KR20150138103A - Electrode for fuel cell, membrane electrode assembly comprising the same and fuel cell comprising the membrane electrode assembly - Google Patents

Abstract

The present invention relates to an electrode for a fuel cell, a membrane electrode assembly including the same, and a fuel cell including the membrane electrode assembly.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an electrode for a fuel cell, a membrane electrode assembly including the membrane electrode assembly, and a fuel cell including the membrane electrode assembly. BACKGROUND OF THE INVENTION 1. Field of the Invention [0001]

The present invention relates to an electrode for a fuel cell, a membrane electrode assembly including the same, and a fuel cell including the membrane electrode assembly.

Recently, as the exhaustion of existing energy resources such as oil and coal is predicted, interest in energy that can replace them is increasing. As one of such alternative energies, fuel cells have attracted particular attention due to their advantages such as high efficiency, no emission of pollutants such as NOx and SOx, and abundant fuel.

A fuel cell is a power generation system that converts the chemical reaction energy of a fuel and an oxidant into electric energy. Hydrogen, hydrocarbons such as methanol and butane are used as fuel, and oxygen is used as an oxidant.

BACKGROUND ART Fuel cells include a polymer electrolyte fuel cell (PEMFC), a direct methanol fuel cell (DMFC), a phosphoric acid fuel cell (PAFC), an alkaline fuel cell (AFC), a molten carbonate fuel cell (MCFC) And a battery (SOFC). Among them, polymer electrolyte fuel cells have been actively studied because they have high energy density and high output. Such a polymer electrolyte fuel cell differs from other fuel cells in that it uses a solid polymer electrolyte membrane instead of a liquid electrolyte.

Korean Patent Publication No. 2003-0076057

The present invention provides an electrode for a fuel cell, a membrane electrode assembly including the same, and a fuel cell including the membrane electrode assembly.

The present invention provides a catalyst layer comprising a catalyst and a hydrophilic material, wherein the hydrophilic material is contained in an amount of 5 parts by weight or more and 10 parts by weight or less based on 100 parts by weight of the catalyst.

The present disclosure also relates to a cathode comprising: a cathode; Anode; And an electrolyte membrane provided between the cathode and the anode, wherein at least one of the cathode and the anode is the electrode.

Further, the present specification provides a fuel cell including the membrane electrode assembly.

One embodiment of the present invention is advantageous in that the performance of the membrane electrode assembly is good even under low humidity conditions.

In one embodiment of the present invention, by increasing the water content of the membrane electrode assembly, it is possible to reduce the influence of the humidity change of the surrounding environment.

1 is a schematic view showing an electricity generation principle of a fuel cell.
2 is a schematic view showing the structure of a membrane electrode assembly for a fuel cell according to an embodiment of the present invention.
3 is a schematic view showing one embodiment of a fuel cell.
4 is a graph of current densities of Example 1-2 and Comparative Example 1-4 at a relative humidity of 100%.
5 is a graph of current densities of Example 1-2 and Comparative Example 1-4 at a relative humidity of 50%.
6 is a graph of current densities of Example 1-2 and Comparative Example 1-4 at a relative humidity of 32%.

Hereinafter, the present invention will be described in detail.

The present invention provides an electrode for a fuel cell comprising a catalyst and a catalyst layer comprising a hydrophilic material.

The thickness of the catalyst layer may be 3 탆 or more and 30 탆 or less.

In this specification, the catalyst is not limited as long as it can serve as a catalyst in a fuel cell, but may include one of platinum, a transition metal, and a platinum-transition metal alloy.

Here, the transition metal is an element of Group 3 to Group 11 in the periodic table, and may be any one of ruthenium, osmium, palladium, molybdenum and rhodium.

Specifically, the catalyst may be selected from the group consisting of platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy, platinum-molybdenum alloy and platinum-rhodium alloy. .

The catalysts can be used not only by themselves but also by being supported on a carbon-based carrier.

Examples of the carbon-based support include graphite, carbon black, acetylene black, denka black, cacao black, activated carbon, mesoporous carbon, carbon nanotube, carbon nanofiber, carbon nanohorn, carbon nano ring, A mixture of two or more selected from the group consisting of fullerene (C ₆₀ ) and Super P black (Super P black) is a preferable example.

In the present specification, the hydrophilic material may include at least one hydrophilic group selected from a hydroxyl group and an amide group.

The hydrophilic material including the hydroxy group may include at least one of polyvinyl alcohol, cellulose, amylose, glycogen, beta glucan, dextrin and galactose.

The hydrophilic substance including the amide group may include at least one of a peptide and a polyacrylamide.

The hydrophilic material preferably comprises polyvinyl alcohol or cellulose.

In one embodiment of the present invention, the content of the hydrophilic substance may be 5 parts by weight or more and 10 parts by weight or less based on 100 parts by weight of the catalyst. In this case, since the hydrophilic material contains water generated by the air reaction with hydrogen and water supplied from the outside, the fuel cell performance is maintained even under low humidification conditions and gas migration in the electrode is not hindered.

In the present invention, the catalyst layer may further include an ionomer. The ionomer provides a path for ions generated by the reaction between the fuel and the catalyst, such as hydrogen or methanol, to move to the electrolyte membrane. The ionomer may specifically be a sulfonated polymer such as Nafion ionomer or sulfonated polytrifluorostyrene.

In the catalyst layer, the content of the ionomer may be 20 parts by weight or more and 60 parts by weight or less based on 100 parts by weight of the catalyst.

The catalyst ink forming the catalyst layer may be composed of a catalyst, a hydrophilic substance, an ionomer and a solvent.

As the solvent contained in the catalyst ink, any one or a mixture of two or more selected from the group consisting of water, butanol, isopropanol, methanol, ethanol, n-propanol, n-butyl acetate and ethylene glycol is preferably used Can be used.

The content of the solvent may be 700 parts by weight or more and 900 parts by weight or less based on 100 parts by weight of the catalyst, and may be 750 parts by weight or more and 850 parts by weight or less, if necessary.

In one embodiment of the present invention, the electrode for a fuel cell may further include a gas diffusion layer provided on one side of the catalyst layer. The gas diffusion layer serves as a current conductor and serves as a passage for reacting gas and water, and has a porous structure. Therefore, the gas diffusion layer may include a conductive base material.

As the conductive base material, any conventional materials known in the art can be used. For example, carbon paper, carbon cloth or carbon felt can be preferably used. It does not.

The thickness of the gas diffusion layer may be 200 탆 or more and 500 탆 or less. In this case, there is an advantage that the reactant gas transfer resistance through the gas diffusion layer is minimized and the optimum state is obtained from the viewpoint of proper water content in the gas diffusion layer.

The present disclosure includes a cathode; Anode; And an electrolyte membrane provided between the cathode and the anode, wherein at least one of the cathode and the anode is the electrode.

In one embodiment of the present specification, the cathode and the anode may each be an electrode for a fuel cell of the present specification. Specifically, the cathode and the anode may be electrodes for a fuel cell including a catalyst layer including a catalyst and a hydrophilic substance, respectively.

In one embodiment of the present invention, the cathode may be an electrode for a fuel cell of the present specification. Specifically, the cathode may be an electrode for a fuel cell including a catalyst and a catalyst layer including a hydrophilic material.

In one embodiment of the present specification, the anode may be an electrode for a fuel cell of the present specification. Specifically, the anode may be a fuel cell electrode including a catalyst layer including a catalyst and a hydrophilic material.

In the case of fuel cell vehicles, high performance in the high current region is important. In order to generate a high current, a corresponding reactant gas is required. However, since the cathode is disadvantageous relative to the anode in terms of reactant gas transfer resistance, it is preferable that the hydrophilic substance is only in the anode.

The reactant gas in the cathode is air. Since the gas involved in the reaction is oxygen in the air, the purity of the anode is disadvantageous compared with the hydrogen, and the molecular size is larger than that of hydrogen. Considering this point, the presence of a hydrophilic substance in the cathode may slow the gas transfer relatively, and the water generated at the cathode may also interfere with gas diffusion. On the other hand, the reactant gas of the anode is pure hydrogen gas, hydrogen is relatively smaller in molecular size than oxygen, and there is no water produced in the anode, so that even if there is a hydrophilic substance, the gas transfer resistance is not larger than that of the cathode. Furthermore, at high currents, dehydration of the electrolyte membrane on the anode side due to electroosmosis is serious, and it is advantageous to have a hydrophilic substance on the anode because the anode is essentially where moisture is required.

The oxidation reaction of the fuel occurs in the catalyst layer of the anode, and the reduction reaction of the oxidant occurs in the catalyst layer of the cathode.

The cathode and the anode may be an electrode including a catalyst layer provided on the electrolyte membrane side and a gas diffusion layer provided on the catalyst layer, respectively.

The process of introducing the catalyst layer can be performed by a conventional method known in the art. For example, the catalyst ink may be directly coated on the electrolyte membrane, or a catalyst layer may be formed on the releasable substrate, followed by thermocompression bonding to the electrolyte membrane, The catalyst layer may be formed by removing the substrate or by coating the gas diffusion layer. The method of coating the catalyst ink is not particularly limited, but spray coating, tape casting, screen printing, blade coating, inkjet coating, die coating or spin coating may be used.

The thickness of the electrolyte membrane may be 5 탆 or more and 50 탆 or less. In this case, there is an advantage that an optimum state is obtained in terms of minimizing the gas cross over of the electrolyte membrane gas and minimizing the proton ion resistance.

In this specification, the electrolyte membrane is provided between the cathode catalyst layer and the anode catalyst layer, and serves as a medium through which protons pass and serves as a separator between air and hydrogen gas. The higher the proton mobility of the electrolyte membrane, the higher the performance of the membrane electrode assembly.

At this time, the proton mobility of the electrolyte membrane is influenced by the humidity, and since the proton is more easily moved as the humidity is higher, the humidity is controlled by the external humidifier in the fuel cell system.

With the trend to simplify the balance of plants in fuel cells, there is a need to eliminate or simplify the external humidifier.

One embodiment of the present disclosure has the advantage that the amount of water exiting the gas diffusion layer is reduced so that the membrane electrode assembly is in a sufficiently wet state, thereby eliminating or simplifying the external humidifier.

One embodiment of the present invention has the advantage of increasing the water content of the membrane electrode assembly.

One embodiment of the present invention has the advantage of improving the performance of the fuel cell under low humidity conditions. Furthermore, one embodiment of the present invention has the advantage of improving the performance of the fuel cell under extremely humid conditions.

The reactant gas of the fuel cell is heated to a temperature of about 10 ° C to 30 ° C (about 10 ° C to 30 ° C) higher than the setting temperature of the humidifier (bubbler) so as not to condense in the gas line through the bubbler, High. At this time, the relative humidity of the battery cell is calculated according to the relative humidity conversion relation based on the temperature of the water in the humidifier through which the reactant gas passes, that is, the dew point temperature and the temperature of the battery cell.

Since the proton ion conductivity of the electrolyte membrane is an important factor in the performance of the membrane electrode assembly, it is highly affected by the relative humidity. Therefore, when measuring the proton conductivity of the electrolyte membrane according to the relative humidity, the relative humidity varies depending on the change in the electrolyte membrane proton conductivity It was distinguished by a large section.

Specifically, in the low humidification condition, the humidity condition refers to the relative humidity measured at the cell temperature of 70 DEG C, and in the present specification, the low humidifying condition is the case where the relative humidity is more than 40% and less than 65% 0% to less than 40%.

When the relative humidity is high humidified, the current density at 0.6 V may be greater than 1000 mA / cm ² .

When the relative humidity is low, the current density at 0.6 V may be greater than 1000 mA / cm ² .

When the relative humidity is extremely humid, the current density at 0.6 V may be greater than 700 mA / cm ² .

In one embodiment of the present invention, by increasing the water content of the membrane electrode assembly, it is possible to reduce the influence of the humidity change of the surrounding environment.

FIG. 1 schematically shows an electricity generating principle of a fuel cell. In a fuel cell, the most basic unit for generating electricity is a membrane electrode assembly (MEA), which includes an electrolyte membrane M and an electrolyte membrane M, And an anode (A) and a cathode (C) formed on both sides of the cathode (C). Referring to Fig. Showing the electricity generating principle of a fuel cell 1, an anode (A) in the hydrogen or methanol, butane and the oxidation of the fuel (F) of the hydrocarbon and so on up the hydrogen ions (H ⁺⁾ and electron (e ^-), such as And the hydrogen ions move to the cathode C through the electrolyte membrane M. In the cathode (C), the hydrogen ions transferred through the electrolyte membrane (M) react with the oxidizing agent (O) such as oxygen, and water (W) is produced. This reaction causes electrons to migrate to the external circuit.

2 schematically shows the structure of a membrane electrode assembly for a fuel cell according to an embodiment of the present invention. The membrane electrode assembly for a fuel cell comprises an electrolyte membrane 10 and a plurality of electrolyte membrane layers 10 facing each other with the electrolyte membrane 10 interposed therebetween And a cathode 50 and an anode 51 positioned thereon.

The cathode includes a cathode catalyst layer 20 and a cathode gas diffusion layer 30 sequentially from the electrolyte membrane 10,

The anode may be provided with the anode catalyst layer 21 and the anode gas diffusion layer 31 sequentially from the electrolyte membrane 10.

In this specification, the electrolyte membrane may be an electrolyte membrane using a solid electrolyte.

In one embodiment of the present invention, the electrolyte membrane may be a polymer electrolyte membrane using a solid polymer electrolyte as an electrolyte.

In one embodiment of the present invention, the electrolyte membrane may be a hydrocarbon-based polymer electrolyte membrane or a fluorinated polymer electrolyte membrane, and the electrolyte membrane may be a hydrocarbon-based polymer electrolyte membrane.

In one embodiment of the present invention, the polymer electrolyte composition forming the polymer electrolyte membrane may include a solvent and a polymer.

The polymer may be at least one hydrocarbon polymer, and conventional materials known in the art may be used.

For example, the polymer may be selected from the group consisting of sulfonated polyetheretherketone, sulfonated polyketone, sulfonated poly (phenylene oxide), sulfonated poly (phenylene sulfide), sulfonated polysulfone, (Phosphonite) polyphosphazene, and a sulfonated polybenzimidazole, and at least one selected from the group consisting of at least one selected from the group consisting of at least one selected from the group consisting of at least one selected from the group consisting of poly (vinylidene fluoride), polycarbonate, sulfonated polystyrene, sulfonated polyimide, sulfonated polyquinoxaline, .

The content of the polymer can be adjusted according to the appropriate IEC (ion exchange capacity) value required for the electrolyte membrane for a fuel cell to be applied. In the case of polymer synthesis for electrolyte membrane production for fuel cells, the polymer can be designed by calculating the ion exchange capacity (IEC) meq./g = mmol / g. The polymer content can be selected so as to be within the range of 0.5 < = IEC <

The weight average molecular weight of the polymer may range from tens of thousands to millions. Specifically, the polymer may have a weight average molecular weight of 10,000 or less.

The solvent for the polymer electrolyte membrane is not particularly limited as long as it is a substance capable of reacting with the polymer to dissolve the polymer, and conventional materials known in the art can be used.

The electrolyte membrane may be formed using the polymer electrolyte composition by a conventional method known in the art. For example, an electrolyte membrane may be formed by casting using the polymer electrolyte composition.

In this specification, the membrane electrode assembly can be produced by a conventional method known in the art, in which the catalyst layer of the anode and the catalyst layer of the cathode are in contact with the electrolyte membrane.

One embodiment of the present invention provides a fuel cell including the membrane electrode assembly.

Another embodiment of the present disclosure relates to a stack comprising two or more membrane electrode assemblies according to the present disclosure and a separator provided between the membrane electrode assemblies; A fuel supply unit for supplying fuel to the stack; And an oxidant supply part for supplying the oxidant to the stack.

3 schematically shows the structure of a fuel cell, which includes a stack 60, an oxidant supply unit 70, and a fuel supply unit 80. [

The stack 60 includes one or more of the membrane electrode assemblies described above and includes a separator interposed therebetween when two or more membrane electrode assemblies are included. The separator serves to prevent the membrane electrode assemblies from being electrically connected and to transfer the fuel and oxidant supplied from the outside to the membrane electrode assembly.

The oxidant supply part 70 serves to supply the oxidant to the stack 60. As the oxidizing agent, oxygen is typically used, and oxygen or air can be injected into the pump 70 and used.

The fuel supply unit 80 serves to supply the fuel to the stack 60 and includes a fuel tank 81 for storing the fuel and a pump 82 for supplying the fuel stored in the fuel tank 81 to the stack 60 Lt; / RTI > As the fuel, gas or liquid hydrogen or hydrocarbon fuel may be used. Examples of hydrocarbon fuels include methanol, ethanol, propanol, butanol or natural gas.

Hereinafter, the present invention will be described in more detail by way of examples. However, the following embodiments are intended to illustrate the present disclosure and are not intended to limit the present disclosure.

 [Manufacturing Example]

1) Manufacture of electrodes not containing polyvinyl alcohol

10.5% by weight catalyst (catalyst with 50% by weight of Pt supported on carbon), 17.3% by weight Nafion ionomer (20% by weight in solvent) based on the total weight of the catalyst layer composition on a polytetrafluoroethylene Comparative Example 1 was prepared by forming a catalyst layer using a catalyst layer composition containing 72.3 wt% of a solvent.

2) Preparation of electrodes containing polyvinyl alcohol

(Catalyst having 50% by weight of Pt supported on carbon), Nafion ionomer (Ionomo dispersed in 20% by weight in a solvent), solvent (water, methanol ) And a polyvinyl alcohol (PVA) as a hydrophilic substance.

As shown in Table 1, the electrodes were prepared in accordance with the content of polyvinyl alcohol in the solid content after drying, in Examples 1-2 and 2-4.

[Table 1]

[Example]

Each pair of electrodes prepared in the above Preparation Example was prepared, and a hydrocarbon-based electrolyte membrane (sulfonated polyether etherketone) was placed therebetween, hot-pressed using a hot press, and PTFE transfer substrates on both sides were removed, (CCM, catalyst coated membrane).

A gas diffusion layer (a gas diffusion layer including a micro porous layer), a bipolar plate, a current collector, and an end plate are formed on both sides of the electrolyte membrane coated with the catalyst prepared thereafter And assembled cell blocks for performance evaluation.

[Experimental Example]

Comparative Example 1 in which PVA is absent, Comparative Example 2 in which the content is 1.5% by weight, Example 1 in which the content is 1.9% by weight, Example 2 in which the content is 3.6% by weight, Comparative Example 3 having a content of 4.0 wt% and Comparative Example 4 having a content of 5.4 wt% were evaluated for performance.

The performance conditions were cell temperature 70 ℃ and atmospheric pressure. Stoichiometry of the flow rate was 1.5 and 2.0 for the anode (hydrogen) and the cathode (air), respectively. The measurement procedure is to measure the current density starting at the first 0 mA / cm ² (Open circuit voltage, OCV) and increasing at 100 mA / cm ² , measuring up to 1500 mA / cm ² and then decreasing the current density to the OCV . The cell temperature was measured in the order of 100%, 50%, and 32% relative humidity at 70 ° C. The performance criterion of the membrane electrode assembly (MEA) was the current density at 0.6 V. The results are shown in Table 2 and Figs. 4 to 6.

 [Table 2]

In Comparative Example 1 in which PVA in the electrode was not added, the relative humidity was 100% and 50%, the current density value at 0.6 V was higher than 1000 mA / cm ² , but at 32%, the performance was lower than 700 mA / cm ² . Comparative Example 2 containing 1.5% by weight of PVA still has the same performance tendency by humidity as Comparative Example 1, and in particular, the improvement effect is not exhibited in the case of extremely low humidification.

On the other hand, in the case of Examples 1 and 2 in which PVA is contained in an amount of 5 parts by weight or more and 10 parts by weight or less based on 100 parts by weight of the catalyst, the performance of the high humidification and the low humidification is maintained, . This allows the PVA to maintain the performance of the fuel cell even in very humid environments because it keeps the water generated by the reaction of hydrogen with air and the water coming from the external humidifier.

However, in Comparative Example 3 in which the amount of PVA is further increased to 4.0 wt%, the current density is low in the case of extremely low humidification. This is because the gas movement in the electrode is not smooth as the amount of PVA increases. This tendency is more remarkable in Comparative Example 4 in which PVA is added up to 5.4% by weight, which shows that high humidification and low humidification performance are also lowered.

10: electrolyte membrane
20, 21: catalyst layer
30, 31: gas diffusion layer
50: cathode
51: anode
60: Stack
70: oxidant supplier
80: fuel supply unit
81: Fuel tank
82: Pump

Claims (11)

A catalyst comprising a catalyst and a hydrophilic material,
Wherein the hydrophilic material is contained in an amount of 5 parts by weight or more and 10 parts by weight or less based on 100 parts by weight of the catalyst. The electrode for a fuel cell according to claim 1, wherein the hydrophilic material comprises at least one hydrophilic group selected from the group consisting of a hydroxyl group and an amide group. The electrode for a fuel cell according to claim 1, wherein the hydrophilic material comprises at least one of polyvinyl alcohol, cellulose, amylose, glycogen, beta glucan, dextrin and galactose. The electrode for a fuel cell according to claim 1, wherein the catalyst comprises one of platinum, a transition metal, and a platinum-transition metal alloy. The electrode for a fuel cell according to claim 4, wherein the transition metal is any one of ruthenium, molybdenum, rhodium, osmium, and palladium. The electrode for a fuel cell according to claim 1, wherein the catalyst layer further comprises an ionomer. The electrode for a fuel cell according to claim 1, further comprising a gas diffusion layer provided on one surface of the catalyst layer. Cathode; Anode; And an electrolyte membrane provided between the cathode and the anode,
Wherein at least one of the cathode and the anode is an electrode according to any one of claims 1 to 7. The membrane electrode assembly according to claim 8, wherein the electrolyte membrane is provided between the cathode catalyst layer and the anode catalyst layer. The membrane-electrode assembly according to claim 8, wherein the electrolyte membrane is a hydrocarbon-based polymer electrolyte membrane. A fuel cell comprising the membrane electrode assembly of claim 8.

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