JPH02281567A - Methanol fuel cell - Google Patents

Abstract

PURPOSE:To largely reduce the weight of a cell by using a separator which comprises a film or sheet formed from synthetic resin and carbon powders, and also providing a methanol supply passage and an air supply passage in the electrode base of a methanol electrode and that of an air electrode, respectively. CONSTITUTION:A separator 4 comprising a flexible and electron conductive film or sheet formed from synthetic resin and carbon powder is used and also a methanol supply passage and an air supply passage are provided in the electrode base of a methanol electrode 1 and that of an air electrode 2, respectively. The above film or sheet is formed as a film or sheet of electrical resistance less than 0.5OMEGAcm<2>, sulfate and methanol resistance, and a methanol transmission coefficient of less than 8X10<-5>mol/cm<2> h(mol/l) under a cell operating temperature condition (about 60 deg.C). The above film or sheet is formed by mixing of carbon powder with polytetrafluoroethylene, polypropylene, polyethylene, vinyl chloride and the like. The thickness of the above film or sheet is from 0.15 to 0.05mm.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a methanol fuel cell, and more particularly to an acidic electrolyte methanol fuel cell that uses methanol as a fuel, air as an oxidizing agent, and an aqueous sulfuric acid solution as an electrolyte.

[Conventional technology]

Fuel cells extract the reaction energy of fuel and oxidizer directly as electrical energy, and have high power generation efficiency.
It is expected to be a new power generation method because it produces less noise and vibration and produces clean exhaust gas. In particular, acid electrolyte methanol fuel cells, which use methanol as fuel and sulfuric acid as electrolyte, operate at normal pressure and relatively low temperature (approximately 60°C), and can be easily miniaturized, so they are widely used as small to medium capacity power sources. It has many uses.

The basic components of this battery are an oxidizer electrode (air electrode), a fuel electrode (methanol electrode), and an electrolyte (ion exchange membrane) to provide ion conductivity between them. is called a unit battery. The output voltage of a unit battery is around 0.5V, and in practice, a large number of unit batteries are connected in series to obtain an output voltage depending on the purpose of use. A common method for constructing a series circuit of unit batteries is to stack unit batteries with separators interposed therebetween. In this case, the separator has the function of electrically connecting the unit cells in series, as well as the function of supplying air to the air electrode and fuel (anolyte: mixed aqueous solution of sulfuric acid and methanol) to the methanol electrode. In other words, an electronically conductive material is used as the separator material (carbon material is usually selected in consideration of corrosion resistance, processability, cost, etc.). A flow path is provided for supplying air to the electrode, and a flow path for supplying fuel (anolyte) to the methanol electrode is provided on the other surface of the separator that is in contact with the methanol electrode. A problem with the fuel cell constructed using the above method is that the weight of the separator is large, which increases the weight of the cell.

FIG. 5 shows the configuration of the conventional battery described above. The battery is constructed by placing carbon separators 4 on both sides of a unit battery consisting of a methanol electrode 1, an ion exchange membrane 3, and an air electrode 2, and by repeatedly stacking a large number of unit batteries (one separator is inserted between each unit battery). ) consists of An anolyte channel 5 is provided on one side of the separator, and while the anolyte flows through this channel, methanol in the anolyte is supplied to the methanol pole 1 and participates in the reaction. On the other hand, an air flow path 6 is provided on the other surface of the separator (back surface in the figure), and while air flows through this flow path, oxygen in the air is supplied to the air electrode 2 and participates in the reaction. The depth of the channel provided in the separator is
In order to smoothly supply the anolyte and air and to smoothly discharge the reaction product, one to several layers are required, and the thickness of the separator becomes larger than that of the separator.

By the way, the separator needs to separate the anolyte and air flowing back to back (this is where the name separator comes from), and it is required to use a material that has low permeability to both liquid (anolyte) and gas (air). The specific gravity of a carbon material that satisfies the above properties usually reaches about 1.5 to 2. The thickness of the separator is increased due to the flow path structure, and its specific gravity is also increased due to its impermeability.As a result, the weight of the carbon separator increases, and the weight of the battery increases.

Solving this problem is particularly important when utilizing this battery as a mobile power source, taking advantage of its suitability as a small to medium capacity power source.

[Problem to be solved by the invention]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above conventional problems and provide a methanol fuel cell that is lighter in weight than conventional ones and is comparable in performance.

[Means to solve the problem]

By not providing a flow path in the separator, which has a relatively high specific gravity, and instead providing the required flow path in the electrode, the inventors have discovered that while maintaining good battery performance, the overall methanol After discovering that the weight of the fuel cell can be significantly reduced and conducting extensive research based on this new knowledge, the present invention was completed.

Therefore, the methanol fuel cell of the present invention has a methanol electrode that electrochemically oxidizes methanol, an air electrode that electrochemically reduces oxygen in the air, and an electrolyte that maintains ionic conductivity between them. In a methanol fuel cell, the methanol fuel cell consists of an ion exchange membrane and a separator that forms an electrical series circuit of the unit cell made up of these membranes and separates the methanol fuel and the air the oxidizer to prevent them from mixing. The separator is made of a flexible and electronically conductive film or sheet made of synthetic resin and carbon powder, and the parts corresponding to the electrodes and air electrodes have an electrical connection function for forming an electrical series circuit of the unit battery. The present invention is characterized in that it has a methanol and air isolating function and that methanol and air supply channels are provided in the electrode substrates of the methanol electrode and the air electrode, each consisting of an electrode substrate and a catalyst layer formed on its surface.

The properties required of the film or sheet made of the synthetic resin and carbon powder are flexibility, electronic conductivity, anolyte resistance, and impermeability to methanol in the anolyte. Electronic conductivity is 005Ω・d or less, preferably 0.2 including contact resistance with electrodes and ion exchange membrane during battery assembly.
Ω・d or less is desirable. For anolyte resistance, 1.5 mol/1 sulfuric acid and 1.5 mo methanol at 60°C
It is the durability against l/l aqueous solution. The impermeability of methanol is 8 × 10-'mol in terms of methanol permeability coefficient.
/ci-h·(mol/ff1) (when there is a difference in methanol concentration on both sides of the membrane, the amount of methanol that permeates through the membrane per hour per 1 cTa of membrane area) or less is required. According to the inventors' studies, a material obtained by kneading carbon powder into a thermoplastic resin and molding it into a film satisfies these conditions. In other words, films made of polytetrafluoroethylene, polypropylene, polyethylene, vinyl chloride, etc. mixed with carbon powder can be applied well, and films made of polytetrafluoroethylene mixed with graphite have excellent flexibility, electronic conductivity, and anolyte resistance. It is excellent in all aspects, including impermeability to methanol, and can be applied particularly well. In addition, from the viewpoint of flexibility and weight reduction, the thickness of the membrane or sheet is
Preferably, it is 0°15LI11 to 0.05+us.

The separator frame is required to have anolyte resistance, and the various plastics mentioned above can be used. Heat-resistant vinyl chloride has excellent anolyte resistance, heat resistance, and processability, and is particularly suitable for use.

The structure of the separator by the separator frame and the conductive film can be achieved by bonding the two with an adhesive, thermal fusion, or mechanical sandwiching.

The substrate material of the methanol electrode is required to have electronic conductivity, anolyte resistance, and methanol permeability for supplying fuel methanol to the catalyst layer, and a porous carbon material can meet these requirements. In porous carbon materials, sheets (nonwoven fabrics) made of carbon fibers have a specific gravity of 0.8 to 0.
．． As small as 4, it can be applied particularly well.

The substrate material of the air electrode is required to have electronic conductivity and gas permeability for supplying oxygen in the air to the catalyst layer, and the same material as the methanol electrode substrate can be suitably used.

[For production]

The separator in the methanol fuel cell of the present invention is composed of a flexible and electronically conductive membrane or sheet made of synthetic resin and carbon powder in the portion corresponding to the methanol electrode and the air electrode. Since the operating temperature is about 60°C, there is no problem with heat resistance, and in the prior art, in order to give the separator the required electrical conductivity, corrosion resistance, permeation resistance to both anolyte and air, etc. This is made of high-density graphite, glassy carbon, etc., but separators made of such materials are inevitably rigid and brittle.
It is difficult to achieve a thickness of approximately ms+ or less. On the contrary, the film or sheet made of the synthetic resin and carbon powder of the present invention not only has the required electrical conductivity, corrosion resistance, permeation resistance, etc., but also is flexible and has a considerably thinner thickness. be able to.

Therefore, when the separator is configured without a flow path as described above, the electrical connection part (current-carrying part) of the separator
The thickness of
Separator weight can be significantly reduced. In addition, since the electrode substrate has air and fuel supply functions, the thickness of the electrode increases, but since the electrode substrate does not need a separation function, lightweight carbon materials can be used, and the increase in electrode weight is small.
Therefore, a significant weight reduction is achieved when looking at the battery as a whole.

Furthermore, since the membrane or sheet constituting the separator is flexible as described above, it fits well with the electrode surface and maintains the required close contact with the electrode surface when the methanol fuel cell is assembled, resulting in good cell performance. It is something to give.

〔Example〕

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples.

Figures 2-(a) and 2-(b) are examples of separators used in the methanol fuel cell of the present invention.

2- In (a) and (c), the separator is composed of a separator frame 11 and a conductive film 12. The conductive film 12 is located at the central notch of the separator frame 11 in the front view, and approximately at the center in the thickness direction of the separator frame in the top view. Therefore, the central notch of the separator frame is divided into two spaces (rooms) by the conductive film. The space on the top surface of the conductive film is connected to an anolite communication hole 13 bored in the separator frame via an anolite duct 14 (which becomes an anolyte flow path when a battery is constructed by stacking a large number of separators), and this space will be described later. This is the room that houses the methanol pole.

On the other hand, the space under the conductive film is connected to the space around the outer periphery of the frame through a plurality of air ducts, and this space becomes a room in which an air electrode, which will be described later, is housed. The conductive film 12 is made of a kneaded mixture of polytetrafluoroethylene and graphite powder, and has a length of 20C11, a width of 10CII, and a thickness of 0.1 mm. The electronic conductivity of conductive M12 is 0.15 Ω·cm”.

The anolyte resistance is good and no change is observed after 2,000 hours of anolyte immersion. The impermeability of methanol is determined by the methanol permeability coefficient of 3. lX10-'n+ol/cm!
・h (a + ol 80.

The separator frame was made of heat-resistant vinyl chloride, and the structure of the separator consisting of the separator frame and the conductive film was achieved by adhering the two together using an adhesive.

Further, by using foamed plastics, ie, foamed plastics having anolyte resistance such as foamed polyethylene, foamed polypropylene, and foamed polytetrafluoroethylene, in the separator frame 11 of FIG. 2, further weight reduction can be achieved.

FIG. 3 shows an example of a methanol electrode used in the methanol fuel cell of the present invention, and FIG. 4 shows an example of an air electrode.

The methanol electrode consists of a methanol electrode substrate 21 and five layers of methanol electrode catalyst coated on one flat surface thereof. The methanol electrode substrate 21 has a length of 20 am, a width of 10 cm+ + a thickness of 3I1 ml, and a width of 4 mm on the opposite side of the catalyst layer of the substrate.
.

An anolyte channel 5 with a depth of 1.8++v+ is provided.

The substrate material of the methanol electrode is a porous carbon plate made of carbon fiber.

Similarly, the air electrode consists of an air electrode substrate 31 and an air electrode catalyst layer coated on one flat surface thereof. air polar group tffE
31 has a length of 20C11 and a width of 10C11. The thickness is 4I,
Width 41. on the side opposite the catalyst layer of the substrate. An air flow path 6 with a depth of 2.8 mm is provided. The substrate material of the air electrode is a porous carbon plate made of carbon fiber, similar to the methanol electrode.

FIG. 1 shows an example of the structure of a methanol fuel cell according to the present invention, using the separator shown in FIG. 2 and the electrodes shown in FIGS. 3 and 4.

In FIG. 1, a methanol electrode and an air electrode shown in FIGS. 3 and 4 are arranged on both sides of an ion exchange membrane, with the catalyst-coated surface facing the ion exchange membrane, thereby forming a unit cell. A separator shown in FIG. 2 is provided on the outside of the electrode. A stacked battery is constructed by repeatedly stacking an air electrode, an ion exchange membrane, a methanol electrode, and a separator, and arranging a pair of current collector plates at both ends. The current collector plate has the function of extracting power from the series circuit of the unit batteries to the outside of the batteries. The anolyte reaches the anolyte channel provided in the methanol electrode from the communication hole of the separator through the anolyte duct, and while flowing through the anolyte channel, methanol is supplied to the methanol electrode catalyst layer,
Thereafter, it is discharged to the outside of the battery through another anorite duct and a communication hole.

On the other hand, air as an oxidizing agent is supplied into the separator from the air duct of the separator and reaches the air flow path of the air electrode 2, and while flowing through the air flow path, it supplies oxygen in the air to the air electrode catalyst layer, and Afterwards, it is exhausted to the outside of the battery through another air duct.

〔Effect of the invention〕

According to the present invention described above, while maintaining good battery performance,
It is possible to significantly reduce the weight of the separator, and as a result, the weight of the battery can be reduced.

[Brief explanation of drawings]

FIG. 1 is a partially exploded perspective view showing one embodiment of the methanol fuel cell of the present invention, and FIGS. 2, 3, and 4 respectively show a separator, a methanol electrode, and an air Diagram showing a specific example of poles, No. 5
The figure is a partially exploded perspective view showing the configuration of a battery according to the prior art. DESCRIPTION OF SYMBOLS 1... Methanol electrode, 2... Air electrode 3... Ion exchange membrane, 4... Separator 5... Anolyte channel,
6...Air flow path 7...Anolyte flow, 8...
Air flow 9... Current collector plate, 11... Separator frame 1
2... Conductive film, 13... Anolyte communication hole 14.
...Anolyte duct, 15...Air duct 21...
- Methanol electrode substrate, 22...methanol electrode catalyst layer 3
1... Air electrode substrate, 32... Air electrode catalyst layer.

Claims (1)

[Claims] 1. A methanol electrode that electrochemically oxidizes methanol, an air electrode that electrochemically reduces oxygen in the air, and ions as an electrolyte to maintain ionic conductivity between them. In a methanol fuel cell consisting of an exchange membrane and a separator that constitutes an electrical series circuit of a unit cell composed of these membranes and separates methanol as a fuel and air as an oxidizer to prevent mixing, a methanol electrode and a separator are used. The part corresponding to the air electrode is made of a separator made of a flexible and electronically conductive film or sheet made of synthetic resin and carbon powder, and has an electrical connection function for constructing an electrical series circuit of the unit battery and methanol. A methanol fuel cell characterized in that it has an air isolation function and that methanol and air supply channels are provided in the electrode substrates of the methanol electrode and the air electrode, which are each composed of an electrode substrate and a catalyst layer formed on its surface. . 2. A flexible and electronically conductive film or sheet made of synthetic resin and carbon powder is produced by kneading carbon powder into a thermoplastic resin such as polytetrafluoroethylene, polypropylene, polyethylene, or vinyl chloride, and then forming a film or sheet into a film or sheet. 2. The methanol fuel cell according to claim 1, wherein the methanol fuel cell is molded as follows. 3. The thickness of the flexible and electronically conductive film or sheet made of synthetic resin and carbon powder is 0.15-0.
Claim 1 or Claim 2 characterized in that the diameter is 05 mm.
The methanol fuel cell described. 4. A flexible and electronically conductive membrane or sheet made of synthetic resin and carbon powder can be used under battery operating temperature conditions (
(approximately 60℃), electrical resistance of 0.5Ω・cm^2 or less, sulfuric acid resistance, methanol resistance, methanol permeability coefficient of 8×
Claim 1, characterized in that it is a film or sheet with a molecular weight of 10^-^5 mol/cm^2.h.(mol/l) or less.
4. The methanol fuel cell according to claim 3. 5. The separator consists of a separator frame and a flexible and electronically conductive film or sheet made of synthetic resin and carbon powder, and the two are bonded by adhesive, thermal fusion, or mechanically sandwiched. The methanol fuel cell according to any one of claims 1 to 4, characterized in that it is an integrated cell. 6. The methanol fuel cell according to any one of claims 1 to 5, wherein the separator frame is made of heat-resistant vinyl chloride. 7. The methanol fuel cell according to any one of claims 1 to 6, wherein the electrode substrate is made of a porous carbon material. 8. The methanol fuel cell according to any one of claims 1 to 7, wherein the porous carbon material is a nonwoven fabric made of carbon fibers.