JP2007115510A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell using no catalyst of an MEA to obtain heat by reacting hydrogen and oxygen in starting at low temperature, capable of preventing damage of the MEA, and deterioration of the drainage capacity in a passage even if a catalyst is arranged on the surface of a gas passage of a separator. <P>SOLUTION: (1) In the fuel cell interposing a membrane-electrode assembly between a pair of separators, a water repellent 51 is arranged together with the catalyst 50 on the surface of the gas passage of the separator. (2) In the fuel cell interposing the membrane-electrode assembly between the pair of separators, the catalyst 50 is arranged on the surface of only an oxidation gas passage out of a fuel gas passage and the oxidation gas passage of the separator. (3) The water repellent 51 is arranged together with the catalyst. (4) In the starting at low temperature, the predetermined amount of fuel gas is supplied to the gas passage where the catalyst 50 is arranged in order to warm the fuel cell. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell, and more particularly, to a fuel cell that can help increase the temperature of the cell and prevent the generated water from freezing.

A fuel cell is formed from a MEA sandwiched between separators. A fuel gas channel, an oxidizing gas channel, and a refrigerant channel are formed in the separator. A fuel cell in which a fuel gas is flowed through the fuel gas flow channel and an oxidizing gas is flowed through the oxidizing gas flow channel generates power and generates water.
When starting at low temperatures, the fuel cell is not yet fully warmed up. When water is generated by power generation, the generated water is frozen in the catalyst layer, diffusion layer, and gas flow path, The supply of the reaction gas flowing through the flow path to the catalyst is hindered, and the power generation performance (startability) at low temperatures is impaired.

In order to suppress this, the following method can be considered.
(B) It is conceivable to obtain heat by supplying hydrogen to the cathode at the time of starting at low temperature and reacting hydrogen and oxygen in the catalyst layer of the membrane-electrode assembly (MEA).
(B) As disclosed in JP 2001-338653 A, in order to prevent catalyst (Pt) poisoning by CO (carbon monoxide), for the purpose of reducing CO contained in the reformed fuel, A method in which a catalyst is supported on the gas flow path surface of the separator, CO contained in the reformed fuel is adsorbed on the catalyst, and a small amount of air is added at regular time intervals to oxidize and remove the adsorbed CO. Since heat is generated when oxidizing the adsorbed CO, it is used to prevent freezing.
JP 2001-338653 A

However, the methods (a) and (b) have the following problems.
In the method (a), since the heat capacity of the MEA is smaller than the heat capacity of the separator and the fuel cell cooling water, the MEA is selectively heated abnormally before the separator and the cooling water are heated. The catalyst layer (electrolyte) is deteriorated by heat.
The method (b) has the following problems.
(B-1) When CO is not contained in the fuel gas, for example, when pure hydrogen is used for the fuel gas, it cannot be used.
Since water is generated in the oxidizing gas flow path, even if a catalyst is arranged in the fuel gas flow path to adsorb CO and burn the CO at regular time intervals, the generated water in the oxidizing gas flow path Does not work directly to prevent freezing.
Also, since CO is not burned during CO adsorption, it does not contribute to the temperature increase of the fuel cell at low temperature start unless there is a sufficient amount of CO adsorption at low temperature start.
(B-2) Further, if a catalyst is disposed on the gas flow path surface of the separator, the drainage performance of the flow path deteriorates, the frequency of flooding increases, and the flooding reduces the supply of reaction gas to the electrode. Performance may deteriorate.

The first object of the present invention is to prevent the MEA catalyst from being used to react with hydrogen and oxygen at low temperature start to obtain heat, so that the MEA can be prevented from being damaged, and the separator has a gas channel surface. An object of the present invention is to provide a fuel cell that does not deteriorate the drainage performance of the flow path even if a catalyst is disposed. --- Solving the problems (b) and (b-2) above.
The second object of the present invention is to avoid the use of an MEA catalyst to obtain heat by reacting hydrogen and oxygen at a low temperature start-up, and it is possible to raise the temperature even in a fuel cell using a fuel gas not containing CO. An object of the present invention is to provide a fuel cell that can directly heat a gas flow path and that can raise the temperature of the fuel cell during cold start. --- Solving the above problems (a) and (b-1).
In addition to the second object, a third object of the present invention is to provide a fuel cell that does not deteriorate the drainage of the flow channel even if a catalyst is disposed on the surface of the gas flow channel of the separator. --- Solving the problems (b), (b-1) and (b-2) above.

The present invention for solving the above problems and achieving the above object is as follows.
(1) A fuel cell in which a membrane-electrode assembly is sandwiched between a pair of separators, wherein a water repellent is provided together with a catalyst on the surface of a gas flow path of the separator.
(2) A fuel cell in which a membrane-electrode assembly is sandwiched between a pair of separators, wherein a catalyst is provided on the surface of only the oxidizing gas channel among the fuel gas channel and the oxidizing gas channel of the separator.
(3) The fuel cell according to (2), wherein a water repellent is provided together with the catalyst.
(4) In order to warm up the fuel cell in the gas flow path provided with the catalyst at a low temperature start, when the gas flow path is a fuel gas flow path, a predetermined amount of oxidizing gas is supplied to the gas flow path. The fuel cell according to any one of (1) and (3), wherein a predetermined amount of fuel gas is supplied when is an oxidizing gas flow path.

According to the fuel cell of the above (1), since the water repellent is provided together with the catalyst on the surface of the gas flow path of the separator, hydrogen and oxygen are allowed to react with the catalyst on the surface of the separator without using the MEA catalyst. Heat can be obtained and damage to the MEA can be prevented.
Further, since the separator catalyst is provided with a water repellent agent together with the catalyst, even if the catalyst is disposed on the gas channel surface of the separator, the drainage property of the channel is not deteriorated.
According to the fuel cell of the above (2), since the catalyst is provided only on the surface of the oxidant gas channel among the fuel gas channel and the oxidant gas channel of the separator, the surface of the separator is not dependent on the MEA catalyst. Heat can be obtained by reacting hydrogen and oxygen with a catalyst, and the MEA can be prevented from being damaged.
In addition, since the catalyst is provided only on the surface of the oxidizing gas flow path, the temperature of the fuel cell using a fuel gas not containing CO can be raised, and the oxidizing gas flow path can be directly heated, so that the temperature of the fuel cell can be raised during low-temperature startup. .
According to the fuel cell of the above (3), since the separator catalyst is provided with the water repellent together with the catalyst, even if the catalyst is disposed on the gas channel surface of the separator, the drainage property of the channel is not deteriorated.
According to the fuel cell of the above (4), in order to warm up the fuel cell at a low temperature start, a predetermined amount of the gas flow path provided with the catalyst is provided when the gas flow path is a fuel gas flow path. Since a predetermined amount of fuel gas is supplied when the gas channel is an oxidizing gas channel, the temperature of the fuel cell can be raised during the period during which the gas is supplied.

Hereinafter, the fuel cell of the present invention will be described with reference to FIGS.
3 to 5 are commonly applicable to all the embodiments of the present invention, FIG. 1 shows a first embodiment of the present invention, and FIG. 2 shows a second embodiment of the present invention.
Components common to all the embodiments of the present invention are denoted by the same reference numerals throughout the embodiments of the present invention.

First, the configuration, operation, and effects of portions common to all the embodiments of the present invention will be described with reference to FIGS. 1 and 3 to 5.
The fuel cell to which the present invention is applied is, for example, a solid polymer electrolyte fuel cell 10. The fuel cell 10 is mounted on, for example, a fuel cell vehicle. However, it may be used other than an automobile.
As shown in FIGS. 3 to 5, the solid polymer electrolyte fuel cell (cell) 10 is formed by stacking a membrane-electrode assembly (MEA) 19 and a separator 18.
The membrane-electrode assembly 19 includes an electrolyte membrane 11 made of an ion exchange membrane, an electrode (anode, fuel electrode) 14 made of a catalyst layer disposed on one surface of the electrolyte membrane 11, and a catalyst layer disposed on the other surface of the electrolyte membrane. Electrode (cathode, air electrode) 17. Between the membrane-electrode assembly and the separator 18, diffusion layers 13 and 16 may be provided on the anode side and the cathode side, respectively. A structure in which the anode side diffusion layer 13, the membrane-electrode assembly 19, and the cathode side diffusion layer 16 are sequentially laminated constitutes a membrane-electrode-diffusion layer assembly.
A cell 10 is formed by stacking a membrane-electrode assembly 19 (which may be a membrane-electrode-diffusion layer assembly, hereinafter the same) and a separator 18 to form a cell stack by stacking the cells 10, and a cell stacking direction of the cell stack Terminals 20, insulators 21, and end plates 22 are arranged at both ends, and end plates 22 at both ends are attached to fastening members (for example, tension plates 24) extending in the cell stacking direction outside the cell stack by bolts and nuts 25. The fuel cell stack 23 is configured by fixing and applying a clamping force in the cell stacking direction to the cell stack.

  The separator 18 is formed with a fuel gas flow path 27 for supplying fuel gas (hydrogen) to the anode 14 on the surface facing the MEA 19 in the power generation region. In the region, an oxidizing gas passage 28 for supplying an oxidizing gas (oxygen, usually air) to the cathode 17 is formed on the surface facing the MEA 19. The separator 18 is also formed with a refrigerant flow path 26 for flowing a refrigerant (usually cooling water) on the surface opposite to the surface facing the MEA 19. In the separator 18, a fuel gas manifold 30, an oxidizing gas manifold 31, and a refrigerant manifold 29 are formed in a non-power generation region around the power generation region. The fuel gas manifold 30 is in communication with the fuel gas passage 27, the oxidizing gas manifold 31 is in communication with the oxidizing gas passage 28, and the refrigerant manifold 29 is in communication with the refrigerant passage 26.

An ionization reaction that converts hydrogen into hydrogen ions (protons) and electrons is performed on the anode 14 side of each cell 10, and the hydrogen ions move through the electrolyte membrane 11 to the cathode 17 side. Water is generated from ions and electrons (electrons generated at the anode of the adjacent MEA come through the separator, or electrons generated at the anode of the cell at one end in the cell stacking direction come to the cathode of the other end cell through an external circuit), Power generation is performed according to the following formula.
Anode side: H ₂ → 2H ⁺ + 2e ⁻
Cathode side: 2H ⁺ + 2e ⁻ + (1/2) O ₂ → H ₂ O

Various fluids are sealed from each other and from the outside. Between the two separators 18 that sandwich the MEA of each cell 10 and between the MEA 19 and the separator 18 are sealed by a first seal member 32, and between adjacent cells 10 is sealed by a second seal member 33. ing.
The first seal member 32 is made of, for example, an adhesive (seal adhesive), and the second seal member 33 is made of, for example, a gasket such as silicone rubber, fluorine rubber, or EPDM (ethylene propylene diene rubber). However, both the first seal member 32 and the second seal member 33 may be made of an adhesive or a gasket.

  The separator 18 is composed of a carbon separator, a metal separator, a combination of a metal separator and a resin frame, a conductive resin separator, or the like. In the case of the metal separator 18, the material of the metal separator 18 is, for example, stainless steel, aluminum or an alloy thereof, titanium or an alloy thereof, magnesium or an alloy thereof, and the like. The metal separator 18 is subjected to surface treatment (conductive treatment for reducing contact resistance, for example, precious metal coating), and an anticorrosion material is applied and an anticorrosion material layer (unsaturated polyester, silicone rubber, fluororubber, EPDM (ethylene propylene diene rubber)) Etc.) are formed. A catalyst 50 and a water repellent 51, which will be described later, are disposed further on the anticorrosive layer.

  As shown in FIG. 1, in a fuel cell 10 in which a membrane-electrode assembly 19 (which may be a membrane-electrode-diffusion layer assembly) is sandwiched between a pair of separators 18 (fuel gas side separator, oxidizing gas side separator) A catalyst 50 (for example, a noble metal catalyst, a surface of the gas channel (at least one of the oxidizing gas channel 28 and the fuel gas channel 27) of the separator 18 is preferably removed). For example, a water repellent 51 (for example, polytetrafluoroethylene or the like) is provided together with Pt or the like. It is desirable that the water repellent 51 does not cover the entire surface of the catalyst 50 with the water repellent 51 so that at least a part of the surface of the catalyst 50 is in contact with the reaction gas flowing in the gas flow path. .

Of the fuel gas channel 27 and the oxidizing gas channel 28 of the separator 18, a catalyst 50 (for example, a noble metal catalyst such as Pt) is provided on the surface 52 (desirably excluding the top surface 53 of the rib) of only one gas channel. ) May be provided. For example, the catalyst 50 is provided on the surface 52 (desirably excluding the top surface 53 of the rib) of only the oxidant gas channel 28 in which the generated water is generated out of the fuel gas channel 27 and the oxidant gas channel 28 of the separator 18. It may be.
Further, when the catalyst 50 is provided only in one of the fuel gas channel 27 and the oxidizing gas channel 28 of the separator 18, the water repellent 51 may be provided together with the catalyst 50. However, without providing the water repellent 51, only the catalyst 50 (the adhesive 54 for attaching the catalyst 50 to the separator surface may be included) may be provided. When the water repellent 51 is provided, the entire surface of the catalyst 50 is not covered with the water repellent 51 so that at least a part of the surface of the catalyst 50 is in contact with the reaction gas flowing through the gas flow path. Is desirable.

  When the gas flow path is the fuel gas flow path 27 in order to warm up the fuel cell in the gas flow path provided with the catalyst 50 at the low temperature start time (starting temperature at which the generated water is frozen). A fixed amount of oxidizing gas is supplied, and when the gas channel is the oxidizing gas channel 28, a predetermined amount of fuel gas is supplied. Here, the predetermined amount means an amount (small amount) at which the fuel cell can be warmed up without causing rapid combustion and causing slow chemical combustion without damaging the membrane 11. Then, when the warm-up is completed, the supply of the reaction gas for warm-up at the time of cold start is stopped.

Further, in addition to the warm-up described above or independently of the warm-up described above, the end cell (one cell at the end) of the cell stack 23 is selectively selected or the end cell and the end cell at the time of cold start. In the vicinity of the cell (2 to 3 cells including the end cells), the temperature is raised by utilizing proton recombination at the cathode due to lack of oxygen (a phenomenon in which H ₂ moves to the cathode). May be.

Next, operations and effects common to all the embodiments will be described.
When the water repellent 51 is provided together with the catalyst 50 on the surfaces of the gas flow paths 27 and 28 of the separator 18, heat is generated by reacting hydrogen and oxygen with the catalyst 50 on the surface of the separator 18, not depending on the catalyst of the MEA 19. Can be obtained, and the MEA 19 can be prevented from being damaged. If heat is obtained by using the MEA catalyst, the film 11 may be damaged by the heat. However, in the present invention, the catalyst 50 on the surface of the separator 18 is used, so that the possibility of damaging the film 11 is eliminated. , Greatly reduced.
In addition, since the catalyst 50 of the separator 18 is provided with the water repellent 51 together with the catalyst 50, the surfaces of the gas flow paths 27 and 28 repel water even when the catalyst 50 is disposed on the surface of the gas flow path of the separator 18. Since the stagnation of water is eliminated, the drainage performance of the gas flow paths 27 and 28 does not deteriorate.

When the catalyst 50 is provided on the surface of only the oxidizing gas channel 28 of the fuel gas channel 27 and the oxidizing gas channel 28 of the separator 18, the surface of the separator 18 is not dependent on the catalyst of the MEA 19 as described above. The catalyst 50 can react hydrogen and oxygen to obtain heat, and can prevent the MEA 19 from being damaged during warm-up.
In addition, since the catalyst 50 is provided only on the surface of the oxidizing gas flow path 28, the temperature of the fuel cell using a fuel gas not containing CO can be increased, and the oxidizing gas flow path 28 can be directly heated. 10 can be heated.

  When the catalyst 50 is provided on the surface of only the oxidizing gas channel 28 of the fuel gas channel 27 and the oxidizing gas channel 28 of the separator 18, and the water repellent 51 is provided together with the catalyst 50 on the catalyst 50 of the separator 18. Even if the catalyst 50 is disposed on the surface of the gas flow path 28 of the separator 18, the drainage performance of the flow path 28 is not deteriorated.

  At the time of cold start (only), in order to warm up the fuel cell 10, when the gas flow path is a fuel gas flow path, a predetermined amount of oxidizing gas is added to the gas flow path provided with the catalyst 50. In the case of the oxidizing gas flow path, since a predetermined amount of fuel gas is supplied, the temperature of the fuel cell can be raised during the period of supplying the gas. Since a predetermined amount of gas is supplied, the oxidation reaction of hydrogen is slow and does not damage the cell. After warm-up, the supply of counter gas for warm-up is stopped.

Next, configurations, operations, and effects unique to each embodiment of the present invention will be described.
[Example 1] --- FIG.
In Example 1 of the present invention, only the catalyst 50 (however, the catalyst 50 is used as the separator) in at least one of the fuel gas channel 27 and the oxidizing gas channel 28 (for example, the oxidizing gas channel 28) of the separator 18. 18 may be provided). The water repellent 51 is not provided.
With respect to its action and effect, since the catalyst 50 is not covered with the water repellent 51, the function of the catalyst 50 can be fully exhibited. However, the water repellency may be lower than when the water repellent 51 is provided.

[Example 2] --- FIG.
In the second embodiment of the present invention, at least one of the fuel gas channel 27 and the oxidizing gas channel 28 of the separator 18 (for example, the oxidizing gas channel 28, but only the fuel gas channel 27 may be provided. ), Both the catalyst 50 and the water repellent 51 are provided.
With respect to its function and effect, since the water repellent 51 is provided, the water repellency of the gas flow path is improved and flooding can be suppressed. However, since a part of the catalyst 50 is covered with the water repellent 51, the function of the catalyst 50 may be slightly deteriorated.

It is sectional drawing of a part of gas flow path of the separator of the fuel cell of Example 1 of this invention. It is sectional drawing of a part of gas flow path of the separator of the fuel cell of Example 2 of this invention. It is a side view of the fuel cell stack incorporating the fuel cell of the present invention. FIG. 4 is an enlarged sectional view of a part of FIG. 3. FIG. 4 is a front view of the cell of FIG. 3.

Explanation of symbols

10 (Solid Polymer Electrolyte Type) Fuel Cell 11 Electrolyte Membranes 13 and 16 Diffusion Layer 14 Anode 17 Cathode 18 Separator 19 MEA
20 Terminal 21 Insulator 22 End plate 23 Fuel cell stack 24 Fastening member (tension plate)
25 Bolt 26 Refrigerant flow path (cooling water flow path)
27 Fuel gas channel 28 Oxidizing gas channel 29 Refrigerant manifold 30 Fuel gas manifold 31 Oxidizing gas manifold 32 First seal member 33 Second seal member 50 Catalyst 51 Water repellent 52 Gas channel (oxidant gas channel and fuel Surface 53 of at least one flow path with gas flow path) top surface 54 of rib

Claims (4)

  A fuel cell in which a membrane-electrode assembly is sandwiched between a pair of separators, wherein a water repellent is provided along with a catalyst on the surface of a gas flow path of the separator.   A fuel cell in which a membrane-electrode assembly is sandwiched between a pair of separators, wherein a catalyst is provided on the surface of only the oxidizing gas channel of the fuel gas channel and the oxidizing gas channel of the separator.   The fuel cell according to claim 2, wherein a water repellent is provided together with the catalyst.   In order to warm up the fuel cell in the gas flow path provided with the catalyst at a low temperature start, a predetermined amount of fuel gas is supplied when the gas flow path is an oxidizing gas flow path, and the gas flow path is a fuel gas. The fuel cell according to any one of claims 1 to 3, wherein a predetermined amount of oxidizing gas is supplied in the case of a flow path.

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