WO2008113257A1

WO2008113257A1 - A method for preparing hydrogen through decomposing sodium borohydride by catalyst

Info

Publication number: WO2008113257A1
Application number: PCT/CN2008/000519
Authority: WO
Inventors: Pei Kang Shen; Mei Wu; Jianying Liang; Yongliang Li; Masaaki Uemura; Yasuhiro Fujita
Original assignee: Sun Yat-Sen University; Sumitomo Corporation
Priority date: 2007-03-20
Filing date: 2008-03-17
Publication date: 2008-09-25
Also published as: CN101041416A; CN100503425C

Abstract

A method for preparing hydrogen through decomposing sodium borohydride by catalyst, comprises: disposing two electrodes in a vessel containing a solution of NaBH4, wherein one of the electrodes is positive electrode and the other is negative electrode; applying a direct current stabilized voltage supply to produce a direct current electric field between the two electrodes; removing sodium metaborate colloid produced from the decomposition of NaBH4, through moving the colloid to the positive electrode by electrophoresis under the effect of the electric field. The method can be applied in convenience, and ensure the decomposing reaction to be carried out in a relatively stable speed.

Description

Method for decomposing hydrogen from sodium borohydride by catalyst

Technical field

The invention relates to a method for producing hydrogen, in particular to a method for decomposing hydrogen from sodium borohydride by a catalyst.

Background technique

Hydrogen is widely used in the chemical industry, and hydrogen energy may become an ideal clean energy source in the future. Its status is unquestionable. However, there are many difficulties in using hydrogen as a fuel cell fuel, mainly due to the lack of convenient, directly usable hydrogen supply methods and safe, efficient, economical and lightweight hydrogen storage technologies. 'Therefore, the key technology for the development of hydrogen-powered vehicles and portable power supplies is the ability to find technologies that safely produce, store and store a certain amount of hydrogen. Proton exchange membrane fuel cells have developed rapidly and are beginning to be commercialized. China has strengthened research work in this area since the early 1990s, and has made some progress in succession. Dalian Institute of Chemical Physics, Changchun Institute of Applied Chemistry, Zhongshan University, Wuhan University of Technology and Tsinghua University have successively developed hydrogen and oxygen. Proton exchange membrane fuel cell stacks, but research work is mainly focused on fuel cell electrode preparation technology and stack assembly technology, but less research on hydrogen generation and storage technology.

The common application of hydrogen is to use a high pressure bottle to store hydrogen, but this method is not only dangerous, but the ultra-high weight that the high pressure bottle itself cannot avoid greatly restricts its application as a portable energy source. A possible approach is to use chemicals to produce hydrogen, which is one of the hottest research directions in the use of chemicals for hydrogen production because of its high hydrogen storage capacity and hydrogen production by hydrolysis alone.

Sodium borohydride is a white crystalline powder with a hydrogen storage capacity of 10.8% (mass fraction) and can be stably present in a vacuum at 400 Torr. Spectral data indicate that the erbium ions are symmetrical tetrahedral structures. Sodium borohydride is a strong reducing agent that reacts with water at room temperature to produce hydrogen. The reaction is as follows: Catalytic

NaBH4+2H ₂ 0 ^ 4H ₂ +NaB0 ₂ (!)

(ΔΗ= - 300 kJ)

Kxeevoy and Jacobson et al. [Kreevoy MM, Jacobson R W. Ventron Alembic, 1979, 15: 2 - 3.] found that the rate of hydrogen production in reaction (1) is strongly dependent on the pH and temperature of the solution, and the relationship can be based on the following experience. Calculation: '

Log ti _/2 = pH - (01034 T - 1192) (2)

Confirmation Where t _1/2 is the half-life (time when NaBH ₄ aqueous solution decomposes _1/2 ) in min; T is the absolute temperature in units.

Schlesinger et al. [Schlesinger HI, Brown C, Finholt AE, et al. J Am Chem Soc, 1953 (75): 215] found that when a catalyst is present, sodium borohydride can be hydrolyzed in a strong alkaline aqueous solution to produce hydrogen and water. Sodium borates. Brown et al. [Brown HC, Brown C A. J Am. Chem. Soc, 1962 (84): 1493] studied a series of metal salts and found that strontium and barium salts were released from NaBH ₄ solution at the fastest rate. hydrogen. At this point, the catalytic decomposition of sodium borohydride has become the mainstream research direction of on-site hydrogen production.

However, there are many difficulties in catalyzing the decomposition of sodium borohydride. First, it is necessary to find a suitable catalyst, and the colloidal poisoning catalyst formed by the reaction of a high concentration sodium borohydride solution makes the controllability of hydrogen decomposition of sodium borohydride to be greatly reduced, so that it cannot be put into practical use. The invention can quickly and easily remove the colloid in the solution.

Under 25 Ό, the solubility of NaBH ₄ in water is 0.55 g / g (H ₂ 0), while the solubility of NaB0 ₂ in water is only 0.28 g / g (H ₂ 0) _0. Therefore, if NaB0 _{2 is} formed by the reaction. Without precipitation, the NaBH ₄ content of the solution must be less than 0.16 g / g (3⁄40). Xia et al. [Xia ZT, Chan SH, J. Power Sources, 2005 (152): 46] also found that when the mass fraction of NaBH ₄ in solution is too high, a large amount of water is consumed in the hydrolysis to cause NaB0 _{2 to be} formed. Directly presented in the form of crystals. Our study also found that when the mass fraction of NaBH ₄ in the solution exceeds 15 wt%, the system after the reaction is neither a transparent solution nor a crystal substance, and the product exists in a colloidal form. The NaBH ₄ decomposition requires hydrogen to produce a catalyst, while the NaBH ₄ solution concentration is greater than 20 wt ° /. At the time, the continuously formed NaB0 ₂ in the solution acts as a colloid on the catalyst, suppressing the catalytic performance of the catalyst, and the decomposition rate of sodium borohydride is lowered. At present, this problem hinders the development and practical application of the NaBH ₄ on-site hydrogen production technology.

Summary of the invention

The object of the present invention is to provide a method for decomposing hydrogen from sodium borohydride by a catalyst. The method of the invention separates the sodium metaborate product in the decomposition process of sodium borohydride from the reaction liquid in time to prevent adhesion to the surface of the catalyst. The performance of the catalyst is lowered to ensure that the decomposition reaction proceeds at a relatively stable rate.

A catalyst for decomposing hydrogen of sodium borohydride of the present invention, wherein two electrodes are added to a container containing a NaBH4 solution, one is a positive electrode and the other is a negative electrode, and a constant current power supply is connected between the two electrodes. Thus, a DC electric field is formed between the two electrodes, and the sodium metaborate colloid produced by the decomposition of NaBH4 is directionally moved and removed in the direction of the positive electrode by the DC electric field.

The voltage of the DC stabilized power supply is 0.3 - 3 volts, typically 0.5 - 2 volts, preferably 0.8 - 1.3 volts. The electrode is a metal electrode, a carbon electrode, a graphite electrode or a surface-treated plastic electrode. The electrodes are placed in various types of sodium borohydride decomposition hydrogen production units, and the placement positions may be different. The invention removes the sodium borohydride decomposition colloid product method, characterized in that the electrodes can be connected in series or in parallel, and can be placed above and below the catalyst, and the positive electrode is placed underneath, so that the sodium metaborate produced is in the same place. In the electric field, the sodium metaborate rate is removed by the interaction of gravity and electric field. Or both the positive and negative electrodes are placed under the catalyst, so that sodium metaborate is completely separated under the catalyst and does not cover the catalyst. It is also possible to place the positive and negative electrodes on both sides of the catalyst so that the produced sodium metaborate moves toward the positive electrode and finally separates at the positive electrode end.

The method of the present invention is based on the following principle: The surface of the dispersed phase colloidal particles is positively charged or negatively charged due to ionization, ion adsorption or ion dissolution at the interface with the polar medium H ₂ 0. . Any ion of the same composition as the sol particle is preferentially adsorbed. In the absence of ions having the same composition as the sol particles, the colloidal particles generally adsorb the anions having weak hydration ability, and the cations having stronger hydration ability remain in the solution. The NaBH ₄ solution is strongly alkaline and contains a large amount of OH- ions. NaB0 ₂ adsorbs Off in the solution and is thus negatively charged. This property is used to separate and remove sodium metaborate by electrophoresis, thereby producing hydrogen production. Sodium metaborate does not cover the catalytic properties of the catalyst.

The process of the present invention ensures that the decomposition reaction proceeds at a relatively stable rate as compared to the prior art of sodium borohydride decomposition to produce hydrogen.

DRAWINGS

Fig. 1 is a schematic diagram of a method for decomposing hydrogen by sodium borohydride.

Fig. 2 is a time-dependent curve of hydrogen production rate for hydrogen production by decomposition of sodium borohydride, curve 1 is a rate-of-time curve of the method of the present invention, and curve 2 is a hydrogen production rate-time curve of the prior art.

Figure 3 is a schematic view of Embodiment 2.

Figure 4 is a schematic view of the embodiment 3.

In Fig. 1, Fig. 3 and Fig. 4, 1 is a sodium borohydride solution; 2 is a negative electrode, 3 is a positive electrode, 4 is a DC stabilized power source, and 5 is a catalyst. - detailed description

The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

As shown in Fig. 2, hydrogen production is decomposed by high concentration (greater than 30 wt% NaBH ₄ ) sodium borohydride under ordinary conditions, and the hydrogen production rate decreases rapidly with time. On the one hand, the concentration of sodium borohydride itself decreases as the decomposition time lengthens, but the main reason for the rapid decline is that the colloidal product covers the surface of the catalyst to reduce its activity. After the electric field is applied, the charged product is removed by electrophoresis to keep the catalyst operating normally. The small decrease in hydrogen production over time is primarily due to a decrease in reactant concentration. As can be seen from the figure, the effect is very obvious.

Example 1 In a vessel containing 30 wt% NaB3⁄4 solution, a stainless steel mesh was used as an electrode, which was placed above and below the catalyst, respectively, as shown in Fig. 1. A voltage of 0.8 V was applied between the two electrodes.

Example 2

In a vessel containing 30 wt% NaBH ₄ solution, four sheets of carbon paper were used as electrodes, which were respectively placed in series on both sides of the catalyst, as shown in FIG. A 3 V DC voltage was applied between the first and last electrodes, and the colloidal product was removed on the side.

Example 3

In a vessel containing 35 wt% NaBH ₄ solution, a conductive plastic was used as an electrode, and both electrodes were placed under the catalyst as shown in FIG. Applying a voltage of 0.5 V between the two electrodes, the colloidal products are removed from below and do not cover the catalyst.

Example 4

In a vessel containing a 25 wt% NaBH ₄ solution, nickel wire was used as an electrode and placed above and below the catalyst as shown in FIG. Applying 13V between the two electrodes, the power supply is a normal chemical battery.

Example 5

In a vessel containing a 30 wt% NaBH ₄ solution, a nickel mesh was used as an electrode and placed above and below the catalyst. A voltage of 2 V is applied between the electrodes, and the power source is a rechargeable secondary battery.

Example 6

In a vessel containing 35 wt% NaBH ₄ solution, a conductive plastic was used as an electrode, and the electrodes were placed above and below the catalyst as shown in FIG. A voltage of 0.3 V was applied between the electrodes, and the colloidal products were removed from below without covering the catalyst.

Claims

Claim

A method for decomposing hydrogen from sodium borohydride by a catalyst, characterized in that: two electrodes are added to a container containing a NaBH ₄ solution, one being a positive electrode and the other being a negative electrode, and a direct current is connected between the two electrodes The stabilized power source forms a DC electric field between the two electrodes. Under the action of a DC electric field, the sodium metaborate colloid produced by the decomposition of NaBH ₄ is removed by electrophoresis in the direction of the positive electrode.

2. The method according to claim 1, wherein the DC stabilized power supply is a low voltage direct current, a chemical battery, a physical battery or a super capacitor formed by alternating voltage rectification.

3. The method according to claim 1, wherein the electrode is a metal electrode, a carbon electrode, a graphite electrode or a surface-treated plastic electrode.

4. The method according to claim 1, characterized in that the two electrodes are placed above and below the catalyst, and the positive electrode is below, so that the sodium metaborate produced is in the electric field, and the bias is caused by the interaction of gravity and electric field. Sodium borate is removed in the direction of the positive electrode to remove so that sodium metaborate does not cover the catalyst.

5. The method according to claim 1, wherein the positive and negative electrodes are disposed on both sides of the catalyst such that the generated sodium metaborate is removed in the direction of the positive electrode, so that sodium metaborate is not covered. On the catalyst.

6. The method of claim 1 wherein said DC regulated power supply has a voltage of 0.3 to 3 volts.

7. The method of claim 1 wherein said DC regulated power supply has a voltage of 0.5 to 2 volts.

8. The method of claim 1 wherein said DC regulated power supply has a voltage of 0.8 to 1.3 volts.