative example product, for example, represents that it is the electrolyte membrane 20 of a fluorine-type ion exchange membrane. Protective F type (protective film type) indicates that different protective films were used for the example product and the comparative product. Further, the number of wet and dry cycles until the leak in the table means the number of cycles until the leak occurs in the vicinity of the film covered portion by the protective film 30.

The example product satisfies Equation 5 in the relationship between the elastic modulus E _m of the electrolyte membrane 20 and the elastic modulus E _f of the protective film 30, and Equation 6 in the relationship between the swelling pressure of the electrolyte membrane 20 and the buckling load of the protective film 30. Fulfill. Comparative sample, although satisfying Equation 6 in relation to the buckling load of the swelling pressure and the protective film 30 of the electrolyte membrane 20, Equation 5 in relation to the electrolyte membrane 20 modulus E _m and the protective film 30 of the elastic modulus E _f Does not meet. In the example product which is the fuel cell 10 of the present example, leaks were observed only after 1245 dry / wet cycles, whereas in the comparative product, leaks were observed in 941 dry / wet cycles. The electrolyte membrane 20 Upon covering at its periphery by the protective film 30, the electrolyte membrane 20 so as to satisfy the equation 5 Equation 6, the elastic modulus E _m is greater than the elastic modulus elastic modulus E _m of the protective film 30, and, It is significant to make the swelling pressure of the electrolyte membrane 20 smaller than the buckling load of the protective film 30, and by defining in this way, the electrolyte in the vicinity of the film-covered portion by the protective film 30. It was confirmed that the durability of the film 20 can be increased.

The difference in the durability of the electrolyte membrane 20 in the vicinity of the film covering portion by the protective film 30 between the comparative example product and the example product can be explained as follows. First, as described above, to satisfy Equation 5, the electrolyte membrane 20, the direction of elastic modulus E _m is greater than the elastic modulus E _f of the protective film 30. Therefore, the electrolyte membrane 20 is constrained at the film-covered portion by the protective film 30, and the constraint is loosened when the electrode is separated from the film-covered portion, but the deformation of the electrolyte membrane 20 due to swelling near the film-covered portion is Since the protective film 30 can be deformed along with film deformation, the protective film 30 is not strongly regulated by the protective film 30.

  In addition, since the swelling pressure generated in the membrane of the electrolyte membrane 20 with the swelling is smaller than the buckling load of the protective film 30 so as to satisfy Formula 6, the swelling pressure of the electrolyte membrane 20 is the buckling of the protective film 30. The load will not be exceeded. As a result, if the mathematical formulas 5 to 6 are satisfied, the protective film 30 does not receive a swelling pressure exceeding the buckling load at the film-covered portion of the protective film 30. In the electrolyte membrane 20 sandwiched between them, the film protection portion and the vicinity thereof are merely repeated so that the contraction and expansion are restored in each cycle of the wet and dry cycle test, and damage caused by wrinkles and breakage is caused. Can be suppressed, and durability can be improved. In addition, since the swelling pressure of the electrolyte membrane 20 increases as the ion exchange capacity IEC of the electrolyte membrane 20 increases as described above, the ion exchange capacity IEC within a range that does not exceed the buckling load of the protective film 30. And proton conductivity can be improved. In this case, the ion exchange capacity IEC can be increased even when the humidification state of the electrolyte membrane 20 is low, so that the protective film 30 satisfies the expressions 5 to 6. If the periphery of the membrane 20 is covered, the power generation capacity can be maintained or improved under low humidification conditions.

And in satisfy | filling Formula 5-Formula 6, it is necessary to consider the groove width L of the gas flow path used as the variable for satisfy | filling Formula 1 or Formula 4 equivalent to this in the Example demonstrated previously. Also in the embodiment, in order to satisfy Equation 1, it is not necessary to consider the sandwiching width L _f of the electrolyte membrane 20 by the protective film 30 that is a variable for satisfying Equation 5 to Equation 6. However, Formula 5 to Formula 6 that define the electrolyte membrane 20 and the protective film 30 can be added to the relationship between the swelling pressure and the buckling load of the electrolyte membrane 20 of Formula 1 described above. Therefore, in the unit cell 15 of the embodiment shown in FIG. 1, the periphery of the electrolyte membrane 20 is covered with the protective film 30, so that the formulas 5 to 6 are satisfied as described above. Then, it is expected that further improvement in durability can be achieved.

  Although the embodiments of the present invention have been described above, the present invention is not limited to such embodiments, and can be implemented in various modes without departing from the scope of the present invention. For example, in FIG. 1, the in-cell fuel gas channel 47 and the in-cell oxidizing gas channel 48 are shown as channels from the front side to the back side of the page or vice versa. And the in-cell oxidizing gas flow channel 48 may be configured to flow so that the gas is perpendicular to the MEA.

DESCRIPTION OF SYMBOLS 10 ... Fuel cell 15 ... Single cell 20 ... Electrolyte membrane 20e ... Peripheral area | region part 20s ... Electrode surface area | region 21 ... Anode 22 ... Cathode 23 ... Anode side gas diffusion layer 24 ... Cathode side gas diffusion layer 25 ... Gas separator 26 ... Gas Separator 30 ... Protective film 32 ... Sealing material 47 ... In-cell fuel gas channel 48 ... In-cell oxidizing gas channel 100 ... Electrode surface region 110 ... Peripheral region L ... Groove width

Claims (2)

A membrane electrode assembly in which both anode and cathode electrodes are joined to both membrane surfaces of an electrolyte membrane is sandwiched between gas diffusion layers, and a gas flow path is provided for gas supply / discharge to the gas diffusion layer. A fuel cell in which the membrane electrode assembly and the gas diffusion layer are sandwiched by a gas flow path member,
The electrolyte membrane has a swelling pressure generated in the membrane as it swells, and a seat on the electrolyte membrane when the deformed electrolyte membrane buckles due to deformation of the electrolyte membrane due to swelling. A fuel cell in which the swelling pressure is smaller than the buckling load in relation to the bending load. The fuel cell according to claim 1,
And a protective film that covers the electrolyte membrane at the periphery of the electrolyte membrane, and a seal member that seals the periphery of the membrane electrode assembly with the protective film interposed therebetween, and the seal member together with the gas diffusion layer and the gas Sandwiched between channel members,
The electrolyte membrane has a property that the elastic modulus of the membrane in a wet state causing swelling is larger than the elastic modulus of the protective film, and the swelling pressure accompanying the swelling is smaller than the buckling load of the protective film.

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