JP2004087344A - Solid polymer fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve heat recovery efficiency by heat radiation from a solid polymer fuel cell by covering a whole surface or a part of the battery with heat-insulating parts from outside of the solid polymer fuel cell. <P>SOLUTION: As for this solid polymer fuel cell, a front face or one part of a laminate laminating a plurality of single cells which make a film-electrode conjugate having a catalyst layer and a hydrogen ion conductive polymer film pinched and held by two sheets of separators for the single cells having gas circulation channels is covered with the heat-insulating parts. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a polymer electrolyte fuel cell.
[0002]
[Prior art]
Polymer electrolyte fuel cells have the advantages of high output, long life, little degradation due to start / stop, low operating temperature (about 70-80 ° C), and no need for precise differential pressure control. Therefore, it is expected to be used in a wide range of applications, such as power supplies for electric vehicles, distributed power supplies for business use and home use.
[0003]
Among these applications, a distributed power source equipped with a polymer electrolyte fuel cell (for example, a cogeneration power generation system) takes out electricity from the polymer electrolyte fuel cell and simultaneously generates heat from the battery during power generation. It is a system that tries to make effective use of energy by recovering as energy.
[0004]
Therefore, in such a distributed power source, it is important how to reduce the heat loss from the fuel cell. However, from such a viewpoint, there is no technology for preventing heat radiation from the polymer electrolyte fuel cell.
[0005]
[Problems to be solved by the invention]
Normally, heat from the fuel cell is taken away by contact with the atmosphere, and there has been a problem that the amount of heat that can be recovered as hot water is reduced. To solve this problem, it is conceivable to cover the fuel cell with a heat insulating material.
[0006]
However, polymer electrolyte fuel cells use a flammable gas containing hydrogen, so if hydrogen leaks from the fuel cell, the hydrogen will stay near the fuel cell due to the heat insulating material used for coating. Therefore, simply covering the fuel cell with a heat insulating material has a problem in practicality.
[0007]
Further, in a typical polymer electrolyte fuel cell, a number of single cells contributing to power generation are arranged in series, and two electrically conductive separators constituting each single cell are exposed to the outside. For this reason, if the separator condenses due to temperature fluctuations, an external short circuit may occur between the separators due to the voltage of the single cell, and simply covering the fuel cell with a heat insulating material has a problem in practicality.
[0008]
Therefore, the present invention aims to prevent such an external short circuit due to stagnation or dew condensation of the flammable gas.
[0009]
[Means for Solving the Problems]
A polymer electrolyte fuel cell is a single cell having a basic structure of a solid polymer electrolyte membrane having a function of transmitting hydrogen ions, electrode layers formed on both sides of the membrane, and a separator arranged so as to sandwich the electrode layer. And usually has a configuration in which a plurality of single cells are connected in series in order to obtain sufficient power.
[0010]
A solid polymer electrolyte membrane having a function of permeating hydrogen ions is generally a polymer obtained by substituting a part of fluorine of a fluoropolymer with sulfonic acid, and having a function of transferring hydrogen ions. If there is, it is applicable to the present invention. For example, fluorine atoms contained in a polymer chain having ethylene tetrafluoride as a basic unit are bonded through about 2 to 5 alkyl chains (such as —CF ₂ CF ₂ — and —CF ₂ CF ₂ (CF ₃ ) —). Thus, there is a polymer film having a sulfonic acid group (—SO ₃ H) at the end of an alkyl chain.
[0011]
The electrode layer is a layer containing platinum or an alloy of a different element such as platinum and ruthenium as an electrode catalyst, and having this electrode catalyst, carbon powder, and a binder.
[0012]
The fuel gas supplied to the polymer electrolyte fuel cell is pure hydrogen or a gas containing hydrogen, and the hydrogen is oxidized on the electrode catalyst by an oxidation reaction (formula 1). At the same time, a reduction reaction of oxygen (formula 2) proceeds on the opposite electrode catalyst. Hydrogen ions generated by the hydrogen oxidation reaction are transferred to the polymer electrolyte membrane, and the hydrogen ions combine with oxygen at the opposite electrode layer to generate water.
[0013]
H ₂ → 2H ⁺⁺ 2e ⁻ (formula 1)
2H ⁺ + 1 / 2O ₂ + 2e ⁻ → H ₂ O (formula 2)
By this battery reaction, the electromotive force of the single cell is about 1.2 V. When a load is connected to generate power, a voltage of about 0.5 to 0.7 V is obtained. Therefore, a plurality of single cells contributing to this power generation are stacked. Thus, a voltage of several tens to several hundreds of volts can be obtained.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the contents of the present invention will be described with reference to examples. The present invention is not limited to the embodiments described below.
[0015]
FIG. 1 shows the configuration of a polymer electrolyte fuel cell. The power generation unit is a single cell 101, and DC power is normally extracted by a multi-stacked cell of several tens or more cells. This single cell 101 is composed of a membrane-electrode assembly in which electrode layers are provided on both surfaces of a solid polymer electrolyte membrane 102 (a membrane composed of 102 and 103 in an enlarged view) and two single cell separators sandwiching the membrane-electrode assembly. A gasket 105 was inserted between the single cell separators 104.
[0016]
An enlarged view of the periphery of the membrane-electrode assembly is shown in FIG. On one side of the single cell separator 104, a groove through which the fuel gas flows is machined. On the other side of the single-cell separator 104, a groove for circulating an oxidizing gas, usually air, is formed.
[0017]
These are laminated, and a positive electrode current collector 113 and a negative electrode current collector 114 are arranged at the ends. Pressure is applied from the outside of the current collectors 113 and 114 by an end plate 109 via an insulating plate 107. Parts fixing the end plate 109 are a bolt 116, a disc spring 117, and a nut 118.
[0018]
The conditions for fixing the laminated body including the single battery (single cell) 101, the cooling water separator 108, the end plate 109, the current collector plates 113, 114, and the like with the fastening parts including the bolts 116, the disc springs 117, and the nuts 118 are as follows. The laminate sandwiched between the two end plates is compressed by a hydraulic press, left as it is for 5 hours, and then the nut 118 is tightened.
[0019]
The fuel gas, the oxidizing gas and the cooling water are supplied to the connector 110 provided on the end plate 109,
It is supplied from 111 and 112 and discharged from the connector provided on the other end plate 109. DC power (output) can be obtained from the positive current collector 113 and the negative current collector 114.
[0020]
In a polymer electrolyte fuel cell, a single cell separator 104 constituting each single cell is usually exposed to the outside. Therefore, there is a problem that the heat recovery rate is reduced due to heat radiation from the fuel cell. However, this embodiment solves the problem by the following means.
[0021]
The means can be realized by covering a part or the whole of the outside of the fuel cell with the heat insulating component 121.
[0022]
The property required for the heat insulating material constituting the heat insulating component 121 is that the heat conductivity is small, and it is desirable that the heat conductivity is lower than the heat conductivity (0.4 W / mK) of general glass wool as the heat insulating material.
[0023]
Further, in consideration of use in cold regions, it is more desirable that the thermal conductivity of the heat insulating material be less than 0.1 W / mK, for example, in the vicinity of 0.02 to 0.03 W / mK.
[0024]
In order to realize such excellent heat insulating properties, a material having a large number of independent air bubbles whose heat insulating material is not connected to the outside is suitable because the thermal conductivity of air is small in a closed state without convection.
[0025]
In addition, the heat insulating component 121 has not only independent air bubbles but also a hole penetrating the heat insulating component 121, which can be achieved by covering a part or the whole outside of the fuel cell.
[0026]
The reason why such a through hole is provided is that by covering the fuel cell with the heat insulating component 121, the retained combustible gas is easily released, and the dew condensation water is easily discharged to the outside.
[0027]
The shape and size of the through-hole are arbitrary, but in order to prevent heat radiation due to convection of the atmosphere, it is necessary that the through-hole has such a degree as to allow a flammable gas or the like to pass therethrough. For transmission of combustible gas, 10 to 1000 μm is preferable, and for transmission of dew condensation water, 1 to 10 mm is preferable.
[0028]
In addition, since hydrogen generally has a lower specific gravity than air, it is easily diffused upward, and heated air is also easily moved to the upper part. A component having a through-hole mainly considering transmission can be arranged.
[0029]
On the other hand, since the dew condensation water easily accumulates on the bottom surface due to gravity, a heat insulating component covering the bottom surface or the side surface of the fuel cell can be a component having a through-hole mainly considering the permeation of the dew condensation water.
[0030]
As an alternative to this, a plurality of plate-shaped heat-insulating parts are arranged on the bottom surface of the fuel cell, and a gap of 1 to 10 mm is provided between the parts to use a heat-insulating part without a through hole. It is also possible.
[0031]
Examples of materials applicable to the heat-insulating components described above include polyurethane foam, styrene foam, foamed rubber, and the like.
[0032]
Further, a foamed rubber material having a flame-retardant, non-flammable and self-extinguishing function can also be applied to the present invention.
[0033]
The heat-insulating component is not particularly limited to the presence or absence of foaming and the type of material, as long as the heat-insulating component has a thermal conductivity smaller than 0.4 W / mK.
[0034]
Note that a fluorine-based electrolyte membrane is used for the solid polymer electrolyte membrane 102 in FIG. 1 and a platinum-based catalyst is used for the catalyst of the catalyst layer 103. The gas diffusion layer 106 has a thickness of 200
Use μm carbon paper.
[0035]
An anode gas flow path having a width of 1 mm and a depth of 0.5 mm is provided on the anode-side separator surface, and a cathode gas flow path having a width of 1 mm and a depth of 0.8 mm is provided on the cathode-side separator surface.
[0036]
The polymer electrolyte fuel cell of the present embodiment has a configuration in which a plurality of 50 single cells are connected in series, and a cooling water separator 108 in which a cooling water flow path is formed for every two cells is inserted.
[0037]
This is because the cooling water is supplied to the cooling water separator 108 by a pump provided outside the battery, and the heat generated inside the battery is provided by a heat exchanger provided in the middle of a cooling water pipe connecting the pump and the battery. In order to collect the
[0038]
Polyurethane foam is used for the heat insulating component 121. These are installed so as to cover the side surfaces (four surfaces) of the fuel cell, and the side surfaces of the heat insulating component 121 are fixed with an adhesive.
[0039]
In order to reduce heat radiation from the end plate 109, an end plate 109 made of ABS resin having a thickness of 40 mm was used. Although not shown in FIG. 1, the end plate 109 may be made of metal, and a heat insulating component may be provided outside the end plate 109 to cover the entire surface of the polymer electrolyte fuel cell.
[0040]
The positive and negative electrode current collector plates 113 and 114 with output terminals protrude the terminal portions of the current collector plate from the holes of the heat insulating component 121. Power can be taken out by connecting this terminal to an external load. The material of these current collector plates was made of nickel. An insulating plate 107 was inserted between the current collector plates 113 and 114 and the end plate 109 to achieve electrical insulation.
[0041]
In this example, the effective area of the electrode capable of generating power was 100 cm ^2, and the output was measured at a current of 50 A. The gas supplied to the anode was hydrogen, the gas supplied to the cathode was air, and the pressure was normal pressure (one atmosphere). The utilization rates of hydrogen and oxygen were 70% and 40%, respectively. The temperature of the cooling water supplied to the cell was set at 70 ± 2 ° C. The battery of this embodiment is designated as S1.
[0042]
A heat-insulating component 132 having no through-hole used in the above-described embodiment, and a heat-insulating component 131 having four fine holes per 100 cm ² having a diameter of 0.1 mm in the heat-insulating component used in the above-described embodiment. And three types of heat insulating parts 133 having holes of 3 mm in diameter and four holes per 100 cm ² were formed in the heat insulating parts used in the above-mentioned examples.
[0043]
Since the heat insulating component 132 is only for the purpose of preventing heat radiation, it was arranged on the side surface of the fuel cell as shown in FIG. The heat insulating component 131 is arranged above the fuel cell because it is assumed that the combustible gas leaks. The heat insulating component 133 was disposed on the bottom surface of the fuel cell in order to discharge dew water. The space between these heat-insulating components and the space between the heat-insulating components and the end plate 119 were fixed with an epoxy resin adhesive. The battery of this embodiment is designated as S2.
[0044]
As a comparative example, a heat-insulating component used in the above-mentioned polymer electrolyte fuel cell was removed, and a conventional fuel cell in which heat insulation was not considered at all was manufactured. The battery of the comparative example is denoted by R.
[0045]
A device in which the batteries S1 and S2 and the battery R of the comparative example were incorporated in the power generation system shown in FIG. 3 was manufactured. The device equipped with the battery S1 is designated A1, the device equipped with the battery S2 is designated A2, and the device equipped with the battery R is designated A3. These devices differ only in the type of battery, but have the same other components and configurations.
[0046]
In FIG. 3, 1001 is natural gas, 1002 is air, 1003 is a reformer, 1005 is a stack of fuel cells, 1006 is distilled water, 1007 is a hot water storage tank, 1008 is a pump for anode gas, and 1009 is a pump for cathode gas. Reference numeral 1010 denotes a circulating water pump, 1011 denotes a heat exchanger, 1012 denotes a fuel cell, 1013 denotes a cathode gas discharge pipe, and 1014 denotes an anode gas discharge pipe.
[0047]
A fuel gas having a hydrogen concentration of 70% was introduced into each device by reforming city gas into the anode, and air was supplied to the cathode.
[0048]
The water temperature of the hot water storage tank 1007 at the start of power generation was 40 ° C., and the temperature of circulating water supplied to the fuel cell 1012 was also 40 ° C. The test was carried out in a constant temperature laboratory having an air conditioner so that the outside air temperature was kept constant at 10 ° C.
[0049]
The utilization rates of hydrogen and oxygen were 70% and 40%, respectively, and were constant for each current. The gas pressure was normal pressure.
[0050]
The current density was set to 0.5 mA / cm ² and a continuous power generation test was performed.
[0051]
The devices A1 and A2 of the present invention were able to obtain hot water at 60 ° C. after about 4 hours by continuous power generation. On the other hand, in the case of the device A3 equipped with the battery R of the comparative example, it took about 5 hours to obtain the same hot water.
It was demonstrated that the heat recovery efficiency was high when A2 was used.
[0052]
【The invention's effect】
By the heat insulating component of the present invention, the efficiency of heat recovery from the polymer electrolyte fuel cell is improved.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a fuel cell in which a heat insulating component of the present invention is arranged.
FIG. 2 is a plan view of a fuel cell in which the heat insulating component of the present invention is arranged.
FIG. 3 is a diagram of a power generation system equipped with the polymer electrolyte fuel cell of the present invention.
[Explanation of symbols]
101 single cell, 102 solid polymer electrolyte membrane, 103 catalyst layer, 104 single cell separator, 105 gasket, 106 gas diffusion layer, 107 insulating plate, 108 cooling water separator, 109 end Plate, 110: Connector for anode gas piping, 111: Connector for cooling water piping, 112: Connector for cathode gas piping, 113, 114: Current collector, 116: Bolt, 117: Disc spring, 118: Nut, 121: Heat insulation 1001, natural gas, 1002, air, 1005, fuel cell stack, 1006, distilled water, 1007, hot water tank, 1008, anode gas pump, 1009, cathode gas pump, 1010, circulating water pump Reference numeral 1011: heat exchanger; 1012: fuel cell; 1013: cathode gas discharge pipe; Gas discharge pipe.

Claims (5)

Front surface or part of a laminate in which a plurality of single cells in which a membrane-electrode assembly having a catalyst layer and a hydrogen ion conductive polymer membrane is sandwiched between two single cell separators having gas flow grooves are sandwiched Solid polymer fuel cell coated with a heat insulating component. 2. The polymer electrolyte fuel cell according to claim 1, wherein the heat insulating component has a bubble or a through hole inside. 3. The polymer electrolyte fuel cell according to claim 1, wherein the thermal conductivity of the heat insulating component is 0.4 W / mK or less. 4. The polymer electrolyte fuel cell according to claim 1, wherein the heat-insulating component has a nonflammable, flame-retardant or self-extinguishing function. A power generation system in which a device for continuously producing a gas containing hydrogen or a device for storing hydrogen and a polymer electrolyte fuel cell are connected via a pipe for flowing a gas containing hydrogen. The power generation system according to claim 1, 2, 3, or 4, wherein the molecular fuel cell generates power using gas containing hydrogen supplied from the device.

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