JP2007048546A - Fuel cell device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent water from remaining in a separator of a fuel cell and thereby prevent freezing of the remaining water in a cold district. <P>SOLUTION: The fuel cell device which is provided with a water supply device for supplying water to an air supply system of the fuel cell has a surface tension conditioned water which has a smaller surface tension than a pure water by being added with a surface tension conditioner into water. This surface tension conditioned water easily leaks into the surface of a separator. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell device. More specifically, the present invention relates to an improvement in technology for preventing water clogging at the air electrode of a fuel cell.

A unit cell of a fuel cell has a configuration in which a polymer solid electrolyte membrane is sandwiched between an air electrode and a hydrogen electrode. Both the air electrode and the hydrogen electrode are formed by sequentially laminating a reaction layer containing a catalyst and a gas diffusion layer from the electrolyte membrane side. A separator provided with a gas flow path is stacked outside the air electrode and the hydrogen electrode. When viewed from the separator, the air electrode of one fuel cell unit cell faces one surface side of the separator, and the hydrogen electrode of another fuel cell unit cell faces the other surface side. This separator prevents the permeation of gas (air, hydrogen gas) and collects the current generated in the unit cell and takes it out.
In such an air supply system that supplies air to the air electrode, water is supplied to maintain the wet state of the fuel cell and / or to cool the fuel cell.

In some cases, water supplied to the air supply system or generated water generated by the reaction of the fuel cell remains in the air flow path of the separator and is blocked. When the air flow path is blocked, air does not spread over the entire air electrode, which may reduce the power generation capacity or make power generation unstable.
Further, if water remains in the air flow path of the separator, the residual water may freeze when the fuel cell after operation is stopped is placed in a sub-freezing environment. Residual water whose volume has expanded due to freezing may cause unexpected mechanical stress on the fuel cell, or the air flow path may be blocked and cannot be activated.
From the above, it is necessary to remove residual water promptly.

In order to remove residual water, conventionally, a surface treatment has been applied to the formation surface of the air flow path in the separator (hereinafter sometimes simply referred to as “separator surface” in this specification). For example, in the fuel cell device described in Patent Document 1, the surface of the separator is made water-repellent to prevent water from adhering to the surface, thereby preventing water from remaining in the air flow path.
In the fuel cell devices described in Patent Documents 2 and 3, the surface of the separator is made hydrophilic so that water can easily flow along the surface. In the so-called water direct injection type fuel cell in which water is directly sprayed onto the air electrode as disclosed in Patent Document 3, the surface of the separator is hydrophilized so that the water is easily wetted with respect to the separator surface. Evaporation is accelerated and the cooling effect is improved.

JP 2002-216786 A JP 2001-93539 A JP 2003-123794 A

However, in the method of surface treatment of the air flow path forming surface of the separator to prevent water from remaining in the air flow path, the water repellency of the surface is caused due to impurities adhering to the air flow path forming surface. Or there exists a possibility that hydrophilicity may fall gradually.
In other words, the conventional technique for preventing water from remaining in the air flow path in the separator has a problem in durability.

As a result of intensive studies to solve the above problems, the present inventor has adjusted the surface tension of the water itself introduced into the air supply system. Recognizing that it can always be prevented from remaining in the water, the present invention has been completed.
That is, in a fuel cell device provided with a water supply device for supplying water to the air supply system of the fuel cell,
A fuel cell apparatus, wherein a surface tension adjusting agent is added to the water to form surface tension adjusting water having a surface tension smaller than that of pure water.
According to the fuel cell device configured as described above, the surface tension adjustment water has a small surface tension, which easily wets the separator surface. Therefore, the surface tension adjusting water easily flows along the separator surface and does not remain in the air flow path. Further, even when used in a cold region, there is no freezing of residual water, so that the fuel cell device starts up quickly (improved mobility). Further, evaporation on the separator surface is promoted, and cooling efficiency is improved.

The fuel cell device according to the second aspect of the present invention is defined as follows. That is,
In the fuel cell device according to the first aspect described above, the surface tension adjustment water has a surface tension as follows:
γg <γl <γs
Where γg is the critical surface tension of the gas diffusion layer on the air electrode side of the fuel cell, γl is the surface tension of the surface tension adjusting water, γs is the critical surface tension of the separator on the air electrode side,
Satisfied.
According to the fuel cell device configured as described above, the surface tension adjusting water is less likely to wet the diffusion layer by making the surface tension γl of the surface tension adjusting water larger than the critical surface tension γg of the gas diffusion layer. This prevents the gas diffusion layer from being clogged with the surface tension adjusting water. Thereby, sufficient gas supply to the reaction layer is ensured, and the output of the fuel cell is stabilized.
Further, by making the surface tension γl of the surface tension adjusting water smaller than the critical surface tension γs of the separator (more specifically, the air flow path forming surface of the separator), the surface tension adjusting water is easily wetted by the separator. Accordingly, the surface tension adjusting water easily flows along the separator surface and does not remain in the air flow path. Therefore, mobility in a cold region is improved. Further, since the surface tension adjusting water is distributed over the entire separator surface, the evaporation is promoted and the cooling capacity of the fuel cell is improved.

The fuel cell device according to the third aspect of the present invention is defined as follows. That is,
In the fuel cell according to the first or second aspect described above, the surface tension adjusting agent is made of a surfactant.
By using the surfactant as the surface tension adjusting agent in this way, the surfactant is inexpensive, and therefore an increase in the manufacturing cost of the fuel cell device can be suppressed.

The fuel cell device according to the fourth aspect of the present invention is defined as follows. That is,
In the fuel cell device according to any one of the first to third aspects described above, the water supply device is a storage unit for the surface tension adjustment water, a surface tension measurement device for measuring the surface tension of the surface tension adjustment water, A surface tension adjusting agent storage unit, and a device for adjusting a supply amount of the surface tension adjusting agent supplied from the surface tension adjusting agent storage unit to the surface tension adjusting water storage unit.
The amount of generated water and the exhaust temperature change according to the load applied to the fuel cell. As a result, there is a possibility that a change occurs in the water content of the recovered surface tension adjustment water. Therefore, in the fuel cell device of this aspect, the surface tension adjustment water surface tension is measured, and the amount of the surface tension adjustment agent is adjusted according to the result, so that the surface tension adjustment water surface tension is maintained within a desired range. be able to.

The fuel cell device according to the fifth aspect of the present invention is defined as follows. That is,
In the fuel cell device according to the first to fourth aspects described above, the water supply device sprays the surface tension adjusting water onto the air electrode of the fuel cell.
In this aspect, the fuel cell device is defined as a so-called direct injection type. In the direct injection type fuel cell device, a large amount of water (surface tension adjustment water in this invention) is sent to the air electrode of the fuel cell, so that the residual water is prevented by appropriately adjusting the surface tension, This improves the startability in cold regions. Further, the evaporation of moisture in the separator is accelerated, and the cooling efficiency of the fuel cell is improved.

Hereafter, each element which comprises this invention is demonstrated.
(Fuel cell device)
The fuel cell device is provided with an air supply system for supplying air to the air electrode of the fuel cell, and a hydrogen supply system for supplying hydrogen to the hydrogen electrode, with the fuel cell as the center. In addition, an auxiliary device such as a cooling device for adjusting the temperature of the fuel cell and a secondary battery or a capacitor for accumulating the generated electric power is optionally provided.

(Water supply device)
The water supply device of the present invention supplies surface tension adjustment water to the air supply system of the fuel cell device. The supply mode is not particularly limited. The surface tension adjustment water is sprayed directly onto the air electrode of the fuel cell as in the so-called water direct injection type in order to maintain the wet state of the fuel cell and prevent the fuel cell from being heated. A type in which tension adjusting water is atomized and introduced into the air supply system can be adopted.
As basic constituent elements of the water supply device, a storage unit for surface tension adjustment water, an introduction unit for introducing the surface tension adjustment water into the air supply system, and a recovery unit for collecting the surface tension adjustment water are provided. As these elements, those of a general-purpose water supply device can be used as they are.

In this invention, it is preferable to maintain the surface tension γl of the surface tension adjusting water within a desired range (γg <γl <γs). Therefore, it is preferable to always monitor the surface tension of the surface tension adjusting water. As a method of monitoring the surface tension, in addition to directly measuring the surface tension of the surface tension adjusting water, the surface tension can be indirectly specified from the specific gravity and transparency of the surface tension adjusting water. That is, if the surface tension adjusting agent is determined in advance, the surface tension and the specific gravity or transparency are related to each other in a one-to-one relationship according to the blending ratio of the surface tension adjusting agent in the surface tension adjusting water.
In accordance with the monitor result of the surface tension of the surface tension adjusting water, the supply of the surface tension adjusting agent is adjusted so that it always falls within a predetermined range. Alternatively, water recovery is adjusted.

(Surface tension regulator)
The surface tension adjusting agent is not particularly limited as long as it is added to water to reduce the surface tension. According to the study of the present inventors, alcohols, ionic surfactants and nonionic surfactants containing ethanol, propanol, ethylene glycol, propylene glycol, glycerin and the like. Desirably, a fluorine-type surfactant which is a nonionic surfactant (for example, Sumitomo 3M, a brand name; Novec) can be mentioned.
From the viewpoint of recovering the surface tension adjusting agent, those having a boiling point equal to or higher than that of water are preferable. As a result, the higher the boiling point, the lower the vapor pressure, and the surface tension adjusting water containing the surface tension adjusting agent can be recovered using the conventional condenser provided in the air discharge system as it is. It is also preferable to provide stability (non-corrosive) to the reaction layer of the air electrode.

Examples of the present invention will be described below.
FIG. 1 shows a schematic configuration of a fuel cell device 1 of an embodiment. As shown in FIG. 1, the fuel cell device 1 is generally composed of a fuel cell stack 10 as a fuel cell main body, a water supply system 20, a hydrogen gas supply system 40, an air supply system 70, and an output system 80.

First, the fuel cell stack 10 will be described. The unit unit of the fuel cell unit cell has a structure in which a solid polymer electrolyte membrane is sandwiched between an air electrode and a fuel electrode. The unit unit has a configuration in which the electrolyte membrane 1 is sandwiched between an oxygen electrode 2 and a hydrogen electrode 3 as shown in FIG. The oxygen electrode 2 is obtained by laminating a gas diffusion layer 3a on a reaction layer 2a. An air flow path is provided on the surface of the separator 5 that faces the oxygen electrode 2, and a part of the air flowing into the air flow path diffuses through the gas diffusion layer 3 a to reach the reaction layer 2 a for the fuel cell reaction. Contribute. Similarly, the hydrogen electrode 3 is obtained by laminating a gas diffusion layer 3b on the reaction layer 3a. A hydrogen channel is provided on the surface of the separator 5 facing the hydrogen electrode 3, and a part of the hydrogen flowing into the hydrogen channel diffuses in the gas diffusion layer 3b and reaches the reaction layer 2b.
A fuel cell stack is formed by alternately stacking a plurality of unit units and separators.
An air manifold 11 is formed above the fuel cell stack 10. A nozzle 29 is attached to the air manifold 11, and surface tension adjusting water is ejected from the nozzle 29. The surface tension adjustment water directly injected from the nozzle 29 is supplied to the entire surface of the air flow path of the fuel cell unit cell, and is used for humidifying the electrolyte membrane and cooling the fuel cell main body.

The surface tension adjusting water 21 is formed by adding a surfactant to the water in the tank 22.
In this embodiment, as shown in FIG. 3, the surface tension γl of the surface tension adjusting water 21 is constantly monitored by the surface tension sensor 103 (step 1). The surface tension γl and the critical surface tension γg of the gas diffusion layer on the air electrode side of the fuel cell are compared (step 3). When the relationship of γg <γl is not satisfied (that is, when γl is γg or less), the pump 101 And the supply of the surfactant is stopped (step 5). Here, since the condensed water contains the generated water, as a result, the proportion of the water in the surface tension adjusting water 21 increases and the surface tension γl increases.

In step 7, the surface tension γl of the surface tension adjusting water 21 is compared with the critical surface tension γs of the separator on the air electrode side (step 7), and when the relationship of γl <γs is not satisfied (when γl becomes γs or more). Then, it is determined that the surface tension γs of the surface tension adjusting water has become too small, the pump 101 is operated to supply the surface tension adjusting agent 21 in the tank 100 to the tank 22, and the ratio of the surfactant in the surface tension adjusting water 21 And thus the surface tension γl is reduced. Furthermore, the ratio of the surface tension adjusting agent in the tank 22 can also be increased by stopping the condensed water recovery pump 38 and closing the recovery adjustment valve 39 to stop the recovery of the condensed water.
The above operation is continued while the water supply system 20 is operating (step 11). Even if the supply rate of the surfactant by the pump 101 is constant, the surface tension γl of the surface tension adjusting water 21 is always maintained in the relationship of γg <γl <γs by repeating the above steps 1 to 9. Can do.

  In the water supply system 20 of the embodiment, a piping unit 30 is connected from a tank 22 to a nozzle 29 via a filter 26, a direct fountain water pump 27, and a direct fountain water supply electromagnetic valve 28. The surface tension adjustment water sucked up from the tank 22 by the direct fountain water pump 27 is adjusted to a desired water pressure by the direct fountain water supply electromagnetic valve 28, blown out from the nozzle 29, and becomes mist in the air manifold 11. Then, the air flow path is entered from the upper opening of the fuel cell unit cell constituting the fuel cell stack by the momentum (initial speed) at the time of blowing, the weight of the mist, the air flow, and the like. Except for what is vaporized in this air flow path and supplied to the air electrode, the surface tension adjustment water is recovered in a condenser 36 provided on the downstream side of the fuel cell stack 10 and is stored in a tank by a condensed water recovery pump 38. Return to 22.

  Here, the surface tension adjustment water supplied to the air manifold passes through the air flow path of the air electrode side separator of each unit cell constituting the fuel cell stack 10 together with the air. At this time, since the surface tension adjusting water has a surface tension smaller than that of pure water, the surface tension adjusting water easily gets wet on the surface of the separator (the surface of the air flow path). Accordingly, the surface tension adjusting water easily flows along the surface of the separator and does not remain in the air flow path. Further, the evaporation from the separator surface is promoted, and the cooling effect on the fuel cell stack is improved.

The tank 22 is provided with a water temperature sensor 24, a tank water level sensor 25, and a heater 23. Reference numeral 37 denotes a filter that prevents foreign substances (dust, insects, etc.) from entering from the outside.
The nozzle 29 preferably jets water directly toward the air flow path inlet. Accordingly, a desired amount of surface tension adjustment water can be supplied to the air flow path regardless of the air supply amount. That is, the supply amount of air and the supply amount of surface tension adjustment water can be controlled independently. The change in the air supply amount and the change in the surface tension adjustment water supply amount are not always required at the same time, and they may be required independently.

  Reference numeral 100 stores a surfactant as a surface tension adjusting agent. The stored surfactant is supplied into the tank 22 by the pump 101. The surface tension of the water to which the surfactant is added, that is, the surface tension adjusting water is directly measured by the sensor 103. The controller 90 controls the amount of the surface tension adjusting agent supplied to the water tank 22 by operating the pump 101 based on the tension of the surface tension adjusting water obtained. In addition, assuming that the amount of water becomes excessive, the recovery adjustment valve 39 prevents the recovered water from being supplied to the water tank.

Next, the hydrogen gas supply system 40 will be described. In this embodiment, a hydrogen storage tank 41 is employed as the hydrogen supply device of the hydrogen gas supply system 40. In addition, a reforming material such as a liquid hydrogen hydrogen cylinder or a water / methanol mixture is reformed in a reformer to generate a hydrogen-rich reformed gas, and the reformed gas is stored in a tank. It can be used as a hydrogen source.
Hydrogen gas in the hydrogen storage tank 41 is supplied to the fuel cell stack 10 via a hydrogen gas pipe 43. A hydrogen primary pressure sensor 46, a hydrogen pressure regulating valve 47, a hydrogen supply electromagnetic valve 48, and a hydrogen secondary pressure sensor 49 are attached to the hydrogen gas pipe 43 to control the supply amount to the fuel cell stack 10. Hydrogen is supplied to the hydrogen storage tank 41 from the outside through a hydrogen filling port 45.

Since all of the hydrogen gas supplied to the fuel cell stack 10 is not consumed, the gas discharged from the fuel cell stack 10 is circulated and used by the circulation system 50. The circulation system 50 includes a circulation pump 51 and a circulation electromagnetic valve 53. The trap 54 captures water from the fuel cell stack 10 and prevents it from entering the circulation system 50 and the hydrogen gas supply system 40. The circulation electromagnetic valve 53 adjusts the flow rate of the circulation system 50. The exhaust solenoid valve 67 is released when the hydrogen gas is exhausted (the decompression solenoid valve 65 is used together when the hydrogen gas is exhausted rapidly). The exhaust from the pressure reducing solenoid valve 65 and the exhaust solenoid valve 67 is mixed with the exhaust of the air supply system 70. This is for diluting the hydrogen gas component contained in the hydrogen gas exhaust.
The outside air introduction electromagnetic valve 63 is opened after the fuel cell stack 10 is stopped, and purges hydrogen gas from the hydrogen gas supply system with outside air. Reference numeral 61 denotes a filter that prevents foreign matter from entering from outside air.

In the air supply system 70, the air taken in by the air fan 73 via the filter 71 is raised to a desired temperature by the heater 75. Reference numeral 76 denotes an outside air temperature sensor, and reference numeral 77 denotes an air inlet temperature sensor in the fuel cell stack. When the air temperature at the air inlet detected by the sensor 77 exceeds the threshold value, the heater is controlled to be turned off.
In a fuel cell device used in a low-temperature environment, it is preferable that the air to be introduced is heated and introduced into the air flow path of each fuel cell unit cell constituting the fuel cell stack 10. As a result, the fuel cell stack 10 is heated to prevent the generated water from freezing, and power generation is possible in the fuel cell stack 10 in a low temperature state.

  According to the fuel cell device configured as described above, surface tension adjustment water obtained by mixing water and a surfactant is introduced into the air electrode side of the fuel cell together with air. Since the surface tension adjusting water has a surface tension smaller than that of pure water, the surface tension adjusting water easily wets the separator surface. As a result, the surface tension adjusting water easily flows along the surface of the separator and does not remain there. Further, when the surface of the separator is wetted widely, its evaporation is promoted, and the cooling effect on the fuel cell is improved.

  The present invention is not limited to the description of the embodiments and examples of the invention described above. Various modifications may be included in the present invention as long as those skilled in the art can easily conceive without departing from the description of the scope of claims.

FIG. 1 is a schematic diagram of a fuel cell apparatus according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing the configuration of the fuel cell unit cell. FIG. 3 is a flowchart showing the operation of the fuel cell device of another embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell apparatus 10 Fuel cell stack 20 Water supply system 21 Surface tension adjusting water 22 Surface tension adjusting water tank 100 Surface tension adjusting agent tank 103 Surface tension sensor

Claims (5)

In a fuel cell device provided with a water supply device for supplying water to an air supply system of the fuel cell,
A fuel cell device, wherein a surface tension adjusting agent is added to the water to form surface tension adjusting water having a surface tension smaller than that of pure water. The surface tension adjusting water has a surface tension as follows:
γg <γl <γs
Where γg is the critical surface tension of the gas diffusion layer on the air electrode side of the fuel cell, γl is the surface tension of the surface tension adjusting water, γs is the critical surface tension of the separator on the air electrode side,
The fuel cell device according to claim 1, wherein: The fuel cell device according to claim 1, wherein the surface tension adjusting agent is made of a surfactant. The water supply device includes a storage unit for the surface tension adjustment water, a surface tension measurement device for measuring a surface tension of the surface tension adjustment water, a storage unit for the surface tension adjustment agent, and a surface tension adjuster from the surface tension adjustment agent storage unit. The fuel cell apparatus according to any one of claims 1 to 3, further comprising a device for adjusting a supply amount of the surface tension adjusting agent supplied to the adjusted water storage unit. 5. The fuel cell device according to claim 1, wherein the water supply device sprays the surface tension adjustment water on an air electrode of the fuel cell.

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