A method for preparing and application of a cellulose biomass all-vanadium liquid flow battery electrode

Abstract

The application provides a preparation method and application of a cellulose biomass full vanadium liquid flow battery electrode, which utilizes treated cellulose biomass and microalgae to improve the specific surface area and activity of a graphite felt electrode material substrate, and performs continuous flow anaerobic fermentation to produce methane and generate carbon-containing gas; biomass material, melamine and sucrose are mixed and dissolved, ultrasonic stirring is performed, then the electrode material substrate is added to perform biomass carbon modification, and finally, an element doped modified biomass carbon electrode is prepared by using nickel oxide and manganese dioxide; the specific surface area of the obtained electrode is significantly improved, the stability of the biomass carbon electrode is improved, and the electrode activity and electronic transmission characteristics are both strengthened; in the preparation process, the treatment liquid and fermentation gas are effectively utilized, zero carbon in the whole life cycle is achieved, solid-liquid-gas comprehensive low-carbon utilization of cellulose biomass is realized, and the application prospect and economic, environmental and social benefits are high.

Description

Technical Field

[0001] This invention relates to vanadium redox flow battery energy storage technology, and particularly to a method for preparing and applying an electrode for a cellulose biomass vanadium redox flow battery. Background Technology

[0002] Vanadium redox flow batteries (VRBs) are a long-term energy storage method with advantages such as high efficiency, strong safety, and long cycle life, making them a promising energy storage route. However, existing VRBs suffer from drawbacks such as poor electrochemical activity, activation loss, and poor electron transfer, which to some extent limit their large-scale development. Electrodes are crucial components of VRBs, significantly influencing electrochemical reaction performance; therefore, the development of high-performance reaction electrodes is necessary.

[0003] Several methods exist for improving the electrochemical performance of existing electrodes: physicochemical treatment and pore structure adjustment; modification with carbon nanotubes, nanoparticles, and graphene to increase the electrochemical surface area; and metal deposition and heteroatom doping. Among these, carbon nanotube modification can improve electron transport performance and energy efficiency, while heteroatom doping can introduce lattice defects into the modified electrode to enhance surface functionality. Electrodes combining both of these treatment methods theoretically possess higher electrochemical performance.

[0004] In the field of energy storage, biomass-modified carbon materials have advantages such as low cost, high activity, and strong stability. In particular, cellulose biomass, such as straw and sugarcane bagasse waste, is an important substrate for the preparation of carbon nanomaterials, and the raw materials are readily available and abundant. Using cellulose biomass to prepare carbon materials to modify electrodes, and optimizing the electrodes through elemental doping to improve their electrochemical performance, has strong application prospects and economic, environmental, and social benefits. However, no relevant research reports have been found to date. Summary of the Invention

[0005] To overcome the problems in the prior art, this application provides a method for preparing and applying a vanadium redox flow battery electrode made from cellulose biomass.

[0006] To achieve the above objectives, the present invention provides a method for preparing a vanadium redox flow battery electrode from cellulose biomass, comprising: (1) hydrolyzing cellulose biomass and reacting it in a high-pressure reactor to obtain product A; (2) adjusting the pH of product A to slightly alkaline, centrifuging, drying the centrifuged solid to obtain biomass material B, and collecting the supernatant after centrifugation as treatment liquid C; (3) placing graphite felt in a vacuum tube furnace under an air atmosphere, heating it at high temperature and keeping it warm to prepare electrode material substrate D; (4) feeding treatment liquid C and anaerobic digested sludge rich in methanogenic bacteria into a continuous flow anaerobic fermentation device, adjusting the pH to alkaline, and carrying out continuous flow anaerobic fermentation under constant temperature conditions. Methanogens are produced, and the hydraulic residence time in the methanogen fermentation tank is controlled to be 15-20 days. The generated gas E is collected. (5) Biomass material B, melamine and sucrose are mixed and dissolved, ultrasonically stirred, and then the electrode material substrate D obtained in step (3) is added. The substrate is magnetically stirred in the atmosphere of gas E, and then placed in a vacuum tube furnace filled with nitrogen atmosphere for high-temperature heating and heat preservation to obtain modified biomass carbon electrode F. (6) Take the ethanol dispersion of nickel oxide and manganese dioxide, add it to the modified biomass carbon electrode F, ultrasonically and dry it, and then place it in a vacuum tube furnace filled with nitrogen atmosphere for high-temperature heating and heat preservation. After cooling, it is washed with alcohol and water and then dried to obtain element-doped modified biomass carbon electrode G.

[0007] Preferably, the cellulose biomass has a cellulose content of 12%-35%.

[0008] Step (1) is a reaction in a high-pressure reactor, where the temperature and pressure are kept constant at 120-150℃ and 10-20MPa for 15-25 min; Step (3) is a high-temperature heating and holding process, where the temperature is heated to 400-700℃ at a rate of 8-15℃ / min and held for 1.5-3 h; Steps (5) and (6) are high-temperature heating and holding processes in a vacuum tube furnace, where the temperature is heated to 800-1000℃ at a rate of 8-15℃ / min and held for 1.5-3 h.

[0009] Preferably, the gas E is mainly composed of 35%-50% methane and 50%-65% carbon dioxide by volume.

[0010] Preferably, in step 4, the fermentation is carried out under continuous flow anaerobic fermentation to produce methanogens at a pH value adjusted to 7.5-9.0 and a constant temperature of 30℃-40℃, with the hydraulic retention time in the methanogenizing fermenter controlled to be 15-20 days.

[0011] Preferably, the centrifugation is performed at 3000-8000 rpm for 3-15 minutes, and multiple centrifugations can be performed.

[0012] Preferably, the mass ratio of nickel oxide to manganese dioxide is (1-2):1.

[0013] Preferably, the cellulose biomass is derived from one or more of sugarcane bagasse, microalgae, straw, and livestock manure.

[0014] As another aspect of the present invention, the present invention provides an application of a vanadium redox flow battery electrode made of cellulose biomass, which uses an element-doped modified biomass carbon electrode G as the working electrode, a platinum electrode as the counter electrode, and an Ag / AgCl electrode as the reference electrode to form a three-electrode system for a vanadium redox flow battery.

[0015] Compared with the prior art, the beneficial effects of the present invention are:

[0016] Existing electrode materials such as carbon felt, graphite felt, carbon paper, and carbon cloth have limited the large-scale development of flow batteries to some extent due to their low hydrophilicity and poor electrochemical performance. A mixture of treated cellulose biomass and melamine, under high temperature, forms a high specific surface area carbon nanotube structure, with a specific surface area of ​​2.5–2.7 m² compared to the unmodified graphite felt. 2 / g significantly increased to 132-146m 2 / g, and after modification with carbon-containing fermentation gas, the specific surface area is further increased to 245-268m². 2 / g. This provides a large number of reactive sites. Treatment with manganese and nickel oxides improves the stability of the biomass carbon electrode, and enhances both electrode activity and electronic conductivity. Compared to the original electrode, the redox couple VO 2+ / VO 2+ The peak potential decreased from 498mV to 410-428mV, while V 3+ / V 2+ The peak potential decreased from 380 mV to 354–366 mV. Furthermore, under acidic conditions, some electrode metal elements slowly entered the electrolyte, and the metal doping of the electrolyte improved the reaction kinetic parameters and activity. Tests showed that at a current density of 100 mA / cm²... 2 At that time, the energy efficiency is higher than 85.0%. The highest energy density ranges from 280 to 288 mW / cm³. 2 Increased to 359–377 mW / cm 2After 1000 cycles, the energy efficiency decreased by no more than 5%, a significant improvement compared to the 20% energy efficiency loss of the original electrode. Cellulose biomass, such as straw and sugarcane bagasse waste, is an important substrate for the preparation of carbon nanomaterials. The raw materials are readily available and abundant, and the main purpose is to increase the specific surface area. This patent uses an anaerobic fermentation method, effectively utilizing the processing liquids and fermentation gases during the preparation process, achieving zero carbon emissions throughout the entire life cycle and realizing the comprehensive low-carbon utilization of cellulose biomass through solid-liquid-gas synthesis. Modifying electrodes with carbon materials prepared from cellulose biomass and optimizing the electrodes through elemental doping enhances their electrochemical performance, demonstrating strong application prospects and significant economic, environmental, and social benefits. Attached Figure Description

[0017] Figure 1 The (a) cellulose biomass material described in Example 1 of this invention has an irregular surface with some grooves and protrusions; (b) the element-doped modified biomass carbon electrode microscopy image shows a filamentous structure with a diameter of 10-50 nm and a large specific surface area.

[0018] Figure 2 The current-voltage curves described in Embodiment 1 of this invention correspond to the peak currents at different scan rates. Compared to the original electrode, the electrode couple VO 2+ / VO2 + and V 3+ / V 2+ The peak potentials of all electrodes decreased, indicating that the electrochemical performance of the electrodes has been improved.

[0019] Figure 3 The current density described in Embodiment 1 of the present invention is 100 mA / cm². 2 The energy efficiency changed after 1000 cycles. After 1000 cycles, the energy efficiency decreased by no more than 5%, which is a significant improvement compared to the 20% energy efficiency loss of the original electrode.

[0020] Figure 4 This is a technical roadmap of the method described in this invention. Detailed Implementation

[0021] To better illustrate the objectives, technical solutions, and advantages of this invention, the following detailed description will be provided in conjunction with specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be construed as limiting the invention in any way.

[0022] The cellulose biomass used in this invention was harvested from farmland and livestock farms in typical rural China. The cellulose biomass originated from one or more of sugarcane bagasse, microalgae, straw, and livestock manure. After collection, the biomass was first sorted manually and by machine to remove impurities such as plastic and glass. It was then sun-dried until the moisture content was below 10%. If sun-drying alone could not guarantee the drying effect, it was placed in a biomass drying oven to ensure drying. The dried biomass was then pre-treated in a grinding device to ensure a particle size of less than 100 μm. The cellulose content in the prepared biomass was 12%–35%. Graphite felt material was purchased from Nanjing Changhong New Materials Co., Ltd. Cellulose, sulfuric acid, hydrochloric acid, sodium hydroxide, anhydrous ethanol, melamine, sucrose, nickel oxide, manganese dioxide, and vanadium oxysulfate (IV) hydrate were purchased from China National Pharmaceutical Group Chemical Reagent Co., Ltd. The anaerobic digestion sludge rich in methanogenic bacteria used in this invention was obtained from any well-functioning methane fermentation tank. Add 5g of cellulose to 500mL of anaerobic activated sludge and enrich for 7 days. When the total organic matter dry weight of the anaerobic activated sludge is higher than 10% and the main bacterial group tested by 16S rRNA is methanococcus, the enrichment is complete and the sludge is placed under anaerobic conditions for later use.

[0023] Example 1

[0024] (1) Weigh 25g of dried and ground cellulose biomass (mass ratio of straw:livestock manure = 1:1) and mix it. Add the mixture to a container and grind it again into fine particles with a particle size of 0.5-50μm. Take 5.5g of the ground fine particles and place them in a beaker, and add 100mL of dilute sulfuric acid solution (0.5wt%). Magnetically stir at 200rpm for 15min to ensure complete hydrolysis of the material. Place the mixture in a high-temperature steam reactor and maintain a constant temperature and pressure of 140℃ and 15MPa. React for 20min and then allow it to cool naturally to room temperature. The heating rate is 5℃ / min. After cooling, remove the solid-liquid mixture from the reactor to obtain product A. Product A is a gray-black slurry and serves as a reaction intermediate in subsequent preparation processes.

[0025] (2) The pH of product A was adjusted to 7.5 using 1 mol / L hydrochloric acid solution and 1 mol / L sodium hydroxide solution. Then, product A was centrifuged at 6000 rpm for 5 min. The centrifuged solid was then added to 30 mL of deionized water and centrifuged three times at 6000 rpm for 5 min each time. The resulting solid was dried in an 80℃ oven for 10 h to obtain biomass material B. Biomass B is a gray-black powder or small lumps. If agglomeration occurs, it needs to be ground to a particle size of less than 50 μm. The supernatant from each centrifugation was collected to obtain treatment solution C.

[0026] (3) Cut the graphite felt material to a side length of 3.5cm. 2 The small pieces were rinsed three times with deionized water and immersed in anhydrous ethanol for 10 minutes, then treated with an ultrasonic device for 30 minutes at a frequency of 50 kHz. Afterward, they were rinsed three times with deionized water. The treated material was dried in an 80°C oven for 10 hours. The dried pieces were then placed in a vacuum tube furnace under air atmosphere and heated to 550°C at a rate of 12°C / min and held for 2 hours. After natural cooling, the electrode material substrate D was removed.

[0027] (4) The treated liquid C was fed into a continuous flow anaerobic fermentation unit. After calculation, 10g of anaerobic digested sludge rich in methanogenic bacteria was added to the volume corresponding to the total dry weight of organic matter. The pH of the liquid in the methanogenic fermenter was then adjusted to 8.0. Methanogenic production was carried out under a constant temperature of 35℃ in a continuous flow anaerobic fermentation unit. The hydraulic retention time (HRT) in the methanogenic fermenter was controlled to be 18 days. The inorganic low-hazard tail liquid of the methanogenic fermentation was discharged into the purification treatment system, and the generated gas E was collected. The main components of E were methane (45%) and carbon dioxide (55%).

[0028] (5) Take 7.2g of a mixture of biomass material B and melamine (mass ratio of 8:1) and add it to 110mL of deionized water, then add 2.6mL of 10% sucrose solution. Stir the mixture until homogeneous. Then, place it in an ultrasonic device at a frequency of 50kHz for 15min to obtain a homogeneous slurry. Transfer the obtained slurry to a magnetic stirring device, add the electrode material substrate D obtained in step (3), and magnetically stir at 300rpm for 20min under the condition of passing gas E at a rate of 12mL / min. Then, place the treated substrate material in a vacuum tube furnace filled with nitrogen atmosphere and heat it to 900℃ at a rate of 12℃ / min and hold for 2h. After cooling to room temperature, remove it to obtain the modified biomass carbon electrode F.

[0029] (6) Take 2.1 g of a solid mixture of nickel oxide and manganese dioxide (mass ratio 1.1:1) and disperse it in 25 mL of 50% ethanol solution. Add the modified biomass carbon electrode F and treat it in an ultrasonic device at a frequency of 50 kHz for 45 min. Then dry it in an oven at 80 ℃ for 10 h and cool it to room temperature. Place the treated electrode in a vacuum tube furnace filled with nitrogen atmosphere and heat it to 700 ℃ at a rate of 12 ℃ / min and hold it for 2 h. After cooling to room temperature, take it out and wash it three times with anhydrous ethanol and then three times with deionized water. Dry it in an oven at 80 ℃ for 10 h to obtain element-doped modified biomass carbon electrode G.

[0030] (7) A three-electrode system for a vanadium redox flow battery was formed, using an element-doped modified biomass carbon electrode G as the working electrode, a platinum electrode as the counter electrode, and an Ag / AgCl electrode as the reference electrode. The electrolytes were 0.1 mol / L LOSO4 and 2.0 mol / L H2SO4, and the ion exchange membrane was a Nafion 212 membrane.

[0031] A mixture of cellulose biomass and melamine, under high temperature, forms high specific surface area structures such as carbon nanotubes, with a specific surface area of ​​2.5–2.7 m² compared to the unmodified graphite felt. 2 / g significantly increased to 146m 2 / g, and after modification with carbon-containing fermentation gas, the specific surface area was further increased to 268m². 2 / g. This provides a large number of reactive sites. Treatment with manganese and nickel oxides improves the stability of the biomass carbon electrode, and enhances both electrode activity and electronic conductivity. Compared to the original electrode, the redox couple VO 2+ / VO2 + The peak potential decreased from 498mV to 410mV, while V 3+ / V 2+ The peak potential decreased from 380mV to 354mV. Furthermore, under acidic conditions, some electrode metal elements slowly entered the electrolyte, and the metal doping of the electrolyte improved the reaction kinetic parameters and activity. Tests showed that at a current density of 100mA / cm²... 2 At that time, the energy conversion efficiency was higher than 86.0%, and after 1000 cycles, the energy efficiency decreased by no more than 5%, which is a significant improvement compared to the 20% energy efficiency loss of the original electrode.

[0032] Example 2

[0033] (1) Weigh 22.5g of dried and ground cellulose biomass (microalgae:livestock manure = 1:1 by mass) and mix it. Add the mixture to a container and grind it again into fine particles with a particle size of 0.5-50μm. Take 5.0g of the ground fine particles and place them in a beaker, and add 100mL of dilute sulfuric acid solution (0.75wt%). Magnetically stir at 175rpm for 12.5min to ensure complete hydrolysis of the material. Place the mixture in a high-temperature steam reactor and maintain a constant temperature and pressure of 160℃ and 12.5MPa. React for 17.5min and then allow it to cool naturally to room temperature. The heating rate is 4℃ / min. After cooling, remove the solid-liquid mixture from the reactor to obtain product A.

[0034] (2) The pH of product A was adjusted to 7.25 using 1 mol / L hydrochloric acid solution and 1 mol / L sodium hydroxide solution. Then, product A was centrifuged at 6500 rpm for 4.5 min. The centrifuged solid was then added to 32.5 mL of deionized water and centrifuged three times at 6500 rpm for 4.5 min each time. The resulting solid was dried in an 80℃ oven for 9 h to obtain biomass material B. Biomass B is a gray-black powder or small lumps. If agglomeration occurs, it needs to be ground to a particle size of less than 50 μm. The supernatant from each centrifugation was collected to obtain treatment solution C.

[0035] (3) Cut the graphite felt material to a side length of 3.25cm. 2 The small pieces were rinsed twice with deionized water and immersed in anhydrous ethanol for 12.5 min, then treated with an ultrasonic device for 35 min at a frequency of 45 kHz. Afterwards, they were rinsed three times with deionized water. The treated material was dried in an 80℃ oven for 9 h. The dried pieces were then placed in a vacuum tube furnace under air atmosphere and heated to 525℃ at a rate of 11℃ / min and held for 2 h. After natural cooling, the electrode material substrate D was removed.

[0036] (4) The treated liquid C is fed into a continuous flow anaerobic fermentation unit and mixed with 9.5g of anaerobic digested sludge rich in methanogenic bacteria by total organic matter dry weight. The pH of the fermentation liquid in the methanogenic fermenter is then adjusted to 7.75. The anaerobic digested sludge rich in methanogenic bacteria comes from any well-functioning methanogenic fermenter. Methanogenic fermentation is carried out under a constant temperature of 35℃ in a continuous flow anaerobic fermentation system. The hydraulic retention time (HRT) in the methanogenic fermenter is controlled to be 18 days. The inorganic low-hazard tail liquid of the methanogenic fermentation is discharged into the purification treatment system, and the generated gas E is collected. The main components of E are methane (40%) and carbon dioxide (60%).

[0037] (5) Take 6.8g of a mixture of biomass material B and melamine (mass ratio of 7.5:1) and add it to 100mL of deionized water, then add 2.8mL of 10% sucrose solution. Stir the mixture until homogeneous. Then, treat it in an ultrasonic device at a frequency of 45kHz for 17.5min to obtain a homogeneous slurry. Transfer the obtained slurry to a magnetic stirrer, add the electrode material substrate D obtained in step (3), and magnetically stir at 325rpm for 17.5min under the condition of passing gas E at a rate of 11mL / min. Then, place the treated substrate material in a vacuum tube furnace filled with nitrogen atmosphere and heat it to 875℃ at a rate of 11℃ / min and hold for 2h. After cooling to room temperature, remove it to obtain the modified biomass carbon electrode F.

[0038] (6) Take 2.05 g of a solid mixture of nickel oxide and manganese dioxide (mass ratio 1.05:1) and disperse it in 22.5 mL of 50% ethanol solution. Add the modified biomass carbon electrode F and treat it in an ultrasonic device at a frequency of 45 kHz for 55 min. Then dry it in an oven at 80 ℃ for 9 h and cool it to room temperature. Place the treated electrode in a vacuum tube furnace filled with nitrogen atmosphere and heat it to 675 ℃ at a rate of 11 ℃ / min and hold it for 2 h. After cooling to room temperature, take it out, wash it twice with anhydrous ethanol, and then wash it three times with deionized water. Dry it in an oven at 80 ℃ for 9 h to obtain element-doped modified biomass carbon electrode G.

[0039] (7) A three-electrode system for a vanadium redox flow battery was formed using an element-doped modified biomass carbon electrode G as the working electrode, a platinum electrode as the counter electrode, and an Ag / AgCl electrode as the reference electrode. The electrolytes were 0.1 mol / L LOSO4 and 2.0 mol / L H2SO4, and the ion exchange membrane was a Nafion 212 membrane. The mixture of cellulose biomass and melamine formed high specific surface area structures such as carbon nanotubes under high temperature, with a specific surface area of ​​2.5–2.7 m² compared to the unmodified graphite felt. 2 / g significantly increased to 139m 2 / g, and after modification with carbon-containing fermentation gas, the specific surface area was further increased to 256m². 2 / g. This provides a large number of reactive sites. Treatment with manganese and nickel oxides improves the stability of the biomass carbon electrode, and enhances both electrode activity and electronic conductivity. Compared to the original electrode, the redox couple VO 2+ / VO2 + The peak potential decreased from 498mV to 419mV, while V 3+ / V 2+ The peak potential decreased from 380mV to 360mV. Furthermore, under acidic conditions, some electrode metal elements slowly entered the electrolyte, and the metal doping of the electrolyte improved the reaction kinetic parameters and activity. Tests showed that at a current density of 100mA / cm²... 2 At that time, the energy conversion efficiency was higher than 85.5%, and after 1000 cycles, the energy efficiency decreased by no more than 5%, which is a significant improvement compared to the 20% energy efficiency loss of the original electrode.

[0040] Example 3

[0041] (1) Weigh 20g of dried and ground cellulose biomass (mass ratio of bagasse: straw = 1:1) and mix it. Add the mixture to a container and grind it again into fine particles with a particle size of 0.5-50μm. Take 4.5g of the ground fine particles and place them in a beaker, and add 100mL of dilute sulfuric acid solution (1wt%). Stir magnetically at 150rpm for 10min to ensure complete hydrolysis of the material. Place the mixture in a high-temperature steam reactor and maintain a constant temperature and pressure of 180℃ and 10MPa. After reacting for 15min, allow it to cool naturally to room temperature. The heating rate is 3℃ / min. After cooling, remove the solid-liquid mixture from the reactor to obtain product A.

[0042] (2) The pH of product A was adjusted to 7 using 1 mol / L hydrochloric acid solution and 1 mol / L sodium hydroxide solution. Then, product A was centrifuged at 7000 rpm for 4 min. The centrifuged solid was then added to 35 mL of deionized water and centrifuged three times at 7000 rpm for 4 min each time. The resulting solid was dried in an 80℃ oven for 8 h to obtain biomass material B. Biomass B is a gray-black powder or small lumps. If agglomeration occurs, it needs to be ground to a particle size of less than 50 μm. The supernatant from each centrifugation was collected to obtain treatment solution C.

[0043] (3) Cut the graphite felt material into pieces with a side length of 3cm. 2 The small pieces were rinsed twice with deionized water and immersed in anhydrous ethanol for 15 minutes, then treated with an ultrasonic device for 40 minutes at a frequency of 40 kHz. Afterwards, they were rinsed twice with deionized water. The treated material was dried in an 80°C oven for 8 hours. The dried pieces were then placed in a vacuum tube furnace under air atmosphere and heated to 500°C at a rate of 10°C / min and held for 2 hours. After natural cooling, the electrode material substrate D was removed.

[0044] (4) The treated liquid C is fed into a continuous flow anaerobic fermentation unit and mixed with 9g of anaerobic digested sludge rich in methanogenic bacteria by total organic matter dry weight. The pH value of the fermentation liquid in the methanogenic fermenter is adjusted to 7.5. The anaerobic digested sludge rich in methanogenic bacteria comes from any well-functioning methanogenic fermenter. Methanogenic fermentation is carried out under a constant temperature of 35℃ in a continuous flow anaerobic fermentation unit. The hydraulic retention time (HRT) in the methanogenic fermenter is controlled to be 18 days. The inorganic low-hazard tail liquid of methanogenic fermentation is discharged into the purification treatment system, and the generated gas E is collected. The main components of E are methane (35%) and carbon dioxide (65%).

[0045] (5) Take 6.4g of a mixture of biomass material B and melamine (mass ratio 7:1) and add it to 90mL of deionized water, then add 3.0mL of 10% sucrose solution. Stir the mixture until homogeneous. Then place it in an ultrasonic device at a frequency of 40kHz for 20min to obtain a homogeneous slurry. Transfer the obtained slurry to a magnetic stirrer, add the electrode material substrate D obtained in step (3), and magnetically stir at 350rpm for 15min under the condition of passing gas E at a rate of 10mL / min. Then place the treated substrate material in a vacuum tube furnace filled with nitrogen atmosphere and heat it to 850℃ at a rate of 10℃ / min and hold for 2h. After cooling to room temperature, remove it to obtain the modified biomass carbon electrode F.

[0046] (6) Take 2g of a solid mixture of nickel oxide and manganese dioxide (mass ratio 1:1) and disperse it in 20mL of 50% ethanol solution. Add the modified biomass carbon electrode F and treat it in an ultrasonic device with a frequency of 40kHz for 60min. Then dry it in an 80℃ oven for 8h and cool it to room temperature. Place the treated electrode in a vacuum tube furnace filled with nitrogen atmosphere and heat it to 650℃ at a rate of 10℃ / min and hold it for 2h. After cooling to room temperature, take it out, wash it twice with anhydrous ethanol, and then wash it twice with deionized water. Dry it in an 80℃ oven for 8h to obtain element-doped modified biomass carbon electrode G.

[0047] (7) A three-electrode system for a vanadium redox flow battery was formed using an element-doped modified biomass carbon electrode G as the working electrode, a platinum electrode as the counter electrode, and an Ag / AgCl electrode as the reference electrode. The electrolytes were 0.1 mol / L LOSO4 and 2.0 mol / L H2SO4, and the ion exchange membrane was a Nafion 212 membrane. The mixture of cellulose biomass and melamine formed high specific surface area structures such as carbon nanotubes under high temperature, with a specific surface area of ​​2.5–2.7 m² compared to the unmodified graphite felt. 2 / g significantly increased to 132m 2 / g, and after modification with carbon-containing fermentation gas, the specific surface area was further increased to 245m². 2 / g. This provides a large number of reactive sites. Treatment with manganese and nickel oxides improves the stability of the biomass carbon electrode, and enhances both electrode activity and electronic conductivity. Compared to the original electrode, the redox couple VO 2+ / VO2 + The peak potential decreased from 498mV to 428mV, while V 3+ / V 2+The peak potential decreased from 380mV to 366mV. Furthermore, under acidic conditions, some electrode metal elements slowly entered the electrolyte, and this metal element doping of the electrolyte improved the reaction kinetic parameters and activity. Tests showed that at a current density of 100mA / cm²... 2 At that time, the energy conversion efficiency was higher than 85.0%, and after 1000 cycles, the energy efficiency decreased by no more than 5%, which is a significant improvement compared to the 20% energy efficiency loss of the original electrode.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing an electrode for a cellulose biomass all-vanadium redox flow battery, characterized in that: include, (1) Hydrolyze cellulose biomass and react it in a high-pressure reactor to obtain product A; (2) Adjust the pH of product A to slightly alkaline, centrifuge, take the solid after centrifugation and dry it to obtain biomass material B, and collect the supernatant after centrifugation as treatment liquid C; (3) The graphite felt is placed in a vacuum tube furnace with an air atmosphere, heated at high temperature and kept at a constant temperature to prepare electrode material substrate D; (4) The treatment liquid C and the anaerobic digested sludge rich in methanogenic bacteria were put into a continuous flow anaerobic fermentation device, the pH value was adjusted to alkaline, and continuous flow anaerobic fermentation to produce methanogens was carried out under constant temperature conditions. The hydraulic retention time in the methanogenic fermentation tank was controlled to be 15-20 days, and the generated gas E was collected. (5) Mix and dissolve biomass material B, melamine and sucrose, stir ultrasonically, add electrode material substrate D obtained in step (3), stir magnetically in the atmosphere of gas E, and then place it in a vacuum tube furnace filled with nitrogen atmosphere for high temperature heating and heat preservation to obtain modified biomass carbon electrode F. (6) Take the ethanol dispersion of nickel oxide and manganese dioxide, add the modified biomass carbon electrode F, sonicate and dry it, and then place it in a vacuum tube furnace filled with nitrogen atmosphere. Heat and keep it at high temperature, cool it, wash it with alcohol and water, and then dry it to obtain the element-doped modified biomass carbon electrode G.

2. The method for preparing the vanadium redox flow battery electrode from cellulose biomass according to claim 1, characterized in that: The cellulose biomass has a cellulose content of 12%-35%.

3. The method for preparing the vanadium redox flow battery electrode from cellulose biomass according to claim 1, characterized in that: Step (1) is a reaction in a high-pressure reactor, where the temperature and pressure are kept constant at 120-150℃ and 10-20MPa for 15-25 min; Step (3) is a high-temperature heating and holding process, where the temperature is heated to 400-700℃ at a rate of 8-15℃ / min and held for 1.5-3 h; Steps (5) and (6) are high-temperature heating and holding processes in a vacuum tube furnace, where the temperature is heated to 800-1000℃ at a rate of 8-15℃ / min and held for 1.5-3 h.

4. The method for preparing the vanadium redox flow battery electrode based on cellulose biomass according to claim 1, characterized in that: The gas E is mainly composed of 35%-50% methane and 50%-65% carbon dioxide by volume.

5. The method for preparing the vanadium redox flow battery electrode based on cellulose biomass according to claim 1, characterized in that: In step 4, the pH value is adjusted to 7.5-9.0, and continuous flow anaerobic fermentation to produce methanogens is carried out under constant temperature conditions of 30℃-40℃. The hydraulic retention time in the methanogenic fermenter is controlled to be 15-20 days.

6. The method for preparing the vanadium redox flow battery electrode from cellulose biomass according to claim 1, characterized in that: The centrifugation process is carried out at 3000-8000 rpm for 3-15 minutes.

7. The method for preparing the vanadium redox flow battery electrode based on cellulose biomass according to claim 1, characterized in that: The mass ratio of nickel oxide to manganese dioxide is (1-2):

1.

8. The method for preparing the vanadium redox flow battery electrode based on cellulose biomass according to claim 1 or 2, characterized in that: The cellulose biomass is derived from one or more of sugarcane bagasse, microalgae, straw, and livestock manure.

9. The application of the electrode obtained by the method according to any one of claims 1-8, characterized in that: A three-electrode system for an all-vanadium redox flow battery was formed, using element-doped modified biomass carbon electrode G as the working electrode, a platinum electrode as the counter electrode, and an Ag / AgCl electrode as the reference electrode.

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