KR20100094892A - Mixed carbon support on catalyst for polymer electrolyte membrane fuel cell, and catalyst for polymer electrolyte membrane fuel cell, and electrode comprising the catalyst, and membrane electrode assembly comprising electrode, and polymer electrolyte membrane fuel cell comprising membrane electrode assembly - Google Patents

Abstract

The present invention is to form a carbon of graphite structure on the surface of the carbon support to ensure the dispersibility of platinum while increasing the durability of the carbon, and to the composite carbon support of the catalyst for polymer electrolyte fuel cell excellent in durability by dispersing platinum on the carbon support It is about.

To this end, a high surface area carbon black is located therein, and a surface carbon layer having a graphite structure is formed on the surface of the carbon black.

According to the above-described configuration, since the carbon layer having a graphite structure is thinly formed on the surface of the existing carbon black, the surface of the carbon support is high because the surface has a graphite structure without any deterioration in fuel cell performance due to its high surface area and platinum dispersibility. There is an effect of suppressing oxidation, and under the fuel cell operating conditions, there is no deterioration in performance due to oxidation of the carbon support, which also significantly increases the life of the fuel cell.

Description

Polymer electrolyte fuel cell comprising a composite carbon support of a catalyst for a polymer electrolyte fuel cell, a catalyst for the polymer electrolyte fuel cell, an electrode containing a catalyst, a membrane-electrode assembly including an electrode, and a membrane-electrode assembly on catalyst for Polymer Electrolyte Membrane Fuel Cell, and catalyst for Polymer Electrolyte Membrane Fuel Cell, and electrode comprising the Catalyst, and Membrane Electrode Assembly comprising electrode, and Polymer Electrolyte Membrane Fuel Cell comprising Membrane Electrode Assembly}

The present invention relates to a polymer electrolyte fuel cell, by forming carbon of the graphite structure on the surface of the carbon support to increase the durability of the carbon while maintaining a high surface area to ensure the dispersion of platinum, and to disperse platinum in the carbon support A composite carbon support of a polymer electrolyte fuel cell catalyst having excellent durability, a polymer electrolyte fuel cell catalyst, an electrode containing a catalyst, a membrane-electrode assembly including an electrode, and a polymer electrolyte fuel cell including a membrane-electrode assembly. It is about.

Polymer Electrolyte Membrane Fuel Cell (PEMFC) is a fuel cell that uses a polymer membrane with hydrogen ion exchange characteristics as an electrolyte, and uses a fuel gas containing hydrogen and air containing oxygen to cause an electrochemical reaction. Generates electricity and heat

The polymer electrolyte fuel cell has the advantages of excellent energy conversion efficiency and high current density even at low temperature, compared to other fuel cells, and thus can be applied to various fields such as electric vehicle power supply, mobile use, military use, and home use. .

However, the biggest problem in commercializing such a polymer electrolyte fuel cell is that the performance of the catalyst gradually decreases with a long time operation or start / stop repetition, thereby degrading the performance of the polymer electrolyte fuel cell. Such a decrease in performance is reported to be due to the decrease in surface area of the cathode (electrode) platinum catalyst as the fuel cell operates.

In general, a polymer electrolyte fuel cell catalyst is used in the form of Pt / C carrying a platinum made of a carbon support nano size having a high active area.

However, the polymer electrolyte fuel cell operates under conditions where carbon corrosion is likely to occur, such as high anode potential, low pH, and high oxygen concentration. While the polymer electrolyte fuel cell is operating, carbon is oxidized in the form of CO or CO ₂ , which reduces the amount of carbon supporting the catalyst. As a result, as the carbon used as the support is oxidized as follows, the active area of platinum is also reduced, causing a problem of deterioration of the performance of the fuel cell.

_{C + H 2 O → CO 2} + 4H + + e - ( oxidation of carbon)

In addition, the presence of platinum in the oxidation of carbon causes its speed to increase. It reacts with platinum to form PtOH and PtOH reacts with carbon to form C _x (OH). Through this continuous reaction, the carbon is oxidized in the form of carbon dioxide to further increase the oxidation rate of carbon.

Accordingly, in order to suppress oxidation of the carbon support for the polymer electrolyte fuel cell as described above, Korean Patent Publication No. 10-2008-0009539 and Korean Patent Publication No. 10-2007-0108405 disclose metal oxide particles on the surface of the carbon support. To improve the durability of the carbon support by introducing.

However, the metal oxide particles have a very low conductivity of electrons, which inevitably degrades the performance of the fuel cell, and the lower conductivity may generate heat to promote oxidation of the carbon support. Therefore, the method of introducing a metal oxide into the carbon support has a problem that can not be a practical solution because it degrades the performance of the fuel cell.

Accordingly, according to recently published articles (Journal of Power Sources 172 (2007) 133-144), Journal of Power Sources 172 (2007) 145-154, Journal of the Electrochemical Society 152 (2005), A2309-A2315) The carbon support of graphite structure is used as a support body of a platinum catalyst, and the durability of a carbon support body is improved.

Carbon of graphite structure is known to hardly oxidize even under fuel cell operating conditions because of its high conductivity and corrosion resistance. In this context, carbon nanotubes are also considered as carbon supports that can inhibit the oxidation of carbon.

As is well known, however, the carbon support of graphite structure has a very low surface area and it is difficult to disperse the platinum nanoparticles on the surface. In addition, in order to disperse platinum in the carbon of the graphite structure, the carbon must be exposed to a very strong acidic atmosphere, and even if such exposure is possible, it is not practically used in a fuel cell because it is not as dispersed as a conventional carbon support. There is a situation.

Accordingly, research on various carbon materials as a carbon support of a catalyst for a polymer electrolyte fuel cell has been actively conducted, but there are still problems with technical limitations that are still not applicable to fuel cells.

The present invention has been made to solve the conventional problems as described above, by forming the carbon of the graphite structure only on the surface of the existing carbon support, while maintaining the high surface area while increasing the durability of the carbon to ensure the dispersion of platinum The present invention provides a composite carbon support of a catalyst for a polymer electrolyte fuel cell.

Another object of the present invention is to disperse platinum or platinum alloy nanoparticles on the composite carbon support, the composite carbon support of the catalyst for polymer electrolyte fuel cell with excellent durability, the catalyst for the polymer electrolyte fuel cell, the electrode comprising a catalyst, There is provided a polymer-electrolyte fuel cell including a membrane-electrode assembly including an electrode and a membrane-electrode assembly.

The composite carbon support of the catalyst for a polymer electrolyte fuel cell of the present invention for achieving the above object has a structure in which a high surface area carbon black is located therein and a surface carbon layer of graphite structure is formed on the carbon black surface. It features.

In addition, the surface carbon layer lattice spacing is 3.44, or less, and the surface carbon layer is formed by chemical vapor deposition (CVD).

Here, the precursor of the surface carbon layer is any one of acetonitrile, styrene, acenaphthene, phenanthrene or any one of these compounds.

And, the chemical vapor deposition temperature is at least 900 ℃ or more, the transport gas uses argon or nitrogen without oxygen.

On the other hand, the platinum is supported on the composite carbon support, characterized in that for producing a polymer electrolyte fuel cell platinum catalyst.

In addition, a platinum-supported catalyst is included in the composite carbon support, characterized in that for producing an electrode for a polymer electrolyte fuel cell.

In addition, the membrane-electrode assembly for a polymer electrolyte fuel cell is produced using the electrode.

Further, there is provided a polymer electrolyte fuel cell comprising the membrane-electrode assembly.

The present invention through the above problem solving means, by forming a thin carbon layer of graphite structure only on the surface of the existing carbon black to produce a composite carbon support, high surface area and platinum dispersibility without reducing fuel cell performance at all, Since the surface has a graphite structure, the carbon support can be inhibited from oxidizing. In particular, under the fuel cell operating conditions, there is no performance deterioration due to oxidation of the carbon support. have.

When described in detail with reference to the accompanying drawings a preferred embodiment of the present invention.

1 is a schematic diagram of a composite carbon support of a catalyst for a polymer electrolyte fuel cell (PEMFC) according to the present invention, wherein carbon black is placed inside, and the surface carbon having a graphite structure on the carbon black surface The layer is deposited by thin deposition.

Here, the carbon black has an irregular orientation of the carbon layers, the lattice spacing of the carbon layer is 3.44 Å or more, and the lattice spacing of Vulcan XC-72 of Cabot, which is currently used most, is about 3.62 Å.

On the other hand, the carbon layer of graphite structure has the carbon layer toward the direction which was comparatively long, and the lattice spacing of a carbon layer should have a value of 3.44 kPa or less. Therefore, the composite carbon support of the present invention is also configured to have a surface carbon layer lattice spacing of 3.44 Å or less so as to have durability in fuel cell operating conditions.

In the composite carbon support having the above structure, the surface carbon layer of the graphite structure may be formed by chemical vapor deposition (CVD). Here, as the graphite precursor for depositing the surface carbon layer, any one of acetonitrile, styrene, acenaphthene, phenanthrene, or a compound thereof may be used.

In the case of chemical vapor deposition, the transport gas necessarily uses argon or nitrogen without oxygen. In addition, the degree of graphitization of the composite carbon support depends on the deposition temperature, which should be at least 900 ° C. or higher.

Hereinafter, the present invention will be described in more detail with reference to preferred examples and comparative examples. Herein, the following embodiments are merely examples to help the understanding of the present invention, and the scope of the present invention is not limited or limited thereto.

≪ Example 1 >

A composite carbon support was prepared using acetonitrile as a graphite precursor on the surface of Vulcan XC-72R, a commercial carbon black manufactured by Cabot. Chemical vapor deposition temperature was 1000 ℃, time was 5 hours, and the transport gas was flowed into the argon at a rate of 50ml / min.

Figure 2 is a photograph of the surface of the commercial carbon black Vulcan XC-72R and the composite carbon support prepared in Example 1 with a transmission electron microscope.

In the case of the commercially available carbon black disposed on the left side, the interlayer lattice spacing of carbon is 3.62 kPa, which is larger than the theoretical lattice spacing of graphite (3.44 kPa), and the lateral connection of the carbon layers as a whole is not slippery. On the other hand, the composite carbon support of Example 1 disposed on the right side has a graphite structure with a lattice spacing of about 3.40 3., and the lateral connection of the surface carbon layer of the graphite structure is also sharper than that of commercial carbon black. Long. Therefore, it can be confirmed that the graphite layer was better formed on the surface of the composite carbon support of <Example 1>.

3 is a result of measuring the surface areas of the commercial carbon black Vulcan XC-72R and the composite carbon support prepared in Example 1 and the commercial graphite powder, respectively, using a nitrogen adsorption / desorption apparatus.

Although the surface area of the composite carbon support was reduced by about half compared to that of the commercial carbon black, it can be seen that it has a very high surface area compared to the commercial graphite powder. It can be seen that the surface area is maintained even after graphitization.

<Example 2>

An electrode slurry was prepared by adding 5 mg of the composite carbon support prepared in Example 1 into a mixed solution of 1 ml of ethanol and 50 µl of Nafion's solution of Dupont. 30 μl of the prepared electrode slurry was dropped on an electrode rod for cyclic voltage current measurement, and dried at 80 ° C. for 1 hour to prepare a working electrode.

Comparative Example 1

5 mg of a commercial carbon black Vulcan XC-72R was added to 1 ml of ethanol and 50 µl of a Nafion solution from Dupont, followed by stirring to prepare an electrode slurry. 30 μl of the prepared electrode slurry was dropped on an electrode rod for cyclic voltage current measurement, and dried at 80 ° C. for 1 hour to prepare a working electrode.

After dipping each working electrode prepared in <Example 2> and <Comparative Example 1> together with the reference electrode and the counter electrode in 1M sulfate electrolyte, 1.2V (vs. RHE) was applied to the working electrode for 30 hours. . Here, the cyclic voltage current was measured at a rate of 20 mV / s from 0 V to 1.2 V every 3 hours to determine the reduced charge amount of quinone / hydroquinone at 0.25 V to 0.65 V. As the surface of carbon is oxidized, the amount of quinone groups increases, so that the amount of reduced charge of quinone / hydroquinone is an index indicating the degree of oxidation of carbon.

Figure 4 shows the relative change in the amount of quinone / hydroquinone reduction charge of the prepared composite carbon support and commercial carbon black. In the case of commercial carbon black, significant oxidation has already occurred during the initial 5 hours and the surface oxidation continues afterwards.

On the other hand, in the case of the composite carbon support electrode manufactured in Example 2, it can be seen that surface oxidation hardly occurs. Therefore, it can be seen that the graphite layer formed on the surface of the carbon black effectively prevents the oxidation of carbon.

<Example 3>

0.5 g of the composite carbon support prepared in <Example 1> was dispersed in 17 ml of 7 M sodium formate solution, and then 0.5 M NaOH aqueous solution was added until the pH reached 9. After slowly dropping 0.4M H ₂ PtCl ₆ aqueous solution so that the amount of platinum supported is 40% by weight in a solution in which the composite carbon support is dispersed, the solution is heated to 80 ° C. and stirred. After 24 hours, the solution was filtered and the powder obtained was washed and dried sufficiently at 80 ° C. to obtain a composite carbon support having platinum dispersed therein.

An electrode slurry was prepared by stirring 5 mg of the composite carbon support prepared with platinum into a mixed solution of 1 ml of ethanol and 50 µl of Nafion's solution of Dupont. 30 μl of the prepared electrode slurry was dropped on an electrode rod for cyclic voltage current measurement, and dried at 80 ° C. for 1 hour to prepare a working electrode.

Comparative Example 2

0.5 g of a commercial carbon black, Vulcan XC-72R, is dispersed in 17 ml of 7 M sodium formate solution, and then 0.5 M NaOH aqueous solution is added until pH is 9. After slowly dropping 0.4M H ₂ PtCl ₆ aqueous solution so that the amount of platinum supported is 40% by weight in a solution in which the composite carbon support is dispersed, the solution is heated to 80 ° C. and stirred. After 24 hours, the solution is filtered and the powder obtained is washed and dried at 80 ° C. to obtain carbon black in which platinum is dispersed.

5 mg of commercially available carbon black in which the prepared platinum was dispersed was added to 1 ml of ethanol and 50 µl of Nafion's solution of Dupont, and stirred to prepare an electrode slurry. 30 μl of the prepared electrode slurry was dropped on an electrode rod for cyclic voltage current measurement, and dried at 80 ° C. for 1 hour to prepare a working electrode.

Each working electrode manufactured in <Example 3> and <Comparative Example 2> was subjected to a circulating voltage of 3,000 times at a rate of 50 mV / s from 0.6 V to 1.0 V in a 0.1 M perchlorate electrolyte together with a reference electrode and a counter electrode. It was. The application of such a cyclic voltage forcibly promotes corrosion of the fuel cell catalyst so that it is possible to know how durable the catalyst is in a short time. Then, the circulating voltage repetition was measured three times at a speed of 20 mV / s from 0 V to 1.2 V every 100 times to calculate the surface area of platinum.

Figure 5 shows the change in the surface area of platinum according to the cyclic voltage repetition of the composite carbon support and commercial carbon black dispersed platinum. Whereas the surface area of platinum dispersed on commercial carbon black had a surface area reduction of about 40% after 3,000 cycles of voltage iteration, platinum dispersed only on the composite carbon support initially showed only a surface area reduction of less than about 10%. It was confirmed that the surface area of was kept constant. Therefore, it can be seen that the composite carbon support proposed in the present invention can significantly improve the life of the fuel cell catalyst.

On the other hand, the present invention has been described in detail only with respect to the specific examples described above it will be apparent to those skilled in the art that various modifications and variations are possible within the technical scope of the present invention, it is natural that such variations and modifications belong to the appended claims. .

1 is a schematic diagram conceptually showing the structure of a composite carbon support according to the present invention;

2 is a transmission electron micrograph showing the surface state of the composite carbon support and the commercial carbon black according to the present invention,

3 is a table comparing the surface area of the composite carbon support, commercial carbon black and graphite powder according to the present invention;

4 is a graph showing a relative change in the amount of quinone / hydroquinone reduction charge of the composite carbon support and the commercial carbon black according to the present invention;

5 is a graph showing the relative electrochemical surface area change of the composite carbon support and the commercial carbon black dispersed platinum according to the present invention.

Claims (9)

A composite carbon support of a catalyst for a polymer electrolyte fuel cell, wherein a high surface area carbon black is disposed therein and a surface carbon layer having a graphite structure is formed on a surface of the carbon black. The composite carbon support of the catalyst for polymer electrolyte fuel cell according to claim 1, wherein the surface carbon layer lattice spacing is 3.44 kPa or less. The composite carbon support of the catalyst for polymer electrolyte fuel cell according to claim 1, wherein the surface carbon layer is formed by chemical vapor deposition (CVD). The composite carbon of the catalyst for polymer electrolyte fuel cell according to claim 3, wherein the precursor of the surface carbon layer is any one of acetonitrile, styrene, acenaphthene, phenanthrene, or any one of these compounds. Support. 4. The composite carbon support of claim 3, wherein the chemical vapor deposition temperature is at least 900 ° C and the transport gas is argon or nitrogen without oxygen. Platinum catalyst for a polymer electrolyte fuel cell, characterized in that the platinum is supported on the composite carbon support according to claim 3. A polymer electrolyte fuel cell electrode comprising a catalyst loaded with platinum on the composite carbon support according to claim 6. A membrane-electrode assembly for a polymer electrolyte fuel cell, which is made of the electrode according to claim 7.  A polymer electrolyte fuel cell comprising the membrane-electrode assembly according to claim 8.

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