KR20060105957A - Co-b catalyst for hydrogen generating reaction using alkaline borohydrides solution and method to prepare the same - Google Patents

Abstract

In the present invention, the hydrogen release using the alkali boron hydride solution, the hydrogen release using the alkali boron hydride solution, characterized in that it comprises any one or both of the oxides of Co and B or the compounds of Co and B It provides a Co-B catalyst for the reaction. Moreover, in this invention, in the manufacturing method of the catalyst for hydrogen release reaction using an alkali boron hydride solution, alkali boron hydride as a reducing agent Reducing Co ²⁺ using the solution (S1); And drying and calcining the precipitated catalyst after reduction, to obtain a catalyst comprising any one or two of oxides of Co and B or a compound of Co and B (S2). Provided is a method for preparing a Co-B catalyst for hydrogen evolution using a solution. Since the Co-B catalyst for hydrogen release reaction using the alkali boron hydride solution according to the present invention has a higher activity of 30-50% or more than the Ru catalyst, which is a noble metal catalyst, it is a non-noble metal catalyst unlike commercial Co metal catalysts. It can replace precious metal catalysts such as expensive Ru.

Boron hydride, ruthenium, hydrogen, catalyst, polymer electrolyte membrane fuel cell

Description

Co-B catalyst for hydrogen generating reaction using alkaline borohydrides solution and method to prepare the same}

1 is a schematic view showing a hydrogen generation experimental apparatus in an experimental example of the present invention.

Figure 2 shows the XRD pattern of each of (a) Co metal powder catalyst of Comparative Example and (b) catalyst prepared in Example according to the present invention.

Figure 3 shows an SEM image of the catalyst prepared in the embodiment of the present invention.

FIG. 4 is a graph showing the effect of temperature upon hydrogen evolution from a 20 wt% NaBH ₄ + 5 wt% NaOH solution using 0.05 g Co-B catalyst (catalyst prepared in Example) in the experimental example of the present invention. .

FIG. 5 shows the effect of the amount of catalyst upon hydrogen evolution from a 20 wt% NaBH ₄ + 5 wt% NaOH solution at 20 ° C. when using a Co-B catalyst (catalyst prepared in Example) in the experimental example of the present invention. It is a graph.

6 shows the effect of NaBH ₄ concentration upon hydrogen evolution from x wt% NaBH ₄ + 5 wt% NaOH solution at 20 ° C. when 0.05 g Co-B catalyst (catalyst prepared in Example) was used in the experimental example of the present invention. Is a graph showing

7 is 20 wt% NaBH ₄ + x at 20 ° C. when 0.05 g Co-B catalyst (catalyst prepared in Example) was used in the experimental example of the present invention. A graph showing the effect of NaOH concentration on hydrogen evolution from wt% NaOH solution.

8 is 20 wt% NaBH ₄ + x at 20 ° C. when 0.05 g Co catalyst (comparative catalyst) was used in the experimental example of the present invention. A graph showing the effect of NaOH concentration on hydrogen evolution from wt% NaOH solution.

FIG. 9 is a graph showing hydrogen generation rate and volume generated from 5 wt% NaBH ₄ + 5 wt% NaOH at 20 ° C. using the catalyst prepared in Example in the Experimental Example of the present invention. FIG.

* Short description of the major reference marks *

5: cooling water 10: reactor

20 mass flow meter 25 personal computer

30: thermostat

1. H.I. Schlesinger, H.C. Brown, A.E. Finholt, J.R. Gilbreath, H. R. Hockstra, and E.K. Hyde: "Sodium Borohydride, Its Hydrolysis and Its Use as a Reducing Agent and in the Generation of Hydrogen", J. Am. Chem. Soc., Vol. 75, 1953, p. 215;

2. S.C. Amendola, S.L. Sharp-Goldman, M.S. Janjua, M.T. Kelly, P.J. Petillo, and M. Binder: "An Ultrasafe Hydrogen Generator: Aqueous, Alkaline Borohydride Solution and Ru Catlayst", J. power sources, Vol. 85, 2000, p. 186;

3. S.C. Amendola, S.L. Sharp-Goldman, M.S. Janjua, N.C. Spencer, M.T. Kelly, P.J. Petillo, and M. Binder: "A Safe, Portable, Hydrogen Gas Generator Using Aqueous Borohydride Solution and Ru Catalyst", Int. J. Hydrog. Energy, 25 (2000) 969;

4. J.-H. Kim, H. Lee, S.-C. Han, H.-S. Kim, M.-S. Song, J.-Y. Lee,: "Production of hydorgen from sodium borohydride in alkaline solution: development of catalyst with high performance". Int. J. Hydrog. Energy, vol. 29, 2004, p. 263;

5. I.-H. Oh, S. K. Park, E. A. Cho, H. Y. Ha, and S.-A. Hong,: "Characteritics of the Monopolar Type Small Polymer Electrolyte Membrane Fuel Cell for Portable Sources", 1st International Conference on Polymer Batteries and Fuel Cells, 2003;

6. D. Hua, Y. Hanxi, A. Xingping, C. Chuansin: "Hydrogen production from catalytic hydrolysis of sodium borohydride solution using nickel boride catalyst". Int. J. Hydrog. Energy, vol. 28, 2003, p. 1095.

The present invention relates to a cobalt-boron catalyst for hydrogen release reaction using an alkali boron hydride solution and a method for producing the same.

Polymer Electrolyte Membrane Fuel Cell (PEMFC) is a fuel cell with high efficiency and power density. To use it as a portable power source, hydrogen, a fuel, must be stored and carried.

As a hydrogen storage method, a method of storing with a high pressure hydrogen gas, a method of storing with a liquid hydrogen gas, a method of storing with a metal hydride, a method of reforming fossil fuels and the like are currently used. However, these methods are difficult to apply to portable fuel cells in terms of hydrogen storage volume, weight, safety, response characteristics, and the like.

Therefore, in order to commercialize a PEMFC for a portable power source, development of a hydrogen storage technology suitable for a portable device must be preceded.

One of the alternatives to the hydrogen storage methods is a method using NaBH ₄ aqueous solution. Hydrogen generation reaction using NaBH ₄ aqueous solution is as shown in the following [Scheme 1].

NaBH ₄ (aq) + 2H ₂ O → 4H ₂ + NaBO ₂ (aq) + heat (217 kJ)

In the acidic or neutral solution, the reaction proceeds without the catalyst, but under strong basic conditions (pH> 13), the reaction proceeds only when contacted with the catalyst to control the rate of hydrogen generation.

The hydrogen storage method using NaBH ₄ has a high energy storage density, a nonflammable reactant and a product, is stable in the atmosphere, harmless to the environment, recyclable of the reactant, and hydrogen can be generated at room temperature. It has many advantages as a storage method (see the prior art document 3). In addition, since hydrogen is generated from the aqueous solution, water vapor is included and released, so that the water supply for driving the fuel cell can be supplied without additional humidification.

Due to these various advantages, many studies have been conducted to apply the hydrogen storage method using the NaBH ₄ to the fuel cell (see the prior art documents 2 to 5).

By the way, in order to release hydrogen stored using NaBH ₄ , the NaBH ₄ aqueous solution must be brought into contact with the catalyst. However, in most of the studies to date, Pt or Ru-based noble metal catalysts have been used (see prior art documents 2 to 3). However, the precious metal catalysts have a big disadvantage in that the cost is low and the economic efficiency is low.

On the other hand, as a non-noble metal catalyst, Ni and Co show activity, but it is reported that hydrogen discharge rate is very low compared with Pt or Ru (refer prior art document 4,5).

Therefore, there is a need for a catalyst for hydrogen release reaction from alkaline NaBH ₄ solution with high hydrogen release rate as a non-noble metal catalyst to replace Pt or Ru.

On the other hand, NaBH ₄ has been used as a hydrogen storage and release medium until now, but there is a great need for developing a boron hydride other than NaBH ₄ as a hydrogen storage release medium and a catalyst used for the hydrogen release reaction of the boron hydride.

Accordingly, the present invention has been made to solve the above problems, an object of the present invention, as a non-noble metal catalyst that can replace the precious metal catalyst Pt or Ru, unlike the conventional commercial Co metal powder catalyst, high activity It is to provide a catalyst for hydrogen release reaction using an alkali boron hydride solution and a method for producing the same.

An object of the present invention as described above is an alkali boron hydride, comprising any one or two of an oxide of Co and B or a compound of Co and B as a catalyst for hydrogen release reaction using an alkali boron hydride solution Achieved by Co-B catalyst for hydrogen release reaction using a solution.

An object of the present invention as described above is an alkali boron hydride as a reducing agent in the method for producing a catalyst for hydrogen release reaction using an alkali boron hydride solution. Reducing Co ²⁺ using the solution (S1); And drying and calcining the precipitated catalyst after reduction, so as to obtain a catalyst comprising one or two of oxides of Co and B or a compound of Co and B (S2). It is achieved by a method for producing a Co-B catalyst for hydrogen release reaction using a digestion solution.

In addition, the step S1 is an alkali boron hydride solution used as the reducing agent, an alkali boron hydride solution of any one of NaBH ₄ , KBH ₄ or LiBH ₄ boron hydride and NaOH or KOH hydroxide Preference is given to using. And, the S2 step is preferably carried out the drying and firing in a nitrogen or hydrogen atmosphere.

As described above, in the present invention, when boron hydrides such as KBH ₄ or LiBH ₄ as well as NaBH ₄ are used as hydrogen storage and release mediums, hydrogen hydride reactions using boron hydride solutions such as NaBH ₄ , KBH ₄ or LiBH ₄ are used. Co-B catalyst is proposed as a high activity non-noble metal catalyst that can be used.

The Co-B catalyst comprises an oxide of Co-B or a compound form of Co-B, such a Co-B catalyst is obtained by reducing Co ²⁺ with an alkali boron hydride solution.

Hereinafter, the present invention will be described in more detail by explaining preferred embodiments of the present invention. However, the present invention is not limited to the following examples, and various forms of embodiments can be implemented within the scope of the appended claims, and the following examples are only common in the art while making the disclosure of the present invention complete. It is intended to facilitate the implementation of the invention to those with knowledge.

<Example>

Co-B Catalyst Preparation

A precursor aqueous solution of CoCl ₂ (Aldrich Inc.) 1 M was prepared to prepare a Co-B catalyst. NaBH ₄ and NaOH aqueous solution were used as reducing agents (ie, alkali borohydride). By using the solution as a reducing agent, in addition to NaBH ₄ , KBH ₄ or LiBH ₄ may be used as the alkali boron hydride, and KOH may be used in addition to NaOH as the hydroxide). The NaBH ₄ generates hydrogen even without a catalyst when dissolved in water, so that NaOH was added to keep the solution in an alkaline state.

In order to prepare a reducing solution, NaOH was first dissolved in distilled water while maintaining the pH of the aqueous solution at 14 or more, NaBH ₄ was dissolved and stirred for at least 4 hours. While maintaining the 1 M CoCl ₂ aqueous solution prepared to control the reaction rate at 0 ℃, 1 g of NaBH ₄ and NaOH aqueous solution was added to reduce the Co ²⁺ .

After the reaction was completely completed, the precipitated powder was filtered using a filter paper and washed with distilled water. The prepared catalyst was dried at 60 ° C. nitrogen atmosphere (or hydrogen atmosphere) and then calcined at 200 ° C. nitrogen atmosphere (or hydrogen atmosphere) for 2 hours. The prepared catalyst was kept sealed in a nitrogen atmosphere and the following experiment was performed.

Comparative Example

In order to compare with the catalyst prepared in this Example, a commercial Co metal powder was prepared and the following experiment was performed.

Experimental Example

Catalytic Characterization and Results

X-Ray Diffraction (XRD), Atomoc Absorption Spectroscopy (AAS), Scanning Electron Microscopy (SEM) and Brunauer-Emmett-Teller (BET) analyzes were performed to investigate the structure and composition, surface morphology and surface area of the catalyst.

Figure 2 shows the XRD pattern of each of (a) the commercial Co metal powder of Comparative Example and (b) the catalyst prepared in Example.

As shown in FIG. 2, XRD spectra of the catalyst of the present Example prepared by the reduction method were obtained by performing XRD analysis on the commercial Co metal powder as a comparative example and the catalyst of the present Example to investigate the structure of the catalyst prepared in powder form. Unlike Co metal powder of Comparative Example, Co ₃ O ₄ peaks were observed. This means that the catalyst of the present embodiment is in an oxide state rather than a metal state.

Meanwhile, AAS analysis was performed to investigate the composition of the prepared catalyst. Table 1 shows the results of elemental analysis of the catalyst prepared in this example by ASS.

Fe Ni Si Mg Mn P B Cu 10 ^-3 10 ^-2 10 ^-2 10 ^-4 10 ^-3 10 ^-3 10 ⁰ 10 ^-3 Na Co Ca Al K Sr S Cl 10 ^-3 10 ⁰ 10 ^-3 10 ^-3 10 ^-3 10 ^-3 10 ^-3 10 ^-3

As shown in Table 1, the composition of the catalyst prepared in this example was found to be composed mostly of Co and B. No oxygen was detected in the AAS analysis.

As such, from the XRD and AAS analysis results, the catalyst of this example is in the form of an oxide of Co-B, such as (Co _x B _y ) ₃ O ₄ , or Co ₃ O ₄ and Co-B compounds such as CoB or Co ₂ B are mixed. I could see that. However, since no peaks of CoB or Co ₂ B were observed in the XRD analysis results, it was determined that the Co-B compound was present even in the presence of a small amount or low crystallinity.

3 shows an SEM image of the catalyst prepared in this example. As shown in Figure 3, it can be seen that the catalyst of the present embodiment is a spherical shape of a relatively uniform particle size. As a result of BET analysis using nitrogen adsorption method, the BET surface area of the catalyst was 77 m ² / g.

Hydrogen Generation Experiment

1 is a schematic view showing a hydrogen generation experimental apparatus of the present experimental example.

As shown in FIG. 1, a NaBH ₄ solution and a catalyst are placed in a reactor 10 having a diameter of 4 cm and a height of 10 cm capable of measuring internal temperature and pressure, and the amount of hydrogen generated is measured by a mass flow meter (MFM). 20 and recorded it with a personal computer 25. Since the hydrogen evolution reaction is an exothermic reaction, a temperature controller 30 is installed outside the reactor, and the cooling water 5 is circulated to maintain a constant temperature of the solution.

In order to investigate the NaBH ₄ hydrogen emission reaction characteristics using the prepared catalyst, the rate of hydrogen evolution was measured while varying the solution temperature, catalyst usage, NaBH ₄ concentration, and NaOH concentration.

In the case of the catalyst prepared in Example, the hydrogen generation result according to the reaction temperature

In order to investigate the effect of reaction temperature on the activity of Co-B catalyst, the rate of hydrogen evolution was measured from 20 wt% NaBH ₄ + 5 wt% NaOH aqueous solution at 10-30 ° C.

FIG. 4 is a graph showing the effect of temperature upon hydrogen generation from a 20 wt% NaBH ₄ + 5 wt% NaOH solution when using 0.05 g Co-B catalyst in the experimental example of the present invention.

As shown in FIG. 4, as in the Ru catalyst, as the catalyst is activated, the reaction rate increases and then becomes constant, indicating that the reaction rate is a zero-order reaction regardless of time. At 10 ° C, hydrogen was generated at 460 mL / min · g, and as the solution temperature increased to 20 ° C and 30 ° C, the rate of hydrogen evolution at 1,800 sec increased from 1,000 mL / min · g to 2,800 mL / min · g. . Considering that the hydrogen generation rate of the Ru powder catalyst at 20 ° C. was about 3,000 mL / min · g, the activity of the non-noble metal Co-B catalyst was found to be quite high.

Hydrogen generation results according to the amount of catalyst prepared in the examples

The rate of hydrogen evolution from 20 wt% NaBH ₄ + 5 wt% NaOH solution at 20 ° C. was measured to investigate the effect of the amount of Co—B catalyst on the activity upon hydrogen evolution.

FIG. 5 is a graph showing the effect of the amount of catalyst upon hydrogen generation from a 20 wt% NaBH ₄ + 5 wt% NaOH solution at 20 ° C. when the Co-B catalyst was used in the experimental example of the present invention.

As shown in FIG. 5, the hydrogen generation rate was measured while varying the amount of Co-B catalyst, and the reaction rate was also initially increased and then showed a substantially constant value. As the amount of the catalyst increased, the maximum reaction rate increased. This is because the higher the amount of catalyst, the more active the initial activation, the reaction heat is not removed locally and the temperature is increased.

On the other hand, even after increasing the amount of catalyst from 0.002 g to 0.09 g, the hydrogen generation rate was almost constant at 1,000 mL / min · g after stabilization. This means that since the Co-B catalyst prepared in the example is a powder type catalyst, it is not affected by the material transfer resistance, and thus the hydrogen generation rate per unit weight is constant regardless of the amount of catalyst used. Therefore, if the hydrogen generated here is used in the fuel cell, the amount of catalyst required for the hydrogen generator can be calculated from the amount of hydrogen consumed in the fuel cell stack.

NaBH for the catalyst prepared in the examples ₄  Hydrogen generation result by concentration

In the case of generating hydrogen using a Co-B catalyst, the hydrogen evolution rate was measured according to the concentration change of NaBH ₄ in order to select the optimal solution condition.

6 is a graph showing the effect of NaBH ₄ concentration upon hydrogen generation from x wt% NaBH ₄ + 5 wt% NaOH solution at 20 ° C. when 0.05 g Co-B catalyst was used in the experimental example of the present invention.

As shown in FIG. 6, as the concentration of NaBH ₄ solution was increased, the rate of hydrogen generation was decreased. However, as increasing to 10 wt%, 20 wt% and 30 wt%, the hydrogen evolution rate decreased from 1,345 mL / min · g to 1,000 mL / min · g and 760 mL / min · g, respectively, at 1,800 seconds. . The reason for the decrease in hydrogen generation rate is that the viscosity of the solution increases with increasing NaBH ₄ concentration, thereby increasing the material transfer resistance.

However, compared with Ru catalyst, the generation rate of hydrogen was decreased with increasing NaBH ₄ concentration, which is lower than the supported catalyst in the case of powder catalyst such as Co-B catalyst prepared in Example. It was judged that.

Example Results of Hydrogen Evolution According to NaOH Concentration

When Co-B catalyst was used, the hydrogen evolution rate was measured according to the concentration of NaOH.

7 is 20 wt% NaBH ₄ + x at 20 ° C. when 0.05 g Co-B catalyst is used in the experimental example of the present invention. A graph showing the effect of NaOH concentration on hydrogen evolution from wt% NaOH solution.

As shown in FIG. 7, when the NaOH concentration was 1 wt%, the hydrogen evolution rate was 550 mL / min · g, but when the NaOH concentration was 3 wt% and 5 wt%, 885 mL / min · g and 1,000 mL / min · g, respectively. 10 ~ 20wt% was about 1,200 mL / min · g. In the case of Ru catalyst, as the NaOH concentration was increased, the hydrogen generation rate was reversed.

This means that the hydrogen generating mechanism is different when the Ru catalyst and the Co-B catalyst are used. In other words, in the case of using the Ru catalyst, when H ⁺ is involved in the hydrogen generating mechanism and the OH ⁻ ion concentration is increased, the generated H ⁺ may be recombined with OH ⁻ to decrease the hydrogen generation rate. On the other hand, in the case of Co-B, OH ^- is involved in the hydrogen evolution reaction, the higher the OH ^- ion concentration is expected to increase the hydrogen generation rate.

Hydrogen generation results according to NaOH concentration

8 is 20 wt% NaBH ₄ + x at 20 ° C. with 0.05 g of Co catalyst of the comparative example. A graph showing the effect of NaOH concentration on hydrogen evolution from wt% NaOH solution.

As shown in Figure 8, the increase in hydrogen generation rate with increasing NaOH concentration was observed even when using a commercial Co metal catalyst, such as the Co-B catalyst of the present embodiment. Furthermore, this phenomenon has been reported for Ni catalysts, but the exact mechanism has not yet been identified.

EXAMPLES Hydrogen Generation Ability for Catalysts

FIG. 9 is a graph showing the rate and volume of hydrogen evolution from 5 wt% NaBH ₄ + 5 wt% NaOH at 20 ° C. with the catalyst prepared in this Example.

The theoretical volume of hydrogen obtainable from a 5 wt% NaBH ₄ solution is 5.07 L at 20 ° C., but as shown in FIG. 9, the final volume of hydrogen obtained in this experiment is 4.77 L, about 94% of the theoretical amount. It can be seen that is released.

In terms of the rate of hydrogen generation, the rate of hydrogen evolution is rapidly increased initially, which is the area where the catalyst is activated. After that, the rate of hydrogen generation remains substantially constant and increases slightly, and then the hydrogen evolution reaction is terminated as the reactants are consumed. The slightly increased rate of hydrogen evolution over time is consistent with the increase of NaOH as the concentration of NaOH increases as the pH increases as the reaction proceeds.

Hydrogen Supply to the Cell Stack

Based on the above results, the catalyst prepared in the present example was adopted in the hydrogen supply system, and hydrogen was supplied to the 2W PEMFC stack (cell phone class). As a result, the stack was successfully operated.

conclusion

In this embodiment, a Co-B catalyst for hydrogen evolution using an aqueous NaBH ₄ solution was prepared by chemical reduction. The catalyst prepared in this example was a Co-B oxide or a Co-B compound, and exhibited a hydrogen generation rate of 1,000 ml / min · g or more. Since it has a higher activity of 30 to 50% than the Ru catalyst, the Co-B catalyst of the present embodiment can replace the expensive Ru catalyst.

On the other hand, using the Co-B catalyst of the present embodiment was measured the hydrogen generation rate according to the solution temperature, catalyst amount, NaBH ₄ concentration, NaOH concentration. Hydrogen evolution was a zero-order reaction in which the reaction rate remained constant over time. The rate of hydrogen evolution increased with increasing solution temperature and increased in proportion to the amount of catalyst used. As the concentration of NaBH ₄ increased, the rate of hydrogen evolution decreased due to an increase in the viscosity of the solution. As the concentration of NaOH increases, the rate of hydrogen evolution increases, and the rate of hydrogen evolution using an alkaline NaBH ₄ aqueous solution increases the pH as the reaction proceeds, so that the rate of hydrogen evolution spontaneously increases over time.

On the other hand, as a result of producing a hydrogen supply system to supply hydrogen to the fuel cell based on the above results it was able to successfully drive the fuel cell.

Co-B catalyst prepared in the present embodiment not only has high activity as a catalyst for hydrogen evolution using alkaline NaBH ₄ aqueous solution, but is also used as a catalyst for hydrogen evolution in other boron hydrides such as KBH ₄ or LiBH ₄ . High activity.

Since the Co-B catalyst for hydrogen release reaction using the alkali boron hydride solution according to the present invention has a higher activity of 30-50% or more than the Ru catalyst, which is a noble metal catalyst, it is a non-noble metal catalyst unlike commercial Co metal catalysts. It can replace precious metal catalysts such as expensive Ru.

Although the present invention has been described in connection with the above-mentioned preferred embodiments, it is possible to make various modifications or variations without departing from the spirit and scope of the invention. Accordingly, the appended claims will cover such modifications and variations as fall within the spirit of the invention.

Claims (4)

As a catalyst for hydrogen release reaction using an alkali boron hydride solution, Co-B catalyst for hydrogen release reaction using an alkali boron hydride solution, characterized in that it comprises an oxide of Co and B or a compound of Co and B. In the method for producing a catalyst for hydrogen release reaction using an alkali boron hydride solution, Alkali boride hydride as reducing agent Reducing Co ²⁺ using the solution (S1); And Alkali borohydride solution, comprising the step (S2) of drying and calcining the precipitated catalyst after reduction to obtain a catalyst comprising any one or both of oxides of Co and B or compounds of Co and B Method for producing a Co-B catalyst for hydrogen evolution reaction using. The method of claim 2, The step S1 is an alkali boron hydride solution used as the reducing agent, using an alkali boron hydride solution in which any one of NaBH ₄ , KBH ₄ or LiBH ₄ boride and a hydroxide of NaOH or KOH is mixed. A method for producing a Co-B catalyst for hydrogen evolution using an alkali boron hydride solution, characterized in that The method of claim 3, wherein The step S2 is a method of producing a Co-B catalyst for hydrogen release reaction using an alkaline boron hydride solution, characterized in that the drying and firing in a nitrogen or hydrogen atmosphere.

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