JPH11191428A - Fuel cell device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To completely recover output so as to attain stabilization by providing a means for eliminating a cover on the surface of a fuel electrode provided along with an air electrode. SOLUTION: A cover 125 on the surface of a fuel electrode 13 holding an electrolyte film 12 jointly with an air electrode 11 is formed by the adhesion of impurities, such as generated water, CO2 and N2 and a high concentration atmosphere near the surface. The cover 125 is eliminated by a physical method of spraying or flowing of fuel gas, shaking-off through vibration or suction to another member, or a chemical method of washing with liquid for dissolving the cover 125 or evaporation of water content, and the effective surface area of the fuel electrode 13 is enlarged. When N2 , O2 or product water from the air electrode 11 adheres to the surface of the fuel electrode 13 supplied with gaseous hydrogen of specified concentration in the closed state of an exhaust valve of a hydrogen supply system 20 at the time of start-up, for instance, gas of low hydrogen partial pressure is exhaust to refresh. The cover 125 is separated by led-in hydrogen made higher in pressure than the specified value. It is preferable that hydrogen exhaust gas be recycled through the air electrode 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell device, and more particularly to an improvement in a fuel electrode.

[0002]

2. Description of the Related Art An ordinary fuel cell has a structure in which an electrolyte membrane is sandwiched between a fuel electrode and an air electrode. Hydrogen gas is supplied to the fuel electrode as fuel gas, while air is supplied to the air electrode to provide an electrolyte membrane. The two are electrochemically reacted via, and electric power is obtained.

[0003] Since fuel exhaust gas discharged from the fuel electrode contains a component (hydrogen) of the fuel gas, a fuel cell apparatus of a type that reuses the fuel gas has been disclosed by the present applicant in Japanese Patent Application Laid-Open No. 9-266004. Is shown in According to the disclosure, most of the hydrogen gas supplied to the fuel electrode is used for the power generation reaction and consumed, but the surplus residual hydrogen gas still flows through the closed loop line (fuel exhaust gas passage) and flows to the air electrode. Introduced directly to

According to the fuel cell device configured as described above, the following operation and effect can be obtained. That is, the hydrogen gas introduced into the air electrode burns on the catalyst layer (Pt) of the air electrode and is converted into water. Thereby, in the case of a solid polymer electrolyte fuel cell in which a solid polymer ion exchange membrane is used for the electrolyte, the water and excess hydrogen gas generated by the normal cell reaction on the air electrode and the air electrode side of the electrolyte membrane are used. The recovered water flows toward the fuel electrode side of the electrolyte membrane whose water concentration is diluted due to the water concentration difference. This makes it possible to maintain and equalize the wet state of the electrolyte membrane on the fuel electrode side. That is, the humidification of the polymer solid electrolyte membrane can be performed from the air electrode side in addition to the conventional humidification from the fuel electrode side, or can be performed only from the air electrode side. When humidification is not performed from the fuel electrode side, it is not necessary to introduce water vapor into the hydrogen gas supplied to the fuel electrode to humidify the fuel gas, so that the utilization efficiency of the hydrogen gas is further improved and stabilized. Further, since the need for a humidifier on the fuel electrode side is eliminated, an auxiliary device for the humidifier can be simplified, and the weight and efficiency of the fuel cell device can be reduced. Furthermore, it is not preferable to discharge the fuel exhaust gas in a state where the surplus hydrogen gas remaining therein is included as it is. This is because hydrogen gas has high activity and may cause an undesired reaction outside the fuel cell device system after discharge.

[0005]

A fuel cell system of the type that reuses fuel exhaust gas may be operated as follows. That is, the flow of the fuel gas is temporarily stopped in order to efficiently use the fuel gas, and as the power generation reaction proceeds, the output of the battery becomes unstable due to the influence of N ₂ , O _2, or generated water passing through the air electrode. Then, the fuel gas is exhausted. As a result, the fuel gas around the fuel electrode is refreshed, and the output of the fuel cell is substantially recovered. However, according to the study of the present inventors, the recovery of the output of the fuel cell sometimes becomes incomplete.

[0006]

Means for Solving the Problems The inventors of the present application have made intensive studies to solve the above-mentioned problems, and as a result, impurities such as generated water, carbon dioxide, and nitrogen adhered to the surface of the fuel electrode, or It has been noticed that the concentration of these impurities in the space around the pole surface increases and the electrode area contributing to the reaction decreases, which contributes to the instability of the output. The present invention has been made based on such new findings by the present inventors. The configuration is as follows. A fuel cell device having a fuel electrode and an air electrode, further comprising means for removing a coating on the surface of the fuel electrode.

[0007]

According to the fuel cell device configured as described above, the coating on the surface of the fuel electrode is removed. As a result, the effective surface area of the fuel electrode becomes larger than before the removal, and the output of the fuel cell is restored. As described above, recovering the output of the fuel cell by removing the coating on the surface of the fuel electrode is particularly effective in a device in which fuel exhaust gas is intermittently introduced into the air electrode. However, it goes without saying that the technology of the present invention can be applied to other types, that is, those in which fuel exhaust gas is directly discharged out of the fuel cell system. Even in this case,
Since the effective surface area of the fuel electrode becomes larger than before the removal, the output of the fuel cell is stabilized.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the above, the method of removing the coating on the surface of the fuel electrode can be appropriately selected according to the properties of the coating on the surface. The removal method is roughly classified into a physical method and a chemical method. The coating on the fuel electrode surface refers to impurities such as generated water, carbon dioxide, and nitrogen attached to the fuel electrode surface, and a high concentration atmosphere of these impurities in a space around the surface of the fuel electrode.

As a physical method, there are a method of applying an impact force to the fuel electrode surface to remove the surface coating, and a method of adsorbing the coating on the fuel electrode surface to another member.

[0010] As the former method, in the embodiment, hydrogen gas is blown toward the fuel electrode surface and circulated along the fuel electrode surface. Thereby, the coating on the fuel electrode surface is removed from the fuel electrode surface by the flow of the hydrogen gas. In addition, by irradiating the surface of the fuel electrode with ultrasonic waves, the coating can be sieved from the surface. Further, the fuel electrode itself may be vibrated. These methods can be used in combination.

As the latter method, there is a method in which an adsorption sheet such as paper is pressed against the surface of the fuel electrode, and this sheet absorbs the surface coating. Further, the surface of the fuel electrode can be washed with a liquid such as water or alcohol. These methods can be used together with the former method described above.

As a chemical method, the surface is washed with a liquid capable of dissolving the surface coating of the fuel electrode. If the coating is water, it is evaporated. Chemical and physical methods can be used in combination.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of a fuel cell device 1 according to the embodiment. FIG. 2 shows a basic unit of the fuel cell main body 10.
As shown in FIG. 1, this device 1 includes a fuel cell main body 10, a hydrogen gas supply system 20 as a fuel gas, an air supply system 30,
It is roughly composed of a water supply system 40.

The unit unit of the fuel cell body 10 has a structure in which a solid polymer electrolyte membrane 12 is sandwiched between an air electrode 11 and a fuel electrode 13. In an actual device, a plurality of the unit units are stacked (fuel cell stack). Air manifolds 14 and 15 are formed above and below the air electrode 11. A mounting hole for mounting the nozzle 41 is formed in the upper manifold 14.

As shown in FIG. 2, the unit of the air electrode 11, solid polymer electrolyte membrane 12, and fuel electrode 13 is sandwiched between a pair of carbon connector plates 16, 17.
A plurality of grooves 18 for circulating air are formed on the surface of the connector plate 16 facing the air electrode 11. Each groove 1
Numeral 8 is formed in the vertical direction and communicates with the manifolds 14 and 15. As a result, the atomized water supplied from the nozzle 41 reaches the lower portion of the air electrode 11 along the groove 18.

Similarly, a groove 19 for flowing hydrogen gas is formed on the surface of the connector plate 17 facing the fuel electrode 13. In the embodiment, a plurality of the grooves 19 are formed in the horizontal direction. The grooves 19 reduce the flow resistance as much as possible so that the flow velocity at the surface of the fuel electrode 13 is increased when the hydrogen gas flows.

Since the air electrode 11 is supplied with water, it is made of a water-resistant material. Further, if a water film is formed thereon, the effective area of the air electrode 11 is reduced.
Material 1 is also required to have high water repellency. As such a material, a gas supply layer (C + PTF
A gas diffusion layer coated with E) was used. A general-purpose Nafion (trade name: DuPont) thin film was used as the solid polymer electrolyte membrane 12. The thickness of the membrane is not particularly limited as long as reverse osmosis of the generated water from the air electrode side is possible. The fuel electrode 13 is formed of the same material as the air electrode 11. This is for the common use of parts.

On the surface of the air electrode 11 and the fuel electrode 13 that is in contact with the electrolyte membrane 12, a well-known platinum-based catalyst used to promote the reaction between oxygen and hydrogen with a certain thickness is uniformly applied. Dispersed in the air electrode 1
1 and a catalyst layer in the fuel electrode 13.

As the hydrogen source 21 of the hydrogen gas supply system 20,
In this embodiment, a hydrogen cylinder made of a hydrogen storage alloy was used. In addition, a reforming material such as a water / methanol mixture is subjected to a reforming reaction in a reformer to generate a hydrogen-rich reformed gas, and this reformed gas is stored in a tank and used as a hydrogen source. You can also. Of course, when the fuel cell device 1 is used while being fixed indoors, the hydrogen pipe can be used as a hydrogen source. The hydrogen source 21 and the fuel electrode 13 are connected by a hydrogen gas supply path 22 via a hydrogen supply pressure regulating valve 23. The pressure regulating valve 23 regulates the pressure of the hydrogen gas supplied to the fuel electrode 13 and may be of a general configuration.

The exhaust gas from the fuel electrode 13 is supplied to the exhaust gas passage 2
4 to an air manifold 14 where it is mixed with air. The exhaust gas passage 24 is provided with a hydrogen exhaust valve 25 for opening and closing the same.

The hydrogen gas supplied to the fuel electrode 13 is used for the power generation reaction and most of the hydrogen gas is consumed. However, the surplus remaining hydrogen gas flows through the exhaust gas passage 24 and passes through the exhaust valve 25 to the air electrode. 11 is introduced. The surplus hydrogen gas supplied to the air electrode 11 in this way is burned on the catalyst and converted into water. This water is supplied to the electrolyte membrane 12. In this manner, in the fuel cell device 1 in which water produced by normal cell reaction and water recovered by combustion of surplus hydrogen gas can be used,
No conventional humidifier is required in each gas path of the hydrogen gas system 20 and the air system 30.

The air electrode 11 is supplied with air from the atmosphere by a blower (not shown). Reference numeral 31 in the figure denotes an air supply path, which is connected to the manifold 14 of the air electrode 11. An air passage 32 for circulating or exhausting the air passing through the air electrode 11 is connected to the lower manifold 15, and the exhaust gas is sent to a circulation passage 35 and an exhaust passage 36 via a condenser 33 for separating water. Can be The ratio of the exhaust gas distributed to the circulation path 35 and the exhaust path 36 is adjusted by the opening degree of the air exhaust pressure regulating valve 34. The purpose of circulating the exhaust gas is to completely burn the excess hydrogen gas introduced into the air electrode 11. The circulation path 35 and the exhaust pressure regulating valve 34 are omitted,
The exhaust gas may be directly discharged to the atmosphere.

The water separated by the condenser 33 is sent to a tank 42. The tank 42 is provided with a water level sensor 43. When the water level in the tank 42 falls below a predetermined value by the water level sensor 43, an alarm 44 flashes to notify the operator of a water shortage.

In the water supply system 40 of the embodiment, a water supply passage 45 is connected from a tank 42 to a nozzle 41 via a pump 46, a water pressure sensor 47 and a pressure regulating valve 48. The water adjusted to a desired water pressure by the pressure regulating valve 48 blows out from the nozzle 41 and becomes a mist in the air manifold 14.
Then, mist-like water is supplied to substantially the entire surface of the air electrode 11 by the momentum (initial speed) at the time of blowing, the own weight of the mist, the air flow, and the like.

The water thus supplied to the surface of the air electrode 11 evaporates by removing latent heat from the surrounding air.
Thereby, evaporation of the water in the electrolyte membrane 12 is prevented.
Further, the water supplied to the air electrode 11 also deprives the air electrode 11 of latent heat, and thus has an effect of cooling it. In particular, when water is supplied at the time of starting, it is possible to prevent the membrane and the catalyst from being damaged by the combustion of hydrogen and air. Further, the water supplied to the air electrode 11 also has an effect of purging the surface of the air electrode 11 (and a function as a purging means). That is, the coating on the surface of the air electrode 11 is removed by the water.

Reference numeral 50 in the figure denotes a voltmeter,
The voltage between the fuel cell 1 and the fuel electrode 13 is measured.

Next, the operation of the fuel cell device 1 according to the embodiment will be described with reference to FIG. The control device 70 and the memory 73 are housed in a control box (not shown in FIG. 1) of the fuel cell device 1. The memory 73 stores a control program that regulates the operation of the control device 70 composed of a computer, and parameters and lookup tables for executing various controls.

First, the operation of the hydrogen gas supply system 20 will be described. At the time of startup, the hydrogen exhaust valve 25 is kept closed, and the hydrogen supply pressure regulating valve 23 is adjusted so that hydrogen gas is supplied to the fuel electrode 13 at a predetermined concentration lower than the explosion limit. When the fuel cell device 1 is operated with the exhaust valve 25 closed, the influence of N ₂ , O _2, or generated water permeating from the air electrode occurs. Furthermore, it adheres to the surface of the fuel electrode 13 to reduce the effective area of the surface. As a result, a stable voltage cannot be obtained.

Therefore, the valve 2 is controlled based on a predetermined rule.
5 is released to exhaust the gas having a reduced hydrogen partial pressure, and the atmosphere gas of the fuel electrode 13 is refreshed. At this time, the pressure of the introduced hydrogen is adjusted to be higher than a predetermined value by adjusting the hydrogen supply pressure regulating valve 23, and a hydrogen gas having a strong flow is caused to flow to the surface of the fuel electrode 13 (at this time, the surface of the fuel electrode 13 is purged. , The coating on the surface is removed.) Thereby, the coating on the surface of the fuel electrode 13 is separated by the flow of the hydrogen gas.
In addition, moisture evaporates. Of course, not all of the coating is removed from the anode surface, but the concentration of the coating on the anode surface will be lower than before no hydrogen flow was introduced. When a large amount of hydrogen gas is used to purge the surface of the fuel electrode, the flown hydrogen gas is effectively used, and the high concentration of hydrogen gas is prevented from being discharged out of the fuel cell system. Therefore, it is preferable to introduce the hydrogen exhaust gas to the air electrode 11 side and reuse it as in the embodiment.

The predetermined rules are stored in the memory 73, and the controller 70 reads and executes the rules from the memory 73 to open and close the valve 25 and adjust the pressure regulating valve 23.

In this embodiment, the output voltage is monitored by the voltmeter 50, and when the output voltage falls below a predetermined threshold, the output voltage drops for a predetermined time (for example, 0.2 kg / cm 2,
Release the exhaust valve 25 (for 1 second). Alternatively, the exhaust valve 25
When the fuel cell device 1 is operated with the valve closed, a time interval at which the output voltage starts to decrease is measured in advance, and the exhaust valve 25 is substantially the same as or slightly shorter than the time interval.
The exhaust valve 25 is intermittently opened and closed so as to be released.

Next, the operation of the air supply system 30 will be described. Outside air is supplied from the air supply path 31 to the air manifold 14 at a constant pressure. On the other hand, part of the exhaust gas is discharged out of the system according to the opening degree of the air exhaust pressure regulating valve 34, and the remainder is circulated through the circulation path 35. That is, since the exhaust gas contains hydrogen, the amount of water generated by burning the hydrogen is adjusted to an appropriate amount to maintain the electrolyte membrane 12 in a wet state, in other words, the water balance of the fuel cell body. The opening degree of the pressure regulating valve 34 can be adjusted so that is optimal.

The control of the opening of the air exhaust pressure regulating valve 34 is also controlled by the control device 70 based on a predetermined rule.
The predetermined rules are stored in the memory 73. In this embodiment, since the water balance of the fuel cell main body 10 is adjusted mainly by the water supply system 40 described later, the opening of the pressure regulating valve 34 may be fixed.

Next, the operation of the water supply system 40 will be described. The water in the tank 42 is pumped by the pump 46. Then, the pressure is adjusted by the injection pressure adjusting valve 48 and the fuel is sprayed from the nozzle 41. As a result, the water is supplied to the air electrode 11 in a liquid state (fog state).

The supply amount of water is controlled by the control device 70 based on a predetermined rule. The predetermined rules are stored in the memory 73. In this embodiment, the water supply system 40 is operated at a constant water pressure every predetermined time (for example, 5 to 10 seconds).

Next, a fuel cell device 101 of another embodiment will be described.
Will be described. Components having the same functions as those in FIG. 1 are denoted by the same reference numerals, and the description thereof will be partially omitted. In this device 101, as shown in FIG.
A vertical groove 119 is formed in the connector plate 117 opposing the groove 3, and hydrogen gas is introduced from above the groove 119. A guide plate 121 is provided near the hydrogen gas inlet, and the introduced hydrogen gas is guided by the guide plate 121 and is sprayed on the surface of the fuel electrode 13 and flows along the surface. The guide plate 121 functions as a means for removing the coating on the surface of the fuel electrode 13. As a result, the surface of the fuel electrode 13 is purged, and the coating 125 is removed. Further, when performing this purging, it is more preferable that a hydrogen supply pressure regulating valve (23 in FIG. 1) is adjusted to introduce hydrogen gas at a pressure higher than usual.

The hydrogen exhaust gas is exhausted from below the connector plate 117 and is introduced into the air introduction passage 31 via the hydrogen exhaust gas passage 124.

The present invention is not at all limited to the description of the above-described embodiments and examples. Various modifications are included in the present invention without departing from the scope of the claims and within the scope of those skilled in the art.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of a fuel cell device according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a basic configuration of the fuel cell body.

FIG. 3 is a schematic diagram showing a control system of the fuel cell device.

FIG. 4 is a schematic diagram showing a configuration of a fuel cell device according to another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 101 Fuel cell device 10 Fuel cell main body 11 Air electrode 12 Electrolyte membrane 13 Fuel electrode 20 Hydrogen supply system 30 Air supply system 40 Water supply system 121 Guide plate 125 Coating

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Goichi Shiraishi 2--19-12 Sotokanda, Chiyoda-ku, Tokyo Inside Equos Research Co., Ltd. (72) Inventor Masataka Ueno 2--19 Sotokanda, Chiyoda-ku, Tokyo No. 12 Inside Equos Research Co., Ltd.

Claims (5)

[Claims] 1. A fuel cell device having a fuel electrode and an air electrode, comprising means for removing a coating on the surface of the fuel electrode. 2. The fuel cell device according to claim 1, wherein said removing means removes a coating on the surface of the fuel electrode by applying a physical force to the surface. 3. The removing means removes a coating on the surface of the fuel electrode by spraying a fuel gas onto the surface of the fuel electrode.
The fuel cell device according to claim 1, wherein: 4. The fuel cell device according to claim 1, wherein said removing means removes the coating on the surface of the fuel electrode by flowing the fuel gas along the surface of the fuel electrode. 5. The fuel gas used for removal is exhausted from the fuel electrode and then introduced into the air electrode.
5. The fuel cell device according to claim 3, wherein: