JPH0864218A - Operating method for solid high polymer electrolyte fuel cell - Google Patents

Abstract

PURPOSE: To provide a solid high polymer electrolyte fuel cell preventing a solid high polymer electrolyte film from being excessively dried or wetted and easy to start. CONSTITUTION: The fuel gas and air reaction gas humidified via humidifiers 24, 25 are fed to the fuel electrode 22 and air electrode 23 of a solid high polymer electrolyte fuel cell 21 respectively. The humidifiers 24, 25 are heat- exchanged with the reaction gas discharged from the solid high polymer electrolyte fuel cell and heated at this time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for operating a solid polymer electrolyte fuel cell, and more particularly to a method for controlling the temperature of a humidifier.

[0002]

2. Description of the Related Art A solid polymer electrolyte fuel cell is formed by disposing an anode and a cathode, which are electrodes, on two main surfaces of a solid polymer electrolyte membrane. Each electrode of the anode or the cathode has an electrode catalyst layer arranged on an electrode base material. The solid polymer electrolyte membrane uses polystyrene type cation exchange membrane with sulfonic acid group as cation conductive membrane, mixed membrane of fluorocarbon sulfonic acid and polyvinylidene fluoride, or trifluoroethylene grafted on fluorocarbon matrix. However, recently, a perfluorocarbon sulfonic acid membrane has been used to extend the life of the fuel cell.

The solid polymer electrolyte membrane has a proton (hydrogen ion) exchange group in the molecule, and when it is saturated with water, it exhibits a specific resistance of 20 Ω · cm or less at room temperature and functions as a proton conductive electrolyte. The saturated water content changes reversibly with temperature. The electrode base material is a porous body and functions as a reaction gas supply means or a reaction gas discharge means and a current collector of the fuel cell. At the anode (fuel electrode) or cathode (air electrode) electrode, a three-phase interface is formed and an electrochemical reaction occurs.

At the anode, the reaction of the formula (1) occurs. H ₂ = 2H ⁺ + 2e (1) At the cathode, the reaction of the formula (2) occurs. 1 / 2O ₂ + 2H ⁺ + 2e = H ₂ O (2) That is, at the anode, hydrogen supplied from the outside of the system produces protons and electrons. The generated protons move toward the cathode in the ion exchange membrane, and the electrons move to the cathode through an external circuit. On the other hand, in the cathode, oxygen supplied from the outside of the system reacts with protons moving from the anode in the ion exchange membrane and electrons moving from the external circuit to generate water.

FIG. 5 is a sectional view showing a solid polymer electrolyte fuel cell. The electrode catalyst layer is laminated on the electrode base material to form the fuel electrode 2 or the air electrode 3. Electrode 2 or 3
Is placed on both main surfaces of a solid polymer electrolyte membrane (also referred to as a solid polymer membrane or polymer membrane) by hot pressing. The solid polymer electrolyte membrane 1 on which the electrodes are arranged is sandwiched by the gas separators 8 and 9 via the current collectors 4 and 5. Although not shown, the gas separators 8 and 9 are provided with cooling water passages for passing cooling water through the current collectors 4 and 5. A fuel passage 6 is provided inside the current collector 4 to flow fuel gas, and an air passage 7 is provided inside the current collector 5 to flow air as an oxidant gas. The gas separators 8 and 9 separate the oxidant gas and the fuel gas from each other.

Such a solid polymer electrolyte fuel cell has a higher power density than a conventional phosphoric acid fuel cell because the solid polymer electrolyte has a high ionic conductivity. Further, since the steady operating temperature of this fuel cell is generally 60 to 100 ° C., the ionic conductivity near room temperature is not so low as that of other fuel cells, and the fuel cell can be operated under load from room temperature.

Since the solid polymer electrolyte membrane 1 contains water inside, it not only functions as an electrolyte, but also prevents cross-leakage in which fuel gas and oxidant gas are mixed with each other. However, in the conventional solid polymer electrolyte fuel cell as described above, the conductivity of the solid polymer electrolyte membrane is greatly influenced by the wettability of the membrane, and therefore the membrane will dry and become conductive when exposed to dry air. The sex becomes worse. That is, in this fuel cell, when a dry reaction gas is supplied, the characteristics of the fuel cell deteriorate due to the drying of the polymer film and the increase in internal resistance due to the decrease in ionic conductivity.

When the dry state is continued, the volume of the polymer film is reduced, so that the electrical contact between the polymer film and the electrode and between the electrode and the current collector becomes poor, and the characteristics of the fuel cell deteriorate. Therefore, in the solid polymer electrolyte fuel cell, the reaction gas is humidified and supplied. FIG. 6 is a layout view showing a solid polymer electrolyte fuel cell including a conventional humidifier. The humidifiers 12 and 12A are for humidifying by passing a reaction gas in water. The humidifier is controlled at a constant temperature, and a reaction gas having a predetermined saturated vapor pressure is supplied to the cells 21 of the fuel cell. The temperature of the humidifier 12, 12A is controlled by the temperature controller 11, 13
Are controlled to temperatures T _{1 and} T ₂ .

FIG. 7 is a layout showing a conventional water spray type humidifier. Make-up water stored in the humidification tank 14 is pump 1
5 is pumped up and sprinkled with water from the upper part of the humidifier 16. The reaction gas is humidified to a predetermined water vapor pressure and supplied to the fuel cell. The control of the amount of humidification was performed by setting the temperature of the humidifier to a predetermined temperature.

[0010]

However, in such a conventional humidifying method, for example, when the water temperature is controlled at 70 ° C., when the operating temperature is raised from room temperature, the amount of humidification is too high and the water vapor condenses inside the cell. The catalyst layer in the electrode gets wet with water, and the electrode reaction does not proceed smoothly. In addition, if the set temperature of the humidifier is set low to prepare for operation from room temperature, there will be no problem near room temperature, but if the temperature of the cell rises, the humidification amount of the reaction gas will be low and as a result dry gas will be supplied to the cell. However, there is a problem that the fuel cell cannot be started properly. We adopted the method of changing the set temperature of the humidifier according to the cell temperature, but the cell operation is very complicated and the energy generated by the battery is consumed because electricity is used as a heat source. There was a problem that it decreased.

The present invention has been made in view of the above points, and an object thereof is to improve the temperature control method of the humidifier in the operation of the solid polyelectrolyte fuel cell to enable easy and stable starting and to improve energy efficiency. Another object of the present invention is to provide a method for operating a solid polymer electrolyte fuel cell, which is excellent.

[0012]

According to the present invention, the above object is to provide a solid polymer electrolyte fuel cell having a solid polymer electrolyte membrane, an electrode, and a gas separator with a humidified fuel gas through a humidifier. In a method for operating a solid polymer electrolyte fuel cell, which supplies reaction gases of an oxidizer gas and an oxidant gas, the humidifier is heated by exchanging heat with an exhaust heat medium from the solid polymer electrolyte fuel cell. It

At this time, as the exhaust heat medium, at least one of the exhaust gas of the solid polymer electrolyte fuel cell and the cooling water is used. Further, it is effective that the exhaust heat medium exchanges heat with the reaction gas before flowing through the humidifier and at least one of the reaction gas after flowing through.

[0014]

[Function] When the humidifier is heated by exchanging heat with the exhaust heat medium from the solid polymer electrolyte fuel cell, the temperature of the humidifier will be linked to the operating temperature of the fuel cell, and the water vapor pressure in the reaction gas will be the solid polymer. It is constantly controlled to the optimum vapor pressure required to prevent the water from drying out from the electrolyte.

Since waste heat is used for heating the humidifier, electricity generated by power generation is not consumed. Further, when the exhaust heat medium exchanges heat with the reaction gas before flowing through the humidifier and at least one of the reaction gases after flowing through the humidifier, the efficiency of utilization of exhaust heat is promoted.

[0016]

Embodiments of the present invention will now be described with reference to the drawings. Example 1 FIG. 1 is a configuration diagram showing a solid polymer electrolyte fuel cell system according to an example of the present invention.

The fuel gas flowing through the fuel electrode 22 is humidified by the humidifier 2.
In 4 the heat is exchanged and the humidifier 24 is heated. In the humidifier, the fuel gas contains water having a water vapor pressure corresponding to the heated temperature. The same thing happens at the cathode. In this way, the water vapor pressure of the reaction gas becomes the water vapor pressure corresponding to the operating temperature of the fuel cell, and the reaction gas does not dry or contain excess water. Example 2 FIG. 2 is a configuration diagram showing a solid polymer electrolyte fuel cell system according to another example of the present invention.

In this case, the reaction exhaust gas does not exchange heat with the humidifier. Instead of the exhaust reaction gas, the cooling water of the fuel cell is used to heat the humidifier. The cooling water circulates through the fuel gas humidifier 26 to the humidifier 27 of the air electrode 23.
Since the humidifier 26 for the fuel gas has a higher temperature than the humidifier 27 for the air electrode 23, the water vapor pressure in the fuel gas becomes higher than the water vapor pressure in the air. Since the fuel electrode has less water than the air electrode, the distribution of the water vapor pressure as described above stabilizes the operation of the fuel cell. Embodiment 3 FIG. 3 is a constitutional view showing a solid polymer electrolyte fuel cell system according to still another embodiment of the present invention.

In this case, both the exhaust gas and the cooling water heat the humidifier. The fuel electrode humidifier 28 is heated by the fuel exhaust gas, while the air electrode humidifier 29 is heated by the air exhaust gas and the cooling water. In this case, the utilization efficiency of exhaust heat is further enhanced. Embodiment 4 FIG. 4 is a constitutional view showing a solid polymer electrolyte fuel cell system according to a further embodiment of the present invention.

The humidifier 30 has a front heat exchanger 32 and a rear heat exchanger 33. The humidifier 31 also has a heat exchanger 34 in the front stage and a heat exchanger 35 in the rear stage. The former heat exchanger prevents the condensation of water in the reaction gas. The latter heat exchanger preheats the reaction gas. When the heat exchangers 32 and 34 in the front stage and the heat exchangers 33 and 35 in the rear stage are provided, the thermal efficiency of utilizing the exhaust heat is improved.

[0021]

According to the present invention, since the humidifier is heated by exchanging heat with the exhaust heat medium from the solid polymer electrolyte fuel cell, the temperature of the humidifier is linked to the operating temperature of the fuel cell. The water vapor pressure inside is constantly controlled to the optimum vapor pressure required to prevent the water from drying out from the solid polymer electrolyte, and the transition from the start of the fuel cell to the steady operation proceeds smoothly and the solid polymer electrolyte is easy to start. Type fuel cell is obtained.

When the exhaust heat medium is heat-exchanged with the reaction gas before flowing through the humidifier and at least one of the reaction gases after flowing through the humidifier, the efficiency of utilization of the exhaust heat is promoted and the electricity obtained by the battery drive is increased. A solid polymer electrolyte fuel cell with high energy efficiency can be obtained in combination with the fact that energy is not consumed.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a solid polymer electrolyte fuel cell system according to an embodiment of the present invention.

FIG. 2 is a configuration diagram showing a solid polymer electrolyte fuel cell system according to another embodiment of the present invention.

FIG. 3 is a configuration diagram showing a solid polymer electrolyte fuel cell system according to still another embodiment of the present invention.

FIG. 4 is a configuration diagram showing a solid polymer electrolyte fuel cell system according to still another embodiment of the present invention.

FIG. 5 is a sectional view showing a solid polymer electrolyte fuel cell.

FIG. 6 is a configuration diagram showing a solid polymer electrolyte fuel cell system including a conventional humidifier.

FIG. 7 is a layout view showing a conventional sprinkler type humidifier.

[Explanation of symbols]

 1 Polymer Membrane 2 Fuel Electrode 3 Air Electrode 4 Current Collector 5 Current Collector 6 Fuel Passage 7 Air Passage 8 Gas Separator 9 Gas Separator 10 Cell 11 Temperature Controller 12 Humidifier 12A Humidifier 13 Temperature Controller 14 Humidification Tank 15 Pump 16 humidifier

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Shinichi Maruyama 1-1, Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd.

Claims (3)

[Claims] 1. A solid polymer electrolyte membrane, an electrode, and a solid polymer electrolyte fuel cell having a gas separator, each of which supplies a humidified fuel gas and an oxidant gas reaction gas through a humidifier. A method for operating a polymer electrolyte fuel cell, comprising heating the humidifier by exchanging heat with an exhaust heat medium from the polymer electrolyte fuel cell. 2. The solid polymer electrolyte fuel according to claim 1, wherein the exhaust heat medium is at least one of exhaust gas from the solid polymer electrolyte fuel cell and cooling water. How to operate the battery. 3. The fuel cell according to claim 1, wherein the exhaust heat medium exchanges heat with at least one of the reaction gas before flowing through the humidifier and the reaction gas after flowing through the humidifier. Method for operating a solid polymer electrolyte fuel cell.