JP2004172111A - Liquid fuel cell and power generator using liquid fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid fuel cell suppressing reaction of liquid fuel during shut down period or low rate power generation period, while increasing absorption of hydrogen gas, achieving high energy density. <P>SOLUTION: The liquid fuel cell comprises a positive electrode 1 for reducing oxygen, a negative electrode 2a including a hydrogen occlusion material, a separator 3 (electrolyte layer) arranged between the positive electrode 1 and the negative electrode 2a, and liquid fuel 4. The negative electrode 2a oxidizes the liquid fuel 4 to produce gas. The liquid fuel cell comprises adjusting means for adjusting the reaction of the liquid fuel 4 oxidized by the negative electrode 2a, according to the amount of electricity to be generated, by utilizing the gas produced from the liquid fuel 4. <P>COPYRIGHT: (C)2004,JPO

Description

  The present invention relates to a liquid fuel cell using a liquid as fuel and a power generator using the same.

  2. Description of the Related Art In recent years, with the spread of cordless devices such as laptop computers and mobile phones, there has been a demand for smaller and higher-capacity secondary batteries as power sources. At present, lithium ion secondary batteries have been put to practical use as secondary batteries having a high energy density and can be reduced in size and weight, and demand for portable power sources is increasing. However, depending on the type of cordless device used, this lithium secondary battery has not yet reached a level where sufficient continuous use time is guaranteed.

  In such a situation, an air battery, a fuel cell, or the like can be considered as an example of a battery that can meet the above demand (for example, see Patent Documents 1 and 2).

  An air battery is a battery that uses oxygen in the air as an active material of a positive electrode. Since most of the internal volume of the battery can be used for filling the negative electrode, a battery suitable for increasing the energy density is used. It is considered to be. However, this air battery has a problem that an alkaline solution used as an electrolytic solution reacts with carbon dioxide in the air and deteriorates.

  In addition, some candidates for the fuel cell to be used are listed as fuel cells, but each has various problems, and a final decision has not been made yet. For example, when pure hydrogen is used as a fuel, it takes time and a huge amount of money to maintain a fuel supply facility such as a hydrogen station. Further, hydrogen is a very light combustible gas, so its handling is difficult, and there is a problem in terms of safety. Further, when gasoline is used as fuel and reforming gasoline to extract hydrogen requires a reformer, there is also a problem that the reforming efficiency is not very high. In addition, when methanol is used as a fuel, a problem similar to that of gasoline occurs when using reformed methanol.Using methanol as fuel without reforming results in lower output and efficiency, resulting in lower fuel efficiency. There is a problem that a certain amount of methanol permeates the electrolyte membrane.

Therefore, sodium borohydride (NaBH ₄ ) has attracted attention as a new hydrogen fuel source. Sodium borohydride generates hydrogen according to the following reaction formula.

(Formula 1)
NaBH ₄ + 2H ₂ O → NaBO ₂ + 4H ₂
Since the above hydrolysis reaction hardly occurs in an alkaline aqueous solution, sodium borohydride can be stably stored in an alkaline aqueous solution, and is expected as a novel hydrogen fuel source.

In recent years, an alkaline fuel cell has been developed in which a battery using a hydrogen storage alloy as a negative electrode is charged with a soluble metal hydride fuel such as NaBH ₄ , KBH ₄ , LiAlH ₄ , KH, or NaH (for example, Patent Reference 3, Patent Document 4.). In this alkaline fuel cell, fuel is supplied to the negative electrode to generate hydrogen, and the hydrogen is temporarily absorbed by the negative electrode to cause a reaction. By absorbing and storing hydrogen in the negative electrode, hydrogen can be used for the reaction according to the discharge rate. The metal hydride as a fuel is used after being dissolved in a liquid such as an aqueous solution. In particular, since NaBH ₄ is stable in an alkaline aqueous solution, it is used after being dissolved in an alkaline aqueous solution. When an air electrode is used as the positive electrode, this alkaline fuel cell can be continuously used as long as fuel and oxygen are supplied.
U.S. Pat. No. 3,419,900 JP-A-60-54177 JP 2002-289252 A (Patent No. 3342699) U.S. Pat. No. 5,599,640

  When an aqueous solution of metal hydride is supplied as fuel to the alkaline fuel cell, a hydrolysis reaction of the metal hydride occurs due to the contact between the fuel and the hydrogen storage alloy as the negative electrode, and even when the fuel cell is not generating power, the fuel in the fuel is not contained in the fuel. The decomposition reaction of the metal hydride continues. In this case, the hydrogen generated by the reaction between the negative electrode and the metal hydride is not used for power generation, but wastes fuel. For this reason, only a part of the prepared fuel can be taken out as electric power, which causes the energy density of the fuel cell to be greatly reduced.

  Here, by using an auxiliary device for controlling the supply of fuel to the negative electrode, useless consumption of fuel can be suppressed. However, in this case, the use of the auxiliary device increases the volume of the entire fuel cell. In addition, the structure of the fuel cell becomes complicated, and it becomes difficult to use the fuel cell as a small portable power supply.

  On the other hand, by giving elasticity to the positive electrode, the electrolyte layer, and the negative electrode and storing hydrogen gas generated by the reaction between the negative electrode and the fuel between the fuel and the negative electrode, the negative electrode and the fuel are only generated during power generation. A fuel cell in contact is also conceivable. For example, a method of imparting elasticity to an integrated body of a positive electrode, an electrolyte layer, and a negative electrode and generating hydrogen gas causes the integrated body to curve to the opposite side to the fuel, thereby cutting off the contact between the negative electrode and the fuel. Conceivable.

  However, in the above method, when a hydrogen storage alloy is used for the negative electrode, it is difficult to give the negative electrode elasticity that can realize the above function. In addition, in the above method, since a high pressure is applied to the hydrogen gas between the negative electrode and the fuel, the hydrogen gas may flow out to the positive electrode side. In order to prevent this, it is necessary to arrange a film-like ion-conductive electrolyte that does not allow gas to pass through the electrolyte layer, which increases the cost. Further, since the positive electrode, the electrolyte, and the negative electrode are repeatedly deformed, the catalyst layer from the positive electrode or the hydrogen storage alloy from the negative electrode easily falls off, and there is a problem in durability of the electrode.

  An object of the present invention is to provide a liquid fuel cell having a high energy density by suppressing the reaction of liquid fuel at the time of stopping power generation or low-rate power generation and increasing the absorption of hydrogen gas.

  The liquid fuel cell of the present invention includes a positive electrode for reducing oxygen, a negative electrode containing a hydrogen storage material, an electrolyte layer disposed between the positive electrode and the negative electrode, and a liquid fuel. A liquid fuel cell in which a gas is generated when fuel is oxidized, wherein a gas generated from the liquid fuel is used to control a reaction in which the liquid fuel is oxidized by the negative electrode according to an amount of generated electricity. It is characterized by having adjusting means.

  Further, the power generation device of the present invention is a power generation device in which a plurality of power generation elements are electrically connected to any one selected from series and parallel, and at least one of the power generation elements includes the liquid fuel cell. It is characterized by being.

  ADVANTAGE OF THE INVENTION This invention can provide the liquid fuel cell of high energy density by suppressing the reaction of the liquid fuel at the time of electric power generation stop or low-rate electric power generation, and increasing the absorption of hydrogen gas.

  Hereinafter, embodiments of the present invention will be described.

  One embodiment of the liquid fuel cell of the present invention includes a positive electrode for reducing oxygen, a negative electrode including a hydrogen storage material, an electrolyte layer disposed between the positive electrode and the negative electrode, and storing a liquid fuel including a metal hydride. And a gas holding portion capable of collecting and holding gas generated from the liquid fuel at a contact portion between the negative electrode and the liquid fuel. The gas holding unit is arranged so that the liquid fuel does not come into contact with the negative electrode while holding the gas generated from the liquid fuel.

  By providing a gas holding part that can collect and hold the gas generated from the liquid fuel at the contact part between the anode and the liquid fuel, the anode and the liquid fuel react when the power generation is stopped or during low-rate power generation to generate electricity. When hydrogen that is not used for the gas is generated, the hydrogen is accumulated in the gas holding unit. When hydrogen is accumulated in the gas holding unit, the contact between the negative electrode and the liquid fuel is cut off by the accumulated hydrogen, and the reaction between the negative electrode and the liquid fuel is stopped. Thereby, wasteful consumption of the liquid fuel can be suppressed, and the energy density of the liquid fuel cell can be improved. During normal power generation of the fuel cell, hydrogen in the gas holding unit is consumed, liquid fuel flows into the gas holding unit, and the negative electrode and the liquid fuel come into contact with each other, so that the negative electrode and the liquid fuel react with each other. Hydrogen is generated, and power generation can be continued.

  When the amount of electricity generated by the liquid fuel cell is large, a large amount of hydrogen stored in the gas holding unit is consumed, so that the amount of liquid fuel flowing into the gas holding unit also increases. Therefore, the area where the anode and the liquid fuel are in contact with each other increases, and a large amount of hydrogen is generated. On the other hand, when the amount of generated electricity is small, the consumption of hydrogen in the gas holding unit is small, so that the amount of liquid fuel flowing into the gas holding unit is also small. Therefore, the area where the anode and the liquid fuel are in contact with each other is reduced, and the generation of hydrogen is also reduced. That is, the reaction between the negative electrode and the liquid fuel can be adjusted according to the amount of generated electricity.

  The structure of the gas holding unit is not particularly limited as long as it has an opening through which the liquid fuel flows and can hold the generated gas on the surface of the negative electrode on the liquid fuel side. Absent. For example, the function of the gas holding part is exhibited by a structure in which a storage part is formed by a partition member between the liquid fuel storage part and the negative electrode so that hydrogen gas generated on the surface of the negative electrode on the liquid fuel side can be collected. Can be done.

  Further, since the gas holding portion is formed in a tubular shape and the installation direction of the tubular portion is set to two or more directions, the generated gas can be held in the gas holding portion regardless of the installation direction of the fuel cell. The power generation efficiency is improved.

  Further, it is preferable that a check valve operated by the pressure of the generated gas is installed at both ends of the tubular gas holding portion so that the liquid fuel and the gas in the tubular portion flow in one direction. Thereby, the liquid fuel circulates, and the utilization rate of the fuel is improved.

  As a material of the gas holding portion, for example, a synthetic resin such as polytetrafluoroethylene, hard polyvinyl chloride, polypropylene, and polyethylene, a stainless steel, and a corrosion-resistant metal such as nickel-plated steel can be used. The type is not particularly limited as long as the material is chemically stable and does not transmit gas.

  It is preferable that the surface of the negative electrode on the gas holding portion side (liquid fuel side) is subjected to a water-repellent treatment. This is because, when generating power using the hydrogen gas accumulated in the gas holding unit, if the surface of the negative electrode is subjected to water repellent treatment, the absorption of hydrogen into the hydrogen storage material as the negative electrode occurs promptly.

  Further, it is preferable that the water repellent treatment is performed by applying a fluororesin to the surface of the negative electrode. This is because fluororesins are excellent in water repellency. Examples of the fluororesin include polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkylvinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, polyvinylidene fluoride, Polychlorotrifluoroethylene and the like can be used.

  Further, a catalyst having at least one function selected from a function of dissociating hydrogen into atoms and a function of oxidizing hydrogen is provided on the surface of the negative electrode on the side of the gas holding portion (liquid fuel side). Is preferred. When a catalyst having a function of dissociating hydrogen into atoms is provided, absorption of hydrogen into the hydrogen storage material can be promoted. In addition, when a catalyst having a function of oxidizing hydrogen is provided, oxidation of hydrogen can be promoted and discharge at the negative electrode can be assisted. This catalyst may be contained in the negative electrode.

  The catalyst only needs to have a function of dissociating hydrogen into atoms or a function of oxidizing hydrogen at the operating temperature of the fuel cell. For example, metals such as Pt, Pd, Rh, and Ni can be used. Among them, Pt is particularly excellent in the above-mentioned catalytic function, and thus can be preferably used.

  Further, this catalyst is preferably supported on porous carbon. By supporting the catalyst on porous carbon, the surface area of the entire catalyst can be increased, the reaction area between hydrogen and the catalyst can be increased, and the dissociation or oxidation reaction of hydrogen can be promoted.

  Further, the carrier supporting the catalyst is preferably carbon. This is because, when the catalyst oxidizes hydrogen, it involves electron transfer. At that time, if carbon having conductivity is used, the reaction proceeds smoothly.

  Further, in order to oxidize the hydrogen generated in the gas holding unit, it is also effective to use a part of the negative electrode as a gas diffusion electrode having a function of oxidizing hydrogen. The surface of the negative electrode containing the hydrogen storage material has a function of oxidizing hydrogen on the surface of the negative electrode by causing a decomposition reaction of metal hydride on the surface of the negative electrode and a gas diffusion electrode performing an oxidation reaction of hydrogen generated on the gas holding portion. This is because hydrogen generated in the gas holding portion can be consumed more efficiently than when a layer is formed.

  The gas diffusion electrode includes a catalyst having a function of dissociating hydrogen into atoms or a function of oxidizing hydrogen. As the catalyst, for example, a metal such as Pt, Pd, Rh, and Ni can be used. Among them, Pt is particularly excellent in the above-mentioned catalytic function, and thus can be preferably used.

  Further, this catalyst is preferably supported on porous carbon. By supporting the catalyst on porous carbon, the surface area of the entire catalyst can be increased, the reaction area between hydrogen and the catalyst can be increased, and the dissociation or oxidation reaction of hydrogen gas can be promoted.

  Further, the carrier supporting the catalyst is preferably carbon. This is because, when the catalyst oxidizes hydrogen, it involves electron transfer. At that time, if carbon having conductivity is used, the reaction proceeds smoothly.

  Further, the gas diffusion electrode preferably contains a fluororesin. This is because fluororesins are excellent in water repellency and can accelerate the dissociation or oxidation reaction of hydrogen gas. Examples of the fluororesin include polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkylvinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, polyvinylidene fluoride, Polychlorotrifluoroethylene and the like can be used.

  In order to separate the liquid fuel from the gas generated by the reaction between the liquid fuel and the negative electrode, it is also effective to arrange the gas-liquid separation membrane at a gas holding portion or at any place connected to the gas holding portion. In particular, when a gas-liquid separation membrane is arranged on the liquid fuel side of the gas diffusion electrode, the generated gas and the liquid fuel are separated, and only the generated gas comes into contact with the gas diffusion electrode. High hydrogen oxidizing ability can be maintained without wetting.

  The gas-liquid separation membrane is a membrane that can separate a gas and a liquid, and may be chemically stable with respect to a liquid fuel. However, a microporous polytetrafluoroethylene membrane is preferably used.

  Further, as the hydrogen storage material, a hydrogen storage alloy or a carbon nanotube is preferable. This is because they have excellent hydrogen storage capacity.

  The electrolyte layer preferably contains an aqueous solution in which at least one selected from the group consisting of KOH, NaOH and LiOH is dissolved. This is because high ionic conductivity can be imparted.

As the liquid fuel, an alkaline aqueous solution in which a metal hydride is dissolved is preferable. This is because metal hydrides can be stably stored in an aqueous alkali solution. The metal hydride may be any compound that undergoes a hydrolysis reaction when it comes into contact with the hydrogen storage material serving as the negative electrode, and at least one selected from the group consisting of NaBH ₄ , KBH ₄ , LiAlH ₄ , KH and NaH. It is preferably one. This is because they can be easily dissolved in water and supply a large amount of hydrogen per unit mass.

  The electromotive force of one liquid fuel cell is 1.23 V or less, and the electromotive force is insufficient to drive many electronic devices. By configuring a power generation device by connecting a plurality of liquid fuel cells in series, an electromotive force capable of driving various electronic devices can be obtained.

  In order to configure a high electromotive force power generation device, the liquid fuel cell of the present invention and other power generation elements such as a fuel cell, a secondary battery, and a capacitor can be connected in series. In addition, by connecting a capacitor or a secondary battery having excellent high-rate discharge characteristics in a shorter time than the liquid fuel cell in parallel with the liquid fuel cell, a high-energy-density power generation device having excellent high-rate discharge characteristics is configured. be able to.

  As a power generation element connected in series or parallel with the liquid fuel cell, a fuel cell that generates power from hydrogen and oxygen is preferable. Since oxygen is contained in air, a special storage unit for oxygen is not required, and only an electrode for reducing oxygen is required, so that a battery having a high energy density is obtained. Since hydrogen generated by the reaction between the metal hydride and the hydrogen storage alloy can be used in the liquid fuel cell of the present invention, a new hydrogen storage unit other than the metal hydride storage unit for the liquid fuel cell can be used. Do not need.

  When a fuel cell using hydrogen as a fuel is connected in series or in parallel with the liquid fuel cell of the present invention in the same power generator, the hydrogen electrode of the fuel cell using hydrogen as a fuel is supplied from the gas holding portion of the liquid fuel cell. It is preferable to provide a conduit for guiding hydrogen to the (negative electrode part). This is because, by using the hydrogen generated from the liquid fuel cell, it is not necessary to newly provide a hydrogen storage unit for the fuel cell using hydrogen as a fuel, and the power generation device can be downsized.

  By providing a gas holding portion capable of collecting and holding gas generated from the liquid fuel at a contact portion between the negative electrode of the liquid fuel cell and the liquid fuel, the negative electrode can be provided when the power generation of the liquid fuel cell is stopped or at a low rate of power generation. Reacts with the liquid fuel to generate hydrogen that is not used for power generation, and the hydrogen is accumulated in the gas holding unit. The stored hydrogen is led by a conduit to the hydrogen electrode of a fuel cell using other hydrogen as fuel. When hydrogen is accumulated in the gas holding portion and the hydrogen electrode portion, the contact between the negative electrode and the liquid fuel is interrupted by the accumulated hydrogen, and the reaction between the negative electrode and the liquid fuel stops. Thereby, wasteful consumption of the liquid fuel can be suppressed, and the energy density of the liquid fuel cell can be improved. During normal power generation of the liquid fuel cell, hydrogen in the hydrogen electrode portion and the gas holding portion is consumed. Liquid fuel flows from the liquid fuel storage portion into the gas holding portion, and the anode and the liquid fuel come into contact again. By doing so, the negative electrode reacts with the liquid fuel to generate hydrogen, and power generation can be continued.

  It is also effective to provide a gas-liquid separation membrane in a conduit for guiding hydrogen to the hydrogen electrode of a fuel cell using hydrogen as fuel to separate liquid fuel and hydrogen. This is because power can be stably generated by supplying only hydrogen to the hydrogen electrode.

  Next, an embodiment of the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 is a sectional view of a liquid fuel cell according to Embodiment 1 of the present invention. The positive electrode 1 is configured by, for example, laminating a carbon layer 1b made of carbon powder having a catalyst supported on porous carbon powder and a gas-liquid separation sheet 1a made of polytetrafluoroethylene. The positive electrode 1 has a function of reducing oxygen, and its performance can be improved by supporting a catalyst on the porous carbon powder. As the catalyst, silver, platinum, ruthenium, iridium oxide, rare earth oxide, manganese oxide, or an alloy containing at least one of silver, platinum, and ruthenium is used. The carbon layer 1b of the positive electrode 1 contains polytetrafluoroethylene resin particles for imparting water repellency.

The negative electrode 2a (hydrogen storage alloy electrode) is formed by fixing a hydrogen storage material to a conductive substrate, and has a function of oxidizing fuel. As the hydrogen storage material, a hydrogen storage alloy or a carbon material such as a carbon nanotube can be used, and a hydrogen storage alloy is particularly suitable. The type of the hydrogen storage alloy is not particularly limited. For example, an AB ₅ type hydrogen storage alloy represented by LaNi ₅ , an AB ₂ type hydrogen storage alloy represented by ZnMn ₂ or a substitute thereof, Magnesium-based A ₂ B-type hydrogen storage alloys represented by Mg ₂ Ni or a substituted body thereof, and solid solution-type vanadium-based hydrogen storage alloys can be used. Among them, MmNi ₅ -based AB ₅ type hydrogen storage alloy in which a misch metal (Mm) which is a mixture of rare earth elements is used and a part of Ni is replaced by Co or the like is particularly preferably used. This is because they have excellent durability and ability to absorb and release hydrogen.

  The conductive substrate of the negative electrode 2a may be any substrate made of a material having corrosion resistance to the electrolyte and capable of obtaining electrical contact from the hydrogen storage material. For example, a nickel or nickel-plated iron punching metal, A foamed metal body or the like is used.

  As the binder for fixing the hydrogen storage material of the negative electrode 2a to the conductive substrate, any material may be used as long as it is chemically stable and sticky in the electrolyte, and for example, polytetrafluoroethylene, latex, or the like is used. be able to. Among them, polytetrafluoroethylene is preferably used because it imparts water repellency to the negative electrode 2a.

  The negative electrode 2b is a gas diffusion electrode having a function of electrochemically oxidizing hydrogen, and is disposed on the same plane as the negative electrode 2a. As this gas diffusion electrode, one having the same configuration as the carbon layer 1b of the positive electrode 1 can be used, and as the catalyst, for example, platinum fine particles can be used. A gas-liquid separation sheet 1a is provided on the surface of the negative electrode 2b on the liquid fuel side. The negative electrodes 2a and 2b are electrically connected in parallel.

  As the electrolyte of the present embodiment, various electrolytes can be used as long as they are liquid, and an alkaline aqueous solution is particularly preferably used. As the alkaline aqueous solution, for example, a solution in which a hydroxide of an alkali metal such as KOH, NaOH, or LiOH is dissolved in water at about 10 to 40% by mass is preferable, and a mixed electrolyte containing a plurality of hydroxides of an alkali metal is preferable. Can also be used.

  In order to form an electrolyte layer while holding the above electrolyte, a separator 3 is disposed between the positive electrode 1 and the negative electrodes 2a and 2b. The material of the separator 3 is not particularly limited as long as it is stable with respect to the electrolyte. For example, a nonwoven fabric made of polypropylene, polyethylene, or the like is used. When water is used as the electrolyte solvent, the surface of the separator 3 is preferably subjected to a hydrophilic treatment.

As a hydrogen supply source of the liquid fuel 4, a metal hydride is used. As the metal hydride, for example, NaBH ₄ , KBH ₄ , LiBH ₄ , LiAlH ₄ , NaAlH ₄ , KAlH ₄ , KH, NaH or the like is used. In particular, NaBH ₄ is preferably used. This is because NaBH ₄ is more stable than other metal hydrides in water or an aqueous alkali solution, and has a mild reaction with the hydrogen storage alloy. The metal hydride as the hydrogen supply source can be used in a state of being dissolved or mixed in the liquid electrolyte.

  The positive electrode 1, the separator 3 and the negative electrodes 2a and 2b constituting the electrolyte layer are each in the form of a sheet, and are laminated in the order of the positive electrode 1, the separator 3 and the negative electrodes 2a and 2b to form an electrode-electrolyte integrated material. I have.

  A fuel tank 5 for storing a liquid fuel 4 is provided adjacent to the negative electrodes 2a and 2b on the side opposite to the separator 3. The fuel tank 5 is made of, for example, a synthetic resin such as polytetrafluoroethylene, hard polyvinyl chloride, polypropylene, or polyethylene, or a corrosion-resistant metal such as stainless steel. However, when the fuel tank 5 is made of metal and a plurality of cells are connected in series to form a fuel cell module, the surface of the fuel tank 5 is insulated so that each cell is not electrically short-circuited. Need to be covered by body.

  At a contact portion between the negative electrodes 2a and 2b and the liquid fuel 4, a gas holding portion 6 capable of collecting and holding gas generated from the liquid fuel 4 is provided. The gas holding unit 6 of the present embodiment is formed by a partition plate 5a provided between the fuel tank 5 as a liquid fuel storage unit and the negative electrodes 2a and 2b. A zigzag groove as shown in FIG. 2 is formed on the surface of the partition plate 5a on the negative electrode side. The gas holding portion 6 forms a tubular portion by the groove portion and the negative electrodes 2a and 2b.

  Check valves 7a and 7b are provided at both ends of the gas holding unit 6 so that the liquid fuel 4 in the gas holding unit 6 and the gas generated from the liquid fuel 4 flow in one direction. When the liquid fuel 4 in the gas holding unit 6 reacts with the negative electrode 2a to generate hydrogen gas, the internal pressure in the gas holding unit 6 increases and the check valve 7a closes. Further, when hydrogen gas is generated, the liquid fuel 4 in the gas holding unit 6 is pushed to the check valve 7b side, and the gas holding unit 6 is filled with hydrogen gas. When power generation is started, the hydrogen gas in the gas holding unit 6 is oxidized by the negative electrode 2b (gas diffusion electrode). At this time, since the inside of the gas holding unit 6 is in a depressurized state, the check valve 7b is closed, and the liquid fuel 4 flows into the gas holding unit 6 from the check valve 7a. With the above-described mechanism, the liquid fuel 4 in the gas holding unit 6 circulates in one direction.

  In order to efficiently circulate the liquid fuel 4, the negative electrodes 2 a and 2 b must be arranged in this order with respect to the flow direction of the liquid fuel 4 in the gas holding unit 6. By doing so, the hydrogen gas in the gas holding unit 6 is consumed by the negative electrode 2b, and only the liquid fuel 4 can return to the fuel tank 5 from the check valve 7b.

  The tube diameter of the tubular portion is preferably small so that the liquid fuel 4 and the hydrogen gas in the gas holding portion 6 are mixed in the tubular portion. Specifically, the tube diameter is preferably 1 to 3 mm, and more preferably 1 to 2 mm. Is more preferred. When the pipe diameter is increased, the liquid fuel 4 and the hydrogen gas are exchanged in the pipe, and the liquid fuel 4 flows to the fuel cell installation surface side. On the other hand, when the pipe diameter is reduced, the liquid fuel 4 and the hydrogen gas can be mixed without being replaced by gravity due to surface tension. Therefore, the circulation causes the liquid fuel 4 and the hydrogen gas to flow in one direction regardless of the direction of gravity. Therefore, the installation direction of the fuel cell of the present embodiment is not limited, and the fuel cell can be position-free.

  A cover plate 8 is provided on the side of the positive electrode 1 opposite to the separator 3, and an air hole 9 is provided in a portion of the cover plate 8 in contact with the positive electrode 1. This allows oxygen in the atmosphere to come into contact with the positive electrode 1 through the air holes 9.

  A current collector 10 is connected to the positive electrode 1 and the negative electrode 2a. The current collector 10 is made of, for example, a noble metal such as platinum or gold, nickel or a nickel-plated corrosion-resistant metal, or carbon. .

  The fuel tank 5 is provided with a fuel supply port 11 for supplying the liquid fuel 4. The liquid fuel 4 is supplied from the fuel supply port 11 and replenished to the fuel tank 5. When the fuel cell generates power, the fuel supply port 11 is sealed so that the liquid fuel 4 does not leak from the fuel cell.

  A gas-liquid separation hole 12a and a gas-liquid separation film 12b are provided on a surface other than the electrode surface side of the fuel tank 5. The gas-liquid separation membrane 12b is provided to prevent the internal pressure in the fuel tank 5 from rising when the hydrogen not consumed by the negative electrode 2b (gas diffusion electrode) is discharged to the fuel tank 5, thereby preventing the tank from bursting. It has the function of discharging only gas out of the tank.

  Further, a rubber seal member 13 is disposed between the gas-liquid separation sheet 1 a of the cover plate 8 and the fuel tank 5.

(Embodiment 2)
FIG. 3 is a sectional view of a liquid fuel cell according to Embodiment 2 of the present invention. In the present embodiment, a negative electrode of the liquid fuel cell of the first embodiment is only the negative electrode 2a (hydrogen storage alloy electrode), a polymer electrolyte fuel cell 16 is newly provided, and the gas holding unit 6 is replaced with the polymer fuel cell 16 It is the structure that led to.

  The positive electrode of the polymer electrolyte fuel cell 16 includes a diffusion layer 15 and a positive electrode catalyst layer 17, and the negative electrode includes the diffusion layer 15 and a negative electrode catalyst layer 18. Further, the solid polymer electrolyte membrane 14 is disposed between the positive electrode catalyst layer 17 and the negative electrode catalyst layer 18. Further, on the liquid fuel side of the anode catalyst layer 18, a gas-liquid separation sheet 1a is disposed. The polymer electrolyte fuel cell 16 generates power using hydrogen generated by the reaction between the negative electrode 2a and the liquid fuel 4 and oxygen in the air. In the present embodiment, a high voltage can be obtained by electrically connecting the two sets of positive and negative electrodes in series.

  Hereinafter, the present invention will be specifically described based on examples. However, the present invention is not limited to the following examples.

(Example 1)
A liquid fuel cell having a structure similar to that of the first embodiment was manufactured as follows.

The positive electrode 1 was produced as follows. 0.25 g of carbon "BP-2000" (trade name) carrying platinum fine particles manufactured by CABOT was added to 30 cm ³ of distilled water, and mixed and stirred for 10 minutes. 0.18 g of an aqueous dispersion of fluoroethylene was added, and the mixture was further mixed and stirred for 20 minutes. Thereafter, 8 cm ³ of n-butanol was added and mixed and stirred for 20 minutes, and further heated to 200 ° C. and mixed and stirred for 20 minutes. Then, aggregates were settled, the supernatant was removed, and the cathode catalyst paste was removed. Obtained. The obtained paste is applied to a 40 mesh nickel mesh plate electrode support and dried to form a carbon layer 1b, which is a polytetrafluoroethylene sheet “Goretex” (trade name, thickness) manufactured by Japan Goretex. Positive electrode 1 was pressure-bonded to a film (gas-liquid separation sheet 1a) having a thickness of 100 µm and a porosity of 50% at a pressure of 9 MPa.

The negative electrode 2a (hydrogen storage alloy electrode) was produced as follows. Composition formula: MmNi _3.48 Co _0.74 Mn _0.4 Al _0.3 (Mm is a misch metal composed of 33 mass% of La, 47 mass% of Ce, 5 mass% of Pr, and 15 mass% of Nd) 100 g of a hydrogen absorbing alloy made of 5 mass% of poly-N 6 g of a vinylacetamide aqueous solution, 0.1 g of carboxymethylcellulose, and 1.3 g of an aqueous dispersion of 50% by mass of latex were added and mixed to obtain a paste containing the negative electrode mixture. The obtained paste was applied and filled on a substrate made of a nickel foam, dried to form a negative electrode mixture layer, and then pressed and formed to obtain a negative electrode 2a.

The negative electrode 2b (gas diffusion electrode) was produced in the same manner as the positive electrode. However, activated carbon carrying platinum fine particles instead of carbon (the ratio of platinum fine particles to the total mass of platinum fine particles and activated carbon was 5% by mass) was used. The amount of platinum applied was 4 mg / cm ² .

The electrolyte used was a 30% by mass aqueous KOH solution, the separator 3 was a 120 μm-thick nonwoven fabric made of sulfonated polypropylene, and the liquid fuel was a 1.6% by mass aqueous NaBH ₄ aqueous solution. As the alkaline aqueous solution, a 29.5% by mass aqueous KOH solution was used.

  In addition, the gas holding part 6 was made into a tubular shape with a cross section of 2 × 2 mm.

(Example 2)
A liquid fuel cell having the same structure as that of the second embodiment was manufactured as follows.

  In this example, as shown in FIG. 3, in the liquid fuel cell manufactured in Example 1, instead of disposing the negative electrode 2b (gas diffusion electrode), the entire negative electrode was used as the negative electrode 2a (hydrogen storage alloy electrode). One battery and one polymer electrolyte fuel cell 16 were combined and produced. The gas holding part 6 of the liquid fuel cell was connected to the gas holding part 6 'of the polymer electrolyte fuel cell 16 as shown in FIG. The liquid fuel cell and the polymer electrolyte fuel cell 16 were electrically connected in series to form a power generator.

The polymer electrolyte fuel cell used in this example was manufactured as follows. First, 50 parts by mass of "Ketjen Black EC" (trade name) manufactured by Lion Akzo, 10 parts by mass of platinum-supported carbon carrying 50 parts by mass of platinum fine particles having an average particle diameter of 3 nm, and 10 parts by mass of Electrochem. 75 parts by mass of a solution of the proton conductive substance "Nafion" (trade name, solid content concentration: 5% by mass), and a polytetrafluoroethylene emulsion solution "D1" (trade name, emulsion concentration: 60 parts by mass) as a fluororesin binder %) And 5 parts by mass of water. These were mixed and dispersed with a homogenizer, applied to a carbon cloth (diffusion layer 15) so that the platinum amount was 0.3 mg / cm ² , and dried. Next, hot pressing was performed at 120 ° C. and 10 MPa for 2 minutes to form electrodes, whereby a positive electrode catalyst layer 17 and a negative electrode catalyst layer 18 were obtained.

  The solid polymer electrolyte membrane 14 is made of “Nafion 117” (trade name) manufactured by DuPont. The solid polymer electrolyte membrane 14 is sandwiched between the cathode catalyst layer 17 and the anode catalyst layer 18 under the conditions of 120 ° C. and 10 MPa. For 3 minutes.

(Comparative Example 1)
FIG. 4 is a sectional view of a conventional liquid fuel cell in Comparative Example 1. This comparative example is the same as Example 1 except that the entire negative electrode was a negative electrode 2a (hydrogen storage alloy electrode), the gas storage portion and the gas-liquid separation hole were not provided, and the installation direction of the battery was changed. It is a structure of. In this comparative example, since the liquid fuel 4 and the negative electrode 2a are always in contact with each other, hydrogen gas continues to be generated even when the power generation of the fuel cell is stopped, and a part of the liquid fuel 4 is wasted. Will be.

(Comparative Example 2)
FIG. 5 is a cross-sectional view of a conventional liquid fuel cell in Comparative Example 2. This comparative example has the same configuration as the comparative example 1 except that a gas-liquid separation hole 12a and a gas-liquid separation film 12b for discharging hydrogen gas generated in the fuel tank 5 are provided.

  Each of the batteries of Examples 1 and 2 and Comparative Examples 1 and 2 was fully filled with liquid fuel, and observation was performed in a state where the positive and negative terminals were open. As a result, in the batteries of Examples 1 and 2, generation of hydrogen gas was stopped within 10 minutes from the start of observation. On the other hand, in the battery of Comparative Example 1, the generation of hydrogen gas continued, the pressure inside the battery increased, and the polytetrafluoroethylene sheet (gas-liquid separation sheet 1a) was damaged, and did not function as a battery. On the other hand, in the battery of Comparative Example 2, the pressure in the battery did not increase because the gas-liquid separation hole 12a and the gas-liquid separation membrane 12b were provided, but until the sodium borohydride in the liquid fuel was completely hydrolyzed. Hydrogen gas generation continued.

Next, after all the used liquid fuel was discharged from each of the cells of Examples 1 and 2 and Comparative Example 2, the liquid fuel was fully charged and the battery voltage was 0.5 V at a current density of 10 mA / cm ^2. , And the discharge capacity was measured. Table 1 shows the results. The discharge capacity was shown as a relative value when the discharge capacity of Example 1 was set to 100%.

表１において、実施例１および実施例２に比べて比較例２の放電容量が小さいのは、比較例２では気体保持部を設けていないので、放電電流の大きさに関係なく一定量の液体燃料が負極と反応しつづけ、放電反応に使用されなかった水素ガスが電池外に放出されたためと考えられる。これに対して、実施例１および実施例２では気体保持部を設けているので、放電反応に使用されなかった水素ガスは電池内に蓄積されるとともに、水素ガスの蓄積部分近傍の負極からは水素ガスが発生しなくなるため、液体燃料が効率よく使用できたものと考えられる。

In Table 1, the reason why the discharge capacity of Comparative Example 2 is smaller than that of Example 1 and Example 2 is that the comparative example 2 does not include a gas holding unit, and therefore a fixed amount of liquid regardless of the magnitude of the discharge current. It is considered that the fuel continued to react with the negative electrode, and hydrogen gas not used for the discharge reaction was released outside the battery. On the other hand, in Example 1 and Example 2, since the gas holding unit is provided, the hydrogen gas not used for the discharge reaction is accumulated in the battery, and the hydrogen gas from the negative electrode in the vicinity of the hydrogen gas accumulation part is not removed. Since no hydrogen gas is generated, it is considered that the liquid fuel could be used efficiently.

  Further, the reason why the discharge capacity of the second embodiment is larger than that of the first embodiment is that the volume of the gas holding portion of the second embodiment is larger than that of the first embodiment only in the portion of the polymer electrolyte fuel cell, and thus the generated hydrogen It is considered that the reaction with the gas occurred efficiently.

  The present invention can provide a liquid fuel cell having a high energy density by suppressing the reaction of liquid fuel at the time of power generation stop or low-rate power generation and increasing the absorption of hydrogen gas, so that a laptop computer can be provided. In addition, a power source of a cordless device such as a mobile phone can be reduced in size and capacity can be increased.

FIG. 2 is a sectional view of the liquid fuel cell according to Embodiment 1 of the present invention. 1 is a perspective view of a fuel tank of a liquid fuel cell according to Embodiment 1 of the present invention. FIG. 5 is a sectional view of a liquid fuel cell according to Embodiment 2 of the present invention. FIG. 4 is a cross-sectional view of a conventional liquid fuel cell in Comparative Example 1. FIG. 9 is a cross-sectional view of a conventional liquid fuel cell in Comparative Example 2.

Explanation of reference numerals

1 positive electrode 1a gas-liquid separation sheet 1b carbon layer 2a negative electrode (hydrogen storage alloy electrode)
2b negative electrode (gas diffusion electrode)
Reference Signs List 3 separator 4 liquid fuel 5 fuel tank 5a partition plate 6 gas holding unit 6 'gas holding unit 7a check valve 7b check valve 8 cover plate 9 air hole 10 current collector 11 fuel supply port 12a gas-liquid separation hole 12b gas-liquid Separation membrane 13 Seal material 14 Solid polymer electrolyte membrane 15 Diffusion layer 16 Solid polymer fuel cell 17 Positive catalyst layer 18 Negative catalyst layer

Claims (25)

A positive electrode for reducing oxygen, a negative electrode containing a hydrogen storage material, an electrolyte layer disposed between the positive electrode and the negative electrode, and a liquid fuel, and a gas when the liquid fuel is oxidized by the negative electrode. A liquid fuel cell in which
A liquid fuel cell, comprising: adjusting means for adjusting a reaction in which the liquid fuel is oxidized by the negative electrode according to the amount of electricity generated by using a gas generated from the liquid fuel.   2. The liquid fuel cell according to claim 1, wherein the adjusting unit includes a gas holding unit that can hold a gas generated from the liquid fuel so as to be in contact with a negative electrode. 3.   3. The liquid fuel cell according to claim 2, wherein the gas holding unit is arranged so that the liquid fuel does not contact the negative electrode while holding a gas generated from the liquid fuel. 4.   The liquid fuel cell according to claim 2, wherein the gas holding unit includes a tubular portion, and the tubular portion is installed in two or more directions.   The liquid fuel cell according to any one of claims 1 to 4, wherein the adjusting means operates by a pressure increased by a gas generated from the liquid fuel.   The liquid fuel cell according to claim 4, wherein the tubular portion further includes a check valve for flowing the liquid fuel and a gas generated from the liquid fuel only in one direction.   7. The liquid fuel cell according to claim 1, wherein the gas generated from the liquid fuel is hydrogen.   The liquid fuel cell according to claim 1, wherein a water-repellent treatment is further performed on a surface of the negative electrode on a liquid fuel side.   The liquid fuel cell according to claim 8, wherein the water-repellent treatment is performed by applying a fluororesin to a surface of the negative electrode.   The fluororesin is polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkylvinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, polyvinylidene fluoride and polychlorotriol. The liquid fuel cell according to claim 9, which is at least one selected from the group consisting of fluoroethylene.   The catalyst having at least one function selected from a function of dissociating hydrogen into atoms and a function of oxidizing hydrogen is further provided on a surface of the negative electrode on a liquid fuel side. A liquid fuel cell according to any one of the above.   The liquid fuel cell according to claim 11, wherein the catalyst includes at least one element selected from the group consisting of Pt, Pd, Rh, and Ni.   13. The liquid fuel cell according to claim 11, wherein the catalyst is supported on porous carbon.   The liquid fuel cell according to any one of claims 1 to 13, wherein a part of the negative electrode includes a gas diffusion electrode having a function of oxidizing hydrogen.   The liquid fuel cell according to claim 14, wherein the gas diffusion electrode includes at least one element selected from the group consisting of Pt, Pd, Rh, and Ni.   The liquid fuel cell according to claim 15, wherein the element is supported on porous carbon.   The gas diffusion electrode is made of polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkylvinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, polyvinylidene fluoride and polychloroethylene. The liquid fuel cell according to any one of claims 14 to 16, comprising at least one selected from the group consisting of trifluoroethylene.   The liquid fuel cell according to any one of claims 1 to 17, further comprising a gas-liquid separation membrane for separating a gas generated from the liquid fuel and the liquid fuel.   19. The liquid fuel cell according to claim 18, wherein the gas-liquid separation membrane comprises a microporous polytetrafluoroethylene membrane.   20. The liquid fuel cell according to claim 1, wherein the hydrogen storage material is any one selected from a hydrogen storage alloy and a carbon nanotube.   21. The liquid fuel cell according to claim 1, wherein the electrolyte layer includes an aqueous solution in which at least one selected from the group consisting of KOH, NaOH, and LiOH is dissolved. Wherein the liquid _{fuel, NaBH 4, KBH 4, LiAlH} 4, liquid fuel cell according to any one of claims 1 to 21 comprising at least one selected from the group consisting of KH and NaH. A plurality of power generation elements, a power generator electrically connected to one selected from series and parallel,
A power generator, wherein at least one of the power generating elements is the liquid fuel cell according to any one of claims 1 to 22.   The power generator according to claim 23, wherein the power generation element other than the liquid fuel cell is a fuel cell that generates power from hydrogen and oxygen.   25. The power generator according to claim 23, further comprising means for guiding gas from the liquid fuel cell to another fuel cell in the same power generator.

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