JPH04132168A - Electrode for liquid fuel battery and liquid fuel battery using same - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is applicable to fuel electrodes and air electrodes of liquid fuel cells that use a reducing agent such as methanol, hydrazine, formalin, or formic acid as a liquid fuel and use air or oxygen as an oxidizing agent. and a liquid fuel cell using the same. More specifically, the present invention relates to an electrode for a fuel cell using methanol as a fuel and a liquid fuel cell using the same.

One of the most important challenges for conventional technology methanol fuel cells is
When methanol fuel is supplied to the fuel electrode in excess, it permeates through the electrolyte layer to the air electrode, and a direct oxidation reaction of the fuel occurs on the air electrode, resulting in a decrease in the performance of the air electrode.

To this end, conventional methanol fuel cells have a structure in which an ion exchange membrane is provided as a diaphragm between the two electrodes to prevent methanol from permeating. Since this ion exchange membrane has proton permeability, it has the role as an electrolyte as well as the above-mentioned role.

Problems to be Solved by the Invention However, in the above conventional configuration, the methanol blocking function was dependent only on the ion exchange membrane, and the air electrode itself did not have any blocking function. Moreover, the ion exchange membranes currently in general use have the drawback of not being able to provide a sufficient methanol blocking function. In addition, due to poor adhesion between the ion exchange membrane and the electrode, air bubbles that have passed through the air electrode and carbon dioxide gas bubbles generated by the decomposition of methanol at the fuel electrode accumulate, impeding the movement of protons. This increases the loss and causes the battery voltage to drop.

The present invention solves the above-mentioned problems, suppresses the deterioration of the characteristics of the air electrode due to methanol permeated from the fuel electrode, brings the ion exchange membrane and electrode into close contact, and provides a higher performance electrode for liquid fuel cells. The purpose of the present invention is to provide a liquid fuel cell using the following methods.

Means for Solving the Problems In order to achieve this object, the liquid fuel electrode of the present invention and the liquid fuel cell using the same are provided by adding a polymer having an ion exchange group inside the air electrode. It has a methanol blocking function. Further, at least one of an oxidizer electrode or a fuel electrode to which a polymer having an ion exchange group is added and an ion exchange membrane are bonded using polymers each having an ion exchange group.

Function: With this configuration, the surface of the catalyst inside the air electrode is covered with a solid polymer electrolyte, which is a proton donor, instead of a conventional electrolyte, such as sulfuric acid. In the case of a conventional liquid electrolyte, methanol dissolved in the electrolyte passes through an ion exchange membrane from the fuel electrode side to the air electrode side, diffuses in the electrolyte inside the air electrode, and reaches the catalyst.

At the air electrode, the reaction of the following formula (1) is progressing, but 3/20°+68 + (36-=3H20・(1
) When methanol is present near the catalyst, a direct oxidation reaction of methanol occurs in the following formula (2), lowering the potential of the air electrode.

CH30H+3/202=CO2+2H20...(2
) In contrast, in the case of the air electrode of the present invention, the solid polymer electrolyte inside the air electrode prevents the diffusion of dissolved methanol,
and selectively permeates protons.

Therefore, the reaction of the above formula (2) is suppressed and the reaction of the formula (1) is allowed to proceed preferentially without impairing the ionic conductivity.

Since the air electrode itself has a methanol blocking function in this way, the methanol blocking function is further improved compared to conventional methanol fuel cells.

In addition, by bonding the oxidizing agent electrode or fuel electrode and the ion exchange membrane using polymers containing ion exchange groups, the ion exchange membrane, the polymer having the ion exchange groups used for bonding, and the oxidizing agent The electrodes and fuel electrodes are strongly bonded to the polymers with ion exchange groups in each electrode.

Therefore, the ion exchange membrane, oxidizer electrode, and fuel electrode are in close contact with each other, and it is possible to prevent air and carbon dioxide gas bubbles from accumulating between the electrode and the ion exchange membrane. Furthermore, in addition to shortening the distance between the two electrodes, the electrodes, adhesive, and ion exchange membrane all contain ion exchange groups, so proton conductivity is maintained and ohmic loss can be significantly reduced.

EXAMPLES Hereinafter, examples of the present invention will be described with reference to the drawings.

(Example 1) FIG. 1 shows a cross-sectional view of a single cell of a methanol fuel cell in a first example of the present invention. In FIG. 1, reference numeral 10 indicates a cation exchange membrane, and in the present invention, a membrane made of a copolymer of tetrafluoroethylene and perfluorovinyl ether is Naf manufactured by DuPont, USA.
ion417 was used. Reference numeral 11 indicates a positive electrode, and reference numeral 12 indicates a negative electrode, both of which were porous electrode plates made of carbon and carrying a platinum-based catalyst. Air was introduced into the air chamber 13 and methanol fuel was introduced into the fuel chamber 14, respectively. Reference numerals 15 and 16 indicate adhesives bonding the electrode and the ion exchange membrane.

FIG. 2 is a schematic enlarged view of a cross section of the positive electrode 11 or the negative electrode 12 in FIG. 1. The electrode has a two-layer structure including a water-repellent layer 22 and a catalyst layer 21. The water-repellent layer is made of fine carbon powder treated with polytetrafluoroethylene (PTFE) to make it water-repellent, and is completely water-repellent and porous, so if it is a positive electrode, it plays the role of supplying air from the air chamber to the inside of the catalyst layer. , the negative electrode serves to supply methanol vapor from the fuel chamber. The catalyst layer is composed of fine carbon powder 26 treated to be water repellent with PTFE 25 and fine carbon powder on which a platinum-based catalyst 27 is supported. The water-repellent portion 26 forms a gas network that supplies air and methanol vapor to the catalyst. In the case of the air electrode of the present invention, a polymer electrolyte 20 having an ion exchange group is provided inside the catalyst layer, and protons supplied from an ion exchange membrane and an adhesive 28 having an ion exchange group are transmitted to the catalyst particles. It has become. On the other hand, in the case of the methanol electrode of the present invention, a polymer electrolyte 20 having an ion exchange group is provided inside the catalyst layer, and the protons generated on the catalyst particles are transferred to an adhesive 28 having an ion exchange group, and an adhesive 28 having an ion exchange group. The structure is such that the information is transmitted to the membrane.

In the case of this example, perfluorinated ion exchange powder of Nafion manufactured by Aldrich Chemical Co., USA was used as the polymer electrolyte.

The above electrode was created by the method described below. First, carbon fine powder carrying 25 wt% of catalyst is impregnated with 10 to 50 wt% of the butanol solution of the polymer electrolyte mentioned above, and after kneading into a paste, this paste is dried at 110°C to remove the butanol solvent. . This dried sample is pulverized to obtain catalyst-supported carbon fine powder with polymer electrolyte.

The air electrode is made by pre-molding a mixture of this catalyst powder and fine carbon powder water-repellent treated with PTFE on a water-repellent layer with a titanium mesh crimped onto it, and then hot-pressing it at 360°C. Created.

The electrode and ion exchange membrane were joined by the method described below.

On the catalyst layer of the electrode prepared as above, apply 1 to 10 μ per 1 d of perfluorinated ion exchange powder, the same as the solution used for the above polymer electrolyte, as an adhesive, and place an ion exchange membrane between the two electrodes. After drying at room temperature, heat to 150°C, maintain stoichiometric pressure for 1 to 5 minutes at 1 to 20 kg per 1 al, cool to room temperature in air, and integrate the electrode and ion exchange membrane. .

The characteristics of a methanol fuel cell using this electrode were determined using the single cell shown in FIG. The methanol fuel supplied was a 2M/l aqueous solution. The measurement temperature was 60°C.

(Example 2) Selemion CMV manufactured by Asahi Glass Co., Ltd. was used as the ion exchange membrane made of a copolymer of styrene and vinylbenzene, and as an adhesive between the ion exchange membrane and the electrode and as a polymer added to the electrode. A polymer made of a copolymer of styrene and vinylbenzene was used.

Addition of the polymer electrolyte to the electrode was performed in the following manner.

Fine carbon powder carrying a catalyst is impregnated into an aqueous solution of a mixture of sodium styrene sulfonate, hexaethylene glycol dimethacrylate as a crosslinking agent, and ammonium persulfate as a polymerization accelerator, and the paste is kneaded at 60°C. Heat for 2 hours to polymerize. This sample is washed with water, dried, and then ground to obtain catalyst-supported carbon fine powder with polymer electrolyte. An electrode is prepared in the same manner as in Example 1 using this fine catalyst powder. This electrode is immersed in approximately 3 M/l sulfuric acid to replace the sodium ions in the sulfonic acid groups of the polymer electrolyte with protons.

The electrode and the ion exchange membrane were joined by the following method.

An aqueous solution containing a mixture of sodium styrene sulfonate, hexaethylene glycol dimethacrylate as a crosslinking agent, and ammonium persulfate as a polymerization accelerator was placed on the catalyst layer of the electrode for 1 d.
The ion exchange membrane is sandwiched between the two electrodes, held under pressure at 60 DEG C. for 1 hour, and washed with water to integrate the electrode and the ion exchange membrane. The electrode integrated with this ion exchange membrane is immersed in approximately 3 M/l sulfuric acid to replace the sodium ions in the sulfonic acid groups of the polymer electrolyte with protons.

The cell configuration, measurement method, and other aspects were exactly the same as in Example 1.

(Example 3) In Example 1, 1. was added to the portion 15.16 of FIG. 1 without bonding the electrode and the ion exchange membrane with the polymer electrolyte.
The procedure was exactly the same as in Example 1 except that 5M/1 sulfuric acid was injected.

(Comparative Example 1) Example 1 was exactly the same as Example fPI 1, except that the electrode and the ion exchange membrane were joined using polytetrafluoroethylene fine particles that were the base of the ion exchange membrane. The joining method is described below. On the catalyst layer of the electrode, polytetrafluoroethylene fine particles are applied as an adhesive at 0.5 to 2 cm per cll, an ion exchange membrane is sandwiched between the two electrodes, and after drying at room temperature, the membrane is heated to 150°C. from 1ea
The stoichiometric pressure is maintained at 1 to 20 kg per f for 1 to 5 minutes, cooled to room temperature in air, and the electrode and ion exchange membrane are integrated.

(Comparative Example 2) In Example 1, 1.
The procedure was exactly the same as in Example 1 except that 5M/1 sulfuric acid was injected and an electrode to which no polymer electrolyte was added was used.

FIG. 3 shows the voltage-current characteristics of methanol fuel cells having structures according to Example 1, Example 2, Example 3, Comparative Example 1, and Comparative Example 2 of the present invention. The characteristics of the fuel cell of Example 1 of the present invention (curve A) show that the cell voltage is 0.45 V at a current density of 60 mA/aIr, and the characteristics of the fuel cell of Example 2 (curve B) also show that the cell voltage is 0.45 V at a current density of 60 mA/aIr. showed similar properties. In addition, the characteristics (curve C) of the battery in which the ion exchange membrane and electrode of Example 3 were not bonded and only the polymer electrolyte was added into the electrode were that the battery voltage at a current density of 60 mA/cm was 0. It showed .43V. On the other hand, the battery of Comparative Example 1 (curve D) in which a polymeric material containing no ion exchange group was used as the adhesive between the ion exchange membrane and the electrode had a current density of 60 mA.
The battery voltage at /al was 0.34V. Also,
In the battery of Comparative Example 2 (curve E) in which 1.5 M/l sulfuric acid was injected without bonding the electrode and the ion exchange membrane with a polymer electrolyte, and the electrode was used with no polymer electrolyte added, the current density was 60 m, The cell voltage at A/aIr was 0.30.

As described above, a comparison between Example 3 and Comparative Example 2 reveals that the fuel cell of the present invention can obtain a higher cell voltage than the conventional fuel cell using an electrode that does not have a methanol blocking function. Ta. Furthermore, from a comparison between Example 1 and Comparative Example 1, it is clear that by bonding the ion exchange membrane and electrode with a polymer having an ion exchange group, proton conductivity is maintained and battery voltage is improved. became.

In addition, in this example, a polymer having an ion exchange group is added to the inside of both the positive electrode and the negative electrode, and both electrodes and the ion exchange membrane are respectively bonded using a polymer containing an ion exchange group. As described above, even when the same treatment was performed on at least one of the electrodes or on the bond between the electrode and the ion exchange membrane, better performance than before was shown. Therefore, even if the treatment of the present invention is applied to at least one of the electrodes and the joint,
A sufficient effect can be obtained.

Further, in this embodiment, a methanol fuel cell is used as an example of a liquid fuel cell, but it is also possible to apply the present invention to a fuel cell using hydrazine, formalin, or the like as a fuel.

Effects of the Invention As described above, the present invention provides a high-performance liquid fuel that can suppress deterioration of air electrode characteristics due to methanol permeating from the fuel electrode by adding a polymer containing an ion exchange group inside the electrode. It is possible to realize a battery electrode and a liquid fuel cell using the same. Further, by bonding the electrode and the ion exchange membrane using a polymer containing an ion exchange group, the adhesion between the two is improved, and a low resistance liquid fuel cell without the retention of air bubbles can be realized.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a methanol fuel cell using the electrode of Example 1 of the present invention, Figure 2 is a schematic cross-sectional view of the electrode of Example 1 of the present invention, and Figure 3 is an example of the present invention and a comparison. FIG. 2 is a diagram of voltage-current characteristics of a methanol fuel cell using an example electrode. 10... Cation exchange membrane, 11... Positive electrode, 12...
・Negative electrode, 13... Air chamber, 14... Fuel chamber, 15.
... Positive electrode adhesive, 16... Negative electrode adhesive, 20... Polymer electrolyte, 21... Catalyst layer, 22... Water repellent layer, 2
3... Air chamber or fuel chamber, 24... Electrolyte chamber, 25... Polytetrafluoroethylene, 26... Fine carbon powder, 27... Platinum catalyst. Name of agent: Patent attorney Akira Koeji, et al.

Claims (4)

[Claims] (1) In a liquid fuel cell consisting of an oxidizer electrode and a fuel electrode, both of which are separated by an ion exchange membrane, a polymer having an ion exchange group is added to the inside of at least one of the two electrodes. An electrode for liquid fuel cells featuring: (2) The electrode for a liquid fuel cell according to claim 1, wherein the polymer is a copolymer of tetrafluoroethylene and perfluorovinyl ether. (3) The electrode for a liquid fuel cell according to claim 1, wherein the polymer is a copolymer of styrene and vinylbenzene. (4) A liquid characterized in that at least one of the oxidizer electrode or the fuel electrode according to claim 1 is bonded to an ion exchange membrane using a polymer containing an ion exchange group. Fuel cell.