JPS59209277A - Fuel cell - Google Patents

Abstract

PURPOSE:To prevent or decrease leakage or flow out of electrolyte by using particles of organic high molecule compound comprising hydrophobic nucleus and surface layer covering the nucleus and having ion group as electrolyte placing between a fuel electrode and an oxidizing agent electrode. CONSTITUTION:Particles 8 of organic high molecule compound comprising hydrophobic nucleus and surface layer covering the nucleus and having ion group 7 is used as electrolyte placing between a fuel electrode 5 and an oxidizing agent electrode 6. For example, particles of copolymer of styrene and styrene sulfonic acid in which sulfonic acid group is distributed on the surface is used as an electrode of methanol fuel cell. The particle is synthesized in such a way that distilled water, styrene as hydrophobic monomer, and sodium styrene sulfonate as ionic monomer are mixed and potassium persulfate as polymerization initiator are added to the mixture and they are stirred in a high speed under a nitrogen atmosphere to polymerize them.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] A new type of heterogeneous organic electrolyte suitable for fuel cells using a gaseous oxidant such as air or a liquid oxidant such as hydrogen peroxide is used. Regarding fuel cells.

[Background of the invention]

Fuel cells directly extract the energy generated by electrochemically reacting fuel and oxidizing agent as electrical energy, and can be used as power sources for power generation equipment, aerospace equipment, unmanned facilities, radio equipment, automobiles, home appliances, etc. It was considered as
Some of them have also been put into practical use.

The main fuel cells include molten carbonate electrolyte fuel cells, 2o, operated at temperatures of about 500-700 tZ'.

There are phosphoric acid electrolyte fuel cells that operate at temperatures around 100°C, alkaline electrolyte fuel cells and acidic electrolyte fuel cells that operate at room temperature to about 100°C or less.

Generally, an aqueous solution of lithium hydroxide, sodium hydroxide, potassium hydroxide, or the like is used as an electrolyte in an alkaline electrolyte fuel cell, and dilute sulfuric acid is used as an electrolyte in an acidic electrolyte fuel cell. The reason for this is that an aqueous solution of a strong electrolyte as described above is the easiest to use as an electrolytic solution with high ionic conductivity at low temperatures.

However, these strong electrolyte aqueous solutions are highly corrosive, and there are restrictions on the materials that can be used to construct the battery, and furthermore, it is necessary to take sufficient care to prevent such electrolytes from leaking outside the battery. Countermeasures against electrolyte leakage are not easy, and various countermeasures have been taken in the past.

In addition, since the electrolyte is an aqueous solution of electrolyte, the electrolyte that should originally accumulate in the electrolyte chamber passes through the porous fuel electrode or oxidizer electrode into the fuel chamber due to the dilution effect due to the concentration gradient between the electrolyte and the fuel or oxidizer. (8) A phenomenon occurs in which the oxidizer leaks into the oxidizer chamber. As a preventive measure against this phenomenon, in the case of fuel cells using liquid fuel, a fuel mixture diluted with electrolyte is supplied to the fuel chamber, and the electrolyte and fuel are By reducing the difference in concentration of electrolyte in the mixture, the outflow of electrolyte from the electrolyte chamber to the fuel chamber is reduced.However, this measure of diluting the fuel with electrolyte is unnecessary for the original function of the battery. In addition, the fk of the fuel becomes lower and the efficiency deteriorates.Also, there are countermeasures such as mixing inorganic powder into the electrolyte and making it into a paste, but the electrolyte is essentially a fuel electrode or an oxidizer electrode. This is not a fundamental countermeasure as long as it can be passed through.

[Purpose of the invention]

An object of the present invention is to provide a fuel cell in which electrolyte leakage or outflow is prevented or reduced.

[Summary of the invention]

The present invention is based on the idea that electrolyte leakage and outflow in conventional fuel cells can be prevented by using an electrolyte that cannot pass through a porous fuel or oxidizer electrode. The present inventors used fine particles of an organic polymer compound with chemically bonded ionic groups on the surface as an electrolyte having the above effect,
When applied to methanol fuel cells, the results were confirmed to be more effective than expected.

Such fine particles are usually obtained as latex (emulsion), but are not limited to latex. In nature, such fine particles mainly exist as natural latex, but they can be artificially produced by copolymerizing ionic monomers and hydrophobic monomers that are poorly soluble in water in an aqueous medium, or by copolymerizing hydrophobic monomers in an aqueous medium. a method of emulsion polymerization or suspension polymerization of a monomer, and graft polymerization of an ionic monomer or grafting an ionic polymer onto the surface of the resulting hydrophobic Borya particles;
The surface of the hydrophobic polymer particles is sulfonated;
It can be synthesized by the sipping method using quaternary ammonium treatment.

Note that the particle size of these particles is not particularly limited, but as long as they do not pass through the porous fuel electrode and oxidizer electrode, it is better to use particles with a smaller particle size. The surface area of the material increases, and the ionic concentration, in other words, the ionic conductivity, increases, making it suitable for use as an electrolyte. For the same reason, it is preferable that the ionic group density on the particle surface is also high.

In acidic electrolyte fuel cells, the ionic group on the particle surface is preferably a strongly acidic ionic group that has a high degree of ionization in water, in other words, has a high ionic conductivity, and specifically, a sulfonic acid group, a sulfuric acid ester group, Examples include phosphonic acid groups and phosphoric ester groups. For the same reason, strong alkaline ionic groups are preferred in alkaline electrolyte fuel cells, and specific examples include quaternary ammonium groups such as trimethylammonium groups and quaternary phosphonium groups such as triphenylphosphonium groups.

The hydrophobic polymer that forms the core of the particles is styrene.

There are homopolymers such as hydrophobic vinyl monomers such as vinyl acetate, acrylonitrile, and methyl methacrylate, olefin monomers such as ethylene and propylene, diene monomers such as butadiene, isoprene, and chloroprene, and copolymers consisting of two or more of the above monomers. Additionally, crosslinking these polymers increases hydrophobicity, mechanical strength of particles,
It is preferable because properties such as heat resistance increase. A polyfunctional compound such as divinylbenzene is used as the crosslinking agent.

Although the structure of the fuel cell of the present invention is not particularly limited, it will be explained below using a methanol fuel cell as an example. FIG. 1 is a schematic diagram showing the principle of a fuel cell according to the present invention.
However, an oxidizing agent 4 such as oxygen or air is supplied to the oxidizing agent chamber 3. An electrolyte layer 9 containing fine particles 8 of an organic polymer compound having ionic groups 7 chemically bonded to the surface thereof and a diaphragm 10 are provided between the fuel electrode 5 and the oxidizer electrode 6. The ionic groups on the particle surface dissociate counterions 11 in the presence of water. These counter ions move within the electrolyte as the cell reaction occurs and are consumed at the oxidizer electrode, but ions of the same type are generated at the fuel electrode and replenished. Specifically, the counter ions 11 are hydrogen ions in the case of an acidic electrolyte, and hydroxide ions in the case of an alkaline electrolyte. The diaphragm 10 is used to prevent or prevent the fuel 2 from oxidizing or burning when it passes through the fuel electrode 5 and the electrolyte layer 9 and reaches the oxidizer electrode 6 to cause a cell reaction, reducing fuel efficiency. Provided to suppress Diaphragm 10
The position is not particularly limited as long as it is between the fuel electrode 5 and the oxidizer electrode 6. Examples of the diaphragm 10 include a cation exchange membrane in the case of an acidic electrolyte and an anion exchange membrane in the case of an anionic electrolyte. The cell reaction in a methanol fuel cell is as follows.

Methanol electrode (negative electrode) CHsOH+HzO→Co! +6H"+66-Oxidizer electrode (positive electrode) FIG. 2 is a perspective view showing the structure of a single cell of a methanol/air fuel cell according to an embodiment of the present invention.

This single cell includes a graphite separator 12 that forms an air chamber and also serves as a current collector, an air electrode 13 adjacent to the separator, an ion exchange membrane 14, and a methanol electrode 1.
7, a methanol electrode 17 fixed to the electrolyte holding frame 16, a fibrous wicking material 19 for supplying methanol from the methanol tank 18 to the fuel chamber by capillary action, and the fuel chamber. It is constructed by sequentially stacking graphite separators 20 which also serve as current collectors. Grooves 21 are formed in the separator 12 to serve as air passages. If the electrolyte is made into a paste, it will be easier to support it on a methanol electrode or the like. In order to make the electrolyte into a paste form, the concentration of the fine particles in an aqueous dispersion of organic polymer particles having chemically bonded ionic groups on the surface is increased, or silicon carbide is added as a thickener to the aqueous dispersion of the fine particles. Insulating fine powder such as fine powder or silica fine powder, or organic fine powder such as ion exchange resin fine powder may be mixed. If such a paste-like electrolyte is applied to the facing surface of the methanol electrode with a frame as described above and/or the facing surface of the fuel electrode, or to one or both sides of the ion exchange membrane, a thin membrane can be easily decomposed. A structure can be created. Furthermore, in the present invention, if methanol or a mixture of methanol and water is supplied from the fuel tank to the fuel chamber using a fibrous wicking material that utilizes capillary action, fuel and electrolyte can be supplied from the fuel tank to the fuel chamber, unlike conventional methanol batteries. It is possible to eliminate the need for auxiliary equipment such as a pump for supplying and circulating the mixture (6 pieces of anolyte). Therefore, in addition to simplifying the construction of four batteries,
Since no power is required, energy efficiency is also increased.

In conventional dilute sulfuric acid electrolyte fuel cells, a large amount of dilute sulfuric acid (50 to 70%
% by volume) had to be mixed.

For this reason, the methanol concentration in the anolite becomes extremely low, and it takes a second
It was difficult to adopt the siphoning financial power formula shown in the figure. However, in the present invention, since the electrolyte is in the form of particles, it does not pass through the porous fuel electrode, and therefore the velyte is not diluted, so there is no need to use an anorite as the fuel. Therefore, since methanol alone or methanol added with a small amount of water required for the reaction can be used as fuel, sufficient methanol can be supplied even with the suction system.

In Figure 2, arrow A is the flow of air, B is the flow of water vapor and air generated by the battery reaction, C is the flow of fuel, D is the flow of carbon dioxide gas generated by the battery reaction, and E is the flow of carbon dioxide released from the battery. It is a flow of carbon dioxide gas.

FIG. 3 is a perspective view showing the appearance of an embodiment of a fuel cell constructed by stacking the single cells shown in FIG. 2. If the electromotive force of a single cell is 0.6V, connecting 20 single cells in series constitutes a fuel cell with an electromotive force of 12V. In FIG. 3, the same symbols as in FIG. 2 mean the same things. A large number of stacked cells are housed in a battery case 22, and a positive terminal 23 and a negative terminal 24 are attached. Fuel is supplied from the boat 25 to the tank 26.

(11) [Embodiments of the invention] Examples of the present invention will be described below.

Example 1 Particles of a copolymer of styrene and styrene sulfonic acid, in which most of the sulfonic acid groups are distributed on the surface of the particles, were used as an electrolyte for a fuel cell using methanol as fuel, as shown in FIG. The particles were prepared by adding 0.8 parts of potassium persulfate as a polymerization initiator to a mixture of 300 parts of distilled water, 50 parts of styrene as a hydrophobic monomer, and 20 parts of sodium styrene sulfonate as an ionic monomer, and heating under a nitrogen atmosphere at a temperature of 60 tT.
The copolymerization reaction was carried out under high speed stirring for 10 hours. In this reaction, since it also acts as an ionic monomaha surfactant, fine oxide particles were produced in the same manner as in ordinary emulsion polymerization. Thereafter, the particles were treated with an acid type cation exchange resin to exchange the counter ions of the sulfonic acid groups on the particle surface from sodium ions to hydrogen ions. An appropriate amount of silicon carbide fine powder is added as a thickener to the aqueous dispersion of electrolyte particles thus obtained, and the mixture is kneaded.
(12) A paste-like electrolyte was obtained. This paste-like electrolyte was interposed in the electrolyte holding frame 16 between the methanol electrode 17 and the cation exchange membrane as the ion exchange membrane 14 to obtain a single cell of a fuel cell. Current (I) - voltage (V) of this single cell
The characteristics are shown in Figure 4.

By making the electrolyte granular in this manner, the electrolyte does not flow out from the electrolyte layer, making it easier to handle and preventing a decrease in battery output even during long-term operation. Furthermore, since the electrolyte no longer flows into the fuel chamber, there is no need to mix the electrolyte with the fuel, and as a result, in the stacked battery shown in Figure 3, there is no short circuit between the electrodes because only the fuel is supplied. In addition, a bomb for fuel supply was no longer required, and the battery output and fuel efficiency were improved, and the fuel supply structure was simplified.

Example 2 The aqueous dispersion of electrolyte particles obtained in Example 1 was concentrated,
A paste-like electrolyte was obtained. This paste-like electrolyte was used as an electrolyte in a methanol fuel cell as shown in FIG. 2 in the same manner as in Example 1.

(13) Due to the high concentration of electrolyte particles, the battery output increased and exhibited good DC-voltage characteristics as shown in FIG. Also,
Even if the thickener was not cooled, since the electrolyte was granular, there was no outflow, and the same effect as in Example 1 was obtained.

Example 3 As an electrolyte for a methanol fuel cell as shown in FIG. 2, particles of an organic polymer compound whose interior was cross-linked and had a sulfonic acid group on the surface were used. Particles are distilled water 30
0.8 parts of potassium persulfate as a polymerization initiator was added to a mixture of 0s, 30 parts of styrene as a hydrophobic monomer, 20 parts of sodium styrene sulfonate as an ionic monomer, and 1.3 parts of divinylbenzene as a crosslinking agent, and the mixture was placed in a nitrogen atmosphere. The copolymerization reaction was carried out under high speed stirring at a temperature of 600C for 10 hours. In this case as well, since the ionic monomer acted as a surfactant, good latex particles were produced as in normal emulsion polymerization. Thereafter, the particles were treated with an acid type cation exchange resin to exchange the counter ions of the sulfonic acid groups on the particle surface from thorium ions to hydrogen ions. The thus obtained aqueous dispersion of electrolyte particles was concentrated to obtain a paste-like d-lyte. This paste-like electrolyte was used in Example 1.
It was used as an electrolyte in a methanol fuel cell as shown in Figure 2 in the same manner as above.

Cross-linking the inside of the electrolyte particles makes it difficult for the particles to swell in water and increases the hydrophobicity of the inside of the particles, making it easier to maintain particle properties even when the concentration of sulfonic acid groups is higher than when internal cross-linking is not done. can. Therefore, since the hydrogen ion concentration in the electrolyte was high, good flow-voltage characteristics were exhibited as shown in FIG.

Furthermore, by cross-linking the inside of the particles, the mechanical strength of the particles increased and the heat resistance of the particles improved, making it difficult for particles to fuse together and reduce the surface area of the particles. Furthermore, since this electrolyte was granular, it did not leak into the fuel chamber, etc., and had the same effect as Example 1.

Example 4 Particles in which polystyrene sulf(15)phonic acid was grafted onto the surface of hydrophobic particles were used as an electrolyte for a methanol fuel cell as shown in FIG. The particles were synthesized as follows. 300 parts of distilled water, 50 parts of styrene as a hydrophobic monomer, and 2 parts of divinylbenzene as a crosslinking agent.
0.5 parts of potassium persulfate and 0.5 parts of sodium bisulfite as polymerization initiators were added to a mixture of 6 parts of 2-hydroxyethyl methacrylate as a monomer giving a graft point, and the mixture was heated at 40C under a nitrogen atmosphere for 10 parts. The copolymerization reaction was carried out while stirring at high speed. As a result, a liquid in which fine particles of the copolymer were dispersed was obtained, although the dispersion stability of ordinary latex is not good. To this aqueous dispersion of fine particles, 50 parts of sodium styrene sulfonate as a grafting monomer and 9 parts of ceric ammonium nitrate as a graft polymerization initiator were added, and the grafting was carried out by stirring at high speed for 8 hours at a temperature of 50C under a nitrogen atmosphere. Polymerization was performed.

Thereafter, the particles were treated with an acid type cation exchange resin to convert the counter ions of the grafted polystyrene sulfonic acid on the particle surface from sodium ions to hydrogen ions. The aqueous dispersion of electrolyte particles thus obtained was concentrated (16) to obtain a paste-like electrolyte. This paste-like electrolyte was used as an "it electrolyte" in a methanol fuel cell as shown in FIG. 2 in the same manner as in Example 1.

The electrolyte particles of this example have a high ion density on the particle surface because the ionic polymer is grafted onto the surface of the particle.
Therefore, even though the hydrogen ion concentration in the electrolyte was high, good current-voltage characteristics were exhibited as shown in FIG. Further, since this electrolyte was also granular, there was no outflow of the electrolyte, and the same effect as in Example 1 was obtained.

〔Effect of the invention〕

Although methanol/air fuel cells have been described in the above embodiments, the present invention is not limited thereto, and can also be applied to fuel cells using other fuels and oxidizers. Further, although a paste-like electrolyte is used as the electrolyte, the basic objective of the present invention, which is to prevent electrolyte leakage and outflow, can be achieved even if a simple aqueous dispersion of electrolyte particles is used.

According to the present invention, it is possible to prevent the electrolyte from flowing out of the electrolyte chamber, thereby providing long-term stability in battery characteristics. In addition, the prevention effect against electrolyte leakage to the outside of the battery has been further improved, making it easy to handle and suitable for use as a mobile power source, a battery for one-time use, or a household power source, especially in places with vibrations. It can be used as a power source. Furthermore, since the electrolyte can be prevented from flowing into the fuel chamber, there is no need to mix the electrolyte into the fuel.As a result, short circuits between the electrodes due to fuel can be prevented, and fuel can be supplied to the fuel chamber without a pump. This makes it possible to improve efficiency and simplify the structure.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram for explaining the principle of the fuel cell of the present invention, Fig. 2 is a partially cutaway perspective view showing the configuration of a single cell of the fuel cell according to the present invention, and Fig. 3 is a schematic diagram for explaining the principle of the fuel cell of the present invention. A perspective view showing the structure of a connected fuel cell, and FIGS. 4 to 7 are graphs showing DC-voltage characteristics of a single cell of a fuel cell according to an embodiment of the present invention. 1... Fuel chamber, 2... Fuel, 3... Oxidizer chamber, 4
... Oxidizer, 5... Fuel electrode, 6... Oxidizer electrode, 7
...Ionic group, 8...Electrolyte particle, 11...Counter ion, 13...Air electrode, (19)

Claims (1)

[Claims] 1. In a fuel cell that directly extracts electrical energy by causing an electrochemical reaction between a fuel electrode and an oxidizer electrode that face each other with an electrolyte in between, the electrolyte has a hydrophobic core and A fuel cell characterized in that it is a particle of an organic polymer compound comprising a surface layer covering the core and having an ionic group. 2. The fuel cell according to claim 1, wherein the particles are latex particles. 3. The fuel cell according to claim 1 or 2, wherein the latex particles are particles of a copolymer of a hydrophobic monomer and an ionic monomer. 4. The fuel cell according to claim 1, wherein the surface layer of the particle is an ionic polymer, and the ionic polymer is grafted onto a hydrophobic core. Fuel cell. 5. The fuel cell according to claim 4, wherein said particles are latex particles. 6. The fuel cell according to any one of claims 1 to 5, wherein the particles are a crosslinked organic polymer compound.