JP3693021B2 - Fuel cell - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a structure of a fuel cell, particularly a polymer electrolyte fuel cell.
[0002]
[Prior art]
In order to reuse the water discharged from the fuel cell for humidification of the cell, there is a device in which a degreasing device is provided outside the fuel cell to remove the impurities of the water discharged from the fuel cell (Japanese Patent Laid-Open No. 2000). -3317033).
[0003]
[Problems to be solved by the invention]
By the way, in the polymer electrolyte fuel cell, since the electrolyte membrane is acidic, the gas diffusion layer (electrode) and the separator in which the gas flow path to the gas diffusion layer is formed (perforated) has acid resistance. Must be. In addition, water is generated on the cathode side as shown in formula (2) described later, and generally the cathode side (gas supplied to the fuel cell, not limited to the cathode) is humidified from the outside during the operation of the fuel cell. For this reason, the gas diffusion layer and the separator must have hydrolysis resistance so as not to react with water in a high temperature environment, and must also have heat resistance that can withstand the power generation temperature. In order to satisfy these three main requirements, after processing various metals to form a gas flow path, the surface is plated with noble metals such as gold or coated with a special paint. I was making it.
[0004]
However, since the cost of manufacturing a separator using such a metal increases, in recent years, the above-mentioned acid resistance and water resistance can be reduced at low cost by obtaining a separator by press molding a material mainly composed of graphite powder and resin. Separators having decomposability and heat resistance functionalities have appeared.
[0005]
When power is actually generated using a separator obtained by molding a material mainly composed of graphite powder and resin, it has been found that the performance of the electrolyte membrane gradually deteriorates or becomes colored. Yes. Examining the cause, it has been found that impurities are contained in condensed water at 60 to 80 ° C., which is formed by cooling a part of the water vapor discharged from the fuel cell. Impurities here are broadly classified into those that are water-soluble and those that are insoluble but have a low melting point (80 ° C. or lower), and are specifically contained in graphite itself, as will be described later. Compounds other than carbon, release agents or curing agents used during molding of separators, compounds derived from modifiers, and unreacted resin monomers (resin components that are insufficiently polymerized and exist as single molecules) ) Etc.
[0006]
When water containing such impurities comes into contact with the gas diffusion layer, the impurities close the pores of the gas diffusion layer and adhere to the surface, and when water containing impurities comes into contact with the electrolyte membrane, By being thermally cured after adhering to the membrane, the gas diffusion layer and the electrolyte membrane are contaminated, thereby reducing the power generation performance.
[0007]
Similarly, when the gas supplied to the fuel cell is humidified from the outside, partially condensed water may dissolve impurities from the separator when the gas passes through the gas flow path of the separator. A similar problem arises.
[0008]
However, just by providing a degreasing device outside the fuel cell as in the conventional device, contamination of the gas diffusion layer and the electrolyte membrane due to such impurities cannot be prevented.
[0009]
In view of the above, the present invention comprises a separator composed mainly of a conductive material and a resin, and is dissolved in water vapor generated by the oxidation reaction of the battery, which is an impurity caused by the separator, or condensed water generated by cooling the water vapor. An object of the present invention is to achieve both reduction in cost and prevention of deterioration in power generation performance by providing an impurity purification means for purifying impurities coming out inside the fuel cell.
[0010]
[Means for Solving the Problems]
According to a first aspect of the present invention, there are provided two gas diffusion layers sandwiching an electrolyte that is an ionic conductor, a separator that is in contact with one of the gas diffusion layers and formed with a gas flow path for supplying fuel gas, and the other of the gas diffusion layers And a separator having a gas flow path for supplying an oxidant in contact with the fuel cell, wherein the separator is composed of a conductive material and a resin as main components, and impurities caused by the separator are the battery. An impurity purifying means for purifying impurities dissolved from the side in contact with the gas diffusion layer into water vapor generated by the oxidation reaction of the water or condensed water generated by cooling the water vapor, and the impurity purifying means comprises adsorption medium for adsorbing said impurities dispersed in the separator wall are a in even without less side in contact with one of the gas diffusion layer forms the gas flow path
[0011]
【The invention's effect】
In the case of a separator composed mainly of a conductive material and a resin, impurities dissolved from the side in contact with the gas diffusion layer contaminate the gas diffusion layer and the electrolyte membrane in water vapor and condensed water generated inside the fuel cell. and, generating less efficient than is lowering, according to the first invention, the adsorption medium dispersed in wall the impurity Te fuel cell internal smell forms the gas diffusion layer side gas flow path of the separators As a result, the power generation efficiency is not lowered and impurities are discharged outside the fuel cell even when a low-cost separator mainly composed of a conductive material and a resin is used. It can also be suppressed.
[0012]
The first invention is particularly effective when at least one of the cathode and the anode (gas diffusion layer) is humidified from the outside by a known means.
[0013]
In addition, when power is generated by reverse osmosis of a part of the water generated on the cathode side without humidification from the outside to the anode side through the electrolyte membrane, it is essential that the water to be reverse osmosis does not contain impurities. Although it is a requirement, according to the first invention, this requirement can be satisfied. Therefore, even when a low-cost separator mainly composed of a conductive material and a resin is used, there is no need for external humidification. It is possible to generate electricity by reverse osmosis of a part of the water generated in step 1 to the anode side through the electrolyte membrane.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.
[0015]
1 is a cross-sectional view of a polymer electrolyte fuel cell 1, FIG. 2 is an exploded view of FIG. 1, and FIG. 3 is a front view showing a gas flow path surface of a separator.
[0016]
1 and 2, gas diffusion layers (electrodes) 3 and 4 having a thickness of about 300 μm on both sides sandwiching a very thin polymer electrolyte membrane 2 of about 30 μm, and a thin plate shape of about 1 mm on the outer side. Separators 5 and 6 are arranged, respectively, and are stacked to constitute one cell.
[0017]
In order to supply an oxidant (usually air) to one gas diffusion layer (cathode) 3 and a fuel gas (usually hydrogen or a hydrogen-containing component) to the other gas diffusion layer (anode) 4, each separator 5, 6 Gas passages 5b and 6b are formed in the side surfaces 5a and 6a on the gas diffusion layer side, respectively.
[0018]
This will be described, for example, as shown in FIG. 3, on the side of the separator 5 on the side in contact with the gas diffusion layer 3 on the side of the gas diffusion layer 3, leaving a central portion 12 and a flat peripheral portion having a constant width around it. 11 is secured, and all the remaining portions except for the elongated portions 13 to 20 in the same plane as the peripheral portion 11 are drilled in the central portion 12, and in the figure, from the upper right to the left, from the left to the right, from the right to the left,. Grooves 21, 22, and 23 that are folded back are formed. That is, if the boundaries between the peripheral edge portion 11 and the central portion 12 are 12a, 12b, 12c, and 12d, the lateral groove 21 having a length, a constant width, and a constant depth from the right boundary 12a to the left boundary 12b. Are formed at intervals of the planar portions 13 to 20, and the first and second, third and fourth, fifth and sixth, seventh and eighth adjacent 2 counted from above. The four lateral grooves 21 are drilled with the same width and the same depth as the lateral grooves 21 along the left boundary 12b, and the second, third, fourth and fifth from the top. Four short connecting grooves 23 in which the second, sixth and seventh, eighth and ninth adjacent lateral grooves 21 are drilled along the right boundary 12a with the same width and depth as the lateral grooves 21. Are communicated with each other.
[0019]
When the grooves 21, 22, and 23 are formed over the entire central portion 12 of the side surface of the separator 5 on the gas diffusion layer 3 side, as shown in FIG. 1 between these grooves and the gas diffusion layer 3. Thus, a space is defined, and the gas passage 5b is formed by this space.
[0020]
In addition, the air inlet 25 penetrating all the stacked cells at the rightmost end of the horizontal groove 21 located at the top in FIG. There is an air outlet 26 penetrating therethrough.
[0021]
Since air of a constant pressure is supplied to the air inlet 25 located at the upper right by an air pump (not shown), the air first flows to the left in the lateral groove 21 located at the uppermost position of the air inlet 25 and turns back when reaching the left end. This time, the second horizontal groove 21 from the top flows to the right, and when it reaches the right end, the third horizontal groove 21 flows from the top to the left again. The air outlet 26 located at is reached.
[0022]
The gas passage 6b formed on the side surface of the other separator 6 on the gas diffusion layer 4 side is also formed in the same manner as the gas passage 5b of the separator 5 shown in FIG.
[0023]
H ₂ (hydrogen gas) supplied to the gas diffusion layer 4 through one gas passage 6b is activated by the catalyst in the gas diffusion layer 4 and decomposed into electrons and hydrogen ions (protons). When this is expressed in chemical formula,
Anode side: H ₂ → 2H ⁺ + 2e ⁻ (1)
It is.
[0024]
The hydrogen ions of the formula (1) move to the gas diffusion layer 3 on the opposite side through the polymer electrolyte membrane 2 through which only hydrogen ions can pass. On the other hand, the electrons of the formula (1) reach the opposite gas diffusion layer 3 after performing electrical work through an external circuit (not shown).
[0025]
Air is supplied to the gas diffusion layer 3 through the gas passage 5b. Oxygen in the air reacts with hydrogen ions and electrons that have passed through the electrolyte membrane 2 to be reduced to H ₂ O (water). The In terms of chemical formula, cathode side: (1/2) O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O (2)
It is.
[0026]
In this case, since the gas passages 5b and 6b are formed in the entire central part of the side surfaces 5a and 6a on the gas diffusion layer side of the two separators 5 and 6, the reactions (1) and (2) described above are performed on the electrolyte membrane 2. This occurs efficiently in almost the entire gas diffusion layers 3 and 4. However, since oxygen used in the above equation (2) is only a part of oxygen in the air, the remaining unused air is discharged from the air outlet 26 to the outside. Similarly, fuel gas that has not been used is discharged outside through a fuel outlet (not shown) provided in the separator 6.
[0027]
Water passages 5d and 6d (water jackets) are respectively formed on the side surfaces 5c and 6c opposite to the gas diffusion layers of the separators 5 and 6, respectively. This is for circulating cooling water for cooling the inside of the fuel cell in operation.
[0028]
Gaskets (silicone rubber, fluororubber, elastomer) 7, 8, 9, 10 for sealing the cooling water flowing through the water passages 5 d, 6 d, the air flowing through the gas passages 5 b, 6 b, and the fuel gas so as not to leak outside. Is housed in a groove provided at the peripheral edge of the separators 5 and 6.
[0029]
In the polymer electrolyte fuel cell 1 configured as described above, since the electrolyte membrane 2 is acidic, the separators 5 and 6 must have acid resistance. In addition, since water is generated on the cathode side as in the above formula (2), it has hydrolysis resistance so that it does not react with water in a high-temperature environment, and also has heat resistance that can withstand the power generation temperature. Must be.
[0030]
In order to obtain a separator that satisfies these requirements and is inexpensive, in the present invention, the separators 5 and 6 are molded using a thermosetting or thermoplastic resin as a binder and graphite powder as a conductive material. impurities of the resin and the conductive material from the separator 5 and 6 for the main component and contaminate the electrolyte membrane 2 and the gas diffusion layers 3 and 4 so that the power generation efficiency is not lowered, the separators 5,6 adsorption medium surface of the gas diffusion layer side (specifically wall surface forming a gas flow path 5b, 6b of the gas diffusion layer side) are dispersed in, for purifying impurities by adsorption of impurities to the adsorption medium.
[0031]
Here, the impurities caused by the separators 5 and 6 in the present invention are mainly compounds and ions. Specifically, it is a metal oxide derived from graphite, a salt such as carbonate or sulfate, and a sulfur compound, and the molded separator includes a resin monomer or a polymer insufficient product, or a resin decomposition product. Furthermore, as an additive, release agents (hydrocarbons, aliphatics, aliphatic amides, esters, alcohols, metal soaps, silicones, etc.) or for improving physical properties and processability Various modifiers are also included.
[0032]
However, the compounds and ions from the separators 5 and 6 are not permanently dissolved, and only the compounds and ions existing mainly on the surfaces and surface layers of the separators 5 and 6 may be dissolved in water. know. Therefore, if the specifications and the molding method of the separators 5 and 6 are determined, the amount of compounds and ions eluted from the separators 5 and 6 (the amount of impurities due to the separators 5 and 6) can be grasped in advance.
[0033]
Therefore, the type, particle size, and amount of the adsorption medium used in the present invention include the material, porosity, and thickness of the gas diffusion layers 3 and 4, and compounds that are eluted from the separators 5 and 6 into water or water at the operating temperature. It is determined comprehensively depending on the amount of ions. Since the thickness of the gas diffusion layers 3 and 4 that are usually used is about 200 to 350 μm on both the anode side and the cathode side, the particle size of the adsorption medium is 50 μm or less, preferably 10 μm or less. The material of the adsorption medium is preferably a single material of carbon, ceramic, or resin or a combination of these.
[0034]
A method of dispersing the (wall surface forming a gas flow path of the gas diffusion layer side in detail) surface of the gas diffusion layer side of the adsorption medium separators 5,6 are not particularly limited.
[0035]
Here, the operation of the present embodiment will be described.
[0036]
In the case of separators 5 and 6 containing graphite powder (conductive material) and resin as main components, impurities dissolved in water vapor or condensed water generated inside the fuel cell are gas diffusion layers 3 and 4 or electrolyte membranes. 2 While it reduce the contaminated power generation efficiency, according to this embodiment, the gas diffusion layer side of the separators 5, 6 and the impurity Te fuel cell interior smell surface (in particular of the gas diffusion layer side gas Since it is adsorbed on the adsorption medium dispersed on the wall surface forming the flow path and purified, the power generation efficiency is lowered even when a low-cost separator mainly composed of graphite powder and resin is used. It is also possible to prevent impurities from being discharged to the outside of the fuel cell.
[0037]
In addition, this embodiment is particularly effective when at least one of the gas diffusion layers 3 and 4 is humidified from the outside by a known means.
[0038]
When generating electricity by reversely osmosis part of the water generated on the cathode side (gas diffusion layer 3 side) through the electrolyte membrane 2 to the anode side (gas diffusion layer 4 side) without external humidification In addition, it is an essential requirement that the water to be reverse osmosis does not contain impurities, but according to the present embodiment, this requirement can be satisfied. Therefore, a molded separator whose main component is a low-cost conductive material and resin. Even in the case of using, it is possible to perform power generation by reverse osmosis of a part of the water generated on the cathode side to the anode side through the electrolyte membrane 2 without humidification from the outside.
[0039]
In addition, when the components of impurities (compounds and ions) can be known in advance (some components are easily dissolved or some components are not dissolved), the components (carbon, ceramic, resin) of the adsorption medium are used. What is necessary is just to adjust according to the component of an impurity. For example, in the case of a separator formed without using a release agent, there is no possibility that a compound derived from the release agent will dissolve, so the adsorption component added for the purpose of adsorbing this compound is omitted and the adsorption medium Configure. Thereby, not only unnecessary adsorption components can be omitted, but also a structure specialized for adsorption of other impurities can be obtained, so that the adsorption efficiency of other impurities can be increased and a greater effect can be obtained.
[0040]
Further, when an elastomer is used for the gaskets 7 and 8, the release agent dissolved in the condensed water may deteriorate the elasticity of the gaskets 7 and 8. However, according to the present embodiment, such a situation is avoided. be able to.
[0052]
In the embodiment, the case where one gas flow path is formed so as to reciprocate as described above with reference to FIG. 3 has been described, but the method of forming the gas flow path is not limited to this. For example, since the pressure loss reduction in the gas flow path, and a single flow path 33 which runs in a transverse direction from the gas flow path inlet 31 (air inlet or hydrogen inlet) as shown in FIG. 4 (a), the flow path The present invention is also applicable to a configuration including a plurality of flow paths 34 branched from 33 and a single aggregate flow path 35 that runs below the outlet 32 (air outlet or hydrogen outlet) in the lateral direction.
[0053]
In this case, it is preferable to install an ion exchange membrane, a porous resin membrane, or a tube on the bottom surface or wall surface of the flow channel rather than dispersing the powder adsorption medium on the bottom surface of the gas flow channel. In addition, an impurity purification means such as the above-described ion exchange membrane capable of adsorbing impurities to the aggregation channel 35 can be provided.
[0054]
Further, there is application of the present invention is also applicable to the case where the gas flow path of the plurality (three in the figure) shown so shown in FIG. 4 (b) is formed so as to reciprocate.
[0055]
In the embodiment, the separators 5 and 6 have been described in the case where the thermosetting or thermoplastic resin is used as a binder and the graphite powder is formed as a conductive material. However, the present invention is not limited to this, and the conductive material is graphite powder. And at least one component of carbon black or metal powder.
[0056]
The separator in the present invention may be formed by injection molding, compression molding, extrusion molding, or any other known method using a material mainly composed of resin and graphite powder or metal powder. Also included is a separator in which a gas flow path is formed on a graphite plate by machining and then impregnated with a resin to improve gas permeability.
[0057]
In the second embodiment, the case where an electrolyte membrane (ion exchange membrane) cut to the same size as the lateral groove 21 is bonded to the lateral groove 21 where the air outlet 26 of the separator 5 is provided is described. An adsorbing medium formed in the form of a powder, tube or sheet using porous carbon, ceramic, resin or a composite thereof is installed in the lateral groove 21 having the outlet 26, and impurities are adsorbed by the adsorbing medium. The impurity may be purified by the above.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a polymer electrolyte fuel cell.
FIG. 2 is an exploded view of FIG.
FIG. 3 is a front view of a separator.
FIG. 4 is a configuration diagram of a gas flow path formed in a separator according to another embodiment.
[Explanation of symbols]
1 Fuel Cell 2 Electrolyte Membrane 3 and 4 Gas Diffusion Layer (Electrode)
5, 6 Separator 5b, 6b Gas flow path

Claims (8)

Two gas diffusion layers sandwiching an electrolyte that is an ionic conductor;
A separator formed with a gas flow path for supplying fuel gas in contact with one of the gas diffusion layers;
A separator having a gas flow path for supplying an oxidant in contact with the other of the gas diffusion layers,
The separator is composed of a conductive material and a resin as main components, and impurities are attributed to the separator and dissolved in water vapor generated by the oxidation reaction of the battery or condensed water generated by cooling the water vapor. Impurity purification means for purifying the fuel is provided inside the fuel cell,
The fuel cell, wherein the impurity purification means is an adsorption medium that is dispersed on a separator wall surface that forms the gas flow path on the side in contact with at least one gas diffusion layer and adsorbs the impurities. 2. The fuel cell according to claim 1 , wherein the adsorption medium is porous carbon, ceramic, resin, or a composite powder thereof. The conductive material is a material using at least one of graphite powder, carbon black, or metal powder, and the separator is formed by molding with the conductive material and a resin as main components. Or the fuel cell of 2 .   The conductive material is a graphite plate, and a gas flow path is formed on the graphite plate by machining and then impregnated with a resin to form a separator. A fuel cell according to claim 1. If that can know the ingredients of the impurities in advance, the fuel cell according to any one of claims 1 to 4, characterized by adjusting the components of the adsorption medium in accordance with the component of the impurities. The fuel cell according to claim 1 , wherein the impurity purification means is provided in a part of a gas flow path. The impurity purification means is an adsorption medium formed into a powder, tube or sheet using porous carbon, ceramic, resin or a composite thereof, and the impurities are adsorbed by the adsorption medium. The fuel cell according to claim 6 . The fuel cell according to claim 6 , wherein when the impurities include ions or compounds, the impurity purification means is means for selectively adsorbing the ions or compounds.

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