JP2003045438A - Low temperature fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small, lightweight, high performance low temperature fuel cell accelerating chemical reaction in an oxygen electrode by accelerating transportation of oxygen gas. SOLUTION: A permanent magnet is arranged in the vicinity of a fuel electrode, in an electrolyte, or in the vicinity of the electrolyte, and by utilizing magnetic attraction acting to paramagnetic oxygen gas, transportation of the oxygen gas is accelerated. Since it is small and lightweight, this fuel cell is used as a power source of a portable personal computer or a fuel cell for an automobile.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small-sized and lightweight low-temperature fuel cell which has improved power generation performance.

[0002]

2. Description of the Related Art In recent years, with the strengthening of global environmental regulations,
Research and development of fuel cells have been promoted as a clean power generation system for generating power using fuel such as hydrogen, and there is a strong demand for its practical application. FIG. 1 shows a principle diagram of a general hydrogen oxygen fuel cell. Since the principle is the same for an air electrode that uses air instead of oxygen, in the present specification, the oxygen electrode will be described as having a meaning including the air electrode. Generally, the oxygen electrode 1 of a fuel cell is composed of a porous plate-shaped electron conductor, and oxygen gas 2 is introduced into one side of the electron conductor, and the opposite side is in contact with the electrolyte 3. There is. When oxygen gas is introduced here, the oxygen gas diffuses in the porous plate toward the electrolyte side, and the reaction in the following formula (1) proceeds in the catalyst layer in the oxygen electrode and the protons in the electrolyte. . The catalyst layer is located near the electrolyte in the oxygen electrode.

[Chemical 1]

In order to improve the efficiency of a low temperature fuel cell, reduction of the overvoltage at the oxygen electrode, which accounts for about 80% of the total overvoltage, is a major issue. This is because the water of the reaction product generated in the porous electrode hinders the transport of oxygen gas, and the transport of oxygen gas to the catalyst layer in the oxygen electrode depends on the diffusion-controlled process, so that the delay of the supply is high. It is the cause of polarization. As a method for solving this problem, an oxygen gas pressurizing device is provided because it is necessary to improve the oxygen gas transport efficiency. This pressurizing device is one of the factors that hinder the practical use of portable or small-sized low-temperature fuel cells.
Further, in order to reduce the cost of the fuel cell, reducing the amount of expensive platinum catalyst used is also a very important issue.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned actual situation in the prior art. That is, the object of the present invention is to promote the chemical reaction by the smooth movement of oxygen gas, eliminating the need for a pressurizing device for oxygen gas or air, and reducing the amount of platinum catalyst used,
An object of the present invention is to provide an inexpensive, high-performance polymer electrolyte fuel cell that is compact and lightweight.

[0005]

First, the inventors of the present invention have found that oxygen gas and bubbles are attracted to a strong permanent magnet as a means for promoting transport of oxygen gas (Wakayama, Jour.
nal of Applied Physics, 69 (1991) 2734, 81 (1997) 298
(0.) and that the magnetic field strength near the catalyst accelerates the catalytic reaction involving oxygen gas (Wakayama, Ja
panese Journal of Applied Physics 39 (2000) L436.) was found. Further, as a result of earnest studies on the utilization of the permanent magnet, the present invention has been completed, focusing on the fact that the reaction at the oxygen electrode is promoted when a strong permanent magnet is arranged at a specific position of the fuel cell. It was

That is, the low temperature fuel cell of the present invention is characterized in that a permanent magnet is arranged in the vicinity of the fuel electrode or in or near the electrolyte. Of course, the present invention can be applied to any fuel cell that operates in a temperature range in which a permanent magnet can be used. Various fuels such as hydrogen gas, methanol, and dimethyl ether can be considered as the fuel used for the fuel electrode. Here, the case where hydrogen is used as the fuel is most commonly described. However, since the gist of the present invention is to improve the efficiency of the oxygen electrode, even a fuel cell using a fuel other than hydrogen will not lose its effectiveness.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. The present invention, in a conventional fuel cell, a permanent magnet is arranged in the vicinity of the fuel electrode or in or near the electrolyte,
A gradient magnetic field is generated in and near the oxygen electrode to attract paramagnetic oxygen gas by magnetic force, which promotes the transport of oxygen gas to the catalyst layer in the oxygen electrode and the reaction is generated by magnetic repulsion. The present invention provides a low-temperature fuel cell with improved efficiency by improving the efficiency of the oxygen electrode by eliminating the water of the substance and improving the reaction efficiency of the oxygen electrode.

In the present invention, the vicinity of the fuel electrode in which the permanent magnet is arranged means a "gradient magnetic field" in which the magnetic field strength increases in the oxygen electrode along the moving direction of the oxygen gas by disposing the permanent magnet. It may be a part that can be generated, usually on the opposite side of the oxygen gas introduction part of the oxygen electrode, so as not to hinder the supply of the fuel gas, for example,
Behind the fuel electrode, in the fuel flow path, before and after the fuel electrode, etc.
The electrolyte or the vicinity thereof may also be a site capable of generating a “gradient magnetic field” in the oxygen electrode. That is, it should be installed in the electrolyte body or at a site adjacent to the oxygen electrode. As the form of the permanent magnet used in the present invention, various shapes such as a plate shape and a granular shape are used alone, or a granular magnet is attached to a wire mesh or the like, or is integrated with a fuel flow path or the like. May be.

FIG. 2A is a schematic diagram showing an example of the structure of the fuel cell according to the present invention. The permanent magnet 6 is installed so as to be adjacent to the fuel flow path 7. In this case, a steep “gradient magnetic field” is generated in the vicinity of the permanent magnet 6. The “gradient magnetic field” generated by the permanent magnet of the present invention refers to a magnetic field having a state in which the magnetic field strength (H) gradually decreases with distance from the permanent magnet.

FIG. 2B shows the distribution of the magnetic field strength (H) generated by the permanent magnet 6. In FIG. 2B, x is the distance from the surface of the permanent magnet, which coincides with the position coordinate in the horizontal direction of FIG. Normally, in a low temperature fuel cell (for example, a polymer electrolyte type), the thickness of the fuel flow path 7 is about 0.05c.
m, the total thickness of the fuel electrode 4 and the electrolyte solution 3 is about 0.1 cm.
Therefore, it is possible to generate a steep gradient magnetic field inside the oxygen electrode 1 and in the vicinity thereof.

As the permanent magnet, specifically, neodymium-iron-boron magnet, samarium-cobalt magnet, ferrite magnet and the like having a desired shape and size can be appropriately selected and used. The permanent magnet varies depending on the type, size, shape, etc. of the magnet used, but the "gradient magnetic field" (dH / dx) is about 0.1 kilogauss / c.
It is preferable to use one that generates a magnetic field of m or more. INDUSTRIAL APPLICABILITY The present invention is used for a low-temperature fuel cell that operates at a temperature below the Curie temperature at which the magnetism of the permanent magnet used is not impaired, and is a polymer electrolyte fuel cell in which a chemical reaction is usually performed at a low temperature of 150 ° C. or less. Especially effective for.

In the present invention, when the permanent magnet itself may undergo a chemical change in the environment of use, the surface of the permanent magnet is covered with a chemically stable substance (not shown) while allowing the magnetic field lines to pass therethrough. Is preferred. Examples of the substance that coats the surface of the magnet include plastics, ceramics, glass, polymers and inorganic compounds. The coating material is preferably electrically conductive. Although the direction of magnetization of the permanent magnet 6 is shown in FIG. 2 parallel to the line connecting the positive and negative electrodes, a perpendicular direction or the like can be appropriately selected. Further, although FIG. 2 shows the case where the magnetic pole close to the oxygen electrode is the S pole, the NS direction may be reversed.

An important matter in the present invention is shown in FIG.
As can be seen in Fig. 1, the permanent magnet is arranged so that the magnetic field strength increases along the moving direction of oxygen gas in the fuel cell. According to the present invention, by using the permanent magnet in this way, the supply of oxygen gas to the catalyst layer is promoted, the chemical reaction of the oxygen electrode is promoted, and the battery performance is improved. As a result, the oxygen gas supply efficiency is improved. It is possible to reduce the conventional pressurizing device provided for increasing the fuel consumption, and to manufacture a small and lightweight fuel cell. These are useful as a power source for a compact electric product such as a portable notebook personal computer and a fuel cell system mounted in an automobile. Furthermore, since the reaction efficiency at the oxygen electrode is improved, the platinum catalyst can be reduced, which leads to cost reduction.

[0014]

Next, the present invention will be described in more detail with reference to the drawings. Example 1 FIG. 3A is a partially enlarged cross-sectional view on the oxygen electrode side of a low temperature fuel cell in which a permanent magnet is installed behind the fuel flow path as shown in FIG. The same applies when a permanent magnet is arranged in or near the electrolyte. The oxygen electrode 1 of the low-temperature fuel cell is composed of a porous carbonaceous material or the like, and a part thereof, in a catalyst layer 1 ′ in which a platinum-based catalyst is present, an ion exchange membrane electrolyte 3 made of perfluorocarbon sulfonic acid or the like. Is in contact with. Oxygen gas moves from the right to the left in the electrode of the porous carbonaceous material, and the reaction proceeds by contacting the electrons and the protons in the electrolyte solution coming from the fuel electrode side in the catalyst layer. The form of oxygen gas during transportation may be gas, microbubbles, or dissolved in water or electrolyte, but the amount of dissolved oxygen in water or electrolyte is extremely small.

Generally, a magnetic force is generated under a gradient magnetic field in which the magnetic field strength changes depending on the position coordinates. The magnetic force (F) acting on a substance is expressed by the product of volume magnetic susceptibility (χ), magnetic field strength (H), and magnetic field gradient (dH / dX) per unit volume as represented by the following equation (2). Be done (Chemical Dictionary, Volume 1, 1
67 pages, Kyoritsu Shuppan (1969). F = χH (dH / dX) (2) The oxygen gas involved in the oxygen electrode reaction has paramagnetism, and its volume magnetic susceptibility is positive and large (+ 1.5 × 10 −7 e.m.
u.), and has the property of being attracted to a magnet by a strong force. In the present invention, oxygen gas and air move in the direction in which the magnetic field strength increases due to the magnetic attractive force represented by the formula (2) and are transported inside the electrode, as indicated by the arrow in FIG. . In this case, the gradient magnetic field H (dH / dX) is 31 kilogauss 2
/ Cm, the magnetic attractive force acting on the oxygen gas can be estimated from Equation (2) to be 4.7 dynes / cm3. Also,
When oxygen gas exists as bubbles in the reaction product water, magnetic buoyancy represented by the following formula (3) acts on the bubbles. F = V (χ _{O 2} −χ ₁ ) H (dH / dX) (3) Here, V is the volume of the bubble and χ ₁ is the volume susceptibility of water or electrolyte. The volume magnetic susceptibility of water is -0.716 x 10-6.
It is emu, and the electrolytic solution has almost the same value, and the force that repels the magnetic field acts. Magnetic buoyancy acts on the bubbles in the direction in which the magnetic field increases, as indicated by the arrow in FIG.
When H (dH / dX) of the gradient magnetic field in the vicinity of the permanent magnet is 31 kilogauss ² / cm, the magnetic buoyancy acting on the oxygen gas can be estimated from Equation (3) to be 27 dynes / cm ³ .

When the permanent magnet is arranged in the vicinity of the fuel electrode or in the electrolyte or in the vicinity thereof as described above, the supply of oxygen gas or oxygen gas bubbles to the oxygen electrode catalyst layer is promoted by the magnetic force, and further reaction is caused. Since the product water is removed from the electrode by magnetic repulsion, the efficiency of the electrode reaction is greatly improved. As a result, unlike the conventional method, there is an advantage that a pressurizing device installed to improve the supply efficiency of oxygen gas is unnecessary.

Embodiment 2 A case where the permanent magnet 6 is installed near the fuel electrode (on the side opposite to the oxygen electrode) as shown in FIG. 2 will be described. A neodymium-iron-boron magnet system (trade name: Neomax, manufactured by Sumitomo Special Metals Co., Ltd.) was used as the permanent magnet, and its shape was as shown in FIG.
As shown in (a), the direction connecting the centers of the N and S poles parallel to the x axis was 1 cm, and the magnetic pole was 2 × 3 cm. Along the direction x connecting both electrodes, the magnetic field strength distribution near the permanent magnet is measured by a Gauss meter [5080 type, F.S. W. Bell Co.] was used for the measurement. However, due to the restriction of the shape of the sensor of the Gauss meter, the magnetic field strength distribution in the vicinity of the small permanent magnet cannot be measured. FIG. 4B shows the measurement result of the magnetic field strength distribution. When the oxygen pole is about 0.2 cm from the surface of the permanent magnet, a gradient magnetic field having a magnetic field strength of 3.2 kilogauss and a magnetic field gradient of 2.6 kilogauss / cm is generated in and near the oxygen pole. From these values, the magnetic attractive force acting on the oxygen gas is estimated to be 1.2 dynes / cm ³ according to the equation (2). The magnetic force acting on the bubbles of oxygen gas is 7.2 dynes / cm ³
It is estimated that Thus, the force of the magnetic field promotes the supply of oxygen gas to the catalyst layer in the oxygen electrode.

Example 3 In a normal fuel cell, a plurality of fuel cells are wired in series. Although the arrangement of the permanent magnets of the one-unit fuel cell has been described in the second embodiment, the S of the permanent magnets 6 in FIG.
Since a similar gradient magnetic field is generated on the pole side, it is possible to apply a gradient magnetic field to two fuel cells with one permanent magnet. Therefore, here, FIG. 5 shows a case where a plurality of permanent magnets are lined up via a spacer. By arranging two fuel cell units in each gap so that the fuel electrode is close to the magnet 6, the permanent magnets can be used efficiently, and the oxygen gas to the catalyst layer in each oxygen electrode can be efficiently used. Can be promoted.

Example 4 By using a permanent magnet in which the magnetic poles and the fuel flow path are integrated, a steeper gradient magnetic field can be generated in the oxygen electrode and in the vicinity thereof. FIG. 6 is an explanatory view showing one mode in which the permanent magnet is arranged behind the fuel flow path 7. FIG. 6A shows a front view of an example of the iron fuel flow path member 8 into which hydrogen fuel is introduced, and its thickness is about 0.05 cm. Other flow path patterns can be appropriately selected. The material of the flow path 8 may be any material that can be easily magnetized, and examples thereof include iron and stainless steel. When the material of the flow channel is liable to chemically change in the use environment, it is preferable to cover the surface with a chemically stable substance (not shown) that allows magnetic field lines to pass through. Examples of the substance to be coated include plastics, ceramics, glass, polymers and inorganic compounds.

As shown in FIG. 6B, the iron fuel flow path member 8 is fixed to the magnetic pole of the permanent magnet 6, and the iron fuel flow path member 8 is arranged so as to be in contact with the fuel electrode 4. The fuel gas flows through the flow path formed by the fuel flow path member 8. In FIG. 6B, the surface of the iron fuel flow path member 8 made of iron that contacts the fuel electrode 4 is the S pole, and a gradient magnetic field as shown in FIG. 6C is generated. In the figure, x is the distance from the surface where the iron fuel flow path member is in contact with the fuel electrode, and coincides with the horizontal position coordinates in FIG. 6B. Since the total layer thickness of the fuel electrode 4 and the electrolyte 3 of a normal low temperature polymer electrolyte fuel cell is about 0.1 cm, a steep gradient magnetic field is generated in and near the oxygen electrode, which is also clear from FIG. As described above, a steep gradient magnetic field is generated in which the magnetic field strength increases as it approaches the catalyst layer. Therefore, the oxygen gas is attracted to the catalyst layer 1'in the oxygen electrode by the magnetic force, and on the contrary, the water of the reaction product is removed from the oxygen electrode, and the oxygen electrode reaction efficiently proceeds by the mass transport by the magnetic force. In this way, it is possible to control and promote the mass transfer involved in the oxygen electrode reaction by magnetic force. In the present invention, the efficiency of the reaction is promoted by using the permanent magnet, and the pressurizing device which requires the power source of the conventional method can be eliminated. Of course, the fuel flow path and permanent magnet integrated type is also applicable to the case of the third embodiment.

Embodiment 5 A fuel cell is generally formed by wiring a plurality of fuel cell units in series. Although the method of disposing the permanent magnets in the plurality of fuel cells has been described in Embodiment 3, FIG.
Other examples will be described below. Two permanent magnets 6
The two blocks are fixed to the U-shaped iron support 9 so as to face each other, and two fuel cell units are arranged between the permanent magnets so that each fuel electrode 4 is in contact with the magnet. Figure 7 (a)
From the thick line in the center, the left and right are the fuel cell units. With this arrangement, the space between the magnets is as shown in FIG.
A gradient magnetic field whose magnetic field strength increases near the magnet as shown in (b) is generated. In this case, a magnetic circuit is created and the distance between the magnets is on the order of 0.1-0.5 cm,
The magnetic field can be applied to the fuel cell unit existing between the magnetic poles with high efficiency as compared with the fourth embodiment. Then, the magnetic force indicated by the arrow acts on the oxygen gas, and the transport of the oxygen gas to the oxygen electrode and its catalyst layer is promoted. Further, there is an advantage that the leakage of the magnetic field to the external space is small.

Example 6 Next, the case where a permanent magnet is arranged inside or near the electrolyte will be described. FIG. 8A shows permanent magnet particles 1.
The case where 0 is arranged between the electrolyte and the catalyst layer is shown. When the permanent magnet particles are arranged in this way, the permanent magnet particles are magnetized using an electromagnet, a pulsed magnetic field, or the like after the fuel cell is formed. The direction of magnetization is appropriately selected such as parallel or perpendicular to the direction in which the oxygen electrode and the fuel electrode are drawn. The permanent magnet particles 10 may be dispersed alone, but as shown in FIG.
May be attached. In this case, since it is strong against vibration and stainless steel is also magnetized, it contributes to the generation of the gradient magnetic field. When the permanent magnet particles are attached to the wire net, the magnetization can be magnetized before the fuel cell is formed. Further, instead of the permanent magnet particles or the magnet particles attached to the wire mesh, a plate-shaped permanent magnet having holes may be used. When the permanent magnet particles 10 and the wire net 11 are corroded by the electrolytic solution, they are covered with a film of a chemically stable substance. When these permanent magnets of various shapes are installed between the electrolyte and the oxygen electrode, the magnetic field strength increases in and near the oxygen electrode along the moving direction of oxygen gas shown in FIG. A "magnetic field" is generated, which facilitates the transport of oxygen gas and also the elimination of the water of reaction products from the electrodes. Further, when the permanent magnet is in the form of particles and coated with an electrically conductive substance, the transport of protons from the electrolyte is not easily hindered. This example can be prepared by adding a permanent magnet particle or a permanent magnet part introduced here to a conventionally known fuel cell.

[0023]

As described above, the present invention has a completely new idea of providing a permanent magnet material in the vicinity of the fuel electrode of a fuel cell or in the electrolyte or in the vicinity thereof, and a gradient magnetic field is provided in and near the oxygen electrode. By generating it, the magnetic force can accelerate the transport of oxygen gas to the catalyst layer in the oxygen electrode, and the magnetic repulsion force can expel the reaction product water from the oxygen electrode. High efficiency can be achieved. In the present invention, the reaction of the oxygen electrode is promoted by the magnetic force, and as a result, the performance of the entire fuel cell system, that is, the power generation performance can be improved, so that the oxygen gas pressurizing device that requires a power source is unnecessary. In addition, it has an excellent advantage that the amount of expensive platinum catalyst used in the catalyst layer can be reduced. Since the low-temperature fuel cell of the present invention is a compact, lightweight and high-performance one, it can be used as a power source for a long time such as a portable notebook computer,
It can be widely used as a fuel cell for automobiles.

[Brief description of drawings]

FIG. 1 is an explanatory diagram related to the principle of a fuel cell.

FIG. 2 is a schematic configuration diagram (a) showing an example of the structure of the fuel cell in the present invention and a graph (b) showing the distribution of the magnetic field intensity (H) generated by the permanent magnet 6. (A) A schematic explanatory view of the present invention and (b) are magnetic field strength distributions.

FIG. 3 is a partially enlarged cross-sectional view (a) on the oxygen electrode side of a low temperature fuel cell in which a permanent magnet is installed behind the fuel flow path of the present invention (a) and a graph (b) of its magnetic field strength distribution.

FIG. 4 is a graph (b) in which the shape of the permanent magnet used in the present invention (a) and the measurement result of the magnetic field strength distribution thereof are plotted.
Is.

FIG. 5 is a layout view of an example in which a plurality of fuel cells according to the present invention are provided with permanent magnets.

FIG. 6 is a fuel flow path (a) of the fuel cell according to the present invention;
It is a block diagram (b) and a graph (c) of magnetic field intensity distribution of an example of an apparatus which integrated a permanent magnet and a fuel channel.

FIG. 7 is a configuration diagram (a) of an example in which two fuel cell units are arranged between permanent magnets according to the present invention, and a graph (b) of the magnetic field strength distribution thereof.

FIG. 8 is a configuration diagram (a) of an example in which permanent magnet particles are arranged between an electrolyte and an oxygen electrode catalyst layer according to the present invention (a) and a graph (b) of its magnetic field strength distribution.

FIG. 9 is a configuration diagram of an example in which a permanent magnet is attached on a wire mesh used in the present invention.

[Explanation of symbols]

1 oxygen pole 1'Catalyst layer in oxygen electrode 2 oxygen gas 3 electrolytes 4 fuel pole 5 hydrogen gas 6 permanent magnet 7 Fuel flow path 8 Iron fuel flow path material 9 Supports 10 Permanent magnet particles 11 wire mesh

Continued front page    F-term (reference) 5H018 AA06 AS02 AS03 CC06 EE02                       EE03 EE05 EE10 EE11 EE13                       EE17 EE18                 5H026 AA06 BB04 CC03 EE02 EE08                       EE11 EE18                 5H027 AA06

Claims (4)

[Claims] 1. A low-temperature fuel cell in which a permanent magnet is arranged near the fuel electrode. 2. A low temperature fuel cell characterized in that a permanent magnet is arranged in or near the electrolyte. 3. The low temperature fuel cell according to claim 1, wherein the magnetic field strength of the permanent magnet increases along the moving direction of the oxygen gas. 4. The low-temperature fuel cell according to claim 1, wherein the permanent magnet has a coating film of a substance that is chemically stable and allows the lines of magnetic force to pass therethrough.