CN111003686A - Novel room temperature hydrogen storage material and preparation method thereof - Google Patents

Abstract

The invention discloses a novel room temperature hydrogen storage material, the expression is Ti₂CT_x，Ti₂CT_xThe material is a two-dimensional layered material and has high-density layered gaps with volume fraction of more than 60 percent and adjustable interlayer spacing of 0.68 nm-0.9 nm; a large number of fluorine functional groups and oxygen-containing functional groups are connected between layers; 1 to 15 percent of Al atoms left after etching are left between the layers. The room temperature hydrogen storage material Ti prepared by the invention₂CT_xThe first hydrogen storage capacity can reach 8.44 wt% and the circulated hydrogen storage capacity is 7.5 wt% at room temperature of 25 deg.C and 50bar (5 MPa). More than 95 percent of stored hydrogen can be rapidly removed (within 5 min) under the conditions of 95 ℃ and 0bar, and the dehydrogenation amount and the dehydrogenation rate are controllable.

Description

Novel room temperature hydrogen storage material and preparation method thereof

Technical Field

The invention belongs to the field of hydrogen storage, and particularly relates to a novel room-temperature hydrogen storage material and a preparation method thereof.

Background

Hydrogen is the most ideal secondary energy source for future human society, and has good combustion performance and high calorific value, so that the hydrogen has attracted extensive attention of international society. The utilization of hydrogen energy relates to three technical links of hydrogen production, hydrogen storage, hydrogen utilization and the like, and the storage and transportation of hydrogen are the key points of hydrogen energy utilization due to the characteristics of dispersibility and intermittence of hydrogen during the utilization, wherein the hydrogen storage is a bottleneck technology. The hydrogen storage system has the characteristics of high energy density, high safety, high hydrogen charging and discharging speed, low cost and the like. The most common storage method at present is to use high pressure gas tanks to store hydrogen as a compressed gas at a pressure in the range of 350 to 700 bar. However, the high pressure tank stores low density hydrogen, and in practical applications (such as hydrogen powered vehicles), excessive pressure is dangerous. Liquid hydrogen, while having a higher power density, is costly to produce at high pressures and low temperatures. At present, the most concerned hydrogen storage method is solid material hydrogen storage, and a large number of researches prove that metal hydrides, porous carbon materials, MOFs, noble metals, composite materials thereof and the like have better hydrogen storage performance. Wherein, most metal hydrides need to store and release hydrogen at higher temperature (200-; by using the material for storing hydrogen by physical adsorption, the capacity of 5 wt% or more can be obtained at the temperature of liquid nitrogen, but the material is limited by low-temperature working conditions; metal/intermetallic compounds such as LaNi₅FeTi can store hydrogen under normal temperature and pressure conditions, but the mass hydrogen storage density of the materials is usually lower than 2 wt%; noble metals Pd, Pt and their composites have high hydrogen storage density, but noble metals are expensive and have the problem of slow dehydrogenation kinetics. The solid hydrogen storage materials reported at present cannot meet the requirements of practical application.

MXene is a novel two-dimensional layered material which is widely concerned in recent years, is carbide or nitride consisting of transition metals, can be obtained by mainly dissociating MAX phase of a layered ceramic material through hydrofluoric acid (HF), has excellent mechanical, electronic, magnetic and other properties, and is mainly applied to the fields of lithium ion battery energy storage, catalysis, sensors, electromagnetic application such as electromagnetic shielding and the like. Although the current related topic groups have studied Ti using local density approximation functional and molecular dynamics simulation methods₂C、Sc₂C and V₂C, etc., but the research of MXene hydrogen storage application is limited to theoretical prediction so far, and no experimental result is reported to beSuccessfully prepare the material with practical hydrogen storage performance.

Disclosure of Invention

The invention aims to provide a novel solid room-temperature hydrogen storage material and a preparation method thereof, wherein MAX phase Ti is prepared by adopting a chemical etching method₂Removing partial Al atoms in layered distribution in AlC to obtain a two-dimensional layered MXene material Ti with a large number of lamellar gaps, wherein 1-15% of Al is remained₂CT_x。

At present, there is Ti₂CT_xIs mainly prepared by using HF to block MAX phase Ti₂Etching and washing AlC ceramic, reacting Al atomic layer in precursor MAX with hydrofluoric acid in solution, allowing acid-etched Al to enter solution, leaving a layer of Al atomic gap in original bulk material, and stripping by means of ultrasound to obtain lamellar Ti₂CT_xThe materials are regularly stacked, so that the material shows higher specific mass capacity and cycling stability in the test of the electrode material of the supercapacitor. Thus, the prior art mainly utilized HF to transform the MAX phase Ti₂All Al atoms in the AlC ceramic are etched away and the layered Ti is obtained by peeling₂CT_xThe material can obtain excellent electrochemical performance. In the process of researching the hydrogen storage performance of the two-dimensional layered MXene material, the invention unexpectedly discovers that the HF is utilized to react with massive MAX phase Ti₂When the AlC ceramic is etched, Ti is added₂When Al atoms in the AlC ceramic are reserved by 1 to 15 percent, the incompletely etched Al atoms can be in Ti₂CT_xThe interlayer of the material plays the role of a bridge and can maintain Ti₂CT_xThe distance of the layered voids of the material and the stability of the structure provide the possibility of storing hydrogen, as shown in fig. 1.

The invention provides a novel room temperature hydrogen storage material, the expression is Ti₂CT_x，Ti₂CT_xThe material is a two-dimensional layered MXene material, has a stacked book-page-shaped layered morphology structure, and has high-density layered gaps with volume fraction of more than 60% and adjustable interlamellar spacing of 0.68-0.9 nm; a large number of fluorine functional groups and oxygen-containing functional groups are connected between layers; 1 to 15 percent of Al atoms left after etching are left between the layers.

Further, Ti₂CT_xThe first hydrogen storage capacity reaches 8.44 wt% at room temperature of 25 ℃ and 50 bar.

Further, Ti₂CT_xThe circulating hydrogen storage capacity was 7.5 wt.% at room temperature 25 ℃ and 50 bar.

Further, Ti₂CT_xAt 95 deg.C and 0bar, over 95% of stored hydrogen is removed within 5 min.

Furthermore, Ti can be realized by changing the external temperature of 25-95 ℃ and the pressure of 0-15 bar₂CT_xThe dehydrogenation amount and the dehydrogenation rate can be controlled.

The invention also provides a preparation method of the novel room-temperature hydrogen storage material, which comprises the following steps:

1) adding a MAX phase Ti₂After sieving AlC powder by a sieve of less than or equal to 200 meshes, pouring the powder into hydrofluoric acid with the concentration of 12 wt%, and fully stirring for t to perform etching reaction, wherein t is more than or equal to 6h and less than 12 h;

2) separating particles obtained after etching from hydrofluoric acid, and washing the particles obtained after separation to be neutral by using deionized water;

3) drying the washed particles in a vacuum oven at 40 ℃ to obtain Ti₂CT_x。

The invention has the beneficial effects that:

1) the whole synthesis process is simple, and large-scale production can be realized;

2) the precursor MAX used in the invention belongs to titanium aluminum carbide ceramics, does not contain noble metal and has low cost;

3) the room temperature hydrogen storage material Ti prepared by the invention₂CT_xThe first hydrogen storage capacity can reach 8.44 wt% and the circulated hydrogen storage capacity is 7.5 wt% at room temperature of 25 deg.C and 50 bar. More than 95% of stored hydrogen can be rapidly removed (within 5 min) at the temperature of 95 ℃ and at the pressure of 0bar, and the control of dehydrogenation amount and dehydrogenation rate can be realized by changing the external temperature (25-95 ℃ at room temperature) and the pressure (0-15 bar).

Drawings

FIG. 1 shows Ti of the present invention₂CT_xPreparation and hydrogen storage schemeA drawing;

FIG. 2 shows Ti etched in example 1 of the present invention₂CT_xSEM picture (upper left corner picture) and HADDF-STEM picture of (A);

FIG. 3 shows Ti etched in example 1 of the present invention₂CT_xA HADDF-STEM map with different layer spacings;

FIG. 4 is a view showing Ti etched in example 1 of the present invention₂CT_xA HADDF-STEM pattern with incompletely etched Al atoms between layers;

FIG. 5 shows Ti etched in example 1 of the present invention₂CT_xXPS test result of Al element (b);

FIG. 6 shows Ti etched in example 1 of the present invention₂CT_xXPS test result of Ti element(s);

FIG. 7 shows Ti etched in example 1 of the present invention₂CT_xXPS test result of F element(s);

FIG. 8 shows Ti etched in example 1 of the present invention₂CT_xXPS test result of C element(s);

FIG. 9 shows Ti etched in example 1 of the present invention₂CT_xXRD curve of (1) and standard PDF card thereof;

FIG. 10 shows Ti etched in example 1 of the present invention₂CT_xThe hydrogen adsorption-desorption cycle curve of (a);

FIG. 11 shows Ti etched according to example 1 of the present invention₂CT_xA low angle XRD profile of the change in the interlayer spacing before and after hydrogen storage;

FIG. 12 shows Ti etched in example 1 of the present invention₂CT_xHydrogen desorption curves at different pressures and temperatures;

FIG. 13 shows Ti etched in example 1 of the present invention₂CT_xThe hydrogen storage stability test result of (1);

FIG. 14 shows Ti etched in examples 1 and 2 of the present invention₂CT_xComparing XRD curves of the two parts;

FIG. 15 shows Ti etched in examples 1 and 2 of the present invention₂CT_xThe hydrogen storage test results are compared with the figure.

Detailed Description

The invention is further described below with reference to the figures and examples.

Example 1

The preparation method of the novel room-temperature hydrogen storage material comprises the following steps:

1) preparing a dilute hydrofluoric acid solution with the concentration of 12 wt% by using 40 wt% concentrated hydrofluoric acid, and placing the dilute hydrofluoric acid solution in a plastic beaker;

2) 2g of Ti₂After sieving the AlC powder by a 200-mesh sieve, slowly pouring the powder into the hydrofluoric acid solution obtained in the step 1);

3) the mixed solution is continuously stirred, so that the phenomenon that the liquid is boiled and splashed due to over violent reaction heat release is avoided;

4) fully stirring for 8 hours at room temperature, and separating the etched particles from an acid solution;

5) repeatedly washing the particles obtained by separation with deionized water until the particles are washed to be neutral;

6) drying the washed particles in a vacuum oven at 40 ℃ to obtain the novel room-temperature hydrogen storage material Ti₂CT_xHaving a layer spacing of 0.68 nm; 2.64% of Al atoms remained after etching are left between the layers.

The Ti produced in the present example will be described below with reference to the accompanying drawings₂CT_xStructural characteristics and hydrogen storage dehydrogenation performance.

FIGS. 2-4 show the novel room temperature hydrogen storage material Ti prepared in example 1₂CT_xAs is apparent from the SEM image of fig. 2, the Ti produced₂CT_xHas a stacked book-page-shaped layered morphology structure, and the interval indicated by white arrows in a HADDF-STEM diagram is the formed uneven interlayer interval. As can be seen from the black arrows in fig. 3, a smaller interlayer spacing of about 0.68nm can be formed in this embodiment, and in addition, the white arrows in fig. 3 indicate the large-sized interlayer spacing formed by completely etching away the interlayer Al atoms.

FIGS. 5 to 8 show Ti₂CT_xXPS test results of Al, Ti, F and C elements of (A) show that Ti is produced₂CT_xA large number of functional groups, mainly fluorine functional groups and oxygen-containing functional groups, are connected between the layers.

In order to maintain proper interlayer spacing, the embodiment 1 of the invention adopts specific etching conditions to enable Ti to be adopted₂CT_xPart of interlayer Al atoms are not completely removed, the existence of Al compounds can be seen from the XRD test result of figure 9, and the interlayer spacing value of the layered structure can be calculated according to the position of the peak in the dotted line frame.

FIG. 10 shows the results of 5 cycles of hydrogen absorption and desorption, Ti, at room temperature at 25 ℃ and a pressure of 50bar₂CT_x7.5 wt% of hydrogen can be reversibly stored, and the XRD result of FIG. 11 also shows Ti₂CT_xThe layered structure of (a) is not destroyed during the hydrogen storage process. And in 5 rounds of hydrogen adsorption-desorption experiments, no significant performance decay was found.

As can be seen from FIG. 12, the Ti produced can be controlled by using different temperatures and pressures₂CT_xWherein the temperature influences the amount of dehydrogenation (whether the absorbed hydrogen is completely released) and the dehydrogenation rate, and under the conditions of low-temperature heating at 95 ℃ and a pressure of 0bar, Ti₂CT_xMore than 90% of the adsorbed hydrogen can be released within 5 minutes, while the pressure influences the dehydrogenation rate.

FIG. 13 shows Ti₂CT_xThe test result of the hydrogen storage stability shows that no obvious gas leakage exists after the hydrogen storage stability test device is placed at room temperature for 7 days, and the storage stability reaches the aim of 2020 of the United states department of energy. Thus, Ti of the present invention₂CT_xHas good hydrogen storage stability.

Example 2

The preparation method of the novel room-temperature hydrogen storage material comprises the following steps:

1) preparing a dilute hydrofluoric acid solution with the concentration of 12 wt% by using 40 wt% concentrated hydrofluoric acid, and placing the dilute hydrofluoric acid solution in a plastic beaker;

2) 2g of Ti₂After sieving the AlC powder by a 200-mesh sieve, slowly pouring the powder into the hydrofluoric acid solution obtained in the step 1);

3) the mixed solution is continuously stirred, so that the phenomenon that the liquid is boiled and splashed due to over violent reaction heat release is avoided;

4) fully stirring for 12 hours at room temperature, and separating the etched particles from an acid solution;

5) repeatedly washing the particles obtained by separation with deionized water until the particles are washed to be neutral;

6) drying the washed particles in a vacuum oven at 40 ℃ to obtain the novel room-temperature hydrogen storage material Ti₂CT_xIt has only a 0.78nm interlayer spacing; at this time, the interlayer Al atoms can be considered to have been completely removed by etching (content)<0.1％)。

The invention can obtain Ti with different interlayer spacing by adjusting the etching time or adjusting the concentration of hydrofluoric acid used in etching₂CT_xTi with smaller interlayer spacing₂CT_xThe hydrogen storage material Ti prepared in example 1 has better hydrogen storage performance₂CT_xAlthough having a non-uniform interlayer spacing, a smaller interlayer spacing of about 0.68nm was used for hydrogen storage, while the hydrogen storage material Ti prepared in example 2 was used₂CT_xIt had only a layer spacing of 0.78nm, and thus it was inferior in hydrogen storage performance to example 1. This is evident from a comparison of the graphs of FIGS. 14 and 15, and the XRD comparison of FIG. 14 shows that the etching time is longer, i.e., L-Ti with lower Al content between layers obtained from example 2₂CT_xTi obtained in example 1₂CT_xWith a larger interlayer spacing. The hydrogen storage test comparison of fig. 15 shows that the example 1 sample having a smaller interlayer distance has a larger hydrogen storage amount.

It will be apparent to those skilled in the art that various modifications and improvements can be made to the embodiments of the present invention without departing from the inventive concept thereof, and these modifications and improvements are intended to be within the scope of the invention.

Claims (6)

1. A novel room-temperature hydrogen storage material is represented by the expression Ti₂CT_xCharacterized by being Ti₂CT_xIs a two-dimensional layered MXene material, has a stacked book page-shaped layered morphology structure and has a volume fractionMore than 60 percent of high-density lamellar gaps and adjustable interlamellar spacing of 0.68 nm-0.9 nm; the interlayer is connected with a fluorine functional group and an oxygen-containing functional group; 1 to 15 percent of Al atoms left after etching are left between the layers.

2. A novel hydrogen storage material at room temperature as claimed in claim 1, characterized by Ti₂CT_xThe first hydrogen storage capacity reaches 8.44 wt% at room temperature of 25 ℃ and 50 bar.

3. A novel hydrogen storage material at room temperature as claimed in claim 1, characterized by Ti₂CT_xThe circulating hydrogen storage capacity was 7.5 wt.% at room temperature 25 ℃ and 50 bar.

4. A novel hydrogen storage material at room temperature as claimed in claim 1, characterized by Ti₂CT_xMore than 95 percent of hydrogen storage capacity is removed within 5min under the conditions of 95 ℃ and 0 bar.

5. A novel hydrogen storage material at room temperature in accordance with claim 1, characterized in that Ti is realized by changing the external temperature from 25 ℃ to 95 ℃ and the pressure from 0bar to 15bar₂CT_xThe dehydrogenation amount and the dehydrogenation rate can be controlled.

6. A method for preparing a novel hydrogen storage material at room temperature according to any one of claims 1 to 5, comprising the steps of:

1) adding a MAX phase Ti₂After sieving AlC powder by a sieve of less than or equal to 200 meshes, pouring the powder into hydrofluoric acid with the concentration of 12 wt%, and fully stirring for t to perform etching reaction, wherein t is more than or equal to 6h and less than 12 h;

2) separating particles obtained after etching from hydrofluoric acid, and washing the particles obtained after separation to be neutral by using deionized water;

3) drying the washed particles in a vacuum oven at 40 ℃ to obtain Ti₂CT_x。

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