NL2032782A - METHOD FOR PREPARING M-MOF NANOMATERIALS WITH ELECTROCATALYTIC ACTIVITY - Google Patents

Abstract

The invention relates to a method for preparing M-MOF nanomaterials with electrocatalytic activity, comprising the following steps: Step S1: Take a certain mass of alkaline hydroxides and dissolve them in distilled water; After stirring well and heating to 95°C, add a certain mass of aqueous solution of FeCl3 and. aqueous solution of fulvic acid; It then continues to age for a certain period of time at a temperature of 95°C; After cooling to room temperature, centrifuge and wash several times with distilled water and absolute ethanol; Finally, place it in the oven to dry before obtaining the precursor; Step SZ: First thoroughly grind the precursor to obtain a homogeneous powder, and then roast the powder in the N 2 -15 atmosphere in a tube furnace; Step S3: After the roasted precursor has returned to room temperature, centrifuge. and wash them several times with distilled water and absolute ethanol, and finally place them in the oven to dry to obtain solid products. in the VOIHI of a black powder; Tagging. these solid products as M—MOFs. The structure of the invention is unique, so that the charge transfer capacity is suitable for the electrocatalytic hydrogen production process, to meet the needs of industrial development, to address the problem of hydrogen energy shortage.

Description

P1554/NLpd METHOD FOR PREPARING M-MOF NANOMATERIALS WITH

ELECTROCATALYTIC ACTIVITY Technological field The invention relates to the technical field under metal-organic frameworks (MOF), more particularly to a method for preparing M-MOF nanomaterials with electrocatalytic activity. Background technology In the past century, the world economy has developed rapidly, the population has grown rapidly, and with it the global need for energy has also grown. A large number of non-renewable primary energy sources such as coal and oil are being consumed on a massive scale, while the associated environmental problems are becoming increasingly serious. The use of traditional fossil fuels is associated with the production of greenhouse gases such as CO2, which is contrary to the concept of environmentally friendly development. H: is ideal and environmentally friendly new fuel energy to solve this problem very well. Burning does not produce greenhouse gases such as CO2, but a large amount of energy. As an energy source with a high energy density, H. has almost three times the heat of combustion of gasoline. At present, the methods for preparing H. mainly include: fossil fuel hydrogen production, biological hydrogen production, photocatalytic hydrogen production, and electrocatalytic hydrogen production. Electrocatalytic hydrolysis of water will be a promising hydrogen production technology in the future. In addition to the development of electrocatalytic technology, the role of catalysts has become increasingly prominent. In the field of traditional catalysts, the catalytic performance of precious metals is excellent, but the production costs are not positive in relation to the economic benefits they bring. The catalytic performance of common metals cannot meet actual production needs. Therefore, improving the catalytic performance of common metals has become a new exploration path. MOFs materials are a new type of materials modified by common metals with high catalytic performance, and have unique advantages and applications in the field of electrocatalysis.

Water electrolysis technology is a clean and pollution-free H; preparation technology with a long development history. Between 1789 and 1800, the phenomenon of water electrolysis was discovered, and after a large number of experimental explorations, the electrolysis water products were H; and O:. Depending on the acidity and alkalinity of the electrolyte, the electrolyzed water can be divided into three systems: alkaline, neutral and acidic; Acidic environments among them are prone to producing strong acid gases, which is easy to cause damage to the production equipment. In industry, alkaline electrolyte systems are often used as mainstream. Seawater is a weak alkaline resource with abundant reserves, so it is widely used in production.

Electrolytic tank has basically configured with power supply, electrode and electrolyte. Figure 1 is a schematic diagram of electrolyzed water in an alkaline system: under the condition of connection to an external power supply, through the action of the electric field, the cathode undergoes a hydrogen evolution reaction (HER}, and the electron is obtained and H 1 is generated Oxygen evolution reaction takes place at the anode to generate O: (OER).

The following processes are the total reaction formula of the electrolysis water equations and the equations in the various electrolytes: Total reaction formula: H,O-H, + 1/20: In neutral or alkaline electrolytes: cathode: 2H,0+2e-—-H? +20H- Anode: 20H--H?0 +1/20:+2e- In acidic electrolyte: cathode: 2H++2e->H; Anode: HO 2H ++ 1/20, + 2e

Mechanism of Electrocatalytic Hydrogen Production: The HER reaction mechanism also differs in different acidic and alkaline electrolytes, including the three primitive reaction steps of Volmer reaction, Heyrovsky reaction, and Tafel reaction. Volmer reaction refers to "electrochemical adsorption" while heyrovsky reaction refers to hydrogen production.

Metal-organic frameworks (MOFs), also known as porous coordination polymers (PCPs), have a certain crystal porous structure. It is itself composed of organic bridging ligands with a polydentate shape, and self-assembled metal nodes. It has very high surface area and porosity, as well as the advantages of flexible structure. MOFs are therefore widely researched and used in the fields such as gas reserve and separation, molecular sensing, photoelectric materials, drug carriers and electrocatalysis.

With the in-depth study of MOFs, the number of publications on MOFs increased exponentially from 1999 to 2020. The development of MOFs shows a good trend, indicating that MOFs have great potential benefits in many areas.

MOF materials combine inorganic metals and organic ligands. In the 1990s, Yaghi et al. first reported on MOFs that attracted widespread attention from researchers. The special topology and regular internal arrangement of MOFs, as well as a variety of pores, provide extensive ideas and feasibility for MOF materials with different functions. The metal nodes of MOFs can construct different kinds of catalytic materials through the targeted selection of catalytically active metal elements, such as Fez*, Ti', zr', Al*', and more. The highly ordered pores of MOFs are one of the most prominent features and have the characteristics of uniform distribution. Theoretical calculations show that the upper limit of the specific surface is about 1.46x104m? :g-1 is. The extremely high porosity and specific surface area of MOFs maximize surface reactions by providing a rich set of active sites. In addition, the variable coordination methods and the rich variety of organic ligands make the composition of MOFs extremely diverse, so that the pore

size and cage size in the MOF structure can be changed by changing the type and number of organic ligands, and in turn the specific surface area of MOFs can be changed.

High surface area and porosity not only increase the contact area of the reactants with the catalyst, but also provide more active sites.

The MoFs materials therefore offer great opportunities for efficient electrocatalysis.

Electrocatalytic applications of MOF nanomaterials The preparation of hydrogen by electrolysis is a clean energy with a high purity.

Among them, a HER reaction occurs.

In this process, because much of the energy cannot be fully utilized, it causes unnecessary energy waste, energy conversion and production capacity are low and cannot be applied in actual hydrogen production.

Therefore, it is necessary to develop an efficient electrocatalyst which in turn reduces the energy consumption of the FER.

After using MOFs in the field of electrocatalysis, electrocatalytic performance includes catalytic activity and chemical stability.

The preparation of electrocatalysts more suitable for actual needs is the goal of scientific research and the goal of industrial production.

As a result, MOF materials will eventually take a prominent position in the field of electrocatalysis.

In this article, starting from the problem of whether electrolyzed water can efficiently catalyze hydrogen production, the above analysis concludes that: Electrocatalyst is the main factor affecting the efficiency of electrolyzed water; Improving electrocatalysts is a viable means of improving the efficiency of hydrogen production.

As a metal source with rich reserves, iron is not only cheap, but also environmentally friendly, and is very suitable as a metal hub for MOFs materials.

There are numerous synthesis methods of MOFs, and only common synthesis methods are listed here, such as: solvent evaporation method is to evenly mix the metal and ligand compounds in the liquid phase without external energy supply, which makes the solvent slowly evaporate and precipitate the crystal-

late, but this method of synthesis is more time consuming; The diffusion method includes the interface diffusion method and the vapor diffusion method, in which the interface diffusion method consists in dissolving the organic ligand and the metal salt respectively by two liquids with large density differences as solvents, and then using the higher density solution as the bottom film. using, and the lower density solution as the upper film, the two layers of films are evenly tiled, and the crystal material is dispersed at the interface between the two layers of the films; The vapor diffusion method is used for the diffusion of highly volatile bad solvent to diffuse into a benign solvent containing metal ions and ligands, reducing the solubility of the complexes and generating the single crystals; This diffusion method has a low yield and lack of selectivity.

Contents of the Invention To solve the above problems, the invention provides a method for preparing M-MOF nanomaterials having electrocatalytic activity, the method significantly reducing costs and being environmentally friendly.

To achieve the above object, the invention offers the following technical solutions: Process for the preparation of M-MOF nanomaterials with electrocatalytic activity, characterized in that it comprises the following steps: Step S1 Prepare Precursor: Taking a certain mass of alkaline hydroxides and dissolve them in distilled water; After stirring well and heating to 95°C, add a certain mass of aqueous solution of FeCl; and aqueous solution of fulvic acid; It then continues to age for a certain period of time at a temperature of 95°C; After cooling to room temperature, centrifuge and wash several times with distilled water and absolute ethanol; Finally, place it in the oven to dry before obtaining the precursor; Step S2 Roasting: First thoroughly grind the precursor to obtain a homogeneous powder, and then roast the powder in the N 2 atmosphere in a tube furnace;

Step S3 Prepare Final Products: After bringing the roasted precursor back to room temperature, centrifuge and wash it several times with distilled water and absolute ethanol, and finally place it in the oven to dry to obtain solid products in the form of a black powder; Label these solid products as M-MOFs.

Preferably, the aging time in step 1 is 4 hours.

Preferably, they are alkaline hydroxides NaOH or KOH.

Preferably, the drying temperature in the drying oven is 60°C.

Preferably, the conditions of the roasting procedure in step S2 are: The heating rate is 5°C/min, remaining for 4 hours after heating to 600°C.

Preferably, M=Fe, FeO.

Preferably, the precursor is a black solid with a metallic sheen.

As can be seen from the above technical solutions, compared with the prior art, the invention includes the following advantages: In economic terms, the production is simple, cheap, easy to obtain, and it is widely used in the fields such as industry, agriculture , medical industry, and more; Structurally, the structure of carbon has a regular pore structure with a certain adsorption and complexation ability, which allows it to adhere or wrap metal particles; As a transition metal, the structure of iron provides strong electron transfer capability suitable for catalytic materials; In terms of size adaptability, by adjusting the molecular weight of humic acid, hundreds of nanometers of humic particles can be obtained, offering the possibility to assemble carbon skeletons of different sizes; In view of hydrophilicity, there have contain hydrophilic functional groups (such as carboxyl groups, phenolic hydroxyl groups, aromatic rings and other active groups) with such pres- tations as metal ion complexation, ion adsorption, redox property and physiological activity, which improve the performance of composite with me-

language materials can be improved.

Illustration In order to more clearly elaborate the embodiments of the invention or the technical solution in the prior art, the following will be a brief introduction to the figures to be used in the description of the embodiments or the prior art. It is to be understood that the figures in the following descriptions are only the embodiments of the invention. For those of ordinary skill in this sector, other drawings can also be obtained without creative effort according to the figures provided.

Figure 1: The accompanying figure refers to the XRD diagram of the materials of M-MOFs (M = Fe, FeO) of the invention before and after roasting.

Figure 2: The accompanying figure refers to the SEM images of the invention.

Figure 3: The accompanying figure refers to the CV diagrams of the materials of M-MOFs (M = Fe, FeO) roasting of the invention before and after firing.

Figure 4: The accompanying figure refers to the linear voltammetry scan curves of the precursor and the materials of M-MOFs (M = Fe, FeO) under HER at different scan rates in the invention.

Figure 5: The accompanying figure refers to the table curves of the materials of M-MOFs (M= Fe, FeO) of the invention before and after roasting.

Figure 6: The accompanying figure refers to the linear voltammetry scan curves of the precursor and the materials of M-MOFs (M = Fe, FeO) under OER at different scan rates in the invention.

Figure 7: The accompanying figure refers to the electrochemical impedance spectral curves of the precursor and the materials of M-MOFs (M = Fe, FeO) of the present invention.

Specific implementation methods The technical solutions are explained clearly and com- pletely below.

explained in detail in combination with specific embodiments of the invention. It is clear that the described embodiments are only partial embodiments of the invention, and not all embodiments. Based on the embodiments of the invention, all other embodiments obtained by ordinary technicians in this field without creative effort fall within the scope of protection of the invention. Execution case:

1. Materials and Methods

1.1 Experimental drugs and experimental devices

1.1.1 Experimental Drugs The main drugs and reagents used in the experiment are listed in Table 1 below. Table 1: Main drugs and reagents used in experiment

1.1.2. Experimental Instruments Name Fashion Formula Purity Manufacturer Ferric Chloride FeCl;e6H,0 299.0% Sinopharm Chemical Reagent Co., Ltd. Hexahydrate Sodium Hydroxide NaOH 296.0% Sinopharm Chemical Reagent Co., Ltd. Absolute ethanol CH3CH;OH 299.7% Tianjin Fuyu Fine Chemical Co., Ltd. potassium hydroxide KOH 285.0% Sinopharm Chemical Reagent Co., Ltd. Fulvic acid Ci4H1208 285% MACKLIN Distilled wa- H,0 Bal Self control ter Nitrogen N, 299.999% Henan Keyi Gases Co, Ltd. NAFION x 0.50% Self-Control The main instruments used in the experiment are shown in Table 2 below.

Table 2: Main Instruments Used in Experiment Instrument Name Model Manufacturer Electric Drum Dryer - DHG - Shanghai Longyue Instrument Equipment Co, Constant Temperature Box - 9023A Ltd. ture Automatic temperature TZL-30F Dandong Tongda Technology Co., Ltd. control cooling device CNC ultrasonic cleaner KQ5200DA Kunshan Ultrasonic Instrument Co., Ltd. Electrochemical Workstation CHI-760E Shanghai Chenhua Instrument Co., Ltd. Shanghai Meiyingpu Instrument Manufacturing Magnetic Stirrer HJ-4A Co., Ltd. X-ray Diffractometer TD-3500 Dandong Tongda Technology Co., Ltd. Electronic Balances BSA2235 Beijing Sartorius Scientific Instrument Co., Ltd. Shanghai Yuzhi Electromechanical Equipment Tube Furnaces 1200 Co., Ltd. Shanghai Lu Xiangyi Centrifuge Instrument Co., High Speed Centrifuge TG16 Ltd. MS-H280- Zhengzhou Yuxiang Instrument Equipment Co, Heated Magnetic Stirrer Pro Ltd. Infrared lamp NL-F6030 Shenzhen Luoli Technology Co., Ltd. Pipette OTF-1200X Hefei Kejing Technology Co., Ltd. Scanning Electron Micro- ZEISS Ge- Carl Zeiss (Shanghai) Management Co., Ltd. scope mini 300

1.2. Preparation and electrocatalytic performance of MM-MFS nanomaterials

1.2.1. Preparation of nanomaterial precursors M-MOFs (M=Fe, FeO) Weigh accurately 12.00g NaOH and dissolve it in 100ml distilled water; After stirring well and heating to 95°C, quickly add 50ml0.4mol/L FeCl: aqueous solution and 50ml 0.02g/ml aqueous fulvic acid solution; It then continues to age for 4 hours at a temperature of 95°C; After cooling to room temperature, centrifuge and wash several times with distilled water and absolute ethanol; Finally, place it in the oven to dry at 60°C to obtain the precursor.

1.2.2. Roasting of nanomaterials of M-MOFs (M=Fe, FeO) First thoroughly grind the precursor to obtain a homogeneous powder, then roast the powder in the N 2 atmosphere in a tube furnace; The heating rate is 5°C/min, and it remains for 4 hours after heating to 600°C. After cooling to room temperature, centrifuge and wash several times with distilled water and absolute ethanol; Finally, put it in the oven to dry to obtain solid products in the form of a black powder; Label these solid products as M-MOFs.

1.3. Characterization test of samples X-ray diffraction (Diffraction of X-rays, XRD) can be used to identify the crystal structure or other structures of the substance in a specific sequence. The setting parameters of the X-ray diffractometer are: the scanning range is 100-800, the angle increment is 0.050, the sampling time is 0.5s, the voltage is 40kV, and the current is 30mA.

Scanning Electron Microscopy (Scanning Electron Microscope, SEM) is an observation tool of morphological structure between transmission electron microscopy and optical microscopy - using a ZEISS Gemini SEM 300 scanning electron microscopy to capture sample morphography with an accelerating voltage of 3kV.

N, adsorption and desorption test

1.4. Electrochemical performance test of samples

1.4.1. Preparation of Working Electrodes The standard method of electrode manufacture is drop coating method. The preparation of the electrodes is usually made with the added organic reagent Nafion, which can improve the adhesion between the sample layer and the conductive substrate. In general, most of the catalysts are used in powder form, and the drop coating method is often widely used in the electrode preparation of catalysts with the advantages of convenience and applicability.

Preparation of working electrodes: (1) Preparation of the drop electrode slurry. Weigh an appropriate amount of samples into the ball centrifuge tube, add approximately 1ml of absolute ethanol and an appropriate amount of Nafion solution, sonicate for 30 minutes to obtain the drop electrode slurry.

(2) Polishing the working electrode. First dissolve the Al:03 polishing powder with ultrapure water, polish it smooth with an even force of 8 marks, polish for 3 minutes each time, and after polishing, rinse it with ultrapure water sonic 2-3 times (not more than 10s at a time). (3) Drip electrode: Pipette 3 µL of the catalyst-containing slurry with a pipette and spread it evenly on the surface of the glassy carbon electrode (D = 3mm, S = 0.07065cm?), dry it with an infrared lamp (not too close nearby to prevent dry cracking after the catalyst has dried due to too high temperature) and add 0.554 of the Nafion diluent solution after drying. If the one-time addition is not successful, the catalyst on the surface of the electrode is sonicated with ethanol and the addition continues after drying.

1.4.2. Cyclic Voltammetry (CV) 1) Cyclic Voltammetry uses the classic three-electrode working system, applying a linear alternating voltage and the auxiliary electrodes at both ends of the working electrode, then performs multiple cyclic scans to determine the current - and record potential information of the redox reaction; By analyzing the recorded waveform data, observe whether the material reaction is reversible, as well as the magnitude of the peak potential and peak current of the reactant. Electrochemical workstation uses CHI-760E model; First connect the three-electrode system, flush the electrolytic cell 2-3 times; at this point the electrolyte is 1 mol/l KOH solution. the green wire is connected to the dry electron (glass-carbon electrode) which has been expanded by drop coating method, the red wire is connected to the counter electrode (platinum electrode or graphite electrode, the platinum electrode being used for this experiment), the white wire is connected to the reference electrode (mercury oxide/mercury electrode or calomel electrode, where the mercury oxide electrode is used for this experiment), the black wire need not be connected, and the platinum electrode can use the platinum electrode or platinum wire electrode. Then power up the electrochemical workstation, open the CHI-760E software, select the control items, click open circuit potential, note the values accurately, input the values to the IR compensation of the control items --- After testing E (V), click Test, record the values in the left residual (ohms). Then multiply by 0.8 (or 0.75, 0.8 is used in this experiment); after entering the values to the remainder (ohms), the two items check Always and Manual, IR Compensation for Next Companies is previously also checked. With each test item change, you must come back to check the box for IR Compensation for Next Companies, which will also be listed later.

2) CV scan for this experiment: Go to the T option and select the Cyclic Votammetry Parameters item. Under alkaline conditions (mercury oxide electrode): the initial potential of the voltage scan range is set to -1V, the upper limit potential is set to 0.2V, and the lower limit potential is set to -1V. The final potential is set to 0.2V {Calomel electrode is used under acidic conditions: the voltage sweep range initial potential is set to -0.2V, the upper limit potential is set to 1V, the lower limit potential is set to 1V, the final potential is set to - set to -0.2V and the alkaline state is used for this experiment). Select the sweep segments (number of scan segments), set them to 200 segments with a scan rate of 110mV/s, 20mV/s, 30mV/s, 50mV/s, 100mV/s sequentially for testing. Sensitivity (Sensitivity): Select 1.e-004 (or 003, 002, but not 005, 006, the sensitivity of this experiment used

1.e-004). Set the experimental parameters, click Start to run the test; Wait until two rounds of the CV images coincide approximately, that is, if it is a stable state, you can stop scanning; switch to different scan speeds to rescan.

1.4.3. Linear Scan Voltammetry (LSV) 1) This is a more fundamental and widespread voltammetry testing technology. The classic three-electrode working system is used to assemble an electrolytic cell. By electrolyzing the diluted solution of the analyte, it is analyzed according to the resulting current-potential curves.

2) LSV scanning for this experiment: After connecting the three-electrode system, it is stabilized by cyclic voltammetry scanning. Go to item T and select the linear scan voltammetry item. Under alkaline conditions (mercury oxidation electrode): the OER voltage sweep range initial potential is set to OV and the lower limit potential is set to 1.4V (Under acidic conditions (calom electrode): the voltage sweep range initial potential of the OER is set to 0.8V, the lower limit potential is set to 1.6V, and the alkaline conditions are used for this experiment), and the scan rate of is set to 10mV/s, 20mV/s, 30mV sequentially /s and 50 mV/s, and 100 mV/s for testing. Sensitivity (Sensitivity): Select 1.e-003 (or 002, but not 005, 006, the sensitivity of this experiment used

1.e-003). Before clicking Start, check IR Compensation for Next Company. Set the experimental parameters and click Start to run the test; wait for the LSV images to coincide about twice, then stop scanning, change the scan speed and scan again.

1.4.4. AC Impedance 1) The AC impedance method is also known as Electrochemical Impedance Spectroscopy (EIS): It uses interfering signal with different frequencies and smaller amplitude to measure the three-electrode system and to determine the change relationship between the electrochemical impedance and the frequencies of the interfering signal.

2) EIS test for this experiment: After connecting the three-electrode system, it is stabilized by cyclic voltammetry scanning. Go to item T and check AC Impedance, select an initial voltage of -0.6V, set a low frequency to 0.01Hz, set a high frequency to 100000Hz, and at this point the amplitude is 5mV. Set the experimental parameters, click Start, wait for the test to complete, and save the data.

2. Results and Analysis

2.1. Results and analyzes for characterization

2.1.1. X-ray diffraction of materials of M-MOFs (M=Fe, FeO) Figure 1 of the invention refers to an XRD diagram before and after roasting of the materials of M-MOFs (M = Fe, FeO). The figure is obtained by analyzing and processing the data measured by XRD with Jade software, and drawing with Origin diagram. As shown in the figure, the precursor has no crystal structure, and the roasted materials of M-MOFs (M=Fe, FeO) have a good crystal structure; The characteristic peak on the crystal surface of (110) is sharper and coincides with the peak of Fe; In the figure, there are only the characteristic peaks of Fe and FeO, and there are no other impurity peaks. The characteristic peaks at the crystal surfaces of (111), (200), (220), (311), (222) are sharp and coincide with the peaks of FeC, indicating that the sample contains Fel. This shows that Fe and FeO were added to MOFs after roasting.

2.1.2. Scanning Electron Microscopy As shown in Figure 2 below, (a) and (b) indicate that it is a SEM diagram of the precursor. From this it can be deduced that the precursor has a two-dimensional layered structure and a very small particle diameter of about 20nm; the distribution of the particles is very uniform and consistent in height, indicating that the iron is evenly distributed above the carbon layer. In Figure 2 below, (c) and (d) indicate that the SEM tragram of the materials of M-MOFs (M = Fe, FeO). It can be seen from this that the carbon particles pack Fe and FeO particles evenly, the packed particles present an "ant's nest" by uniform distribution, and have a three-dimensional porous spherical composite stereostructure. The stereo structure gives it a high porosity, and can increase the contact area between the interface between the catalytic material and the electrolyte, thereby improving the catalytic performance. Part of the reason why the catalytic performance of the materials of M-MOFs (M = Fe, FeO) is higher than that of precursors is due to their three-dimensional structure superior to two-dimensional structure.

2.2 Results and Analysis of Electrochemical Performance Tests

2.2.1 Cyclic Voltammetry Scan Curve Figure 3 shows the CV diagram of the materials of M-MOFs (M=Fe, FeO) before and after roasting. The figure is obtained by analyzing and processing the data measured by chi760e with Excel software, and drawing with Origin diagram. The figure respectively indicates the cyclic voltammetry scanning curve of precursors and materials of M-MOFs (M=Fe, FeO) at a scanning rate of 10 mV/s. As shown in the figure, the precursor has no obvious redox peak and it can be speculated that the catalytic performance of the precursor will not be very good, and the conclusion will be further explained in LSV; For the roasted materials of M-MOFs (M = Fe, FeO), it can be clearly seen that there are a few redox peaks, indicating that there is a reversible process, proving that the electrode is a typical redox electrode (also known as a Faraday electrode). The redox peak in the materials of M-MOFs (M=Fe, FeO) is very broad, and it can be concluded that the envelope structure of materials of M-MOFs (M=Fe, FeO) makes the interface between the active substance and electrolyte has a relatively strong charge transfer at the interface, resulting in a broader redox peak. The feasibility of the materials of M-MOFs (M=Fe, FeO) as a high performance catalytic material is further elucidated.

2.2.2. Linear voltammetry scan curve and Table curve below

HER Figure 4 shows the LSV diagram of the materials of M-MOFs (M=Fe, FeO) before and after roasting. The figure is obtained by analyzing and processing the data measured by chi7é0e with Excel software, and drawing with Origin diagram. The figure respectively indicates that the cyclic voltammetry scan-

curve of HER at different scanning speeds. As shown in the figure, both the precursor and materials of M-MOFs (M = Fe, FeQ) have the best electrocatalytic HER performance at a sweep rate of 10mV/s. At a current density of 10mAcm-2, the overpotential of the precursor is 541.65mV and the overpotential of the materials of M-MOFs (M = Fe, FeO) is only 147.6 mV, proving that the materials of M-MOFs ( M = Fe, FeO) has obtained better electrocatalytic HER performance after roasting than the precursor. The excellent HER performance is due not only to the high conductivity of the material itself, which improves the charge transfer rate between the electrolyte and the working electrode, but also to the synergy between Fe and FeO, and the unique chemical structure of the catalyst .

Figure 5 shows the Tefel curve of the materials of M-MOFs (M=Fe, FeO) before and after roasting. The figure is obtained by analyzing and processing the data measured by chi7é0e with Excel software, and drawing with Origin diagram. Table slope is an important evaluation standard for measuring electrocatalytic HER kinetics. As shown in the figure, the roasted materials M-MOFs (M = Fe, FeO) perform a small Table slope, which are 177.5 mV/dec and 191.0 mV/dec, respectively, further proving that the HER process of the materials of M-MOF's (M = Fe, FeQ) is the fastest. The roasted materials of M-MOFs (M = Fe, FeO) are shown to have higher electrocatalytic performance.

Figure 6 (C) and (D}) shows the Tefel curve of the materials of M-MOFs (M=Fe, FeQ) before and after roasting. The figure is obtained by analyzing and processing the data measured by chi760e with Excel software, and drawing with Origin diagram. Figures 6(c) and (d) are linear voltammetry scan curves under OER at different scan rates. As shown in the figure, both the precursor and the materials of M-MOFs (M = Fe, Fel) perform the best electrocatalytic OER at a sweep rate of 100mV/s. When the current density is 10mAcm-2, the overpotential of the precursor is 2.555V, and the overpotential of the materials of M-MOFs (M = Fe, FeO) is 2.403V. Although the overpotentials of the two are relatively large, but the OER

performance of the roasted materials of M-MOFs (M = Fe, FeO) is still better than the OER performance of the precursor, further indicating that the roasted material is better.

2.2.3. AC impedance analysis Figure 7 below shows the electrochemical impedance spectrum of precursors and materials of M-MOF/s (M = Fe, FeO), from which it can be concluded that they have a very small hemispherical arc in the high frequency range. The materials of M-MOFs (M = Fe, FeO) have a lower electrochemical impedance, indicating that the active material has a high mass transfer rate. This is due to the fact that the packed Fe and FeO particles increase the contact area of the boundary falcon, increasing the area of activity ratio. The extremely small AC impedance of the materials of M-MOFs (M=Fe, FeO) further proves their suitability in the field of catalytic hydrogen production.

3. Conclusion and discussion MOF complexes offer many advantages, including low cost, environmental friendliness, surface area and high porosity. This experiment uses iron salt and humic acid as basic raw materials, and mainly has the following advantages: In economic terms, the production is simple, cheap, easy to obtain, and it is widely used in the fields such as industry, agriculture, medical industry, and more ; Structurally, the structure of carbon has a regular pore structure with a certain adsorption and complexation ability, which allows it to bond or wrap metal particles; As a transition metal, iron's structure gives it strong electron transfer ability suitable for catalytic materials; In terms of size adaptability, by adjusting the molecular weight of humic acid, hundreds of nanometers of humic particles can be obtained, offering the possibility to assemble carbon skeletons of different sizes; In view of hydrophilicity, it contains hydrophilic functional groups (such as carboxyl groups, phenolic hydroxyl groups, aromatic rings and other active groups) with prestige such as metal ion complexation, ion adsorption, redox property and physiological activity, which can improve the performance of composite with metal materials become.

In this experiment, the precursor is obtained by solvent evaporation method and the materials of M-MOFs (M = Fe, FeQ) are obtained after roasting. Characterized by X-ray diffraction techniques and scanning electron microscopy, the morphological structure is characterized, showing that it included Fe and FeO, as well as a packaged structure; Finally, the electrochemical performance test is performed, the cyclic voltammetry curve is analyzed and its reversibility is determined, and the feasibility and efficiency of electrocatalytic hydrogen production are proven after the HER analysis. The electrochemical impedance spectrum indicates that it has a high mass transfer rate. In general, the unique structure of the nanomaterials of M-MOF's (M = Fe, FeO) makes the charge transfer capacity suitable for electrocatalytic hydrogen production processes, to meet the needs of industrial development, to solve the problem of hydrogen energy shortage to deal with.

Each execution case in this manual is described in a progressive manner. For each implementation case, emphasis is placed on the differences from other implementation cases, while the same or similar parts between each implementation case may refer to each other. For the devices listed in the execution cases, they are described relatively simply because they correspond to the method used in the execution cases.

For related points, please refer to the notes to the method section.

According to the above description of the public embodiments, professionals in this field can practice or use the invention. For professionals in this field, multiple modifications to these embodiments are very easy to perform. The general principles defined herein may be practiced in other embodiments without departing from the spirit or scope of the invention. Accordingly, the invention will not be limited to these embodiments shown herein, but will have the broadest scope consistent with the principles and novel features set forth herein.

Claims (7)

CONCLUSIONS A method for preparing M-MOF nanomaterials with electrocatalytic activity, characterized in that it comprises the following steps: Step S1 Preparing Precursor: Take a certain mass of alkaline hydroxides and dissolve them in distilled water; After stirring well and heating to 95°C, add a certain mass of aqueous solution of FeCl; and aqueous solution of fulvic acid; It then continues to age for a certain period at a temperature of 95°C; After cooling to room temperature, centrifuge and wash several times with distilled water and absolute ethanol; Finally, place it in the oven to dry to obtain the precursor; Step S2 Roasting: First thoroughly grind the precursor to obtain a homogeneous powder, then roast the powder in the N 2 atmosphere in a tube furnace; Step S3 Prepare Final Products: After bringing the roasted precursor back to room temperature, centrifuge and wash it several times with distilled water and absolute ethanol, and finally place it in the oven to dry to obtain solid products in the form of a black powder; Label these solid products as M-MOF/s. A method for preparing M-MOF nanomaterials with electrocatalytic activity according to claim 1, characterized in that the aging time in step 1 is 4 hours. A method for preparing M-MOF nanomaterials with electrocatalytic activity according to claim 1 characterized in that they are alkaline hydroxides NaOH or KOH. The method for preparing M-MOF nanomaterials with electrocatalytic activity according to claim 1, characterized in that the drying temperature in the drying oven is 60°C. The method for preparing M-MOF nanomaterials having electrocatalytic activity according to claim 1, characterized in that the conditions of the roasting procedure in step S2 are: The heating rate is 5°C/min, and remain 4 hours after heating to 600 °C. The method for preparing M-MOF nanomaterials with electrocatalytic activity according to claim 1, characterized in that M=Fe, FeO. The method for preparing M-MOF nanomaterials with electrocatalytic activity according to claim 1, characterized in that the precursor is a black solid with a metallic luster.