KR101181856B1 - A electrode for fuel cell and a fuel cell and membrane/electrode assembly comprising the same - Google Patents

Abstract

The present invention relates to a fuel cell electrode and a fuel cell comprising the same, the fuel cell electrode comprising a catalyst layer; A porous layer comprising large conductive particles and small conductive particles having different sizes of particles; And a gas diffusion layer made of a conductive substrate. The fuel cell may include at least one membrane / electrode assembly including an anode electrode and a cathode electrode disposed to face each other, and a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode; And a separator in which a flow channel is formed to contact any one of an anode electrode and a cathode electrode of the membrane / electrode assembly to supply gas, wherein at least one of the anode electrode and the cathode electrode comprises: a catalyst layer; A porous layer comprising large conductive particles and small conductive particles having different sizes of particles; And a gas diffusion layer made of a conductive substrate.

Fuel cell, porous layer, conductive particles, gas diffusion layer

Description

ELECTRODE FOR FUEL CELL AND A FUEL CELL AND MEMBRANE / ELECTRODE ASSEMBLY COMPRISING THE SAME

1 is a view schematically showing a porous layer of an electrode of a fuel cell of the present invention.

2 is a view showing an operating state of a fuel cell including a polymer electrolyte membrane.

<Description of the symbols for the main parts of the drawings>

1: fuel cell 3: anode electrode

5: cathode electrode 7: polymer electrolyte membrane

[Industrial use]

The present invention relates to a fuel cell electrode, a membrane / electrode assembly including the same, and a fuel cell, and more particularly, to improve the performance of a battery by optimizing the porosity of a porous layer including conductive particles having different particle sizes. The present invention relates to a fuel cell electrode and a membrane / electrode assembly including the same, and a fuel cell.

BACKGROUND ART [0002]                         

A fuel cell is a power generation system that directly converts the chemical reaction energy of hydrogen and oxygen contained in hydrocarbon-based materials such as methanol, ethanol and natural gas into electrical energy.

Fuel cells are classified into phosphoric acid fuel cells, molten carbonate fuel cells, solid oxide fuel cells, polymer electrolyte or alkaline fuel cells, etc., depending on the type of electrolyte used. Each of these fuel cells operates on essentially the same principle, but differs in the type of fuel used, operating temperature, catalyst, electrolyte, and the like.

Among these, the polymer electrolyte fuel cell (PEMFC), which is being developed recently, has superior output characteristics compared to other fuel cells, has a low operating temperature, fast start-up and response characteristics, and a mobile power source such as an automobile. Of course, it has a wide range of applications, such as distributed power supply for homes, public buildings and small power supply for electronic devices.

Such a PEMFC basically includes a stack, a reformer, a fuel tank, a fuel pump, and the like to constitute a system. The stack forms the body of the fuel cell, and the fuel pump supplies the fuel in the fuel tank to the reformer. The reformer reforms the fuel to generate hydrogen gas and supplies the hydrogen gas to the stack. Thus, the PEMFC supplies fuel in the fuel tank to the reformer by operation of a fuel pump, reforming the fuel in the reformer to generate hydrogen gas, and electrochemically reacting the hydrogen gas and oxygen in a stack to generate electrical energy. Let's do it.

In such a fuel cell system, a stack that substantially generates electricity includes a unit cell including a membrane electrode assembly (MEA) and a separator (also called a bipolar plate) that adheres to both surfaces thereof. It has a stacked structure of several to several tens. The membrane / electrode assembly has a structure in which an anode electrode and a cathode electrode are coupled with an electrolyte membrane interposed therebetween. The separator separates the respective membrane / electrode assemblies and serves as a passage for supplying hydrogen gas and oxygen required for the reaction of the fuel cell to the anode electrode and the cathode electrode of the membrane / electrode assembly, and the anode electrode of each membrane / electrode assembly. Simultaneously serves as a conductor that connects the cathode electrode in series. Hydrogen gas is supplied to the anode electrode through the separator, while oxygen is supplied to the cathode electrode. In this process, an oxidation reaction of hydrogen gas occurs at an anode electrode, and a reduction reaction of oxygen occurs at a cathode electrode, thereby generating electricity due to the movement of electrons generated, and additionally generating heat and moisture.

SUMMARY OF THE INVENTION An object of the present invention is to provide a fuel cell electrode and a membrane / electrode assembly including the same, and a fuel cell, which can improve the efficiency of a battery by optimizing porosity by including conductive particles having different particle sizes in a porous layer. It is to.

In order to achieve the above object, there is provided a fuel cell electrode comprising a catalyst layer, a porous layer including large conductive particles and small conductive particles having different sizes of particles, and a gas diffusion layer made of a conductive substrate.

The present invention also includes an anode electrode and a cathode electrode positioned opposite to each other, and a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode, wherein at least one of the anode electrode and the cathode electrode is a catalyst layer, a large conductivity having different sizes of particles. A fuel cell membrane / electrode assembly comprising a porous layer including particles and small conductive particles, and a gas diffusion layer made of a conductive substrate.

The invention also includes at least one membrane / electrode assembly comprising an anode electrode and a cathode electrode positioned opposite each other, and a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode; And a separator in which a flow channel for supplying a gas is provided to contact any one of an anode electrode and a cathode electrode of the membrane / electrode assembly.

At least one of the anode electrode and the cathode electrode provides a fuel cell including a catalyst layer, a porous layer including large conductive particles and small conductive particles having different sizes of particles, and a gas diffusion layer made of a conductive substrate.

Hereinafter, the present invention will be described in more detail.

The electrode of a fuel cell is generally composed of a catalyst layer and a gas diffusion layer (GDL), and includes a porous layer having an optimized porosity in order to enhance the gas diffusion effect of the gas diffusion layer and effectively discharge water formed from the electrode. do.

The catalyst layer comprises a so-called metal catalyst which catalyzes the related reaction (oxidation of hydrogen and reduction of oxygen), and includes platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy or It is preferred to include at least one catalyst selected from platinum-M alloys (M = Ga, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn). It is more preferable to include at least one catalyst selected from platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy, platinum-cobalt alloy or platinum-nickel. These metal catalysts are preferably supported by a carrier and used. As the carrier, carbon such as acetylene black, graphite, or the like may be used, or inorganic fine particles such as alumina or silica may be used. In the case of using the noble metal supported on the carrier as a catalyst, a commercially available one may be used, or a noble metal supported on the carrier may be prepared and used. The process of supporting the precious metal on the carrier is well known in the art, and thus detailed description thereof will be omitted.

The porous layer is used to enhance the gas diffusion effect, and serves to uniformly supply gas to the catalyst layer and transfer electrons formed in the catalyst layer to the gas diffusion layer. In addition, the cathode should be able to effectively discharge the water generated by the reduction reaction. Gas diffusion and water discharge have a great influence on the morphology of the porous layer and are controlled by macropores rather than micropores. In general, the porous layer located between the catalyst layer and the gas diffusion layer is prepared by containing conductive powder particles having a small particle diameter, such as carbon powder, carbon black, acetylene black, activated carbon, and the like. In the case of using only conductive powder particles having a small particle diameter, it is difficult to effectively control gas diffusion and water discharge. Therefore, in the present invention, the porosity of the porous layer is controlled to efficiently diffuse the gas and discharge the water by mixing the large conductive powder particles having a large particle size with the small conductive powder particles having a small particle size at an appropriate ratio.

1 is a view schematically showing a porous layer of the present invention. As shown in FIG. 1, the porous layer contains macropores of 2 to 25 micrometers, preferably 10 to 25 micrometers, and micropores of 0.01 to 0.1 micrometers. The average pore size of the porous layer is preferably in the range of 0.1 to 15 micrometers, more preferably in the range of 1 to 5 micrometers.

In the present invention, the porous layer is manufactured using large conductive particles and small conductive particles having different sizes of particles. The average particle size of the large conductive particles is preferably in the range of 2 to 25 micrometers, more preferably in the range of 10 to 25 micrometers. It is preferable that the average particle size of the said small electroconductive particle exists in the range of 0.01-0.1 micrometer. In the present invention, the thickness of the porous layer is in the range of 30 to 40 micrometers.

It is preferable to mix and use the said large electroconductive particle and the small electroconductive particle in the weight ratio of 90-80: 10-10. In the case where the large conductive particles and the small charged particles are in the above ranges, fuel diffusion and water discharge can be easily controlled, thereby improving battery performance.

In the present invention, as the small conductive particles, all of the conductive powder particles that are conventionally used as a material for forming the porous layer may be used. Examples of such small conductive particles include carbon powder, carbon black, acetylene black, activated carbon, and the like. As the large conductive particles, graphite or vulcans such as natural graphite and artificial graphite may be preferably used. In the case of using the graphite, the electron conductivity is better than the conventional conductive powder particles, so that the limiting current can be applied at a lower voltage in the high current region, thereby improving the performance of the battery. Can be.

The porous layer is prepared by coating a conductive substrate with a composition including large conductive particles having different particle sizes, small conductive particles, a binder resin, and a solvent. As the binder resin, polytetrafluoroethylene (PTFE), polyvinylidene fluoride, copolymer of polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), polyvinyl alcohol, cellulose acetate and the like are preferably used. The solvent may be alcohol such as ethanol, isopropyl alcohol, ethyl alcohol, n-propyl alcohol, butyl alcohol, water, dimethylacetamide (DMAc), dimethylformamide, dimethyl sulfoxide (DMSO), N-methyl Pyrrolidone, tetrahydrofuran and the like can be preferably used. The coating process may be a screen printing method, a spray coating method or a coating method using a doctor blade, a gravure coating method, a dip coating method, a silk screen method, a painting method, etc., depending on the viscosity of the composition, but is not limited thereto.

The gas diffusion layer plays a role of supporting the fuel cell electrode while diffusing the reaction gas into the catalyst layer to easily access the reaction gas to the catalyst layer. The gas diffusion layer is generally composed of a conductive substrate. The carbon paper, carbon cloth, carbon felt, or the like may be used. The conductive substrate may be used by water repellent treatment with polytetrafluoroethylene (PTFE).

In the fuel cell, the cathode electrode and the anode electrode are not distinguished by materials but in their role, and the fuel cell electrode is divided into an anode electrode for hydrogen oxidation and a cathode electrode for reducing oxygen. Therefore, the fuel cell electrode of the present invention can be used for both the cathode electrode and the anode electrode. That is, in a fuel cell, hydrogen or fuel is supplied to the anode electrode and oxygen is supplied to the cathode electrode, thereby generating electricity by an electrochemical reaction between the anode electrode and the cathode electrode. An oxidation reaction of hydrogen or organic fuel occurs at the anode electrode and a reduction reaction of oxygen occurs at the cathode electrode to generate a voltage difference between the two electrodes.

In accordance with the present invention, the electrode having the porous layer is preferably used as a cathode because water can be easily discharged.

FIG. 2 is a view schematically showing an operating state of a fuel cell 1 including an anode electrode 3, a cathode electrode 5, and a polymer electrolyte membrane 7. The electrode of the present invention may be used as the anode electrode 3 and the cathode electrode 5. The polymer electrolyte membrane 7 may be any polymer as long as it has hydrogen ion conductivity, and preferably a perfluoro polymer, a benzimidazole polymer, a polyimide polymer, a polyetherimide polymer, or a polyphenylene sulfide. Type polymer, polysulfone type polymer, polyether sulfone type polymer, polyether ketone type polymer, polyether-etherketone type polymer, polyphenylquinoxaline type polymer and the like can be used, and specific examples thereof include poly (perfluorosulfur) Fluoric acid), poly (perfluorocarboxylic acid), tetrafluoroethylene and fluorovinylether copolymers containing sulfonic acid groups, defluorinated sulfonated polyetherketones, aryl ketones or poly (2,2 '-(m -Phenylene) -5,5'-bibenzimidazole) (poly (2,2 '-(m-phenylene) -5,5'-bibenzimidazole)), poly (2,5-benzimidazole), etc. Polybenzimidazole, etc. are available It may be, but is not limited thereto. In general, the polymer electrolyte membrane has a thickness of 10 to 200㎛.

The fuel cell is manufactured by inserting a membrane / electrode assembly between a gas flow channel and a separator having a cooling channel to manufacture a unit cell, stacking the same, and manufacturing a stack, and then inserting the membrane / electrode assembly between two end plates. can do. Fuel cells can be readily manufactured by conventional techniques in the art.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only one preferred embodiment of the present invention and the present invention is not limited to the following examples.

Example 1-3 Preparation of Electrode and Unit Battery

Platinum-supported carbon powder (Pt / C), polytetrafluoroethylene polymer and ethanol were mixed with a solvent to prepare a coating composition for forming a catalyst layer. In addition, graphite particles and large conductive particles were mixed with carbon black, polytetrafluoroethylene polymer and ethanol with a small conductive particle to prepare a coating composition for forming a porous layer. The graphite particles and carbon black were mixed and used in a weight ratio of 90:10 (Example 1), 85:15 (Example 2), and 80:20 (Example 3). The coating composition for forming the porous layer was coated on carbon paper to form a porous layer having a thickness of 30 to 40 micrometers, and then coating the coating composition for forming a catalyst layer to prepare an electrode.

The electrode was used as an anode electrode and a cathode electrode, and a Nafion (manufactured by DuPon) polymer membrane was placed therebetween and hot rolled to prepare a membrane / electrode assembly (MEA).

The prepared membrane / electrode assembly is inserted between two gaskets, and then inserted into two separators in which a gas flow channel and a cooling channel of a predetermined shape are formed, and then compressed between the copper end plates. Prepared.

(Comparative Example 1)

A battery was manufactured in the same manner as in the above example except that the porous layer was prepared using only carbon black.

Examples 1 to 3, in which the porous layer was formed by mixing the graphite particles and carbon black, showed that the water discharge performance was more than two times better than that of Comparative Example 1.

In the fuel cell electrode of the present invention, a porous layer including conductive particles having different particle sizes is disposed between the catalyst layer and the gas diffusion layer, thereby optimizing the porosity of the porous layer to effectively diffuse gas and discharge water, thereby improving battery efficiency. Can be improved excellently.

Claims (16)

Catalyst layer; A porous layer comprising large conductive particles and small conductive particles having different sizes of particles; And A gas diffusion layer made of a conductive substrate, The thickness of the porous layer is a fuel cell electrode that is in the range of 30 to 40 micrometers. The method of claim 1, wherein the catalyst layer is platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy and platinum-M alloy (M = Ga, Ti, V, Cr, Mn, Fe, Co) And at least one transition metal selected from the group consisting of Ni, Cu, and Zn). The fuel cell electrode of claim 1, wherein the porous layer includes macropores of 2 to 25 micrometers and micropores of 0.01 to 0.1 micrometer. The electrode of claim 1, wherein the average particle size of the large conductive particles is in the range of 10 to 25 micrometers. The electrode of claim 1, wherein the average particle size of the small conductive particles is in the range of 0.01 to 0.1 micrometers. delete The fuel cell electrode according to claim 1, wherein the large conductive particles and the small conductive particles are mixed in a weight ratio of 90 to 80: 10 to 20. The electrode for a fuel cell of claim 1, wherein the large conductive particles are graphite or vulcan. The electrode of claim 1, wherein the small conductive particles are at least one selected from the group consisting of carbon powder, carbon black, acetylene black, activated carbon, and mixtures thereof. The electrode of claim 1, wherein the porous layer is prepared by coating a composition including large conductive particles, small conductive particles, a binder resin, and a solvent. The method of claim 10, wherein the binder resin is polytetrafluoroethylene (PTFE), polyvinylidene fluoride, polyvinylidene fluoride- hexafluoropropylene copolymer (PVdF-HFP), polyvinyl alcohol, cellulose acetate And at least one electrode selected from the group consisting of a mixture thereof. The solvent of claim 10, wherein the solvent is alcohol such as ethanol, isopropyl alcohol, ethyl alcohol, n-propyl alcohol, butyl alcohol, water, dimethylacetamide (DMAc), dimethylformamide, dimethyl sulfoxide (DMSO), An electrode for a fuel cell, which is at least one selected from the group consisting of N-methylpyrrolidone, tetrahydrofuran, and mixtures thereof. An anode electrode and a cathode electrode disposed opposite to each other, and a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode, At least one of the anode electrode and the cathode electrode according to any one of claims 1 to 5 and claim 7 to claim 12 for fuel cell membrane assembly. The method of claim 13, wherein the polymer electrolyte membrane is perfluoro-based polymer, benzimidazole-based polymer, polyimide-based polymer, polyetherimide-based polymer, polyphenylene sulfide-based polymer, polysulfone-based polymer, polyether sulfone-based polymer, Polyether ketone-based polymer Polyether-ether ketone-based polymer, and polyphenylquinoxaline-based polymer is at least one selected from the group consisting of fuel cell membrane electrode assembly. At least one membrane / electrode assembly comprising an anode electrode and a cathode electrode positioned opposite each other, and a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode; And a separator in which a flow channel for supplying a gas is provided to contact any one of an anode electrode and a cathode electrode of the membrane / electrode assembly. At least one of the anode electrode and the cathode electrode is at least one of the anode electrode and the cathode electrode according to any one of claims 1 to 5 and 7 to 12. The method of claim 15, wherein the polymer electrolyte membrane is perfluoro-based polymer, benzimidazole-based polymer, polyimide-based polymer, polyetherimide-based polymer, polyphenylene sulfide-based polymer, polysulfone-based polymer, polyether sulfone-based polymer, A polyether ketone-based polymer A polyether-ether ketone-based polymer, and a polyphenylquinoxaline-based polymer is at least one selected from the group consisting of a fuel cell.

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