JP3866534B2 - Fuel cell - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel cell. More specifically, the present invention relates to a small fuel cell having a simple structure that does not use a forced oxygen and fuel supply mechanism.
[0002]
[Background Art and Problems to be Solved by the Invention]
In recent years, in the field of electronic devices, portable electronic devices such as portable information terminals, mobile phones, and video cameras are rapidly spreading. Accordingly, as a power source for using these devices, development of a portable power source that has a high energy density and can be used for a long time is required.
As such a power source, secondary batteries are currently the mainstream, and research and development are actively conducted. Recently, the performance of nickel-metal hydride batteries and lithium-ion batteries has been improved, and the position as a power source for portable electronic devices is being built.
[0003]
However, depending on the type of portable electronic device, it has not reached a level that guarantees sufficient continuous use time. In addition, due to environmental problems, it is necessary to collect used batteries for recycling.
Therefore, development of an air battery and a fuel cell is expected as a battery having a high energy density to replace the secondary battery. However, the air battery has a problem that the self-discharge rate is large because the alkaline electrolyte reacts with carbon dioxide in the air and deteriorates with time.
[0004]
On the other hand, in the fuel cell, the fuel supplied to the negative electrode is oxidized to separate protons and electrons, and the protons conduct through the electrolyte membrane and react with oxygen supplied to the positive electrode to generate electric power.
Thus, the fuel cell directly converts the combustion energy of the fuel into electric energy, and the energy conversion efficiency is very high. In addition, since only water is generated during power generation, the load on the environment is very low.
[0005]
Moreover, it can be used continuously as long as the supply of fuel and oxygen is continued. In recent years, a polymer film has been used as an electrolyte film, and a fuel cell can be used at a relatively low temperature from room temperature to 90 ° C., so that it can be applied to a small electronic device.
However, in a fuel cell, water is generated at the positive electrode during power generation. If the water is not removed efficiently, electrons that have passed through the electrolyte membrane and reached the positive electrode cannot react with oxygen on the positive electrode, resulting in power generation efficiency. There is a disadvantage that leads to a decrease in. Furthermore, the fuel supplied to the negative electrode side is consumed with power generation, and the power generation efficiency decreases as the concentration decreases. Therefore, in order to increase the power generation efficiency in the fuel cell, an oxygen supply mechanism that forcibly distributes oxygen to the positive electrode and a fuel supply mechanism that forcibly distributes and supplies fuel to the negative electrode are necessary. However, since these forced oxygen and fuel supply mechanisms are bulky, the entire fuel cell also becomes large, which is inappropriate for use as a compact power source for portable electronic devices.
[0006]
Japanese Unexamined Patent Publication No. 2000-268835 discloses a fuel cell that does not use a forced oxygen supply mechanism. In the fuel cell, a positive electrode and a negative electrode are arranged to face each other through an electrolyte membrane, and a fuel holding portion is provided adjacent to the negative electrode so that fuel is supplied to the negative electrode by movement by natural diffusion. Yes. In addition, a ventilation structure is provided on the opposite side of the positive electrode to the electrolyte membrane, and external air is supplied to the positive electrode by natural diffusion through the gap, while the generated water is removed by natural evaporation, and the foreign matter is linearly directly. It can prevent reaching the positive electrode.
However, even in such a fuel cell, oxygen and fuel are diffused and the rate of spontaneous evaporation of generated water is slow, so oxygen and fuel supply and water removal from the positive electrode and the negative electrode are not sufficient. There is a need for further shortening of startup time and increase in power generation efficiency.
[0007]
[Means for Solving the Problems]
In the present invention, a fuel cell in which a positive electrode and a negative electrode are housed in a container with an electrolyte membrane sandwiched therebetween, the container has a fuel holding gap, a surplus fuel discharge port and a fuel supply port leading to the fuel holding space on the negative electrode side. The surplus fuel discharge port has a radius of 1/5 to 1/2 of the radius of the fuel supply port in circular conversion, and when the fuel is a gas, the fuel When the size of the supply port is a circle, the radius is 2 mm to 0.5 mm, and when the fuel is liquid, the size of the fuel supply port is a circle, and the radius is 4 mm to 1 mm. A combustion furnace equipped with a surplus fuel discharge port is installed, and the combustion furnace is filled with an oxidation filter made of a material carrying a metal catalyst. A small fuel cell with higher efficiency is supplied.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The fuel cell of the present invention is mainly composed of an electrolyte membrane, a positive electrode, a negative electrode, and a container.
[0009]
As the negative electrode and positive electrode used in the present invention, a water-repellent treated porous substrate such as carbon, carbon paper, carbon molded body, carbon sintered body, sintered metal, foam metal, and metal fiber aggregate should be used. Can do. These electrodes may further be used with a catalyst layer. For the catalyst layer, a carbon material containing a transition metal and platinum alloy such as platinum, iron, nickel, cobalt, ruthenium or the like, or fine particles of oxides thereof as a catalyst can be used. Platinum is preferred when the fuel is pure hydrogen, and platinum-ruthenium alloy is preferred when it contains hydrocarbons. The amount of the catalyst is about 5 to about 50% by weight, preferably about 10 to about 20% by weight, based on the electrode.
[0010]
The catalyst layer can be attached to the electrode by the following method. For example, a mixture of fine metal powders of platinum and ruthenium is supported as it is or on a carbon having a large surface area, and mixed with an alcohol solution containing polytetrafluoroethylene or a solid polymer electrolyte that acts as a binder and a water repellent, A method of spraying onto a porous electrode such as carbon paper and bonding it to a solid polymer electrolyte by hot pressing or the like (US Pat. No. 5,599,638), or a mixture of fine powders of platinum and ruthenium or its oxides as a solid This is mixed with an alcohol solution containing a polymer electrolyte, this catalyst mixture solution is applied onto a polytetrafluoroethylene plate, dried and then peeled off from the polytetrafluoroethylene plate, and transferred onto a porous electrode such as carbon paper. , A method of bonding to a solid polymer electrolyte by hot pressing or the like (X. Ren et al., J Electrochem.Soc., 143, L12 (1996)), and the like.
[0011]
The electrolyte membrane includes a copolymer of a trifluoroethylene derivative, a phosphoric acid-impregnated polybenzimidazole resin, a resin having a sulfonic acid group, a phosphonic acid group, a phenolic hydroxyl group or a fluorine-containing carbon sulfonic acid group as a cation exchange group, PSSA Examples thereof include those made of -PVA (polystyrene sulfonate polyvinyl alcohol copolymer), PSSA-EVOH (polystyrene sulfonate ethylene vinyl alcohol copolymer), and the like. Among them, those made of an ion exchange resin having a fluorine-containing carbon sulfonic acid group are preferable, and specifically, a Nafion membrane manufactured by DuPont, a Flemion membrane manufactured by Asahi Glass, and an Aciplex membrane manufactured by Asahi Kasei are used. . The solid polymer electrolyte membrane is obtained by forming a resin precursor into a film shape by a known method such as hot press molding, roll molding, extrusion molding, and the like, followed by hydrolysis and acidification treatment. It can also be obtained by a solvent casting method from a solution in which a fluorine-based cation exchange resin is dissolved in a solvent such as alcohol.
[0012]
The fuel holding gap is a space for holding the supplied fuel to supply it to the negative electrode. By providing the surplus fuel discharge port and the fuel supply port so as to communicate with the fuel holding gap, when the fuel is supplied from the fuel supply port, the gas having a reduced fuel concentration remaining in the fuel holding gap is excessive. The fuel is extruded from the fuel discharge port, and new fuel is smoothly supplied. Accordingly, the concentration of the fuel held in the fuel holding gap increases, and the fuel is supplied at a high concentration to the negative electrode, so that the power generation efficiency is improved. Further, since the fuel is smoothly supplied to the negative electrode, the startup time is shortened. The fuel holding gap is a space formed between the negative electrode and the container, and the size thereof is appropriately adjusted according to the size of the entire fuel cell. For example, it may have a volume of about 10% of the size of the container.
[0013]
The sizes of the fuel supply port and the surplus fuel discharge port are appropriately adjusted in consideration of the size of the container. When the fuel is a gas, there is no particular limitation. However, when the fuel is a liquid, it is difficult to supply the fuel if the radius of the fuel supply port is too small. Therefore, the fuel supply port preferably has a radius of about 1 mm or more.
In the fuel cell of the present invention, preferably, the surplus fuel discharge port is smaller than the fuel supply port. At this time, when the surplus fuel discharge port is smaller than the fuel supply port, the fuel supply pressure is temporarily maintained, which is preferable. For this reason, even when more fuel than the fuel holding gap can hold is supplied to the fuel holding gap, excess fuel is discharged from the excess fuel discharge port, and the pressure in the fuel holding gap is kept constant. Abnormal pressure is applied to prevent damage. Specifically, when the fuel supply port and the surplus fuel discharge port are substantially circular, and the fuel is gas, the radius of the fuel supply port is about 2 mm to about 0.5 mm, and the surplus fuel discharge port The size of the outlet radius is about 1 mm to about 0.1 mm. When the fuel is liquid, the radius of the fuel supply port is about 4 mm to about 1 mm, and the radius of the surplus fuel discharge port is about 2 mm to about 0.5 mm. When the fuel supply port and the surplus fuel discharge port are not circular, the sizes are considered as in the case where they are almost circular.
[0014]
In the fuel cell of the present invention, preferably, the container is provided with an outside air storage space and an outside air vent communicating therewith on the positive electrode side.
The outside air storage space is a space for supplying oxygen to the positive electrode. The positive-side container is provided with an external air vent, and an external air storage gap is formed between the fuel cell container and the positive electrode, so that the positive electrode is positioned in the vicinity of the outer surface to facilitate contact with the external air and the positive electrode It is possible to prevent foreign matter from coming into contact with. The outside air storage space is a space formed between the positive electrode and the container, and the size thereof is appropriately adjusted according to the size of the entire fuel cell. For example, it may have a volume of about 10% of the size of the container.
Outside air vent circles, rectangles, etc., may have any shape, those having about 0.1 mm ² ~ about 10 mm ² per 1 is preferable as the area. The number is preferably 1 to 100.
[0015]
In the fuel cell of the present invention, the outside air storage gap is preferably filled with an outside air holding material.
The outside air holding material is filled in the outside air storage gap, but may be one that completely fills the gap or a part thereof. In the case of satisfying a part, it may be disposed entirely or partially with respect to the positive electrode between the outside air vent provided in the container and the positive electrode. In any case, it may have an arbitrary thickness with respect to the width between the container and the positive electrode. As the form when the outside air retaining material is provided, as a sheet, a mesh or wool-like line, a line woven in a net-like shape, a thin line is compressed into a plate, granular, etc. Any form is acceptable. Specifically, a linear material is woven in a net-like shape, and a linear material is agglomerated like steel wool. Nickel, stainless steel, aluminum, and iron can be used as the material for the outside air retaining material. Furthermore, the water generated by the reaction at the positive electrode can be efficiently removed by the water repellent treatment by covering the outside air holding material with polytetrafluoroethylene or the like. The outside air holding material plays a role of holding outside air supplied from the outside air vent and supplying oxygen to the positive electrode by natural diffusion.
[0016]
In the fuel cell of the present invention, preferably, the outside air holding material is made of an electrically conductive material. That is, an organic conductive material represented by iodine-added polyacetylene (conductive polymer) or polymer material having electrical conductivity, specifically having an electrical conductivity at room temperature of 10 ³ S / cm or more. If the outside air holding material is made of an electrically conductive resin or the like in which a metal conductor is dispersed, the current collector also serves as a current collector. Therefore, the current collecting effect is improved, so that a higher current value can be obtained. Further, an independent layer may be formed as a current collector separately from the outside air holding material between the outside air holding material and the positive electrode. At this time, the current collector is formed of the same or different material as the outside air holding material.
[0017]
The fuel cell of the present invention is preferably further provided with a check valve at the fuel supply port. From the check valve, it is possible to prevent the back flow of the fuel, and as a result, it is possible to prevent the contamination of the unused fuel by the reactant. The check valve is not particularly limited as long as it is normally used for preventing the backflow of liquid or gas. For example, the check valve is released only when hydrogen of fuel is supplied from the fuel tank to the fuel supply port. Can be used. The air staying in the fuel holding gap is discharged from the surplus fuel discharge port so as to be pushed out by the supplied fuel. Therefore, the air staying in the fuel holding gap does not flow back to the fuel tank, and the fuel is supplied in a constant manner in the fuel holding air. As a result, stable power generation is performed.
[0018]
In the fuel cell of the present invention, preferably, a combustion furnace having an outside air intake / exhaust hole is connected to the surplus fuel discharge port.
The fuel furnace removes excess fuel that is not held in the fuel holding material after being supplied or is not consumed in the negative electrode, or carbon monoxide discharged as a result of the reaction in the negative electrode. This is a space for oxidizing and decomposing surplus fuel before it is discharged. Since it is sufficient that at least oxygen be mixed in the combustion furnace, it may be in a state where air introduced from the outside air intake / exhaust hole exists. The shape of the outside air intake / exhaust hole is not limited to a rectangular shape. In the case of a hole form, it is preferable to provide 10 to 200 holes having a hole diameter of about 0.5 mm to about 2 mm, but the number is not particularly limited.
[0019]
In the fuel cell of the present invention, the combustion furnace is preferably filled with an oxidation filter made of a material carrying a metal catalyst. By passing through the oxidation filter inside the combustion furnace, excess fuel in the exhausted gas is catalytically oxidized and decomposed to make it harmless, and exhausted from the outside air intake and exhaust hole together with the air remaining in the fuel holding gap. Thus, the fuel concentration in the fuel holding gap can be kept above a certain level. At this time, in the combustion furnace, there is a risk of high temperature due to the reaction heat of the oxidation reaction, so it is desirable to equip a heat insulating material made of glass wool or the like between the combustion furnace and the battery body.
[0020]
As the oxidation filter, porous ceramics such as alumina and silica, carbon fiber, carbon paper and the like can be used. As the metal catalyst supported on the oxidation filter, a noble metal such as platinum, or a transition metal such as palladium, manganese, nickel, etc., alone or in combination, has an average pore size of about 10 μm to about 500 μm, preferably about 20 μm to about 100 μm. Things can be used. However, the catalyst on the oxidation filter is preferably a metal that is less reactive than the catalyst used for the negative electrode. This is because if a catalyst having a higher adsorbing power than the catalyst used for the negative electrode is installed in the combustion furnace, the fuel is oxidized and decomposed in the combustion furnace before it is adsorbed to the negative electrode, and the concentration of the fuel decreases. It is. For example, when the catalyst used for the negative electrode is platinum, nickel can be used as the catalyst used for the oxidation filter.
[0021]
In the fuel cell of the present invention, preferably, a fuel tank is further connected to the fuel supply port.
The fuel cell of the present invention is characterized in that the fuel tank is made of a soft resin. In the present invention, the soft resin is a resin having a glass transition point of room temperature or lower, more specifically, low density polyethylene (specific gravity 0.91 to 0.93), polypropylene, polyethylene terephthalate, and the like. When the fuel tank is made of a soft resin, if the fuel tank is crushed, the fuel can be supplied to the negative electrode more quickly and smoothly as necessary. The fuel tank stores gas such as hydrogen or liquid fuel (hydrocarbon such as methanol) according to the type of fuel cell. Moreover, in order to produce | generate fuel by reaction, you may generate | occur | produce a fuel by reaction when storing a reaction raw material and supplying it to a fuel cell.
[0022]
In the fuel cell of the present invention, the fuel holding gap is filled with a fuel holding material.
As the fuel holding material, when supplying hydrogen as a fuel, a fuel holding material made of a porous carbon material or a hydrogen storage alloy composed of an alloy such as La-Ni, Ti-Fe, Mg-Ni alone or in combination is used. Can be used. Moreover, when supplying a liquid as a fuel, what made stainless steel, nickel, etc. with a high corrosion resistance in the shape of a wool and a mesh can be used, and the bigger fuel holding effect can be anticipated. When the fuel holding material is made of an electrically conductive material, it can also serve as a current collector, thus improving the current collection effect. Further, an independent layer may be formed as a current collector separately from the fuel holding material between the fuel holding material and the negative electrode. At that time, the current collector is formed of the same or different material as the fuel holding material.
[0023]
The fuel cell of the present invention preferably further has a gas diffusion layer made of a porous carbon material such as carbon paper or carbon fiber between each of the positive electrode and the negative electrode and the current collector. The gas diffusion layer plays a role of supplying air and fuel to the positive electrode and the negative electrode, respectively. When the gas diffusion layer is made of an electrically conductive material, it can also serve as a current collector.
[0024]
As a container, you may have what kind of form according to the form of the portable electronic device used, and its use. As the material of the container, in addition to acrylic resin, those having a glass transition point of room temperature or higher, specifically polystyrene, polycarbonate, hard polyvinyl chloride (added with 0-5% plasticizer), polydenylene oxide, etc. Hard resin can be used.
[0025]
The fuel cell of the present invention can be used particularly in a form incorporated in a small electronic device such as a portable information terminal, a mobile phone, and an electronic device (for example, an electronic device).
[0026]
【Example】
Hereinafter, the present invention will be described in detail. The following examples are general, and the present invention is not limited to these examples.
FIG. 1 shows an external configuration of a fuel cell according to an embodiment of the present invention, and FIG. 2 shows a schematic cross-sectional structure along the broken line shown in FIG. FIG. 3 is an enlarged view of a portion surrounded by a broken line in FIG.
[0027]
Example 1
In the fuel cell according to the present invention, in FIG. 1, a positive electrode 12 and a negative electrode 11 are arranged to face each other with an electrolyte membrane 13 therebetween, and a fuel holding gap 11d and an outside air storage gap are provided on the opposite side of the electrolyte membrane 13 of each pole. 12d. On the positive electrode side of the container for storing the fuel cell, there are five 2 mm × 5 mm rectangular outside air vents 1 and on the negative electrode side a φ1 mm fuel supply port 11e provided with a check valve 11f and a smaller φ0.5 mm diameter φ0.5 mm. A surplus fuel discharge port 11g is provided. The outside air storage gap 12d is loaded with an outside air holding material 12h in which a φ50 μm nickel wire is woven in a net shape. The fuel holding gap 11d is connected to the fuel tank 14 through the fuel supply port 11e. The fuel tank 14 stores fuel or unreacted substances for fuel generation. Further, a fuel furnace 15 provided with 120 holes of φ1.25 mm as the outside air outlet / exhaust hole 4 was connected to the surplus fuel discharge port 11g. The fuel furnace 15 was filled with 5 g of a conductive nickel-supporting porous ceramic having an average pore diameter of 50 μm as an oxidation filter 16 and 2 g of glass wool as a heat insulating material 17.
[0028]
As the catalyst material, a catalyst-integrated electrolyte membrane in which catalyst layers 11b and 12b in which 5 g of 10% by weight of platinum-supported carbon was attached to both surfaces of an electrolyte membrane 13 made of Nafion (registered trademark) manufactured by DuPont was fixed by hot pressing was used. . The catalyst layer-integrated electrolyte membrane is held by gas diffusion layers 11a and 12a made of carbon fiber and current collectors 11c and 12c made of stainless steel mesh, held in a battery container 10 made of acrylic resin, and a silicone adhesive. Fixed.
[0029]
Terminals 2 and 3 made of copper were connected to the current collectors 11c and 12c, respectively.
When fuel hydrogen is supplied from the fuel tank 14 to the fuel supply port 11e, the check valve 11f is released, and the air retained in the fuel holding gap 11d is pushed out from the surplus fuel discharge port 11g, and fuel is supplied to the fuel holding gap 11d. Was supplied and stable power generation was performed.
[0030]
【The invention's effect】
By the fuel supply as described above, the entire fuel cell is reduced in size. By providing the surplus fuel discharge port and the fuel supply port, exhausting the surplus fuel and combusting it removes the air that has accumulated in the fuel holding part, so that the cell performance is efficiently exhibited from the initial energization. . In addition, since the fuel is smoothly supplied, the power generation efficiency is improved and the startup time is further shortened.
[Brief description of the drawings]
FIG. 1 shows an external configuration of a fuel cell according to an embodiment of the present invention.
FIG. 2 shows a schematic cross-sectional structure along the broken line shown in FIG.
FIG. 3 shows an enlarged view of a portion surrounded by a broken line in FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Outside air vent 2 Negative electrode terminal 3 Positive electrode terminal 4 Outside air intake port / exhaust hole 10 Battery container 11 Negative electrode 11a Gas diffusion layer 11b Catalyst layer 11c Negative electrode current collector 11d Fuel holding gap 11e Fuel supply port 11f Check valve 11g Excess fuel discharge Outlet 11h Fuel holding material 12 Positive electrode 12a Gas diffusion layer 12b Catalyst layer 12c Positive electrode current collector 12d Outside air storage gap 12h Outside air holding material 13 Electrolyte membrane 14 Fuel tank 15 Combustion furnace 16 Oxidation filter 17 Heat insulating material

Claims (10)

A fuel cell in which a positive electrode and a negative electrode are housed in a container with an electrolyte membrane interposed therebetween,
The container includes, on the negative electrode side, a fuel holding gap, a surplus fuel discharge port and a fuel supply port that communicate with the fuel holding gap, and the size of the surplus fuel discharge port is one of the radius of the fuel supply port in circular conversion. When the fuel is a gas, the size of the fuel supply port is a circle with a radius of 2 mm to 0.5 mm, and when the fuel is a liquid The fuel supply port has a radius of 4 mm to 1 mm in circular conversion,
A fuel cell in which a combustion furnace having an outside air intake / exhaust hole is connected to the surplus fuel discharge port, and the combustion furnace is filled with an oxidation filter made of a material carrying a metal catalyst .   2. The fuel cell according to claim 1, wherein the container is provided with an outside air storage gap and an outside air vent leading to the outside air storage gap on the positive electrode side.   The fuel cell according to claim 1 or 2, wherein the outside air storage gap is filled with an outside air holding material. The fuel cell according to claim 3 , wherein the outside air holding material is made of an electrically conductive material. The fuel cell according to the check valve, any one of claims 1-4, characterized in that provided in the fuel supply port. When the fuel is gas, the size of the fuel supply port is a radius of 2 mm to 0.5 mm in terms of a circle, and the size of the surplus fuel discharge port is a radius of 1 mm to 0.1 mm in terms of a circle. When the fuel is a liquid, the size of the fuel supply port is a radius of 4 mm to 1 mm in terms of a circle, and the size of the surplus fuel discharge port is a radius of 2 mm to 0.5 mm in terms of a circle. The fuel cell according to any one of the above. The fuel cell according to any one of claims 1 to 6, wherein the metal catalyst is a metal having a lower reactivity than a catalyst used for the negative electrode.   The fuel cell according to any one of claims 1 to 7, wherein a fuel tank is installed in connection with the fuel supply port. The fuel cell according to claim 8, wherein the fuel tank is made of a soft resin.   The fuel cell according to claim 1, wherein the fuel holding gap is filled with a fuel holding material.

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