Method for preparing flexible porous carbon nanofiber micro-fuel cell cathode material through electrostatic spinning and application of flexible porous carbon nanofiber micro-fuel cell cathode material

Abstract

The invention discloses a method for preparing a flexible porous carbon nanofiber micro-fuel cell cathode material through electrostatic spinning. The method comprises the following steps: firstly, uniformly mixing carbon nanotubes and polytetrafluoroethylene dispersion liquid; dissolving polyvinyl alcohol in water, and adding the boric acid solution into the polyvinyl alcohol aqueous solution; mixing the two solutions to obtain an electrostatic spinning precursor solution, and carrying out spinning treatment; the preparation method comprises the following steps: preparing a polymer fiber material, drying, pre-oxidizing to be brown, and carbonizing the pre-oxidized polymer fiber material to obtain the flexible porous carbon nanofiber micro-fuel cell cathode material. The microbial fuel cell constructed on the basis of the flexible porous carbon nanofiber micro-fuel cell cathode material has relatively high cathode oxygen reduction performance, relatively high power output density and long cycle stability, and is expected to be put into practical application in the aspects of sewage treatment and energy recovery.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of microbial fuel cells, and relates to a method for preparing a flexible porous carbon nanofiber microbial fuel cell cathode material by electrospinning and application thereof. BACKGROUND

[0002] Microbial fuel cells (MFCs) have attracted much attention in recent years as an innovative technology that integrates pollution treatment and energy recovery. MFC systems use microorganisms as biological catalysts to generate electrons by degrading and oxidizing organic matter, which are then transferred to the terminal electron acceptor through conductive materials to achieve bioelectricity generation. Over the past century, with the discovery of excellent conductive bacteria, the application of high-efficiency electron transfer mediators, and the improvement and modification of electrode materials, the power of MFC systems has been greatly improved and has shown potential for large-scale application. Generally, various organic substrates, such as carbohydrates, starch, chitin, cellulose, organic acids, proteins, amino acids, organic pollutants, and other toxic waste chemicals, can be used in MFC power generation systems. In addition, wastewater from various sources, such as domestic, municipal, food industry, paper mill, pig farming, textile, brewery / distillery, metal pollution, mining industry, and ocean sediments, can also serve as reaction substrates for MFC systems to generate electricity while purifying water. MFC technology provides the possibility of sustainable production of energy and recovery of high-value products such as hydrogen (H2), methane (CH4), and hydrogen peroxide (H2O2) from organic waste. Compared with conventional pollution control technologies, MFCs do not require additional energy and can simultaneously achieve energy and resource recovery, with the advantages of being clean, efficient, and environmentally friendly, and have great development potential.

[0003] As a green energy technology that combines biological technology and electrochemical principles, microbial fuel cells (MFCs) can convert the chemical energy of organic matter into electrical energy through microbial metabolism, and have shown advantages in wastewater treatment and other fields. However, the current low power density and high material cost seriously limit its practical application, with the performance bottleneck of cathode materials being particularly prominent. Traditional carbon-based materials such as activated carbon and carbon paper have good biocompatibility and chemical stability, but their low specific surface area and low electron transfer efficiency result in slow oxygen reduction reaction kinetics, with energy conversion efficiency often below 10% and power density generally below 200 mW / m 2 ; glassy carbon electrodes can increase the power density to 300-500 mW / m 2 , but their preparation process is complex, the cost is 10-20 times that of ordinary carbon materials, and the high-temperature sintering energy consumption is high and difficult to degrade, which violates the initial intention of green technology. Therefore, it is necessary to design and prepare cathode materials with high biocompatibility to maintain microbial activity, high specific surface area (such as carbon nanotubes, which can reach 1000-2000 m2 / g) carbon nanomaterials with increased reaction sites, high conductivity to accelerate electron transmission, high electron extraction efficiency, and controllable cost (which can be reduced to less than 1 / 5 of the cost of a glassy carbon electrode), which become a key optimization path for breaking through the technical barriers of MFC power output and promoting the industrial application of MFCs. SUMMARY

[0004] The present application provides a flexible porous carbon nanofiber micro fuel cell cathode material prepared by electrospinning to solve the problems of low electrode biological capacity, low electron extraction efficiency, and high material cost in the prior art.

[0005] Another object of the present application is to provide the use of the above-mentioned flexible porous carbon nanofiber micro fuel cell cathode material prepared by electrospinning in the construction of a microbial fuel cell.

[0006] The object of the present application is achieved by the following technical solutions.

[0007] A method for preparing a flexible porous carbon nanofiber micro fuel cell cathode material by electrospinning, comprising the following steps:

[0008] S1: mixing and uniformly mixing carbon nanotubes and polytetrafluoroethylene dispersion liquid;

[0009] S2: dissolving polyvinyl alcohol in water, and then adding a boric acid solution to the polyvinyl alcohol aqueous solution;

[0010] S3: adding the mixed solution in step S1 to the mixed solution in step S2, and stirring to obtain an electrospinning precursor solution;

[0011] S4: performing spinning treatment on the electrospinning precursor solution in step S3;

[0012] S5: drying the polymer fiber precursor obtained in step S4, then pre-oxidizing it to brown, and then carbonizing the pre-oxidized polymer fiber material to obtain the flexible porous carbon nanofiber micro fuel cell cathode material.

[0013] Preferably, the diameter of the carbon nanotubes in step S1 is 4-8 nm, and the length is 0.5-2 µm; the relative molecular mass of the polyvinyl alcohol in step S2 is 78000-145000 g / mol.

[0014] Preferably, the mass ratio of polyvinyl alcohol, polytetrafluoroethylene, and carbon nanotubes is 4:6:0.06.

[0015] Preferably, the mass fraction of the boric acid solution in step S2 is 3-6 wt%; and the amount of the boric acid solution added is 25-50 µL of boric acid per 10 g of polyvinyl alcohol solution.

[0016] Preferably, the electrostatic spinning voltage in step S4 is 10-15 KV, the flow rate is 1-1.5 mL / h, and the distance between the nozzle and the collector is 15-20 cm.

[0017] Preferably, the temperature for drying in step S5 is 60-80 ℃, and the time is 8-12 h.

[0018] Preferably, the pre-oxidation temperature is 250-300 ℃, the temperature is raised at a rate of 5 ℃ per minute, and the holding time is 1.5-2 h; the carbonization temperature is 800-1000 ℃, the temperature is raised at a rate of 5 ℃ per minute, and the holding time is 1.5-2 h.

[0019] The present application also protects the flexible porous cage-like electrospun carbon nanofiber electrode material obtained by the method. The average diameter of the fiber is about 400 nm, the average pore size is 3.213 nm, the specific surface area is 787 m 2 / g, and the total pore volume is 0.633 cm 3 / g. The material has high toughness, high specific surface area, porous structure, and good biocompatibility, is conducive to the formation of a dense biological membrane on the surface of the cathode, and promotes the oxygen reduction activity of the cathode of the microbial fuel cell; the CNTs as the framework of the material not only increase the toughness of the material, but also promote electron transfer due to the excellent electrical conductivity, thereby greatly improving the output power of the microbial fuel cell; the anode, the cathode, and the proton exchange membrane of the microbial fuel cell are assembled into a microbial fuel cell, and the power density and long cycle stability of the microbial fuel cell are obviously improved compared with the comparative sample, and the microbial fuel cell has application in the field of low-cost and high-performance microbial fuel cells.

[0020] The present application further protects a microbial fuel cell comprising the flexible porous cage-like electrospun carbon nanofiber electrode material.

[0021] Preferably, the microbial fuel cell comprises an anode, a cathode, and a proton exchange membrane, the anode is a carbon cloth uniformly loaded with 0.02 mg / cm 2 Pt / C catalyst, and naphthol is used as a binder; the cathode is the flexible porous cage-like electrospun carbon nanofiber electrode material; and the proton exchange membrane is Nafion 211.

[0022] Preferably, the electrolyte in the cathode chamber is an M9 buffer solution containing 4 g / L glucose as a carbon source, and the electrolyte is purged with oxygen for 30 minutes to remove dissolved nitrogen. The anode electrolyte is an M9 salt solution with 1 M glucose as an electron donor.

[0023] Compared with the prior art, the present application has the following advantages:

[0024] The flexible porous cage-shaped electrospun carbon nanofiber electrode material is used in the cathode of the microbial fuel cell, has a three-dimensional sponge-like three-dimensional structure, the structure is stacked by carbon fibers, coated with CNT, and each carbon fiber is uniformly distributed with a hole structure. The electronegative heteroatoms of B and N can improve the electronic conductivity of PCNF by changing the electron cloud of C atoms. The internal carbon nanotubes enhance the flexibility of the PCNF film, and the high porosity and heterogeneous elements can promote the electrochemical reaction. The raw materials PTFE and PVA used to make the material have good biocompatibility. Escherichia coli is inoculated in the PCNF film matched with the size of the bacterial pore. The surface morphology of the C-FPCNF electrode material is observed by scanning electron microscope, the PCNF electrode is mainly composed of carbon fibers crossing and overlapping each other, and presents a cage structure, and the size of each cage structure is between 0.5-5 µm. The size is matched with the size of most microbial cells 0.5-3 µm, so that the microorganisms can be relatively independent to colonize in the PCNF, so as to fully utilize the broad inner surface and form high-density culture. A large number of mesoporous structures of 10-20 nm are uniformly distributed on each carbon fiber, which is beneficial to direct electron transfer and material exchange between bacteria and carbon base, shortens the diffusion path of oxygen and substrate, accelerates the ORR reaction kinetics, and synchronously promotes the rapid discharge of metabolic products (such as CO2 and H⁺), avoids the inhibition of local pH imbalance on the activity of bacteria. The microbial fuel cell has high cathode oxygen reduction performance, high power output density and long cycle stability, and is expected to be applied in sewage treatment and energy recovery. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The scanning electron microscope (SEM) picture of the flexible porous carbon nanofiber obtained in Example 1. Figure 1 The picture obtained by magnifying to 2 µm.

[0026] Figure 2 The scanning electron microscope (SEM) picture of the flexible porous carbon nanofiber obtained in Example 1. Figure 2 The picture obtained by magnifying to 200 nm.

[0027] Figure 3 The transmission electron microscope (TEM) picture of the flexible porous carbon nanofiber obtained in Example 1. Figure 3 The picture obtained by magnifying to 500 nm.

[0028] Figure 4 The transmission electron microscope (TEM) picture of the flexible porous carbon nanofiber obtained in Example 1. Figure 4 The picture obtained by magnifying to 200 nm.

[0029] Figure 5Nitrogen adsorption-desorption image of the flexible porous carbon nanofiber obtained in Example 1.

[0030] Figure 6 Pore size distribution curve of the flexible porous carbon nanofiber obtained in Example 1.

[0031] Figure 7 Linear sweep voltammetry (LSV) graph of the flexible porous carbon nanofiber for the cathode of the microbial fuel cell obtained in Example 2.

[0032] Figure 8 Cyclic voltammetry (CV) graph of the flexible porous carbon nanofiber for the cathode of the microbial fuel cell obtained in Example 2.

[0033] Figure 9 Electrochemical impedance spectroscopy (EIS) of the flexible porous carbon nanofiber for the cathode of the microbial fuel cell obtained in Example 2.

[0034] Figure 10 Power density graph of the flexible porous carbon nanofiber for the cathode of the microbial fuel cell obtained in Example 2.

[0035] Figure 11 200h long cycle stability performance graph of the flexible porous carbon nanofiber for the cathode of the microbial fuel cell obtained in Example 2. DETAILED DESCRIPTION

[0036] The technical solutions of the present application will be described in detail below with specific embodiments of the present application. It should be pointed out that the provided embodiments only represent a part of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0037] The test methods used in the embodiments of the present application are all conventional methods unless otherwise specified; the materials, reagents, etc. used are commercially available reagents and materials unless otherwise specified, and the commercially available raw materials are used after removing insoluble impurities and the like by general filtration methods.

[0038] Example 1: Electrospinning preparation of flexible porous carbon nanofiber microbial fuel cell cathode material of the present application

[0039] 1) 0.0288 g of CNTs and 4.8 g of PTFE were weighed using an electronic analytical balance and added to a beaker, a magnetic rotor was added, the beaker was placed on a magnetic stirrer to stir at a speed of 400 rpm, the CNTs were mixed with the PTFE, then the beaker was placed in an ultrasonic cleaner and ultrasonic treatment was carried out for 30 min until the CNTs were completely mixed with the PTFE; 1.92 g of PVA was weighed and placed in a new beaker, 17.28 mL of deionized water and a magnetic rotor were added, the beaker was placed in a digital constant temperature magnetic stirrer, heated in a water bath at 85°C, and stirred at a speed of 200 rpm for 2 h until the PVA was completely dissolved in the deionized water; 4 g of BA was weighed and added to the beaker, 100 mL of water was added, and the BA was stirred with a glass rod until it was completely dissolved; 48 μL of the BA solution was measured and added to the cooled PVA solution, and the mixture was stirred with a glass rod until it was uniform; the uniform CNTs and PTFE suspension was then added to the PVA and BA mixture, and the mixture was placed on a magnetic stirrer and stirred at a speed of 600 rpm overnight to obtain a uniform, precipitate-free electrospinning precursor solution;

[0040] 2) The electrospinning precursor solution was added to a 10 mL syringe, the syringe was installed on a microsyringe pump, the injection speed was controlled by the microsyringe pump to be 1 mL / h; the spinning voltage was adjusted by a high-voltage direct-current power supply device to be 15 kV; the distance between the nozzle and the receiving device was adjusted by moving the iron stand to be 20 cm; then the electrospinning experiment was started.

[0041] 3) The obtained polymer fiber precursor was placed in a 60°C vacuum oven and dried for 12 h to completely remove the residual solvent; then the release paper was separated from the polymer fiber membrane precursor, and the obtained polymer fiber membrane was placed in a clean porcelain boat and placed in a muffle furnace to be pre-oxidized at a temperature increasing rate of 5°C per minute to 280°C until the polymer fiber membrane was completely brown; finally, the brown polymer fiber membrane was placed in a clean porcelain boat and placed in a nitrogen-filled tube furnace to be high-temperature carbonized at a temperature increasing rate of 5°C per minute to 1000°C for 2 h until the flexible porous cage-shaped carbon nanofiber structure was formed.

[0042] The morphology of the porous carbon fiber was observed using a field emission electron microscope, and the specific surface area, pore size distribution, and total pore volume of the porous carbon fiber were measured using a specific surface area and pore size analyzer. The average diameter of the fiber is about 400 nm, the average pore size is 3.213 nm, the specific surface area is 787 m 2 / g, and the total pore volume is 0.633 cm 3 / g.

[0043] Example 2: Construction of a microbial fuel cell based on the electrospinning of the present application to prepare a flexible porous carbon nanofiber micro fuel cell cathode material

[0044] The reagents used are as follows:

[0045] Materials: carbon cloth, Nafion 211 proton exchange membrane

[0046] Reagents: 40% Pt / C catalyst, 5% naphthol solution

[0047] The microbial fuel cell of the present example is a double-chamber microbial fuel cell, which comprises an anode, a cathode, and the internal working volume is 50 mL, separated by a proton exchange membrane. The anode comprises an electrode substrate and a modified material coated on the surface of the electrode substrate, and a flexible porous carbon nanofiber micro fuel cell cathode material as the cathode.

[0048] The specific construction and operation process of the microbial fuel cell of the present example is as follows:

[0049] 1) Preparation of microbial fuel cell anode: pour a 5% naphthol solution and anhydrous ethanol solution into a test tube and mix them evenly to obtain a binder solution; add Pt / carbon powder catalyst to the binder solution and mix the Pt / carbon powder catalyst with the binder solution evenly to form a binder solution containing catalyst; evenly drop the binder solution containing catalyst on one side surface layer of a carbon cloth substrate (2×2 cm 2 ) with a pipette, and then place it in a 60°C air blowing box for drying for 4 h, which completes the preparation of the anode of the microbial fuel cell; the volume ratio of the naphthol solution to the anhydrous ethanol solution is 0.2:1, and the added Pt / carbon powder anode catalyst is a commercial 40% Pt / C with a loading of 2 mg / cm 2 .

[0050] 2) Assembly of MFCs: use the carbon cloth containing Pt / C catalyst prepared in step 1) as the anode; use the carbon nanofiber prepared in example 1 as the cathode, and assemble the microbial fuel cell with Nafion 211 proton exchange membrane as the separation membrane, which is recorded as C-FPCNF-MFC.

[0051] 3) Running MFCs: The preserved E. coli BL21 strain was first resuscitated and revived in 5 mL of LB liquid medium. The bacterial solution was placed in a shaker at 37 °C for at least 12 hours. Then 200 μL of the bacterial suspension was taken and placed in another culture bottle containing 200 mL of fresh LB medium for further growth. When the optical density (OD600) value of the final bacterial solution was about 1.5, the cells were collected by centrifugation (5000 rpm, 5 min), washed twice with deionized water and then poured into a culture bottle containing 50 mL of LB medium, and the cathode electrode was placed in the culture bottle, and cultured for 24 h until the E. coli adhered to the cathode electrode; the cathode was taken out of the culture solution containing E. coli, and M9 buffer solution containing 4 g / L glucose as a carbon source was injected into the cathode chamber as an electrolyte, and the cathode chamber was purged with oxygen for 30 minutes to remove dissolved nitrogen; the anode was injected with M9 salt solution containing 1 M glucose as an electron donor as an electrolyte.

[0052] The concentrations of the solutes in the LB medium in this example are shown in Table 1, and the concentrations of the solutes in the M9 buffer solution containing 4 g / L glucose as a carbon source are shown in Table 1-2; the anode electrolyte and the cathode electrolyte only differ in the content of glucose, and the C-FPCNF-MFC is started.

[0053] Table 1 Concentrations of solutes in the LB medium

[0054] Table 2 Concentrations of solutes in the M9 buffer solution containing 4 g / L glucose as a carbon source -1 Concentrations of solutes in the M9 buffer solution containing 4 g / L glucose as a carbon source

[0055] Comparative Example 1

[0056] The microbial fuel cell of this comparative example differs from the microbial fuel cell of Experimental Example 1 only in that the cathode of the microbial fuel cell of this comparative example is untreated carbon cloth, denoted as CC-MFC; and the porous carbon nanofiber without CNT, denoted as PCNF.

[0057] Test Experimental Example

[0058] Experimental Example 1: Oxidation performance

[0059] The electrochemical experiment proves that under the same conditions of wild E. coli cell adhesion, C-FPCNF has more excellent electrocatalytic ORR performance than carbon cloth and PCNF. The CV test was carried out under O2 saturation conditions, and the results are shown in Figure 1. Figure 7It can be seen that the carbon cloth, PCNF and C-FPCNF materials all have obvious reduction peak signals, and the peak current density of the cells on the C-FPCNF is 5.13 mA / cm 2 , which is much higher than that of the carbon cloth (2.15 mA / cm 2 ), and significantly enhances the ORR activity.

[0060] Linear sweep voltammetry (LSV) measurement as Figure 8 shows that the C-FPCNF with cells has higher ORR catalytic activity, and the limiting current density is ~1.5 mA / cm 2 , which is obviously higher than that of the carbon cloth with cells (~0.9 mA / cm 2 ). Electrochemical impedance spectroscopy (EIS) analysis shows that Figure 9 , compared with the carbon cloth with cells, the C-FPCNF with cells has a smaller semicircle, showing a lower charge transfer resistance, indicating that the electrode material has a faster electron transfer efficiency.

[0061] Experimental Example 2: Electricity generation performance

[0062] Polarization-power density curve Figure 10 shows that the open-circuit voltage of the C-FPCNF-MFCs is 0.75 V, which is higher than that of the wild E. coli (0.7 V); the maximum power density of the C-FPCNF-MFCs reaches 350 μW / cm, which is about 2.8 times higher than that of the wild E. coli (80.2 μW / cm). Long cycle stability test as Figure 11 shows that the MFC stably maintains the output voltage between 690 and 740 V under 400 h test, and the voltage output stability is good. During the period, the liquid is changed for 3 times, and the voltage after the liquid change can still reach the initial voltage, and the material reusability is superior.

[0063] Experimental Example 3: Morphology of cathode microorganisms

[0064] The morphology of the cathode biofilm of the CC-MFCs and the C-FPCNF-MFCs after running for 200 h is observed by using a scanning electron microscope. It can be obviously seen that the amount of microorganisms attached to the cathode of the C-FPCNF-MFCs is more, and the biofilm is more dense, while the cathode biofilm of the CC-MFCs is relatively sparse.

[0065] Obviously, the above examples of the present application are only examples for clearly illustrating the technical solutions of the present application, and are not a limitation on the specific embodiments of the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the claims of the present application shall be included in the protection scope of the claims of the present application.

Claims

1. A method for preparing a flexible porous carbon nanofiber micro fuel cell cathode material by electrospinning, characterized in that, Comprising the following steps: S1: mixing and uniformly mixing carbon nanotubes and polytetrafluoroethylene dispersion liquid; S2: dissolving polyvinyl alcohol in water, and then adding boric acid solution into the polyvinyl alcohol aqueous solution; S3: adding the mixed solution in step S1 into the mixed solution in step S2, and stirring to obtain an electrospinning precursor solution; S4: performing spinning treatment on the electrospinning precursor solution in step S3; S5: drying the polymer fiber precursor obtained in step S4, then pre-oxidizing into brown, and then carbonizing the pre-oxidized polymer fiber material to obtain the flexible porous carbon nanofiber micro fuel cell cathode material.

2. The method for preparing flexible porous carbon nanofiber micro fuel cell cathode material by electrospinning according to claim 1, characterized in that, The diameter of the carbon nanotubes in step S1 is 4-8 nm, and the length is 0.5-2 µm; the relative molecular mass of the polyvinyl alcohol in step S2 is 78000-145000 g / mol.

3. The method for preparing flexible porous carbon nanofiber micro fuel cell cathode material by electrospinning according to claim 1 or 2, characterized in that, The mass ratio of polyvinyl alcohol, polytetrafluoroethylene and carbon nanotubes is 4:6:0.

06.

4. The method for preparing flexible porous carbon nanofiber micro fuel cell cathode material by electrospinning according to claim 3, characterized in that, The mass fraction of the boric acid solution in step S2 is 3-6 wt%; the addition amount of the boric acid solution is 25-50 µL of boric acid per 10-20 g of polyvinyl alcohol solution.

5. The method for preparing flexible porous carbon nanofiber micro fuel cell cathode material by electrospinning according to claim 1, characterized in that, The electrospinning voltage in step S4 is 10-15 KV, the flow rate is 1-1.5 mL / h, and the distance between the nozzle and the collector is 15-20 cm.

6. The method for preparing flexible porous carbon nanofiber micro fuel cell cathode material by electrospinning according to claim 1, characterized in that, The drying temperature in step S5 is 60-80 ℃, and the time is 8-12 h.

7. The method for preparing flexible porous carbon nanofiber micro fuel cell cathode material by electrospinning according to claim 6, characterized in that, The pre-oxidation temperature is 250-300 ℃, with a temperature rise of 5 ℃ per minute, and the holding time is 1.5-2 h; the carbonization temperature is 800-1000 ℃, with a temperature rise of 5 ℃ per minute, and the holding time is 1.5-2 h.

8. The flexible porous cage-like electrospun carbon nanofiber electrode material obtained by the method of any one of claims 1 to 7.

9. A microbial fuel cell, characterized by, Comprising the flexible porous cage-like electrospun carbon nanofiber electrode material of claim 8.

10. The application of the flexible porous cage-like electrospun carbon nanofiber electrode material of claim 8 in the cathode of a microbial fuel cell.

Images