KR20060095407A - Development of paste typed catalyst on hydrogen generation from nabh - Google Patents

Abstract

The present invention relates to the development of a paste type catalyst electrode in hydrogen generation using an alkali boron hydride (NaBH ₄ ) alkaline solution.

The present invention is a form of a catalyst electrode used for hydrogen generation of NaBH ₄ alkaline solution, using a paste-type catalyst electrode to prepare various catalyst materials (Ni, Co, Pt, etc.) and paste-forming additives (binders, thickeners, substrates). To develop high performance paste cathode and catalyst material through optimization.

Description

Development of paste type catalyst electrode for hydrogen generation of alkali boron hydrides {Development of paste typed catalyst on hydrogen generation from NaBH}

1 is a paste (cathode) cathode manufacturing process.

2 is a Substrate effect on the rate of hydrogen evolution according to the reaction time.

3 is a life characteristics of the catalyst electrode according to the type of substrate (maximum generation rate reference).

Figure 4 is a hydrogen generation characteristics according to the type of binder used in the paste production.

5 is a graph showing the effect on the NaBH ₄ hydrogen evolution rate according to the type of various catalysts used in the paste catalyst electrode.

Figure 6 is a graph showing the hydrogen evolution rate with time of the Filamentary Ni-Co mixture and nano-sized Co on C catalyst for Co catalyst.

Alkaline boron hydride (NaBH ₄ ) generates hydrogen through hydrolysis with water (H ₂ O).

NaBH ₄ + 2H ₂ O → NaBO ₂ + 4H ₂ ----------------- (1)

NaBH ₄ has a high hydrogen storage capacity of 10.8 wt.% H. When stored in alkaline solution, NaBH ₄ can store hydrogen stably for a long time and use the same infra as the existing gas station. In addition, by-product NaBO ₂ is an environmentally friendly material, and can be recycled to NaBH ₄ after use. Because of these properties, NaBH ₄ is known as an advantageous material as a hydrogen storage and generation device for PEMFC (proton exchange membrane fuel cell), hydrogen engine (Hydrogen engine) system, and many studies have been conducted.

Hydrogen evolution from NaBH ₄ , which is dissolved and safely stored in such alkaline solutions, is achieved through the use of solid catalysts. Therefore, the development of high performance solid catalyst in hydrogen generation of NaBH ₄ alkaline solution is the most important core technology.

Looking at the study on the hydrogen generation of NaBH ₄ to use the solid catalyst of the Russian Korovov etc., LaNi _4.5 T _0.5 hydrogen generation of the (T = Mn, Cr, Co , Fe, Cu, Al) NaBH 4 by using the hydrogen storage alloy Suda et al. Investigated the hydrolysis characteristics of NaBH ₄ using fluorinated metal hydride.

In the case of hydrogen generation using hydrogen storage alloys, the Ni phase present in nano-size without eluting from the surface of the alloy shows a catalytic effect, and is used for heat management of the generator system through endothermic-exothermic reaction. It has the advantage of low price of materials. However, when the amount of Ni phase present on the surface of the alloy is small, considering the hydrogen generation characteristics of the total catalyst amount, the overall performance such as hydrogen generation rate and generation amount was insufficient.

Amendola et al., On the other hand, used a nano-size Ru catalyst on IRA-400 resin, while Kojima et al., Japan, used a Pt catalyst on LiCoO ₂ to improve the hydrolysis characteristics of NaBH ₄ . Observation confirmed excellent hydrogen generation characteristics, but these methods had a disadvantage that the catalyst manufacturing process is very complicated and the catalyst is expensive.

Therefore, the development of effective and inexpensive catalysts for the hydrolysis reaction of NaBH ₄ should be made. In the literatures dealing with the catalyst for the hydrolysis reaction of NaBH ₄ , HCBrown et al. Showed excellent catalytic effect on hydrolysis in the order of Pt, Rh, Ru, Co, Ni, and Os, Pd, Fe, etc. Reported.

Among them, Co and Ni show low over-potential for hydrogen generation in basic atmosphere and inert properties that do not elute in strong alkali solution. Therefore, Co and Ni can be used as excellent catalyst materials for NaBH ₄ hydrogen generation. have.

In addition to the type of catalyst, the type of catalyst electrode applied in the system is also a very important parameter for performance. Conventionally, a catalyst electrode in which powder is simply sprayed onto a system or a powder is filled in a box-shaped mesh is used.

However, this type has the disadvantage that it is difficult to reuse the catalyst electrode and the space occupied in the system is large. On the other hand, since the paste-type catalyst electrode has a plate-like shape, it takes up little space in the system and is easy to deform so that a flexible system design is possible. Has the advantages of the process. In addition, through the optimization of the additive (agent) to enter the paste has the advantage that the performance is easy to improve.

The catalyst materials used to generate NaBH ₄ hydrogen were noble-metal catalysts such as Pt and Ru and metal hydrides. Precious metal catalysts have excellent hydrogen generation performance, but because they are expensive materials, they need to be replaced due to their low price competitiveness. In the case of hydrogen storage alloys, they have low performance due to the small portion of Ni phase acting as catalytic layer on the catalyst surface. Has a problem. Therefore, Ni and Co, which are effective in hydrogen generation reaction and relatively inexpensive, are used as catalyst materials.

In addition, it is intended to prepare a paste-type catalyst electrode and apply it to the system. Paste-type catalyst electrode can be used continuously, and because it is plate-shaped, it takes the smallest volume in the system, is easy to deform, and is a simple manufacturing process that is currently industrialized. do. In addition, the paste-type catalyst electrode is intended to improve the performance of the NaBH ₄ system because it is easy to improve the performance according to the optimization of the additives (binder, thickener, substrate) used.

In order to achieve the above object, the present invention provides a catalyst electrode in the form of paste in a hydrogen generating system using a NaBH ₄ alkaline solution, is installed in the reaction tube, while the NaBH ₄ alkaline solution is injected into the reaction tube surface Induces a hydrogen evolution reaction. The generated hydrogen gas is measured by the flow meter connected to the reaction tube, and the hydrogen generation rate can be measured in real time through interfacing with the computer.

1 shows a paste catalyst electrode manufacturing process.

The catalyst material, the thickener (adjust the paste concentration), the binder (binder) is mixed and mixed for 2 hours through a mixer to prepare a paste and then the paste is loaded on the substrate. The final shape of the plate can then be prepared by wrapping it with sus-mesh through drying, rolling and cutting.

The catalyst material is used the hydrogen storage alloy of Spherical Ni, Filamentary Ni, Co, Ni-Co mixture, nano sized Co on C, ZrV 0 .8 Ni 1 .2, LaAl 0 .5 Ni 4 .5. Thickener uses HPMC (Hydroxi-pluoro-methyl-cellulose) solution (2.0wt.%, 3600cps). The binder was evaluated in a strong base atmosphere, using a PTFE (polytetrafluorothylene) emulsion and a SBR (stylenebutadienerubber) emulsion, which have a high molecular weight. The performance was evaluated using foam.

The NaBH ₄ alkaline solution was prepared by dissolving NaBH ₄ in a concentration of 10-18 wt% in KOH solutions of pH 13 and 14.

2 shows the hydrogen evolution rates for various substrates.

The catalyst is Ni in spherical form, NaBH ₄ fuel was used as a solution of NaBH ₄ 1M in 1M KOH solution (pH = 14), 20% by weight PTFE was used as the bnder material in the preparation of the cathode. Carbon substrate, Ni mesh, and Ni foam were used as substrates, and their characteristics were compared by hydrogen generation rate. As can be seen from the results, the effect of substrate shape on the hydrogen evolution rate could not be observed.

However, as a result of measuring the life characteristics of each catalyst electrode, the carbon paper and Ni-mesh showed a sharp decrease in performance after 5 to 20 cycles, which is due to the dropping of the catalyst material. there was.

In the case of Ni foam, no drop of catalyst was observed after 50 cycles, and there was no deterioration in performance. See FIG. 3.

This result appears to be due to the strong bonding between the catalyst material and the substrate due to the 3 d-network structure of the Ni foam. In addition, Ni-foam can load a large amount of catalyst in the same volume. In this study, Ni foam was selected as the substrate of the catalyst electrode.

The binder used to prepare the paste must be stable in a strong base atmosphere and have a strong bonding force. Therefore, in this study, hydrogen evolution rate was measured by using PTFE emulsion, which is used as a binder of conventional fuel cells or Ni-MH cells, and SBR, a kind of industrial bond.

4 shows better results with SBR, because PTFE has hydrophobic while SBR has hydrophilic. Hydrophilic SBR allows NaBH ₄ solution to be smoothly fed into the cathode, allowing larger catalyst area to participate in the hydrolysis reaction. Therefore, we selected SBR as the binder.

5 shows the hydrogen evolution rate according to the type of catalyst. The catalyst is Filamenatary Ni (~ 100 mn), Spherical Ni (~ 5um), Co (~ 5um), LaNi 4 .5 Al 0 .5 (<20um), ZrV 0.8 Ni 1.2 (<20um) was used.

It can be seen that the initial hydrogen generation rate (characteristic reaching the maximum hydrogen generation rate) reaches the maximum value within 30 seconds regardless of the type of catalyst. Such characteristics can be said to be very encouraging when compared to the initial operation waiting time of 20 minutes or more in the case of a hydrogen generator using a conventional reformer.

On the other hand, the maximum hydrogen evolution rate is related to the type of catalyst, and Co and Filamentary Ni catalyst poles show the best results with the maximum generation rates of 211 m1 / min.-g catalyst and 165.7 ml / min.-g catalyst , respectively. I could see that looks.

The intrinsic catalytic activity (ml / min.m ² ) of each catalyst electrode was analyzed by the specific surface area analysis of the pasted catalytic electrode through BET, and Co was 122.6 ml / min.m ² . It was confirmed that the catalyst effect on NaBH ₄ hydrolysis was more than two times higher, and the excellent performance of the filamentary Ni was due to the increase of the reaction area due to the large specific surface area (5.86 m ² / g).

6 shows the hydrogen evolution characteristics of the filamentary Ni-Co mixture (20:80 wt.%) And the nano-sized Co on C catalyst. Both catalysts showed excellent results with maximum hydrogen evolution rate increased by more than 30% compared to particle size micro sized Co catalyst.

In particular, in the case of the Filamentary Ni-Co mixture catalyst, the performance was increased by enabling the infiltration of NaBH ₄ solution through the formation of fine pores inside the cathode, and the performance of the nano-sized Co on C catalyst was improved by the size effect. Is interpreted as Such Co based catalysts are much lower in price than Pt and Ru catalysts and can be expected as high performance and low cost catalysts for hydrogen evolution in NaBH ₄ alkaline solutions.

Currently, hydrogen storage includes gas storage, liquid storage, and solid storage. The dual gas storage method has a problem that the system is large due to the small storage capacity. The liquid hydrogen storage method has a larger storage density (70 g / liter) than the liquid storage method, but liquefies hydrogen by lowering it below the liquefaction point of -235 ° C. As a method of storage, it is not suitable as a hydrogen storage method in terms of economics because of the problem that a large amount of energy is consumed and a cryogenic container having a large thermal insulation is used so as not to vaporize during storage.

The hydrogen storage alloy, which is a solid storage method, should also be preceded by the development of a hydrogen storage alloy having excellent hydrogen storage capacity and hydrogenation reaction rate. In addition, the study of carbon-based hydride, which is being actively researched in recent years, is a situation in which the reproducibility and reliability of the system are still insufficient.

On the other hand, the hydrogen storage method using NaBH _{4 is known} to be capable of hydrogen storage in the liquid state and the hydrogen storage density per unit weight (5wt% to 20wt%) is much larger than other hydrogen storage media developed so far. Therefore, various industrial fields using hydrogen energy (Hydrogen storage system for fuel cell, Fuel storage system for hydrogen car, Ni / MH secondary battery which is the driving source of electric vehicle and small electronic device, Heat-pump system for automobile air-conditioner, Automobile initial It is the most suitable storage medium for soot removal system, heat-upgrading system using industrial waste, etc. and it can be applied in various ways.

In the above, the present invention has been illustrated and described with reference to specific preferred embodiments, but the present invention is not limited to the above-described embodiments, and the general knowledge in the technical field to which the present invention belongs does not depart from the spirit of the present invention. Various changes and modifications will be made by the person who owns it.

Claims (5)

In a hydrogen generation system using NaBH ₄ alkaline solution, The reaction tube is provided with a catalyst electrode in the form of a paste, NaBH ₄ alkaline solution is injected into the reaction tube to generate hydrogen gas at the surface of the cathode, and the generated hydrogen gas is measured through a flow meter connected to the reaction tube. ₄ Hydrogen storage and generator for alkaline solution. The hydrogen storage and generation apparatus of a NaBH ₄ alkaline solution according to claim 1, which uses a catalyst electrode in the form of a paste prepared from a binder of polytetrafluorothylene (PTFE) and a stylenebutadienerubber (SBR) emulsion. According to claim 1, hydrogen storage and generation of NaBH ₄ alkaline solution using a paste-type catalyst electrode prepared with a thickening agent HPMC (Hydroxi-pluoro-methyl-cellulose) solution (2.0wt.%, 3600cps) Device. The hydrogen storage and generation apparatus of NaBH ₄ alkaline solution using carbon paper, Ni-mesh, and Ni-foam as a substrate for loading a paste. The method according to claim 1, wherein the catalyst material used in the paste catalyst electrode is Filamenatary Ni (~ 100 mn), Spherical Ni (~ 5um), Flake Ni, Ni on Carbon, Co, Co on Carbon, LaNi _5.0-x Al _x ( x = 0 ~ 5.0), hydrogen storage and generator of NaBH ₄ alkaline solution using ZrV _x Ni _{2 .0-x} (x = 0 ~ 2.0).

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