JP2024128178A - Fuel Cells - Google Patents

Abstract

To provide a fuel cell which can suppress oxidation degradation of a resin sheet.SOLUTION: A fuel cell includes: a membrane electrode gas diffusion layer assembly; a resin frame arranged in the periphery of the membrane electrode gas diffusion layer assembly; a pair of separators for sandwiching the membrane electrode gas diffusion layer assembly and the resin frame; and a resin sheet, wherein the resin sheet is continuously arranged in a surface direction from a first region on a surface of the resin frame to a second region on a surface of an exposed electrolyte membrane of the membrane electrode gas diffusion layer assembly, and in a third region where an outer peripheral edge part of the first gas diffusion layer of the membrane electrode gas diffusion layer assembly does not face the resin sheet, and faces the resin frame and is adjacent to the first region, and the resin frame does not face the resin sheet, the outer peripheral edge part of the first gas diffusion layer and the resin frame are joined to each other by the resin frame.SELECTED DRAWING: Figure 1

Description

This disclosure relates to fuel cells.

Various technologies have been proposed regarding fuel cells (FCs), such as those disclosed in Patent Document 1.

JP 2016-162651 A

In Patent Document 1, a UV-curable adhesive is used to seal the inside of the cell to prevent cross leakage, but the UV-curable adhesive has a low molecular weight and is difficult to increase in molecular weight, so it deteriorates quickly when the molecular gap is broken and has low oxidation resistance. In addition, the adhesive is exposed and is easily oxidized. Deterioration is particularly noticeable in environments where oxygen is generated, such as lunar rovers.
In sealing the inside of the cell, a resin sheet (cover sheet) can be used instead of a UV-curable adhesive.
However, in a fuel cell that uses oxygen (O ₂ ) as an oxidant gas, oxidative degradation of the fuel cell due to oxygen is a problem, particularly degradation at the cathode (Ca) inlet through which oxygen flows.
Antioxidants can be used as a measure to suppress oxidative deterioration. Antioxidants such as phenolic resins can be used in the shell layers at both ends of the resin frame in the lamination direction. Also, an antioxidant such as Ce can be used in the mesoporous layer (MPL) of the cathode gas diffusion layer (CaGDL).
However, if an antioxidant such as phenol is added to the resin sheet (cover sheet) placed between the resin frame and the MEGA to prevent cross leakage, it will easily dissolve on the power generation section, causing a deterioration in the performance of the fuel cell. Also, there is a problem that inorganic substances such as Ce do not dissolve in the resin and cannot be made into a sheet.

This disclosure was made in consideration of the above-mentioned circumstances, and its main objective is to provide a fuel cell that can suppress oxidative deterioration of the resin sheet.

The present disclosure provides a fuel cell having the following features:
a resin frame disposed around the membrane electrode gas diffusion layer assembly; a pair of separators sandwiching the membrane electrode gas diffusion layer assembly and the resin frame; and a resin sheet, the resin sheet being disposed continuously in a planar direction from a first region on a surface of the resin frame to a second region on a surface of an exposed electrolyte membrane of the membrane electrode gas diffusion layer assembly, the outer periphery of a first gas diffusion layer of the membrane electrode gas diffusion layer assembly not facing the resin sheet but facing the resin frame, adjacent to the first region, and in a third region where the resin frame does not face the resin sheet, the outer periphery of the first gas diffusion layer and the resin frame are joined by the resin frame.

The fuel cell disclosed herein can suppress oxidative deterioration of the resin sheet.

FIG. 1A is a schematic cross-sectional view showing an example of a fuel cell according to the present disclosure, and FIG. 1B is a partially enlarged view of FIG. 1A to 1C are schematic cross-sectional views showing an example of a method for manufacturing a fuel cell according to the present disclosure.

The present disclosure provides a fuel cell having the following features:
a resin frame disposed around the membrane electrode gas diffusion layer assembly; a pair of separators sandwiching the membrane electrode gas diffusion layer assembly and the resin frame; and a resin sheet, the resin sheet being disposed continuously in a planar direction from a first region on a surface of the resin frame to a second region on a surface of an exposed electrolyte membrane of the membrane electrode gas diffusion layer assembly, the outer periphery of a first gas diffusion layer of the membrane electrode gas diffusion layer assembly not facing the resin sheet but facing the resin frame, adjacent to the first region, and in a third region where the resin frame does not face the resin sheet, the outer periphery of the first gas diffusion layer and the resin frame are joined by the resin frame.

In the present disclosure, the cathode-side gas diffusion layer and the resin frame are bonded together to prevent the end of the resin sheet (cover sheet) from being exposed to oxygen, thereby preventing oxidation degradation of the resin sheet (cover sheet). The shell layer of the resin frame (three-layer sheet) is melted and brought into close contact with the MPL of the cathode-side gas diffusion layer, preventing the end of the resin sheet (cover sheet) from being exposed to oxygen.
The resin sheet (cover sheet) is made of a material with a higher molecular weight than the UV-curing adhesives used in conventional technology, so it is less susceptible to oxidation degradation than the UV-curing adhesives used in conventional technology, and because it is sandwiched between the cathode-side gas diffusion layer and the resin frame (three-layer sheet), oxidation degradation can be suppressed without the use of an antioxidant. This makes it possible to prevent gas from entering from the end of the adhesive layer of the resin frame.

FIG. 1(1) is a schematic cross-sectional view showing an example of a fuel cell according to the present disclosure, and FIG. 1(2) is a partially enlarged view of FIG.
As shown in Fig. 1 (1), the resin sheet is continuously arranged in the surface direction from the first region on the surface of the resin frame to the second region on the surface of the exposed electrolyte membrane of the membrane electrode gas diffusion layer assembly, and the outer peripheral portion of the cathode side gas diffusion layer, which is the first gas diffusion layer of the membrane electrode gas diffusion layer assembly, does not face the resin sheet and faces the resin frame. As shown in Fig. 1 (2), the cathode side gas diffusion layer may be composed of a substrate and an MPL, and in a third region adjacent to the first region and in which the resin frame does not face the resin sheet, the outer peripheral portion of the cathode side gas diffusion layer and the resin frame are joined by the resin frame. Specifically, the resin frame and the MPL of the cathode side gas diffusion layer are bonded by the first shell layer of the resin frame.

FIG. 2 is a schematic cross-sectional view showing an example of a method for producing a fuel cell according to the present disclosure.
As shown in FIG. 2 , (1) a resin frame is prepared, (2) a resin sheet is arranged on the resin frame so that a part of the resin sheet has a protruding portion that protrudes in a planar direction and is not in contact with the resin frame, (3) an AnMEGA is prepared, a resin sheet is arranged on the surface of the electrolyte membrane of the AnMEGA so that at least a part of the protruding portion of the resin sheet is in contact with the surface, and the resin sheet is hot-pressed to bond the resin sheet and the resin frame and also to bond the resin sheet and the electrolyte membrane, and (4) a CaGDL is arranged on the Ca catalyst layer of the AnMEGA to form a MEGA. The outer peripheral edge of the CaGDL is opposed to the resin frame in a third region beyond the first region of the resin frame, and the CaGDL and the resin frame are heat-pressed to bond the CaGDL and the resin frame, and as shown in (4'), the ends of the resin sheet are covered with the CaGDL and the resin frame to prevent gas intrusion, and (5) a pair of separators are positioned to sandwich the MEGA and the resin frame, and heat-pressed to sandwich the pair of separators to bond the resin frame and the pair of separators, thereby obtaining a fuel cell according to the present disclosure.

In this disclosure, the fuel gas and the oxidant gas are collectively referred to as reactant gas or gas. The reactant gas supplied to the anode is the fuel gas (sometimes referred to as the anode gas), and the reactant gas supplied to the cathode is the oxidant gas (sometimes referred to as the cathode gas). The fuel gas is a gas that mainly contains hydrogen and may be hydrogen. The oxidant gas is a gas that contains oxygen and may be oxygen, air, dry air, etc.

A single cell of the fuel cell according to the present disclosure comprises a membrane electrode gas diffusion layer assembly, a resin frame arranged around the membrane electrode gas diffusion layer assembly, a pair of separators sandwiching the membrane electrode gas diffusion layer assembly and the resin frame, and a resin sheet.
The fuel cell of the present disclosure may be one having only one unit cell, or may be a fuel cell stack in which a plurality of unit cells are stacked.
The number of unit cells stacked in the fuel cell stack is not particularly limited, and may range from 2 to several hundred.
In this disclosure, both the single cell and the fuel cell stack may be referred to as a fuel cell.

The membrane electrode gas diffusion layer assembly (MEGA) comprises, in this order, an anode side gas diffusion layer (AnGDL), an anode catalyst layer, an electrolyte membrane, a cathode catalyst layer, and a cathode side gas diffusion layer (CaGDL).
In the present disclosure, the AnMEGA is composed of a membrane electrode assembly (MEA) and an anode-side gas diffusion layer. The MEA is composed of an electrolyte membrane, and an anode catalyst layer and a cathode catalyst layer that sandwich the electrolyte membrane.

The cathode (oxidant electrode) includes a cathode catalyst layer and a cathode-side gas diffusion layer.
The anode (fuel electrode) includes an anode catalyst layer and an anode-side gas diffusion layer.
The cathode catalyst layer and the anode catalyst layer are collectively referred to as catalyst layers.
The catalyst layer may include, for example, a catalytic metal that promotes an electrochemical reaction, an electrolyte having proton conductivity, and a carrier having electron conductivity.
As the catalytic metal, for example, platinum (Pt) and alloys of Pt and other metals (for example, Pt alloys mixed with cobalt and nickel, etc.) can be used.
The electrolyte may be a fluorine-based resin, etc. As the fluorine-based resin, for example, a Nafion solution, etc. may be used.
The catalytic metal is supported on a carrier, and in each catalyst layer, the carrier supporting the catalytic metal (catalyst-supporting carrier) and the electrolyte may be present together.
The support for supporting the catalytic metal may be, for example, a carbon material such as carbon that is generally available commercially.

The cathode side gas diffusion layer and the anode side gas diffusion layer are collectively referred to as a gas diffusion layer (GDL).
The GDL may be composed of a substrate and a mesoporous layer (MPL).
The GDL may have a substrate on the side in contact with the separator, and an MPL on the side in contact with the catalyst layer.
The substrate may be a gas-permeable conductive member or the like.
Examples of the substrate include porous carbon bodies such as carbon cloth and carbon paper, and porous metal bodies such as metal mesh and foamed metal.
The MPL may comprise a mixture of a water repellent resin, such as PTFE, and a conductive material, such as carbon black.
The MPL may contain an antioxidant such as Ce. The antioxidant can prevent the generation of radicals.

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

The single cell has a resin frame.
The resin frame is disposed around the outer periphery of the membrane electrode gas diffusion layer assembly, and is disposed between the cathode separator and the anode separator.
The resin frame may have a framework, an opening, and a hole.
The framework is the main part of the resin frame that connects to the membrane electrode gas diffusion layer assembly.
The opening is a holding region for the membrane electrode gas diffusion layer assembly, and is a region penetrating a part of the framework to accommodate the membrane electrode gas diffusion layer assembly. The opening may be located at a position in the resin frame where the framework is disposed around (the outer periphery of) the membrane electrode gas diffusion layer assembly, and may be located in the center of the resin frame.
The holes in the resin frame allow reaction gases and fluids such as a cooling medium to flow in the stacking direction of the unit cells. The holes in the resin frame may be aligned and arranged so as to communicate with the holes in the separators.
The resin frame may have a three-layer structure including a frame-shaped core layer and two frame-shaped shell layers, i.e., a first shell layer and a second shell layer, provided on both sides of the core layer. The first shell layer and the second shell layer may be provided in a frame shape on both sides of the core layer, similar to the core layer.

The core layer may be a structural member having gas sealing and insulating properties, and may be formed of a material whose structure does not change even under the temperature conditions during thermocompression bonding in the manufacturing process of the fuel cell. Specifically, the material of the core layer may be, for example, polyethylene, polypropylene (PP), PC (polycarbonate), PPS (polyphenylene sulfide), PET (polyethylene terephthalate), PEN (polyethylene naphthalate), PA (polyamide), PI (polyimide), PS (polystyrene), PPE (polyphenylene ether), PEEK (polyether ether ketone), cycloolefin, PES (polyether sulfone), PPSU (polyphenyl sulfone), LCP (liquid crystal polymer), epoxy resin, or other resin. The material of the core layer may be a rubber material such as EPDM (ethylene propylene diene rubber), fluorine-based rubber, or silicon-based rubber.
The thickness of the core layer may be 5 μm or more, or may be 30 μm or more, from the viewpoint of ensuring insulation, and may be 100 μm or less, or may be 90 μm or less, from the viewpoint of reducing the cell thickness.

The first and second shell layers may have properties such as high adhesion to other substances, softening under temperature conditions during thermocompression bonding, and a lower viscosity and melting point than the core layer, in order to bond the core layer to the anode separator and the cathode separator and ensure sealing properties. Specifically, the first and second shell layers may be thermoplastic resins such as polyester and modified olefin, or may be thermosetting resins such as modified epoxy resins, or may be maleic acid modified PP (trade name: Admer), etc.
The resin constituting the first shell layer and the resin constituting the second shell layer may be the same type of resin or different types of resin.
The shell layer may include a phenolic antioxidant.
By providing shell layers on both sides of the core layer, adhesion between the resin frame and the two separators by hot pressing becomes easier.
The thickness of each of the first shell layer and the second shell layer may be 5 μm or more, or may be 30 μm or more, from the viewpoint of ensuring adhesion, and may be 100 μm or less, or may be 40 μm or less, from the viewpoint of reducing the cell thickness.

The first shell layer provided on one surface of the core layer may be bonded to the cathode separator and the first gas diffusion layer. The second shell layer provided on the other surface of the core layer may be bonded to the anode separator. The resin frame may be sandwiched between a pair of separators.

The single cell includes a pair of separators that sandwich a resin frame and a membrane electrode gas diffusion layer assembly. One of the pair of separators is an anode separator, and the other is a cathode separator. In the present disclosure, the anode separator and the cathode separator are collectively referred to as separators.
The separator may have holes forming manifolds such as supply holes and exhaust holes for passing fluids such as reactant gases and cooling media in the stacking direction of the unit cells.
As the cooling medium, cooling water such as a mixed solution of ethylene glycol and water can be used to prevent freezing at low temperatures, or cooling air can be used as the cooling medium.
Examples of the supply hole include a fuel gas supply hole, an oxidant gas supply hole, and a coolant supply hole.
Examples of the exhaust hole include a fuel gas exhaust hole, an oxidant gas exhaust hole, and a coolant exhaust hole.
The separator may have a reactant gas flow path on the surface in contact with the gas diffusion layer, and may have a coolant flow path on the surface opposite to the surface in contact with the gas diffusion layer for maintaining a constant temperature of the fuel cell.
The separator may have ribs that define flow paths such as a reactant gas flow path and a coolant flow path.
The separator may be a gas-impermeable conductive member. The conductive member may be, for example, dense carbon made by compressing carbon to make it gas-impermeable, or a press-formed metal (e.g., iron, aluminum, stainless steel, etc.) plate. The separator may also have a current collecting function.
The shape of the separator may be rectangular, horizontally elongated hexagonal, horizontally elongated octagonal, circular, oval, or the like.

The fuel cell stack has manifolds, such as an inlet manifold to which the supply holes communicate, and an outlet manifold to which the exhaust holes communicate.
Examples of the inlet manifold include an anode inlet manifold, a cathode inlet manifold, a coolant inlet manifold, etc. The anode inlet manifold and the cathode inlet manifold are collectively referred to as a gas inlet manifold.
Examples of the outlet manifold include an anode outlet manifold, a cathode outlet manifold, a cooling medium outlet manifold, etc. The anode outlet manifold and the cathode outlet manifold are collectively referred to as a gas outlet manifold.
The gas inlet manifold and the gas outlet manifold are collectively referred to as the reaction gas manifold.

The resin sheet is disposed continuously in the planar direction from a first region on the surface of the resin frame to a second region on the surface of the exposed electrolyte membrane of the membrane electrode-gas diffusion layer assembly.
The outer peripheral edge of the first gas diffusion layer of the membrane electrode gas diffusion layer assembly does not face the resin sheet, but faces the resin frame. In the present disclosure, the first gas diffusion layer is a cathode side gas diffusion layer or an anode side gas diffusion layer, and may be a cathode side gas diffusion layer.
In a third region adjacent to the first region and in which the resin frame does not face the resin sheet, the outer peripheral edge of the first gas diffusion layer and the resin frame are joined by the resin frame (specifically, the shell layer).
The resin sheet may be made of a polyamide resin such as nylon 12 or nylon 11, or maleic acid modified PP (trade name: Admer).

Claims (1)

1. A fuel cell comprising:
the fuel cell comprises a membrane electrode gas diffusion layer assembly, a resin frame arranged around the membrane electrode gas diffusion layer assembly, a pair of separators sandwiching the membrane electrode gas diffusion layer assembly and the resin frame, and a resin sheet;
the resin sheet is disposed continuously in a planar direction from a first region on a surface of the resin frame to a second region on a surface of the exposed electrolyte membrane of the membrane electrode-gas diffusion layer assembly,
an outer peripheral edge portion of the first gas diffusion layer of the membrane electrode gas diffusion layer assembly does not face the resin sheet and faces the resin frame;
A fuel cell characterized in that in a third region adjacent to the first region and in which the resin frame does not face the resin sheet, the outer peripheral edge of the first gas diffusion layer and the resin frame are joined by the resin frame.

Images