KR100785043B1 - Co-b catalyst/structured support for hydrogen generating using alkaline borohydrides solution and method for preparing the same - Google Patents

Abstract

A cobalt-boron catalyst/carrier for generating hydrogen and a method for manufacturing the same are provided to improve the activity of the catalyst, reduce the loss of catalyst in a continuous circulation type reaction, and substitute for noble metal catalysts, by manufacturing the cobalt-boron catalyst/carrier using an alkaline borohydride solution. A cobalt-boron catalyst/carrier for generating hydrogen is manufactured by using an alkaline borohydride solution. One or two types of cobalt-boron catalysts are supported on a carrier, wherein the one or two types of cobalt-boron catalysts are cobalt-boron oxides or cobalt-boron compounds except cobalt-carbon oxides. The alkaline borohydride solution is prepared by mixing one hydroxide selected from NaOH and KOH into one borohydride selected from NaBH4, KBH4, and LiBH4.

Description

Co-B catalyst / structured support for hydrogen generating using alkaline borohydrides solution and method for preparing the same}

1 is a photograph (a) of a porous carrier and a photograph (b) of a catalyst / carrier according to an embodiment of the present invention.

Figure 2 shows the molar ratio by the ICP results of the catalyst prepared in this example.

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

4 is a graph showing the amount of hydrogen released according to the change of precursor concentration (precursor).

5 shows each XRD pattern according to the heat treatment temperature when the Co-B catalyst / support of the present embodiment is heat treated.

FIG. 6 shows respective SEM images according to the heat treatment temperatures of the catalyst / carrier prepared in this example.

FIG. 7 is a graph showing the effect of calcination temperature upon hydrogen generation from a 25 wt% NaBH ₄ + 3 wt% NaOH solution in the case of Co-B / Ni.

8 is a graph showing the physical catalyst loss rate with time of the Co-B catalyst prepared by firing temperature in the experimental example of the present invention.

* Short description of the major reference marks *

10: hydrogen evolution reactor 11: agitator

12: thermocouple 13: temperature control device

14 mass wander meter 15 water jacket

20: hydrogen generation flow 31: cooling water inflow

32: cooling water outflow 40: NaBH ₄ solution

50: Co-B / Ni

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 (hereinafter referred to as "Co-B") catalyst / support for hydrogen release reaction using an alkali boron hydride solution and a method for producing the same.

In the present specification, "Co-B catalyst" means a catalyst which is either one or two of an oxide to which Co and B are bonded or a compound to which Co and B are bonded (except for an oxide to which Co and B are bonded).

In the present specification, "catalyst / support" means that the catalyst is supported on the support.

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

As the hydrogen storage method, a high pressure hydrogen gas storage method, a liquid hydrogen gas storage method, a metal hydride storage method, a fossil fuel reforming method and the like are used.

However, existing methods are difficult to apply to portable fuel cells in terms of hydrogen storage volume and weight, safety and response characteristics.

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

One alternative to the existing hydrogen storage methods is the use of aqueous NaBH ₄ 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 a catalyst, but under strong basic conditions (pH> 13), the reaction proceeds only when contacted with the catalyst, and thus the rate of hydrogen evolution can be controlled by the addition of a base condition and a catalyst. See 2>.

As such, when hydrogen is stored using NaBH ₄ , the energy storage density is high, and the reactants and the product are nonflammable. It also has the advantage of being stable in the atmosphere, harmless to the environment, and allowing the recycling of the reactants. Further, hydrogen can be generated even at room temperature (see the prior art document 3). In addition, since hydrogen is generated from the aqueous solution, water is released, including water vapor, and thus, it is possible to supply water required for driving the fuel cell without additional humidification.

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

However, as described above, in order to release hydrogen stored using NaBH ₄ , the catalyst must be contacted with an aqueous NaBH ₄ solution. For this purpose, a noble metal catalyst of the Pt or Ru series was used in the past. See 3>.

However, since the precious metal catalysts are expensive, there is a problem that significantly lowers the economics of the entire PEMFC.

As a result, studies have been conducted to use non-noble metal catalysts rather than noble metal catalysts, but non-metal catalysts such as Ni and Co have been reported to have very low hydrogen release rates compared to Pt or Ru even though they exhibit activity. See references 4 and 5>.

Therefore, there is a great need for the development of a non-metal catalyst capable of increasing the rate of hydrogen release as a non-noble metal catalyst to replace Pt or Ru.

On the other hand, there is also an existing need for a study wherein the available catalyst with possible use of different boron hydride NaBH ₄ solution in addition came with a solution of NaBH ₄ as a hydrogen evolution reaction solution as the hydrogen storage media.

In addition, the conventional non-noble metal catalyst does not exhibit any problems when using a batch hydrogen discharge reactor as a powder form, but the disadvantage that the loss of the catalyst is inevitable in the continuous reaction system, in particular in the circulating supply process of the reactants In addition, the conventional non-noble metal catalyst has a problem of low reactivity and durability, so there is also a need for a solution.

Accordingly, the present invention is to solve the problems of the prior art as described above, the object of the present invention is a non-noble metal catalyst that can replace the expensive noble metal catalyst, high hydrogen release rate, NaBH ₄ as well as other boron Co-B catalyst / support for hydrogen release reaction using alkali boron hydride solution, which can be used for hydrogen release reaction of hydride, and has low catalyst loss rate, high reactivity and long-term durability in continuous reaction system, and its It is to provide a manufacturing method.

An object of the present invention as described above is a catalyst for hydrogen release reaction using an alkali boron hydride solution, and any one of an oxide to which Co and B are bonded or a compound to which Co and B are bonded (excluding oxides to which Co and B are bonded). Or a Co-B catalyst / carrier for hydrogen release reaction using an alkali boron hydride solution, characterized in that two Co-B catalysts are supported in the carrier.

The alkali boron hydride is NaBH ₄ , KBH ₄ Or LiBH ₄ It is preferable to mix the hydroxide of either NaOH or KOH with any one of the boron hydrides.

Preferably, the catalyst is an oxide in which Co and B are bonded, and the oxide preferably has a composition of Co and B of Co _1.5-3.0 B ₁ .

The support is preferably any one of a metal foam, carbon felt, carbon woven, or carbon nanotubes.

An object of the present invention as described above is a method for producing a Co-B catalyst / carrier for hydrogen release reaction using an alkali boron hydride solution, in which a support is used to support Co ²⁺ in a support, and an alkali boron as a reducing agent. Hydride Reducing the Co ²⁺ using a solution (S1); And drying, drying, and calcining the Co-B catalyst, which is one or two of the oxides of Co and B bonded or the compounds of Co and B bonded (except the oxides of Co and B bonded) supported on the carrier after reduction. It is achieved by the method for producing a Co-B catalyst / support for hydrogen release reaction using an alkaline boron hydride solution, characterized in that (S2).

The step S1 is preferably using CoCl ₂ as the precursor and the carrier carrying Co ^{2 +,} to dipping (dipping) the carrier in the alkali boron hydride solution at a constant rate.

In the step S1, the concentration of the precursor is preferably 30wt%.

The step S1 is an alkaline boron hydride solution used as the reducing agent NaBH ₄ , KBH ₄ Or LiBH ₄ It is preferable to use the alkali boron hydride solution which mixed the hydroxide of any one of NaOH or KOH with the boron hydride in any one of these.

The step S1 is preferably dried, dried and calcined in a nitrogen or hydrogen atmosphere.

In the step S1, the firing temperature during the firing is preferably 200 to 300 ° C, more preferably 200 to 250 ° C.

It is preferable to repeat the step S1 for densification of the Co-B catalyst in the support.

The step S1 is preferably used any one of the metal foam (foam), carbon felt (carbon felt), carbon woven (carbon woven) or carbon nanotube (carbon nanotube) as the support.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the present invention is not limited to the following specific examples, only the following examples are intended to facilitate the implementation of the invention to those skilled in the art while at the same time making the disclosure of the present invention complete, Various forms of modifications are possible within the scope of the appended claims.

<Example: Co-B catalyst / support preparation>

1 is a photograph (a) of a porous carrier and a photograph (b) of a catalyst / carrier according to an embodiment of the present invention.

First, an aqueous solution of CoCl ₂ (Aldrich Inc.), a precursor, was prepared to prepare the catalyst / carrier. As the carrier, for example, porous carriers such as metal foam, carbon felt, carbon woven, carbon nanotube, and the like may be used, and they are excellent in durability and economy. In the present Example, especially Ni foam was used as a support body.

A NaBH ₄ solution was used as the reducing agent, but NaBH ₄ generated hydrogen even without a catalyst when dissolved in water, so that the solution was kept in an alkaline state by adding NaOH to suppress it. In order to prepare the reducing solution, NaOH was first dissolved in distilled water to keep the pH of the aqueous solution at 14 or higher, NaBH ₄ was dissolved, and then stirred for 4 hours or more.

The precursor by varying the concentration of CoCl ₂ was loaded first supporting Co ^{2 +} ions in Ni chain form. NaBH ₄ The carrier was dipped at a constant speed in an aqueous solution so that Co-B was supported in the carrier.

On the other hand, the process was repeated 5 to 20 times to perform the densification to increase the concentration of Co-B in the carrier.

Subsequently the reaction was terminated completely and washed with distilled water.

The prepared catalyst was dried in a 60 ° C. nitrogen atmosphere (or hydrogen atmosphere), and then calcined in 200, 250, 300, 400, and 500 ° C. nitrogen atmosphere (or hydrogen atmosphere) for 2 to 4 hours. Meanwhile, in the following FIGS. 5 and 6, the respective temperatures are sequentially indicated by (a), (b), (c), (d) and (e). That is, (a) shows 200 degreeC, (b) shows 250 degreeC, (c) shows 300 degreeC, (d) shows 400 degreeC, and (e) shows 500 degreeC.

The catalyst prepared as described above was stored in a sealed container in a nitrogen (or methanol solution) atmosphere, and the following experiment was performed.

Experimental Example

As described below, in this experiment, X-ray diffraction (XRD), Inductively Coupled Plasma Mass Spectrometer (ICP-MS), and Scanning Electron Microscopy (SEM) analysis were performed to investigate the structure and composition, surface shape, and surface area of the catalyst. Was performed. By analyzing the crystallinity, shape and durability of the catalyst prepared after firing as described above, it is possible to prepare the most effective non-noble metal catalyst in the case of using the carrier.

First, the ICP analysis was performed to investigate the molar ratio of cobalt and boron in the catalyst, and FIG. 2 shows the molar ratio due to the ICP result of the catalyst prepared in this example.

As shown in Figure 2, it can be seen that the composition of the catalyst prepared in this embodiment is mostly composed of Co and B.

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

As shown in FIG. 3, the NaBH ₄ solution 40 and the preparation are prepared in a hydrogen discharge reactor 10 having a diameter of 10 cm and a height of 20 cm, in which a stirrer 11 is installed and can measure the temperature and pressure therein. Co-B / Ni (50) was added and the amount of hydrogen released from the hydrogen discharge stream 20 was measured through a mass flow meter (MFM) 14 and recorded on a personal computer. Since the thermocouple 12 was installed inside the reactor and the hydrogen generation reaction was an exothermic reaction, a temperature control device 13 including a temperature sensor (NI USB 9211) was installed outside the reactor. Cooling water was circulated through the inlet 31 and the outlet 32 of the cooling water to maintain a constant temperature of the solution. On the other hand, a water jacket 15 was installed around the hydrogen discharge reactor.

4 is a graph showing the amount of hydrogen generated according to the change in precursor concentration.

As shown in FIG. 4, as the concentration of the precursor is increased, the amount of hydrogen generation is also increased, particularly when the concentration of the precursor is 30 wt%.

Or more ICP analysis and the catalyst carrier of this embodiment from the hydrogen release rate results appeared to be high in the form of oxide is the most reactive, such as _{Co 1 .5-3.0 B 1, Co 3} O 4 and Co ₂ CoB or as B It was found that Co-B compounds were mixed.

FIG. 5 shows each XRD pattern according to the heat treatment temperature of the Co-B catalyst / support of the present embodiment.

As shown in FIG. 5, as a result of performing XRD analysis to investigate the structure of the catalyst formed in the support, in the XRD spectrum of the catalyst of this example prepared by the reduction method, a distinct crystalline peak was observed at a firing temperature of 200 ° C. or lower. It was not detected.

These results indicate that Co-B of amorphous structure is formed in the carrier. The structure of amorphous Co-B is known to be formed at 2θ value of 40 ~ 50 ° as shown in previous results. In this example as well, fine peaks were detected.

When the firing temperature of 300 ℃ is applied to the metal Co peak is observed and at 400 ℃ the amorphous structure is observed again, this result is a phenomenon that appears when the crystallinity of the metal Co is changed from HCP to FCC. On the other hand, the firing temperature of 500 ℃ caused metal Co formation.

As such, according to the present experimental example, it was determined that the catalyst structure capable of acting as a catalyst for hydrogen emission was effectively maintained when a calcination temperature of 300 ° C. or lower was applied.

6 shows an SEM image of the catalyst / support prepared in this Example.

As shown in FIG. 6, the catalyst / support according to the heat treatment of the present embodiment has a tangled state structure when a firing temperature of 200 ° C. or less is applied, and a catalyst structure having a more obvious shape at 300 ° C. Was observed. At 400 ° C, an unclear structure was formed again, and in the case of a catalyst fired at 500 ° C, small spheres were regularly aggregated.

Thus, from the XRD analysis and SEM results, it was found that the catalyst / support of the present example changed in structure, shape and shape according to the firing temperature.

On the other hand, in order to investigate the NaBH ₄ hydrogen emission reaction characteristics using the prepared catalyst / carrier, the rate of hydrogen evolution was measured while changing the firing temperature. In order to investigate the effect of calcination temperature on the activity of Co-B catalyst / support, NaBH ₄ and NaOH concentrations were fixed at 25wt% and 3wt%. The reaction temperature was constantly adjusted to 40 ° C. using a chiller. The amount of catalyst in the catalyst / carrier used was 0.06 ± 0.005 g.

FIG. 7 is a graph showing the effect of calcination temperature upon hydrogen generation from a 25 wt% NaBH ₄ + 3 wt% NaOH solution in the case of Co-B / Ni.

As shown in FIG. 7, in the case of the catalyst itself prepared in a state in which no calcination is applied (DRY state), the amount of hydrogen generated is 5000 mL / min · g, and the amount of hydrogen generated per weight is increased by 3 to 5 times than the same catalyst in the form of nano powder Was observed.

In the case of the catalyst having a calcination temperature of 200 ~ 250 ℃ it was confirmed that the maximum generation of hydrogen of 7000 ~ 7300mL / min.g, it was found that the best generating capacity. It was found that the catalyst calcined at 300 ° C. had a value of 5000 mL / min · g similar to the amount of hydrogen generated when the catalyst in the DRY state was used. When the firing temperature was applied at 300 ° C. or higher, that is, at 400 ° C. and 500 ° C., the amount of hydrogen generation decreased, and hydrogen generation rates of 4000 mL / min · g and 1850 mL / min · g were observed, respectively.

The difference in the amount of hydrogen generated by the firing temperature is due to the crystalline structure of the catalyst in the carrier and the form and shape of the metal Co observed in the SEM and XRD. In the case of metal Co, hydrogen generating ability from NaBH ₄ is known to be very low, and the rate of generation in this experimental example also depends heavily on the metal Co activity.

On the other hand, in order to observe the degree of loss due to the intense hydrogen generation of the Co-B catalyst in the support, that is, durability, the catalyst / support prepared by firing temperature was put in an ultrasonic cleaner to observe the physical loss rate of the catalyst.

8 is a graph showing the physical loss rate with time of the Co-B catalyst prepared by firing temperature in the experimental example of the present invention.

As shown in FIG. 8, the highest weight loss and a decrease of 40 to 50% were observed when the firing temperature was 200 ° C. or lower, and the higher the firing temperature, that is, the lower the loss rate was, the more crystalline metal cobalt was formed. Could.

conclusion

In this embodiment, a Co-B catalyst for hydrogen evolution using alkaline NaBH ₄ aqueous solution was prepared by chemical reduction so as to be supported in a porous Ni carrier.

The Co-B catalyst prepared in this Example was an oxide in which Co and B are bonded or a compound in which Co and B is bonded (except for oxides in which Co and B are bonded), and hydrogen of 7,000 ml / min · g or more at a baking temperature of 250 ° C. The rate of occurrence was shown. On the other hand, when considering the catalyst loss rate was found that the preferred firing temperature range is 200 ~ 250 ℃.

Since it has 3 to 5 times higher activity than that of the conventional powder Co-B catalyst, the Co-B catalyst / support of the present embodiment can replace the expensive Ru catalyst and the powder Co-B catalyst. .

Based on the above results, a hydrogen supply system was fabricated and hydrogen was supplied to the fuel cell, thereby successfully driving the fuel cell.

The densified Co-B / carrier catalyst prepared in this example has high activity as a catalyst for hydrogen release reaction using alkaline NaBH ₄ aqueous solution, and also releases hydrogen in other boron hydrides such as KBH ₄ or LiBH ₄ . It can be used as a catalyst for the reaction and shows high activity as well.

The Co-B catalyst / carrier for hydrogen release reaction using the alkali boron hydride solution of the present invention is 5-7 times higher than Ru catalyst which is a noble metal catalyst, and 3-5 times higher than Co-B catalyst in nano powder form. It has at least twice as high activity (at least 30% activity per unit volume). Furthermore, the loss of the catalyst is 50% or more lower in the continuous cyclic reaction than the Co-B catalyst in the form of nanopowder. Therefore, it is possible to replace the precious metal catalysts such as Co-B and expensive Ru in the form of non-noble metal catalysts. In addition, it can be used for hydrogen release reaction of other boron hydrides as well as NaBH ₄ , and has high reactivity and long-term durability. Therefore, it can be effectively used in the manufacture of mobile fuel cell energy system, thereby lowering its manufacturing cost.

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 (12)

A catalyst for hydrogen release reaction using an alkali boron hydride solution, wherein a Co-B catalyst, which is one or two of an oxide bonded by Co and B or a compound bonded by Co and B (excluding an oxide bonded by Co and B), is supported. Co-B catalyst / support for hydrogen release reaction using an alkali boron hydride solution, characterized in that supported on. The method of claim 1, The alkali boron hydride is NaBH ₄ , KBH ₄ Or LiBH ₄ Co-B catalyst / support for hydrogen release reaction using an alkali boron hydride solution, characterized in that any one of the hydroxides of NaOH or KOH mixed with the boron hydride. The method of claim 1, The catalyst is an oxide in which Co and B are bonded, and the composition of Co and B is Co _1.5-3.0 B ₁ Co-B catalyst / support for hydrogen release reaction using an alkali boron hydride solution. The method of claim 1, The support is for hydrogen release reaction using an alkali boron hydride solution, characterized in that any one of a metal foam (carbon), carbon felt (carbon felt), carbon woven (carbon woven) or carbon nanotube (carbon nanotube) Co-B catalyst / support. In the production method of Co-B catalyst / support for hydrogen release reaction using an alkali boron hydride solution, Co ²⁺ is supported in the support using a precursor, and an alkali boron hydride is used as a reducing agent. Reducing the Co ²⁺ using a solution, Co-B which is any one or two of the oxides of Co and B bonded to the carrier or the compound of Co and B bonded (except the oxides of Co and B bonded) Obtaining a catalyst (S1); And Drying and calcining the Co-B catalyst supported on the support (S2); Method of producing a Co-B catalyst / support for hydrogen release reaction using an alkali boride hydride solution comprising a. The method of claim 5, The step S1 is with packages using CoCl ₂ as the precursor and carrying a Co ^{2 +} in the bearing member, can be an alkali boron to the bearing member to hydride alkali boron solution characterized in that the dipping (dipping) at a constant speed a solution Process for preparing Co-B catalyst / support for hydrogen release reaction. The method of claim 6, The step S1 is a method of producing a Co-B catalyst / support for hydrogen release reaction using an alkali boron hydride solution, characterized in that the concentration of the precursor to 30wt%. The method of claim 5, The step S1 is an alkaline boron hydride solution used as the reducing agent NaBH ₄ , KBH ₄ Or LiBH ₄ Co-B catalyst / carrier for hydrogen release reaction using an alkali boron hydride solution characterized by using an alkali boron hydride solution in which any one of the hydroxide of NaOH or KOH is mixed with any one of the boron hydride Manufacturing method. The method of claim 5, The step S2 is a method of producing a Co-B catalyst / support for hydrogen release reaction using an alkali boron hydride solution, characterized in that the drying and firing in a nitrogen or hydrogen atmosphere. The method of claim 5, The S2 step is a method of producing a Co-B catalyst / support for hydrogen release reaction using an alkali boron hydride solution, characterized in that the firing temperature during the firing to 200 ~ 250 ℃. The method of claim 5, Method for producing a Co-B catalyst / support for hydrogen release reaction using an alkali boron hydride solution, characterized in that to repeat the step S1 for densification of the Co-B catalyst in the support. The method of claim 5, The step S1 is an alkali boride hydride solution, characterized in that using any one of metal foam (foam), carbon felt (carbon felt), carbon woven (carbon woven) or carbon nanotube (carbon nanotube) as the carrier Method for producing a Co-B catalyst / support for hydrogen release reaction using.

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