Fuel cell

Abstract

The present invention provides a fuel cell capable of suppressing a decrease in power generation performance. The fuel cell has at least a power generation unit and a pair of diaphragms that sandwich the power generation unit, the pair of diaphragms have grooves that constitute a flow path, the power generation unit includes a gas diffusion layer, and in the region of the power generation unit, the surface pressure on the upstream side in the flow direction of the oxidant gas is greater than the surface pressure on the downstream side in the flow direction of the oxidant gas.

Description

Technical Field

[0001] The present disclosure relates to a fuel cell. Background Art

[0002] Various techniques have been proposed for fuel cells such as those disclosed in Patent Documents 1-2.

[0003] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2008-171598

[0004] Patent Document 2: Japanese Unexamined Patent Application Publication No. 2006-147501

[0005] A technique for making the surface pressure distribution of a fuel cell uniform is disclosed in Patent Document 1. On the downstream side in the flow direction of the oxidant gas in the fuel cell, the gas diffusion resistance is more dominant than the resistance. Therefore, if the surface pressure of the fuel cell is too high, the gas diffusion resistance becomes large, and there is a possibility that the power generation performance of the fuel cell decreases. Summary of the Invention

[0006] The present disclosure has been made in view of the above actual situation, and its main object is to provide a fuel cell capable of suppressing a decrease in power generation performance.

[0007] That is, the present disclosure includes the following aspects.

[0008] <1> A fuel cell, wherein

[0009] the fuel cell has at least a power generation unit and a pair of separators sandwiching the power generation unit,

[0010] the pair of separators has grooves forming flow paths,

[0011] the power generation unit includes a gas diffusion layer,

[0012] in the region of the power generation unit, the surface pressure on the upstream side in the flow direction of the oxidant gas is greater than the surface pressure on the downstream side in the flow direction of the oxidant gas.

[0013] <2> The fuel cell according to <1>, wherein

[0014] in a state where the gas diffusion layer is not pressurized, the thickness of the gas diffusion layer on the upstream side in the flow direction of the oxidant gas is greater than the thickness of the gas diffusion layer on the downstream side in the flow direction of the oxidant gas.

[0015] <3> The fuel cell according to <1> or <2>, wherein

[0016] the density of the gas diffusion layer on the upstream side in the flow direction of the oxidant gas is greater than the density of the gas diffusion layer on the downstream side in the flow direction of the oxidant gas.

[0017] <4> The fuel cell according to any one of <1> to <3>, wherein

[0018] The depth of the groove on the upstream side of the flow direction of the oxidant gas is greater than the depth of the groove on the downstream side of the flow direction of the oxidant gas.

[0019] <5> The fuel cell according to any one of <1> to <4>, wherein

[0020] One of the pair of diaphragms is a cathode diaphragm and the other is an anode diaphragm.

[0021] The cathode diaphragm has the groove that constitutes the oxidant gas flow path.

[0022] When the entire region of the oxidant gas flow path is set to 100%, the upstream side in the flow direction of the oxidant gas is the region from 30% to 70% on the oxidant gas inlet side of the oxidant gas flow path.

[0023] The fuel cell of the present disclosure can suppress a decrease in power generation performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic view showing an example when looking down at the cathode diaphragm of the fuel cell of the present disclosure.

[0025] Figure 2 It is a schematic view showing another example when looking down at the cathode diaphragm of the fuel cell of the present disclosure.

[0026] Figure 3 It is a schematic view showing another example when looking down at the cathode diaphragm of the fuel cell of the present disclosure. DETAILED DESCRIPTION

[0027] Hereinafter, embodiments related to the present disclosure will be described. Among them, matters required for the implementation of the present disclosure in matters other than those specifically mentioned in this specification (for example, general configurations and manufacturing processes of fuel cells that do not constitute features of the present disclosure) can be grasped as design matters of those skilled in the art based on the prior art in the art. The present disclosure can be implemented based on the content disclosed in this specification and common technical knowledge in the art.

[0028] In addition, the dimensional relationships (length, width, thickness, etc.) in the drawings do not reflect actual dimensional relationships.

[0029] In the present disclosure, the gas supplied to the anode of the fuel cell is a fuel gas (anode gas), and the gas supplied to the cathode of the fuel cell is an oxidant gas (cathode gas). The fuel gas is a gas mainly containing hydrogen and may be hydrogen. The oxidant gas is a gas containing oxygen and may be oxygen, air, etc. In the present disclosure, the fuel gas and the oxidant gas are collectively referred to as reaction gases or gases.

[0030] In the present disclosure, a fuel cell is provided.

[0031] The above fuel cell has at least a power generation part and a pair of diaphragms sandwiching the power generation part.

[0032] The above pair of diaphragms has grooves forming flow paths.

[0033] The above power generation part includes a gas diffusion layer.

[0034] In the region of the above power generation part, the surface pressure on the upstream side in the flow direction of the oxidant gas is greater than the surface pressure on the downstream side in the flow direction of the oxidant gas.

[0035] In the present disclosure, means for the surface pressure distribution for improving the power generation performance of the fuel cell are provided. In the prior art, by giving as uniform a surface pressure as possible in the power generation part of the cell core and reducing the resistance of the fuel cell with a surface pressure above a specified value, the power generation performance of the fuel cell is improved. However, depending on the part of the power generation part, there are regions where a high surface pressure is preferable and regions where a low surface pressure is preferable, and the optimal power generation performance cannot be obtained. Since the gas diffusion resistance is more dominant than the resistance on the downstream side in the flow direction of the oxidant gas in the cell core, if the surface pressure is high, the gas diffusion layer is damaged, and thus the gas diffusion resistance increases and the power generation performance of the fuel cell becomes low.

[0036] In the present disclosure, as the surface pressure distribution in the flow direction of the oxidant gas, by making the upstream side in the flow direction > the downstream side in the flow direction, the reduction of resistance is prioritized on the upstream side in the flow direction, and the reduction of gas diffusion resistance is prioritized on the downstream side in the flow direction, resulting in an appropriate power generation state. The surface pressure distribution is controlled by setting the distribution of the thickness of the gas diffusion layer, the density of the gas diffusion layer, or the height of the flow path to achieve the structure.

[0037] For various applications such as vehicles, when the auxiliary machine power such as an air compressor is operated by suppressing it to a value of 2 or less in terms of the air stoichiometric ratio, since the oxygen partial pressure in about 1 / 3 of the downstream side in the flow direction of the oxidant gas flow path decreases, concentration overvoltage is likely to occur.

[0038] In a proton-conducting fuel cell, since power generation is carried out by protons and oxygen meeting on the cathode side, it is necessary for oxygen to move to the catalyst surface in the presence of the generated moisture. Therefore, the surface pressure design of the present disclosure is suitable for a proton-conducting fuel cell in which gas diffusion on the cathode side is likely to be a problem.

[0039] In a fuel cell of the type that generates products on the anode side, in a fuel cell using a gas diffusion layer having surface pressure dependence, the same surface pressure design as on the cathode side can be carried out based on the flow direction of the anode gas.

[0040] Regarding the flow path type, compared with a porous body flow path where gas supply is more uniform, etc., it is more suitable for a groove flow path type where gas diffusion is likely to be affected under the rib (rib). The groove flow path type can be a groove flow path without a throttle portion or a groove flow path with a throttle portion.

[0041] The fuel cell of the present disclosure can be used when mounted on a moving body such as a vehicle, or can be used when mounted on a vehicle. In addition, the fuel cell of the present disclosure can be used when mounted on a fixed power generation system such as a generator.

[0042] The vehicle can be a fuel cell vehicle or the like. As a moving body other than a vehicle, for example, railways, ships, airplanes, etc. can be cited.

[0043] In addition, the fuel cell of the present disclosure can be used when mounted on a moving body such as a vehicle that can also travel using the power of a secondary battery.

[0044] The moving body and the fixed power generation system can include the fuel cell of the present disclosure. The moving body can have drive units such as a motor, an inverter, and a hybrid control system.

[0045] The hybrid control system can be a system that can use the output of the fuel cell and the power of the secondary battery in combination to make the moving body travel.

[0046] The fuel cell can have only one single cell (cell), or can be a fuel cell stack (battery stack) in which a plurality of cells are stacked.

[0047] In the present disclosure, both the cell and the fuel cell stack are sometimes referred to as a fuel cell.

[0048] The number of cells stacked in the fuel cell stack is not particularly limited, and can be, for example, 2 to several hundred.

[0049] The cell of the fuel cell has at least a power generation part and a pair of diaphragms that sandwich the power generation part.

[0050] The shape of the power generation part can be rectangular when viewed from above.

[0051] The power generation part has at least a gas diffusion layer.

[0052] The power generation unit may include a membrane electrode assembly (MEA) including an electrolyte membrane and two electrodes sandwiching the electrolyte membrane.

[0053] The electrolyte membrane may be a solid polymer electrolyte membrane. Examples of the solid polymer electrolyte membrane include fluorine-based electrolyte membranes such as thin films of perfluorosulfonic acid containing moisture, and hydrocarbon-based electrolyte membranes. As the electrolyte membrane, for example, it may be a Nafion membrane (manufactured by DuPont).

[0054] One of the two electrodes is an anode (fuel electrode), and the other is a cathode (oxidant electrode).

[0055] The electrode includes a catalyst layer and may include a gas diffusion layer as needed. The power generation unit may be a membrane electrode gas diffusion layer assembly (MEGA). In this case, the cell may include a cathode separator, an anode separator, and a membrane electrode gas diffusion layer assembly disposed between the cathode separator and the anode separator.

[0056] The membrane electrode gas diffusion layer assembly sequentially has an anode-side gas diffusion layer, an anode catalyst layer, an electrolyte membrane, a cathode catalyst layer, and a cathode-side gas diffusion layer.

[0057] The anode catalyst layer and the cathode catalyst layer are collectively referred to as the catalyst layer.

[0058] The anode-side gas diffusion layer and the cathode-side gas diffusion layer are collectively referred to as the gas diffusion layer.

[0059] The catalyst layer includes a catalyst, and the catalyst may include a catalyst metal that promotes an electrochemical reaction, an electrolyte having proton conductivity, and a carrier having electron conductivity, etc.

[0060] As the catalyst metal, for example, platinum (Pt), and alloys composed of Pt and other metals (for example, Pt alloys mixed with cobalt and nickel, etc.) can be used. The catalyst metal used as the cathode catalyst and the catalyst metal used as the anode catalyst may be the same or different.

[0061] As the electrolyte, it may be a fluorine-based resin, etc. As the fluorine-based resin, for example, Nafion solution, etc. can be used.

[0062] The above catalyst metal is supported on a carrier, and in each catalyst layer, the carrier supporting the catalyst metal (catalyst-supported carrier) and the electrolyte may be mixed together.

[0063] Examples of the carrier for supporting the catalyst metal include carbon materials such as commercially available carbon.

[0064] The gas diffusion layer (GDL) may be composed of a base material and a microporous layer (MPL).

[0065] 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.

[0066] The substrate may be a conductive component with gas permeability, etc.

[0067] Examples of the substrate include carbon porous bodies such as carbon cloth and carbon paper, and metal porous bodies such as metal mesh and foamed metal.

[0068] The MPL may include a mixture of a hydrophobic resin such as PTFE and a conductive material such as carbon black.

[0069] The MPL may include an antioxidant such as Ce. By means of the antioxidant, the generation of free radicals can be prevented.

[0070] The cell may include a resin frame for insulation disposed on the outer side (periphery) in the plane direction of the membrane electrode assembly disposed between the anode separator and the cathode separator. The resin frame is formed into a plate-like and frame-like shape using a thermoplastic resin, and seals the space between the anode separator and the cathode separator while holding the membrane electrode assembly in its central region. As the resin frame, resins such as PE, PP, PET, and PEN can be used, for example. The resin frame may be a three-layer sheet composed of three layers with an adhesive layer disposed on the surface layer.

[0071] In order to seal each gas, the fuel cell stack may have gaskets, resin sheets, etc. between the cells. The resin sheet may be the above-mentioned resin frame.

[0072] The separator collects the current generated by power generation and functions as a partition wall. The separator is disposed on both sides in the stacking direction of the power generation unit in such a manner that a pair of separators sandwich the power generation unit. One of the pair of separators is the anode separator and the other is the cathode separator. The anode separator and the cathode separator are collectively referred to as the separator.

[0073] The pair of separators has grooves forming flow paths.

[0074] The anode separator may have grooves forming a fuel gas flow path on the surface on the power generation unit side.

[0075] The cathode separator may have grooves forming an oxidant gas flow path on the surface on the power generation unit side.

[0076] The separator may have holes such as supply holes and discharge holes forming a manifold for allowing fluids such as reaction gases and refrigerants to flow in the stacking direction of the cell.

[0077] Examples of the refrigerant include water, a mixed solvent of water and ethylene glycol, etc.

[0078] As the separator, for example, it can be formed of compressed carbon into an airtight dense carbon, and stamped metal (such as iron, titanium, stainless steel, etc.).

[0079] In the region of the power generation section of the fuel cell, the surface pressure on the upstream side of the flow direction of the oxidant gas is greater than the surface pressure on the downstream side of the flow direction of the oxidant gas.

[0080] From the viewpoint of setting the surface pressure distribution in the region of the power generation section of the fuel cell, in a state where the gas diffusion layer is not pressurized, the thickness of the gas diffusion layer on the upstream side of the flow direction of the oxidant gas can be greater than the thickness of the gas diffusion layer on the downstream side of the flow direction of the oxidant gas. In a state where the gas diffusion layer is not pressurized, the thickness of at least one of the anode-side gas diffusion layer and the cathode-side gas diffusion layer on the upstream side of the flow direction of the oxidant gas can be greater than the thickness of the gas diffusion layer on the downstream side of the flow direction of the oxidant gas. In a state where the gas diffusion layer is not pressurized, the thickness of the cathode-side gas diffusion layer on the upstream side of the flow direction of the oxidant gas can be greater than the thickness of the cathode-side gas diffusion layer on the downstream side of the flow direction of the oxidant gas. In a state where the gas diffusion layer is not pressurized, the thickness of the anode-side gas diffusion layer on the upstream side of the flow direction of the oxidant gas can be greater than the thickness of the anode-side gas diffusion layer on the downstream side of the flow direction of the oxidant gas. In a state where the gas diffusion layer is pressurized, the thickness of the gas diffusion layer on the upstream side of the flow direction of the oxidant gas can be the same as the thickness of the gas diffusion layer on the downstream side of the flow direction of the oxidant gas.

[0081] From the viewpoint of setting the surface pressure distribution in the region of the power generation section of the fuel cell, the density of the gas diffusion layer on the upstream side of the flow direction of the oxidant gas can be greater than the density of the gas diffusion layer on the downstream side of the flow direction of the oxidant gas. The density of at least one of the anode-side gas diffusion layer and the cathode-side gas diffusion layer on the upstream side of the flow direction of the oxidant gas can be greater than the density of the gas diffusion layer on the downstream side of the flow direction of the oxidant gas. The density of the cathode-side gas diffusion layer on the upstream side of the flow direction of the oxidant gas can be greater than the density of the cathode-side gas diffusion layer on the downstream side of the flow direction of the oxidant gas. The density of the anode-side gas diffusion layer on the upstream side of the flow direction of the oxidant gas can be greater than the density of the anode-side gas diffusion layer on the downstream side of the flow direction of the oxidant gas.

[0082] The material of the gas diffusion layer on the upstream side of the flow direction of the oxidant gas can be different from or the same as the material of the gas diffusion layer on the downstream side of the flow direction of the oxidant gas.

[0083] The flow direction of the fuel gas can be the same as the flow direction of the oxidant gas or a countercurrent.

[0084] From the perspective of setting a surface pressure distribution in the region of the power generation unit of the fuel cell, the depth of the grooves in the separator on the upstream side in the flow direction of the oxidant gas can be greater than the depth of the grooves in the separator on the downstream side in the flow direction of the oxidant gas. The depth of the grooves in at least one of the anode separator and the cathode separator on the upstream side in the flow direction of the oxidant gas can be greater than the depth of the grooves in the separator on the downstream side in the flow direction of the oxidant gas. The depth of the grooves in the cathode separator on the upstream side in the flow direction of the oxidant gas can be greater than the depth of the grooves in the cathode separator on the downstream side in the flow direction of the oxidant gas. The depth of the grooves in the anode separator on the upstream side in the flow direction of the oxidant gas can be greater than the depth of the grooves in the anode separator on the downstream side in the flow direction of the oxidant gas.

[0085] In the present disclosure, when the entire region of the oxidant gas flow path is set to 100%, the upstream side in the flow direction of the oxidant gas can be a region from 30% to 70% starting from the oxidant gas inlet side of the oxidant gas flow path, or a region from 50% to 70%, or a region of 70%.

[0086] In the present disclosure, when the entire region of the oxidant gas flow path is set to 100%, the downstream side in the flow direction of the oxidant gas can be a region from 30% to 70% starting from the oxidant gas outlet side of the oxidant gas flow path, or a region from 30% to 50%, or a region of 30%.

[0087] The surface pressure distribution can be designed according to the operating conditions of the fuel cell, the specifications of the flow paths of the separator, and the specifications of the MEGA, etc.

[0088] For example, the surface pressure in the region of 70% starting from the oxidant gas inlet side of the oxidant gas flow path can be made higher than the surface pressure in the region of 30% starting from the oxidant gas outlet side of the oxidant gas flow path.

[0089] Figure 1 It is a schematic diagram showing an example when observing the cathode separator of the fuel cell of the present disclosure from above.

[0090] Figure 1 The cathode separator 100 of the fuel cell has one oxidant gas flow path 10.

[0091] Figure 2 It is a schematic diagram showing another example when observing the cathode separator of the fuel cell of the present disclosure from above.

[0092] Figure 2 The cathode separator 200 of the fuel cell has one oxidant gas flow path 20.

[0093] One oxidant gas flow path 20 branches into a plurality of flow paths on the upstream side 40 in the flow direction of the oxidant gas, and the branched plurality of flow paths merge on the downstream side 50 in the flow direction of the oxidant gas.

[0094] Figure 3 It is a schematic diagram showing another example when observing the cathode separator of the fuel cell of the present disclosure from above.

[0095] Figure 3 The cathode separator 300 of the fuel cell has a plurality of oxidant gas flow paths 30.

[0096] In Figures 1 to 3 When optimizing the supply amount of the oxidant gas F in consideration of fuel efficiency, the concentration overvoltage generally increases in the range of about 30% on the downstream side of the oxidant gas flow path. Therefore, the surface pressure in the upstream side 40 in the flow direction of the oxidant gas, that is, the area of 70% from the oxidant gas inlet side of the oxidant gas flow path, is higher than the surface pressure in the downstream side 50 in the flow direction of the oxidant gas, that is, the area of 30% from the oxidant gas outlet side of the oxidant gas flow path. Among them, since the range in which the concentration overvoltage is dominant varies depending on the supply amount of the oxidant gas F, the specifications of the oxidant gas flow path, and the ease of supply of the oxidant gas F to the power generation part due to the specifications of the GDL, the optimum value of the surface pressure distribution design changes. Therefore, the surface pressure distribution can be designed according to these conditions.

[0097] Explanation of reference numerals:

[0098] 10... oxidant gas flow path; 20... oxidant gas flow path; 30... oxidant gas flow path; 40... upstream side in the flow direction of the oxidant gas; 50... downstream side in the flow direction of the oxidant gas; 100... cathode separator; 200... cathode separator; 300... cathode separator; F... oxidant gas.

Claims

1. A fuel cell, wherein, the fuel cell has at least a power generation part and a pair of diaphragms sandwiching the power generation part, the pair of diaphragms has grooves forming a flow path, the power generation part includes a gas diffusion layer, in the area of the power generation part, the surface pressure on the upstream side of the flow direction of the oxidant gas is greater than the surface pressure on the downstream side of the flow direction of the oxidant gas.

2. The fuel cell according to claim 1, wherein, in a state where the gas diffusion layer is not pressurized, the thickness of the gas diffusion layer on the upstream side of the flow direction of the oxidant gas is greater than the thickness of the gas diffusion layer on the downstream side of the flow direction of the oxidant gas.

3. The fuel cell according to claim 1, wherein, the density of the gas diffusion layer on the upstream side of the flow direction of the oxidant gas is greater than the density of the gas diffusion layer on the downstream side of the flow direction of the oxidant gas.

4. The fuel cell according to claim 1, wherein, the depth of the groove on the upstream side of the flow direction of the oxidant gas is greater than the depth of the groove on the downstream side of the flow direction of the oxidant gas.

5. The fuel cell according to claim 1, wherein, one of the pair of diaphragms is a cathode diaphragm and the other is an anode diaphragm, the cathode diaphragm has the groove forming the oxidant gas flow path, when the entire area of the oxidant gas flow path is set to 100%, the upstream side of the flow direction of the oxidant gas is the area from 30% to 70% starting from the oxidant gas inlet side of the oxidant gas flow path.

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