A graphite felt / manganese cobalt oxide nanowire electrode and its preparation method, and a lignin-based fuel cell.

Abstract

The application discloses a graphite felt / manganese cobalt oxide nanowire electrode and a preparation method thereof, and a lignin-based fuel cell. The preparation steps of the graphite felt / manganese cobalt oxide nanowire electrode include the following steps: dissolving Mn(NO3)2.6H2O, Co(NO3)2.6H2O, urea and ammonium fluoride in water to obtain a hydrothermal reaction solution; placing the graphite felt in the hydrothermal reaction solution, and performing a hydrothermal reaction in a high-pressure reaction kettle; taking out the sample after the reaction, washing, and drying to obtain the graphite felt / manganese cobalt oxide nanowire electrode. The graphite felt / manganese cobalt oxide nanowire electrode is used for assembling the lignin-based fuel cell, and high power density of the lignin-based fuel cell and efficient conversion of biomass energy to electric energy are realized. In addition, low-molecular-weight lignin is prepared synchronously, and the lignin has important significance for high-value utilization of lignin, ecological environment protection and energy crisis alleviation.

Description

Technical Field

[0001] This invention belongs to the field of high-value utilization of lignin, specifically relating to a graphite felt / manganese cobalt oxide nanowire electrode and its preparation method, and a lignin-based fuel cell. Background Technology

[0002] With the depletion of fossil fuels, finding renewable energy alternatives has become an urgent need. Lignin, as a renewable energy source, is the most abundant aromatic polymer in nature besides petroleum. The paper industry produces large amounts of lignin daily as a byproduct, but most of it is treated as waste and burned to generate heat or for power generation. To further enhance its utilization value and reduce carbon dioxide emissions, researchers have adopted many strategies, such as using lignin as a precursor for carbon-based materials, preparing lignin hydrogels, and converting lignin into ultraviolet-protective absorbers. However, complex process conditions and high energy consumption limit their further large-scale application. Developing simple and energy-efficient methods for utilizing lignin still faces significant challenges.

[0003] In response to the national call for "carbon peaking and carbon neutrality," replacing traditional fossil fuels with lignin for power generation is an effective way to achieve high-value utilization of lignin. Currently, a series of fuel cell technologies for converting biomass energy into electricity have been developed, such as solid oxide fuel cells (SOFCs), microbial fuel cells (MFCs), and biomass flow fuel cells (BFFCs), which utilize high temperatures, redox couple-mediated degradation, or microbial catalysis to degrade biomass for power generation. Solid oxide fuel cells (SOFCs) are unsuitable for large-scale deployment due to their high energy consumption caused by high temperatures. Microbial fuel cells (MFCs), which utilize microbial degradation of lignin for power generation, suffer from low power density (<0.1 mW / cm³) due to the poor degradation ability of microorganisms. 2 In comparison, biomass flow fuel cells have received widespread attention due to their advantages such as high power density, low operating temperature, and wide applicability.

[0004] Previous studies have shown that biomass flow fuel cells using lignin as fuel often require redox active materials as electron carriers, which is the reason for the high performance of lignin-based fuel cells. Now, PMO has been developed. Ox / PMO Re Fe 3+ / Fe 2+ [Fe(CN)6] 3- / [Fe(CN)6] 4- Cu 2+ / Cu + TiO 2+ / Ti 3+Redox couples are used. However, the addition of redox-active substances makes the electron transport pathway relatively complex, and the number of alternative redox couples is limited. Furthermore, the introduced redox-active substances are difficult to separate from the degraded lignin after the reaction, making the solid residue difficult to reuse and polluting the environment if directly emitted. In addition, the power density of batteries using lignin as fuel is still far lower than that of fuel cells using glucose, starch, or bagasse as fuel. To address this problem, existing technologies disclose methods such as heating, microbial degradation, and light irradiation; however, these methods all have shortcomings:

[0005] 1) Heating to increase electron transport and electrochemical reaction rates is a common method to improve the performance of biomass fuel cells. However, when used for lignin power generation, excessively high temperatures can cause lignin to condense and become difficult to completely degrade, and the electrolyte preheating process is slow and energy-intensive. 2) Microbial degradation of lignin is also a method to achieve lignin power generation, but microorganisms are easily deactivated by pH or temperature, severely affecting the continuous and stable operation of the fuel cell, and microbial fuel cells have low power density. 3) Existing photocatalysis methods, although simple to operate, environmentally friendly, and low-cost, suffer from low photocatalytic activity of redox couples, resulting in insufficient degradation of lignin and low power density of the fuel cell. 4) Electrocatalysis is one of the potential technologies to achieve efficient power generation without adding redox-active substances to the electrolyte. However, the electrode material commonly used in biomass fuel cells is unmodified graphite felt. This carbon material has advantages such as high stability and high conductivity, but graphite felt electrodes have disadvantages such as small specific surface area, poor wettability, and low electrochemical catalytic activity, so new modification methods need to be studied. Summary of the Invention

[0006] To address the shortcomings and deficiencies of existing technologies, the primary objective of this invention is to provide a method for preparing a graphite felt / manganese cobalt oxide nanowire electrode. This invention utilizes a hydrothermal method to grow manganese cobalt oxide nanowires on the surface of graphite felt. The prepared graphite felt / manganese cobalt oxide nanowire electrode exhibits excellent electrocatalytic activity and a large specific surface area. Using it as an electrocatalyst can improve electron transport rate and the specific surface area of ​​the electrochemical reaction, thereby efficiently degrading lignin macromolecules and simultaneously generating clean electrical energy.

[0007] Another object of the present invention is to provide a graphite felt / manganese cobalt oxide nanowire electrode prepared by the above method.

[0008] Another object of the present invention is to provide a lignin-based fuel cell constructed using the aforementioned graphite felt / manganese cobalt oxide nanowire electrode. This lignin-based fuel cell exhibits high power density and high open-circuit voltage, and the materials used are inexpensive, readily available, safe, and environmentally friendly. The present invention uses a lignin alkaline solution as the anode electrolyte, vanadium sulfate and nitric acid as the cathode electrolyte, oxygen as the cathode regenerator, graphite felt / manganese cobalt oxide nanowires as the anode electrode material, and graphite felt as the cathode electrode material, assembling them into a lignin-based fuel cell. The resulting battery exhibits high power density and high open-circuit voltage, and the materials used are inexpensive, readily available, safe, and environmentally friendly.

[0009] The objective of this invention is achieved through the following technical solution:

[0010] A method for preparing a graphite felt / manganese cobalt oxide nanowire electrode includes the following steps:

[0011] Mn(NO3)2·6H2O, Co(NO3)2·6H2O, urea and ammonium fluoride were dissolved in water to obtain a hydrothermal reaction solution. Graphite felt was placed in the hydrothermal reaction solution and subjected to a hydrothermal reaction in a high-pressure reactor at a certain temperature. After the reaction was completed, the sample was taken out, washed and dried to obtain a graphite felt / manganese cobalt oxide nanowire electrode.

[0012] Preferably, the molar ratio of Mn(NO3)2·6H2O, Co(NO3)2·6H2O, urea and ammonium fluoride is 0.5-3:1-3:7-12:3-6, more preferably 1:2:10:4.

[0013] Preferably, the graphite felt is calcined before use to remove the organic matter adhering to its surface. The calcination temperature is 200-600℃, the calcination time is 0.5-20h, and the heating rate is 1-50℃ / min.

[0014] Preferably, the hydrothermal reaction temperature is 20–200°C, and the hydrothermal reaction time is 1–20 h.

[0015] More preferably, the hydrothermal reaction temperature is 50–150°C, and the hydrothermal reaction time is 5–7 hours.

[0016] Preferably, the washing solution is at least one of ethanol, deionized water, and acetone.

[0017] Applications of graphite felt / manganese cobalt oxide nanowire electrodes in lignin-based fuel cells include:

[0018] (1) Anode electrolyte is prepared by dissolving lignin in an alkaline solution, and cathode electrolyte is prepared by using pentavalent vanadium salt, acid solution and cathode regeneration oxidant. Graphite felt electrode is used as cathode electrode, and graphite felt / manganese cobalt oxide nanowire electrode prepared in this invention is used as anode electrode. The lignin-based fuel cell is then assembled.

[0019] (2) The electrolyte and battery are preheated to a certain temperature, and the cathode electrolyte and anode electrolyte are respectively supplied to the cathode and anode chambers of the battery by a peristaltic pump, so that the lignin-based fuel cell can operate.

[0020] Preferably, the lignin in step (1) is at least one of enzymatically hydrolyzed lignin, pre-hydrolyzed lignin, sodium lignin sulfonate, and alkali lignin.

[0021] Preferably, the alkali in step (1) is one or two of KOH, NaOH and ammonia water.

[0022] Preferably, the concentration of hydroxide ions in the alkali in the anolyte in step (1) is 0.05 to 20.0 mol / L, more preferably 0.1 to 3 mol / L, and most preferably 0.2 to 2 mol / L.

[0023] Preferably, the lignin molecule content in the anolyte in step (1) is 1-100 g / L, more preferably 5-70 g / L, and most preferably 10-50 g / L.

[0024] Preferably, the pentavalent vanadium salt in step (1) is selected from at least one of vanadium pentoxide, vanadium sulfate, and vanadium nitrate.

[0025] Preferably, the acid solution in step (1) is selected from at least one of hydrochloric acid aqueous solution, sulfuric acid aqueous solution and nitric acid aqueous solution.

[0026] Preferably, the cathode regeneration oxidant in step (1) is selected from at least one of nitric acid, oxygen, hydrogen peroxide or potassium permanganate.

[0027] Preferably, the concentration of pentavalent vanadium salt in the cathode electrolyte in step (1) is 0.05 to 5 mol / L.

[0028] Preferably, the concentration of acid in the cathode electrolyte in step (1) is 0.05 to 8.0 mol / L.

[0029] Preferably, in the cathode regeneration oxidant of step (1), the concentration of nitric acid is 0.01 to 8 mol / L, and the flow rate of oxygen is 1 to 100 mL / min.

[0030] Preferably, the heating temperature in step (2) is 10 to 120°C, that is, the operating temperature of the lignin-based fuel cell is 10 to 120°C.

[0031] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0032] 1. The graphite felt / manganese cobalt oxide nanowire electrode prepared by the present invention using inexpensive and environmentally friendly transition metals has a high specific surface area and excellent electrocatalytic activity. Moreover, the preparation process is simple, and the optimal preparation process does not require calcination treatment.

[0033] 2. The graphite felt / manganese cobalt oxide nanowire electrode prepared by this invention is applied to lignin-based fuel cells and has a higher power density compared with other similar designs.

[0034] 3. The anolyte used in the lignin-based fuel cell of the present invention does not require the introduction of an external redox couple to assist electron transport, which simplifies the electron transfer and lignin separation and purification process after degradation. Furthermore, it can be used for direct power generation without preheating the electrolyte, thus avoiding lignin condensation, simplifying the power generation process, and reducing energy consumption.

[0035] 4. The lignin-based fuel cell of this invention directly electrocatalytically oxidizes lignin on the electrode to generate electricity, without the need for the introduction of microorganisms. It is less susceptible to influence from other factors, allowing the fuel cell to operate continuously and stably. The application of modified electrodes can significantly increase the lignin oxidation rate and electron transport rate, thereby greatly improving the performance of the fuel cell.

[0036] 5. The lignin-based fuel cell of the present invention uses a manganese cobalt oxide micro-nano modified carbon felt electrode, which has the advantages of large specific surface area and high catalytic activity. Therefore, it can induce a large number of lignin macromolecules to undergo deep degradation, thereby improving the various performance characteristics of the lignin-based fuel cell. Attached Figure Description

[0037] Figure 1 The current density-voltage-output power graph is shown for the lignin-based fuel cell constructed with graphite felt / manganese cobalt oxide nanowire electrodes with different hydrothermal times in Example 1.

[0038] Figure 2 The image shows a SEM image of the graphite felt / manganese cobalt oxide nanowire electrode prepared by hydrothermal treatment for 5 hours in Example 1.

[0039] Figure 3 The graph shows the current density-voltage-output power of the lignin-based fuel cell constructed with graphite felt / manganese cobalt oxide nanowire electrodes before and after calcination treatment in Example 2.

[0040] Figure 4 The image shows the XRD patterns of manganese cobalt oxide nanowires before and after calcination treatment in Example 2.

[0041] Figure 5 The current density-voltage-output power graph is shown for the lignin-based fuel cells constructed with anolytes of different NaOH concentrations in Example 3.

[0042] Figure 6The current density-voltage-output power graph is shown for the lignin-based fuel cells constructed with different types of lignin anode electrolytes in Example 4.

[0043] Figure 7 The current density-voltage-output power graph is shown for the lignin-based fuel cells constructed with anolytes of different lignin concentrations in Example 5.

[0044] Figure 8 This is a long-term, stable discharge diagram of the lignin-based fuel cell assembled using graphite felt / manganese cobalt oxide nanowire electrodes in Example 6.

[0045] Figure 9 The current density-voltage-output power graph is shown for the lignin-based fuel cell constructed with graphite felt electrodes as a comparative example 1.

[0046] Figure 10 The current density-voltage-output power graphs are for lignin-based fuel cells constructed with graphite felt / copper-doped manganese cobalt oxide nanowire electrodes and graphite felt electrodes with different copper doping contents, as shown in Comparative Example 2.

[0047] Figure 11 The current density-voltage-output power graphs for the lignin-based fuel cells constructed using graphite felt / iron-doped manganese cobalt oxide nanowire electrodes and graphite felt electrodes, as shown in Comparative Example 3.

[0048] Figure 12 The current density-voltage-output power graphs are for the lignin-based fuel cells constructed using graphite felt / CoS electrodes and graphite felt electrodes, as shown in Comparative Example 4.

[0049] Figure 13 Current density-voltage-output power graphs for lignin-based fuel cells constructed using graphite felt / manganese cobalt oxide electrodes and graphite felt electrodes, as shown in Comparative Example 10.

[0050] Figure 14 SEM image of the graphite felt / manganese cobalt oxide electrode prepared for Comparative Example 10. Detailed Implementation

[0051] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. The raw materials involved in the present invention can all be purchased directly from the market, and for process parameters not specifically specified, conventional techniques can be referred to.

[0052] The alkali lignin, sodium lignin sulfonate, and enzymatically hydrolyzed lignin used in the following examples and comparative examples were all purchased from Shandong Longli Biotechnology Co., Ltd. The graphite felt used in the following examples and comparative examples was purchased from Taiwan Carbon Energy. Before use, it was calcined to remove surface organic matter. The calcination temperature was 420℃, the calcination time was 4 hours, and the heating rate was 5℃ / min.

[0053] Example 1: Effect of graphite felt / manganese cobalt oxide nanowire electrodes prepared with different hydrothermal times on fuel cells

[0054] 1. Preparation of graphite felt / manganese cobalt oxide nanowire electrode: 5 mmol Co(NO3)2·6H2O, 2.5 mmol Mn(NO3)2·6H2O, 10 mmol NH4F, and 25 mmol urea were dissolved in 70 ml of deionized water to prepare four mixed solutions. Each solution was then impregnated with a 5 cm × 0.5 cm × 0.5 cm graphite felt and placed in a high-pressure reactor for hydrothermal treatment at 120 °C for 1 h, 3 h, 5 h, and 7 h, respectively. After the reaction, the samples were removed, washed several times with deionized water, and dried.

[0055] 2. Preparation of anolyte: Weigh 2g of NaOH and dissolve it in 50ml of deionized water. Then weigh 1g of enzymatically hydrolyzed lignin and add it to the solution. Stir for 10 minutes and then filter to obtain the anolyte of lignin alkaline solution.

[0056] 3. Preparation of the cathode electrolyte: Weigh 20g of vanadium pentoxide powder and add it to a beaker containing 524ml of deionized water, and stir at room temperature. Then, slowly add 76ml of concentrated sulfuric acid (98.3% by mass) to the solution. Next, add 4ml of nitric acid (68% by mass), and continue stirring the solution until it becomes a clear, bright yellow solution. Let it stand for 24 hours to obtain the high-valence vanadium cathode electrolyte. Measure 100ml of this solution as the cathode electrolyte.

[0057] 4. Battery System Construction and Electrical Performance Testing: Four battery systems were constructed, each using graphite felt / manganese cobalt oxide nanowires with different hydrothermal times as the anode electrode, with other structures remaining identical. Graphite felt / manganese cobalt oxide nanowires were filled into the S-shaped flow channels within the anode graphite plate as the anode electrode, and graphite felt was filled into the S-shaped flow channels within the cathode graphite plate as the cathode electrode. The graphite plate, load (LED light) wires, and fixing end plates were then assembled in the following order: metal cover plate, anode graphite plate containing graphite felt / manganese cobalt oxide nanowires, polytetrafluoroethylene film, Nafion 211 film, polytetrafluoroethylene film, cathode graphite plate containing graphite felt, and metal cover plate. The battery and load were connected with wires. The electrolyte from step 2 was added to the anode electrolyte tank, and the electrolyte from step 3 was added to the cathode electrolyte tank. The anode electrolyte tank was connected to the anode inlet and outlet of the battery, and the cathode tank was connected to the cathode inlet and outlet of the battery using tubes. Oxygen was introduced into the cathode electrolyte tank at a flow rate of 40 mL / min, and the battery was operated at 90°C.

[0058] The battery's electrical performance was tested using the scanning current method, and the results are as follows: Figure 1As shown, with increasing hydrothermal time, the graphite felt / manganese cobalt oxide nanowire electrode grown hydrothermally for 7 hours exhibits the best battery performance, with a maximum voltage of 1.53V and a maximum current density of 642.7mA / cm². 2 The maximum power density is 157.16 mW / cm³. 2 The battery performance of graphite felt / manganese cobalt oxide nanowire electrodes grown hydrothermally for 5 hours is not much different from that grown hydrothermally for 7 hours, indicating that 5 hours is the optimal hydrothermal time from the perspective of energy saving.

[0059] The SEM image of the graphite felt / manganese cobalt oxide nanowire electrode grown hydrothermally for 5 hours in this embodiment is as follows: Figure 2 As shown, the originally smooth graphite felt surface is uniformly coated with manganese cobalt oxide nanowires and exhibits a needle-like radial morphology, indicating that manganese cobalt oxide nanowires can be grown well on the graphite felt surface under these conditions.

[0060] Example 2: Effects of graphite felt / manganese cobalt oxide nanowire electrodes on fuel cells before and after calcination treatment

[0061] 1. Preparation of graphite felt / manganese cobalt oxide nanowire electrode: 5 mmol Co(NO3)2·6H2O, 2.5 mmol Mn(NO3)2·6H2O, 10 mmol NH4F, and 25 mmol urea were dissolved in 70 ml of deionized water. A 5 cm × 0.5 cm × 0.5 cm graphite felt was then added and impregnated. The mixture was placed in a high-pressure reactor and hydrothermally heated at 120 °C for 5 h. After the reaction, the sample was removed, washed several times with deionized water, and dried (the dried sample was used as the graphite felt / manganese cobalt oxide nanowire electrode before calcination).

[0062] The dried sample was placed in a muffle furnace and calcined at 350℃ for 2 hours to obtain the calcined graphite felt / manganese cobalt nanowire electrode. The heating rate was 5℃ / min.

[0063] 2. Preparation of anolyte: Weigh 2g of NaOH and dissolve it in 50ml of deionized water. Then weigh 1g of enzymatically hydrolyzed lignin and add it to the solution. Stir for 10 minutes and then filter to obtain the anolyte of lignin alkaline solution.

[0064] 3. The preparation of the cathode electrolyte is the same as in Example 1.

[0065] 4. Battery System Construction and Electrical Performance Testing: Two battery systems were constructed, using graphite felt / manganese cobalt oxide nanowires before and after the calcination treatment as the anode electrodes, with other structures remaining the same. Graphite felt / manganese cobalt oxide nanowires were filled into the S-shaped flow channels within the anode graphite plate as the anode electrode, and graphite felt was filled into the S-shaped flow channels within the cathode graphite plate as the cathode electrode. The graphite plate, load (LED light) wires, and fixing end plates were then assembled in the following order: metal cover plate, anode graphite plate containing graphite felt / manganese cobalt oxide nanowires, polytetrafluoroethylene film, Nafion 211 film, polytetrafluoroethylene film, cathode graphite plate containing graphite felt, and metal cover plate. The battery and load were connected with wires. The electrolyte from step 2 was added to the anode electrolyte tank, and the electrolyte from step 3 was added to the cathode electrolyte tank. The anode electrolyte tank was connected to the anode inlet and outlet of the battery, and the cathode tank was connected to the cathode inlet and outlet of the battery using tubes. Oxygen was introduced into the cathode electrolyte tank at a flow rate of 40 mL / min, and the battery was operated at 90°C.

[0066] The battery's electrical performance was tested using the scanning current method, and the results are as follows: Figure 3 As shown, the uncalcined graphite felt / manganese cobalt oxide nanowire electrode exhibits the best battery performance, with a maximum voltage of 1.5V and a maximum current density of 646.61 mA / cm². 2 The maximum power density is 152.64 mW / cm³. 2 This indicates that the performance of the battery can be significantly improved by using uncalcined graphite felt / manganese cobalt oxide nanowire electrodes with a small amount of hydroxide doping.

[0067] The XRD patterns of the manganese cobalt oxide nanowires before and after calcination in this embodiment are as follows: Figure 4 As shown.

[0068] Example 3: Effect of Anode Electrolytes Prepared with Different NaOH Concentrations on Fuel Cells

[0069] 1. Preparation of graphite felt / manganese cobalt oxide nanowire electrode: 5 mmol Co(NO3)2·6H2O, 2.5 mmol Mn(NO3)2·6H2O, 10 mmol NH4F, and 25 mmol urea were dissolved in 70 ml of deionized water. A 5 cm × 0.5 cm × 0.5 cm graphite felt was then added and impregnated. The mixture was placed in a high-pressure reactor and hydrothermally heated at 120 °C for 5 h. After the reaction was complete, the sample was removed, washed several times with deionized water, and dried.

[0070] 2. Preparation of anolyte: Weigh 1g, 2g, and 4g of NaOH and dissolve them in 50ml of deionized water respectively. Then weigh three 1g portions of enzymatically hydrolyzed lignin and add them to the NaOH solutions respectively. After stirring for 10min, filter to obtain anolytes of lignin alkaline solutions with different NaOH concentrations. The NaOH concentrations are 0.5M, 1M, and 2M.

[0071] 3. The preparation of the cathode electrolyte is the same as in Example 1.

[0072] 4. Battery System Construction and Electrical Performance Testing: Graphite felt / manganese cobalt oxide nanowires are filled into the S-shaped flow channels within the anode graphite plate to serve as the anode electrode, and graphite felt is filled into the S-shaped flow channels within the cathode graphite plate to serve as the cathode electrode. Then, the graphite plate, load (LED light) wires, and fixed end plates are assembled into the battery in the following order: metal cover plate, anode graphite plate containing graphite felt / manganese cobalt oxide nanowires, polytetrafluoroethylene film, Nafion 211 film, polytetrafluoroethylene film, cathode graphite plate containing graphite felt, and metal cover plate. The battery and load are connected with wires. The electrolyte from step 2 is added to the anode electrolyte tank, and the electrolyte from step 3 is added to the cathode electrolyte tank. The anode electrolyte tank is connected to the anode inlet and outlet of the battery, and the cathode tank is connected to the cathode inlet and outlet of the battery. Oxygen is introduced into the cathode electrolyte tank at a flow rate of 40 mL / min, and the battery is operated at 90°C.

[0073] The battery's electrical performance was tested using the scanning current method, and the results are as follows: Figure 5 As shown, the battery with 2M NaOH anolyte exhibits the best performance, with a maximum voltage of 1.5V and a maximum current density of 772.59 mA / cm². 2 The maximum power density is 179.46 mW / cm³. 2 .

[0074] Example 4: The effect of anolytes prepared with different lignin types on fuel cells

[0075] 1. Preparation of graphite felt / manganese cobalt oxide nanowire electrode: 5 mmol Co(NO3)2·6H2O, 2.5 mmol Mn(NO3)2·6H2O, 10 mmol NH4F, and 25 mmol urea were dissolved in 70 ml of deionized water. A 5 cm × 0.5 cm × 0.5 cm graphite felt was then added and impregnated. The mixture was placed in a high-pressure reactor and hydrothermally heated at 120 °C for 5 h. After the reaction was complete, the sample was removed, washed several times with deionized water, and dried.

[0076] 2. Preparation of anolyte: Weigh three 4g portions of NaOH and dissolve them in 50ml of deionized water respectively. Then weigh 1g of enzymatically hydrolyzed lignin, 1g of alkali lignin, and 1g of sodium lignin sulfonate and add them to the NaOH solution respectively. Stir for 10min and then filter to obtain lignin alkaline solutions of different lignin types as anolytes.

[0077] 3. The preparation of the cathode electrolyte is the same as in Example 1.

[0078] 4. Battery System Construction and Electrical Performance Testing: Graphite felt / manganese cobalt oxide nanowires are filled into the S-shaped flow channels within the anode graphite plate to serve as the anode electrode, and graphite felt is filled into the S-shaped flow channels within the cathode graphite plate to serve as the cathode electrode. Then, the graphite plate, load (LED light) wires, and fixed end plates are assembled into the battery in the following order: metal cover plate, anode graphite plate containing graphite felt / manganese cobalt oxide nanowires, polytetrafluoroethylene film, Nafion 211 film, polytetrafluoroethylene film, cathode graphite plate containing graphite felt, and metal cover plate. The battery and load are connected with wires. The electrolyte from step 2 is added to the anode electrolyte tank, and the electrolyte from step 3 is added to the cathode electrolyte tank. The anode electrolyte tank is connected to the anode inlet and outlet of the battery, and the cathode tank is connected to the cathode inlet and outlet of the battery. Oxygen is introduced into the cathode electrolyte tank at a flow rate of 40 mL / min, and the battery is operated at 90°C.

[0079] The battery's electrical performance was tested using the scanning current method, and the results are as follows: Figure 6 As shown, the battery with alkali lignin added to the anolyte exhibits the best performance, with a maximum power density of 192.04 mW / cm³. 2 .

[0080] Example 5: Effect of Anodic Electrolytes Prepared with Different Lignin Concentrations on Fuel Cells

[0081] 1. Preparation of graphite felt / manganese cobalt oxide nanowire electrode: 5 mmol Co(NO3)2·6H2O, 2.5 mmol Mn(NO3)2·6H2O, 10 mmol NH4F, and 25 mmol urea were dissolved in 70 ml of deionized water. A 5 cm × 0.5 cm × 0.5 cm graphite felt was then added and impregnated. The mixture was placed in a high-pressure reactor and hydrothermally heated at 120 °C for 5 h. After the reaction was complete, the sample was removed, washed several times with deionized water, and dried.

[0082] 2. Preparation of anolyte: Weigh 2g of NaOH and dissolve it in 50ml of deionized water. Then weigh 1g and 2g of enzymatically hydrolyzed lignin, add them to the solutions respectively, stir for 10min and filter to obtain lignin alkaline solutions of anolyte with different lignin concentrations.

[0083] 3. The preparation of the cathode electrolyte is the same as in Example 1.

[0084] 4. Battery System Construction and Electrical Performance Testing: Graphite felt / manganese cobalt oxide nanowires are filled into the S-shaped flow channels within the anode graphite plate to serve as the anode electrode, and graphite felt is filled into the S-shaped flow channels within the cathode graphite plate to serve as the cathode electrode. Then, the graphite plate, load (LED light) wires, and fixed end plates are assembled into the battery in the following order: metal cover plate, anode graphite plate containing graphite felt / manganese cobalt oxide nanowires, polytetrafluoroethylene film, Nafion 211 film, polytetrafluoroethylene film, cathode graphite plate containing graphite felt, and metal cover plate. The battery and load are connected with wires. The electrolyte from step 2 is added to the anode electrolyte tank, and the electrolyte from step 3 is added to the cathode electrolyte tank. The anode electrolyte tank is connected to the anode inlet and outlet of the battery, and the cathode tank is connected to the cathode inlet and outlet of the battery. Oxygen is introduced into the cathode electrolyte tank at a flow rate of 40 mL / min, and the battery is operated at 90°C.

[0085] The battery's electrical performance was tested using the scanning current method, and the results are as follows: Figure 7 As shown, the battery exhibits the best performance with the addition of 2g of lignin-enzymatically hydrolyzed anolyte, exhibiting a maximum voltage of 1.6V and a maximum current density of 792.74mA / cm². 2 The maximum power density is 209.56 mW / cm³. 2 .

[0086] Example 6: Investigation of Long-Term Continuous Stable Discharge of Lignin-Based Fuel Cells

[0087] 1. Preparation of graphite felt / manganese cobalt oxide nanowire electrode: 5 mmol Co(NO3)2·6H2O, 2.5 mmol Mn(NO3)2·6H2O, 10 mmol NH4F, and 25 mmol urea were dissolved in 70 ml of deionized water. A 5 cm × 0.5 cm × 0.5 cm graphite felt was then added and impregnated. The mixture was placed in a high-pressure reactor and hydrothermally heated at 120 °C for 5 h. After the reaction was complete, the sample was removed, washed several times with deionized water, and dried.

[0088] 2. Preparation of anolyte: Weigh 40g of NaOH and dissolve it in 500ml of deionized water. Then weigh 5g of enzymatically hydrolyzed lignin and add it to the solution. Stir for 10 minutes and then filter to obtain the lignin alkaline solution anolyte.

[0089] 3. Preparation of the cathode electrolyte: Weigh 20g of vanadium pentoxide powder and add it to a beaker containing 524ml of deionized water, and stir at room temperature. Then, slowly add 76mL of concentrated sulfuric acid (98.3% by mass) to the solution. Next, add 4ml of nitric acid (68% by mass), and continue stirring the solution until it becomes a clear, bright yellow solution. Let it stand for 24 hours to obtain the high-valence vanadium cathode electrolyte.

[0090] 4. Battery System Construction and Electrical Performance Testing: Graphite felt / manganese cobalt oxide nanowires are filled into the S-shaped flow channels within the anode graphite plate to serve as the anode electrode, and graphite felt is filled into the S-shaped flow channels within the cathode graphite plate to serve as the cathode electrode. Then, the graphite plate, load (LED light) wires, and fixed end plates are assembled into the battery in the following order: metal cover plate, anode graphite plate containing graphite felt / manganese cobalt oxide nanowires, polytetrafluoroethylene film, Nafion 211 film, polytetrafluoroethylene film, cathode graphite plate containing graphite felt, and metal cover plate. The battery and load are connected with wires. The electrolyte from step 2 is added to the anode electrolyte tank, and the electrolyte from step 3 is added to the cathode electrolyte tank. The anode electrolyte tank is connected to the anode inlet and outlet of the battery, and the cathode tank is connected to the cathode inlet and outlet of the battery. Oxygen is introduced into the cathode electrolyte tank at a flow rate of 40 mL / min, and the battery is operated at 90°C.

[0091] The test was conducted using the constant current discharge method, and the results are as follows: Figure 8 As shown, at a voltage of 0.3V, this battery can achieve continuous and stable discharge for more than 9 hours.

[0092] Comparative Example 1: The effect of using graphite felt as the anode electrode on lignin-based fuel cells

[0093] 1. Preparation of anolyte: Weigh 2g of NaOH and dissolve it in 50ml of deionized water. Then weigh 1g of enzymatically hydrolyzed lignin and add it to the solution. Stir for 10min and filter to obtain the anolyte of lignin alkaline solution.

[0094] 2. The preparation of the cathode electrolyte is the same as in Example 1.

[0095] 3. Battery System Construction and Electrical Performance Testing: Fill the S-shaped flow channels within the graphite plate with graphite felt. Then, assemble the battery in the following order: graphite plate, load (LED light) wires, fixed end plate, etc., in the following sequence: metal cover plate, anode graphite plate containing graphite felt, PTFE film, Nafion 211 film, PTFE film, cathode graphite plate containing graphite felt, and metal cover plate. Connect the battery and load with wires. Add the electrolyte from step 2 to the anode electrolyte tank, and add the electrolyte from step 3 to the cathode electrolyte tank. Connect the anode electrolyte tank to the anode inlet and outlet of the battery, and the cathode tank to the cathode inlet and outlet of the battery. Introduce oxygen into the cathode electrolyte tank at a flow rate of 40 mL / min, and operate the battery at 90°C.

[0096] The battery's electrical performance was tested using the scanning current method, and the results are as follows: Figure 9 As shown, the maximum voltage is 1.45V and the maximum current density is 397.44mA / cm². 2 The maximum power density is 108.54 mW / cm³. 2However, its performance is not as good as that of the graphite felt / manganese cobalt oxide nanowire electrode in Example 1. Therefore, the graphite felt / manganese cobalt oxide nanowire electrode can achieve efficient degradation of lignin and coupled power generation.

[0097] Comparative Example 2: The effect of using graphite felt / copper-doped manganese cobalt oxide nanowires with different copper doping contents as anode electrodes on lignin-based fuel cells

[0098] 1. Preparation of graphite felt / copper-doped manganese cobalt oxide nanowire electrodes with different copper doping contents: 5 mmol Co(NO3)2·6H2O, 2.5 mmol Mn(NO3)2·6H2O, 10 mmol NH4F, and 25 mmol urea were dissolved in 70 ml of deionized water, and two aliquots of this solution were prepared. 1.25 mmol and 0.5 mmol Cu(NO3)2·3H2O were added to each aliquot, and 5 cm × 0.5 cm × 0.5 cm graphite felts were then impregnated. The aliquots were placed in a high-pressure reactor and hydrothermally heated for 5 h. After the reaction, the samples were removed, washed several times with deionized water, and dried.

[0099] 2. Preparation of anolyte: Weigh 2g of NaOH and dissolve it in 50ml of deionized water. Then weigh 1g of enzymatically hydrolyzed lignin and add it to the solution. Stir for 10 minutes and then filter to obtain the anolyte of lignin alkaline solution.

[0100] 3. The preparation of the cathode electrolyte is the same as in Example 1.

[0101] 4. Battery System Construction and Electrical Performance Testing: Two battery systems were constructed, using graphite felt / copper-doped manganese cobalt oxide nanowires with different copper doping contents as the anode electrodes, with other structures remaining the same. Graphite felt / copper-doped manganese cobalt oxide nanowires were filled into the S-shaped flow channels within the anode graphite plate as the anode electrode, and graphite felt was filled into the S-shaped flow channels within the cathode graphite plate as the cathode electrode. The graphite plate, load (LED light) wires, and fixing end plates were then assembled in the following order: metal cover plate, anode graphite plate containing graphite felt / copper-doped manganese cobalt oxide nanowires, polytetrafluoroethylene film, Nafion 211 film, polytetrafluoroethylene film, cathode graphite plate containing graphite felt, and metal cover plate. The battery and load were connected with wires. The electrolyte from step 2 was added to the anode electrolyte tank, and the electrolyte from step 3 was added to the cathode electrolyte tank. The anode electrolyte tank was connected to the anode inlet and outlet of the battery, and the cathode tank was connected to the cathode inlet and outlet of the battery using tubes. Oxygen was introduced into the cathode electrolyte tank at a flow rate of 40 mL / min, and the battery was operated at 90°C.

[0102] The battery's electrical performance was tested using the scanning current method, and the results are as follows: Figure 10 As shown, the constructed fuel cell has a maximum voltage of 1.4V and a maximum power density of 144.58mW / cm³. 2Both the voltage and power density are lower than those of this application, indicating that copper doping does not significantly improve the electrocatalytic performance of manganese cobalt oxide, and therefore does not significantly increase the power density of the battery. This shows that not all types of transition metal compounds can electrocatalyze the depolymerization of lignin and accelerate the electron transport rate; only transition metal compounds with specific compositions and structures have the effect of electrocatalyzing the depolymerization of lignin and accelerating the electron transport rate.

[0103] Comparative Example 3: The effect of using graphite felt / iron-doped manganese cobalt oxide as an anode electrode on lignin-based fuel cells

[0104] 1. Preparation of graphite felt / iron-doped manganese cobalt oxide nanowire electrode: 1.25 mmol Fe(NO3)3·9H2O, 5 mmol Co(NO3)2·6H2O, 2.5 mmol Mn(NO3)2·6H2O, 10 mmol NH4F, and 25 mmol urea were dissolved in 70 ml of deionized water. A 5 cm × 0.5 cm × 0.5 cm graphite felt was then added and impregnated. The mixture was placed in a high-pressure reactor and hydrothermally heated for 5 h. After the reaction was complete, the sample was removed, washed several times with deionized water, and dried.

[0105] 2. Preparation of anolyte: Weigh 2g of NaOH and dissolve it in 50ml of deionized water. Then weigh 1g of enzymatically hydrolyzed lignin and add it to the solution. Stir for 10 minutes and then filter to obtain the anolyte of lignin alkaline solution.

[0106] 3. The preparation of the cathode electrolyte is the same as in Example 1.

[0107] 4. Battery System Construction and Electrical Performance Testing: Graphite felt / iron-doped manganese cobalt oxide nanowires are filled into the S-shaped flow channels within the anode graphite plate to serve as the anode electrode. Graphite felt is filled into the S-shaped flow channels within the cathode graphite plate to serve as the cathode electrode. Then, the graphite plate, load (LED light) wires, and fixed end plates are assembled into the battery in the following order: metal cover plate, anode graphite plate containing graphite felt / iron-doped manganese cobalt oxide nanowires, polytetrafluoroethylene film, Nafion 211 film, polytetrafluoroethylene film, cathode graphite plate containing graphite felt, and metal cover plate. The battery and load are connected with wires. The electrolyte from step 2 is added to the anode electrolyte tank, and the electrolyte from step 3 is added to the cathode electrolyte tank. The anode electrolyte tank is connected to the anode inlet and outlet of the battery, and the cathode tank is connected to the cathode inlet and outlet of the battery. Oxygen is introduced into the cathode electrolyte tank at a flow rate of 40 mL / min, and the battery is operated at 90°C.

[0108] The battery's electrical performance was tested using the scanning current method, and the results are as follows: Figure 11 As shown, the constructed fuel cell has a maximum voltage of 1.51V and a maximum power density of 135.22mW / cm³. 2The power density is lower than that of this application, indicating that iron doping does not significantly improve the electrocatalytic performance of manganese cobalt oxide, and therefore does not significantly increase the power density of the battery. This shows that not all kinds of transition metal compounds can electrocatalyze the depolymerization of lignin and accelerate the electron transport rate. Only transition metal compounds with specific compositions and structures have the effect of electrocatalyzing the depolymerization of lignin and accelerating the electron transport rate.

[0109] Comparative Example 4: The effect of using graphite felt / CoS as the anode electrode on lignin-based fuel cells

[0110] 1. Preparation of graphite felt / CoS electrode: 2 mmol Co(NO3)2·6H2O, 10 mmol urea, and 25 mmol sublimed sulfur were dissolved in a mixed solution containing 23.33 ml ethylene glycol and 46.67 ml DMF. After stirring for 1 h, a 5 cm × 0.5 cm × 0.5 cm graphite felt was added for impregnation, and the mixture was placed in a high-pressure reactor and hydrothermally heated at 180 °C for 12 h. After the reaction was completed, the sample was removed, washed several times with ethanol, and dried.

[0111] 2. Preparation of anolyte: Weigh 4g of NaOH and dissolve it in 50ml of deionized water. Then weigh 2g of enzymatically hydrolyzed lignin and add it to the solution. Stir for 10 minutes and then filter to obtain the anolyte of lignin alkaline solution.

[0112] 3. The preparation of the cathode electrolyte is the same as in Example 1.

[0113] 4. Battery System Construction and Electrical Performance Testing: Graphite felt / CoS is filled into the S-shaped flow channel within the anode graphite plate as the anode electrode, and graphite felt is filled into the S-shaped flow channel within the cathode graphite plate as the cathode electrode. Then, the graphite plate, load (LED light) wires, and fixed end plates are assembled into the battery in the following order: metal cover plate, anode graphite plate containing graphite felt / CoS, PTFE film, Nafion 211 film, PTFE film, cathode graphite plate containing graphite felt, and metal cover plate. The battery and load are then connected with wires. The electrolyte from step 2 is added to the anode electrolyte tank, and the electrolyte from step 3 is added to the cathode electrolyte tank. The anode electrolyte tank is connected to the anode inlet and outlet of the battery, and the cathode tank is connected to the cathode inlet and outlet of the battery. Oxygen is introduced into the cathode electrolyte tank at a flow rate of 40 mL / min, and the battery is operated at 90°C.

[0114] The battery's electrical performance was tested using the scanning current method, and the results are as follows: Figure 13 As shown, the constructed fuel cell has a maximum voltage of 1.38V and a maximum power density of 138.54mW / cm³. 2 Both the voltage and power density are lower than those in this application.

[0115] Comparative Example 5: CuCl2 / TiOSO4 co-mediated lignin-based fuel cell (referencing Chemical Engineering Journal 452(2023)139266)

[0116] 1. Preparation of anolyte: Dissolve 61.4g of copper chloride dihydrate and 30mL of concentrated hydrochloric acid in deionized water, then add 6g of straw and 45g of titanium oxysulfate, add water to make up to 180mL of mixed solution, stir evenly, heat to 90℃, keep warm for 3h to obtain copper-titanium synergistic degradation of straw electrolyte.

[0117] 2. Preparation of cathode electrolyte: Weigh 20g of vanadium pentoxide powder and add it to a beaker containing deionized water. Stir at room temperature, then add 100mL of concentrated sulfuric acid (98.3% by mass) to the solution and stir for 12h to prepare a 500mL solution. Then add 2mL of nitric acid (68% by mass) and continue stirring until it turns bright yellow. Let it stand for 24h to obtain the high-valence vanadium cathode electrolyte.

[0118] 3. Battery System Construction and Electrical Performance Testing: The copper-titanium co-degradation straw electrolyte prepared in step 1 was added separately to an 80℃ anolyte tank, while the cathode electrolyte prepared in step 2 was stored in an 80℃ cathode electrolyte tank. The anolyte tank was connected to the anode inlet and outlet of the battery, and the cathode tank was connected to the cathode inlet and outlet of the battery. Simultaneously, high-purity oxygen was introduced into the cathode electrolyte tank at a flow rate of 40 mL / min to reduce tetravalent vanadium, thus regenerating the cathode electrolyte. Oxygen was then introduced into the cathode electrolyte tank, and the battery was operated at 80℃.

[0119] The electrical performance of the fuel cell was tested using the scanning current method. The constructed fuel cell exhibited a maximum voltage of 0.56V and a maximum current density of 830.2mA / cm². 2 The maximum power density is 131 mW / cm³. 2 Both the voltage and power density are far lower than those in this application.

[0120] Comparative Example 6: Fe 3+ / TiO2 composite system with different light sources catalyzing lignin degradation and coupled power generation (referencing patent: CN114551953A)

[0121] 1. Preparation of anolyte: Dissolve 6.75 g of ferric chloride hexahydrate, 2.0 g of nano-titanium dioxide (60 nm), and 4.2 mL of concentrated hydrochloric acid (12 mol / L) in deionized water. Then add 1 g of sodium lignosulfonate to prepare a 25 mL mixed solution consisting of 1 mol / L FeCl3 + 80 g / L nano-titanium dioxide + 40 g / L sodium lignosulfonate (H2O). +The solutions (at a concentration of 2 mol / L) were mixed and transferred to a photoreactor, then placed under sunlight (approximately 30°C) for 4 hours to prepare a solar-induced degradation anolyte. Two more 25 mL portions of the mixture were prepared using the same method and irradiated under xenon lamp and ultraviolet light (room temperature 30°C), respectively, for 4 hours to obtain xenon lamp-induced degradation anolytes and ultraviolet light-induced degradation anolytes, respectively.

[0122] 2. Preparation of cathode electrolyte: 10 g of V₂O₅ was added to 22 mL of water under vigorous stirring. Then, 38 mL of concentrated H₂SO₄ (98%) was added dropwise to the V₂O₅ suspension in an ice bath. The reaction was allowed to proceed for 20 hours. Finally, 1 mL of nitric acid (42%) was added to obtain the cathode electrolyte (vanadium ion concentration 0.8 mol / L, H₂SO₄ concentration 42%). + Concentration: 2.2 mol / L.

[0123] 3. Battery System Construction and Electrical Performance Testing: Fill the S-shaped flow channels within the graphite plate with graphite felt. Then, assemble the battery in the following order: graphite plate, load (LED light) wires, fixed end plate, etc., in the order of metal cover plate, anode graphite plate, polytetrafluoroethylene film, Nafion 117 film, polytetrafluoroethylene film, cathode graphite plate, and metal cover plate. Connect the battery and load with wires. Add the anode electrolyte from step 1 to the anode electrolyte tank at room temperature, and add the cathode electrolyte from step 2 to the cathode electrolyte tank. Then, connect the anode electrolyte tank to the anode inlet / outlet and anode pump of the battery, and connect the cathode tank to the cathode inlet / outlet and cathode pump of the battery to complete the assembly of the power generation device. Introduce oxygen into the cathode electrolyte tank at a flow rate of 40 mL / min, and operate the battery at 80°C.

[0124] After starting the power generation unit, the battery's electrical performance was tested using the scanning current method. The results showed that the battery composed of electrolyte treated with sunlight exhibited the best performance, with a maximum voltage of 0.54V and a maximum current density of 532.7mA / cm². 2 The maximum power density is 64.5 mW / cm³. 2 In comparison, batteries with electrolytes treated with ultraviolet light performed the second best, while batteries with electrolytes treated with hydrogen light performed the worst. Fe 3+ The lignin-based fuel cell constructed using the / TiO2 composite photocatalytic system has a much lower voltage and power density than that described in this application, and lignin cannot be effectively degraded to generate electricity.

[0125] Comparative Example 7: Solar-induced hybrid lignin-based fuel cell (refer to Nat. Commun. 5 (2014) 1–8.)

[0126] 1. Preparation of anolyte: Weigh 10.95g of phosphomolybdic acid (H3(PMo)2)12 O 40 Dissolve the lignin in 20 ml of deionized water, then add 0.3 g of enzymatically hydrolyzed lignin to the solution. Maintain the mixture at 6°C using a circulating water bath. Irradiate the reaction solution with sunlight for 8 hours using a SoLux solar simulator until the solution changes from yellow to dark blue, with the light source 10 cm away from the solution surface.

[0127] 2. Battery system construction and electrical performance testing: The anode uses 5 layers of carbon cloth as the electrode, and the cathode electrode uses 5 layers of carbon cloth with a loading of 60 mg / cm³. 2 A 5% Pt / C catalyst was used, separated by a Nafion 117 membrane. The anolyte prepared in step 1 was added to an anolyte bath at 25°C. The anolyte bath was connected to the anode inlet and outlet of the battery using a tube. High-purity oxygen was introduced into the cathode bath at a flow rate of 40 mL / min.

[0128] The electrical performance of the fuel cell was tested using the scanning current method. The constructed fuel cell exhibited a maximum voltage of 0.36V and a maximum current density of 3.3mA / cm². 2 The maximum power density is 0.55 mW / cm³. 2 Both the voltage and power density are far lower than those in this application.

[0129] Comparative Example 8: Methylene Blue-Mediated Lignin-Based Fuel Cells

[0130] 1. Preparation of anolyte: Weigh 1.6g of methylene blue and dissolve it in 50ml of deionized water. Then add a certain amount of concentrated sulfuric acid (98.3% by mass) to make its concentration in the solution 1mol / L. Add 2g of sodium lignosulfonate to the solution and react the mixture at 45℃ for 5h.

[0131] 2. Preparation of cathode electrolyte: Weigh 13g FeCl3 and dissolve it in 100ml deionized water, then add a certain amount of concentrated sulfuric acid (mass fraction 98.3%) to make its concentration in the solution 1mol / L.

[0132] 3. Battery System Construction and Electrical Performance Testing: The methylene blue-degraded lignin electrolyte prepared in step 1 was added separately to a 90℃ anolyte bath, and the catholyte prepared in step 2 was stored in a 90℃ catholyte bath. The anolyte bath was connected to the anode inlet and outlet of the battery, and the cathode bath was connected to the cathode inlet and outlet of the battery. Simultaneously, high-purity oxygen was introduced into the catholyte bath at a flow rate of 40 mL / min to reduce iron ions and regenerate the catholyte. A proton exchange membrane was used as the ion exchange membrane.

[0133] The electrical performance of the fuel cell was tested using the scanning current method. The constructed fuel cell had a maximum voltage of 0.56V and a maximum power density of 11.41mW / cm³. 2 Both the voltage and power density are far lower than those in this application.

[0134] Comparative Example 9: Hierarchical nickel-iron-phosphide (NiFeP) nanosheets as anode catalysts for lignin-based fuel cells

[0135] 1. Synthesis of NiFeP: First, nickel foam (2cm × 5cm) was ultrasonically treated for 15 minutes each in 6M HCl, ethanol, and water. Then, the cleaned nickel foam was immersed in a solution containing 4 mmol NH4F, 10 mmol urea, 4 mmol Ni(NO3)2·6H2O, 4 mmol Fe(NO3)3·9H2O, and 40 mL H2O. The mixture was transferred to a 50 mL high-pressure reactor and hydrothermally treated at 120 °C for 6 h. After hydrothermal treatment, the nickel foam was separated from the solution, ultrasonically washed at room temperature, and dried at 60 °C. The nickel foam and 1.0 g NaH2PO2·H2O were placed in two ceramic boats in a tube furnace, with the NaH2PO2·H2O positioned upstream of the gas flow. The furnace was heated to 300 °C at a heating rate of 2 °C / min and held at this temperature for 2 h under argon protection. After synthesis, the nickel foam was cut into 2cm × 2.5cm pieces and used directly as the anode.

[0136] 2. Preparation of anolyte: Weigh 2.8g KOH and dissolve it in 50ml deionized water. Then weigh 2.5g of enzymatically hydrolyzed lignin and add it to the solution. Stir for 10min and filter to obtain the anolyte of lignin alkaline solution.

[0137] 3. Preparation of cathode electrolyte: Weigh 13.5g of ferric chloride hexahydrate and dissolve it in 100ml of deionized water to obtain the cathode electrolyte of ferric chloride solution.

[0138] 4. Battery System Construction and Electrical Performance Testing: The battery consists of two graphite bipolar plates, serving as the anode and cathode electrodes, respectively. A membrane electrode assembly (MEA) is sandwiched between the two bipolar plates, dividing the fuel cell into an anode chamber and a cathode chamber. The effective area is 5 cm². 2 The MEA consists of an anode, a Nafion membrane, and carbon cloth as the cathode backing layer. A peristaltic pump continuously circulates the prepared anolyte and catholyte through the cathode and anode chambers at a flow rate of 20 ml / min. The battery operates at 90°C.

[0139] The electrical performance of the fuel cell was tested using the scanning current method. The constructed fuel cell had a maximum voltage of 1.49V and a maximum power density of 24mW / cm³. 2 The power density is much lower than that of this application.

[0140] Comparative Example 10: Morphology of graphite felt / manganese cobalt oxide electrodes prepared with different raw material ratios and power generation performance of the assembled batteries

[0141] 1. Preparation of graphite felt / manganese cobalt oxide nanosphere electrode: 2 mmol Co(NO3)2·6H2O, 1 mmol Mn(NO3)2·6H2O, 5 mmol NH4F, and 5 mmol urea were dissolved in 50 ml of deionized water. A 5 cm × 0.5 cm × 0.5 cm graphite felt was then added and impregnated. The mixture was placed in a high-pressure reactor and hydrothermally heated at 140 °C for 6 h. After the reaction was complete, the sample was removed, washed several times with deionized water, and dried.

[0142] 2. Preparation of anolyte: Weigh 2g of NaOH and dissolve it in 50ml of deionized water. Then weigh 1g of enzymatically hydrolyzed lignin and add it to the solution. Stir for 10 minutes and then filter to obtain the anolyte of lignin alkaline solution.

[0143] 3. The preparation of the cathode electrolyte is the same as in Example 1.

[0144] 4. Battery System Construction and Electrical Performance Testing: Graphite felt / manganese cobalt oxide is filled into the S-shaped flow channel within the anode graphite plate as the anode electrode, and graphite felt is filled into the S-shaped flow channel within the cathode graphite plate as the cathode electrode. Then, the graphite plate, load (LED light) wires, and fixing end plates are assembled into the battery in the following order: metal cover plate, anode graphite plate containing graphite felt / manganese cobalt oxide, polytetrafluoroethylene film, Nafion 211 film, polytetrafluoroethylene film, cathode graphite plate containing graphite felt, and metal cover plate. The battery and load are connected with wires. The electrolyte from step 2 is added to the anode electrolyte tank, and the electrolyte from step 3 is added to the cathode electrolyte tank. The anode electrolyte tank is connected to the anode inlet and outlet of the battery, and the cathode tank is connected to the cathode inlet and outlet of the battery. Oxygen is introduced into the cathode electrolyte tank at a flow rate of 40 mL / min, and the battery is operated at 90°C.

[0145] The battery's electrical performance was tested using the scanning current method, and the results are as follows: Figure 13 As shown, a lignin-based fuel cell using graphite felt / manganese cobalt oxide nanospheres as the anode has a voltage of 1.4V and a maximum power density of 134.45mW / cm³. 2 The battery performance is lower than that of batteries using graphite felt / manganese cobalt oxide nanowires as the anode electrode.

[0146] The SEM images of the graphite felt / manganese cobalt oxide electrode in this comparative example are as follows: Figure 14 As shown, when the raw material concentration is low, graphite felt / manganese cobalt oxide nanowire electrodes cannot be prepared; instead, graphite felt / manganese cobalt oxide nanosphere electrodes are prepared, and their distribution on the graphite felt surface is relatively scattered, which is not conducive to catalytic degradation of lignin for power generation.

[0147] Summarize

[0148] Table 1 is a comprehensive comparison of the above embodiments and comparative examples in terms of operating temperature, open-circuit voltage, and maximum power density.

[0149] Table 1. Comprehensive Comparison of Lignin-Based Fuel Cell Systems

[0150]

[0151]

[0152] Comparing all the examples and comparative examples, it is evident that the battery with the best power generation performance is the lignin-based fuel cell system constructed using enzymatically hydrolyzed lignin as a raw material in Example 5, with an open-circuit voltage of 1.6V and a maximum power density of 209.56mW / cm³. 2 This is far higher than the comparative ratio.

[0153] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A lignin-based fuel cell comprising an anolyte, a catholyte, a cathode electrode and an anode electrode, characterized in that: The anode electrolyte is prepared by dissolving lignin in an alkaline solution, the cathode electrolyte is prepared by using pentavalent vanadium salt, acid solution and cathode regenerative oxidant, the cathode electrode is graphite felt electrode, and the anode electrode is graphite felt / manganese cobaltate nanowire electrode; The graphite felt / manganese cobaltate nanowire electrode is prepared by the following steps: dissolving Mn(NO3)2·6H2O, Co(NO3)2·6H2O, urea and ammonium fluoride in water to obtain a hydrothermal reaction solution; placing the graphite felt in the hydrothermal reaction solution, and performing hydrothermal reaction in a high-pressure reaction kettle; taking out the sample after the reaction, washing, drying to obtain the graphite felt / manganese cobaltate nanowire electrode; the molar ratio of Mn(NO3)2·6H2O, Co(NO3)2·6H2O, urea and ammonium fluoride is 0.5-3:1-3:7-12:3-6; the temperature of the hydrothermal reaction is 20-200℃, and the time of the hydrothermal reaction is 1-20h.

2. A lignin-based fuel cell according to claim 1, wherein, The lignin is at least one of enzymatic hydrolysis lignin, pre-hydrolysis lignin, sodium lignosulfonate and alkali lignin; the alkali is one or two of KOH, NaOH and ammonia water.

3. The lignin-based fuel cell of claim 1, wherein, The concentration of hydroxyl ions of the alkali in the anode electrolyte is 0.05-5.0mol / L. The content of lignin molecules in the anode electrolyte is 1-100g / L.

4. The lignin-based fuel cell of claim 1, wherein, The operating temperature of the lignin-based fuel cell is 10-120℃.

5. The lignin-based fuel cell of claim 1, wherein, The molar ratio of Mn(NO3)2·6H2O, Co(NO3)2·6H2O, urea and ammonium fluoride is 1:2:10:

4.

6. The lignin-based fuel cell of claim 1, wherein, The temperature of the hydrothermal reaction in the preparation of the graphite felt / manganese cobaltate nanowire electrode used in the anode of the lignin-based fuel cell is 50-150℃, and the time of the hydrothermal reaction is 5-7h.

7. The lignin-based fuel cell of claim 1, wherein, The graphite felt is calcined to remove the organic matters attached on the surface before use, the calcination temperature is 200-600℃, the calcination time is 0.5-20h, and the heating rate is 1-50℃ / min.

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