JP2011096466A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell having improved output performance, especially a compact liquid fuel direct supply type fuel cell. <P>SOLUTION: The fuel cell includes a membrane/electrode assembly 1 including an anode 6 that includes an anode catalytic layer 11, and an anode gas diffusion layer 12 provided on one surface of the anode catalytic layer, a cathode 5 that includes a cathode catalytic layer 8, and a cathode gas diffusion layer 9 provided on one surface of the cathode catalytic layer, and an electrolyte membrane 7 disposed between the anode catalytic layer 11 and the cathode catalytic layer 8. In the fuel cell, at least one of the anode catalytic layer 11 and the cathode catalytic layer 8 includes a noble metal weight density of not less than 0.2 g/cc and not more than 0.8 g/cc satisfying the following formula (1), 1≤(T<SB>a</SB>/T<SB>c</SB>), where T<SB>c</SB>is a thickness of the cathode catalytic layer and T<SB>a</SB>is a thickness of the anode catalytic layer. <P>COPYRIGHT: (C)2011,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, small fuel cells have attracted attention in place of lithium ion secondary batteries. In particular, a direct methanol fuel cell (DMFC) using methanol as a fuel is more difficult to handle hydrogen gas than a fuel cell using hydrogen gas, and the organic fuel is reformed to generate hydrogen. There is no need for a device to create, and it is excellent in miniaturization.

  In DMFC, methanol is oxidized and decomposed at an anode (for example, a fuel electrode) to generate carbon dioxide, protons, and electrons. On the other hand, in the cathode (for example, 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.

  Here, there is an idea of increasing the amount of catalyst as a method of stably increasing the output. However, since noble metals such as Pt are generally used for the catalyst and tend to be expensive, a method of producing high output while suppressing the amount of catalyst is desirable. Furthermore, for miniaturization, it is desirable to make the film electrode assembly as thin as possible.

  Patent Document 1 discloses that the thickness of a catalyst layer using polyethersulfone as a binder and the thickness of a gas diffusion layer of the catalyst layer are defined. Patent Document 2 discloses that the thickness of the catalyst layer using polyvinylidene fluoride as a binder and the thickness of the gas diffusion layer of the catalyst layer are defined.

  Patent Document 3 uses a cathode catalyst layer in which a plurality of layers having different ratios of the mass of the polymer electrolyte to the mass of the conductive support are laminated along the direction of the gas diffusion layer from the polymer electrolyte membrane, and the average of the anode catalyst layer A fuel cell membrane electrode assembly having a thickness smaller than the average thickness of the cathode catalyst layer is disclosed.

  Patent Document 4 discloses a fuel cell membrane-electrode assembly in which the average thickness of the anode catalyst layer is smaller than the average thickness of the cathode catalyst layer.

  However, polyethersulfone and polyvinylidene fluoride used for the binder of the catalyst layer in Patent Documents 1 and 2 are inferior in proton conductivity, and thus cannot provide high output. In addition, if the average thickness of the anode catalyst layer is smaller than the average thickness of the cathode catalyst layer as in Patent Documents 3 and 4, fuel crossover will occur remarkably when using fuel containing methanol, leading to a decrease in output. .

Japanese Patent Laid-Open No. 10-092439 Japanese Patent Laid-Open No. 10-092440 JP 2008-176990 A WO2005 / 106994A1

  An object of this invention is to provide the fuel cell excellent in output performance.

A fuel cell according to the present invention includes an anode catalyst layer, and an anode including an anode gas diffusion layer provided facing one surface of the anode catalyst layer;
A cathode including a cathode catalyst layer, and a cathode gas diffusion layer provided facing one side of the cathode catalyst layer;
A membrane electrode assembly including an electrolyte membrane disposed between the anode catalyst layer and the cathode catalyst layer;
The anode catalyst layer and the cathode catalyst layer have a noble metal weight density of 0.2 g / cc or more and 0.8 g / cc or less, and satisfy the following formula (1).

1 ≦ (T _a / T _c ) (1)
However, the T _c in the thickness of the cathode catalyst layer, T _a is the thickness of the anode catalyst layer.

  ADVANTAGE OF THE INVENTION According to this invention, the fuel cell excellent in output performance can be provided.

The internal perspective sectional view showing the fuel cell concerning an embodiment. The perspective view which shows the fuel distribution mechanism of the fuel cell of FIG. FIG. 2 is a schematic cross-sectional view showing a main part of the fuel cell of FIG. 1. The cross-sectional schematic diagram of the fuel cell which concerns on another embodiment.

  Embodiments of the present invention will be described below with reference to the drawings.

  1 is an internal perspective sectional view showing a fuel cell according to an embodiment of the present invention, FIG. 2 is a perspective view showing a fuel distribution mechanism of the fuel cell of FIG. 1, and FIG. It is a cross-sectional schematic diagram which shows the principal part of a fuel cell.

  The fuel cell 100 includes a membrane electrode assembly 1, a fuel storage unit 3 that stores liquid fuel F, a flow path 4 that connects the fuel supply unit 2 and the fuel storage unit 3, a fuel introduction unit 30, and fuel introduction A fuel supply unit 2 that supplies fuel to the unit 30 and an oxidant introduction unit (oxygen introduction unit) 40 are provided.

  The membrane electrode assembly 1 includes an anode (fuel electrode) 5, a cathode (air electrode) 6, and a proton conductive electrolyte membrane 7 disposed between the anode 5 and the cathode 6.

  The anode 5 has an anode catalyst layer 8 provided facing one surface of the electrolyte membrane 7 and an anode gas diffusion layer 9 laminated on the anode catalyst layer 8. The cathode 6 has a cathode catalyst layer 11 provided facing the other surface of the electrolyte membrane 7 and a cathode gas diffusion layer 12 laminated on the cathode catalyst layer 11.

  The electrolyte membrane 7 includes a proton conductive material, such as a fluorine-based resin having a sulfonic acid group (trade name Nafion (registered trademark) manufactured by DuPont or Flemion (registered trademark) manufactured by Asahi Glass Co., Ltd.). Perfluorosulfonic acid polymer, etc.), hydrocarbon resins having a sulfonic acid group, inorganic substances (for example, tungstic acid, phosphotungstic acid, lithium nitrate, etc.) are used, but are not limited thereto.

  The anode gas diffusion layer 9 and the cathode gas diffusion layer 12 can be formed from, for example, a paper, a nonwoven fabric, a woven fabric, a knitted fabric, or a conductive porous film made of a fiber such as carbon or a conductive polymer. However, it is preferably formed from carbon paper. Any gas diffusion layer may be provided with water repellency or may not be provided with water repellency. For the water repellent treatment, a fluorine resin such as polytetrafluoroethylene (PTFE) can be used.

The anode gas diffusion layer 9 serves to uniformly supply fuel to the anode catalyst layer 8 and also serves as a current collector for the anode catalyst layer 8.
The cathode gas diffusion layer 12 serves to uniformly supply the oxidant to the cathode catalyst layer 11 and also serves as a current collector for the cathode catalyst layer 11.
The anode catalyst layer 8 includes an anode catalyst and a polymer electrolyte such as a perfluoropolysulfonic acid polymer electrolyte. The cathode catalyst layer 11 includes a cathode catalyst and a polymer electrolyte such as a perfluoropolysulfonic acid polymer electrolyte. The anode catalyst and the cathode catalyst contain a noble metal. As the noble metal, for example, a single metal such as Pt, Ru, Rh, Ir, Os, and Pd, which is a platinum group element, an alloy containing a platinum group element, or the like is used. Specifically, Pt—Ru and Pt—Mo having strong resistance to methanol and carbon monoxide are suitable as the catalyst on the anode side, and platinum, Pt—Ni, Pt—Co and the like are suitable as the catalyst on the cathode side. However, the present invention is not limited to these. Either a supported catalyst using a conductive support such as a carbon material or an unsupported catalyst can be used. As the support, particulate carbon such as activated carbon or graphite, or fibrous carbon can be used.

  As the polymer electrolyte used in the catalyst layer, for example, a perfluoropolysulfonic acid polymer electrolyte can be used. Perfluoropolysulfonic acid-based polymer electrolytes can use fluorine-based resins having sulfonic acid groups. Specifically, the product name Nafion (registered trademark) manufactured by DuPont and the product name Flemion manufactured by Asahi Glass Co., Ltd. Perfluorosulfonic acid polymers such as (registered trademark). In the catalyst layer, the perfluoropolysulfonic acid polymer electrolyte is used to bind the catalyst to the gas diffusion layer and to conduct protons generated by the electrochemical reaction. In addition, perfluoropolysulfonic acid-based polymer electrolytes increase the proton conductivity of the electrode and contribute to the improvement of output performance.

  A rubber O-ring 15 is disposed between the electrolyte membrane 7 and the cover plate 16 and between the electrolyte membrane 7 and the fuel supply unit 2 so as to surround the membrane electrode assembly (MEA) 1. These prevent fuel leakage and oxidant leakage.

  The oxidant introduction part (oxygen introduction part) 40 has a function of taking in an oxidant such as air from the outside and supplying it to the MEA 1. Thus, the oxidant introduction part 40 includes a member arranged in this manner. The oxidant introduction unit 40 includes, for example, the conductive layer 13 provided to face the cathode gas diffusion layer 12, the moisturizing layer 18, and the cover plate 16, but is not limited to this configuration. In addition, the configuration without the conductive layer 13 and the moisture retaining layer 18 can be obtained.

  The conductive layer 13 is provided as necessary. For example, a porous layer (for example, a mesh) or a foil body made of a metal material such as gold or nickel, or a conductive metal material such as stainless steel (SUS) is made of gold. A composite material coated with a highly conductive metal such as is used.

  The moisture retaining layer 18 is disposed between the cover plate 16 and the cathode 6 as necessary. The moisturizing layer 18 is impregnated with a part of the water generated in the cathode catalyst layer 11 to suppress the transpiration of water and has a function of diffusing a part of the generated water to the anode side. The cathode gas diffusion layer also has a function of uniformly introducing air as an oxidant to promote uniform diffusion of the oxidant to the cathode catalyst layer 11. The moisturizing layer 18 is composed of a flat plate made of, for example, a polyethylene porous film.

The cover plate 16 has a plurality of through holes 16a as openings for taking in air as an oxidant. The cover plate 16 adjusts the intake amount of air, and the adjustment is performed by changing the number and size of the air inlets. It also plays a role of increasing the adhesion by pressurizing the MEA and the moisturizing layer. The cover plate 16 can be made of a metal such as SUS304, but is not limited thereto. By providing such a cover plate 16, the oxidant can be naturally supplied to the cathode 6 without using a blower for supplying the oxidant. Note that the oxidizing agent is not limited to air, and a gas containing O ₂ can be used.

  A fuel distribution mechanism 2 as a fuel supply unit is disposed on the anode 5 side of the membrane electrode assembly 1. The fuel supply unit 2 has a fuel discharge port facing the fuel intake surface of the fuel introduction unit 40, and supplies fuel to the fuel introduction unit 40 through the fuel discharge port. The fuel distribution mechanism 2 is connected to the fuel storage unit 3 through a flow path 4 of liquid fuel F such as piping. Liquid fuel F is introduced into the fuel distribution mechanism 2 from the fuel storage portion 3 through the flow path 4. The flow path 4 is not limited to piping independent of the fuel distribution mechanism 2 and the fuel storage unit 3. For example, when the fuel distribution mechanism 2 and the fuel storage unit 3 are stacked and integrated, a flow path of the liquid fuel F that connects them may be used. The fuel distribution mechanism 2 may be connected to the fuel storage unit 3 through the flow path 4.

  The mechanism for feeding the liquid fuel F from the fuel storage unit 3 to the fuel distribution mechanism 2 is not particularly limited. For example, when the installation location at the time of use is fixed, the liquid fuel F can be dropped from the fuel storage unit 3 to the fuel distribution mechanism 2 and fed using gravity. Further, by using the flow path 4 filled with a porous body or the like, liquid can be fed from the fuel storage unit 3 to the fuel distribution mechanism 2 by capillary action. Furthermore, liquid feeding from the fuel storage unit 3 to the fuel distribution mechanism 2 may be performed by a pump 17 as shown in FIG. Alternatively, if the fuel is supplied from the fuel distribution mechanism 2 to the membrane electrode assembly 1, a fuel cutoff valve may be arranged instead of the pump 17. In this case, the fuel cutoff valve is provided to control the supply of the liquid fuel F through the flow path.

  The pump 17 functions as a supply pump that simply supplies liquid fuel from the fuel storage unit 3 to the fuel distribution mechanism 2, and functions as a circulation pump that circulates excess liquid fuel supplied to the fuel cells. It does not provide. The fuel cell equipped with this pump does not circulate the fuel, so the configuration is different from the conventional active method, and the configuration is different from the pure passive method such as the conventional internal vaporization type, so-called semi-passive type. Applicable. The type of the pump that functions as the fuel supply means is not particularly limited, but a rotary vane pump that can feed a small amount of liquid fuel with good controllability and can be reduced in size and weight, It is preferable to use an electroosmotic pump, a diaphragm pump, a squeezing pump, or the like. The rotary vane pump feeds liquid by rotating wings with a motor. The electroosmotic flow pump uses a sintered porous body such as silica that causes an electroosmotic flow phenomenon. A diaphragm pump drives a diaphragm with an electromagnet or piezoelectric ceramics to send liquid. The squeezing pump presses a part of a flexible fuel flow path and squeezes the fuel. Among these, it is more preferable to use an electroosmotic pump or a diaphragm pump having piezoelectric ceramics from the viewpoint of driving power, size, and the like. When the pump is provided as described above, the pump is electrically connected to the control means (not shown), and the supply amount of the liquid fuel supplied to the fuel supply unit is controlled by the control means.

  As shown in FIG. 1, the fuel distribution mechanism 2 includes at least one fuel inlet 21 into which the liquid fuel F flows through the flow path 4 and a plurality of fuel exhausts that discharge the liquid fuel F and its vaporized components. A fuel distribution plate 23 having an outlet 22 is provided. As shown in FIG. 1, the fuel distribution plate 23 is provided with a gap 24 serving as a liquid fuel passage led from the fuel injection port 21. The plurality of fuel discharge ports 22 are directly connected to the gaps 24 that function as fuel passages.

  The fuel distribution plate 23 is made of, for example, a vaporized component of liquid fuel or a material that does not allow liquid fuel to permeate. Specifically, for example, polyethylene terephthalate (PET) resin, polyethylene naphthalate (PEN) resin, polyimide resin, and the like. Consists of. Here, in the fuel cell, the liquid fuel introduced into the fuel distribution mechanism 2 is guided to the fuel introduction unit 30 from a plurality of openings of the fuel distribution plate 23, and the vaporized component of the liquid fuel is the entire surface of the anode (fuel electrode). Supplied against. As described above, the fuel distribution plate 23 can equalize the amount of fuel supplied to the anode (fuel electrode).

  The liquid fuel F introduced into the fuel distribution mechanism 2 from the fuel inlet 21 enters the gap 24 and is guided to the plurality of fuel outlets 22 through the gap 24 functioning as a fuel passage. For example, a gas-liquid separator (not shown) that transmits only the vaporized component of the liquid fuel and does not transmit the liquid component may be disposed in the plurality of fuel discharge ports 22. As a result, the vaporized component of the liquid fuel is supplied to the anode 5 of the membrane electrode assembly 1. The vaporized component of the liquid fuel is discharged from a plurality of fuel discharge ports 22 toward a plurality of locations of the fuel introduction unit 30.

A plurality of fuel discharge ports 22 are provided on the surface of the fuel distribution plate 23 facing the fuel introduction portion 30 so that fuel can be supplied to the entire membrane electrode assembly 1. The number of the fuel discharge ports 22 may be two or more, but there are 0.1 to 10 / cm ² fuel discharge ports 22 in order to equalize the fuel supply amount in the surface of the membrane electrode assembly 1. It is preferable to form as follows.

  The liquid fuel F introduced into the fuel distribution mechanism 2 described above is guided to the plurality of fuel discharge ports 22 via the gaps 24. Since the gap 24 of the fuel distribution mechanism 2 functions as a buffer, fuel of a specified concentration is discharged from the plurality of fuel discharge ports 22, respectively. Since the plurality of fuel discharge ports 22 are arranged so that fuel is supplied to the entire surface of the membrane electrode assembly 1, the amount of fuel supplied to the membrane electrode assembly 1 can be made uniform.

  The fuel storage unit 3 stores liquid fuel F corresponding to the membrane electrode assembly 1. Examples of the liquid fuel F include methanol fuels such as aqueous methanol solutions of various concentrations and pure methanol. The liquid fuel F is not necessarily limited to methanol fuel. The liquid fuel F may be, for example, an ethanol fuel such as an ethanol aqueous solution or pure ethanol, a propanol fuel such as a propanol aqueous solution or pure propanol, a glycol fuel such as a glycol aqueous solution or pure glycol, dimethyl ether, formic acid, or other liquid fuel. In any case, the liquid fuel F corresponding to the membrane electrode assembly 1 is stored in the fuel storage unit 3.

  The type and concentration of the liquid fuel are not limited. However, the characteristics of the fuel distribution mechanism 2 having a plurality of fuel discharge ports 22 become more apparent when the fuel concentration is high. For this reason, the fuel cell can particularly exhibit its performance and effects when a methanol aqueous solution or pure methanol having a concentration of 80% or more is used as the liquid fuel.

  The fuel introduction unit 30 has a function of supplying the fuel discharged from the fuel discharge port 22 of the fuel distribution mechanism 2 to the MEA 1, and a member disposed between the anode gas diffusion layer 9 and the fuel distribution mechanism 2 is provided. It is included in this fuel introduction part 30. The fuel introduction part 30 is provided facing the anode gas diffusion layer 9 and has a fuel intake surface in contact with the fuel discharge port 22 of the fuel distribution mechanism 2. Here, the fuel intake surface refers to the surface of the layer in contact with the fuel discharge port 22 of the fuel distribution mechanism 2 on the fuel discharge port 22 side.

  The fuel introduction part 30 shown in FIG. 1 includes a conductive layer 14 and a fuel diffusion layer 19 provided facing the anode gas diffusion layer 9. However, the present invention is not limited to this, and the fuel diffusion layer 19 may not be included, or other layers may be included.

  The conductive layer 14 is provided as necessary. For example, a porous layer (for example, a mesh) or a foil body made of a metal material such as gold or nickel, or a conductive metal material such as stainless steel (SUS) is made of gold. A composite material coated with a highly conductive metal such as is used.

  The fuel diffusion layer 19 has a surface in contact with the fuel discharge port 22 of the fuel supply unit 2 and plays a role of uniformly diffusing the fuel discharged from the fuel discharge port 22 to the anode 5 as vaporized fuel.

  The fuel released from the fuel distribution mechanism 2 is introduced into the MEA 1 via the fuel introduction unit 30. In the MEA 1, the fuel diffuses through the anode gas diffusion layer 9 and is supplied to the anode catalyst layer 8. When methanol fuel is used as the fuel, an internal reforming reaction of methanol shown in the following formula (A) occurs.

CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻ Formula (A)
Protons (H ⁺ ) generated by the internal reforming reaction are conducted through the electrolyte membrane 7 and reach the cathode catalyst layer 11. Gaseous fuel (for example, air) supplied from the cathode gas diffusion layer 12 diffuses through the cathode gas diffusion layer 12 and is supplied to the cathode catalyst. The air supplied to the cathode catalyst causes the reaction shown in the following formula (B). By this reaction, water is generated and a power generation reaction occurs.

(3/2) O ₂ + 6H ⁺ + 6e ⁻ → 3H ₂ O Formula (B)
Water generated by the power generation reaction is supplied from the cathode 6 to the anode catalyst layer 8 through the electrolyte membrane 7.

  The fuel cell described above includes an anode catalyst layer, an anode having an anode gas diffusion layer provided facing one side of the anode catalyst layer, a cathode catalyst layer, and one of the cathode catalyst layer. A membrane electrode assembly is provided that includes a cathode having a cathode gas diffusion layer provided facing the surface, and an anode catalyst layer and an electrolyte membrane disposed between the cathode catalyst layer. The anode catalyst layer and the cathode catalyst layer have a noble metal weight density of 0.2 g / cc or more and 0.8 g / cc or less, and satisfy the following formula (1).

1 ≦ (T _a / T _c ) (1)
However, the T _c in the thickness of the cathode catalyst layer, T _a is the thickness of the anode catalyst layer.

In the present invention, when the thickness T _a of the anode catalyst layer is equal to or thicker than the thickness T _c of the cathode catalyst layer, the weight density of at least one of the anode catalyst layer and the cathode catalyst layer is 0.2 g / cc or more. It has been found that when the amount is 0.8 g / cc or less, both the initial output and the output retention rate of the fuel cell are improved.

  That is, when the above formula (1) is satisfied, if the noble metal weight density of both the anode catalyst layer and the cathode catalyst layer is less than 0.2 g / cc, the catalyst amount is insufficient and sufficient output can be obtained. Can not. On the other hand, when the noble metal weight density of both the anode catalyst layer and the cathode catalyst layer exceeds 0.8 g / cc, both the anode catalyst layer and the cathode catalyst layer are compressed excessively. As a result, the fuel diffusion efficiency in the anode catalyst layer and the air intake efficiency in the cathode catalyst layer are reduced, so that the output is reduced.

  By making the noble metal weight density of at least one of the anode catalyst layer and the cathode catalyst layer 0.2 g / cc or more, the catalyst amount of at least one of the anode catalyst layer and the cathode catalyst layer becomes sufficient. The output can be improved. In addition, by making the noble metal weight density of at least one of the anode catalyst layer and the cathode catalyst layer 0.8 g / cc or less, the fuel diffusion efficiency or the air intake efficiency is improved, so that the initial output and the output maintenance ratio are improved. Can do. In particular, when the noble metal weight density of both the anode catalyst layer and the cathode catalyst layer is 0.2 g / cc or more and 0.8 g / cc or less, the amount of catalyst in both the anode catalyst layer and the cathode catalyst layer becomes sufficient. Since both the fuel diffusion efficiency and the air intake efficiency are improved, the initial output and the output maintenance rate can be greatly improved.

  A more preferable range of the noble metal weight density (ρa) in the anode catalyst layer is 0.5 g / cc or more and 0.7 g / cc or less. A more preferable range of the catalyst noble metal weight density (ρc) in the cathode catalyst layer is 0.3 g / cc or more and 0.6 g / cc or less.

The upper limit value of (T _a / T _c ) is desirably 7. By setting the value of (T _a / T _c ) to 7 or less, the thickness of the anode catalyst layer relative to the cathode catalyst layer becomes appropriate, and fuel diffusion proceeds smoothly, so that sufficient output can be obtained. it can. The upper limit value of (T _a / T _c ) is more preferably 4.25. By setting the amount to 4.25 or less, it is possible to avoid a relatively small amount of the catalyst on the cathode, thereby improving the life characteristics.

It is desirable that the noble metal weight density (ρa) of the anode catalyst layer is 0.2 g / cc or more and 0.8 g / cc or less, and the cathode satisfies the following formula (2).

0.1 ≦ (T _c / C _d ) ≦ 0.5 (2)
Where C _d is the thickness of the cathode and T _c is the thickness of the cathode catalyst layer.

By setting the value of the ratio of (T _c / C _d ) to 0.1 or more when the noble metal weight density (ρa) of the anode catalyst layer is 0.2 g / cc or more and 0.8 g / cc or less, the cathode Thus, both the initial output and the output retention ratio can be further improved by the synergistic effect of the cathode and the anode. On the other hand, by making the value of the ratio of (T _c / C _d ) 0.5 or less, so-called flooding in which H ₂ O generated by the power generation reaction becomes liquid water and covers the cathode gas diffusion layer is prevented. Therefore, the air intake efficiency is improved, and both the initial output and the output maintenance rate can be further improved. The cathode thickness C _d is desirably 250μm or 400μm or less. As a result, the initial output and the output maintenance ratio can be further improved.

  Moreover, it is desirable that the noble metal weight density of the cathode catalyst layer is 0.2 g / cc or more and 0.8 g / cc or less, and the anode satisfies the following formula (3).

0.1 ≦ (T _a / A _d ) ≦ 0.6 (3)
However, the A _d in the thickness of the anode, T _a is the thickness of the anode catalyst layer.

By setting the value of (T _a / A _d ) to 0.1 or more when the catalyst noble metal weight density (ρc) in the cathode catalyst layer is 0.2 g / cc or more and 0.8 g / cc or less, the anode Thus, both the initial output and the output retention ratio can be further improved by the synergistic effect of the cathode and the anode. On the other hand, by setting the value of (T _a / A _d ) to 0.6 or less, it is possible to increase both the proton conductive ability of the anode catalyst layer and the gas diffusion ability of the anode gas diffusion layer. It is possible to suppress the fuel efficiency. As a result, both the initial output and the output maintenance rate can be further improved. The thickness A _d of the anode is preferably not less than 330 [mu] m 650 .mu.m or less. As a result, the initial output and the output maintenance ratio can be further improved.

The thickness T _e of the electrolyte membrane is preferably not more than 180 [mu] m.

The thickness T from the outer surface to Irimen preparative fuel in the fuel inlet portion 30, i.e., the thickness C _o of the oxidizing agent inlet part 40, the membrane electrode assembly thickness having an opening portion 16a of the oxidizing agent inlet part 40 The total thickness of T _M and the thickness A _f of the fuel introduction part 30 (hereinafter referred to as cell thickness T) is not particularly limited, but can be 700 μm or more and 900 μm or less.

  The fuel cell according to the present embodiment is not limited to the structure shown in FIGS. 1 to 3, and can be configured as shown in FIG. 4, for example. In addition, the same member as demonstrated in FIGS. 1-3 is attached | subjected the same code | symbol, and description is abbreviate | omitted.

  The fuel diffusion layer 19 of the fuel introduction unit 30 includes a diffusion sheet (product name Sunmap manufactured by Nitto Denko) 51, a gas-liquid separation membrane 52, and a polytetrafluoroethylene (PTFE) membrane 53 in this order from the fuel supply unit 2 side. Are stacked. The conductive layer 14 is laminated on the PTFE film 53. The surface of the diffusion sheet 51 is in contact with the fuel discharge port 22 of the fuel supply unit 2. The gas-liquid separation membrane separates the vaporized component of the liquid fuel and the liquid fuel, and passes the vaporized component to the anode (fuel electrode) side. This gas-liquid separation membrane is made of a material that is inert to liquid fuel and does not dissolve, and is formed into a sheet. Specifically, silicone rubber, low-density polyethylene (LDPE) thin film, polyvinyl chloride (PVC) thin film, polyethylene It is made of a material such as a terephthalate (PET) thin film, a fluororesin (for example, polytetrafluoroethylene (PTFE), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), etc.), or a microporous film. The gas-liquid separation membrane is configured so that fuel and the like do not leak from the periphery. The PTFE membrane suppresses the permeation of water vapor and prevents an excessive amount of water vapor from being supplied to the anode.

  A resin frame (not shown) may be provided between the gas-liquid separation membrane and the anode. The space surrounded by the frame functions as a vaporized fuel storage chamber (so-called vapor pool) that temporarily stores the vaporized fuel that has diffused through the gas-liquid separation membrane, and also functions as a reinforcing plate that tightly contacts the membrane electrode assembly To do. Due to the effect of suppressing the amount of permeated methanol in the vaporized fuel storage chamber and the gas-liquid separation membrane, it is possible to avoid supplying a large amount of vaporized fuel to the anode catalyst layer at once. The frame is a short frame, and is made of engineering plastic having high chemical resistance such as polyetheretherketone (PEEK: trademark of Victorex).

  The oxidant introduction part 40 has a multilayer structure in which the conductive layer 13, the PTFE film 54, the moisture retention layer 18, the reinforcing plate 55, and the cover plate 56 are laminated in this order from the cathode 6 side. The reinforcing plate 55 and the cover plate 56 are made of, for example, SUS, and each has a plurality of openings (not shown) for taking in air as an oxidant. The PTFE membrane 54 is impregnated with a part of the water generated in the cathode catalyst layer 11 to suppress the transpiration of water and promote the uniform diffusion of air to the cathode catalyst layer 11.

  First, the thickness of each constituent member is measured by the following method.

  The MEA is taken out of the fuel cell, cut and embedded in the resin so that the cross section can be seen. The MEA embedded in the resin is polished so that the cross section becomes flat to obtain a measurement sample. For example, when the electrode has a rectangular shape, the electrode is cut parallel to the longitudinal direction at the center in the direction orthogonal to the longitudinal direction. Then, a total of three cut surfaces at positions near the center of 10% of the length in the longitudinal direction are taken out from the center and both ends of the cut surface. The subsequent results are the average values of these three locations.

  SEM photograph (1000 times) of SEI (secondary electron image) and BEI (reflected electron image) of the cut surface is confirmed for the measurement sample, and within 25% of the left and right of the field of view from the center in the image seen in the field of view. The thickness at the position (10 locations) obtained by dividing the cross section of the object into nine equal parts and the maximum thickness and the minimum thickness in this range are measured, and the average value is defined as the average thickness, which is the thickness of each component.

  Next, the noble metal weight and the noble metal weight density are measured by the following methods.

From the MEA of the fuel cell whose thickness has been measured, the MEA cut out for measuring the amount of noble metal is first peeled off to the anode and the cathode. Next, the whole area is cut out to ² cm ² and placed in a container, 250 mL of a hydrochloric acid / nitric acid mixed solution is added, and a thermal decomposition treatment is performed at 140 ° C. for 2 hours. Here, when the MEA is composed of a plurality of cells, the cut-out from the MEA is the central portion in the planar direction of each cell. When part of the anode catalyst layer or part of the cathode catalyst layer remains when the anode and cathode are peeled from the MEA, the part is scraped off with a jig.

  The obtained liquid after thermal decomposition is subjected to (xmL) ICP measurement (pressure acid decomposition-ICP emission spectroscopy). As the apparatus, IRIS Advantage manufactured by Thermo Fisher Scientific Co., Ltd. was used.

  The measurement conditions are as shown below.

Platinum (in the case of Pt)
Integration time 2 sec
Number of integrations 5times
Photomal voltage H
High frequency output 1.2kW
Metering height 10mm
Carrier gas flow rate 0.9L / min
Plasma gas flow rate 16L / min
Auxiliary gas flow rate 0.5L / min
Slit width Normal wavelength 214.4nm
Ruthenium (Ru) integration time 2 sec
Number of integrations 5times
Photomal voltage H
High frequency output 1.2kW
Metering height 15mm
Carrier gas flow rate 0.9L / min
Plasma gas flow rate 16L / min
Auxiliary gas flow rate 0.5L / min
Slit width Normal wavelength 240.3nm
From the amount of precious metal obtained by ICP measurement (y μg), the amount of sample used for ICP measurement (XmL), and the acid volume for dissolution of 250 mL, the amount of precious metal in the sample is calculated by the following equation.

The amount of noble metal in the sample (μg) = (y / X) × 250. A precious metal weight per unit area (mg / cm ² ) is calculated from the obtained precious metal amount (μg) and the sample area.

And precious metal weight density is computed by the following formula | equation.

Noble metal weight density ρ (g / cm ³ ) = ρ (g / cc) = Noble metal amount in sample / sample area / catalyst layer thickness The fuel cell applicable to the present invention has a liquid fuel and an oxidant because of its form. Active type fuel cell that supplies the fuel using an auxiliary device such as a pump, a passive type (internal vaporization type) fuel cell that supplies a vaporized component of liquid fuel to the anode, and a semi-passive type fuel cell shown in FIG. It is done. The active fuel cell employs a system in which a fuel made of an aqueous methanol solution is supplied to the anode of the MEA while being adjusted by a pump so that the amount thereof is constant, and air is also supplied to the cathode by a pump. In the passive type fuel cell, a system in which vaporized methanol is naturally supplied to the anode of the MEA and natural air is also supplied to the cathode and no extra equipment such as a pump is provided. In the semi-passive type fuel cell, the fuel supplied from the fuel storage part to the membrane electrode assembly is used for the power generation reaction, and is not circulated thereafter and returned to the fuel storage part. The semi-passive type fuel cell is different from the active method because it does not circulate the fuel, and does not impair the downsizing of the device. Further, the semi-passive type fuel cell uses a pump for supplying fuel, and is different from a pure passive type such as an internal vaporization type. In this semi-passive type fuel cell, a fuel cutoff valve may be arranged in place of the pump as long as fuel is supplied from the fuel storage portion to the membrane electrode assembly. In this case, the fuel cutoff valve is provided to control the supply of liquid fuel through the flow path.

  The fuel cell of the above-described embodiment is effective when various liquid fuels are used, and the type and concentration of the liquid fuel are not limited. Further, the above-described embodiment has been described by taking a semi-passive type using a pump for supplying fuel as an example of the configuration of the fuel cell main body, but for a purely passive type fuel cell such as an internal vaporization type However, the present invention can be applied.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Example 1)
<Production of anode>
A platinum-supporting carbon (carbon carrier: ketjen black, platinum content: 50% by mass) particles 8%, a perfluorosulfonic acid polymer composed of DE2020 (manufactured by DuPont), and a solvent are mixed by a homogenizer to obtain about 20 A slurry with a% solid content was prepared, and this was applied to one side of a compressed carbon paper (TGP-H-120 manufactured by Toray Industries, Inc.), which is an anode gas diffusion layer, using a die coater. This was dried at room temperature to form an anode catalyst layer.

<Production of cathode>
Platinum ruthenium-supported carbon (carbon carrier: ketjen black, platinum content: 50% by mass) particles 7% and perfluorosulfonic acid polymer made of DE2020 (manufactured by DuPont) are mixed with a homogenizer to give about 15% A slurry was prepared, and applied to one surface of carbon paper (TGP-H-090 manufactured by Toray Industries, Inc.), which is a cathode gas diffusion layer, and dried to form a cathode catalyst layer.

<Production of MEA>
As the electrolyte membrane, a solid electrolyte membrane made of Nafion 112 (manufactured by DuPont) was used. First, the electrolyte membrane and the cathode were overlapped so that the catalyst layer was on the electrolyte membrane side, and the electrolyte membrane cathode was further overlapped. An anode was placed on the opposite side of the anode so that the catalyst layer was on the electrolyte membrane side, and pressed under conditions of a temperature of 150 ° C. and a pressure of 40 kgf / cm ² to prepare a membrane electrode assembly (MEA). The electrode area was 12 cm ² for both the cathode and anode.

  This membrane / electrode assembly was sandwiched between gold foils having a plurality of openings for taking in air and vaporized methanol to form an anode conductive layer having a thickness of 60 μm and a cathode conductive layer having a thickness of 60 μm.

  The laminate in which the membrane electrode assembly (MEA), the anode conductive layer, and the cathode conductive layer were laminated was sandwiched between two resin frames. A rubber O-ring was sandwiched between the cathode side of the membrane electrode assembly and one frame, and between the anode side of the membrane electrode assembly and the other frame, respectively.

  The anode side frame was fixed by screwing to the liquid fuel storage chamber through a gas-liquid separation membrane. A 0.2 mm thick silicone sheet was used for the gas-liquid separation membrane. On the other hand, on the cathode side frame, a porous plate having a porosity of 28% and a thickness of 750 μm was arranged to form a moisture retaining layer. On this moisturizing layer, a stainless steel plate (SUS304) having a thickness of 2 mm with air inlets (4 mm diameter, 64 holes) for air intake is arranged to form a cover plate, and screwed Fixed.

  Pure methanol is injected into the liquid fuel storage chamber of the fuel cell formed as described above while controlling the cathode temperature to 55 ° C. with a pump. In an environment of a temperature of 25 ° C. and a relative humidity of 50%, the initial output and the output retention rate were measured by the following method, and the results are shown in Table 1 below.

In an environment where the temperature was 25 ° C. and the relative humidity was 50%, pure methanol having a purity of 99.9% by weight was supplied to the fuel cell produced as described above. A constant voltage power supply is connected to control the current flowing through the fuel cell so that the output voltage of the fuel cell becomes constant at 0.35 V (per 1 MEA). At this time, the output density obtained from the fuel cell is controlled. Measured. Here, the output density (mW / cm ² ) of the fuel cell is obtained by multiplying the current density flowing through the fuel cell (current value per 1 cm ² area of the power generation unit (mA / cm ² )) by the output voltage of the fuel cell. Is. The initial output is obtained by averaging the output density of 10 to 20 hours from the start of power generation. The output maintenance ratio is obtained by dividing the output density after 1000 hours by the initial output in%.

Further, the thickness of each constituent member is measured by the method described above, and the cell thickness T, the catalyst layer thickness ratio (T _a / T _c ), the cathode thickness ratio (T _c / C _d ), and the anode The thickness ratio (T _a / A _d ) is also shown in Table 1 below. The oxygen introducing section 40 has a cover plate, the moisture retaining layer, the conductive layer and the frame, the thickness C _o of the oxygen introduction part 40 was 1710Myuemu. The cathode thickness C _d is 310 .mu.m, the anode having a thickness of A _d is 470μm, 50μm thickness of the electrolyte membrane T _e, the thickness T _M of the membrane electrode assembly was 830 microns. The fuel introduction part 30 had a gas-liquid separation membrane, a conductive layer and a frame, and the thickness A _f of the fuel introduction part 30 was 450 μm.

  Further, the noble metal weight density of each of the cathode catalyst layer and the anode catalyst layer was measured by the method described above, and the results are shown in Table 1 below.

(Examples 2-9)
By changing the thickness of the cathode catalyst layer and the anode catalyst layer by changing the pressing conditions during MEA fabrication, the cell thickness T, the noble metal weight density, the catalyst layer thickness ratio (T _a / T _c ), A fuel cell was manufactured in the same manner as in Example 1 except that the cathode thickness ratio (T _c / C _d ) and the anode thickness ratio (T _a / A _d ) were changed as shown in Table 1 below. . The initial output and output retention rate of the obtained fuel cell were measured under the same conditions as in Example 1, and the results are shown in Table 1 below.

(Example 10)
An attempt was made to produce a membrane electrode assembly including an anode having a catalyst layer thickness ratio (T _a / T _c ) of 1.55 and an anode catalyst layer having a noble metal weight density of 0.889 g / cc. At this time, the anode catalyst layer was destroyed, and a membrane electrode assembly could not be obtained.

As is apparent from Table 1, the weight density of at least one of the cathode catalyst layer and the anode catalyst layer is 0.2 g / cc or more and 0.8 g / cc or less, and the thickness ratio (T _a / T _c ) is One or more Examples 1 to 8 have an initial output or an output maintaining as compared with Example 9 in which the thickness ratio (T _a / T _c ) is less than 1 although the noble metal weight density of the anode catalyst layer is within the above range. It can be seen that the rate is high and the output performance is excellent.

  By comparing Examples 1 to 7, Examples 1 to 5 in which the noble metal weight density of both the cathode catalyst layer and the anode catalyst layer is 0.2 g / cc to 0.8 g / cc It can be seen that both are superior to Examples 6 and 7 in which the noble metal weight density of only one of the cathode catalyst layer and the anode catalyst layer satisfies the above range.

Further, by comparing Example 1 to Example 5 and Example 8, the cathode thickness ratio (T _c / C _d ) and the anode thickness ratio (T _a / A _d ) satisfy the expressions (2) and (3). In Examples 1 to 5, both the initial output and the output retention ratio are superior to Example 8 (the cathode thickness ratio (T _c / C _d ) does not satisfy the formula (2)). Recognize.

  The present invention can be applied to various fuel cells using liquid fuel. Further, the specific configuration of the fuel cell, the supply state of the fuel, and the like are not particularly limited. In the implementation stage, the constituent elements can be modified and embodied without departing from the technical idea of the present invention. Furthermore, various modifications are possible, such as appropriately combining a plurality of constituent elements shown in the above embodiment, or deleting some constituent elements from all the constituent elements shown in the embodiment. Embodiments of the present invention can be expanded or modified within the scope of the technical idea of the present invention, and these expanded and modified embodiments are also included in the technical scope of the present invention.

  DESCRIPTION OF SYMBOLS 1 ... Membrane electrode assembly (MEA), 2 ... Fuel supply part (fuel distribution mechanism), 3 ... Fuel accommodating part, 4 ... Flow path, 5 ... Anode, 6 ... Cathode, 7 ... Electrolyte membrane, 8 ... Anode catalyst layer , 9 ... Anode gas diffusion layer, 11 ... Cathode catalyst layer, 12 ... Cathode gas diffusion layer, 13 ... Cathode conductive layer, 14 ... Anode conductive layer, 15 ... O-ring, 16 ... Cover plate, 16a ... Opening, 17 ... Pump, 18 ... moisturizing layer, 21 ... fuel inlet, 22 ... fuel outlet, 23 ... fuel distribution plate, 24 ... gap, 30 ... fuel inlet, 40 ... oxidant inlet, 100 ... fuel cell.

Claims (7)

An anode including an anode catalyst layer, and an anode gas diffusion layer provided facing one side of the anode catalyst layer;
A cathode including a cathode catalyst layer, and a cathode gas diffusion layer provided facing one side of the cathode catalyst layer;
A membrane electrode assembly including an electrolyte membrane disposed between the anode catalyst layer and the cathode catalyst layer;
The anode catalyst layer and the cathode catalyst layer have a noble metal weight density of 0.2 g / cc or more and 0.8 g / cc or less and satisfy the following formula (1).
1 ≦ (T _a / T _c ) (1)
However, the T _c in the thickness of the cathode catalyst layer, T _a is the thickness of the anode catalyst layer. 2. The fuel cell according to claim 1, wherein the anode catalyst layer has a noble metal weight density of 0.2 g / cc or more and 0.8 g / cc or less, and the cathode satisfies the following expression (2).
0.1 ≦ (T _c / C _d ) ≦ 0.5 (2)
Where C _d is the thickness of the cathode and T _c is the thickness of the cathode catalyst layer. The cathode thickness C _d is the fuel cell according to claim 2, wherein a is 250μm or more 400μm or less. 2. The fuel cell according to claim 1, wherein the cathode catalyst layer has a noble metal weight density of 0.2 g / cc or more and 0.8 g / cc or less, and the anode satisfies the following expression (3).
0.1 ≦ (T _a / A _d ) ≦ 0.6 (3)
However, the A _d in the thickness of the anode, T _a is the thickness of the anode catalyst layer. The thickness A _d of the anode, the fuel cell according to claim 4, wherein the at least 330 [mu] m 650 .mu.m or less.   The fuel cell according to claim 1, wherein a thickness of the electrolyte membrane is 180 μm or less. An oxidant introduction part provided facing the cathode diffusion layer and having an opening for taking in an oxidant on the outer surface;
A fuel introduction portion provided facing the anode diffusion layer and having a fuel intake surface; and a fuel discharge port facing the fuel intake surface of the fuel introduction portion, and the fuel introduction portion passing through the fuel discharge port. A fuel supply unit for supplying fuel to
The fuel cell according to any one of claims 1 to 6, wherein a thickness from the outer surface of the oxidant introduction portion to the fuel intake surface of the fuel introduction portion is 700 µm or more and 900 µm or less.

Images