JP2008153200A - Electrode for solid polymer fuel cell, manufacturing method of solid polymer fuel cell, and solid polymer fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode for a solid polymer fuel cell in which high catalyst activity is obtained while securing good fuel permeation, without generating a by-product difficult in treatment. <P>SOLUTION: The electrode for the solid polymer fuel cell is composed of a gas diffusion layer 2 having conductivity and ventilation performance and a catalyst layer 3 including a metal catalyst 6 carried on a catalyst carrier 5 and an ion exchange resin 7. The catalyst carrier 5 is constructed of a carbon layer consisting of carbon nanotubes of cup-stack type with a diameter of 50-200 nm and a length of 100 μm or less, and the metal catalyst 6 is carried by sputtering on the catalyst carrier 5. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrode for a solid polymer fuel cell comprising a gas diffusion layer having conductivity and air permeability, and a catalyst layer containing a metal catalyst supported on a catalyst support and an ion exchange resin, and a solid polymer fuel The present invention relates to a battery electrode manufacturing method and a polymer electrolyte fuel cell.

  A polymer electrolyte fuel cell is composed of a membrane-electrode assembly in which both sides of a solid electrolyte membrane are sandwiched between an anode catalyst electrode and a cathode catalyst electrode.

  The anode catalyst electrode and the cathode catalyst electrode each include a gas diffusion layer having conductivity and air permeability, a catalyst layer containing a metal catalyst supported on a catalyst support and an ion exchange resin, and the catalyst layer is in contact with the solid electrolyte membrane It has a structure.

  The catalyst layer is constructed by supporting a metal catalyst such as platinum or a platinum alloy on a catalyst carrier having a large surface area such as carbon black, and applying this together with an ion exchange resin onto the gas diffusion layer. It is obtained by doing.

  In order to support a metal catalyst such as platinum or platinum alloy on a catalyst support such as carbon black, a method generally called a wet method is employed.

JP 2004-359724 A

  As an example of such a wet method, a reduction reaction of chloroplatinic acid with ethanol can be exemplified, and according to this, platinum is supported on carbon black, but it is necessary to spend several days for the supporting work. At the same time, it is difficult to process the waste liquid from the manufacturing process. As waste liquid, by-products such as chlorine, ethyl chloride, hydrogen chloride, etc. and alkaline solution with pH adjustment etc. are generated, in addition to the problem of its production efficiency, there is a problem that waste liquid treatment costs arise, leading to an increase in manufacturing cost. there were.

  In addition, since the metal catalyst loading site on the catalyst carrier is arbitrary, for example, when the metal catalyst is supported in the pores on the surface of the catalyst carrier, the metal catalyst is disconnected from the fuel gas. There is also a problem that since the catalytic reaction does not occur, it does not contribute to the improvement of the output of the entire fuel cell. In fact, in the wet method, the solution penetrates into the pores on the surface of the carbon black, and a metal catalyst such as platinum is supported, so that contact with the ion exchange resin that controls proton conduction is insufficient, and as a catalyst It is said that there are many metal catalysts that do not fulfill this function. Furthermore, some supported metal catalysts grow as secondary particles in the course of the reaction, and metal particles that do not contribute to the catalytic reaction are formed in the particles.

  In addition, in the wet method, it is very difficult to control the particle diameter of the metal catalyst on the catalyst carrier, and the specific surface area of the metal catalyst is sufficiently small and cannot be uniformly controlled. Therefore, in order to improve the power generation characteristics of the polymer electrolyte fuel cell, it is necessary to carry a large amount of metal catalyst, which is economically inefficient.

  Furthermore, in order for the supported metal catalyst to fully exhibit its catalytic activity and improve the output of the polymer electrolyte fuel cell, so-called three-phase is used so that the metal catalyst, the fuel and the ion exchange resin are in contact at the same time. It is necessary to form an interface, but in the conventional method, since the ion exchange resin and the conductive catalyst carrier supporting the metal catalyst are mixed and applied, the path through which the fuel permeates is lost, or the metal catalyst Problems such as loss of contact with fuel due to being covered with ion exchange resin itself, and metal catalysts supported on the opposite side of the solid polymer electrolyte membrane are three-dimensionally delivering protons to the electrolyte membrane. There is also a problem that it is not possible to sufficiently perform the operation, and does not contribute to the improvement of the power generation amount of the entire fuel cell.

  For these many reasons, in the catalyst layer of a general fuel cell, the amount of metal catalyst such as platinum or platinum alloy that actually contributes to the power generation reaction is the total metal catalyst supported in the catalyst layer. It is said that it is only 10 to 30% by weight of the amount.

  In view of the above-mentioned problems, an object of the present invention is to provide an electrode for a polymer electrolyte fuel cell capable of obtaining high catalytic activity while ensuring good fuel permeability without generating by-products that are difficult to process, It exists in the point which provides the manufacturing method of the electrode for polymer electrolyte fuel cells, and a polymer electrolyte fuel cell.

  In order to achieve the above-described object, the characteristic configuration of the electrode for a polymer electrolyte fuel cell according to the present invention includes a gas diffusion layer having conductivity and air permeability, as described in claim 1 of the claims. A polymer electrolyte fuel cell electrode comprising a metal catalyst supported on a catalyst support and a catalyst layer containing an ion exchange resin, wherein the catalyst support is composed of a carbon layer, and the metal catalyst is the catalyst. This is in that it is supported on the support by sputtering.

  According to the above-described configuration, by appropriately adjusting various sputtering conditions, the particle size distribution and loading amount of the metal catalyst supported on the catalyst support made of the carbon layer can be suitably controlled. It is possible to provide a polymer electrolyte fuel cell electrode having high catalytic activity without causing problems of production efficiency and waste liquid treatment as in the method.

  Further, when the carbon layer is composed of carbon particles having a primary particle diameter of 1 to 100 nm, it is preferable in that resistance polarization is reduced due to high conductivity and concentration polarization is reduced, and the diameter is 50 to 200 nm. When composed of carbon fibers having a length of 100 μm or less, the activation polarization is reduced by sputtering and the catalytic activity is improved, and the resistance polarization is lowered by high conductivity, and the concentration polarization can be lowered. Is preferable.

  Furthermore, if the carbon fiber is a carbon nanotube, a sufficient surface area for supporting a required amount of the metal catalyst can be secured, which is preferable. When adopting a cup stack type carbon nanotube having a hollow structure inside as a carbon nanotube, the carbon network layers are only bonded by weak van der Waals forces between the carbon network layers. The length can be easily adjusted, and the end faces of the inner and outer surfaces of the structure in which the carbon network layer is laminated in a cup shape are exposed to the outside. The catalyst can be suitably dispersed and supported.

  Further, it is preferable that the metal catalyst is supported on the carbon layer so that the catalyst layer has air permeability, that is, the metal catalyst is preferably dispersed and supported on the carbon layer without forming a membrane. The gas permeability can be ensured and power can be generated efficiently.

If the particle diameter of the metal catalyst is in the range of 1 to 10 nm, the gas permeability of the fuel gas can be ensured and the metal catalyst can be sufficiently in contact with the fuel gas in the catalyst layer, so that a high catalytic reaction can be obtained. The amount of the metal catalyst supported is more preferably 0.5 mg / cm ² or less.

  The characteristic configuration of the above-described method for producing an electrode for a polymer electrolyte fuel cell includes an application step of applying carbon particles or carbon fibers dispersed in an organic solvent on the upper surface of a gas diffusion layer having conductivity and air permeability, It consists of a film forming step of forming a gas diffusion layer-carbon layer composite film by sintering at a high temperature after coating, and a metal catalyst supporting step of sputtering a metal catalyst on the formed composite film.

  In other words, the internal resistance generated between the layers can be reduced by the gas diffusion layer-carbon layer composite film produced by applying carbon particles or carbon fibers on the gas diffusion layer, thereby reducing the power generation efficiency. This can be effectively prevented, and by adopting the sputtering method, the particle size distribution and supported amount of the metal catalyst can be suitably controlled.

  The sputtering treatment time is preferably 15 seconds or more and less than 90 seconds, so that the metal catalyst can be evenly dispersed with an appropriate particle size while ensuring air permeability of the fuel gas.

  Then, using the above-described solid polymer type fuel cell electrode as an anode catalyst electrode and a cathode catalyst electrode, the catalyst layer of the anode catalyst electrode is bonded to one surface of the solid polymer electrolyte membrane, and the cathode catalyst is bonded to the other surface. By joining the electrode catalyst layers, a highly efficient fuel cell can be obtained.

  As described above, according to the present invention, an electrode for a polymer electrolyte fuel cell capable of obtaining high catalytic activity while ensuring good fuel permeability without generating a by-product that is difficult to process, A method for producing an electrode for a molecular fuel cell and a polymer electrolyte fuel cell can be provided.

  Hereinafter, preferred embodiments of a polymer electrolyte fuel cell employing the polymer electrolyte fuel cell electrode according to the present invention will be described.

  FIG. 1 shows an example of an embodiment of a polymer electrolyte fuel cell according to the present invention. The solid polymer fuel cell 1 is configured by joining an anode catalyst electrode 4a (4) and a cathode catalyst electrode 4b (4) to both surfaces of a solid polymer electrolyte membrane 8, respectively.

  The anode catalyst electrode 4a (4) and the cathode catalyst electrode 4b (4) are a metal catalyst supported on the gas diffusion layer 2 (2a, 2b) having conductivity and air permeability and the catalyst support 5 (5a, 5b). 6 (6a, 6b) and a catalyst layer 3 (3a, 3b) including an ion exchange resin 7, and each catalyst layer 3 (3a, 3b) is disposed so as to face the solid polymer electrolyte membrane 8. ing.

  The gas diffusion layer 2 is composed of carbon paper or carbon cloth having conductivity and air permeability. In general, carbon fibers processed into a woven fabric, nonwoven fabric, paper, or cloth can be suitably used as those having both gas permeability and conductivity.

  Further, the catalyst carrier 5 is composed of a material having a surface area sufficient to carry a required amount of the metal catalyst 6 and also having electron conductivity. Specifically, carbon such as furnace black and channel black, graft carbon, etc. Carbon particles, carbon fibers containing carbon nanotubes, and the like are used.

  After applying carbon particles or carbon fibers as the catalyst support 5 in advance on the gas diffusion layer 2, the metal catalyst 6 is supported on the carbon particles or carbon fibers by sputtering. The sputtering treatment time is preferably less than 90 seconds, particularly preferably 15 to 60 seconds.

  When carbon is used as the catalyst support 5, the specific surface area of the carbon decreases with the particle size and affects the supported amount and uniform dispersibility of the metal catalyst, so the primary particle size is in the range of 1 to 100 nm. It is preferable to use carbon particles, and it is particularly preferable to use carbon particles in the range of 1 to 50 nm.

  When carbon fibers are used as the catalyst support 5, it is preferable to use carbon fibers having a diameter of 50 to 200 nm and a fiber length of 100 μm or less and 1 μm or more for the same reason.

  It is also possible to use carbon nanotubes in the above numerical range as the carbon fiber, and in particular, it has a structure in which one graphene sheet is wound in a cylindrical shape, a diameter of 0.7 to 70 nm, and a length of about several tens of μm. When carbon nanotubes made of carbon crystals are used, they are extremely suitable as a catalyst support in the present invention because of their specific surface area and conductivity.

  There are various types of carbon nanotubes such as a single-wall type, a multi-wall type, and a carbon horn type, which are known as materials having very excellent characteristics such as strength, conductivity, and thermal conductivity. In particular, cup-stacked carbon nanotubes are different from ordinary concentric carbon nanotubes in that the cups with open bottoms are stacked and have a large hollow structure inside, and the length depends on the number of cups stacked. Since adjustment is possible, it is extremely useful in that the amount of the metal catalyst supported can be controlled by appropriately selecting the length of the cup-stacked carbon nanotube. A cup-stacked carbon nanotube having a diameter of 80 to 120 nm can be easily formed to a length of 100 μm or less by, for example, ball milling.

  In general, in order to obtain good power generation characteristics of a fuel cell, it is necessary to optimize the three types of activation polarization, resistance polarization, and concentration polarization. Three types of optimization: reduction of activation polarization by catalyst loading (improvement of catalyst activity), reduction of resistance polarization by high conductivity equal to or higher than that of existing carbon black or carbon nanotube, and reduction of concentration polarization by length control Is possible. Particularly in reducing concentration polarization, the use of a length of 5 μm to 50 μm, more preferably 5 μm to 15 μm, improves the performance over existing materials.

  The step of applying carbon particles or carbon fibers to the gas diffusion layer 2 will be described. First, carbon particles or carbon fibers are dispersed in an organic solvent using a paint shaker, a ball mill, or the like, and the obtained carbon dispersion solution is sprayed. The coating is applied to the gas diffusion layer 2 by a dipping method, a doctor blade method, a screen printing method, etc., and after the application, the solvent is evaporated by sintering at a temperature higher than the vaporization temperature of the solvent used, and the gas diffusion layer − A composite film of carbon layers is formed. The type of the organic solvent is selected according to the type of carbon, and is not particularly limited. However, when a cup stack type carbon nanotube is used, a polar organic solvent can be exemplified, and N-methylpyrrolidone is particularly preferable.

A step of supporting the metal catalyst 6 using the sputtering method is performed on the catalyst support 5 of the gas diffusion layer-carbon layer composite formed as described above. The catalyst 6 has a function of promoting the electrode reaction, and platinum Pt or a platinum alloy is preferably used. In addition, gold Au, silver Ag, iridium Ir, palladium Pd, ruthenium Ru, osmium Os, nickel Ni, tungsten Metals containing at least one selected from W, molybdenum Mo, manganese Mn, yttrium Y, vanadium V, niobium Nb, titanium Ti, and rare earth metals can be used, and carbides such as molybdenum carbide Mo ₂ C can be used. It is also possible. These catalysts may be used alone or in combination, or some or all of them may be used in the form of an alloy.

  The average particle diameter of the metal catalyst 6 is preferably in the range of 1 to 10 nm, more preferably in the range of 2 to 5 nm, because the smaller the average particle diameter, the larger the effective electrode area and the better the catalytic activity. Here, when the metal catalyst 6 is supported by sputtering, it is necessary to adjust various conditions so that a thin film of the metal catalyst 6 is not formed. This is because when the thin film of the metal catalyst 6 is formed, the metal catalyst 6 covers the entire surface of the catalyst layer 3 and inhibits the movement of the raw material and the water required for humidifying the raw material.

  The sputtering treatment time is preferably less than 90 seconds, and more preferably 15 seconds to 60 seconds or less. The RF output value during sputtering is not particularly limited, but is preferably 100 W or more.

  The catalyst layer 3 can be joined to the solid polymer electrolyte membrane 8 and used as a fuel cell MEA (Membrane Electrode Assembly). When joining both, it is preferable to apply the ion exchange resin 7 in order to obtain a path through which protons pass between the metal catalyst 6 and the solid polymer electrolyte membrane 8.

  As the ion exchange resin 7, a material having at least high proton conductivity is preferable, and various Nafion (DuPont registered trademark: Nafion) manufactured by DuPont, ion exchange resin manufactured by Dow Chemical Co., etc. are preferably exemplified.

  The content of the ion exchange resin 7 applied to the catalyst layer 3 is not particularly limited, but is preferably 50 to 2000% by weight with respect to the total amount of the supported metal catalyst 6. The ion exchange resin can be applied to the electrode catalyst layer by using a spray method, a dipping method, a doctor blade method, a screen printing method, or the like.

  Further, the joining of the catalyst layer 3 and the solid polymer electrolyte membrane 8 can be performed using a hot press apparatus or the like.

  1 g of cup-stacked carbon nanotubes (provided by GSI Creos Co., Ltd., type: 24PS) and 70 g of 5 mmφ zirconia beads were treated in a paint shaker for 5 minutes. Thereafter, 2 mL of N-methylpyrrolidone (hereinafter referred to as NMP) was added, and the mixture was similarly treated with a paint shaker for 10 minutes.

  This operation was repeated four times, and finally a 60-minute paint shaker treatment was performed to obtain approximately 10 mL of a cup-stacked carbon nanotube-dispersed NMP solution.

This solution was applied to one side of carbon paper and carbon cloth (both manufactured by Toray Industries, Inc .: TGP-H), which had been cut to 5 cm ² in advance, using a doctor blade. The carbon cloth was treated with Teflon (registered trademark of DuPont) in advance to have water repellency in order to prevent water accumulation during power generation.

  The cup-stacked carbon nanotube laminated carbon paper and the cloth thus obtained were dried in a hot air oven at 230 ° C. for 2 hours to completely evaporate NMP. The weights of the cup-stacked carbon nanotubes laminated on the carbon paper and the carbon cloth were 0.124 g and 0.186 g, respectively.

Next, the metal catalyst was supported by sputtering on the cup-stacked carbon nanotube laminated carbon paper and the cloth using a sputtering apparatus manufactured by ULVAC. Sputtering was performed using platinum as a target, argon as an inert gas, and using a DC power supply, with a vacuum of 3.6 × 10 ³ Torr, an RF output of 300 W, and a sputtering temperature of 24 ° C. Sputtering was performed for 15 seconds, 30 seconds, and 60 seconds, respectively.

  The cup-stacked carbon nanotube-laminated carbon paper and the cloth were fixed to the surface of the support in the sputtering apparatus using a double-sided tape so that the surface on which the cup-stacked carbon nanotubes were laminated was sputtered.

The amount of platinum supported when subjected to sputtering for 15 seconds, when conducted 0.029 mg / ^cm 2, 60 seconds when conducted 0.017 mg / ^cm 2, 30 seconds was 0.057 mg / cm ² . A transmission electron micrograph of the platinum particles 6 supported on the cup-stacked carbon nanotube 5 is shown in FIG. Finally, the Alfrich Nafion solution (5 weight percent solution) adjusted to the same amount as the supported platinum was added to the cup-stacked carbon nanotube laminated carbon paper supporting the platinum particles and the cloth with a doctor blade. And dried in vacuo at 80 degrees to obtain a platinum-supported electrode catalyst film.

  The MEA was created by the following procedure. A Dupont Nafion212 membrane, which had been subjected to a cleaning treatment in advance, was cut into a size of 5 cm square. The electrode catalyst film supporting platinum was sandwiched from both sides of the Nafion 212 film so that the supported platinum was directed to the Nafion 112 film side, and bonded by a hot press apparatus. The bonding temperature was 120 ° C., the pressure was 3 MPa, and the time was 10 minutes. In this way, an MEA was produced in which the side to which the electrode catalyst film using carbon paper was bonded was the anode, and the side to which the electrode catalyst film using carbon cloth was bonded was the cathode.

  The obtained MEA was incorporated into a single cell (EFC05-01SP) manufactured by Toyo Technica and evaluated as a fuel cell. In the evaluation, hydrogen gas was supplied to the anode side and oxygen gas was supplied to the cathode side as fuel. Both gases were supplied at a rate of 500 cc / min and a gas temperature of 120 ° C. The temperature of the cell body was 80 ° C. The IV characteristics were evaluated and the power generation characteristics as shown in FIG. 3 were obtained.

  FIG. 4 shows the power generation characteristics when the sputtering time is 15 seconds and the RF output is 300 W and 100 W.

[Comparative example]
In the above example, an MEA was fabricated using the same method except that the sputtering treatment time was 90 seconds. The amount of platinum carried was 0.084 mg / cm ² .

  FIG. 3 shows the IV characteristics when the power generation characteristics of the obtained MEA were measured in the same manner as the method shown in Example 1. Despite the increased amount of platinum supported, the IV characteristics are not improved.

  FIG. 5 shows a transmission electron micrograph of platinum particles supported on cup-stacked carbon nanotubes under such conditions. It can be seen that the platinum particles are aggregated and supported so as to cover the cup-stacked carbon nanotubes.

  In the above-described embodiments, the case where the carbon layer which is a catalyst carrier is configured using cup-stacked carbon nanotubes has been described. However, the catalyst carrier according to the present invention is described in the column of means for solving the problems. In any case, a solid polymer fuel cell electrode having good characteristics can be obtained by supporting a metal catalyst by sputtering.

Explanatory drawing of the polymer electrolyte fuel cell by this invention Transmission electron micrograph of platinum particles supported on cup-stacked carbon nanotubes by sputtering according to the present invention Power generation characteristics when the sputtering time is changed Power generation characteristics when changing RF output of sputtering equipment Transmission electron micrograph of platinum particles supported on cup-stacked carbon nanotubes by sputtering with proportionality

Explanation of symbols

1: solid polymer fuel cells 2, 2a, 2b: gas diffusion layers 3, 3a, 3b: catalyst layer 4: catalyst electrode 4a: anode catalyst electrode 4b: cathode catalyst electrodes 5, 5a, 5b: catalyst carrier 6, 6a, 6b: Metal catalyst 7: Ion exchange resin 8: Solid polymer electrolyte membrane

Claims (10)

An electrode for a polymer electrolyte fuel cell comprising a gas diffusion layer having electrical conductivity and air permeability, and a catalyst layer containing a metal catalyst supported on a catalyst support and an ion exchange resin,
An electrode for a polymer electrolyte fuel cell, wherein the catalyst support is composed of a carbon layer, and the metal catalyst is supported on the catalyst support by sputtering.   2. The polymer electrolyte fuel cell electrode according to claim 1, wherein the carbon layer is composed of carbon particles having a primary particle diameter of 1 to 100 nm or carbon fibers having a diameter of 50 to 200 nm and a length of 100 μm or less.   3. The polymer electrolyte fuel cell electrode according to claim 2, wherein the carbon fiber is a carbon nanotube.   The electrode for a polymer electrolyte fuel cell according to claim 3, wherein the carbon nanotube is a cup-stacked carbon nanotube having a hollow structure therein.   5. The polymer electrolyte fuel cell electrode according to claim 1, wherein the metal catalyst is supported on the carbon layer so that the catalyst layer has air permeability.   The electrode for a polymer electrolyte fuel cell according to any one of claims 1 to 5, wherein the particle diameter of the metal catalyst is in the range of 1 to 10 nm. The solid polymer fuel cell electrode according to any one of claims 1 to 6, wherein the supported amount of the metal catalyst is 0.5 mg / cm ² or less. A method for producing an electrode for a polymer electrolyte fuel cell according to any one of claims 1 to 7,
An application step of applying carbon particles or carbon fibers dispersed in an organic solvent on the upper surface of the gas diffusion layer having conductivity and air permeability, and a composite film of the gas diffusion layer and the carbon layer by sintering at a high temperature after application A method for producing an electrode for a polymer electrolyte fuel cell comprising a film forming step of forming a metal catalyst and a metal catalyst supporting step of sputtering a metal catalyst on the formed composite membrane.   The method for producing an electrode for a polymer electrolyte fuel cell according to claim 8, wherein the sputtering treatment time is 15 seconds or more and less than 90 seconds.   The electrode for a polymer electrolyte fuel cell according to any one of claims 1 to 7 is used as an anode catalyst electrode and a cathode catalyst electrode, and a catalyst layer of the anode catalyst electrode is bonded to one surface of a solid polymer electrolyte membrane, A polymer electrolyte fuel cell in which a catalyst layer of the cathode catalyst electrode is bonded to the other surface.