JP2008117563A - Water-repellent paste for fuel cell electrode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide water-repellent paste for a fuel cell electrode with a void ratio of a water-repellent layer increased by blending an appropriate amount of fibrous filler and thereby improving a gas diffusion property and a removing capacity of product moisture for characteristics improvement of the fuel cell. <P>SOLUTION: As against a void ratio of 66% in a comparison example 1 not containing a fibrous filler, an execution example 1 has a void ratio of 71%, an execution example 2 has that of 75%, an execution example 3 has that of 84%, and an execution example has that of 87%, all toward improvement. Especially, as a content of carbon fiber is increased as a fibrous filler from the example 1 to that 2, and that 3, a void ratio is increased from 71%, to 75% and 84%. An MEA is manufactured with the use of water-repellent paste for the fuel cell electrode in correspondence with the execution examples 1 to 4 and the comparison example 1, and each battery performance is measured. It is found that a voltage generated becomes larger as a void ratio is increased. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a water-repellent paste for a fuel cell electrode that forms a diffusion layer of an electrode used in a polymer electrolyte fuel cell, and particularly to increase the output of the polymer electrolyte fuel cell by increasing the porosity. The present invention relates to a water repellent paste for a fuel cell electrode.

  In a polymer electrolyte fuel cell, a cathode side electrode and an anode side electrode are formed on both sides of a polymer electrolyte membrane. Usually, the cathode side electrode and the anode side electrode are carbon carrying a catalyst such as platinum. A catalyst layer made of black and ion exchange resin, a particulate conductive filler such as carbon black powder for imparting conductivity to a carbon substrate such as carbon cloth or carbon paper, and polytetrafluoro for imparting water repellency It is constituted by a gas diffusion layer formed by applying a water-repellent paste kneaded with a fluorine resin dispersion such as ethylene (hereinafter referred to as “PTFE”) dispersion.

  Here, simply applying a mixture of particulate conductive filler and fluororesin dispersion causes clogging of the space in the gas diffusion layer, reducing gas diffusibility and the ability to remove generated water (drainage). It has been found that the performance of the fuel cell deteriorates.

  In view of this, the invention disclosed in Patent Document 1 proposes a fuel cell characterized by having fibrous carbon in at least a part of the interface between the catalyst layer and / or the gas diffusion layer with the catalyst layer. As a result, the fuel cell can suppress “wetting” in the catalyst layer, reduce electric resistance, secure a gas flow path, improve gas permeability, and easily perform humidification control. It is going to be.

  In the invention disclosed in Patent Document 2, carbon fiber having a fiber diameter of 1 μm to 100 μm and an aspect ratio of 50 or more in the water-repellent layer is 0.1 M to 0.2 M when the content of carbon particles is M. By making the catalyst layer and / or the diffusion layer contained in a proportion, the fuel cell does not have a closed space inside and has a catalyst layer and / or a diffusion layer excellent in gas permeability and conductivity. .

Furthermore, in the invention disclosed in Patent Document 3, the water-repellent layer of the gas diffusion layer includes a water-repellent resin / conductive particles and a selectively hydrophobic-treated fiber, A fuel cell characterized by containing 10% by weight to 50% by weight with respect to the conductive powder is proposed. As a result, gas diffusion with excellent gas diffusibility and drainage performance is possible without excess water accumulating as in the case of using a hydrophilic fiber such as carbon fiber as the fiber material, resulting in insufficient drainage. The fuel cell has a layer.
JP 2004-119398 A JP 2005-294115 A JP 2006-92920 A

  However, in the techniques described in Patent Document 1 and Patent Document 2 described above, the water repellent that forms a part of the gas diffusion layer by applying the water repellent paste even though the gas permeation passage can be secured. Since there is no change in the point of layer formation, the porosity of the gas diffusion layer is reduced and the gas diffusibility and the ability to remove generated water are reduced, especially the ability to remove generated water (drainage) is greatly increased. There was a problem that it was unavoidable to decrease.

  Moreover, in the technique described in the above-mentioned patent document 3, since the fiber material must be subjected to a hydrophobic treatment, fluorine gas treatment for heating the fiber material in a fluorine gas atmosphere to fluorinate the surface, PTFE, etc. Hydrophobic resin coating treatment that coats the surface of the fiber with a fluororesin is required, a manufacturing process becomes longer, and an apparatus for performing the hydrophobic treatment process is also required. There was a problem of increased costs.

  Furthermore, the present inventors have found that even when a hydrophilic fiber such as carbon fiber is used as the fiber, the drainage performance is not necessarily deteriorated and the performance as a fuel cell is improved. . Therefore, the present invention increases the porosity of the water-repellent layer by producing a water-repellent paste for a fuel cell electrode by blending an appropriate amount of fibrous filler, thereby improving the gas diffusibility and the ability to remove generated water. An object of the present invention is to provide a water-repellent paste for a fuel cell electrode capable of improving the characteristics of the fuel cell.

  A water-repellent paste for a fuel cell electrode according to the invention of claim 1 is a water-repellent paste for forming a gas diffusion layer of a solid polymer fuel cell mainly composed of a polymer electrolyte membrane. It contains a conductive filler, a fluorine resin dispersion, and a fibrous filler. Here, the “particulate conductive filler” includes carbon black, the “fluorinated resin dispersion” includes PTFE dispersion, and the “fibrous filler” includes acicular titanium oxide, zinc oxide whisker, Examples include potassium titanate fiber.

  The water repellent paste for a fuel cell electrode according to the invention of claim 2 is the structure of claim 1, wherein the fibrous filler is a conductive fibrous filler having conductivity. Here, examples of the “conductive fibrous filler having conductivity” include carbon fibers and carbon nanotubes.

  The water repellent paste for a fuel cell electrode according to the invention of claim 3 is the structure of claim 1 or claim 2, wherein the amount of the fibrous filler added is a combination of the particulate conductive filler and the fibrous filler. It is what is 20 to 100 weight% of the whole filler.

  A water-repellent paste for a fuel cell electrode according to a fourth aspect of the invention is a water-repellent paste for forming a gas diffusion layer of a solid polymer fuel cell mainly composed of a polymer electrolyte membrane. It contains only a conductive fibrous filler having conductivity and a fluororesin dispersion. Here, examples of the “conductive fibrous filler” include carbon fibers and carbon nanotubes.

  The water-repellent paste for a fuel cell electrode according to the invention of claim 5 is the one according to any one of claims 1 to 4 further including a pore forming agent. Here, examples of the “pore-forming agent” include polylactic acid particles.

  The water repellent paste for a fuel cell electrode according to a sixth aspect of the present invention is the structure according to any one of the first to fifth aspects, wherein the fibrous filler (including the conductive fibrous filler) has a diameter of 0.1 μm. It is in the range of ˜15 μm, and the length is in the range of 1 μm to 1 mm.

  A water-repellent paste for a fuel cell electrode according to the invention of claim 1 is a water-repellent paste for forming a gas diffusion layer of a solid polymer fuel cell mainly composed of a polymer electrolyte membrane. It contains a conductive filler, a fluorine resin dispersion, and a fibrous filler. Here, the “particulate conductive filler” includes carbon black, the “fluorinated resin dispersion” includes PTFE dispersion, and the “fibrous filler” includes acicular titanium oxide, zinc oxide whisker, Examples include potassium titanate fiber.

  In this way, by including the fibrous filler in the water repellent paste for the fuel cell electrode, the fibrous filler is entangled with each other to form a space, so that the water repellent for the fuel cell electrode is formed on a substrate such as carbon paper. By applying and baking the paste, the porosity of the formed water repellent layer is increased. Therefore, when the fuel cell electrode (anode and cathode) is formed integrally with the catalyst layer and the fuel cell is further configured and operated, the gas diffusibility and the ability to remove generated water are large, which is excellent. It shows power characteristics (generated voltage).

  In this way, a water repellent paste for a fuel cell electrode is produced by blending an appropriate amount of fibrous filler to increase the porosity of the water repellent layer, thereby improving the gas diffusibility and the ability to remove generated water. It becomes the water-repellent paste for fuel cell electrodes which can improve the characteristic of a battery.

  In the water repellent paste for a fuel cell electrode according to the invention of claim 2, the fibrous filler is a conductive fibrous filler having conductivity. Here, examples of the “conductive fibrous filler having conductivity” include carbon fibers and carbon nanotubes.

  In this way, the water repellent paste for fuel cell electrodes is formed on a substrate such as carbon paper in order to form a space by including the fiber filler in the water repellent paste for fuel cell electrodes so that the fibrous fillers are entangled with each other. By applying and baking, the porosity of the formed water-repellent layer is increased. Furthermore, in addition to the effect of the first aspect, since the fibrous filler has conductivity, the conductivity of the gas diffusion layer as a whole is improved, and electric power can be taken out efficiently.

  Thus, by producing a water repellent paste for a fuel cell electrode by blending an appropriate amount of conductive fibrous filler having conductivity, the porosity of the water repellent layer is increased and the conductivity is also increased. A water-repellent paste for a fuel cell electrode capable of improving the characteristics of the fuel cell by improving the gas diffusibility and the ability to remove generated water.

  In the water repellent paste for a fuel cell electrode according to the invention of claim 3, the addition amount of the fibrous filler is 20% by weight to 100% by weight of the total filler including the particulate conductive filler and the fibrous filler. This is because when the amount of the fibrous filler added is less than 20% by weight of the whole filler, only a small effect of increasing the porosity of the water repellent layer can be obtained.

  Moreover, when the addition amount of a fibrous filler is 100 weight% of the whole filler, at least one part of a fibrous filler needs to be a conductive fibrous filler which has electroconductivity.

  Thus, by producing a water repellent paste for a fuel cell electrode by blending an appropriate amount of conductive fibrous filler having conductivity, the porosity of the water repellent layer is increased and the conductivity is also increased. A water-repellent paste for a fuel cell electrode capable of improving the characteristics of the fuel cell by improving the gas diffusibility and the ability to remove generated water.

  A water-repellent paste for a fuel cell electrode according to a fourth aspect of the invention is a water-repellent paste for forming a gas diffusion layer of a solid polymer fuel cell mainly composed of a polymer electrolyte membrane. It contains only a conductive fibrous filler having conductivity and a fluororesin dispersion. Here, examples of the “conductive fibrous filler” include carbon fibers and carbon nanotubes.

  When the conductive fibrous filler is used, the conductivity of the water-repellent layer can be ensured by the conductive fibrous filler, so there is no need to blend a non-fibrous particulate conductive filler such as carbon black. . Thus, the water repellent formed by simply applying a conductive fibrous filler such as carbon fiber and a fluorine resin dispersion such as PTFE dispersion to a base material such as carbon paper and baking it. A water repellent paste for a fuel cell electrode in which the porosity of the layer is increased can be obtained.

  Thus, by producing a water repellent paste for a fuel cell electrode by blending an appropriate amount of a conductive fibrous filler, the porosity of the water repellent layer is increased and the conductivity is also increased. The water repellent paste for a fuel cell electrode can improve the characteristics of the fuel cell by improving the ability to remove the generated water.

  The water-repellent paste for a fuel cell electrode according to the invention of claim 5 is obtained by further adding a pore forming agent. Here, examples of the “pore-forming agent” include polylactic acid particles. Accordingly, in addition to the effect described in any one of claims 1 to 4, a space is generated after firing at the position where the pore-forming agent was present, so that the porosity is further increased.

  In this way, a water repellent paste for a fuel cell electrode is produced by blending an appropriate amount of fibrous filler to increase the porosity of the water repellent layer, thereby improving the gas diffusibility and the ability to remove generated water. It becomes the water-repellent paste for fuel cell electrodes which can improve the characteristic of a battery.

  In the water repellent paste for a fuel cell electrode according to the invention of claim 6, the diameter of the fibrous filler (including the conductive fibrous filler) is in the range of 0.1 μm to 15 μm and the length is 1 μm to 1 mm. Within the range, more preferably within the range of 1 μm to 50 μm.

  The inventors of the present invention have conducted extensive experimental research on the size of the fibrous filler (including conductive fibrous filler) to be blended in the water-repellent paste for fuel cell electrodes. As a result, the diameter of the fibrous filler is 0.1 μm. It is found that the most preferable result is obtained when the length is in the range of ˜15 μm and the length is in the range of 1 μm to 1 mm, more preferably in the range of 1 μm to 50 μm, and the present invention is completed based on this finding. It has been made.

  Thus, the porosity of the water-repellent layer is increased by producing a water-repellent paste for a fuel cell electrode by blending an appropriate amount of fibrous filler having an appropriate diameter and length, thereby increasing gas diffusibility and generated moisture. The water repellent paste for a fuel cell electrode can improve the characteristics of the fuel cell by improving the removal ability of the fuel cell.

  Hereinafter, a water-repellent paste for a fuel cell electrode according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a cross-sectional view showing the structure of a gas diffusion layer formed by applying a water repellent paste for a fuel cell electrode according to an embodiment of the present invention to a substrate and baking it. FIG. 2 is a graph showing power characteristics of an MEA (Membrane Electrode Assembly) produced using the water-repellent paste for fuel cell electrodes according to the embodiment of the present invention.

  First, a method for producing a water-repellent paste for a fuel cell electrode according to an embodiment of the present invention and a method for evaluating a porosity will be described. The water repellent paste for a fuel cell electrode according to the present embodiment includes carbon black as a particulate conductive filler, PTFE dispersion as a fluororesin dispersion, and carbon fiber as a fibrous filler (conductive fibrous filler). A paste-like mixture containing polylactic acid or the like as a pore-forming agent.

  In the present embodiment, the water-repellent paste for fuel cell electrodes of Examples 1 to 4 was prepared by changing the components and the composition as the water-repellent paste for fuel cell electrodes, and a conventional fuel cell electrode as Comparative Example 1 A water repellent paste was also prepared. The formulations of Examples 1 to 4 and Comparative Example 1 are shown in Table 1.

  As shown in Table 1, Example 1 and Example 2 are carbon black as a particulate conductive filler, PTFE dispersion as a fluororesin dispersion, and fibrous filler (conductive fibrous filler). And a carbon fiber as a water-repellent paste for a fuel cell electrode, which corresponds to the inventions of claim 1 and claim 2. Further, Example 3 is a water-repellent paste for a fuel cell electrode containing only carbon fibers as a conductive fibrous filler having conductivity as a filler and PTFE dispersion as a fluororesin dispersion, This corresponds to the fourth invention. Furthermore, Example 4 is a water-repellent paste for fuel cell electrodes containing carbon fiber, PTFE dispersion and polylactic acid as a pore-forming agent, and corresponds to the invention of claim 5.

  The carbon fiber as the fibrous filler (conductive fibrous filler) has a diameter of 0.15 μm and a length of 20 μm, and corresponds to the invention of claim 6. Furthermore, the carbon fiber content as the fibrous filler in Example 1 is 20% by weight of the total filler combined with carbon black, and the carbon fiber content in Example 2 is 40% by weight of the total filler. In Examples 3 and 4, since the content is 100% by weight, both satisfy the conditions of the invention of claim 3.

  The “other” component shown in Table 1 is mostly water, and the rest contains a small amount of surfactant. Therefore, the “other” component is a solvent for mixing each component of carbon black, PTFE dispersion, carbon fiber, and polylactic acid into a paste, and disappears after firing.

  These blending components of Examples 1 to 4 and Comparative Example 1 were mixed sufficiently to prepare 5 types of water-repellent pastes for fuel cell electrodes. And each paste was baked at 350 degreeC and the porosity of the obtained baked product was measured with the porosimeter. The measurement results of the porosity are shown in the bottom row of Table 1. As shown in Table 1, Example 1 has a porosity of 71 compared to Comparative Example 1 which is a conventional water-repellent paste and does not contain a fibrous filler, compared with a porosity of 66%. %, Example 2 has a porosity of 75%, Example 3 has a porosity of 84%, and Example 4 has a porosity of 87%.

  In particular, as Example 1, Example 2 and Example 3 and the content rate of carbon fiber as a fibrous filler increased, the porosity also increased rapidly to 71%, 75% and 84%. Thus, it is considered that the porosity is increased by forming a space in the water repellent paste for a fuel cell electrode by entwining carbon fibers as fibrous fillers.

  Next, using these water-repellent pastes for fuel cell electrodes according to Examples 1 to 4 and Comparative Example 1, MEA (Membrane Electrode Assembly) was respectively produced and the battery performance was measured. did. FIG. 1 shows the structure of the gas diffusion layer in the produced MEA. As shown in FIG. 1, by applying a water repellent paste for a fuel cell electrode to carbon paper 5 (thickness: about 200 μm) as a base material and baking it, carbon fibers 3 as a fibrous filler and fluororesin A water repellent layer 2 (thickness: about 100 μm) made of PTFE 4 is formed.

  The gas diffusion layer 1 shown in FIG. 1 relates to Example 3 made of 100% conductive fibrous filler in the present embodiment. In the case of Example 1 and Example 2, the gas diffusion layer 1 is repellent. The water layer 2 further contains carbon black. The thus formed gas diffusion layer 1 according to the present embodiment was closely attached to the catalyst layers formed on both sides with the polymer electrolyte membrane interposed therebetween, thereby producing an MEA (membrane electrode assembly).

The operating conditions of MEA are: hydrogen utilization rate 80%, air utilization rate 45%, anode humidification condition is 57 ° C with bubbler, cathode humidification condition is 60 ° C with bubbler, and water (dry air) ratio when converted to 1 atm. (0.21 mol / 0.25 mol). As a result, as shown in FIG. 2, it was found that the generated voltage increases as the porosity increases. The experimental results shown in FIG. 2 are, in order from the left, Comparative Example 1, Example 1, Example 2, Example 3, and Example 4, and the generated voltage when the current value is 0.8 A / cm ² is shown. It is shown.

  In Comparative Example 1, the porosity is 66% and the generated voltage of MEA is 570 mV, whereas in Example 1, the porosity is 71%, the generated voltage of MEA is 600 mV, and in Example 2, the porosity is 75. %, The generated voltage of MEA was 610 mV, in Example 3, the porosity was 84%, the generated voltage of MEA was 630 mV, in Example 4, the porosity was 87%, and the generated voltage of MEA was also 630 mV.

  Thus, the porosity of the water repellent layer increases as the content of the carbon fiber as the fibrous filler increases, and the generated voltage of the fuel cell (MEA) increases as the porosity increases. Thus, in the water repellent paste for a fuel cell electrode according to the present embodiment, the porosity of the water repellent layer is increased by blending an appropriate amount of fibrous filler to produce a water repellent paste for a fuel cell electrode. As a result, the gas diffusibility and the ability to remove generated water can be improved, and the characteristics of the fuel cell can be improved.

  In the present embodiment, the case where carbon fiber as conductive fibrous filler having conductivity is used as the fibrous filler has been described. However, the fibrous filler is not limited to this, and acicular titanium oxide. In addition, non-conductive fibers such as zinc oxide whiskers and potassium titanate fibers can also be used.

  In carrying out the present invention, other configurations, components, materials, blending, shapes, sizes, manufacturing methods, and the like of the water-repellent paste for fuel cell electrodes are not limited to the present embodiment.

FIG. 1 is a cross-sectional view showing the structure of a gas diffusion layer formed by applying a water repellent paste for a fuel cell electrode according to an embodiment of the present invention to a substrate and baking it. FIG. 2 is a graph showing power characteristics of an MEA (Membrane Electrode Assembly) produced using the water-repellent paste for fuel cell electrodes according to the embodiment of the present invention.

Explanation of symbols

1 Gas diffusion layer 2 Water repellent layer 3 Fibrous filler 4 Fluororesin

Claims (6)

A water-repellent paste for forming a gas diffusion layer of a polymer electrolyte fuel cell composed mainly of a polymer electrolyte membrane,
A water-repellent paste for a fuel cell electrode, comprising a particulate conductive filler, a fluororesin dispersion, and a fibrous filler.   The water-repellent paste for a fuel cell electrode according to claim 1, wherein the fibrous filler is a conductive fibrous filler having conductivity.   The addition amount of the said fibrous filler is 20 to 100 weight% of the whole filler which match | combined the said particulate conductive filler and the said fibrous filler, The Claim 1 or Claim 2 characterized by the above-mentioned. Water repellent paste for fuel cell electrodes. A water-repellent paste for forming a gas diffusion layer of a polymer electrolyte fuel cell composed mainly of a polymer electrolyte membrane,
A water repellent paste for a fuel cell electrode, comprising only a conductive fibrous filler having conductivity as a filler and a fluororesin dispersion.   The water repellent paste for a fuel cell electrode according to any one of claims 1 to 4, further comprising a pore forming agent.   The fuel according to any one of claims 1 to 5, wherein the fibrous filler has a diameter in a range of 0.1 µm to 15 µm and a length in a range of 1 µm to 1 mm. Water repellent paste for battery electrodes.

Images