JP5003056B2 - Fuel cell - Google Patents

Description

  The present invention relates to a fuel cell, and more particularly, to a direct methanol fuel cell suitable for a drive power source of a portable electronic device.

  In recent years, due to remarkable progress of portable electronic devices such as mobile phones, PDAs, and notebook personal computers, the power consumption of these devices has increased while the usage time has become longer. For this reason, a battery that is a driving power source is strongly required to have a high capacity in addition to being light and thin.

  By the way, a lithium ion secondary battery has been frequently used as a mounting power source for portable electronic devices. This battery has a high driving voltage and a large battery capacity, and has been improved in performance to match the progress of portable electronic devices.

  However, the performance improvement of lithium ion secondary batteries is now approaching the limits in terms of materials and structure, and it has become difficult to satisfy the demand as a drive power source corresponding to the progress of portable electronic devices. Yes.

  As a new high-capacity power supply that breaks down the current situation, fuel cells that have a power supply capacity several times higher than that of lithium-ion secondary batteries and have the potential to replace lithium-ion secondary batteries have been proposed. It was.

  The basic structure of a fuel cell has a structure in which a solid electrolyte membrane capable of ion migration is sandwiched between an anode containing a catalyst and a cathode. The components of the fuel cell are called by various names. The anode is also called a fuel electrode because it is a negative electrode or an electrode that oxidizes fuel. The cathode is a positive electrode or oxygen (usually oxygen in the air) is reduced. Because it is an electrode, it is also called an air electrode. Here, they are collectively referred to as an anode and a cathode.

  When fuel is supplied to the anode and oxygen is supplied to the cathode, an electrochemical reaction occurs in each of the electrodes by the action of the catalyst contained in the electrodes, and current can be taken out using the fuel as a supply source.

  In a fuel cell that generates power by such a mechanism, continuous power generation is possible by continuously supplying fuel and oxygen. Therefore, the fuel cell can be used in the same manner as a secondary battery repeatedly used by a charging operation by replenishing fuel and oxygen.

  FIG. 3 is a basic configuration diagram of the fuel cell, FIG. 3 (A) is a plan view, and FIG. 3 (B) is a schematic sectional view.

  FIG. 3A is a plan view of the fuel cell 10 as viewed from above with the battery housing 1 opened, and the power generation unit 2 is disposed at the center. A fuel tank 6 is disposed on the right side of the power generation unit 2 in the figure, and a fuel supply line 61 is disposed from the fuel tank 6 to the power generation unit 2. A control circuit 7 is arranged on the left side. A gas exchange unit 12 is disposed on the upper side and the lower side of the power generation unit 2 in the drawing so that oxygen (air) can be taken in and generated water vapor and carbon dioxide gas can be discharged.

  FIG. 3B is a cross-sectional view taken along the line Y-Y in FIG. 3A, and the basic configuration of the power generation unit 2 is a layer configuration in which the cathode 21 and the anode 22 sandwich the solid electrolyte layer 23. . Both the cathode 21 and the anode 22 are formed by layering carbon powder carrying a catalyst with a binder.

  The anode 22 includes, for example, a platinum-ruthenium alloy-supported catalyst, and oxidizes the fuel vaporized by the liquid fuel to generate protons and electrons. The generated protons move to the cathode 21 through the solid electrolyte layer 23 having ion conductivity. The cathode 21 includes, for example, a platinum-supported catalyst, and generates water by reducing oxygen.

  By the way, the fuel cell is classified into various types depending on the type of electrolyte and fuel. The power source of the portable electronic device can be operated at a low temperature near room temperature, can be configured in a small size, is strong against vibration, A direct methanol fuel cell (DMFC) that supplies an aqueous methanol solution as a fuel to the anode is considered to be preferable because it includes a solid electrolyte that is easy to produce.

  At present, a large number of direct methanol fuel cells are well known, but can be classified into various types according to the fuel supply system and the state of the fuel to the electrode structure constituting the anode.

  Naturally vaporized passive direct methanol fuel cells that vaporize fuel naturally and supply it by gravity, capillary action, and natural diffusion can supply high-concentration methanol and discharge reaction products with a simple structure. it can.

  In other words, the natural vaporization type passive direct methanol fuel cell has the advantage of minimizing the amount of water vapor that is generated at the cathode and discharged outside the system during power generation, since the moisture contained in the methanol fuel is small.

  However, many fuel-diluted direct methanol fuel cells are derived not only from water produced at the cathode during power generation, but also from water obtained by diluting fuel (for example, see Patent Document 1).

  By the way, in the method using a methanol aqueous solution having a high concentration close to 100%, the water necessary for the power generation reaction of fuel oxidation at the anode is the natural water diffused through the electrolyte membrane to the anode by the natural diffusion of the water generated during power generation at the cathode of the counter electrode. There is no need to add water to the fuel for transportation.

  Therefore, it is possible to reduce the amount of water vapor by the amount of water that dilutes the fuel, and the water vapor that is released comes only from the water that is inevitably produced by the power generation reaction. As a result, problems caused by water vapor such as dew condensation outside the fuel cell can be reduced to a minimum (see, for example, Patent Document 2).

  On the other hand, in order to operate a direct methanol fuel cell using a high-concentration methanol solution close to 100% concentration, the evaporation of water generated at the cathode is controlled and suppressed below a certain amount, and the water supply to the anode is controlled. It is necessary to work efficiently.

  As one of such means, there is a method in which a space surrounded by a casing is arranged near the anode, and a gas exchange port is provided in a part of the space. In this method, the diffusion of water vapor in the atmosphere is suppressed by the gas exchange port, and the relative humidity in the space is maintained at a high humidity to suppress the evaporation of water from the anode.

  By the way, according to this method, when a temperature difference occurs between the fuel cell main body and the housing, a part of the water vapor from the cathode is condensed inside the housing. This dew condensation phenomenon is an advantageous characteristic in terms of reducing the release of water vapor out of the fuel cell system and controlling the temperature inside the housing.

  However, if this condensed water moves and leaks into a device equipped with a fuel cell, the use environment of the user is greatly impaired. In addition, fixing of condensed water is indispensable because water leakage causes damage to the circuit.

  Conventionally, there are several proposals for a method for managing condensed water in such a casing.

  One of the proposals discloses a fuel cell having a recovery cartridge that absorbs generated water into a water-absorbing polymer. However, with this method, there is a problem that the downsizing of the apparatus is difficult and the operation such as cartridge replacement becomes complicated. Moreover, since the water-absorbing polymer used here generally has high water absorption performance, the water is naturally evaporated after water supply and dried at a low rate. For this reason, there has been a problem that periodic replacement of the collection card ridge cannot be avoided (see, for example, Patent Document 3).

There is also a proposal for treating the generated water generated at the cathode by providing a water-absorbing / hydrophobic portion having both hydrophilicity and hydrophobicity in the casing of the fuel cell. However, such a polymer material having both hydrophilicity and hydrophobicity is generally an expensive material in many cases. Therefore, a lower cost method is desired (for example, refer to Patent Document 4).
Japanese Patent No. 3413111 JP 2006-040882 A JP 2003-203668 A JP 2006-344346 A

  As described above, in order to operate a direct methanol fuel cell using a high concentration methanol aqueous solution close to 100% in order to realize high energy density in the fuel cell, it is generated at the cathode. Water management and control are important.

  However, for the new problem of fixing the dew condensation water generated due to the temperature difference in the space in the housing provided for the management of the generated water, the troublesome replacement of the recovery cartridge and the expensive absorbent material There was a problem such as using.

  Therefore, the present invention has a hydrophilic porous membrane that faces the space provided in the power generation unit and the battery casing and allows water vapor to pass but does not allow water to pass, and once the water vapor passing through the porous membrane has condensed, An object of the present invention is to provide a fuel cell that prevents the condensed water from leaking from the battery casing until it evaporates.

The problem described above is that, in claim 1, a power generation unit in which a cathode for reducing oxygen to an active material and an anode for oxidizing fuel are disposed with a solid electrolyte membrane interposed therebetween, and fuel is supplied to the power generation unit. In a fuel cell comprising a fuel supply unit that is supplied in a form and a housing in which a space is disposed in the vicinity of the cathode, the fuel cell is disposed on the inner surface of the battery housing in the vicinity of the cathode that faces the space, and allows water vapor to pass therethrough but water A porous porous membrane that does not pass through, and an inner surface of the battery casing in the vicinity of the cathode that faces the space, and the porous membrane is stretched over the entire opening of the condensed water holding portion The fuel cell is configured to include a dew condensation water holding unit .

That is, in the fuel cell of the present invention, a hydrophilic porous membrane that allows water vapor to pass but does not allow water to pass is disposed on the inner surface in the vicinity of the cathode facing the space provided in the housing.

  As a result, in fuel cells using high-concentration aqueous methanol, especially in fuel cells for ultra-small devices such as mobile phones, it is possible to control water leakage at a low price by preventing condensation in the water retention space. it can.

Further , in claim 1 , there is a dew condensation water holding portion drilled in the inner surface of the battery casing near the cathode facing the space, and the porous membrane is stretched over the opening of the dew condensation water holding portion. It is solved by configured fuel cell as.

  That is, the inner surface of the battery casing at the part where the porous membrane is disposed is formed, and the concave portion is used as the dew condensation water holding portion. And the porous membrane is stretched | stretched so that the opening whole surface of the condensed water holding part may be covered with a lid | cover.

  Then, although the gas such as water vapor passes through the porous membrane, the liquid such as water having viscosity does not pass through the porous membrane, so that the water vapor flows into the condensed water holding portion through the porous membrane. However, even if the flowing water vapor condenses in the dew condensation water holding part, the dew condensation water does not pass through the porous membrane, so that it can be prevented that the water vapor is held by the dew condensation water holding part and leaks.

Next, in claim 2 , the porous membrane is solved by the fuel cell according to claim 1, wherein the pore diameter is configured not to exceed 0.01 mmφ.

  In other words, a porous membrane that prevents dew condensation in the space cannot easily be retained by the surface free energy (surface tension) of water if the pore diameter is too small, but if it is too large, water will leak from the pore. Therefore, the preferable pore diameter does not exceed 0.01 mmφ.

Then, in claim 3, condensation water holding section is solved by a fuel cell according to claim 1, wherein the thickness is configured so as not to exceed 2 mm.

  In other words, an excessively large space for holding water generated at the cathode not only goes against reducing the size of the fuel cell itself, but also the volume of the space is large and the water retention of the porous membrane does not function sufficiently. Therefore, the thickness of the space should not exceed 2 mm, and the atmosphere containing water in the space should be in sufficient contact with the porous membrane.

  In the present invention, a porous membrane that allows water vapor to pass but does not pass water is disposed on the inner surface of the battery casing facing the space provided between the cathode of the power generation unit and the battery casing. And the water vapor | steam produced | generated by the cathode is passed through a porous membrane, and the water which condensed has prevented it from leaking from a porous membrane.

  As a result, especially in fuel cells using high-concentration methanol, not only does water vapor condensate generated by methanol crossover prevent leakage from the battery housing, but it also manages and controls the water produced by the cathode. It can be carried out.

FIG. 1 is an explanatory view of an embodiment of a fuel cell according to the present invention. FIG. 1 (A) is a partially cutaway plan view, FIG. 1 (B) is an XX cross-sectional view of FIG. ) Shows a schematic cross-sectional view of the power generation unit, FIG. 2 is a schematic flow chart of the power generation operation of the fuel cell of the present invention, FIG. 2 (A) is the start of power generation, FIG. 2 (B) is the power generation, 2 (C) shows the end of power generation, and FIG. 2 (D) shows no power generation.
〔Example〕
FIG. 1A is a plan view of the fuel cell 10 according to the present invention when the battery casing 1 is opened and seen from above, and the power generation unit 2 is arranged at the center. A fuel tank 6 is disposed on the right side of the power generation unit 2 in the figure, and a fuel supply line 61 is disposed from the fuel tank 6 to the power generation unit 2. A control circuit 7 is arranged on the left side. Further, gas exchange ports 11 are arranged on the upper side and the lower side of the power generation unit 2 in the drawing so that the generated water vapor and the like can be discharged.

  A porous membrane 4 is disposed on the back side of the power generation unit 2 where the power generation unit 2 is cut out. The depth direction of the porous membrane 4 in the drawing is formed in a concave shape in the battery housing 1 to form a condensed water holding unit 5. ing. The porous membrane 4 is stretched so that the cover covers the entire opening of the condensed water holding unit 5. Thus, since the dew condensation water holding part 5 is perforated in the battery casing 1, even if this configuration is added, the size of the fuel cell 1 itself is not different from the conventional one.

  FIG. 1B is a cross-sectional view taken along the line XX in FIG. 1A and shows a main part of the fuel cell of the present invention. A power generation unit 2 is housed in the central portion of the battery casing 1 of the fuel cell 10. The basic configuration of the power generation unit 2 is a layer configuration in which the cathode 21 and the anode 22 sandwich the solid electrolyte layer 23 as shown in the schematic cross-sectional view of FIG. Both the cathode 21 and the anode 22 are formed by layering carbon powder carrying a catalyst with a binder.

  The anode 22 includes, for example, a platinum-ruthenium alloy supported catalyst: TEC61E54 (manufactured by Tanaka Kikinzoku Co., Ltd.), and methanol of liquid fuel introduced from a fuel storage unit (not shown) is oxidized together with water by the action of the catalyst. Protons and electrons are generated. The generated protons move to the cathode 21 through the solid electrolyte layer 23 having ion conductivity.

  For the solid electrolyte layer 23, for example, an ion conductive solid polymer film such as perfluorosulfonic acid (trade name: Nafion 112, manufactured by DuPont) is used.

  In the cathode 21, oxygen is reduced together with protons that have moved through the solid electrolyte layer 23 by the action of the catalyst to become an active material, and generate water. Examples of the catalyst include a platinum-supported catalyst: TEC10E50E (manufactured by Tanaka Kikinzoku Co., Ltd.).

  The surface area of the power generation unit 2 is 80 mm × 40 mm. A space 3 having a thickness of 2 mm is provided between the battery case 1 facing the power generation unit 2. A concave portion having a depth of 0.5 mm is provided on the inner surface of the battery housing 1 facing the space 3, and the concave portion serves as a dew condensation water holding portion 5. Further, the porous membrane 4 is stretched so that the entire opening portion of the condensed water holding portion 5 is covered with a lid.

  The porous membrane 4 is a hydrophilic filter that transmits gas such as water vapor but does not transmit viscous liquid such as water. For example, Durapore membrane filter HVLP14250 (manufactured by Nihon Millipore) is used. .

  FIG. 2 is a schematic flow chart of the power generation operation of the embodiment of the present invention. The action and effect of the porous membrane 4 before and after the power generation operation are shown in FIG. 1 (B). The fuel cell will be described with reference to a schematic cross-sectional view. In the figure, the part with a halftone dot pattern indicates the presence of water vapor, and the arrow indicates the direction of movement of the water vapor.

  FIG. 2A shows the internal state of the battery casing 1 of the fuel cell 10 at the start of power generation, and fuel methanol is oxidized by a catalytic reaction at the anode of the power generation unit 2 to generate protons. The protons move through the solid electrolyte layer to the cathode, and water is generated by the action of the catalyst together with oxygen.

  In the direct methanol fuel cell using high-concentration methanol as the fuel, the water generated at the cathode causes the temperature of the power generation unit 2 to rise due to the so-called methanol crossover that occurs when methanol permeates through the solid electrolyte layer. In addition, water vapor is generated as indicated by an arrow 81, and the relative humidity in the vicinity of the cathode facing the space 3 increases.

  Next, FIG. 2 (B) shows the state of the inside of the battery casing 1 of the fuel cell 10 during power generation, and the amount of water vapor indicated by a halftone dot pattern as the generation and temperature increase of water in the power generation unit 2 further progresses. Will increase. The water vapor passes through the porous membrane 4 as indicated by an arrow 82, and is condensed due to a temperature difference between the power generation unit 2 and the battery casing 1, and begins to accumulate in the condensed water holding unit 5 as liquid water. At the same time, discharge starts from the gas exchange port 11 in the direction of the arrow 83. The release of water vapor from the gas exchange port 11 determines the evaporation rate of water from the power generation unit 2.

  Next, FIG. 2C shows the internal state of the battery housing 1 of the fuel cell 10 when the power generation is finished, and the temperature of the power generation unit 2 decreases and the evaporation of water stops. The water vapor filling the space 3 is discharged from the gas exchange port 11 in the direction of the arrow 84. However, the water accumulated in the dew condensation water holding unit 5 has viscosity, so if it remains in the liquid state, it cannot pass through the porous membrane 4 and leak into the space 3 and remains in the dew condensation water holding unit 5. ing.

  Next, FIG. 2 (D) shows the internal state of the battery casing 1 of the fuel cell 10 when no power is generated, and the water accumulated in the condensed water holding part 5 spontaneously evaporates and permeates the porous membrane 4. Then, it evaporates gently in the direction of the arrow 85 and is discharged into the space 3, and is discharged out of the battery casing 1 from the gas exchange port 11 as indicated by the arrow 86.

  In the series of power generation operations illustrated in FIG. 2, the battery housing 1 is made of transparent plastic so that the inside of the housing can be visually observed. In addition, the power generation unit 2 arranges the battery housing 1 so that the longitudinal direction of 80 mm is perpendicular to the floor surface, repeats the power generation for 3 hours → the power generation for 4 hours, that is, discharges the generated water five times, Visual observation confirmed the behavior of the condensed water inside the body 1 from the outside.

As a result, even when the repetition was repeated five times, the dew condensation water in the dew condensation water holding unit 5 was held, and there was no inconvenience that it moved to the outside and caused so-called water leakage.
[Comparative Example 1]
In the fuel cell having the same configuration as that of the example, a test similar to that of the example was performed in a state where the hydrophilic porous membrane was stretched on the dew condensation water holding portion and not the configuration according to the present invention.

As a result, at the end of the first power generation, a large amount of liquid droplets that seemed to overflow from the condensed water holding part were found in the lower part of the space of the battery casing.
[Comparative Example 2]
In the fuel cell having the same configuration as that of the example, in the state where a general acrylic water-absorbing polymer was applied to a thickness of 200 μm instead of the hydrophilic porous membrane stretched on the condensed water holding portion. A test similar to the example was performed.

  As a result, at the end of the fourth power generation, as in Comparative Example 1, a large amount of liquid droplets that seemed to overflow from the dew condensation water holding part were observed in the lower part of the space of the battery casing.

  Thus, according to the present invention, in a direct methanol fuel cell using a highly concentrated aqueous methanol solution, which is considered to have particularly good power generation efficiency, as a liquid fuel, water generated at the anode is used to generate power by crossover of methanol. The problem that water vapor is generated by the temperature rise of the part and then dew condensation and water leakage from the battery housing can be effectively avoided by a simple mechanism.

  The catalyst included in the cathode or anode and the material constituting the solid electrolyte layer are commercially available by various manufacturers and are not limited to those exemplified in the embodiments, and various modifications are possible. .

  Further, the hydrophilic porous membrane can be applied as long as it is a material having a characteristic of permeating water vapor but not liquid water, and various modifications are possible.

  In addition, the space provided between the power generation unit in the battery casing and the depth of the concavity of the dew condensation water holding unit are the specifications determined for downsizing and thinning the fuel cell. Of course, those exceeding the range are also included in the technical matters of the present invention.

  Further, the present invention is more effective in a direct methanol fuel cell using a methanol aqueous solution having a high concentration of methanol as fuel, but can be applied to a large concentration range and various modifications are possible.

It is typical sectional drawing of the Example of this invention. It is a flowchart of typical electric power generation operation | movement of the fuel cell of this invention. It is explanatory drawing of the Example of the fuel cell of this invention.

Explanation of symbols

1 Battery housing
DESCRIPTION OF SYMBOLS 11 Gas exchange port 2 Electric power generation part 21 Cathode 22 Anode 23 Solid electrolyte layer 3 Space 4 Porous membrane 5 Condensation water holding part 6 Fuel tank 7 Control circuit 81, 82, 83, 84, 85, 86 (It shows the direction through which water vapor flows ) Arrow 10 Fuel cell

Claims (3)

A power generation unit in which a cathode that reduces oxygen to an active material and an anode in which fuel is oxidized sandwiches a solid electrolyte membrane, a fuel supply unit that vaporizes and supplies fuel to the power generation unit, and the vicinity of the cathode In a fuel cell comprising a battery casing with a space arranged in
A hydrophilic porous membrane disposed on the inner surface of the battery case near the cathode facing the space, allowing water vapor to pass but not water;
A dew condensation water holding portion that is formed in the inner surface of the battery casing in the vicinity of the cathode facing the space, and the porous membrane is stretched over the entire opening of the dew condensation water holding portion;
Fuel cell characterized in that it comprises a. The fuel cell according to claim 1, wherein the porous membrane has a pore diameter not exceeding 0.01 mmφ. 2. The fuel cell according to claim 1, wherein the dew condensation water holding part has a thickness not exceeding 2 mm.

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