JP2005243270A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve an electric property of a fuel cell having a permeation membrane interposed between a fuel electrode and an oxidant electrode, using an alkaline aqueous solution of a metal-hydrogen complex compound, for example, sodium borohydrate as fuel. <P>SOLUTION: A metal ion, for example, a sodium ion generated by electrode reaction at the fuel electrode is diffused by a water-absorbent buffer material 6 by interposing a water-absorbent buffer material 6 between the fuel electrode 51 and the permeation membrane 3, and an effective sodium ion passing area on the permeation membrane is improved. Further, the movement of a sodium hydroxide into an oxidant electrode 41 is prevented and a water content in the permeation membrane is stabilized by interposing the buffer material between the oxidant electrode and the permeation membrane since the buffer material 6 absorbs the metal hydroxide, for example, a sodium hydroxide generated at the permeation membrane side of the oxidant electrode. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fuel cell to which a fuel liquid comprising an alkaline aqueous solution of a metal hydrogen complex compound such as tetrahydroborate is supplied.

A fuel cell is a device that continuously supplies fuel and an oxidant to the negative electrode and the positive electrode, respectively, and converts the energy obtained by the chemical reaction that takes place into electrical energy. Collecting. For example, a fuel cell that reforms methanol to extract a hydrogen-rich gas and uses this hydrogen-rich gas as a fuel has been well known, but recently, a borohydride such as sodium borohydride (NaBH4). A fuel cell (borohydride fuel cell) using a complex compound liquid fuel has been studied. For example, sodium borohydride (NaBH4) is stable in an alkaline aqueous solution, BH4 ^- the BO2 ^- theoretical voltage from the electrochemical potential is baser when converting to high, also to generate hydrogen There are advantages such as no need for a reformer. This type of fuel cell is described in Patent Document 1.

  For example, Patent Document 1 describes a borohydride fuel cell shown in FIG. In this fuel cell, an insulating case body 11 such as a resin is partitioned into two regions by a permeable membrane 12 made of a polymer electrolyte membrane, and an oxidant electrode 13 is formed on one surface side of the permeable membrane 12 in one region. The fuel electrode 14 is provided in contact with the other surface side of the permeable membrane 12 in the other region. As the oxidant electrode 13 and the fuel electrode 14, for example, a granular sintered body such as nickel or a porous body such as foam is used as a base material, and a surface thereof plated with a noble metal such as platinum or palladium is used. Further, an oxidant passage 15 for allowing an oxidant, for example, air, to flow therethrough is formed between the oxidant electrode 13 and one side surface of the case body 11, and the fuel electrode 14 and the other side surface of the case body 11 A fuel flow path portion 16 for allowing fuel to flow therethrough is formed.

  In such a fuel cell, for example, when humidified air is allowed to flow through the oxidant flow path portion 15 and fuel that is an alkaline aqueous solution of sodium borohydride (NaBH4) is allowed to flow through the fuel flow path portion 16, In the fuel electrode 14, an eight-electron reaction mainly occurs as shown in the following formula (1).

NaBH4 + 8NaOH → NaBO2 + 6H2O + 8Na ⁺ + 8e ⁻ (1)
Sodium ions (Na ⁺ ) generated at the fuel electrode 14 pass through the permeable membrane 12 and move to the oxidant electrode 13, and the electrons are transferred to the oxidant electrode 13 through a circuit (not shown) connected to the outside. In the oxidizer electrode 13, as shown in the following formula (2), electrons are transferred through a circuit connected to the outside, and oxygen (O 2) and water (H 2 O) supplied as oxidizer from the outside The sodium ions that have moved from the permeable membrane 12 react with each other by a catalytic action to generate sodium hydroxide. There is also a reaction in which hydrogen ions moving from the permeable membrane 12 react with oxygen to produce water.

2O 2 + 4H 2 O + 8Na ⁺ + 8e ⁻ → 8 NaOH (2)
FIG. 16 shows the basic structure of the fuel cell, but in a fuel cell stack that is actually used, the permeable membrane 12, the oxidant electrode 13, and the fuel electrode 14 are configured as a membrane / electrode assembly that is overlapped with each other by an adhesive. Has been. However, since the permeable membrane 12 is made of a polymer electrolyte membrane made of, for example, a cation permeable membrane, if both surfaces of the permeable membrane 12 are in direct contact with the oxidant electrode 13 and the fuel electrode 14, respectively, There is a risk of damaging the membrane surface of the permeable membrane 12 when the fabrication process or structure is incorporated into the fuel cell. If the permeable membrane 12 is damaged in this manner, the fuel leaks and the required electrical characteristics cannot be obtained.

  Further, as shown in the above equation (1), sodium ions generated at the fuel electrode 14 pass through the permeable membrane 12 and move to the oxidizer electrode 13, but one side of the fuel electrode 14 that contacts the permeable membrane 12. In this case, the sodium ions ionized by the catalytic reaction are not uniformly dispersed over the entire surface of the permeable membrane 12, so that the effective passage area of sodium ions in the permeable membrane 12 is not utilized. Further, in the fuel electrode 14, the reactions of the following formulas (3) and (4) occur, so that the generated hydrogen gas bubbles are adsorbed on the surface of the permeable membrane 12. There is a problem that the effective passage area of sodium ions is reduced, and as a result, the output voltage is lowered.

^{BH4 - + 8OH - → BO2 -} + 6H2O + 8e - ...... (3)
BH4 ⁻ + 4OH ⁻ → BO2 ⁻ + 2H2O + 2H2 + 4e ⁻ (4)
Furthermore, as described above, the reaction of the formula (2) occurs on one surface side of the oxidant electrode 13 that contacts the permeable membrane 12, and sodium hydroxide (NaOH) generated on the surface portion on this one surface side is generated. There is a problem that the oxidant electrode 13 which is a porous body accumulates inside the oxidant electrode 13 and the catalytic reaction in the oxidant electrode 13 is inhibited. Furthermore, the moisture of the permeable membrane is lost due to evaporation and the movement resistance of sodium ions is increased. This also causes a decrease in output.

JP 2002-50375 (FIG. 2)

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a fuel cell in which electric resistance is improved by reducing the movement resistance of a permeable membrane with respect to ionized metal ions. Still another object of the present invention is to provide a fuel cell that improves electrical characteristics by suppressing metal hydroxide accumulated in the oxidizer electrode.

  The present invention relates to a fuel cell in which a permeable membrane is interposed between a fuel electrode and an oxidizer electrode and an alkaline aqueous solution of a metal hydride complex is used as a fuel, and a water absorbing buffer material between the fuel electrode and the permeable membrane. Is provided. In this fuel cell, the buffer material may also serve as a fuel flow path. In this case, the fuel electrode and the buffer material may be provided with a flow path portion constituted by a liquid flow diffuser for allowing the fuel to flow, or the permeable membrane of the fuel electrode may be provided. The structure provided with the flow path part provided in the other side and allowing a fuel to flow through may be sufficient.

  In still another aspect of the present invention, in a fuel cell in which a permeable membrane is interposed between a fuel electrode and an oxidant electrode and an alkaline aqueous solution of a metal hydride complex is used as a fuel, water absorption is performed between the oxidant electrode and the permeable membrane. A characteristic buffer material is provided. In this fuel cell, it is preferable to provide a discharge port for discharging a metal hydroxide absorbed by the buffer material, such as a sodium hydroxide aqueous solution.

  For example, carbon paper, carbon cloth (woven fabric) or non-woven fabric is used as the buffer material. The metal hydrogen complex compound is, for example, a borohydride complex compound.

  According to the present invention, by interposing a water-absorbing buffer material between the fuel electrode and the permeable membrane, the fuel is absorbed by the buffer material and retained. For this reason, metal ions such as sodium ions in the fuel move while diffusing in the buffer material, that is, the buffer material acts as a buffer against the flow of metal ions, so the effective passage area of metal ions in the permeable membrane is improved As a result, the passage of metal ions becomes smooth and the electrical characteristics are improved.

  According to another invention, a metal that is a product of an electrode reaction (power generation product) generated on the oxidant electrode side by interposing a water-absorbing buffer material between the oxidant electrode and the permeable membrane. Hydroxides such as aqueous sodium hydroxide are absorbed by the buffer material. For this reason, movement to the inside of the oxidizer electrode is prevented, and the moisture content in the permeable membrane is stabilized, and the increase in sodium ion migration resistance is eliminated, so that the electrical characteristics are improved.

[First Embodiment]
A basic configuration of the first embodiment of the fuel cell according to the present invention will be described with reference to FIGS. 1 and 2. In FIG. 1, reference numeral 2 denotes a rectangular case body, and the inside of the case body 2 is divided into an oxidant electrode (positive electrode) chamber 4 and a fuel electrode (negative electrode) chamber 5 by a permeable membrane 3. In the oxidant electrode chamber 4, a plate-like oxidant electrode 41 is provided so that one surface side thereof is in contact with the permeable membrane 3, and between the other surface side of the oxidant electrode 41 and the case body 2, For example, a flow path portion 42 through which an oxidizing agent such as air flows is formed. An oxidant supply path 43 and a discharge path 44 are connected to the flow path portion 42. The oxidant supply path 43 is connected to the oxidant supply path 43 from the upstream side by an oxidant supply source 45, a supply pump 46, a humidifying means 47, and a heating means. 48 are provided in this order.

  A plate-like fuel electrode 51 is disposed in the fuel electrode chamber 5 so as to face the permeable membrane 3. Between the one surface side of the fuel electrode 51 and the permeable membrane 3, for example, a thickness of 0 made of carbon paper, for example, is formed. A buffer material 6 having a water absorption of 25 mm is interposed. More specifically, the buffer material 6 is configured as a planar body that forms a layer having the same size as the effective area of the permeable membrane 3. Further, a first flow path portion 52 through which fuel flows is formed between the other surface side of the fuel electrode 51 and the case body 2. A fuel supply path 70 and a discharge path 71 are connected to the first flow path portion 52, and a supply pump 72 is interposed in the fuel supply path 70. A fuel storage tank 73 as a fuel supply source is interposed between the upstream side of the fuel supply path 70 and the downstream side of the discharge path 71, and a fuel circulation path is constituted by the fuel supply path 70 and the discharge path 71. ing.

In the fuel cell described above, an insulating material is advantageous as a material constituting the case body 2, and for example, insulating ceramics, resins, metal oxides, and the like are used. As the permeable membrane 3, for example, a polymer electrolyte membrane made of a cation permeable membrane or the like can be used. As the cation permeable membrane, for example, a trade name “Nafion” (manufactured by DuPont) can be used. An anion permeable membrane or a bipolar permeable membrane that transmits both cations and anions can be used. In this embodiment, a boiling sodium hydroxide aqueous solution obtained by immersing the “Nafion” and boiling it is used. "Nafion" is a state in which SO3 ^- ions are bonded to carbon in the fluororesin using a fluororesin as a skeleton, and hydrogen ions (H ⁺ ) are adsorbed to these ions. Therefore, when boiling with sodium hydroxide, hydrogen ions (H ⁺ ) are replaced by sodium ions (Na ⁺ ). That is, in the above-mentioned commercially available permeable membrane, the exchange group is sulfonic acid type (SO3H), but it is changed to sodium type (SO3Na) by treatment with an aqueous solution of sodium hydroxide.

  As the oxidant electrode 41 and the fuel electrode 51, platinum dispersed carbon or metal such as iron, nickel, chromium, copper, platinum, palladium, or an alloy of these metals is used, and power generation efficiency and durability are good and low. In terms of cost, a nickel or nickel-chromium alloy porous body, such as a granular sintered body or foam, is used as a base material, and a catalyst layer is formed by plating a catalyst made of noble metal such as platinum or palladium on the surface. Etc. are used. In the first embodiment, as the oxidant electrode 41 and the fuel electrode 51, for example, those having catalyst layers formed on both surfaces of a porous base material are used.

  As the fuel electrode 51, the above electrode material may be used, but a hydrogen storage alloy or a hydride thereof is particularly preferable. This hydrogen storage alloy or its hydride is not particularly limited as long as it can reversibly absorb and release hydrogen. For example, Mg2Ni alloy, Mg2Ni alloy such as Mg2Ni and Mg eutectic alloy, A2B type Alloys, ZrNi2 alloys, TiNi2 alloys and other Laves phase AB2 alloys, ABFe alloys such as TiFe alloys, AB5 alloys such as LaNi5 alloys, and BCC alloys such as TiV2 alloys You can choose arbitrarily.

  Among these, LaNi4.7Al0.3 alloy, MmNi0.35Mn0.4Al0.3Co0.75 alloy (where Mm is Misch metal), MmNi3.75Co0.75Mn0.20Al0.30 alloy (where Mm is Misch metal), Ti0.5Zr0.5Mn0.8Cr0.8Ni0.4, Ti0.5Zr0.5Mn0.5Cr0.5Ni, Ti0.5Zr0.5V0.75Ni1.25, Ti0.5Zr0.5V0.5Ni1.5, Ti0.1Zr0.9V0.2Mn0. 6Co0.1Ni1.1, MmNi3.87Co0.78Mn0.10Al0.38 (where Mm is Misch metal).

  The performance of these hydrogen storage alloys or hydrides thereof can be significantly improved by subjecting the surface to fluorination treatment. That is, by performing such a fluorination treatment, corrosion resistance to the contacting negative electrode solution is imparted, and a high power generation capacity can be maintained for a long time. This fluorination treatment is performed, for example, by immersing a hydrogen storage alloy or a hydride thereof in an aqueous solution containing a fluorinating agent and fluorinating the surface.

  The oxidant supplied to the oxidant electrode 41 may be oxygen gas or air. However, in order for the reaction of formula (2) described above to proceed, as shown in FIG. It is preferable that moisture be included in the humidifier 47, for example. The oxidizing agent is not limited to a gas, and may be an aqueous solution of an active oxygen generator, for example, an aqueous solution of a peroxide such as hydrogen peroxide.

  As the fuel, an alkali aqueous solution of a metal hydride complex is used. Examples of the metal hydride complex include hydrogenation such as sodium borohydride (NaBH4), potassium borohydride (KBH4), or lithium borohydride (LiBH4). Examples of the boron complex compound include lithium aluminum hydride (LiAlH4) and zinc borohydride (Zn (BH4) 2). As the alkaline aqueous solution, for example, an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide can be used. If the concentration of the aqueous alkali solution is too high, the metal-hydrogen complex compound becomes difficult to dissolve, so it is preferably selected within the range of 30% by weight, for example, 20% by weight. The metal hydrogen complex compound is preferably used at a concentration of, for example, 0.1 to 50% by weight in consideration of the desired power generation capacity and solubility in an alkaline aqueous solution.

  Generally, carbon paper, carbon cloth (woven fabric), and nonwoven fabric are preferably used as the buffer material 6 because they have electrical conductivity and corrosion resistance. In addition, a sheet or nonwoven fabric made of pulp or the like imparted with corrosion resistance, or a nonwoven fabric made of a synthetic polymer such as polyvinyl alcohol can be used. In addition, when using the said sheet | seat and a nonwoven fabric, it is preferable when ensuring the electroconductivity to infiltrate the pigment containing carbon.

  Next, the operation of this embodiment will be described with reference to FIGS. An oxidant such as air from the oxidant supply source 45 is supplied to the flow path portion 42 of the oxidant electrode chamber 4 by the supply pump 46. Here, before supplying the oxidizing agent to the flow path portion 42, the humidifier 47 humidifies the absolute temperature to, for example, about 30 to 70%, and further the heater 48 heats to a necessary temperature, for example, 40 to 90 ° C. The air that has flowed through the flow path portion 42 is discharged from the discharge path 44.

  On the other hand, for example, a fuel obtained by dissolving sodium borohydride in sodium hydroxide is supplied from the fuel storage tank 73 to the first flow path portion 52 of the fuel electrode chamber 5 by the supply pump 72. In this example, the fuel discharged from the first flow path portion 52 is returned to the fuel storage tank 73 and circulated. The fuel permeates into the fuel electrode 51, which is a porous body. At this time, as described in the section of the prior art, the 8-electron reaction represented by the formula (4) (corresponding to the formula (1) described above). It is considered that the four-electron reaction represented by the formula (5) has also occurred.

NaBH 4 +8 NaOH → NaBO 2 + 6H 2 O + 8Na ⁺ + 8e ⁻ (4)
NaBH 4 + 4NaOH → NaBO 2 + 2H 2 O + 2H 2 + 4Na ⁺ + 4e ⁻ (5)
In this way, electrons are taken out from the fuel electrode 51 to the circuit connected to the outside, and sodium ions in the fuel move to the oxidant electrode chamber 4 side through the buffer material 6 and the permeable membrane 3 holding the fuel. However, sodium hydroxide is generated from sodium ions, oxygen, and moisture as shown in the above-described equation (2).

  According to such an embodiment, since the water-absorbing buffer material 6 is interposed between the permeable membrane 3 and the fuel electrode 51, the following effects are obtained. Sodium ions, which are metal ions ionized by the electrode reaction at the fuel electrode 51, freely move while diffusing in the buffer material 6 that has been retained. Since the sodium ions diffused by the buffer material 6 are uniformly dispersed over the entire surface of the permeable membrane 3 that is in surface contact with the buffer material 6, the effective passage area of sodium ions in the permeable membrane 3 is improved. Smooth passage of sodium ions.

  Further, as described in the conventional item, on the one surface side of the fuel electrode 51 in contact with the permeable membrane 3, the following expressions (6) and (7) (corresponding to the expressions (3) and (4) described above) Generated by the generation of hydrogen gas in the four-electron reaction shown in the following equation (6) generated on the permeable membrane 3 side of the fuel electrode 51 as the electrode reaction at the fuel electrode 51 proceeds. The trapped air bubbles are trapped in the water-absorbing buffer material 6, so that the adhesion to the permeable membrane 3 is reduced. As a result, the passage area of sodium ions in the permeable membrane 3 is improved and the passage of sodium ions is smooth. Therefore, the electrical characteristics are improved as is apparent from the examples described later.

^{BH4 - + 8OH - → BO2 -} + 6H2O + 8e - ...... (6)
BH4 ⁻ + 4OH ⁻ → BO2 ⁻ + 2H2O + 2H2 + 4e ⁻ (7)
Further, the fuel electrode 51 and the permeable membrane 3 are not brought into direct contact with each other, and a water-absorbing buffer material is interposed therebetween, thereby suppressing the occurrence of damage to the membrane surface of the permeable membrane 3 and oxidizing from the fuel electrode chamber 5. This is useful for preventing fuel leakage to the agent electrode chamber 4.

[Second Embodiment]
The basic configuration of the second embodiment of the fuel cell according to the present invention will be described with reference to FIG. In this fuel cell, the structure is devised so that fuel is supplied to the water retention buffer material 3 interposed between the fuel electrode 51 and the permeable membrane 3 in the fuel cell of the first embodiment. . That is, the fuel supply flow path 70 and the discharge path 71 are provided with a flow dividing supply path 74 and a flow dividing discharge path 75, respectively, and the flow dividing supply path 74 and the flow dividing discharge path 75 are connected to the upper side and the lower side of the cushioning material 6, respectively. The fuel is supplied from the diversion supply path 74 to the buffer material 6, and the fuel is discharged from the diversion discharge path 75 through the buffer material 6. In this case, by setting the thickness of the buffer material 6 to, for example, 0.25 mm, the buffer material 6 serves as a fuel flow path portion.

  Describing the operation of this embodiment, the fuel supplied to the flow path portion 52 and the buffer material 6 permeates from one side and the other side of the fuel electrode 51, which is a porous body, as described above. An 8-electron reaction and a 4-electron reaction occur. Sodium ions, which are metal ions freed by the electrode reaction, pass through the permeable membrane 3 while diffusing through the buffer material 6 retained by the fuel, and reach the oxidant electrode 41 on the oxidant electrode chamber 4 side. As shown in the above-described equation (2), sodium hydroxide is generated from sodium ions, oxygen and moisture.

  Even with such a structure, the same effect as that of the fuel cell according to the first embodiment can be obtained, and the buffer material 6 serves as a fuel flow path portion. And the fuel can be brought into contact from both the other side. Then, since new fuel diffuses to the surface of the fuel electrode 51 on the side of the permeable membrane 3, an active electrode reaction occurs in this portion, and free sodium ions pass through the buffer electrode 6 without passing through the fuel electrode 51. Therefore, the movement resistance of sodium ions is further reduced.

[Third Embodiment]
The basic configuration of the third embodiment of the fuel cell according to the present invention will be described with reference to FIG. This fuel cell is the same as that of the fuel cell of the first embodiment, but is a liquid flow diffuser that forms a second flow path portion of fuel between the fuel electrode 51 and the buffer material 6, for example, a net-like shape formed in a plate shape. A nickel net 53 as a structure is interposed. That is, the fuel supply flow path 70 and the discharge path 71 are provided with a flow dividing supply path 76 and a flow dividing discharge path 77, respectively, and the flow dividing supply path 76 and the flow dividing discharge path 77 are connected to the upper side and the lower side of the nickel net, respectively. The fuel is supplied from the diversion supply path 76 to the nickel net 53, and the fuel is discharged from the diversion discharge path 77 through the nickel net 53. The second flow path portion of the fuel between the fuel electrode 51 and the buffer material 6 is not limited to the net-like structure such as the nickel net 51, but contacts the fuel electrode 53 when the fuel flows through the flow path portion. It is preferable to stir the fuel so that the fuel can be diffused and replaced as much as possible. Therefore, a network structure that can also be referred to as a diffusion layer in terms of a structure in which the fuel flows while colliding rather than a simple space. preferable. Other examples of the second flow path part include a porous sheet and a foamed sheet.

  The operation of this embodiment will be described with reference to (a) of FIG. 5. The fuel supplied to the first flow path portion 52 exhibits the above-described operation, and the fuel supplied to the nickel net 53 Since it is diffused by the nickel net 53, the stirring action at that time works to move downstream while contacting and penetrating the fuel electrode 51. At this time, sodium borohydride, which is the fuel flowing through the nickel net 53, contacts the catalyst layer on the surface of the fuel electrode 51 to cause an electrode reaction. As a result, sodium ions, which are charge carriers, become free, The sodium ions diffuse through the buffer material 6 retained by the fuel and pass through the permeable membrane 3 to reach the oxidant electrode 41 on the oxidant electrode chamber 4 side. As shown, sodium hydroxide is produced from sodium ions, oxygen and moisture.

  Even with such a structure, the same effects as those of the first embodiment can be obtained, and the nickel net 53 as the second flow path portion is interposed between the fuel electrode 51 and the buffer material 6. Therefore, since the sodium ions generated by the electrode reaction on the one surface side of the fuel electrode 51 in contact with the nickel net 53 do not pass through the fuel electrode 51, the fuel electrode 51 does not become a resistance and reaches the permeable membrane 3 smoothly. be able to. Therefore, since the resistance when sodium ions move from the fuel electrode chamber 5 to the oxidant electrode chamber 4 side is small, it is possible to suppress a decrease in output voltage that occurs with an increase in current.

  Further, although it is effective to use the nickel net 53 as described above, in the case where no buffer material is interposed between the nickel net 53 and the permeable membrane 3, as shown in the image diagram shown in FIG. Sodium ions in the permeable membrane 3 do not diffuse uniformly and pass through the permeable membrane 3 as they are. That is, since the nickel net 53 is a net-like structure, sodium ions cannot pass through the net-like portion and pass through only from spaces other than the net-like portion, so that the effective area in the permeable membrane 3 is limited. Will be. On the other hand, when the buffer material 6 is interposed between the permeable membrane 3 and the nickel net 53, sodium ions that have passed through the nickel net 53 are absorbed by the buffer material 6 as shown in the image diagram of FIG. Then, a large number of sodium ions are once trapped in the buffer material 6 and moved to the permeable membrane 3, so that the passage area of sodium ions in the permeable membrane 3 is improved.

[Fourth Embodiment]
A basic configuration of the fourth embodiment of the fuel cell according to the present invention will be described with reference to FIG. In the fuel cell according to the first embodiment, instead of interposing the buffer material 6 between the fuel electrode 51 and the permeable membrane 3, for example, between the oxidant electrode 41 and the permeable membrane 3, It is characterized in that the same cushioning material 6 as described above is provided. Further, on the side of the oxidant electrode chamber 4, a discharge path 49 a that is a discharge port for discharging a metal hydroxide such as a sodium hydroxide aqueous solution is provided on the lower surface side of the buffer material 6.

  As described above, the reaction of the formula (2) occurs on one side of the oxidant electrode 41 in contact with the buffer material 6, and the water-absorbing buffer material 6 uses the sodium hydroxide aqueous solution generated on this one side. Absorb. Then, the aqueous sodium hydroxide solution accumulated in the buffer material 6 descends in the buffer material 6 due to gravity and is discharged from the discharge path 49a.

  Further, as shown in FIG. 6B, the oxidizer electrode 41 may be provided with a large number of through holes 49b serving as discharge ports for a metal hydroxide, for example, a sodium hydroxide aqueous solution. In this case, the liquid in the buffer material 6 is drawn by the negative pressure generated by supplying the oxidizing agent to the flow path portion 42, and the aqueous sodium hydroxide solution accumulated in the buffer material 6 is discharged through the through hole 49b. Will be.

  According to this embodiment, by interposing the water-absorbing buffer material 6 between the oxidant electrode 41 and the permeable membrane 3, the product of the electrode reaction (power generation) generated on one surface side of the oxidant electrode 41. The product (metal hydroxide) such as sodium hydroxide aqueous solution is absorbed by the buffer material 6. For this reason, the movement of the water accompanying sodium ions into the oxidizer electrode 41 is suppressed, and in addition, the moisture content in the permeable membrane 3 is stabilized. Stabilize.

  Further, by causing a water-absorbing buffer material to intervene between the oxidant electrode 41 and the permeable membrane 3 without directly contacting them, the occurrence of damage to the membrane surface of the permeable membrane 3 is suppressed, and the fuel electrode chamber 5 This is useful for preventing fuel leakage to the oxidant electrode chamber 4.

[Fifth Embodiment]
Next, an example that further embodies the above-described embodiment will be described with reference to FIGS. In this example, the unit cells of the third embodiment shown in FIG. 4 are stacked to constitute a fuel cell stack. However, in this specification, the fuel cell stack is referred to as a fuel cell. In the following description, the same reference numerals are given for the portions corresponding to FIG. 7A and 6B are separators (bipolar plates) made of, for example, a conductive material, and the permeable membrane 3 is disposed between the separators 6A and 6B. The buffer material 6, the nickel net 53, and the fuel electrode 51 described above are disposed between the permeable membrane 3 and one separator 6A, and the oxidant electrode 41 is disposed between the permeable membrane 3 and the other separator 6B. As shown in FIG. 8, a plurality of unit cells 60 including a fuel electrode 51, a nickel net 53, a buffer material 6, a permeable membrane 3, an oxidant electrode 41, and gaskets 7A and 7B described later are provided via separators 6A and 6B. These are stacked, and this stack is fixed between the end plates 100 and 101. The fuel electrode 51, the nickel net 53, the buffer material 6 and the oxidant electrode 41 are fixed to each other with, for example, an adhesive, and constitute a membrane / electrode assembly (MEA).

  Grooves forming curved paths are formed on the front surface (front surface in FIG. 7) and back surface (rear surface) of each separator 6A, 6B. The groove on the front surface side of each separator 6A, 6B is an oxidant flow path 61, and the groove on the back surface side is a fuel flow path 62. The flow path 61 corresponds to the first flow path portion 42 of the third embodiment. In FIG. 7, the back side of the separator 6A is shown at the left end. 7A and 7B are gaskets, and windows 71 are formed in the gaskets 7A and 7B, respectively. The fuel electrode 51, the nickel net 53, and the buffer material 6 are closely fitted in the window 71 of one gasket 7A, and the oxidant electrode 41 is closely fitted in the window 71 of the other gasket 7B.

  A discharge port 63 is formed at the upper left end of the oxidant flow path 61 in the separator 6A, and the permeation membrane 3 and the gaskets 7A, 7B have holes 31, 72, 72 at portions corresponding to the discharge port 63, respectively. Is drilled. Accordingly, the oxidant supplied to the supply end 61a at the lower right end of the flow path 61 flows through the flow path 61 and is discharged from the discharge port 63, and is supplied to the flow path 61 of the separator 6B through the holes 72, 31, and 72. The end 61a is reached.

  FIG. 9 is a view showing a state where the fuel electrode 51 and the nickel net 53 are attached to the separator 6A, and FIG. 10 is a view showing the back side of the separator 6A. In this example, the flow path 62 of the separator 6 </ b> A has a fuel supply port 64 formed at the upper left end of the flow path 62 in FIG. 10, and the fuel supplied therefrom flows into the flow path 62 and the nickel net 53. It goes to the discharge end 65 at the lower right end of the flow path 62. The area in which the flow path 62 is formed is substantially rectangular, but the inlet side and the outlet side protrude slightly from the square area to the left and right as indicated by reference numerals 62b and 62c, and one surface of the nickel net is the protruding part. It is made the same size as the rectangle except for.

  A fuel electrode 51 is interposed between the separator 6A and the nickel net 53 in a state where both surfaces thereof are in contact with the separator 6A and the nickel net 53, respectively. The width of the fuel electrode 51 (the length in the left-right direction in FIG. 9) is the same as that of the nickel net 53, but the length in the vertical direction is shorter than that of the nickel net 53. The net 53 is closer to the inside than the upper end and the lower end of the net 53 by about half the width of the flow path 62 (the width of the two grooves 62a). Accordingly, as can be seen from FIG. 9, spaces (communication paths) 66 and 67 surrounded by the portion of the nickel net 53 protruding from the upper and lower sides of the fuel electrode 51 and the gasket 7A are formed, and the upper fuel supply port 64 is the space 66. The nickel net 53 communicates with the lower portion (discharge side) of the nickel net 53 through the space 67 and communicates with the fuel discharge end 65.

  In the permeable membrane 3 and the gaskets 7A and 7B, holes (holes 73 of the gasket 7A are shown in FIG. 9) are formed at positions corresponding to the discharge end 65, and the discharge end 65 discharges. The fuel thus obtained passes through each hole and reaches a fuel supply port that is hidden in FIG. 7 in the flow path 62 of the separator 6B. Therefore, in this example, the hole 73 of the gasket 7A corresponds to the fuel discharge port.

  Next, the operation of this embodiment will be described with reference to FIGS. 11 and 12. The fuel sent to the separator supply port 64 flows into the bent flow path 62 formed of a groove formed in the separator 6A. Through the communication passage 66, the nickel net 53 flows in from the portion protruding from the fuel electrode 51 at the upper end portion in the figure, flows through the nickel net 53 as shown by the arrow 102 in FIG. To the discharge end 65. Both of these fuels reach the supply end of the fuel flow path 62 formed on one side of the separator 6B through the hole 32 of the permeable membrane 3 and the discharge port 73 of the gasket 7B as shown in FIG. . Further, as described above, the oxidant supplied to the inlet side of the flow path 61 of the separator 6B, for example, humidified air, flows through the flow path 61 of the separator 6B.

  Also in such an embodiment, the same effect as the effect of the third embodiment is obtained. The unit cells of the first, second, and fourth embodiments may be stacked and similarly configured as a fuel cell stack, and the same effects as the effects of the first, second, and fourth embodiments. Can be obtained.

  In the fuel cells of the first to fifth embodiments, a water absorbing buffer material may be interposed between the oxidant electrode and the permeable membrane and between the fuel electrode and the permeable membrane. That is, in the first to third and fifth embodiments, a configuration in which the buffer material 6 is interposed between the permeable membrane 3 and the oxidant electrode 41, that is, a configuration in which the fourth embodiment is combined. Also good. In this way, the occurrence of damage on both sides of the permeable membrane 3 can be suppressed, and fuel leakage from the fuel electrode chamber 5 to the oxidant electrode chamber 4 can be prevented. In the second and third embodiments, the first flow path portion 52 does not necessarily have to be provided. In this case, the fuel electrode 51 may not be a porous body, for example, the permeable membrane 3 side. Alternatively, a catalyst layer may be used.

  Next, an experiment conducted for confirming the effect of the present invention will be described.

(Experimental example)
A. Example 1
After 13.6 g of Zr0.9Ti0.1Mn0.6V0.2Co0.1Ni1.1 alloy powder having an average particle diameter of 2 to 5 μm treated with fluorination and 1.36 g of PTFE powder, which is a fluororesin, were rubbed together, The catalyst layer was formed on both surfaces of a Ni foam (80 mm long, 84.6 mm wide, 0.8 mm thick) as a base material. And after wrapping this Ni foam with a 100 mesh Ni net | network, these were crimped | bonded by the roll press and the plate-shaped fuel electrode of thickness 0.5mm was produced. As the oxidant electrode, an oxidant electrode in which platinum particles as a catalyst were dispersed and supported on the surface of carbon black (80 mm length, 84.6 mm width, 0.2 mm thickness) as a base material was used.

  A permeable membrane made of a cation exchange membrane (made by DuPont, trade name: Nafion) is provided between the fuel electrode and the oxidizer electrode, and carbon paper (vertical) is used as a buffer material between the fuel electrode and the permeable membrane. 80 mm, width 84.6 mm, thickness 0.25 mm) (manufactured by Toyobo Co., Ltd.) and these were tightly joined to produce a fuel cell having the structure shown in FIG. The relationship between the output voltage and output current of this fuel cell was examined. As for this measurement method, as shown in FIG. 13, a load resistor 202 is connected to the fuel cell 200 via a constant current source 201, and the constant current source 201 is changed by changing the parameters of the constant current source 201 while keeping the load resistor 202 constant. The output voltage of the fuel cell was measured by changing the current output from the fuel cell. The measurement conditions are as follows. The fuel supplied to the fuel electrode is prepared by dissolving 10% by weight of sodium borohydride in a 20% by weight sodium hydroxide aqueous solution, adjusting the temperature to 60 ° C., and at a flow rate of 0.135 liters / minute. Supplied to the pole. The oxidizing agent supplied to the oxidizing agent electrode was humidified to 60 ° C. with a humidifier and supplied to the oxidizing agent electrode at a flow rate of 5 liters / minute.

B. Comparative Example 1
A fuel cell was fabricated in the same manner as in Example 1 except that no carbon paper was interposed between the fuel electrode and the permeable membrane, and the output voltage of this fuel cell was examined under the same measurement conditions.

(Results and discussion)
FIG. 14 shows the results of Example 1 and Comparative Example 1, and is a characteristic diagram in which the vertical axis represents power density (mW / cm 2) and the horizontal axis represents current density (A / cm 2). As can be seen from FIG. 13, the maximum values of current density and power density of Comparative Example 1 are 0.27 A / cm 2 and 155 mW / cm 2, respectively, whereas the maximum values of current density and power density of Example 1 are Thus, the current is 0.35 A / cm 2 and 195 mW / cm 2, so that more current and power can be extracted from the fuel cell in which the carbon paper is interposed between the fuel electrode and the oxidant electrode.

  FIG. 15 shows the change in power density over time in the state where the current density was maintained at 0.2 A / cm 2 in Example 1 and Comparative Example 1, and the vertical axis represents the power density (mW / cm 2). It is the characteristic view which took elapsed time (min) on the axis | shaft. As can be seen from FIG. 15, it can be understood that the fuel cell in which the carbon paper is interposed between the fuel electrode and the permeable membrane has a smaller power density drop with respect to the elapsed time.

It is sectional drawing which shows the outline of 1st Embodiment of the fuel cell which concerns on this invention. It is explanatory drawing which shows the effect | action of the said embodiment. It is sectional drawing which shows the outline of 2nd Embodiment of the fuel cell which concerns on this invention. It is sectional drawing which shows the outline of 3rd Embodiment of the fuel cell which concerns on this invention. It is explanatory drawing which shows the effect | action of the said embodiment. It is sectional drawing which shows the outline of 4th Embodiment of the fuel cell which concerns on this invention, and a perspective view which shows a part of fuel cell. It is a disassembled perspective view which shows the outline of 5th Embodiment of the fuel cell which concerns on this invention. It is a perspective view which shows the external appearance of the said 5th Embodiment concretely. It is a perspective view which shows a part of fuel cell shown in FIG. It is a top view which shows the separator shown in FIG. It is an AA perspective view which cuts and shows a part of fuel cell shown in FIG. It is sectional drawing which shows the outline of 5th Embodiment of the fuel cell which concerns on this invention. It is a circuit diagram for measuring the output voltage and output power of a fuel cell. It is the characteristic view which showed the voltage measurement of each fuel cell. It is the characteristic view which showed the voltage measurement of each fuel cell. It is sectional drawing which shows the outline of the conventional fuel cell.

Explanation of symbols

2 Case body 3 Permeation membrane 4 Oxidant electrode chamber 41 Oxidant electrode 42 Channel portion 49a Discharge passage 49b Through hole 5 Fuel electrode chamber 51 Fuel electrode 52 First channel portion 53 Nickel net 6 Buffer material 61 Channel 62 Flow Path 6A, 6B Separator 7A, 7B Gasket

Claims (8)

In a fuel cell in which a permeable membrane is interposed between a fuel electrode and an oxidant electrode and an alkaline aqueous solution of a metal hydride complex is used as a fuel,
A fuel cell, wherein a water-absorbing buffer material is provided between the fuel electrode and the permeable membrane. In a fuel cell in which a permeable membrane is interposed between a fuel electrode and an oxidant electrode and an alkaline aqueous solution of a metal hydride complex is used as a fuel,
A fuel cell, wherein a water-absorbing buffer material is provided between the oxidant electrode and the permeable membrane.   3. The fuel cell according to claim 2, further comprising a discharge port for discharging the metal hydroxide absorbed by the buffer material.   2. The fuel cell according to claim 1, wherein the buffer material also serves as a fuel flow path.   2. The fuel cell according to claim 1, further comprising a flow path portion formed of a liquid flow diffuser for allowing fuel to flow between the fuel electrode and the buffer material.   6. The fuel cell according to claim 4, further comprising a flow path portion provided on the opposite side of the fuel electrode to the permeable membrane side for allowing fuel to flow therethrough.   The fuel cell according to any one of claims 1 to 6, wherein the cushioning material is carbon paper, carbon cloth (woven fabric), or nonwoven fabric. 8. The fuel cell according to claim 1, wherein the metal hydride complex compound is a borohydride complex compound.

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