JP2002050375A - Liquid fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve reaction efficiency by liquidizing the supply source of hydrogen as a fuel and oxygen oxidizing the fuel in a fuel cell in which hydrogen as a fuel source and oxygen as a substance of oxidizing the fuel are used. SOLUTION: In the fuel cell in which one side is formed as a positive electrode and the other is formed as a negative electrode by separating by a transmission membrane, an active oxygen generating water solution as a positive electrode liquid and an alkaline water solution of metal hydrogen complex compound as a negative electrode liquid are used, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel liquid fuel cell for supplying, as a liquid, a substance supplied to a negative electrode and a substance oxidizing a fuel supplied to a positive electrode.

[0002]

2. Description of the Related Art In a fuel cell, a fuel is continuously supplied to a negative electrode and a material for oxidizing the fuel is continuously supplied to a positive electrode to cause a chemical reaction, and a change in free energy at that time is directly converted into electric energy. Although it is a device that generates power, the fuel supplied to the negative electrode so far is hydrogen, methane, a hydrocarbon such as gasoline, a gas or liquid such as methyl alcohol, and the fuel supplied to the positive electrode as a substance that oxidizes the fuel. Gases such as air have been mainly used.

For example, the simplest system is a hydrogen-oxygen fuel cell as shown in FIG. This material comprises a positive electrode 1 and a negative electrode 2 made of a material in which platinum black is adhered to a porous carbon plate as a catalyst, and a dilute sulfuric acid aqueous solution or a phosphoric acid aqueous solution is filled between both electrodes as an electrolyte 3. Hydrogen gas and air are supplied to the oxidizing gas chamber 5. When the external circuit 6 between the electrodes is closed, electrons flow from the negative electrode through the external circuit 6 to the positive electrode to generate power. Depending on the type of electrolyte, this fuel cell is called an acidic electrolyte fuel cell, an alkaline fuel cell, a solid electrolyte fuel cell, a molten salt fuel cell, or the like, and depending on the type of fuel, a hydrogen-oxygen fuel cell, a methane fuel cell, a hydrazine fuel cell, or the like. It is called a battery or a methanol fuel cell.

[0004] On the other hand, there is also known an alloy using a hydrogen storage alloy as a hydrogen supply source, a hydrogen electrode (negative electrode), a hydrogen gas permeable membrane or a mixed gas separation membrane of a fuel cell. However, if the fuel and the substance that oxidizes the fuel can be supplied as a liquid, the reaction can be performed smoothly, the efficiency is improved, and the handling is easy. Using hydrogen storage alloy until
Further, there has been no known fuel cell in which both the fuel and the substance oxidizing the fuel are supplied as liquids.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a fuel cell using hydrogen as a fuel source and oxygen as a substance for oxidizing fuel, in which the source of hydrogen for fuel and the source of oxygen for oxidizing fuel are made liquid. Thus, the present invention has been made for the purpose of improving the reaction efficiency and facilitating the control of the supply conditions.

[0006]

The inventors of the present invention have conducted various studies on a hydrogen supply source and an oxygen supply source for a fuel cell. As a result, an alkaline aqueous solution of a metal hydride complex compound was used as a hydrogen supply source. It has been found that both the fuel and the substance that oxidizes the fuel can be supplied in liquid form by using the aqueous solution of the active oxygen generator as the source, and the present invention has been accomplished based on this finding.

That is, according to the present invention, in a fuel cell in which one is formed into a positive electrode portion and the other is formed into a negative electrode portion by using a permeable membrane, an active oxygen generator aqueous solution is used as a positive electrode solution, and a metal hydride complex compound is used as a negative electrode solution. The present invention provides a liquid fuel cell characterized by using an alkaline aqueous solution.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A liquid fuel cell according to the present invention will be described below with reference to the accompanying drawings. FIG. 2 is a side cross-sectional view showing the structure of the fuel cell of the present invention. The inside of a casing 7 is divided into two by a permeable membrane 8, one of which has a positive electrode 1 and the other has a negative electrode 2. The positive electrode is supplied with active oxygen from an active oxygen generator aqueous solution 9 in contact therewith, and the negative electrode 2 is supplied with active hydrogen from an alkaline aqueous solution of a metal hydride complex compound 10 in contact therewith. You.

[0009] In the fuel cell having such a configuration, the negative electrode 2, two protons and two electrons from molecular hydrogen is produced as shown in the following ^{_{formula, H 2 → 2H + + 2e}} - On the other hand, in the positive electrode 1, it produces hydroxyl ions as shown in the following equation by reactive oxygen and _{water, O + H 2 O + 2e} - → 2OH - the hydroxide ions react with protons produced in the anode 2 Regenerate water as follows: 2OH ⁻ + 2H ⁺ → 2H ₂ O Therefore, if the positive terminal 13 and the negative terminal 14 are connected, an electromotive force is generated between both terminals.

As the material forming the casing 7, metals, alloys, metal oxides, insulating ceramics, plastics, and the like are used, and it is advantageous to use an insulating material for each electrode. Further, the permeable membrane 8 separating the positive electrode portion and the negative electrode portion needs to be made of a material having corrosion resistance to both the positive electrode solution and the negative electrode solution. The permeable membrane 8 may be an anion permeable membrane, that is, a membrane that transmits hydroxyl ions generated by the reaction of active oxygen with water in the positive electrode and does not transmit protons generated in the negative electrode, or a cation permeable membrane, That is, it may be one that transmits protons generated at the negative electrode and does not transmit hydroxyl ions generated at the positive electrode. If desired, a bipolar permeable membrane that transmits both ions can also be used. A typical example of such a permeable membrane is a membrane obtained by introducing a sulfonic acid group or a quaternary ammonium base into a styrene-divinylbenzene copolymer, or polyvinyl benzyl trimethyl ammonium chloride or sodium polystyrene sulfonate with water-acetone. A membrane obtained by dissolving in sodium bromide, an acrylonitrile-sodium methacrylsulfonate copolymer membrane, and the like. These permeable membranes can be easily obtained as commercial products. Particularly preferred are proton-permeable polymer electrolyte membranes such as Nafion (trade name of cation-permeable membrane, manufactured by DuPont).

Next, as the electrode material of the positive electrode and the negative electrode in the present invention, for example, carbon or iron in which carbon or platinum is dispersed,
Metals such as nickel, chromium, copper, platinum and palladium and alloys thereof are used. Power generation efficiency and durability are good, and in terms of low cost, a porous body of nickel or nickel-chromium alloy, for example, a granular sintered body or foam as a base material,
It is preferable that the surface is plated with a noble metal such as platinum or palladium. As the positive electrode, a conductive material in which a reduction reaction of oxygen easily proceeds on the surface is preferable. Also,
An oxygen breathing material, that is, a material capable of reversibly absorbing and releasing oxygen in contact with oxygen gas can also be used for the positive electrode.

As the negative electrode, the above-mentioned electrode materials may be used, but a hydrogen storage alloy or a hydride thereof is particularly preferable. The hydrogen storage alloy or its hydride is not particularly limited as long as it can absorb and release hydrogen reversibly. For example, Mg ₂ Ni alloy, eutectic alloy of Mg ₂ Ni and Mg, ₂ Ni-based alloy, ZrNi ₂ alloy, Laves phase system AB ₂ type alloy such as TiNi ₂ alloy, T
It can be arbitrarily selected from an AB type alloy such as an iFe type alloy, an AB ₅ type alloy such as a LaNi ₅ type alloy, and a BCC type alloy such as a TiV ₂ type alloy.

Among these, LaNi _4.7 Al is preferred.
_{0.3 alloy, MmNi 0.35 Mn 0.4 Al 0 .3} Co 0.75 alloy (wherein Mm is misch metal), MmNi _3.75 Co
_0.75 Mn _{0. 20} Al _0.30 alloy (wherein Mm is misch _{metal), Ti 0.5 Zr 0.5 Mn 0.8} Cr 0 .8 Ni 0.4, Ti 0.5
Zr _0.5 Mn _0.5 Cr _0.5 Ni, Ti _0.5 Zr _0.5 V _0.75 N
_{i 1.2 5, Ti 0.5 Zr 0.5} V 0.5 Ni 1.5, Ti 0.1 Zr 0.9
V _0.2 Mn _0.6 Co _0.1 Ni _1.1 , MmNi _3.87 Co _0.78 M
n _0.10 Al _0.38 (where Mm is misch metal).

The performance of these hydrogen storage alloys or their hydrides can be significantly enhanced by subjecting the surface to fluorination treatment. That is, by performing such a fluorination treatment, corrosion resistance to the contacting negative electrode solution is provided, and a high power generation capacity can be maintained for a long period of time.

This fluorination treatment is performed, for example, by immersing a hydrogen storage alloy or a hydride thereof in an aqueous solution containing a fluorinating agent and fluorinating the surface. As the fluorinating agent-containing aqueous solution, an aqueous solution containing fluorine ions and alkali ions is usually used. For example, an aqueous solution containing alkali fluoride at a concentration of about 0.2 to 20% by mass is added to an aqueous solution containing hydrogen fluoride. To adjust the pH to 2.0 to 6.5.
Degree, preferably in the range of 4.0 to 6.0. The alkali fluoride used at this time is not particularly limited, and ones that are easily soluble in water, such as sodium fluoride, potassium fluoride, and ammonium fluoride, are preferable, and potassium fluoride is particularly preferable. These alkali fluorides may be used alone or in combination of two or more.

The preferable concentration of the alkali fluoride in the aqueous solution containing a fluorinating agent is 0.3 to 3% by mass in the case of sodium fluoride, 0.5 to 5% by mass in the case of potassium fluoride, and 0.1 to 3% by mass in the case of ammonium fluoride. It is in the range of 5 to 8% by mass. If the concentration of the alkali fluoride is lower than the above range, it takes a long time to form the fluorinated surface, which is not practical, and if the concentration is higher than the above range, it is difficult to form a fluorinated surface with a sufficient thickness. The stabilizing effect becomes insufficient.

The amount of hydrogen fluoride required to adjust the above pH range is usually 1 to 3 mol for sodium fluoride and 0.2 to 3 for potassium fluoride per mol of alkali fluoride. Mol, 0.2-1 for ammonium fluoride
Range of moles.

In order to form a fluorinated surface on a hydrogen storage alloy or its hydride using an aqueous solution containing a fluorinating agent, the surface is immersed in the aqueous solution containing a fluorinating agent, and the fluorinated alloy or the hydride is usually immersed in an aqueous solution under a normal pressure. About 80 ° C, preferably 30 to 60 ° C
Is maintained until a fluorinated surface having a sufficient thickness is formed on the surface, that is, about 0.01 to 1 μm. The time required for this is about 1 to 60 minutes.

The electrode in the present invention may be configured as a bipolar electrode having one side as an anode and the other side as a cathode. The shape of the electrode is arbitrary, and may be various shapes such as a sheet, a tube, a cylinder, a cuboid, and a sphere according to the purpose. Further, it can be formed into a foam, colloid, or powder.

Next, in the liquid fuel cell of the present invention,
The metal hydride complex compound constituting the negative electrode solution, for example, the general formula ^{_{M I M III H 4-n}} R n (I) or _{^{M II (M III H 4-}} n R n) 2 (II) (M in the formula ^I is an alkali metal, M ^II is an alkaline earth metal or zinc, M ^III is boron, aluminum or gallium, R is a hydrocarbon group, a hydrocarbyloxy group or an acyloxy group, and n is an integer of 0 to 3) There are metal hydride complexes represented.

In these formulas, M ^I is an alkali metal such as lithium, sodium, potassium, rubidium and the like, and M ^II is an alkaline earth metal such as magnesium,
Calcium, strontium or zinc, and M ^III is boron, aluminum or gallium. R is a hydrocarbon group such as a methyl group, an ethyl group, a propyl group, a butyl group, a phenyl group, a methoxy group, an ethoxy group,
n-propoxy group, iso-propoxy group, n-butoxy group, iso-butoxy group, sec-butoxy group, te
It is a hydrocarbyloxy group such as rt-butoxy group, 2-methoxyethoxy group or 2-ethoxymethoxy group or an acyloxy group such as acetoxy group or propionyloxy group.

Accordingly, gold represented by the general formula (I)
Examples of the genus hydrogen complex compounds include sodium borohydride
(NaBH_Four), Potassium borohydride (KBH_Four),water
Lithium aluminum nitride (LiAlH_Four), Trimet
Sodium borohydride [NaBH (OC
H_Three)], Sodium triacetoxyborohydride [N
aBH (OCOCH_Three)_Three], Triphenoxy borohydride
Sodium sodium [NaBH (OC ₆H_Five)_Three], Hydrogenated birds
Lithium ethyl boron [Li (C_TwoH_Five)_ThreeBH], hydrogen
Lithium tri-s-butyl boron [Li (s-C
_FourH₉)_ThreeBH], lithium tributylborohydride [L
i (nC_FourH₉)_ThreeBH], tri-s-butyl hydride
Potassium iodide [K (s-C_FourH₉)_ThreeBH], hydrogenated birds
Potassium phenylboron [K (C₆H_Five)_ThreeBH], bird
Lithium methoxy aluminum hydride [LiAlH (O
CH_Three)_Three], Lithium monoethoxy aluminum hydride
[LiAlH_Three(OC_TwoH_Five)], Tri-tert-but
Lithium aluminum oxyhydride, bis-hydride (2-me
Toxiethoxy) aluminum sodium etc.
be able to. Further, a metal represented by the general formula (II)
Examples of the hydrogen complex compound include zinc borohydride [Zn
(BH_Four)_Two], Calcium borohydride [Ca (B
H_Four)_Two], Zinc tetramethoxy zinc borohydride [Zn [B
(OCH_Three)_TwoH_Two]_Two], Hexaethoxyborohydride
Lucium [Ca [B (OC_TwoH_Five)_ThreeH]_Two]
be able to. These metal hydride complexes are known.
And commercially available as a reagent for selective hydrogenation.

In the present invention, it is necessary to dissolve this metal hydride complex compound in an alkaline aqueous medium and use it as an aqueous solution. In this case, a water-miscible solvent such as an alcohol can be mixed with the water of the medium as required.

Alkaline substances added into water to form an alkaline medium include lithium hydroxide,
There are alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and quaternary alkyl ammonium compounds such as tetramethylammonium hydroxide and tetraethylammonium hydroxide.

In the present invention, an alkaline medium is prepared by dissolving these alkaline substances at a concentration of at least 5% by mass, preferably at least 10% by mass in a predetermined solvent. The upper limit of the concentration is the saturation concentration of the alkaline substance. However, if the concentration is too high, the metal hydride complex compound is difficult to dissolve. Therefore, it is preferable to select the concentration within the range of 30% by mass or less.

The metal hydride complex compound is generally preferably used in a concentration of 0.1 to 50% by mass in consideration of the desired power generation capacity and solubility in an alkaline aqueous solution. In addition, in order to improve the ionic conductivity of the electrolytic solution, lithium hydroxide may be added in a small amount, for example, 0.01 to 0.1% by mass.

In the fuel cell of the present invention, the amount of power generation can be easily controlled by adjusting the flow rate and temperature of the liquid, since the negative electrode liquid itself serves as a hydrogen supply source, and since gaseous hydrogen does not substantially exist in the negative electrode. A small-diameter pipe can be used, making it easier to control pressure and flow rate.

Next, in the liquid fuel cell of the present invention, an aqueous solution of an active oxygen generator is used as a positive electrode solution for oxidizing hydrogen, ie, a fuel generated at the negative electrode portion. As the active oxygen generating agent aqueous solution, for example, hydrogen peroxide,
Hydroperoxide (R'OOH), dialkyl peroxide (R'OOR '), diacyl peroxide [(R'CO
O) ₂ ], and an aqueous solution of a peroxide such as a peroxide ester (R'COOOR ") (where R 'and R" are an alkyl group or an aryl group), particularly hydrogen peroxide, benzoyl peroxide, Di-tert-butyl peroxide is preferred because it is the easiest to use. These aqueous solutions are used at a concentration of 1 to 40% by mass, and particularly preferred is an aqueous solution of hydrogen peroxide having a concentration of 2 to 5% by mass. Phosphoric acid, uric acid, hippuric acid, barbital, acetanilide, etc. may be added to these aqueous active oxygen generator aqueous solutions as stabilizers, if desired.
It can be added at a concentration ranging from 01 to 0.1% by mass.

In the liquid fuel cell of the present invention, the positive electrode solution, ie, an aqueous solution of an active oxygen generator, and the negative electrode solution, ie, an alkaline aqueous solution of a metal hydride complex, are supplied through conduits 11 and 12.
When the activity of these liquids decreases, the liquids are drawn out by three-way valves 17 and 18 provided in the respective pipelines 11 and 12, and new ones are generated. Either replace the liquid or continuously draw out the used liquid and replenish it with new liquid to maintain power generation.

The liquid fuel cell of the present invention can be made completely liquid by using an alkaline aqueous solution of a metal hydrogen complex compound as the negative electrode solution and using an active oxygen generator aqueous solution as the positive electrode solution. A much larger amount of oxygen can be supplied than when air or oxygen gas is used as the oxygen source. For example, a 2% aqueous hydrogen peroxide solution 1
When 00 ml is used, the amount of oxygen is about 22 times that when air is used. The fuel cell of the present invention may be configured by connecting unit cells in series or in parallel.

[0031]

Next, the present invention will be described in more detail with reference to examples.

Example 1 Nickel porous material (average pore diameter 400 μm, porosity 9
Plate-like body 9%) of (100 × 70 × 1.15 mm) as a base material, this powder (average particle size 75μm of the hydrogen storage alloy _{(LaNi 4.7 Al 0 .3))} 7.5g of water 1.5g And dried, and then roll pressed
A plate-like electrode (45 × 70 × 1 mm) used as a negative electrode was manufactured by compression molding with a load of 0 ton / m. Separately, four plates (475 × 700 × 1.15 mm) of the same nickel porous material as described above were stacked to form a positive electrode. In a beaker of 1 liter volume, the above-mentioned negative electrode and positive electrode were arranged in parallel and opposed at an interval of 2 mm, and a proton exchange polymer electrolyte membrane (manufactured by DuPont Co., Ltd .;
Product name "Nafion NE-424")
Isolated. Next, on the negative electrode side, 20 ml of a solution obtained by dissolving KBH ₄ at a concentration of 2% by mass in a 30% by mass aqueous solution of KOH.
And 18 ml of a 3% by mass aqueous solution of H ₂ O ₂ (containing 0.01% by mass of phosphoric acid) were simultaneously injected into the positive electrode side.
The temperature was maintained at 5 ° C., the negative electrode and the positive electrode were connected by a conductor, and the relationship between the generated voltage and the generated current was measured. The result is shown in FIG.

Example 2 In Example 1, after generating electricity for 100 minutes, almost no generated voltage was recognized. Therefore, the negative electrode solution and the positive electrode solution were newly replaced, and the same experiment was repeated four times.
The change of the voltage thus obtained is shown below. 1st time 1.21V 2nd time 1.35V 3rd time 1.46V 4th time 1.53V In this way, it can be seen that the voltage approaches the theoretical value (1.641V) with each repetition.

Example 3 Mg ₂ Ni was immersed in an aqueous solution containing 2% by mass of sodium fluoride and 2% by mass of hydrogen fluoride, and fluorinated at 50 ° C. for 20 minutes. The hydrogen-absorbing alloy powder (average particle diameter 60 μm) thus obtained was subjected to a plate-like body (100 × 70 × 1.15 mm) of a nickel porous material in the same manner as in Example 1.
, Dried, and compression-molded to produce a negative electrode (45 x 70 x 1 mm). Separately, PdCl _{2 2} g / liter, 35 mass% HCl 4 ml / liter, NH ₄ OH
(28% by mass as NH ₃ ) 160 g / liter, Na
Using a plating solution containing 10 g / liter of H ₂ PO ₂ .2H ₂ O, five electrodes obtained by performing electroless plating at 50 ° C. for 10 minutes were stacked to form a positive electrode. Using the negative electrode and the positive electrode obtained in this manner, power was generated under the same conditions as in Example 1. After a discharge time of 5 hours, a voltage of 0.7 V and a current density of 300 were obtained.
mA / dm ² was measured.

Example 4 Instead of a 3% by mass aqueous solution of H ₂ O ₂ as a negative electrode solution, 5% by mass was used.
Electric power was generated under the same conditions as in Example 3 except that an aqueous solution of acetyl peroxide was used. As a result, at a discharge time of 5 hours, a voltage of 0.7 V and a current density of 450 mA / dm ² were obtained.

COMPARATIVE EXAMPLE The same treatment as in Example 1 was carried out using the negative electrode liquid of Example 1 and contacting compressed air (0.35 liter / min) as an oxygen supply source.
V, and the current density was 342 mA / dm ² . From this example, it can be seen that according to the present invention, both the voltage and the current density are significantly improved as compared with the conventional one.

[0037]

According to the present invention, both the fuel to be supplied to the negative electrode and the substance to oxidize the fuel to be supplied to the positive electrode can be continuously supplied as a liquid, so that a complete liquid fuel can be efficiently generated. A battery is obtained.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing the structure of a hydrogen-oxygen fuel cell of the simplest system.

FIG. 2 is a side sectional view showing the structure of the fuel cell of the present invention.

FIG. 3 is a graph showing a relationship between a generated voltage and a generated current in the first embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Electrolyte 4 Fuel gas chamber 5 Oxidant gas chamber 6 External circuit 7 Casing 8 Permeable membrane 9 Active oxygen generator aqueous solution 10 Alkaline aqueous solution of metal hydrogen complex compound 11, 12 Pipeline 13 Positive terminal 14 Negative terminal 15 , 16 Pump 17, 18 Three-way valve

[Procedure amendment]

[Submission date] October 24, 2001 (2001.10.
24)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0036

[Correction method] Change

[Correction contents]

COMPARATIVE EXAMPLE In Example 1, compressed air (0.3
(5 liters / minute) while contacting with each other except that the voltage was 1.35 V and the current density was 34.
It was ² mA / dm ² . From this example, it can be seen that according to the present invention, both the voltage and the current density are significantly improved as compared with the conventional one.

Claims (4)

[Claims] 1. A fractionation by a permeable membrane, one of which is a positive electrode part,
A liquid fuel cell, wherein the other is formed in a negative electrode part, wherein an aqueous solution of an active oxygen generator is used as a positive electrode solution and an alkaline aqueous solution of a metal hydrogen complex compound is used as a negative electrode solution. 2. The liquid fuel cell according to claim 1, wherein an aqueous solution of an active oxygen generator and an alkaline aqueous solution of a metal hydride complex are continuously supplied to the positive electrode portion and the negative electrode portion, respectively. 3. The liquid fuel cell according to claim 1, wherein the active oxygen generator is at least one selected from water-soluble peroxides. 4. A metal-hydrogen complex compound has the general formula _{^{M I M III H 4-n}} R n or _{^{M II (M III H 4-}} n R n) 2 (M I is an alkali metal in the formula, M ^II is Alkaline earth metal or zinc, M ^III is boron, aluminum or gallium, R is a hydrocarbon group, hydrocarbyloxy group or acyloxy group, and n is an integer of 0 to 3) 4. The liquid fuel cell according to claim 1, which is at least one member selected from the group consisting of: