CN117702181A - Ultrasonic-assisted preparation method and application of OER catalyst - Google Patents
Ultrasonic-assisted preparation method and application of OER catalyst Download PDFInfo
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- CN117702181A CN117702181A CN202311762898.1A CN202311762898A CN117702181A CN 117702181 A CN117702181 A CN 117702181A CN 202311762898 A CN202311762898 A CN 202311762898A CN 117702181 A CN117702181 A CN 117702181A
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- 239000003054 catalyst Substances 0.000 title claims abstract description 46
- 238000002360 preparation method Methods 0.000 title claims abstract description 30
- 238000004729 solvothermal method Methods 0.000 claims abstract description 85
- 238000006243 chemical reaction Methods 0.000 claims abstract description 31
- 239000000463 material Substances 0.000 claims abstract description 22
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- 238000000967 suction filtration Methods 0.000 claims abstract description 7
- 238000004140 cleaning Methods 0.000 claims abstract description 5
- 238000001035 drying Methods 0.000 claims abstract description 5
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 19
- ZMXDDKWLCZADIW-UHFFFAOYSA-N N,N-Dimethylformamide Chemical compound CN(C)C=O ZMXDDKWLCZADIW-UHFFFAOYSA-N 0.000 claims description 15
- OYFRNYNHAZOYNF-UHFFFAOYSA-N 2,5-dihydroxyterephthalic acid Chemical compound OC(=O)C1=CC(O)=C(C(O)=O)C=C1O OYFRNYNHAZOYNF-UHFFFAOYSA-N 0.000 claims description 10
- 239000008367 deionised water Substances 0.000 claims description 7
- 229910021641 deionized water Inorganic materials 0.000 claims description 7
- 150000003839 salts Chemical class 0.000 claims description 7
- 150000002815 nickel Chemical class 0.000 claims description 6
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 4
- 229910021578 Iron(III) chloride Inorganic materials 0.000 claims description 4
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Chemical compound NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 claims description 4
- 239000004202 carbamide Substances 0.000 claims description 4
- RBTARNINKXHZNM-UHFFFAOYSA-K iron trichloride Chemical group Cl[Fe](Cl)Cl RBTARNINKXHZNM-UHFFFAOYSA-K 0.000 claims description 4
- VCJMYUPGQJHHFU-UHFFFAOYSA-N iron(3+);trinitrate Chemical group [Fe+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O VCJMYUPGQJHHFU-UHFFFAOYSA-N 0.000 claims description 4
- KBJMLQFLOWQJNF-UHFFFAOYSA-N nickel(ii) nitrate Chemical group [Ni+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O KBJMLQFLOWQJNF-UHFFFAOYSA-N 0.000 claims description 2
- 230000000694 effects Effects 0.000 abstract description 12
- 239000001301 oxygen Substances 0.000 abstract description 11
- 229910052760 oxygen Inorganic materials 0.000 abstract description 11
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 abstract description 9
- 238000001556 precipitation Methods 0.000 abstract description 2
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 58
- 239000012621 metal-organic framework Substances 0.000 description 16
- 239000001257 hydrogen Substances 0.000 description 14
- 229910052739 hydrogen Inorganic materials 0.000 description 14
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 13
- 239000013078 crystal Substances 0.000 description 13
- 238000000034 method Methods 0.000 description 12
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- 238000000157 electrochemical-induced impedance spectroscopy Methods 0.000 description 6
- 238000004833 X-ray photoelectron spectroscopy Methods 0.000 description 5
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- 238000002441 X-ray diffraction Methods 0.000 description 4
- 238000000026 X-ray photoelectron spectrum Methods 0.000 description 4
- 239000010411 electrocatalyst Substances 0.000 description 4
- -1 hydrogen ions Chemical class 0.000 description 4
- 239000011229 interlayer Substances 0.000 description 4
- 229910021645 metal ion Inorganic materials 0.000 description 4
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 4
- 150000001450 anions Chemical class 0.000 description 3
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- 229910014033 C-OH Inorganic materials 0.000 description 2
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- 229910014570 C—OH Inorganic materials 0.000 description 2
- 229910001030 Iron–nickel alloy Inorganic materials 0.000 description 2
- 238000001237 Raman spectrum Methods 0.000 description 2
- KJTLSVCANCCWHF-UHFFFAOYSA-N Ruthenium Chemical compound [Ru] KJTLSVCANCCWHF-UHFFFAOYSA-N 0.000 description 2
- VREFGVBLTWBCJP-UHFFFAOYSA-N alprazolam Chemical compound C12=CC(Cl)=CC=C2N2C(C)=NN=C2CN=C1C1=CC=CC=C1 VREFGVBLTWBCJP-UHFFFAOYSA-N 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
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- 239000006227 byproduct Substances 0.000 description 2
- 150000004770 chalcogenides Chemical class 0.000 description 2
- 238000012512 characterization method Methods 0.000 description 2
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- 229940032296 ferric chloride Drugs 0.000 description 2
- 229940044631 ferric chloride hexahydrate Drugs 0.000 description 2
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- 239000002803 fossil fuel Substances 0.000 description 2
- 125000002887 hydroxy group Chemical group [H]O* 0.000 description 2
- 150000002500 ions Chemical class 0.000 description 2
- NQXWGWZJXJUMQB-UHFFFAOYSA-K iron trichloride hexahydrate Chemical compound O.O.O.O.O.O.[Cl-].Cl[Fe+]Cl NQXWGWZJXJUMQB-UHFFFAOYSA-K 0.000 description 2
- 239000003446 ligand Substances 0.000 description 2
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- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 description 1
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- 229910052741 iridium Inorganic materials 0.000 description 1
- GKOZUEZYRPOHIO-UHFFFAOYSA-N iridium atom Chemical compound [Ir] GKOZUEZYRPOHIO-UHFFFAOYSA-N 0.000 description 1
- 238000004502 linear sweep voltammetry Methods 0.000 description 1
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- 229910052976 metal sulfide Inorganic materials 0.000 description 1
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- 229910000510 noble metal Inorganic materials 0.000 description 1
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Abstract
The invention discloses an ultrasonic-assisted preparation method and application of an OER catalyst. In an embodiment, the OER catalyst is a MOF or LDH material and the ultrasound-assisted preparation method comprises the steps of: s1, preparing a reaction solution; s2, carrying out solvothermal reaction on the reaction solution under the ultrasonic condition; wherein the ultrasonic power is set to be 200-500W, and the reaction time is 15-30 min; and S3, carrying out suction filtration, cleaning and drying on the obtained product. Compared with the traditional solvothermal method, the ultrasonic-assisted solvothermal method disclosed by the invention has the advantages of shorter time and higher efficiency, and the prepared MOF or LDH material has higher oxygen precipitation activity and stability in an alkaline environment.
Description
Technical Field
The invention relates to the technical field of OER electrocatalysis; more particularly, it relates to an ultrasound-assisted preparation method of MOF or LDH material and its application as OER catalyst.
Background
The existing industrial hydrogen production method mainly comprises fossil fuel hydrogen production, industrial by-product hydrogen production, electrolytic water hydrogen production and the like, and the problems of high carbon dioxide emission, unavoidable environmental pollution and the like of the fossil fuel hydrogen production and the industrial by-product hydrogen production lead to the fact that the hydrogen production method is not sustainable and is not an optimal scheme. The hydrogen production by water electrolysis is a relatively better hydrogen production mode at present because of the sustainable and low pollution advantages.
The method for producing hydrogen by electrolyzing water is based on an electrochemical principle, and water molecules are decomposed into hydrogen and oxygen by adding electrolyte into water and then electrifying between two electrodes. In the process of producing hydrogen by electrolysis of water, water molecules are decomposed into hydrogen ions and oxygen ions by the electrolyte, and then the ions move along the direction of an electric field until reaching two electrodes. On the surface of these electrodes, the hydrogen ions get electrons and then combine with another hydrogen ion to form hydrogen gas (HER); at the same time, the oxygen ions lose electrons and combine to form Oxygen (OER). In the whole water splitting process, the anode Oxygen Evolution Reaction (OER) has slow dynamic reaction due to the multi-electron transfer process, and is a key factor for limiting the efficiency of the whole water splitting device. The design of a high efficiency OER electrocatalyst is therefore critical to reduce the overpotential for the water electrolysis reaction.
The most effective OER catalysts at present are still noble metal oxides of iridium and ruthenium (IrO) 2 And RuO (Ruo) 2 Etc.), their scarcity and high cost severely limit their large-scale application. Thus, researchers have been looking for more cost effective alternatives. Some materials with significant OER activity include perovskite, spinel, layered structure type materials, metal sulfides, metal nitrides, metal organic compounds, and non-metallic electrocatalysts, among others. Many of these materials exhibit excellent OER properties under experimental conditions, but also have respective advantages and disadvantages. For example, perovskite, while highly active and stable, is complex and costly to prepare; spinel materials, although stable, have relatively low activity; layered structure type materials, although highly active, have poor stability; although the metal chalcogenide has high activity and good stability, the preparation cost is high and the metal chalcogenide is harmful to the environment; although the metal nitride has high activity and good stability, the preparation cost is high and the metal nitride is harmful to the environment; although the metal organic compound has high activity and good stability, the preparation cost is high and the metal organic compound is harmful to the environment; the nonmetallic electrocatalyst has high activity and good stability, but has higher preparation cost.
Metal Organic Frameworks (MOFs) are porous crystalline materials composed of metal/metal clusters and organic ligands by formation of coordination bonds. The electrochemical reaction can be easier to occur due to the characteristics of larger porosity and full exposure of active sites, so that the OER activity is improved; the electronic structure and the crystal morphology of the metal organic framework can be regulated and controlled by changing the types of central atoms and ligands in the metal organic framework, so that the metal organic framework can be used for OER reactions under different conditions; in addition, the metal organic frame material has good stability and peroxidation resistance, so that the metal organic frame material can be kept stable in a wider temperature range and pH value. Compared with other OER catalysts, the metal organic framework has lower preparation cost and simple preparation method, can be modified more easily by changing ligands and central atoms, and has good application prospect.
LDHs (layered double hydroxides) are a complex assembled from positively charged host laminates and negatively charged anions under covalent bond attachment. It has high adjustability, the chemical composition of the main laminate is adjustable, and the type and amount of anions between layers can be changed. Thus, LDHs can be flexibly designed to achieve different properties by merely modifying the metal ions of the host plate layers or modifying the type and amount of anions between the layers. Taking NiFe-LDHs as an example, due to adjustable Ni 2+ And Fe (Fe) 3+ And has better catalytic activity on OER reaction.
However, the morphology of the MOF and LDH materials synthesized by the conventional solvothermal method is not regulated, so that the specific surface areas of the MOF and LDH materials are generally smaller, which means that the active centers of the MOF and LDH materials are not fully exposed and participate in the reaction when the MOF and LDH materials are used as catalysts, and the catalytic effect of the MOF and LDH materials is not improved. In addition, the conventional preparation process is carried out at high temperature using an autoclave, and the reaction usually lasts for more than 10 hours or even several days, which brings inconvenience to the synthesis of both.
Disclosure of Invention
The first aspect of the invention discloses an ultrasonic-assisted preparation method of an OER catalyst, wherein the OER catalyst is MOF or LDH material; the ultrasonic-assisted preparation method comprises the following steps:
s1, preparing a reaction solution;
s2, carrying out solvothermal reaction on the reaction solution under ultrasonic conditions; wherein the ultrasonic power is set to be 200-500W, and the reaction time is 15-30 min;
and S3, carrying out suction filtration, cleaning and drying on the obtained product.
According to one embodiment of the present invention, the OER catalyst is MIL-88b (Fe) -2OH.
Further, 2, 5-dihydroxyterephthalic acid and an iron salt are dissolved in N, N-dimethylformamide in a predetermined ratio in step S1 to obtain the reaction solution.
Further, the ferric salt is ferric chloride, and the molar ratio of the 2, 5-dihydroxyterephthalic acid to the ferric chloride to the N, N-dimethylformamide is 1:1:65.
According to another embodiment of the invention, the OER catalyst is a NiFe-LDH.
Further, in step S1, ferric salt, nickel salt and urea are dissolved in a proper amount of deionized water according to a preset proportion, so as to obtain the reaction solution.
Further, the molar ratio of the iron salt, the nickel salt and the urea is 1:1:10.
Further, the iron salt is ferric nitrate and the nickel salt is nickel nitrate.
According to one embodiment of the present invention, step S3 is performed by alternately cleaning with absolute ethanol and deionized water.
The second aspect of the invention discloses application of the catalyst material obtained by the ultrasonic-assisted preparation method in OER reaction.
The technical scheme of the invention has the following beneficial effects:
compared with the traditional solvothermal method, the ultrasonic-assisted solvothermal method for preparing the MOF or LDH material is simpler, more convenient and faster, shorter in time and higher in efficiency.
Compared with the traditional solvothermal method, the MOF or LDH material catalyst prepared by the ultrasonic-assisted solvothermal method has higher oxygen precipitation activity and stability in an alkaline environment.
In order to more clearly illustrate the technical solution and advantages of the present invention, the present invention will be described in further detail below with reference to the accompanying drawings and detailed description.
Drawings
FIG. 1 is an XRD pattern of an MIL-88b (Fe) -2OH sample prepared by an ultrasonic assisted solvothermal method;
FIG. 2 is an XRD pattern for a conventional solvothermal preparation of MIL-88b (Fe) -2OH sample;
FIG. 3 is an SEM image of an ultrasonic assisted solvothermal method for preparing MIL-88b (Fe) -2OH sample;
FIG. 4 is an SEM image of a conventional solvothermal preparation of MIL-88b (Fe) -2OH sample;
FIG. 5 is a C1s high resolution X-ray photoelectron spectroscopy (XPS) spectrum of MIL-88b (Fe) -2OH prepared by an ultrasonic assisted solvothermal method and MIL-88b (Fe) -2OH prepared by a traditional solvothermal method;
FIG. 6 is an O1s high resolution X-ray photoelectron spectroscopy (XPS) spectrum of MIL-88b (Fe) -2OH prepared by an ultrasonic assisted solvothermal method and MIL-88b (Fe) -2OH prepared by a traditional solvothermal method;
FIG. 7 is a graph of high resolution X-ray photoelectron spectroscopy (XPS) of the ultrasonic assisted solvothermal method for MIL-88b (Fe) -2OH and the traditional solvothermal method for MIL-88b (Fe) -2 OH;
FIG. 8 is a graph showing IR corrected polarization of MIL-88b (Fe) -2OH prepared by an ultrasonic assisted solvothermal method and MIL-88b (Fe) -2OH prepared by a conventional solvothermal method at 1.0M KOH and at room temperature;
FIG. 9 is a Taphil plot of an ultrasound-assisted solvothermal method for MIL-88b (Fe) -2OH and a conventional solvothermal method for MIL-88b (Fe) -2OH during an electrocatalytic oxygen evolution reaction;
FIG. 10 shows the double layer capacitance (C) of MIL-88b (Fe) -2OH prepared by ultrasonic assisted solvothermal method and MIL-88b (Fe) -2OH prepared by traditional solvothermal method in electrocatalytic oxygen evolution reaction dl ) A graph;
FIG. 11 is an Electrochemical Impedance Spectroscopy (EIS) diagram of an ultrasound-assisted solvothermal method for MIL-88b (Fe) -2OH and a traditional solvothermal method for MIL-88b (Fe) -2OH in an electrocatalytic oxygen evolution reaction;
FIG. 12 shows an ultrasonic assisted solvothermal method for preparing MIL-88b (Fe) -2OH and a conventional solvothermal method for preparing MIL-88b (Fe) -2OH at 1.0M KOH, 100mA/cm 2 A stability profile at current density, room temperature;
FIG. 13 is an XRD pattern for a NiFe-LDH catalyst prepared using an ultrasonic assisted solvothermal method and a conventional solvothermal method;
FIG. 14 is a Raman spectrum of NiFe-LDH catalyst prepared by ultrasonic assisted solvothermal method and conventional solvothermal method;
FIG. 15 shows polarization curves (a), tafel curves (b), cdl curves (c) and Eis curves (d) for NiFe-LDH catalysts prepared by ultrasonic assisted solvothermal method and conventional solvothermal method.
Detailed Description
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, but the described embodiments are presented for purposes of illustration and explanation only and are not intended to limit the scope of the present invention.
Example 1
Example 1 an MILs-88 b (Fe) -2OH catalyst (labeled Fe-MOF-U) was prepared using an ultrasonic assisted solvothermal process, which was prepared by the steps of:
s1, 3.00g of 2, 5-dihydroxyterephthalic acid (C 8 H 6 O 6 ) And 4.05g of ferric chloride hexahydrate (FeCl) 3 ·6H 2 O) was dissolved in 75ml of N, N-dimethylformamide to prepare a reaction solution;
s2, transferring the reaction solution into an ultrasonic reaction kettle for solvothermal reaction, wherein the temperature is set to 120 ℃, the ultrasonic power is set to 300W, and the reaction time is 30min;
and S3, carrying out suction filtration on the obtained product, alternately flushing with absolute ethyl alcohol and deionized water for three times in the suction filtration process, and then drying the sample in an oven with the set temperature of 50 ℃ for 12 hours.
Comparative example 1
Comparative example 1 MILs-88 b (Fe) -2OH catalyst (labeled Fe-MOF-S) was prepared using a conventional solvothermal process, which differs from example 1 in that: ultrasound is not carried out in the solvothermal reaction process, and the reaction time is 12 hours.
Example 2
Example 2 a NiFe-LDH catalyst was prepared using an ultrasonic assisted solvothermal method comprising the following steps:
s1, 0.606g Fe (NO) 3 ) 3 ·9H 2 O、0.435g Ni(NO 3 ) 2 ·6H 2 O and 0.909g CO (NH) 2 ) 2 (molar ratio of the three1:1:10) in 108ml deionized water to prepare a reaction solution;
s2, transferring the reaction solution into an ultrasonic reaction kettle for solvothermal reaction, wherein the temperature is set to 120 ℃, the ultrasonic power is set to 300W, and the reaction time is 30min;
and S3, carrying out suction filtration on the obtained product, alternately flushing with absolute ethyl alcohol and deionized water for three times in the suction filtration process, and then drying the sample in an oven with the set temperature of 65 ℃ for 12 hours.
Comparative example 2
Comparative example 2 NiFe-LDH was prepared using a conventional solvothermal method, which differs from example 2 in that: ultrasound is not carried out in the solvothermal reaction process, and the reaction time is 12 hours.
Structural morphology and performance characterization of MIL-88b (Fe) -2OH
As can be seen from fig. 1 and 2, the main diffraction peak of MILs-88 b (Fe) -2OH prepared in example 1 and comparative example 1 is at 2θ=9.2 °,10.3 °,16.8 °,18.4 °,18.6 °, and compared with the standard PDF card of MILs-88 b (Fe) -2OH, the diffraction peak is basically not shifted, but the dominant crystal plane of crystal growth is significantly changed, which indicates that the introduction of ultrasonic waves changes the crystal growth mechanism, so that the growth speed is accelerated or slowed down, and the purpose of adjusting crystal morphology is achieved.
As shown in the SEM diagram of FIG. 3, MIL-88b (Fe) -2OH prepared by an ultrasonic assisted solvothermal method belongs to a trigonal system, two ends of two crystals are relatively sharp, and the whole crystals are hexagonal prisms in a shuttle shape, but the crystals grow irregularly and are partially broken.
As shown in the SEM diagram of FIG. 4, MIL-88b (Fe) -2OH prepared by the traditional solvothermal method also belongs to a trigonal system, two ends of two crystals are relatively sharp, and the whole is a hexagonal prism in a shuttle shape, but the size of the crystals is obviously larger than that of a sample prepared by an ultrasonic auxiliary solvothermal method, and the crystals are more complete.
FIG. 5 is a C1s high resolution XPS spectrum of MIL-88b (Fe) -2OH samples prepared by an ultrasonic assisted solvothermal method and a traditional solvothermal method, and the high resolution C1s XPS spectrum confirms that the MIL-88b (Fe) -2OH samples synthesized by the ultrasonic assisted solvothermal method and the traditional solvothermal method have the compositions of aromatic rings C=C/C-C (284.84 eV and 284.62 eV), C-O/C-OH (286.40 eV and 286.12 eV) and carboxylate groups O=C-O (288.84 eV and 288.42 eV).
FIG. 6 is a graph of O1s high resolution XPS of MIL-88b (Fe) -2OH samples prepared by ultrasonic assisted solvothermal method and traditional solvothermal method, wherein the O1s XPS peak at 531.8eV and 531.68eV is attributed to C-OH bond, and the shift of binding energy of Fe-O bond at 530.2eV and 530.6eV indicates that the bond length is changed by introducing ultrasonic wave, which is beneficial to improving OER catalytic activity.
FIG. 7 is a high resolution XPS spectrum of Fe2p for preparing MIL-88b (Fe) -2OH samples by ultrasonic assisted solvothermal method and conventional solvothermal method, wherein four characteristic peaks of the sample by ultrasonic assisted solvothermal method are respectively attributed to Fe 3+ (710.24 eV and 723.84 eV) and related oscillation concomitant peaks (715.24 eV and 729.24 eV), while the high-resolution XPS spectrum at Fe2p of MIL-88b (Fe) -2OH prepared by traditional solvothermal method can also convolve four characteristic peaks, respectively attributed to Fe 3+ (710 eV and 723.8 eV) and the associated oscillation concomitant peaks (714.4 eV and 732 eV).
The electrocatalytic properties of two samples of MILs-88 b (Fe) -2OH for OER reactions were tested by Linear Sweep Voltammetry (LSV) and Cyclic Voltammetry (CV) under the following conditions: three electrode cell systems, oxygen saturated 1.0M KOH solution, room temperature.
FIG. 8 shows MIL-88b (Fe) -2OH prepared by the ultrasonic assisted solvothermal method of example 1 and the conventional solvothermal method of comparative example 1 at 1mV s -1 Polarization curve obtained by IR correction at low scan rate. Wherein MIL-88b (Fe) -2OH prepared by ultrasonic assisted solvothermal method is 10mA cm -2 Exhibits 221mV overpotential at current density that is approximately 14mV lower than MIL-88b (Fe) -2OH (235 mV) prepared by conventional solvothermal methods. This result shows that the catalytic activity of the OER of MIL-88b (Fe) -2OH prepared by the ultrasonic assisted solvothermal method of example 1 is more remarkable.
FIG. 9 shows the Tafil slope obtained for MIL-88b (Fe) -2OH prepared by the ultrasonic assisted solvothermal method of example 1 and the conventional solvothermal method of comparative example 1 based on the polarization curve. Wherein, the Tafel slope of the MIL-88b (Fe) -2OH catalyst by the ultrasonic auxiliary solvothermal method is 53.30mV dec -1 Compared with traditional solvothermal MIL method-88b (Fe) -2OH catalyst (54.42 mV dec -1 ) Small, indicating a greater advantage in OER process reaction kinetics.
FIG. 10 shows the double layer capacitance (C) obtained based on cyclic voltammograms for MIL-88b (Fe) -2OH prepared by the ultrasonic assisted solvothermal method of example 1 and the conventional solvothermal method of comparative example 1 dl ). C of ultrasonic assisted solvothermal MIL-88b (Fe) -2OH catalyst dl The value was 16.71mF cm -2 This is compared with the conventional solvothermal MIL-88b (Fe) -2OH catalyst (9.52 mF cm) -2 ) Two times larger, demonstrating a greater electrochemically reactive surface area.
FIG. 11 is an Electrochemical Impedance Spectroscopy (EIS) of MIL-88b (Fe) -2OH (Fe-MOF-S) prepared by the ultrasonic assisted solvothermal method of example 1 and the conventional solvothermal method of comparative example 1, and it can be seen that the semi-circle radius of the MIL-88b (Fe) -2OH catalyst prepared by the ultrasonic assisted solvothermal method is significantly smaller than that of the MIL-88b (Fe) -2OH catalyst prepared by the conventional solvothermal method, demonstrating that the MIL-88b (Fe) -2OH catalyst has a smaller charge transfer resistance in the electrochemical reaction process.
FIG. 12 is a graph of MIL-88b (Fe) -2OH prepared by ultrasonic assisted solvothermal method of example 1 and MIL-88b (Fe) -2OH prepared by conventional solvothermal method of comparative example 1 at 1.0M KOH, 100mA/cm 2 Current density, stability at room temperature.
Compared with the traditional solvothermal method, the catalytic activity of the MIL-88b (Fe) -2OH catalyst prepared by adopting the ultrasonic auxiliary solvothermal method in the embodiment of the invention is obviously better in alkaline OER medium, because ultrasonic waves can generate cavitation bubble effect in the solution, super hot spots are formed in the reaction solution, crystals preferentially and rapidly nucleate and grow on the super hot spots, and the super hot spots can damage the complete structure of the crystal growth and manufacture defects, so that the overall OER performance of the catalyst is promoted.
Structural morphology and performance characterization of NiFe-LDH
FIG. 13 is an XRD pattern of a NiFe-LDH catalyst prepared by the ultrasonic assisted solvothermal method of example 2 (labeled as NiFe-LDH-US30min in the figure) and a NiFe-LDH catalyst prepared by the conventional solvothermal method (labeled as NiFe-LDH in the figure). Wherein all diffraction peaks of both catalyst samples can be indexed as LDH (PDF: 380715), whichIt was shown that NiFe-LDH samples synthesized by both methods have typical layered double hydroxide (or hydrotalcite-like compound) structural features and high crystallinity, i.e. hydroxyl and trivalent (Fe 3+ ) And divalent cations (Ni) 2+ ) Coordination forms a hydrotalcite-like body.
As shown in the Raman spectrum of FIG. 14, the NiFe-LDH prepared by the two methods is 292cm in length -1 And 277cm -1 There is a peak due to vibration of HO-Ni (Fe) -OH, respectively at 681cm -1 And 713cm -1 There is a peak generated by vibration of M-O-M and M-O between a metal ion interlayer and a hydroxyl layer in NiFe-LDH, and NiFe-LDH prepared by ultrasonic assisted solvothermal method (labeled as NiFe-LDH-UTS in the figure) is 1084cm -1 There appears a distinct peak, which is probably due to the cavitation bubble effect induced by ultrasound, mixed into the NiFe metal ion interlayer to replace OH-NO 3 - Resulting in that. Both samples were also at 1582cm -1 And 1663cm -1 There is one peak each, which may correspond to the peak exhibited by water molecules under raman spectroscopy, indicating that both process-prepared NiFe-LDH samples contain some water, which may be present between NiFe metal ion interlayers.
By O 2 Saturated 1mol/L KOH was used as electrolyte and the electrocatalytic OER performance of two different samples of NiFe-LDH prepared at room temperature was investigated. The polarization curve in FIG. 15a is at 1 mV.s under the above conditions -1 Obtained at a scanning rate of (a). As can be seen from FIG. 15a, the temperature is 10 mA.cm -2 Compared to traditional solvothermal preparation of NiFe-LDH (307 mV), the ultrasound assisted solvothermal preparation of NiFe-LDH catalyst shows a lower overpotential of 254 mV. As shown in FIG. 15b, the Tafil slope (51.2 mV. Dec -1 ) Is lower than that of NiFe-LDH prepared by a traditional solvothermal method (72.49 mV.dec) -1 ) This indicates faster OER kinetics for NiFe-LDHs prepared by ultrasound assisted solvothermal methods.
Electrochemically active surface area (ECSA) of electrocatalyst and electrochemical double layer capacitance (C dl ) Proportional, which can be measured byScan rate-dependent Cyclic Voltammetry (CV) of the non-faraday region. C (C) dl The value of (c) may be represented by the equation Δj= (j) a -j c ) Calculated according to FIG. 15C, the observed C of NiFe-LDH prepared by ultrasonic assisted solvothermal method dl The value was 14.5 mF.cm -2 Whereas NiFe-LDH prepared using conventional solvothermal methods has only 8.09mF cm -2 。
To further demonstrate the kinetics of the electrode reactions during OER catalysis, electrochemical Impedance Spectroscopy (EIS) tests were performed. As shown in fig. 15d, the radius of the curve for NiFe-LDH prepared using the ultrasonic assisted solvothermal method is much smaller than for NiFe-LDH prepared using the conventional solvothermal method, indicating that the charge transfer on the NiFe-LDH surface prepared using the ultrasonic assisted solvothermal method is much faster with a fast OER kinetics process. This may be due to the fact that the structure of the prepared NiFe-LDH is relatively loose, the interlayer spacing is relatively large, which is favorable for the diffusion of ions to active substances, or the cavitation bubble effect induced by the ultrasonic energy in the reaction solution causes the partial NiFe-LDH to be peeled off from the three-dimensional structure, thus forming a two-dimensional NiFe-LDH nano-sheet with more catalytic activity.
In conclusion, compared with the traditional solvothermal method, the ultrasonic-assisted solvothermal method has the advantages of shorter time, higher efficiency and higher OER catalytic performance in alkaline environment for preparing the MOF or LDH material.
Claims (10)
1. An ultrasonic-assisted preparation method of an OER catalyst, wherein the OER catalyst is MOF or LDH material; the ultrasonic-assisted preparation method is characterized by comprising the following steps of:
s1, preparing a reaction solution;
s2, carrying out solvothermal reaction on the reaction solution under ultrasonic conditions; wherein the ultrasonic power is set to be 200-500W, and the reaction time is 15-30 min;
and S3, carrying out suction filtration, cleaning and drying on the obtained product.
2. The ultrasound-assisted preparation method of OER catalyst according to claim 1, characterized by: the OER catalyst is MIL-88b (Fe) -2OH.
3. The ultrasound-assisted preparation method of OER catalyst according to claim 2, characterized by: in step S1, 2, 5-dihydroxyterephthalic acid and ferric salt are dissolved in N, N-dimethylformamide according to a preset proportion, so as to obtain the reaction solution.
4. The ultrasound-assisted preparation method of OER catalyst according to claim 3, characterized in that: the ferric salt is ferric chloride, and the mol ratio of the 2, 5-dihydroxyterephthalic acid to the ferric chloride to the N, N-dimethylformamide is 1:1:65.
5. The ultrasound-assisted preparation method of OER catalyst according to claim 1, characterized by: the OER catalyst is NiFe-LDH.
6. The ultrasound-assisted preparation method of OER catalyst according to claim 5, characterized by: in the step S1, ferric salt, nickel salt and urea are dissolved in proper deionized water according to a preset proportion, so as to obtain the reaction solution.
7. The ultrasound-assisted preparation method of OER catalyst according to claim 6, characterized by: the molar ratio of the ferric salt to the nickel salt to the urea is 1:1:10.
8. The ultrasound-assisted preparation method of OER catalyst according to claim 6, characterized by: the ferric salt is ferric nitrate, and the nickel salt is nickel nitrate.
9. The ultrasound-assisted preparation method of OER catalyst according to claim 1, characterized by: in the step S3, anhydrous ethanol and deionized water are adopted for alternate cleaning.
10. Use of the catalyst material obtained by the ultrasound-assisted preparation method of any one of claims 1 to 9 in OER reactions.
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