JP2016072133A - Fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell arranged so that a liquid fuel can be supplied to a cathode catalyst layer efficiently, which enables the increase in power generation efficiency.SOLUTION: A fuel cell 3 comprises: an electrolyte membrane 64; an anode electrode 65 supplied with a liquid fuel; a cathode electrode 66 supplied with oxygen; and an anode-side diffusion layer 67 disposed to face the anode electrode 65 and having pores 90. The pores 90 are formed so that the size thereof becomes larger from its lower side upward. The liquid fuel is supplied to the anode electrode 65 from its lower side upward.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a fuel cell mounted on a vehicle or the like, and particularly to a fuel cell including a gas diffusion layer.

  Conventionally, as a fuel cell, a solid polymer fuel cell is known in which an anode to which liquid fuel is supplied and a cathode to which air is supplied face each other with an electrolyte membrane made of a solid polymer membrane interposed therebetween. Yes.

  Further, as an electrode and an electrolyte membrane employed in a fuel cell, an electrolyte membrane, an anode electrode (fuel side catalyst layer) joined to one surface of the electrolyte membrane, and a cathode electrode (air) joined to the other surface of the electrolyte membrane A membrane electrode assembly (MEA) including a side catalyst layer) is known.

  For example, a membrane-electrode assembly, an anode-side GDL integrated seal laminated on one side of the membrane-electrode assembly, and a cathode-side GDL integrated seal laminated on the other side of the membrane-electrode assembly A fuel cell is proposed in which the anode-side GDL integrated seal includes an anode-side diffusion layer made of a gas-permeable material, and the cathode-side GDL integrated seal includes a cathode-side diffusion layer made of a gas-permeable material ( For example, see Patent Document 1.)

JP2013-51036A

  However, in the fuel cell described in Patent Document 1, air is supplied to the cathode via the cathode side diffusion layer, and liquid fuel is supplied to the anode via the anode side diffusion layer. Thereby, at the cathode, oxygen and water react to generate hydroxide ions. Then, the hydroxide ions pass through the membrane-electrode assembly and react with the liquid fuel at the anode to generate an electromotive force.

  Here, in the anode, gas is generated by the reaction between the hydroxide ions and the liquid fuel. Therefore, the liquid fuel supplied to the anode has more gas in the supply direction downstream of the liquid fuel than in the supply direction upstream. included. Therefore, the amount of liquid fuel supplied to the anode is relatively small downstream in the liquid fuel supply direction and relatively large upstream in the supply direction.

  Moreover, the liquid fuel supplied to the anode may permeate the electrolyte membrane without reacting at the anode and leak to the cathode. The amount of liquid fuel leaking to the cathode is relatively small when the amount of gas contained in the liquid fuel is large, and relatively large when the amount of gas contained in the liquid fuel is small. For this reason, the amount of liquid fuel leaking to the cathode is such that a relatively large amount of liquid fuel leaks to the cathode upstream in the liquid fuel supply direction.

  As a result, there is a problem in that the amount of liquid fuel supplied to the anode further decreases downstream in the liquid fuel supply direction, and power generation efficiency decreases.

  Therefore, an object of the present invention is to provide a fuel cell that can efficiently supply liquid fuel to the anode catalyst layer and can improve power generation efficiency.

  The fuel cell of the present invention is disposed on one surface in the thickness direction of the electrolyte layer, the electrolyte layer, an anode catalyst layer to which liquid fuel is supplied, and disposed on the other surface in the thickness direction of the electrolyte layer. A cathode catalyst layer to be supplied; and at least one of the anode catalyst layer and the cathode catalyst layer and a gas diffusion layer having a plurality of pores arranged to face the thickness direction, the anode catalyst layer comprising: The liquid fuel is configured to be supplied from one of the orthogonal directions orthogonal to the thickness direction to the other, and the size of the plurality of pores increases from one to the other in the orthogonal direction. It is characterized by.

  Moreover, it is preferable that the size of the plurality of pores is continuously increased from one to the other in the orthogonal direction.

  The gas diffusion layer is preferably disposed on one side of the anode catalyst layer in the thickness direction.

  In the fuel cell of the present invention, liquid fuel is supplied to the anode catalyst layer from one side in the orthogonal direction to the other side. Therefore, the size of the plurality of pores increases from the upstream to the downstream in the liquid fuel supply direction. That is, the size of the plurality of pores is relatively small upstream in the liquid fuel supply direction and relatively large downstream in the liquid fuel supply direction.

  When such a gas diffusion layer having a plurality of pores is disposed so as to face the anode catalyst layer, the liquid fuel passes through the plurality of pores and is supplied to the anode catalyst layer. Here, among the plurality of pores, the size of the pores upstream in the liquid fuel supply direction is relatively small, so that the liquid fuel is excessively supplied to the anode catalyst layer upstream in the liquid fuel supply direction. And the leakage of the liquid fuel to the cathode catalyst layer can be suppressed.

  On the other hand, among the plurality of pores, the size of the pores downstream in the liquid fuel supply direction is relatively large, so even if the gas contained in the liquid fuel increases downstream in the liquid fuel supply direction, the liquid The fuel can be efficiently supplied to the anode catalyst layer.

  Further, when the gas diffusion layer having a plurality of pores is disposed so as to face the cathode catalyst layer, air passes through the plurality of pores and is supplied to the cathode catalyst layer. Here, among the plurality of pores, the size of the pores upstream in the liquid fuel supply direction is relatively small. For example, even if the liquid fuel leaks into the cathode catalyst layer, the liquid fuel passes through the pores. Thus, it is possible to suppress discharge from the gas diffusion layer facing the cathode catalyst layer. As a result, the gas diffusion layer facing the cathode catalyst layer traps liquid fuel containing moisture and improves power generation efficiency.

  By these, the power generation efficiency can be improved.

FIG. 1 is a schematic configuration diagram of an electric vehicle equipped with an embodiment of a fuel cell of the present invention. FIG. 2 is a schematic configuration diagram showing a cell of the fuel cell shown in FIG. 3A is a schematic view showing a processed sheet for producing the cathode side diffusion layer and the anode side diffusion layer shown in FIG. FIG. 3B is a schematic diagram showing the cathode side diffusion layer and the anode side diffusion layer shown in FIG. 2. FIG. 4 is a schematic view showing a modification of the cathode side diffusion layer and the anode side diffusion layer according to the present invention.

1. Overall Configuration of Electric Vehicle As shown in FIG. 1, the electric vehicle 1 is a hybrid vehicle that selectively uses a fuel cell 3 and a battery 53 as power sources, and is equipped with a fuel cell system 2.

The fuel cell system 2 includes a fuel cell 3, a fuel supply / exhaust unit 4, an air supply / exhaust unit 5, a control unit 6, and a power unit 7.
(1) Fuel Cell The fuel cell 3 is a direct liquid fuel type fuel cell to which liquid fuel is directly supplied, and is disposed on the lower center side of the electric vehicle 1.
(2) Fuel Supply / Discharge Unit The fuel supply / discharge unit 4 is disposed on the rear side of the fuel cell 3 in the electric vehicle 1. The fuel supply / discharge unit 4 includes a fuel tank 21, a fuel supply line 23, a fuel recirculation line 24, and an exhaust line 25.

  The fuel tank 21 is disposed on the rear side of the fuel cell 3 with an interval. The fuel tank 21 has a substantially box shape and is configured to store liquid fuel containing a fuel component.

  Examples of the fuel component include hydrogen-containing liquid fuels containing hydrogen atoms in the molecule, and specific examples include alcohols such as methanol, ethers having an alkyl group such as dimethyl ether, and hydrazines. Preferably, alcohols and hydrazines are used, and more preferably, hydrazines are used.

Examples of hydrazines include hydrazine (NH ₂ NH ₂ ), hydrated hydrazine (NH ₂ NH ₂ .H ₂ O), hydrazine carbonate ((NH ₂ NH ₂ ) ₂ CO ₂ ), and hydrazine hydrochloride (NH ₂ NH _2). HCl), hydrazine sulfate (NH ₂ NH ₂ .H ₂ SO ₄ ), monomethyl hydrazine (CH ₃ NHNH ₂ ), dimethyl hydrazine ((CH ₃ ) ₂ NNH ₂ , CH ₃ NHNHCH ₃ ), carboxylic hydrazide ((NHNH ₂ ) ₂ CO).

Among such hydrazines, preferably, hydrazines containing no carbon, that is, hydrazine, hydrated hydrazine, hydrazine sulfate, and the like. Hydrazine, hydrated hydrazine, hydrazine sulfate, etc. do not generate CO and CO ₂ and do not cause poisoning of the catalyst. Therefore, durability can be improved and substantially zero emission can be realized. it can.

  Such fuel components can be used alone or in combination of two or more.

  The fuel supply line 23 is a pipe for supplying liquid fuel from the fuel tank 21 to the fuel cell 3. The supply direction upstream end of the fuel supply line 23 is connected to the lower end of the fuel tank 21. A downstream end of the fuel supply line 23 in the supply direction is connected to a fuel supply port 82 (see FIG. 2 described later) of the fuel cell 3. The fuel supply line 23 includes a first pump 26.

  The first pump 26 is interposed in the middle of the fuel supply line 23. Examples of the first pump 26 include known liquid feed pumps such as rotary pumps such as rotary pumps and gear pumps, and reciprocating pumps such as piston pumps and diaphragm pumps. The first pump 26 is driven to supply the liquid fuel in the fuel tank 21 to the fuel cell 3.

  The fuel return line 24 is a pipe for returning liquid fuel from the fuel cell 3 to the fuel tank 21. The upstream end of the fuel recirculation line 24 in the recirculation direction is connected to a fuel discharge port 83 (see FIG. 2 described later) of the fuel cell 3. The downstream end of the fuel return line 24 in the return direction is connected to the upper end of the fuel tank 21. The fuel return line 24 includes a gas-liquid separator 27.

  The gas-liquid separator 27 is interposed in the middle of the fuel recirculation line 24. The gas-liquid separator 27 separates liquid fuel and gas (gas).

The exhaust line 25 is a pipe for exhausting the gas separated by the gas-liquid separator 27 from the electric vehicle 1 to the outside. The upstream end of the exhaust line 25 in the exhaust direction is connected to the gas-liquid separator 27. The downstream end of the exhaust line 25 in the exhaust direction is open to the atmosphere. In the middle of the exhaust line 25, a purification device (not shown) for detoxifying and debromating the gas is interposed.
(3) Air Supply / Exhaust Unit The air supply / exhaust unit 5 is disposed on the front side of the fuel cell 3 in the electric vehicle 1. The air supply / discharge part 5 includes an air supply line 41 and an air discharge line 42.

  The air supply line 41 is a pipe for supplying air from the outside of the electric vehicle 1 to the fuel cell 3. The upstream end of the air supply line 41 in the supply direction is open to the atmosphere. The downstream end of the air supply line 41 in the supply direction is connected to an air supply port 85 (described later, see FIG. 2) of the fuel cell 3. The air supply line 41 includes a second pump 43.

  The second pump 43 is interposed in the air supply line 41. Examples of the second pump 43 include a known air supply pump such as an air compressor. The second pump 43 supplies air from the outside of the electric vehicle 1 to the fuel cell 3 by driving. In the middle of the air supply line 41, a humidifier (not shown) for humidifying the air passing through the air supply line 41 is connected (intervened).

The air discharge line 42 is a pipe for discharging air from the fuel cell 3 to the outside of the electric vehicle 1. The upstream end of the air discharge line 42 in the discharge direction is connected to an air discharge port 86 (see FIG. 2 described later) of the fuel cell 3. The downstream end of the air discharge line 42 in the discharge direction is open to the atmosphere.
(4) Control Unit The control unit 6 includes an ECU 51.

  The ECU 51 is a control unit (i.e., Electronic Control Unit) that executes electrical control in the electric vehicle 1, and includes a microcomputer including a CPU, a ROM, a RAM, and the like.

The ECU 51 is electrically connected to each of the first pump 26 and the second pump 43.
(5) Power unit The power unit 7 is disposed in a so-called engine room at the front end of the electric vehicle 1. The power unit 7 includes a motor 52 and a battery 53.

  The motor 52 is electrically connected to the fuel cell 3. The motor 52 converts electrical energy output from the fuel cell 3 into mechanical energy as the driving force of the electric vehicle 1. Examples of the motor 52 include known three-phase motors such as a three-phase induction motor and a three-phase synchronous motor.

  The battery 53 is electrically connected to the wiring between the fuel cell 3 and the motor 52. Examples of the battery 53 include a known secondary battery such as a nickel metal hydride battery or a lithium ion battery.

2. As shown in FIG. 2, the fuel cell 3 includes a membrane / electrode assembly 61, a fuel supply member 62 disposed on one side (anode side) of the membrane / electrode assembly 61, and a membrane / electrode assembly. An air supply member 63 disposed on the other side (cathode side) of 61, and an anode side diffusion layer 67 as an example of a gas diffusion layer disposed between the membrane-electrode assembly 61 and the fuel supply member 62; A stack structure in which a plurality of fuel cells (unit cells) having a cathode side diffusion layer 68 as an example of a gas diffusion layer disposed between the membrane / electrode assembly 61 and the air supply member 63 are stacked. (See FIG. 1). In FIG. 2, only one of the plurality of unit cells is represented as the fuel cell 3, and the other unit cells are omitted.

  The membrane / electrode assembly 61 includes an electrolyte membrane 64 as an example of an electrolyte layer, an anode electrode 65 as an example of an anode catalyst layer disposed on one surface in the thickness direction of the electrolyte membrane 64, and a thickness direction of the electrolyte membrane 64. The cathode electrode 66 is provided as an example of the cathode catalyst layer disposed on the other surface.

  In the following description, the thickness direction of the electrolyte membrane 64 (the left-right direction in FIG. 2) is simply the thickness direction, and the direction orthogonal to both the thickness direction and the up-down direction is the width direction. Moreover, the up-down direction is an example of the orthogonal direction, the lower side is an example of the orthogonal direction, and the upper side is an example of the other side of the orthogonal direction.

  The electrolyte membrane 64 is formed of an anion exchange type or cation exchange type polymer electrolyte membrane.

  The thickness of the electrolyte membrane 64 is, for example, 5 μm or more, preferably 10 μm or more, for example, 50 μm or less, preferably 35 μm or less.

  The anode electrode 65 is formed of, for example, a catalyst carrier that supports a catalyst. Further, the catalyst may be directly formed as the anode electrode 65 without using the catalyst carrier.

  The thickness of the anode electrode 65 is, for example, 10 μm or more, preferably 20 μm or more, for example, 200 μm or less, preferably 100 μm or less.

  The cathode electrode 66 is formed of, for example, a catalyst carrier that supports a catalyst, similarly to the anode electrode 65.

  In the cathode electrode 66, for example, a transition metal is supported on a complex formed of a complex-forming organic compound and / or a conductive polymer and carbon (hereinafter, this complex is referred to as a “carbon composite”). It may be formed of a material.

  The thickness of the cathode electrode 66 is, for example, 10 μm or more, preferably 20 μm or more, for example, 300 μm or less, preferably 150 μm or less.

  The anode side diffusion layer 67 is laminated (arranged) on one side with respect to the anode electrode 65, and is arranged so as to face the anode electrode 65 from one side in the thickness direction.

  The cathode side diffusion layer 68 is laminated (arranged) on the other side with respect to the cathode electrode 66, and is arranged so as to face the cathode electrode 66 from the other side in the thickness direction.

  The fuel supply member 62 is made of a gas impermeable conductive member and supplies liquid fuel to the anode electrode 65. The fuel supply member 62 is formed with, for example, a groove having a concave shape, which is recessed from the surface thereof. The surface of the fuel supply member 62 in which the groove is formed is in opposed contact with the anode electrode 65 through the anode-side diffusion layer 67. As a result, a fuel supply path 81 is formed between the one surface of the anode electrode 65 and the other surface of the fuel supply member 62 (the surface on which the groove is formed) for bringing the fuel component into contact with the entire anode electrode 65. The

  In the fuel supply path 81, a fuel supply port 82 for allowing the fuel component to flow into the fuel supply member 62 is formed at the lower end, and a fuel discharge port 83 for discharging the fuel component from the fuel supply member 62 is provided at the upper end. Is formed.

  The air supply member 63 is made of a gas impermeable conductive member and supplies air to the cathode electrode 66. The air supply member 63 is formed with a groove that is recessed from the surface thereof, for example, a distorted shape. The air supply member 63 has a grooved surface in contact with the cathode electrode 66 through the cathode side diffusion layer 68. Thus, an air supply path 84 for bringing air into contact with the entire cathode electrode 66 is formed between the other surface of the cathode electrode 66 and one surface of the air supply member 63 (the surface on which the groove is formed). .

In the air supply path 84, an air supply port 85 for allowing air to flow into the air supply member 63 is formed at the upper end portion, and an air discharge port 86 for discharging air from the air supply member 63 is formed at the lower end portion. Has been.
3. As shown in FIG. 3B, each of the anode side diffusion layer 67 and the cathode side diffusion layer 67 and the cathode side diffusion layer 68 has a substantially rectangular shape as viewed from the thickness direction, more specifically, in the vertical direction. It has a substantially rectangular shape that extends.

  Each of the anode side diffusion layer 67 and the cathode side diffusion layer 68 is a gas diffusion layer (GDL) having pores 90 for allowing gas to pass therethrough, and is made of a gas permeable material.

  Examples of the gas permeable material include carbon paper, carbon cloth, and carbon fiber nonwoven fabric. Further, the gas permeable material may be treated with fluorine as necessary. Among such gas permeable materials, carbon paper and carbon cloth are preferable. The carbon paper is prepared by weaving a bundle 91 of carbon fibers.

  For example, when each of the anode side diffusion layer 67 and the cathode side diffusion layer 68 is formed of carbon cloth, the texture of the carbon cloth is configured as a plurality of pores 90.

  The plurality of pores 90 are arranged over the whole of the anode side diffusion layer 67 and the cathode side diffusion layer 68. The shape of each of the plurality of pores 90 is not particularly limited, but when the pores 90 are carbon cloth weaves, the shape is substantially rectangular when viewed from the thickness direction.

  The size of the plurality of pores 90 increases continuously from the bottom to the top.

  That is, the plurality of pores 90 include a plurality of pores 90 having different sizes. More specifically, the smallest pore 90A having the smallest size, the largest pore 90B having the largest size, and the smallest pore 90A having the smallest size. Medium pores 90C that are larger and smaller than the largest pores 90B.

  The minimum pore 90 </ b> A is disposed at the lower end of each of the anode side diffusion layer 67 and the cathode side diffusion layer 68.

  The dimension L1 in the width direction of the minimum pore 90A is, for example, 15 μm or more, preferably 20 μm or more, for example, 30 μm or less, preferably 25 μm or less. The vertical dimension L2 of the minimum pore 90A is, for example, 15 μm or more, preferably 20 μm or more, for example, 30 μm or less, preferably 25 μm or less.

Further, the opening area of the minimum pore 90A is, for example, 5.625 × 10 ⁻⁷ % or more, preferably 1.0 × 10 ⁻⁶ % with respect to the area of the anode side diffusion layer 67 or the cathode side diffusion layer 68. For example, it is 2.25 × 10 ⁻⁶ % or less, preferably 1.56 × 10 ⁻⁶ % or less.

  The maximum pores 90 </ b> B are disposed at the upper ends of the anode side diffusion layer 67 and the cathode side diffusion layer 68.

  The dimension L3 in the width direction of the maximum pore 90B is, for example, 40 μm or more, preferably 45 μm or more, for example, 60 μm or less, preferably 55 μm or less. The vertical dimension L4 of the maximum pore 90B is, for example, 45 μm or more, preferably 50 μm or more, for example, 60 μm or less, preferably 55 μm or less.

Further, the opening area of the maximum pore 90B is, for example, 4.0 × 10 ⁻⁶ % or more, preferably 5.06 × 10 ⁻⁶ % with respect to the area of the anode side diffusion layer 67 or the cathode side diffusion layer 68. For example, it is 9.0 × 10 ⁻⁶ % or less, preferably 7.56 × 10 ⁻⁶ % or less. The opening area of the maximum pore 90B is, for example, 180% or more, preferably 324% or more, for example, 1600% or less, preferably 625% or less with respect to the opening area of the minimum pore 90A.

  The middle pore 90C is disposed between the minimum pore 90A and the maximum pore 90B in each of the anode side diffusion layer 67 and the cathode side diffusion layer 68.

  The dimension L5 in the width direction of the middle pore 90C is, for example, 30 μm or more, preferably 35 μm or more, for example, 45 μm or less, preferably 40 μm or less. The vertical dimension L6 of the middle pore 90C is, for example, 30 μm or more, preferably 35 μm or more, for example, 45 μm or less, preferably 40 μm or less.

Further, the opening area of the medium pore 90C is, for example, 2.25 × 10 ⁻⁶ % or more, preferably 3.06 × 10 ⁻⁶ % with respect to the area of the anode side diffusion layer 67 or the cathode side diffusion layer 68. For example, it is 5.06 × 10 ⁻⁶ % or less, preferably 4.0 × 10 ⁻⁶ % or less. Further, the opening area of the medium pore 90C is, for example, 136% or more, preferably 306.25% or more, for example, 900% or less, preferably 506.25% or less with respect to the opening area of the minimum pore 90A. Yes, for example, 25% or more, preferably 41% or more, for example 81% or less, preferably 64% or less with respect to the opening area of the maximum pore 90B.

  Thus, when the pores 90 are rectangular when viewed from the thickness direction, the average width direction dimension of the plurality of pores 90 is, for example, 20 μm or more, preferably 25 μm or more, for example, 35 μm or less, preferably 30 μm or less. The average vertical dimension of the plurality of pores 90 is, for example, 20 μm or more, preferably 25 μm or more, for example, 35 μm or less, preferably 30 μm or less.

  The total opening area of the plurality of pores 90 is, for example, 50% or more, preferably 60% or more, for example, 80% or less, with respect to the area of the anode side diffusion layer 67 or the cathode side diffusion layer 68. Preferably, it is 70% or less.

  In order to manufacture each of the anode side diffusion layer 67 and the cathode side diffusion layer 68, for example, as shown in FIG. 3A, a processed sheet 92 made of carbon cloth is viewed upward from the thickness direction. Cut into a substantially trapezoidal shape that is narrow.

  The width direction dimension of the lower base X of the processed sheet 92 is, for example, 120% or more, preferably 130% or more, for example, 200% or less, preferably, with respect to the width direction dimension of the upper base Y of the processed sheet 92. 190% or less.

  The vertical dimension of the height Z of the processed sheet 92 is, for example, 50% or more, preferably 60% or more, for example, 100% or less, preferably with respect to the width direction dimension of the lower base X of the processed sheet 92. 90% or less.

  Each of the plurality of pores 90 (texture) of the processed sheet 92 has the same size (dimension).

  Then, both end edges in the width direction of the upper portion of the processed sheet 92 are pulled outward in the width direction so that the processed sheet 92 is substantially rectangular when viewed from the thickness direction.

  Then, the size of the plurality of pores 90 (texture) of the processed sheet 92 is increased so as to gradually increase gradually from the lower side to the upper side.

Thereby, as shown in FIG. 3B, each of the anode side diffusion layer 67 and the cathode side diffusion layer 68 is produced.
4). As shown in FIG. 1, when the first pump 26 operates as shown in FIG. 1, liquid fuel is supplied from the fuel supply port 82 to the fuel supply path 81 as shown in FIG. 2. Then, the liquid fuel passes through the fuel supply path 81 from below to above. At this time, the liquid fuel passes through the plurality of pores 90 of the anode side diffusion layer 67 and is supplied to the anode electrode 65 as shown in FIGS. 2 and 3B. That is, the liquid fuel is supplied to the anode electrode 65 from below to above and comes into contact with the anode electrode 65.

  As shown in FIG. 1, when the second pump 43 is activated, air is supplied from the air supply port 85 to the air supply path 84 as shown in FIG. 2. Then, the air passes through the air supply path 84 from the upper side to the lower side. At this time, air passes through the plurality of pores 90 of the cathode side diffusion layer 68 and is supplied to the cathode electrode 66 as shown in FIGS. 2 and 3B. That is, air is supplied to the cathode electrode 66 from the upper side to the lower side, and comes into contact with the cathode electrode 66.

Then, an electrochemical reaction occurs in each electrode (the anode electrode 65 and the cathode electrode 66), and an electromotive force is generated. For example, when the electrolyte membrane 64 is an anion exchange type solid polymer membrane and the fuel component is hydrazine, the electrochemical reaction is represented by the following formulas (1) to (3).
(1) N ₂ H ₄ + 4OH ⁻ → N ₂ + 4H ₂ O + 4e ⁻ (reaction at the anode electrode 65)
(2) O ₂ + 2H ₂ O + 4e ⁻ → 4OH ⁻ (reaction at the cathode electrode 66)
(3) N ₂ H ₄ + O ₂ → N ₂ + 2H ₂ O (reaction in the entire fuel cell 3)
That is, at the anode electrode 65 supplied with hydrazine, hydrazine (N ₂ H ₄ ) reacts with hydroxide ions (OH ⁻ ) generated by the reaction at the cathode electrode 66 to react with nitrogen (N ₂ ) and water. (H ₂ O) is generated and electrons (e ⁻ ) are generated (see the above formula (1)).

In the cathode electrode 66, electrons (e ⁻ ), water (H ₂ O), and oxygen (O ₂ ) in the air flowing through the air supply path 84 react to generate hydroxide ions (OH ⁻ ). (See the above formula (2)).

The generated hydroxide ions (OH ⁻ ) pass through the electrolyte membrane 64 and reach the anode electrode 65, and the reaction of the above formula (1) occurs.

  Then, when the electrochemical reaction at the anode electrode 65 and the cathode electrode 66 is continuously generated, the reaction represented by the above formula (3) occurs in the fuel cell 3 as a whole, and the electromotive force is generated in the fuel cell 3. Will occur. That is, the fuel cell 3 consumes the fuel component to generate power.

In addition, the above electrochemical reaction is expressed by the following formulas (4) to (6) when the electrolyte membrane 64 is an anion exchange type solid polymer membrane and the liquid fuel is methanol.
(4) CH ₃ OH + 6OH ⁻ → CO ₂ + 5H ₂ O + 6e ⁻ (reaction at the anode electrode 65)
(5) O ₂ + 2H ₂ O + 4e ⁻ → 4OH ⁻ (reaction at the cathode electrode 66)
(6) CH ₃ OH + 3 / 2O ₂ → CO ₂ + 2H ₂ O (reaction in the entire fuel cell 3)
5. Operational Effect In the fuel cell 3, as shown in FIG. 2, the liquid fuel is supplied to the anode electrode 65 from below to above. That is, in each of the anode-side diffusion layer 67 and the cathode-side diffusion layer 68, the size of the plurality of pores 90 increases from upstream to downstream in the liquid fuel supply direction S as shown in FIG. 3B. Therefore, the size of the plurality of pores 90 is relatively small upstream in the liquid fuel supply direction S and relatively large downstream in the liquid fuel supply direction S.

  In the above power generation operation, when the liquid fuel is supplied to the anode-side diffusion layer 67, the liquid fuel passes through the plurality of pores 90 and is supplied to the anode electrode 65 as shown in FIGS. Here, among the plurality of pores 90, the size of the pores 90 upstream of the liquid fuel supply direction S, that is, the lower pores 90 (for example, the minimum pores 90A) is relatively small.

  Thereby, upstream of the liquid fuel supply direction S, liquid fuel can be prevented from being excessively supplied to the anode electrode 65, and liquid fuel can be prevented from leaking to the cathode electrode 66.

  On the other hand, among the plurality of pores 90, the size of the pore 90 downstream in the liquid fuel supply direction S, that is, the upper pore 90 (for example, the maximum pore 90B) is relatively large.

  Therefore, as shown in the above formulas (1) and (4), even if gas is generated by the reaction at the anode electrode 65 and the gas contained in the liquid fuel increases, the liquid fuel is supplied downstream in the supply direction S. The liquid fuel can be supplied to the anode electrode 65 relatively more than upstream in the supply direction S. That is, the liquid fuel can be efficiently supplied to the anode electrode 65.

  In the above power generation operation, when air is supplied to the cathode side diffusion layer 68, the air passes through the plurality of pores 90 and is supplied to the cathode electrode 66. Here, among the plurality of pores 90, the size of the pore 90 upstream in the liquid fuel supply direction S, that is, the lower pore 90 (for example, the minimum pore 90A) is relatively small. Therefore, even if liquid fuel leaks to the cathode electrode 66, it can be suppressed that the liquid fuel is discharged from the cathode side diffusion layer 68 through the lower pore 90. As a result, the cathode side diffusion layer 68 traps the liquid fuel containing moisture. By these, the power generation efficiency can be improved.

  In the above embodiment, as shown in FIG. 3B, each of the plurality of pores 90 is formed in a substantially rectangular shape when viewed from the thickness direction, but the shape of the pores 90 is not particularly limited.

  For example, as shown in FIG. 4, each of the plurality of pores 90 may have a substantially circular shape when viewed from the thickness direction, or may be a polygon when viewed from the thickness direction.

  In the above embodiment, as shown in FIG. 3B, the size of the plurality of pores 90 is configured to increase continuously from the bottom to the top, but as shown in FIG. You may comprise so that it may become large.

  When the size of the plurality of pores 90 increases stepwise, each of the anode-side diffusion layer 67 and the cathode-side diffusion layer 68 includes a first portion 93 in which a plurality of minimum pores 90A are formed and a plurality of maximum pores 90B. A second portion 94 to be formed and a third portion 95 in which a plurality of medium pores 90C are formed are provided.

  The first portion 93 is a lower end portion of each of the anode side diffusion layer 67 and the cathode side diffusion layer 68. The plurality of minimum pores 90A formed in the first portion 93 have the same size.

  The second portion 94 is an upper end portion of each of the anode side diffusion layer 67 and the cathode side diffusion layer 68. The plurality of maximum pores 90B formed in the second portion 94 have the same size and are larger than the minimum pore 90A.

  The third portion 95 is a substantially central portion in the vertical direction of each of the anode side diffusion layer 67 and the cathode side diffusion layer 68 and is a portion between the first portion 93 and the second portion 94. The plurality of medium pores 90C formed in the third portion 95 have the same size, which is larger than the minimum pore 90A and smaller than the maximum pore 90B.

  In order to produce such an anode side diffusion layer 67 and cathode side diffusion layer 68, the first part 93, the second part 94, and the third part 95 are separately prepared and joined together.

  FIG. 4 shows a form in which the size of the plurality of pores 90 increases in three stages from the bottom to the top, but the number of stages is not limited to this.

  In such a modification, each of the anode side diffusion layer 67 and the cathode side diffusion layer 68 has a joint. In order to inhibit the diffusion of liquid fuel and air, such a joint is more preferable in the above-described embodiment than in this modification.

  In the above embodiment, each of the anode side diffusion layer 67 and the cathode side diffusion layer 68 has the plurality of pores 90 that increase in size from the bottom to the top. However, the present invention is not limited to this. Only the plurality of pores 90 included in the diffusion layer 67 may be increased in size from the lower side toward the upper side, and only the plurality of pores 90 included in the cathode side diffusion layer 68 may be increased in size from the lower side toward the upper side. It may be made larger.

  Although not shown, the cathode side diffusion layer 68 may include a microporous layer disposed between the cathode electrode 66 and the cathode side diffusion layer 68.

  Also according to these modified examples, the same effects as those of the above embodiment can be obtained.

  Moreover, the said embodiment and modification can be combined suitably.

3 Fuel Cell 64 Electrolyte Membrane 65 Anode Electrode 66 Cathode Electrode 67 Anode Side Diffusion Layer 68 Cathode Side Diffusion Layer 90 Multiple Porosities

Claims (3)

An electrolyte layer;
An anode catalyst layer disposed on one surface in the thickness direction of the electrolyte layer and supplied with liquid fuel;
A cathode catalyst layer disposed on the other surface in the thickness direction of the electrolyte layer and supplied with oxygen;
A gas diffusion layer that is disposed so as to face at least one of the anode catalyst layer and the cathode catalyst layer in the thickness direction and has a plurality of pores;
The anode catalyst layer is configured so that liquid fuel is supplied from one of the orthogonal directions orthogonal to the thickness direction toward the other,
The fuel cell according to claim 1, wherein the size of the plurality of pores increases from one to the other in the orthogonal direction.   2. The fuel cell according to claim 1, wherein the size of the plurality of pores continuously increases from one to the other in the orthogonal direction.   The fuel cell according to claim 1, wherein the gas diffusion layer is disposed on one side of the anode catalyst layer in the thickness direction.

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