JP4476558B2 - Fuel cell and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a solid polymer fuel cell using a solid polymer having ion conductivity as an electrolyte.
[0002]
[Prior art]
Conventionally, a fuel cell is known as a device that directly converts chemical energy of a fuel into electric energy. In this fuel cell, a fuel cell is usually formed with a pair of porous electrodes composed of a fuel electrode and an oxygen electrode facing each other with an electrolyte layer holding an electrolyte interposed therebetween, and a fuel gas such as hydrogen on the back surface of the fuel electrode And an oxidant such as air is brought into contact with the back surface of the oxygen electrode to take out electrical energy from the two electrodes using the electrochemical reaction generated at this time. According to the fuel cell, as long as the fuel gas and the oxidant are supplied, electric energy can be extracted with high conversion efficiency. Therefore, practical research is actively conducted as a power generation system advantageous for energy saving and environmental conservation. This fuel cell is called an alkali type (AFC), a phosphoric acid type (PAFC), a molten carbonic acid type (MCFC), a solid oxide type (SOFC), a solid polymer type (PEFC), or the like depending on the type of electrolyte.
[0003]
Among these, recently, a polymer electrolyte fuel cell has been attracting attention as a next-generation energy source. This fuel cell has two types of electrodes, that is, a fuel electrode and an oxygen electrode. Electricity is generated by oxidizing fuel at the fuel electrode and reducing oxygen at the positive electrode. The product in the positive electrode is an aqueous solution including water.
[0004]
Now, oxygen used in the positive electrode can be supplied from the air. Therefore, since it is sufficient to hold only fuel as a reactant in the fuel cell, the fuel cell has an advantage of high energy density. However, in such a fuel cell, an aqueous solution generated on the positive electrode stays on the positive electrode, which inhibits oxygen diffusion and hinders efficient operation of the fuel cell. In order to solve this problem, a method of using a blower to skip generated water is used. (See Patent Document 1)
[0005]
[Patent Document 1]
JP-A-6-188008 (page 3-5, FIG. 42)
[0006]
[Problems to be solved by the invention]
However, according to the conventional method, the energy density is lowered because the structure is complicated and the volume is increased. In addition, since power is consumed by the blower, there is a problem that the energy density is further reduced. In particular, the power source of a small portable device is limited in size and needs to be lightweight. However, when a fuel cell for a small portable device is configured by a conventional method, the volume in which the fuel is put becomes small and it is difficult to obtain effective energy. Therefore, it is not particularly suitable as a power source for small portable devices.
[0007]
An object of the present invention is to remove an aqueous solution generated on an electrode in a positive electrode of a polymer electrolyte fuel cell without consuming electric power and without greatly increasing the volume and reducing the energy density of the fuel cell. To do.
[0008]
[Means for Solving the Problems]
In order to solve the above problems, a fuel cell of the present invention includes a positive electrode attached with a catalyst having a function of selectively reducing oxygen electrochemically, a negative electrode attached with a catalyst for electrochemically oxidizing fuel, and bipolar electrodes. A cation-permeable solid polymer membrane is provided to be spaced apart from each other, an absorbent material that absorbs the aqueous solution generated on the electrode is provided around the positive electrode, and the positive electrode has a structure that transports the aqueous solution to the absorbent material. Thereby, since the aqueous solution produced | generated or condensed on the positive electrode is conveyed by the absorber and absorbed around the positive electrode, the aqueous solution does not stay in the positive electrode. Therefore, in order to remove the aqueous solution generated on the positive electrode, it is possible to remove the aqueous solution without using electric power, having a complicated structure, and hardly changing the volume.
[0009]
Furthermore, the hydrophilic material of the hydrophilic portion of the present invention is arranged so that the concentration increases from the center of the electrode toward the outside. Thereby, the liquid amount of the aqueous solution produced | generated on the positive electrode increases so that the outer peripheral part of a positive electrode, and the contact site | part of an absorber and aqueous solution increases. Therefore, the aqueous solution absorption efficiency of the absorbent material is improved, and the amount of aqueous solution removed from the positive electrode can be increased.
[0010]
Furthermore, a flow path is formed in the hydrophilic material forming portion. Thereby, the aqueous solution produced | generated on the positive electrode is sucked up by a hydrophilic part, and is conveyed to an absorber. Further, it is absorbed by the absorbent and removed from the positive electrode. Accordingly, there is an effect that a product such as an aqueous solution stays on the channel or the channel is not clogged by the channel formed of the hydrophilic material.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0012]
A schematic structure of the fuel cell of the present invention is shown in FIG. As shown in the figure, the fuel cell of the present invention is provided with a solid polymer electrolyte membrane 1 having ion conductivity and a gas separation function. The polymer electrolyte membrane 1 only needs to be capable of transmitting protons, and for example, a material such as Nafion (trademark) is used. A pair of gas diffusion electrodes composed of a negative electrode 2 and a positive electrode 3 are arranged so as to sandwich the solid polymer electrolyte membrane 1. A reaction catalyst layer containing a catalyst such as Pt is formed on the surface of each of the electrodes 2 and 3 in contact with the electrolyte membrane 1. Carbon or the like is used as a support to hold a catalyst such as Pt in each of the electrodes 2 and 3. As a structure for transporting the aqueous solution generated on the surface of the positive electrode 3 to the absorbent 5 provided around the positive electrode 3, the hydrophilic portion 4 is disposed on the surface of the positive electrode 3 that faces the surface in contact with the polymer electrolyte membrane 1. Further, an absorbent 5 is disposed on the outer periphery of the hydrophilic portion 4 as a structure for removing the conveyed aqueous solution around the positive electrode 3. A unit cell is composed of the hydrophilic portion 4, the absorbent 5, the solid polymer electrolyte membrane 1, and the electrodes 2 and 3. A structure for transporting the aqueous solution generated on the positive electrode 3 to the absorbent 5 provided around the positive electrode is disposed on the positive electrode 3, and the aqueous solution is removed by the absorbent 5, whereby oxygen is generated on the positive electrode 3 during power generation of the fuel cell. It has a function of removing the generated aqueous solution that inhibits diffusion. This eliminates the need for electric power, does not have a complicated structure, and can remove the aqueous solution with almost no change in volume, so that highly efficient power generation can be performed.
[0013]
Further, the hydrophilic portion 4 is provided as a structure for transporting the aqueous solution generated at the positive electrode to the absorbent material 5. The hydrophilic portion 4 has a function of transporting the aqueous solution to the absorbent material 5. The material constituting the hydrophilic portion 4 is preferably a hydrophilic material having high wettability, and can be arbitrarily selected from hydrophilic materials such as titanium oxide. An absorbent such as an absorbent resin was used as the absorbent 5 and was arranged on the outer periphery of the hydrophilic portion 4. The hydrophilic portion 4 has a function of sucking up the aqueous solution generated on the positive electrode 3 and transporting it to the absorbent material 5. The absorbent 5 has a function of sequentially absorbing the aqueous solution sucked up by the hydrophilic portion 4 and storing the aqueous solution. Thereby, the aqueous solution produced | generated on the positive electrode 3 does not stay. Therefore, inhibition of oxygen diffusion can be prevented.
[0014]
Since the polymer electrolyte fuel cell has a relatively low operating temperature (room temperature to 100 ° C.), among the water supplied for humidification, the water not absorbed by the electrolyte and the product generated by the reaction May exist in a liquid state. This aqueous solution has a problem that the diffusibility of gas to the electrode catalyst layer is hindered and the output of the fuel cell is lowered. Therefore, in the case where inhibition of gas diffusibility by the aqueous solution is a problem, a structure for removing the aqueous solution generated or condensed on the electrode may be used for both the positive electrode 3 and the negative electrode 2.
[0015]
Further, the structure of the positive electrode is such that the positive electrode 3 is composed of a hydrophilic portion 4 made of a hydrophilic material and the reaction catalyst as independent layers, and the hydrophilic portion is arranged on the surface of the positive electrode 3 facing the surface in contact with the polymer electrolyte membrane 1. To do. As a result, the aqueous solution generated on the positive electrode 3 can be efficiently sucked up without stagnation. Therefore, the electrode performance is not deteriorated with time.
[0016]
Moreover, the hydrophilic part 4 was formed by hold | maintaining the paste containing a hydrophilic material and a binder on the water-repellent-treated carbon support body. Thereby, moderate intensity | strength and a softness | flexibility can be given. Moreover, the aqueous solution produced | generated on the positive electrode 3 can be hold | maintained on the hydrophilic material between the support body of the carbon to which the water repellent process of the positive electrode 3 and the hydrophilic part 4, for example, a carbon sheet. Therefore, there is an effect that the absorbent 5 can quickly absorb the outside of the carbon sheet, that is, the outside of the fuel cell without leaking with the aqueous solution. Moreover, there is also an effect that the polymer electrolyte membrane 1 is hardly damaged by giving appropriate flexibility.
[0017]
Further, as the binder, for example, any of the group consisting of polytetrafluoroethylene (PTFE), poly-N-vinylacetamide (PNVA), polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), and styrene butadiene rubber (SBR). You can choose any one. The binder content is desirably 1.0% by weight to 10.0% by weight with respect to the weight of the hydrophilic material powder. Thereby, the effect | action which binds hydrophilic materials mutually is expressed. Further, in the fuel cell, the hydrophilic portion 4 is dried when not in operation and when the power generation amount is small. Moreover, when there is much electric power generation amount, the hydrophilic part 4 will become wet. Although the hydrophilic portion 4 may lose its shape due to the change in volume accompanying the change in humidity of the hydrophilic portion 4, the present invention has an effect of suppressing the loss of shape of the hydrophilic portion 4.
[0018]
Further, a flow path was formed in the hydrophilic portion 4. The shape of this flow path may be spiral or serpentine. Furthermore, it may be curved or straight. The width of the flow path is preferably 0.1 mm to 20 mm, and the distance between the flow paths is also preferably 0.1 mm to 20 mm. However, this is not restrictive. Thereby, when the fuel cells are stacked in series and used, the hydrophilic portion 4 can be used as a separator. Furthermore, since the flow path is formed of a hydrophilic material, a product such as an aqueous solution does not stay on the flow path or clog the flow path. Thereby, the product does not hinder the flow of air and oxygen.
[0019]
Furthermore, the hydrophilic part 4 and the positive electrode 3 may not be provided separately, but a powdery hydrophilic material may be mixed with the positive electrode 3. In this case, as shown in FIG. 3, the absorber 5 is arranged on the outer periphery of the positive electrode 6 mixed with the hydrophilic material powder. Here, FIG. 3 is a side sectional view of a structure showing an example of the present invention, in which a solid polymer electrolyte membrane 1 having ion conductivity is provided. A pair of gas diffusion electrodes composed of a negative electrode 2 and a positive electrode 6 are arranged so as to sandwich the solid polymer electrolyte membrane 1. A reaction catalyst layer containing a catalyst such as Pt is formed on the surfaces of the positive electrodes 2 and 6 that are in contact with the electrolyte membrane 1. In order to hold a catalyst such as Pt in the positive electrode 6, carbon or the like is used as a support. Further, in the positive electrode 6, a powdered hydrophilic material is mixed for conveying the aqueous solution. As a structure for removing the conveyed aqueous solution around the positive electrode 6, an absorbent material 5 is arranged on the outer periphery of the hydrophilic portion 4. These hydrophilic portion 4, absorbent material 5, solid polymer electrolyte membrane 1 and electrodes 2, 6 constitute a single battery. Thereby, it is possible to make it the volume substantially the same as the conventional positive electrode. Moreover, since the aqueous solution produced | generated with the reaction catalyst gets wet with a hydrophilic material immediately after reaction, and aqueous solution can be conveyed to an absorber, retention of aqueous solution can be suppressed more.
[0020]
Further, as the hydrophilic material of the hydrophilic portion 4, for example, hydrophilicity such as titanium oxide, zinc oxide, tin oxide, niobium oxide, tungsten oxide, molybdenum oxide, zirconium oxide, strontium titanate, potassium sulfide, cadmium sulfide, zinc sulfide, etc. Any one of the group of materials can be chosen arbitrarily. By selecting a hydrophilic material having high wettability, the aqueous solution generated on the positive electrode 3 is quickly sucked up, the aqueous solution is removed from the positive electrode 3, and the aqueous solution is sequentially applied to the absorbent 5 disposed on the outer periphery of the hydrophilic portion 4. It has a function to convey. As a result, the aqueous solution produced on the positive electrode 3 does not stay and oxygen diffusion is not inhibited, so that the operation of the fuel cell is stabilized.
[0021]
Furthermore, the hydrophilic material of the hydrophilic portion 4 is arranged so that the concentration increases from the center of the electrode toward the outer periphery of the electrode. The shape may be distributed circularly or squarely. A method of producing the hydrophilic portion 4 having a concentration gradient is, for example, producing a plurality of mixtures having different mixing ratios of the water-repellent carbon powder and the hydrophilic material, arranging them in the order of concentration, and forming a film by pressing. Is. Alternatively, the mixture of the carbon powder and the hydrophilic material may be spin-coated on the positive electrode 3, and the carbon powder may be further applied to the central recess to form a film. Thereby, a large amount of the aqueous solution sucked up by the hydrophilic material is retained on the outer peripheral portion of the hydrophilic portion 4 having a high concentration of the hydrophilic material. And the water quantity which contacts the absorber 5 arrange | positioned on the outer periphery of the hydrophilic part 4 can be increased, and aqueous solution is absorbed in the absorber 5 efficiently one by one. As a result, the aqueous solution produced on the positive electrode 3 is removed from the positive electrode without stagnation, so that the problem of inhibition of oxygen diffusion can be solved, and the fuel cell can be stably produced from a low current density to a high current density. It becomes possible to drive.
[0022]
In addition, the method for producing a fuel cell according to the present invention includes a step of fixing a reaction catalyst having a function of selectively reducing oxygen electrochemically to a cation-permeable solid polymer membrane, an aqueous solution on the reaction catalyst layer, and A step of fixing a hydrophilic portion holding a hydrophilic material having high wettability, a step of fixing an absorbent of an aqueous solution along the outer periphery of the positive electrode formed in this way, and a catalyst for electrochemically oxidizing fuel Forming an attached negative electrode so as to be separated from the positive electrode through the cation-permeable solid polymer membrane. Examples of the fixing method include thermocompression bonding and adhesion. Therefore, by controlling the temperature, pressure, and weight of the fixing agent, it is possible to manufacture a structure that removes the aqueous solution with high reproducibility and high straightness.
[0023]
Furthermore, a hydrophilic part was formed by holding a paste containing a hydrophilic material and a binder on a water-repellent carbon support.
[0024]
【Example】
Next, the present invention will be described in more detail with reference to examples.
[0025]
(Example 1) PEFC
As the electrolyte, a polymer electrolyte membrane made of a cation exchange membrane (manufactured by DuPont, product name “Nafion NE-112”), which is a polymer electrolyte membrane, was used. The catalyst electrode-conjugate is composed of an electrode in which platinum is dispersed at a rate of 1 mg / cm (product name “EC-20-10-7” manufactured by Electrochem Co., Ltd.) as a positive electrode and a negative electrode, and 0.1 mg / cm on the electrode. A Nafion solution (manufactured by Aldrich, Nafion solution) was applied at a rate of cm, and hot pressing was performed on both sides of the polymer electrolyte membrane.
[0026]
Titanium oxide was used as the hydrophilic material, and polytetrafluoroethylene (PTFE) was used as the binder. In preparing the hydrophilic portion 4 composed of 0.5 mg / cm 2 of titanium oxide, 2.0 wt% PTFE was used as the binder content with respect to the weight of the hydrophilic material powder. On one side of the support of a carbon sheet (manufactured by Toray Industries, Inc., “Product Name TGP-H-030” (110 μm)) obtained by mixing a hydrophilic material and a binder into a paste. Created by hot pressing. An absorbent resin (Sumitomo Seika Co., Ltd., trade name “Aquakeep 10SH”) was used for the absorbent material 5 and arranged on the outer periphery of the hydrophilic portion 4. In addition, a heater 7 was disposed outside thereof.
[0027]
These were arranged as shown in FIG. FIG. 4 is a side sectional view showing the structure of Example 1, in which a solid polymer electrolyte membrane 1 having ion conductivity is provided. A pair of gas diffusion electrodes composed of a negative electrode 2 and a positive electrode 3 are arranged so as to sandwich the solid polymer electrolyte membrane 1. A reaction catalyst layer containing a catalyst such as Pt is formed on the surface of each of the electrodes 2 and 3 in contact with the electrolyte membrane 1. Carbon or the like is used as a support to hold a catalyst such as Pt in each of the electrodes 2 and 3. As a structure for transporting the aqueous solution generated on the surface of the positive electrode 3 to the absorbent 5 provided around the positive electrode 3, the hydrophilic portion 4 is disposed on the surface of the positive electrode 3 that faces the surface in contact with the polymer electrolyte membrane 1. Further, an absorbent 5 is disposed on the outer periphery of the hydrophilic portion 4 as a structure for removing the conveyed aqueous solution around the positive electrode 3. Further, a heater 7 is disposed on the outer periphery of the absorbent material 5. A unit cell is constituted by the hydrophilic portion 4, the absorbent material 5, the heater 7, the solid polymer electrolyte membrane 1, and the electrodes 2 and 3. Thus, in order to remove the aqueous solution generated on the positive electrode 3, the fuel cell is stably operated until the high current density is obtained without removing the aqueous solution without changing the volume almost without changing the volume. It became possible. Further, by arranging the heater 7, the aqueous solution absorbed by the absorbent 5 evaporates, and it becomes possible to operate the fuel cell stably for a long time.
[0028]
(Example 2) DMFC
As the electrolyte, a polymer electrolyte membrane made of a cation exchange membrane (manufactured by DuPont, product name “Nafion NE-117”) was used as the polymer electrolyte membrane. The catalyst electrode-junction was prepared by using an electrode in which platinum was dispersed at a rate of 1 mg / cm 2 (manufactured by Electrochem, product name “EC-20-10-7”) as a positive electrode and a negative electrode, and 0.1 mg / cm on the electrode. A Nafion solution (manufactured by Aldrich, Nafion solution) was applied at a rate of cm2, and hot pressing was performed on both sides of the polymer electrolyte membrane. Poly-N-vinylacetamide (PNVA) was used for the absorbent material 5, and the hydrophilic portion 4 was prepared in the same manner as in Example 1 and arranged as shown in FIG.
[0029]
In the fuel cell according to the present invention, methanol crossover occurs, but the crossover fuel is stored together with the water generated by the absorbent 5, so that it can be reused later, and the fuel utilization efficiency is improved. Connected.
[0030]
(Embodiment 3) Direct fuel cell FIG. 2 shows a schematic cross-sectional structure of this embodiment. As shown, a solid polymer electrolyte membrane 21 having ion conductivity is provided. The hydrophilic portion 24 and the absorbent material 25 were prepared in the same manner as in Example 2. Using a hydrogen storage alloy 22 as a negative electrode and a platinum-supported carbon electrode (manufactured by Electronchem) on which 16 wt% of platinum is supported as an oxygen electrode 23, a hydrophilic portion 24 made of 0.5 mg / cm 2 of titanium oxide was created. Using a polymer electrolyte membrane 21 made of a cation exchange membrane (manufactured by DuPont, product name “Nafion NE-117”) as an electrolyte, a fuel cell having the structure shown in FIG. 2 was prepared.
[0031]
A negative electrode and a positive electrode are arranged so as to sandwich the solid polymer electrolyte membrane. A reaction catalyst layer containing a catalyst such as Pt is formed on the surface of the positive electrode in contact with the electrolyte membrane. In order to hold a catalyst such as Pt in the positive electrode, carbon or the like is used as a support. As a structure for transporting the aqueous solution generated on the surface of the positive electrode to an absorbent provided around the positive electrode, a hydrophilic portion is disposed on the surface of the positive electrode facing the surface in contact with the polymer electrolyte membrane. Furthermore, as a structure for removing the conveyed aqueous solution around the positive electrode, an absorbent material is disposed on the outer periphery of the hydrophilic portion. A hydrogen storage alloy was disposed on the negative electrode. A unit cell is composed of these hydrophilic portion, absorbent material, solid polymer electrolyte membrane and electrode. Next, a solution prepared by dissolving NaBH4 at a concentration of 10 wt% in a 20 wt% NaOH aqueous solution is supplied to the hydrogen electrode side as an electrolyte and a fuel supply source, and air is simultaneously supplied to the oxygen electrode side, The current-voltage characteristics between the hydrogen electrode and the oxygen electrode were measured at. The result is shown as a solid line in FIG. For comparison, the results of obtaining the current-voltage characteristics of a conventional fuel cell that does not use the hydrophilic portion 24 and the absorbent material 25 are shown as wavy lines in FIG. 5 as a graph.
[0032]
The hydrophilic portion 24 of the present invention was disposed on the electrode, and the generated or crossed over alkaline water was absorbed, and the influence of the alkaline water on the external environment could be improved.
[0033]
【The invention's effect】
According to the mechanism for removing the aqueous solution generated or condensed on the electrode of the present invention, the generated or condensed aqueous solution staying on the positive electrode can be removed, so that a high load is applied to the fuel cell, that is, a large amount of current is taken out. In addition, it was confirmed that power generation can be performed more efficiently than when no mechanism for removing the aqueous solution generated or condensed on the electrode is used. As a result, the problem of inhibition of oxygen diffusion can be solved, and the fuel cell can be stably operated from a low current density to a high current density.
[Brief description of the drawings]
FIG. 1 shows an example of a fuel cell according to the present invention.
FIG. 2 is a view showing another example of a fuel cell according to the present invention.
FIG. 3 is a view showing another example of a fuel cell according to the present invention.
FIG. 4 is a schematic cross-sectional view of a fuel cell showing an embodiment of the present invention.
FIG. 5 is a current-voltage characteristic curve of an example of the present invention and a comparative example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1,21 Polymer electrolyte membrane 2 Negative electrode 3 Positive electrode 4 Hydrophilic part 5 Absorbent material 6 Electrode mixed with hydrophilic material 7 Heater 22 Hydrogen storage alloy

Claims (8)

A positive electrode with a catalyst for reducing oxygen;
A negative electrode with a catalyst for oxidizing the fuel;
A solid polymer electrolyte membrane sandwiched between the positive electrode and the negative electrode;
A hydrophilic material made of a hydrophilic material provided on the surface of the positive electrode facing the surface of the solid polymer film so that the aqueous solution generated on the surface of the positive electrode is transported around the positive electrode. And
In order to absorb and remove the aqueous solution conveyed by the hydrophilic part, comprising an absorbent material provided on the outer periphery of the hydrophilic part and around the electrode of the positive electrode ,
Fuel cell concentration distribution of the hydrophilic material, characterized in the Rukoto from the center of the cathode electrode is arranged to be higher toward the outer periphery of the electrode.   The fuel cell according to claim 1, wherein the hydrophilic portion includes a paste containing the hydrophilic material and a binder, and a support body that holds the paste.   The fuel cell according to claim 2, wherein the support is made of water-repellent carbon.   The fuel cell according to claim 1, wherein the hydrophilic portion has a flow path that absorbs the aqueous solution generated on the surface of the electrode of the positive electrode and conveys the aqueous solution to the absorbent material. A positive electrode in which a catalyst for reducing oxygen and a powdered hydrophilic material are mixed;
A negative electrode with a catalyst for oxidizing the fuel;
A solid polymer electrolyte membrane sandwiched between the positive electrode and the negative electrode;
An absorbent provided on an outer periphery of the positive electrode so as to remove the aqueous solution generated in the positive electrode and transported by the hydrophilic material around the positive electrode;
A fuel cell comprising: The fuel cell according to any one of claims 1 to 5, characterized in that it comprises a arranged a heater on the outer periphery of the absorbent material. Fixing a reaction catalyst for reducing oxygen to a solid polymer film to form a positive electrode;
A step of fixing a hydrophilic portion holding a hydrophilic material whose concentration distribution is increased from the center portion of the positive electrode toward the outer periphery of the electrode;
Fixing the water absorbing material along the outer periphery of the positive electrode;
Forming a negative electrode attached with a catalyst for oxidizing fuel so as to be separated from the positive electrode through the solid polymer film;
A method of manufacturing a fuel cell comprising: 8. The method of manufacturing a fuel cell according to claim 7 , further comprising a step of forming the hydrophilic portion by holding a paste containing the hydrophilic material and a binder on a support.

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