KR20140136256A - Method and process of metal catalyst for fuel cell using a complex compound, and fuel cell electrode adopting the catalyst and fuel cell comprising the electrode - Google Patents

Abstract

The present invention relates to a metal catalyst for a fuel cell using a complex compound and, more particularly, to a method for manufacturing a metal catalyst for a fuel cell comprising the steps of: forming a carbon-based catalyst substrate doped with a chelating agent by mixing a carbon-based catalyst substrate, a chelating agent and a first solvent, adding a reducing agent and thereby conducting primary reduction; forming a transition metal precursor-mixed solution by mixing transition metal precursors in a second solvent; and forming a metal catalyst by dispersing the carbon-based catalyst substrate doped with the chelating agent in the transition metal precursor-mixed solution, adding a reducing agent and thereby conducting secondary reduction. According to the present invention, the electrochemical efficiency of a metal catalyst can be increased while not including platinum or reducing the content thereof and an economical fuel cell can be manufactured by realizing maximal efficiency in the manufacture thereof.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and a device for manufacturing a metal catalyst for a fuel cell using a complex compound, an electrode for a fuel cell and a fuel cell using the same,

The present invention relates to a method for producing a metal catalyst for a fuel cell using a complex, and a method for producing a metal catalyst for a fuel cell, which comprises a step of doping a chelating agent on the surface of a carbon- A method for manufacturing a metal catalyst for a fuel cell, and an electrode and a fuel cell for a fuel cell using the same.

Today, due to environmental pollution problems and depletion of resources, interest in alternative energy is increasing. Especially, energy-efficient fuel cells are attracting much attention as energy conversion devices. Industrial, household, and vehicle-powered power supplies.

The types of fuel cells can be classified by electrolytes and include a proton exchange membrane fuel cell (PEMFC), a direct methanol fuel cell (DMFC), an alkaline fuel cell (AFC) ) And phosphoric acid fuel cells (PAFCs).

BACKGROUND ART Electrode catalysts for producing electricity from an electrochemical reaction are mainly composed of transition metals and precious metals, and particularly, platinum-based precious metals have high current density, high resistance to chemical attack, and low temperature And excellent electrochemical reactivity at the same time. The platinum-based noble metal, which provides a great advantage in the oxidation-reduction reaction, is currently the mainstream of electrode catalysts used in fuel cells.

However, due to the high cost of rare metals such as platinum-based precious metals, research and development efforts have been made to overcome economic difficulties over the past several decades in order to commercialize them, and it has been reported that platinum usage per kW should be reduced to 0.2 g or less .

Currently, studies on alloy catalyst materials that do not use platinum at all or reduce the amount of pure platinum are being actively conducted, but it is a fact that there is a real difficulty in applying to the fuel cell electrode as the activity of the platinum catalyst so far developed , Research and development of a method for minimizing the loss of platinum in the development and reaction of an alloy catalyst material using a small amount of platinum compared to pure platinum will be required.

Accordingly, the present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a metal catalyst for a fuel cell which can improve the efficiency of the electrical conductivity and improve the performance by reducing the metal catalyst loss during the electrochemical reaction, And a method for producing the catalyst.

It is another object of the present invention to provide a fuel cell electrode including the metal catalyst for a fuel cell and a fuel cell including the same.

In order to solve the above problems,

According to an aspect of the present invention, there is provided a method for producing a carbon-based catalyst, comprising: mixing a carbon-based catalyst carrier, a chelating agent, and a first solvent; Mixing a transition metal precursor with a second solvent to form a transition metal precursor mixture; Dispersing the carbonaceous catalyst carrier doped with the chelating agent into the transition metal precursor mixture, and adding a reducing agent to the metal catalyst to form a metal catalyst, thereby forming a metal catalyst.

In another aspect, the present invention provides an electrode for a fuel cell comprising a metal catalyst for a fuel cell manufactured according to the above-described manufacturing method.

In yet another aspect, the present invention provides a fuel cell including the electrode for a fuel cell.

According to the present invention, a chelating agent is doped to a carbon-based catalyst support, thereby making it possible to manufacture a metal catalyst for a fuel cell having a high electrochemical efficiency while reducing the content of transition metals, thereby contributing to the production of an economical fuel cell. In addition, through the two step reduction process, it is possible to exhibit the maximum carrying efficiency in the production of the metal catalyst for the fuel cell.

Figure 1 is a graphical representation of a metal catalyst prepared according to some embodiments of the present invention, 1.0M H ₂ SO ₄ A graph showing the results of the cyclic current density-voltage curve measured in the electrolytic solution.
Figure 2 is a graphical representation of a metal catalyst prepared according to some embodiments of the present invention in 1.0 M H ₂ SO ₄ + 2.0M CH ₃ OH A graph showing the results of the cyclic current density-voltage curve measured in the electrolytic solution.
Figure 3 shows a transmission electron microscope (TEM) photograph of a metal catalyst prepared according to some embodiments of the present invention. (A): Example 1, (b): Comparative Example 1, (2): Comparative Example 2)
4 is a graph showing the results of X-ray diffraction analysis (XRD) of metal catalysts prepared according to some embodiments of the present invention.

Hereinafter, the present invention will be described in detail.

According to an aspect of the present invention, there is provided a method for preparing a carbon-based catalyst carrier, comprising: mixing a carbon-based catalyst carrier, a chelating agent, and a first solvent, and adding a reducing agent to perform a primary reduction to form a chelating agent- Mixing a transition metal precursor with a second solvent to form a transition metal precursor mixture; Dispersing the carbonaceous catalyst carrier doped with the chelating agent into the transition metal precursor mixture, and adding a reducing agent to the metal catalyst to form a metal catalyst, thereby forming a metal catalyst.

As described above, the production method according to the present invention is to improve the activity of the catalyst by controlling the particle size of the metal catalyst and uniformly dispersing the metal catalyst by doping with the chelating agent. In the metal catalyst, And is 1.5 to 2.5 nm.

The chelate-doped carbon-based catalyst carrier provides a property of increasing the deposition of metal ions on the catalyst carrier and stabilizing the loading process of the metal catalyst, and such characteristics can be explained by the chelating effect. In general, covalent bonds form bonds by sharing and sharing electrons with each other, but in coordination bonding, only one atom unilaterally provides electrons and the other atom accepts electrons to form a bond. The chelating agent provides unidirectional electrons to the metal ion to form a stable coordination bond, so that the chelating agent-doped carbon-based catalyst carrier forms coordination bonds with the metal ion in more than one place. As the chelating agent and the transition metal form strong bonds, the transition metal particles can be dispersed evenly on the carbon-based catalyst carrier, and the effect of preventing the size of the transition metal particles from being developed can be obtained. do.

In addition, the manufacturing method according to the present invention increases the deposition yield by carrying out a two-step reduction process. When a carbon-based catalyst carrier, a chelating agent, and a transition metal precursor are all mixed and reduced by a one-step reduction process, a chelating agent having a strong binding force with a transition metal is combined with a transition metal before being doped in the carbon- Which results in lowering the yield of carrying. Therefore, it is possible to obtain the best carrying yield by dividing the carbon-based catalyst carrier by the two-step reduction process and reliably doping the chelating agent, and then supporting the transition metal precursor on the carbon-based catalyst carrier doped with the chelating agent.

In order to facilitate understanding of the manufacturing method of the present invention as described above, it will be described in detail as follows.

First, a carbon-based catalyst support and a chelating agent are mixed with a first solvent, followed by a primary reduction by adding a reducing agent to form a chelate-doped carbon-based catalyst support. This is a step of chemically reducing a chelating agent to a carbon-based catalyst carrier, and the carbon-based catalyst carrier is at least one selected from the group consisting of activated carbon, carbon black, graphene and carbon nanotubes having good electrical conductivity and a wide surface area It is preferable to use them.

The chelating agent may be selected from the group consisting of EDTA, EGTA, ethylenediamine, diethyltriamine, trientine, tetraethylenepentamine, pentaethylenehexamine, hexaethyleneheptamine, dipropylenetriamine, tripropylenetetramine, (2-aminopropyl) -ethanediamine oxine, and o -phenanthroline may be selected from the group consisting of hexamethylenetetramine, pentapropylene hexamine, hexapropyleneequetimine, (2-aminoethyl) -propanediamine,

The first solvent may be at least one selected from the group consisting of ethanol, methanol, ethylene glycol, diethylene glycol, triethylene glycol, and mixtures thereof. More preferably, the chelating agent having water- , And after the addition of the reducing agent, the carbon-based catalyst carrier should be stirred at 55 ° C to 60 ° C for 12 to 24 hours so that the chelating agent can be sufficiently doped, and the reducing agent may be sodium bromide, hydrazine , Sodium hydroxide and formaldehyde may be selected and used.

Also, in the above step, the content ratio of the carbon-based catalyst carrier to the chelating agent is preferably 1: 1 to 10.5. When the added amount of the chelating agent is less than the lower limit, the reaction with the carbon-based catalyst carrier is not smoothly carried out, and thus the carbon-based catalyst carrier doped with the chelating agent is not sufficiently formed. The byproducts are excessively generated in the solution due to the agglomeration phenomenon of the metal catalyst, and thus the efficiency of supporting the metal catalyst is lowered.

Next, the transition metal precursor is mixed with the second solvent to form a transition metal precursor mixture. Wherein the transition metal precursor is selected from the group consisting of Pt, Pd, Ru, Co, Ni, T and Ti, ), And the second solvent may be at least one selected from the group consisting of water, urea, ethylene glycol, diethylene glycol, triethylene glycol or a mixture thereof Can be used.

The transition metal precursor is preferably added in an amount of 10 to 30 wt% based on the carbon-based catalyst support. If the addition amount of the transition metal precursor is below the lower limit, there is a problem that the amount of the transition metal to be supported is insufficient. If the amount exceeds the upper limit, there is a problem that the unreacted compounds are agglomerated and the size of the metal catalyst particle is increased I can not.

The content of the transition metal precursor is preferably 0.01 to 10 mg / ml relative to the second solvent, more preferably 12 to 24 hours so that the transition metal precursor can be dispersed smoothly It should be well dispersed in the solvent.

Then, the carbon-based catalyst carrier doped with the chelating agent is dispersed in the transition metal precursor mixture, and a reducing agent is added thereto to form a metal catalyst by secondary reduction. This is a step of supporting the transition metal particles on the carbon-based catalyst carrier, and the mixture of the transition metal precursor mixture and the chelating agent-doped carbon-based catalyst carrier is titrated to pH 10 to 12 using an additive, And more preferably at 80 to 170 占 폚 for 4 hours to 5 hours at 200 to 600 rpm.

The transition metal particles can be more smoothly dispersed in the carbon-based catalyst carrier in the temperature range and the stirring speed range, and the reducing agent is selected from the group consisting of sodium bromohydride, hydrazine, sodium hydroxide and formaldehyde Can be used.

According to another aspect of the present invention, there is provided an electrode for a fuel cell comprising a metal catalyst for a fuel cell manufactured according to the above-described manufacturing method.

According to another aspect of the present invention, there is provided a fuel cell including the electrode for a fuel cell.

Hereinafter, the present invention will be described in more detail with reference to examples, but the scope of the present invention is not limited thereto.

Example

≪ Example 1 > Preparation of platinum catalyst by EDTA-2Na doping treatment and two-step reduction process

A carbon-based catalyst carrier solution prepared by dispersing 0.2 g of graphene oxide (GO) in 50 ml of methanol and a chelating agent solution prepared by dispersing 2.1 g of EDTA-2Na in 50 ml of methanol were mixed, And the mixture was heated and stirred at 55 to 60 ° C for 12 hours at 250 rpm and then cooled to room temperature (25 ° C).

100 ml of methanol was added to the first mixture to disperse and dilute the mixture. The mixture was filtered to obtain a powder, washed with methanol, ethanol or distilled water using a centrifuge, and freeze-dried for 24 hours.

Next, the lyophilized EDTA-doped graphene oxide (EDTA-GO) was dispersed in a platinum precursor mixture prepared by dispersing 0.058 g of chloroplatinic acid salt (H ₂ PtCl ₆ .6H ₂ O) in 53 ml of ethylene glycol , And the solution was titrated to pH 12 with 1.0 M NaOH aqueous solution and reduced. The mixture was heated and stirred at 120 rpm for 4 hours at 350 rpm, and cooled to room temperature (25 캜).

After filtering to obtain the powder of the second mixed solution, it was washed with methanol, ethanol or distilled water using a centrifuge and freeze-dried for 24 hours.

< Comparative Example  1> EDTA -2 Na  Doping and 1 Step  Preparation of Platinum Catalyst by Reduction Process

A carbon-based catalyst carrier solution prepared by dispersing 0.2 g of graphene oxide (GO) in 50 ml of methanol and a chelating agent solution prepared by dispersing 2.1 g of EDTA-2Na in 50 ml of methanol were mixed and ultrasonicated for 60 minutes &Lt; / RTI &gt;

0.058 g of chloroplatinic acid salt (H ₂ PtCl ₆ .6H ₂ O) was dispersed in the mixed solution, and the solution was titrated to pH 12 using 1.0 M NaOH aqueous solution and reduced. The mixture was heated at 120 ° C. for 4 hours at 350 rpm, Followed by cooling to room temperature (25 DEG C).

The cooled mixture solution was filtered to obtain a powder, washed with methanol, ethanol or distilled water using a centrifuge, and lyophilized for 24 hours.

< Comparative Example  2> 1 Step  Preparation of Platinum Catalyst by Reduction Process

0.058 g of chloroplatinic acid salt (H ₂ PtCl ₆ .6H ₂ O) was dispersed in 53 ml of ethylene glycol and titrated to pH 12 using 1.0 M aqueous NaOH solution for reduction.

Grapein oxide (GO) was added to the reduced mixed solution and dispersed by ultrasonic treatment for 20 minutes. Then, the mixture was heated and stirred at 120 rpm for 4 hours at 350 rpm, and then cooled to room temperature (25 캜).

The cooled mixture solution was filtered to obtain a powder, washed with methanol, ethanol or distilled water using a centrifuge, and lyophilized for 24 hours.

Experimental Example

< Experimental Example  1> Electrochemical properties

Three electrode experiments were performed on the metal catalysts for fuel cells prepared according to the Examples and Comparative Examples, and the results are shown in FIGS. 1 and 2. FIG. The relative electrode, the reference electrode, and the working electrode were immersed in an electrolyte (1.0 M H ₂ SO ₄ or 1.0 MH ₂ SO ₄ + 2.0M CH ₃ OH) to measure the circulating current density-voltage curve.

1, platinum catalysts prepared by EDTA-2Na doping and 2-step reduction processes according to Example 1 have a wider hydrogen adsorption peak than platinum catalysts prepared according to Comparative Example 1 and Comparative Example 2 Can be confirmed. This indicates that the performance of the platinum catalyst is improved by the process of doping the carbon-based catalyst carrier with EDTA-2Na and the two-step reduction process.

The above hydrogen absorption peaks can be compared on the basis of the electrochemical active surface area (ESA), and the electrochemically active surface area (ESA) can be determined by the direct contact area when the platinum catalyst reacts with the fuel Can be calculated from the following equation.

(ESA: electrochemically active surface area, [M]: weight of metal reacting with metal and fuel in electrode catalyst, Q _H : hydrogen adsorption area)

The electrochemically active surface area (ESA) calculated from the above equation is expressed in units of m ² / g, and the results are shown in Table 1.

Types of Electrode Catalyst ESA  (m ² / g) Example 1 Pt / EDTA-GO (2 steps) 64 Comparative Example 1 Pt / EDTA-GO (1step) 55 Comparative Example 2 Pt / GO 36

Referring to Table 1, the Pt / EDTA-GO (2Step) electrode catalyst prepared according to Example 1 exhibited the highest electrochemically active surface area (ESA) of 64 m ² / g, / EDTA-GO (1Step) The electrochemically active surface area (ESA) of the electrocatalyst was 55 m ² / g, and the Pt / GO electrode catalyst prepared according to Comparative Example 2 had an electrochemically active surface area (ESA) of 36 m ² / g.

From the above results, it can be seen that the larger the active surface area of the electrode catalyst, the wider the hydrogen adsorption peak, and it can be confirmed that the direct hydrogen adsorption of the platinum catalyst by the EDTA-2Na doping treatment and the two step reduction process of the carbon- As the area increases, the current density and the activity of the catalyst are improved.

FIG. 2 shows the results of cyclic current density-voltage curves measured on a platinum catalyst prepared according to Examples and Comparative Examples in a 1.0 M H ₂ SO ₄ + 2.0 M CH ₃ OH electrolyte. Generally, a cell reaction in the presence of a methanol electrolyte shows a peak due to a reaction between metal particles and methanol, and a peak due to a reaction in which reaction intermediates such as carbon monoxide (CO) strongly adsorb to metal particles. If the intermediate product such as carbon monoxide (CO) is strongly adsorbed on the metal catalyst particles, the electrochemically active surface area (ESA) of the electrode catalyst is reduced, which causes the efficiency of the battery to be lowered.

Referring to FIG. 2, two oxidation peaks can be identified. The first peak (I _F ) is a peak indicating the degree of oxidation of methanol. The second peak (I _R ) Of the adsorbent. The above I _F And I _R , The I _F / I _R ratio according to the present invention describes the electrocatalytic function of the electrode surface, and the higher the ratio, the less the adsorption of carbon monoxide (CO), which is an intermediate carbon species, on the surface of the electrocatalyst.

I _{F ,} I _R according to the above result And I _F / I _R ratio are shown in Table 2.

Types of Electrode Catalyst I _F ( mA / cm ² ) I _R ( mA / cm ² ) I _F / I _R Ratio Example 1 Pt / EDTA-GO (2 steps) 3.8 1.1 3.45 Comparative Example 1 Pt / EDTA-GO (1step) 2.6 0.8 3.25 Comparative Example 2 Pt / GO 1.8 0.6 3.00

Referring to Table 2, the Pt / EDTA-GO (2Step) electrode catalyst prepared according to Example 1 exhibited the highest I _F / I _R ratio of 3.45, and Pt / EDTA-GO (1Step) electrode catalyst was 3.25, and the Pt / GO electrode catalyst prepared according to Comparative Example 2 had an I _F / I _R ratio of 3.00. This indicates that the degree of adsorption of the intermediate carbon species on the surface of the Pt / EDTA-GO electrode catalyst prepared according to Example 1 is reduced, thereby increasing the electrochemically active surface area (ESA) of the electrode catalyst, The performance of the second embodiment is improved.

<Experimental Example 2> Crystallinity analysis

In order to analyze the crystallization degree and the particle size of the metal catalyst for a fuel cell manufactured according to the examples and the comparative examples, a transmission electron microscope (TEM) and an X-ray diffractometer (XRD PHILIPS, Xpert PRO MRD) The results are shown in FIG. 3 and FIG.

Referring to FIG. 3, it can be seen that the Pt / EDTA-GO (2Step) electrode catalyst prepared according to Example 1 has a very uniform distribution of small size metal catalyst particles, In the case of the Pt / EDTA-GO (1 step) electrode catalyst, it was confirmed that metal catalyst particles of a small size were uniformly distributed, but that some agglomerated metal catalyst particles were distributed. In the case of the Pt-GO electrode catalyst, large particles are distributed by the aggregation of the metal catalyst particles as a whole.

In addition, X- ray pattern exhibited by the diffraction (XRD), and is to confirm information on a random grid of light scattering from the lattice interval of each metal, by default, the integrated value (intensity), and each 2 θ (degree) Is given. X- ray diffraction analysis (XRD) pattern of the case of pure platinum is the [111] structure in each of 2 θ angle of 39 °, the [200] structure at 46 °, and the [220] structures appear in the 68 °, this Values refer to values when the diffraction peak is at maximum.

Referring to FIG. 4, it can be seen that the peak shifts due to the EDTA doping treatment on graphene oxide (GO), and more specifically, the value of 2 θ is changed from 39 ° to 40.5 °, from 46 ° to 46.3 °, from 68 ° 68.35 °, respectively. This means that the doping treatment of graphene oxide (GO), which is a catalyst carrier, with EDTA improves the loading efficiency of the platinum catalyst.

From the above results, the particle size of the electrode catalyst was calculated using the following Scherer's equation.

(the average size of the particles,?: the wavelength of the X-ray (= 1.54056 ? ),? _max : the angle at which the peak is at its peak , B _{2 ?:} the peak width at half the height of the maximum peak)

The average size of the platinum catalyst particles calculated from the above formula is shown in Table 3.

Types of Electrode Catalyst Average size of particles ( nm ) Example 1 Pt / EDTA-GO (2 steps) 2.3 Comparative Example 1 Pt / EDTA-GO (1step) 2.8 Comparative Example 2 Pt / GO 3.6

Referring to Table 3, it can be seen that the Pt / EDTA-GO (2Step) electrode catalyst prepared according to Example 1 has the smallest average particle size. From the above results, it can be seen that as the particle size of the electrode catalyst decreases, the electrochemically active surface area (ESA) directly contacting with the fuel increases and the activity of the electrode catalyst increases.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but variations and modifications may be made by those skilled in the art without departing from the scope and spirit of the invention. Do.

Claims (14)

Mixing the carbon-based catalyst carrier, the chelating agent and the first solvent, and adding a reducing agent to the carbon-based catalyst carrier to form a chelate-doped carbon-based catalyst carrier;
Mixing a transition metal precursor with a second solvent to form a transition metal precursor mixture;
Dispersing the carbonaceous catalyst carrier doped with the chelating agent in the transition metal precursor mixture, and adding a reducing agent to the metal catalyst carrier to form a metal catalyst. The method according to claim 1,
Wherein the metal catalyst for a fuel cell has a diameter of 1.5 to 2.5 nm. The method according to claim 1,
Wherein the carbon-based catalyst carrier is at least one selected from the group consisting of activated carbon, carbon black, graphene, and carbon nanotubes. The method according to claim 1,
The chelating agent may be selected from the group consisting of EDTA, EGTA, ethylenediamine, diethyltriamine, trientine, tetraethylenepentamine, pentaethylenehexamine, hexaethyleneheptamine, dipropylenetriamine, tripropylenetetramine, (2-aminopropyl) -ethanediamine oxine and &lt; RTI ID = 0.0 &gt; o -phenanthroline, &lt; / RTI &gt; characterized in that the fuel is at least one selected from the group consisting of pentapropylene hexamine, hexapropylene & A method for producing a metal catalyst for a battery. The method according to claim 1,
Wherein the content ratio of the carbon-based catalyst carrier to the chelating agent is 1: 1 to 10.5. The method according to claim 1,
Wherein the first solvent is at least one selected from the group consisting of ethanol, methanol, ethylene glycol, diethylene glycol, triethylene glycol, and mixtures thereof. The method according to claim 1,
Wherein the transition metal precursor is at least one transition metal selected from the group consisting of Pt, Pd, Ru, Co, Ni, W and Ti. Wherein the metal compound is a compound containing at least one metal element selected from the group consisting of iron and iron. The method according to claim 1,
Wherein the transition metal precursor is added in an amount of 10 to 30 wt% based on the carbon-based catalyst support. The method according to claim 1,
Wherein the second solvent is at least one selected from the group consisting of urea, ethylene glycol, diethylene glycol, triethylene glycol, and mixtures thereof. The method according to claim 1,
Wherein the transition metal precursor is mixed at a rate of 0.01 to 10 mg / ml with respect to the second solvent. The method according to claim 1,
Wherein the reducing agent is at least one selected from the group consisting of sodium borohydride, hydrazine, sodium hydroxide, and formaldehyde. 12. A metal catalyst for a fuel cell produced by the production method according to any one of claims 1 to 11. An electrode for a fuel cell comprising the metal catalyst for a fuel cell according to claim 12. 14. A fuel cell comprising an electrode for a fuel cell according to claim 13.

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