JPS61168875A - Fuel cell - Google Patents

Abstract

PURPOSE:To maintain the amount of electrolyte constant to obtain steady electric output for a long time by circulating part of oxidizing agent exhaust gas of a fuel cell to return to the cell, and controlling heat quantity added to added water based on the exhaust gas temperature. CONSTITUTION:A cell stack 10 consists of cells each of which comprises a fuel electrode, oxidizing agent electrode, and ion exchange film containing sulfuric acid and placed between both electrodes. A water content controller 7 is installed in an oxidizing agent supply hole 11 to the stack 10. A correction device 13 feedback controls the temperature of an oxidizing agent supply unit 12 so as to keep 40 deg.C and the controller 7 controls the amount of oxidizing agent electrode exhaust gas. The water content in the oxidizing agent supplied to the stack 10 is controlled so as to keep a water vapor partial pressure of 5-8%, and the electrolyte retaining amount is kept constant and steady electric output is obtained for a long time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a fuel cell, and particularly to a fuel cell improved so that the amount of electrolyte can be kept constant.

[Background of the invention]

Regarding fuel cells, the invention published in JP-A-39-3162 and the invention published in JP-A-58-112264 are known.

Fuel cells supply fuel and an oxidizing agent and allow an electrochemical reaction to proceed on electrodes to directly extract electrical energy, and are expected to be put into practical use as a power source that can obtain electrical energy with high efficiency. especially.

Among those that use liquid fuel as a portable small power source, methanol-air acid electrolyte fuel cells C and below.

Methanol fuel cells (abbreviated as methanol fuel cells) are attracting attention.

As shown in FIG. 4, the unit configuration of this type of fuel cell is as shown in FIG.
A fuel cell is constructed by stacking these ion exchange membranes (containing sulfuric acid). In such a fuel cell that uses a liquid electrolyte as an electrolyte, it is important to maintain a stable amount of electrolyte. In particular, in gas diffusion electrodes, battery performance changes significantly depending on the initial amount of electrolyte retained and fluctuations in the amount retained due to evaporation, scattering, etc. during operation. If the amount of electrolyte retained is small, the electrode area will become smaller and the internal resistance of the battery will increase.
If the retained amount is too large, the electrode will be covered and the electrode area will be reduced, which may lead to a decrease in battery performance. In particular, during battery operation, there is a problem in that the amount of electrolyte retained is reduced due to evaporation. For this reason, it is important to maintain the amount of electrolyte retained during battery operation, and for this purpose, it is necessary to supply water to the battery in consideration of the balanced amount of electrolyte retained during battery operation.

Regarding fuel cells that use liquid fuel, including the methanol fuel cell 1, no inventions that take the above into account have been made yet.As for hydrogen-oxygen gas fuel cells, the above-mentioned Japanese Patent Laid-Open No. 39-3162, which uses an alkaline electrolyte, This method involves bubbling water at room temperature with hydrogen and oxygen gas to both the hydrogen and oxygen electrodes, respectively, to supply water equal to the amount of steam at room temperature. cannot be maintained.

In addition, Japanese Patent Application Laid-Open No. 58-112264 using a phosphoric acid electrolyte
In this method, current is passed through the electrolyte in the battery to find the resistance, and water vapor is added from outside to maintain the resistance at a predetermined value, thereby keeping the concentration of the electrolyte constant at a predetermined concentration. be. The above proposal has problems in that it requires an external power source and water vapor, and the control system becomes complicated.

Next, the retention of electrolyte liquid volume will be explained in detail. As already described with reference to FIG. 4, the fuel cell has a fuel electrode 1, an oxidizer electrode 2, and an electrolyte 3 as its main components, and two separators 4. It is equipped with 4. The electrode is composed of, for example, a catalyst layer 6 in which a catalyst containing one or more platinum group elements as a main component is supported on a conductive porous carrier, which is coated and bonded onto a conductive porous substrate 5. A battery is constructed by stacking these unit batteries. When forming unit cells or stacking them to form a battery, an electrolytic solution is applied to the oxidizer electrode 2, which is a gas diffusion electrode, in order to ensure sufficient movement of hydrogen ions in the electrochemical reaction and to reduce contact resistance. hold it.

Figure 2 shows the relationship between the amount of electrolyte held in the oxidizer electrode and the initial battery voltage of the unit battery at a current haze of 60*A/- (set at 60°C). In places where the amount of electrolyte is small, the reaction area on the electrode is small due to a lack of electrolyte, and in places where there is a large amount of electrolyte held, the catalyst surface is covered with electrolyte and the reaction area is reduced, resulting in a decrease in performance. From this,
In order to improve battery performance, it is important to maintain the amount of electrolyte retained at a predetermined value. This result indicates the performance of the battery at the initial stage of operation, and the amount of electrolyte retained is sufficient at the start of operation.

However, by continuing to operate for a long time, the electrolyte concentrates to the equilibrium concentration at the operating temperature of 60°C, which causes a problem in that the amount of electrolyte retained is insufficient and the battery performance deteriorates. In consideration of the layer structure, attempts were made to increase the initial amount of electrolyte retained and to use an electrolyte with a high electrolyte concentration, but the result was that it took a long time for the electrical performance to stabilize and the battery voltage was low.

From the above, in order to improve battery voltage and maintain long-term performance, it is necessary to consider the state of the electrolyte during operation. It is necessary to maintain the retention amount at .

[Purpose of the invention]

The present invention has been made in view of the above-mentioned circumstances, and it is an object of the present invention to provide a fuel cell that can maintain a constant amount of electrolyte and stabilize electrical output over a long period of time.

[Summary of the invention]

First, the basic principle of the fuel cell of the present invention created to achieve the above object will be explained below.

As a result of intensive studies in the development of this fuel cell, the inventors found that the amount of electrolyte retained in the oxidizer electrode in a unit cell during operation (at 60°C) is at an equilibrium value due to the retained sulfuric acid and water vapor partial pressure. We focused on what is fixed. This relationship is shown in FIG.

The present invention utilizes the water concentration dependence described above, and controls the water concentration in the oxidant supplied to the oxidizer electrode to be constant at a predetermined concentration.

In order to achieve the above object (maintaining a constant amount of electrolyte) based on the above-mentioned principle, the first invention uses a gas containing oxygen as an oxidizing agent and uses an electrolyte that does not have an equilibrium composition under operating conditions. The fuel cell used is characterized in that it is provided with means for circulating a portion of the oxidizer exhaust gas from the fuel cell and returning it into the fuel cell.

Moreover, in order to achieve the same object as the above, the second invention is as follows:
A fuel cell using an oxygen-containing gas as an oxidizing agent and an electrolyte that does not have an equilibrium composition under operating conditions, further comprising a device for adding water to the oxidizing agent supplied to the fuel cell, and further comprising: The device for adding water uses the exhaust gas of the fuel cell as a heat source and has a function of controlling the amount of steam generated by controlling the amount of heat given to the added water based on the temperature of the exhaust gas. do.

[Embodiments of the invention]

The fuel electrode 1 described with reference to FIG. 4 is constructed as follows in this embodiment.

1.15 g of catalyst powder supporting 50 ut% of platinum and ruthenium was added to carbon powder (Furnace Black: trade name, manufactured by Cabot Corporation), mixed with 2 ml of distilled water and kneaded well.
Add 1 mg of FH (manufactured by Daikin, trade name: Polyfron Disverge Di, 2.5 times diluted) and mix. This paste was evenly applied to carbon paper (E-715: trade name, manufactured by Kureha Chemical Co., Ltd.) 100 x 128 cm, and after drying,
The fuel electrode configured as above and fired for about 30 minutes in a nitrogen atmosphere at 0° C. is named fuel electrode electrode A.

Next, the oxidizer electrode 2 described with reference to FIG.

This embodiment is configured as follows.

Catalyst powder with 30 ut% of platinum supported on carbon powder
．． After adding 77 g of distilled water and mixing, add and mix 0.55 mjl of Polyflon dispersion Dl solution, apply the mixture to carbon vapor 100 x 128-
After air-drying, the oxidizer electrode was calcined in air at 300"C for about 30 minutes.The oxidizer electrode was configured to hold 4.5 ol/41 sulfuric acid as an electrolyte in the catalyst layer of this electrode. Name it.

Example 1 This example is a methanol fuel cell equipped with an oxidant supply hole equipped with a device for controlling the water concentration in the oxidant. The outline of its appearance is shown in Fig. 1.

The aforementioned fuel electrode A and oxidizer electrode B constituted a battery stack 10 of a laminated cell in which an ion exchange membrane containing dilute sulfuric acid (CMV: trade name, manufactured by Chiya Kasei Co., Ltd.) was interposed as an electrolyte between the electrodes. . A moisture concentration control device 7 was provided in the oxidizing agent supply hole 11 to the battery stack 10. FIG. 5 is a schematic diagram of the water concentration control device (1). The correction device 1 adjusts the temperature of the oxidizing agent supply section 12 to 40°C.
3, the amount of gas discharged from the oxidizer electrode was adjusted by feedback control. Moisture concentration control device! By providing (1), it was possible to control the moisture in the oxidizing agent supplied to the battery stack 1o within a water vapor partial pressure range of 5 to 8%.

Example 2 This example is the same fuel cell as Example 1 except that the oxidant supply hole 11 is equipped with a water concentration control device (II). A schematic diagram of the apparatus (n) is shown in FIG.

Moisture in the oxidant supplied to the oxidizer electrode is detected by a moisture detector 18, and a correction device 13 adjusts the amount of circulating part of the oxidizer electrode exhaust gas containing produced water. When the moisture detector was set so that the water vapor partial pressure was 6%,
It was possible to control the moisture in the oxidizing agent within a water vapor partial pressure range of 5 to 7%.

Example 3 This fuel cell is the same as Example 1 except that the oxidizing agent supply hole 11 is equipped with a water concentration control device (m). A schematic diagram of the device (II) is shown in FIG. 7, steam generation section 1
9 was detected by the temperature detection unit 20, and the correction device 13 performed feedback control to maintain the temperature of the steam generating unit at 40°C, and the circulation amount of the oxidizer electrode exhaust gas (50 to 55°C) was adjusted. . By providing the device (II), moisture in the oxidizing agent supplied to the battery stack 10 can be reduced to 5 to 50%.
It was possible to control the water vapor partial pressure within a range of 6%.

Using the above-mentioned Examples 1 and 2.3, the current density was 60i+A.
/aJ was subjected to a continuous test of 600 hours. In the fuel tank 9, there is 1 methanol/oil/a-sulfuric acid 1
．． Filled with 5 ■ o 41 / Jl of anorite.

This anolite was circulated to the cell stack, and methanol and water were supplied to maintain the fuel concentration. FIG. 8 shows the relationship between energization time and output power in the above test.

The solid line curve (1) shows the output power of Example 1, the broken line curve (...) shows the output power of Example 2, and the dashed-dotted curve (ffl) shows the output power of Example 3. .

The two-dot chain curve indicates the output power of a conventional fuel cell shown as a comparative example, and the configuration of this conventional example is as follows. That is, it is the same as Example 1 except that a water concentration control device is not installed to supply the oxidizing agent, and air is supplied by a fan.

[Effects of the Invention] When the present invention is applied as shown in each of Examples 1 and 2.3 above, it is possible to maintain the water concentration in the oxidizing agent within a predetermined concentration range. Since the amount of electrolyte retained can be maintained, the performance of the fuel cell can be improved and the output power of the fuel cell can be maintained for a long time without fluctuation.

[Brief explanation of drawings]

FIG. 1 is a schematic external perspective view of an embodiment of the present invention. Figure 2 is a chart showing the relationship between the electrolyte retention amount of the oxidizer electrode and unit cell voltage, Figure 3 is a diagram showing the relationship between water vapor partial pressure and electrolyte retention amount, and Figure 4 is the methanol - A unit configuration diagram of an air acid electrolyte fuel cell. FIG. 5 to FIG. 7 are explanatory diagrams of a water concentration control device constructed by applying the present invention, respectively. FIG. 8 is a diagram for explaining the present invention in detail. 1... Fuel electrode, 2... Oxidizer electrode, 3... Electrolyte,
4...Separator, 5...Carbon paper, 6...
・Catalyst layer.

Claims (1)

[Claims] 1. In a fuel cell that uses a gas containing oxygen as an oxidant and uses an electrolyte that does not have an equilibrium composition under operating conditions, a part of the oxidizer exhaust gas of the fuel cell is circulated. A fuel cell characterized by being provided with means for returning the fuel into the fuel cell. 2. The means for circulating a portion of the oxidant exhaust gas has a structure that includes means for detecting the temperature of the fuel cell and controls the circulation flow rate of the oxidizer exhaust gas based on the detected temperature. A fuel cell according to claim 1, characterized in that: 3. The means for circulating a portion of the oxidizing agent exhaust gas includes means for detecting the moisture concentration in the oxidizing agent exhaust gas,
Claim 1, characterized in that the structure is such that the circulating flow rate of the oxidant exhaust gas is controlled based on the detected temperature.
The fuel cell described in Section. 4. The fuel cell according to claim 1, wherein the oxygen-containing gas is air. 5. The fuel cell according to claim 1, wherein the fuel cell uses liquid fuel as fuel. 6. The fuel cell according to claim 5, wherein the liquid fuel is methanol. 7. A fuel cell using a gas containing oxygen as an oxidizing agent and an electrolyte that does not have an equilibrium composition under operating conditions, further comprising a device for adding water to the oxidizing agent supplied to the fuel cell, The water adding device described above uses the exhaust gas of the fuel cell as a heat source and has a function of controlling the amount of steam generated by controlling the amount of heat given to the added water based on the temperature of the exhaust gas. It is characterized by 8. The fuel cell according to claim 7, wherein the oxygen-containing gas is air. 9. The fuel cell according to claim 7, wherein the fuel cell uses liquid fuel as fuel. 10. The fuel cell according to claim 7, wherein the liquid fuel is methanol.