JP5153083B2 - Fuel cell - Google Patents

Description

  The present invention relates to a fuel cell in which liquid fuel is supplied directly to an anode.

  A fuel cell is a device that generates electrical energy from hydrogen and oxygen, and can achieve high power generation efficiency. The main feature of the fuel cell is direct power generation that does not go through the process of thermal energy and kinetic energy as in the conventional power generation method, so high power generation efficiency can be expected even on a small scale, and there is little emission of nitrogen compounds, Noise and vibration are also small, so the environment is good. In this way, the fuel cell can effectively use the chemical energy of fuel and has environmentally friendly characteristics, so it is expected as an energy supply system for the 21st century, from space use to automobiles and portable devices. It is attracting attention as a promising new power generation system that can be used for various applications from large-scale power generation to small-scale power generation.

  Among them, solid polymer fuel cells are characterized by low operating temperature and high power density compared to other types of fuel cells. In particular, as a form of solid polymer fuel cells, direct methanol A fuel cell (Direct Methanol Fuel Cell: DMFC) is attracting attention. In DMFC, an aqueous methanol solution as a fuel is directly supplied to the anode without modification, and electric power is obtained by an electrochemical reaction between the aqueous methanol solution and oxygen, and carbon dioxide is emitted from the anode to the cathode by this electrochemical reaction. The product water is discharged as a reaction product. Aqueous methanol solution has higher energy per unit volume than hydrogen, and is suitable for storage and has a low risk of explosion, so it can be used in automobiles and mobile devices (cell phones, notebook personal computers, PDAs, MP3 players, Use for power sources such as digital cameras or electronic dictionaries (books) is expected.

FIG. 7 is a cross-sectional view showing a schematic configuration of a conventional DMFC. The DMFC has a membrane electrode assembly in which a fuel electrode 530 and an air electrode 560 are provided with an electrolyte membrane 500 interposed therebetween. The fuel electrode 530 includes an anode catalyst layer 510 and an anode diffusion layer 520. The air electrode 560 includes a cathode catalyst layer 540 and a cathode diffusion layer 550. The fuel electrode 530 is pressed by a rib 572 provided on the casing 570. Similarly, the air electrode 560 is pressed by a rib 582 provided in the casing 580. Such a configuration is also disclosed in Patent Document 1.
JP 2005-209584 A

  In the conventional DMFC, in order to reduce the contact resistance of the diffusion layer, the catalyst layer, and the electrolyte membrane, it is necessary to tighten using a fastening member such as a nut or a bolt. For this reason, each member of DMFC has been required to have a strength sufficient to withstand the clamping pressure. In particular, the diffusion layer, the catalyst layer, and the like had to be thickened to ensure strength. Further, since ribs are necessary to hold down the diffusion layer, the structure of the DMFC is complicated and enlarged, which hinders diffusion of fuel, air and products. Further, there has been a problem that miniaturization and maintenance become difficult and the cost increases.

  The present invention has been made in view of these problems, and an object of the present invention is to provide a technique for simplifying and thinning the structure of the DMFC without impairing the diffusibility of fuel, air and products.

One embodiment of the present invention is a fuel cell. The fuel cell includes an electrolyte membrane, an anode catalyst layer and a cathode catalyst layer provided across the electrolyte membrane, a fuel chamber for storing liquid fuel directly supplied to the anode catalyst layer, and the anode catalyst layer Or a current collector made of a flat metal sheet in contact with the cathode catalyst layer and provided with a plurality of pores in a direction substantially perpendicular to the surface direction, and the pore portion of the current collector The side surface is tapered from both sides, and the apex of the side surface of the pore is embedded in the anode catalyst layer or the cathode catalyst layer .

  According to the fuel cell of this aspect, the current collector and the catalyst layer are kept in close contact without using a support such as a rib. Thereby, by reducing the members for bringing the current collector and the catalyst layer into close contact with each other, the structure of the fuel cell can be simplified, maintenance can be facilitated, and the manufacturing cost can be reduced. In addition, since the load applied to the casing of the fuel cell by a fastening member such as a bolt or a nut can be reduced, the thickness of the casing catalyst layer or the like of the fuel cell can be reduced, and the overall size of the fuel cell can be reduced. Can be made compact.

In the fuel cell of the above aspect, Runode part or all of the current collector is embedded in the anode catalyst layer or cathode catalyst layer, the anchor effect between the current collector and the catalyst layer, the current collector and the catalyst layer Adhesion can be further improved.

  In the fuel cell of the above aspect, the surface of the current collector may be coated with a corrosion-resistant metal.

  According to this aspect, while improving the electroconductivity of a collector, it can suppress that the metal which comprises a collector is eluted, and can improve the operation stability of a fuel cell.

  In the fuel cell of the above aspect, the plurality of pores provided in the current collector may be regularly arranged.

  According to this aspect, since the aperture ratio in the surface direction of the current collector is uniform, it is possible to suppress the diffusibility of fuel and air from being varied depending on the location, and to improve the operational stability of the fuel cell.

  According to the present invention, since the contact resistance is reduced without pressing the current collector and the electrode, the fuel cell can be reduced in size.

  FIG. 1 is an exploded perspective view of a fuel cell according to an embodiment. 2A and 2B are cross-sectional views along the line A-A ′ in FIG. 1.

  The fuel cell 10 includes a plurality of cells 11 arranged on a plane. Each cell 11 includes a membrane electrode assembly including an anode catalyst layer 12, a cathode catalyst layer 14, and an electrolyte membrane 16 sandwiched between the anode catalyst layer 12 and the cathode catalyst layer 14. The anode catalyst layer 12 is supplied with a methanol aqueous solution or pure methanol (hereinafter referred to as “methanol fuel”). Air is supplied to the cathode catalyst layer 14. The fuel cell 10 generates power by an electrochemical reaction between methanol in methanol fuel and oxygen in air.

  The electrolyte membrane 16 preferably exhibits good ion conductivity in a wet state, and functions as an ion exchange membrane that moves protons between the anode catalyst layer 12 and the cathode catalyst layer 14. The electrolyte membrane 16 is formed of a solid polymer material such as a fluorine-containing polymer or a non-fluorine polymer. Etc. can be used. Examples of the sulfonic acid type perfluorocarbon polymer include Nafion (manufactured by DuPont: registered trademark) 112. Examples of non-fluorine polymers include sulfonated aromatic polyetheretherketone and polysulfone.

  An electrolyte membrane 16 is bonded to one surface of the anode catalyst layer 12, and a current collector 18 is bonded to the other surface of the anode catalyst layer 12. This structure can be obtained by mounting the current collector 18 on the electrolyte membrane 16 after the anode catalyst layer 12 is formed by spray coating, screen printing, transfer method or the like. Details of the current collector 18 will be described later. An anode side gasket 40 is provided on the peripheral edge of the electrolyte membrane 16 on the anode catalyst layer 12 side. An anode side housing 26 is installed via an anode side gasket 40, and a fuel chamber 70 in which methanol fuel is stored is formed by the anode side housing 26. Note that the end of each current collector 18 in the longitudinal direction is pressed by the anode side gasket 40. The methanol fuel stored in the fuel chamber 70 is supplied directly to the anode catalyst layer 12.

  An opening 27 is provided in the main surface of the anode housing 26. A gas-liquid separation filter 28 is installed inside the opening 27. The gas generated at the anode passes through the gas-liquid separation filter 28, passes through the opening 27, and is discharged to the outside. The anode-side housing 26 desirably has characteristics such as methanol resistance, acid resistance, and mechanical rigidity.

  Examples of the material constituting the anode-side housing 60 include metal materials such as stainless steel metals and titanium alloys, or synthetic resins such as acrylic resins, epoxies, and glass epoxy resins.

  The anode side housing 26 has a fuel suction part (not shown) for sucking methanol fuel from a fuel tank (not shown) provided outside the fuel cell 10, and methanol fuel is contained in the fuel chamber 70. Is replenished as appropriate.

The electrolyte membrane 16 is bonded to one surface of the cathode catalyst layer 14, and the current collector 20 is bonded to the other surface of the cathode catalyst layer 14. The configuration of the current collector 20 is the same as that of the current collector 18. A cathode side gasket 42 is provided on the peripheral edge of the electrolyte membrane 16 on the cathode catalyst layer 14 side. A cathode side housing 34 is installed via a cathode side gasket 42. Note that the ends of the current collectors 20 in the longitudinal direction are pressed by the cathode side gasket 42.
An air intake port 36 for air intake is provided on the main surface of the cathode side housing 34. The air that flows in from the air intake port 36 reaches the cathode catalyst layer 14. As the material constituting the cathode side housing 34, the materials exemplified for the anode side housing 26 can be used.

  Each cell 11 is electrically connected in series. Specifically, in adjacent cells, the current collector 18 of one cell and the other current collector 20 are connected by a wiring 24.

  Hereinafter, the current collector used in the present embodiment will be described. Since the current collector 18 and the current collector 20 have the same configuration, the current collector 18 will be described as an example.

  The properties required for the base material of the current collector 18 include conductivity and rigidity. As a base material with such characteristics, copper-based materials such as oxygen-free copper, tough pitch copper, phosphor bronze, brass and beryllium copper, nickel alloys such as kovar, permalloy, nichrome, amber and inconel, SUS, molybdenum and aluminum Examples include a flat metal sheet made of an alloy or the like.

  The base material of the current collector 18 is preferably coated with a metal having corrosion resistance such as gold or platinum. The layer thickness of the metal having corrosion resistance is, for example, 100 nm or less. The metal having corrosion resistance can be coated on the base material of the current collector 18 by sputtering, plating, or the like. By covering the base material of the current collector 18 with a metal having corrosion resistance, the conductivity of the current collector is improved while suppressing costs, and the base metal constituting the current collector 18 is eluted. It is possible to suppress this, and as a result, the operation stability of the fuel cell can be improved.

  Since the current collector 18 is rigid, the current collector 18 and the anode catalyst layer 12 are kept in close contact with each other even when the current collector 18 is not pressed by a support such as a rib. Thereby, by reducing the members for bringing the current collector 18 and the anode catalyst layer 12 into close contact with each other, the structure of the fuel cell can be simplified, maintenance can be facilitated, and the manufacturing cost can be reduced. Further, since the load applied to the casing of the fuel cell by a fastening member such as a bolt or nut can be reduced, the thickness of the casing of the fuel cell, the catalyst layer, etc. can be reduced, and the overall size of the fuel cell can be reduced. Can be made compact.

  The current collector 18 is provided with a plurality of pores in a direction substantially perpendicular to the surface direction. Such pores can be obtained by forming a mask having an opening of a predetermined shape on a metal sheet by lithography and then selectively etching the metal sheet using an etching method. The liquid fuel is supplied to the anode catalyst layer 12 through the pores provided in the current collector 18.

  It is desirable that the plurality of pores provided in the current collector 18 be regularly arranged. According to this, since the aperture ratio in the surface direction of the current collector 18 becomes uniform, it is possible to suppress the diffusibility of fuel and air from being varied depending on the location, and to improve the operational stability of the fuel cell.

  The shape of the pores provided in the current collector 18 can be a polygon, and it is desirable to form a (regular) triangle, (regular) quadrangle, (regular) hexagon, or a combination of two or more of these.

  FIG. 3 is a microscopic image of a current collector actually produced using SUS as a base material. In this example, the pores are regular hexagons, and the current collector 18 has a honeycomb structure. By making the current collector 18 have a honeycomb structure, the rigidity can be further enhanced while efficiently providing pores.

  Table 1 shows examples of dimensions of the current collector having a honeycomb structure. In Table 1, a, b, and c are the distance from the center of the pore to the side of the regular hexagon, the distance between the sides of the adjacent regular hexagon, and the length of one side of the regular hexagon (see FIG. 4). The aperture ratio is obtained by the following equation.

Opening ratio = total area of pores / (total area of pores + occupied area of current collector) × 100

  When a power generation test was performed using a current collector with a honeycomb structure of each size, it was confirmed that all of them had good adhesion between the current collector and the electrode, and an output could be obtained sufficiently and stably. In addition, from the viewpoint of ensuring the diffusibility of fuel and air, the aperture ratio of the current collector 18 is desirably 50 to 90%.

  A preferred form of the cross-sectional shape of the current collector 18 is a trapezoidal shape having the side on the electrode side as a long side (see FIG. 5). By making the cross section of the current collector 18 trapezoidal, the bottom area of the current collector 18 increases, so the contact area between the current collector 18 and the anode catalyst layer 12 increases. As a result, the contact resistance between the current collector 18 and the anode catalyst layer 12 is reduced.

  FIG. 6 is a diagram illustrating an example of a connection structure between the current collector 18 and the anode catalyst layer 12. In this example, the bottom of the current collector 18 is embedded in the anode catalyst layer 12. Thereby, the adhesiveness of the electrical power collector 18 and the anode catalyst layer 12 improves further, and it is suppressed that the electrical power collector 18 peels from the anode catalyst layer 12. FIG. When the current collector 18 is embedded in the anode catalyst layer 12, a taper is provided on both sides of the pore portion of the current collector 18 from both sides so that the apex of the pore side surface is embedded in the anode catalyst layer 12. desirable. The typical angle of the taper on the side surface of the pore (θ shown in FIG. 6B) is 60 to 70 °. According to this, the adhesion between the current collector 18 and the anode catalyst layer 12 is further improved. The current collector having the cross-sectional shape shown in FIG. 6 can be obtained by etching in a state where resists are provided on both sides as a mask.

  The structure in which the current collector 18 is embedded in the anode catalyst layer 12 is obtained by a method in which the anode catalyst layer 12a is formed by a spray method or the like after the current collector 18 is installed on the anode catalyst layer 12a serving as a base material. be able to.

  In the example of FIG. 6, the current collector 18 is partially embedded in the anode catalyst layer 12, but the entire current collector 18 is embedded in the anode catalyst layer 12 with the surface of the current collector 18 exposed. It may be.

  The present invention is not limited to the above-described embodiments, and various modifications such as design changes can be added based on the knowledge of those skilled in the art. The form can also be included in the scope of the present invention.

1 is an exploded perspective view of a fuel cell according to an embodiment. 2A is a cross-sectional view of the fuel cell according to the embodiment, taken along the line A-A ′ of FIG. 1. 2B is a cross-sectional view of the fuel cell according to the embodiment, taken along the line B-B ′ of FIG. 1. It is a microscope image of the electrical power collector actually produced using SUS for a base material. It is a figure which shows the various dimensions of the electrical power collector which has a honeycomb structure. It is a figure which shows the cross-sectional shape of a collector. It is a figure which shows an example of the connection structure of a collector and an anode catalyst layer. FIG. 6A is a plan view of the current collector and the anode catalyst layer. FIG. 6B is a cross-sectional view taken along line C-C ′ of FIG. It is sectional drawing which shows the structure of the conventional DMFC.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Fuel cell, 12 Anode catalyst layer, 14 Cathode catalyst layer, 16 Electrolyte membrane, 18, 20 Current collector, 26 Anode side housing, 34 Cathode side housing.

Claims (4)

An electrolyte membrane;
An anode catalyst layer and a cathode catalyst layer provided across the electrolyte membrane;
A fuel chamber for storing liquid fuel supplied directly to the anode catalyst layer;
A current collector made of a flat metal sheet in contact with the anode catalyst layer or the cathode catalyst layer and provided with a plurality of pores in a direction substantially perpendicular to the surface direction ;
A fuel cell , wherein a taper is provided on both sides of a pore portion of a current collector, and a vertex of the pore side surface is embedded in an anode catalyst layer or a cathode catalyst layer . The fuel cell according to claim 1, wherein a surface of the current collector is coated with a corrosion-resistant metal . The fuel cell according to claim 1, wherein a plurality of pores provided in the current collector are regularly arranged . 4. The fuel cell according to claim 3, wherein the plurality of pores provided in the current collector have a hexagonal shape, and the current collector has a honeycomb structure .

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