JP2009283350A - Power generator and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology which suppresses deterioration of power generation performance in a polymer electrolyte fuel cell. <P>SOLUTION: A power generator includes: a solid polymer electrolyte membrane consisting of a first solid polymer material having proton conductivity; an anode catalyst layer arranged on one face side of the solid polymer electrolyte membrane; a cathode catalyst layer which is arranged on the other face side of the solid polymer electrolyte membrane and includes a catalyst, a first carbon material, and a second solid polymer material having proton conductivity; and an interlayer which does not include a catalyst and includes a second carbon material, a third solid polymer material having proton conductivity, and is arranged between the solid polymer electrolyte membrane and the cathode catalyst layer. The weight ratio of the third solid polymer material to the second carbon material included in the interlayer is higher than the weight ratio of the second solid polymer material to the first carbon material included in the cathode catalyst layer. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fuel cell.

  There is a fuel cell in which an anode and a cathode are provided on both sides of a solid polymer electrolyte membrane, and a fuel gas containing hydrogen and an oxidant gas containing oxygen are supplied to obtain an electromotive force by an electrochemical reaction. In such a fuel cell, a membrane-electrode assembly (hereinafter also referred to as “MEA”) in which a solid polymer electrolyte membrane, an anode, and a cathode are joined is generally used.

  The anode and the cathode include a catalyst layer in which an electrochemical reaction is performed, and a gas diffusion layer in which fuel gas and oxidant gas are diffused and supplied to the catalyst layer. The catalyst layer is mainly composed of a catalyst, a carrier supporting the catalyst, and a proton conductive solid polymer material (hereinafter also referred to as “ionomer”). As the catalyst, platinum, platinum alloy or the like is used, and as the carrier, carbon fine particles such as carbon black are often used.

  During operation of the fuel cell, for example, a potential of about 1 V is generated in the cathode catalyst layer, so that the catalyst (for example, platinum) becomes ions. Since the electrolyte membrane does not contain a catalyst, catalyst ions move through the ionomer contained in the cathode catalyst layer and reach the electrolyte membrane due to the concentration gradient of the catalyst. As described above, when the catalyst is eluted from the cathode catalyst layer to the electrolyte membrane, the amount of the catalyst contained in the cathode catalyst layer is reduced, so that the electrochemical reaction in the cathode catalyst layer is suppressed and the power generation performance may be reduced. . In order to solve such a problem, a technique for suppressing elution of the catalyst from the catalyst layer to the electrolyte membrane has been proposed (see, for example, Patent Documents 1 to 3).

JP 2006-236631 A JP 2007-242423 A JP 2007-005292 A

  For example, the fuel cell described in Patent Document 1 is configured to include a buffer layer between the cathode catalyst layer and the solid polymer electrolyte membrane. The buffer layer mainly includes a catalyst, a carrier supporting the catalyst, and an ionomer. By providing the buffer layer, elution of the catalyst from the cathode catalyst layer to the solid polymer electrolyte membrane is suppressed.

  However, in the fuel cell described in Patent Document 1, since the buffer layer contains a catalyst, an electrochemical reaction occurs in the buffer layer. In addition, since the buffer layer contains more ionomer than the cathode catalyst layer, it tends to be water-containing, so flooding is caused by water moving from the solid polymer electrolyte membrane or water generated by an electrochemical reaction. There was a risk that the power generation performance would be reduced.

  This invention is made | formed in view of such a subject, and it aims at providing the technique which suppresses the fall of electric power generation performance in a polymer electrolyte fuel cell.

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

[Application Example 1] A power generator,
A solid polymer electrolyte membrane comprising a first solid polymer material having proton conductivity;
An anode catalyst layer disposed on one side of the solid polymer electrolyte membrane;
A cathode catalyst layer disposed on the other surface side of the solid polymer electrolyte membrane, comprising a catalyst, a first carbon material, and a second solid polymer material having proton conductivity;
An intermediate layer that does not include a catalyst, includes a second carbon material, and a third solid polymer material having proton conductivity, and is disposed between the solid polymer electrolyte membrane and the cathode catalyst layer When,
With
The second solid polymer material relative to the first carbon material included in the cathode catalyst layer is a weight ratio of the third solid polymer material relative to the second carbon material included in the intermediate layer. The power generator is higher than the weight ratio.

  According to this configuration, since the intermediate layer includes the second carbon material, it is possible to suppress the catalyst from eluting from the cathode catalyst layer. Further, since the intermediate layer does not contain a catalyst, an electrochemical reaction hardly occurs in the intermediate layer, and flooding in the intermediate layer can be suppressed. Further, the weight ratio of the third solid polymer material to the second carbon material contained in the intermediate layer is greater than the weight ratio of the second solid polymer material to the first carbon material contained in the cathode catalyst layer. Therefore, it is difficult for the intermediate layer to prevent proton movement. Therefore, it is possible to suppress a decrease in power generation performance.

[Application Example 2] In the power generator according to Application Example 1,
The intermediate layer has a thickness of 2 μm or more.

  If it does in this way, the fall of the power generation performance by the driving | operation of a fuel cell can be suppressed more.

  Note that the present invention can be realized in various forms, for example, in the form of a fuel cell including a power generator, a fuel cell system including the fuel cell, a moving body equipped with the fuel cell system, and the like. can do.

Next, embodiments of the present invention will be described in the following order based on examples.
A. Example:
A1. Fuel cell configuration:
A1-1. Structure of seal member integrated MEA:
A1-1-1. Electrolyte membrane:
A1-1-2. Cathode catalyst layer and anode catalyst layer:
A1-1-3. Middle layer:
A1-1-4. Anode side diffusion layer and cathode side diffusion layer:
A1-1-5. Seal member:
A1-2. Composition of anode side porous body and cathode side porous body:
A2. Effects of the embodiment:
B. Variations:

A. Example:
A1. Fuel cell configuration:
FIG. 1 is a cross-sectional view schematically showing a cross-sectional configuration of a fuel cell 100 as a first embodiment of the present invention. In FIG. 1, the AA cut surface in FIG. 2 mentioned later is shown. The fuel cell 100 is a solid polymer fuel cell that generates power using hydrogen and air.

  As shown in FIG. 1, in the fuel cell 100, an anode-side porous body 410 and an anode-side separator 310 are laminated in this order on the anode side of a seal member-integrated MEA (Membrane-Electrode Assembly) 200. The cathode side porous body 430 and the cathode side separator 330 are laminated on the cathode side in that order. In FIG. 1, a part of a portion where a plurality of seal member integrated MEAs 200, an anode side porous body 410, an anode side separator 310, a cathode side porous body 430, and a cathode side separator 330 are stacked is shown. Is not shown. Hereinafter, the anode side separator 310 and the cathode side separator 330 are also collectively referred to as separators 310 and 330.

  A cooling water separator in which a cooling water channel for flowing cooling water is formed is disposed between the anode side separator 310 and the cathode side separator 330 (not shown) at a predetermined interval. By circulating the cooling water through the cooling water separator, the heat generated with the electrode reaction of the fuel cell 100 is removed, and the internal temperature of the fuel cell 100 is kept within a predetermined range.

  The anode-side separator 310 has a plurality of concave and convex ribs 312 on the surface facing the anode-side porous body 410. Similarly, a plurality of concave and convex ribs 332 are formed on the cathode-side separator 330 on the surface facing the cathode-side porous body 430. The separators 310 and 320 sandwich the MEA 210 from both sides, thereby forming flow paths through which hydrogen as the anode gas and air as the cathode gas flow.

  The air supplied to the fuel cell 100 passes through a cathode gas supply manifold (not shown), passes through a flow path formed by the rib 332 of the cathode side separator 330, flows into the cathode side porous body 430, and is cathode side porous. While being distributed in the body 430, it is supplied to the MEA 210 and used for the electrode reaction. Cathode exhaust gas containing air that has not been used for the electrode reaction is discharged to a cathode exhaust gas discharge manifold (not shown), and is discharged out of the fuel cell 100 through the cathode exhaust gas discharge manifold (not shown).

  Similarly, the hydrogen supplied to the fuel cell 100 flows through the fuel cell 100 and is used for the electrode reaction, and the anode exhaust gas containing hydrogen that is not used for the electrode reaction is discharged out of the fuel cell 100.

  In this embodiment, the anode-side separators 310 and 330 are made of stainless steel flat plates, but other metal flat plates such as titanium and aluminum may be used, and carbon flat plates may be used. It may be used.

  Further, in this embodiment, the anode side porous body 410 and the cathode side porous body 430 are illustrated as being disposed between the MEA 210 and the separators 310 and 330, respectively, but the anode side porous body 410, A configuration in which the cathode-side porous body 430 is not provided, that is, a configuration in which the MEA 210 and the separators 310 and 330 abut may be adopted.

A1-1. Structure of seal member integrated MEA:
FIG. 2 is a plan view showing a planar configuration of the seal member integrated MEA 200. As shown in FIG. 2, the seal member-integrated MEA 200 is configured such that a frame-shaped seal member 220 is formed integrally with the MEA 210 on the outer periphery of the MEA 210 having a substantially square outer shape.

  3 is an enlarged cross-sectional view showing an X1 portion in FIG. As shown in FIG. 3, the MEA 210 is laminated on one surface of an electrolyte membrane 212 in the order of an anode catalyst layer 214 and an anode side diffusion layer 215, and on the other surface, an intermediate layer 218, a cathode catalyst layer 216, and a cathode side diffusion. The layers 217 are stacked in this order. The MEA 210 in this embodiment is the power generator in the claims, the electrolyte membrane 212 is in the solid polymer electrolyte membrane in the claims, the anode catalyst layer 214 is in the anode catalyst layer in the claims, and the cathode catalyst layer 216 is the cathode in the claims. The intermediate layer 218 corresponds to the catalyst layer and the intermediate layer in claims.

A1-1-1. Electrolyte membrane:
In this embodiment, as the electrolyte membrane 212, a polymer electrolyte membrane (Nafion (registered trademark)) formed of a fluorinated sulfonic acid polymer as a proton conductive solid polymer material is used. The polymer electrolyte membrane is not limited to Nafion (registered trademark), and other fluorine-based sulfonic acid membranes such as Aciplex (registered trademark) and Flemion (registered trademark) may be used. Further, for example, a fluorine-based phosphonic acid film, a fluorine-based carboxylic acid film, a fluorine-hydrocarbon-based graft film, a hydrocarbon-based graft film, an aromatic film, or the like may be used. Moreover, you may use the composite polymer film which strengthened mechanical characteristics containing reinforcement materials, such as PTFE and a polyimide.

A1-1-2. Cathode catalyst layer and anode catalyst layer:
FIG. 4 is an explanatory diagram for explaining the configuration of the cathode catalyst layer and the intermediate layer in the fuel cell 100 of the present embodiment. In FIG. 4, the cross-sectional configurations of the electrolyte membrane 212, the intermediate layer 218, and the cathode catalyst layer 216 are enlarged and conceptually shown.

  FIG. 4A shows the initial state of the cathode catalyst layer 216 and the intermediate layer 218. As shown in the figure, the cathode catalyst layer 216 is formed by coating carbon black C carrying platinum P as a catalyst with ionomer I, which is a polymer material having proton conductivity. In this example, Ketjen (registered trademark) is used as the carbon black C, and Nafion (registered trademark) is used as the ionomer I in the same manner as the electrolyte membrane 212. In the cathode catalyst layer 216, ionomer I: carbon black C = 0.75: 1 (weight ratio). The anode catalyst layer 214 has the same configuration as the cathode catalyst layer 216.

  In this example, platinum is used as the catalyst, but various other metals such as rhodium, palladium, iridium, osmium, ruthenium, rhenium, gold, silver, nickel, cobalt, lithium, lanthanum, strontium, yttrium, etc. Can be used. An alloy in which two or more of these are combined can also be used.

  In this embodiment, Ketjen (registered trademark) is used as the carbon black C as the catalyst carrier, but a different carbon black may be used. For example, Vulcan XC-72 (trade name), acetylene black, channel black, thermal black, furnace black, or the like may be used. Moreover, it is not limited to carbon black, and various carbon materials such as natural graphite powder, artificial graphite powder, mesocarbon microbeads (MCMB), and multi-walled carbon nanotubes (MWCNT) can be used.

  The platinum P in this example is the catalyst in the claims, the carbon black C contained in the cathode catalyst layer 216, the first carbon material in the claims, and the ionomer I contained in the cathode catalyst layer 216 in the claims. It corresponds to the second solid polymer material, respectively.

A1-1-3. Middle layer:
As shown in FIG. 4A, the intermediate layer 218 is formed by coating carbon black C with an ionomer I having proton conductivity. In this example, Ketjen (registered trademark) is used as the carbon black C as in the cathode catalyst layer 216, and Nafion (registered trademark) is used as the ionomer I in the same manner as the cathode catalyst layer 216. The intermediate layer 218 is disposed between the electrolyte membrane 212 and the cathode catalyst layer 216, and functions to suppress elution of platinum P from the cathode catalyst layer 216 to the electrolyte membrane 212, as will be described later. The carbon black C contained in the intermediate layer 218 in this example corresponds to the second carbon material in the claims, and the ionomer I contained in the intermediate layer 218 corresponds to the third solid polymer material in the claims, respectively. To do.

In the intermediate layer 218, ionomer I: carbon black C = 2: 1 (weight ratio). That is, the weight ratio of ionomer I to carbon black C in the intermediate layer 218 is higher than that in the cathode catalyst layer 216. As described above, when the ratio of the ionomer I is increased, protons (H ⁺ ) easily move in the intermediate layer 218, so that it is considered that a decrease in power generation performance due to the provision of the intermediate layer 218 can be suppressed.

  FIG. 5 is a diagram showing the initial performance (IV characteristics) of the fuel cell 100 of this example together with Comparative Examples 1 and 2. FIG. 5 shows initial performance measured using each fuel cell under a predetermined low humidification condition.

  The fuel cell of Comparative Example 1 has the same configuration as the fuel cell 100 of the present example except that the composition of the intermediate layer is different. The intermediate layer in the fuel cell of Comparative Example 1 was coated with carbon black C (Ketjen (registered trademark)) with Ionomer I (Nafion (registered trademark)) in the same manner as the intermediate layer 218 of the fuel cell 100 in the present example. The weight ratio is ionomer I: carbon black C = 0.75: 1.

  The fuel cell of the comparative example 2 is different from the fuel cell 100 of the present embodiment in that the intermediate layer 218 is not provided, and other configurations are the same as those of the fuel cell 100 of the present embodiment. . That is, the fuel cell of Comparative Example 2 has the same configuration as the conventional fuel cell.

As shown in the figure, the fuel cell 100 of the present example shows substantially the same initial performance as the fuel cell of Comparative Example 2, whereas the fuel cell of Comparative Example 1 is earlier than the fuel cell of Comparative Example 2. The performance is bad. This is because, in the fuel cell 100 of this example, the weight ratio of the ionomer I to the carbon black C in the intermediate layer is higher than that of the fuel cell of the comparative example 1 (that is, the ionomer I content is high). This is probably because (H ⁺ ) is easy to move.

As described above, the cathode catalyst layer 216 in the fuel cell 100 of the present example is ionomer I: carbon black C = 0.75: 1 (weight ratio). That is, the intermediate layer in the fuel cell of Comparative Example 1 has the same weight ratio of ionomer I and carbon black C as that of the cathode catalyst layer 216. On the other hand, the weight ratio of ionomer I to carbon black C in the intermediate layer 218 of the fuel cell 100 of this example is higher than that of the cathode catalyst layer 216. That is, when the weight ratio of ionomer I to carbon black C in the intermediate layer is higher than that of the cathode catalyst layer 216, it is considered that the initial performance of the fuel cell can be maintained without hindering the movement of protons (H ⁺ ).

  In this example, the weight ratio of the ionomer I to the carbon black C in the intermediate layer 218 is 2, but this ratio is not limited to 2, and is higher than the weight ratio in the cathode catalyst layer 216. It is sufficient that the elution of (catalyst) can be suppressed.

A1-1-4. Anode side diffusion layer and cathode side diffusion layer:
As the anode side diffusion layer 215 and the cathode side diffusion layer 217, carbon felt subjected to water repellent processing is used. For example, water repellent processing can be performed by impregnating carbon felt with a mixed solution obtained by mixing carbon and Teflon (registered trademark). Note that only the contact surface of the anode side diffusion layer 215 that contacts the anode catalyst layer 214 and the contact surface of the cathode side diffusion layer 217 that contacts the cathode catalyst layer 216 may be subjected to water repellent processing, or the anode side diffusion layer. 215 and the entire cathode side diffusion layer 217 may be subjected to water repellent finishing. In this embodiment, in order to improve drainage, the anode-side diffusion layer 215 and the cathode-side diffusion layer 217 are subjected to water repellent processing. However, the water-repellent processing may not be performed.

A1-1-5. Seal member:
The seal member 220 is formed by injection molding using silicone rubber. When molding the seal member 220, silicone rubber is impregnated in the voids inside the anode catalyst layer 214, the cathode catalyst layer 216, the intermediate layer 218, the anode side diffusion layer 215, and the cathode side diffusion layer 217, so-called The seal member 220 and the MEA 210 are coupled by the anchor effect.

  As shown in FIG. 2, the seal member 220 includes a cathode gas supply through-hole 106s, a cathode exhaust gas discharge through-hole 108s, an anode gas supply through-hole 102s, an anode exhaust gas discharge through-hole 104s, and a cooling water supply through-hole. One hole 110s and one cooling water discharge through hole 112s are formed. And the seal line SL for preventing the leakage of the reaction gas is formed. Each through hole constitutes a manifold for supplying and discharging reaction gas and cooling water together with the through holes formed in the separators 310 and 330.

A1-2. Composition of anode side porous body and cathode side porous body:
As shown in FIG. 1, the anode side porous body 410 and the cathode side porous body 430 have a substantially rectangular planar shape whose outer shape substantially coincides with the inner frame of the seal member 220 of the seal member integrated MEA 200. It is. In the present embodiment, an expanded metal made of stainless steel having corrosion resistance is used as the anode side porous body 410 and the cathode side porous body 430. The anode-side porous body 410 and the cathode-side porous body 430 are not limited to expanded metal, but use a stainless steel powder, a metal porous body created by slurry foaming, a punching metal, a carbon porous body, etc. Various porous bodies having conductivity can be used. The anode side porous body 410 and the cathode side porous body 430 in this example correspond to the reaction gas flow path forming part in the claims.

A2. Effects of the embodiment:
The effect of the fuel cell 100 of the present embodiment will be described in comparison with the fuel cell of Comparative Example 2 used for measuring the initial performance shown in FIG. The fuel cell of Comparative Example 2 is a fuel cell that does not include the intermediate layer 218 (that is, the same configuration as the conventional fuel cell).

  FIG. 8 is an explanatory diagram conceptually showing the initial state and the operating state of the cathode catalyst layer in the fuel cell of Comparative Example 2. In FIG. 8, the cross-sectional structures of the electrolyte membrane 212 and the cathode catalyst layer 216 are enlarged and conceptually shown. The cathode catalyst layer 216 in the fuel cell of Comparative Example 2 was made of carbon black C (Ketjen (registered trademark)) carrying platinum P as a catalyst, ionomer I (Nafion), as in the cathode catalyst layer 216 in this example. (Registered trademark)). That is, platinum P exists in the cathode catalyst layer 216 and is supported on the carbon black C (FIG. 8A). The electrolyte membrane 212 does not have platinum P.

FIG. 8B shows the state of the cathode catalyst layer 216 when the fuel cell of Comparative Example 2 is in operation. During operation of the fuel cell 100, a potential of about 1 V is applied to the cathode catalyst layer 216, for example. Then, a part of platinum P supported on the carbon black C in the cathode catalyst layer 216 becomes platinum ions (Pt ²⁺ ). Since the electrolyte membrane 212 does not contain platinum, platinum ions (Pt ²⁺ ) in the cathode catalyst layer 216 move through the ionomer I in the cathode catalyst layer 216 and elute into the electrolyte membrane 212 due to the concentration gradient. .

  Since the electrolyte membrane 212 is made of ionomer I (Nafion (registered trademark)) and does not contain carbon black C, platinum ions easily move. In particular, in the cathode catalyst layer 216, platinum P in the vicinity of the boundary with the electrolyte membrane 212 is easily eluted. Then, as shown in FIG. 8B, in the cathode catalyst layer 216, the platinum P content is reduced in the vicinity of the boundary with the electrolyte membrane 212.

  FIG. 9 is a diagram showing IV characteristics in the fuel cell of Comparative Example 2. FIG. 9 shows a comparison of IV characteristics before and after the durability test. The IV characteristics shown in FIG. 9 indicate the initial characteristics of the fuel cell of Comparative Example 2 and the IV characteristics after performing a predetermined durability test. The IV characteristics shown in FIG. 8 are measured under low humidification conditions of a cell temperature of 80 ° C., an anode side dew point of 45 ° C., and a cathode side dew point of 55 ° C. As shown in the drawing, the power generation performance of the fuel cell after the durability test is lower than that before the durability test (initial state).

  Under the above conditions, the electrochemical reaction in the cathode catalyst layer 216 is considered to occur mainly near the boundary with the electrolyte membrane 212. As described above, in the fuel cell of Comparative Example 2, it is considered that when the fuel cell is operated, the content of platinum P in the vicinity of the boundary with the electrolyte membrane 212 in the cathode catalyst layer 216 decreases, so that the power generation efficiency decreases. .

  Next, the fuel cell 100 of the present embodiment will be described. As shown in FIG. 4A, in the initial state, the cathode catalyst layer 216 is formed by coating carbon black C carrying platinum P as a catalyst with ionomer I as described above. That is, platinum P exists in the cathode catalyst layer 216 and is supported on the carbon black C. The intermediate layer 218 and the electrolyte membrane 212 do not have platinum P.

  FIG. 4B shows the state of the cathode catalyst layer 216 and the intermediate layer 218 when the fuel cell 100 is in operation.

During the operation of the fuel cell 100, the cathode catalyst layer 216 is applied with a potential of about 1 V, for example, as in Comparative Example 2. Then, a part of platinum P supported on the carbon black C in the cathode catalyst layer 216 becomes platinum ions (Pt ²⁺ ). Since the intermediate layer 218 does not contain platinum, platinum ions (Pt ²⁺ ) in the cathode catalyst layer 216 move in the ionomer I in the cathode catalyst layer 216 and move to the intermediate layer 218 due to the concentration gradient. And However, the intermediate layer 218 made of the ionomer I containing carbon black C has fewer sulfonic acid groups per unit area than the electrolyte membrane 212, that is, a path for moving platinum ions (Pt ²⁺ ) ( Since there are few platinum ion movement paths), it is considered that platinum ions (Pt ²⁺ ) hardly move in the intermediate layer 218. Therefore, elution of platinum P as a catalyst from the cathode catalyst layer 216 to the electrolyte membrane 212 can be suppressed.

Further, during the operation of the fuel cell 100, ionized H ⁺ (proton) in the anode catalyst layer 214 passes through the electrolyte membrane 212 and reaches the intermediate layer 218, and passes through the ionomer I included in the intermediate layer 218. It moves to reach the cathode catalyst layer 216. In the cathode catalyst layer 216, the supplied oxygen (O ₂ ), protons (H ⁺ ) moved from the anode side, and electrons (e ⁻ ) supplied via the separators 310 and 330, Water (H ₂ O) is produced. Although the intermediate layer 218 contains carbon black C, the content of ionomer I (weight ratio of ionomer I to carbon black C) is higher than that of the cathode catalyst layer 216, so that the movement of protons (H ⁺ ) is inhibited. It is hard to be done.

  FIG. 6 is a diagram showing the amount of platinum P transferred to the electrolyte membrane 212 in the fuel cell 100 of the present embodiment in comparison with the fuel cell of Comparative Example 2. In FIG. 6, the amount of platinum P in the electrolyte membrane 212 in the fuel cell of Comparative Example 2 is shown as 1. After the fuel cell 100 of this example and the fuel cell of Comparative Example 2 were operated under the same durability conditions, the electrolyte membrane was burned and aqua regia (concentrated hydrochloric acid and concentrated nitric acid in a volume of 3: 1) 2 shows a result of quantitative analysis by ICP-MS (Inductively Coupled Plasma Mass Spectrometer).

  As shown in the drawing, the amount of platinum P contained in the electrolyte membrane 212 of the fuel cell 100 of this example is smaller than the amount of platinum contained in the electrolyte membrane of the fuel cell of Comparative Example 2. That is, according to the fuel cell 100 of the present embodiment, elution of platinum P from the cathode catalyst layer 216 to the electrolyte membrane 212 can be suppressed.

  FIG. 7 is a diagram showing IV characteristics in the fuel cell 100 of the present example and the fuel cell of Comparative Example 2 after the durability test. The IV characteristics shown in FIG. 7 are measured by using each fuel cell after performing a predetermined endurance test under low humidification conditions of a cell temperature of 80 ° C., an anode side dew point of 45 ° C., and a cathode side dew point of 55 ° C. Yes. As shown in the figure, the power generation performance of the fuel cell 100 of this example is improved compared to the fuel cell of Comparative Example 2.

As described above, according to the fuel cell 100 of the present embodiment, the elution of platinum P from the cathode catalyst layer 216 to the electrolyte membrane 212 is suppressed by providing the intermediate layer 218. In addition, by making the weight ratio of ionomer I to carbon black C in the intermediate layer 218 higher than that in the cathode catalyst layer 216, the movement of protons (H ⁺ ) from the anode catalyst layer 214 to the cathode catalyst layer 216 is not hindered. I am doing so. As a result, it is possible to suppress a decrease in power generation performance accompanying the operation of the fuel cell.

  Further, in the fuel cell 100 of the present embodiment, the intermediate layer 218 does not contain platinum P as a catalyst. Therefore, no electrochemical reaction occurs in the intermediate layer 218, and no water is generated, so that flooding is unlikely to occur in the intermediate layer 218. Therefore, for example, compared with the fuel cell described in Patent Document 1 described above, it is possible to suppress a decrease in power generation performance due to flooding.

In addition, the fuel cell 100 according to the present embodiment is particularly effective in suppressing a decrease in power generation performance, particularly when operated under low humidification conditions (for example, anode side dew point 45 ° C., cathode side dew point 55 ° C.). is there. Under low humidification conditions, protons (H ⁺ ) hardly move through the ionomer I. Therefore, protons (H ⁺ ) hardly reach the cathode side diffusion layer 217 side of the cathode catalyst layer 216. Therefore, when the platinum P in the vicinity of the electrolyte membrane 212 is eluted in the cathode catalyst layer 216, the power generation performance is significantly reduced. Therefore, suppressing the elution of platinum P by the intermediate layer 218 is effective in suppressing the decrease in power generation performance.

B. Variations:
The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

  (1) In the above embodiment, the intermediate layer 218 is provided only between the electrolyte membrane 212 and the cathode catalyst layer 216, but may be provided between the electrolyte membrane 212 and the anode catalyst layer 214. In general, since the anode catalyst layer 214 has a potential of 0 V, platinum P as a catalyst is not ionized, so that the catalyst is hardly eluted into the electrolyte membrane 212. However, for example, after the operation of the fuel cell 100 is stopped, the anode gas and the cathode gas may be switched and supplied to the fuel cell 100 so that unnecessary power generation is not performed. In such a case, a potential is applied to the anode catalyst layer 214 side, so that the catalyst may be eluted. In such a case, by providing the intermediate layer 218 between the electrolyte membrane 212 and the anode catalyst layer 214, elution of the catalyst into the electrolyte membrane 212 can be suppressed.

  (2) In the above embodiment, the same ionomer I (polymer electrolyte membrane (Nafion (registered trademark)) formed of a fluorosulfonic acid polymer) is used in the electrolyte membrane 212, the cathode catalyst layer 216, and the intermediate layer 218. However, a different ionomer (a solid polymer material having proton conductivity) may be used for each layer.

  In the above embodiment, the same carbon black C (Ketjen (registered trademark)) is used in the cathode catalyst layer 216 and the intermediate layer 218, but different carbon blacks may be used. Further, for example, different carbon materials may be used from carbon black, natural graphite powder, artificial graphite powder, mesocarbon microbeads (MCMB), multi-walled carbon nanotubes (MWCNT), and the like. That is, in the cathode catalyst layer 216 and the intermediate layer 218, the same carbon material may be used, or different carbon materials may be used. Even if it does in this way, the effect similar to the said Example can be acquired.

  (3) In the above embodiment, the intermediate layer 218 having a thickness of 2 μm is illustrated, but the thickness of the intermediate layer 218 is not limited to 2 μm. FIG. 10 is a diagram showing the voltage drop rate with respect to the thickness of the intermediate layer. The voltage drop rate is a generated voltage after the durability test with respect to the initial state. As shown in the figure, voltage drop is suppressed when the thickness of the intermediate layer is 2 μm or more. However, if the intermediate layer is too thick, proton conductivity is hindered, which may reduce power generation performance. Therefore, it is preferably 6 μm or less, more preferably 4 μm or less.

  (4) In the above-described embodiment, a separator having a groove-like reaction gas channel formed on a plane has been shown. However, the configuration of the separator is not limited to the above-described embodiment. For example, three layers in which an anode facing plate that contacts the anode side porous body 410, a cathode facing plate that contacts the cathode side porous body 430, and an intermediate plate sandwiched between the cathode facing plate and the anode facing plate are laminated. It may have a structure, a flat surface may be a smooth surface, and a groove may not be formed.

  As a separator having a three-layer structure, for example, a through hole that forms a manifold for supplying and discharging reaction gas and cooling water is formed in the peripheral portion of each plate. A supply port for supplying anode gas to the anode side porous body 410 is formed in the anode facing plate, and similarly, a supply port for supplying cathode gas to the cathode side porous body 430 is formed in the cathode facing plate. Is done. The intermediate plate is formed with a through-hole for connecting the above-described supply port and each manifold. By stacking the three plates, a flow path for supplying the anode gas and the cathode gas flowing through the manifold to the anode side porous body 410 and the cathode side porous body 430 is formed.

  In the separator having such a configuration, for example, the anode facing plate, the cathode facing plate, and the intermediate plate are thin plates made of stainless steel, and are manufactured by metal bonding or resin bonding. Instead of stainless steel, other metals such as titanium and aluminum may be used. In addition, since each of these plates is exposed to cooling water, it is preferable to use a metal with high corrosion resistance.

1 is a cross-sectional view schematically showing a cross-sectional configuration of a fuel cell 100 as a first embodiment of the present invention. It is a top view which shows the planar structure of seal member integrated MEA200. It is an expanded sectional view which expands and shows the X1 part in FIG. It is explanatory drawing for demonstrating the structure of the cathode catalyst layer 216 and the intermediate | middle layer 218 in the fuel cell 100 of a present Example. It is a figure which shows the initial stage performance (IV characteristic) in the fuel cell 100 of a present Example with Comparative Examples 1 and 2. FIG. FIG. 6 is a diagram showing the amount of platinum P moved to the electrolyte membrane 212 in the fuel cell 100 of the present embodiment in comparison with the fuel cell of Comparative Example 2. It is a figure which shows IV characteristic in the fuel cell 100 of the present Example after a durability test, and the fuel cell of the comparative example 2. FIG. 6 is an explanatory diagram conceptually showing an initial state and an operating state of a cathode catalyst layer in a fuel cell of Comparative Example 2. FIG. 6 is a diagram showing IV characteristics in a fuel cell of Comparative Example 2. FIG. It is a figure which shows the voltage fall rate with respect to the thickness of an intermediate | middle layer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Fuel cell 102s ... Through-hole for anode gas supply 104s ... Through-hole for anode exhaust gas discharge 106s ... Through-hole for cathode gas supply 108s ... Through-hole for cathode exhaust gas discharge 110s ... Through-hole for cooling water supply 112s ... For discharge of cooling water Through hole 200 ... MEA with integrated seal member
210 ... MEA
DESCRIPTION OF SYMBOLS 212 ... Electrolyte membrane 214 ... Anode catalyst layer 215 ... Anode side diffusion layer 216 ... Cathode catalyst layer 217 ... Cathode side diffusion layer 218 ... Intermediate layer 220 ... Seal member 310 ... Anode side separator 312, 332 ... Rib 330 ... Cathode side separator 410 ... Anode-side porous body 430 ... Cathode-side porous body P ... Platinum C ... Carbon black I ... Ionomer SL ... Seal line

Claims (3)

A power generator,
A solid polymer electrolyte membrane comprising a first solid polymer material having proton conductivity;
An anode catalyst layer disposed on one side of the solid polymer electrolyte membrane;
A cathode catalyst layer disposed on the other surface side of the solid polymer electrolyte membrane, comprising a catalyst, a first carbon material, and a second solid polymer material having proton conductivity;
An intermediate layer that does not include a catalyst, includes a second carbon material, and a third solid polymer material having proton conductivity, and is disposed between the solid polymer electrolyte membrane and the cathode catalyst layer When,
With
The second solid polymer material relative to the first carbon material included in the cathode catalyst layer is a weight ratio of the third solid polymer material relative to the second carbon material included in the intermediate layer. The power generator is higher than the weight ratio. The power generator according to claim 1,
The intermediate layer has a thickness of 2 μm or more. A fuel cell,
A power generator according to claim 1 or 2,
A reaction gas flow path forming section for supplying a reaction gas used for an electrochemical reaction in the power generation body to the power generation body;
A fuel cell comprising:

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