JP2006179263A - Control of minute crack of carbon coating at manufacturing of gdl electrode layer for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coating of a gaseous diffusion layer (GDL) for a fuel cell or a battery. <P>SOLUTION: The coating contains carbon black, fluoro-polymer, and dispersion liquid of either graphite particles or carbon particles. A size of the coating is substantially larger than that of the carbon black, and the coating is endowed with a structural integration to achieve minimization of cracks. A size of the carbon black particle is within the range of around 13 to 95 nm. The carbon particle may be substituted by either that of chopped carbon fiber, a flake or a platelet of carbon or graphite, carbon nanotube, carbon fibril, or carbon whisker. The carbon particle can take a large length to diameter ratio. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a coating applied to the surface of a gas diffusion layer or electrode of a fuel cell or battery containing carbon or graphite particles.

  The gas diffusion layer (“GDL”) of a fuel cell or battery, which may be non-woven or woven carbon fiber, is generally electrically connected between the GDL and the membrane or bipolar plate in the fuel cell. To form a contact, one or more sides are coated with a substance. Such coatings can be made from a mixture of fluoropolymers such as carbon black (also referred to as acetylene black or amorphous black) and Teflon. Other materials such as particles of various sizes to control desired properties such as enhanced conductivity and to support the catalyst can also be included.

  In order to increase the fuel efficiency of a fuel cell or battery, the size and porosity of the coating must be controlled. Porosity affects a variety of functions, including the formation of another pathway that controls the flow of fuel to the catalyst and membrane, adjustment of the amount of water near the membrane, and support of the catalyst itself.

  The coating is formed by an aqueous dispersion with a low solids content. When removing large amounts of fluid, cracks (“mud cracks”) frequently occur in the coating on the surface of the GDL. A typical crack includes a coating defect consisting of a broken portion of the cured film exposing a bare substrate. This coating defect usually occurs during the manufacture of a coated substrate when the coating is very brittle or the adhesion to the substrate is very weak. Cracks become more pronounced when a thicker coating is applied on the surface of the GDL substrate. The more severe the crack, the less effective the GDL is to perform some of its functions. FIG. 1 shows an example of such a crack in the coating on the surface of the GDL.

  Methods for removing coating cracks such as binder weight gain, drying rate control, continuous thin pass coating and solid weight gain have been used in the past but have not been successful. Even if the amount of the binder was increased, there was no effect in preventing cracks in this application. It was practically impossible to carry out a drying speed that seemed to be effective. The pass coating could not be made too thin and the solids could not be increased. This is because the coating process is hindered.

  The present invention provides a coating on the gas diffusion layer or electrode of a fuel cell or battery that minimizes cracking. The coating consists of carbon black, a fluoropolymer, and an aqueous dispersion of one of graphite particles and carbon particles. The size of most particles is substantially larger than the size of carbon black particles, for example, in the range of about 13-95 nm. The carbon particles may be cut or chopped carbon fibers, carbon or graphite flakes or platelets, carbon nanotubes, carbon fibrils, or carbon whiskers.

  The length to diameter ratio of the carbon particles may be large.

  Other features and advantages of the present invention will be understood upon reading the following detailed description of the illustrated embodiments, with reference to the accompanying drawings, in which corresponding components are designated with the same reference numerals. .

  In the case of the present invention, the aqueous dispersion is applied as a coating to the GDL substrate of a battery or fuel cell (such as a methanol type fuel cell). The dispersion can include carbon black, fluoropolymer, and carbon or graphite particles, and can also include a surfactant. The ratio of fluoropolymer to carbon black falls within the range of 5/95 to 70/30 by weight. The particles can comprise 25% to 70% of the total coating weight. The addition of these particles can increase structural integrity and increase the solids content of the dispersion without increasing viscosity. As a result, the coating of the present invention reduces the cracking of the GDL coating layer to a minimum.

  Carbon black is a black and amorphous carbon pigment made by pyrolyzing natural hydrocarbons. In general, there are three different types of carbon black (ie, furnace black, channel black and lamp black). Its nominal purity is approximately 98.5% to 99.6%. The size of the carbon black particles is about 13 nm to 95 nm. Carbon black may be spherical.

  The size of most particles may be substantially larger than the size of the carbon black particles. The particles can have a length that is greater than their diameter. The ratio of length to diameter is in the range of 1.5 to 10,000. The particles may include short length fibers such as cut carbon or graphite fibers, carbon or graphite flakes or small plates, carbon or graphite nanotubes, carbon or graphite fibrils, or carbon or graphite whiskers. it can. The fiber diameter is 6-20 microns and the fiber length is 10-500 microns. The length of the flakes or small plates is 1 to 500 microns. Nanotubes, fibrils and whiskers have a diameter of 5 to 100 nm and a length of 5 to several hundred microns. Introducing these fibers as a coating compound reduces mud cracking during drying to a minimum.

  FIG. 2 shows a coating on the surface of a GDL containing chopped carbon fiber. As can be seen from this figure, there are no visible cracks in the coating.

  In addition to preventing cracking in the coating, introducing particles can improve the conductivity of the coating.

  GDL substrates are from fibrous carbon preforms, which may be short in length, paper, unidirectional tape, woven and non-woven tissues (woven and non-woven), including knitted ones, and stitch-bonded multiaxial structures. Can be made. The coating can be applied by various techniques such as dip coating, doctor blade, knife, spray, roll or slot.

  The electrode may be a single bent piece that can be inserted into an adjacent cell. Alternatively, the electrodes can be made from two pieces and connected so that the two connected pieces function as one electrode. A membrane can be provided between the electrodes so that ions can pass through the membrane.

  FIG. 3 is a schematic diagram of the fuel cell 100. The fuel cell 100 can include, among other things, a current collector 102, a gas passage 104, a GDL 105, a catalyst layer 106, and a proton exchange membrane 107 arranged as shown in FIG.

Therefore, the introduction of particles can significantly reduce the amount of cracking in the coating prepared on the GDL substrate. With these particles, a total coating amount of up to 300 g / m ² can be applied with a minimum number of cracks. This mixture is particularly advantageous in the case of methanol fuel cells because methanol fuel cells require a thicker coating than hydrogen fueled fuel cells.

  Although preferred embodiments of the present invention and variations thereof have been described in detail, the present invention is not limited to these embodiments themselves and variations thereof, and those skilled in the art will recognize the invention described in the claims. It should be understood that various other modifications and changes can be made without departing from the spirit and scope.

2 is a drawing of a coating on a gas diffusion layer structure having cracks. 2 is a drawing of a coating on a gas diffusion layer structure according to an embodiment of the present invention. 1 is a drawing of an example of a fuel cell to which the coating of the present invention can be applied.

Explanation of symbols

100 Fuel Cell 102 Current Collector 104 Gas Passage 105 GDL
106 catalyst layer 107 proton exchange membrane

Claims (24)

A coating for a gas diffusion layer of a fuel cell or battery, comprising carbon black, a fluoropolymer, and one of graphite or carbon particles, wherein some of the particles are substantially larger in size than the carbon black. Larger coating that provides structural integrity to the coating and minimizes cracking. The coating of claim 1, wherein the carbon black particle size is in the range of about 13-95 nm. The coating of claim 1, wherein the particles are chopped carbon fiber. The coating of claim 1, wherein the particles are carbon or graphite flakes or small plates. The coating of claim 1, wherein the particles are carbon nanotubes. The coating of claim 1, wherein the particles are carbon fibrils. The coating of claim 1, wherein the particles are carbon whiskers. The coating of claim 1, wherein the particles have a large length / diameter ratio. A method for coating a GDL substrate of a fuel cell or battery comprising:
Preparing a dispersion of one of carbon black, fluoropolymer, and graphite or carbon particles;
Applying the dispersion to the substrate to coat the substrate;
A method wherein the particles are substantially larger in size than the carbon black, providing structural integrity to the coating and minimizing its cracking. The method of claim 9, wherein the size of the carbon black particles is in the range of about 13-95 nm. The method of claim 1, wherein the particles are chopped carbon fiber. 10. The method of claim 9, wherein the particles are carbon or graphite flakes or small plates. The method of claim 9, wherein the particles are carbon nanotubes. The method of claim 9, wherein the particles are carbon fibrils. The method of claim 9, wherein the particles are carbon whiskers. The method of claim 9, wherein the particles have a large length / diameter ratio. An article for use in a fuel cell or battery, wherein the article is a GDL having a substrate coated with a dispersion comprising carbon black, a fluoropolymer, and one of graphite or carbon particles; An article in which some of the particles are substantially larger in size than the carbon black, providing structural integrity to the coating and minimizing its cracking. The article of claim 17, wherein the size of the carbon black particles is in the range of about 13-95 nm. The article of claim 17, wherein the particles are chopped carbon fiber. The article of claim 17, wherein the particles are carbon or graphite flakes or small plates. The article of claim 17, wherein the particles are carbon nanotubes. The article of claim 17, wherein the particles are carbon fibrils. The article of claim 17, wherein the particles are carbon whiskers. The article of claim 17, wherein the particles have a large length / diameter ratio.

Images