Fe-N-C-at-MXene composite material, synthesis method thereof and application of Fe-N-C-at-MXene composite material in microbial fuel cell
By using Fe-NC@MXene composite material as the cathode catalyst for microbial fuel cells, the problems of high internal resistance in electron transfer and easy material contamination were solved, achieving efficient oxygen reduction reaction and improved battery output voltage, reducing costs and improving stability.
Patent Information
- Application Number
- CN202512009500.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-29
- Publication Date
- 2026-03-27
AI Technical Summary
Microbial fuel cells suffer from problems such as high internal resistance in electron transport, high cost and easy contamination of electrode materials, instability of proton exchange membranes, and susceptibility of microbial activity to environmental interference, which limit their power density and long-term stability.
Fe-NC@MXene composite material was used as the cathode catalyst. MIL-101(Fe)@MXene composite material was grown in situ and melamine was introduced for high-temperature pyrolysis to construct a multi-level structure, thereby improving electron transport and catalytic activity.
It significantly improves oxygen reduction reaction activity and battery output voltage, reduces costs, and enhances battery stability and durability, demonstrating excellent catalytic performance and long-term operational reliability.
Smart Images
Figure CN121748416A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a Fe-NC@MXene composite material, its synthesis method, and its application in microbial fuel cells, belonging to the field of microbial fuel cell technology. Background Technology
[0002] Microbial fuel cells (MFCs) are similar in basic working principle to traditional fuel cells. Microorganisms in the anode chamber metabolize and decompose organic matter, releasing electrons and protons. Electrons are transported to the cathode via an external circuit to form an electric current, while protons migrate through a proton exchange membrane to the cathode chamber, where they combine with oxygen and electrons to produce water, thus generating electrical energy. This process avoids reliance on traditional metal catalysts. These microorganisms (such as bacteria) can generate electricity by metabolizing organic matter and degradable substrates (such as wastewater), while simultaneously degrading organic matter in wastewater. A major advantage of MFCs is their ability to operate stably under adverse environmental conditions such as low temperatures and their capacity to utilize a variety of degradable substrates as fuel, making them a promising sustainable green energy technology with broad application prospects.
[0003] Despite these challenges, MFCs still face numerous obstacles that severely restrict their large-scale commercial application in practical engineering. First, low power density is one of the core issues hindering MFC development. Due to the high internal resistance during electron transfer from microorganisms to the electrodes, the overall system output power is insufficient to meet industrial energy output demands. Second, electrode materials and reactor configurations still need optimization. Highly conductive, corrosion-resistant electrode materials with surfaces suitable for microbial adhesion are expensive, while inexpensive materials often have limited performance, making it difficult to balance cost and performance. Furthermore, the proton exchange membrane between the anode and cathode chambers is not only costly but also easily contaminated or clogged, affecting proton transport efficiency and long-term stable system operation.
[0004] In terms of microorganisms, the current understanding of electron transfer mechanisms (especially extracellular electron transport) is insufficient, which limits the screening and targeted modification of highly efficient power-generating strains. During long-term operation, MFC systems are easily affected by environmental factors such as pollutants, pH changes, or nutrient depletion, leading to reduced or even inactive microorganisms, which affects power generation efficiency and service life.
[0005] Although platinum-based catalysts, especially the widely used Pt / C catalysts, have long been considered the most promising electrode materials due to their excellent overall performance and commercial potential, many problems in practical applications, such as high cost, poor durability, and unavoidable poisoning effects, limit their long-term stability and challenge their practical use. Therefore, the search for electrode materials with higher stability, economy, and sustainability has become particularly important. Summary of the Invention
[0006] The purpose of this invention is to provide a Fe-NC@MXene composite material, its synthesis method, and its application in microbial fuel cells. This invention employs an in-situ growth strategy on a monolayer Ti3C2T... x MIL-101(Fe) was constructed on the surface of MXene to form a well-bonded MIL-101(Fe)@MXene composite material. Melamine was then introduced as a nitrogen source, and synergistic nitrogen doping and carbonization were achieved through high-temperature pyrolysis to construct a multi-level Fe-NC@MXene composite material with high specific surface area and abundant active sites. This composite material can be used as a cathode catalyst in microbial fuel cells and exhibits excellent catalytic activity.
[0007] The technical solution to achieve the purpose of this invention is as follows:
[0008] The synthesis method of Fe-NC@MXene composite material involves first synthesizing MIL-101(Fe)@MXene composite material in situ via hydrothermal method, and then mixing MIL-101(Fe)@MXene with melamine followed by pyrolysis treatment, including the following steps:
[0009] (1) Preparation of MIL-101(Fe)@MXene composite material:
[0010] According to Ti3C2T x The mass ratio of MXene, FeCl3·6H2O, and terephthalic acid (H2BDC) is 1:13:8, in Ti3C2T x FeCl3·6H2O and terephthalic acid were added sequentially to the MXene suspension to obtain a precursor solution. The precursor solution was then subjected to a hydrothermal reaction under inert gas protection at 120±10℃. After the reaction was completed, the solid was collected by centrifugation, washed, and vacuum dried to obtain the MIL-101(Fe)@MXene composite material.
[0011] (2) Synthesis of Fe-NC@MXene composite material:
[0012] MIL-101(Fe)@MXene and melamine were ground until uniformly mixed, and then pyrolyzed under nitrogen protection at 800±50℃ to obtain Fe-NC@MXene composite material.
[0013] Furthermore, in step (1), the inert gas is nitrogen or argon.
[0014] Furthermore, in step (1), the hydrothermal reaction time is more than 24 hours.
[0015] Furthermore, in step (1), the vacuum drying temperature is 60°C and the drying time is 12h.
[0016] Furthermore, in step (1), the washing method is to wash repeatedly with N,N-dimethylformamide (DMF) and ethanol in sequence.
[0017] Furthermore, in step (2), the mass ratio of MIL-101(Fe)@MXene to melamine is 1:5.
[0018] Furthermore, in step (2), the temperature is increased to 800±50℃ at a rate of 5℃ / min.
[0019] This invention provides Fe-NC@MXene composite materials prepared by the above-described method.
[0020] The present invention also provides the application of the above-mentioned Fe-NC@MXene composite material as a cathode catalyst in microbial fuel cells.
[0021] Furthermore, the specific application method is as follows: Fe-NC@MXene composite material is added to a mixed solution of isopropanol and water with a volume ratio of 3:1, 5wt% Nafion solution is added, and after ultrasonic dispersion, the dispersion is uniformly coated on the surface of the gas diffusion layer as a cathode, and the activated carbon fiber brush is used as an anode to assemble a microbial fuel cell.
[0022] Furthermore, the loading of Fe-NC@MXene composite material on the surface of the gas diffusion layer is 0.2 mg / cm². 2 .
[0023] This invention uses FeCl3·6H2O as a metal precursor, Fe 3+ Through electrostatic adsorption and coordination with functional groups on the MXene surface, active sites are provided for the nucleation of MOF crystals. Then, terephthalic acid is added as an organic ligand. During the hydrothermal reaction, MIL-101(Fe) crystals preferentially grow on the MXene surface, benefiting from the growth of Fe. 3+The enrichment of MIL-101(Fe) and the promoting effect of the MXene two-dimensional platform inhibited the aggregation of free MIL particles, maintained the high specific surface area and open pore structure of MIL-101(Fe), and improved the exposure of active sites, resulting in a MIL-101(Fe)@MXene composite material with uniform surface crystal distribution and complete structure. This composite material has good interfacial contact and electronic coupling efficiency, which is beneficial to the improvement of charge transport and catalytic performance. Subsequently, through the mixed pyrolysis of MIL-101(Fe)@MXene and melamine, the organic ligands in MIL-101(Fe) underwent thermal decomposition and transformed into a porous carbon framework. At the same time, melamine decomposed to generate abundant nitrogen-containing intermediates (such as NH3, -CN, -NH2, etc.), which synergistically reacted with Fe species under high temperature. During the pyrolysis process, MXene was transformed into a TiC / TiOx structure, providing conductive channels and stabilizing the overall structure, finally yielding the Fe-NC@MXene composite material.
[0024] Compared with the prior art, the present invention has the following advantages:
[0025] (1) The prepared composite material exhibits excellent ORR activity. In cyclic voltammetry (CV) testing, the reduction peak potential of Fe-NC@MXene (0.75V) is significantly higher than that of commercial Pt / C catalyst (0.65V), and its cathode current density is significantly higher than that of Pt / C. In linear sweep voltammetry (LSV) testing, the half-wave potential of Fe-NC@MXene is 0.79V, which is slightly higher than that of Pt / C (0.77V), showing ORR kinetic performance comparable to that of noble metal catalysts; (2) In microbial fuel cell (MFC) performance testing, the average output voltage of Fe-NC@MXene reaches 0.53V, which is 1.51 times higher than that of commercial Pt / C (0.35V). In 140h continuous discharge testing, the battery voltage fluctuation of this material is extremely small, and its stability is significantly better than that of Pt / C, showing excellent long-term operational reliability; (3) The raw materials of the material are inexpensive and the preparation process is simple, which greatly reduces the assembly cost of microbial fuel cells.
[0026] MIL-101 (Fe), as a material with a metal-organic framework structure, exhibits excellent catalytic performance in the field of electrocatalysis due to its superior porous structure, metal center, and high specific surface area. By combining it with monolayer MXene and preparing Fe-NC@MXene composite catalysts through an in-situ growth strategy, significant catalytic performance was demonstrated. The advantages of this composite material are reflected in the following aspects: (1) The metal center (Fe) in MIL-101 (Fe) provides abundant active sites, which can effectively catalyze the oxygen reduction reaction (ORR) and improve the diffusion rate of reactants by regulating its pore structure; (2) MXene, as a conductive framework, enhances the electronic conductivity of the composite material, enabling the catalyst to maintain efficient current transmission during the reaction and reducing the energy barrier of the electrocatalytic reaction; (3) High-temperature carbonization treatment not only enhances the thermal stability of the catalyst, but also effectively improves the electrochemical stability and durability of the catalyst; (4) By introducing nitrogen atoms to achieve nitrogen doping, the electronic structure of the catalyst is optimized, and the active sites of nitrogen-containing groups are increased. These nitrogen sites further improve the activity and selectivity of the catalytic reaction, especially playing an important role in the adsorption and activation of oxygen molecules. Attached Figure Description
[0027] Figure 1 The CV curves for Fe-NC@MXene and the comparative example in alkaline solution are shown.
[0028] Figure 2 The LSV curves are for Fe-NC@MXene and the comparative example.
[0029] Figure 3 Voltage-time plots of Fe-NC@MXene and comparative applications in microbial fuel cells at 10 mA constant current discharge. Detailed Implementation
[0030] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.
[0031] In the following embodiments, a single-layer Ti3C2T is used. x MXene References (Downes M, Shuck CE, McBride B, et al. Comprehensive synthesis of Ti3C2T) xFrom MAX phase to MXene[J]. Nature Protocols, 2024, 19(6): 1807-1834.) was prepared by selectively etching the aluminum layer in the Ti3AlC2 precursor through in-situ generation of hydrofluoric acid. Specifically, 2g of LiF was dissolved in 35 mL of concentrated hydrochloric acid and stirred at room temperature for 30 minutes. Then, 4g of Ti3AlC2 powder was slowly added to the mixed solution and stirred continuously at 40°C for 40 hours to etch Ti3AlC2 using the HF generated during the reaction. After the reaction, the Ti3AlC2 was washed by centrifugation with deionized water multiple times until the supernatant was neutral. Finally, the Ti3AlC2 was further washed with ethanol to promote interlayer hydration and exfoliation, thereby obtaining the exfoliated Ti3C2T x MXene.
[0032] Example 1
[0033] 1. Preparation of MIL-101(Fe)@MXene composite material:
[0034] MIL-101(Fe)@MXene composite material was synthesized in situ via a hydrothermal method. First, 20 mg of exfoliated Ti3C2T... x MXene was dispersed in 20 mL of deionized water and sonicated for 30 minutes to obtain a homogeneous dispersion. Then, 270 mg of FeCl3·6H2O was added as a metal precursor, and the mixture was stirred for 30 minutes to allow Fe to dissolve. 3+ Electrostatic adsorption and coordination with functional groups on the MXene surface provide active sites for MOF crystal nucleation. 166 mg of terephthalic acid was then added as an organic ligand, and the mixture was transferred to a reaction vessel. Under nitrogen protection, the reaction was carried out at 120°C for 24 hours. During this process, MIL-101(Fe) crystals preferentially grew on the MXene surface, benefiting from the growth of Fe... 3+ The enrichment of MIL particles and the promoting effect of the MXene two-dimensional platform inhibited the aggregation of free MIL particles, maintaining the high specific surface area and open pore structure of MIL-101(Fe) and improving the exposure of active sites. After the reaction, the product was separated by centrifugation and repeatedly washed with DMF and ethanol, and then vacuum dried at 60°C for 12 hours to obtain a MIL-101(Fe)@MXene composite material with uniform surface crystal distribution and complete structure. This composite material has good interfacial contact and electronic coupling efficiency, which is beneficial to the improvement of charge transport and catalytic performance.
[0035] 2. Synthesis of Fe-NC@MXene:
[0036] To construct Fe-N xA conductive composite electrocatalyst with active sites was developed by pyrolysis of a mixture of MIL-101(Fe)@MXene and melamine. Specifically, 100 mg of dried MIL-101(Fe)@MXene composite material and 500 mg of melamine were thoroughly ground. Under nitrogen protection, the mixture was heated to 800 °C at a rate of 5 °C / min. The organic ligands in MIL-101(Fe) underwent thermal decomposition, transforming into a porous carbon framework. Simultaneously, melamine decomposed to generate abundant nitrogen-containing intermediates (such as NH3, -CN, -NH2, etc.), which synergistically reacted with Fe species under high temperature. During the pyrolysis process, MXene was converted into TiC / TiO. x The structure provides conductive channels and stabilizes the overall structure, ultimately yielding the Fe-NC@MXene composite material.
[0037] Comparative Example 1
[0038] This comparative example is largely the same as Example 1, except that melamine is not added for nitrogen doping, and Fe@MXene / C composite material is obtained directly by pyrolysis.
[0039] Comparative Example 2
[0040] This comparative example is largely the same as Example 1, except that Ti3C2T is not added. x MXene was used to prepare Fe-NC composite materials.
[0041] Comparative Example 3
[0042] This comparative example is largely the same as Example 1, except that the heating rate is increased from 5°C / min to 10°C / min.
[0043] The results showed that when the heating rate increased to 10 °C / min, the pyrolysis and reconstruction of the carbonization / nitridation process became more intense and uneven, which easily aggravated the migration and aggregation of Fe species, thereby shortening the Fe-N transition time. x The effective formation window of coordination sites and the reduced proportion of highly dispersed active centers lead to a decrease in catalytic performance and batch consistency. Simultaneously, the asynchronous nature of rapid outgassing and framework carbonization worsens pore structure regulation, manifesting as pore collapse or widened pore size distribution, and weakens the interfacial coupling and conductive network continuity between the carbon layer and MXene, further hindering the stable construction of specific surface area and mass transfer channels. The oxygen reduction peak measured in the CV curve is only at 0.65 V.
[0044] Comparative Example 4
[0045] This comparative example is largely the same as Example 1, except that Ti3C2T xThe mass ratio of MXene, FeCl3·6H2O, and terephthalic acid was adjusted from 1:13:8 to 2:13:8.
[0046] The results showed that doubling the MXene content while keeping the Fe source and ligand feed constant significantly reduced the Fe / BDC supply per unit mass of MXene in the system. This easily led to a decrease in the coverage, thinning of the crystal layer, or reduction in crystallinity of MIL-101(Fe) in situ growth on the MXene surface, which in turn affected Fe-N during the subsequent co-carbonization process with melamine. x The effective formation and anchoring of potential active sites are limited, and the site density is diluted. Simultaneously, increased MXene lamellar content increases the tendency for re-stacking, and when the MOF / carbon phase "spacer support" is insufficient, it is more likely to cause pore blockage and narrowing of mass transfer pathways, thus hindering the stable construction of specific surface area and pore structure. Ultimately, this may manifest as a decrease in the upper limit of the ORR activity of the composite material and poor batch-to-batch consistency. The oxygen reduction peak measured in the CV curve is only at 0.67 V.
[0047] Example 2
[0048] The Fe-NC@MXene catalyst samples prepared in Example 1, the Fe@MXene / C catalyst prepared in Comparative Example 1, and the Fe-NC catalyst samples prepared in Comparative Example 2 were respectively added to a mixed solution of isopropanol and water with a volume ratio of 3:1. 5 wt% Nafion solution was added, and after ultrasonic dispersion, the dispersion was uniformly coated onto the surface of a gas diffusion layer as the working electrode. The size of the gas diffusion layer was 2 cm × 2 cm, and the loading of each catalyst sample was 0.2 mg·cm³. -2 A three-electrode system was constructed using a graphite rod as the counter electrode and Ag / AgCl as the reference electrode. In 0.1 mol L... -1 After continuously bubbling oxygen into the KOH solution for 1 h to ensure full electrolyte saturation, cyclic voltammetry (CV) and linear sweep voltammetry (LSV) tests were performed using an electrochemical workstation. A commercial Pt / C catalyst was used as a comparison.
[0049] like Figure 1 As shown, the Fe-NC@MXene sample exhibited a distinct oxygen reduction peak in the CV curve, with a peak position of 0.76 V, slightly higher than Fe@MXene / C (0.68 V), Fe-NC (0.69 V), and commercial Pt / C (0.69 V). This result indicates that Fe-NC@MXene has higher oxygen adsorption and utilization efficiency in the oxygen reduction reaction. Furthermore, Fe-NC@MXene had the largest CV curve area, indicating a greater number of active sites and the highest electrochemical reactivity.
[0050] Further LSV test results ( Figure 2 The results show that the half-wave potential (E) of Fe-NC@MXene is... 1 / 2 The onset potential is 0.79 V, slightly higher than that of commercial Pt / C (0.75 V); its onset potential is as high as 0.84 V, which is significantly better than other comparative samples, indicating that the Fe-NC@MXene composite material exhibits excellent electrocatalytic activity and reaction kinetics in alkaline systems and has the potential to replace noble metal catalysts for oxygen reduction reactions.
[0051] Example 3
[0052] 1. Activation of carbon fiber brushes: Immerse the carbon fiber brushes in acetone solution for at least 4 hours, and rinse three times with deionized water; immerse the carbon fiber brushes in a beaker containing 1M dilute hydrochloric acid for 4 hours, rinse again with deionized water until neutral, and finally dry in an oven. Place the pretreated carbon fiber brushes in a ceramic boat, put them in a tube furnace, set the program to increase the temperature to 450℃ at 5℃ / min, and hold the temperature for 2 hours; after the tube furnace cools naturally to room temperature, remove the carbon fiber brushes, sonicate them with deionized water for 2 hours, and dry them in an oven to obtain activated carbon fiber brushes.
[0053] 2. The Fe-NC@MXene catalyst samples prepared in Example 1, the Fe@MXene / C catalyst prepared in Comparative Example 1, and the Fe-NC catalyst samples prepared in Comparative Example 2 were respectively added to a mixed solution of isopropanol and water with a volume ratio of 3:1. 5 wt% Nafion solution was added, and after ultrasonic dispersion, the dispersions were uniformly coated onto the surface of a gas diffusion layer. The size of the gas diffusion layer was 2 cm × 2 cm, and the loading of each catalyst sample was 0.2 mg·cm³. -2 After being vacuum dried at 60 °C for 2 h, the material was fixed onto a platinum electrode to serve as the cathode of the microbial fuel cell. The anode was an activated carbon fiber brush. The anode culture medium was tryptone soybean broth (TSB) solution, and the cathode culture medium was simulated seawater. Together, they formed a single-chamber MFC system. The simulated seawater consisted of: 10 L deionized water, 245.3 g sodium chloride, 52 g magnesium chloride, 40.9 g sodium sulfate, 11.6 g calcium chloride, 6.95 g potassium chloride, 2.01 g sodium bicarbonate, 1.01 g potassium bromide, 0.27 g boric acid, 0.25 g strontium chloride, and 0.03 g sodium fluoride. A simulated seawater concentration of 3.5 wt% was obtained.
[0054] A constant current discharge of 10 mA was performed in the blue electric discharge test system, and the voltage-time curve was recorded. The results are as follows: Figure 3As shown, the Fe-NC@MXene cathode exhibited the highest steady-state output voltage, reaching 1.085 V, which was higher than that of Fe@MXene / C (0.983 V), Fe-NC (1.045 V), and Pt / C (1.024 V), respectively. Notably, during the first 250 hours of continuous discharge, the Fe-NC@MXene cathode maintained a consistently high output voltage without significant performance degradation, indicating that this electrode material possesses good electrochemical activity and durability. However, when the discharge time was extended to 360 hours, the voltage decreased significantly, indicating that the catalytic performance of the cathode began to decline. Further analysis suggests that this phenomenon may be related to the following factors: (1) During long-term operation, oxygen reduction products (such as peroxides or hydroxyl intermediates) may accumulate on the electrode surface, leading to the covering of local reaction sites and increasing interfacial charge transfer impedance; (2) Under continuous operation, the metabolic activity of microorganisms gradually decreases, and the anode biofilm may partially detach or undergo metabolic inhibition, thereby reducing electron transfer efficiency; (3) Long-term reduction of dissolved oxygen in the cathode region may also change the local pH environment, causing partial inactivation of the metal-nitrogen active center or breakage of Fe-N bonds, weakening the stability of ORR active sites. Voltage decay may be caused by multiple factors, including changes in the structure of the electrode catalytic center, microbial inactivation, and deterioration of interfacial reaction kinetics.
[0055] In summary, Fe-NC@MXene achieves a synergistic improvement in efficient oxygen reduction reaction activity and excellent electrochemical stability by constructing Fe-NC active centers in situ on the MXene framework. As an MFC cathode catalyst, it can not only significantly improve output voltage and energy conversion efficiency, but also has long-term structural stability and anti-deactivation ability, providing a new technical approach for high-performance, low-cost microbial fuel cell cathode materials.
Claims
1. A method for synthesizing Fe-NC@MXene composite materials, characterized in that, Includes the following steps: (1) Preparation of MIL-101(Fe)@MXene composite material: According to Ti3C2T x The mass ratio of MXene, FeCl3·6H2O, and terephthalic acid is 1:13:8, in Ti3C2T x FeCl3·6H2O and terephthalic acid were added sequentially to the MXene suspension to obtain a precursor solution. The precursor solution was then subjected to a hydrothermal reaction under inert gas protection at 120±10℃. After the reaction was completed, the solid was collected by centrifugation, washed, and vacuum dried to obtain the MIL-101(Fe)@MXene composite material. (2) Synthesis of Fe-NC@MXene composite material: MIL-101(Fe)@MXene and melamine were ground until uniformly mixed, and then pyrolyzed under nitrogen protection at 800±50℃ to obtain Fe-NC@MXene composite material.
2. The synthesis method according to claim 1, characterized in that, In step (1), the inert gas is nitrogen or argon.
3. The synthesis method according to claim 1, characterized in that, In step (1), the hydrothermal reaction time is more than 24 hours, the vacuum drying temperature is 60℃, and the drying time is 12 hours.
4. The synthesis method according to claim 1, characterized in that, In step (1), the washing method is to wash repeatedly with N,N-dimethylformamide (DMF) and ethanol in sequence.
5. The synthesis method according to claim 1, characterized in that, In step (2), the mass ratio of MIL-101(Fe)@MXene to melamine is 1:
5.
6. The synthesis method according to claim 1, characterized in that, In step (2), the temperature is increased to 800±50℃ at a rate of 5℃ / min.
7. The Fe-NC@MXene composite material prepared by any one of the preparation methods according to claims 1 to 6.
8. The application of the Fe-NC@MXene composite material according to claim 7 as a cathode catalyst in microbial fuel cells.
9. The application according to claim 8, characterized in that, The specific application method is as follows: Fe-NC@MXene composite material is added to a mixed solution of isopropanol and water with a volume ratio of 3:1, 5wt% Nafion solution is added, and after ultrasonic dispersion, the dispersion is uniformly coated on the surface of the gas diffusion layer as a cathode, and the activated carbon fiber brush is used as an anode to assemble a microbial fuel cell.
10. The application according to claim 9, characterized in that, The loading of Fe-NC@MXene composite material on the surface of the gas diffusion layer is 0.2 mg / cm². 2 .