A catalyst utilizing strain gradient induced magnetic enhancement and magnetic field response and a method for preparing the same

Abstract

The application discloses a kind of catalyst using strain gradient induced magnetic enhancement and magnetic field response and preparation method thereof, the catalyst is the alloy film of wrinkle morphology with strain gradient, by being tied to alloy film, the alloy film of wrinkle morphology with strain gradient is obtained.Due to the expansion and shrinkage in the temperature rising and falling of NaCl substrate, and the weak van der Waals binding between film and substrate, the film presents self-supporting wrinkle morphology on the substrate.The film with wrinkle morphology is simple in preparation process, and the wrinkle degree and wrinkle density of the film can be adjusted by controlling the high and low of annealing temperature.After introducing strain gradient, the saturation magnetization of wrinkle film at room temperature is enhanced by an order of magnitude compared with flat film.In addition, under the action of external magnetic field, the hydrogen evolution and oxygen evolution reaction activity of wrinkle film as catalyst is obviously improved.

Description

Technical Field

[0001] This invention relates to the field of new materials technology, and in particular to a catalyst that utilizes strain gradient-induced magnetic enhancement and magnetic field response, and its preparation method. Background Technology

[0002] Pulsed laser deposition systems utilize high-energy pulsed lasers, focused by a focusing system, to ablate a solid target, generating a plasma plume. This plasma plume reaches the target substrate surface, ultimately forming a uniform thin film. The resulting films are not only uniform in thickness and have a composition close to that of the solid target, but the film preparation process is also simple, allowing for flexible adjustment of geometric parameters, laser parameters, and film growth process parameters to obtain high-quality films.

[0003] Due to the strong interaction between the thin film and the substrate, films prepared using pulsed laser deposition systems are almost always constrained by a hard substrate and have a flat and uniform surface morphology. Typically, obtaining substrate-free films requires the introduction of a sacrificial layer and detailed knowledge of etching chemistry; therefore, there is an urgent need to develop new processes for preparing unconstrained films with unique morphologies. Furthermore, the properties of unconstrained functional material films can be tuned through strain and strain gradients, thereby broadening their application range.

[0004] To overcome the shortcomings of existing thin film preparation processes, this invention provides a process for obtaining substrate-free constrained alloy thin films, and achieves enhanced magnetic properties and improved electrocatalytic activity of the wrinkled thin films under an external magnetic field by introducing a strain gradient. Summary of the Invention

[0005] Objective of the invention: The objective of this invention is to provide a catalyst with strong magnetic properties and high electrocatalytic activity that utilizes strain gradient-induced magnetic enhancement and magnetic field response; another objective of this invention is to provide a method for preparing the above-mentioned catalyst.

[0006] Technical solution: The present invention provides a catalyst that utilizes strain gradient-induced magnetic enhancement and magnetic field response. The catalyst is an alloy thin film with a strain gradient and a wrinkled morphology. The alloy thin film with a strain gradient and a wrinkled morphology is obtained by binding the alloy thin film.

[0007] Preferably, the thickness of the alloy film is 14nm-135nm.

[0008] Preferably, the alloy film comprises a multi-element alloy or a single metal with good ductility.

[0009] On the other hand, the present invention provides a method for preparing a catalyst that utilizes strain gradient-induced magnetic enhancement and magnetic field response, the preparation method comprising the following steps:

[0010] 1) Deposit an alloy thin film on a NaCl single crystal substrate;

[0011] 2) The alloy film is annealed in situ to room temperature, and the wrinkle size and wrinkle density are controlled by adjusting the annealing temperature.

[0012] 3) Unconstrained, flat films can be obtained by directly picking up from NaCl substrates;

[0013] 4) Using adhesive to bind and peel the film on the NaCl substrate can produce a wrinkled film with strain gradient.

[0014] As a further improvement to the above scheme, in step 1), the substrate temperature is 400℃-450℃.

[0015] As a further improvement to the above scheme, in step 1), the thickness of the alloy film is 14nm-135nm.

[0016] As a further improvement to the above scheme, in step 1), the method for depositing alloy thin films on the NaCl single crystal substrate is pulsed laser deposition or laser-assisted molecular beam epitaxy.

[0017] As a further improvement to the above scheme, in step 1), the alloy film includes a multi-element alloy or a single metal with good ductility.

[0018] As a further improvement to the above scheme, in step 2), the annealing temperature is 400-500℃.

[0019] As a further improvement to the above scheme, in step 2), the method for controlling the wrinkle degree and wrinkle density of the wrinkle morphology is as follows: increasing the annealing temperature results in a larger wrinkle degree and a lower wrinkle density; decreasing the annealing temperature results in a smaller wrinkle degree and a higher wrinkle density.

[0020] This invention discloses a magnetically enhanced and magnetically responsive catalyst induced by a strain gradient. An alloy target is deposited on a NaCl substrate using pulsed laser deposition at a high growth temperature to form a uniform thin film. During in-situ annealing, the expansion and contraction of the NaCl substrate during heating and cooling, along with the weak van der Waals bonding between the film and the substrate, results in a self-supporting wrinkled morphology. The wrinkle degree and density can be adjusted by controlling the annealing temperature. Unconstrained, flat films can be directly picked up from the NaCl substrate using tweezers, while wrinkled films with a strain gradient are obtained by binding and peeling the film from the NaCl substrate using adhesive. The wrinkled film, after introducing a strain gradient, exhibits an order of magnitude increase in room temperature saturation magnetization compared to the flat film. Under an external magnetic field, the wrinkled film shows a significant positive response compared to the negative effects exhibited by the flat film as a catalyst, resulting in improved hydrogen evolution and oxygen evolution performance.

[0021] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0022] (1) The preparation process of this catalyst that induces magnetic enhancement and magnetic field response is simple.

[0023] (2) Adjustable fold morphology can be achieved by changing the annealing temperature.

[0024] (3) The idea of ​​introducing a strain gradient into the thin film through the expansion and contraction of the substrate, the weak van der Waals bonding between the interfaces and the transfer of adhesive is ingenious.

[0025] (4) For some multi-element alloys or metallic elements with good ductility, the preparation process can be repeated. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a catalyst preparation process that utilizes strain gradient-induced magnetic enhancement and magnetic field response, provided as an embodiment of the present invention.

[0027] Figure 2 The images shown are optical microscope images of the wrinkled film prepared in Example 1 of the present invention. S1 is an optical microscope image of the wrinkled film before transfer, and S2 is an optical microscope image of the wrinkled film after transfer.

[0028] Figure 3 This is an optical microscope image of the flat film prepared in Comparative Example 1 of the present invention.

[0029] Figure 4 These are optical microscope images of the wrinkled films prepared in the comparative examples of the present invention. S1 is an optical microscope image of the wrinkled film of Comparative Example 2; S3 is an optical microscope image of the wrinkled film of Comparative Example 3.

[0030] Figure 5 The room temperature hysteresis loops of the wrinkled thin film and the flat thin film in the embodiments of the present invention are shown.

[0031] Figure 6 The figures show the hydrogen evolution performance of the wrinkled film and the flat film as catalysts in this embodiment of the invention, respectively, under no magnetic field and under a magnetic field.

[0032] Figure 7 The diagram shows the oxygen evolution performance of the wrinkled film and the flat film as catalysts in this embodiment of the invention, respectively, under no magnetic field and under a magnetic field. Detailed Implementation

[0033] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0034] Example 1

[0035] like Figure 1 As shown, this embodiment of the invention provides a method for preparing a catalyst that utilizes strain gradient-induced magnetic enhancement and magnetic field response. The preparation method includes the following steps:

[0036] 1) First, at a growth temperature of 450℃, an alloy thin film is prepared on a NaCl single crystal substrate (1cm×1cm) using a pulsed laser deposition system. The thickness of the CrMnFeCoNi alloy thin film can be controlled between 14nm and 135nm depending on the number of laser pulses (5000-40000 pulses).

[0037] 2) Based on the required wrinkle size and wrinkle density, maintain the temperature of the alloy film at 450℃ and anneal for 30 minutes.

[0038] 3) Turn off the temperature control switch and wait for the alloy film to cool down to room temperature naturally in a high vacuum environment, so as to form the corresponding wrinkled morphology.

[0039] 4) Unconstrained flat films (1cm×1cm) can be directly picked up from the NaCl substrate using tweezers, while wrinkled films (1cm×1cm) with strain gradients can be obtained by binding and peeling the films on the NaCl substrate with adhesive. Thus, a catalyst with magnetic enhancement and magnetic field response induced by strain gradient is prepared.

[0040] Figure 2 This is an optical microscope image of the wrinkled film finally prepared in Example 1.

[0041] In the above preparation method, the thickness of the CrMnFeCoNi alloy film has little effect on the catalytic performance of the catalyst. Therefore, films of different thicknesses can be obtained by adjusting the number of laser pulses according to actual application requirements.

[0042] Comparative Example 1

[0043] Comparative Example 1 provides a flat film catalyst, which is prepared by the following steps: keeping steps (1) to (3) of Example 1 unchanged, the flat film catalyst can be directly picked up from the NaCl substrate by tweezers.

[0044] Figure 3 This is an optical microscope image of the flat film finally prepared for Comparative Example 1.

[0045] Figure 1 In the diagram, S1 shows the preparation of an alloy thin film on a NaCl single crystal substrate at 450℃ using a pulsed laser deposition system. The substrate size is 1cm×1cm, and the film has high flatness at this temperature. S2 shows the naturally formed wrinkled morphology of the alloy thin film during in-situ annealing to room temperature. S3 shows the use of adhesive to bind and peel the film on the NaCl substrate to obtain a wrinkled film with strain gradient.

[0046] Hysteresis Loop Measurement: Room-temperature hysteresis loops of both flat and wrinkled thin films were measured using a superconducting quantum interference device (SQI) manufactured by Quantum Design, Inc. The room-temperature hysteresis loop data were recorded in four parts: 10 kilo-Oerst to 0 Oerst, 0 Oerst to -10 kilo-Oerst, -10 kilo-Oerst to 0 Oerst, and 0 Oerst to 10 kilo-Oerst. Furthermore, the superconducting magnet was demagnetized by oscillation at 300 K before each measurement to ensure no residual magnetic flux in the tested thin film.

[0047] Figure 5 Hysteresis loop measurements revealed that the saturation magnetization of the wrinkled film was increased tenfold compared to the flat film after introducing a strain gradient. The wrinkled film was the catalyst finally prepared in Example 1, while the flat film was the catalyst prepared in Comparative Example 1.

[0048] Hydrogen evolution and oxygen evolution performance testing: Hydrogen evolution and oxygen evolution performance tests were conducted at room temperature using a CHI 660E electrochemical workstation (Shanghai Chenhua, China) equipped with a standard three-electrode electrochemical cell (using 1 molar potassium hydroxide solution as the electrolyte). The reference electrode was mercury / mercuric oxide, the counter electrode was made of graphite rod, and flat and wrinkled films were used as the working electrodes. Linear sweep voltammetry of the hydrogen evolution and oxygen evolution reactions was performed at a scan rate of 5 mV / s and compensated for according to their resistance values.

[0049] Figure 6 and Figure 7The wrinkled film and the flat film were used as electrochemical catalysts, respectively, and their hydrogen evolution and oxygen evolution performance under no magnetic field and with a magnetic field were studied. S1 shows that the hydrogen evolution and oxygen evolution catalytic performance of the wrinkled film is significantly improved under an external magnetic field, while S2 shows that the flat film exhibits a negative effect as a catalyst under an external magnetic field. The wrinkled film is the catalyst finally prepared in Example 1. The flat film is the catalyst prepared in Comparative Example 1.

[0050] Example 2

[0051] This invention provides a method for preparing a catalyst that utilizes strain gradient-induced magnetic enhancement and magnetic field response. The difference between this method and Example 1 is that in step (1), the growth temperature of the CrMnFeCoNi alloy thin film is 400℃; in step (2), the annealing temperature is 400℃; the steps and conditions are the same as in Example 1. The hydrogen evolution and oxygen evolution performance of the wrinkled film prepared by the above method is comparable to that of the wrinkled film prepared in Example 1.

[0052] Example 3

[0053] This invention provides a method for preparing a catalyst that utilizes strain gradient-induced magnetic enhancement and magnetic field response. The difference between this method and Example 1 is that in step (1), the growth temperature of the CrMnFeCoNi alloy thin film is 450℃; in step (2), the annealing temperature is 500℃; the steps and conditions are the same as in Example 1. The hydrogen evolution and oxygen evolution performance of the wrinkled film prepared by the above method is comparable to that of the wrinkled film prepared in Example 1.

[0054] Comparative Example 2

[0055] This comparative example provides a method for preparing a catalyst that utilizes strain gradient-induced magnetic enhancement and magnetic field response. The difference between this method and Example 1 is that in step (2), the annealing temperature is 250°C; the steps and conditions are the same as in Example 1.

[0056] like Figure 4 As shown in (S1), the wrinkled film prepared by the above method has the following morphological characteristics: high wrinkle density but low wrinkle degree. Since the film and the substrate are strongly bonded, the film will be torn and damaged after peeling. Therefore, its hydrogen evolution and oxygen evolution performance is much worse than that of Example 1.

[0057] Comparative Example 3

[0058] This comparative example provides a method for preparing a catalyst that utilizes strain gradient-induced magnetic enhancement and magnetic field response. The difference between this method and Example 1 is that in step (2), the annealing temperature is 650°C; the steps and conditions are the same as in Example 1.

[0059] like Figure 4As shown in (S2), the wrinkled film prepared by the above method has the following morphological characteristics: large wrinkle degree but low wrinkle density. Since its wrinkle morphology (i.e. strain gradient) is difficult to be preserved during the transfer process, its hydrogen evolution and oxygen evolution performance is far worse than that of Example 1.

[0060] Comparative Example 4

[0061] This comparative example provides a method for preparing a catalyst that utilizes strain gradient-induced magnetic enhancement and magnetic field response. The difference between this method and Example 1 lies in the different single-crystal substrates. In this comparative example, alloy catalysts are prepared on MgO, SrTiO3, and Al2O3 single-crystal substrates, respectively. On these single-crystal substrates, it is impossible to form wrinkled morphologies similar to those on NaCl single-crystal substrates. The resulting films are smooth and tightly bonded to the MgO, SrTiO3, and Al2O3 single-crystal substrates. The preparation method includes the following steps:

[0062] 1) First, at a growth temperature of 450℃, an alloy thin film was prepared on a 0.5cm×0.5cm single crystal substrate of MgO, SrTiO3 and Al2O3 using a pulsed laser deposition system. The thickness of the alloy thin film was controlled at 100nm.

[0063] 2) Anneal the alloy film in situ at 450℃ for 30 minutes;

[0064] 3) Turn off the temperature control switch and wait for the alloy film to cool down to room temperature naturally in a high vacuum environment, so as to form a smooth morphology.

[0065] The thin film prepared by the above method cannot form the wrinkled morphology in Example 1.

[0066] This invention provides a method for preparing a strain gradient-induced magnetic enhancement and magnetic field-responsive catalyst. Compared with traditional thin film deposition methods, this method overcomes the limitation of only growing substrate-constrained films, providing a novel peelable, self-supporting wrinkled morphology with adjustable wrinkle morphology. Simultaneously, by using adhesive to bind and peel the film on a NaCl substrate to introduce a strain gradient, the magnetic properties and catalytic performance under a magnetic field of the film are significantly improved. The entire operation process is simple and has certain application prospects. It should be noted that those skilled in the art can make several improvements without departing from the principle of this invention. For example, in addition to depositing certain multi-element alloys or elemental metals, this method can also be used to introduce a strain gradient and obtain corresponding wrinkled films for some functional materials with good ductility and strength. Alternatively, alloy films can be prepared using vacuum deposition methods such as magnetron sputtering. These improvements should also be considered within the scope of protection of this invention.

Claims

1. A method for preparing a catalyst that utilizes strain gradient-induced magnetic enhancement and magnetic field response, characterized in that, The preparation method includes the following steps: 1) Deposit an alloy thin film on a NaCl single crystal substrate; 2) The alloy film is annealed in situ to room temperature, and the wrinkle size and wrinkle density are controlled by adjusting the annealing temperature; the annealing temperature is 400-500℃. 3) Unconstrained, flat films can be obtained by directly picking up from NaCl substrates; 4) By using adhesive to bind and peel the film on the NaCl substrate, a wrinkled film with strain gradient can be obtained.

2. The method for preparing a catalyst utilizing strain gradient-induced magnetic enhancement and magnetic field response according to claim 1, characterized in that, In step 1), the substrate temperature is 400℃-450℃.

3. The method for preparing a catalyst utilizing strain gradient-induced magnetic enhancement and magnetic field response according to claim 1, characterized in that, In step 1), the thickness of the alloy film is 14 nm-135 nm.

4. The method for preparing a catalyst utilizing strain gradient-induced magnetic enhancement and magnetic field response according to claim 1, characterized in that, In step 1), the method for depositing alloy thin films on NaCl single crystal substrates is pulsed laser deposition or laser-assisted molecular beam epitaxy.

5. The method for preparing a catalyst utilizing strain gradient-induced magnetic enhancement and magnetic field response according to claim 1, characterized in that, In step 1), the alloy film includes a multi-element alloy with good ductility.

6. The method for preparing a catalyst utilizing strain gradient-induced magnetic enhancement and magnetic field response according to claim 1, characterized in that, In step 2), the method to control the wrinkle degree and wrinkle density of the wrinkle morphology is as follows: increasing the annealing temperature results in a larger wrinkle degree and a lower wrinkle density; decreasing the annealing temperature results in a smaller wrinkle degree and a higher wrinkle density.

7. A catalyst prepared using the method of claim 1, characterized in that, The catalyst is an alloy film with a strain gradient and a wrinkled morphology. The alloy film with a strain gradient and a wrinkled morphology is obtained by binding the alloy film.

8. The catalyst according to claim 7, characterized in that, The thickness of the alloy film is 14 nm-135 nm.

9. The catalyst according to claim 7, characterized in that, Alloy films include multi-element alloys with good ductility.

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