JP2008097977A - Fuel supply method, fuel cell system and portable electronic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel supply method and a fuel cell system, which suppresses CO poisoning of a fuel electrode catalyst by oxidizing CO adsorbed on the surface of the fuel electrode catalyst without damaging constitution members of a fuel cell. <P>SOLUTION: Fuel for the fuel cell and a metal peroxide are mixed, and the fuel for the fuel cell is supplied to a fuel electrode of a unit fuel cell. Preferably, the fuel for the fuel cell, the metal peroxide, and water are mixed, the fuel for the fuel cell is supplied to the fuel electrode of the unit fuel cell. The fuel for the fuel cell having high dissolved oxygen concentration is supplied to the fuel electrode, and CO poisoning of the fuel electrode catalyst is suppressed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel supply method to a fuel electrode in a fuel cell system, a fuel cell system, and a portable electronic device.

  In recent years, countermeasures against environmental and resource problems have become important, and as one of the countermeasures, development of fuel cells capable of generating electricity by directly supplying organic solvent and water as liquid fuel has been active. Has been done.

  In particular, a direct methanol fuel cell that uses methanol as a liquid fuel and can generate electricity by directly supplying methanol without reforming or gasifying it has a simple structure and is smaller and lighter. Since it is easy, it is promising as various distributed power sources and portable power sources including consumer power sources for portable small electronic devices and computers.

In the direct methanol fuel cell, as shown by the following formulas (1) to (3), an aqueous methanol solution is supplied to the fuel electrode (anode) side, and air as an oxidant gas is supplied to the air electrode (cathode) side. At the fuel electrode, methanol and water react to generate carbon dioxide, and hydrogen ions and electrons are released. At the air electrode, oxygen in the air passes through the electrolyte. And water is generated, and an electromotive force is generated in the external circuit. And the produced | generated water is discharged | emitted from the air electrode side with the air which did not contribute to reaction, and the produced | generated carbon dioxide is discharged | emitted from the fuel electrode side with the methanol aqueous solution which did not contribute to reaction.
(Fuel electrode) CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻ (1)
(Air electrode) 6H ⁺ + 3/2 O ₂ + 6e ⁻ → 3H ₂ O (2)
(All reactions) CH ₃ OH + 3 / 2O ₂ → CO ₂ + 2H ₂ O (3)

  Such a direct methanol fuel cell can take out six electrons from one molecule of methanol as long as the reactions shown in the above formulas (1) to (3) occur smoothly. Since the potential is almost the same as that of hydrogen, a fuel cell with a high energy density should be theoretically possible. However, the reaction rate of methanol at the fuel electrode is slow, intermediates are generated, and the like, so that the output characteristics do not reach the conventional fuel cell using hydrogen.

For example, when an electrode carrying a Pt catalyst is used in the fuel electrode of the fuel cell, the reaction at the fuel electrode of methanol in the electrode carrying the Pt catalyst is expressed by the following equations (4) to (7). It is thought to progress.
CH ₃ OH → CH ₂ OH + H ⁺ + e ⁻ (4)
CH ₂ OH → CHOH + H ⁺ + e ⁻ (5)
^{CHOH → CHO + H + + e} - ... (6)
^{CHO → CO + H + + e} - ... (7)

  Methanol adsorbs on the Pt catalyst surface of the fuel electrode and proceeds from the above formula (4) to (6) or (7), but the reaction does not proceed here. This is because the CO adsorbed firmly on the Pt catalyst surface is not easily oxidized as the reaction proceeds, so that all the active sites on the Pt catalyst surface are occupied by CO.

  In order to reduce CO poisoning of the Pt catalyst, in a direct methanol fuel cell, an alloy of Pt and Ru is generally used as a fuel electrode catalyst (anode catalyst).

When an alloy of Pt and Ru is used as the fuel electrode catalyst (anode catalyst), Ru decomposes water and adsorbs OH as shown in the following formula (8).
H ₂ O → Ru—OH _ad + H ⁺ + e ⁻ (8)

The OH adsorbed on Ru oxidizes CO adsorbed on the surface of the Pt catalyst in the vicinity to CO ₂ as shown in the following formula (9).
Pt-CO _ad + Ru-OH _ad
→ Pt + Ru + CO ₂ + H ⁺ + e ⁻ (9)

Since CO ₂ produced by the above formula (9) does not adsorb on the Pt catalyst surface, it is separated from the Pt catalyst surface. And methanol adsorb | sucks to the Pt catalyst surface again, reaction from said Formula (4) to (6) or (7) advances continuously, and an electric current can be taken out. However, even in this case, since the reaction rates of the above formulas (8) and (9) are slow, the output from the fuel cell is small and an intermediate is also generated, resulting in energy loss.

In order to avoid such a problem, it is necessary to efficiently oxidize the CO adsorbed on the surface of the Pt catalyst and convert it to CO ₂ . Therefore, by supplying hydrogen peroxide as an oxidizing agent together with the fuel for the fuel cell to the fuel electrode (anode), CO adsorbed on the surface of the fuel electrode catalyst is oxidized to CO ₂ , so that the CO coverage of the fuel electrode catalyst is increased. A method for avoiding poison has been proposed (see Patent Document 1).
JP 2002-343403 A

  However, since the method described in Patent Document 1 has an extremely strong oxidizing power of hydrogen peroxide, the hydrogen peroxide supplied to the fuel electrode together with the fuel for the fuel cell is an electrolyte membrane or product constituting the fuel cell. There was a problem of deteriorating members and the like.

  Accordingly, the present invention provides a fuel supply method and a fuel cell system that can oxidize CO adsorbed on the surface of a fuel electrode catalyst and prevent CO poisoning of the fuel electrode catalyst without damaging components of the fuel cell. The purpose is to provide.

  In order to solve the above problems, the present invention provides a fuel supply method characterized by mixing a fuel for a fuel cell and a metal peroxide and supplying the fuel cell fuel to a fuel electrode of a fuel cell. (Claim 1).

For example, metal peroxides such as magnesium peroxide and calcium peroxide release oxygen by contact with water as shown in the following formulas (10) and (11).
MgO ₂ + H ₂ O → Mg (OH) ₂ + 1 / 2O ₂ (10)
_{CaO 2 + H 2 O → Ca} (OH) 2 + 1 / 2O 2 ... (11)

Oxygen generated by the reactions shown in the above formulas (10) and (11) can quickly oxidize CO adsorbed on the surface of the fuel electrode catalyst by the reaction of the fuel cell fuel at the fuel electrode to CO _2. Therefore, the fuel cell fuel having a high dissolved oxygen concentration is supplied to the fuel electrode by supplying the fuel cell fuel and metal peroxide mixture to the fuel electrode as in the above invention (invention 1). As a result, CO poisoning of the fuel electrode catalyst can be suppressed.

  In the said invention (invention 1), it is preferable to mix the said fuel for fuel cells, the said metal peroxide, and water, and to supply the said fuel cell fuel to the said fuel electrode (invention 2). According to this invention (invention 2), when the metal peroxide and water are brought into contact with each other, oxygen is released by the reaction between the metal peroxide and water, and a fuel for fuel cells having a higher dissolved oxygen concentration is obtained. This can be supplied to the fuel electrode, whereby CO poisoning of the fuel electrode catalyst can be more effectively suppressed.

  In the above inventions (Inventions 1 and 2), the metal peroxide and / or metal cations derived from the metal peroxide are removed from a mixture of the fuel for fuel cells and the metal peroxide, Preferably, the fuel cell fuel is supplied to the fuel electrode.

Among metal peroxides, alkali metals and alkaline earth metals have a relatively large ionization tendency and are likely to become cations. Therefore, when such metal cations are supplied to the fuel electrode, the fuel electrode moves to the air electrode. Although there is a possibility that the movement of the hydrogen ions (H ⁺⁾ is inhibited according to the present invention (claim 3), without the metal cation to the fuel electrode is supplied, the fuel cell system stable You can drive.

  In the said invention (Invention 1-3), it is preferable that the said metal peroxide is a magnesium peroxide and / or a calcium peroxide (Invention 4). Magnesium peroxide and calcium peroxide are excellent in oxygen release properties, and oxygen is gradually released. Therefore, according to this invention (claim 4), oxygen is rapidly released from the metal peroxide. Therefore, the risk of explosion or the like can be avoided, and the safety of the fuel cell system can be improved.

  In the said invention (Invention 1-4), it is preferable that the said fuel for fuel cells is alcohol (Invention 5), In this invention (Invention 5), the said alcohol is methanol. (Claim 6).

  The present invention also provides a fuel cell system comprising: a fuel cell having a fuel electrode; and a mixing unit for mixing a fuel for a fuel cell and a metal peroxide (Claim 7).

  Furthermore, the present invention provides a fuel cell system comprising: a fuel cell having a fuel electrode; and a mixing unit that mixes fuel for a fuel cell, a metal peroxide, and water. ).

  According to the above inventions (Inventions 7 and 8), CO poisoning of the fuel electrode catalyst in the fuel cell system can be suppressed.

  In the said invention (invention 7 and 8), the removal part which removes the said metal peroxide and / or the metal cation derived from the said metal peroxide is provided in the upstream of the fuel electrode of the said fuel cell. (Claim 9).

Among metal peroxides, alkali metals and alkaline earth metals have a relatively large ionization tendency and are likely to become cations. Therefore, when such metal cations are supplied to the fuel electrode, the fuel electrode moves to the air electrode. The movement of hydrogen ions (H ⁺ ) may be hindered. However, according to the above invention (invention 9), the metal peroxide and / or metal cation is trapped in the removal section, so that the fuel The metal cation is not supplied to the electrode, and the fuel cell system can be stably operated.

  Furthermore, the present invention provides a portable electronic device that is driven using electricity generated by the fuel cell system according to the above inventions (inventions 7 to 9) (invention 10).

  According to the present invention, a fuel supply method and a fuel cell system that can oxidize CO adsorbed on the surface of a fuel electrode catalyst and prevent CO poisoning of the fuel electrode catalyst without damaging components of the fuel cell. Can be provided.

Hereinafter, a fuel supply method according to an embodiment of the present invention will be described.
The fuel supply method according to this embodiment mixes fuel cell fuel and metal peroxide, and supplies the fuel cell fuel to the fuel electrode of the fuel cell. Preferably, the fuel for the fuel cell, the metal peroxide, and water are mixed, and the fuel for the fuel cell is supplied to the fuel electrode of the fuel cell.

  Examples of the fuel for the fuel cell include alcohols, ethers, hydrocarbons, acetals, formic acids and the like, but are not particularly limited thereto. Specifically, as a fuel for a fuel cell, lower fat having 1 to 4 carbon atoms such as methanol, ethanol, denatured alcohol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, tert-butanol, ethylene glycol and the like. Aromatic alcohols; Ethers such as dimethyl ether, methyl ethyl ether and diethyl ether; Hydrocarbons such as propane and butane; Acetals such as dimethoxymethane and trimethoxymethane; Formic acids such as formic acid and methyl formate Can do. These may be used individually by 1 type, and 2 or more types may be mixed and used for them. Among these, it is preferable to use methanol which is a fuel of the direct methanol fuel cell.

Examples of the metal peroxide include potassium peroxide, sodium peroxide, magnesium peroxide, calcium peroxide, barium peroxide, lithium peroxide and the like. These metal peroxides may be used singly or in an arbitrary mixture. Since metal peroxide releases oxygen when it comes into contact with water, a fuel cell fuel with a high dissolved oxygen concentration can be obtained by supplying a fuel cell fuel, a mixture of metal peroxide and water to the fuel electrode. Can be supplied to the fuel electrode, so that CO generated by the reaction of the fuel cell fuel at the fuel electrode catalyst can be quickly oxidized to CO ₂ to suppress CO poisoning of the fuel electrode catalyst. it can. Examples of the fuel electrode catalyst include, but are not limited to, a Pt catalyst, a Pt—Ru catalyst, a Pt—Ni catalyst, a Pt—Co catalyst, and a Pt—Fe catalyst.

  The shape of the metal peroxide is not particularly limited, but is preferably in the form of particles (fine particles). Since the metal peroxide is in the form of particles, the reactivity between the metal peroxide and water is improved, and the dissolved oxygen concentration in the fuel for the fuel cell is increased, so that CO poisoning of the fuel electrode catalyst is effective. The amount of oxygen that can be suppressed is supplied to the fuel electrode.

  The particle size of the metal peroxide is preferably 1 to 1000 μm. If the particle size of the metal peroxide is within the above range, an amount of oxygen capable of effectively suppressing CO poisoning of the fuel electrode catalyst can be supplied to the fuel electrode.

  Of these metal peroxides, magnesium peroxide and calcium peroxide are preferably used. Magnesium peroxide and calcium peroxide are excellent in sustained release of oxygen and release oxygen slowly when in contact with water, so there is no risk of explosion due to sudden release of oxygen, and safety. In terms of surface.

  The mixing ratio of the fuel for the fuel cell and the metal peroxide is preferably 0.01 to 1 part by mass of the metal peroxide with respect to 1 part by mass of the fuel for the fuel cell. If the mixing ratio of the fuel for the fuel cell and the metal peroxide is within the above range, the amount of CO poisoning of the fuel electrode catalyst that can be effectively suppressed when the metal peroxide is brought into contact with water. Oxygen can be supplied to the fuel electrode.

  When a metal peroxide and water are mixed with the fuel for the fuel cell and the mixture is supplied to the fuel electrode, the blending ratio of the fuel for the fuel cell in the entire mixture is preferably 3 to 30% by mass. If the blending ratio of the fuel cell fuel in the whole mixture exceeds 30% by mass, crossover or the like may occur, and if it is less than 3% by mass, power generation is not efficiently performed and a desired output cannot be obtained. There is a fear.

  As a method of supplying a fuel cell fuel, metal peroxide and water mixture to the fuel electrode, for example, a method of supplying a fuel cell fuel, metal peroxide and water mixture as a liquid (liquid supply method) ), A method of vaporizing a mixture of a fuel aqueous solution for a fuel cell and a metal peroxide and supplying it as a gas (vaporization supply method).

  In the case of the liquid supply method, for example, each fuel cartridge having a fuel cell fuel container, a metal peroxide container, and a water container is prefilled with fuel cell fuel, metal peroxide, and water. Alternatively, the fuel for the fuel cell, the metal peroxide, and water may be mixed, and the mixture may be forcibly supplied to the fuel electrode with a pump, or the fuel for the fuel cell, the metal peroxide, and water may be mixed in advance. The mixed mixture may be filled in a fuel cartridge, and the mixture may be forcibly supplied to the fuel electrode with a pump. Further, a mixture of fuel for fuel cell, metal peroxide, and water may be spontaneously supplied to the fuel electrode by capillary action through the porous diffusion layer.

  In the case of the liquid supply method, it is preferable that the metal peroxide and the metal cation are removed from the fuel cell fuel on the upstream side of the fuel electrode, and the fuel cell fuel is supplied to the fuel electrode. Most metal peroxides are peroxides of alkali metals or alkaline earth metals, and alkali metals and alkaline earth metals have a higher ionization tendency than other metals (for example, transition metals), and metal cations. However, if metal cations are present in the fuel electrode, the movement of hydrogen ions from the fuel electrode to the air electrode may be hindered. It is preferable to do.

  The method for removing the metal peroxide and the metal cation from the fuel for the fuel cell is not particularly limited. For example, the metal peroxide and the metal cation are removed by an anion exchange membrane, a column filled with a cation exchange resin, or the like. A method is mentioned. These anion exchange membranes, cation exchange resin packed columns, etc. may be provided on the upstream side of the fuel electrode. For example, an anion exchange membrane may be provided at the outlet of the fuel cartridge. A column filled with a cation exchange resin may be provided in the flow path between the outlet of the cartridge and the fuel electrode.

  In the case of the vaporization supply method, a fuel cell fuel aqueous solution and metal peroxide fine particles held in a porous material or the like are contained in a fuel cartridge, and the fuel cell fuel aqueous solution is vaporized at room temperature to fuel the fuel cell fuel It may be supplied to the electrode, or the fuel cartridge may be heated to vaporize the aqueous fuel cell fuel solution to supply the fuel cell fuel to the fuel electrode. Since the dissolved oxygen concentration in the fuel aqueous solution for fuel cells is increased by holding the aqueous fuel solution for fuel cells and metal peroxide fine particles in the porous material, etc., the fuel for fuel cells vaporized from the porous material is used as fuel. By supplying to the electrode, CO poisoning of the fuel electrode catalyst can be suppressed. Further, by holding the aqueous fuel cell fuel solution in the porous material, the fuel cell fuel is more easily vaporized than in the liquid state, and the fuel cell fuel vaporized even at room temperature can be supplied to the fuel electrode.

  In the case of the vaporization supply method, the fuel cartridge is preferably made of metal. Utilizing the reaction heat generated by the reaction at the fuel electrode of the fuel cell fuel in order to vaporize the fuel aqueous solution for the fuel cell because the fuel cartridge is made of a material having high thermal conductivity such as metal. Can do. In this case, the material of the fuel cartridge is preferably a versatile and low-cost metal such as copper, aluminum, steel, and stainless steel, but is not particularly limited thereto.

  The fuel cell system to which fuel for the fuel cell is supplied by the fuel supply method described above is not particularly limited. For example, the direct methanol fuel cell system, the polymer electrolyte fuel cell system, the solid oxide type Examples thereof include a fuel cell system.

  The fuel cell system to which fuel for the fuel cell is supplied by the fuel supply method described above is, for example, by electrically connecting the fuel cell system to a portable electronic device such as a mobile phone, a notebook computer, or a digital camera. It can be suitably used as a power source for these portable electronic devices.

  The embodiment described above is described for facilitating understanding of the present invention, and is not described for limiting the present invention. Therefore, each element disclosed in the above embodiment is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to the following Example at all.

[Example 1] Measurement of dissolved oxygen concentration After adding 1 g of calcium peroxide to 100 g of deionized water, the solution was allowed to stand at room temperature (27 ° C), and the dissolved oxygen concentration in deionized water was measured at regular intervals. Similarly, after adding 1 g of magnesium peroxide to 100 g of deionized water, the solution was allowed to stand at room temperature (27 ° C.), and the dissolved oxygen concentration in the deionized water was measured at regular intervals. The dissolved oxygen concentration in deionized water was measured using a dissolved oxygen meter (trade name: OM-51, manufactured by Horiba, Ltd.).
The results are shown in FIG.

  As shown in FIG. 1, it was confirmed that the dissolved oxygen concentration in the deionized water was increased by bringing the deionized water into contact with calcium peroxide and magnesium peroxide. It was also confirmed that magnesium peroxide has a tendency to increase the dissolved oxygen concentration more slowly than calcium peroxide.

Example 2 Current-Voltage Measurement An electrode coated with a catalyst layer was thermocompression bonded to a Nafion 112 membrane (manufactured by DuPont) to prepare a membrane electrode assembly (MEA). The electrode area was 20 cm ² , Pt—Ru / C (Pt: Ru = 2: 1, mass ratio) was used as the fuel electrode catalyst, and Pt / C was used as the air electrode catalyst. This MEA was incorporated into a self-made experimental fuel cell, and current-voltage measurement was performed. Note that a potentio / galvanostat (trade name: HA-151, manufactured by Hokuto Denko) was used as a galvanostat for current-voltage control.

1 g of calcium peroxide was added to 100 g of a 3% by mass aqueous methanol solution, supplied to the fuel electrode at a flow rate of 10 mL / min, and after confirming that the voltage was stabilized at a constant current, current-voltage curve measurement was performed. In addition, it measured also about the methanol aqueous solution which has not added calcium peroxide as a comparative example. When supplying an aqueous methanol solution added with calcium peroxide to the fuel electrode, a column packed with a cation exchange resin (product name: Monosphere 650C, manufactured by Dow Chemical Co., Ltd.) to remove calcium ions eluted in the aqueous methanol solution. Was provided in the flow path between the fuel cartridge and the fuel electrode. Note that room air was supplied to the air electrode at a flow rate of 0.15 L / min.
The results are shown in FIG.

  As shown in FIG. 2, it was confirmed that the cell performance was improved by adding calcium peroxide to the fuel. When calcium peroxide was added, the maximum output was improved by 5.7% compared to the case where calcium peroxide was not added.

  The present invention is useful for preventing performance deterioration of a fuel cell system due to CO poisoning of the fuel electrode catalyst.

4 is a graph showing the measurement results of dissolved oxygen concentration in Example 1. 6 is a graph showing a current-voltage curve measurement result in Example 2.

Claims (10)

  A fuel supply method comprising: mixing a fuel cell fuel and a metal peroxide, and supplying the fuel cell fuel to a fuel electrode of a fuel cell.   The fuel supply method according to claim 1, wherein the fuel for the fuel cell, the metal peroxide, and water are mixed, and the fuel for the fuel cell is supplied to the fuel electrode.   Removing the metal peroxide and / or metal cations derived from the metal peroxide from a mixture of the fuel cell fuel and the metal peroxide, and supplying the fuel cell fuel to the fuel electrode; The fuel supply method according to claim 1 or 2.   The fuel supply method according to claim 1, wherein the metal peroxide is magnesium peroxide and / or calcium peroxide.   The fuel supply method according to claim 1, wherein the fuel for the fuel cell is an alcohol.   The fuel supply method according to claim 5, wherein the alcohol is methanol. A fuel cell having a fuel electrode;
A fuel cell system comprising a mixing unit for mixing a fuel for a fuel cell and a metal peroxide. A fuel cell having a fuel electrode;
A fuel cell system comprising: a fuel cell fuel, a mixing unit for mixing metal peroxide and water.   The removal part which removes the said metal peroxide and / or the metal cation derived from the said metal peroxide is provided in the upstream of the fuel electrode of the said fuel cell. The fuel cell system described in 1.   A portable electronic device that is driven by using electricity generated by the fuel cell system according to claim 7.

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