Biochar-polyurethane carbon anode material, preparation method thereof, microbial fuel cell and application

Abstract

The invention discloses a biochar-polyurethane carbon anode material, a preparation method thereof, a microbial fuel cell and application, biochar, polyol, triethanolamine, water and isocyanate are added into a mold to be mixed to obtain a mixture, the mixture reacts under stirring until white floating foam appears, then standing foaming is performed, carbonization is performed after the material is cured, and the biochar-polyurethane carbon anode material is obtained. The internal resistance of a double-chamber microbial fuel cell constructed by taking the carbonized biochar-polyurethane material as an anode of MFCs is not greater than 3.00 omega, the highest voltage stably exceeds 620 mV, the maximum area power density exceeds 800 mW m <-2 >, and the COD removal rate of the biochar-polyurethane carbon anode material disclosed by the invention reaches 97.24%.

Description

Technical Field

[0001] This invention belongs to the field of microbial fuel cell technology, specifically relating to a biochar-polyurethane carbon anode material and its preparation method, as well as microbial fuel cells and their applications. Background Technology

[0002] Microbial fuel cells (MFCs) are devices that utilize electrogenic bacteria to degrade organic matter in wastewater, converting its chemical energy into electrical energy, thus simultaneously achieving efficient and green wastewater treatment. In the anode chamber, electrogenic bacteria decompose organic matter in the wastewater through their own oxidative metabolism under anaerobic conditions, achieving wastewater purification. During this process, electrons released from the anode chamber flow into the cathode through an external circuit, while released protons pass through the proton exchange membrane in the middle of the cell and enter the cathode. The cathode chamber receives electrons and protons, and an oxygen reduction reaction occurs at the cathode, thereby completing the entire wastewater treatment and electricity generation process.

[0003] Generally, the anode is not only a carrier for electrogenic bacteria but also a conductor for electron transfer, thus significantly affecting the performance of MFCs. For this reason, biochar is widely used in MFCs due to its good biocompatibility, excellent conductivity, and sufficient chemical stability. In addition, it is inexpensive and readily available. However, current biochar anodes are mostly fabricated by coating or depositing onto the surface of a substrate electrode. While this improves performance to some extent, it is expensive to prepare and has poor long-term operational stability.

[0004] Liu et al. fabricated a three-dimensional anode by depositing carbon black onto a polyurethane sponge using Nafion solution. The anode had a resistance of approximately 33 Ω and a maximum output power density of 926 mW / m³. -2 It is 2.2 times that of carbon cloth electrodes, but carbon black will fall off during long-term operation, causing a decline in battery performance.

[0005] Pérez-Rodríguez et al. prepared a three-dimensional anode by rapidly mixing graphite and carbon nanofibers with polyols, adding isocyanate, and then subjecting the mixture to high-speed stirring and foaming. While the preparation process was simple, the cost was high, and the anode exhibited a high resistance of 1051.11 Ω and a maximum power density of only 232.32 mW / m². -3 . Summary of the Invention

[0006] Based on the shortcomings of the existing technology, the first objective of this invention is to provide a method for preparing biochar-polyurethane carbon anode material.

[0007] The second objective of this invention is to provide a biochar-polyurethane carbon anode material prepared by the above-described preparation method.

[0008] A third objective of this invention is to provide a microbial fuel cell.

[0009] The fourth objective of this invention is to provide an application of microbial fuel cells.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] This invention provides a method for preparing a biochar-polyurethane carbon anode material. Biochar, polyol, triethanolamine, water and isocyanate are added to a mold and mixed to obtain a mixture. The mixture is reacted under stirring until white foam appears, and then allowed to stand to foam. After the material is solidified, it is carbonized to obtain the biochar-polyurethane carbon anode material.

[0012] The biochar-polyurethane carbon material provided by this invention comprises polyurethane formed by the condensation polymerization of isocyanate and polyol. The reaction of water and isocyanate promotes foaming and chain extension, while simultaneously replacing nitrogen doping sites, which is beneficial for the subsequent formation of NC active sites. Triethanolamine not only catalyzes the gelation and foaming reactions, but also introduces nitrogen elements during carbonization to form NC active sites and improve the electrochemical performance of the electrode. The introduction of biochar can enhance the conductivity and biocompatibility of the electrode on the one hand, and on the other hand, it can efficiently utilize the nitrogen elements in the carbonization process of polyurethane foam electrode to form a large number of NC active sites and increase the active area of ​​the electrode.

[0013] In a preferred embodiment, the polyol is selected from polyester polyols and / or polyether polyols, and more preferably a mixture of polyester polyols and polyether polyols.

[0014] Experiments have shown that polyester polyols can form a honeycomb porous structure with a high specific surface area, which is beneficial for the attachment of microorganisms but not for the fixation of the battery. The mixture of polyether polyol and polyester polyol not only retains the porosity of the electrode but also enhances its toughness, giving the electrode a certain mechanical strength and enabling it to better maintain its shape.

[0015] In a further preferred embodiment, the polyol is a mixture of polyester polyol and polyether polyol in a mass ratio of 7-9:1. Experiments have shown that controlling the ratio of polyester polyol to polyether polyol within this range yields optimal performance; however, adding too much polyether polyol leads to a decrease in the mechanical strength and solvent resistance of the electrode after carbonization.

[0016] In a preferred embodiment, the isocyanate is a polymeric isocyanate. Experiments have shown that the foaming time of polymeric isocyanate is only 1-3 minutes, which can significantly improve reaction efficiency.

[0017] In a preferred embodiment, the mixture, by mass ratio, is biochar: polyol: triethanolamine: water: isocyanate = 0.1 ~ 2.0 : 5.0 ~ 10.0 : 0.1 ~ 0.5 : 0.05 ~ 0.5 : 3.0 ~ 5.0.

[0018] Experiments have shown that when the mass of each component is controlled within the above-mentioned range, the final biochar-polyurethane carbon anode material exhibits the best performance.

[0019] In the preferred embodiment, the reaction temperature under stirring is 30-40°C. o C.

[0020] In actual operation, the reaction is carried out in a water bath. After stirring until white foam appears, the mold is removed from the water bath and left to stand to foam.

[0021] In a preferred embodiment, the carbonization process is as follows: first, carbonization is carried out at 4 to 6... o Heating rate increased to 200~350 °C / min. o Keep warm at 0.5 to 1.5 hours, then at 2 to 4 degrees Celsius. o Heating rate increased to 800 ~ 1000 °C / min o Temperature range: C, heat treatment for 2.0 to 4.0 hours. The carbonization process provided by this invention, first stage: 200 to 350°C. o The electrode is kept at a temperature of 0.5 to 1.5 h to remove water and residual additives, allowing for electrode structure restructuring and pore formation, resulting in a well-developed porous structure and N–C doping active sites, thus enhancing the electrochemical activity of the electrode. The second stage involves heating to 800 °C. o C ~ 1000 o Incubation at C for 2.0h ~ 4.0h forms a conductive carbon skeleton, enhancing the conductivity of the material. The carbonized biochar-polyurethane material has a porous structure and a large specific surface area. The large pores facilitate substrate diffusion, while the small pores facilitate the colonization of electrogenic bacteria, thereby improving the electrochemical performance of the battery.

[0022] In actual operation, the carbonized product is cut to the specifications of a microbial fuel cell, and then the material is clamped with titanium wire clamps to obtain biochar-polyurethane carbon anode material.

[0023] The present invention also provides a biochar-polyurethane carbon anode material prepared by the above preparation method.

[0024] The present invention also provides a microbial fuel cell, wherein the anode chamber of the microbial fuel cell is made of the biochar-polyurethane carbon anode material.

[0025] In a preferred embodiment, the microbial fuel cell is an H-type dual-chamber microbial fuel cell, the cathode chamber is made of modified carbon felt, and the anode chamber and cathode chamber are separated by a modified Nafion 117 proton exchange membrane.

[0026] In a further preferred embodiment, the modified carbon felt is obtained as follows: after washing the carbon felt with deionized water, it is soaked in a mixed solution containing dilute nitric acid and hydrogen peroxide for 0.5 to 1.5 hours, then rinsed with deionized water and soaked for 0.5 to 1 hour, and finally wrapped with sealing film. After making dense small holes on the surface of the sealing film, it is dried to obtain the final product.

[0027] In the mixed solution, the volume ratio of dilute nitric acid to hydrogen peroxide is 2.5~3.5:1;

[0028] The concentration of the dilute nitric acid is 0.5~2 mol / L.

[0029] The above modifications remove impurities from the carbon felt surface, strengthen surface active sites, and improve electron transfer efficiency.

[0030] A further preferred embodiment is that the modified Nafion 117 proton exchange membrane is obtained by first immersing the Nafion 117 proton exchange membrane in a 4-6% (w / w) hydrogen peroxide solution at 60-80 °C. o Soak at C for 0.5-1 hour, then rinse repeatedly with deionized water and soak for 0.5-1 hour. Finally, soak in 4-6% dilute sulfuric acid at 60-80 °C. o Soak at C for 0.5-1 hour, then rinse repeatedly with deionized water and soak for 0.5-1 hour.

[0031] The above treatment removes impurities from the surface of the Nafion 117 proton exchange membrane, reduces interfacial contact resistance, and activates proton-conducting groups to form continuous proton transport channels, thereby improving the membrane's proton conductivity.

[0032] The present invention also provides an application of a microbial fuel cell, wherein the microbial fuel cell is used to treat organic wastewater.

[0033] The advantages and effects of this invention are as follows:

[0034] The biochar-polyurethane carbon anode material provided by this invention is prepared in a one-pot process using biochar, polyol, triethanolamine, water, and isocyanate. Polyurethane is formed through the condensation polymerization of isocyanate and polyol. The reaction of water and isocyanate promotes foaming and chain extension, while simultaneously replacing nitrogen-doped sites, which is beneficial for the subsequent formation of NC active sites. Triethanolamine not only catalyzes the gelation and foaming reactions but also introduces nitrogen elements during carbonization, forming NC active sites and improving the electrochemical performance of the electrode. The introduction of biochar enhances the conductivity and biocompatibility of the electrode and efficiently utilizes the nitrogen elements generated during the carbonization process of the polyurethane foam electrode to form a large number of NC active sites, increasing the active area of ​​the electrode. The carbonization process is divided into two stages, the first stage being 200... o C ~ 350 oThe electrode is kept at a temperature of 0.5 to 1.5 degrees Celsius to remove water and residual additives, allowing for electrode structure remodeling and pore formation, resulting in a well-developed porous structure. The second stage involves maintaining the electrode at 800 degrees Celsius. o C ~ 1000 o Incubation at C for 2.0h to 4.0h forms a conductive carbon framework and NC active sites, enhancing the material's conductivity. The carbonized biochar-polyurethane material possesses a porous structure and a large specific surface area. Macropores facilitate substrate diffusion, while micropores promote the colonization of electrogenic bacteria, thereby improving the battery's electrochemical performance.

[0035] The dual-chamber microbial fuel cell constructed using carbonized biochar-polyurethane material as the anode of MFCs in this invention exhibits an internal resistance not exceeding 3.00 Ω, a maximum stable voltage exceeding 620 mV, and a maximum areal power density exceeding 800 mW / m². -2 The COD removal rate of this invention reaches 97.24%.

[0036] The preparation process of this invention is simple, the experimental conditions are mild, and the raw material cost is low, reducing costs by about 90% compared to traditional biochar-based electrodes. Attached Figure Description

[0037] Figure 1 The images show the biochar-polyurethane carbon anode material before and after carbonization.

[0038] Figure 2 Cyclic voltammetry curves of MFCs prepared from carbonized biochar-polyurethane carbon anodes with different raw material ratios.

[0039] Figure 3 Chronoamperometry of MFCs prepared from carbonized biochar-polyurethane carbon anodes with different raw material ratios.

[0040] Figure 4 Electrochemical impedance spectroscopy of MFCs prepared from carbonized biochar-polyurethane carbon anodes with different raw material ratios.

[0041] Figure 5 The relationship between time and output voltage for MFCs made from carbonized biochar-polyurethane carbon anodes with different raw material ratios.

[0042] Figure 6 Power density and polarization curves of MFCs prepared from carbonized biochar-polyurethane carbon anodes with different raw material ratios.

[0043] Figure 7 The COD removal rate of MFCs made from carbonized biochar-polyurethane carbon anodes with different raw material ratios is shown in the figure. Detailed Implementation

[0044] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Of course, the described examples are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative effort are all within the scope of protection of the present invention.

[0045] Example 1

[0046] In this embodiment, the application of carbonized biochar-polyurethane carbon anode in a microbial fuel cell is carried out according to the following steps:

[0047] Step 1: Take 3 molds and place them in a 35°C container. o In a water bath (C), add 5.0g polyester polyol, 0.1g triethanolamine, 0.1g deionized water, and 3.0g isocyanate to mold 1 in sequence; add 4.5g polyester polyol, 0.5g polyether polyol, 0.1g triethanolamine, 0.1g deionized water, and 3.0g isocyanate to mold 2 in sequence; and add 0.1g biochar, 4.5g polyester polyol, 0.5g polyether polyol, 0.1g triethanolamine, 0.1g deionized water, and 3.0g isocyanate to mold 3 in sequence. After stirring until white foam appears, remove the mold and let it stand at room temperature to foam and solidify.

[0048] Step 2: After demolding the materials from Step 1, place them separately into an atmosphere furnace. Under N2 protection, first heat at 5°C. o Heat up to 300 °C / min o Pre-carbonization is carried out by holding at C for 1 hour, followed by 3 o Temperature increased to 800 °C / min o The carbonized electrode material is obtained by holding it at temperature for 2 hours.

[0049] Step 3: Rinse the material obtained in Step 2 with deionized water and then cut it into pieces with dimensions of 3 × 3 × 0.5 cm. 3 The mass is not limited, and the materials are connected and fixed with titanium wire, and are referred to as: polyester electrode, polyether polyester electrode, biochar-polyether polyester electrode.

[0050] Step 4: Place the electrodes from Step 3 into the anode chamber, add anolyte and anaerobic granules from the wastewater treatment plant to the anode chamber; add catholyte to the cathode chamber, and the cathode is a pretreated carbon felt of the same size.

[0051] The anode chamber and cathode chamber are separated by a Nafion 117 proton exchange membrane, and the anode and cathode are connected by an external 1000Ω resistor to assemble the microbial fuel cell.

[0052] The anolyte is wastewater composed of sodium acetate, trace element solution, and mineral solution. The preparation steps of the anolyte are as follows: add 1.0g of yeast extract, 1mL of trace element solution, and 3.294g of sodium acetate to 1000mL of mineral solution and dissolve them completely.

[0053] Further specifying the steps for preparing the mineral solution, the steps are as follows: Add 400-700 mL of deionized water to a beaker, then add 0.42 g of potassium dihydrogen phosphate, 1.26 g of dipotassium hydrogen phosphate, 0.315 g of magnesium chloride, 0.075 g of calcium chloride dihydrate, 0.2 g of ammonium chloride, 0.33 g of potassium chloride, and 0.30 g of sodium chloride in sequence. After dissolving completely, transfer the solution to a 1000 mL volumetric flask, add deionized water to bring the volume to 1000 mL, mix well, and then pour into a sterile container for sealing and storage.

[0054] Further specifying the steps for preparing the trace element solution, the steps are as follows: Add 400-700 mL of deionized water to a beaker, then add 50.0 g of ferrous chloride tetrahydrate, 1.25 g of zinc chloride, 12.5 g of manganese chloride tetrahydrate, 1.25 g of ammonium molybdate tetrahydrate, 3.75 g of cobalt chloride hexahydrate, 2.5 g of nickel chloride hexahydrate, 0.75 g of copper chloride dihydrate, and 1.25 g of boric acid in sequence. After fully dissolving, transfer the solution to a 1000 mL volumetric flask, add deionized water to bring the volume to 1000 mL, mix well, and then pour the solution into a sterile container for sealing and storage.

[0055] To further define the process, the steps for preparing the cathodic solution are as follows: add 16.46 g of potassium ferricyanide to 1000 mL of PBS buffer and dissolve it completely.

[0056] Further specifying the steps for preparing the PBS buffer, the steps are as follows: Add 1000 mL of deionized water to a beaker, then add 11.54 g of disodium hydrogen phosphate, 2.77 g of sodium dihydrogen phosphate, 0.31 g of ammonium chloride and 0.13 g of potassium chloride in sequence. After dissolving completely, adjust the pH to 7.2-7.4 with sodium hydroxide, and finally pour into a sterile container and seal for storage.

[0057] The assembled dual-chamber microbial fuel cell was connected to a data acquisition card, and voltage data was automatically recorded every 600 seconds. After several cycles of operation, when the voltage reached its maximum stable value, the electrochemical performance of the cell was measured using an electrochemical workstation after 6 hours of open-circuit operation. At the same time, the external circuit resistance was changed from large to small (9000Ω ~ 100Ω), the output voltage was recorded, and the polarization curve and power density curve were calculated and plotted.

[0058] Performance testing

[0059] Electrochemical performance of microbial fuel cells fabricated with biochar-polyurethane carbon anodes

[0060] Figure 2 The figures show the cyclic voltammetry curves of MFCs prepared from carbonized biochar-polyurethane carbon anodes with different raw material ratios prepared in the examples. This experiment used a three-electrode system: the anode as the working electrode, the cathode as the counter electrode, and Ag / AgCl as the reference electrode. From the curves, it can be seen that the biochar-polyether polyester anode has the largest capacitance area, the most active sites, and the strongest charge storage capacity.

[0061] Furthermore, through Figure 3 Chronoamperometry (COP) plots of MFCs prepared from carbonized biochar-polyurethane carbon anodes with different raw material ratios corroborate the CV curve results. This experiment used a three-electrode system: the anode as the working electrode, the cathode as the counter electrode, and Ag / AgCl as the reference electrode. The system was charged for 0.5 h under open circuit conditions and then discharged for 10 min. The entire process was carried out at a constant voltage of 0.75 V. The curves show that the biochar-polyether polyester anode has the largest current area and generates and stores the most charge.

[0062] Figure 4 The images show the electrochemical impedance spectroscopy of MFCs prepared from carbonized biochar-polyurethane carbon anodes under different raw material ratios in the examples. This experiment used a three-electrode system: the anode as the working electrode, the cathode as the counter electrode, and Ag / AgCl as the reference electrode. From the curves, it can be seen that the biochar-polyether polyester anode has the lowest resistance value, only 2.17Ω, which is less than that of commercial carbon felt and other polyurethane anodes.

[0063] Electrical performance of microbial fuel cells fabricated using biochar-polyurethane carbon anodes

[0064] Figure 5 The graph shows the relationship between time and output voltage of MFCs made from carbonized biochar-polyurethane carbon anodes under different raw material ratios in the examples. It can be seen from the graph that the highest voltage of the biochar-polyether polyester anode is 624.62mV, the single cycle period reaches 6 days, and it is consistently higher than that of commercial carbon felt and other polyurethane anodes.

[0065] Figure 6 The figures show the power density and polarization curves of MFCs prepared from carbonized biochar-polyurethane carbon anodes under different raw material ratios in the examples. It can be seen from the figures that the biochar-polyether polyester electrode has the highest output power density, with a maximum area power density of 821.78 mW / m². -2 The maximum volumetric power is 16.43 Wm. -3 It is speculated that the addition of biochar may have enhanced the conductivity and biocompatibility of the polyurethane electrode, promoting the attachment of electrogenic bacteria and the rate of extracellular electron transfer.

[0066] Organic matter degradation capacity of microbial fuel cells made with biochar-polyurethane carbon anodes

[0067] After the microbial fuel cell has operated stably for several cycles, the influent and effluent of the anolyte are collected for COD testing. To prevent exceeding the measurement range, the effluent does not need to be diluted. The influent is diluted 50 times, and 2 mL is added to a digestion tube. Then, 2 mL of potassium dichromate standard solution, 0.5 mL of 10% (v / v) dilute sulfuric acid, and 3 mL of 5 g / L sulfuric acid-silver sulfate solution are added to the digestion tube in sequence. After thorough mixing, the mixture is incubated at 165°C. o Digestion was performed in a C-type digester for 40 minutes. After the temperature dropped to room temperature, a UV spectrophotometer was used for comparative analysis. Before analysis, a blank sample was used to zero the sample, and the COD values ​​of the influent and effluent were recorded separately to calculate the COD removal rate over a complete cycle.

[0068] from Figure 7 It can be found that the biochar-polyurethane carbon anode of the present invention has the highest COD removal rate of 97.24% when measured using the above method. Other polyurethane electrodes also exceed those of commercial carbon felt anodes, indicating that the assembled microbial fuel cell has a good degradation ability for organic matter in wastewater.

Claims

1. A method for preparing a biochar-polyurethane carbon anode material, characterized in that: Biochar, polyol, triethanolamine, water and isocyanate are added to a mold and mixed to obtain a mixture. The mixture is stirred until white foam appears, then allowed to stand and foam. After the material is cured, it is carbonized to obtain biochar-polyurethane carbon anode material.

2. The method for preparing a biochar-polyurethane carbon anode material according to claim 1, characterized in that: The polyol is selected from polyester polyols and / or polyether polyols; The isocyanate is a polymeric isocyanate.

3. The method for preparing a biochar-polyurethane carbon anode material according to claim 2, characterized in that: The polyol is a mixture of polyester polyol and polyether polyol in a mass ratio of 7 to 9:

1.

4. The method for preparing a biochar-polyurethane carbon anode material according to claim 1, characterized in that: In the mixture, by mass ratio, biochar: polyol: triethanolamine: water: isocyanate = 0.1 ~ 2.0 : 5.0 ~ 10.0 : 0.1 ~ 0.5 : 0.05 ~ 0.5 : 3.0 ~ 5.

0.

5. The method for preparing a biochar-polyurethane carbon anode material according to claim 1, characterized in that: The reaction temperature under stirring is 30-40°C. o C; The carbonization process is as follows: first, at 4 to 6... o Heating rate increased to 200 ~ 350 °C / min o Keep warm at 0.5 to 1.5 hours, then at 2 to 4 degrees Celsius. o Heating rate increased to 800~1000 °C / min. o C, keep warm for 2.0 ~ 4.0 hours.

6. A biochar-polyurethane carbon anode material prepared by the preparation method according to any one of claims 1-5.

7. A microbial fuel cell, characterized in that: The anode chamber of the microbial fuel cell is made of the biochar-polyurethane carbon anode material as described in claim 6.

8. A microbial fuel cell according to claim 7, characterized in that: The microbial fuel cell is an H-type dual-chamber microbial fuel cell, with the cathode chamber made of modified carbon felt and the anode and cathode chambers separated by a modified Nafion 117 proton exchange membrane.

9. A microbial fuel cell according to claim 8, characterized in that: The modified carbon felt is obtained as follows: after washing the carbon felt with deionized water, it is soaked in a mixed solution containing dilute nitric acid and hydrogen peroxide for 0.5 to 1.5 hours, then rinsed with deionized water and soaked for 0.5 to 1 hour. Finally, it is wrapped with sealing film, and after making dense small holes on the surface of the sealing film, it is dried. In the mixed solution, the volume ratio of dilute nitric acid to hydrogen peroxide is 2.5~3.5:1; The concentration of the dilute nitric acid is 0.5~2 mol / L; The modified Nafion 117 proton exchange membrane was obtained by first soaking the Nafion 117 proton exchange membrane in a 4-6% hydrogen peroxide solution at 60-80°C. o Soak at C for 0.5-1 hour, then rinse repeatedly with deionized water and soak for 0.5-1 hour. Finally, soak in 4-6% dilute sulfuric acid at 60-80°C. o Soak at C for 0.5-1 hour, then rinse repeatedly with deionized water and soak for another 0.5-1 hour.

10. The application of a microbial fuel cell according to any one of claims 7-9, characterized in that: The microbial fuel cell is used to treat organic wastewater.

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