KR20060019851A - Electrode for fuel cell and a fuel cell system comprising the same - Google Patents

Abstract

The present invention relates to a fuel cell electrode and a fuel cell including the same, more particularly, at least one catalyst metal is selected from the group consisting of silicon (Si), germanium (Ge), tin (Sn) and lead (Pb). A fuel cell electrode having a catalyst layer and an electrode base supported on a catalyst carrier made of a Group 4B element or an alloy containing the same, and a fuel cell system including the same.

The present invention uses materials such as silicon, germanium, tin, and lead as carriers for supporting catalytic metals, which not only has an electrical conductivity higher than or equal to that of a fuel cell electrode employing conventional carbon, but is also inexpensive and reduces production costs. Can be achieved.

Catalytic Metal, Group 4B, Catalyst Carrier, Electrode Base, Electric Conductivity, Fuel Cell

Description

Electrode for fuel cell and fuel cell system including same TECHNICAL FIELD {{Electrode FOR FUEL CELL AND A FUEL CELL SYSTEM COMPRISING THE SAME}

1 is an exploded perspective view showing the structure of a stack of a fuel cell system according to the present invention.

[Industrial use]

The present invention relates to a fuel cell electrode having a catalyst layer and an electrode base supported by a catalyst carrier comprising an element in which the catalyst metal comprises an element corresponding to group 4B of the periodic table, and a fuel cell system including the same.

 [Private Technology]

A fuel cell is an electrochemical cell and is a power generation system that directly converts energy generated by electrochemical reaction between fuel (hydrogen or methanol) and oxidant (oxygen or air) to electrical energy.

The fuel cell electrode is a core part of the fuel cell, and generates electrochemical energy through the oxidation reaction of hydrogen and the reduction reaction of oxygen at the anode and cathode electrodes, and to increase the rate of electrochemical reaction such as oxidation and reduction. Is essentially used.

Specifically, the structure of the fuel cell electrode is largely divided into a catalyst layer and an electrode substrate (or also referred to as a 'substrate layer') for supporting it.

The catalyst layer is a region in which the reactants are actually electrochemically reacted to generate electricity in the electrode. In general, a catalyst having a high activity is preferable because the reduction of oxygen is very slow compared to the oxidation of hydrogen.

Platinum (Pt) is known to be the most suitable material for forming a catalyst layer, but there is a problem that it is not suitable for mass production as an expensive metal. In recent years, platinum has been alloyed with transition metals or base metals such as ruthenium (Ru), iron (Fe), cobalt (Co), chromium (Cr), and nickel (Ni), or catalyst carriers with excellent electrical conductivity. It is supported by using.

Carbon-based powders are mainly used as the catalyst carrier, and carbon-based powders having various particle diameters and pore sizes and specific surface areas ranging from several nm to several tens of mm are used.

However, the carbon-based powder is an expensive material produced by burning or pyrolyzing petroleum-based raw materials. Moreover, when the price of the petroleum-based raw material of the carbon-based powder is increased, an inevitable increase in price is caused, and it is urgent to develop a material that can replace the carbon-based powder.

 An object of the present invention for solving the above problems is to provide a fuel cell electrode having a catalyst layer containing an element corresponding to the group 4B of the periodic table as a catalyst carrier for supporting the catalytic metal.

In addition, another object of the present invention is to provide a fuel cell system having the fuel cell electrode described above.

In order to achieve the above object, the present invention provides a fuel cell electrode having a catalyst layer and an electrode base supported on a catalyst carrier, the catalyst metal comprising an element corresponding to group 4B of the periodic table.

In this case, the element corresponding to Group 4B of the periodic table is at least one material selected from the group consisting of silicon (Si), germanium (Ge), tin (Sn) and lead (Pb).

Preferably, the catalyst carrier is used alone, blended with carbon-based powder, or alloyed with another metal.

The carbon powder is carbon black, ketjen black, acetylene black, activated carbon powder, fullerene (C60), carbon nanotube At least one selected from the group consisting of carbon nanofibers, carbon nanowires, carbon nanowires, carbon nanohorns, and carbon nanorings may be used.

In addition, the alloyable metal is titanium (Ti), strontium (Sr), cerium (Ce), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel ( Ni), copper (Cu), zinc (Zn), aluminum (Al), molybdenum (Mo), selenium (Se), palladium (Pd), tungsten (W), iridium (Ir), osmium (Os), rhodium ( Rh), niobium (Nb) and tantalum (Ta).

In addition, the present invention,

A membrane-electrode assembly disposed on both sides of the polymer electrolyte membrane and the polymer electrolyte membrane, the catalyst metal including a catalyst layer supported on a catalyst carrier comprising an element corresponding to group 4B of the periodic table, and a fuel cell electrode having an electrode base; An electricity generator including separators disposed on both sides of the membrane-electrode assembly;

A fuel supply unit supplying a fuel containing hydrogen to the electricity generation unit; And,

It provides a fuel cell system including an oxygen supply unit for supplying oxygen to the electricity generation unit.

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

The electrode of the fuel cell is composed of a catalyst layer and an electrode base for supporting the same, and is located between a polymer electrolyte membrane and a separator (or referred to as a bipolar plate), and is divided into an anode and a cathode to oxidize hydrogen and oxygen. The reduction reaction generates electrochemical energy.

In the present invention, a catalyst metal is used as a material constituting the catalyst layer, and an element corresponding to group 4B of the periodic table is used as a catalyst carrier for supporting the catalyst metal.

Elements of Group 4B of the periodic table are silicon (Si), germanium (Ge), tin (Sn), and lead (Pb). The silicon and germanium are intrinsic semiconductors. Tin and lead are also metals with good electrical properties.

The Group 4B element is excellent in electrical conductivity and has electrical properties equivalent to or higher than that of the carbon-based powder used as a conventional catalyst carrier, and has excellent corrosion resistance to the operating environment of the fuel cell system, thereby replacing the carbon-based powder. Can be.

The catalyst carrier including the Group 4B element is preferably in a powder state, and should have fine pores to sufficiently support the metal catalyst, and the catalyst layer should be uniformly formed on the electrode substrate, thereby limiting the particle size.

Preferably, the catalyst carrier according to the present invention has a specific surface area of 10 m ² / g to 900 m ² / g so that the metal catalyst can be sufficiently supported in consideration of the catalyst loading of the electrode to be finally obtained. In addition, the size of the particle size is also used in the range of 0.1 nm to 10 mm, preferably 10 nm to 1 mm, wherein if the size of the particle diameter is less than the above range, the formed catalyst layer is too dense to increase the resistance during mass transfer, the range If it exceeds, it becomes difficult to form the catalyst layer by coating.

The catalyst carrier may be used by using at least one group 4B element selected from the group consisting of silicon, germanium, tin, and lead as listed above, or by blending with carbon powder in another powder state.

The carbon-based powder is a material that is widely used as a conventional catalyst carrier, carbon black, ketjen black, acetylene black, activated carbon powder, fullerene (C ₆₀ ), Carbon nanotubes, carbon nanofibers, carbon nanowires, carbon nano-horns and carbon nano rings One or more selected from is possible.

The carbon-based powder blended with the catalyst carrier according to the present invention forms a uniform catalyst layer and uses a range similar to the particle diameter and specific surface area of the catalyst carrier so as to uniformly control the amount of the metal catalyst supported thereon. It is used by mixing less than 10000 weight part with respect to parts. In this case, when the content of the carbon-based powder exceeds the above range, the cost of the entire fuel cell system is caused by the use of expensive carbon-based powder.

In addition to such blending with carbon, the catalyst carrier containing the element of Group 4B according to the present invention is used by alloying with a metal having excellent conductivity. Alloyable metals include titanium (Ti), strontium (Sr), cerium (Ce), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni) , Copper (Cu), zinc (Zn), aluminum (Al), molybdenum (Mo), selenium (Se), palladium (Pd), tungsten (W), iridium (Ir), osmium (Os), rhodium (Rh) , Niobium (Nb) and tantalum (Ta) and alloy with at least one metal selected from the group consisting of.

At this time, the alloy containing a Group 4B element also forms a uniform catalyst layer, and uses a range similar to the particle diameter and specific surface area of the catalyst carrier to uniformly control the amount of metal catalyst supported, 100 parts by weight of the catalyst carrier It is used by mixing less than 1000 parts by weight. At this time, when the content of the carbon-based powder exceeds the above range, only the carbon properties appear, there is a problem that there is no effect of blending.

Formation of the catalyst layer including the catalyst carrier as described above may be a method commonly used in the art.

Typically, after the catalyst metal precursor and the catalyst carrier are dispersed in water or an organic solvent, heat treatment is performed at 150 to 350 ° C. for 0.5 to 5 hours in a hydrogen atmosphere to reduce the fine pores of the catalyst carrier through the reduction reaction of the catalyst metal precursor. It is converted into catalytic metal particles within.

At this time, if the heat treatment temperature is too low, the reduction reaction of the catalytic metal precursor is insufficient, if too high chemical deformation of the constituent material may occur, it is preferable to carry out within the above range. In addition, if the heat treatment time is too short, the reduction rate to the metal catalyst particles is low, and even if it is long, the reduction rate no longer increases, so it is performed within the above range.

The catalytic metal precursor may be chlorides, nitrates, sulfates or mixtures of these catalyst metals or mixtures of precursors of different metal catalysts.

Catalytic metals that can be used include platinum (Pt), ruthenium (Ru), osmium (Os), iron (Fe), cobalt (Co), chromium (Cr), nickel (Ni), mixtures thereof, and alloys thereof. It may be at least one metal selected from.                     

The catalyst metal supported on the catalyst carrier is prepared in a slurry state and wet-coated on the electrode base to form an electrode for a fuel cell.

The wet coating process is simple and the surface contact ability between the formed catalyst layer and the polymer electrolyte membrane is increased because the catalyst metal material is applied to the porous electrode substrate in a solution state, leading to an increase in the output of the fuel cell. Such a wet coating method is not limited in the present invention, and conventional methods such as screen printing, spray coating or coating using a doctor blade may be used depending on the viscosity of the composition. At this time, the coating amount or coating thickness of the slurry is not particularly limited, and is appropriately adjusted in consideration of the composition of the slurry, that is, the catalyst loading amount of the electrode to be obtained.

The electrode base serves as a support for supporting the electrode, and at the same time, a diffusion function for uniformly supplying a reaction gas such as fuel gas or air from the gas flow path of the bipolar plate to the catalyst in the catalyst layer, and by reaction in the catalyst layer. It serves to quickly discharge the generated water into the gas flow path, and also serves to challenge the electrons required for the reaction or generated during the reaction. The electrode base that can be used is preferably any one selected from carbon paper, carbon cloth, and carbon felt, and more preferably polytetrafluoroethylene; It is used by water repellent treatment with hydrophobic polymer such as PTFE).

As such, the fuel cell electrode having a catalyst layer including a metal catalyst on the electrode base and a catalyst carrier including a Group 4B element of the periodic table for supporting the metal catalyst is preferably applied to a fuel cell system.

Fuel cell system provided with an electrode for a fuel cell according to the present invention,

A membrane-electrode assembly disposed on both sides of the polymer electrolyte membrane and the polymer electrolyte membrane, the catalyst metal including a catalyst layer supported on a catalyst carrier comprising an element corresponding to group 4B of the periodic table, and a fuel cell electrode having an electrode base; An electricity generator including separators disposed on both sides of the membrane-electrode assembly;

A fuel supply unit supplying a fuel containing hydrogen to the electricity generation unit; And,

An oxygen supply unit for supplying oxygen to the electricity generating unit.

Specifically, as shown in FIG. 1, the electricity generating unit 11 forms a stack of minimum units for generating electricity by arranging the separators 16 on both sides of the membrane-electrode assembly 12 at the center thereof. In addition, a plurality of end plates 13 are provided to form a stack 10 having a stacked structure, and the end 10 of the stack 10 is in close contact with the plurality of electricity generating units 11. The plate 13 has injection portions 13a and 13b and discharge portions 13c and 13d for injecting and discharging hydrogen containing fuel and oxidant gas.

The membrane-electrode assembly 12 includes an anode electrode and a cathode electrode on both sides of the polymer electrolyte membrane, and functions to oxidize / reduce hydrogen gas and oxygen in air. The separator 16 functions as a conductor that forms a gas passage for supplying hydrogen gas and air to both sides of the membrane-electrode assembly 12 and connects the anode electrode and the cathode electrode in series.                     

In particular, in the present invention, by employing an element corresponding to group 4B of the periodic table as a catalyst layer of the electrode for fuel cells, such as the anode and the cathode constituting the membrane-electrode assembly 12, as a catalyst carrier for supporting it, It has the same electrical conductivity as that of the carbon powder used as the catalyst carrier, and can be used as a substitute for the carbon powder, and the price is low, thereby inducing a reduction in the price of the overall fuel cell system and increasing the competitiveness of the product. .

Hereinafter, 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 Fabrication of a Unit Cell Comprising a Pt-Si Catalyst Layer

0.4 g of platinum chloride (PtCl, 98%) was added to 200 ml of tetrahydrofuran, followed by stirring at 50 ° C. for 3 hours to sufficiently dissolve. In another reactor, 0.6 g of powdered silicon was added to 200 ml of tetrahydrofuran so that the mass ratio of the catalyst to the support was 40:60, followed by stirring at 50 ° C. for 3 hours to sufficiently dissolve the platinum chloride. The solution was mixed and stirred for 5 hours.

The obtained mixed reaction solution was heated to 150 ° C. to remove the solvent in the reaction solution, charged into a furnace, and heat-treated under hydrogen atmosphere at 100 ° C. for 6 hours to prepare platinum particles (Pt / Si) supported on silicon. It was.

In order to form a catalyst layer using the obtained Pt / Si powder, 20 parts by weight of Pt / Si powder (Pt content 20wt%) and 13.4 parts by weight of Nafion were added to 66.6 parts by weight of a mixed solvent of water / isopropyl alcohol (4/1). After mixing, sonication for 30 minutes and stirring for 3 hours using a magnetic stirrer to prepare a slurry.

The slurry obtained was slurry coated on an electrode substrate made of carbon felt and then dried to prepare an anode and a cathode electrode having a catalyst layer having a thickness of 60 μm.

The anode and cathode electrodes were stacked on both sides of the Nafion 112 membrane and hot-pressed at a temperature of 120 ° C. for about 3 minutes at a load of 100 kgf / cm ² to form a membrane-electrode assembly. Next, a bipolar plate was fastened to both sides of the membrane-electrode assembly to prepare a unit cell.

Example 2 Fabrication of Unit Cell Comprising Pt-Ge Catalyst Layer

A unit cell was prepared in the same manner as in Example 1, except that germanium (Ge) was used as a catalyst carrier.

Example 3 Fabrication of a Unit Cell Comprising a Pt-Sn Catalyst Layer

A unit cell was prepared in the same manner as in Example 1, except that tin (Sn) was used as a catalyst carrier.

Example 4 Fabrication of a Unit Cell Comprising a Pt-Pb Catalyst Layer

A unit cell was prepared in the same manner as in Example 1, except that lead (Pb) was used as a catalyst carrier.

Example 5 Fabrication of Unit Cell Comprising Pt / Si-C Catalyst Layer

A unit cell was prepared in the same manner as in Example 1, except that carbon black was mixed and mixed with silicon powder in a weight ratio of 50:50 in the supporting step of Example 1.

Example 6 Fabrication of Unit Cell Comprising Pt / Si-Ni Catalyst Layer

A unit cell was manufactured in the same manner as in Example 1, except that the Si-Ni alloy was used instead of the silicon powder.

Comparative Example 1 Preparation of a Unit Cell Comprising a Pt / C Catalyst Layer

A unit cell was prepared in the same manner as in Example 1, except that carbon black was used as the catalyst carrier.

Experimental Example 1

Hydrogen air in a humidified state at a temperature of 70 ° C. and an atmospheric pressure of the unit cells prepared in Examples and Comparative Examples was introduced into a unit battery cell, and voltages according to current densities were measured.

division Voltage Current density (A / cm ² ) Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Comparative Example 1 0 0.94 0.91 0.89 0.88 0.93 0.92 0.91 0.2 0.91 0.86 0.87 0.86 0.87 0.83 0.93 0.6 0.68 0.62 0.63 0.64 0.62 0.53 0.64 0.8 0.53 0.54 0.55 0.51 0.51 0.47 0.54 One 0.47 0.43 0.47 0.42 0.44 0.36 0.48

According to the above Table 1, it was confirmed that the unit cell prepared according to the embodiment of the present invention showed an output equal to or higher than that of the comparative example using the conventional carbon black.

As described above, according to the present invention, an electrode for a fuel cell including a catalyst layer supported on a carrier containing a catalyst metal containing an element corresponding to group 4B of the periodic table was produced.

As the catalyst carrier of the fuel cell electrode, Group 4B elements are excellent in electrical conductivity, and can not only replace carbon used as a conventional catalyst carrier, but also are inexpensive and can lower the production cost of the electrode for fuel cell. It can be usefully applied.

Claims (14)

A catalyst layer supported by a catalyst carrier comprising an element of the catalytic metal corresponding to group 4B of the periodic table; And A fuel cell electrode having an electrode base. The method of claim 1, wherein the element corresponding to Group 4B of the periodic table includes at least one selected from the group consisting of silicon (Si), germanium (Ge), tin (Sn), and lead (Pb). Fuel cell electrode. The fuel cell electrode according to claim 1, wherein the element corresponding to Group 4B of the periodic table is a porous powder. The electrode of claim 3, wherein the porous powder has a specific surface area of 10 m ² / g to 900 m ² / g. The electrode of claim 3, wherein the porous powder has a particle size of 1 nm to 10 mm. The fuel cell electrode as claimed in claim 1, wherein the catalyst carrier further comprises a carbon-based powder. 7. The fuel cell electrode according to claim 6, wherein the carbon-based powder is contained in an amount of less than 10000 parts by weight based on 100 parts by weight of an element of Group 4B. The method of claim 6, wherein the carbon-based powder is carbon black, ketjen black, acetylene black, activated carbon powder, fullerene (C ₆₀ ), carbon nanotubes (carbon nano tube), carbon nano fiber (carbon nano fiber), carbon nano wire (carbon nano wire), carbon nano horn (carbon nano horn) and one or more selected from the group consisting of carbon nano ring (carbon nano ring) A fuel cell electrode comprising a. The electrode of claim 1, wherein the catalyst carrier further comprises an alloy material alloyed with a Group 4B element and an alloying element. 10. The electrode of claim 9, wherein the alloying material is contained in an amount of less than 1000 parts by weight based on 100 parts by weight of the 4B group element. The method of claim 9, wherein the alloying element is titanium (Ti), strontium (Sr), cerium (Ce), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), Nickel (Ni), Copper (Cu), Zinc (Zn), Aluminum (Al), Molybdenum (Mo), Selenium (Se), Palladium (Pd), Tungsten (W), Iridium (Ir), Osmium (Os), A fuel cell electrode, characterized in that at least one metal selected from the group consisting of rhodium (Rh), niobium (Nb) and tantalum (Ta). The method of claim 1, wherein the catalytic metal is platinum (Pt), ruthenium (Ru), osmium (Os), iron (Fe), cobalt (Co), chromium (Cr) and nickel (Ni) and mixtures thereof The fuel cell electrode, characterized in that at least one metal selected from the group. The electrode of claim 1, wherein the electrode base material is one selected from the group consisting of carbon paper, carbon cloth, and carbon felt. A membrane comprising a polymer electrolyte membrane and a fuel cell electrode of claim 1 having a catalyst layer supported on a catalyst carrier comprising an element corresponding to group 4B of the periodic table and having an electrode base, the catalyst metal being disposed on both sides of the polymer electrolyte membrane. An electrical generator including an electrode assembly and separators disposed on both sides of the membrane-electrode assembly; A fuel supply unit supplying a fuel containing hydrogen to the electricity generation unit; And, A fuel cell system comprising an oxygen supply unit for supplying oxygen to the electricity generation unit.

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