JP2010113927A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell having a closed passage for improving drainage performance. <P>SOLUTION: The fuel cell includes a membrane electrode assembly, a gas diffusion layer, and a separator arranged on the opposite side to the membrane electrode assembly of the gas diffusion layer. A first closed passage in which the exit of reaction gas to be supplied to the membrane electrode assembly is closed and a second closed passage in which the entrance of the reaction gas is closed are provided adjacently, and the hydrophobicity of surface of the gas diffusion layer which faces the portion of the separator provided between the first closed passage and the second closed passage is lower than the hydrophobicity of the surface of the gas diffusion layer which faces the center in width direction of the first closed passage, and the hydrophobicity of the surface of the gas diffusion layer which faces the center in the width direction of the second closed passage. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fuel cell, and more particularly, to a fuel cell including a closed channel in which one end of a channel is closed.

  A fuel cell includes a membrane electrode structure (hereinafter referred to as an “electrolyte membrane”) and electrodes (an anode catalyst layer and a cathode catalyst layer) disposed on both sides of the electrolyte membrane. , And may be referred to as “MEA”), and an electric energy generated by the electrochemical reaction is taken out to the outside. Among fuel cells, a polymer electrolyte fuel cell (hereinafter sometimes referred to as “PEFC”) used in a home cogeneration system, an automobile, or the like can be operated in a low temperature region. This PEFC has been attracting attention as a power source and portable power source for electric vehicles because of its high energy conversion efficiency, short start-up time, and small and light system.

  A single cell of PEFC includes an MEA and a pair of current collectors (separators) that sandwich a laminate including the MEA, and the MEA exhibits proton conduction performance by being kept in a water-containing state. Contains a proton conducting polymer. During operation of PEFC, a hydrogen-containing gas (hereinafter referred to as “hydrogen”) is supplied to the anode, and an oxygen-containing gas (hereinafter referred to as “air”) is supplied to the cathode. The hydrogen supplied to the anode is separated into protons and electrons under the action of the catalyst contained in the anode catalyst layer, and the protons generated from the hydrogen reach the cathode catalyst layer through the anode catalyst layer and the electrolyte membrane. On the other hand, electrons reach the cathode catalyst layer through an external circuit, and through such a process, electric energy can be extracted. Then, protons and electrons that have reached the cathode catalyst layer react with oxygen contained in the air supplied to the cathode catalyst layer under the action of the catalyst contained in the cathode catalyst layer, so that water is produced. Generated.

  In order to continue the power generation of PEFC, it is necessary to continuously supply hydrogen and air to the MEA. On the other hand, when liquid water (liquid water) existing in the single cell stays in the reaction gas flow path or the like, diffusion of hydrogen and / or air is inhibited by the liquid water. If the diffusion of hydrogen and / or air is hindered, the power generation performance of the PEFC is reduced. Therefore, in order to improve the power generation performance of the PEFC, it is necessary to discharge liquid water out of the single cell.

  On the other hand, a PEFC including a separator having a closed channel in which one end (an inlet or an outlet) of the channel is blocked has been developed. If it is a form having a closed channel, hydrogen and air that have circulated through a closed channel (hereinafter sometimes referred to as an “entry channel”) whose outlet is blocked are sandwiched between a pair of separators. To reach a closed channel (hereinafter, sometimes referred to as “outlet channel”) through which the inlet is blocked through the laminate, and to be discharged out of the single cell through the outlet channel. It becomes possible to increase the diffusibility of hydrogen and air supplied to the laminate.

  As a technique related to such a PEFC having a closed channel, for example, Patent Document 1 discloses a layer (hereinafter referred to as “gas diffusion layer”) having both conductivity and air permeability between the MEA and the separator. ) And a layer made of a hydrophilic substance (hereinafter referred to as “hydrophilic layer”) is disclosed between the gas diffusion layer and the separator.

JP 2004-79457 A

  In the technique disclosed in Patent Document 1, since a hydrophilic layer is disposed between the gas diffusion layer and the separator, it is possible to move water generated in the cathode catalyst layer during operation to the hydrophilic layer. Become. However, since the hydrophilicity of the hydrophilic layer is higher than that of the closed channel formed in the separator, it is difficult for the technique disclosed in Patent Document 1 to move liquid water from the hydrophilic layer to the closed channel. is there. For this reason, the technique disclosed in Patent Document 1 has a problem that it is difficult to discharge liquid water out of the single cell (improve drainage).

  Then, this invention makes it a subject to provide the fuel cell which has the obstruction | occlusion flow path which can improve drainage.

In order to solve the above problems, the present invention takes the following means. That is,
The present invention includes a membrane electrode structure, a gas diffusion layer disposed on at least one of the membrane electrode structures, and a separator disposed on the opposite side of the membrane electrode structure with respect to the gas diffusion layer. A first closed channel in which an outlet of a reactive gas supplied to the membrane electrode structure is closed on a surface of the separator on the gas diffusion layer side, and a second closed channel in which an inlet of the reactive gas is closed The surface of the gas diffusion layer that is provided so as to be adjacent to each other and faces a portion of the separator (hereinafter sometimes referred to as a “convex portion”) provided between the first closed channel and the second closed channel. Than the hydrophobicity of the surface of the gas diffusion layer facing the center in the width direction of the first closed channel and the hydrophobicity of the surface of the gas diffusion layer facing the center of the second closed channel in the width direction. It is a fuel cell characterized by being low.

  Here, in the present invention, "a separator disposed on the opposite side of the gas diffusion layer from the membrane electrode structure" means that the gas diffusion layer exists between the membrane electrode structure and the separator. It means that a membrane electrode structure, a gas diffusion layer, and a separator are provided.

  According to the present invention, for example, even when the fuel cell is operated under the condition that liquid water is present in the closed portion of the first closed channel, the convex portion and the surface of the separator having relatively low hydrophobicity. The liquid water can be moved to a region including the surface of the gas diffusion layer. And according to this invention, the liquid water moved to the site | part with relatively low hydrophobicity is sent to a 2nd obstruction | occlusion flow path with the reaction gas which goes to a 2nd obstruction | occlusion flow path from a 1st obstruction | occlusion flow path. It can be moved, and liquid water can be discharged out of the single cell through the outlet of the second closed channel. Therefore, according to the present invention, it is possible to provide a fuel cell having a closed channel that can improve drainage.

  For the purpose of improving the performance by improving the diffusibility of the reaction gas supplied to the laminate including the MEA, a PEFC having a closed channel has been developed. However, if the PEFC is operated under the condition that liquid water can exist in the closed channel, liquid water may stay in the closed portion of the incoming channel or the outgoing channel. When the liquid water stays in this way, the diffusion of the reaction gas is inhibited by the staying liquid water, so that the performance of PEFC is lowered. Therefore, it is important to improve the discharge performance (drainage) of liquid water in order to suppress the performance degradation of PEFC. As a result of intensive studies from such a viewpoint, the inventors of the present invention provided a relatively hydrophobic portion and a relatively hydrophobic portion in the gas diffusion layer, and the convexity sandwiched between the closed channels. By relatively lowering the hydrophobicity of the surface of the gas diffusion layer facing the portion and relatively increasing the hydrophobicity of the gas diffusion layer portion facing the center of the widthwise direction of the blocked flow path, As a result, it was found that liquid water can be prevented from staying in the water and the present invention was completed.

  The present invention has been made on the basis of such knowledge, and its main gist is to provide a fuel cell having a closed channel that can improve drainage.

  The present invention will be described below with reference to the drawings. In addition, the form shown below is an illustration of this invention and this invention is not limited to the form shown below.

  FIG. 1 is a cross-sectional view schematically showing an example of a fuel cell according to the present invention. 1 is the thickness direction of the separator, the left-right direction of FIG. 1 is the flow path width direction of the closed flow path provided in the separator, and the back / front direction of FIG. 1 is the reaction gas flow direction. is there. In order to facilitate understanding of the present invention, some reference numerals are omitted in FIG. FIG. 2 is an enlarged view of a part of the cathode catalyst layer, the gas diffusion layer, and the separator described in FIG. 2 is the thickness direction of the separator, the left-right direction of FIG. 2 is the channel width direction of the closed channel provided in the separator, and the back / front direction of FIG. 2 is the reaction gas flow direction, The arrows in FIG. 2 indicate the direction of movement of water generated during operation of the fuel cell of the present invention. FIG. 3 is a plan view showing a form example of a separator disposed on the anode catalyst layer side. The arrows in FIG. 3 indicate the direction of hydrogen flow. FIG. 4 is a plan view showing a form example of the separator disposed on the cathode catalyst layer side. The arrows in FIG. 4 indicate the direction of air flow.

  As shown in FIGS. 1 and 2, the fuel cell 10 of the present invention includes an electrolyte membrane 1, an anode catalyst layer 2 formed on one surface of the electrolyte membrane 1, and the anode catalyst layer 2. An MEA 4 including a cathode catalyst layer 3 formed on the surface opposite to the surface of the electrolyte membrane 1, a gas diffusion layer 5 disposed on the anode catalyst layer 2 side, and a cathode catalyst layer 3 side. A gas diffusion layer 6, a separator 7 disposed on the gas diffusion layer 5 side, and a separator 8 disposed on the gas diffusion layer 6 side.

  In the fuel cell 10, the gas diffusion layer 5 has a highly hydrophobic portion 5a having a relatively high hydrophobicity and low hydrophobic portions 5b, 5b,. The hydrophobicity of the part 5a is higher than the hydrophobicity of the low hydrophobic parts 5b, 5b,. The gas diffusion layer 6 has a highly hydrophobic portion 6a having relatively high hydrophobicity and low hydrophobic portions 6b, 6b,... Having relatively low hydrophobicity, and the hydrophobicity of the highly hydrophobic portion 6a. Is higher than the hydrophobicity of the low hydrophobic portions 6b, 6b,. Moreover, as shown in FIG.1 and FIG.3, the separator 7 is the entrance channel 7x, 7x, ... which is an obstruction | occlusion passage by which the exit was obstruct | occluded by the obstruction | occlusion member 9,9 ... , Which are closed channels whose inlets are blocked by the projections 7z, 7z located between the input channels 7x, 7x,... And the output channels 7y, 7y,. ,…have. 1, 2, and 4, the separator 8 includes the inflow channels 8 x, 8 x,..., Which are closed channels whose outlets are blocked by the blocking members 9, 9,. Are located between the exit channels 8y, 8y,... And the exit channels 8y, 8y,. It has convex portions 8z, 8z,.

  As shown in FIG. 1, in the gas diffusion layer 5, the low hydrophobic portions 5 b, 5 b,... Are arranged in a region including the surface facing the convex portions 7 z, 7 z,. The region of the gas diffusion layer 5 other than... Is a highly hydrophobic portion 5a. Similarly, as shown in FIGS. 1 and 2, in the gas diffusion layer 6, the low hydrophobic portions 6 b, 6 b,... Are arranged in a region including the surface facing the convex portions 8 z, 8 z,. The region of the gas diffusion layer 6 other than the sex sites 6b, 6b,... Is a highly hydrophobic site 6a.

  During operation of the fuel cell 10, hydrogen supplied through the inflow channels 7 x, 7 x,... Passes through the gas diffusion layer 5 and reaches the anode catalyst layer 2, and the catalyst ( For example, platinum and the like. The same applies hereinafter.) The reaction is performed to separate protons and electrons. Protons generated in this way move to the cathode catalyst layer 3 through the proton conductors contained in the anode catalyst layer 2, the electrolyte membrane 1, and the cathode catalyst layer 3, and are generated in the anode catalyst layer 2. The electrons reach the cathode catalyst layer 3 via an external circuit. On the other hand, during operation of the fuel cell 10, the air supplied through the inflow channels 8 x, 8 x,... Passes through the gas diffusion layer 6 to reach the cathode catalyst layer 3 and reaches the cathode catalyst layer 3. Oxygen contained in the air reacts with protons and electrons moving from the anode catalyst layer 2 to the cathode catalyst layer 3 under the action of the catalyst contained in the cathode catalyst layer 3, thereby Generated.

  In order to reduce the conduction resistance of protons traveling from the anode catalyst layer 2 to the cathode catalyst layer 3 through the proton conductor, the MEA 4 needs to be in a water-containing state. Therefore, during operation of the fuel cell of the present invention, humidified hydrogen is supplied via the inlet channels 7x, 7x,..., And humidified air is supplied via the inlet channels 8x, 8x,. . In the fuel cell 10, among the hydrogen supplied through the inflow channels 7 x, 7 x,..., Hydrogen not used for the reaction in the anode catalyst layer 2 passes through the anode catalyst layer 2 and the gas diffusion layer 5. To the outlet channels 7y, 7y,... And discharged through the outlets of the outlet channels 7y, 7y,. That is, supply is made through the inflow channels 7x, 7x,... By having the inflow channels 7x, 7x,... With the outlets closed and the outflow channels 7y, 7y,. The forced hydrogen can be forced to flow into the anode catalyst layer 2, and the hydrogen diffused through the anode catalyst layer 2 can be discharged through the outlets of the outlet channels 7y, 7y,. Therefore, according to the fuel cell 10, the region of the gas diffusion layer 5 facing the convex portions 7z, 7z,... (Low hydrophobic portions 5b, 5b,...) And the anode catalyst layer facing the convex portions 7z, 7z,. Hydrogen can be diffused also in the second region. On the other hand, air that has not been used for the reaction in the cathode catalyst layer 3 out of the air supplied through the inflow channels 8x, 8x,... It reaches the paths 8y, 8y,... And is discharged through the outlets of the outlet channels 8y, 8y,. That is, supply is made via the inflow channels 8x, 8x,... By having the inflow channels 8x, 8x,... With the outlets closed and the outflow channels 8y, 8y,. The forced air can be forced to flow into the cathode catalyst layer 3, and the air diffused through the cathode catalyst layer 3 can be discharged through the outlets of the outlet channels 8y, 8y,. Therefore, according to the fuel cell 10, the region of the gas diffusion layer 6 facing the convex portions 8z, 8z,... (Low hydrophobic portions 6b, 6b,...) And the cathode catalyst layer facing the convex portions 8z, 8z,. The air can be diffused also in the third area.

  The water generated in the cathode catalyst layer 3 during the operation of the fuel cell 10 moves in the direction indicated by the arrow in FIG. More specifically, it is as follows.

  The cathode catalyst layer 3 has a hydrophilic region and a hydrophobic region. Therefore, the water generated in the cathode catalyst layer 3 reaches the interface between the cathode catalyst layer 3 and the gas diffusion layer 6 through the hydrophilic region included in the cathode catalyst layer 3. Here, the hydrophobicity of the hydrophobic region included in the cathode catalyst layer 3 is higher than the hydrophobicity of the highly hydrophobic portion 6 a included in the gas diffusion layer 6. Therefore, the water pushed out from the cathode catalyst layer 3 by producing a large amount of water reaches the highly hydrophobic portion 6 a of the gas diffusion layer 6. The water that has reached the highly hydrophobic portion 6a then moves to the inflow channels 8x, 8x,... And the outflow channels 8y, 8y,..., Or to the low hydrophobic portions 6b, 6b,. Moving.

  Thus, at least a part of the water generated in the cathode catalyst layer 3 reaches the inflow channels 8x, 8x,. As described above, since the outlet of the inlet channel is blocked, in the prior art, liquid water tends to stay at the outlet of the inlet channel of the separator disposed on the cathode catalyst layer side. However, in the fuel cell 10, the low hydrophobic portions 6 b, 6 b,... Are arranged on a part of the gas diffusion layer 6 including the surface facing the convex portions 8 z, 8 z,. A highly hydrophobic portion 6 a is disposed in the region of the gas diffusion layer 6 other than the above. Therefore, the liquid water present at the outlets of the inflow channels 8x, 8x,... Moves to the low hydrophobic portions 6b, 6b,. Here, as described above, in the fuel cell 10, there is an air flow from the inflow channels 8x, 8x,... To the outflow channels 8y, 8y,. The air flow also exists. Therefore, according to the fuel cell 10, the liquid water that has reached the low hydrophobic portions 6b, 6b,... Via the inflow channels 8x, 8x,. And the liquid water can be discharged through the outlet channels 8y, 8y,. Therefore, according to the fuel cell 10 of the present invention having the high hydrophobic portion 6a and the low hydrophobic portions 6b, 6b,..., Drainage can be improved. Therefore, according to the fuel cell 10 of the present invention, the occurrence of flooding on the cathode catalyst layer 3 side can be suppressed.

  Furthermore, during the operation of the conventional fuel cell, liquid water may remain at the outlet of the inlet channel of the separator disposed on the anode catalyst layer side. However, in the fuel cell 10, the low hydrophobic portions 5 b, 5 b,... Are arranged on a part of the gas diffusion layer 5 including the surface facing the convex portions 7 z, 7 z,. A highly hydrophobic portion 5 a is disposed in the region of the gas diffusion layer 5 other than the above. Therefore, the liquid water present at the outlets of the entrance channels 7x, 7x,... Moves to the low hydrophobic portions 5b, 5b,... Having a lower degree of hydrophobicity than the high hydrophobic portion 5a. Here, as described above, in the fuel cell 10, there is a flow of hydrogen from the inflow channels 7x, 7x,... To the outflow channels 7y, 7y,. There is also a flow of such hydrogen. Therefore, according to the fuel cell 10, liquid water that has reached the low hydrophobic portions 5b, 5b,... Via the inflow channels 7x, 7x,. And the liquid water can be discharged through the outlet channels 7y, 7y,. Therefore, according to the fuel cell 10 of the present invention having the high hydrophobic portion 5a and the low hydrophobic portions 5b, 5b,..., Drainage can be improved. Therefore, according to the fuel cell 10 of the present invention, the occurrence of flooding not only on the cathode catalyst layer 3 side but also on the anode catalyst layer 2 side can be suppressed.

  In the above description of the fuel cell 10 according to the present invention, the gas diffusion layer 5 is provided with the high hydrophobic portion 5a and the low hydrophobic portions 5b, 5b,. Although the form provided with the sex parts 6b, 6b,... Is exemplified, the fuel cell of the present invention is not limited to the form. In the fuel cell of the present invention, the gas diffusion layer disposed on the anode catalyst layer side or the gas diffusion layer disposed on the cathode catalyst layer side has substantially uniform hydrophobicity over the entire region. It is also possible to adopt a form. However, from the viewpoint of improving the air diffusibility by suppressing the situation in which liquid water stays in the vicinity of the outlet of the inlet channel of the separator disposed on the cathode catalyst layer side, the cathode catalyst layer It is preferable that a highly hydrophobic portion and a low hydrophobic portion are disposed in the gas diffusion layer disposed on the side. In addition, from the standpoint of a configuration in which liquid water stays in the vicinity of the outlet of the separator inlet channel disposed on the anode catalyst layer side through which hydrogen having a slower flow rate than air flows, etc. It is preferable that a highly hydrophobic portion and a low hydrophobic portion are disposed in the gas diffusion layer disposed on the anode catalyst layer side.

  In the above description regarding the fuel cell 10 of the present invention, the gas diffusion layer 5 is provided on the anode catalyst layer 2 side and the gas diffusion layer 6 is provided on the cathode catalyst layer 3 side. The fuel cell is not limited to this form. The fuel cell of the present invention may be configured such that the gas diffusion layer is provided only between the anode catalyst layer and the separator or between the cathode catalyst layer and the separator. Thus, in the fuel cell of the present invention, when the gas diffusion layer is provided only on one of the anode catalyst layer side and the cathode catalyst layer side, the gas diffusion layer is divided into a highly hydrophobic portion and a low hydrophobic portion. A gas diffusion layer having

  In the fuel cell 10 of the present invention, the method for producing the gas diffusion layer 5 is particularly limited as long as the gas diffusion layer 5 including the high hydrophobic portion 5a and the low hydrophobic portions 5b, 5b,. It is not a thing and a well-known method can be used. As a method for producing the gas diffusion layer 5, for example, the gas diffusion layer in which the masking member is arranged at the place where the low hydrophobic portions 5b, 5b,. The form etc. can be mentioned. If produced by such a method, the gas diffusion layer 5 in which the portion where the masking member is not disposed is defined as a highly hydrophobic portion 5a, and the portion where the masking member is disposed is defined as a low hydrophobic portion 5b, 5b,. Can be produced. The gas diffusion layer 6 can be produced by the same method as the gas diffusion layer 5.

It is sectional drawing which shows the example of a form of the fuel cell 10 of this invention. It is sectional drawing which expands and shows a part of fuel cell 10 of this invention. FIG. 6 is a plan view showing an example of the form of a separator 7. FIG. 5 is a plan view showing an example of the form of a separator 8.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electrolyte membrane 2 ... Anode catalyst layer 3 ... Cathode catalyst layer 4 ... MEA (membrane electrode structure)
5 ... Gas diffusion layer 5a ... High hydrophobic part 5b ... Low hydrophobic part 6 ... Gas diffusion layer 6a ... High hydrophobic part 6b ... Low hydrophobic part 7 ... Separator 7x ... Inlet channel (first closed channel)
7y ... Outlet channel (second closed channel)
7z ... convex part 8 ... separator 8x ... entering flow path (first closed flow path)
8y ... Outlet channel (second closed channel)
8z ... convex part 9 ... closing member 10 ... fuel cell

Claims (1)

A membrane electrode structure, a gas diffusion layer disposed on at least one of the membrane electrode structures, and a separator disposed on the opposite side of the membrane electrode structure with respect to the gas diffusion layer,
On the surface of the separator on the gas diffusion layer side, a first closed flow path in which an outlet of a reactive gas supplied to the membrane electrode structure is closed, and a second closed flow in which an inlet of the reactive gas is closed Roads are prepared next to each other,
The hydrophobicity of the surface of the gas diffusion layer facing the portion of the separator provided between the first closed channel and the second closed channel faces the center in the width direction of the first closed channel. The fuel cell, wherein the hydrophobicity of the surface of the gas diffusion layer and the hydrophobicity of the surface of the gas diffusion layer facing the center in the width direction of the second closed channel are lower.

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