Lignin-based non-noble metal catalyst for flow battery and preparation method of lignin-based non-noble metal catalyst

Abstract

The invention discloses a preparation method of a lignin-based non-noble metal catalyst for a flow battery. The lignin-based non-noble metal catalyst is prepared by adopting nitrogen-doped reduced graphene oxide, sulfur / nitrogen-doped lignin, iron phthalocyanine and nitrate hexahydrate as raw materials, and the catalyst shows excellent oxygen reduction (ORR) and oxygen evolution (OER) bifunctional catalytic activity. When the lignin-based non-noble metal catalyst is applied to a lignin flow battery, the lignin-based non-noble metal catalyst shows good power generation performance, the open-circuit voltage is about 1.3 V, and the maximum power density can reach 162mW / cm < 2 >. In addition, the preparation process is simple, the production cost is low, on one hand, platinum carbon and other noble metal catalysts are expected to be replaced, and on the other hand, high-added-value utilization of industrial lignin is achieved. The industrial lignin is applied to the oxygen reduction and oxygen evolution reaction catalyst, and the industrial lignin is converted into electric energy and other chemicals.

Description

Technical Field

[0001] This invention belongs to the field of flow battery technology, and specifically relates to a lignin-based non-precious metal catalyst for flow batteries and its preparation method. Background Technology

[0002] Lignin fuel cells, as a type of fuel cell, have been widely reported due to their advantages such as widely available and renewable raw materials and high energy density. However, current lignin fuel cells also suffer from drawbacks, including reliance on precious metal catalysts such as platinum and iridium, insufficient output power density to meet practical application requirements, and a complex lignin oxidation discharge mechanism. Furthermore, approximately 5 billion tons of lignin are produced globally annually through photosynthesis, and about 300 million tons of industrial lignin are produced annually during pulp and paper production. However, only a small portion of this industrial lignin is utilized at high value; the majority is directly burned as fuel. Therefore, developing a highly efficient non-precious metal catalyst to significantly improve the power generation efficiency of lignin fuel cells is extremely urgent. Summary of the Invention

[0003] In view of the problems existing in the background art, the purpose of this invention is to provide a lignin-based non-precious metal catalyst for flow batteries and its preparation method.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: A first aspect of the present invention provides a method for preparing a lignin-based non-noble metal catalyst for flow batteries, comprising the following steps: S1. Urea and graphene oxide are added to deionized water, ultrasonically mixed, dried, and calcined to obtain nitrogen-doped reduced graphene oxide. S2. Melamine and thiourea are added to N,N-dimethylformamide and stirred to dissolve. Then lignin and ammonium chloride are added and stirred continuously. The solvent is evaporated, dried, and calcined to obtain sulfur / nitrogen-doped lignin. S3. Nitrogen-doped reduced graphene oxide, iron phthalocyanine, sulfur / nitrogen-doped lignin and nitrate hexahydrate are mixed, added to deionized water, stirred, ultrasonicated, centrifuged, dried, and finally calcined under nitrogen protection, then ground and pulverized to obtain a lignin-based non-precious metal catalyst. Preferably, in step S1, the calcination temperature is 300-500℃ and the calcination time is 1-4h. Preferably, in step S2, the calcination temperature is 600-1000℃ and the calcination time is 1-3h. 1. Preferably, in step S2, the mass ratio of melamine to thiourea is 1:1-3; the mass ratio of lignin to ammonium chloride is 1:1-3; and the mass ratio of the melamine and thiourea mixture to the lignin and ammonium chloride mixture is 1:1-3. Preferably, in step S3, the calcination temperature is 600-1200℃, and the calcination time is 1-3 hours. Preferably, in step S3, the mass ratio of nitrogen-doped reduced graphene oxide, sulfur-nitrogen-doped sulfate lignin, phthalocyanine iron, and nitrate hexahydrate is (1-3):(1-3):(0.1-0.5):(0.5-2). Preferably, in step S3, the calcination temperature is 600–1100°C, and the calcination time is [missing information]. Preferably, the hexahydrate nitrate is manganese nitrate hexahydrate, nickel nitrate hexahydrate, or cobalt nitrate hexahydrate.

[0005] A second aspect of the present invention provides a lignin-based non-precious metal catalyst prepared by the above-described preparation method.

[0006] A third aspect of the present invention provides the application of the above-described lignin-based non-precious metal catalyst in a lignin flow battery. Preferably, the loading of the lignin-based non-precious metal catalyst as a cathode catalyst in the flow battery is 0.5–5 mg / cm³. 2 Alternatively, when the lignin-based iron-manganese alloy catalyst is used as the anode catalyst in a flow battery, its loading is 2–20 mg / cm³. 2 .

[0007] Compared with the prior art, the present invention has the following beneficial effects: (1) The lignin-based non-precious metal catalyst prepared by this invention not only has excellent catalytic activity for oxygen reduction reaction, but also has certain catalytic activity for oxygen evolution reaction. This invention not only uses industrial lignin as a catalyst, but also converts industrial lignin into electrical energy and small molecule chemical substances, providing a new solution for the high-value utilization of industrial lignin, which is of great significance for biomass conversion and utilization and energy conservation and environmental protection. (2) The preparation method of the present invention is simple to operate and easy to promote industrialization, thus having broad application prospects. The present invention not only uses industrial lignin as a catalyst, but also uses lignin as fuel for power generation, which greatly improves the utilization rate of industrial lignin and is of great significance for the high added value utilization and energy conservation and environmental protection of industrial lignin. Attached Figure Description

[0008] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Figure 1 Here is a SEM image of the lignin-based iron-manganese alloy catalyst prepared in Example 1; Figure 2 The image shows a TEM image of the lignin-based iron-manganese alloy catalyst prepared in Example 1. Figure 3 The XPS full spectrum of the lignin-based iron-manganese alloy catalyst prepared in Example 1 is shown below. Figure 4 The image shows the XRD results of the lignin-based iron-manganese alloy catalyst prepared in Example 1. Figure 5 This is a comparison of the ORR activities of the catalysts prepared in Examples 1-3; Figure 6 This is a comparison of the OER activities of the catalysts prepared in Examples 1-3; Figure 7 The diagram shows the open-circuit voltage and power density of the lignin-based iron-manganese alloy catalyst prepared in Example 1 when applied to a lignin flow battery. Detailed Implementation

[0009] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will understand that the invention may be implemented in other embodiments without these specific details.

[0010] Example 1 (1) Add 5g of urea to 25mL of deionized water, then add 20% (based on the mass of urea) of graphene oxide and sonicate for 0.5h, dry at 60℃ for 24h, and then calcine at 400℃ for 2h in a tube furnace under nitrogen protection to obtain nitrogen-doped reduced graphene oxide. (2) Melamine and thiourea were added to 100 mL of N-N dimethylformamide solution at a mass ratio of 1:1 and stirred at 80 °C for 30 minutes to dissolve. Then, lignin and ammonium chloride were added at a mass ratio of 1:1 (the total mass of lignin and ammonium chloride was equal to the total mass of melamine and thiourea), and stirred for 30 minutes. Finally, the N-N dimethylformamide was evaporated at 100 °C, and the reactants were transferred to an oven and dried at 60 °C for 12 h. The mixture was then placed in a tube furnace and calcined at 600 °C for 2 h under a nitrogen atmosphere to obtain sulfur / nitrogen-doped lignin. (3) The obtained nitrogen-doped reduced graphene oxide was mixed with ferrophthalocyanine at a mass ratio of 1:1, and then sulfur-nitrogen-doped lignin (at a mass ratio of 1:1 to nitrogen-doped reduced graphene oxide) was added; then manganese nitrate hexahydrate (at a mass ratio of 1:0.5 to ferrophthalocyanine) was added, mixed, and then added to 50 mL of deionized water. The mixture was stirred for 24 h, sonicated for 1 h, centrifuged, and dried in an oven at 60 °C for 12 h; finally, it was placed in a tube furnace and calcined at 600 °C for 2 h under nitrogen protection. After cooling, it was ground to obtain the lignin-based iron-manganese alloy catalyst. The SEM, TEM, XPS, and XRD results are shown in the figure. Figure 1-4 . Depend on Figure 1 The results show that the catalyst prepared in Example 1 has a 3D structure, with nanoscale iron-manganese alloy uniformly covering the surfaces of nitrogen-doped reduced graphene oxide and sulfur / nitrogen-doped lignin. Depend on Figure 2 The results show thin, gauze-like graphene, rectangular-structured nano-phthalocyanine iron, and dot-like iron-manganese alloy nanoparticles. Depend on Figure 3 The results showed that Fe and Mn elements were detected on the catalyst surface by XPS full-spectrum scanning. Depend on Figure 4 The results showed that a characteristic peak of iron phthalocyanine was detected at a diffraction angle of 25.9°, and a characteristic peak of manganese was detected at a diffraction angle of 43°. Based on the above results, it can be concluded that the present invention has successfully prepared a lignin-based iron-manganese alloy catalyst.

[0011] Example 2 (1) 5g of urea was added to 25mL of deionized water, then 20% (based on the mass of urea) of graphene oxide was added and ultrasonicated for 1h, dried at 60℃ for 24h, and then calcined at 500℃ for 2h in a tube furnace under nitrogen protection to obtain nitrogen-doped reduced graphene oxide. (2) Melamine and thiourea were added to 100 mL of N-N dimethylformamide solution at a mass ratio of 1:1 and stirred at 80 °C for 30 minutes to dissolve. Then, lignin and ammonium chloride were added at a mass ratio of 1:2 (the total mass of lignin and ammonium chloride was 1.5 times the total mass of melamine and thiourea), and stirred for 30 minutes. Finally, N-N dimethylformamide was evaporated at 110 °C, and the reactants were transferred to an oven and dried at 60 °C for 12 h. The mixture was then placed in a tube furnace and calcined at 700 °C for 2 h under a nitrogen atmosphere to obtain sulfur / nitrogen-doped lignin. (3) The nitrogen-doped reduced graphene oxide obtained was mixed with phthalocyanine iron at a mass ratio of 2:1, and then sulfur-nitrogen-doped lignin (at a mass ratio of 1:1 to nitrogen-doped reduced graphene oxide) was added; then nickel nitrate hexahydrate (at a mass ratio of 1:1 to phthalocyanine iron) was added, mixed and added to 50 ml of deionized water, stirred for 24 h, then sonicated for 1 h, then centrifuged and dried in an oven at 70 °C for 12 h; finally, it was placed in a tube furnace and calcined at 700 °C for 2 h under nitrogen protection, cooled and ground to obtain lignin-based nickel-iron alloy catalyst.

[0012] Example 3 (1) 5g of urea was added to 25mL of deionized water, then 30% (based on the mass of urea) of graphene oxide was added and ultrasonicated for 2h, dried at 80℃ for 24h, and then calcined at 800℃ for 2h in a tube furnace under nitrogen protection to obtain nitrogen-doped reduced graphene oxide. (2) Melamine and thiourea were added to 100 mL of N-N dimethylformamide solution at a mass ratio of 1:1 and stirred at 120 °C for 30 minutes to dissolve. Then, lignin and ammonium chloride were added at a mass ratio of 1:3 (the total mass of lignin and ammonium chloride was twice the total mass of melamine and thiourea), and stirred for 30 minutes. Finally, the N-N dimethylformamide was evaporated at 180 °C, and the reactants were transferred to an oven and dried at 100 °C for 12 h. The mixture was then placed in a tube furnace and calcined at 1000 °C for 2 h under a nitrogen atmosphere to obtain sulfur / nitrogen-doped lignin. (3) Nitrogen-doped reduced graphene oxide and phthalocyanine iron were mixed at a mass ratio of 10:1, and then sulfur-nitrogen-doped lignin (at a mass ratio of 3:1 to nitrogen-doped reduced graphene oxide) was added; then cobalt nitrate hexahydrate (at a mass ratio of 1:2 to phthalocyanine iron) was added, mixed and added to 50 ml of deionized water, stirred for 24 h, sonicated for 1 h, centrifuged, and dried in an oven at 100 °C for 12 h; finally, it was placed in a tube furnace and calcined at 1100 °C for 2 h under nitrogen protection. After cooling, the catalyst was ground to obtain the lignin-based cobalt-iron alloy catalyst.

[0013] Example 4 (1) 5g of urea was added to 25mL of deionized water, then 40% (based on the mass of urea) of graphene oxide was added and ultrasonicated for 1.5h, dried at 70℃ for 24h, and then calcined at 600℃ for 2h in a tube furnace under nitrogen protection to obtain nitrogen-doped reduced graphene oxide. (2) Melamine and thiourea were added to 100 mL of N-N dimethylformamide solution at a mass ratio of 1:2 and stirred at 100 °C for 30 minutes to dissolve. Then, lignin and ammonium chloride were added at a mass ratio of 1:2 (the total mass of lignin and ammonium chloride was 3 times the total mass of melamine and thiourea), and stirred for 30 minutes. Finally, the N-N dimethylformamide was evaporated at 160 °C, and the reactants were transferred to an oven and dried at 90 °C for 12 h. The mixture was then placed in a tube furnace and calcined at 800 °C for 2 h under a nitrogen atmosphere to obtain sulfur / nitrogen-doped lignin. (3) Nitrogen-doped reduced graphene oxide and phthalocyanine iron were mixed at a mass ratio of 5:1, and then sulfur-nitrogen-doped lignin (at a mass ratio of 2:1 to nitrogen-doped reduced graphene oxide) was added; then manganese nitrate hexahydrate (at a mass ratio of 1:1.5 to phthalocyanine iron) was added, mixed, and then added to 50 ml of deionized water. The mixture was stirred for 24 h, then sonicated for 1 h, then centrifuged, and dried in an oven at 90 °C for 12 h; finally, it was placed in a tube furnace and calcined at 900 °C for 2 h under nitrogen protection. After cooling, it was ground to obtain the lignin-based iron-manganese alloy catalyst.

[0014] Experimental Example 1 Prepare 50 ml of a 0.1 mol / L anhydrous ethanol solution of sucrose, and then add the catalyst prepared in Example 1 (at an amount of 2 mg / cm³). 2 Place a 4*4*0.4cm graphite felt in the oven, sonicate for 1 hour, and then dry in an oven at 60℃ for 6 hours. To prepare lignin anode fuel with a concentration of 10 g / L: dissolve lignin in a 2 mol / L sodium hydroxide alkaline solution and add a 0.3 mol / L potassium ferricyanide solution, then heat in a water bath or oil bath at 60°C for 2 hours. To prepare the cathode electrolyte for a lignin-based flow fuel cell, a 0.1 mol / L vanadium sulfate solution was used, with the addition of 0.02 mol / L nitric acid. A 1*1 cm [piece of electrolyte] was cut. 2 Graphite felt and 2*2cm 2 A proton exchange membrane lignin-based liquid flow fuel cell was assembled. The fuel cell operated at a temperature of 20°C, and no oxygen was introduced into the cathode. First, the oxygen reduction reaction (ORR) performance of the catalyst was tested using a Chenhua electrochemical workstation (CHI660D) with a three-electrode system. Mercuric oxide was used as the reference electrode, a graphite rod as the counter electrode, and glassy carbon as the working electrode. A Shengerno rotating ring-disc electrode apparatus was also used. 0.1M potassium hydroxide solution was used as the electrolyte, and the test was conducted under oxygen saturation. Linear sweep voltammetry (LSV) was used to test the ORR activity of the catalyst at a rotation speed of 1600 rpm. For the oxygen evolution reaction (OER) test, 1M potassium hydroxide solution was used as the electrolyte, and other test conditions were the same as for the ORR test. The lignin flow battery was tested using a Xinwei battery testing system. The power curve of the flow battery was tested using a multi-segment constant current discharge method. RuO2 and Pt / C were used as controls. The results are shown in Table 1 and [Table data missing]. Figure 5-7 .

[0015] Experimental Example 2 Prepare 50 ml of a 0.2 mol / L anhydrous ethanol solution of sucrose, and then add the catalyst prepared in Example 2 (at an amount of 2 mg / cm³). 2 Then place a 4*4*0.4cm graphite felt inside, sonicate for 1 hour, and then dry in an oven at 60-100℃ for 6 hours; To prepare lignin anode fuel with a concentration of 50 g / L, lignin was dissolved in a 6 mol / L sodium hydroxide alkaline solution, and a 1 mol / L potassium ferricyanide solution was added. The mixture was then heated in a water bath or oil bath at 120°C for 2 hours. To prepare the cathode electrolyte for a lignin-based flow fuel cell, a 5 mol / L vanadium sulfate solution was used, with the addition of 1 mol / L nitric acid. A 1*1 cm piece was cut... 2 Graphite felt and 2*2cm 2 A lignin-based flow fuel cell was assembled using a proton exchange membrane. The fuel cell operates at a temperature of 100°C, and no oxygen is introduced into the positive electrode. First, the oxygen reduction reaction (ORR) performance of the catalyst was tested using a Chenhua electrochemical workstation (CHI660D) with a three-electrode system. Mercuric oxide was used as the reference electrode, a graphite rod as the counter electrode, and glassy carbon as the working electrode. A Shengerno rotating ring-disc electrode apparatus was also used. 0.1M potassium hydroxide solution was used as the electrolyte, and the test was conducted under oxygen saturation. Linear sweep voltammetry (LSV) was used to test the ORR activity of the catalyst at a rotation speed of 1600 rpm. For the oxygen evolution reaction (OER) test, 1M potassium hydroxide solution was used as the electrolyte, and other test conditions were the same as for the ORR test. The lignin flow battery was tested using a Xinwei battery testing system. The power curve of the flow battery was tested using a multi-segment constant current discharge method. RuO2 and Pt / C were used as controls. The results are shown in Table 1 and [Table data missing]. Figure 5-6 .

[0016] Experimental Example 3 Prepare 50 ml of a 0.5 mol / L anhydrous ethanol solution of sucrose, and then add the catalyst prepared in Example 3 (addition amount of 10 mg / cm³). 2 Then place a 4*4*0.4cm graphite felt inside, sonicate for 1 hour, and then dry in an oven at 100℃ for 6 hours; To prepare lignin anode fuel with a concentration of 30 g / L: dissolve lignin in a 3 mol / L sodium hydroxide alkaline solution, add a 0.2 mol / L potassium ferricyanide solution, and then heat in a water bath or oil bath at 100°C for 2 hours. To prepare the cathode electrolyte for a lignin-based flow fuel cell, a 3 mol / L vanadium sulfate solution was used, with the addition of 0.1 mol / L nitric acid. A 1*1 cm [piece of electrolyte] was cut. 2 Graphite felt and 2*2cm 2 A proton exchange membrane lignin-based liquid flow fuel cell was assembled. The fuel cell operates at a temperature of 80°C, and no oxygen is introduced into the positive electrode. First, the oxygen reduction reaction (ORR) performance of the catalyst was tested using a Chenhua electrochemical workstation (CHI660D) with a three-electrode system. Mercuric oxide was used as the reference electrode, a graphite rod as the counter electrode, and glassy carbon as the working electrode. A Shengerno rotating ring-disc electrode apparatus was also used. 0.1M potassium hydroxide solution was used as the electrolyte, and the test was conducted under oxygen saturation. Linear sweep voltammetry (LSV) was used to test the ORR activity of the catalyst at a rotation speed of 1600 rpm. For the oxygen evolution reaction (OER) test, 1M potassium hydroxide solution was used as the electrolyte, and other test conditions were the same as for the ORR test. The lignin flow battery was tested using a Xinwei battery testing system. The power curve of the flow battery was tested using a multi-segment constant current discharge method. RuO2 and Pt / C were used as controls. The results are shown in Table 1 and [Table data missing]. Figure 5-6 .

[0017] Test Example 4 Prepare 50 ml of a 0.3 mol / L anhydrous ethanol solution of sucrose, and then add the catalyst prepared in Example 4 (addition amount of 5 mg / cm³). 2 Then place a 4*4*0.4cm graphite felt inside, sonicate for 1 hour, and then dry in an oven at 80℃ for 6 hours; To prepare lignin anode fuel with a concentration of 20 g / L, lignin was dissolved in a 2 mol / L sodium hydroxide alkaline solution, and a 0.5 mol / L potassium ferricyanide solution was added. The mixture was then heated in a water bath or oil bath at 80°C for 2 hours. To prepare the cathode electrolyte for a lignin-based liquid flow fuel cell, a 0.5 mol / L vanadium sulfate solution was used, with the addition of 0.2 mol / L nitric acid. A 1*1 cm [piece of electrolyte] was cut. 2Graphite felt and 2*2cm 2 A proton exchange membrane lignin-based liquid flow fuel cell was assembled. The fuel cell operates at a temperature of 90°C, and no oxygen is introduced into the positive electrode. First, the Chenhua electrochemical workstation CHI660D was used with a three-electrode system. Mercuric oxide was used as the reference electrode, a graphite rod as the counter electrode, and glassy carbon as the working electrode. A Shengerno rotating ring-disc electrode apparatus was used to test the catalyst's oxygen reduction reaction (ORR) performance. A 0.1M potassium hydroxide solution was used as the electrolyte, and the test was conducted under oxygen saturation. Linear sweep voltammetry (LSV) was used to test the catalyst's ORR activity at a rotation speed of 1600 rpm. For the oxygen evolution reaction (OER) test, a 1M potassium hydroxide solution was used as the electrolyte, and other test conditions were the same as for the ORR test. The lignin flow battery was tested using a Xinwei battery testing system, and the power curve of the flow battery was measured using a multi-segment constant current discharge method. The results are shown in Table 1. Table 1 Depend on Figure 5 The results show that, based on LSV testing and analysis of the catalyst's ORR performance, the iron-manganese alloy catalyst exhibits the best ORR performance due to its highest limiting current density and half-wave potential, both reaching 2.5 mA / cm². -1 With a voltage of 0.83V, it surpasses commercial platinum-carbon and other alloy catalysts. Depend on Figure 6 The results show that, for the comparison of OER performance, the catalysts being compared are at 10 mA / cm². -1 Regarding the overpotential at the OER, among the five catalysts, commercial RuO2 had the lowest overpotential, thus exhibiting the best OER performance. However, the (lignin-based) iron-manganese alloy catalyst also showed certain OER catalytic performance, exceeding that of the commercial platinum-carbon catalyst. Depend on Figure 7 The results show that when the (lignin-based) iron-manganese alloy catalyst with the best catalytic performance is applied to the lignin flow battery, the battery exhibits an open-circuit voltage close to 1.2V and a flow rate of 162mW / cm². 2 Its maximum power density is an outstanding performance in the field of lignin-based liquid flow fuel cells.

[0018] This invention is not limited to the specific embodiments described above. Any modifications made by those skilled in the art based on the above concept without creative effort are within the scope of protection of this invention.

Claims

1. A method for the preparation of a lignin-based non-precious metal catalyst for a flow battery, characterized by, The method comprises the following steps: S1, adding urea and graphene oxide into deionized water, ultrasonic mixing, drying, calcining to obtain nitrogen-doped reduced graphene oxide; S2, adding melamine and thiourea into N,N-dimethylformamide, stirring and dissolving, then adding lignin and ammonium chloride, continuing to stir, evaporating to remove the solvent, drying, calcining to obtain sulfur / nitrogen-doped lignin; S3, mixing nitrogen-doped reduced graphene oxide, iron phthalocyanine, sulfur / nitrogen-doped lignin and manganese nitrate hexahydrate, adding into deionized water, stirring, ultrasonic mixing, centrifuging, drying, finally calcining under nitrogen protection, grinding to obtain lignin-based non-noble metal catalyst.

2. The method for preparing the lignin-based non-precious metal catalyst according to claim 1, characterized in that, In step S1, the mass of the graphene oxide is 15%-25% of the mass of the urea.

3. The method for preparing the lignin-based non-precious metal catalyst according to claim 1, characterized in that, In step S1, the calcining temperature is 300-500℃, and the calcining time is 1-4h.

4. The method for preparing the lignin-based non-precious metal catalyst according to claim 1, characterized in that, In step S2, the mass ratio of the melamine and the thiourea is 1:1-3; the mass ratio of the lignin and the ammonium chloride is 1:1-3; the mass ratio of the mixture of the melamine and the thiourea to the mixture of the lignin and the ammonium chloride is 1:1-3.

5. The method for preparing the lignin-based non-precious metal catalyst according to claim 1, characterized in that, In step S2, the calcining temperature is 600-1000℃, and the calcining time is 1-3h.

6. The method for preparing the lignin-based non-precious metal catalyst according to claim 1, characterized in that, In step S3, the mass ratio of the nitrogen-doped reduced graphene oxide, the sulfur / nitrogen-doped lignin, the iron phthalocyanine and the manganese nitrate hexahydrate is (1-3):(1-3):(0.1-0.5):(0.5-2).

7. The method for preparing the lignin-based non-precious metal catalyst according to claim 1, characterized in that, In step S3, the calcining temperature is 600-1200℃, and the calcining time is 1-3h.

8. The method for preparing the lignin-based non-precious metal catalyst according to claim 1, characterized in that, The manganese nitrate hexahydrate, the nickel nitrate hexahydrate or the cobalt nitrate hexahydrate.

9. Application of the lignin-based non-noble metal catalyst prepared by the method of any one of claims 1-8 in a liquid flow battery.

10. Use according to claim 9, wherein The loading amount when the lignin-based non-noble metal catalyst is used as a cathode catalyst of a flow battery is 0.5-5 mg / cm 2 ; When the lignin-based non-noble metal catalyst is used as an anode catalyst of a flow battery, the loading amount of the lignin-based non-noble metal catalyst is 2 to 20 mg / cm 2 .

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