JP2007005163A - Direct methanol fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a direct methanol fuel cell system capable of preventing inhibition of stable operation of a system due to fuel shortage. <P>SOLUTION: The direct methanol fuel cell system is provided with a fuel cell main body 1 equipped with proton-conductive polymer solid electrolyte 4, a pair of air electrode 5 and a fuel electrode 3 arranged at both sides, a fuel tank 2 storing liquid fuel to be supplied to the fuel electrode 3, a fuel supply tube 10 guiding the liquid fuel inside the fuel tank 2 into the fuel electrode 3 of the fuel cell main body 1, and an air guide-in tube 11 guiding oxygen in the air into the air electrode 5 of the fuel cell main body 1. The fuel supply tube 10 is constituted of a material transmitted by electromagnetic waves, to enable to contribute to a stable operation of the system by detecting a propagation state of the electromagnetic waves according to existence or non-existence of the liquid fuel in the fuel supply tube 10. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a direct methanol fuel cell system capable of generating electricity by directly supplying an organic solvent and water. More specifically, the present invention relates to a power generation unit in which a plurality of fuel cell bodies are stacked from a fuel tank. The present invention relates to a system having a function of easily detecting whether liquid fuel is present in a fuel supply pipe into which liquid fuel is introduced.

  In recent years, dealing with environmental problems and resource problems has become important, and fuel cells are being actively developed as one of the countermeasures. In particular, solid polymer fuel cells and direct methanol fuel cells using proton conductive polymer solid electrolyte as an electrolyte have the feature that they can generate electricity by directly supplying fuel without gasification or reforming. Therefore, the structure is simple, and it is easy to reduce the size and weight, and is attracting attention as a distributed power source and a portable power source.

  In this direct methanol fuel cell, a fuel cell body, in which an air electrode and a fuel electrode are joined to both sides of a proton conductive polymer solid electrolyte, is sandwiched between graphite separator plates, and a large number of them are stacked to form a power generation unit. ing. The air electrode is formed by applying a carbon powder carrying a platinum catalyst on the surface of a porous carbon paper, and the fuel electrode is formed by applying a carbon powder carrying a platinum-ruthenium catalyst on the surface of the same carbon paper. .

  In the direct methanol fuel cell, when an aqueous methanol solution having a concentration of about 3% by weight is supplied to the fuel electrode as a liquid fuel (reducing agent) and air is supplied to the air electrode as an oxidant, the fuel electrode undergoes a fuel reaction. Carbon dioxide gas is generated from the air, and water is generated from the air electrode to generate an electromotive force. The generated carbon dioxide gas and water are discharged from the exhaust side together with the waste fuel and waste air. In such a direct methanol fuel cell, the remaining amount of the methanol aqueous solution in the fuel tank is accurately detected and replenished, or if the fuel tank is a cartridge type, it should be replaced quickly. However, it is indispensable for the stable operation of the fuel cell. In addition, it must be possible to detect that the aqueous methanol solution is flowing smoothly in the fuel supply pipe for introducing the liquid fuel from the fuel tank to the power generation unit.

  Known methods for detecting the remaining amount of aqueous methanol solution include a method for visually detecting the level of the aqueous methanol solution, a method for detecting with a float sensor, and a method for detecting with a photosensor.

Moreover, as a method for detecting that the aqueous methanol solution is flowing smoothly in the fuel supply pipe, a method described in Patent Document 1 is known. Although the method described in Patent Document 1 does not detect that the aqueous methanol solution is flowing smoothly, a light-transmitting tube is provided in a part of the liquid supply path, and light is emitted from the side of the tube. Attach a photosensor with a detection unit consisting of a light receiving unit and a light receiving unit, and read the change in the amount of light when the light projected from the light emitting unit passes through the wall surface of the tubular body and enters the light receiving unit over time It detects the presence or absence of liquid in the tube.
Japanese Patent Laid-Open No. 2003-248812

  In the above direct methanol fuel cell, the method of visually detecting the liquid level of the aqueous methanol solution has a problem in terms of reliability, and the method of detecting by a float sensor or a photo sensor has a problem in terms of the number of parts. In addition, in order to detect the liquid level of the fuel tank by the above-described method, visual processing must be provided in the fuel tank, or a float sensor or photosensor must be provided in the fuel tank. The direct methanol fuel cell using a tank has a problem in cost.

  In order to solve the above-described problems, the present invention provides a proton conductive polymer solid electrolyte, a fuel cell main body including a pair of air electrodes and fuel electrodes disposed on both sides thereof, A fuel tank that contains liquid fuel; a fuel supply pipe that introduces liquid fuel in the fuel tank into the fuel electrode of the fuel cell body; and an air introduction pipe that introduces oxygen in the air into the air electrode of the fuel cell body; And a direct methanol fuel cell system having a power generation unit in which a plurality of the fuel cell main bodies are stacked, the fuel supply pipe is made of a material that transmits electromagnetic waves, and the presence or absence of liquid fuel in the fuel supply pipe The present invention has a function of detecting the propagation state of electromagnetic waves and detecting the presence or absence of liquid fuel in the fuel supply pipe (Claim 1), and the direct methanol fuel cell system includes A high-concentration fuel tank for storing the high-concentration liquid fuel, and a high-concentration fuel supply pipe for introducing the high-concentration liquid fuel from the high-concentration fuel tank to the fuel tank. It has a function to detect the presence or absence of high-concentration liquid fuel in the high-concentration fuel supply pipe by detecting the propagation state of electromagnetic waves due to the presence or absence of high-concentration liquid fuel in the high-concentration fuel supply pipe. According to the present invention (Claim 2), the electromagnetic wave is ultraviolet light, visible light, infrared light or a combination thereof, and the fuel supply pipe is made of fluororesin, polypropylene, polyethylene, or silicon resin. It is made of an organic solvent-resistant and electromagnetic wave-transmitting material (claim 4).

  The present invention also detects the presence or absence of liquid fuel in the fuel supply pipe or the high-concentration fuel supply pipe by detecting the change caused by the air mixed into the fuel supply pipe or the high-concentration fuel supply pipe. (5), the high-concentration liquid fuel in the high-concentration fuel tank is reduced, so that air is mixed into the high-concentration fuel supply pipe, and a change in the propagation state of electromagnetic waves due to the air is detected. And an additional signal of the high-concentration liquid fuel is sent out (Claim 6), and the supply of the liquid fuel from the fuel tank to the fuel cell main body is stopped, whereby air is mixed into the fuel supply pipe, A change in the propagation state of the electromagnetic wave is detected and a system operation stop signal is transmitted (claim 7).

  Since the present invention is as described above, it is not necessary to provide visual processing in the fuel tank, or to provide a float sensor or photo sensor in the fuel tank, and all of the fuel supply pipes are electromagnetic waves. Therefore, it can contribute to the improvement of the cost of the direct methanol fuel cell using the cartridge type fuel tank.

Hereinafter, embodiments of the present invention will be described.
Example 1
FIG. 1 is a diagram showing a configuration of a direct methanol fuel cell system according to Embodiment 1 of the present invention.

  In FIG. 1, a fuel cell main body 1 includes a pair of fuel electrodes 3 and an air electrode 5 disposed on both sides of a proton conductive polymer solid electrolyte 4, and accommodates liquid fuel supplied to the fuel electrode 3. A fuel supply pipe 10 is provided between the fuel tank 2 and the fuel tank 2, and an air introduction pipe 11 for introducing oxygen in the air to the air electrode 5 through an air blower 21 is provided. ing. The power generation unit 6 includes a graphite fuel electrode side separator (not shown) on the opposite side of the surface of the fuel electrode 3 that is in contact with the proton conductive polymer solid electrolyte 4, and a proton conductivity of the air electrode 5. 40 graphite air electrode side separators (not shown) are arranged on the opposite side of the surface in contact with the solid polymer electrolyte 4 and are laminated. The fuel electrode side separator and the air electrode side separator may be located in the middle of the power generation unit so that the respective functions are provided on both sides of one plate.

  The fuel supply pipe 10 is made of a material that transmits electromagnetic waves in order to detect the presence or absence of liquid fuel. For example, when infrared rays are used as electromagnetic waves and a sensor in which an infrared light emitting diode and an infrared phototransistor are combined is used, a silicon tube is used for the fuel supply pipe 10 and liquid fuel is present in the fuel supply pipe 10. The sensor is arranged so that the electromagnetic wave irradiated from the infrared light emitting diode can be received by the infrared phototransistor through the silicon tube so that it can be detected. The material of the fuel supply pipe 10 can be changed as appropriate according to the type of electromagnetic wave used. That is, polypropylene and polyethylene can be used as materials other than silicon resin, and ultraviolet rays and visible rays can be used as electromagnetic waves other than infrared rays.

Using the direct methanol fuel cell system having such a structure, a methanol aqueous solution having a concentration of 3% by weight is accommodated as a liquid fuel in the fuel tank 2, the air flow rate is 5 liters / minute, and the fuel flow rate is 100 milliliters. Operating at a constant current density (100 mA / cm ² ) and a constant temperature (60 ° C.) to measure the current-voltage characteristics, and to the silicon tube as the fuel supply pipe 10 The output of the provided sensor was measured.

  As a result, while the liquid fuel is continuously supplied from the fuel tank 2, the current-voltage characteristic is stable and the output of the sensor shows a constant voltage value. When the liquid level in the vicinity of the liquid level detection line, the liquid fuel supplied from the fuel tank 2 is intermittent, and the current-voltage characteristics and the sensor output tend to be pulsed and unstable. It was.

  In the fuel tank 2, when the liquid level of the liquid fuel is lowered and near the liquid level detection line, air is mixed into the silicon tube as the fuel supply pipe 10 and part of the infrared rays of the sensor diffuses. By being done.

  Next, in a situation where there is sufficient liquid fuel in the fuel tank 2, when the silicon tube as the fuel supply pipe 10 is cut during operation, no output can be obtained from the sensor disposed in the silicon tube. It was recognized that the current-voltage characteristics declined rapidly.

From this, it can be seen that the occurrence of a failure that prevents the liquid fuel from being delivered to the fuel cell main body 1 was detected, and stopping the operation of the system by this signal can contribute to the safe operation of the system.
(Example 2)
FIG. 2 is a diagram showing a configuration of a direct methanol fuel cell system according to Embodiment 2 of the present invention. Components having the same functions as those in FIG. .

  In the second embodiment, a high concentration fuel tank 22 for storing high concentration liquid fuel and a high concentration fuel supply pipe 23 for introducing high concentration liquid fuel from the high concentration fuel tank 22 to the fuel tank 2 are provided. The concentration fuel supply pipe 23 is made of a material that transmits electromagnetic waves, and the presence or absence of the high concentration liquid fuel in the high concentration fuel supply pipe 23 can be detected by a change in the propagation state of the electromagnetic waves.

Using the direct methanol fuel cell system having such a configuration, a methanol aqueous solution having a concentration of 3% by weight is accommodated as a liquid fuel in the fuel tank 2, and a high concentration liquid fuel is contained in the high concentration fuel tank 22. , Containing an aqueous methanol solution having a concentration of 60% by weight, operating at a constant current density (100 mA / cm ² ) and a constant temperature (60 ° C.) with an air flow rate of 5 liters / minute, While measuring a current-voltage characteristic, the output of the sensor provided in the silicon tube as the high concentration fuel supply pipe 23 was measured. The high concentration liquid fuel was dropped from the high concentration fuel tank 22 into the fuel tank 2 at a constant rate so that the methanol concentration of the liquid fuel in the fuel tank 2 was maintained at 3% by weight.

  As a result, while the high-concentration liquid fuel is continuously supplied from the high-concentration fuel tank 22, the current-voltage characteristics are stable and the sensor output also shows a constant voltage value. When the liquid level of the high-concentration liquid fuel in the tank 22 is near the bottom surface, the high-concentration liquid fuel supplied from the high-concentration fuel tank 22 becomes intermittent, and the sensor output becomes pulsated and unstable. Thus, a decrease in voltage was observed.

  In the high concentration fuel tank 22, when the liquid level of the high concentration liquid fuel is near the bottom surface, air is mixed into the silicon tube as the high concentration liquid fuel supply pipe 23, and a part of the infrared rays of the sensor is This is due to the fact that the methanol concentration in the fuel tank 2 decreases due to a decrease in the supply amount of the high-concentration liquid fuel while being diffused.

  Next, in a situation where there is sufficient high-concentration liquid fuel in the high-concentration fuel tank 22, the silicon tube as the high-concentration liquid fuel supply pipe 23 was cut during operation. From the sensor disposed on the silicon tube, It was recognized that the output could not be obtained and the voltage dropped rapidly.

  From this, it can be seen that when the high-concentration liquid fuel in the high-concentration fuel tank 22 runs out, or the occurrence of a failure in which the high-concentration liquid fuel is not sent to the fuel tank 2 can be detected. The need for additional liquid fuel can be known, and shutting down the system with this signal can contribute to safe operation of the system.

  In Examples 1 and 2 described above, a membrane made of Nafion (registered trademark) 117 manufactured by DuPont was used as the proton conductive polymer solid electrolyte, and Pt- Using a carbon paper coated with Ru / C catalyst and Pt / C catalyst, the fuel cell body 1 is integrated into a membrane-electrode assembly (MEA) by a hot press method. It is sandwiched and laminated by a graphite separator plate.

  The above experiments were performed with the operating temperature, liquid fuel concentration, fuel flow rate, air flow rate, and current density kept constant, but it was also confirmed that detection was possible when these were arbitrarily changed.

  Further, in the above-described experiment, the material of the fuel supply pipe 10 and the high-concentration liquid fuel supply pipe 23 is made of silicon resin. However, it has resistance to organic solvents such as fluororesin, polypropylene, and polyethylene, and electromagnetic wave permeability. The resin is not particularly limited as long as it is a resin.

  In the direct methanol fuel cell system described above, sensors are provided in the fuel supply pipe 10 and the high-concentration liquid fuel supply pipe 23, but a liquid level detector is also provided in the fuel tank 2 and the high-concentration fuel tank 22. The reason why the sensor output could not be obtained is that the liquid level in the fuel tank 2 or the high-concentration fuel tank 22 has decreased, or that a problem has occurred in the liquid fuel supply system. You can make things understandable. That is, when a normal output is obtained from a sensor that detects the liquid level of the fuel tank 2 or the liquid level of the high concentration fuel tank 22, the liquid fuel supply system or the high concentration liquid fuel supply system is defective. It is thought that has occurred.

  According to the present invention, the presence or absence of liquid fuel in the fuel supply pipe for supplying liquid fuel from the fuel tank to the fuel cell main body can be easily detected. It can contribute to the stable operation of the system without causing a pole, and the industrial applicability of the direct methanol fuel cell system is great.

It is the figure which showed the structure of the direct methanol type fuel cell system which concerns on Example 1 of this invention. It is the figure which showed the structure of the direct methanol type fuel cell system which concerns on Example 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell main body 2 Fuel tank 3 Fuel electrode 4 Proton conductive polymer solid electrolyte 5 Air electrode 6 Sensor 10 Fuel supply pipe 11 Air introduction pipe 20 Fuel pump 21 Air blower 22 High concentration fuel tank 23 High concentration liquid fuel supply pipe

Claims (7)

Proton conductive polymer solid electrolyte, fuel cell main body provided with a pair of air electrode and fuel electrode disposed on both sides thereof, a fuel tank containing liquid fuel to be supplied to the fuel electrode, and the fuel cell A fuel supply pipe for introducing the liquid fuel in the fuel tank into the fuel electrode of the main body and an air introduction pipe for introducing oxygen in the air into the air electrode of the fuel cell main body, and a plurality of the fuel cell main bodies are stacked. In the direct methanol fuel cell system provided with the power generation section, the fuel supply pipe is made of a material that transmits electromagnetic waves, and the propagation state of the electromagnetic waves due to the presence or absence of liquid fuel in the fuel supply pipe is detected to detect the propagation state of the electromagnetic waves in the fuel supply pipe. A direct methanol fuel cell system having a function of detecting the presence or absence of liquid fuel. 2. The direct methanol fuel cell system according to claim 1, further comprising a high concentration fuel tank for storing high concentration liquid fuel, and a high concentration fuel supply pipe for introducing the high concentration liquid fuel from the high concentration fuel tank to the fuel tank. The high-concentration fuel supply pipe is made of a material that transmits electromagnetic waves, and the propagation state of the electromagnetic waves due to the presence or absence of the high-concentration liquid fuel in the high-concentration fuel supply pipe is detected to detect the high-concentration liquid fuel in the high-concentration fuel supply pipe. A direct methanol fuel cell system having a function of detecting the presence or absence of fuel. 3. The direct methanol fuel cell system according to claim 1, wherein the electromagnetic waves are ultraviolet rays, visible rays, infrared rays or a combination thereof. 3. The direct methanol type according to claim 1, wherein the fuel supply pipe or the high-concentration fuel supply pipe is made of an organic solvent-resistant electromagnetic wave-transmitting material made of fluororesin, polypropylene, polyethylene, or silicon resin. Fuel cell system. 5. The direct methanol fuel cell system according to claim 1, wherein air mixed in the fuel supply pipe or the high-concentration fuel supply pipe changes the propagation state of electromagnetic waves, and detects this change to supply fuel. A direct methanol fuel cell system that detects the presence or absence of liquid fuel in a pipe or a high concentration fuel supply pipe or the presence or absence of high concentration liquid fuel in a high concentration fuel supply pipe. 6. The direct methanol fuel cell system according to claim 5, wherein air is mixed into the high-concentration fuel supply pipe due to a decrease in the high-concentration liquid fuel in the high-concentration fuel tank, and a change in the propagation state of electromagnetic waves due to the air is detected. A direct methanol fuel cell system, wherein an additional signal of high-concentration liquid fuel is transmitted. 6. The direct methanol fuel cell system according to claim 5, wherein air is mixed into the fuel supply pipe by stopping the supply of liquid fuel from the fuel tank to the fuel cell body, and a change in the propagation state of electromagnetic waves due to the air is detected. A direct methanol fuel cell system characterized by transmitting a system stop signal.

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