JP5164691B2 - Fuel transport mechanism of direct alcohol fuel cell - Google Patents

Description

  The present invention relates to a fuel cell that can be used as a power source for various electric devices ranging from small devices such as notebook computers, mobile phones, and small video cameras to large devices such as automobiles and homes, and more particularly to the fuel supply device thereof. It is about.

  Direct alcohol type fuel cells are capable of generating electricity at relatively low temperatures, and have higher fuel energy densities due to the use of liquid fuels compared to fuel cells using flammable gases, and as a result Since the fuel container can be reduced in size, and hydrogen gas that is difficult to store is not used as fuel, the configuration of the entire fuel cell can be reduced. Therefore, it is a fuel cell that is promising as a power source for small portable devices such as notebook computers, mobile phones, and small video cameras.

  Conventional direct alcohol fuel cells have problems such as a small amount of electric power generated compared to a fuel cell using hydrogen gas as a fuel, and improvement of generated electric power has been an issue.

  Direct methanol fuel cells using methanol as the liquid fuel are divided into a liquid supply type that supplies liquid fuel directly to the battery body by a fuel supply method to the battery body, and a vaporization supply type that supplies vaporized methanol to the battery body. Broadly divided.

In the former liquid supply type methanol fuel cell, when methanol is supplied to the fuel side of the cell main body, the methanol permeates through an electrode made of a mesh-like metal and further forms a porous gas diffusion layer. Permeate to reach the catalyst layer. When methanol and water of the same amount or more reach or exist in the catalyst layer composed of a platinum / ruthenium mixture, the methanol is decomposed into carbon dioxide, protons, and electrons.
CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻
The carbon dioxide generated at this time is released to the outside through the gas diffusion layer and the electrode through which the fuel has permeated. The generated protons pass through the electrolyte membrane and move to the air supply side. Furthermore, the generated electrons pass through the porous gas diffusion layer, which is a conductor, and are captured by the electrodes, and move through the circuit formed between the electrodes on the opposite side (air supply side) to generate electricity. To do.

  The structure of the electrode is desirably a mesh shape so that liquid and gas can be easily transmitted and electricity can be easily captured. The electrode material is preferably a metal such as titanium, iron or copper plated with a noble metal such as platinum or gold so as not to be subject to electrical corrosion.

  The gas diffusion layer is preferably made of carbon fiber or carbon paper, which is easy to transmit liquid and gas, and is a good electrical conductor, like the electrode. More preferably, the material constituting the gas diffusion layer may be subjected to a hydration treatment so that the liquid can easily pass therethrough. In the hydration treatment, carbon fiber or the like is generally impregnated with tin oxide or the like.

On the air supply side, oxygen contained in the air sucked by the standard atmospheric pressure reaches the catalyst layer via the electrode and gas diffusion layer on the air supply side, and in the proton and electrolyte membrane that has moved from the fuel supply side, together with electrons Reaction produces water.
3 / 2O ₂ + 6H ⁺ + 6e ⁻ → 3H ₂ O

  In the above-described general methanol fuel cell, when the required power is to be stably taken out, it is necessary to supply methanol in a liquid state under the standard pressure without using external power. Is not sufficient for the stable extraction. Therefore, conventionally, a small pump is used to forcibly supply the fuel electrode while controlling the flow rate of methanol.

  When a similar fuel cell is used in a portable small electronic device such as a mobile phone, the fuel supply pump as described above cannot be adopted from the viewpoint of its size. In general, electric power is required to control the pump, and when a part of the electric power generated by the fuel cell is used for driving the pump, the output power of the entire fuel cell is reduced.

  As the latter vaporization supply type methanol fuel cell, a method of vaporizing methanol fed by a conventional pump and supplying it by a blower is known. The electrode reaction performance is higher than that of the liquid supply type, but this method also requires an auxiliary device such as a vaporizer, which leads to an increase in the size of the apparatus.

  Conventionally, it has been proposed to use a fuel supply medium having a wick structure that causes capillary action instead of a pump. By using the wick structure, a passive structure can be adopted instead of an active structure like a conventional fuel cell. In addition, since the energy supply related to the fuel supply can be suppressed as much as possible and the fuel supply structure can be suppressed to be small, the possibility of the power supply for small portable devices described above can be further increased.

  An example in which a fuel supply medium having a wick structure is proposed is described in the following patent document. Patent Documents 1 and 2 are configured to introduce liquid fuel into a stack using a capillary phenomenon. The liquid fuel introduced into the stack is vaporized by the reaction heat of the power generation unit and supplied to the power generation unit. By supplying the vaporized fuel, the electrode reactivity is increased and the output power is improved. Further, the gaseous fuel in the fuel vaporization layer is kept almost saturated. Therefore, liquid fuel is vaporized by the amount of fuel consumed by the cell reaction. Furthermore, liquid fuel is introduced into the unit cell by capillary action as much as it is vaporized.

  Further, in Patent Document 2, in addition to the structure of Patent Document 1, the pressure inside the fuel storage container is kept constant by mechanical pressure such as a spring sealed in the fuel storage container.

Japanese Patent No. 3442688 Japanese Patent No. 3668069

  The fuel cells described in Patent Documents 1 and 2 are configured to keep the pressure inside the fuel container constant and to push out liquid fuel and introduce it into the stack by the wick capillary phenomenon. Therefore, since the fuel supply amount is linked to the fuel consumption amount, the fuel supply amount depends on the fuel consumption amount of the power generation unit. Further, there is a risk that the fuel supply amount will be insufficient when the fuel cell is started. Furthermore, in order to adjust the fuel supply amount, it is necessary to increase or decrease the area of the unit cell.

  The present invention has been made paying attention to the above technical problem, and provides a fuel transportation mechanism for a direct alcohol fuel cell capable of stably supplying fuel without depending on the fuel consumption of the power generation unit. It is intended to provide.

  In order to achieve the above object, the invention of claim 1 is directed to generating a non-condensable gas by a catalytic reaction from a liquid gas generating agent, pressurizing the fuel with the non-condensable gas, and transporting it to the power generation unit. In the alcohol fuel cell, a porous member that fixes the catalyst and allows the non-condensable gas to permeate without allowing the liquid gas generating agent to permeate the non-condensable gas to the fuel. It arrange | positions in the pipe line to supply, It is characterized by the above-mentioned.

  According to a second aspect of the present invention, in the first aspect of the invention, the porous member is formed in a bottomed cylindrical shape with one end closed and the other end opened, and It is characterized by being inserted concentrically into a pipeline that feeds fuel and dividing the upstream side and the downstream side of the pipeline.

  A third aspect of the invention is characterized in that, in the first or second aspect of the invention, the porous member is formed of a porous ceramic.

  According to the first aspect of the present invention, since the liquid gas generating agent does not permeate the porous member, the reaction efficiency between the liquid gas generating agent and the catalyst fixed to the porous member can be improved.

  According to the invention of claim 2, in addition to the same effect as that of the invention of claim 1, since the porous member is formed in a bottomed cylindrical shape, it is compared with the case where the catalyst is fixed on a flat surface. Thus, the area for fixing the catalyst can be increased. Moreover, since it is inserted in the conduit for supplying the non-condensable gas to the fuel, space can be saved. Furthermore, since the porous member is formed in a bottomed cylindrical shape and inserted into the pipeline, the upstream side and the downstream side of the pipeline can be partitioned from the shape.

  According to the invention of claim 3, in addition to the effect similar to the effect of the invention of claim 1 or 2, since the porous member is formed of porous ceramic, the degree of freedom in shape design can be obtained and assembled. It is possible to improve the performance. Moreover, since the material is ceramic, heat resistance can be obtained.

  Next, a fuel transport mechanism of a direct alcohol fuel cell according to the present invention will be described based on examples. FIG. 1 schematically shows a porous member 1 according to the present invention. In the mechanism according to the present invention, alcohol as fuel is pumped by the non-condensable gas 2 and supplied to a power generation unit (not shown). The porous member 1 in the present invention has a porous structure that does not allow the liquid gas generating agent 3 that generates the non-condensable gas 2 to permeate but allows the non-condensable gas 2 generated by the catalytic reaction to permeate. Yes. A catalyst 4 for generating the non-condensable gas 2 from the liquid gas generating agent 3 by a catalytic reaction is fixed in these holes or surfaces. Therefore, for example, when the liquid gas generating agent 3 contacts the inner wall surface 1a, the non-condensable gas 2 generated by the catalytic reaction passes through the porous member 1 and is led out from the outer wall surface 1b to the conduit 5. On the other hand, when it contacts the outer wall surface 1b, the non-condensable gas 2 generated by the catalytic reaction passes through the porous member 1 and is led out from the inner wall surface 1a to the conduit 5. As a result, since the liquid gas generating agent 3 does not permeate the porous member 1, it is possible to prevent or suppress leakage of the unreacted liquid gas generating agent 3.

  FIG. 2 schematically shows an example in which the porous member 1 is inserted into a conduit 5 that supplies the non-condensable gas 2. A gap generated between the porous member 1 and the pipe line 5 is filled with a sealing material 6 such as an O-ring 6 so that the liquid gas generating agent 3 is not leaked. A wick 7 is inserted in contact with the inner wall 1 a of the porous member 1. Therefore, the liquid gas generating agent 3 is fed by the capillary force generated by the wick 7. When the liquid gas generating agent 3 fed by the capillary force generated by the wick 7 comes into contact with the inner wall surface 1a, the non-condensable gas 2 generated by the catalytic reaction passes through the porous member 1 from the outer wall surface 1b. It is led out to the pipeline 5. On the contrary, when the wick 7 is provided in contact with the outer wall surface 1b, the liquid gas generating agent 3 is supplied to the outer wall surface 1b by the wick 7, and the non-condensable gas 2 generated by the catalytic reaction is generated. It passes through the porous member 1 and is led out from the inner wall surface 1 a to the pipe 5. As a result, the gap formed between the porous member 1 and the pipe line 5 is filled with the sealing material 6 such as the O-ring 6, thereby preventing or suppressing leakage of the unreacted liquid gas generating agent 3. Can do. Moreover, it is possible to prevent or suppress the non-condensable gas 2 generated by the catalytic reaction from flowing backward. Furthermore, since the wick 7 is used to supply the liquid gas generating agent 3, the liquid gas generating agent 3 can be supplied without stagnation.

  FIG. 3 schematically shows an apparatus for evaluating the amount of oxygen generated by the fuel transport mechanism of a direct alcohol fuel cell according to the present invention. The liquid gas generating agent 3 is configured to be stored in the gas generating agent tank 8. Moreover, the gas generating agent 3 is comprised so that it may introduce | transduce into the porous member 1 inserted in the inside of the pipe line 5 by the wick 7 which has capillary force. The amount of the non-condensable gas 2 introduced into the porous member 1 and generated by the catalytic reaction was collected in the beaker 9 and measured by the water displacement method. FIG. 4 shows a simplified enlarged view of the porous member 1 and the wick 7 inserted into the pipe line 5 in FIG.

As the liquid gas generating agent 3, 3 vol% hydrogen peroxide solution 3 diluted with water was used. Manganese dioxide 4 was used as the catalyst 4 for decomposing the hydrogen peroxide 3 and generating the non-condensable gas 2. Hydrogen peroxide 3 is decomposed by the catalytic action of manganese dioxide 4 to generate oxygen 3 which is a non-condensable gas 3.
2H ₂ O ₂ → 2H ₂ O + O ₂

Manganese dioxide 4 was fixed to the porous member 1 by sintering. Specifically, the porous member 1 previously washed is immersed in manganese nitrate (hexahydrate) diluted with ethanol so as to have a concentration of 10 vol% for 30 minutes at 105 ° C. for 1 hour. After drying, it was supported by heating at 400 ° C. for 1 hour in an oxygen atmosphere.
Mn (NO ₂ ) → MnO ₂ + NO ₂
Platinum other than manganese dioxide 4 may be used for the catalyst 4 for decomposing hydrogen peroxide 3. As the porous member 1, an alumina tube 1 having an average pore diameter of 10 μm was used.

  FIG. 5 shows the oxygen generation amount of the alumina tube 1 configured as described above. As a comparison object, the above-described glass wick ex1 and 1.5 times longer glass wick ex2 and twice as long glass wick ex3 are used as a reference based on the length of the alumina tube 1 described above. The manganese dioxide 4 was immobilized and evaluated by the same method as described above. The thickness of the glass wick was the same as that of the alumina tube 1. As a result, compared with the case where the catalyst 4 was fixed to the wick 7, the amount of oxygen generated when the catalyst 4 was fixed to the porous member 1 was the largest. That is, the amount of decomposition of the hydrogen peroxide solution 3 by the catalyst 4 depends on the amount of the catalyst 4, and particularly depends on the surface area on which the catalyst 4 is immobilized, so it can be said that the effective area of the porous member 1 is wide. In other words, compared with the case where the catalyst 4 is fixed to the wick 7, the porous member 1 has a large effective area on which the catalyst 4 is fixed, so that a sufficient oxygen generation amount can be secured. In addition, since the effective area is large, it can contribute to miniaturization of the fuel cell.

  FIG. 6 shows the result of adjusting the average pore diameter of the alumina tube 1 and confirming the presence or absence of leakage of the hydrogen peroxide solution 3 from the gap formed between the pipe 5 and the porous member 1. When the average pore diameter measured after the catalyst 4 was fixed was smaller than 50 μm, no leakage of the hydrogen peroxide solution 3 was observed from the gap. On the contrary, when the average pore diameter was larger than 50 μm, leakage of the hydrogen peroxide solution 3 from the gap was observed. When the hydrogen peroxide solution 3 leaks from the gap, the amount of contact between the catalyst 4 fixed to the porous member 1 and the hydrogen peroxide solution 3 decreases, so the amount of oxygen generated decreases. Therefore, the catalytic reaction between the catalyst 4 and the hydrogen peroxide solution 3 can be optimized by adjusting the average pore diameter of the porous member 1 to be smaller than 50 μm.

  In addition, although the example which used the alumina for the porous member 1 was shown in the example mentioned above, you may use the other material which can adjust an average hole diameter to the range shown in FIG.

It is a figure which shows typically the porous member in this invention. It is a figure which shows typically the example of arrangement | positioning of the porous member in this invention. It is a figure which shows typically the apparatus which evaluates the non-condensable gas generation amount of the porous member in this invention. It is a figure which shows typically the porous member and wick which were inserted in the pipe line. It is a figure which shows typically the oxygen generation amount of the porous member in this invention. It is a figure which shows typically the relationship between the average hole diameter of the porous member in this invention, and the presence or absence of the leakage of hydrogen peroxide water.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Porous member, 2 ... Non-condensable gas, 3 ... Gas generating agent, 4 ... Catalyst, 5 ... Pipe line.

Claims (3)

In a direct alcohol fuel cell that generates a non-condensable gas from a liquid gas generant by a catalytic reaction, pressurizes the fuel with the non-condensable gas, and transports the fuel to a power generation unit.
A porous member that fixes the catalyst and allows the non-condensable gas to permeate without allowing the liquid gas generating agent to permeate is provided in a pipe that supplies the non-condensable gas to the fuel. A fuel transport mechanism for a direct alcohol fuel cell, wherein the fuel transport mechanism is arranged.   The porous member is formed in a bottomed cylindrical shape with one end closed and the other end opened, and is inserted concentrically into a conduit for sending the non-condensable gas to the fuel. 2. The fuel transport mechanism for a direct alcohol fuel cell according to claim 1, wherein an upstream side and a downstream side of the pipe are partitioned.   3. The fuel transport mechanism for a direct alcohol fuel cell according to claim 1, wherein the porous member is made of porous ceramic.

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