JP2009070570A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell which can supply a liquid fuel uniformly and efficiently and can improve an output. <P>SOLUTION: The fuel cell includes a fuel electrode, an electrolyte membrane which is arranged neighboring with the fuel electrode and transmits cations from the fuel electrode, an oxidant electrode which is arranged to face the fuel electrode with the electrolyte membrane in-between and makes the cations transmitting the electrolyte membrane reacted with the cations, a fuel supplying mechanism for supplying the liquid fuel to the fuel electrode, and a fuel diffusion layer which is arranged on a side of the fuel supplying mechanism and a fuel absorbing layer arranged on a side of the fuel electrode, both arranged between the fuel electrode and the fuel supplying mechanism. The fuel absorbing layer has a plurality of layers having different wettabilities against the liquid fuel in a thickness direction, and a layer arranged on the side of the fuel electrode is made of a material having a higher wettability than that of the layer arranged on the side of the fuel diffusion layer and, moreover, can impregnate more liquid fuel in itself than the fuel diffusion layer. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel cell including a fuel electrode, an electrolyte membrane, and an oxidant electrode.

  A fuel cell is a generator that generates electricity by supplying a hydrogen-containing gas or organic alcohol or the like and an oxygen-containing gas to an electrode. Usually, a fuel electrode and an oxidant electrode face each other through an electrolyte membrane. The basic structure is arranged. In such a basic structure, hydrogen is oxidized on the fuel electrode, and the generated hydrogen ions are transferred to the oxidant electrode side through the electrolyte membrane. In the oxidant electrode, the transferred hydrogen ions and the supplied oxygen are transferred. Reacts to produce water, and electrons circulate through an external circuit to produce electrical energy.

  The fuel cell is attracting attention as a clean power generation system because it generates less load on the environment due to power generation. Among fuel cells, a polymer electrolyte fuel cell using a solid polymer membrane having a hydrogen ion conductor as an electrolyte membrane has been proposed for use as a mobile power source for space use and vehicle use.

  Here, FIG. 11 is a cross-sectional view schematically showing a polymer electrolyte fuel cell 101 as disclosed in, for example, Japanese Patent Application Laid-Open No. 2003-86192 (Patent Document 1) as an example of a conventional typical fuel cell. FIG. The polymer electrolyte fuel cell 101 of the example shown in FIG. 11 includes a power generation element 102 in which a fuel electrode 103 and an oxidant electrode 104 are arranged to face each other with an electrolyte membrane 105 interposed therebetween, for example. Flow path plates 106 and 107 are disposed on both sides of the power generation element 102, respectively, and a fuel flow path 108 for supplying fuel to the fuel electrode 103 and an oxidant flow for supplying oxidant to the oxidant electrode 104. A passage 109 is formed.

  As a fuel for a polymer electrolyte fuel cell, methanol that can provide high energy efficiency and high output is currently promising. In general, a diluted fuel obtained by diluting the fuel with water to about 1 to 3 mol / l is used. Further, as the oxidant, it is common to use oxygen contained in the atmosphere. The chemical reactions occurring at the fuel electrode and the oxidant electrode are expressed by the following reaction formulas (1) and (2).

CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻ (1)
3 / 2O ₂ + 6H ⁺ + 6e ⁻ → 3H ₂ O (2)
In the polymer electrolyte fuel cell 101 as shown in FIG. 11, a fuel diffusion layer 110 is usually interposed between the fuel electrode 103 and the fuel flow path plate 106, and the liquid fuel passes through this fuel diffusion layer 110 and the fuel electrode 103 to be supplied. Similarly, an oxidant diffusion layer 111 is interposed between the oxidant electrode 104 and the oxidant flow path plate 107, and the oxidant is supplied to the oxidant electrode 104 through the oxidant diffusion layer 111. The Here, FIG. 12 is a partially enlarged view showing the vicinity of the fuel diffusion layer 110 of the conventional polymer electrolyte fuel cell 101 shown in FIG. 11 and 12, in order for liquid fuel to be always supplied to the fuel electrode 103, the liquid fuel has a flow in a direction from the fuel flow path 108 side toward the fuel electrode 103 side. Is desired.

  However, as shown in FIG. 12, since the liquid fuel in the fuel flow path 108 flows in one direction (direction A in FIG. 12) while diffusing into the fuel diffusion layer 110, the pressure in the fuel flow path 108 is increased. Is reduced by the pressure loss along the direction, and the amount of the liquid fuel that permeates the fuel diffusion layer 110 is more likely to decrease as it becomes downstream in the direction. For this reason, the supply of the liquid fuel to the fuel electrode 103 may become uneven, or a portion where the supply of the liquid fuel is insufficient may occur. A fuel cell having a portion where supply of liquid fuel to the fuel electrode 103 is insufficient causes a problem that sufficient output cannot be obtained. In particular, when trying to stack a fuel cell in a smaller volume, it is necessary to reduce the cross section of the fuel flow path and reduce the thickness of the flow path plate. The supply of liquid fuel to the electrodes tends to be uneven.

In the structure as shown in FIG. 11, in order to supply a sufficient amount of liquid fuel to the fuel electrode 103, a method of feeding the liquid fuel by a fuel pump or the like installed outside can be considered. However, in this case, a part of the electric power generated by the fuel cell is used for the operation of the fuel pump and the like, leading to deterioration of the power generation efficiency of the entire fuel cell.
JP 2003-86192 A

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a fuel cell capable of supplying liquid fuel uniformly and efficiently and improving output. is there.

  The fuel cell of the present invention includes a fuel electrode that generates cations from liquid fuel, an electrolyte membrane that is disposed adjacent to the fuel electrode and that allows cations from the fuel electrode to pass therethrough, and is opposed to the fuel electrode through the electrolyte membrane. And an oxidant electrode that reacts the cation and the oxidant that have passed through the electrolyte membrane, a fuel supply mechanism for supplying liquid fuel to the fuel electrode, and an intervening between the fuel electrode and the fuel supply mechanism A fuel diffusion layer disposed on the fuel supply mechanism side and a fuel absorption layer disposed on the fuel electrode side, and the fuel absorption layer has two or more layers having different wettability with respect to the liquid fuel in the thickness direction. The layer disposed on the fuel electrode side is formed of a material having higher wettability than the layer disposed on the fuel diffusion layer side, and is configured so that more liquid fuel can be impregnated inside than the fuel diffusion layer. It is characterized by

  In the fuel cell of the present invention, it is preferable that the fuel absorption layer is configured to have a higher absorption rate in the surface direction with respect to the liquid fuel than the fuel diffusion layer.

  Further, in the fuel cell of the present invention, the layer disposed on the fuel electrode side of the fuel absorption layer has a higher absorption rate in the plane direction with respect to the liquid fuel than the layer disposed on the fuel diffusion layer side of the fuel absorption layer. It is preferable that it is comprised.

  In the fuel cell of the present invention, it is preferable that the layer disposed on the fuel electrode side of the fuel absorption layer includes a fibrous material extending radially in the plane direction. In this case, the fibrous material is more preferably hydrophilic.

  In the fuel cell of the present invention, the layer disposed on the fuel diffusion layer side of the fuel absorption layer preferably has a smaller thickness than the layer disposed on the fuel electrode side of the fuel absorption layer.

The fuel cell of the present invention preferably has one or more holes penetrating in the thickness direction.
In the fuel cell of the present invention, the side surface of the fuel absorption layer is preferably covered with a material that is impermeable to liquid fuel.

  In the fuel cell of the present invention, it is preferable that a conductive film is formed on the surface of the layer disposed on the fuel diffusion layer side of the fuel absorption layer.

  According to the fuel cell of the present invention, the fuel absorption layer is configured to be able to impregnate more liquid fuel than the fuel diffusion layer, so that the liquid fuel discharged from the fuel diffusion layer or the fuel flow path Can be efficiently absorbed in the fuel absorption layer, and the liquid fuel necessary for the fuel electrode can be supplied from the fuel absorption layer, thereby improving the output of the fuel cell. The fuel absorption layer has two or more layers having different wettability with respect to the liquid fuel in the thickness direction, and the layer disposed on the fuel electrode side is higher in wettability than the layer disposed on the fuel diffusion layer side. In the fuel absorption layer, the flow direction of the liquid fuel can be controlled and the supply of the liquid fuel to the fuel electrode becomes uneven or the supply of the liquid fuel is insufficient. Does not occur. As a result, a fuel cell can be provided in which liquid fuel can be supplied uniformly and efficiently, and output can be improved.

  FIG. 1 is a cross-sectional view schematically showing a preferred example fuel cell 1 of the present invention. The fuel cell 1 of the present invention includes a fuel electrode 3, an electrolyte membrane 4 disposed adjacent to the fuel electrode 3, and an oxidant electrode 5 disposed opposite to the fuel electrode 3 through the electrolyte membrane 4. The power generation element 2 configured is basically provided. In addition to the basic configuration described above, the fuel cell 1 of the present invention has a fuel supply mechanism for supplying liquid fuel to the fuel electrode 3 (in the example shown in FIG. 1, the side adjacent to the electrolyte membrane 4 of the fuel electrode 3 is A fuel flow path plate 6) having a fuel flow path 7 provided on the opposite side, a fuel diffusion layer 8 disposed on the fuel supply mechanism side between the fuel supply mechanism and the fuel electrode 3, and a fuel The fuel absorbing layer 9 disposed on the electrode 3 side is interposed.

  The fuel electrode 3 in the fuel cell 1 of the present invention is realized by a resin layer containing a metal catalyst, but can be made of a conventionally known material, and a platinum-ruthenium alloy or the like is used as an example of the metal catalyst. In addition, alloys such as platinum and gold, platinum and osmium, platinum and rhodium can be used. Further, as the resin layer of the fuel electrode 3, for example, a perfluoroalkyl sulfonic acid resin is used.

  The electrolyte membrane 4 in the fuel cell 1 of the present invention can be made of a conventionally known material regardless of whether it is an organic material or an inorganic material as long as it is a proton-conductive heat-resistant and acid-resistant material. A sulfonic acid group-containing perfluorocarbon (Nafion 117 (manufactured by DuPont)) can be used. In addition, as long as the electrolyte membrane 4 in the fuel cell 1 of the present invention has a proton-conducting function, it may be realized by a structure in which the electrolyte membrane is embedded in another base material.

  Further, the oxidant electrode 5 in the fuel cell 1 of the present invention is realized by, for example, a resin layer containing a metal catalyst, as in the case of the fuel electrode 3 described above. What was formed with the appropriate material used widely can be used. The metal catalyst that can be used for the oxidant electrode 5 is not particularly limited, and platinum, platinum-ruthenium alloy, platinum-gold alloy, platinum-osmium alloy, platinum-rhodium alloy, and the like are preferably used. Since the influence of poisoning by CO is small on the oxidant electrode side, platinum can be used. The resin material used for forming the oxidant electrode 5 is not particularly limited, and can be made of a conventionally known material. For example, a perfluoroalkylsulfonic acid resin is used.

In the fuel cell 1 of the present invention, the power generating element 2 composed of the fuel electrode 3, the electrolyte membrane 4 and the oxidant electrode 5 described above generates power by the following fuel cell reaction. First, liquid fuel (for example, a mixture of methanol (CH ₃ OH) and water (H ₂ O)) is supplied from the fuel flow path plate 6 to the fuel electrode 3 through the fuel diffusion layer 8 and the fuel absorption layer 9. Then, cations (for example, hydrogen ions (H ⁺ )) are generated from the liquid fuel at the fuel electrode 3. At this time, carbon dioxide as an electron and exhaust gas is generated together with the cation. The cations generated at the fuel electrode 3 permeate the electrolyte membrane 4 and move to the oxidant electrode 5 side. On the other hand, electrons generated by the fuel electrode 3 are guided from the fuel electrode 3 to the oxidant electrode 5 via an external circuit (not shown). The cation transferred to the oxidant electrode 5 reacts with the oxidant (for example, oxygen (O ₂ )) and electrons at the oxidant electrode 5 to generate water. That is, for example, the liquid fuel is a mixture of methanol (CH ₃ OH) and water (H ₂ O), and the cation generated at the fuel electrode 3 is hydrogen ion (H ⁺ ), which is supplied to the oxidant electrode 5. When the oxidizing agent to be used is oxygen (O ₂ ), chemical reactions as shown in the following reaction formulas (1) and (2) occur.

CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻ (1)
3 / 2O ₂ + 6H ⁺ + 6e ⁻ → 3H ₂ O (2)
The fuel cell of the present invention further includes a mechanism (fuel supply mechanism) for supplying liquid fuel to the fuel electrode 3 described above. FIG. 1 shows, as an example, a case where a fuel supply mechanism is realized by a fuel flow path plate 6 having a fuel flow path 7 disposed on the opposite side of the fuel electrode 3 from the side adjacent to the electrolyte membrane 4. ing. In this case, the fuel flow path plate 6 is not particularly limited as long as it is an appropriate substrate that is not permeable to liquid fuel. For example, a metal substrate, a silicon substrate, a glass substrate, a resin substrate, or the like is used. Can be realized. Among these, from the viewpoint of mass productivity, a silicon substrate compatible with an existing silicon device manufacturing process is preferable. In FIG. 1, a fuel flow path plate 6 is formed of a silicon substrate on which a fuel flow path 7 is formed by microfabrication. An example of realizing is shown. The shape and size of the fuel flow path 7 are not particularly limited as long as the fuel flow path 7 forms a flow path for supplying liquid fuel to the fuel diffusion layer 8. Further, the fuel supply mechanism in the fuel cell of the present invention is not limited to the fuel flow path plate 6 having the fuel flow path 7 as shown in FIG. 1, for example, adjacent to the liquid fuel storage tank, It may be realized by a porous material capable of transporting liquid fuel to the fuel diffusion layer 8 by capillary action.

  The fuel diffusion layer 8 disposed on the fuel supply mechanism side between the fuel supply mechanism and the fuel electrode 3 described above includes, for example, carbon paper, a sintered body of carbon, porous silicon, porous silicon oxide, A porous material such as a sintered metal such as nickel or a foam metal is used. Among them, it is preferable that the fuel diffusion layer 8 is realized by carbon paper that is chemically stable and can carry a catalyst on the fiber. The fuel diffusion layer 8 is usually made of a material having a porosity of about 70 to 80%.

  In the fuel cell 1 of the present invention, the fuel absorption layer 9 disposed on the fuel electrode 3 side between the fuel supply mechanism and the fuel electrode 3 described above has two or more layers having different wettability with respect to the liquid fuel in the thickness direction. And the layer disposed on the fuel electrode 3 side is made of a material having higher wettability than the layer disposed on the fuel diffusion layer 8 side, and the entire fuel absorption layer 9 is more than the fuel diffusion layer 8. The main feature is that it is configured so that a large amount of liquid fuel can be impregnated therein. According to the fuel cell 1 of the present invention, the fuel absorption layer 9 can be impregnated with more liquid fuel than the fuel diffusion layer 8, so that the fuel diffusion layer 8 or the fuel flow path can be obtained. The liquid fuel discharged from the fuel cell 7 is efficiently absorbed by the fuel absorption layer 9, and the necessary liquid fuel can be supplied from the fuel absorption layer 9 to the fuel electrode 3, thereby improving the output of the fuel cell. . In addition, the fuel absorption layer 9 has two or more layers having different wettability with respect to the liquid fuel in the thickness direction, and the layer disposed on the fuel electrode 3 side is more wettable than the layer disposed on the fuel diffusion layer 8 side. By being formed of a high material, the flow direction of the liquid fuel can be controlled in the fuel absorption layer 9, and the supply of the liquid fuel to the fuel electrode 3 becomes uneven or the supply of the liquid fuel There will be no shortage. As a result, the fuel cell 1 can be provided in which the liquid fuel can be supplied uniformly and efficiently, and the output can be improved.

  As described above, the fuel absorption layer 9 is realized so that more liquid fuel can be impregnated inside than the fuel diffusion layer 8. In other words, for the formation of the fuel absorption layer 9, a structure or material that easily absorbs and permeates liquid fuel is selected. Specifically, the fuel absorption layer has a methanol absorption capacity of 1.66 g / g, whereas the fuel absorption layer has a methanol absorption capacity of 4.55 g / g. Note that the fuel absorption layer 9 can be impregnated with more liquid fuel than the fuel diffusion layer 8 by, for example, measuring the weight before and after the fuel absorption layer and the fuel diffusion layer are impregnated with the liquid fuel. Can do.

  In the fuel cell of the present invention, the fuel absorption layer 9 can be impregnated with liquid fuel more than the fuel diffusion layer 8, so that the liquid fuel that has been discharged unevenly from the fuel diffusion layer 8 can be absorbed quickly by the fuel absorption layer 9. And penetrates into the fuel absorption layer 9. In general, since the fuel diffusion layer 8 is configured to be impregnated with liquid fuel rather than the fuel electrode 3, the fuel absorption layer 9 can be impregnated with liquid fuel rather than the fuel electrode 3. As a result, the fuel electrode 3 is less likely to penetrate liquid fuel than the fuel absorption layer 9, and a sufficient amount of liquid fuel is temporarily accumulated in the fuel supply layer 9. The liquid fuel temporarily impregnated in the layer 9 will be supplied.

Here, FIG. 2 is a partially enlarged view showing the vicinity of the fuel absorption layer 9 of the fuel cell 1 of the present invention. In FIG. 2, the fuel absorption layer 9 is simplified as one layer for convenience. As described above, the fuel absorption layer 9 allows the liquid fuel to penetrate more easily than the fuel diffusion layer 8, and the liquid fuel is temporarily accumulated in the fuel absorption layer 9. For this reason, in the fuel cell 1 of the present invention, unlike the conventional fuel cell having no fuel absorbing layer as shown in FIGS. 11 and 12, the flow of the fuel flow path 7 as shown in FIG. It is hard to be influenced by the nonuniformity of the liquid fuel that permeates the fuel diffusion layer 8 due to the pressure loss along the direction of. In addition, since the fuel absorption layer 9 adjacent to the fuel electrode 3 can contain a large amount of liquid fuel, the fuel cell operates at a high output, and a large amount of liquid fuel is consumed due to the reaction at the fuel electrode 3. However, the liquid fuel can be uniformly supplied to the fuel electrode 3 without causing a local supply shortage of the liquid fuel. Further, in the fuel cell 1 of the present invention, the fuel absorption layer 9 impregnated with a large amount of liquid fuel is provided adjacent to the fuel electrode 3 side of the fuel diffusion layer 8, so that CO ₂ as a reaction product can be obtained. There is also an advantage that emissions are not easily inhibited.

  Here, FIG. 3 shows a fuel cell when the fuel absorption layer is provided as in the present invention (solid line in the figure) and when the fuel absorption layer is not provided as in the conventional example (broken line in the figure). Is a graph showing the comparison of output characteristics, wherein the vertical axis represents output (au) and the horizontal axis represents current (mA). As shown in FIG. 3, when the fuel absorption layer is provided as in the fuel cell of the present invention, the liquid fuel is uniformly supplied to the fuel electrode, and the fuel absorption layer is not provided as in the conventional example. It can be seen that a higher output can be obtained than FIG. 3 shows, for example, a conventionally known and generally used current source, a battery characteristic measuring circuit including a voltmeter, a liquid fuel supply pump (manufactured by ISMATEC), and a mass flow controller for adjusting the air flow rate. The result measured using (made by STEC) is shown.

  Further, even when a fuel absorption layer capable of impregnating more liquid fuel than the fuel diffusion layer is provided between the fuel diffusion layer and the fuel electrode, when the fuel absorption layer is only one layer. It is difficult to obtain a stable flow of liquid fuel in the direction from the fuel diffusion layer side to the fuel electrode side. Therefore, in the fuel cell of the present invention, as described above, the fuel absorption layer 9 has two or more layers having different wettability with respect to the liquid fuel in the thickness direction, and the layer disposed on the fuel electrode 3 side is the fuel diffusion layer. It is made of a material having higher wettability than the layer disposed on the layer 8 side.

  Here, FIG. 4 is a partially enlarged view showing the vicinity of the fuel absorbing layer 9 in the fuel cell 1 of the present invention. FIG. 4 shows a case where the fuel absorption layer 9 is realized by two layers of a first absorption layer 11 arranged on the fuel supply mechanism side and a second absorption layer 12 arranged on the fuel electrode 3 side. ing. In addition, the fuel absorption layer in this invention should just be two or more layers, and is not limited to a two-layer structure as shown in FIG. In the example shown in FIG. 4, the liquid fuel discharged from the fuel diffusion layer 8 first passes through the first absorption layer 11 disposed on the fuel diffusion layer 8 side, and then the second fuel disposed on the fuel electrode 3 side. It passes through the absorption layer 12 and is carried to the fuel electrode 3. At this time, if the first absorbent layer has higher wettability than the second absorbent layer, the liquid fuel is difficult to permeate from the first absorbent layer to the second absorbent layer. The liquid fuel returns to the diffusion layer. In the fuel cell of the present invention, the second absorbent layer 12 disposed on the fuel electrode 3 side is configured to have higher wettability than the first absorbent layer 11 disposed on the fuel diffusion layer 8 side. Liquid fuel is likely to permeate from the first absorbent layer 11 to the second absorbent layer 12. In addition, since liquid fuel is fed into the fuel diffusion layer 8 from the fuel flow path 7, the fuel diffusion layer 8 is normally kept at a higher pressure than the fuel absorption layer 9, and the second absorption layer Since the pressure in 12 is not sufficiently high, the liquid fuel does not return to the fuel diffusion layer 8 side. Thereby, the liquid fuel can be efficiently held in the fuel absorption layer 9 adjacent to the fuel electrode 3, and the fuel cell 1 having a stable battery output can be realized. Furthermore, as described above, the liquid fuel has a property that it is difficult to return, so that the output dependency on the installation direction when using the fuel cell is reduced, and even when the fuel electrode side is arranged on either the upper or lower side. There is also an advantage that a constant output can be obtained.

  On the other hand, even if there are two or more layers having different wettability with respect to the liquid fuel in the thickness direction between the fuel diffusion layer and the fuel electrode, they are arranged on the fuel diffusion layer side of the fuel absorption layer. When the wetted layer has a higher wettability with respect to the liquid fuel than the layer disposed on the fuel electrode side, the liquid fuel is retained in the layer disposed on the fuel diffusion layer side, and the layer disposed on the fuel electrode side Therefore, the amount of liquid fuel in the immediate vicinity of the fuel electrode is insufficient, and the battery output is reduced. Further, in this case, the layer disposed on the fuel diffusion layer side of the fuel absorption layer cannot perform the function of suppressing the backflow of the liquid fuel to the fuel diffusion layer. For example, in order to prevent this, Even if the layer for preventing the backflow of the liquid fuel is formed at the interface with the fuel flow path, the liquid fuel will flow back into the fuel diffusion layer, so the amount of the liquid fuel contained in the fuel absorption layer May be insufficient. In addition, it is conceivable to form a layer for suppressing the back flow of the liquid fuel described above on the surface of the fuel diffusion layer adjacent to the fuel absorption layer, but the fuel diffusion layer is usually denser than the fuel absorption layer. Therefore, when such a layer is formed, there is a problem that the movement of liquid fuel from the fuel diffusion layer to the fuel absorption layer is also hindered. Therefore, as in the fuel cell of the present invention, the fuel absorption layer is realized so that the layer disposed on the fuel electrode 3 side is formed of a material having higher wettability than the layer disposed on the fuel diffusion layer 8 side. Thus, the above-described effects can be exhibited with a simple configuration and without causing problems.

  In addition, the “wetting property” of the fuel absorption layer with respect to the liquid fuel is generally evaluated by a contact angle formed between the water droplet and the material surface when a predetermined amount of water droplet is brought into contact with the surface of the material placed horizontally. (Droplet method) property. That is, the smaller the contact angle measured by the droplet method, the higher the wettability. In the fuel cell 1 of the present invention, the above-described fuel absorption layer is realized by forming the layer disposed on the fuel electrode 3 side with a material having higher wettability than the layer disposed on the fuel diffusion layer 8 side. Therefore, in the fuel absorption layer 9, the first absorption layer 11 disposed on the fuel diffusion layer 8 side has hydrophobicity, and the second absorption layer 12 disposed on the fuel electrode 3 side is obtained. It is preferable that has hydrophilicity. Here, “hydrophilic” in the present invention means that the contact angle measured by the above-described droplet method is 40 degrees or less, and “hydrophobic” means that the contact angle measured similarly is 90 °. It means that it is more than degree. As a particularly suitable case, the first absorption layer 11 is formed of a hydrophobic material having a contact angle of about 100 degrees (for example, a material in which a hydrophobic film is formed on the surface of a fibrous material made of polypropylene or polyethylene). An example in which the second absorbent layer 12 is formed of a superhydrophilic material having a contact angle of 10 degrees or less (for example, a highly absorbent fibrous material mainly composed of cellulose) can be given.

  The fuel cell 1 of the present invention is also preferably configured such that the fuel absorption layer 9 has a higher absorption speed in the surface direction with respect to the liquid fuel than the fuel diffusion layer 8. In the present invention, the “absorption rate in the plane direction” with respect to the liquid fuel refers to the absorption rate of the liquid fuel in the direction along the plane perpendicular to the thickness direction of the fuel absorption layer 9. Note that the fuel absorption layer is configured so that the absorption speed in the plane direction with respect to the liquid fuel is larger than that of the fuel diffusion layer. For example, the 2.3 cm × 0.5 cm square dry fuel diffusion layer and the fuel absorption This can be confirmed by contacting a part of the layer with methanol and measuring the time required for the entire surface of the fuel diffusion layer and the fuel absorption layer to be filled with methanol. Specifically, the case where the time measured in this way was 1 minute 18 seconds in the fuel diffusion layer, but 0 minute 2 seconds in the fuel absorption layer is exemplified. Such a difference in the absorption speed with respect to the surface direction with respect to the liquid fuel is adjusted by, for example, using fibrous materials having different wettability for the fibrous materials constituting the layers, or using fibrous materials having different shapes. Can do.

  FIG. 5 is a partially enlarged view showing the vicinity of the fuel absorption layer 9 when the fuel absorption layer 9 is configured to have a higher absorption rate for liquid fuel than the fuel diffusion layer 8. In FIG. 5, for convenience, the fuel absorption layer 9 is shown as a single layer in a simplified manner. Since the pressure in the fuel flow path 7 decreases due to the pressure loss along the flow of the liquid fuel in the fuel flow path 7, the amount of liquid fuel passing through the fuel diffusion layer 8 does not decrease as it becomes downstream in the above direction. As described above. At this time, the fuel absorption layer 9 is configured so that the absorption speed in the surface direction with respect to the liquid fuel is larger than that of the fuel diffusion layer 8, so that the fuel supply to the fuel diffusion layer 8 is performed as shown in FIG. Even if this is not uniform, a large amount of fuel can be discharged from the fuel diffusion layer 8 and the liquid fuel can be quickly and uniformly absorbed in the surface direction of the fuel absorption layer 9. As a result, the liquid fuel can be supplied uniformly with respect to the surface direction of the fuel electrode 3, and even in a situation where a large amount of liquid fuel is consumed by the reaction at the fuel electrode 3, the surface direction of the fuel electrode 3 can be quickly achieved. The liquid fuel can be supplied uniformly.

  Here, FIG. 6 shows a case where the fuel absorption layer is configured so that the absorption speed in the surface direction with respect to the liquid fuel is larger than that of the fuel diffusion layer (solid line in the figure), and the fuel absorption layer and the fuel diffusion layer. Is a graph showing the comparison of the output characteristics of the fuel cell with respect to the case where the absorption speed in the plane direction with respect to the liquid fuel is equivalent (broken line in the figure), the vertical axis is the output (au), the horizontal The axis is current (mA). From FIG. 6, when the fuel absorption layer is configured so that the absorption speed in the surface direction with respect to the liquid fuel is larger than that in the fuel diffusion layer, the absorption in the surface direction with respect to the liquid fuel between the fuel absorption layer and the fuel diffusion layer. It can be seen that a higher output is obtained compared to the case where the speeds are equal. FIG. 6 shows, for example, a conventionally known and generally used current source, a battery characteristic measuring circuit including a voltmeter, a liquid fuel supply pump (manufactured by ISMATEC), and a mass flow controller (STEC) for adjusting the air flow rate. The results of measurement using a

  Further, in the fuel cell of the present invention, the layer disposed on the fuel electrode side of the fuel absorption layer has a higher absorption rate in the plane direction with respect to the liquid fuel than the layer disposed on the fuel diffusion layer side of the fuel absorption layer. It is preferable that it is comprised. As a result, even if the region where the liquid fuel is supplied from the layer disposed on the fuel diffusion layer side in the fuel absorption layer to the layer disposed on the fuel electrode side is limited, the liquid is partially Liquid fuel is quickly and uniformly diffused from the portion where the fuel has passed with respect to the surface direction of the layer disposed on the fuel electrode side of the fuel absorption layer, and the liquid fuel is reliably absorbed in the layer disposed on the fuel electrode side, The effect that it can hold | maintain is show | played. Note that the layer disposed on the fuel electrode side of the fuel absorption layer is configured so that the absorption speed in the surface direction with respect to the liquid fuel is greater than the layer disposed on the fuel diffusion layer side of the fuel absorption layer. As in the case of the fuel absorption layer and the fuel diffusion layer described above, it can be confirmed by measuring the time required until the entire surface is filled with methanol. Such a difference in the absorption speed with respect to the surface direction with respect to the liquid fuel is adjusted by, for example, using fibrous materials having different wettability for the fibrous materials constituting the layers, or using fibrous materials having different shapes. Can do.

  In the fuel cell of the present invention, it is preferable that the layer disposed on the fuel electrode side of the fuel absorption layer includes a fibrous material extending radially in the plane direction. Here, FIG. 7 is a diagram schematically showing the fibrous material 16 that can be included on the side of the fuel absorption layer of the present invention disposed on the fuel electrode side of the fuel absorption layer. The fibrous material 16 that can be included in the layer disposed on the fuel electrode side of the fuel absorbing layer described above has a radially extending shape as shown in FIG. It is disposed so as to be parallel to a plane substantially perpendicular to the thickness direction of the layer disposed on the fuel electrode side of the absorption layer, and is included in the layer disposed on the fuel electrode side of the fuel absorption layer. By including the fibrous material 16 in this manner, the liquid fuel can be transported by the radially extending fibrous material 16, and the liquid fuel can be transported faster with respect to the surface direction of the layer disposed on the fuel electrode side. Will be able to diffuse.

  Here, FIG. 8 shows a case where the layer disposed on the fuel electrode side of the fuel absorption layer includes a fibrous material extending radially in the plane direction (solid line in the drawing) and a case where the layer does not include the fibrous material ( The broken line in the figure is a graph showing the comparison of the output characteristics of the fuel cell, where the vertical axis is the output (au) and the horizontal axis is the current (mA). From FIG. 8, when the layer disposed on the fuel electrode side of the fuel absorption layer includes a fibrous material extending radially in the plane direction, a higher output can be obtained as compared with the case where the fibrous material is not included. You can see that This is because the layer disposed on the fuel electrode side of the fuel absorption layer as described above can absorb liquid fuel uniformly and quickly with respect to the surface direction, and supply of the liquid fuel to the fuel electrode can be performed. This is thought to be due to the promotion. FIG. 8 shows, for example, a conventionally known and generally used current source, a battery characteristic measuring circuit including a voltmeter, a liquid fuel supply pump (manufactured by ISMATEC), and a mass flow controller (STEC) for adjusting the air flow rate. The results of measurement using a

  In the fuel cell of the present invention, it is preferable that the fibrous material 16 described above has hydrophilicity. Here, “hydrophilic” indicates that the contact angle measured by the droplet method is 40 degrees or less, as described above. By including the hydrophilic fibrous material 16 in the layer disposed on the fuel electrode side of the fuel absorption layer in this manner, the layer disposed on the fuel diffusion layer side of the fuel absorption layer and the fuel electrode side Even in a state where the layer disposed on the surface of the fibrous material 16 is in partial contact with the entire surface, the liquid fuel easily propagates on the surface of the fibrous material 16, so that the layer disposed on the fuel diffusion layer side The liquid fuel can be smoothly conveyed to the layer disposed on the fuel electrode side.

  Specifically, as the fibrous material (preferably having hydrophilicity) that can be included in the layer disposed on the fuel electrode side of the fuel absorbing layer described above, a highly absorbing fibrous material mainly composed of cellulose is used. It is preferable. Such a fibrous material can be formed, for example, by bundling a plurality of thin fibers formed of the materials described above. In addition, it is preferable that the fibrous material has a fine uneven portion on the surface along the fiber direction, and by having such an uneven portion, the liquid fuel extends along the recessed portion like a groove. The liquid fuel can be absorbed more smoothly.

  In the fuel cell of the present invention, it is preferable that the layer disposed on the fuel diffusion layer side of the fuel absorption layer has a smaller thickness than the layer disposed on the fuel electrode side of the fuel absorption layer. The layer disposed on the fuel electrode side of the fuel absorption layer only needs to be able to impregnate the liquid fuel, but the larger the thickness, the more liquid fuel can be held, and the more liquid fuel that can be held leads to high output as a battery. . The preferred thickness of the layer disposed on the fuel electrode side of the fuel absorption layer is 50 μm or more. The layer arranged on the fuel diffusion layer side of the fuel absorption layer has a low wettability with respect to the liquid fuel as compared with the layer arranged on the fuel electrode side. Can be fulfilled. Further, if the thickness of the layer disposed on the fuel diffusion layer side of the fuel absorption layer is excessive, it becomes difficult to permeate the fuel. As an example, the layer thickness of the layer disposed on the fuel diffusion layer side of the fuel absorption layer may be 5 μm or more and less than 50 μm. For example, as an example of a fuel cell used for a fine device, since the thickness usable as a fuel absorption layer is 200 μm or less, it is applied to a fuel cell in which the thickness usable as a fuel absorption layer is limited. In this case, a limited thickness can be efficiently used by reducing the thickness of the layer disposed on the fuel diffusion layer side of the fuel absorption layer.

  In the fuel cell of the present invention, it is preferable that the fuel absorption layer has one or more holes penetrating in the thickness direction. In FIG. 1, the fuel absorption layer 9 is formed on the surface of the first absorption layer 11 disposed on the fuel diffusion layer 8 side, the second absorption layer 12 disposed on the fuel electrode 3 side, and the second absorption layer 12. An example is shown in which a plurality of through-holes 21 that have a conductive film 26 (described later) and that penetrate the fuel absorption layer 9 in the thickness direction are formed. As described above, carbon dioxide is generated in the reaction at the fuel electrode 3, but this carbon dioxide forms a void in the fuel absorption layer (for example, forms a fuel absorption layer) when the above-described through hole is not formed. It is discharged from the gap between the fibrous materials. In the configuration shown in FIG. 1, since the through-hole 21 described above is formed in the fuel absorption layer 9, a large amount of carbon dioxide is easily discharged from the discharge port (not shown) to the outside of the fuel cell through the through-hole 21. Become. Thus, unlike the case where the above-described through holes are not formed, there is an advantage that even when the battery is operated at a high current and the amount of generated carbon dioxide increases, carbon dioxide can be discharged without delay.

  In the fuel cell of the present invention, the side surface of the fuel absorption layer is preferably covered with a material impermeable to liquid fuel. As described above, the fuel absorption layer contains a large amount of liquid fuel, but there is a possibility that the liquid fuel leaks from the side surface side of the fuel absorption layer. In this case, not only the utilization efficiency of the liquid fuel is lowered, but also a crossover of the liquid fuel from the periphery of the fuel electrode into the electrolyte membrane is caused. Since the side surface of the fuel absorption layer is covered with a material that is impermeable to the liquid fuel, such leakage of the liquid fuel can be prevented. The material for covering the side surface of the fuel absorption layer is not particularly limited as long as it is impermeable to liquid fuel, and examples thereof include polydimethylsiloxane (PDMS), fluorocarbon, and the like, and a layer formed of these materials. It is preferable to cover the side surface of the fuel absorption layer with an object or a film-like object.

  Furthermore, in the fuel cell of the present invention, it is preferable that a conductive film is formed on the surface of the layer disposed on the fuel electrode side of the fuel absorption layer. As described above, FIG. 1 shows an example in which the conductive film 26 is formed on the surface of the second absorption layer 12 disposed on the fuel electrode 3 side of the fuel absorption layer 9. In the conventional fuel cell, the charge generated by the fuel cell reaction is currently collected by using a fuel diffusion layer or a fuel electrode or by introducing a conductive mesh on the fuel electrode. However, there is a problem that the electric resistance value is high in a fuel diffusion layer and a fuel electrode made of carbon sheets or the like that are usually used. In addition, when a conductive mesh is introduced, the contact between the fuel electrode and the fuel diffusion layer is deteriorated, and there is a problem that the supply of liquid fuel is hindered. For this reason, as in the example of FIG. 1, the conductive film 26 is formed on the surface of the layer (second absorption layer 12) disposed on the fuel electrode 3 side of the fuel absorption layer 9. The membrane 26 can serve as a collecting electrode for collecting electric charges generated by the fuel cell reaction, and does not cause the above-described problems.

  The material for forming the conductive film 26 is not particularly limited as long as it is a conductive material that can be formed into a film shape. For example, a noble metal material such as Au, Pt, Ru, Rh, and Ir, or Use of these alloys or conductive oxides of these metal elements is preferable because a conductive film having stable characteristics can be obtained particularly in the long term and can contribute to the stability of the performance of the fuel cell. The thickness of the conductive film 26 is not particularly limited, but microscopically, the conductive film is formed so as to cover the fiber surface constituting the fuel absorption layer, and the thicker the conductive film, the more liquid Since the fuel absorption capacity may be reduced, the thickness of the conductive film is preferably less than half the fuel absorption layer thickness.

  As described above, the fuel cell of the present invention has a feature in a configuration in which a specific fuel absorption layer is interposed between the fuel diffusion layer and the fuel electrode. The present invention is not limited, and a conventionally known appropriate configuration can be adopted. For example, in FIG. 1, the side of the oxidant electrode 5 opposite to the side adjacent to the electrolyte membrane 4 is an oxidant in which an oxidant channel 32 is formed as a oxidant supply mechanism (oxidant supply mechanism). The fuel cell 1 of the example in which the flow-path board 31 was provided through the oxidizing agent diffusion layer 33 is shown.

  As the oxidant flow path plate 31, a material that is not permeable to liquid and oxygen, which is an oxidant, such as a metal substrate, a silicon substrate, a glass substrate, and a resin substrate can be used. Similarly, a silicon substrate in which the oxidant flow path 32 is formed by fine processing can be suitably used. Of course, a plate-like object that does not have an oxidant flow path and is formed with holes through which air can pass may be used as the oxidant supply mechanism.

  Further, as the oxidant diffusion layer 33, as with the fuel diffusion layer 8 described above, carbon paper, a sintered body of carbon, porous silicon, porous silicon oxide, sintered metal such as nickel, and porous material such as foam metal. The material can be used, but is not limited thereto. In addition, the water produced | generated in the oxidant electrode 5 by the fuel cell reaction mentioned above diffuses in this oxidant diffusion layer 33, and is discharged | emitted out of a fuel cell from a discharge port (not shown).

  If the fuel cell of this invention has the above characteristics, the manufacturing method will not be restrict | limited in particular. Here, FIG. 9 is a figure which shows the method of producing the fuel flow-path board 6 in steps. The fuel flow path plate 6 and the oxidant flow path plate 31 used in the fuel cell according to the present invention are formed of an appropriate substrate material 41 (FIG. 9A) as shown in FIG. Further, the fuel channel 7 (or the oxidant channel 32) is formed by performing microfabrication using known photolithography and Deep-RIE methods (FIG. 9B).

  FIG. 10 is a diagram showing in steps the method for producing the fuel absorbing layer 9 shown in FIG. The layer (the first absorption layer 11 in the example shown in FIG. 1) disposed on the fuel diffusion layer 8 side of the fuel absorption layer 9 can be formed using a fibrous material made of, for example, polypropylene, polyethylene or the like. Further, a layer (second absorbing layer 12 in the example shown in FIG. 1) disposed on the fuel electrode 3 side of the fuel absorbing layer 9 is formed using a fibrous material made of a material mainly composed of cellulose. These layers are laminated by using a known method described in, for example, JP-A-8-066425 (Reference 1) (FIG. 10A). Next, one or more through-holes 21 penetrating in the thickness direction using a known laser ablation method, punching, drilling or other mechanical punching means are formed in the laminate of the first absorption layer 11 and the second absorption layer 12. It forms (FIG.10 (b)). Further, a conductive material such as Au is deposited on the surface of the second absorption layer 12 by a known sputtering method or the like to form a conductive film 26 (FIG. 10C). In addition, it is preferable that the fiber material which forms the 2nd absorption layer 12 has the density of the surface which forms the electroconductive film 26 higher than the inside, and the metal particle sputter | spattered by this to the depth of a fiber material more than necessary. There is an advantage that high conductivity can be obtained while preventing entry.

  The fuel electrode 3 and the oxidant electrode 5 that are formed by laminating the metal materials as described above are arranged so as to face each other with the electrolyte membrane 4 therebetween, and the power generation element 2 is manufactured. Furthermore, the fuel absorption layer 9 manufactured as described above, the fuel diffusion layer 8 and the oxidant diffusion layer 33 formed using general carbon paper, the fuel flow path plate 6 manufactured as described above and the oxidation By sequentially laminating the agent flow path plates 31, the fuel cell 1 of the present invention as shown in FIG. 1 can be manufactured.

It is sectional drawing which shows typically the fuel cell 1 of a preferable example of this invention. It is a figure which expands and shows the vicinity of the fuel absorption layer 9 of the fuel cell 1 of this invention partially. When the fuel absorption layer is provided as in the present invention (solid line in the figure) and when the fuel absorption layer is not provided as in the conventional example (broken line in the figure), the output characteristics of the fuel cell are compared. The vertical axis represents output (au), and the horizontal axis represents current (mA). It is a figure which expands and shows the vicinity of the fuel absorption layer 9 of the fuel cell 1 of this invention partially. FIG. 3 is a diagram showing a part of the vicinity of the fuel absorption layer 9 in an enlarged manner when the fuel absorption layer 9 is configured to have a higher absorption rate for liquid fuel than the fuel diffusion layer 8. When the fuel absorption layer is configured so that the absorption speed in the surface direction with respect to the liquid fuel is larger than the fuel diffusion layer (solid line in the figure), the surface direction with respect to the liquid fuel between the fuel absorption layer and the fuel diffusion layer Is a graph showing a comparison of the output characteristics of the fuel cell with respect to the case where the absorption rate is equivalent (broken line in the figure), where the vertical axis is output (au) and the horizontal axis is current (mA). is there. It is a figure which shows typically the fibrous material 16 which may be contained in the side arrange | positioned at the fuel electrode side of the fuel absorption layer in the fuel cell of this invention. When the layer arranged on the fuel electrode side of the fuel absorption layer includes a fibrous material extending radially in the plane direction (solid line in the figure) and when not including the fibrous material (broken line in the figure) FIG. 5 is a graph showing comparison of output characteristics of fuel cells, where the vertical axis represents output (au) and the horizontal axis represents current (mA). It is a figure which shows the method of producing the fuel flow-path board 6 in steps. It is a figure which shows the method of producing the fuel absorption layer 9 shown in FIG. 1 in steps. FIG. 1 is a cross-sectional view schematically showing a solid polymer fuel cell 101 as disclosed in, for example, Japanese Patent Application Laid-Open No. 2003-86192 as an example of a conventional typical fuel cell. FIG. 12 is a partially enlarged view showing the vicinity of a fuel diffusion layer 110 of the polymer electrolyte fuel cell 101 of the conventional example shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Fuel cell, 2 Power generation element, 3 Fuel electrode, 4 Electrolyte membrane, 5 Oxidant electrode, 6 Fuel flow path plate, 7 Fuel flow path, 8 Fuel diffusion layer, 9 Fuel absorption layer, 11 1st absorption layer, 12 1st 2 absorbent layers, 16 fibrous material, 21 through-hole, 26 conductive film, 31 oxidant flow path plate, 32 oxidant flow path, 33 oxidant diffusion layer.

Claims (9)

A fuel electrode that generates cations from liquid fuel;
An electrolyte membrane disposed adjacent to the fuel electrode and permeable to cations from the fuel electrode;
An oxidant electrode disposed opposite to the fuel electrode through the electrolyte membrane and reacting the cation and permeate the electrolyte membrane with the oxidant;
A fuel supply mechanism for supplying liquid fuel to the fuel electrode;
A fuel diffusion layer disposed between the fuel electrode and the fuel supply mechanism, disposed on the fuel supply mechanism side, and a fuel absorption layer disposed on the fuel electrode side;
The fuel absorption layer has two or more layers having different wettability with respect to the liquid fuel in the thickness direction, and the layer disposed on the fuel electrode side is formed of a material having higher wettability than the layer disposed on the fuel diffusion layer side. And a fuel cell configured to be able to impregnate more liquid fuel than the fuel diffusion layer.   2. The fuel cell according to claim 1, wherein the fuel absorption layer is configured to have a higher absorption rate in a plane direction with respect to the liquid fuel than the fuel diffusion layer.   The layer disposed on the fuel electrode side of the fuel absorption layer is configured such that the absorption speed in the surface direction with respect to the liquid fuel is larger than the layer disposed on the fuel diffusion layer side of the fuel absorption layer. Or the fuel cell of 2.   The fuel cell according to any one of claims 1 to 3, wherein the layer disposed on the fuel electrode side of the fuel absorption layer includes a fibrous material extending radially in the plane direction.   The fuel cell according to claim 4, wherein the fibrous material has hydrophilicity.   The fuel cell according to claim 1, wherein the layer disposed on the fuel diffusion layer side of the fuel absorption layer has a smaller thickness than the layer disposed on the fuel electrode side of the fuel absorption layer.   The fuel cell according to claim 1, wherein the fuel absorption layer has one or more holes penetrating in the thickness direction.   The fuel cell according to any one of claims 1 to 7, wherein a side surface of the fuel absorption layer is covered with a material impermeable to liquid fuel.   The fuel cell according to claim 1, wherein a conductive film is formed on a surface of a layer disposed on the fuel diffusion layer side of the fuel absorption layer.

Images