Polymer electrolyte fuel cell

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

Regarding the polymer electrolyte type fuel cell, particularly regarding the electrode which is a component thereof.

【0002】

[Conventional technology]

In the electrode of the polymer electrolyte fuel cell, the area of the so-called three-phase interface formed by the pores serving as the supply path of the reaction gas, the hydrogen ion conductive polymer electrolyte, and the catalyst material which is an electron conductor is large or small. However, it affects the discharge performance of the battery. Conventionally, in order to increase the three-phase interface and reduce the amount of noble metal used as a catalyst material, attempts have been made to mix and disperse a hydrogen ion conductive polymer electrolyte in the catalyst material. For example, in the techniques described in Japanese Patent Publication No. 62-61118 and Japanese Patent Publication No. 62-61119, a mixture of a solution in which a polymer electrolyte is dispersed and a catalyst material is applied onto a polymer electrolyte membrane. A method of reducing the catalyst material after hot pressing with the electrode material has been proposed.

【0003】

Further, Japanese Patent Application Laid-Open No. 2-48632 proposes a method in which a porous electrode is molded, a solution in which an ion exchange membrane resin is dispersed is sprayed on the electrode, and the electrode and the ion exchange membrane are hot-pressed. .. Further, Japanese Patent Application Laid-Open No. 3-184266 proposes a method in which a polymer resin surface is coated with a polymer electrolyte, and Japanese Patent Application Laid-Open No. 3-295172 proposes a method in which a polymer electrolyte powder is mixed in an electrode. Further, Japanese Patent Application Laid-Open No. 5-36418 proposes a method in which a polymer electrolyte, a catalyst, carbon powder and a fluororesin are mixed and formed into a film to form an electrode. Further, in the technique described in US Patent No. 5211984, a solution in which a polymer electrolyte, a catalyst and a carbon powder are dispersed in an ink form is prepared by using glycerin or tetrabutylammonium salt as a solvent, and this is polytetrafluoro. A method of molding on an ethylene (hereinafter referred to as PTFE) film and then transferring to the surface of the solid polymer electrolyte membrane, or replacing the exchanging group of the solid polymer electrolyte membrane with Na type, and the above ink on the surface of the membrane. A method of applying a state dispersion liquid, heating and drying at 125 ° C or higher, and substituting the exchange group with an H type again has been reported.

【0004】

However, in the above-mentioned polymer electrolyte fuel cell, peroxide is generated by the battery reaction in the catalyst layer formed at the interface between the solid polymer electrolyte membrane and the electrode. The generated peroxide becomes a peroxide radical while diffusing, and deteriorates the electrolyte. In a fuel cell, fuel is oxidized at the fuel electrode and oxygen is reduced at the oxygen electrode, but side reactions occur in addition to these main reactions. A typical example is the production of hydrogen peroxide (H2O2).

【0005】

Hydrogen peroxide generated on these electrodes separates from the electrodes due to diffusion or the like and moves into the electrolyte. This hydrogen peroxide is a substance with strong oxidizing power and oxidizes many organic substances that make up the electrolyte.

【0006】

In order to suppress the deterioration of the electrolyte membrane due to such peroxide, for example, Japanese Patent Application Laid-Open No. 6-103992 also discloses a technique of supporting a catalyst metal in the electrolyte and decomposing the peroxide. .. Further, Japanese Patent Application Laid-Open No. 2001-118591 discloses a technique for dispersing and blending a transition metal oxide having a catalytic ability to catalytically crack peroxide in an electrolyte material.

【0007】

[Problems to be Solved by the Invention]

However, the deterioration of the electrolyte due to the peroxide does not occur only in the electrolyte membrane, but also decomposes the hydrogen ion conductive polymer electrolyte in the catalyst layer. The decomposition of the electrolyte by the peroxide becomes remarkable in the presence of heavy metals, so that the decomposition occurs more actively in the catalyst layer.

【0008】

Further, in the electrode, the diffusibility of the reaction gas must be ensured, and it is difficult to dispose a large amount of the polymer electrolyte in the catalyst layer. Therefore, even if a small amount of the polymer electrolyte is decomposed, a large proportion of the polymer electrolyte is lost.

【0009】

Deterioration of the electrolyte due to peroxide in the polymer electrolyte fuel cell causes more damage to the hydrogen ion conductive polymer electrolyte arranged in the catalyst layer than the electrolyte membrane itself. Further, the decomposition of the hydrogen ion conductive polymer electrolyte is remarkable on the oxidant gas side.

【0010】

Due to such decomposition of the hydrogen ion conductive polymer electrolyte, the power generation efficiency of the fuel cell decreases with the lapse of operating time. When the humidity of the oxidant gas to be supplied is high and sufficient water is supplied to the catalyst layer, the concentration of peroxide in the catalyst layer is diluted and discharged from the catalyst layer together with the water generated by power generation. Therefore, the decomposition of the hydrogen ion conductive polymer electrolyte is not remarkable. However, when the humidity of the supplied oxidant gas is low, the concentration of peroxide in the catalyst layer becomes high, which causes serious decomposition of the hydrogen ion conductive polymer electrolyte and causes a significant deterioration in power generation efficiency. ..

【0011】

[Means for solving problems]

The present invention solves the above-mentioned problems. By rapidly decomposing the peroxide generated on the surface of the catalyst, the decomposition of the hydrogen ion conductive polymer electrolyte is suppressed, and the humidity of the supplied oxidant gas is low. Even in this case, the purpose is to maintain good power generation efficiency for a long period of time.

【0012】

Therefore, the polymer electrolyte fuel cell of the present invention has a hydrogen ion conductive polymer electrolyte membrane, a pair of electrodes arranged at positions sandwiching the hydrogen ion conductive polymer electrolyte membrane, and one of the electrodes. In a fuel cell provided with a pair of separators having a gas flow path for supplying and discharging fuel gas and supplying and discharging oxidizing agent gas to the other, the electrode includes a catalyst layer in contact with the hydrogen ion conductive polymer electrolyte membrane. However, at least one catalyst layer of the electrode is characterized by having a hydrogen ion conductive polymer electrolyte, conductive carbon particles carrying catalyst particles, and a peroxide decomposition catalyst.

【0013】

At this time, it is effective to arrange the peroxide decomposition catalyst at the interface between the hydrogen ion conductive polymer electrolyte membrane and the catalyst layer.

【0014】

In the above, it is effective to electronically insulate between the peroxide decomposition catalyst and the electrode. Further, it is effective to support the peroxide decomposition catalyst on the electrically insulating particles. Further, it is desirable that the peroxide decomposition catalyst is a metal selected from ruthenium, manganese, cobalt, chromium, nickel, iridium, iron and vanadium, an oxide thereof, or an alloy containing the metal.

【0015】

BEST MODE FOR CARRYING OUT THE INVENTION

As the peroxide decomposition catalyst, it is desirable to use a metal having a good affinity for oxygen. Examples of such metals include ruthenium, manganese, cobalt, chromium, nickel, iridium, iron and vanadium. These metals may be used alone, or may be alloyed with other metals. The oxides of these metals also show good peroxide decomposability.

【0016】

In order to reduce the amount of these metals used and exert effective hydrogen peroxide decomposition properties, it is necessary to support the hydrogen peroxide decomposition catalyst on a carrier in the form of fine particles to increase the specific surface area of the catalyst. is there. As the carrier, carbon black, zirconia, alumina, zeolite, silica and the like can be used.

【0017】

These peroxide decomposition catalysts may be mixed in the catalyst layer of the electrode, but the surface potential of the catalyst in electrical contact with the electrode becomes the same as that of the electrode, and hydrogen peroxide is effectively used. Cannot be disassembled. For this reason, it is desirable that the catalyst be electrically insulated from the electrodes. A catalyst supported on a conductive carrier such as carbon black insulates some catalysts because they cannot maintain electrical contact with the electrodes when mixed in the catalyst, but insulates this more effectively. For that purpose, it is effective to coat with a hydrogen ion conductive polymer electrolyte in advance.

【0018】

Further, if a catalyst supported on an insulating carrier such as zirconia, alumina, zeolite, or silica is used, the electrode can be easily insulated from the electrode.

【0019】

[Example]

Next, an embodiment of the present invention will be specifically described.

【0020】

(Example 1) As a peroxide decomposition catalyst, 2 g of a catalyst in which an alloy of ruthenium and platinum is supported on carbon black (TEC61E54 manufactured by Tanaka Kikinzoku, Pt concentration 30% by weight, Ru concentration 24% by weight) has electronic insulation. 11 g of a solution in which a hydrogen ion conductive polymer electrolyte was dispersed (manufactured by Asahi Glass Co., Ltd., product name: Flemion, 9 wt% ethanol solution) was mixed under a nitrogen atmosphere, dried and solidified, and then crushed to hydrogen. Approximately 3 g of a peroxide decomposition catalyst coated with an ionic conductive polymer electrolyte was obtained.

【0021】

5 g of catalyst with platinum supported on carbon black as a catalyst for fuel cell electrodes (TEC10E50E manufactured by Tanaka Kikinzoku, Pt concentration 50% by weight), and 25 g of solution in which hydrogen ion conductive polymer electrolyte is dispersed (manufactured by Asahi Glass, product name: Flemion). , 9% by weight ethanol solution) and 5 g of water were added and mixed, and the mixture was applied to the surface of the polypropylene sheet with a bar coder and dried to obtain an oxidizing agent electrode side catalyst layer. As for the coating amount of the catalyst layer, the platinum content is 1 cm.²It was adjusted to 0.3 mg per unit.

【0022】

When this polypropylene sheet with a catalyst layer was cut into 6 cm squares, 500 ml of 3% hydrogen peroxide solution was added, and the amount of oxygen generated was measured, good hydrogen peroxide decomposability was shown as shown in Fig. 1.

【0023】

A hydrogen ion conductive polymer electrolyte membrane (manufactured by Japan Gore-Tex Co., Ltd .: Gore-Select, film thickness 30 μm) is sandwiched between the above-mentioned two sets of polypropylene sheets with a catalyst layer so that the catalyst layer is on the inside, and 130 ° C. After hot pressing for 10 minutes with, the polypropylene sheet was removed and sandwiched between carbon papers (manufactured by Toray, TGP-H-120, film thickness 360 μm) to form an electrode membrane bonded body (MEA). The structure is shown in Fig. 2. Using the above MEA, a cell (single cell) for measuring fuel cell characteristics was assembled and tested. Figure 3 shows a single-cell configuration diagram.

【0024】

The temperature of the single cell is set to 75 ° C, and as an active material, hydrogen gas is humidified at a dew point of 70 ° C on the negative electrode side, and the utilization rate is 80%. Prepared to 40%, current density 200mA / cm²When the discharge test was carried out while passing the current, the cell voltage hardly decreased even after long-term operation. Figure 4 shows the change in cell voltage over time.

【0025】

In the above, as the peroxide decomposition catalyst, a catalyst in which an alloy of ruthenium and platinum is supported on carbon black is used, but instead, ruthenium, platinum-cobalt alloy, platinum-chromium alloy, platinum-nickel alloy, iridium, etc. Even when a catalyst (all manufactured by E-TEK) in which a platinum-iridium alloy, a platinum-iron alloy, a platinum-vanadium alloy, a platinum-cobalt-chromium alloy, or a platinum-cobalt-nickel alloy is supported on carbon black is used. Although there was a slight decrease in performance, almost the same results were obtained.

【0026】

(Comparative Example 1) 5 g of catalyst in which platinum is supported on carbon black as a catalyst for fuel cell electrodes (TEC10E50E manufactured by Tanaka Kikinzoku, Pt concentration 50% by weight), 25 g of solution in which hydrogen ion conductive polymer electrolyte is dispersed (manufactured by Asahi Glass Co., Ltd.) Name: Flemion, 9% by weight ethanol solution), 5 g of water was added and mixed, and the mixture was applied to the surface of the polypropylene sheet with a bar coder and dried to form an oxidant electrode side catalyst layer. As for the coating amount of the catalyst layer, the platinum content is 1 cm.²It was adjusted to 0.3 mg per unit.

【0027】

When this polypropylene sheet with a catalyst layer was cut into 6 cm squares and the hydrogen peroxide decomposability was examined in the same manner as in Example 1, the hydrogen peroxide decomposability was not good as shown in FIG.

【0028】

Using this catalyst layer, an electrode membrane junction (MEA) was prepared in the same manner as in Example 1, and a cell (single cell) for measuring fuel cell characteristics was assembled and tested. When the discharge test was performed in the same manner as in Example 1, the cell voltage decreased with the lapse of the operating time. Figure 4 shows the change in cell voltage over time.

【0029】

(Example 2) A catalyst in which 1 g of manganese oxide powder (manufactured by Kanto Chemical Co., Ltd.) is supported as a peroxide decomposition catalyst and platinum is supported on carbon black as a catalyst for a fuel cell electrode (TEC10E50E manufactured by Tanaka Kikinzoku, Pt concentration 50% by weight). , 25 g of a solution in which a hydrogen ion conductive polymer electrolyte is dispersed (manufactured by Asahi Glass, product name: Flemion, 9 wt% ethanol solution) and 5 g of water are added and mixed, and the mixture is applied to the surface of the polypropylene sheet with a barcoder. By drying, it became an oxidizing agent electrode side catalyst layer. As for the coating amount of the catalyst layer, the platinum content is 1 cm.²It was adjusted to 0.3 mg per unit.

【0030】

When this polypropylene sheet with a catalyst layer was cut into 6 cm squares and the hydrogen peroxide decomposability was examined in the same manner as in Example 1, good hydrogen peroxide decomposability was shown as shown in FIG.

【0031】

Using this catalyst layer, an electrode membrane junction (MEA) was prepared in the same manner as in Example 1, and a cell (single cell) for measuring fuel cell characteristics was assembled and tested. When the discharge test was performed in the same manner as in Example 1, the cell voltage hardly decreased even after long-term operation. Figure 4 shows the change in cell voltage over time.

【0032】

Further, in this example, the same catalyst layer was used for the fuel electrode side and the oxidant electrode side, but when the catalyst layer on the fuel electrode side was replaced with the catalyst layer of Comparative Example 1, the same discharge test was performed. Almost the same result was obtained.

【0033】

The same result was obtained when cobalt oxide and ruthenium oxide were used instead of manganese oxide.

【0034】

(Example 3) 15.0 g of a 10 wt% ruthenium chloride aqueous solution was dissolved in 1000 ml of water.

【0035】

10 g of zirconia powder (manufactured by Kanto Chemical Co., Inc.) was added thereto, and 60 ml of a 5% sodium hydroxide aqueous solution was added dropwise to adjust the pH to 5. The precipitate was filtered and dried, and heated to 400 ° C. under a nitrogen atmosphere to obtain a peroxide decomposition catalyst in which ruthenium was supported on the surface of zirconia.

【0036】

1 g of peroxide decomposition catalyst, 5 g of catalyst in which platinum is supported on carbon black as a catalyst for fuel cell electrodes (TEC10E50E made by Takashi Tanaka, Pt concentration 50% by weight), and 25 g of solution in which hydrogen ion conductive polymer electrolyte is dispersed (Asahi Glass) , Product name: Flemion, 9% by weight ethanol solution), 5 g of water was added and mixed, and the mixture was applied to the surface of the polypropylene sheet with a bar coder and dried to obtain an oxidant electrode side catalyst layer. As for the coating amount of the catalyst layer, the platinum content is 1 cm.²It was adjusted to 0.3 mg per unit.

【0037】

When this polypropylene sheet with a catalyst layer was cut into 6 cm squares and the hydrogen peroxide decomposability was examined in the same manner as in Example 1, good hydrogen peroxide decomposability was shown as shown in FIG.

【0038】

Using this catalyst layer, an electrode membrane junction (MEA) was prepared in the same manner as in Example 1, and a cell (single cell) for measuring fuel cell characteristics was assembled and tested. When the discharge test was performed in the same manner as in Example 1, the cell voltage hardly decreased even after long-term operation. Figure 4 shows the change in cell voltage over time.

【0039】

The same result was obtained when alumina, zeolite, and silica were used instead of zirconia.

【0040】

(Example 4) As the peroxide decomposition catalyst, a catalyst in which an alloy of ruthenium and platinum is supported on carbon black (TEC61E54 manufactured by Tanaka Kikinzoku, Pt concentration 30% by weight, Ru concentration 24% by weight) is used, and the same as in Example 1. About 3 g of a peroxide decomposition catalyst coated with a hydrogen ion conductive polymer electrolyte was obtained.

【0041】

To this, 5 g of water and 10 g of ethylene glycol were added and mixed by a ball mill, and applied by a screen printing method to one side of a hydrogen ion conductive polymer electrolyte membrane (manufactured by Japan Goretex Co., Ltd .: Gore-Select, film thickness 30 μm). The amount of catalyst applied is 1 cm for platinum content.²It was adjusted to 0.1 mg per unit.

【0042】

This hydrogen ion conductive polymer electrolyte membrane is sandwiched between polypropylene sheets with a catalyst layer similar to Comparative Example 1 so that the catalyst layer is on the inside, and an electrode film junction (MEA) is prepared as in Example 1 to prepare a fuel. A cell (single cell) for measuring battery characteristics was assembled and tested. At that time, the surface coated with the peroxide decomposition catalyst was set as the oxidant electrode side.

【0043】

When the discharge test was carried out in the same manner as in Example 1, the cell voltage hardly decreased even after long-term operation. Figure 4 shows the change in cell voltage over time.

【0044】

[Effect of the invention]

As described above, the present invention maintains high power generation efficiency for a long period of time by arranging a peroxide decomposition catalyst in the catalyst layer or at the interface between the hydrogen ion conductive polymer electrolyte membrane and the catalyst layer. A molecular electrolyte type fuel cell can be provided.

[Simple explanation of drawings]

[Figure 1]

The figure which showed the 1st characteristic of the battery of the 1st to 3rd Example and the comparative example of this invention. [Figure 2]

The figure which showed the structure of MEA which is a component of the battery which is an Example of this invention. [Fig. 3]

The figure which showed the structure of the single cell of the battery which is an Example of this invention. [Fig. 4]

The figure which showed the 2nd characteristic of the battery of the 1st to 4th Example and the comparative example of this invention. [Explanation of symbols]

21 Hydrogen ion conductive polymer electrolyte membrane 22 Catalyst layer 23 Porous electrode 24 MEA 31 Separator 32 gas flow path 33 single cell