CN1546495A - Nano metal complex hydrogen-storage material and its preparation method - Google Patents

Abstract

The invention discloses a novel nano metallic organic complexes hydrogen storing material, wherein vacuum saturated vapour reaction method is employed to prepare the nano lines of metallic organic complexes Ag (TCNQ) and Cu (TCNQ), and solution chemical reaction method is utilized to prepare the nanometer-micrometre scale pipe shaped Ag(TCNQ) and (TCNQ) metallic organic complexes.

Description

Nano metal organic complex hydrogen storage material and preparation method thereof

Technical Field

The invention belongs to the technical field of nano hydrogen storage materials in the field of novel energy and a preparation method thereof.

Background

Hydrogen energy is a renewable, ideal clean energy source. The hydrogen has high combustion value, wide resources and no pollution, and the water generated after combustion can be used as the raw material for hydrogen production for repeated recycling. Therefore, the gradual change to the utilization of hydrogen energy is a necessary trend in the development of energy field in this century because of the environmental protection and the trend of shortage of petrochemical fuels. Hydrogen fuel cells are gaining considerable attention in many countries as a secondary energy source. However, one of the technical problems that has prevented the practical use thereof is hydrogen storage technology.

The current hydrogen storage technology mainly comprises: compressed gas hydrogen storage, liquefied hydrogen storage, metal hydride hydrogen storage, and the like. The compressed gas has low hydrogen storage density, high pressure and poor safety; the hydrogen storage in the liquid state needs low-temperature isolation of 20K, which is not economical; the hydrogen storage alloy is an energy storage material developed in the last 70 th century, and compared with other modes, the hydrogen storage alloy has high hydrogen storage density per unit volume, good safety and low hydrogen storage density by weight.

The one-dimensional nano material has very high specific surface area and special effects and properties which are not possessed by some conventional materials, so the one-dimensional nano material is expected to become an advantageous hydrogen storage material to be applied to fuel cells. The most studied are metal hydrides and nanocarbon materials, including carbon nanotubes (Dillon AC, Jones KM, Bekkedahl TA, et al [ J ]. Nature 1997; 386: 377-. But the hydrogen storage amount can not reach the practical required level. Recently, a new Metal-organic hydrogen storage material, namely a Metal-organic framework (Nathaniel l.rosi, Juergen Eckert, mohammed eddaooudi et al [ J ]. Sciences, 300: 1127-.

Disclosure of Invention

The invention aims to obtain a nano metal organic complex hydrogen storage material with large specific surface area and high hydrogen storage capacity.

The invention aims to obtain a preparation method of a nano metal organic complex hydrogen storage material, which has simple preparation process, low temperature and no need of a catalyst.

The hydrogen storage material of the nano metal organic complex is a metal organic complex of metal Ag or Cu and 7, 7, 8, 8-tetracyanoquinodimethane TCNQ (7, 7, 8, 8-tetracyanoquinodimethane), wherein the complex is an orthorhombic structure, nano wires or nano tubes in a layered structure are orderly arranged and have interlayer spacing, and the diameter of the nano wires or the nano tubes is between 3.20 and 3.50 Å and is between 100nm and 2.0 mu m.

The invention uses a vacuum saturated vapor reaction method to prepare the nanowire, and the specific process is as follows (as shown in figure 1):

① preparing a metal Ag or Cu film with a thickness of 10-20nm on a substrate (silicon wafer, glass, quartz wafer, etc.) by vacuum evaporation or other methods;

② the sample with thin film and organic material TCNQ prepared in the previous step are placed in a container (such as glass tube) simultaneously, the molar ratio of metal to TCNQ is 1: 1. to complete the reaction, the amount of TCNQ may be slightly excessive to 1: 1.5.

③ vacuumizing the container to 1-5 × 10^-3Sealing the container by Pa, and separating the container from a vacuum system;

④ the vacuum container is heated in an oven and maintained at the required temperature for a certain time, so that the metal film on the substrate will react with the saturated vapor of TCNQ to finally generate Ag (TCNQ) or Cu (TCNQ) metal organic complex nano-wires on the substrate, wherein the maintenance temperature can be 80-140 ℃, the maintenance time can be 15-40 minutes, the vacuum container is heated in the oven at 100 ℃ and 120 ℃, and the maintenance reaction time is 20-30 minutes, which is a better reaction condition.

The invention uses a solution chemical reaction method to prepare the micro-nano tube, and the specific process is as follows:

① A saturated solution of TCNQ in acetonitrile was prepared.

TCNQ powder is generally an earthy yellow powder, differing in purity or brand by brand, slightly differing in color. The TCNQ powder was slowly added to a beaker containing acetonitrile with constant stirring with a glass rod until the added TCNQ powder no longer dissolved, at which time a saturated solution of TCNQ in acetonitrile was obtained.

② A silver film or copper film with a thickness of about 10-20nm is grown on the cleaned substrate (silicon wafer, glass, quartz wafer, etc.) by vacuum coating method, and the coating condition can be vacuum evaporation coating condition.

③ soaking the film in saturated solution of TCNQ acetonitrile for 1-10 s to see that the film slowly turns blue, taking out the substrate, and washing with acetonitrile to remove the residual liquid.

The vacuum degree of the solution chemical reaction method for plating the film is 1-5 multiplied by 10^-3Pa is better, the film layer is uniform and stable, the film coating rate is better controlled to be 0.5-5 Å/s, the film layer prepared in the range completely reacts with TCNQ, and the prepared film is most suitable for being soaked in TCNQ acetonitrile saturated solution for 2-5 seconds.

In the present invention, hydrogen storage properties of Ag (TCNQ) and Cu (TCNQ) in a nanostructure were measured using a quartz crystal microbalance method (QCM).

The quartz crystal oscillation method is commonly used in the vacuum coating process, and can monitor the deposition thickness of the film in real time. The method is used for measuring the hydrogen storage performance of the material. According to the basic principle of QCM, a mass of material is deposited on a quartz wafer with a change in resonant frequency of:

$\mathrm{\Δf}=-\frac{2{f_0}^2\mathrm{\Δm}}{A\sqrt{\mathrm{\μ\ρ}}}=-\mathrm{C\Δm}-------\left(1\right)$

in the formula f₀Is the initial resonant frequency of the quartz wafer; Δ m is the increment of mass; a is the surface area; μ is shear modulus (2.947X 10)¹¹gcm^-1s^-2) (ii) a ρ is the density of quartz (2.648 gcm)^-3). From the formula (1), C is a constant relating to the quartz crystal. Therefore, within a certain range, the change of the resonance frequency of the quartz crystal and the change of the mass of the substance adsorbed on the surface of the quartz crystal are linear changes. I.e. the decrease in the frequency of the wafer measured in the experiment corresponds to the mass of hydrogen adsorbed by the sample.

The specific test apparatus is shown in fig. 2.

The metal organic complex of the invention has the following characteristics:

(1) the specific surface area is large. SEM images of Ag (TCNQ) nanowire arrays are shown in FIG. 3. The arrangement of nanowires was relatively uniform and there was a gap, and it was found that the specific surface area was large.

(2) The metal organic complex has a loose crystal structure, has gaps inside, is in a layered structure, has the interlayer spacing of 3.22 Å and is larger than H₂The molecular dynamics diameter (about 2.89 Å) is shown in figure 4, the X-ray polycrystalline diffraction analysis result of the Ag (TCNQ) nanowire sample prepared by the invention is shown in figure 5, wherein 28.43 degrees is the diffraction peak of the Si (111) surface, and the rest are Ag (TCNQ) peaks, and compared with the data of the prior person, the crystal structure of the Ag (TCNQ) nanowire sample is consistent with the crystal structure reported by the Shields and belongs to an orthorhombic system.

(3) The presence of polycrystals in the sample; some defects and the like may occur when preparing the sample.

The invention adopts a vacuum saturated vapor method to prepare metal organic complex Ag (TCNQ) and Cu (TCNQ) nanowire arrays. The preparation process is simple, the growth temperature is low, and a catalyst is not needed. The grown nano-wire is vertical to the substrate, the array is arranged orderly, certain gaps are formed, the specific surface area is large, and a novel hydrogen storage material with practical value can be developed.

Drawings

FIG. 1 is a schematic diagram of a vacuum saturated vapor reaction process.

Fig. 2 is a schematic view of a hydrogen storage amount measuring apparatus.

FIG. 3 is an SEM image of an Ag (TCNQ) nanowire array.

FIG. 4 shows the crystal structure of Ag (TCNQ).

FIG. 5 is an X-ray diffraction pattern of Ag (TCNQ) nanowires.

Figure 6 is a graph of the change in resonant frequency of a nanowire sample over time.

Fig. 7 is a graph of the change in resonant frequency of a blank wafer over time.

Fig. 8 is a comparison of the hydrogen storage process for the sample and blank wafer.

FIG. 1 is a metal film; 2 is TCNQ powder; 3 is a substrate; 4 is a vacuum chamber; 5 is a vacuum system; 6, a film thickness measuring instrument and a computer system thereof; 7 is a hydrogen chamber; 8 is a sample chamber; and 9 is a vacuum system.

Detailed Description

Example 1:

ag (TCNQ) nanowire sample preparation

An array of ag (tcnq) nanowires was prepared using the vacuum saturated vapor reaction method shown in fig. 1. The initial resonance frequency of the sample is f₁A quartz wafer with 66001118Hz silver electrodes. After a layer of Ag film with thickness of about 10nm is plated by vacuum evaporation method, its resonant frequency is changed into f₂6000624 Hz; the sample was then placed in a glass tube together with TCNQ and evacuated to a vacuum of 2X 10^-3And Pa, sealing the glass tube. Heating in an oven at 100 deg.C for 40 min. Obtaining Ag (TCNQ) nanowire sample on quartz wafer, and measuring the resonance frequency f₃＝5996682Hz。

2. Measurement of Hydrogen storage amount

The test apparatus used is shown in fig. 2. The testing steps are as follows:

(1) putting the sample prepared in the embodiment 1 into a small vacuum chamber, and starting a computer control system to measure the resonance frequency of the sample in real time;

(2) pumping the vacuum chamber until the vacuum degree reaches 5 × 10^-3Pa, recording the air extraction processThe change of the resonant frequency of the medium sample;

(3) opening an inflation valve, slowly inflating hydrogen, and recording the change condition of the resonant frequency of the sample in the inflation process;

(4) after the hydrogen pressure reached one atmosphere, it was kept for 5-6 hours until the resonance frequency stabilized at a certain value, and this value was recorded.

In order to increase the reliability of the experimental results, the invention also tests the blank quartz wafer according to the above steps.

3. Computing

(1) Frequency change of Ag (TCNQ) nanowires

Under the condition that the silver electrode does not participate in the reaction, the change amount of the mass of the Ag (TCNQ) nanowire corresponding to the resonance frequency of the wafer is considered as follows: f. of₁-f₃4436 Hz. However, in experimental analysis, the silver electrode is found to participate in the reaction, so that the initial resonant frequency of the wafer is corrected in the calculation process. By

(0＜σ＜1) (2)

It can be calculated that there is a mass correspondence Δ f in the electrode_Ag1593 Hz. Therefore, the actual change of the mass of the Ag (TCNQ) nanowire on the substrate corresponding to the resonance frequency of the wafer is as follows: Δ f_Ag(TCNQ)＝(f₁+Δf_Ag)-f₃＝4436+1593＝6029Hz。

(2) Hydrogen storage capacity by weight

The change of the resonance frequency of the quartz crystal oscillation sample of the Ag (TCNQ) nanowire and the blank quartz crystal oscillation piece along with time in the hydrogen absorption test process is shown in fig. 3 and 4. As can be seen from FIG. 3, the initial resonant frequency of the sample before the start of hydrogen gas filling is F₂5996688 Hz; after hydrogen absorption its resonant frequency becomes F₃5996606Hz, frequency variation Δ F_H2Is 82 Hz; but is blankThe frequency variation of the wafer during this process was only 10Hz respectively, and their comparison is shown in fig. 5. Multiple tests show that the above results can be repeated, and the relative error of each test is 2% of the total weight of the composition. It can be seen that our measurement system is stable.

The principle of QCM is as follows:

$\left(3\right)------\frac{\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="2"\; label="F\; H"\; filenames="A20031010908100093.png"\; state="\{\{state\}\}">F</figure-callout>}}_{H_{}}}{{\mathrm{\&Delta;f}}_{\mathrm{Ag}\left(\mathrm{TCNQ}\right)}}=\frac{{\mathrm{\&Delta;m}}_{{\mathrm{<figure-callout\; id="2"\; label="H"\; filenames="A20031010908100093.png"\; state="\{\{state\}\}">H</figure-callout>}}_2}}{{\mathrm{\&Delta;m}}_{\mathrm{Ag}\left(\mathrm{TCNQ}\right)}}$

therefore, the weight hydrogen storage amount is:

$\left(4\right)------\mathrm{wt}\%=\frac{\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="2"\; label="F\; H"\; filenames="A20031010908100093.png"\; state="\{\{state\}\}">F</figure-callout>}}_{H_{}}}{{\mathrm{\&Delta;<figure-callout\; id="2"\; label="F\; H"\; filenames="A20031010908100093.png"\; state="\{\{state\}\}">F</figure-callout>}}_{H_{}}+{\mathrm{\&Delta;f}}_{\mathrm{AgTCNQ}}}\&times;100\%$

the weight hydrogen storage amount of the quartz crystal oscillation sample grown with Ag (TCNQ) nano-wires under normal temperature and pressure is 1.34 percent by substituting the experimental data into the formula (4).

Example 2

Cu (TCNQ) nanowires were also prepared by a vacuum saturated vapor reaction method. The specific growth conditions are: the thickness of the Cu film plated by vacuum evaporation is 20 nm; the vacuum degree in the glass tube is pumped to 5 multiplied by 10^-3Sealing under Pa; putting the mixture into an oven, heating the mixture to 140 ℃, reacting the mixture for 15 minutes, and taking the mixture out. An array of nanowires grown perpendicular to the substrate is also obtained.

Example 3

Ag (TCNQ) micro-nano-tubes are prepared by a solution chemical reaction method. The specific preparation conditions are as follows: the thickness of the Ag film plated by vacuum evaporation is 10 nm; the degree of vacuum during vapor deposition was 1X 10^-3Pa; putting the mixture into TCNQ acetonitrile solution to react for 2 seconds; taking out and putting into acetonitrile for washing. The micro-nano tube with the diameter range of 200nm-2 mu m is obtained.

Example 4

The Cu (TCNQ) micro-nano tube is prepared by a solution chemical reaction method. The specific preparation conditions are as follows: the thickness of the Ag film plated by vacuum evaporation is 20 nm; the degree of vacuum during vapor deposition was 5X 10^-3Pa; putting the mixture into TCNQ acetonitrile solution to react for 10 seconds; taking out and putting into acetonitrile for washing. Micro-nano-tubes with the diameter of 500nm-2.5 μm are obtained.

Claims (7)

1.A hydrogen-storing nano-class metal-organic complex as hydrogen-bearing material is prepared from Ag or Cu and 7, 7, 8, 8-tetracyanoquinodimethane (7, 7, 8, 8-tetracyanoquinodimethane), TCNQ, and features that said metal-organic complex is orthorhombic structure, nano-wire or nano-tube with laminated structure, 3.20-3.50 Å of layer spacing and 100nm-2.0 microns of diameter.

2. The method for preparing a nano metal organic complex hydrogen storage material according to claim 1, wherein the metal organic complex nano wire is prepared by a vacuum saturated vapor reaction:

(1) preparing a layer of metal Ag or Cu film with the thickness of 10-20nm on a substrate;

(2) placing the substrate with the thin film and organic material TCNQ in a container, and vacuumizing to 1-5 × 10^-3Pa；

(3) And (3) heating the vacuumized container in an oven at the temperature of 80-140 ℃ for 15-40 minutes to obtain the metal organic complex nanowire.

3. The method for preparing the hydrogen storage material of the nano metal organic complex as claimed in claim 2, wherein the temperature for heating the container which is vacuumized is 100-120 ℃ and the holding time is 20-30 minutes.

4. The method for preparing a nano metal organic complex hydrogen storage material according to claim 1, wherein the metal organic complex micro-nano tube is prepared by a solution chemical reaction method:

(1) preparing a TCNQ acetonitrile saturated solution;

(2) growing a layer of Ag film or Cu film with the thickness of 10-20nm on the substrate by a vacuum coating method;

(3) immersing the prepared film into a saturated solution of acetonitrile for 1-10 seconds to obtain the metal organic complex micro-nano tube.

5. The method for producing a nanometal organic complex hydrogen storage material according to claim 4, wherein the degree of vacuum for depositing the Ag film or the Cu film is 1 to 5X 10^-3Pa。

6. The method for producing a nanometal organic complex hydrogen storage material according to claim 4, wherein the thickness of the deposited Ag film or Cu film is 10 to 20 nm.

7. The method for preparing a nanometal organic complex hydrogen storage material according to claim 4, wherein the prepared film is immersed in a saturated solution of acetonitrile for 2 to 5 seconds.

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