JP2022053736A - Fuel cell - Google Patents

Abstract

To provide a fuel cell enabling degradation of the performance thereof to be suppressed.SOLUTION: A fuel cell is provided, comprising one or more single cells each having: a membrane electrode assembly in which a pair of electrodes are arranged on both sides of an electrolyte film; and two separators that sandwich and hold the membrane electrode assembly. Each separator has: a flow channel for flowing fluid in a plane direction of the separator; and a supply hole and a discharge hole for flowing the fluid flow in a lamination direction of the single cells. The separator has three or more flow channels in at least a part of a range from the supply hole to the discharge hole on the same plane. A hydrophilicity of at least one of two flow channels arranged at both ends among the three or more the flow channels is higher than that of the other flow channels.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to fuel cells.

A fuel cell (FC) is used as a fuel gas in a fuel cell stack (hereinafter, may be simply referred to as a stack) in which one single cell or a plurality of single cells (hereinafter, may be referred to as a cell) are laminated. It is a power generation device that extracts electric energy by an electrochemical reaction between hydrogen (H ₂ ) and oxygen (O ₂ ) as an oxidizing agent gas. In the following, the fuel gas and the oxidant gas may be simply referred to as "reaction gas" or "gas" without particular distinction.
A single cell of this fuel cell is usually composed of a membrane electrode assembly (MEA: Membrane Electrode Assembly) and, if necessary, two separators sandwiching both sides of the membrane electrode assembly.
In the membrane electrode assembly, a catalyst layer and a gas diffusion layer (GDL) are sequentially formed on both sides of a solid polymer electrolyte membrane having proton (H ⁺ ) conductivity (hereinafter, also simply referred to as “electrolyte membrane”), respectively. Has a structure that has been modified. Therefore, the membrane electrode assembly may be referred to as a membrane electrode gas diffusion layer assembly (MEGA).
The separator usually has a structure in which a groove as a fluid flow path is formed on the surface in contact with the gas diffusion layer. This separator also functions as a current collector for the generated electricity.
At the fuel electrode (anode) of the fuel cell, hydrogen 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 moves to the oxidizing agent electrode (cathode). The simultaneously generated electrons work through an external circuit and move to the cathode. Oxygen 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 the excess water permeates the gas diffusion layer and is discharged to the outside of the system.

Various studies have been conducted on fuel cells used in vehicles of fuel cell vehicles (hereinafter sometimes referred to as vehicles).
For example, Patent Document 1 discloses a fuel cell that improves the drainage property of residual water remaining in a fuel gas flow path.

Japanese Unexamined Patent Publication No. 2013-118125

In a fuel cell provided with a separator having three or more flow paths between the fluid supply hole and the discharge hole, the flow path at the end of the separator (flow path on the non-power generation side) is compared with other flow paths. Therefore, there is a problem that the pressure loss becomes high, water tends to stay, the flow of fluid is obstructed, and the performance of the fuel cell deteriorates.

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 capable of suppressing deterioration of performance.

In the present disclosure, a fuel cell comprising one or more single cells including a membrane electrode assembly in which a pair of electrodes are arranged on both sides of an electrolyte membrane and two separators sandwiching the membrane electrode assembly. ,
The separator has a flow path for flowing the fluid in the plane direction of the separator, and a supply hole and a discharge hole for flowing the fluid in the stacking direction of the single cell.
The separator has at least a part of three or more flow paths from the supply hole to the discharge hole in the same plane.
Provided is a fuel cell characterized in that the hydrophilicity of at least one of the two channels arranged at both ends of the three or more channels is higher than that of the remaining channels.

According to the present disclosure, it is possible to provide a fuel cell capable of suppressing deterioration in performance.

It is a schematic schematic diagram which shows an example of the separator provided in the fuel cell of this disclosure. It is a schematic schematic diagram which shows an example of the fuel cell stack of this disclosure.

In the present disclosure, a fuel cell comprising one or more single cells including a membrane electrode assembly in which a pair of electrodes are arranged on both sides of an electrolyte membrane and two separators sandwiching the membrane electrode assembly. ,
The separator has a flow path for flowing the fluid in the plane direction of the separator, and a supply hole and a discharge hole for flowing the fluid in the stacking direction of the single cell.
The separator has at least a part of three or more flow paths from the supply hole to the discharge hole in the same plane.
Provided is a fuel cell characterized in that the hydrophilicity of at least one of the two channels arranged at both ends of the three or more channels is higher than that of the remaining channels.

With the widespread use of fuel cell vehicles (FCVs), fuel cells are required to be smaller and have higher performance. Due to the densification of the flow path and GDL, the performance of the fuel cell deteriorates due to the deterioration of gas diffusivity due to poor drainage such as flooding. During power generation of a fuel cell, the temperature environment at the end of the separator surface is lower than that of the central part, and the end flow path is relatively longer than the in-plane inner flow path, creating an environment in which water easily collects and drainage is reduced. However, there is a problem that a partial gas shortage occurs depending on the power generation state, and the power generation performance of the fuel cell deteriorates due to deterioration of the catalyst layer.
According to the present disclosure, the wettability (hydrophilicity) of at least one of the flow paths at both ends in the cell surface, which is a portion where water tends to collect in the flow path of the separator, is compared with that of the other flow paths. By changing the coating amount or type of the surface treatment so as to be large, the drainage property can be improved and the deterioration of the power generation performance of the fuel cell (deterioration of the catalyst layer) can be suppressed.

The fuel cell of the present disclosure includes at least one single cell including a membrane electrode assembly in which a pair of electrodes are arranged on both sides of an electrolyte membrane and two separators sandwiching the membrane electrode assembly.
If necessary, the single cell of the fuel cell may be provided with a frame-shaped resin sheet that is arranged between two separators and adheres the separators to each other.

The fuel cell may be a fuel cell stack which is a laminated body in which a plurality of single cells are laminated.
The fuel cell stack is a laminated body in which a plurality of single cells of a fuel cell are laminated. In the present disclosure, the fuel cell may be only one single cell or may be a fuel cell stack.
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.
The fuel cell stack may optionally have a gasket between the separators of each single cell adjacent to each other. The gasket may be formed of, for example, silicone rubber or the like.

One of the pair of electrodes is the oxidant electrode and the other is the fuel electrode.
The oxidant electrode includes an oxidant electrode catalyst layer and a gas diffusion layer.
The fuel electrode includes a fuel electrode catalyst layer and a gas diffusion layer.
The oxidant electrode catalyst layer and the fuel electrode catalyst layer may include, for example, a catalyst metal that promotes an electrochemical reaction, an electrolyte having proton conductivity, carbon particles having electron conductivity, and the like.
As the catalyst metal, for example, platinum (Pt), 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 electrolyte may be a fluororesin or the like. As the fluororesin, for example, a Nafion solution or the like may be used.
The catalyst metal is supported on carbon particles, and carbon particles (catalyst particles) carrying the catalyst metal and an electrolyte may be mixed in each catalyst layer.
The carbon particles for supporting the catalyst metal (supporting carbon particles) are, for example, water-repellent carbon particles whose water repellency is enhanced by heat-treating commercially available carbon particles (carbon powder). May be used.

The gas diffusion layer may be a conductive member or the like having gas permeability.
Examples of the conductive member include a carbon porous body such as carbon cloth and carbon paper, a metal mesh, and a metal porous body such as foamed metal.

The electrolyte membrane may be 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 separator has a flow path for flowing the fluid in the plane direction of the separator, and a supply hole and a discharge hole for flowing the fluid in the stacking direction of a single cell.
The fluid may be a reaction gas, a refrigerant (cooling water), or the like. 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, a refrigerant supply hole, and the like.
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, oxidant gas supply holes, refrigerant supply holes, fuel gas discharge holes, oxidant gas discharge holes, and refrigerant discharge holes.

The fuel cell stack has 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.

The separator may have a reaction gas flow path on the surface in contact with the gas diffusion layer as a flow path. Further, the separator may have a refrigerant flow path for keeping the stack temperature constant on a surface opposite to the surface in contact with the gas diffusion layer as a flow path.
When the separator is an anode-side separator, it has one or more fuel gas supply holes, oxidant gas supply holes, refrigerant supply holes, fuel gas discharge holes, oxidant gas discharge holes, and refrigerant discharge holes, respectively, and has an anode. The surface in contact with the side gas diffusion layer has a fuel gas flow path for flowing fuel gas from the fuel gas supply hole to the fuel gas discharge hole, and the surface opposite to the surface in contact with the anode side gas diffusion layer has a refrigerant from the refrigerant supply hole. It may have a gas flow path through which the gas flows through the discharge hole.
When the separator is a separator on the cathode side, it has one or more fuel gas supply hole, oxidant gas supply hole, refrigerant supply hole, fuel gas discharge hole, oxidant gas discharge hole, and refrigerant discharge hole, and the cathode. The surface in contact with the side gas diffusion layer has an oxidant gas flow path for flowing the oxidant gas from the oxidant gas supply hole to the oxidant gas discharge hole, and the refrigerant is on the surface opposite to the surface in contact with the cathode side gas diffusion layer. It may have a gas flow path for flowing a gas from a supply hole to a gas discharge hole.
The separator may be a gas-impermeable conductive member or the like. The conductive member may be, for example, a dense carbon obtained by compressing carbon to make it impermeable to gas, a press-molded metal plate (for example, iron, aluminum, titanium, stainless steel, etc.) or the like. Further, the separator may have a current collecting function.

The separator has three or more flow paths in at least a part from the supply hole to the discharge hole in the same plane. The same surface of the separator is either the front surface or the back surface when there is a front surface and a back surface of the separator. The separator may have at least three or more flow paths from the supply hole to the discharge hole on both the front surface and the back surface.
The number of flow paths of the separator may be at least three or more in at least a part from the supply hole to the discharge hole, and the upper limit of the number of flow paths is not particularly limited and can be appropriately set depending on the scale of the separator. In addition, the flow path of the separator branches from the supply hole into three or more flow paths at the flow path branch, and three or more flow paths merge at the flow path confluence in front of the discharge hole to form one flow path. You may be doing it. Further, the width of each flow path is not particularly limited and can be appropriately set depending on the scale of the separator.

The separator is provided as long as the hydrophilicity of at least one of the two flow paths (end flow paths) arranged at both ends of the three or more flow paths in the same plane is higher than that of the remaining flow paths. good.
Further, from the viewpoint of improving the performance of the fuel cell, the separator has the hydrophilicity of both end flow paths of the two end flow paths arranged at both ends of the three or more flow paths in the same plane. It may be higher than the remaining in-plane internal flow path.
In addition, when there are five or more flow paths in the same plane of the separator, from the viewpoint of suppressing the difference in hydrophilicity performance, the hydrophilicity of the intermediate level is between the two levels of hydrophilicity in the plane of the separator. Region, that is, three levels of hydrophilicity are provided in the plane of the separator to maximize the hydrophilicity of the end flow paths at both ends, and the hydrophilicity of the two in-plane internal flow paths adjacent to these regions. May be lower than the end flow path so that the hydrophilicity of one central in-plane internal flow path is the lowest.
By making the flow path of the separator hydrophilic, it is possible to prevent the cross section of the flow path from being blocked by water, causing the reaction gas flow to deteriorate, causing gas shortage, and deteriorating the catalyst layer.

As a surface treatment method for imparting hydrophilicity to the flow path of the separator, for example, a mixture of columnar or plate-shaped carbon or the like mixed with an epoxy resin or the like by designating a coating range is used as a hydrophilic layer to have a thickness of several μm. It may be applied to the flow path of the separator as described above.
The coating method is not particularly limited, and examples thereof include a doctor blade method, a metal mask printing method, an electrostatic coating method, a dip coating method, a spray coating method, a roll coating method, a gravure coating method, and a screen printing method.
The hydrophilicity can be different between the flow paths of the separator depending on the component ratio of the hydrophilic layer, the thickness, and the like.
Further, by changing the coating method of the hydrophilic layer, it is possible to make a difference in hydrophilicity between the flow paths of the separator.

When the in-plane flow path of the separator is long, the pressure loss is higher than when the flow path is short. It is necessary to balance the hydrophilicity of each flow path. Therefore, when the flow path is long, the hydrophilicity of the flow path may be increased to suppress the growth of water droplets as compared with the case where the flow path is short, and the cross-sectional area of the flow path may be larger than when the flow path is short.
In addition, the end flow paths located at both ends in the surface of the separator have a low temperature environment during power generation of the fuel cell, and even if the structure has the same flow path length as the other in-plane internal flow paths, due to the growth of water droplets. Since the cross-sectional area of the flow path is reduced, it is necessary to increase the hydrophilicity.
The flow path of the conventional separator has improved hydrophilicity so that the wet spread becomes long when water droplets are dropped on the flow path during power generation of the fuel cell, and the Wet / Dry pressure loss is one of the design indicators of the flow path. The ratio is small. As the wetting spread length becomes shorter, the Wet / Dty pressure drop ratio becomes larger. That is, if the water droplets are likely to spread in the flow path at the time of Wet, the flow path is not easily blocked by the water droplets, and it is possible to easily secure a desired flow path cross-sectional area. On the other hand, if the water droplets are difficult to spread in the flow path at the time of Wet, the flow path is easily blocked by the water droplets and it is difficult to secure a desired cross-sectional area of the flow path.

The two end flow paths at both ends of the separator are lower in temperature and environmentally than the in-plane internal flow paths near the center, and water pools are likely to occur. When the shape of the separator of a single cell is rectangular, it becomes longer as it approaches the vicinity of both ends in the plane of the separator in the design of the flow path, the pressure loss increases, and water tends to collect. In addition, the cross-sectional area of the flow path cannot be sufficiently secured due to the design, the pressure loss increases, and water tends to collect in the flow path.

Therefore, the flow paths of the separator of the fuel cell stack are classified into the following four types of flow paths (1) to (4) from the viewpoint of the difference in the temperature environment during power generation of the fuel cell.
(1) A flow path other than the in-plane inner flow path of the inner single cell separator arranged at other than both ends of the fuel cell stack (hereinafter, the in-plane inner flow path or the in-plane inner flow path of the inner single cell separator). It may be called 1))
(2) With the flow path at the inner end of the inner single cell separator arranged outside both ends of the fuel cell stack (hereinafter, the end flow path of the inner single cell separator or the end flow path (2)). May be called)
(3) A flow path other than the in-plane ends of the outer separator of the outer single cell arranged at both ends of the fuel cell stack (hereinafter, the in-plane inner flow path or the in-plane inner flow path of the outer separator of the outer single cell). (Sometimes referred to as (3))
(4) Flow paths at both ends in the plane of the outer separator of the outer single cell arranged at both ends of the fuel cell stack (hereinafter, end flow paths or end flow paths of the outer separator of the outer single cell). May be called)

FIG. 1 is a schematic schematic diagram showing an example of a separator (separator of an inner single cell) included in the fuel cell of the present disclosure.
The separator 50 shown in FIG. 1 has a supply hole 10, a discharge hole 20, a flow path branching portion 30, and a flow path merging portion 40, and has six in-plane internal flow paths (1) and two end flows. The paths (2) are arranged in parallel, and the end flow path (2) is subjected to surface treatment having a higher hydrophilicity than the in-plane internal flow path (1). As a result, the amount of water or gas staying in the flow path can be reduced, and deterioration of the catalyst layer due to lack of gas can be suppressed. The arrow shown in FIG. 1 indicates the direction in which the fluid flows.
The supply hole 10 is either a fuel gas supply hole, an oxidant gas supply hole, or a refrigerant supply hole. When the supply hole 10 is a fuel gas supply hole, the discharge hole 20 is a fuel gas discharge hole, and the in-plane internal flow path (1) and the end flow path (2) are fuel gas flow paths.
When the supply hole 10 is an oxidant gas supply hole, the discharge hole 20 is an oxidant gas discharge hole, and the in-plane internal flow path (1) and the end flow path (2) are oxidant gas flow paths. ..
When the supply hole 10 is a refrigerant supply hole, the discharge hole 20 is a refrigerant discharge hole, and the in-plane internal flow path (1) and the end flow path (2) are refrigerant flow paths.

FIG. 2 is a schematic schematic diagram showing an example of the fuel cell stack of the present disclosure.
In the outer separator 60 of the end single cell (outer single cell) arranged at the end of the fuel cell stack 100 shown in FIG. 2, the in-plane internal flow path (3) and the end flow path (4) are arranged in parallel. The end channel (4) is arranged and has a surface treatment that is more hydrophilic than the in-plane internal channel (3). In the outer separator 60 shown in FIG. 2, the supply hole, the discharge hole, the flow path branching portion, the flow path merging portion, and the like are omitted for convenience.

The flow path of the separator of the fuel cell stack of the prior art is likely to be flooded in the order of (4)>(3)>(2)> (1). The temperature environment of the in-plane internal flow path (3) of the outer separator of the outer single cell at the stack end at the time of stacking single cells is lower than that of other separators of other laminated inner single cells, and water stays there. The hydrophilicity of the surface may be higher than that of the two end flow paths (2) of the separators of other laminated inner single cells so as not to run out of gas.
In the present disclosure, for example, the hydrophilicity of the flow path by surface treatment may be increased in the order of (4)>(3)>(2)> (1). For example, the hydrophilicity may be changed by changing the coverage (hydrophilicity) to four levels by one kind of surface treatment. Further, the hydrophilicity may be changed by different components of the two types of surface treatments. For example, (4): difference in surface treatment B component> (3): difference in surface treatment B> (2): difference in surface treatment A component> (1): difference in surface treatment A may be obtained in descending order of hydrophilicity of the hydrophilic layer.

An example of the hydrophilicity evaluation of the separator is as follows.
Observe the spread length of the water droplets due to the dripping of water into the flow path of the separator. When water droplets are dropped from a height of several mm, for example, when the wet spread length of surface treatment A exceeds 5 mm and the wet spread length of surface treatment B exceeds 10 mm, surface treatment B is more hydrophilic. The property is clearly high, and it is possible to suppress a decrease in the cross-sectional area of the flow path (increase in pressure loss) due to a pool of water in the flow path. Further, the hydrophilicity may be evaluated by examining the distribution of the wet spread length of the flow path in the plane of the separator.

10 Supply hole 20 Discharge hole 30 Flow path branch 40 Flow path confluence 50 Separator 60 Outer separator 100 Fuel cell stack (1) In-plane inner flow path of inner single cell separator (2) Inner single cell separator end Flow path (3) In-plane inner flow path of the outer separator of the outer single cell (4) End flow path of the outer separator of the outer single cell

Claims (1)

A fuel cell comprising one or more single cells comprising a membrane electrode assembly in which a pair of electrodes are arranged on both sides of an electrolyte membrane and two separators sandwiching the membrane electrode assembly.
The separator has a flow path for flowing the fluid in the plane direction of the separator, and a supply hole and a discharge hole for flowing the fluid in the stacking direction of the single cell.
The separator has at least a part of three or more flow paths from the supply hole to the discharge hole in the same plane.
A fuel cell characterized in that the hydrophilicity of at least one of the two channels arranged at both ends of the three or more channels is higher than that of the remaining channels.

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