JP2005294229A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a fuel cell supply device which is small, has proper starting performance, and can maintain appropriately the wet conditions of an electrolyte membrane in a fuel cell using a liquefied gas. <P>SOLUTION: The fuel cell has a fuel supply device, in which the liquefied gas is dissolved into water via a hollow fiber membrane from a container filled with the liquefied gas, and this water solution is used as a fuel for the fuel cell. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell using an aqueous solution of liquefied gas as fuel.

  Fuel cells are attracting attention because of their low environmental impact and high overall efficiency.

  In recent years, methanol direct fuel cells (DMFC) that supply methanol directly to the anode have attracted attention, particularly in mobile device applications. Methanol reacts as shown in (Chemical Formula 1) at the anode.

(Chemical Formula 1) CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻
Since methanol is a liquid at room temperature, it is a desirable fuel from the viewpoint of convenience when carrying the fuel. However, in order to use methanol widely, the problem of regulations must be solved. Recently, a fuel cell using dimethyl ether (hereinafter, DME) as a fuel other than methanol has been known (for example, see Non-Patent Document 1).

  DME is a kind of liquefied gas that becomes liquid when pressurized even at room temperature. If it is placed in a pressurized container, the energy density can be increased like methanol. DME reacts as shown in (Chemical Formula 2) at the anode.

(Chemical Formula 2) CH ₃ OCH ₃ + 3H ₂ O → 2CO ₂ + 12H ⁺ + 12e ⁻
In a system having only DME as fuel and recovering water, the energy density can theoretically be higher than that of methanol.

  As can be seen from the above (Chemical Formula 2), water is necessary for the actual reaction at the anode. Accordingly, as a method of actually using DME as fuel for a fuel cell, a method of using DME gas that is humidified by bubbling DME gas whose flow rate is controlled by a flow rate regulator into water is known (for example, Non-patent document 1).

Further, in the polymer electrolyte fuel cell, when the solid polymer as the electrolyte membrane is dried, the resistance of the entire fuel cell is increased, and the power generation characteristics are greatly deteriorated. In order to prevent this, a method of humidifying a gas used as fuel for a fuel cell using a hollow fiber membrane is known (for example, see Patent Document 1).
New Energy and Industrial Technology Development Organization 2001 Results Report “Research and Development of Polymer Electrolyte Fuel Cell” Research on Polymer Electrolyte Fuel Cell (PEFC) Fueled with Dimethyl Ether (DME) JP-A-8-273687

  However, in the method of Non-Patent Document 1, it is difficult to adjust the amount of water in the DME gas and there is a limit to the amount that can be humidified with water, so that the electrolyte membrane of the fuel cell can be easily dried. There is a problem that resistance increases and battery characteristics deteriorate. Furthermore, although the humidification rate is improved by increasing the temperature of the water to be bubbled, there are problems that energy is required to increase the temperature and that it takes time until the temperature increases or decreases.

  On the other hand, Patent Document 1 describes using a hollow fiber membrane as a means for humidifying a gas. When this method is used, the humidification speed becomes faster than that in Non-Patent Document 1. However, even if this method is used in a fuel cell using DME as fuel and water is supplied to the DME gas through a hollow fiber membrane and humidified, the electrolyte membrane is brought into an appropriate moisture-retaining state in the entire operating range of the fuel cell. It is difficult to maintain. That is, the amount of water introduced into the fuel cell by humidifying the DME gas has a limit depending on the temperature, and humidification of the electrolyte membrane of the fuel cell may be insufficient. A method of raising the gas temperature to increase the amount of moisture in the gas is also conceivable. However, there is a problem that the amount of energy is required and it takes time until the temperature rises or falls. . That it takes time to reach the desired temperature means that the startability of the fuel cell is poor.

  In order to solve the above-described conventional problems, the fuel cell of the present invention using an aqueous solution obtained by mixing liquefied gas and water as fuel, and having a gas-liquid mixing section for dissolving the liquefied gas in water through a hollow fiber membrane. It is characterized by.

  In this case, since an aqueous solution in which liquefied gas is dissolved in water is used as fuel in the fuel cell, there is sufficient water in the fuel cell, and the electrolyte membrane of the fuel cell in any temperature range or power generation state Can remain sufficiently wet. Further, since the liquefied gas and water are mixed through the hollow fiber membrane, the dissolution rate of the liquefied gas in water is high, and sufficient fuel can be sent to the fuel cell. As a result, a fuel in which a sufficient amount of liquefied gas and water is mixed can be sent to the fuel cell regardless of the outside air temperature and the power generation state, and the start-up is fast and stable power generation can be achieved.

  Furthermore, the liquefied gas evaporated from the container filled with the liquefied gas is pressurized against the hollow fiber membrane, and the liquefied gas can be obtained simply by contacting water and the pressurized liquefied gas through the hollow fiber membrane. Can be dissolved in water, making it extremely simpler and smaller than conventional devices that require the humidification of the electrolyte membrane and the flow rate of liquefied gas to match the power generation state of the fuel cell. Excellent in terms of cost reduction and energy efficiency.

  Furthermore, it is desirable that a regulator be provided between the container filled with the liquefied gas and the gas-liquid mixing unit. This is because the pressure in the container filled with the liquefied gas varies depending on the temperature, so that when the liquefied gas is directly dissolved in water, the pressure at the time of dissolution also varies if there is no regulator. It is also possible to control the amount of liquefied gas dissolved in water by changing the pressure of the regulator.

  Furthermore, it is desirable to have a pressure control unit that controls the pressure in the gas-liquid mixing unit.

  The liquefied gas is vaporized and has a certain pressure. For this reason, when the liquefied gas is dissolved in water through the hollow fiber membrane, it is possible to prevent the aqueous solution from leaking to the outside by maintaining the pressure of the aqueous solution in which the liquefied gas is dissolved at a predetermined value. . For example, if somewhere in the fuel cell system is at atmospheric pressure, the aqueous solution in which the liquefied gas is dissolved leaks more and more, and the fuel cell system structure is such that the pressure is transmitted to the fuel cell. If so, the fuel cell itself is required to have high pressure resistance. In this case, in order to prevent leakage of the fuel cell, it is necessary to increase the tightening pressure or to increase the tightening portion not involved in power generation, which leads to an increase in size.

  Furthermore, it is desirable to have a flow rate control unit that controls the flow rate of supplying fuel to the fuel cell, and the flow rate control unit controls the flow rate according to the pressure and temperature in the gas-liquid mixing unit. This is because the solubility of water and liquefied gas is physically determined by pressure and temperature, and at the same time, the concentration of liquefied gas in the aqueous solution also changes. In this way, even if the concentration of the liquefied gas in the aqueous solution changes, the flow rate is adjusted according to the pressure and temperature of the aqueous solution in which the liquefied gas is dissolved in water, so that a desired amount of fuel is supplied to the fuel cell. It becomes possible to send. When the temperature is constant, the liquefied gas concentration in the aqueous solution can be specified by keeping the pressure at a certain value, and by combining this with the flow control device, it is possible to send the desired amount of fuel to the fuel cell. Become. A pump may be used to send the aqueous solution in which the liquefied gas is dissolved to the fuel cell, but since the aqueous solution in which the liquefied gas is dissolved has pressure, this pressure difference is used to substitute the pump with a valve or the like. It is also possible to do.

  The liquefied gas used as fuel is preferably DME. This is because when the gas is reformed and directly used for power generation without being converted to hydrogen, DME can obtain a larger output than other liquefied gases such as butane and diethyl ether.

  An aqueous solution in which liquefied gas and water are mixed is used as the fuel, but the fuel is heated before being sent to the power generation unit of the fuel cell, or after being sent, it is heated within the power generation unit of the fuel cell. It may be in a vaporized state.

  According to the present application, it is possible to reduce the size of a fuel cell using liquefied gas as a fuel, good startability, and appropriate maintenance of the wet state of the electrolyte membrane, so that a stable output can be obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 is a schematic view of a gas-liquid mixing unit for dissolving a liquefied gas in water through a hollow fiber membrane in the present invention. The liquefied gas 1 is sent from the container 2 filled with the liquefied gas 1 through the regulator 3 to the gas-liquid mixing unit 4 from the gas inlet a. At this time, the gas outlet b is closed, and the liquefied gas 1 is not exhausted. By doing so, the pressure of the liquefied gas 1 in the gas-liquid mixing unit 4 can be controlled only by the regulator 3, and it is not necessary to discharge the fuel, which leads to an improvement in fuel utilization efficiency.

  A large number of hollow fiber membranes 5 are arranged in the gas-liquid mixing unit 4, and the water 20 introduced from the liquid inlet c comes into contact with the liquefied gas 1 through the hollow fiber membrane 5, and the liquefied gas 1 is dissolved in the water 20. To do. The aqueous solution 21 in which the liquefied gas 1 is dissolved is discharged from the liquid outlet d. With the above configuration, since the contact area between the liquefied gas 1 and the water 20 can be increased by the hollow fiber membrane 5, the liquefied gas 1 can be saturated with respect to the water 20 in a short time. Further, by controlling the pressure with the regulator 3, the liquefied gas 1 can be supplied to the gas-liquid mixing section 4 at a stable pressure even if the pressure in the container 2 changes. Can be stabilized. The hollow fiber membrane 5 is preferably a hydrophobic membrane that allows the liquefied gas 1 to permeate but does not allow water 20 to permeate. As the gas-liquid mixing unit 4, for example, a hollow fiber membrane module called Liquicel manufactured by Celgard can be used. At this time, the inside of the hollow fiber membrane 5 may be the liquefied gas 1 and the outside may be the water 20, or the inside of the hollow fiber membrane 5 may be the water 20 and the outside may be the liquefied gas 1.

  FIG. 2 is a schematic diagram of the fuel cell according to Embodiment 1 of the present invention. A device 6 for sending the aqueous solution 21 to the anode of the fuel cell 13, a device 7 for sending an oxidant such as air to the fuel cell 13, and a gas-liquid separation for discharging carbon dioxide, which is a reaction product generated from the anode of the fuel cell 13. The apparatus 8, the apparatus 9 for sending the aqueous solution 22 containing the remaining liquefied gas after removing carbon dioxide to the hollow fiber membrane 5, and the water for recovering the water that is the reaction product generated at the cathode of the fuel cell 13 A recovery device 10 and a device 11 for feeding the recovered water for use as water for dissolving the liquefied gas are provided.

  Here, it is desirable that each of the device 6, the device 9, and the device 11 also serves as a check valve. By playing the role of the check valve, the back flow in the entire system is prevented, and the fuel cell 13 can be stably operated. In addition, an area 12 including the gas-liquid mixing unit 4 surrounded by the regulator 3, the device 6, the device 9, and the device 11 includes a pressure sensor 14 that measures the pressure of the aqueous solution, and can monitor the pressure. . Furthermore, the pressure of the aqueous solution 21 in the area 12 can be controlled by the regulator 3, the device 6, the device 9, and the device 11. Furthermore, the temperature of the aqueous solution 21 in which the liquefied gas is dissolved can be monitored by the temperature sensor 15. From the pressure in the area 12 and the temperature indicated by the temperature sensor 15, it is possible to calculate the amount of the liquefied gas 1 dissolved in the water 20. By doing so, it is possible to send an appropriate amount of the aqueous solution 21 to the fuel cell 13.

  In the apparatus 6, a liquid pump can be used, and liquid feeding is possible even with a structure such as a pressure valve utilizing the pressure applied to the aqueous solution 21 in which the liquefied gas is dissolved.

  FIG. 3 shows a schematic diagram of the power generation unit of the fuel cell according to the present invention. The power generation unit 40 has a structure in which the proton conducting membrane 31 is sandwiched between the anode catalyst layer 32 and the cathode catalyst layer 33, and further, on each catalyst layer, an anode diffusion layer 34 and a cathode diffusion layer 35. Is installed. Further, the periphery of the anode diffusion layer 34 and the cathode diffusion layer 35 is sealed with gaskets 36 and 37 that have an effect of preventing fluid from leaking to the surroundings and regulating the compression of the diffusion layer and the catalyst layer. . Further, the anode diffusion layer 34 and the gasket 36, and the cathode diffusion layer 35 and the gasket 37 are sandwiched between separators 38 and 39 each having a groove through which a fluid flows. Although not shown, actually, in order to press and hold the power generation unit 40, end plates on both sides, current collecting plates for taking out electricity, and the like are required.

(Embodiment 2)
FIG. 4 shows a schematic diagram of a fuel cell according to Embodiment 2 of the present invention. When the apparatus 6 is adjusted so that the minimum amount of fuel necessary for power generation of the fuel cell 13 is sent, the gas-liquid separator 8 and the apparatus 9 in FIG. 2 can be omitted, as shown in FIG. It can also take a configuration. In this case, since it is assumed that some liquid is contained in the exhaust of the anode, the water recovery device 10 may be used.

  It should be noted that substances exhausted outside the fuel cell system, such as exhaust after passing through the water recovery device 10, may be purified by catalytic combustion or the like.

  As described above, according to the present invention, the fuel cell system using the liquefied gas as the fuel can be downsized, the startability is good, and the wet state of the electrolyte membrane can be appropriately maintained so that a stable output can be obtained. Can provide.

  INDUSTRIAL APPLICABILITY According to the present invention, it is very useful for a fuel cell using an aqueous solution obtained by mixing liquefied gas and water as a fuel. In particular, when dimethyl ether is used as the liquefied gas, a large output can be obtained as compared with other liquefied gases, which is very useful for improving the energy density of the fuel cell.

Schematic of the gas-liquid mixing part of the fuel cell in Embodiment 1 of the present invention Schematic of the fuel cell in Embodiment 1 of the present invention Schematic of the power generation part of the fuel cell in the present invention Schematic of the fuel cell in Embodiment 2 of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquefied gas 2 Container 3 Regulator 4 Gas-liquid mixing part 5 Hollow fiber membrane 6 Apparatus which sends aqueous solution to an anode 7 Apparatus which sends oxidant 8 Gas-liquid separation apparatus for discharging | emitting carbon dioxide 9 The aqueous solution containing residual liquefied gas Device for sending to hollow fiber membrane 10 Water recovery device 11 Device for sending recovered water for use as water for dissolving liquefied gas 12 Area 13 Fuel cell 14 Pressure sensor 15 Temperature sensor 20 Water 21 Aqueous solution 22 Residual remaining Aqueous solution containing liquefied gas a Gas inlet b Gas outlet c Liquid inlet d Liquid outlet 31 Proton conducting membrane 32 Anode catalyst layer 33 Cathode catalyst layer 34 Anode diffusion layer 35 Anode diffusion layer 36, 37 Gasket 38 , 39 Separator 40 Power generation unit

Claims (5)

In a fuel cell using an aqueous solution obtained by mixing a liquefied gas and water as a fuel,
A fuel cell having a gas-liquid mixing part for dissolving the liquefied gas in the water through a hollow fiber membrane. A regulator is provided between the container filled with the liquefied gas and the gas-liquid mixing unit,
The fuel cell according to claim 1. A pressure control unit for controlling the pressure in the gas-liquid mixing unit;
The fuel cell according to claim 1 or 2. A flow rate control unit that controls a flow rate of supplying the fuel to the fuel cell, and the flow rate control unit controls the flow rate according to pressure and temperature in the gas-liquid mixing unit;
The fuel cell according to any one of claims 1 to 3. The liquefied gas is dimethyl ether;
The fuel cell according to any one of claims 1 to 4.

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