JP2022106440A - Fuel cell - Google Patents

Abstract

To provide a fuel cell comprising a gas diffusion layer which has drainability, conductivity, and rigidity.SOLUTION: A fuel cell comprises: a membrane electrode assembly in which catalyst layers are bonded to both faces of an electrolyte membrane; a first gas diffusion layer which is bonded, on one side, to the membrane electrode assembly; and a separator. The separator has gas passage grooves separated from each other by a rib, and the rib comes into contact with the first gas diffusion layer. The first gas diffusion layer has a drain groove which does not penetrate the first gas diffusion layer in its thickness direction. The drain groove is formed only in a contact region with the rib. The drain groove communicates with the gas passage grooves in the width direction of the first gas diffusion layer.SELECTED DRAWING: Figure 3

Description

The present disclosure relates to fuel cells.

A fuel cell (FC) is a fuel cell stack (hereinafter, may be simply referred to as a stack) in which a plurality of single cells (hereinafter, may be referred to as a cell) are laminated, and a fuel gas such as hydrogen and oxygen are added. It is a power generation device that extracts electrical energy by an electrochemical reaction with an oxidant gas such as air. In the following, the fuel gas and the oxidant gas may be simply referred to as "reaction gas" or "gas" without particular distinction. Further, both a single cell and a fuel cell stack in which single cells are stacked may be referred to as a fuel cell.
At the fuel electrode (anode) of the fuel cell, hydrogen (H ₂ ) as a fuel gas supplied from the gas flow path and the gas diffusion layer is protonated by the catalytic action of the catalyst layer, passes through the electrolyte membrane, and passes through the electrolyte membrane to the oxidant electrode (oxidant electrode). Move to the cathode). The electrons generated at the same time work through an external circuit and move to the cathode. Oxygen (O ₂ ) as an oxidant gas supplied to the cathode reacts with protons and electrons on the cathode to produce water. The generated water gives an appropriate humidity to the electrolyte membrane, and excess water permeates the gas diffusion layer (GDL, hereinafter simply referred to as a diffusion layer) and is discharged to the outside of the system.

Various techniques have been proposed for fuel cells used in a fuel cell vehicle (hereinafter sometimes referred to as a vehicle).
For example, Patent Document 1 discloses that a plurality of holes are formed only in a contact region with a rib portion of a separator of a gas diffusion layer in order to improve drainage.

Further, Patent Document 2 discloses a technique of providing orthogonal grid-like grooves on the diffusion layer in order to discharge water accumulated in the diffusion layer.

Japanese Unexamined Patent Publication No. 2010-231922 Japanese Unexamined Patent Publication No. 2007-299654

The gas diffusion layer of the fuel cell is required not to retain the liquid water generated during power generation and to improve the drainage property during scavenging.
The hole portion described in Patent Document 1 is a through hole, which reduces the density and rigidity of the gas diffusion layer. The decrease in density reduces the conductivity required for the gas diffusion layer, and the decrease in rigidity causes the deflection in the contact region with the ribs of the separator to increase, resulting in a decrease in the gas permeability required for the gas diffusion layer.

The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a fuel cell provided with a gas diffusion layer having drainage property, conductivity, and rigidity.

In the present disclosure, a membrane electrode assembly in which catalyst layers are bonded to both sides of an electrolyte membrane and a membrane electrode assembly are used.
A first gas diffusion layer bonded to the membrane electrode assembly on one side,
With a separator,
The separator has a gas flow path groove separated by ribs, and the ribs come into contact with the first gas diffusion layer.
The first gas diffusion layer has a drainage groove that does not penetrate in the thickness direction of the first gas diffusion layer.
The drainage ditch is formed only in the contact area with the rib.
The drainage ditch provides a fuel cell characterized in communicating with the gas flow path ditch in the width direction of the first gas diffusion layer.

The fuel cell of the present disclosure has drainage, conductivity, and rigidity, and particularly has a gas diffusion layer that easily drains a large amount of liquid water generated during high-load power generation without retaining it, so that the power generation performance can be improved. ..

FIG. 1 is a diagram showing the relationship between the surface pressure and resistance of each gas diffusion layer when the gas diffusion layer has a through hole and when it does not. FIG. 2 shows a case where the gas diffusion layer has a through hole in the fuel cell and thus the gas diffusion layer is bent, and a case where the gas diffusion layer does not have a through hole and the gas diffusion layer is not bent. It is a figure which shows the result of having measured the pressure loss of each fuel cell in the case. FIG. 3 is a schematic cross-sectional view showing an example of the fuel cell of the present disclosure. FIG. 4 shows the fall angles of a diffusion layer (conventional technique) in which a drainage groove having a groove width of 0.1 mm is provided on the flow path of the separator and a diffusion layer (no groove: the present disclosure) in which the drainage groove is not provided on the flow path of the separator. It is a figure which shows the result of having measured. FIG. 5 corresponds to a fuel cell having a diffusion layer having no groove, a fuel cell having a diffusion layer having a groove in both a region abutting the flow path of the separator and a region abutting the rib, and a rib of the separator. It is a figure which shows the result of having measured the drainage time by scavenging for each fuel cell of the fuel cell provided with the diffusion layer which has a groove only in the contact area. FIG. 6 is a schematic top view of the fuel cell when the separator is seen through the diffusion layer showing an example of the fuel cell of the present disclosure. FIG. 7 is a schematic top view of the fuel cell when the separator is seen through the diffusion layer showing another example of the fuel cell of the present disclosure. FIG. 8 is a schematic top view of the fuel cell when the separator is seen through the diffusion layer showing another example of the fuel cell of the present disclosure.

In the present disclosure, a membrane electrode assembly in which catalyst layers are bonded to both sides of an electrolyte membrane and a membrane electrode assembly are used.
A first gas diffusion layer bonded to the membrane electrode assembly on one side,
With a separator,
The separator has a gas flow path groove separated by ribs, and the ribs come into contact with the first gas diffusion layer.
The first gas diffusion layer has a drainage groove that does not penetrate in the thickness direction of the first gas diffusion layer.
The drainage ditch is formed only in the contact area with the rib.
The drainage ditch provides a fuel cell characterized in communicating with the gas flow path ditch in the width direction of the first gas diffusion layer.

FIG. 1 is a diagram showing the relationship between the surface pressure and resistance of each gas diffusion layer when the gas diffusion layer has a through hole and when it does not.
As shown in FIG. 1, it can be seen that when the gas diffusion layer is provided with a through hole, the conductivity of the gas diffusion layer is lowered as compared with the case where the through hole is not provided.
Further, if the gas diffusion layer is provided with a through hole, the substrate density (rigidity) of the gas diffusion layer is lowered.
FIG. 2 shows a case where the gas diffusion layer has a through hole in the fuel cell and thus the gas diffusion layer is bent, and a case where the gas diffusion layer does not have a through hole and the gas diffusion layer is not bent. It is a figure which shows the result of having measured the pressure loss of each fuel cell in the case.
As shown in FIG. 2, it can be seen that when the gas diffusion layer is bent, the pressure loss is larger than when the gas diffusion layer is not bent. As a result, since the gas diffusion layer has through holes, the rigidity of the gas diffusion layer decreases, and when the rigidity of the gas diffusion layer decreases, the deflection of the gas diffusion layer that abuts under the rib of the separator increases, and the gas flow. It is thought that the road will be narrowed and the pressure loss will increase.
Based on the above findings, the present disclosers provide a drainage groove that does not penetrate in the thickness direction only in the contact region of the gas diffusion layer with the rib portion of the separator, and communicate the drainage groove with the gas flow path of the separator. It was found that the liquid water under the gas flow path can be collected and the gas can be made conductive to promote the removal of the liquid water and improve the drainage property while ensuring the conductivity and rigidity.

FIG. 3 is a schematic cross-sectional view showing an example of the fuel cell of the present disclosure.
The fuel cell shown in FIG. 3 has a first separator, a first gas diffusion layer, MEA, a second gas diffusion layer, and a second separator, and the first separator is a flow path (gas flow path groove) separated by ribs. The first gas diffusion layer has a drainage groove that does not penetrate in the thickness direction of the first gas diffusion layer, the drainage groove is formed only in the contact region with the rib, and the drainage groove is the first gas. It communicates with the flow path in the width direction of the diffusion layer.
The first separator may be a cathode side separator or an anode side separator. One of the first separator and the second separator is a cathode side separator and the other is an anode side separator. The first separator and the second separator are collectively referred to as a separator.
Although the second gas diffusion layer shown in FIG. 3 does not have a drainage groove, the second gas diffusion layer may have a drainage groove like the first gas diffusion layer. The first gas diffusion layer and the second gas diffusion layer are collectively referred to as a gas diffusion layer or a diffusion layer.

The fuel cell may be a fuel cell stack in which a plurality of single cells of the fuel cell are stacked.
The number of stacked single cells is not particularly limited, and may be, for example, 2 to several hundreds or 2 to 200.
The fuel cell stack may include end plates at both ends of the single cell stacking direction.

A single cell of a fuel cell includes a membrane electrode assembly (MEA: Membrane Electrode Assembly) in which catalyst layers are bonded to both sides of an electrolyte membrane, a first gas diffusion layer bonded to the membrane electrode assembly on one side, a separator, and the like. Has.
The membrane electrode assembly has an anode catalyst layer, an electrolyte membrane, and a cathode catalyst layer in this order.

The fuel cell of the present disclosure has at least a first gas diffusion layer bonded to the membrane electrode assembly on one side, and usually has a second gas diffusion layer bonded to the membrane electrode assembly on the other side. That is, the single cell of the fuel cell of the present disclosure has a membrane electrode gas diffusion layer conjugate (MEGA) having an anode side gas diffusion layer, an anode catalyst layer, an electrolyte membrane, a cathode catalyst layer, and a cathode side gas diffusion layer in this order. You may be doing it.
The cathode (oxidizing agent electrode) includes a cathode catalyst layer and, if necessary, a cathode side gas diffusion layer.
The anode (fuel electrode) includes an anode catalyst layer and, if necessary, an anode-side gas diffusion layer.
The cathode side gas diffusion layer and the anode side gas diffusion layer are collectively referred to as a gas diffusion layer.
The first gas diffusion layer in the present disclosure may be a cathode side gas diffusion layer or an anode side gas diffusion layer. One of the first gas diffusion layer and the second gas diffusion layer is a cathode side gas diffusion layer, and the other is an anode side gas diffusion layer.

The first gas diffusion layer has a drainage groove that does not penetrate in the thickness direction of the first gas diffusion layer, the drainage groove is formed only in the contact region with the rib of the separator, and the drainage groove is the first gas diffusion layer. It communicates with the gas flow path groove of the separator in the width direction of. The second gas diffusion layer may not have a drainage groove, and like the first gas diffusion layer, a drainage groove that does not penetrate in the thickness direction of the second gas diffusion layer is used as a rib of the second separator. The drainage groove may be communicated with the gas flow path groove of the second separator in the width direction of the second gas diffusion layer.

FIG. 4 shows the fall angles of a diffusion layer (conventional technique) in which a drainage groove having a groove width of 0.1 mm is provided on the flow path of the separator and a diffusion layer (no groove: the present disclosure) in which the drainage groove is not provided on the flow path of the separator. It is a figure which shows the result of having measured.
As shown in FIG. 4, in the case of the size of the droplet generated in the flow path, it can be seen that the rolling angle is smaller (= the water movement resistance is smaller) in the configuration without the groove. This indicates that the diffusion layer having the drainage groove on the flow path of the separator has a worse drainage property in the flow path than the diffusion layer having no drainage groove on the flow path of the separator.

In a structure in which the groove (drainage groove) provided in the diffusion layer overlaps the flow path (flow path portion) of the separator, the diffusion layer is usually surface-coated with PTFE and thus has water repellency. Since the coat by PTFE is peeled off and becomes hydrophilic, a hydrophilic-water-repellent boundary is created between the part where the coat by PTFE is present, and the resistance force during water movement due to surface tension increases, resulting in liquid water. It causes retention, and the drainage property in the flow path is worse than when the diffusion layer has a structure without a drainage groove.

The present disclosures include a fuel cell having a diffusion layer without a groove, a fuel cell having a diffusion layer having a groove in both a region abutting a flow path of a separator and a region abutting a rib, and a rib of a separator. For each fuel cell of a fuel cell having a diffusion layer having a groove only in the region in contact with the fuel cell, a jig capable of visualizing the liquid water existing in the flow path and under the rib is used at an output of 3 A / cm ² . After generating power for 30 seconds, the time required for drainage by scavenging was measured.
FIG. 5 corresponds to a fuel cell having a diffusion layer having no groove, a fuel cell having a diffusion layer having a groove in both a region abutting the flow path of the separator and a region abutting the rib, and a rib of the separator. It is a figure which shows the result of having measured the drainage time by scavenging for each fuel cell of the fuel cell provided with the diffusion layer which has a groove only in the contact area.
As shown in FIG. 5, it can be seen that the time required for drainage of the fuel cell provided with the diffusion layer having a groove only in the region in contact with the rib of the separator was the shortest.
In the present disclosure, the location where the drainage ditch of the diffusion layer is provided is limited to under the rib of the separator so that the drainage ditch of the diffusion layer does not overlap the flow path portion of the separator, thereby creating a hydrophilic-water repellent boundary. do not have. As a result, the water accumulated in the diffusion layer can be quickly discharged without deteriorating the drainage property in the flow path.
Since the present disclosure can be realized only by changing the process of punching the diffusion layer without adding parts, it is possible to suppress the manufacturing cost and improve the drainage property of the diffusion layer.

The gas diffusion layer of the present disclosure may be a carbon porous body such as carbon cloth and carbon paper, or a metal porous body such as a metal mesh or a metal foam.

The cathode catalyst layer and the anode catalyst layer are collectively referred to as a catalyst layer.
The catalyst layer may include a catalyst such as a metal that promotes an electrochemical reaction, an electrolyte, and a carrier such as carbon particles having electron conductivity.
As the catalyst (catalyst metal), for example, platinum (Pt) and an alloy composed of Pt and another metal (for example, a Pt alloy in which cobalt, nickel and the like are mixed) and the like can be used.

The catalyst is supported on a carrier such as carbon particles, and in each catalyst layer, a carrier carrying a catalyst metal (catalyst-supporting carrier) and an electrolyte may be mixed.
As the carrier for supporting the catalyst, for example, water-repellent carbon particles whose water repellency has been enhanced by heat-treating commercially available carbon particles (carbon powder) may be used.

The electrolyte membrane may be, for example, a solid polymer electrolyte membrane. Examples of the solid polymer electrolyte membrane include a fluorine-based electrolyte membrane such as a thin film of perfluorosulfonic acid containing water, a hydrocarbon-based electrolyte membrane, and the like. The electrolyte membrane may be, for example, a Nafion membrane (manufactured by DuPont) or the like.

The single cell may have a microporous layer (MPL) between the catalyst layer and the gas diffusion layer, if necessary. The microporous layer may contain a mixture of a water repellent resin such as PTFE and a conductive material such as carbon black.

The single cell is provided with a separator so that the rib and the first gas diffusion layer are in contact with each other. The single cell may include two separators (first separator and second separator) that sandwich both sides of the membrane electrode gas diffusion layer bonded body. One of the two separators is the anode side separator and the other is the cathode side separator. In the present disclosure, the anode-side separator and the cathode-side separator are collectively referred to as a separator.
The separator may have a plurality of ribs and a plurality of gas flow path grooves separated by the ribs, and the ribs and the first gas diffusion layer may be in contact with each other. When the single cell has a second separator, the second separator may have a plurality of ribs and a plurality of gas flow path grooves separated by the ribs, and the ribs and the second gas diffusion layer are in contact with each other. It may be in contact.
The separator may have a reaction gas flow path on the surface in contact with the gas diffusion layer. Further, the separator may have a refrigerant flow path for keeping the temperature of the fuel cell constant on the surface opposite to the surface in contact with the gas diffusion layer.
The separator may have a supply hole and a discharge hole for flowing the reaction gas and the refrigerant in the stacking direction of the single cell. As the refrigerant, for example, a mixed solution of ethylene glycol and water can be used in order to prevent freezing at a low temperature. The reaction gas is a fuel gas or an oxidant gas. The fuel gas may be hydrogen or the like. The oxidant gas may be oxygen, air, dry air or the like.
Examples of the supply hole include a fuel gas supply hole, an oxidant gas supply hole, and a refrigerant supply hole.
Examples of the discharge hole include a fuel gas discharge hole, an oxidant gas discharge hole, a refrigerant discharge hole, and the like.
The separator may have one or more fuel gas supply holes, one or more oxidant gas supply holes, or one or more refrigerant supply holes. It may have one or more fuel gas discharge holes, one or more oxidant gas discharge holes, or one or more refrigerant discharge holes.
When the separator is an anode-side separator, it may have one or more fuel gas supply holes, or may have one or more oxidant gas supply holes, and one or more refrigerant supply holes. May have one or more fuel gas discharge holes, may have one or more oxidant gas discharge holes, and may have one or more refrigerant discharge holes. The anode-side separator may have a fuel gas flow path for flowing fuel gas from the fuel gas supply hole to the fuel gas discharge hole on the surface in contact with the anode-side gas diffusion layer, and the anode-side gas diffusion may be performed. A gas flow path for flowing a gas from a gas supply hole to a gas discharge hole may be provided on a surface opposite to the surface in contact with the layer.
When the separator is a cathode side separator, it may have one or more fuel gas supply holes, or may have one or more oxidant gas supply holes, and one or more refrigerant supply holes. May have one or more fuel gas discharge holes, may have one or more oxidant gas discharge holes, and may have one or more refrigerant discharge holes. The cathode side separator may have an oxidant gas flow path for flowing the oxidant gas from the oxidant gas supply hole to the oxidant gas discharge hole on the surface in contact with the cathode side gas diffusion layer. A refrigerant flow path for flowing the refrigerant from the refrigerant supply hole to the refrigerant discharge hole may be provided on the surface opposite to the surface in contact with the gas diffusion layer on the cathode side.
The separator may be a gas-impermeable conductive member or the like. The conductive member may be, for example, dense carbon obtained by compressing carbon to make it gas impermeable, a press-molded metal (for example, iron, aluminum, stainless steel, etc.) plate or the like. Further, the separator may have a current collecting function.

The fuel cell stack may have a manifold such as an inlet manifold in which each supply hole communicates and an outlet manifold in which each discharge hole communicates.
Examples of the inlet manifold include an anode inlet manifold, a cathode inlet manifold, and a refrigerant inlet manifold.
Examples of the outlet manifold include an anode outlet manifold, a cathode outlet manifold, and a refrigerant outlet manifold.

If the drainage groove of the first gas diffusion layer does not penetrate in the thickness direction of the first gas diffusion layer and communicates with the gas flow path groove of the separator in the width direction of the first gas diffusion layer, the plane thereof. The visual shape is not particularly limited, and in the contact region with the rib, a set of two drainage grooves may form an orthogonal grid shape, or a plurality of drainage grooves may be arranged in parallel with each other. , A plurality of drainage ditches may be arranged in a curved shape. When the second gas diffusion layer has a drainage ditch, the shape of the drainage ditch in a plan view is the same as that of the first gas diffusion layer.
FIG. 6 is a schematic top view of the fuel cell when the separator is seen through the diffusion layer showing an example of the fuel cell of the present disclosure. The diffusion layer included in the fuel cell shown in FIG. 6 is provided with a grid-like diffusion layer groove (drainage groove) orthogonal to the region in contact with the rib of the separator.
FIG. 7 is a schematic top view of the fuel cell when the separator is seen through the diffusion layer showing another example of the fuel cell of the present disclosure. The diffusion layer included in the fuel cell shown in FIG. 7 is provided with a plurality of diffusion layer grooves (drainage grooves) parallel to each other in a region in contact with the rib of the separator.
FIG. 8 is a schematic top view of the fuel cell when the separator is seen through the diffusion layer showing another example of the fuel cell of the present disclosure. As shown in FIG. 8, the plurality of diffusion layer grooves (drainage grooves) do not necessarily have to be provided in parallel with each other.

Claims (1)

A membrane electrode assembly in which catalyst layers are bonded to both sides of the electrolyte membrane,
A first gas diffusion layer bonded to the membrane electrode assembly on one side,
With a separator,
The separator has a gas flow path groove separated by ribs, and the ribs come into contact with the first gas diffusion layer.
The first gas diffusion layer has a drainage groove that does not penetrate in the thickness direction of the first gas diffusion layer.
The drainage ditch is formed only in the contact area with the rib.
A fuel cell characterized in that the drainage ditch communicates with the gas flow path ditch in the width direction of the first gas diffusion layer.

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