A lignin-based fuel cell

Abstract

The present application belongs to the field of high-value utilization of biomass waste, and particularly relates to a lignin-based fuel cell. The lignin-based fuel cell comprises an anode electrolyte and a cathode electrolyte, wherein the anode electrolyte comprises lignin and alkali. The lignin is at least one of alkali lignin, sodium lignosulfonate, enzymatic hydrolysis lignin and pre-hydrolysis lignin. The present application adopts a lignin solution as an anode electrolyte to construct a lignin-based self-power generation fuel cell system, without additional addition of an electron transfer agent and an oxidant, so that the lignin can realize low-temperature (25-90 DEG C) high-efficiency power generation (the highest power density is 159.9 mW / cm 2 ), and can be simultaneously subjected to structural modification, so that the lignin macromolecule is degraded into small molecules containing rich active functional groups, and has good application prospect in the fields of high polymer materials and fine chemicals.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of high-value utilization of biomass waste, and particularly relates to a lignin-based fuel cell. BACKGROUND

[0002] At present, people have developed various fuel cell technologies using lignocellulose and its derivatives as raw materials, mainly four kinds: solid oxide fuel cell, direct carbon fuel cell, microbial fuel cell, and biomass flow fuel cell. Solid oxide fuel cell and direct carbon fuel cell need to operate under harsh conditions of high temperature (500-1000℃), which does not conform to the concept of green development. Microbial fuel cell can operate at room temperature and normal pressure, but the low output power limits its popularization and application. Biomass flow fuel cell can realize electric energy output at a lower temperature and is a new type of efficient and green power generation technology. The currently disclosed biomass flow fuel cells all need to add catalytic oxidants to degrade biomass and transfer electrons, thereby realizing power generation. For example, polyoxometalate, K3[Fe(CN)6], FeCl3, CuCl2, etc. are used as oxidants and electron carriers to degrade biomass such as glucose, starch, straw, and sugarcane residue at low temperature (≤110℃) to realize power generation. Some researchers have also proposed biomass flow fuel cells driven by light, which use photocatalysts to decompose biomass and capture their electrons, and use photo-thermal catalysis to convert biomass into high-power output electricity. However, the existing various biomass flow cell technologies not only increase the cost due to the additional addition of catalytic oxidants, but also have other shortcomings, such as the presence of impurity ions in the oxidized and degraded biomass, long pre-degradation time of biomass heating (light), and low power density of the cell. In addition, the current biomass flow fuel cells simply use catalytic oxidants to oxidize biomass, without developing and utilizing different characteristics of different types of biomass. Lignin is the second largest renewable biomass resource after cellulose. Compared with cellulose, lignin has functional groups such as phenolic hydroxyl and alcoholic hydroxyl that can release electrons, and therefore is a good fuel cell power generation raw material.

[0003] Although the biomass flow fuel cell is a green and clean power generation technology, it has four shortcomings:

[0004] (1) The oxidized and degraded biomass contains impurity ions (Fe 3+ , Cu 2+ , etc.);

[0005] (2) The pre-degradation time of biomass heating (light) is long (usually 1-10h), which requires additional energy consumption;

[0006] (3) The cell operates at a high temperature (about 100℃) and has a low power density (usually less than 100mW / cm 2 );

[0007] (4) In the existing acid system battery, alkali lignin, enzymatic lignin and the like have poor solubility.

[0008] The current biomass flow fuel cell technology mainly uses metal salts to oxidize biomass, and the metal salts are converted from high valence state to low valence state (a process of storing electrons), thereby preparing an anode electrolyte with low potential, and forming a potential difference with a cathode electrolyte, so as to realize the transfer of anode and cathode electrons and output electric energy. However, the metal salts (such as FeCl3, CuCl2, etc.) used will cause the oxidized biomass to contain impurity ions, and the impurity ions will be complexed with the biomass, so that the impurity ions cannot be completely removed, which will affect the development and utilization of the downstream products of the biomass. At the same time, the time for synchronously preparing the anode electrolyte by heating and pre-degradation of the biomass is relatively long (usually 1-10h), and this part of heating needs additional energy consumption, thereby reducing the net output electric energy of the battery system. Moreover, the heating and pre-degradation is an intermittent process, which leads to that the battery system cannot be continuously operated in industry. In addition, the currently disclosed biomass flow fuel cell is an acid system, and alkali lignin, enzymatic lignin and the like have poor solubility under acid conditions, and have good solubility under alkaline conditions, so it is necessary to develop an alkaline fuel cell system. SUMMARY

[0009] In order to solve the defects and shortcomings of the prior art, the present application provides a lignin-based fuel cell. The fuel cell provided by the present application can release electrons from part of the functional groups and valence bonds of lignin under the action of the potential difference between the anode and the cathode, thereby supplying power to the outside and synchronously degrading lignin into small molecules. No catalytic oxidant is needed as an electron transfer body, and no pre-degradation is needed. Therefore, compared with the prior art, the problems of residual catalytic oxidant and energy consumption in pre-degradation are avoided. Furthermore, the anode electrolyte of the present application adopts an alkaline system, and alkali lignin, enzymatic lignin and the like have high solubility, high energy density and are not easy to block the battery, thereby solving the problems of low solubility and easy precipitation of alkali lignin, enzymatic lignin and the like under acid conditions, and blocking the battery.

[0010] The object of the present application is achieved by the following technical solutions:

[0011] A lignin-based fuel cell comprises an anode electrolyte and a cathode electrolyte, wherein the anode electrolyte comprises lignin and an alkali.

[0012] Preferably, the lignin is at least one of alkali lignin, sodium lignosulfonate, enzymatic lignin, pre-hydrolysis lignin and the like.

[0013] Preferably, the alkali is at least one of NaOH, KOH, ammonia and the like.

[0014] Preferably, the concentration of the base in the anolyte is 0.001-8 mol / L, more preferably 0.1-4 mol / L, and most preferably 1-2 mol / L.

[0015] Preferably, the content of the lignin in the anolyte is 0.01-80 g / L, more preferably 0.1-60 g / L, and most preferably 0.5-40 g / L.

[0016] Preferably, the operating temperature of the lignin-based fuel cell is 10-100℃, more preferably 10-90℃, and most preferably 25-90℃.

[0017] The catholyte comprises a pentavalent vanadium salt, an acid solution, and a cathode regenerative oxidant.

[0018] Preferably, the pentavalent vanadium salt is selected from at least one of vanadium pentoxide, vanadyl sulfate, and vanadyl nitrate.

[0019] Preferably, the acid solution is selected from at least one of an aqueous hydrochloric acid solution, an aqueous sulfuric acid solution, and an aqueous nitric acid solution.

[0020] Preferably, the cathode regenerative oxidant is selected from at least one of nitric acid, oxygen, hydrogen peroxide, or potassium permanganate.

[0021] Preferably, the concentration of the pentavalent vanadium salt in the catholyte is 0.05-5 mol / L.

[0022] The concentration of the acid in the catholyte is 0.05-8.0 mol / L.

[0023] When the cathode regenerative oxidant is nitric acid, its concentration in the catholyte is 0.01-8 mol / L; when the cathode regenerative oxidant is oxygen, its flow rate is 30-100 mL / min.

[0024] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0025] 1. Based on the liquid flow fuel cell technology, the present application realizes the room-temperature high-efficiency conversion of lignin into electric energy without adding an electron transport body and an oxidant. The open-circuit voltage (up to 1.67 V), power density (the maximum power density is 159.9 mW / cm 2 ), long-time discharge stability, and other power generation performances of the cell under optimal conditions are at the leading level in the existing research.

[0026] 2. The present application modifies the structure of lignin while generating electricity. The low-molecular-weight lignin obtained after electricity generation has potential applications in high-molecular-weight materials and fine chemicals. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 Current density-voltage-output power graph of the lignin-based fuel cell based on different concentrations of NaOH for Example 1 was constructed.

[0028] Figure 2 Current density-voltage-output power graph of the lignin-based fuel cell based on different operating temperatures for Example 2 was constructed.

[0029] Figure 3 Current density-voltage-output power graph of the lignin-based fuel cell based on different kinds of lignin for Example 3 was constructed.

[0030] Figure 4 Time-current density-voltage graph of long-time operation of the cell for Example 4.

[0031] Figure 5 Molecular weight comparison graph of alkali lignin before and after 8h continuous power generation for Example 5.

[0032] Figure 6 Two-dimensional nuclear magnetic resonance spectrum of alkali lignin before and after power generation: (a) side chain region of original alkali lignin; (b) side chain region of alkali lignin after 4h power generation; (c) aromatic region of original lignin; (d) aromatic region of alkali lignin after 4h power generation for Example 6.

[0033] Figure 7 Current density-voltage-output power graph of the cell operated at room temperature for Example 7.

[0034] Figure 8 Time-current-voltage graph of long-time operation of the stack at room temperature for Example 8.

[0035] Figure 9 Current density-voltage-output power graph of the cell constructed by heating degradation of alkali lignin with potassium ferricyanide at different temperatures for Comparative Example 1.

[0036] Figure 10 Current density-voltage-output power graph of the cell constructed by light degradation of alkali lignin with potassium ferricyanide under different light sources for Comparative Example 2.

[0037] Figure 11 Current density-voltage-output power graph of the cellulose-based fuel cell for Comparative Example 3. DETAILED DESCRIPTION

[0038] The present application will be further described in conjunction with the examples and the accompanying drawings, but the embodiments of the present application are not limited thereto. The raw materials involved in the present application can be directly purchased from the market. For the process parameters not specifically mentioned, the conventional techniques can be referred to.

[0039] The alkali lignin, sodium lignosulfonate and enzymatic hydrolysis lignin used in the following examples and comparative examples were purchased from Shandong Longli Biological Technology Co., Ltd.

[0040] Example 1: Comparison of performance of lignin-based fuel cells based on different concentrations of NaOH solution in anode

[0041] 1. Preparation of anode electrolyte: 2 portions of 50 mL NaOH solution (concentration of 1 mol / L and 2 mol / L, respectively) were prepared, and 2 g of alkali lignin was added to each portion, which was stirred until completely dissolved to prepare the anode electrolyte.

[0042] 2. Preparation of cathode electrolyte: 2 g of V2O5 powder and 7.6 mL of concentrated sulfuric acid (mass fraction 98.3%) were measured and added to deionized water and stirred until uniform, and then 0.4 mL of concentrated nitric acid (mass fraction 68%) was added to prepare a 50 mL solution. This solution was prepared in two portions.

[0043] 3. Construction of cell system and test of power generation performance: the anode electrolyte prepared in step 1 was added to the anode electrolyte tank, and the cathode electrolyte prepared in step 2 was added to the cathode electrolyte tank. The anode electrolyte tank was connected to the anode inlet and outlet of the cell with a tube, and the cathode tank was connected to the cathode inlet and outlet of the cell. The operating temperature of the cell was 90°C. At the same time, high-purity oxygen was introduced into the cathode tank at a flow rate of 40 mL / min to reduce the tetravalent vanadium and regenerate the cathode electrolyte. The electrical performance of the cell was tested by the scanning current method, and the results are shown in Figure 1 It can be seen that the power generation performance of the cell constructed by high-concentration NaOH solution is better than that of the cell constructed by low-concentration NaOH solution. This is because high-concentration NaOH can make the dissolution of alkali lignin more sufficient, which enhances the electron transfer kinetics, and higher NaOH concentration also makes the acid-base concentration difference between the anode and the cathode higher, thereby increasing the electron transfer rate of the electrode reaction.

[0044] Example 2: Comparison of performance of lignin-based fuel cells based on different operating temperatures

[0045] 1. Preparation of anode electrolyte: 3 portions of 50 mL NaOH solution (concentration of 2 mol / L) were prepared, and 2 g of alkali lignin was added to each portion, which was stirred until completely dissolved to prepare the anode electrolyte.

[0046] 2. Preparation of cathode electrolyte: 2 g of V2O5 powder and 7.6 mL of concentrated sulfuric acid (mass fraction 98.3%) were measured and added to deionized water and stirred until uniform, and then 0.4 mL of concentrated nitric acid (mass fraction 68%) was added to prepare a 50 mL solution. This solution was prepared in three portions.

[0047] 3. Cell system construction and power generation performance test: The anolyte prepared in step 1 was added to the anolyte tank, and the catholyte prepared in step 2 was added to the catholyte tank. The anolyte tank was connected to the anode inlet and outlet of the cell with a tube, and the cathode tank was connected to the cathode inlet and outlet of the cell. The operating temperature of the three groups of cells was 70, 80, and 90°C, respectively. At the same time, high-purity oxygen was introduced into the cathode tank at a flow rate of 40 mL / min to reduce the tetravalent vanadium and regenerate the catholyte. The electrical performance of the cell was tested by the scanning current method, and the results are shown in Figure 2 As the temperature increases, the power generation performance of the cell is better. Increasing the temperature can accelerate the electron transfer rate, thereby obtaining higher output power.

[0048] Example 3: Comparison of the performance of lignin-based fuel cells based on different types of lignin

[0049] 1. Preparation of anolyte: Prepare 3 portions of 50 mL NaOH solution (concentration 2 mol / L), and add alkali lignin, enzymatic lignin, and lignin sulfonate sodium with a mass of 2 g each, and stir until completely dissolved to prepare the anolyte.

[0050] 2. Preparation of catholyte: Measure 2 g of V2O5 powder and 7.6 mL of concentrated sulfuric acid (mass fraction 98.3%) and add to deionized water and stir until uniform, then add 0.4 mL of concentrated nitric acid (mass fraction 68%) and prepare 50 mL of solution. Prepare 3 portions of this solution.

[0051] 3. Cell system construction and power generation performance test: The anolyte prepared in step 1 was added to the anolyte tank, and the catholyte prepared in step 2 was added to the catholyte tank. The anolyte tank was connected to the anode inlet and outlet of the cell with a tube, and the cathode tank was connected to the cathode inlet and outlet of the cell. The operating temperature of the three groups of cells was 70, 80, and 90°C, respectively. At the same time, high-purity oxygen was introduced into the cathode tank at a flow rate of 40 mL / min to reduce the tetravalent vanadium and regenerate the catholyte. The electrical performance of the cell was tested by the scanning current method, and the results are shown in Figure 3 As shown in the figure, when enzymatic lignin is used as a power generation raw material, the power generation performance is the best, with an open-circuit voltage of 1.67 V and a maximum power density of 159.9 mW / cm 2 Due to the differences in the content of phenolic hydroxyl and alcoholic hydroxyl groups and the differences in the structure of side chain groups in different types of lignin, the power generation performance of the cell composed of different types of lignin is different.

[0052] Example 4: Continuous and stable power generation test (90°C)

[0053] 1. Preparation of anolyte: 500 mL of NaOH solution (2 mol / L) was prepared, 5 g of alkali lignin was added and stirred until completely dissolved to obtain an anolyte.

[0054] 2. Preparation of catholyte: 20 g of V2O5 powder and 76 mL of concentrated sulfuric acid (mass fraction 98.3%) were measured and added to deionized water and stirred until uniform, and then 4 mL of concentrated nitric acid (mass fraction 68%) was added to prepare a 500 mL solution.

[0055] 3. Construction of battery system and test of power generation performance: the anolyte prepared in step 1 was added to the anolyte tank, and the catholyte prepared in step 2 was added to the catholyte tank. The anolyte tank was connected to the anode inlet and outlet of the battery with a tube, and the catholyte tank was connected to the cathode inlet and outlet of the battery. The battery was operated at a temperature of 90°C. At the same time, the catholyte tank was added with concentrated nitric acid (mass fraction 68%) at a rate of 0.5 mL / min, and oxygen was introduced at a rate of 40 mL / min to reduce the tetravalent vanadium ions and regenerate the catholyte. The continuous power generation test was carried out at a voltage of 0.4 V, and the results are shown in Figure 4 . The output current density of the battery was stable at 360 mA / cm 2 , and there was no obvious current fluctuation. The battery was stably operated for 8 h, indicating that the battery had good continuity and stability.

[0056] Example 5: Test of molecular weight of lignin before and after power generation

[0057] 1. Extraction of lignin after power generation: the alkali lignin solution of the anode in Example 4 was neutralized with hydrochloric acid until the solution was neutral, and solid was precipitated. After centrifugation, washing and drying, the alkali lignin after power generation was obtained.

[0058] 2. Acetylation of lignin: the original alkali lignin and the lignin after power generation were respectively diluted in 2 mL of pyridine / acetic anhydride (1:1 by volume) and stirred in the dark for 72 hours. After the reaction was completed, the product was added to a hydrochloric acid solution, filtered, centrifuged and freeze-dried.

[0059] 3. GPC test: after acetylation, the two kinds of lignin were respectively dissolved in THF, and the molecular weight distribution of each kind of lignin was determined by GPC (Agilent 1260), and the results are shown in Figure 5 . The GPC data are shown in Table 1. The weight average molecular weight and the number average molecular weight of the lignin after power generation decreased compared with the original alkali lignin, indicating that the macromolecular lignin was oxidatively degraded into small molecular lignin. The decrease of PDI (polymer dispersity index) indicates that the molecular weight distribution of the lignin becomes more uniform after power generation.

[0060] Table 1 GPC data

[0061]

[0062] Example 6: Two-dimensional nuclear magnetic test before and after power generation

[0063] 1. Extraction of lignin after power generation: The alkali lignin solution after power generation for 4h was neutralized with hydrochloric acid until the solution was neutral, and solid was precipitated. After centrifugation, washing and drying, the alkali lignin after power generation was obtained.

[0064] 2. Two-dimensional nuclear magnetic test: The original lignin and the lignin after power generation for 4h were respectively dissolved in deuterated reagent, and a 600MHz all-digital superconducting nuclear magnetic resonance instrument (NMR) was used for testing, and the results are shown in Figure 6 From the two-dimensional nuclear magnetic results, it can be seen that the structures of β-O-4, β-β, β-5, Gly and the like are damaged to different degrees, and part of the side chain is broken, but the aromatic structure of lignin is basically retained, and the lignin does not undergo polycondensation.

[0065] Example 7: Cell running at room temperature (25℃)

[0066] 1. Preparation of anode electrolyte: 50mL of NaOH solution (concentration 2mol / L) was prepared, 2g of alkali lignin was added and stirred until completely dissolved to prepare the anode electrolyte.

[0067] 2. Preparation of cathode electrolyte: 2g of V2O5 powder and 7.6mL of concentrated sulfuric acid (mass fraction 98.3%) were weighed and added to deionized water and stirred uniformly, and then 0.4mL of concentrated nitric acid (mass fraction 68%) was added to prepare a 50mL solution.

[0068] 3. Construction of cell system and test of power generation performance: The anode electrolyte prepared in step 1 was added to the anode electrolyte tank, and the cathode electrolyte prepared in step 2 was added to the cathode electrolyte tank. The anode electrolyte tank was connected to the anode inlet and outlet of the cell with a tube, and the cathode tank was connected to the cathode inlet and outlet of the cell. The operating temperature of the cell was room temperature (25℃). At the same time, high-purity oxygen was introduced into the cathode tank at a flow rate of 40mL / min to reduce tetravalent vanadium and regenerate the cathode electrolyte. The electrical performance of the cell was tested by the scanning current method, and the results are shown in Figure 7 The constructed cell at room temperature runs normally, the open circuit voltage reaches 1.36V, the maximum power density reaches 57.0mW / cm 2 , and no additional energy is needed for heating during power generation at room temperature, realizing direct output of electrical energy.

[0069] Example 8: Continuous and stable power generation test (25℃)

[0070] 1. Preparation of anode electrolyte: 500 mL of NaOH solution (2 mol / L) was prepared, 5 g of alkali lignin was added and stirred until completely dissolved to prepare the anode electrolyte.

[0071] 2. Preparation of cathode electrolyte: 20 g of V2O5 powder and 76 mL of concentrated sulfuric acid (mass fraction 98.3%) were measured and added to deionized water and stirred until uniform, and then 4 mL of concentrated nitric acid (mass fraction 68%) was added to prepare a 500 mL solution.

[0072] 3. Power generation performance test using a battery stack: the anode electrolyte prepared in step 1 was added to the anode electrolyte tank, and the cathode electrolyte prepared in step 2 was added to the cathode electrolyte tank. The anode electrolyte tank was connected to the anode inlet and outlet of the battery stack with a tube, and the cathode tank was connected to the cathode inlet and outlet of the battery stack. The battery operating temperature was 25℃. At the same time, the cathode electrolyte tank was added with concentrated nitric acid (mass fraction 68%) at a rate of 0.5 mL / min, and oxygen was introduced at a rate of 40 mL / min to reduce the tetravalent vanadium ions with oxygen, thereby regenerating the cathode electrolyte. The continuous power generation test was carried out at a voltage of 0.5 V, and the results are shown in Figure 8 . The output current of the battery stabilized at 900 mA without obvious current fluctuation, and the stable operation lasted for 2 h, indicating that the battery had good continuity and stability.

[0073] Comparative Example 1: Comparison of power generation performance of fuel cells based on pre-degradation of alkali lignin by heating potassium ferricyanide at different temperatures

[0074] 1. Preparation of anode electrolyte: 6.585 g of K3[Fe(CN)6] and 4 g of NaOH were weighed and added to deionized water and stirred until uniform to prepare a 50 mL solution. Then 2 g of alkali lignin was added and stirred until completely dissolved. The above solution was prepared in three portions and pre-degraded at 50, 70 and 90℃ for 30 min to prepare three anode electrolytes.

[0075] 2. Preparation of cathode electrolyte: 6.585 g of K3[Fe(CN)6] and 4 g of NaOH were weighed and added to deionized water and stirred until uniform to prepare a 50 mL solution as the cathode electrolyte. This solution was prepared in three portions.

[0076] 3. Battery system construction and power generation performance test: the anode electrolyte prepared in step 1 was added to the anode electrolyte tank, and the cathode electrolyte prepared in step 2 was added to the cathode electrolyte tank. The anode electrolyte tank was connected to the anode inlet and outlet of the battery with a tube, and the cathode tank was connected to the cathode inlet and outlet of the battery. The operating temperatures of the three groups of batteries were 50, 70 and 90℃, respectively. At the same time, high-purity oxygen was introduced into the cathode tank at a flow rate of 40 mL / min to reduce ferricyanide with oxygen, thereby regenerating the cathode electrolyte. The electrical performance of the battery was tested by the scanning current method, and the results are shown inFigure 9 As shown, the power generation performance is best when the battery operates at 90℃. Under heating driving, the alkali lignin in the anode electrolyte tank reacts with [Fe(CN)6] 3− to generate [Fe(CN)6] 4− , transports [Fe(CN)6] 4− to the anode to release electrons and regenerate [Fe(CN)6] 3− , [Fe(CN)6] 3− returns to the anode electrolyte tank for recycling. The electrons released by the anode are transferred to the cathode through an external circuit to achieve power generation. Higher pre-degradation temperature helps to improve the conversion rate of [Fe(CN)6] 3− , and higher battery operating temperature helps to improve the electron transport rate. Therefore, by increasing the pre-degradation temperature and the battery operating temperature, the power generation performance of the battery can be improved.

[0077] Comparative Example 2: Comparison of power generation performance of fuel cells constructed based on potassium ferricyanide light pre-degradation of alkali lignin under different light sources

[0078] 1. Preparation of anode electrolyte: weigh 6.585g K3[Fe(CN)6] and 4g NaOH, add deionized water and stir until uniform, prepare 50mL solution. Add 2g alkali lignin and stir until completely dissolved. The above solution is prepared in two portions, which are respectively irradiated under xenon lamp and sunlight for 30min to prepare two anode electrolytes.

[0079] 2. Preparation of cathode electrolyte: weigh 6.585g K3[Fe(CN)6] and 4g NaOH, add deionized water and stir until uniform, prepare 50mL solution as cathode electrolyte. This solution is prepared in two portions.

[0080] 3. Construction of battery system and test of power generation performance: add the anode electrolyte prepared in step 1 to the anode electrolyte tank, and add the cathode electrolyte prepared in step 2 to the cathode electrolyte tank. Connect the anode electrolyte tank with the anode inlet and outlet of the battery with a tube, and connect the cathode tank with the cathode inlet and outlet of the battery. At the same time, pass high-purity oxygen into the cathode tank at a flow rate of 40mL / min to reduce ferricyanide and regenerate the cathode electrolyte. The electrical performance of the battery is tested by scanning current method, and the results are shown in Figure 10 As shown, the power generation performance of the xenon lamp irradiation group is better than that of the sunlight irradiation group, because the xenon lamp used in the laboratory is controlled by a stable power supply to keep the light intensity constant, which can supply stable light energy to the reaction system. However, the sunlight in nature usually cannot output light energy stably, which determines the conversion rate of [Fe(CN)6] 3− and the degradation degree of alkali lignin, thereby affecting the power generation performance of the battery.

[0081] Comparative Example 3: Cellulose-based fuel cell system power generation performance

[0082] 1. Preparation of anode electrolyte: 50 mL of NaOH solution (2 mol / L) was prepared, 0.25 g of cellulose was added and stirred until completely dissolved to prepare the anode electrolyte.

[0083] 2. Preparation of cathode electrolyte: 2 g of V2O5 powder and 7.6 mL of concentrated sulfuric acid (mass fraction 98.3%) were weighed and added to deionized water and stirred until uniform, then 0.4 mL of concentrated nitric acid (mass fraction 68%) was added to prepare a 50 mL solution.

[0084] 3. Cell system construction and power generation performance test: the anode electrolyte prepared in step 1 was added to the anode electrolyte tank, and the cathode electrolyte prepared in step 2 was added to the cathode electrolyte tank. The anode electrolyte tank was connected to the anode inlet and outlet of the cell with a tube, and the cathode tank was connected to the cathode inlet and outlet of the cell. The cell was operated at a temperature of 90°C. At the same time, high-purity oxygen was introduced into the cathode tank at a flow rate of 40 mL / min to reduce the tetravalent vanadium and regenerate the cathode electrolyte. The electrical performance of the cell was tested by the scanning current method, and the results are shown in Figure 11 , the open-circuit voltage is only 1.32 V, and the maximum power density is only 60.1 mW / cm 2 . It can be seen that the power generation performance of the cellulose-based fuel cell system is far inferior to that of the lignin-based fuel cell system. This is because the abundant alcohol hydroxyl and phenolic hydroxyl structures of lignin can release electrons, and the solubility of lignin in alkaline conditions is higher than that of cellulose. The above two conditions make the lignin-based fuel cell have greater energy storage capacity and faster electron transmission rate, thus obtaining more excellent power generation performance.

[0085] Comparative Example 4: Power generation performance of fuel cell constructed by heating and pre-degrading straw with copper chloride

[0086] 1. Preparation of anode electrolyte: 17.05 g of copper chloride dihydrate and 8.33 mL of concentrated hydrochloric acid were dissolved in deionized water, then 1.67 g of straw was added, the mixture was stirred and then heated to 90°C, and the reaction was maintained for 3 h to prepare the anode electrolyte.

[0087] 2. Preparation of cathode electrolyte: 2 g of V2O5 powder and 7.6 mL of concentrated sulfuric acid (mass fraction 98.3%) were weighed and added to deionized water and stirred until uniform, then 0.4 mL of concentrated nitric acid (mass fraction 68%) was added to prepare a 50 mL solution.

[0088] 3. Cell system construction and power generation performance test: The anolyte prepared in step 1 was added to the anolyte tank, and the catholyte prepared in step 2 was added to the catholyte tank. The anolyte tank was connected to the anode inlet and outlet of the cell with a tube, and the catholyte tank was connected to the cathode inlet and outlet of the cell. The cell was operated at a temperature of 90°C. At the same time, high-purity oxygen was introduced into the catholyte tank at a flow rate of 40 mL / min to reduce the tetravalent vanadium and regenerate the catholyte. The electrical performance of the cell was tested by the scanning current method, and the test results are shown in Table 2.

[0089] Example 5: Power generation performance of a fuel cell constructed by heating and pre-degrading glucose with iron chloride

[0090] 1. Preparation of anolyte: 20.27 g of iron chloride hexahydrate and 13.9 mL of concentrated hydrochloric acid were dissolved in deionized water, and then only 4.5 g of glucose was added to prepare a mixed solution of 50 mL. After stirring uniformly, it was heated to 90°C and kept for 1 h to prepare the anolyte.

[0091] 2. Preparation of catholyte: 2 g of V2O5 powder and 7.6 mL of concentrated sulfuric acid (mass fraction of 98.3%) were added to deionized water and stirred uniformly, and then 0.4 mL of concentrated nitric acid (mass fraction of 68%) was added to prepare a 50 mL solution.

[0092] 3. Cell system construction and power generation performance test: The anolyte prepared in step 1 was added to the anolyte tank, and the catholyte prepared in step 2 was added to the catholyte tank. The anolyte tank was connected to the anode inlet and outlet of the cell with a tube, and the catholyte tank was connected to the cathode inlet and outlet of the cell. The cell was operated at a temperature of 90°C. At the same time, high-purity oxygen was introduced into the catholyte tank at a flow rate of 40 mL / min to reduce the tetravalent vanadium and regenerate the catholyte. The electrical performance of the cell was tested by the scanning current method, and the test results are shown in Table 2.

[0093] Example 6: Lignin-based fuel cell with Pt / C catalyst loaded on the cathode

[0094] 1. Preparation of anolyte: (1) Heating pretreatment method: 0.5 g of alkali lignin was prepared into a 100 mL suspension, and then mixed with 100 mL of 5 mol / L NaOH solution. The solution was placed in a round-bottom flask and heated in a water bath at 80°C for 2 h. Then the treated alkali lignin solution was mixed with methyl viologen (MV) solution uniformly according to a volume ratio of 2:1. (2) Light pretreatment method: The suspension of alkali lignin was mixed with an equal volume of 5 mol / L NaOH solution, and then treated under ultraviolet light with a wavelength of 253.7 nm for 24 h. The mixture was mixed with MV solution uniformly according to a volume ratio of 2:1.

[0095] 2. Preparation of cathode catalytic membrane: carbon cloth was immersed in 60% FTFE and burned in a muffle furnace to make a hydrophobic carbon cloth with a FTFE mass fraction of 30%; a suspension made of carbon black and 40% FTFE was evenly applied to one side of the carbon cloth to make a diffusion layer of the carbon cloth, and the other side was a catalytic layer, a suspension made of 10% Pt / C catalyst, isopropyl alcohol and Nafion solution was applied. Air dry overnight, the cathode catalytic membrane is completed.

[0096] 3. Cell system construction and power generation performance test: the fuel cell shell was assembled by two 10 mm thick organic glass plates and a 20 mm thick organic glass middle plate, the center chamber was a cylindrical inner chamber with a diameter of 30 mm and a total volume of 12 mL, and there were two holes on the top. The reference electrode (saturated calomel electrode) and the counter electrode (platinum wire electrode) can be inserted from the two holes on the top of the center chamber. The cathode catalytic membrane and the nickel mesh anode were placed on both sides of the cylindrical inner chamber, the nickel wire passed through the two sides of the middle plate and spanned the chamber diameter position to tightly contact the electrodes, the gasket was placed and tightened with screws to prevent liquid leakage. Among them, the cathode side is not sealed, the purpose is to expose the air cathode to the air, so that oxygen enters from one side and plays a role in the reaction. The electrical performance of the cell was tested by scanning current method, and the test results are shown in Table 2.

[0097] Comparative Example 7: lignin-based fuel cell with layered nickel iron phosphide (NiFeP) as anode catalyst

[0098] 1. Preparation of NiFeP: nickel foam (2 cm x 5 cm) was ultrasonically pretreated in 6 mol / L hydrochloric acid, ethanol and water for 15 min, respectively. 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 water. Ni / Fe was prepared in a molar ratio of 10 / 0, 9 / 1, 7 / 3, 5 / 5. The mixture was transferred to a high-pressure kettle, sealed, and reacted at 120°C for 6 hours to hydrothermally grow NiFe layered double hydroxide (NiFe-LDH) on the nickel foam. During the hydrothermal process, the nickel foam was separated from the solution, ultrasonically rinsed, and dried at 60°C. In order to convert NiFe-LDH to NiFeP, the synthesized NiFe-LDH on the nickel foam and 1.0 g NaH2PO2·H2O were placed in a tube furnace, heated to 300°C at a rate of 2 ℃ min -1

[0099] ​2. Preparation of catholyte and anolyte: 6.757 g of FeCl3-6H2O and 8.4 mL of hydrochloric acid were weighed and added to deionized water and stirred to prepare a 50 mL solution as the catholyte. 2.5 g of alkali lignin was dissolved in 50 mL of KOH solution with a concentration of 1 mol / L as the anolyte.

[0100] 3. Cell system construction and power generation performance test: The cell was composed of two graphite bipolar plates (anode and cathode). The membrane electrode assembly (MEA) was sandwiched between the bipolar plates to separate the fuel cell into anode and cathode chambers. The active area of the MEA was 5 cm 2 The MEA was composed of an anode, a Nafion membrane, and a carbon cloth as a cathode substrate. The catalyst prepared in step 1 was placed on the anode, and the catholyte and anolyte were pumped into the cathode and anode chambers by a pump, and the cell was operated at 90°C. The electrical performance of the cell was tested by the scanning current method, and the test results are shown in Table 2.

[0101] Comparative Example 8: Comparison of lignin-based fuel cell performance based on different catholytes

[0102] 1. Preparation of anolyte: 3 portions of 50 mL NaOH solution (concentration of 2 mol / L) were prepared, and 2 g of alkali lignin was added to each portion and stirred until completely dissolved to prepare the anolyte.

[0103] 2. Preparation of catholyte:

[0104] (1) Preparation of K3[Fe(CN)6] solution: 6.585 g of K3[Fe(CN)6] and 4 g of NaOH were weighed and added to deionized water and stirred to prepare a 50 mL solution.

[0105] (2) Preparation of 4-HO-TEMPO solution: 3.4448 g of 4-HO-TEMPO and 2.925 g of NaCl were weighed and added to deionized water and stirred to prepare a 50 mL solution.

[0106] (3) Preparation of FeCl3 solution: 6.757 g of FeCl3-6H2O and 8.4 mL of hydrochloric acid were weighed and added to deionized water and stirred to prepare a 50 mL solution.

[0107] 3. Battery system construction and power generation performance test: The anode electrolyte prepared in step 1 was added to the anode electrolyte tank, and the cathode electrolyte prepared in step 2 was added to the cathode electrolyte tank. The anode electrolyte tank was connected to the anode inlet and outlet of the battery with a tube, and the cathode tank was connected to the cathode inlet and outlet of the battery. The battery operating temperature was 90°C, and the cathode electrolyte of the three groups of batteries was K3[Fe(CN)6] solution, 4-HO-TEMPO solution and FeCl3 solution, respectively. At the same time, high-purity oxygen was introduced into the cathode tank at a flow rate of 40 mL / min to regenerate the cathode electrolyte. The electrical performance of the battery was tested by the scanning current method, and the results are shown in Table 2.

[0108] Summary

[0109] Table 2 is a comprehensive comparison of the operating temperature, open-circuit voltage, maximum power density, etc. of the above examples and comparative examples.

[0110] Table 2 is a comprehensive comparison of the operating temperature, open-circuit voltage, maximum power density, etc. of the above examples and comparative examples.

[0111]

[0112] Comparing all examples and comparative examples, it can be seen that the battery with the best power generation performance is the lignin-based fuel cell system constructed using enzymatic lignin as the raw material in Example 3, with an open-circuit voltage of 1.67 V and a maximum power density of 159.9 mW / cm 2 , which is much higher than that of Comparative Example 1 and Comparative Example 2.

[0113] In addition, Example 8 proves that the battery of the present application can operate at room temperature (25°C), and when operating at room temperature, the open-circuit voltage can reach 1.36 V and the maximum power density can reach 57.0 mW / cm 2 .

[0114] The battery in Comparative Example 1 needs a pre-degradation process before operation, needs an additional oxidizing agent, needs additional energy consumption, and the operation is relatively complex. Moreover, pre-degradation is an intermittent process, which leads to the inability of the power generation device to operate continuously, thereby restricting its industrial application.

[0115] The battery in Comparative Example 2 needs a pre-degradation process under light before operation, although it can save energy by using sunlight and other energy compared to heating pre-degradation, but it still needs a relatively complex operation, and the battery performance is poor, which is not conducive to its popularization and application in industry.

[0116] The open-circuit voltage of the cellulose-based fuel cell system constructed using cellulose as the raw material in Comparative Example 3 is only 1.32 V, and the maximum power density is only 60.1 mW / cm 2, far lower than the embodiment 3 of the present application, because the lignin-rich alcohol hydroxyl, phenolic hydroxyl structure can release electrons, and the solubility of lignin in alkaline conditions is higher than that of cellulose, the above two conditions make the lignin-based fuel cell have greater energy storage capacity and faster electron transmission rate, thus obtaining more excellent power generation performance.

[0117] Comparative examples 4 and 5 use straw and glucose as power generation raw materials, additionally add catalytic oxidants, and perform heating pre-degradation, but the open-circuit voltage and power density are still lower than that of the embodiment 3, which also illustrates the superiority of the present application.

[0118] Comparative example 6 prepares a cathode catalytic film containing noble metal Pt, performs heating or light pre-treatment on lignin, and adds MV solution as a catalytic oxidant, but the highest power density is only 0.0335 mW / cm 2 and 0.0371 mW / cm 2 , far lower than the present application.

[0119] Comparative example 7 uses NiFeP as an anode catalyst, but the catalytic effect is not obvious, and the highest power density is only 24 mW / cm 2 .

[0120] Comparative example 8 uses different kinds of cathode electrolyte to construct lignin-based fuel cells, and the power generation performance of the three groups of cells is poor.

[0121] It can be seen that the method proposed in the present application is based on biomass flow fuel cell technology, and the lignin-specific structure is improved and innovated, and under the condition of not adding additional oxidants, lignin is converted into electric energy at low temperature or even room temperature. The battery of the present application operates under optimal conditions, and the power generation performance such as open-circuit voltage, power density, long-time discharge stability is in the leading level among similar batteries. At the same time, the low molecular weight lignin obtained after power generation has potential applications in high polymer materials, fine chemicals and the like.

[0122] The above embodiments are the preferred embodiments of the present application, but the embodiments of the present application are not limited by the above embodiments, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application shall be equivalent replacement methods, and all shall be included in the protection scope of the present application.

Claims

1. A lignin-based fuel cell comprising an anode electrolyte and a cathode electrolyte, characterized in that, The anode electrolyte comprises lignin and alkali, and no additional electron transfer agent and oxidant are needed, the lignin is directly oxidized as fuel in the discharging process; the cathode electrolyte comprises pentavalent vanadium salt, acid solution and cathode regenerative oxidant.

2. A lignin-based fuel cell according to claim 1, wherein, The lignin is at least one of alkali lignin, sodium lignosulfonate, enzymatic hydrolysis lignin and pre-hydrolysis lignin.

3. The lignin-based fuel cell of claim 1, wherein, The alkali is at least one of NaOH, KOH and ammonia water.

4. The lignin-based fuel cell of claim 1, wherein, The concentration of alkali in the anode electrolyte is 0.001-8 mol / L, and the content of lignin is 0.01-80 g / L.

5. The lignin-based fuel cell of claim 1, wherein, The concentration of alkali in the anode electrolyte is 0.1-4 mol / L, and the content of lignin is 0.1-60 g / L.

6. The lignin-based fuel cell of claim 1, wherein, The concentration of alkali in the anode electrolyte is 1-2 mol / L, and the content of lignin is 0.5-40 g / L.

7. The lignin-based fuel cell of claim 1, wherein, The operation temperature of the lignin-based fuel cell is 10-100℃.

8. A lignin-based fuel cell according to claim 7, wherein, The pentavalent vanadium salt is at least one of vanadium pentoxide, vanadyl sulfate and vanadyl nitrate; the acid solution is at least one of hydrochloric acid aqueous solution, sulfuric acid aqueous solution and nitric acid aqueous solution; and the cathode regenerative oxidant is at least one of nitric acid, oxygen, hydrogen peroxide and potassium permanganate.

9. The lignin-based fuel cell of claim 1, wherein, The concentration of pentavalent vanadium salt in the cathode electrolyte is 0.05-5 mol / L, and the concentration of acid in the cathode electrolyte is 0.05-8.0 mol / L. When the cathode regenerative oxidant is nitric acid, the concentration thereof in the cathode electrolyte is 0.01-8 mol / L; and when the cathode regenerative oxidant is oxygen, the flow rate thereof is 30-100 mL / min.

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