Graphite felt / high-entropy MOF electrode, lignin-based fuel cell and method for co-production of aviation fuel components

Abstract

The invention discloses a graphite felt / high-entropy MOF electrode, a lignin-based fuel cell and a method for co-producing aviation fuel components. The graphite felt / high-entropy MOF electrode is obtained by dissolving various soluble metal salts and 2, 5-dihydroxy terephthalic acid in a solvent for hydrothermal reaction and generating high-entropy MOF on the surface of the graphite felt in situ. When the graphite felt / high-entropy MOF electrode is used for assembling the lignin-based liquid flow fuel cell, high-power density output of the lignin-based liquid flow fuel cell and efficient conversion from biomass energy to electric energy are successfully realized. After long-time power generation of the flow battery, lignin macromolecules can be promoted to be efficiently and directionally depolymerized into an aircraft fuel precursor to generate C8-C16 micromolecular substances, the main micromolecular substances are C10-C11, the micromolecular substances can be further subjected to hydrodeoxygenation to prepare aircraft fuel, and the flow battery has very great commercial prospects and utilization values.

Description

Technical Field

[0001] The present invention belongs to the field of high-value utilization of lignin, and particularly relates to a graphite felt / high-entropy MOF electrode, a lignin-based fuel cell, and a method for co-producing aviation fuel components. Background Art

[0002] The trend of reducing the use of fossil fuels globally is becoming increasingly significant, which has prompted the development and utilization of clean energy to attract more attention. Therefore, it is urgent to actively develop clean and renewable energy. Biomass energy has great potential as a renewable energy source, and the conversion of biomass into clean electric energy has always been a research direction that has received much attention. Currently, most of the anodic oxidants used in reported biomass fuel cells are polyoxometalates (POMs), which are complex in synthesis, poor in solubility, and expensive in price, restricting their wide application. In addition, the graphite felt electrode materials used in this type of battery have disadvantages such as poor wettability, small specific surface area, and low electrocatalytic activity, resulting in a large interfacial resistance between the electrolyte and the electrode, usually restricting the power density of the biomass fuel cell and leading to poor battery output performance, thus making it difficult to meet the actual needs.

[0003] As one of the three main components of biomass, lignin has a large reserve, is renewable, and has a low cost. However, at present, most industrial lignin is disposed of by incineration or direct discharge. The fuel cell system is a clean and efficient energy conversion technology that can be used to convert lignin into electric energy. However, most of the fuel cells studied currently have problems such as high working temperature, low energy utilization efficiency, and low power density, making it difficult to achieve efficient conversion of lignin directly into electric energy. In comparison, redox-type biomass fuel cells can directly and efficiently convert lignocellulosic biomass into electric energy at a relatively low temperature.

[0004] Lignin is one of the important components of biomass. As an abundant renewable resource, due to its structural characteristics, it is often used in energy storage batteries to improve the instability brought by traditional materials. The lignin fuel cells reported currently integrate the advantages of redox-type biomass fuel cells, can directly convert lignin into electric energy at low temperature, and have a higher power generation efficiency than other types of fuel cells such as microbial fuel cells. However, when lignin is used as a fuel, it needs to be modified through thermodynamic, chemical, or biological processes before it can be applied, resulting in low energy utilization efficiency and slow electron transfer rate, making the battery output power density low and the stability poor. Secondly, the internal graphite felt electrode has strong hydrophobicity and a small specific surface area, resulting in a slow electron transfer rate at the electrolyte-electrode interface, restricting the performance improvement and application research of this type of battery.

[0005] At present, the conversion of biomass into aviation fuel can effectively maintain the carbon balance, improve the environment, and promote energy conservation, emission reduction, and energy transformation. As a renewable energy source, the conversion of biomass into aviation fuel helps to enhance the stability and security of energy supply and reduce dependence on the external energy market. Its conversion into aviation fuel contributes to the optimization and transformation of the energy structure. By increasing the application of biomass energy in the aviation field, the dependence on fossil energy can be reduced, the diversity and sustainability of energy utilization can be improved, and commercial application can reduce the operating costs of airlines and increase economic benefits. Biomass aviation fuel has the same chemical composition as fossil fuel. Aviation fuel contains C8-C 16 chain hydrocarbons, naphthenes, and aromatic compounds, and the composition varies depending on the manufacturer and raw materials. Currently, the depolymerization of lignin mainly relies on pyrolysis, but the energy recovery is insufficient, resulting in waste of resources.

[0006] Therefore, there is an urgent need for a method to efficiently convert biomass into aviation fuel, construct a low-temperature and high-efficiency lignin fuel cell, generate electricity while oxidizing and degrading industrial lignin, and co-produce aviation fuel components. Summary of the Invention

[0007] To solve the disadvantages and deficiencies of the prior art, the primary object of the present invention is to provide a method for preparing a graphite felt / high-entropy MOF electrode. The present invention uses hydrothermal synthesis technology to successfully grow high-entropy MOF in-situ on the graphite felt substrate. The prepared electrode has excellent electrocatalytic activity, a large specific surface area, and a faster electron transfer rate. Using this electrode to assemble a lignin fuel cell is beneficial to the oxidation of lignin, thereby enabling efficient degradation of lignin macromolecules and co-producing electric energy and aviation fuel components simultaneously.

[0008] Another object of the present invention is to provide a graphite felt / high-entropy MOF electrode prepared by the above method.

[0009] Another object of the present invention is to provide a lignin-based fuel cell constructed with the above graphite felt / high-entropy MOF electrode.

[0010] The present invention uses a lignin alkaline solution as the anolyte, vanadyl sulfate and nitric acid as the catholyte, oxygen as the catholyte regenerant, graphite felt / high-entropy MOF as the anode electrode material, and graphite felt as the cathode electrode material to assemble a lignin-based fuel cell. The obtained fuel cell has a high power density and an open-circuit voltage, and the materials used are inexpensive, easily available, safe, and environmentally friendly.

[0011] Another object of the present invention is to provide a method for co-producing aviation fuel components using the above lignin-based fuel cell.

[0012] After long-term power generation by the lignin-based fuel cell of the present invention, it can produce mainly C8-C 16Small molecule substances, similar to small molecule substances of aviation fuel precursors, are expected to prepare aviation fuel through hydrodeoxygenation, and have broad application prospects and utilization values.

[0013] The object of the present invention is achieved by the following technical solutions:

[0014] A preparation method of a graphite felt / high-entropy MOF composite material, comprising the following steps:

[0015] Dissolve soluble cobalt salt, soluble nickel salt, soluble copper salt, soluble manganese salt, soluble molybdenum salt and 2,5-dihydroxyterephthalic acid in a solvent, add graphite felt, and carry out hydrothermal reaction in a high-pressure reaction kettle. After the reaction is completed, take out the graphite felt sample, wash it, and dry it to obtain the graphite felt / high-entropy MOF composite material.

[0016] Preferably, the molar ratio of the soluble cobalt salt, soluble nickel salt, soluble copper salt, soluble manganese salt, and soluble molybdenum salt is (0.5-1.5):(0.5-1.5):(0.5-1.5):(0.5-1.5):(0.5-1.5).

[0017] Preferably, the soluble cobalt salt, soluble nickel salt, soluble copper salt, soluble manganese salt, and soluble molybdenum salt are CoCl5·6H2O, NiCl2·6H2O, CuCl2, MnCl2·4H2O, and MoCl5 respectively.

[0018] Preferably, the concentration of the soluble cobalt salt, soluble nickel salt, soluble copper salt, soluble manganese salt, and soluble molybdenum salt in the solvent is 0.01-0.18 mol / L, more preferably 0.09-0.13 mmol / L.

[0019] Preferably, the molar ratio of the soluble cobalt salt and 2,5-dihydroxyterephthalic acid is (0.5-1.5):(1-4).

[0020] Preferably, the solvent is N,N-dimethylformamide, anhydrous ethanol and water with a volume ratio of (10-15):(0.5-1.5):(0.5-1.5).

[0021] Preferably, the temperature of the hydrothermal reaction is 20-200 °C, and the time is 2-24 h; more preferably, the temperature of the hydrothermal reaction is 60-130 °C, and the time is 4-24 h; most preferably, the temperature of the hydrothermal reaction is 60-130 °C, and the time is 4-12 h.

[0022] Preferably, the washing solution is at least one of ethanol, deionized water and acetone.

[0023] A graphite felt / high-entropy MOF composite material prepared by the above preparation method.

[0024] The application of the above-mentioned graphite felt / high-entropy MOF composite material in a lignin-based fuel cell.

[0025] The present invention also provides a lignin-based fuel cell, which includes an anolyte and an anode electrode; wherein the anolyte is a lignin alkali solution, and the anode electrode is the above-mentioned graphite felt / high-entropy MOF composite material.

[0026] Preferably, the concentration of lignin in the lignin alkali solution is 1-100 g / L, more preferably 1-80 g / L, still more preferably 5-70 g / L, and most preferably 10-50 g / L.

[0027] Preferably, the concentration of hydroxide ions in the lignin alkali solution is 0.02-10 mol / L, more preferably 0.05-3 mol / L, and most preferably 0.2-2 mol / L.

[0028] Preferably, in the lignin alkali solution, the alkali used is at least one of NaOH, KOH, and ammonia water.

[0029] Preferably, in the lignin alkali solution, the lignin used is at least one of enzymatic hydrolysis lignin, prehydrolysis lignin, lignin sulfonate, and alkali lignin.

[0030] Preferably, the lignin-based fuel cell further includes a catholyte, and the catholyte includes a pentavalent vanadium salt, an acid solution, and an oxidant for cathode regeneration.

[0031] More preferably, the pentavalent vanadium salt is at least one of vanadium pentoxide, vanadyl nitrate, and vanadyl sulfate; the concentration of the pentavalent vanadium salt in the catholyte is 0.05-5 mol / L.

[0032] More preferably, the acid solution is at least one of hydrochloric acid aqueous solution, sulfuric acid aqueous solution, and nitric acid aqueous solution; the concentration of the acid solution is 0.05-8.0 mol / L.

[0033] More preferably, the oxidant is at least one of nitric acid and oxygen; the concentration of nitric acid in the catholyte is 0.01-8 mol / L; the flow rate of oxygen introduced into the catholyte is 10-120 mL / min.

[0034] Preferably, the lignin-based fuel cell further includes a cathode electrode; the cathode electrode is a graphite felt.

[0035] Preferably, the operating temperature of the lignin-based fuel cell is 20-120 °C, more preferably 60-110 °C.

[0036] The present invention also provides a method for co-producing aviation fuel components by using the above lignin-based fuel cell, comprising the following steps:

[0037] Operate the above lignin-based fuel cell at 20-120 °C. The lignin in the anolyte undergoes a depolymerization reaction. Extract the depolymerization products and then perform hydrodeoxygenation treatment to obtain aviation fuel components.

[0038] Preferably, the operating temperature of the lignin-based fuel cell is 60-110 °C.

[0039] Preferably, the solvent for extraction is at least one of ethyl acetate, isopropyl acetate, and butyl acetate.

[0040] Preferably, the temperature of the hydrodeoxygenation treatment is 150-210 °C and the time is 6-10 h.

[0041] Preferably, the hydrodeoxygenation treatment is carried out under the action of a catalyst, and the catalyst is at least one of Pt / C catalyst and Fe-based catalyst; the mass ratio of the depolymerization product to the catalyst is (0.5-1):(3-5).

[0042] Preferably, the hydrodeoxygenation treatment is carried out in a high-pressure reactor, and the solvent is at least one of cyclohexane and n-octane; the ratio of the depolymerization product to the solvent is 0.5-1.5 mg:0.5-1.5 mL.

[0043] Preferably, the hydrogen pressure of the hydrodeoxygenation treatment is 3-5 MPa.

[0044] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0045] 1. The present invention uses low-cost and environmentally friendly transition metals, which are low in cost, cheap in price, and high in cost performance. A graphite felt / high-entropy MOF electrode is prepared. The high-entropy alloy catalyst breaks through the limitations of traditional single-component catalysts and introduces the concept of multi-component components, providing a new idea for more efficient catalyst design. This electrode not only has a high specific surface area and excellent electrocatalytic activity, but also has a simple preparation process and can achieve the best effect without going through complex calcination steps.

[0046] 2. When the graphite felt / high-entropy MOF electrode in the present invention is applied to a lignin-based fuel cell, its power density far exceeds that of similar designs reported currently, and its performance is particularly outstanding.

[0047] 3. The anolyte of the lignin-based fuel cell of the present invention does not require the additional addition of a redox couple to assist electron transfer, thus simplifying the processes of electron transfer and subsequent separation and purification of lignin. In addition, the cell can directly generate electricity using unpreheated anolyte, effectively avoiding the condensation phenomenon of lignin, further simplifying the power generation process and reducing energy consumption. The lignin-based fuel cell of the present invention generates electrical energy by directly electrocatalytically oxidizing lignin on the electrode, and the application of the graphite felt / high-entropy MOF electrode significantly improves the oxidation rate of lignin and the electron transfer efficiency, thereby greatly enhancing the overall performance of the fuel cell.

[0048] 4. The graphite felt / high-entropy MOF electrode of the present invention itself has good corrosion resistance and thermal stability, is suitable for harsh catalytic environments, presents a large number of active sites through the inherent synergistic effect of severe lattice distortion and tunable electronic structure, and can adjust the catalytic performance by adjusting the composition and structure of the high-entropy alloy. It has excellent electrocatalytic activity, and the synthesized MOF material has a highly controllable structure, a large specific surface area, and good stability. Therefore, the lignin-based fuel cell of the present invention can induce the deep degradation of a large number of lignin macromolecules, thereby comprehensively improving the performance indexes of the fuel cell.

[0049] 5. The main products of the lignin flow fuel cell constructed by the graphite felt / high-entropy MOF electrode of the present invention during long-term power generation are C8 - C 16 small molecules, and the most concentrated ones are in C 10 -C 11 , which can be further hydrodeoxygenated to prepare aviation fuel, having broad application prospects and utilization value. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 It is the current density-voltage-output power diagram of the lignin flow fuel cell constructed by the CoNiCuMnMo-MOF / GF electrode in Example 1.

[0051] Figure 2 It is the XRD diagram of the CoNiCuMnMo-MOF / GF electrode in Example 1, where HEA-MOF / GF in the figure is CoNiCuMnMo-MOF / GF.

[0052] Figure 3 It is the current density-voltage-output power diagram of the lignin flow fuel cell constructed by the CoNiCuMnMo-HEO / GF electrode in Comparative Example 1.

[0053] Figure 4Current density-voltage-output power diagram of the lignin-based flow fuel cell constructed with CoNiCuMnMo-MOF / GF electrodes prepared with different metal concentrations in Example 2. In the figure, HEA-MOF / GF is CoNiCuMnMo-MOF / GF.

[0054] Figure 5 Current density-voltage-output power diagram of the lignin-based flow fuel cell constructed with CoNiCuMnMo-MOF / GF electrodes prepared with different hydrothermal reaction times in Example 3. In the figure, HEA-MOF / GF is CoNiCuMnMo-MOF / GF, and HEA / GF is CoNiCuMnMo / GF.

[0055] Figure 6 LSV and EIS diagrams of the electrochemical test of the CoNiCuMnMo-MOF / GF electrode in Example 4.

[0056] Figure 7 SEM diagram of the CoNiCuMnMo-MOF / GF electrode in Example 4.

[0057] Figure 8 Diagram of the electron transfer rate and energy release after long-term power generation of enzymatic lignin in Example 5.

[0058] Figure 9 GC-MS diagram of the degradation products after long-term power generation of enzymatic lignin in Example 5.

[0059] Figure 10 Current density-voltage-output power diagram of the lignin-based flow fuel cell constructed with a graphite felt electrode in Comparative Example 2.

[0060] Figure 11 Current density-voltage-output power diagram of the lignin-based flow fuel cell constructed with the CoNiCuMnMo-MOF / GF electrode before calcination and the CoNiCuMnMo-HEO / GF electrode after calcination in Comparative Example 3. Detailed implementation manners

[0061] The present invention will be further described in detail below with reference to the embodiments and the drawings, but the implementation manners of the present invention are not limited thereto.

[0062] In the present invention, "room temperature" is generally calculated as 10-30 °C unless otherwise specified.

[0063] The enzymatic lignin used in the following examples and comparative examples of the present invention was purchased from Shandong Longli Biotechnology Co., Ltd. The graphite felt was purchased from Carbon Energy, Taiwan Province, China, and was ultrasonically cleaned in absolute ethanol, acetone, hydrochloric acid solution with a volume concentration of 75%, and deionized water before use.

[0064] The electrical properties (current density, voltage, output power) of the battery prepared by the present invention were tested by the scanning current method.

[0065] All raw materials used in the following examples and comparative examples of the present invention are commercially available products.

[0066] Example 1: Preparation and performance study of CoNiCuMnMo-MOF / GF electrode

[0067] 1. The graphite felt was pretreated before use. It was ultrasonically cleaned in acetone for 15 min, rinsed several times with deionized water, then transferred to a 75% (by volume) hydrochloric acid solution for ultrasonic cleaning for 15 min. After the ultrasonic cleaning was completed, it was rinsed several times with deionized water and then transferred to concentrated nitric acid for ultrasonic cleaning for 15 min. Finally, after rinsing several times with deionized water, the carbon cloth was immersed in anhydrous ethanol for use.

[0068] 2. Preparation of CoNiCuMnMo-MOF / GF electrode: 3 mmol of CoCl₅·6H₂O, 3 mmol of NiCl₂·6H₂O, 3 mmol of CuCl₂, 3 mmol of MnCl₂·4H₂O, 3 mmol of MoCl₅, and 9 mmol of 2,5-dihydroxyterephthalic acid were dissolved in a mixed solvent of 39 ml of N,N-dimethylformamide, 3 ml of anhydrous ethanol, and 3 ml of water to obtain a hydrothermal reaction solution; a 5 cm × 0.5 cm × 0.5 cm graphite felt was pasted with medical tape and placed in the hydrothermal reaction solution to allow it to react fully in the solution. The hydrothermal reaction was carried out in a high-pressure reaction kettle at 120 °C for 24 h. After the reaction was completed, the sample was taken out, washed several times with deionized water, and dried to obtain a graphite felt / high-entropy MOF electrode.

[0069] 3. Preparation of anodic electrolyte: Weigh 4 g of NaOH and dissolve it in 50 ml of deionized water, and stir for 10 min. Then weigh 2 g of enzymatically hydrolyzed lignin, add it to the solution, stir for 10 min and then filter to obtain the anodic electrolyte of lignin alkaline solution.

[0070] 4. Preparation of cathodic electrolyte: Weigh 20 g of vanadium pentoxide powder and add it to a beaker containing 524 ml of deionized water, and stir at room temperature. Then take 76 ml of concentrated sulfuric acid with a mass fraction of 98.3%, slowly add it to the solution, and continue stirring. After 24 h, add 4 ml of pure nitric acid, and continue stirring the solution until it forms a clear solution, showing a bright yellow color, and let it stand for 72 h to obtain the cathodic electrolyte of high-valent vanadium. Take 100 ml from it as the cathodic electrolyte.

[0071] 5. Assembly and electrical property measurement of the battery: A battery system was constructed. The LFFC (liquid flow fuel cell) consisted of two all-carbon graphite electrodes with serpentine flow channels and had a total effective area of 1 cm 2The graphite felt was filled in the cathode flow channel of the battery system, and the graphite felt / high entropy MOF electrode was filled in the anode flow channel of the battery system. The anolyte and catholyte were stirred at a rate of 10 mL min -1 The flow rate of nitric acid was pumped into LFFC. -1 The oxygen is injected into the cathode at a flow rate of 2+ Oxidized to VO2 + The cathode electrolyte was regenerated. The LFFC system was operated at 90°C. The sample cell performance was tested by the 857 flow battery test system.

[0072] The electrical performance of the battery was tested using the scanning current method. The results are as follows: Figure 1 As shown in Figure 2, the maximum power density of the CoNiCuMnMo-MOF / GF electrode is 261.03 mW / cm 2 , with good battery performance.

[0073] The XRD spectrum of CoNiCuMnMo-MOF / GF in Example 1 is as follows Figure 2 As shown, it can be seen that the peaks at 25.7° and 43.9° correspond to the (002) and (101) crystal planes of carbon. The other peaks are all caused by MOF. In other words, the main peaks of CoNiCuMnMo-MOF / GF can be indexed with MOFs.

[0074] Comparative Example 1: Preparation and performance study of CoNiCuMnMo-HEO / GF high entropy oxide electrode

[0075] 1. The graphite felt is pre-treated before use. It is ultrasonically cleaned in acetone for 15 minutes, rinsed several times with deionized water, and then transferred to a 75% volume concentration hydrochloric acid solution for ultrasonic cleaning for 15 minutes. After the ultrasound, it is rinsed several times with deionized water and then transferred to concentrated nitric acid for ultrasonic cleaning for 15 minutes. Finally, it is rinsed several times with deionized water and the carbon cloth is soaked in anhydrous ethanol for standby use.

[0076] 2. Preparation of CoNiCuMnMo-HEO / GF electrode: Dissolve 3 mmol of CoCl₅·6H₂O, 3 mmol of NiCl₂·6H₂O, 3 mmol of CuCl₂, 3 mmol of MnCl₂·4H₂O, and 3 mmol of MoCl₅ in a mixed solvent of 39 ml of N,N-dimethylformamide, 3 ml of absolute ethanol, and 3 ml of water to obtain a hydrothermal reaction solution; Paste the pretreated graphite felt of 5 cm×0.5 cm×0.5 cm with medical tape and place it in the hydrothermal reaction solution to allow it to react fully in the solution. Carry out hydrothermal reaction in a high-pressure reactor at 120 °C for 24 h. After cooling to room temperature, wash the prepared sample several times with deionized water and dry it overnight in an oven at 60 °C to obtain a graphite felt / high-entropy oxide electrode.

[0077] 3. Preparation of anolyte: Weigh 4 g of NaOH and dissolve it in 50 ml of deionized water, and stir for 10 min. Then weigh 2 g of enzymatically hydrolyzed lignin, add it to the solution, stir for 10 min and then filter to obtain the anolyte of lignin alkaline solution.

[0078] 4. Preparation of catholyte: Weigh 20 g of vanadium pentoxide powder and add it to a beaker containing 524 ml of deionized water, and stir at room temperature. Then take 76 ml of concentrated sulfuric acid with a mass fraction of 98.3%, slowly add it to the solution, and keep stirring. After 24 h, add 4 ml of nitric acid, and keep stirring the solution until it forms a clear solution, showing bright yellow, and let it stand for 72 h to obtain the catholyte of high-valent vanadium. Measure 100 ml from it as the catholyte.

[0079] 5. Assembly and electrical performance measurement of the battery: Construct a battery system. The LFFC consists of two all-carbon graphite electrodes with serpentine flow channels and is separated by a Nafion 211 membrane with a total effective area of 1 cm 2 . The graphite felt is filled in the cathode flow channel of the battery system, and the CoNiCuMnMo-HEO / GF high-entropy oxide electrode is filled in the anode flow channel of the battery system. The anolyte and catholyte are pumped into the LFFC at a flow rate of 10 mL min -1 . Under the catalysis of nitric acid, oxygen is injected into the cathode at a flow rate of 40 mL min -1 to oxidize the VO 2+ generated at the cathode into VO₂ + , realizing the regeneration of the catholyte. The LFFC system operates at 90 °C. The performance of the sample cell is tested by an 857 flow battery test system.

[0080] The electrical performance of the battery is tested by the scanning current method, and the results are as Figure 3As shown, when the CoNiCuMnMo-HEO / GF electrode is used as the anode electrode, the maximum power density of the battery is 242.41 mW / cm 2 , compared with the maximum power density of 261.03 mW / cm in Example 1 2 , it can be seen that the performance is significantly better after adding the MOF framework in Example 1.

[0081] Example 2: Influence of CoNiCuMnMo-MOF / GF electrodes prepared with different metal concentrations on fuel cells.

[0082] 1. The graphite felt is pretreated before use. It is ultrasonically cleaned in acetone for 15 min, rinsed several times with deionized water, then transferred to a hydrochloric acid solution with a volume concentration of 75% for ultrasonic cleaning for 15 min. After the ultrasonic cleaning is completed, it is rinsed several times with deionized water and then transferred to concentrated nitric acid for ultrasonic cleaning for 15 min. Finally, after rinsing several times with deionized water, the carbon cloth is immersed in absolute ethanol for later use.

[0083] 2. Preparation of CoNiCuMnMo-MOF / GF electrodes: 3 mmol CoCl5·6H2O, 3 mmol NiCl2·6H2O, 3 mmol CuCl2, 3 mmol MnCl2·4H2O, 3 mmol MoCl5, and 9 mmol 2,5-dihydroxyterephthalic acid are dissolved in a mixed solvent of 39 ml N,N-dimethylformamide, 3 ml absolute ethanol, and 3 ml water to obtain the first group of hydrothermal reaction solutions; 4 mmol CoCl5·6H2O, 4 mmol NiCl2·6H2O, 4 mmol CuCl2, 4 mmol MnCl2·4H2O, 4 mmol MoCl5, and 12 mmol 2,5-dihydroxyterephthalic acid are dissolved in a mixed solvent of 39 ml N,N-dimethylformamide, 3 ml absolute ethanol, and 3 ml water to obtain the second group of hydrothermal reaction solutions; 6 mmol CoCl5·6H2O, 6 mmol NiCl2·6H2O, CuCl2, 6 mmol MnCl2·4H2O, 6 mmol MoCl5, and 18 mmol 2,5-dihydroxyterephthalic acid are dissolved in a mixed solvent of 39 ml N,N-dimethylformamide, 3 ml absolute ethanol, and 3 ml water to obtain the third group of hydrothermal reaction solutions; The pretreated 5 cm × 0.5 cm × 0.5 cm graphite felt is pasted with medical tape and placed in the hydrothermal reaction solution respectively, so that it can react fully in the solution. The hydrothermal reaction is carried out in a high-pressure reaction kettle at 120 °C for 24 h. After the reaction is completed and cooled to room temperature, the samples are taken out. The prepared samples are washed several times with deionized water and dried overnight in an oven at 60 °C to obtain three graphite felt / high-entropy MOF electrodes.

[0084] 3. Preparation of anolyte: Weigh 4 g of NaOH and dissolve it in 50 ml of deionized water, and stir for 10 min. Then weigh 2 g of enzymatically hydrolyzed lignin, add it to the solution, stir for 10 min and then filter to obtain the anolyte of lignin alkaline solution.

[0085] 4. Preparation of catholyte: Weigh 20 g of vanadium pentoxide powder and add it to a beaker containing 524 ml of deionized water, and stir at room temperature. Then take 76 ml of concentrated sulfuric acid with a mass fraction of 98.3%, slowly add it to the solution, and keep stirring. After 24 h, add 4 ml of nitric acid, and keep stirring the solution until it forms a clear solution, showing a bright yellow color, and let it stand for 72 h to obtain the catholyte of high-valent vanadium. Measure 100 ml from it as the catholyte.

[0086] 5. Assembly and electrical performance measurement of the battery: Construct 3 groups of battery systems. The LFFC consists of two all-carbon graphite electrodes with serpentine flow channels and is separated by a Nafion 211 membrane with a total effective area of 1 cm 2 . Graphite felt is filled in the cathode flow channels of the three groups of battery systems, and each of the three graphite felt / high-entropy MOF electrodes obtained from the above operations is filled in the anode flow channels of one group of battery systems. The anolyte and catholyte are pumped into the LFFC at a flow rate of 10 mL min -1 . Under the catalysis of nitric acid, oxygen is injected into the cathode at a flow rate of 40 mL min -1 to oxidize the VO 2+ generated at the cathode into VO2 + , realizing the regeneration of the catholyte. The LFFC system operates at 90 °C. The performance of the sample cell is tested by an 857 flow battery test system.

[0087] The electrical performance of the battery is tested by the scanning current method, and the results are as Figure 4 shown. The battery performance of the graphite felt / high-entropy MOF electrode obtained by using 6 mmol of each metal salt as the third group of hydrothermal reaction solutions is the best, with a maximum voltage of 1.5 V, a maximum current density of 772.59 mA / cm 2 , and a maximum power density of 366.62 mW / cm 2 . The maximum power density of the graphite felt / high-entropy MOF electrode obtained by using 4 mmol of each metal salt as the third group of hydrothermal reaction solutions is the second best, which is 333.91 mW / cm 2 , proving that the graphite felt / high-entropy MOF electrode obtained by using 6 mmol of each metal salt as the third group of hydrothermal reaction solutions has more prominent battery performance.

[0088] Example 3: Influence of CoNiCuMnMo-MOF / GF electrodes with different reaction times on fuel cells

[0089] 1. The graphite felt is pretreated before use. It is ultrasonically cleaned in acetone for 15 min, rinsed several times with deionized water, then transferred to a hydrochloric acid solution with a volume concentration of 75% and ultrasonically cleaned for 15 min. After the ultrasonic cleaning, it is rinsed several times with deionized water again and then transferred to concentrated nitric acid for ultrasonic cleaning for 15 min. Finally, after rinsing several times with deionized water, the carbon cloth is soaked in absolute ethanol for later use.

[0090] 2. Preparation of the graphite felt / high-entropy MOF electrode: Dissolve 6 mmol CoCl₅·6H₂O, 6 mmol NiCl₂·6H₂O, 6 mmol CuCl₂, 6 mmol MnCl₂·4H₂O, 6 mmol MoCl₅, and 18 mmol 2,5-dihydroxyterephthalic acid in a mixed solvent of 39 ml N,N-dimethylformamide, 3 ml absolute ethanol, and 3 ml water to obtain a hydrothermal reaction solution; Paste the pretreated graphite felt of 5 cm×0.5 cm×0.5 cm with medical tape and place it in the hydrothermal reaction solution to allow it to react fully in the solution. Carry out hydrothermal reactions at 120 °C in a high-pressure reaction kettle for 4 h, 6 h, and 12 h respectively. After the reaction, take out the samples, wash them several times with deionized water, and dry them to obtain three kinds of graphite felt / high-entropy MOF electrodes.

[0091] 3. Preparation of the anolyte: Weigh 4 g of NaOH and dissolve it in 50 ml of deionized water, and stir for 10 min. Then weigh 2 g of enzymatically hydrolyzed lignin, add it to the solution, stir for 10 min and then filter to obtain the anolyte of the lignin alkali solution.

[0092] 4. Preparation of the catholyte: Weigh 20 g of vanadium pentoxide powder and add it to a beaker containing 524 ml of deionized water, and stir at room temperature. Then take 76 ml of concentrated sulfuric acid with a mass fraction of 98.3%, slowly add it to the solution, and continue stirring. After 24 h, add 4 ml of nitric acid, and continue stirring the solution until it forms a clear solution, showing a bright yellow color, and let it stand for 72 h to obtain the catholyte of high-valent vanadium. Take 100 ml from it as the catholyte.

[0093] 5. Assembly and electrical performance measurement of the battery: Construct 3 groups of battery systems. The LFFC consists of two all-carbon graphite electrodes with serpentine flow channels and is separated by a Nafion 211 membrane with a total effective area of 1 cm 2 . The graphite felt is filled in the cathode flow channels of the three groups of battery systems, and each of the three kinds of graphite felt / high-entropy MOF electrodes obtained from the above operations is filled in the anode flow channels of one group of battery systems. The anolyte and catholyte are pumped into the LFFC at a flow rate of 10 mL min -1 . Under the catalysis of nitric acid, oxygen is injected into the cathode at a flow rate of 40 mL min -1 to oxidize the VO 2+ generated at the cathode into VO₂+ to achieve the regeneration of the catholyte. The LFFC system operates at 90 °C. The performance of the sample cell is tested by an 857 flow battery test system.

[0094] The electrical performance of the battery is tested by the cyclic voltammetry method, and the results are as Figure 5 shown. The graphite felt / high-entropy MOF electrode has the best battery performance after 12 h of hydrothermal reaction. The maximum voltage is 1.58 V, and the maximum current density is 1454.1 mA / cm 2 , and the maximum power density is 545.48 mW / cm 2 . The battery performance of the hydrothermal reaction for 4 h and 6 h is lower. It is proved that the graphite felt / high-entropy MOF electrode has the best battery performance at 12 h of hydrothermal reaction, which is more conducive to the oxidation of lignin.

[0095] Example 4: Electrochemical activity of the CoNiCuMnMo-MOF / GF electrode

[0096] 1. The graphite felt is pretreated before use. It is ultrasonically cleaned in acetone for 15 min, rinsed several times with deionized water, then transferred to a 75% (by volume) hydrochloric acid solution for ultrasonic cleaning for 15 min. After ultrasonic cleaning, it is rinsed several times with deionized water and then transferred to concentrated nitric acid for ultrasonic cleaning for 15 min. Finally, after rinsing several times with deionized water, the carbon cloth is immersed in absolute ethanol for later use.

[0097] 2. Preparation of the graphite felt / high-entropy MOF electrode: 6 mmol of CoCl5·6H2O, 6 mmol of NiCl2·6H2O, 6 mmol of CuCl2, 6 mmol of MnCl2·4H2O, 6 mmol of MoCl5, and 18 mmol of 2,5-dihydroxyterephthalic acid are dissolved in a mixed solvent of 39 ml of N,N-dimethylformamide, 3 ml of absolute ethanol, and 3 ml of water to obtain a hydrothermal reaction solution; a 5 cm × 0.5 cm × 0.5 cm graphite felt is pasted with medical tape and placed in the hydrothermal reaction solution to allow it to react fully in the solution. The hydrothermal reaction is carried out in a high-pressure reaction kettle at 120 °C for 12 h. After the reaction is completed, the sample is taken out, washed repeatedly with deionized water, and dried to obtain the graphite felt / high-entropy MOF electrode.

[0098] 3. Preparation of graphite felt / high-entropy oxide electrode: Dissolve 6 mmol of CoCl₅·6H₂O, 6 mmol of NiCl₂·6H₂O, 6 mmol of CuCl₂, 6 mmol of MnCl₂·4H₂O, and 6 mmol of MoCl₅ in a mixed solvent of 39 ml of N,N-dimethylformamide, 3 ml of absolute ethanol, and 3 ml of water to obtain a hydrothermal reaction solution; Paste a 5 cm×0.5 cm×0.5 cm graphite felt with medical tape and place it in the hydrothermal reaction solution to allow it to react fully in the solution. Carry out hydrothermal reaction in a high-pressure reactor at 120 °C for 12 h. After the reaction, take out the sample, wash it with deionized water multiple times, and dry it to obtain the graphite felt / high-entropy oxide electrode.

[0099] 4. Preparation of NaOH solution: Weigh 8 g of NaOH and dissolve it in 100 ml of deionized water to obtain a 2 mol / L NaOH solution.

[0100] 5. Using a Gamry electrochemical workstation, with a standard Ag / AgCl electrode as the reference electrode, a graphite rod as the counter electrode, and the prepared graphite felt / high-entropy MOF electrode and graphite felt / high-entropy oxide electrode as the working electrodes. Test using linear sweep voltammetry. The test range is from 1.5 V to -0.5 V versus the reversible hydrogen electrode (RHE) and scan at a rate of 5 mV / s in 2 mol / L NaOH solution. The electrode potential calculation formula is E RHE = E Ag / AgCl + 0.197 V + 0.059 V×pH. Electrochemical impedance spectroscopy (EIS) is carried out in the frequency range of 20 kHz to 0.01 Hz with an amplitude of 5 mV.

[0101] The test results are as Figure 6 shown. It can be concluded that the graphite felt / high-entropy MOF electrode with MOF has a smaller overpotential and a smaller impedance than the graphite felt / high-entropy oxide electrode without MOF at a current density of 50 mA / cm 2 . It is proved that the graphite felt / high-entropy MOF electrode with high-entropy organic framework MOF has better reaction kinetics and electrochemical activity.

[0102] In this example, the SEM pattern of the CoNiCuMnMo-MOF / GF electrode is as Figure 7 shown. It can be seen that the morphology of the high-entropy MOF is a blocky shape formed by the stacking of flakes on carbon fibers, and the distribution is relatively uniform.

[0103] Example 5: Long-term power generation of a flow battery to prepare a precursor of aviation fuel

[0104] 1. The graphite felt is pretreated before use. It is ultrasonically cleaned in acetone for 15 min, rinsed several times with deionized water, then transferred to a hydrochloric acid solution with a volume concentration of 75% and ultrasonically cleaned for 15 min. After the ultrasonic cleaning is completed, it is rinsed several times with deionized water and then transferred to concentrated nitric acid for ultrasonic cleaning for 15 min. Finally, after rinsing several times with deionized water, the carbon cloth is immersed in absolute ethanol for later use.

[0105] 2. Preparation of the graphite felt / high-entropy MOF electrode: 6 mmol of CoCl₅·6H₂O, 6 mmol of NiCl₂·6H₂O, 6 mmol of CuCl₂, 6 mmol of MnCl₂·4H₂O, 6 mmol of MoCl₅, and 18 mmol of 2,5-dihydroxyterephthalic acid are dissolved in a mixed solvent of 39 ml of N,N-dimethylformamide, 3 ml of absolute ethanol, and 3 ml of water to obtain a hydrothermal reaction solution; the pretreated graphite felt of 5 cm × 0.5 cm × 0.5 cm is pasted with medical tape and placed in the hydrothermal reaction solution so that it can fully react in the solution. The hydrothermal reaction is carried out in a high-pressure reaction kettle at 120 °C for 12 h. After the reaction is completed, the sample is taken out, washed several times with deionized water, and dried to obtain the graphite felt / high-entropy MOF electrode.

[0106] 3. Preparation of the anolyte: Weigh 8 g of NaOH and dissolve it in 100 ml of deionized water, and stir for 10 min. Then weigh 1 g of enzymatically hydrolyzed lignin and add it to the solution. After stirring for 20 min, filter it to obtain 100 ml of the anolyte of the lignin alkaline solution.

[0107] 4. Preparation of the catholyte: Weigh 20 g of vanadium pentoxide powder and add it to a beaker containing 524 ml of deionized water, and stir at room temperature. Then take 76 ml of concentrated sulfuric acid with a mass fraction of 98.3% and slowly add it to the solution, and keep stirring. After 24 h, add 4 ml of nitric acid, and keep stirring the solution until it forms a clear solution, showing a bright yellow color. Let it stand for 72 h to obtain the catholyte of high-valent vanadium. Measure 600 ml from it as the catholyte.

[0108] 5. Assembly of the battery: Construct a battery system. The LFFC consists of two all-carbon graphite electrodes with serpentine flow channels and is separated by a Nafion 211 membrane with a total effective area of 1 cm 2 The graphite felt is filled in the cathode flow channel, and the graphite felt / high-entropy MOF electrode obtained from the above operations is filled in the anode flow channel. The anolyte and catholyte are pumped into the LFFC at a flow rate of 10 mL min -1 Under the catalysis of nitric acid, oxygen is injected into the cathode at a flow rate of 40 mL min -1 to oxidize the VO 2+ generated at the cathode into VO₂ +, realizing the regeneration of the catholyte. The LFFC system operates at 90 °C. The performance of the sample cell is tested by an 857 flow battery test system.

[0109] 6. The constant current discharge method is adopted for testing, and a long-term continuous discharge experiment is carried out on the lignin-based fuel cell at a voltage of 0.3 V. During this period, when the molar concentration of C8-C 16 components in the anolyte reaches 20%, power generation is stopped. As Figure 8 shown. At a voltage of 0.3 V, 1 g of enzymatically hydrolyzed lignin can generate 500 mW h of electricity.

[0110] 7. The obtained anolyte is extracted with ethyl acetate, and the extracted solution is the co-produced aviation fuel precursor component, and the products in the extracted solution are sent for GC-MS testing. The sample is directly injected for GC-MS analysis after being filtered through a 0.22 μm microporous filter membrane. The chromatographic column is HP-5MS (30.0 m × 250 μm, 0.25 μm); the initial temperature is maintained at 40 °C for 1 min, heated to 120 °C at a rate of 5 °C / min, and then heated to 280 °C at a rate of 10 °C / min and maintained for 15 min; the vaporization chamber temperature is 280 °C; the transfer line temperature is 300 °C; the carrier gas is He; the carrier gas flow rate is 1.0 mL / min; the split ratio is 20:1, and the injection volume is 1 μL. Mass spectrometry conditions: EI source; electron energy 70 eV; ion source temperature 230 °C; quadrupole 150 °C; scan mode is Scan; the scan mass range is 20-500 μ.

[0111] The test results are as Figure 9 shown. From Figure 9 it can be seen that the products of long-term power generation of the flow fuel cell include straight-chain hydrocarbons, aromatic hydrocarbons, and cycloalkanes, and small molecule substances of C8-C 16 can be produced after long-term power generation, which are similar to aviation fuel precursors and can be further hydrodeoxygenated to prepare aviation fuel, having great commercial prospects and utilization value.

[0112] Example 6: A method for preparing an aviation fuel component using the co-produced aviation fuel precursor solution by power generation, the steps are as follows:

[0113] The extracted solution in Example 5 is subjected to heat evaporation solvent treatment to obtain a solid lignin degradation product; 0.01 g of this lignin degradation product, 0.05 g of Pt / C catalyst powder (brand: Macklin, manufacturer: Guangzhou Rongman Biotechnology Co., Ltd., product number: P822267-1g) and 10 mL of cyclohexane solvent are added to a high-pressure reaction kettle. After removing the air in the reaction kettle, 5 MPa of high-pressure hydrogen is charged, and the mixture is heated and stirred at 180 °C for 8 h, and then the product yield is detected by a gas chromatograph. Hexane is used as an internal standard, and the conversion rate, yield, and selectivity are calculated by the internal standard method. The calculation formulas are as follows:

[0114]

[0115] Among them, f i and f s are the correction factors of the analyte and the internal standard respectively, which are calculated by the effective carbon number method. A i and A s are the peak areas of the analyte and the internal standard respectively, m s is the mass of the internal standard, and m i is the mass of the analyte. The results show that the yield of aviation fuel components is about 25%, and the conversion rate is about 69%.

[0116] Comparative Example 2: Influence of Graphite Felt as Anode Electrode on Lignin Flow Fuel Cell

[0117] 1. The graphite felt is pretreated before use. It is ultrasonically cleaned in acetone for 15 min, rinsed several times with deionized water, then transferred to a 75% (by volume) hydrochloric acid solution for ultrasonic cleaning for 15 min. After the ultrasonic cleaning is completed, it is rinsed several times with deionized water and then transferred to concentrated nitric acid for ultrasonic cleaning for 15 min. Finally, after rinsing several times with deionized water, the carbon cloth is immersed in absolute ethanol for later use.

[0118] 2. Preparation of the anolyte: Weigh 4 g of NaOH and dissolve it in 50 ml of deionized water, and stir for 10 min. Then weigh 2 g of enzymatically hydrolyzed lignin and add it to the solution. After stirring for 10 min, filter it to obtain the anolyte of the lignin alkaline solution.

[0119] 3. Preparation of the catholyte: Weigh 20 g of vanadium pentoxide powder and add it to a beaker containing 524 ml of deionized water, and stir at room temperature. Then take 76 ml of concentrated sulfuric acid with a mass fraction of 98.3% and slowly add it to the solution, and keep stirring. After 24 h, add 4 ml of nitric acid, and keep stirring the solution until it forms a clear solution, showing a bright yellow color. Let it stand for 72 h to obtain the catholyte of high-valent vanadium. Take 100 ml from it as the catholyte.

[0120] 4. Assembly and electrical performance measurement of the battery: The LFFC consists of two all-carbon graphite electrodes with serpentine flow channels and is separated by a Nafion 211 membrane with a total effective area of 1 cm 2 . The graphite felt is filled in the cathode flow channel, and the graphite felt is filled in the anode flow channel. The anolyte and the catholyte are pumped into the LFFC at a flow rate of 10 mL min -1 . Under the catalysis of nitric acid, oxygen is injected into the cathode at a flow rate of 40 mL min -1 to oxidize the VO 2+ generated at the cathode into VO2 +, realizing the regeneration of the catholyte. The LFFC system operates at 90 °C. The performance of the sample cell was tested by an 857 flow battery test system.

[0121] The electrical performance of the battery was tested by the scanning current method, and the results are as Figure 10 shown. The maximum voltage is 1.45 V, and the maximum current density is 465.62 mA / cm 2 , and the maximum power density is 139.09 mW / cm 2 . The performance is far from being as excellent as that of the graphite felt / high-entropy MOF electrode obtained by hydrothermal reaction for 12 h in Example 3. Therefore, the use of the graphite felt / high-entropy MOF electrode can achieve the efficient degradation of lignin and power generation.

[0122] Comparative Example 3: Influence of the calcined CoNiCuMnMo-HEO / GF(N2) electrode on the fuel cell

[0123] 1. The graphite felt was pretreated before use. It was ultrasonically cleaned in acetone for 15 min, rinsed several times with deionized water, then transferred to a 75% (by volume) hydrochloric acid solution for ultrasonic cleaning for 15 min. After the ultrasonic cleaning, it was rinsed several times with deionized water and then transferred to concentrated nitric acid for ultrasonic cleaning for 15 min. Finally, after rinsing several times with deionized water, the carbon cloth was immersed in absolute ethanol for later use.

[0124] 2. Preparation of the CoNiCuMnMo-HEO / GF(N2) electrode: Dissolve 3 mmol of CoCl5·6H2O, 3 mmol of NiCl2·6H2O, 3 mmol of CuCl2, 3 mmol of MnCl2·4H2O, 3 mmol of MoCl5, and 9 mmol of 2,5-dihydroxyterephthalic acid in a mixed solution of 39 ml of N,N-dimethylformamide, 3 ml of absolute ethanol, and 3 ml of water to obtain a hydrothermal reaction solution; Use medical tape to paste two pretreated graphite felts with dimensions of 5 cm × 0.5 cm × 0.5 cm and place them in the hydrothermal reaction solution so that they can react fully in the solution. Carry out hydrothermal reaction in a high-pressure reaction kettle at 120 °C for 24 h. After the reaction, take out the sample, wash it several times with deionized water, and dry it to obtain two CoNiCuMnMo-MOF / GF electrodes. Take one of the dried samples and place it in a muffle furnace, and calcine it in N2 at 500 °C for 2 h to obtain the calcined CoNiCuMnMo-HEO / GF(N2) electrode, with a heating rate of 5 °C / min.

[0125] 3. Preparation of the anolyte: Weigh 4 g of NaOH and dissolve it in 50 ml of deionized water, and stir for 10 min. Then weigh 2 g of enzymatically hydrolyzed lignin, add it to the solution, stir for 10 min, and then filter to obtain the anolyte of the lignin alkali solution.

[0126] 4. Preparation of the catholyte: Weigh 20 g of vanadium pentoxide powder and add it to a beaker containing 524 ml of deionized water, and stir at room temperature. Then take 76 ml of concentrated sulfuric acid with a mass fraction of 98.3%, slowly add it to the solution, and continue stirring. After 24 h, add 4 ml of nitric acid, and keep stirring the solution until it forms a clear solution, showing a bright yellow color. Let it stand for 72 h to obtain the catholyte of high-valent vanadium. Measure 100 ml from it as the catholyte.

[0127] 5. Assembly and electrical performance measurement of the battery: Construct 2 sets of battery systems. The LFFC consists of two all-carbon graphite electrodes with serpentine flow channels and is separated by a Nafion 211 membrane with a total effective area of 1 cm 2 . Graphite felt is filled in the cathode flow channels of the two sets of battery systems. The CoNiCuMnMo-MOF / GF electrode and the calcined CoNiCuMnMo-HEO / GF(N2) electrode obtained from the above operations are each filled in the anode flow channels of one set of battery systems. The anolyte and catholyte are pumped into the LFFC at a flow rate of 10 mL min -1 . Under the catalysis of nitric acid, oxygen is injected into the cathode at a flow rate of 40 mL min -1 to oxidize the VO 2+ generated at the cathode into VO2 + , realizing the regeneration of the catholyte. The LFFC system operates at 90 °C. The performance of the sample cell is tested by an 857 flow battery test system.

[0128] The electrical performance of the battery is tested by the scanning current method, and the results are as Figure 11 shown. The maximum power density of the calcined CoNiCuMnMo-HEO / GF(N2) electrode is 250 mW / cm 2 . Compared with the uncalcined CoNiCuMnMo-MOF electrode under the same conditions, the performance is worse, proving that the CoNiCuMnMo-MOF / GF electrode is more conducive to improving the battery performance and the oxidation of lignin, and the power density of the battery corresponding to the calcined CoNiCuMnMo-HEO / GF(N2) electrode is much lower than the power density under the optimal conditions of Example 3.

[0129] Comparative Example 4 CoNiFe-LDH / NF nanowire electrode for lignin flow fuel cell

[0130] 1. Preparation of CoNiFe-LDH / NF nanowire electrode: Dissolve 2 mmol of Co(NO3)2·6H2O, 1 mmol of NiCl2·6H2O, 0.5 mmol of FeCl3·6H2O, 5 mmol of NH4F, and 5 mmol of urea in 50 mL of deionized water. Add a 4 cm×1 cm×0.7 cm nickel foam for impregnation, and place it in a high-pressure reaction kettle for hydrothermal reaction at 140 °C for 6 h. After the reaction, take out the sample, wash it with deionized water, and dry it to obtain the CoNiFe-LDH / NF nanowire electrode.

[0131] 2. Preparation of anolyte:

[0132] Weigh 4 g of NaOH and dissolve it in 50 ml of deionized water, and stir for 10 min. Then weigh 2 g of enzymatically hydrolyzed lignin, add it to the solution, stir for 10 min and then filter to obtain the anolyte of lignin alkaline solution.

[0133] 3. Preparation of catholyte:

[0134] Weigh 20 g of vanadium pentoxide powder and add it to a beaker containing 524 ml of deionized water, and stir at room temperature. Then take 76 ml of concentrated sulfuric acid with a mass fraction of 98.3%, slowly add it to the solution, and keep stirring. After 24 h, add 4 ml of nitric acid, and keep stirring the solution until it forms a clear solution, showing a bright yellow color. Let it stand for 72 h to obtain the catholyte of high-valent vanadium. Measure 100 ml from it as the catholyte.

[0135] 4. Construction of battery system and electrical performance test: Construct a battery system. The LFFC is composed of two all-carbon graphite electrodes with serpentine flow channels and separated by a Nafion 211 membrane with a total effective area of 1 cm 2 . The graphite felt is filled in the cathode flow channel, and the CoNiFe-LDH / NF nanowire electrode obtained from the above operations is filled in the anode flow channel. The anolyte and catholyte are pumped into the LFFC at a flow rate of 10 mL min -1 . Under the catalysis of nitric acid, oxygen is injected into the cathode at a flow rate of 40 mL min -1 to oxidize the VO 2+ generated at the cathode into VO2 + , realizing the regeneration of the catholyte. The LFFC system operates at 90 °C. The performance of the sample cell is tested by an 857 flow battery test system.

[0136] The electrical performance of the battery is tested by the scanning current method. For the constructed fuel cell, the maximum voltage is 1.56 V, and the maximum power density is 263.5 mW / cm 2 . The power density is much lower than that in Example 3 of this application.

[0137] Comparative Example 5: Using a nickel foam anode loaded with a solid electrocatalyst for a lignin flow fuel cell

[0138] 1. Preparation of the CoS@Ni foam electrode: Cut the nickel foam into sheets of 2 cm 2 ×3 cm 2 and ultrasonically wash it successively with concentrated hydrochloric acid, absolute ethanol, and deionized water. Then dry the nickel foam in an oven at 60 °C for 1 h. Mix 0.05 mol / L CoCl2 and 0.5 mol / L CH4N2S to prepare the electrodeposition solution. Prepare the CoS@Ni foam electrode by chronoamperometry at a constant voltage of -1 V vs Ag / AgCl for 30 minutes. Wash the prepared CoS@Ni foam electrode with deionized water and dry it at 60 °C for 1 h.

[0139] 2. Preparation of the anolyte: Weigh 4 g of NaOH and dissolve it in 50 ml of deionized water, and stir for 10 min. Weigh another 2 g of enzymatically hydrolyzed lignin, add it to the solution, stir for 10 min and then filter to obtain the anolyte of the lignin alkaline solution.

[0140] 3. Preparation of the catholyte: Weigh 20 g of vanadium pentoxide powder and add it to a beaker containing 524 ml of deionized water, and stir at room temperature. Then take 76 ml of concentrated sulfuric acid with a mass fraction of 98.3%, slowly add it to the solution, and continue stirring. After 24 h, add 4 ml of nitric acid, and continue stirring the solution until it forms a clear solution, showing a bright yellow color, and let it stand for 72 h to obtain the catholyte of high-valent vanadium. Measure 100 ml from it as the catholyte.

[0141] 4. Assembly and electrical performance measurement of the battery: Construct a battery system. The LFFC consists of two all-carbon graphite electrodes with serpentine flow channels and is separated by a Nafion 211 membrane with a total effective area of 1 cm 2 . The graphite felt is filled in the cathode flow channel, and the CoS@Ni foam electrode obtained from the above operations is filled in the anode flow channel. The anolyte and catholyte are pumped into the LFFC at a flow rate of 10 mL min -1 . Under the catalysis of nitric acid, oxygen is injected into the cathode at a flow rate of 40 mL min -1 to oxidize the VO 2+ generated at the cathode into VO2 + , realizing the regeneration of the catholyte. The LFFC system operates at 90 °C. The performance of the sample cell is tested by an 857 flow battery test system.

[0142] Test the battery performance by the scanning current method. For the constructed fuel cell, the maximum voltage is 1.38 V, and the maximum power density is 176 mW / cm 2 . It can be seen that both the voltage and the power density are much lower than those in Example 3 of this application.

[0143] Table 1 is a comprehensive comparison of the above-mentioned examples and comparative examples in terms of operating temperature, open-circuit voltage, maximum power density, etc.

[0144] Comprehensive Comparison of Lignin-based Flow Fuel Cell Systems in Table 1

[0145]

[0146]

[0147] Comparing all the examples and comparative examples, it can be seen that the fuel cell with the best power generation performance is the lignin-based fuel cell system prepared by hydrothermal reaction for 12 h to prepare the electrocatalyst and using enzymatically hydrolyzed lignin as the raw material in Example 3, with an open-circuit voltage of 1.58 V and a maximum power density of 545.48 mW / cm 2 , which is much higher than that of the comparative example.

[0148] The above examples are the preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above examples. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A preparation method of a graphite felt / high-entropy MOF composite material, characterized in that, It includes the following steps: Dissolve soluble cobalt salt, soluble nickel salt, soluble copper salt, soluble manganese salt, soluble molybdenum salt and 2,5-dihydroxyterephthalic acid in a solvent, add graphite felt, and conduct a hydrothermal reaction in a high-pressure reaction kettle. After the reaction is completed, take out the graphite felt sample, wash it, and dry it to obtain a graphite felt / high-entropy MOF composite material.

2. The preparation method of the graphite felt / high-entropy MOF composite material according to claim 1, wherein, The molar ratio of the soluble cobalt salt, soluble nickel salt, soluble copper salt, soluble manganese salt, and soluble molybdenum salt is (0.5 - 1.5):(0.5 - 1.5):(0.5 - 1.5):(0.5 - 1.5):(0.5 - 1.5); and / or, the soluble cobalt salt, soluble nickel salt, soluble copper salt, soluble manganese salt, and soluble molybdenum salt are CoCl5·6H2O, NiCl2·6H2O, CuCl2, MnCl2·4H2O, and MoCl5 respectively; and / or, the concentration of the soluble cobalt salt, soluble nickel salt, soluble copper salt, soluble manganese salt, and soluble molybdenum salt in the solvent is 0.01 - 0.18 mol / L; and / or, the molar ratio of the soluble cobalt salt and 2,5-dihydroxyterephthalic acid is (0.5 - 1.5):(1 - 4); and / or, the temperature of the hydrothermal reaction is 20 - 200 °C, and the time is 2 - 24 h; and / or, the solvent is N,N-dimethylformamide, absolute ethanol, and water with a volume ratio of (10 - 15):(0.5 - 1.5):(0.5 - 1.5).

3. A graphite felt / high-entropy MOF composite material obtained by the preparation method according to any one of claims 1 - 2.

4. Application of the graphite felt / high-entropy MOF composite material according to claim 3 in a lignin-based fuel cell.

5. A lignin-based fuel cell, characterized in that, It includes an anolyte and an anode electrode; wherein the anolyte is a lignin alkaline solution, and the anode electrode is the graphite felt / high-entropy MOF composite material according to claim 3.

6. The lignin-based fuel cell according to claim 5, wherein, The concentration of lignin in the lignin alkaline solution is 1 - 100 g / L; and / or, the concentration of hydroxide ions in the lignin alkaline solution is 0.02 - 10 mol / L; and / or, in the lignin alkaline solution, the alkali used is at least one of NaOH, KOH, and ammonia water; and / or, in the lignin alkaline solution, the lignin used is at least one of enzymatic hydrolysis lignin, prehydrolysis lignin, lignin sulfonate, and alkali lignin.

7. The lignin-based fuel cell according to claim 5 or 6, characterized in that, It further includes a catholyte, and the catholyte includes a pentavalent vanadium salt, an acid solution, and an oxidant; and / or, the pentavalent vanadium salt is at least one of vanadium pentoxide, vanadyl nitrate, and vanadyl sulfate; and / or, the concentration of the pentavalent vanadium salt in the catholyte is 0.05 - 5 mol / L; and / or, the acid solution is at least one of hydrochloric acid aqueous solution, sulfuric acid aqueous solution, and nitric acid aqueous solution; and / or, the concentration of the acid solution is 0.05 - 8.0 mol / L; and / or, the oxidant is at least one of nitric acid and oxygen; the concentration of nitric acid in the catholyte is 0.01 - 8 mol / L; and / or, the flow rate of oxygen introduced into the catholyte is 10 - 120 mL / min; And / or, further comprising a cathode electrode; the cathode electrode is a graphite felt; And / or, the operating temperature of the lignin-based fuel cell is 20-120 °C.

8. A method for co-producing aviation fuel components using the lignin-based fuel cell described in claims 5 to 7, characterized in that, Comprising the following steps: Operating the above lignin-based fuel cell at 20-120 °C, the lignin in the anolyte undergoes a depolymerization reaction, extracting the depolymerization products, and then performing hydrodeoxygenation treatment to obtain aviation fuel components.

9. The method according to claim 8, wherein The operating temperature of the lignin-based fuel cell is 80-110 °C; And / or, the solvent for extraction is at least one of ethyl acetate, isopropyl acetate, and butyl acetate.

10. The method according to claim 8 or 9, characterized in that, The temperature of the hydrodeoxygenation treatment is 150-210 °C, and the time is 6-10 h; And / or, the hydrodeoxygenation treatment is carried out under the action of a catalyst, and the catalyst is at least one of a Pt / C catalyst and an Fe-based catalyst; the mass ratio of the depolymerization product to the catalyst is (0.5-1):(3-5); And / or, the hydrodeoxygenation treatment is carried out in a high-pressure reactor, and the solvent is at least one of cyclohexane and n-octane; the ratio of the depolymerization product to the solvent is 0.5-1.5 mg:0.5-1.5 mL; And / or, the hydrogen pressure of the hydrodeoxygenation treatment is 3-5 MPa.

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