Preparation method and application of low-crystallinity NiFe LDH three-dimensional nanosheet array catalyst

Abstract

The invention relates to a preparation method and application of a low-crystallinity NiFe LDH three-dimensional nanosheet array catalyst. The preparation method comprises the following steps: removing surface impurities and oxide layers of nickel foil by using strong acid, ultrapure water and absolute ethyl alcohol respectively; the treated nickel foil is placed in an electrolyte composed of 1 mmol to 20 mmol of FeSO4, 1 mmol to 10 mmol of H3BO3 and a saturated KCl aqueous solution, and the low-crystallinity NiFe LDH three-dimensional nanosheet array catalyst is prepared through a pulse electrodeposition method. The NiFe LDH-B / NF amorphous / crystal nanosheet with excellent OER performance is prepared by taking nickel foil as a framework to replace foamed nickel through a pulse electrodeposition method. The electrocatalytic performance of the film material can be promoted, and the problem that traditional ultrasonic waves have no obvious influence on oxygen evolution performance is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrocatalysis, and in particular relates to a preparation method and application of a low-crystalline NiFe LDH three-dimensional nanosheet array catalyst. The catalyst has good acoustic wave responsiveness and OER activity, is a non-precious metal catalyst, and can be used to assist in oxygen evolution by electrolysis of water. Background Art

[0002] With the widespread use of renewable energy around the world, the need to store unstable energy in the form of stable chemical energy (such as hydrogen energy) is becoming increasingly urgent. Water electrolysis technology driven by renewable energy is an important way to achieve sustainable hydrogen production. However, water electrolysis requires an additional overpotential to overcome the activation energy barrier, resulting in energy loss. Currently, many electrolytic cells rely on precious metal electrodes and lack efficient catalysts to reduce the overpotential. In particular, compared with the cathode hydrogen evolution reaction (HER), the anode oxygen evolution reaction (OER) has slower kinetics, becoming the main bottleneck limiting battery efficiency. Therefore, the development of high-performance and highly stable anode electrocatalysts is crucial to improving the efficiency of water electrolysis.

[0003] Excellent electrocatalysts can significantly reduce the activation overpotential required for electrocatalysis, and the introduction of ultrasound can compensate for the ohmic loss in the system caused by the kinetic overpotential. The application of ultrasound in the field of water electrolysis mainly optimizes the reaction kinetics and mass transfer process through its physical effects (such as cavitation effect and acoustic streaming effect), thereby improving the HER and OER efficiency. Usually, ultrasound is emitted by a generator and then transmitted to the electrolytic cell through a medium such as water to interfere with the electrocatalyst electrolysis of water. Since the loss of ultrasound during propagation needs to be considered, the ultrasonic power used is usually large, and long-term radiation on the electrocatalyst will damage its service life. Therefore, it is necessary to improve the device for applying ultrasound to solve the problem of ultrasound loss service life and further improve the performance of ultrasound-assisted water electrolysis. Summary of the invention

[0004] In view of the deficiencies in the prior art, the technical problem to be solved by the present invention is to provide a preparation method and application of a low-crystalline NiFeLDH three-dimensional nanosheet array catalyst, so as to solve the deficiencies in the prior art of the lack of catalysts having both good ultrasonic effect and excellent OER activity, as well as the problems that the traditional sound wave-assisted electrocatalytic oxygen evolution effect is not significant and the traditional sound wave device damages the stability of the catalyst.

[0005] The technical solution adopted by the present invention to solve the technical problem is:

[0006] In a first aspect, the present invention provides a method for preparing a low-crystalline NiFe LDH three-dimensional nanosheet array catalyst, the preparation method comprising: removing surface impurities and an oxide layer from a nickel foil using a strong acid, ultrapure water, and anhydrous ethanol, respectively; placing the treated nickel foil in a solution containing 1 to 20 mmol FeSO 4 1~10mmol H 3 BO 3 Low-crystalline NiFe LDH three-dimensional nanosheet array catalyst was prepared by pulse electrodeposition in an electrolyte consisting of a saturated KCl aqueous solution.

[0007] Furthermore, the specific process of the preparation method is:

[0008] S1. Place 1-100 μm nickel foil in a 1-3M H ion strong acid solution for ultrasonic treatment to remove the NiOx layer that may exist on its surface, then rinse with ultrapure water and ethanol, and blow dry with dry analytical pure argon gas;

[0009] S2, 1-20 mmol FeSO 4 1~10mmol H 3 BO 3 Add to 50 mL of saturated KCl aqueous solution and stir evenly to obtain an electrolyte;

[0010] S3, using pulse deposition method to perform electrochemical treatment, using a two-electrode system, wherein both electrodes are nickel foils pre-treated in step S1, the two electrodes are placed in parallel, 1.5-3 cm apart from each other, and the electrolyte described in step S2 is used; the pulse current density applied in the pulse electrodeposition method is ±10-100 mA / cm 2 , pulse frequency is 0~20Hz, pulse period is 0~1000;

[0011] S4. After the electrochemical treatment is completed, the electrode is taken out from the electrolyte, rinsed with ultrapure water and anhydrous ethanol, and placed in a vacuum oven for drying at 50-70°C for 8-16 hours to obtain a low-crystalline NiFe LDH three-dimensional nanosheet array catalyst.

[0012] Furthermore, in step S1, the thickness of the nickel foil is 8-20 μm, and the strong acid is: H 2 SO 4 solution or 1-3M HCl solution; in step S2, FeSO 4 The concentration is 1~5mmol, H 3 BO 3 The concentration is 1 to 3 mmol;

[0013] In step S3, the pulse current density applied is ±30-60 mA / cm 2 , the pulse frequency is 4~8Hz, and the pulse period is 500~800.

[0014] In a second aspect, the present invention provides a low-crystalline NiFe LDH three-dimensional nanosheet array catalyst obtained by the preparation method, wherein the microscopic morphology of the catalyst is composed of a large number of wrinkled nanosheets, and there are crystalline regions and non-crystalline regions inside the nanosheets.

[0015] Furthermore, Fe, Ni, O and B elements in the nanosheets of the catalyst are uniformly dispersed on the surface thereof.

[0016] In a third aspect, the present invention provides an application of the catalyst according to claim 4, wherein a low-crystalline NiFe LDH three-dimensional nanosheet array catalyst is used as a working electrode for electrocatalytic oxygen evolution, and the low-crystalline NiFe LDH three-dimensional nanosheet array catalyst is recorded as NiFe LDH-B / NF, and the specific application process is as follows:

[0017] One side of NiFe LDH-B / NF is the adhesive surface, and the other side is the test surface. Use AB glue to adhere the adhesive surface of NiFe LDH-B / NF to the substrate of the interdigital electrode, 1.5-3mm away from the photolithographic pattern on the interdigital electrode. Use a scraper to hang off the excess AB glue and dry it for 2.5-5 hours.

[0018] Subsequently, the electrolytic cell was adhered to the interdigital electrode with AB glue, the electrolytic cell covered the working electrode, and the inside of the electrolytic cell was divided into a working electrode covering area and a substrate area, and then dried overnight to obtain an in-situ hybrid acoustic wave electrolytic cell;

[0019] A 1.0 M potassium hydroxide solution was prepared as an electrocatalytic electrolyte, and nitrogen was introduced into the in-situ hybrid sonic electrolysis cell to drive out the air;

[0020] Using NiFe LDH-B / NF as the working electrode, graphite as the counter electrode, and saturated calomel electrode as the reference electrode, the electrochemical workstation was connected to carry out the electrocatalytic oxygen evolution reaction in the electrocatalytic electrolyte.

[0021] The RF source is connected to the signal amplifier, and then connected to a resistor with a resistance of 50 ohms, and then connected to the interdigital electrodes; a DC power supply is used to provide a DC power of 32V to the signal amplifier; during the electrocatalytic oxygen evolution test, the RF source causes the interdigital electrodes to convert an RF signal with a frequency of 5-15MHZ and a level of 0-108dbm into an acoustic signal through the signal amplifier to assist oxygen evolution and test its overpotential.

[0022] Furthermore, the substrate of the interdigitated electrode is a lithium niobate single crystal, and the photolithographic pattern converts the electrical signal into an acoustic wave signal. The acoustic wave is transmitted by the lithium niobate single crystal of the substrate and propagates to the working electrode adhered to the single crystal. At the same time, the single crystal not covered by the working electrode propagates the acoustic wave into the electrolyte, jointly promoting the oxygen evolution performance of the electrocatalyst in the form of bulk acoustic waves and surface acoustic waves.

[0023] Furthermore, without surface ultrasound, the working electrode was subjected to a current density of 20 mA cm -2 The overpotential of NiFe LDH-B / NF was 294 mV under the condition of surface ultrasound at a current density of 20 mA cm -2 The overpotential of NiFe LDH-B was 237 mV; Ultrasonic wave reduced the overpotential of NiFe LDH-B from 294 mV to 237 mV @ 20 mA cm -2 , Tafel slope decreases by 66mV·dec -1 , ultrasound increases the current density at 500mV by no less than two times.

[0024] In a fourth aspect, the present invention provides an in-situ hybrid acoustic electrolysis system, characterized in that the system comprises:

[0025] RF source: transmits an RF signal with a frequency of 5-15MHz and a level of 0-9dbm;

[0026] DC power supply: Provide 32V DC power to the signal amplifier;

[0027] Signal amplifier: used to amplify the RF signal strength of the radio frequency source;

[0028] Interdigitated electrode: It includes a 28.0mm×47.0mm×0.5mm single crystal piezoelectric substrate on which a comb-shaped transducer electrode pattern is photoetched to convert electrical signals into acoustic signals;

[0029] Electrolytic cell: A regular quadrangular prism made of glass, with the upper and lower surfaces not sealed;

[0030] Assembly: First, glue the working electrode to the outside of the pattern on the interdigital electrode with AB glue, then cover the working electrode with the electrolytic cell, and glue the bottom of the electrolytic cell to the substrate of the interdigital electrode with AB glue. The working electrode is not completely covered in the electrolytic cell, and some areas of the substrate are exposed; then, use a BNC-N port adapter to connect the RF source and the signal amplifier, and then use the N port-electrode clamp to connect the signal amplifier to the interdigital electrode; then connect the signal amplifier to the DC power supply, so that the transmitted electrical signal of the RF source is amplified by the signal amplifier and converted into an acoustic wave signal by the interdigital electrode; finally, add KOH solution to the electrolytic cell, insert the counter electrode and reference electrode, and then connect the electrochemical workstation to perform relevant tests.

[0031] Furthermore, the size of the electrolytic cell in the system is 13.0 mm×13 mm×24.5 mm×1 cm.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) The present invention prepares NiFe LDH-B / NF amorphous / crystalline nanosheets with excellent OER performance by using nickel foil as the skeleton instead of nickel foam through pulse electrodeposition.

[0034] (2) The in-situ hybrid acoustic wave electrolysis cell of the present invention can promote the electrocatalytic performance of thin film materials, overcoming the problem that conventional ultrasonic waves have little effect on oxygen evolution performance.

[0035] (3) Surface acoustic waves can reduce the oxygen evolution overpotential of NiFe LDH-B / NF by up to 57 mV, and increase the current density at 500 mV by 2.1 times, with excellent acoustic wave response performance. Surface acoustic waves significantly enhance the oxygen evolution performance of NiFe LDH-B / NF, which is much greater than the effect of traditional ultrasound on oxygen evolution performance.

[0036] (4) The overpotential in water decomposition is mainly caused by activation, ohmic and concentration overpotentials. Although the activation and ohmic overpotentials can be reduced by optimizing the catalyst to improve the OER performance, the improvement of HER and OER performance also leads to the accumulation and increase of bubbles on the electrodes. The high content of bubbles in the solution hinders the transmission of the electrolyte and increases the solution resistance. The accumulation of bubbles on the electrodes acts as an insulating barrier, disrupting the electrolysis process. The catalyst prepared by the present invention and its application method can effectively weaken the ohmic and concentration overpotentials caused by bubbles, effectively remove hydrogen bubbles, improve the hydrogen evolution performance, and have a favorable effect on the oxygen evolution reaction without destroying the stability of the catalyst, significantly reducing the overpotential.

[0037] (5) The self-supporting working electrode prepared by the present invention has excellent OER activity, and the improvement of OER by surface acoustic waves is much greater than that by conventional ultrasound, and the electrolyte is not heated, causing less damage to the material itself. In addition, surface acoustic wave devices are easier to characterize in situ than conventional ultrasound devices, which facilitates the study of the microscopic mechanism of acoustic wave-assisted water electrolysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a physical picture of the in-situ hybrid acoustic electrolysis cell.

[0039] Figure 2 Linear sweep voltammetry curves of the oxygen evolution reaction in water electrolysis with or without 10MHz acoustic wave assistance on nickel foils of different thicknesses.

[0040] Figure 3Figures 2 and 3 are the characterization results of NiFe LDH-B, where (a)-(b) are TEM images of NiFe LDH-B; (c) energy dispersive analysis (EDX) element distribution map and electron diffraction map of NiFe LDH-B.

[0041] Figure 4 The oxygen evolution performance test results of different samples are shown in Figure 1, where (a) is the LSV curve, (b) is the Tafel slope, (c) is the EIS graph, and (d) is the double layer C dl picture.

[0042] Figure 5 The oxygen evolution performance test results of different samples with and without ultrasound are shown in Figure 2, where (a) is the LSV curve, (b) is the Tafel slope, (c) is the EIS graph, and (d) is the double layer C dl picture.

[0043] Figure 6 It is a schematic diagram of the simulation structure of the in-situ mixed acoustic electrolysis system in the present invention.

[0044] Figure 7 This is a physical picture of the in-situ mixed acoustic electrolysis system of the present invention. DETAILED DESCRIPTION

[0045] The present invention will be described in detail below through the accompanying drawings and in combination with embodiments, and the advantages and implementation methods of the present invention will become more obvious. The contents shown in the accompanying drawings are only used to explain the present invention and do not constitute any limitation to the present invention in any sense.

[0046] The present invention provides a method for preparing a low-crystalline NiFe LDH three-dimensional nanosheet array catalyst. The method comprises removing surface impurities and an oxide layer from nickel foils of a certain area and different thicknesses using a strong acid (H2+ concentration of 1 to 3 M), ultrapure water and anhydrous ethanol, wherein the strong acid may be H2+ with a concentration of 0.8 to 1.2 mol / L. 2 SO 4 solution, 1-3M HCl solution, etc. The treated nickel foil is placed in a solution containing 1-20mmolFeSO 4 , 40mM (mMol / mL) H 3 BO 3 Low-crystalline NiFe LDH-B / NF was prepared by pulse electrodeposition in an electrolyte consisting of a saturated KCl aqueous solution.

[0047] Use AB glue to glue NiFe LDH-B / NF as the working electrode to the interdigital electrode, 1.5-3 mm away from the photolithographic pattern, use a scraper to hang off the excess AB glue, and dry for 3 hours. Then, glue the electrolytic cell to the interdigital electrode with AB glue, and the electrolytic cell covers the working electrode, leaving a 1 cm area of ​​the working electrode inside the electrolytic cell.2 , and then dried overnight to obtain an in-situ hybrid sonic electrolytic cell.

[0048] The specific preparation and application process is as follows:

[0049] 1. Preparation process

[0050] S1. Place a 1-100 μm nickel foil (with a test surface and an adhesive surface) in a 1-3 M HCl solution for ultrasonic treatment for 10 minutes to remove the NiOx layer that may exist on its surface, then rinse with ultrapure water and ethanol, and blow dry with dry analytical pure argon.

[0051] S2, 1-20 mmol FeSO 4 1~10mmol H 3 BO 3 Add to 50 mL of saturated KCl aqueous solution and stir evenly to obtain an electrolyte;

[0052] S3. Electrochemical treatment is carried out in a two-electrode system, where both electrodes are pre-cleaned nickel foils, placed in parallel and about 1.5-3 cm apart. The pulse current density applied in the pulse electrodeposition method is ±10-100 mA / cm 2 , pulse frequency is 0~20Hz, pulse period is 0~1000;

[0053] S4. After the electrochemical treatment is completed, the electrode is taken out from the electrolyte, rinsed with ultrapure water and anhydrous ethanol, and placed in a vacuum oven for drying at 60° C. for 8 to 16 hours to obtain a low-crystalline NiFe LDH three-dimensional nanosheet array catalyst.

[0054] Preferably, in step S1, a nickel foil with a thickness of 10 μm is selected and ultrasonically treated in a 3 mol / L HCl solution for 10 minutes, and then rinsed three times with water and ethanol in sequence.

[0055] In step S2, 1 mmol of FeSO 4 , 2mmol H 3 BO 3 Add it into a saturated KCl aqueous solution and stir for 5 min to obtain a uniform electrolyte.

[0056] In step S3, the pulse current density applied is ±50 mA / cm 2 , the pulse frequency is 5Hz, and the pulse period is 750.

[0057] In step S4, drying is performed in a vacuum drying oven for 8 hours.

[0058] 2. Application process of acoustic wave assisted electrocatalytic oxygen evolution

[0059] F1. Mix glue A and glue B in a mass ratio of 3:1 and stir evenly;

[0060] F2. Use AB glue to adhere the prepared low-crystalline NiFe LDH three-dimensional nanosheet array catalyst to the interdigital electrode, 1.5-3 mm away from the photolithographic pattern on the interdigital electrode, use a scraper to hang off the excess AB glue, and dry for 3 hours;

[0061] F3. Use AB glue to stick the electrolytic cell to the interdigital electrodes. Cover the working electrode completely in the electrolytic cell, leaving some space to expose the substrate of the interdigital electrodes. The area of ​​the working electrode left inside the electrolytic cell is 1cm. 2 , and then dried overnight to obtain an in-situ hybrid sonic electrolytic cell.

[0062] F4, prepare 1.0M potassium hydroxide solution as the electrocatalytic electrolyte, and introduce nitrogen to drive away the air;

[0063] F5. Use NiFe LDH-B / NF as the working electrode, graphite as the counter electrode, and saturated calomel electrode as the reference electrode. Connect to an electrochemical workstation and carry out electrocatalytic oxygen evolution reaction in the electrolyte.

[0064] F6. Connect the RF source to the signal amplifier, and connect a 50 ohm resistor, and then connect the interdigital electrodes; use a DC power supply to provide the signal amplifier with a DC power of 32V. During the electrocatalytic oxygen evolution test, the RF source converts an RF signal with a frequency of 5-15MHZ and a level of 0-108dbm into an acoustic signal through the signal amplifier to assist oxygen evolution and test its overpotential.

[0065] Example 1

[0066] First, a 10 μm nickel foil was placed in a 3 M HCl solution for ultrasonic treatment for 10 min, then rinsed with ultrapure water and ethanol, and blown dry with dry analytical grade argon. 50 mL of 20 mM FeSO 4 , 40 mM H 3 BO 3 The electrochemical treatment was carried out in a two-electrode system, where both electrodes were pre-cleaned nickel foils with an area of ​​1*1cm 2 , the two electrodes are placed parallel to each other, about 3 cm apart.

[0067] The pulse current density applied in the experiment was ±50 mA / cm 2, the pulse frequency is 5Hz, and the pulse period is 750. After the electrochemical treatment is completed, the electrode is removed from the electrolyte, rinsed with ultrapure water and ethanol, and dried in a vacuum box for 8 hours. Mix glue A and glue B in a mass ratio of 3:1 and stir evenly. Use AB glue to glue the nickel foil to the interdigital electrode, 3mm away from the photolithographic pattern, use a scraper to hang out the excess AB glue, and dry it for 3 hours. Subsequently, use AB glue to glue the electrolytic cell to the interdigital electrode, and the working electrode area left inside the electrolytic cell is 1cm 2 , and then dried overnight to obtain an in situ sonic electrochemical cell.

[0068] In this embodiment, the substrate of the interdigitated electrode is a lithium niobate single crystal. The photolithographic pattern can convert electrical signals into acoustic wave signals. The acoustic waves are transmitted by the lithium niobate single crystal of the substrate to the nickel foil adhered to the single crystal. At the same time, the single crystal not covered by the nickel foil can transmit the acoustic waves to the electrolyte, and jointly promote the oxygen evolution performance of the electrocatalyst in the form of body acoustic waves (inside the nickel foil body) and surface acoustic waves (surface in contact with the electrolyte).

[0069] application

[0070] Prepare 1.0M potassium hydroxide solution as electrocatalytic electrolyte, introduce nitrogen to drive away air. NiFe LDH-B / NF is used as working electrode, graphite is used as counter electrode, saturated calomel electrode is used as reference electrode, connected to electrochemical workstation, and electrocatalytic oxygen evolution reaction is carried out in electrolyte.

[0071] Without surface ultrasound, the working electrode was -2 The overpotential is 294mV.

[0072] Then, the RF source was connected to the signal amplifier, and then connected to a 50 ohm resistor, and then connected to the interdigital electrodes. During the electrocatalytic oxygen evolution test, the interdigital electrodes converted an RF signal with a frequency of 10 MHZ and a level of 60 dBm into an acoustic signal. NiFe LDH-B / NF was tested at a current density of 20 mA cm -2 The overpotential is 237mV.

[0073] Under the same test conditions, if nickel foam of the same thickness is used as the carrier of the working electrode, the attenuation of ultrasound is relatively strong and cannot play a role in reducing the overpotential in the electrocatalytic oxygen evolution test.

[0074] from Figure 3TEM shows that the microscopic morphology of NiFe LDH-B / NF is composed of a large number of wrinkled nanosheets, and there are crystalline regions (the lattice spacing of the crystalline region is 0.216nm) and amorphous regions (Amorphous) inside the nanosheets. In addition, elemental mapping analysis of NiFe-LDH-B nanosheets shows that Fe and Ni, O, and B elements are uniformly dispersed on their surface.

[0075] The present application can play a role in reducing overpotential at higher current density, and the catalyst has high ultrasonic responsiveness, which is greatly improved with the assistance of ultrasound.

[0076] Comparative Example 1

[0077] In this embodiment, only the thickness of the nickel foil is changed to test the related performance of water electrolysis and oxygen evolution with or without the assistance of surface ultrasound at different thicknesses.

[0078] Figure 2 The vertical axis is the current density when electrolyzing water for oxygen evolution, and the horizontal axis is the voltage when electrolyzing water for oxygen evolution. The figure shows the LSV curves of oxygen evolution of nickel foil with thickness of 4um, 8um, and 10um with and without the assistance of sound waves. -2 The overpotentials at the locations are 849mV, 716mV, and 670mV respectively. When there is sound wave, the overpotentials at 50mA cm -2 The overpotentials at the 10 μm thick nickel foil are 837 mV, 699 mV, and 643 mV, respectively. After applying the sound wave, the overpotential of the 10 μm thick nickel foil drops the most, by only 27 mV. The nickel foil itself has a relatively low response to ultrasound.

[0079] Comparative Example 2

[0080] First, a 10 μm nickel foil was placed in a 3 M HCl solution for 10 min of ultrasonic treatment, then rinsed with ultrapure water and ethanol, and blown dry with dry analytical grade argon. 4 The electrochemical treatment was carried out in a two-electrode system, where both electrodes were pre-cleaned nickel foils with an area of ​​1*1cm 2 The two electrodes were placed in parallel and about 3 cm apart. The pulse current density applied in the experiment was ±50 mA / cm 2 , the pulse frequency was 5 Hz, and the pulse period was 750. After the electrochemical treatment was completed, the electrode was taken out from the electrolyte, rinsed with ultrapure water and ethanol, and dried in a vacuum box for 8 hours. NiFe LDH / NF catalyst was obtained.

[0081] The results show that the electrocatalytic oxygen evolution reaction in the electrolyte can be carried out without ultrasound assistance at a current density of 20 mA cm -2 The overpotential is 303mV.

[0082] Comparative Example 3

[0083] First, a 10 μm nickel foil was placed in a 3M HCl solution for 10 min of ultrasonic treatment, then rinsed with ultrapure water and ethanol, and blown dry with dry analytical grade argon. 3 BO 3 The electrochemical treatment was carried out in a two-electrode system, where both electrodes were pre-cleaned nickel foils with an area of ​​1*1cm 2 The two electrodes were placed in parallel and about 3 cm apart. The pulse current density applied in the experiment was ±50 mA / cm 2 , the pulse frequency was 5 Hz, and the pulse period was 750. After the electrochemical treatment was completed, the electrode was taken out from the electrolyte, rinsed with ultrapure water and ethanol, and dried in a vacuum box for 8 hours. Ni LDH-B / NF catalyst was obtained.

[0084] The results show that the electrocatalytic oxygen evolution reaction in the electrolyte can be carried out without ultrasound assistance at a current density of 20 mA cm -2 The overpotential is 346mV.

[0085] like Figure 4 As shown in Figure 2, NiFe-LDH-B exhibits excellent intrinsic catalytic activity with an OER overpotential of 294 mV@20 mA cm -2 , which is much lower than NiFe-LDH (303mV) and Ni-LDH-B (346mV). In addition, the OER activity of different electrocatalysts was also evaluated by Tafel plots. The Tafel slope of NiFe-LDH-B was 98mV dec. -1 , much smaller than NiFe-LDH (111mV dec -1 )、Ni-LDH-B(120mV dec -1 ). The low Tafel slope value of NiFe-LDH-B indicates that it has excellent kinetic performance for OER reaction. NiFe-LDH-B has the lowest charge transfer resistance R ct and the maximum double layer capacitance C dl It shows that NiFe-LDH-B has extremely strong electron transfer kinetics and electrochemical active area.

[0086] Ultrasonication reduces the overpotential of NiFe LDH-B from 294 mV to 237 mV@20 mA cm -2( Figure 5 In a), the Tafel slope decreases by 66 mV·dec -1 ( Figure 5 b), the charge transfer resistance is reduced by 0.7Ω( Figure 5 In c), the electrochemical active area increased by 4.75 cm 2 ( Figure 5 d). Ultrasound increased the current density at 500 mV by 2.1 times. The fact that the charge transfer resistance and electroactive area did not change significantly indicates that the significant improvement in performance is not only due to the effect of ultrasonic cleaning on the surface, but also because the ultrasound played a role in assisting oxygen evolution.

[0087] Example 2

[0088] The in-situ hybrid acoustic electrolysis cell system of this embodiment is as follows: Figure 1 and Figure 6 , 7 As shown, including:

[0089] RF source: transmits an RF signal with a frequency of 5-15MHz and a level of 0-9dbm.

[0090] DC power supply: Provides 32V DC power to the signal amplifier.

[0091] Signal amplifier: Amplifies the RF signal strength of 5dbm to 60dbm.

[0092] Interdigitated electrode: It consists of a 28.0 (horizontal direction) × 47.0 × 0.5 mm single crystal piezoelectric (128° Y-rotation, X-propagation lithium niobate) substrate, on which a comb transducer electrode (pattern) is photolithographically formed, consisting of 30 pairs of 10 nm and 200 nm thick gold layers with an opening size of 5.6 mm, which can convert electrical signals into acoustic signals.

[0093] Electrolytic cell: A rectangular electrolyte chamber of 13.0 mm (horizontally) × 13 mm × 24.5 mm × 1 cm (thickness) is formed of glass, with the upper and lower surfaces not sealed.

[0094] Assembly: First, glue the working electrode to the outside of the pattern on the interdigital electrode with AB glue, then cover the electrolytic cell on the working electrode, and glue the bottom of the electrolytic cell to the substrate of the interdigital electrode with AB glue. The working electrode is not completely covered in the electrolytic cell, and some areas of the substrate are exposed. Thus, an in-situ hybrid acoustic electrolytic cell is obtained.

[0095] Then, use a BNC-N port adapter to connect the RF source and the signal amplifier, and then use an N port-electrode clamp to connect the signal amplifier to the interdigital electrode. Then connect the signal amplifier to a DC power supply, so that the transmitted electrical signal of the RF source can be amplified by the signal amplifier and converted into an acoustic wave signal by the interdigital electrode. Finally, add KOH solution to the electrolytic cell, insert the counter electrode and reference electrode, and then connect the electrochemical workstation to perform relevant tests.

[0096] The embodiments of the present invention are described in detail above, but the contents are only preferred embodiments of the present invention and cannot be considered to limit the scope of implementation of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the present invention.

[0097] Any matters not described in the present invention are applicable to the prior art.

Claims

1. A method for preparing a low-crystalline NiFe LDH three-dimensional nanosheet array catalyst, characterized in that: The preparation method comprises the following steps: using strong acid, ultrapure water and anhydrous ethanol to remove surface impurities and an oxide layer from nickel foil respectively; placing the treated nickel foil in an electrolyte consisting of 1 to 20 mmol FeSO4, 1 to 10 mmol H3BO3 and a saturated KCl aqueous solution, and preparing a low-crystalline NiFe LDH three-dimensional nanosheet array catalyst by a pulse electrodeposition method.

2. The preparation method according to claim 1, characterized in that: The specific process of the preparation method is: S1. Place 1-100 μm nickel foil in a strong acid solution of 1-3 M H ions for ultrasonic treatment to remove the NiOx layer that may exist on its surface, then rinse with ultrapure water and ethanol, and blow dry with dry analytical pure argon gas; S2. Add 1-20 mmol of FeSO4 and 1-10 mmol of H3BO3 to 50 mL of saturated KCl aqueous solution and stir evenly to obtain an electrolyte; S3, using pulse deposition method to perform electrochemical treatment, using a two-electrode system, wherein both electrodes are nickel foils pre-treated in step S1, the two electrodes are placed in parallel, 1.5-3 cm apart from each other, and the electrolyte described in step S2 is used; the pulse current density applied in the pulse electrodeposition method is ±10-100 mA / cm 2 , pulse frequency is 0~20Hz, pulse period is 0~1000; S4. After the electrochemical treatment is completed, the electrode is taken out from the electrolyte, rinsed with ultrapure water and anhydrous ethanol, and placed in a vacuum oven for drying at 50-70°C for 8-16 hours to obtain a low-crystalline NiFe LDH three-dimensional nanosheet array catalyst.

3. The preparation method according to claim 1, characterized in that: In step S1, the thickness of the nickel foil is 8-20 μm, and the strong acid is: a H2SO4 solution with a concentration of 0.8-1.2 mol / L or a 1-3 M HCl solution; in step S2, the concentration of FeSO4 is 1-5 mmol, and the concentration of H3BO3 is 1-3 mmol; In step S3, the pulse current density applied is ±30-60 mA / cm 2 , the pulse frequency is 4~8Hz, and the pulse period is 500~800.

4. A low-crystalline NiFe LDH three-dimensional nanosheet array catalyst obtained by the preparation method according to any one of claims 1 to 3, characterized in that: The microscopic morphology of the catalyst is composed of a large number of wrinkled nanosheets, and there are crystalline regions and non-crystalline regions inside the nanosheets.

5. The catalyst according to claim 4, characterized in that In the nanosheets of the catalyst, Fe, Ni, O and B elements are uniformly dispersed on the surface thereof.

6. Use of the catalyst according to claim 4, characterized in that: The low-crystalline NiFe LDH three-dimensional nanosheet array catalyst is used as a working electrode in electrocatalytic oxygen evolution. The low-crystalline NiFe LDH three-dimensional nanosheet array catalyst is denoted as NiFe LDH-B / NF. The specific application process is as follows: One side of NiFe LDH-B / NF is the adhesive surface, and the other side is the test surface. Use AB glue to adhere the adhesive surface of NiFe LDH-B / NF to the substrate of the interdigital electrode, 1.5-3mm away from the photolithographic pattern on the interdigital electrode. Use a scraper to hang off the excess AB glue and dry it for 2.5-5 hours. Subsequently, the electrolytic cell was adhered to the interdigital electrode with AB glue, the electrolytic cell covered the working electrode, and the inside of the electrolytic cell was divided into a working electrode covering area and a substrate area, and then dried overnight to obtain an in-situ hybrid acoustic wave electrolytic cell; A 1.0 M potassium hydroxide solution was prepared as an electrocatalytic electrolyte, and nitrogen was introduced into the in-situ hybrid sonic electrolysis cell to drive out the air; Using NiFe LDH-B / NF as the working electrode, graphite as the counter electrode, and saturated calomel electrode as the reference electrode, the electrochemical workstation was connected to carry out the electrocatalytic oxygen evolution reaction in the electrocatalytic electrolyte. The RF source is connected to the signal amplifier, and then connected to a resistor with a resistance of 50 ohms, and then connected to the interdigital electrodes; a DC power supply is used to provide a DC power of 32V to the signal amplifier; during the electrocatalytic oxygen evolution test, the RF source causes the interdigital electrodes to convert an RF signal with a frequency of 5-15MHZ and a level of 0-108dbm into an acoustic signal through the signal amplifier to assist oxygen evolution and test its overpotential.

7. The use according to claim 6, characterized in that: The substrate of the interdigitated electrode is a lithium niobate single crystal. The photolithographic pattern converts the electrical signal into an acoustic wave signal. The acoustic wave is transmitted by the lithium niobate single crystal of the substrate and propagates to the working electrode adhered to the single crystal. At the same time, the single crystal not covered by the working electrode propagates the acoustic wave into the electrolyte, jointly promoting the oxygen evolution performance of the electrocatalyst in the form of bulk acoustic waves and surface acoustic waves.

8. The use according to claim 6, characterized in that: Without surface ultrasound, the working electrode was -2 The overpotential of NiFe LDH-B / NF is 294 mV. Under the condition of surface ultrasound, the current density of NiFe LDH-B / NF is 20 mA cm -2 The overpotential of NiFe LDH-B was 237mV; Ultrasonic wave reduced the overpotential of NiFe LDH-B from 294mV to 237mV@20mAcm -2 , Tafel slope decreases by 66mV·dec -1 , ultrasound increases the current density at 500mV by no less than two times.

9. An in-situ mixed acoustic electrolysis system, characterized in that: The system comprises: RF source: transmits an RF signal with a frequency of 5-15MHz and a level of 0-9dbm; DC power supply: Provide 32V DC power to the signal amplifier; Signal amplifier: used to amplify the RF signal strength of the radio frequency source; Interdigitated electrode: It includes a 28.0mm×47.0mm×0.5mm single crystal piezoelectric substrate on which a comb-shaped transducer electrode pattern is photoetched to convert electrical signals into acoustic signals; Electrolytic cell: A regular quadrangular prism made of glass, with the upper and lower surfaces not sealed; Assembly: First, glue the working electrode to the outside of the pattern on the interdigital electrode with AB glue, then cover the working electrode with the electrolytic cell, and glue the bottom of the electrolytic cell to the substrate of the interdigital electrode with AB glue. The working electrode is not completely covered in the electrolytic cell, and some areas of the substrate are exposed; then, use a BNC-N port adapter to connect the RF source and the signal amplifier, and then use the N port-electrode clamp to connect the signal amplifier to the interdigital electrode; then connect the signal amplifier to the DC power supply, so that the transmitted electrical signal of the RF source is amplified by the signal amplifier and converted into an acoustic wave signal by the interdigital electrode; finally, add KOH solution to the electrolytic cell, insert the counter electrode and reference electrode, and then connect the electrochemical workstation to perform relevant tests.

10. The system according to claim 9, characterized in that The dimensions of the electrolytic cell in the system are 13.0 mm x 13 mm x 24.5 mm x 1 cm.

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