JP2009099262A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the output performance of a fuel cell. <P>SOLUTION: The fuel cell has: an electrolyte membrane; a cathode electrode catalyst layer which is formed on one face of the electrolyte membrane and in which an electrochemical reaction is generated; a gas diffusion layer which is arranged on the cathode electrode catalyst layer and in which a reaction gas utilized for the electrochemical reaction is diffused; and a hydrophobic layer which is formed on a face contacting with the cathode electrode catalyst layer in the gas diffusion layer which has hydrophobic characteristics, and has a flow passage forming part to form a flow passage between the cathode electrode catalyst layer. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel cell.

  In a fuel cell, it is known that the generated water generated by the electrochemical reaction stays in the cathode electrode catalyst layer, or the electrolyte membrane dries and the proton conductivity decreases, so that the voltage of the fuel cell decreases. ing. In order to solve at least a part of this problem, a water retention layer is provided between the cathode electrode catalyst layer and the gas diffusion layer, and the water retention layer prevents a decrease in proton conductivity by supplying necessary moisture to the electrolyte membrane. Is known (Patent Document 1). Further, a technique is known in which an intermediate layer having a gap is provided between the cathode electrode catalyst layer and the electrolyte membrane, and the generated water is discharged from the intermediate layer to prevent the generated water from staying in the cathode electrode catalyst layer. (Patent Document 2). In addition, by making the joint surface of the gas diffusion layer with the cathode electrode catalyst layer hydrophobic, and providing the cathode electrode catalyst layer with the generated water, a concave generated water flow path is provided on the side of the gas diffusion layer facing the separator. A technique for discharging generated water staying in a gas diffusion layer as water vapor is known (Patent Document 3).

Japanese Patent No. 3778506 JP 2005-174646 A JP 2006-4787 A

  However, if a water retention layer is provided between the cathode electrode catalyst layer and the gas diffusion layer, when excessive product water is generated by an electrochemical reaction, the product water stays in the water retention layer, and this is the cathode electrode of the oxidizing gas. There is a possibility that the diffusion into the catalyst layer may be hindered. Further, when an intermediate layer having a gap is provided between the cathode electrode catalyst layer and the electrolyte membrane, protons need to move through the intermediate layer in addition to the electrolyte membrane for electrochemical reaction. In addition, the contact area between the electrolyte membrane and the cathode electrode catalyst layer is reduced by the gap. As a result, the power generation efficiency of the fuel cell may be reduced. If the bonding surface of the gas diffusion layer with the cathode electrode catalyst layer is made hydrophobic and a concave generated water flow path is provided on the side of the gas diffusion layer facing the separator, the hydrophobic bonding surface of the gas diffusion layer causes the catalyst layer to enter the catalyst layer. There is a risk that the generated water may stay or the generated water in the flow path provided on the side facing the separator may stay in the vicinity of the oxidizing gas outlet along the flow of the oxidizing gas, degrading the output performance of the fuel cell. There is a problem to make.

  The present invention has been made to solve at least a part of the above-described conventional problems, and an object thereof is to improve the output performance of a fuel cell.

  In order to solve at least a part of the above problems, the present invention employs the following aspects.

  A first aspect of the present invention provides a fuel cell. A fuel cell according to a first aspect of the present invention includes an electrolyte membrane, a cathode electrode catalyst layer that is formed on one surface of the electrolyte membrane and causes an electrochemical reaction, and is disposed on the cathode electrode catalyst layer, A gas diffusion layer for diffusing a reaction gas used for an electrochemical reaction and a surface of the gas diffusion layer in contact with the cathode electrode catalyst layer, having hydrophobicity and flowing between the cathode electrode catalyst layer And a hydrophobic layer having a flow path forming portion for forming a path.

  According to the fuel cell of the first aspect of the present invention, by providing a hydrophobic layer having hydrophobicity on the surface of the gas diffusion layer in contact with the cathode electrode catalyst layer, the generated water stays in the gas diffusion layer. This can be suppressed. Further, by forming a flow path between the cathode electrode catalyst layer and the flow path forming portion, the generated water can be discharged, and retention of the generated water in the cathode electrode catalyst layer can be suppressed. Thereby, the retention of the produced water that inhibits the supply of the reaction gas supplied to the electrochemical reaction to the cathode electrode catalyst layer can be suppressed, and the output performance of the fuel cell can be improved.

  The fuel cell according to the first aspect of the present invention further includes a supply port for supplying the reaction gas to the gas diffusion layer and an exhaust port for discharging the reaction gas from the gas diffusion layer, The flow path forming unit may form a flow path that guides the generated water from the vicinity of the discharge port to the vicinity of the supply port. In this case, the generated water can be moved from the vicinity of the discharge port to the vicinity of the supply port by the flow path formed by the flow path forming unit, and the stay of the generated water in the vicinity of the discharge port can be suppressed.

  In the fuel cell according to the first aspect of the present invention, the flow path forming portion has a groove-shaped portion communicating from the vicinity of the discharge port to the vicinity of the supply port, and the flow path is formed by the groove-shaped portion. May be. In this case, since the groove-shaped portion communicates from the vicinity of the discharge port to the vicinity of the supply port, the generated water can move from the vicinity of the discharge port to the vicinity of the supply port through the flow path formed by the groove-shaped portion, It is possible to suppress the generated water from staying in the vicinity of the discharge port.

  In the fuel cell according to the first aspect of the present invention, the flow path forming portion may include a plurality of the groove-shaped portions. In this case, the generated water can be moved from the vicinity of the discharge port to the vicinity of the supply port in a wide range of the cathode electrode catalyst layer by the plurality of groove-shaped portions, and the discharge performance of the generated water can be further improved.

  In the fuel cell according to the first aspect of the present invention, the surface of the groove portion may be hydrophilic. In this case, since the surface of the groove-like portion is hydrophilic, the generated water can easily move through the flow path formed by the groove-like portion, and thus the discharge performance of the generated water can be improved.

  In the fuel cell according to the first aspect of the present invention, the supply port and the discharge port may be disposed in the vicinity of the opposing end portions of the separator. In this case, the generated water in the vicinity of the discharge port disposed in the vicinity of the end of the separator can be moved to the vicinity of the supply port disposed in the vicinity of the end opposite to the end in which the discharge port is disposed. The generated water in the vicinity of the discharge port can be discharged and the generated water can be supplied in the vicinity of the supply port, and the output performance of the fuel cell can be improved by maintaining the wet state of the electrolyte membrane in the vicinity of the supply port.

  In the present invention, the various aspects described above can be combined as appropriate or applied with a part omitted.

  Hereinafter, a fuel cell according to the present invention will be described based on examples with reference to the drawings.

A. First Example A1. Fuel cell configuration:
FIG. 1 is a schematic cross-sectional view showing a schematic configuration of a single cell constituting a fuel cell as one embodiment of the present invention. The unit cell 10 includes an electrolyte membrane 20, an anode catalyst layer 21 and a cathode catalyst layer 22 that are electrodes formed on each surface of the electrolyte membrane 20, and a gas that sandwiches the electrolyte membrane 20 on which the electrodes are formed from both sides. Diffusion layers 23 and 24 and gas separators 25 and 26 disposed further outside the gas diffusion layers 23 and 24 are provided.

  The fuel cell of this example is a solid polymer fuel cell, and the electrolyte membrane 20 includes a solid polymer electrolyte that exhibits proton conductivity in a wet state. The anode catalyst layer 21 and the cathode catalyst layer 22 include, for example, platinum or a platinum alloy as a catalyst. More specifically, the anode catalyst layer 21 and the cathode catalyst layer 22 include carbon particles supporting the catalyst and an electrolyte similar to the polymer electrolyte constituting the electrolyte membrane 20. The anode catalyst layer 21 and the cathode catalyst layer 22 together with the electrolyte membrane 20 constitute an MEA (Membrane Electrode Assembly) 30.

  The gas diffusion layers 23 and 24 can be formed of a conductive member having gas permeability, such as carbon paper or carbon cloth, metal mesh, or foam metal. Each of the gas diffusion layers 23 and 24 is formed as a flat plate-like member, serves as a flow path for a gas used for an electrochemical reaction, and serves for current collection. The gas diffusion layer 24 of the present embodiment includes a hydrophobic layer and a water flow path which will be described later on the surface in contact with the cathode catalyst layer 22.

  The gas separators 25 and 26 are formed in a plate shape by a gas impermeable conductive member, for example, a member made of compressed carbon or stainless steel. Each of the gas separators 25 and 26 has a predetermined convex portion. By this convex portion, a single-cell fuel gas flow path 27 through which a fuel gas containing hydrogen flows is formed between the gas separator 25 and the gas diffusion layer 23. In addition, an in-single cell oxidizing gas passage 28 through which an oxidizing gas containing oxygen flows is formed between the gas separator 26 and the gas diffusion layer 24 by the convex portion.

  Further, a sealing member such as a gasket is disposed on the outer peripheral portion of the single cell 10 (not shown) in order to ensure the gas sealing property of the fuel gas and the oxidizing gas in the single cell. In addition, the fuel cell of this embodiment has a stack structure in which a plurality of single cells 10 are stacked. The outer periphery of the stack structure is parallel to the stacking direction of the single cells 10 and is fuel gas or oxidation. A plurality of gas manifolds through which gas flows are provided (not shown). The fuel gas flowing through the fuel gas supply manifold is distributed to the anode side of each unit cell 10, passes through each unit cell fuel gas flow path 27 while being subjected to an electrochemical reaction, and gathers in the fuel gas discharge manifold. Similarly, the oxidant gas flowing through the oxidant gas supply manifold is distributed to the cathode side of each single cell 10, passes through the oxidant gas flow path 28 in each single cell while being subjected to an electrochemical reaction, and reaches the oxidant gas discharge manifold. Gather.

A2. Channel structure:
A structure of a flow path through which produced water generated by an electrochemical reaction moves will be described with reference to FIG. FIG. 2 is an explanatory view illustrating a flow path provided on the gas diffusion layer. FIG. 2 is different from FIG. 1 in that the membrane surface is horizontal and the anode catalyst layer 21 is above the cathode catalyst layer 22. As shown in the figure, the gas separator 26 includes an oxidizing gas supply port 51 and an oxidizing gas discharge port 52. Each of the oxidizing gas supply port 51 and the oxidizing gas discharge port 52 is disposed in the vicinity of the opposite sides of the gas separator 26. The oxidizing gas flowing through the oxidizing gas supply manifold described above is supplied into the single cell 10 from the oxidizing gas supply port 51, passes through the oxidizing gas flow path 28 in the single cell, and is then discharged from the oxidizing gas discharge port 52. Collected in the discharge manifold.

  A flow path 42 is provided on the surface of the gas diffusion layer 24 in contact with the cathode catalyst layer 22. In the present embodiment, the flow path 42 is a groove-shaped portion having a V-shaped cross-sectional shape. The cross-sectional shape of the flow path 42 is not particularly limited, and may be U-shaped or a U-shaped groove. A plurality of the flow paths 42 are arranged substantially in parallel in the direction connecting the oxidizing gas upstream portion in the vicinity of the oxidizing gas supply port 51 and the oxidizing gas downstream portion in the vicinity of the oxidizing gas discharge port 52 in the gas separator 26. The depth and width of the groove of the channel 42 are not particularly defined, but are preferably about 0.1 to 2 μm. The interval between the flow paths 42 is not particularly limited, but is preferably about 10 times the groove width, for example. The flow path 42 can be formed using, for example, an excimer laser or an ultrashort pulse laser.

  FIG. 3 is a schematic cross-sectional view showing an enlarged joint surface between the cathode catalyst layer and the gas diffusion layer. Contrary to FIG. 2, the cathode catalyst layer 22 is shown to be on the upper side of the electrolyte membrane. As shown in FIG. 3, a hydrophobic layer 41 is formed on the gas diffusion layer 24 on the surface in contact with the cathode catalyst layer 22 having the flow path 42. The hydrophobic layer 41 is a gas diffusion layer made of a mixed paste of carbon or a conductive material similar thereto and a hydrophobic binder resin such as polytetrafluoroethylene (PTFE) or tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA). It is formed by coating. The channel 42 is processed by a laser to modify the surface of the groove-like portion, so that even the channel formed on the surface of the hydrophobic layer 41 has hydrophilicity.

A3. Channel function:
The function of the gas diffusion layer provided with a flow path through which produced water generated by the electrochemical reaction moves will be described. As indicated by the wavy line x in FIG. 3, the oxidizing gas is diffused from the gas diffusion layer 24 to the cathode catalyst layer 22 via the hydrophobic layer 41. Since the hydrophobic layer 41 is hydrophobic, the generated water generated by the electrochemical reaction in the cathode catalyst layer 22 is suppressed from moving to the gas diffusion layer 24 and guided to the flow path 42 as indicated by the wavy line w. As a result, it is possible to prevent the generated water from staying at the interface between the gas diffusion layer 24 and the cathode catalyst layer 22 at a portion other than the flow path 42, and the oxidizing gas is inhibited by the generated water at a portion other than the flow path 42. Without being supplied to the cathode catalyst layer 22.

  4 is a schematic cross-sectional view including a 4-4 cross section of FIG. As shown in the figure, the oxidizing gas flows in the single cell oxidizing gas flow path 28 in a certain direction. Part of the generated water generated by the electrochemical reaction permeates the hydrophobic layer 41 as water vapor and is discharged along the flow of the oxidizing gas inside the oxidizing gas channel 28 in the single cell. Some of the generated water moves as liquid water toward the upstream portion of the oxidizing gas that tends to be in a dry state in the flow path 42. Thereby, retention of the produced water in the downstream portion of the oxidizing gas can be suppressed. Moreover, the electrolyte membrane upstream of the oxidizing gas can be humidified by the generated product water that has moved.

  According to the fuel cell of the first embodiment described above, the produced water generated by the electrochemical reaction moves in the flow path 42, so that the produced water can be prevented from staying in the vicinity of the oxidizing gas discharge port 52. Thereby, the discharge performance of produced water can be improved and the output performance of a fuel cell can be improved.

  According to the first embodiment, the generated water in the vicinity of the oxidizing gas discharge port can be moved to the vicinity of the oxidizing gas supply port by the flow path 42. As a result, the generated water in the downstream portion of the oxidizing gas can be used to humidify the electrolyte membrane in the upstream portion of the oxidizing gas, preventing a decrease in proton conductivity and improving the output performance of the fuel cell.

  According to the first embodiment, the hydrophobic layer 41 is formed on the surface of the gas diffusion layer 24 in contact with the cathode catalyst layer 22. Thereby, the generated water in the cathode is suppressed from moving into the gas diffusion layer 24, and the retention of the generated water in the gas diffusion layer that inhibits the electrochemical reaction can be suppressed.

  According to the first embodiment, the surface of the gas diffusion layer 24 has a plurality of groove portions that are flow paths of generated water. Thereby, the generated water can be moved from the vicinity of the discharge port to the vicinity of the supply port in a wide range of the cathode electrode catalyst layer, and the discharge performance of the generated water can be further enhanced.

  According to the first embodiment, the groove portion surface can be modified to be hydrophilic by processing the groove portion with a laser. Thereby, the flow path 42 becomes hydrophilic so that the generated water can be easily moved, and the discharge performance of the generated water can be further improved.

B. Second embodiment:
In the second embodiment, a fuel cell will be described in which a groove portion is not formed as a flow path of generated water on the surface of the gas diffusion layer 24. In the second embodiment, each component having the same reference numeral as that in the first embodiment has the same structure and function as each component in the first embodiment.

  FIG. 5 is a schematic cross-sectional view showing an enlarged joint surface between the cathode catalyst layer and the gas diffusion layer in the second embodiment. As in the first embodiment, the gas diffusion layer 24 has a hydrophobic layer 41 formed on the surface in contact with the cathode catalyst layer 22. The surface of the hydrophobic layer 41 is modified by plasma treatment, and the hydrophobic layer 41 includes a hydrophilic portion 43 having hydrophilicity. The hydrophilic portion 43 forms a gap through which generated water can move between the surface of the cathode catalyst layer 22. Since the hydrophobic layer 41 is hydrophobic, the generated water generated by the electrochemical reaction in the cathode catalyst layer 22 is suppressed from moving to the gas diffusion layer 24 and guided to the hydrophilic portion 43 as indicated by the wavy line w ′. The hydrophilic portion 43 has a function similar to that of the flow path 42 in the first embodiment as a flow path of the generated water. In the fuel cell according to the second embodiment, the generated water generated by the electrochemical reaction forms a gap formed between the hydrophilic portion 43 and the cathode catalyst layer 22 from the vicinity of the oxidizing gas discharge port 52 to the vicinity of the oxidizing gas supply port 51. , The generated water is discharged from the vicinity of the oxidizing gas discharge port 52, and the electrolyte membrane in the vicinity of the oxidizing gas supply port 51 is humidified.

  According to the second embodiment, the generated water generated by the electrochemical reaction moves through the gap formed between the hydrophilic portion 43 and the cathode catalyst layer 22 without providing the channel of the groove portion. As a result, similar to the first embodiment, the generated water can be prevented from staying in the vicinity of the oxidizing gas discharge port 52, the generated water discharge performance can be improved, and the output performance of the fuel cell can be improved.

  According to the second embodiment, the hydrophobic layer 41 can be modified to be hydrophilic also by plasma treatment, and the generated water easily moves through the void formed between the hydrophilic portion 43 and the cathode catalyst layer 22. It is possible to improve the discharge performance of the produced water.

C. Third embodiment:
In the third embodiment, a fuel cell having a hydrophilic layer on the surface of the gas diffusion layer 24 will be described. Also in the third embodiment, each component having the same reference numeral as that in the first embodiment has the same structure and function as each component in the first embodiment.

  FIG. 6 is a schematic cross-sectional view showing an enlarged joint surface between the cathode catalyst layer and the gas diffusion layer in the third embodiment. As in the first embodiment, the gas diffusion layer 24 has a hydrophobic layer 41 formed on the surface in contact with the cathode catalyst layer 22. The gas diffusion layer 24 according to the third embodiment further includes a hydrophilic surface 44 on the surface of the hydrophobic layer 41. The hydrophilic surface 44 is formed by a surface treatment method such as arc discharge. The hydrophilic surface 44 needs to have such a thickness that the generated water does not stay. For example, it is preferably about 1 molecule, about 0.001 to 0.01 μm.

  According to the third embodiment, since the generated water generated by the electrochemical reaction moves in the space formed between the hydrophilic surface 44 and the cathode catalyst layer 22, grooves and voids are formed on the surface of the gas diffusion layer. It is possible to suppress the retention of generated water in the vicinity of the oxidizing gas discharge port 52 without forming the above. Thereby, the output performance of the fuel cell can be improved.

  According to the third embodiment, the hydrophilic surface 44 does not have a thickness in which the generated water stays, and the hydrophobic layer 41 prevents the generated water from permeating into the gas diffusion layer. The product water can be prevented from staying in the gas diffusion layer.

  According to the third embodiment, a hydrophilic surface 44 that is hydrophilic is formed on the surface of the hydrophobic layer 41. For this reason, the generated water can easily move in the space formed between the hydrophilic surface 44 and the cathode catalyst layer 22, and the discharge performance of the generated water can be further improved.

D. Modification D1. Modification 1:
In the first embodiment, the oxidant gas flow path 28 in the single cell in the gas separator 26 is shown in a substantially straight line, but the oxidant gas flow path 28 in the single cell can be implemented even in a curved shape. FIG. 7 is an explanatory diagram illustrating a single cell according to a modification. For example, even in the gas separator 26 having the serpentine-shaped single-cell oxidizing gas flow path 28, the generated water in the downstream portion of the oxidizing gas in the vicinity of the oxidizing gas discharge port 52 flows into the upstream portion of the oxidizing gas in the vicinity of the oxidizing gas supply port. It can be implemented by forming the flow path so as to be movable.

D2. Modification 2:
In the first embodiment, the flow path 42 in the gas diffusion layer 24 is substantially straight, but if the generated water can move from the downstream portion of the oxidizing gas to the upstream portion of the oxidizing gas, it may be curved or short. Or the width may change or the direction of each groove-like portion may be different. Further, the flow path 42 may be formed by a collection of recesses.

D3. Modification 3
Although the hydrophobic layer 41 is configured as a part of the gas diffusion layer 24 in the embodiment, it may be configured as an intermediate layer sandwiched between the gas diffusion layer and the cathode.

D4. Modification 4
In the first embodiment, the surface of the gas diffusion layer 24 is made hydrophobic except for the flow path 42, but a hydrophilic surface including the flow path 42 may be formed as in the third embodiment.

D5. Modification 5
In the embodiment, the oxidizing gas supply port 51 and the oxidizing gas discharge port 52 are arranged in the vicinity of the opposing sides of the gas separator 26, but the oxidizing gas supply port 51 and the oxidizing gas discharge port 52 are close to each other. In other cases, the generated water in the downstream portion of the oxidizing gas in the vicinity of the oxidizing gas discharge port 52 can be implemented by forming a flow path of the generated water so that it can move to the upstream portion of the oxidizing gas in the vicinity of the oxidizing gas supply port. .

  Although various embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and it goes without saying that various configurations can be adopted without departing from the spirit of the present invention.

It is a cross-sectional schematic diagram showing the schematic structure of the single cell which comprises the fuel cell as one Example of this invention. It is explanatory drawing which illustrated the flow path provided on the gas diffusion layer. It is the cross-sectional schematic diagram which expanded and showed the joining surface of a cathode catalyst layer and a gas diffusion layer. It is a cross-sectional schematic diagram containing 4-4 cross section of FIG. It is the cross-sectional schematic diagram which expanded and showed the joint surface of the cathode catalyst layer and gas diffusion layer in a 2nd Example. It is the cross-sectional schematic diagram which expanded and showed the joint surface of the cathode catalyst layer and gas diffusion layer in a 3rd Example. It is explanatory drawing which illustrated the single cell which concerns on a modification.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Single cell 20 ... Electrolyte membrane 21 ... Anode catalyst layer 22 ... Cathode catalyst layer 23, 24 ... Gas diffusion layer 25, 26 ... Gas separator 27 ... Fuel gas flow path in single cell 28 ... Oxidation gas flow path in single cell 41 ... hydrophobic layer 42 ... flow path 43 ... hydrophilic portion 44 ... hydrophilic surface 51 ... oxidizing gas supply port 52 ... oxidizing gas discharge port

Claims (6)

A fuel cell,
An electrolyte membrane;
A cathode electrode catalyst layer formed on one surface of the electrolyte membrane and causing an electrochemical reaction;
A gas diffusion layer disposed on the cathode electrode catalyst layer and diffusing a reaction gas used for the electrochemical reaction;
A fuel comprising: a hydrophobic layer formed on a surface of the gas diffusion layer in contact with the cathode electrode catalyst layer, having a hydrophobic property and having a flow channel forming portion that forms a flow channel with the cathode electrode catalyst layer. battery. The fuel cell according to claim 1, further comprising:
A supply port for supplying the reaction gas to the gas diffusion layer, and a discharge port for discharging the reaction gas from the gas diffusion layer, comprising a separator disposed on the gas diffusion layer,
The said flow path formation part is a fuel cell which forms the flow path which guides the said generated water from the said discharge port vicinity to the said supply port vicinity. The fuel cell according to claim 1 or 2,
The said flow path formation part has a groove-shaped part connected from the said discharge port vicinity to the said supply port vicinity, The fuel cell which forms the said flow path with the said groove-shaped part. The fuel cell according to claim 3, wherein
The flow path forming portion is a fuel cell having a plurality of the groove-shaped portions. The fuel cell according to claim 3 or 4,
A fuel cell in which the surface of the groove-like portion is hydrophilic. The fuel cell according to any one of claims 2 to 5,
The supply port and the discharge port are fuel cells arranged in the vicinity of opposing ends of the separator.

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