CN1546366A

CN1546366A - Aluminum-containing nano complex hydrogen storage material and its preparation method

Info

Publication number: CN1546366A
Application number: CNA2003101090806A
Authority: CN
Inventors: 孙大林; 陈国荣; 徐华华
Original assignee: Fudan University
Current assignee: Fudan University
Priority date: 2003-12-04
Filing date: 2003-12-04
Publication date: 2004-11-17
Anticipated expiration: 2023-12-04
Also published as: CN1304276C

Abstract

The invention relates to a process for preparing nano complex compound hydrogen storing material LiAlH4, NaAlH4 and KalH4, which comprises mixing LiH or NaH or Ka with pure Al powder, adding small amount of catalyst containing titanium, zirconium and ferrum, mechanically grinding 3-25 hours at the presence of hydrogen atmosphere. According to the invention, no organic solvent is needed to directly realize the material nanocrystallization.

Description

Aluminum-containing nano complex hydrogen storage material and preparation method thereof

Technical Field

The invention belongs to the technical field of functional materials, and particularly relates to a preparation method of a nano complex hydrogen storage material. The prepared material can be used as a hydrogen storage material to provide a hydrogen source for a fuel cell.

Background

Facing the double pressure of the increasing shortage of petroleum resources and the deterioration of ecological environment, the utilization of hydrogen energy as a clean energy source to replace the existing energy source based on petrochemical fuels has become a global consensus. Therefore, the development and utilization of new energy technologies related to hydrogen have been highlighted by many countriesThe contents. Important results obtained in some fields, such as fuel cells, electric vehicles, etc., are also being developed toward industrialization. It is anticipated that the world's energy economy will revolutionize from a carbon-based energy economy to a hydrogen-based energy economy, referred to as the "hydrogen economy". The introduction of the hydrogen economy concept forces the industry to place new demands on hydrogen storage capacity of hydrogen storage materials (1) of up to 5-6.5 wt. -%]Schlapbach L，Zuttel A，Nature，2001，414，353；[2]Bogdanovic B, Schwickardi m.j. alloyscomp, 1997; 253-254: 1). To achieve this goal, the research focus in this field since 1996 has been expanded from traditional metal hydrides to micro-nanostructured hydrogen storage materials and NaAlH₄A typical complex hydrogen storage material. NaAlH₄The effective hydrogen storage amount of the catalyst can reach 5.6 wt%. From the reported experimental results of thermodynamic and kinetic properties, the NaAlH₄The hydrogen storage material is feasible, but the following two defects are urgently overcome. The disadvantage is that the existing NaAlH₄The synthesis method of (2) requires not only high temperature (more than 170 ℃) and high pressure (more than 15MPa) reaction conditions, but also the use of flammable organic solvents, such as triethylaluminum, tetrahydrofuran, acetone, and the like. This method is high in cost, poor in safety, and extremely difficult in waste liquid treatment. Secondly, the NaAlH prepared by the method has the defect that₄The low-temperature hydrogen release dynamic performance is poor. For example, the hydrogen evolution at 120 ℃ over 3 hours is only 2.5 wt%, much lower than the theoretical capacity of the material, 5.6 wt%. The material can only completely discharge hydrogen when the temperature reaches 140-160 ℃. The two disadvantages not only hinder the exertion of potential properties of the material, but also bring certain limitations to practical application.

Disclosure of Invention

The invention aims to obtain an aluminum-containing nano complex hydrogen storage material with simple preparation method, low cost and good performance and a preparation method thereof.

The chemical molecular formula of the material is MALH₄M is an alkali metal element Li, or Na, or K, and the particle size of the material is 5-500 nm.

The invention adopts a mechanical grinding method to prepare a nano-complex MAlH₄Where M represents an alkali metal such as Li, Na or K.Produced MALH₄Can be used as hydrogen storage material.

The nano complex MAlH of the invention₄The preparation steps are as follows:

(1) mixture of equimolar amounts of MH and Al

Weighing equal molar weight of MH and high-purity Al powder at room temperature under the protection atmosphere of inert gas nitrogen or argon. Where MH is an alkali metal hydride, where M is Li, or Na or K. Then mixing the two powders, stirring uniformly, adding 0.5-15mol of inorganic substance containing titanium, zirconium and iron or organic complex catalyst, and mixing uniformly. It is silver gray. Catalysts added, e.g. TiCl₄，TiF₃，Ti(Obu)₄，Zr(OPr)₄，FeCl₂And the like.

(2) Homogenization of the powder mixture

And (3) placing the mixed powder obtained in the step (1) into a tungsten carbide or stainless steel container, sealing the container, and then placing the container on a high-energy ball mill for grinding for 5-60 minutes to further homogenize the mixed powder. The grinding apparatus and grinding process are shown in fig. 1. After grinding, the powder was brown.

(3) After the step (2) is finished, introducing 5-13MPa of high-purity hydrogen (the purity is 99.999%) into the reaction vessel, and continuously grinding for 5-20 hours.

(4) And (4) after the step (3) is finished, taking a brownish black powder sample out of the container under the protection of inert gas. The resulting sample was confirmed by X-ray diffraction to contain 65% of MAlH₄. This indicates that during mechanical grinding, the following chemical reactions occur:

(1)

m in the formula (1) represents Li, or Na or K. The analysis of the particle size shows that MAlH₄The particle size of (a) is between 5 and 500 nm.

According to the invention, after mixing an alkali metal hydride MH and high-purity Al powder in equal molar quantity, putting the mixture into a reactor, and simultaneously putting a tungsten carbide grinding ball with the diameter of 10-15mm, wherein the weight ratio of the grinding ball to the mixture powder is preferably (120-150) to 1.

A small amount of hexane or pentane is added into the mixture powder to prevent the powder from caking and blocking during grinding.

According to the invention, if 5 to 20 mol% of TiCl is added in the above-mentioned step (3)₄Or TiCl₃Or TiE₃Or Ti (OBu)₄As catalyst, MAlH in equation (1)₄The production rate of (c) increased from 65% to 85%. The particle size is 5-350 nm. These results show that the addition of the titanium-containing catalyst not only catalyzes the reaction (1) but also refines the MALH₄The particle size of (a).

The invention adopts the MAlH prepared by a mechanical method₄The method is simple, the cost is low, and the hydrogen release rate is higher than the MALH with micron size₄It is a new hydrogen storage material with high commercial value.

Nano complex MAlH prepared by the invention₄Can be used as a hydrogen storage carrier in the fuel cell to provide a hydrogen source for the fuel cell.

Drawings

FIG. 1 is an X-ray diffraction pattern of a sample of example 1.

Fig. 2 is a graph of the hydrogen discharge amount versus the hydrogen discharge time at a temperature of 120 c. In the figure 1 is NaAlH prepared by the invention₄Titanium-containing catalyst, 2 is NaAlH prepared by the invention₄Free of titanium catalyst, 3 is a high temperature and high pressure synthesized NaAlH₄。

Detailed Description

Example 1

Nano complex NaAlH₄The preparation steps are as follows:

(1) mixing of equimolar amounts of NaH and Al

Weighing equal molar weight of NaH and Al powder at room temperature under the protection of inert gas nitrogen. Then, the two powders are mixed and stirred uniformly to be silver gray.

(2) Homogenization of the powder mixture

Placing the mixed powder obtained in the step (1) in a tungsten carbide container, and putting a tungsten carbide grinding ball with the diameter of 10 mm. The weight ratio of the grinding balls to the mixed powder is as follows: 120: 1. A small amount of hexane was added to the mixed powder to prevent the powder from caking and caking during the grinding process. The container was sealed and then ground in a high energy ball mill for 20 minutes to further homogenize the mixed powder. After grinding, the powder was brown.

(3) And (3) after the step (2) is finished, introducing high-purity hydrogen (the purity is 99.999%) with the pressure of 5MPa into the reaction container, and continuously grinding for 6 hours.

(4) And (4) after the step (3) is finished, taking a brownish black powder sample out of the container under the protection of inert gas. The sample obtained was confirmed to contain 65% of NaAlH by X-ray diffraction₄. This indicates that during the mechanical grinding process, a chemical reaction occurs in which

(2)

The particle size analysis shows that the NaAlH₄The particle size of (a) is between 5 and 500 nm.

(5) Further experiments prove that if 5 mol% of Ti (OBu) is added in the step (3)₄As the catalyst, NaAlH in the formula (2)₄The production rate of (c) increased from 65% to 85%. The particle size is 5-350 nm. The X-ray diffraction spectrum of the sample is shown in FIG. 1.

The preparation method is as above, mixing with equimolar LiH or KH and Al powders, the weight ratio of grinding ball to mixture powder is 150: 1, introducing high-purity hydrogen gas with 12MPa into the reactor, grinding for 16 hours, and adding TiCl 18 mol% of the powder₄Catalyst to obtain LiAlH with good hydrogen storage effect₄And kAlH₄A material.

Example 2

With NaAlH₄For example, FIG. 2 compares the hydrogen evolution amount with the hydrogen evolution time at the same temperature of 120 ℃. As can be seen from the figure, the present inventionPrepared nano complex NaAlH₄The initial hydrogen release rate of the catalyst is higher than that of micron NaAlH synthesized at high temperature and high pressure under the condition of adding or not adding titanium catalyst₄. The hydrogen discharge rate is increased from small to largeThe sequence is as follows:

micron NaAlH₄<nano NaAlH without catalyst₄Nano NaAlH containing titanium catalyst₄。

Claims

1. An Al-contained nano complex hydrogen-storing material with chemical molecular formula of MAlH₄M is an alkali metal element Li, or Na, or K, and the particle size of the material is 5-500 nm.

2. The method for preparing the aluminum-containing nanocomplex hydrogen storage material as claimed in claim 1, wherein the method comprises

(1) Under the protection atmosphere of inert gas at room temperature, mixing equimolar amount of alkali metal hydride MH and high-purity Al powder, and adding 0.5-15 mol% of inorganic substance or organic complex catalyst containing titanium, zirconium and iron for uniform mixing;

(2) placing the mixed powder obtained in the step (1) in a reactor, sealing and then carrying out vacuum degassing;

(3) introducing hydrogen gas with pressure of 5-13Mpa into the sealed reactor, and grinding in a ball mill for 5-20 hr to obtain nanometer MAlH₄。

3. The method for preparing the aluminum-containing nanocomplex hydrogen storage material as claimed in claim 2, wherein the equimolar amounts of the alkali metal hydride MH and the high purity Al powder are mixed and then placed in the reactor, and the tungsten carbide grinding balls having a diameter of 10-15mm are placed therein, the weight ratio of the grinding balls to the mixture powder being (120-): 1.

4. The method for preparing a hydrogen storage material containing aluminum-containing nanocomplexes as claimed in claim 3, wherein an appropriate amount of hexane or pentane is further added to the mixture powder.

5. The method for preparing the aluminum-containing nanocomplex hydrogen storage material as claimed in claim 2, wherein TiCl is added in step (1)₄Or TiCl₃Or TiF₃Or Ti (OBu)₄Is used as catalyst and is added in 5-20 mol% of the powder.

6. The aluminum-containing nanocomplex hydrogen storage material MALH as set forth in claim 1 or 2₄The hydrogen storage material is used for providing a hydrogen source for the fuel cell.