KR20050121932A - A electrode for fuel cell and a fuel cell 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 comprising a platinum-transition metal alloy catalyst; And a gas diffusion layer made of a conductive substrate, wherein a quantity of Coulomb of week bonding (Qw) when hydrogen adsorbed on the platinum surface is oxidized is 100 Coulomb / g of Pt or more. The fuel cell includes at least one membrane / electrode assembly including an anode and a cathode electrode facing each other, and a polymer electrolyte membrane located between the anode and the cathode electrode; And a bipolar plate having a flow channel for supplying a gas in contact with one of the anode and the cathode of the membrane / electrode assembly, wherein at least one of the anode and the cathode is made of the electrode.

Description

A fuel cell electrode and a fuel cell including the same {A ELECTRODE FOR FUEL CELL AND A FUEL CELL COMPRISING THE SAME}

[Industrial use]

The present invention relates to a fuel cell electrode and a fuel cell including the same, and more particularly, to a fuel cell electrode and a fuel cell including the same, which can improve the efficiency of the fuel cell with a fast reaction rate and excellent reaction activity. .

[Prior art]

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 the fuel pump, reforming the fuel in the reformer to generate hydrogen gas, and electrochemically reacting the hydrogen gas and oxygen in the stack to generate electrical energy. Let's do it.

In such a fuel cell system, a stack that substantially generates electricity is stacked with several to several tens of unit cells including a membrane electrode assembly (MEA) and a bipolar plate that adheres to both sides thereof. Has a structure. 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 bipolar plate 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 for each membrane / electrode assembly. It simultaneously serves as a conductor that connects the anode and cathode electrodes in series. Hydrogen gas is supplied to the anode electrode through the bipolar plate, while oxygen is supplied to the cathode electrode. In this process, an oxidation reaction of hydrogen gas occurs at the anode electrode, and a reduction reaction of oxygen occurs at the cathode electrode, thereby generating electricity due to the movement of electrons generated, and additionally generating heat and moisture.

An object of the present invention is to provide a fuel cell electrode and a fuel cell including the same that can improve the efficiency of the fuel cell by the fast reaction speed and excellent reaction activity.

In order to achieve the above object, a catalyst layer comprising a platinum-transition metal alloy catalyst; And a gas diffusion layer made of a conductive substrate, wherein a quantity of coulomb of week bonding (Qw) when hydrogen adsorbed on the platinum surface is oxidized is 100 Coulomb / g of Pt or more.

The invention also includes at least one membrane / electrode assembly comprising an anode and a cathode electrode positioned opposite each other, and a polymer electrolyte membrane positioned between the anode and the cathode electrode; And a bipolar plate having a flow channel for supplying a gas in contact with one of an anode and a cathode of the membrane / electrode assembly.

At least one of the anode and the cathode electrode comprises a catalyst layer comprising a platinum-transition metal alloy catalyst; And a gas diffusion layer made of a conductive substrate, the fuel cell having a quantity of Coulomb of week bonding (Qw) of 100 Coulomb / g of Pt or more when hydrogen adsorbed on the platinum surface is oxidized.

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

The catalyst for a fuel cell catalyzes the oxidation reaction of hydrogen of an anode electrode and the reduction reaction of oxygen of a cathode electrode, and platinum is used preferably.

Hydrogen ions generated at the anode electrode react with oxygen adsorbed on the platinum catalyst of the cathode to generate water. At this time, if hydrogen is so strongly adsorbed to the platinum catalyst, water is difficult to desorb after the reaction. Therefore, the bonding force of hydrogen adsorbed on the surface of the platinum catalyst is closely related to the catalytic activity. That is, if the binding force is too strong, desorption reaction of water hardly occurs after the reduction reaction, and the overall reaction rate is lowered, thereby reducing the efficiency of the fuel cell.

In the present invention, by inserting a transition metal in the platinum lattice structure to change the distance between the platinum atoms to adjust the bonding force that the hydrogen is adsorbed to the platinum atom to improve the catalytic activity excellent. The quantity of Coulomb of week bonding (Qw) when the hydrogen adsorbed on the platinum surface in the platinum-transition metal alloy is more than 100 Coulomb / g of Pt, preferably 110 to 140 Coulomb / g of Pt Adjust to be within the range of. The charge amount represents the adsorption intensity of hydrogen, and when it is adjusted in the above range, it shows excellent catalytic activity.

Cobalt, iron, chromium, nickel and the like are preferable as the transition metal. The platinum and the transition metal preferably form an alloy at a molar ratio of 40:60 to 60:40, and more preferably form an alloy at a molar ratio of 50:50. When the molar ratio of platinum and transition metal is out of the above range, it is difficult to form an alloy having a desirable hydrogen adsorption intensity.

In the platinum-transition metal alloy catalyst of the present invention, the transition metal is inserted into the platinum lattice structure to control the size of the catalyst particles in the range of 40 to 60 mm 3. In this range, the activity of the catalyst particles (mass activity) is best controlled.

 The platinum-transition metal alloy catalyst may be prepared by mixing a platinum-containing material and a transition metal-containing material, followed by drying and heat treatment. The platinum-containing material may use platinum supported on a carrier commonly used in fuel cells. Specific examples of the carrier include carbon, alumina, silica, and the like. Of these, preferably platinum supported using carbon as a carrier can be used, and in this case, the carbon is more preferably acetylene black, graphite or the like.

Platinum supported by the carrier may be commercially available, or may be used by supporting platinum on the carrier. The process of supporting platinum on the carrier is well known in the art, and thus detailed description thereof will be omitted.

In addition, the transition metal-containing material includes a transition metal, and any compound that can form a platinum-transition metal alloy may be used, but preferably includes a compound including cobalt, iron, chromium, nickel, and the like. It can use more than 1 type, More preferably, it can use 1 or more types of metal halide, nitrate, hydrochloride, sulfate, or amine containing the said metal, Most preferably metal containing iron, nickel, chromium, cobalt, etc. One or more selected from halides or nitrates can be used.

The transition metal-containing material is mixed and used in a liquid phase, and preferably, the metal-containing material may be used in a solution state in which alcohol, water, or a mixture of alcohol and water is dissolved. The solution preferably has a concentration of 0.1 to 1 M of the transition metal-containing material.

After the mixture is prepared by mixing the platinum-containing material and the transition metal-containing material, it is dried. The drying process is a process of evaporating a solvent, such as water and alcohol, included in the mixture, according to a conventional drying process.

After drying the mixture, the heat treatment is performed, and the heat treatment is preferably performed at a temperature of 500 to 800 ° C. in a reducing atmosphere, and more preferably 600 to 800 ° C. It is preferable that heat processing time is 1 to 5 hours. If the heat treatment temperature is less than 500 ℃ or the heat treatment time is less than 1 hour, it is difficult to form the alloy. If the heat treatment temperature is higher than 800 ℃ or heat treatment time is more than 5 hours, the particle size of the alloy catalyst particles is too large, the catalyst activity is lowered Not desirable

In the reducing atmosphere during the heat treatment, a hydrogen gas, a nitrogen gas, or a mixed gas of hydrogen and nitrogen may be used.

In the platinum-transition metal alloy catalyst of the present invention, an electrode including a catalyst layer is prepared by coating a composition mixed with a binder resin and a solvent on a conductive substrate (gas diffusion layer).

The binder resin may be a fluorine-containing polymer such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), or a rubber-based polymer such as styrene-butadiene rubber. The solvent may be N-methylpyrrolidone (NMP), alcohol such as isopropyl alcohol, water and the like.

The coating method of the composition is not particularly limited. For example, doctor blade method, dip method, reverse roll method, direct roll method, gravure method, extrusion method, brush Law and the like can be used.

Alternatively, the composition may be filmed and then laminated with a conductive substrate to prepare an electrode.

As the conductive substrate, carbon paper, carbon cloth, carbon felt, or the like may be used. The conductive substrate serves to support the catalyst layer and at the same time serves as a gas diffusion passage for delivering the reaction gas to the catalyst layer. The conductive substrate can also be used after water repellent treatment with a fluorine-based polymer such as polytetrafluoroethylene.

The electrode for a fuel cell of the present invention may further include a microporous layer to enhance the gas diffusion effect between the catalyst layer and the catalyst support layer. The microporous layer serves to uniformly supply the reaction gas to the catalyst layer and to transfer electrons formed in the catalyst layer to the catalyst support layer. In general, it may include a conductive powder having a small particle diameter, such as carbon powder, carbon black, acetylene black, activated carbon, and the like.

The microporous layer is prepared by coating a conductive substrate with a composition comprising a conductive powder, a binder resin, and a solvent. As the fluorine-based binder resin, a fluorine-based binder resin such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), or a polymer such as styrene-butadiene rubber (SBR) may be used. The solvent may be N-methylpyrrolidone (NMP), alcohol such as isopropyl alcohol, water and the like. The coating process may be screen printing, spray coating, or a coating method using a doctor blade according to the viscosity of the composition, but is not limited thereto.

In the fuel cell, the cathode and the anode electrode are not distinguished by materials but in their role, and the fuel cell electrode is divided into an anode for hydrogen oxidation and a cathode for reducing oxygen. Therefore, the fuel cell electrode of the present invention can be used for both the cathode and the anode electrode.

FIG. 1 is a view schematically showing an operating state of a fuel cell 1 including an anode 3, a cathode 5, and a polymer electrolyte membrane 7. The electrode of the present invention may be used as the anode 3 and the cathode 5 electrodes. In particular, it is preferable to use the platinum-transition metal alloy catalyst as the cathode. Referring to FIG. 1, when hydrogen gas or fuel is supplied to the anode 3, an electrochemical oxidation reaction occurs and is oxidized while being ionized with hydrogen ions H ⁺ and electrons e ⁻ . Ionized hydrogen ions move to the cathode 5 through the polymer electrolyte membrane 7 and electrons move to the cathode 5 through an external circuit. The hydrogen ions transferred to the cathode 5 cause an electrochemical reduction reaction with oxygen supplied to the cathode 5 to generate heat of reaction and water, and electrical energy is generated by the movement of electrons.

The polymer electrolyte membrane 7 is made of a hydrogen ion-conductive polymer material, that is, an ionomer, and is generally a fluorine-based polymer, a ketone-based polymer, a benzimidazole-based polymer, an ester-based polymer, an amide-based polymer, or an imide-based polymer. , Sulfonic polymers, styrene polymers, etc. may be used. Specific examples thereof include poly (perfluorosulfonic acid), poly (perfluorocarboxylic acid), and tetrafluoroethylene and fluoro containing sulfonic acid groups. Vinyl ether copolymers, defluorinated sulfide polyether ketones, aryl ketones, poly (2,2 '-(m-phenylene) -5,5'-bibenzimidazole) (poly (2,2'-(m -phenylene) -5,5'-bibenzimidazole)), poly (2,5-benzimidazole), polyimide, polysulfone, polystyrene, polyphenylene and the like can be used, but is not limited thereto.

The fuel cell inserts a membrane / electrode assembly between a gas flow channel and a bipolar plate on which a cooling channel is formed to fabricate a unit cell, stacks it, and manufactures a stack, and then inserts it between two end plates. Can be prepared. Fuel cells can be readily manufactured by conventional techniques in the art.

The electrode for fuel cells of the present invention is applicable to all fuel cells, and is particularly preferably applied to polymer electrolyte fuel cells (PEMFC) and direct methanol cells (DMFC).

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

A 1 M aqueous solution of CoCl ₂ was added dropwise to a commercial platinum / carbon (Pt / C) catalyst (platinum content 10 wt%) by Johnson Matthey Co. and mixed. At this time, it mixed so that the molar ratio of platinum: cobalt might be 50:50. The mixture was dried at 100 ° C. for 1 hour and then heat-treated at 600 ° C. for 2.5 hours in the presence of a mixed gas of hydrogen and nitrogen (10% by volume of hydrogen and 90% by volume of nitrogen) to prepare a platinum-transition metal catalyst.

Example 2

A platinum-transition metal catalyst was prepared in the same manner as in Example 1 except that the heat treatment temperature was 700 ° C.

Comparative Example 1

Johnson Matthey Co. commercial platinum / carbon (Pt / C) catalyst

Comparative Example 2

A platinum-transition metal catalyst was prepared in the same manner as in Example 1 except that the heat treatment temperature was 900 ° C.

Comparative Example 3

A platinum-transition metal catalyst was prepared in the same manner as in Example 1 except that the heat treatment temperature was 1100 ° C.

Electrode for fuel cell by coating a composition prepared by mixing 100 parts by weight of the catalyst of Examples 1 to 2 and Comparative Examples 1 to 3, 10 parts by weight of polytetrafluoroethylene polymer and 100 parts by weight of isopropyl alcohol with a solvent Was prepared. The electrode was used as an anode and a cathode, and a Nafion (manufactured by DuPont) polymer membrane was placed therebetween, fired at 100 degrees for 30 seconds, 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 bipolar plates in which a gas flow channel and a cooling channel of a predetermined shape are formed, and then compressed between copper end plates. The battery was prepared.

Example 1, 2 using a platinum plate as the electrode and the counter electrode, 1 MH ₂ S0 ₄ aqueous solution as the electrolyte, and a saturated calomel electrode (SCE) as the standard electrode by cyclic voltammetry And the quantity of Coulomb of week bonding (Qw) when hydrogen adsorbed on the platinum surface of each catalyst of Comparative Examples 1 to 3 was oxidized. At this time, the scanning speed was 10 mV / sec.

In addition, for the electrodes of Examples 1, 2 and Comparative Examples 1 to 3 were measured the current density at 600mV compared to the hydrogen reference electrode. The measured current value was divided by the weight of the catalyst to calculate mass activity. The results are shown in Table 1 below.

TABLE 1

Alloy components Alloy composition ratio Heat treatment temperature (℃) Catalyst particle size Qw (Coul / Pt g) Weight Activity (A / g) Example 1 Pt-Co 1: 1 600 53.5 117 752 Example 2 Pt-Co 1: 1 700 42.9 137 678 Comparative Example 1 Pt - No heat treatment <30 125 461 Comparative Example 2 Pt 1: 1 900 64.3 79.0 418 Comparative Example 3 Pt 1: 1 1100 103 64.2 400

As shown in Table 1, the platinum-cobalt alloys of Examples 1 to 2 prepared according to the present invention were adjusted to a range excellent in catalytic activity, and the amount of charge when hydrogen adsorbed on the platinum surface was oxidized ( Qw; Quantity of Coulomb of week bonding) is 100 Coulomb / g of Pt, it can be seen that the weight activity indicating the catalytic activity is also very good. Although the platinum catalyst of Comparative Example 1 showed a charge amount of 100 Coulomb / g of Pt, it was found that the catalytic activity was low because the particle size was too small. The platinum-cobalt alloy catalysts of Comparative Examples 1 and 2 had large particle sizes and Qw. Too low the catalytic activity was low.

In the fuel cell catalyst of the present invention, the alloy particle size and the amount of charge when hydrogen adsorbed on the surface of platinum are oxidized to a range excellent for catalytic activity, thereby improving the efficiency of the fuel cell due to the fast reaction rate and excellent reaction activity. have.

1 is a view schematically 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

5: cathode 7: polyelectrolyte membrane

Claims (16)

A catalyst layer comprising a platinum-transition metal alloy catalyst; And A fuel cell electrode comprising a gas diffusion layer made of a conductive substrate and having a quantity of Coulomb of week bonding (Qw) of 100 Coulomb / g of Pt or more when hydrogen adsorbed on the platinum surface is oxidized. The fuel cell electrode according to claim 1, wherein a charge amount (Qw) of the hydrogen adsorbed on the platinum surface is oxidized is 110 to 140 Coulomb / g of Pt. The electrode of claim 1, wherein the transition metal is selected from the group consisting of cobalt, iron, chromium, nickel, and mixtures thereof. The electrode of claim 1, wherein the platinum and the transition metal form an alloy at a molar ratio of 40:60 to 60:40. The electrode of claim 1, wherein the platinum-transition metal alloy catalyst has a catalyst particle size in the range of 40 to 60 Hz. The electrode of claim 1, wherein the platinum-transition metal alloy catalyst is prepared by mixing a platinum-containing material and a transition metal-containing material, followed by drying and heat treatment. The electrode for a fuel cell of claim 1, wherein the heat treatment is performed at a temperature of 500 to 800 ° C. The electrode for a fuel cell of claim 1, wherein the heat treatment is performed in a reducing atmosphere. At least one membrane / electrode assembly comprising an anode and a cathode electrode positioned opposite each other, and a polymer electrolyte membrane positioned between the anode and the cathode electrode; And a bipolar plate having a flow channel for supplying a gas in contact with one of an anode and a cathode of the membrane / electrode assembly. At least one of the anode and the cathode electrode comprises a catalyst layer comprising a platinum-transition metal alloy catalyst; And a gas diffusion layer made of a conductive substrate, wherein a quantity of Coulomb of week bonding (Qw) when hydrogen adsorbed on the platinum surface is oxidized is 100 Coulomb / g of Pt or more. 10. The fuel cell of claim 9, wherein a quantity of coulomb of week bonding (Qw) is 110 to 140 Coulomb / g of Pt when hydrogen adsorbed on the platinum surface is oxidized. The fuel cell of claim 9, wherein the transition metal is selected from the group consisting of cobalt, iron, chromium, nickel, and mixtures thereof. The fuel cell of claim 9, wherein the platinum and the transition metal form an alloy at a molar ratio of 40:60 to 60:40. 10. The fuel cell of claim 9, wherein the platinum-transition metal alloy catalyst has a catalyst particle size in the range of 40 to 60 Hz. The fuel cell of claim 9, wherein the platinum-transition metal alloy catalyst is prepared by mixing a platinum-containing material and a transition metal-containing material, followed by drying and heat treatment. The fuel cell of claim 9, wherein the heat treatment is performed at a temperature of 500 to 800 ° C. 11. The fuel cell of claim 9, wherein the heat treatment is performed in a reducing atmosphere.