JP2006269126A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell in which methanol of a prescribed concentration can be supplied uniformly to a power generating part, and which is hardly affected by the external environmental factor such as temperature. <P>SOLUTION: It is possible to provide the fuel cell which is equipped with a liquid fuel tank 26 that houses a fuel and has an opening to lead out vaporization component of the fuel, a vapor-liquid separation film 25 that is arranged and installed so as to seal the opening of this liquid fuel tank 26 and that makes the vapor-liquid component of the fuel permeate the film, a film electrode joint assembly 16 constituted of an electrolyte film 15 pinched by a fuel electrode and an air electrode, a hydrophobic porous film arranged and installed between the fuel electrode side of this film electrode joint assembly 16 and the vapor-liquid separation film 25, and a polymer swelling membrane 22 that is arranged and installed on the vapor-liquid separation film 25 side of this porous film and which adjusts fuel concentration supplied to the fuel cell, and which suppresses crossover of methanol, and which is hardly affected by the external environmental factor such as the temperature. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell, and more particularly to a small liquid fuel direct supply type fuel cell.

  In recent years, advances in electronic technology have led to downsizing, higher performance, and portability of electronic devices. In portable electronic devices, there is an increasing demand for higher energy density of batteries used. For this reason, there is a demand for a secondary battery having a high capacity while being lightweight and small.

  In response to the demand for such secondary batteries, for example, lithium ion secondary batteries have been developed. In addition, the operation time of portable electronic devices tends to increase further, and in lithium ion secondary batteries, the improvement of energy density is almost limited from the viewpoint of materials and structure, which is further demanded. It is becoming impossible to respond.

  Under such circumstances, small fuel cells are attracting attention instead of lithium ion secondary batteries. In particular, direct methanol fuel cells (DMFC) using methanol as fuel require more difficult handling of hydrogen gas and devices that produce hydrogen by reforming organic fuel, compared to fuel cells using hydrogen gas. It is thought that it is excellent in miniaturization.

  In DMFC, methanol is oxidatively decomposed at the fuel electrode to generate carbon dioxide, protons and electrons. On the other hand, in the air electrode, water is generated by oxygen obtained from air, protons supplied from the fuel electrode through the electrolyte membrane, and electrons supplied from the fuel electrode through an external circuit. In addition, power is supplied by electrons passing through the external circuit.

  In the DMFC, in order to advance power generation with such a configuration, a pump for supplying methanol and a blower for feeding air are provided as auxiliary devices, and a DMFC having a complicated form as a system has been developed. Therefore, it is difficult to reduce the size of the DMFC having this structure.

  Therefore, rather than supplying methanol with a pump, downsizing is promoted by providing a membrane that allows methanol molecules to pass between the methanol tank and the power generation element, allowing methanol to permeate, and bringing the methanol tank closer to the power generation element. It was. For air intake, a small DMFC was constructed by installing an air inlet directly attached to the power generation element without using a blower. However, it is difficult for such a small DMFC to send a certain amount of methanol to the power generation element when it is affected by external environmental factors such as temperature instead of the mechanism being simplified. For this reason, it has been difficult to achieve stable and high output.

Therefore, in order to control the methanol supply amount, a technique is disclosed in which a porous body is installed between the fuel tank portion and the negative electrode to reduce the methanol supply amount (see, for example, Patent Document 1).
JP 2004-171844 A

  However, in the conventional fuel cell configuration described above, the methanol supplied by the capillary force of the porous body is easily affected by the external environment, and methanol of a predetermined concentration that is always uniformized through the porous body is used as the fuel electrode. It was difficult to supply power to the power supply, and it was difficult to stabilize the power generation state.

  Therefore, the present invention has been made to solve the above-described problem, and provides a fuel cell that can uniformly supply methanol at a predetermined concentration to a power generation portion and is not easily affected by external environmental factors such as temperature. The purpose is to provide.

  In order to achieve the above object, a fuel cell of the present invention is provided in a fuel supply part having an opening for containing fuel and deriving a vaporized component of the fuel, and an opening part of the fuel supply part, An electromotive part composed of a gas-liquid separation membrane that allows the vaporized component of the fuel to permeate, a fuel electrode, an air electrode, and an electrolyte membrane sandwiched between the fuel electrode and the air electrode, and fuel for the electromotive part A hydrophobic porous membrane disposed between the pole side and the gas-liquid separation membrane, and a fuel concentration supplied to the fuel electrode, which is disposed on the gas-liquid separation membrane side of the porous membrane. And a fuel concentration adjusting layer.

  According to this fuel cell, by providing the fuel concentration adjustment layer, it is possible to adjust the concentration and supply amount of the fuel supplied to the fuel electrode, thus mitigating the effects of fluctuations in the amount of fuel vaporization in the fuel supply unit. Thus, the fuel having a predetermined concentration can be uniformly supplied to the fuel electrode.

  According to the fuel cell of the present invention, it is possible to provide a fuel cell that can uniformly supply methanol at a predetermined concentration to the power generation portion and is hardly affected by external environmental factors such as temperature.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 schematically shows a cross-sectional view of a direct methanol fuel cell 10 according to an embodiment of the present invention.

  As shown in FIG. 1, a fuel cell 10 includes a fuel electrode composed of a fuel electrode catalyst layer 11 and a fuel electrode gas diffusion layer 12, an air electrode composed of an air electrode catalyst layer 13 and an air electrode gas diffusion layer 14, and a fuel electrode. A membrane electrode assembly (MEA) 16 composed of a proton (hydrogen ion) conductive electrolyte membrane 15 sandwiched between the catalyst layer 11 and the air electrode catalyst layer 13 is configured as an electromotive unit. is doing.

  Examples of the catalyst contained in the fuel electrode catalyst layer 11 and the air electrode catalyst layer 13 include, for example, platinum group elements such as Pt, Ru, Rh, Ir, Os, and Pd, as well as alloys containing platinum group elements. And so on. Specifically, Pt—Ru or Pt—Mo having strong resistance to methanol or carbon monoxide is used as the fuel electrode catalyst layer 11, and platinum or Pt—Ni is used as the air electrode catalyst layer 13. Although preferable, it is not necessarily limited to these. Further, a supported catalyst using a conductive support such as a carbon material or an unsupported catalyst may be used.

  Examples of the proton conductive material that constitutes the electrolyte membrane 15 include fluorinated resins having a sulfonic acid group, such as perfluorosulfonic acid polymer (Nafion (trade name, manufactured by DuPont), Flemion (trade name, Asahi Glass Co., Ltd.)), sulfonic acid group-containing hydrocarbon resins, and inorganic substances such as tungstic acid and phosphotungstic acid, but are not limited thereto.

  The fuel electrode gas diffusion layer 12 laminated on the fuel electrode catalyst layer 11 serves to uniformly supply fuel to the fuel electrode catalyst layer 11 and also serves as a current collector for the fuel electrode catalyst layer 11. On the other hand, the air electrode gas diffusion layer 14 laminated on the air electrode catalyst layer 13 serves to uniformly supply the oxidant to the air electrode catalyst layer 13 and also serves as a current collector for the air electrode catalyst layer 13. Yes. A fuel electrode conductive layer 17 is stacked on the fuel electrode gas diffusion layer 12, and an air electrode conductive layer 18 is stacked on the air electrode gas diffusion layer 14. The fuel electrode conductive layer 17 and the air electrode conductive layer 18 are formed of a porous layer such as a mesh made of a conductive metal material such as gold.

  Rubber O-rings 19 and 20 are interposed between the electrolyte membrane 15 and the fuel electrode conductive layer 17 and between the electrolyte membrane 15 and the air electrode conductive layer 18, so that fuel leakage from the membrane electrode assembly 16 occurs. And prevent oxidant leakage.

  In addition, a hydrophobic porous film 21 and a polymer swelling film 22 are laminated on the fuel electrode conductive layer 17 in this order. The laminated body including the polymer swelling film 22 and the air electrode conductive layer 18 is sandwiched between frames 23 and 24 (here, rectangular frames) configured in a shape corresponding to the outer edge shape of the fuel cell 10. Yes. The frames 23 and 24 are formed of, for example, a thermoplastic polyester resin such as polyethylene terephthalate (PET).

  The fuel electrode side frame 23 is a liquid fuel tank that functions as a fuel supply unit via a gas-liquid separation membrane 25 that functions as a vapor-phase fuel permeable membrane that transmits only the vaporized component of the liquid fuel and does not transmit the liquid fuel. 26.

  The gas-liquid separation membrane 25 is disposed so as to close an opening provided for deriving a vaporized component of the fuel in the liquid fuel tank 26. The gas-liquid separation film 25 separates the vaporized component of the fuel and the liquid fuel, and further vaporizes the liquid fuel. Specifically, the gas-liquid separation film 25 can be made of a material such as silicone rubber.

  Further, on the liquid fuel tank 26 side of the gas-liquid separation membrane 25, there is a gas-liquid separation function similar to that of the gas-liquid separation membrane 25, and a permeation adjustment membrane (illustrated) for adjusting the permeation amount of the vaporized component of the fuel. No) may be provided. The adjustment of the permeation amount of the vaporized component by the permeation amount adjusting film is performed by changing the aperture ratio of the permeation amount adjusting film. This permeation amount adjusting film can be made of, for example, a material such as polyethylene terephthalate. By providing this permeation amount adjusting film, it is possible to perform gas-liquid separation of the fuel and to adjust the supply amount of the vaporized component of the fuel supplied to the fuel electrode catalyst layer 11 side.

  Here, the liquid fuel stored in the liquid fuel tank 26 is a methanol aqueous solution having a concentration exceeding 50 mol% or pure methanol. The purity of pure methanol is preferably 95% by weight or more and 100% by weight or less. The vaporized component of liquid fuel means vaporized ethanol when liquid ethanol is used as the liquid fuel, and vaporized component of methanol and water when methanol aqueous solution is used as the liquid fuel. It means an air-fuel mixture consisting of components.

  The porous membrane 21 has hydrophobicity and prevents water from entering from the fuel electrode gas diffusion layer 12 side through the porous membrane 21 to the polymer swelling membrane 22 side, while the polymer swelling through the porous membrane 21 is prevented. The vaporized component of the liquid fuel can be transmitted from the membrane 22 side to the fuel electrode gas diffusion layer 12 side. Specific examples of the material for the porous film 21 include polytetrafluoroethylene (PTFE) and a water-repellent treated silicone sheet.

  By disposing the porous membrane 21 between the fuel electrode conductive layer 17 and the polymer swelling film 22, water generated in the air electrode catalyst layer 13 passes through the electrolyte membrane 15 due to, for example, an osmotic pressure phenomenon. When the reaction to move to the fuel electrode catalyst layer 11 is promoted, the moved water is prevented from entering the polymer swelling membrane 22 or the gas-liquid separation membrane 25 side below it. Can do. As a result, for example, the vaporized fuel storage chamber 27 and the like are not filled with water, so that the space is not reduced. Therefore, the vaporization of the fuel in the liquid fuel tank 26 can be prevented from proceeding. In addition, by holding water between the fuel electrode catalyst layer 11 and the porous membrane 21, it is possible to replenish water in the fuel electrode catalyst layer 11, for example, no water is supplied from the liquid fuel tank 26. This is effective when pure methanol is used as fuel. In addition, the movement of water from the air electrode catalyst layer 13 side to the fuel electrode catalyst layer 11 side due to the osmotic pressure phenomenon changes the number and size of the air inlets 30 of the surface layer 29 installed on the moisturizing layer 28, It can be controlled by adjusting the opening area and the like.

  The polymer swelling film 22 functions as a fuel concentration adjustment layer for adjusting the concentration and supply amount of fuel supplied to the fuel electrode catalyst layer 11, vaporizes in the liquid fuel tank 26, and the gas-liquid separation film 25 is formed. The vapor-phase methanol that has passed through is absorbed until it reaches a limit concentration that can be absorbed, that is, a saturation concentration, and methanol that exceeds the saturation concentration is supplied to the fuel electrode catalyst layer 11 side. As a material constituting the polymer swelling film 22, for example, a cellulose, acrylic, or vinyl polymer can be used. Specifically, methyl cellulose and the like are used for cellulose, polybutyl methacrylate and the like are used for acrylic, and polyvinyl butyrate is used for vinyl.

  Here, the polymer forming the polymer swelling film 22 has a functional group such as an OH group, a carboxyl group, and a sulfone group, and thus has an interaction with methanol, and the release of methanol from the polymer swelling film 22. The amount is not easily affected by external temperature or the like. Therefore, a substantially constant concentration of methanol can be supplied to the fuel electrode catalyst layer 11 side regardless of the external temperature or the like. The saturated concentration of methanol in the polymer swelling film 22 varies depending on the functional group of the polymer forming the polymer swelling film 22, but can be adjusted by, for example, the thickness of the polymer swelling film 22. .

  Further, the polymer swelling film 22 can reversibly change from a non-gel film state to a gel film state with a temperature change in a predetermined range. For example, when methylcellulose is used as the polymer swelling film 22, when the temperature rises to about 50 to 70 ° C., the polymer layer gels due to the thermal gelation effect. Since this thermal gelation effect is reversible with respect to temperature, when the temperature returns to room temperature, the gelation is eliminated and the original polymer film is restored. Thereby, for example, in the liquid fuel tank 26, the vaporization of the liquid fuel is promoted, and the polymer swelling film 22 is gelated even in a state where the operating temperature (for example, about 50 to 70 ° C.) at which methanol is excessively supplied is reached. Therefore, it is possible to prevent excessive supply by reducing the diffusion rate of methanol to the fuel electrode catalyst layer 11 side. On the other hand, when the temperature drops to room temperature, the original polymer membrane is restored, so that the methanol diffusion rate to the fuel electrode catalyst layer 11 side is returned to the normal state at the room temperature when methanol supply is not excessive. Can do. Thus, a large amount of vaporized fuel can be avoided from being supplied to the fuel electrode catalyst layer 11 at a time, and the occurrence of methanol crossover (MCO) can be suppressed. Moreover, methanol with a substantially constant concentration can be supplied to the fuel electrode catalyst layer 11 side regardless of the external temperature or the like.

  Further, the space surrounded by the frame 23 between the polymer swelling membrane 22 and the gas-liquid separation membrane 25 temporarily accommodates the vaporized fuel that has diffused through the gas-liquid separation membrane 25, and further the concentration of the vaporized fuel. The vaporized fuel storage chamber 27 makes the distribution uniform. The vaporized fuel storage chamber 27 is preferably formed in order to temporarily store the vaporized fuel that has diffused through the gas-liquid separation membrane 25 and to make the concentration distribution of the vaporized fuel uniform. The fuel cell 10 may be configured without forming the storage chamber 27.

  Here, a porous membrane (not shown) may be disposed between the polymer swelling membrane 22 and the gas-liquid separation membrane 25 in order to prevent the polymer swelling membrane 22 from peeling or falling. The porous membrane is preferably disposed so as to contact the surface of the polymer swelling membrane 22 on the liquid fuel tank 26 side. The porous membrane is made of, for example, a material such as PTFE (polytetrafluoroethylene), and a membrane having a maximum pore diameter of about 10 to 100 μm is used. The reason that the maximum pore diameter is within this range is that when the pore diameter is smaller than 10 μm, the methanol permeability is too low, and when it is larger than 100 μm, liquid methanol passes through.

  On the other hand, a moisture retaining layer 28 is laminated on the frame 24 on the air electrode side, and a surface layer 29 having a plurality of air inlets 30 for taking in air as an oxidant is laminated on the moisture retaining layer 28. Has been. The surface layer 29 is also made of a metal such as SUS304, for example, because it also serves to pressurize the laminated body including the membrane electrode assembly 16 and enhance its adhesion. The moisturizing layer 28 impregnates a part of the water generated in the air electrode catalyst layer 13 to play a role of suppressing water evaporation, and by uniformly introducing an oxidant into the air electrode gas diffusion layer 14, It also has a function as an auxiliary diffusion layer that promotes uniform diffusion of the oxidant to the air electrode catalyst layer 13.

  The moisturizing layer 28 is made of, for example, a material such as a polyethylene porous film, and a film having a maximum pore diameter of about 20 to 50 μm is used. The reason for setting the maximum pore diameter within this range is that the air permeability decreases when the pore diameter is smaller than 20 μm, and the water evaporation becomes excessive when the pore diameter is larger than 50 μm. The moisturizing layer 28 is preferably installed, but the fuel cell 10 may be configured without using the moisturizing layer 28. In that case, it is preferable to install the surface layer 29 on the frame 24 on the air electrode side to adjust the water storage amount and water evaporation of the air electrode catalyst layer 13, but without using the surface layer 29. The fuel cell 10 may be configured.

  Next, the operation of the fuel cell 10 described above will be described.

The liquid fuel (for example, methanol aqueous solution) in the liquid fuel tank 26 is vaporized, and the vaporized mixture of methanol and water vapor passes through the gas-liquid separation membrane 25 and is temporarily stored in the vaporized fuel storage chamber 27, and the concentration distribution is To be uniform. The air-fuel mixture once stored in the vaporized fuel storage chamber 27 enters the polymer swelling film 22 where methanol is absorbed by the polymer swelling film 22. When the polymer swelling film 22 reaches a saturated state, methanol is released from the polymer swelling film 22, passes through the porous film 21 and the fuel electrode conductive layer 17 together with water vapor, and is further diffused in the fuel electrode gas diffusion layer 12. The fuel electrode catalyst layer 11 is supplied. The air-fuel mixture supplied to the fuel electrode catalyst layer 11 causes an internal reforming reaction of methanol represented by the following formula (1).
CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻ Formula (1)

  In addition, when pure methanol is used as the liquid fuel, there is no supply of water vapor from the liquid fuel tank 26. Therefore, water generated in the air electrode catalyst layer 13, water in the electrolyte membrane 15 and the like are described as methanol. The internal reforming reaction of the formula (1) is generated, or the internal reforming reaction is generated by another reaction mechanism that does not require water, regardless of the internal reforming reaction of the above formula (1).

Protons (H ⁺ ) generated by the internal reforming reaction are conducted through the electrolyte membrane 15 and reach the air electrode catalyst layer 13. The air taken in from the air inlet 30 of the surface layer 29 diffuses through the moisture retention layer 28, the air electrode conductive layer 18, and the air electrode gas diffusion layer 14 and is supplied to the air electrode catalyst layer 13. The air supplied to the air electrode catalyst layer 13 causes the reaction shown in the following formula (2). By this reaction, water is generated and a power generation reaction occurs.
(3/2) O ₂ + 6H ⁺ + 6e ⁻ → 3H ₂ O Formula (2)

  The water generated in the air electrode catalyst layer 13 by this reaction diffuses in the air electrode gas diffusion layer 14 and reaches the moisturizing layer 28, and a part of the water in the surface layer 29 provided on the moisturizing layer 28. The transpiration from the air inlet 30 is inhibited by the surface layer 29 from the remaining water. In particular, when the reaction of Formula (2) proceeds, the amount of water whose transpiration is inhibited by the surface layer 29 increases, and the amount of water stored in the air electrode catalyst layer 13 increases. In this case, the water storage amount of the air electrode catalyst layer 13 becomes larger than the water storage amount of the fuel electrode catalyst layer 11 as the reaction of the formula (2) proceeds. As a result, a reaction in which water generated in the air electrode catalyst layer 13 moves to the fuel electrode catalyst layer 11 through the electrolyte membrane 15 is promoted by the osmotic pressure phenomenon. Therefore, compared to the case where the supply of moisture to the fuel electrode catalyst layer 11 is dependent only on the vapor vaporized from the liquid fuel tank 26, the supply of moisture is promoted, and the internal reforming reaction of methanol in the above-described equation (1) is performed. Can be promoted. As a result, the output density can be increased and the high output density can be maintained for a long period of time.

  Further, even when a methanol aqueous solution with a methanol concentration exceeding 50 mol% or pure methanol is used as the liquid fuel, the water that has moved from the air electrode catalyst layer 13 to the fuel electrode catalyst layer 11 is used for the internal reforming reaction. Therefore, it is possible to stably supply water to the fuel electrode catalyst layer 11. Thereby, the reaction resistance of the internal reforming reaction of methanol can be further reduced, and the long-term output characteristics and load current characteristics can be further improved. Further, the liquid fuel tank 26 can be downsized.

  As described above, according to the direct methanol fuel cell 10 of one embodiment, the porous membrane 21 and the polymer swelling membrane 22 are laminated so that the porous membrane 21 is on the fuel electrode catalyst layer 11 side. By constituting the fuel cell 10, the polymer swelling film 22 absorbs the vaporized methanol and becomes saturated, and then the methanol can be released to the fuel electrode catalyst layer 11 side. As a result, the influence of the change in the amount of vaporized methanol in the liquid fuel tank 26 can be mitigated, and methanol having a predetermined concentration can be uniformly supplied to the fuel electrode catalyst layer 11.

  Furthermore, since the polymer swelling film 22 can reversibly change from a non-gel film state to a gel film state with a temperature change in a predetermined range, it is substantially constant regardless of the external temperature or the like. A methanol concentration can be supplied to the fuel electrode catalyst layer 11 side. Further, since the porous membrane 21 has hydrophobicity, water on the fuel electrode catalyst layer 11 side can be prevented from entering the polymer swelling membrane 22 and the gas-liquid separation membrane 25 side.

  In each of the above embodiments, a direct methanol fuel cell using a methanol aqueous solution or pure methanol as the liquid fuel has been described. However, the liquid fuel is not limited to these. For example, the present invention can also be applied to a liquid fuel direct supply type fuel cell using ethyl alcohol, isopropyl alcohol, butanol, dimethyl ether, or the like, or an aqueous solution thereof.

  Next, the fuel cell 10 is configured by laminating the porous membrane 21 and the polymer swelling membrane 22 so that the porous membrane 21 is on the fuel electrode catalyst layer 11 side, so that excellent output characteristics can be obtained. The following examples illustrate.

Example 1
The fuel cell according to the present invention was produced as follows.

  First, platinum-supported graphite particles were mixed with DE2020 (trade name: manufactured by DuPont) and a homogenizer to prepare a slurry, which was applied to carbon paper as an air electrode gas diffusion layer. And this was dried at normal temperature and the air electrode was produced.

  Further, carbon particles carrying platinum ruthenium alloy fine particles were mixed with DE2020 manufactured by Wako Pure Chemical Industries, Ltd. and a homogenizer to prepare a slurry, which was applied to carbon paper as a fuel electrode gas diffusion layer. And this was dried at normal temperature and the fuel electrode was produced.

As the electrolyte membrane, a fixed electrolyte membrane Nafion 112 manufactured by DuPont was used. The electrolyte membrane was sandwiched between an air electrode and a fuel electrode, pressed at a temperature of 120 ° C. and a pressure of 30 kgf / cm ² , and membrane electrode joining was performed. A body (MEA) was prepared. The electrode area was 12 cm ² for both the air electrode and the fuel electrode.

  Subsequently, the membrane electrode assembly was sandwiched between gold foils having a plurality of holes for taking in air and vaporized methanol to form a fuel electrode conductive layer and an air electrode conductive layer.

  Subsequently, a porous film made of polytetrafluoroethylene having hydrophobicity was formed on the surface of the fuel electrode conductive layer. Furthermore, methylcellulose dissolved in water was applied to the surface of the porous membrane on the side different from the fuel electrode conductive layer side to a thickness of about 20 μm and sufficiently dried at room temperature to form a polymer swelling layer.

  A laminate in which the membrane electrode assembly (MEA), the fuel electrode conductive layer, the air electrode conductive layer, the porous membrane, and the polymer swelling layer were laminated was sandwiched between two resin frames. In addition, a rubber O-ring was sandwiched between the air electrode side of the membrane electrode assembly and one frame, and between the fuel electrode side of the membrane electrode assembly and the other frame, respectively. .

  Also, the fuel electrode side frame was fixed to the liquid fuel tank by screwing through a gas-liquid separation membrane. A silicone sheet was used for the gas-liquid separation membrane. On the other hand, a porous plate was disposed on the air electrode side frame to form a moisture retention layer. On this moisturizing layer, a stainless steel plate (SUS304) with a thickness of 2 mm formed with air inlets (4 mm diameter, 64 holes) for air intake is arranged to form a surface layer, and by screwing Fixed.

  5 ml of pure methanol was injected into the liquid fuel tank of the fuel cell formed as described above, and the maximum output value was measured from the current value and the voltage value in an environment of a temperature of 25 ° C. and a relative humidity of 50%. Moreover, the maximum value of the surface temperature of the fuel cell was measured with a thermocouple attached to the surface of the surface layer.

As a result of the measurement, the maximum value of the output was 12.2 mW / cm ² and the maximum value of the surface temperature of the fuel cell was 32.4 ° C.

(Example 2)
The configuration of the fuel cell used in Example 2 was that the polymer swelling layer was coated with polyvinyl alcohol in a thickness of about 20 μm on the surface on the side different from the fuel electrode conductive layer side of the porous membrane, and sufficiently at room temperature. The configuration of the fuel cell of Example 1 is the same as that of Example 1 except that it is formed by drying. The measurement method and measurement conditions for the maximum output value and the maximum surface temperature of the fuel cell are the same as the measurement method and measurement conditions in Example 1.

As a result of the measurement, the maximum value of the output was 11.7 mW / cm ² and the maximum value of the surface temperature of the fuel cell was 31.5 ° C.

(Example 3)
The configuration of the fuel cell used in Example 3 is a sum of a polymer swelling layer and a polyperfluoroalkylsulfonic acid dissolved in water and isopropyl alcohol on the surface of the porous membrane on the side different from the fuel electrode conductive layer side. The configuration of the fuel cell of Example 1 is the same as that of Example 1 except that the optically pure DE2020 was applied to a thickness of about 20 μm and sufficiently dried at room temperature. The measurement method and measurement conditions for the maximum output value and the maximum surface temperature of the fuel cell are the same as the measurement method and measurement conditions in Example 1.

As a result of the measurement, the maximum value of the output was 11.2 mW / cm ² , and the maximum value of the surface temperature of the fuel cell was 31.2 ° C.

Example 4
The configuration of the fuel cell used in Example 4 is the same as that of the fuel cell used in Example 1. Using this fuel cell, 5 ml of pure methanol was injected into the liquid fuel tank of the fuel cell, and the maximum value of the output and the maximum value of the surface temperature of the fuel cell were measured in an environment of a temperature of 65 ° C. and a relative humidity of 50%. . The method for measuring the maximum value of the output and the maximum value of the surface temperature of the fuel cell is the same as the measuring method in Example 1.

As a result of the measurement, the maximum value of the output was 14.5 mW / cm ² , and the maximum value of the surface temperature of the fuel cell was 67.2 ° C.

(Comparative Example 1)
The configuration of the fuel cell used in Comparative Example 1 is that of the fuel cell of Example 1 except that the polymer swelling layer is not formed on the surface of the porous membrane on the side different from the fuel electrode conductive layer side. Is the same. The measurement method and measurement conditions for the maximum output value and the maximum surface temperature of the fuel cell are the same as the measurement method and measurement conditions in Example 1.

As a result of the measurement, the maximum value of the output was 10.2 mW / cm ² , and the maximum value of the surface temperature of the fuel cell was 38.6 ° C. In addition, the fuel consumption of the liquid fuel tank is fast, and the time until the fuel becomes empty is short.

(Comparative Example 2)
The configuration of the fuel cell used in Comparative Example 2 is the same as that of the fuel cell used in Comparative Example 1. Using this fuel cell, 5 ml of pure methanol was injected into the liquid fuel tank of the fuel cell, and the maximum value of the output and the maximum value of the surface temperature of the fuel cell were measured in an environment of a temperature of 65 ° C. and a relative humidity of 50%. . The method for measuring the maximum value of the output and the maximum value of the surface temperature of the fuel cell is the same as the measuring method in Example 1.

As a result of the measurement, the maximum value of the output was 9.8 mW / cm ² , and the maximum value of the surface temperature of the fuel cell was 85.3 ° C.

(Examination of measurement results of Examples and Comparative Examples)
Table 1 shows the measurement results of Examples 1 to 4 and Comparative Examples 1 and 2 described above.

  From the measurement results shown in Table 1, the maximum value of the output of Examples 1 to 4 was higher than that of Comparative Examples 1 and 2. As a result, it has been clarified that the formation of the polymer swelling layer on the surface of the porous membrane on the side different from the fuel electrode conductive layer side is a factor for improving the output.

  Moreover, when the maximum value of the output in Example 1 and the maximum value of the output in Example 4 were compared, Example 4 showed a higher value. The fuel cells used in Example 1 and Example 4 are the same, but the operating temperatures are different, being 25 ° C. in Example 1 and 65 ° C. in Example 4. From this, it was found that the maximum value of the output becomes higher when the operating temperature is higher in the measured temperature range.

  On the other hand, when the maximum output value in Comparative Example 1 and the maximum output value in Comparative Example 2 were compared, Comparative Example 1 showed a higher value. In Comparative Example 1 and Comparative Example 2, the fuel cells used are the same, but the operating temperatures are different, being 25 ° C. in Comparative Example 1 and 65 ° C. in Comparative Example 2. Therefore, in the fuel cell in which the polymer swelling layer is not formed on the surface of the porous membrane different from the fuel electrode conductive layer side, the measurement is different from the cases of Examples 1 to 4 in which the polymer swelling layer is formed. In the temperature range within the range, the maximum value of the output hardly changed.

  Further, when the maximum output value in Example 4 was compared with the maximum output value in Comparative Example 2, Example 4 showed a value about 1.5 times higher. In Example 4 and Comparative Example 2, the operating conditions such as the operating temperature are the same, but in Example 4, the polymer swelling layer is formed, and in Comparative Example 2, the polymer swelling layer is not formed. From this, when the operating temperature is 65 ° C., in the liquid fuel tank, the vaporization of the liquid fuel is promoted and the supply of methanol tends to be excessive. In the fuel cell of Comparative Example 2 having no polymer swelling layer, It is thought that the output decreased because the excessive supply could not be suppressed, the fuel concentration increased in the fuel electrode catalyst layer, and methanol crossover (MCO) occurred vigorously. On the other hand, in the fuel cell of Example 4 having a polymer swelling layer, a high output is obtained even in such a situation. By providing the polymer swelling layer, crossover of methanol is suppressed. It is thought that it was possible.

  Here, when the methanol crossover occurs, the methanol that has moved to the air electrode catalyst layer directly reacts with oxygen present in the vicinity of the air electrode catalyst layer to generate water and carbon dioxide. Since this reaction is an exothermic reaction, the temperature rises. Furthermore, since oxygen is used for the exothermic reaction, the oxygen concentration in the air electrode catalyst layer is lowered, the potential is lowered, and the output is lowered.

  As described above, in the comparative example, when the operating temperature is 65 ° C. (Comparative Example 2), the maximum output value is lower than that at 25 ° C. (Comparative Example 1). In this case, it is considered that this methanol crossover occurred vigorously.

  In addition, in the case of Examples 1 to 4, the maximum value of the surface temperature is a temperature increase of less than 10 ° C. with respect to the operating temperature. This is a temperature rise exceeding ℃, and in the case of Comparative Example 2, the temperature rise is about 20 ℃. In Comparative Examples 1 and 2, since the polymer swelling layer was not provided, methanol crossover occurred vigorously, and the above exothermic reaction occurred vigorously in the air electrode catalyst layer. Compared with the case of 4, it is thought that the temperature rise became remarkable.

  As described above, by forming a polymer swelling layer on the surface of the porous membrane that is different from the fuel electrode conductive layer side, a fuel cell that suppresses methanol crossover, has high output, and has little temperature rise is provided. It became clear that we could do it. Further, it has been clarified that the formation of the polymer swelling layer can provide a fuel cell that is hardly affected by external environmental factors such as temperature.

1 is a cross-sectional view of a direct methanol fuel cell according to an embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Fuel cell, 11 ... Fuel electrode catalyst layer, 12 ... Fuel electrode gas diffusion layer, 13 ... Air electrode catalyst layer, 14 ... Air electrode gas diffusion layer, 15 ... Electrolyte membrane, 16 ... Membrane electrode assembly, 17 ... Fuel Electrode conductive layer, 18 ... Air electrode conductive layer, 19, 20 ... O-ring, 21 ... Porous membrane, 22 ... Polymer swelling membrane, 23,24 ... Frame, 25 ... Gas-liquid separation membrane, 26 ... Liquid fuel tank, 27 ... vaporized fuel storage chamber, 28 ... moisturizing layer, 29 ... surface layer, 30 ... air inlet.

Claims (10)

A fuel supply section containing fuel and having an opening for deriving a vaporized component of the fuel;
A gas-liquid separation membrane disposed in an opening portion of the fuel supply unit and permeable to a vaporized component of the fuel;
An electromotive part composed of a fuel electrode, an air electrode, and an electrolyte membrane sandwiched between the fuel electrode and the air electrode;
A hydrophobic porous membrane disposed between the fuel electrode side of the electromotive unit and the gas-liquid separation membrane;
A fuel cell comprising: a fuel concentration adjusting layer that is disposed on the gas-liquid separation membrane side of the porous membrane and adjusts a fuel concentration supplied to the fuel electrode.   2. The fuel cell according to claim 1, wherein the fuel concentration adjusting layer comprises a polymer swelling layer capable of absorbing gas-phase fuel until a predetermined concentration is reached.   3. The fuel cell according to claim 2, wherein the polymer swelling layer reversibly changes from a non-gel film state to a gel film state with a temperature change in a predetermined range.   The polymer swelling layer has at least an OH group, a carboxyl group, a sulfone group, or an ester group obtained by reacting at least two of the OH group, the carboxyl group, and the sulfone group in an polymer skeleton, an ether 4. The fuel cell according to claim 2, further comprising a group.   The fuel cell according to claim 1, wherein the porous membrane is mainly composed of polytetrafluoroethylene.   The fuel cell according to claim 1, wherein a porous membrane is disposed between the polymer swelling layer and the gas-liquid separation membrane.   2. The fuel cell according to claim 1, wherein a permeation amount adjusting membrane for adjusting a permeation amount of a vaporized component of the fuel is disposed on the fuel supply side of the gas-liquid separation membrane.   The fuel cell according to any one of claims 1 to 7, wherein the fuel is a methanol aqueous solution having a concentration exceeding 50 mol% or liquid methanol.   9. The fuel cell according to claim 1, wherein a moisturizing layer impregnated with water generated by the air electrode is disposed on the air electrode side of the electromotive unit. 10.   10. The fuel cell according to claim 1, wherein a surface layer having a plurality of air inlets is provided on a side different from the air electrode side of the moisture retention layer.

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