Preparation method and application of cr-ni fe mof / cellulose aerogel composite material

Abstract

The application discloses a kind of methods for synthesizing MOFs / cellulose aerogel composite electrode material and its electrocatalytic oxygen evolution application, belong to electrocatalytic functional material preparation process technical field.It is specifically disclosed a kind of preparation method of Cr-NiFe MOF / cellulose aerogel electrode material, including the following steps, Cr source, Ni source and Fe source are dissolved in deionized water and are added to the solution of N,N dimethylformamide containing terephthalic acid, after stirring uniformly, transfer to Teflon reaction kettle, 160 DEG C is reacted 24h and obtains Cr-NiFe MOF;Subsequently, the obtained Cr-NiFe MOF powder is dispersed in carboxymethyl cellulose solution, a certain amount of acetone is added, after mixing uniformly at 80 DEG C, liquid nitrogen freezing is carried out, then 48h of freeze drying can be obtained Cr-NiFe MOF / cellulose aerogel composite material.This composite electrode material when used as electrocatalytic oxygen evolution material, show superior activity and extremely high stability.Especially, at 10mA·cm-2, show 235mV of low overpotential, tafel slope is 53.7mV·dec-1, stability is more than 210h, is one of the best aerogel composite materials of catalytic performance at present, has good application prospect in catalysis and energy conversion field.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of preparation processes of electrocatalytic functional materials, and more particularly to a general synthesis strategy of MOF-based / cellulose aerogel composite materials and application of the MOF-based / cellulose aerogel composite materials in electrocatalytic oxygen evolution under alkaline conditions. BACKGROUND

[0002] Hydrogen energy, as a clean energy, has attracted much attention due to its flexibility, high efficiency, low carbon emission, wide application range and other advantages. Producing hydrogen energy through a low-carbon and efficient method is a key challenge, and water electrolysis is a promising strategy to solve this problem. Synthesizing electrocatalysts that improve the reaction kinetics of the oxygen evolution reaction (OER) is the most effective way to improve the efficiency of water electrolysis. Cellulose aerogels prepared from carboxymethyl cellulose have the advantages of low cost, green and renewable, high specific surface area, easy-to-control porous structure, stable electrocatalytic performance and the like. However, due to the poor pore structure of the cellulose aerogel itself, its electrocatalytic performance is not ideal, and it is necessary to introduce a low-cost and high-activity subunit to improve its electrochemical performance.

[0003] In recent years, although there are studies on electrode materials using aerogels as substrates for electrocatalytic oxygen evolution, the catalytic activity and stability are still not ideal. Metal-organic frameworks (MOFs) have the advantages of easy-to-control modification and good catalytic activity, and can be used as a subunit to improve the electrocatalytic performance of cellulose-based aerogels. The preparation of MOFs / cellulose aerogel composite electrode materials combines the advantages of both, which not only avoids the agglomeration of MOFs to provide more active sites, but also effectively promotes the diffusion and ion conduction of electrolytes due to the porous structure of the aerogel, thereby greatly improving the electrochemical performance. Therefore, it is very challenging to develop a low-cost, mild and widely applicable method to allow MOF particles to grow uniformly and firmly on the aerogel substrate to reduce agglomeration and improve stability. SUMMARY

[0004] The application aims to provide a preparation method of Cr-NiFe MOF / cellulose aerogel composite material and its application in electrocatalytic oxygen evolution reaction, so as to solve the problem that the development of water electrolysis technology is limited by the high overpotential of anode oxygen evolution reaction. The application improves the activity of NiFe MOF by doping high-valence metal Cr, and adjusts the doping ratio to achieve the best catalytic activity. The whole process is mild, low-cost and universal, and its catalytic activity and corrosion resistance can be comparable to noble metal catalysts, and has the prospect of large-scale application.

[0005] In order to achieve the above application purposes, the application provides the following technical solutions:

[0006] The preparation method of the Cr-NiFe MOF / cellulose aerogel composite material comprises the following steps:

[0007] S1, Preparation of carboxymethyl cellulose solution: carboxymethyl cellulose and NaOH were dissolved in deionized water and stirred uniformly to obtain a carboxymethyl cellulose solution of a certain concentration;

[0008] S2, Preparation of Cr-NiFe MOF material:

[0009] S2.1, Ni(NO3)2·6H2O, Fe(NO3)3·9H2O and Cr(NO3)3·9H2O were dissolved in deionized water and stirred to form solution A;

[0010] S2.2, terephthalic acid was dissolved in organic solvent N,N-dimethylformamide and stirred uniformly to form solution B;

[0011] S2.3, solution A was added dropwise to solution B, and after stirring for a period of time, it was transferred to an autoclave for hydrothermal reaction;

[0012] S2.4 After the reaction was cooled to room temperature, it was washed multiple times and dried overnight to obtain Cr-NiFe MOF;

[0013] S3, Preparation of Cr-NiFe MOF / cellulose aerogel electrode material: the obtained Cr-NiFe MOF powder was dispersed in the carboxymethyl cellulose solution, a certain amount of acetone was added, and the mixture was uniformly mixed at a certain temperature, then liquid nitrogen freezing and subsequent freeze-drying were performed to obtain Cr-NiFe MOF / cellulose aerogel composite material.

[0014] Preferably, the amount of carboxymethyl cellulose in S1 is 350-370 mg, and the amount of NaOH is 15-25 mg. The above carboxymethyl cellulose and NaOH are dissolved in 10-15 ml of deionized water.

[0015] Preferably, the amount of Ni(NO3)2·6H2O and Fe(NO3)3·9H2O in S2.1 is 1-2 mmol and 0.75-1.25 mmol, respectively, and the amount of Cr(NO3)3·9H2O is 0.1-0.3 mmol, and the amount of terephthalic acid is 2-4 mmol.

[0016] Preferably, the solution A in S2.1 is 10-20 mL of deionized water, and the solution B in S2.2 is 10-20 mL of N,N-dimethylformamide solution.

[0017] Preferably, the hydrothermal reaction conditions in S2.3 are heating at 150-170°C for 24h; the washing agent includes but is not limited to deionized water and anhydrous ethanol.

[0018] Preferably, the amount of the Cr-NiFe MOF in S3 is 0.3-0.5 g, the amount of the acetone is 0.2-0.4 mL, and the amount of the deionized water is 10-20 mL.

[0019] Preferably, the temperature of the reaction after the uniform mixing in S3 is controlled to be 70-90 DEG C, the reaction time is 2-4 h, the freezing time of the liquid nitrogen is 5-15 min, and the freeze-drying time is 48 h.

[0020] A Cr-NiFe MOF / cellulose aerogel electrode material prepared by the above method.

[0021] Use of the Cr-NiFe MOF / cellulose aerogel electrode material prepared as above in electrocatalytic oxygen evolution under alkaline conditions.

[0022] Compared with the prior art, the application provides a preparation method of a Cr-NiFe MOF / cellulose aerogel composite material and application thereof, and has the following beneficial effects:

[0023] (1) The preparation method provided in the application has low cost, simple and universal synthesis method, and greatly reduces the cost of the catalyst, since the synthesis raw material of the synthesized Cr-NiFe MOF / cellulose aerogel composite material is mainly nickel salt, iron salt, chromium salt and carboxymethyl cellulose.

[0024] (2) In the application, the widely available carboxymethyl cellulose is used as a raw material to synthesize the cellulose aerogel with a three-dimensional network interconnected structure as a substrate, and the MOF particles are uniformly loaded. The combination of the MOF structure from the brittle powder crystal state to the flexible multi-layer cellulose aerogel carrier exposes more active sites, greatly accelerates the mass transfer, and improves the activity of the catalyst.

[0025] (3) In the application, the Cr-NiFe MOF / cellulose aerogel exhibits excellent electrocatalytic oxygen evolution performance and super-long corrosion resistance under alkaline conditions. Not only is the cost of the Cr-NiFe MOF / cellulose aerogel much lower than that of the current industrial catalyst RuO2, but also the activity is significantly better than that of the commercial catalyst. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The XRD pattern of the Cr-NiFe MOF / cellulose aerogel mentioned in the embodiments of the application;

[0027] Figure 2 The SEM pattern of the Cr-NiFe MOF / cellulose aerogel mentioned in the embodiments of the application, wherein (a) the scale is 150 mu m, and (b) the scale is 10 mu m;

[0028] Figure 3TEM, HAADF STEM and elemental Mapping images of the Cr-NiFe MOF / cellulose aerogel composite mentioned in the embodiments of the present application, wherein (a) is a TEM image with a scale of 500 nm, (b) is a HAADF STEM image with a scale of 200 nm, and (c-g) are elemental Mapping images with a scale of 200 nm;

[0029] Figure 4 FT-IR image of the Cr-NiFe MOF / cellulose aerogel composite mentioned in the embodiments of the present application;

[0030] Figure 5 XPS image of the Cr-NiFe MOF / cellulose aerogel composite mentioned in the embodiments of the present application;

[0031] Figure 6 LSV curve of the Cr-NiFe MOF / cellulose aerogel composite mentioned in the embodiments of the present application in 1M KOH electrolyte;

[0032] Figure 7 Tafel slope of the Cr-NiFe MOF / cellulose aerogel composite mentioned in the embodiments of the present application;

[0033] Figure 8 Double-layer capacitance (C dl ) value measured at 1.15V vs. RHE of the Cr-NiFe MOF / cellulose aerogel composite mentioned in the embodiments of the present application;

[0034] Figure 9 EIS image of the Cr-NiFe MOF / cellulose aerogel composite mentioned in the embodiments of the present application;

[0035] Figure 10 Long-term stability test of the Cr-NiFe MOF / cellulose aerogel composite mentioned in the embodiments of the present application. DETAILED DESCRIPTION

[0036] The specific implementation of the present application is further described below in combination with examples, but the protection scope of the present application is not limited by these specific implementations, but is determined by the claims in the appendix. If not specifically stated, the raw materials used are market-purchased conventional products.

[0037] Example 1

[0038] The preparation method of the Cr-NiFe MOF / cellulose aerogel composite electrode material comprises the following steps:

[0039] (1) Preparation of Cr-NiFe MOF

[0040] Cr-NiFe MOF was synthesized by a simple one-step solvothermal method. Typically, 1.5 mmol of Ni(NO3)2.6H2O, 1 mmol of Fe(NO3)3.9H2O and (0.125, 0.25, 0.375 and 0.5 mmol) of Cr(NO3)3.9H2O were dissolved in 15 ml of deionized water and stirred for 30 min, noted as solution A. Then, 3 mmol of terephthalic acid was dissolved in 15 ml of N,N dimethylformamide solution and stirred well, noted as solution B. Solution A was slowly added to solution B and stirred for 1 h. The mixed solution was transferred to a hydrothermal reactor and heated at 160 °C for 24 h. It was washed with ethanol and deionized water several times and vacuum dried at 70 °C overnight to obtain 5%, 10%, 15%, 20% Cr-doped NiFe MOF, respectively.

[0041] (2) Preparation of Cr-NiFe MOF / cellulose aerogel

[0042] Take 0.4 g of the above prepared Cr-NiFe MOF, add 0.36 g of carboxymethyl cellulose, 20 mg of NaOH, 0.3 mL of acetone, and dissolve in 15 ml of deionized water, react in an oil bath at 80 °C for 3 h, cool to room temperature and freeze with liquid nitrogen. Then, freeze-drying for 48 h to obtain the final sample of Cr-NiFe MOF / cellulose aerogel.

[0043] Example 2

[0044] Preparation of NiFe MOF / cellulose aerogel composite electrode material, including the following steps:

[0045] (1) Preparation of NiFe MOF

[0046] NiFe MOF was synthesized by a simple one-step solvothermal method. Typically, 1.5 mmol of Ni(NO3)2.6H2O and 1 mmol of Fe(NO3)3.9H2O were dissolved in 15 ml of deionized water and stirred for 30 min, noted as solution A. Then, 3 mmol of terephthalic acid was dissolved in 15 ml of N,N dimethylformamide solution and stirred well, noted as solution B. Solution A was slowly added to solution B and stirred for 1 h. The mixed solution was transferred to a hydrothermal reactor and heated at 160 °C for 24 h. It was washed with ethanol and deionized water several times and vacuum dried at 70 °C overnight to obtain NiFe MOF.

[0047] (2) Preparation of NiFe MOF / cellulose aerogel

[0048] To 0.4 g of the NiFe MOF prepared above, 0.36 g of carboxymethyl cellulose, 20 mg of NaOH, 0.3 mL of acetone were dissolved in 15 mL of deionized water and reacted in an oil bath at 80 °C for 3 h, cooled to room temperature and frozen with liquid nitrogen. Subsequently, freeze-dried for 48 h to obtain the sample NiFe MOF / cellulose aerogel.

[0049] Example 3

[0050] Preparation of Cr-NiFe MOF electrode material, comprising the following steps:

[0051] (1) Preparation of 10% Cr-NiFe MOF

[0052] Cr-NiFe MOF was synthesized by a simple one-step solvothermal method. Typically, 1.5 mmol of Ni(NO3)2·6H2O, 1 mmol of Fe(NO3)3·9H2O and 0.25 mmol of Cr(NO3)3·9H2O were dissolved in 15 mL of deionized water and stirred for 30 min, denoted as solution A. Then, 3 mmol of terephthalic acid was dissolved in 15 mL of N,N-dimethylformamide solution and stirred uniformly, denoted as solution B. Solution A was slowly added to solution B and stirred for 1 h. The mixed solution was transferred to a hydrothermal reactor and heated at 160 °C for 24 h. It was washed with ethanol and deionized water several times and vacuum dried at 70 °C overnight to obtain 10% Cr-NiFe MOF.

[0053] Example 4

[0054] (1) Preparation of cellulose aerogel electrode material

[0055] To 0.36 g of carboxymethyl cellulose and 20 mg of NaOH, acetone was dissolved in 15 mL of deionized water and reacted in an oil bath at 80 °C for 3 h, cooled to room temperature and frozen with liquid nitrogen. Subsequently, freeze-dried for 48 h to obtain the cellulose aerogel.

[0056] In summary, Figure 1 X-ray powder diffraction patterns of the products obtained in Examples 1, 3, 4 were obtained. Both 10% Cr-NiFe MOF and 10% Cr-NiFe MOF / cellulose aerogel showed three obvious peaks at 9.59°, 16.02° and 18.09°, which was consistent with the crystal structure of Ni MOF (No. 985792, CCDC). The peaks at 22.94, 24.06, 25.89 and 32.14 in Cr-NiFe MOF / cellulose aerogel belonged to the characteristic peaks of cellulose aerogel. It showed that the Cr-NiFe MOF / cellulose aerogel was successfully prepared and had good crystallinity at the same time.

[0057] Figure 2 SEM images of 10% Cr-NiFe MOF / cellulose aerogel were obtained for Example 1. It shows the interconnected network structure, MOF is uniformly dispersed on the skeleton of aerogel Figure 2 a-b).

[0058] Figure 3 TEM, HAADF-STEM and EDS elemental mapping images of the product were obtained for Example 1. TEM images of 10% Cr-NiFe MOF / cellulose aerogel clearly show the lamellar structure of aerogel and nanosphere and nanorod structure of 10% Cr-NiFe MOF Figure 3 a). HAADF-STEM and EDS elemental mapping Figure 3 b-g) spectra show that Cr, Ni, Fe elements are uniformly distributed on the nanosphere, while only Cr and Ni elements can be observed on the nanorod, which proves that the incorporation of Cr is conducive to the formation of nanorod structure.

[0059] Figure 4 Infrared spectroscopy tests were performed on the products of Examples 1 and 3 to analyze the functional groups in 10% Cr-NiFe MOF and 10% Cr-NiFe MOF / cellulose aerogel catalysts. The O-H stretching vibration peak is at 3453 cm -1 , the peak at 2806 cm -1 is the stretching vibration of -CH2, and the two characteristic peaks at 1472 and 1355 cm -1 belong to the symmetric and asymmetric vibrations of -COOH, respectively. Compared with Cr-NiFe MOF, the intensity of the -COOH characteristic peak of the material after compounding with cellulose aerogel is higher, which proves the successful compounding of Cr-NiFe MOF and cellulose aerogel.

[0060] Figure 5 XPS tests were performed on the products of Examples 1 and 2 to determine the elements and valence states of 10% Cr-NiFe MOF / cellulose aerogel and NiFe MOF / cellulose aerogel. Figure 5 a As can be seen from the full spectrum, the catalyst contains Ni, Fe, Cr, C and O elements. The Ni 2p spectrum of Cr-NiFe MOF / cellulose aerogel and NiFe MOF / cellulose aerogel is shown in Figure 5 b. The binding energy at 856.03 and 873.98 eV is attributed to Ni 2+ 2p 3 / 2 and Ni 2+ 2p 1 / 2, and two satellite peaks at 861.13 eV and 880.52 eV. Compared with NiFe MOF / cellulose aerogel, the binding energy of Cr-NiFe MOF / cellulose aerogel shifted about 0.7 eV to the negative direction. Figure 5 In c, the high-resolution spectrum of Fe 2p shows that the peaks of Fe 2p 3 / 2 and Fe 2p 1 / 2 are at 711.18 and 724.65 eV, respectively, and the satellite peak is at 717.67 eV, indicating that the Fe element exists in the +3 valence. Similarly, compared with NiFe MOF / cellulose aerogel, the binding energy of Cr-NiFe MOF / cellulose aerogel shifted about 0.3 eV to the negative direction of Fe 2p. After Cr doping, the binding energy of Ni 2p and Fe 2p shifted to the negative direction, which indicates that there is a strong electronic interaction between NiFe MOF and Cr. Figure 5 In d, the Cr 2p of Cr-NiFe MOF / cellulose aerogel shows two groups of peaks corresponding to Cr 2p 3 / 2 and 2p 1 / 2 , in which the peaks at 577.52 and 587.63 eV correspond to Cr 3+ , and the peaks at 579.98 and 591.71 eV correspond to Cr 6+ .

[0061] Figure 6 The electrochemical LSV tests of the products obtained in Examples 1, 2, 3 and 4 at a scan rate of 5 mV·S -1 , were carried out to evaluate the OER activity of the composite electrode catalyst, and all the measured potential results were referenced to the reversible hydrogen electrode (vs. RHE). Figure 6 a It is determined that the catalytic performance is best when the Cr doping amount is 10% as in Example 1, which only needs to provide a low overpotential of 235 mV to drive 10 mA cm -2 . At the same time, Figure 5 b shows that the catalytic activity of Cr-NiFe MOF / cellulose aerogel (235 mV) is much better than that of NiFe MOF / cellulose aerogel (298 mV) and Cr-NiFe MOF (317 mV), cellulose aerogel (381 mV), and also better than that of the commercial catalyst RuO2 (310 mV). It is shown that the doping of Cr and the compounding of MOF and aerogel together promote the improvement of OER.

[0062] Figure 7 The Tafel slopes of the products obtained in Examples 1, 2, 3 and 4 and commercial RuO2 were obtained to study the reaction kinetics. The Tafel slope of 10% Cr-NiFe MOF / cellulose aerogel is only 53.7 mV·dec -1The 5% Cr-NiFe MOF / cellulose aerogel sample with a lower Cr doping ratio than other samples (87.1 mV·dec) -1 ), 15% Cr-NiFe MOF / cellulose aerogel (53.7mV·dec) -1 ), 20% Cr-NiFe MOF / cellulose aerogel (76.3 mV·dec) -1 The value was also much smaller than that of other comparative samples, NiFe MOF / cellulose aerogel (82.4 mV·dec). -1 ), Cr-NiFe MOF (70.3mV·dec) -1 ), cellulose aerogel (173.7 mV·dec) -1 ),RuO2(103.4mV·dec -1 The results show that Cr doping significantly improves the OER reaction kinetics of the catalyst, and its reaction kinetics are further enhanced after being combined with cellulose aerogel.

[0063] Figure 8 Cdl was tested on the products obtained in Examples 1, 2, 3, and 4. The assessment of the electrochemical active surface area (ECSA) is crucial for studying the number of catalytically active sites. Cdl can be used to estimate its electrochemical active surface area. For example... Figure 8 As shown, the Cdl of 10% Cr-NiFe MOF / cellulose aerogel is 27.9 mF·cm. -2 Higher than NiFe MOF / cellulose aerogel (21.1 mF·cm⁻¹). -2 ), 10% Cr-NiFe MOF (16.1mF·cm -2 ) and cellulose aerogel (10.1 mF·cm -2 The exposed area of ​​active sites in 10% Cr-NiFeMOF / cellulose aerogel is significantly larger than that in uncomposite MOF and cellulose aerogel materials, demonstrating that the combination of the two can provide a better electrocatalytic site for OER.

[0064] Figure 9 Impedance tests were performed on the products obtained in Examples 1, 2, 3 and 4. The charge transfer resistance of the 10% Cr-NiFe MOF / cellulose aerogel in 1M KOH was 1.98Ω, showing the lowest impedance value. This further demonstrates that the incorporation of Cr and its combination with cellulose aerogel reduced the kinetic barriers in the OER process.

[0065] Figure 10 This is a long-term stability test for Example 1. Figure 10aIt is shown that the current density of the catalyst for oxygen evolution reaction remains good stability at each test potential after 1000 cycles of CV, and there is no obvious recession before and after the cycle. When the current density is 10 mA·cm -2 , the catalyst can be stable for more than 210 h Figure 10 b).

[0066] In combination with the above, it can be known that the Cr-NiFe MOF / cellulose aerogel prepared by the present application exhibits excellent electrocatalytic oxygen evolution performance and super-long time corrosion resistance under alkaline conditions, and not only its cost is much lower than the current industrial catalyst RuO2, but also its activity is obviously better than the commercial catalyst.

[0067] The above is only the preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can make equivalent replacement or change according to the technical scheme and the inventive concept of the present application within the technical range disclosed by the present application, which should be covered in the protection scope of the present application.

Claims

1. A method for preparing Cr-NiFe MOF / cellulose aerogel composite material, characterized in that, Includes the following steps: S1. Preparation of carboxymethyl cellulose solution: Dissolve carboxymethyl cellulose and NaOH in deionized water and stir until homogeneous to obtain a carboxymethyl cellulose solution of a certain concentration; Preparation of S2, Cr-NiFe MOF materials: S2.1 Dissolve Ni(NO3)2·6H2O, Fe(NO3)3·9H2O and Cr(NO3)3·9H2O in deionized water and stir, and label this solution A; the amounts of Ni(NO3)2·6H2O and Fe(NO3)3·9H2O used are 1~2 mmol and 0.75~1.25 mmol, respectively, and the amount of Cr(NO3)3·9H2O used is 0.1~0.3 mmol; The amount of deionized water used in solution A is 10-20 mL; S2.2 Dissolve terephthalic acid in the organic solvent N,N-dimethylformamide and stir until homogeneous, denoted as solution B; the amount of terephthalic acid used is 2~4 mmol; solution B is 10~20 mL of N,N-dimethylformamide solution; S2.3 Add solution A dropwise to solution B, continue stirring for a period of time, and then transfer to a hydrothermal reactor for hydrothermal reaction; The hydrothermal reaction conditions are heating at 150~170 ℃ for 24 h; S2.4 After the reaction is cooled to room temperature, the product is washed multiple times and dried overnight to obtain Cr-NiFe MOF; the washing agents used include deionized water and anhydrous ethanol. S3. Preparation of Cr-NiFe MOF / cellulose aerogel electrode material: The obtained Cr-NiFe MOF powder was dispersed in a carboxymethyl cellulose solution, a certain amount of acetone was added, and the mixture was mixed evenly at a certain temperature. After the reaction was complete, the mixture was frozen in liquid nitrogen and then freeze-dried to obtain the Cr-NiFe MOF / cellulose aerogel composite material.

2. The method for preparing the Cr-NiFe MOF / cellulose aerogel composite material according to claim 1, characterized in that, The amount of carboxymethyl cellulose used in S1 is 350~370 mg, and the amount of NaOH is 15~25 mg. The above carboxymethyl cellulose and NaOH are dissolved in 10~15 ml of deionized water.

3. The method for preparing the Cr-NiFe MOF / cellulose aerogel composite material according to claim 1, characterized in that, The amount of Cr-NiFe MOF used in S3 is 0.3~0.5 g, and the amount of acetone used is 0.2~0.4 mL.

4. The method for preparing the Cr-NiFe MOF / cellulose aerogel composite material according to claim 1, characterized in that, After the mixture in S3 is thoroughly mixed, the reaction temperature is controlled at 70~90℃ and the reaction time is 2~4 h; the liquid nitrogen freezing time is 5~15 min; and the freeze-drying time is 48 h.

5. A Cr-NiFe MOF / cellulose aerogel electrode material prepared by any one of the methods described in claims 1-4.

6. The application of the Cr-NiFe MOF / cellulose aerogel electrode material prepared as described in claim 5 in the electrocatalytic oxygen evolution under alkaline conditions.

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