JPH097620A - Polymer electrolyte fuel cell power generator - Google Patents

Abstract

(57) [Summary] [Objective] The concentration of carbon monoxide in the fuel reformed gas supplied to the fuel electrode is reduced to several ppm, and the deterioration of cell characteristics due to poisoning of the platinum catalyst of the electrode is suppressed. A fuel gas humidifier 2A that humidifies the fuel reformed gas reformed by a reformer 6 and a CO shift converter 7 and supplies it to a fuel electrode of a fuel cell body 1 is provided with an alloy catalyst of copper and zinc. The platinum mesh 10 with the added CO oxidation catalyst is provided to oxidize carbon monoxide remaining in the fuel reformed gas, reduce the concentration of carbon monoxide, and supply the carbon monoxide to the fuel electrode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polymer electrolyte fuel cell power generator, and more particularly to a structure of a fuel gas supply system.

[0002]

2. Description of the Related Art FIG. 5 is a sectional view showing a general basic structure of a fuel cell main body of a polymer electrolyte fuel cell power generator. As shown in the figure, a fuel electrode 22 and an air electrode 2 are formed on both sides of an ion conductive polymer membrane 21 used as an electrolyte.
3 is arranged, a current collector 24 having a fuel gas passage 26 is arranged outside the fuel electrode 22, and a current collector 25 having an air passage 27 is arranged outside the air electrode 23. The basic unit of the cell is formed between 28 and 29. Although only the basic unit is shown in FIG. 5, the fuel cell body is constructed by stacking the basic units.

In this solid polymer type fuel cell, the polymer membrane used for the electrolyte has a high ionic conductivity, so that a high output density can be obtained as compared with the conventional phosphoric acid type fuel cell and molten carbonate type fuel cell. It is characterized by being Further, the steady-state operating temperature of the present fuel cell is generally about 80 ° C., but since the ionic conductivity near room temperature does not decrease as in other types of fuel cells, it is possible to perform load operation even at room temperature. .

However, the ionic conductivity of the polymer membrane is greatly affected by the wetness of the membrane, and when the fuel gas or air is supplied in a dry state, the water content in the polymer membrane evaporates and the membrane is dried and becomes conductive. The rate drops. Therefore, the polymer electrolyte fuel cell employs a method of humidifying and supplying the reaction gas such as fuel gas and air. FIG. 6 is a basic configuration diagram of a reaction gas supply system of a conventional polymer electrolyte fuel cell power generator. The fuel gas is reformed by adding steam by the reformer 6, and further the carbon monoxide contained in the CO shift converter 7 is converted into carbon dioxide to be reformed gas, which is fed into the humidified water of the fuel gas humidifier 2. After being sent and passed in the form of bubbles to be humidified, it is supplied to the fuel electrode of the fuel cell body 1 schematically shown. The fuel gas humidifier 2 has a temperature sensor 4
2 and a heater 41 are installed, and the humidifying level of the fuel gas is controlled to be constant by controlling the temperature of the humidifying water to a constant temperature by the temperature controller 4. On the other hand, air is similarly humidified in the air humidifier 3 including the temperature sensor 52, the heater 51, and the temperature controller 5, and then supplied to the air electrode of the fuel cell body 1. The exhaust gas discharged after the power generation reaction is performed in the fuel cell main body 1 has its water content condensed and removed by the fuel exhaust gas condenser 8 and the air exhaust gas condenser 9, respectively, and is then discharged as a dry exhaust gas.

[0005]

As described above, in the conventional polymer electrolyte fuel cell power generator, by adopting the method of supplying the reaction gas by humidifying it, it is possible to prevent the polymer membrane from drying and to improve the conductivity. It is driving while avoiding the decrease of
As already mentioned, the operating temperature of the polymer electrolyte fuel cell is about 80 ° C, which is lower than that of other types of fuel cells. Therefore, due to the trace amount of carbon monoxide of 100 ppm or less remaining in the reformed gas, There is a problem that the platinum catalyst in the electrode is poisoned and the battery performance is deteriorated.

As a method for lowering the carbon monoxide concentration in the fuel reformed gas, a carbon monoxide combustor, a carbon monoxide adsorption column,
Alternatively, a method using a carbon monoxide selective permeable membrane may be considered, but the carbon monoxide combustor contains the risk of explosion because it mixes oxygen, and moreover, carbon monoxide cannot be completely removed and the concentration is 100 ppm or less. It is difficult to lower the concentration, and in addition, unreacted oxygen reacts with hydrogen at the fuel electrode to cause polarization, resulting in deterioration of cell characteristics. Further, in the method using the carbon monoxide adsorption column or the carbon monoxide selective permeable membrane, a large power of about 20% of the power generation amount is required, so that the system efficiency of the power generation device is significantly reduced.

In addition to the above, a method has been proposed in which a small amount of air is mixed into the fuel reformed gas to cause oxidative combustion on the surface of the platinum catalyst of the electrode. However, this method is accompanied by the risk of explosion and Since the oxidation reaction is performed on the fuel electrode, there is a drawback that polarization occurs and the cell performance deteriorates. The present invention has been made in consideration of such a situation, and an object thereof is to reduce the concentration of carbon monoxide in the fuel reformed gas supplied to the fuel electrode to several ppm and to poison the platinum catalyst of the electrode. An object of the present invention is to provide a polymer electrolyte fuel cell power generation device in which deterioration of cell performance due to the suppression is suppressed.

[0008]

To achieve the above object, in the present invention, a reformer, or a fuel gas reformed by a reformer and a carbon monoxide shift converter is introduced and humidified. In a polymer electrolyte fuel cell power generator having a humidifier for supplying to a fuel electrode of a fuel cell main body, the humidifier is provided with an oxidizing means for oxidizing carbon monoxide in the introduced fuel gas, As the oxidizing means, a catalyst composed of platinum or palladium, ruthenium, cobalt, copper or zinc, or an alloy catalyst composed of a combination of any two or more of them is used.

Alternatively, the humidifying water of the humidifier for supplying air to the air electrode of the fuel cell body and the air exhaust gas discharged from the air electrode are introduced to the oxidizing means to condense the water. At least one of the condensed water of the air exhaust gas condenser that discharges the dry exhaust gas is used.

[0010]

As described above, the reformer of the fuel gas system is provided with the oxidizing means, and the oxidizing means is composed of a catalyst made of any one of platinum and palladium, or a combination of two or more kinds thereof. If an alloy catalyst is used, carbon monoxide contained in the fuel gas chemically changes into carbon dioxide and hydrogen by the reaction of the formula (1) on the catalyst in the presence of water.

[0011]

Embedded image CO + H ₂ O → CO ₂ + H ₂ (1) This reaction is an exothermic reaction with an enthalpy change of −41 [kJ / mol] and is advantageous at low temperatures. Furthermore, CO ₂ , H
₂ , the partial pressure of CO is displayed as P (CO ₂ ), P (H ₂ ), P (CO),
When the partial pressure of water vapor is expressed by P (H ₂ O), the pressure equilibrium constant Kp of this reaction is expressed by the equation (2).

[0012]

## STR00002 ## Kp = P (CO ₂ ) .P (H ₂ ) / [P (CO) .P (H ₂ O)] (2) At the operating temperature of the polymer electrolyte fuel cell of 80 ° C.,
Kp = 7.831 × 10 ^{4, which} is a very large value, and in the case of a fuel gas obtained by reforming natural gas, containing H ₂ at about 75% and CO ₂ at about 25%, the monoxide contained in the fuel gas is included. Carbon concentration 9.7 p
It can be reduced to pm. Therefore, poisoning of the platinum catalyst of the electrode is prevented, and deterioration of battery performance is avoided.

Further, in the humidifier for humidifying air to supply it to the air electrode of the fuel cell main body and the air exhaust gas condenser for guiding the air exhaust gas from the air electrode to condense water, the solubility of oxygen in water is reduced. 1.68 at 70 ° C
Since it is × 10 ^-5 , 1.87 × 10 ^-4 [mol / l] of oxygen is dissolved in the humidifying water of the humidifier and the condensed water of the condenser. Therefore, if at least one of the humidifying water and the condensed water is supplied to the humidifier for humidifying the fuel gas, the carbon monoxide contained in the fuel gas is easily oxidized by oxygen in the humidifier as shown in the following equation. Becomes carbon dioxide.

[0014]

2CO + O ₂ → 2CO ₂ (3) Assuming a polymer electrolyte fuel cell with an output of 1 kW,
It is necessary to supply 19 [l / min] of reformed fuel gas with a hydrogen utilization rate of 70%.
At 100 ppm, 8.48 × 10 ^-5 [mol / min] carbon monoxide will be supplied. Therefore, if the humidifying water of the air humidifier and the condensed water of the air exhaust gas condenser are combined to supply 1 [l / min] to the humidifier of fuel gas, dissolved oxygen will be 1.87 × 10 ⁻⁴ [mol / min]. Will be supplied,
The carbon monoxide contained in the fuel gas is almost completely oxidized according to equation (3), and the concentration of carbon monoxide in the fuel gas sent from the humidifier to the fuel electrode of the fuel cell main body is several pp.
can be reduced to m. Therefore, poisoning of the platinum catalyst of the electrode is prevented, and deterioration of battery performance is avoided.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a basic configuration diagram showing a reaction gas supply system of a first embodiment of the polymer electrolyte fuel cell power generator of the present invention. Components having the same functions as those of the conventional example shown in FIG. 6 are designated by the same reference numerals, and duplicate description will be omitted. The difference between the present embodiment and the conventional example is the configuration of the fuel gas humidifier 2A, and the heater 4 for controlling the humidifying water to a constant temperature.
In addition to 1, the temperature sensor 42 and the temperature controller 4, a platinum mesh 10 with a CO oxidation catalyst is provided.

An alloy catalyst of copper and zinc is used as the CO oxidation catalyst of this embodiment, and the fuel containing 100 to 1000 ppm of CO that is reformed by the reformer 6 and the CO shift converter 7 remains. In the fuel gas humidifier 2A, the gas comes into contact with the catalyst and water vapor by bubbling to be humidified, and at the same time, CO
Is oxidized and converted to CO ₂ and H ₂ , so the CO concentration of the fuel gas after passing through the fuel gas humidifier 2A is 5 to 10 ppm.
Fall to.

FIG. 2 shows the cell voltage-current density characteristics of the polymer electrolyte fuel cell power generator having the structure of this embodiment.
This is shown in comparison with the characteristics of the conventional example having the above configuration. As shown in the figure, in the conventional example, when the reaction gas amount was increased and the current density was increased, the cell voltage was drastically decreased, but in the present example, the decrease in cell voltage was suppressed,
Good characteristics are obtained. This is because the CO concentration of the reformed gas sent to the fuel electrode was reduced to 10 ppm or less, and the poisoning of the electrode catalyst was suppressed.

In the present embodiment, an alloy catalyst of copper and zinc is used as the CO oxidation catalyst, but the CO oxidation catalyst is not limited to this, and platinum or palladium, which has a similar oxidation catalytic action, Even when a catalyst of ruthenium, cobalt, copper, zinc is used alone or in combination of two or more, C of the reformed gas sent to the fuel electrode is similarly used.
It is possible to reduce the O concentration and suppress the poisoning of the electrode catalyst to avoid the deterioration of the battery performance.

FIG. 3 is a basic block diagram showing a reaction gas supply system of a second embodiment of the solid polymer fuel cell power generator of the present invention. A feature of the present embodiment is that a pipe is provided between the fuel gas humidifier 2 and the air humidifier 3, and the humidifying water of the air humidifier 3 is supplied to the fuel gas humidifier 2. In this configuration, since the humidifying water of the fuel gas humidifier 2 contains oxygen by taking in the humidifying water of the air humidifier 3 in which oxygen is dissolved, it is reformed by the reformer 6 and the CO shift converter 7. Remaining CO in the fuel gas introduced as
The CO concentration of the fuel gas after passing through the fuel gas humidifier ₂ is changed to O ₂ and H ₂ , and is reduced to 10 ppm or less. Therefore, poisoning of the electrode catalyst is suppressed, and deterioration of battery performance is avoided.

FIG. 4 is a basic configuration diagram showing a reaction gas supply system of a third embodiment of the solid polymer fuel cell power generator of the present invention. The feature of the present embodiment is that a pipe is provided between the fuel gas humidifier 2 and the air exhaust gas condenser 9 and the condensed water of the air exhaust gas condenser 9 is supplied to the fuel gas humidifier 2. Also in this configuration, as in the second embodiment of FIG. 3, since the humidifying water of the fuel gas humidifier 2 contains oxygen, CO remaining in the introduced fuel gas is oxidized and the fuel gas is humidified. The CO concentration of the fuel gas after passing through the reactor 2 is
It will be reduced to 10 ppm or less, and poisoning of the electrode catalyst will be suppressed, and deterioration of battery performance will be avoided.

In place of the above construction, the air humidifier 3
A pipe is provided between the fuel gas humidifier 2 and both the air exhaust gas condenser 9 and the fuel gas humidifier 2, and the humidifying water of the air humidifier 3 and the condensed water of the air exhaust gas condenser 9 are simultaneously supplied to the fuel gas humidifier 2. However, it is obvious that the same effect can be obtained without needing to illustrate it.

[0022]

As described above, according to the present invention, the fuel gas reformed by the reformer or the reformer and the carbon monoxide shifter is introduced and humidified to the fuel electrode of the fuel cell main body. In the polymer electrolyte fuel cell power generator including the humidifier for supplying the fuel to the fuel electrode, the humidifier is provided with an oxidizing means for oxidizing carbon monoxide in the introduced fuel gas. It has become possible to obtain a polymer electrolyte fuel cell power generator in which the concentration of carbon monoxide in the gas is reduced and the deterioration of the cell performance due to the poisoning of the electrode catalyst is suppressed. In particular, if a catalyst composed of platinum or palladium, ruthenium, cobalt, copper, or zinc, or an alloy catalyst composed of a combination of two or more of these is used for the above-mentioned oxidizing means, The carbon monoxide is oxidized by the carbon monoxide, and the concentration of carbon monoxide in the fuel gas supplied to the fuel electrode is effectively reduced.Therefore, deterioration of the cell performance due to poisoning of the electrode catalyst is suppressed. It is suitable as a battery power generator.

Further, the humidifying water of the humidifier for supplying air to the air electrode of the fuel cell main body and the exhaust gas discharged from the air electrode are introduced to the oxidizing means to condense the moisture. If at least one of the condensed water of the air exhaust gas condenser that discharges the dried exhaust gas is used, the carbon monoxide is oxidized by the oxygen dissolved in these humidifying water and condensed water, and the fuel supplied to the fuel electrode is supplied. Since the concentration of carbon monoxide in the gas is effectively reduced, it is suitable as a polymer electrolyte fuel cell power generation device in which the deterioration of the cell performance due to the poisoning of the electrode catalyst is suppressed.

[Brief description of drawings]

FIG. 1 is a first solid polymer fuel cell power generator according to the present invention.
Basic configuration diagram showing the reaction gas supply system of the embodiment

FIG. 2 is a characteristic diagram showing cell voltage-current density characteristics of the polymer electrolyte fuel cell power generator according to the first embodiment in comparison with a conventional example.

FIG. 3 is a second solid polymer fuel cell power generator according to the present invention.
Basic configuration diagram showing the reaction gas supply system of the embodiment

FIG. 4 is a third part of the polymer electrolyte fuel cell power generator of the present invention.
Basic configuration diagram showing the reaction gas supply system of the embodiment

FIG. 5 is a sectional view showing a general basic structure of a fuel cell main body of a polymer electrolyte fuel cell power generator.

FIG. 6 is a basic configuration diagram of a reaction gas supply system of a conventional polymer electrolyte fuel cell power generator.

[Explanation of symbols]

 1 Fuel cell main body 2 Fuel gas humidifier 2A Fuel gas humidifier 3 Air humidifier 4 Temperature controller 5 Temperature controller 6 Reformer 7 CO shifter 8 Fuel exhaust gas condenser 9 Air exhaust gas condenser 41 Heater 42 Temperature sensor 51 Heater 52 temperature sensor

Claims (3)

[Claims] 1. A solid polymer having a reformer, or a humidifier for introducing and humidifying the fuel gas reformed by the reformer and the carbon monoxide shift converter and supplying the humidified gas to the fuel electrode of the fuel cell body. A solid polymer fuel cell power generator, wherein the humidifier comprises an oxidizing means for oxidizing carbon monoxide in the introduced fuel gas. 2. The oxidizing means is platinum or palladium,
The solid polymer fuel cell power generator according to claim 1, which is a catalyst composed of ruthenium, cobalt, copper, or zinc, or an alloy catalyst composed of a combination of two or more of them. . 3. The oxidizing means guides humidifying water of a humidifier for introducing air to humidify it to the air electrode of the fuel cell main body, and air exhaust gas discharged from the air electrode to condense water for drying. The polymer electrolyte fuel cell power generator according to claim 1, comprising at least one of condensed water of an air exhaust gas condenser that discharges exhaust gas.