Preparation method of Fe-N-S-C catalyst and application of Fe-N-S-C catalyst in microbial fuel cell cathode

Abstract

The invention belongs to the technical field of air cathode materials of microbial fuel cells, and relates to a preparation method of a Fe-N-S-C catalyst, and the preparation method comprises the following steps: S1, adding ZIF-8 into a solvent for dispersion, and then adding ferric salt; then introducing a sulfur source to obtain a Fe-N-S-C precursor; and S2, calcining the precursor obtained in the step S1 under the protection of argon. Fe-Nx active sites in the Fe-N-S-C catalyst are utilized to provide enough electrochemical active sites, so that adhesion of bacteria and formation of a biological membrane are facilitated, signal conduction and charge transfer between cells are facilitated, and the extracellular electron transfer rate is increased. The Fe-N-S-C catalyst modified electrode attached with the bacillus subtilis biological membrane not only has excellent electro-catalysis ORR activity in a half battery, but also still shows good biological power generation capacity when being used as a catalytic material of an MFC air cathode to be assembled into a total battery, and has a relatively strong application prospect.

Description

Technical Field

[0001] This invention belongs to the field of air cathode material technology for microbial fuel cells, and relates to a method for preparing Fe-NSC catalyst and its application in the cathode of microbial fuel cells. Background Technology

[0002] With the increasing global population and rapid economic development, human demand for energy is growing daily, leading to increasingly severe energy problems and a continuous increase in the need for new clean energy sources. Microbial fuel cell (MFC) technology utilizes microbial metabolism to generate electrons and protons from organic pollutants in wastewater, directly converting chemical energy into electrical energy. While generating energy, it can also address the treatment of domestic and industrial wastewater, showing broad application prospects in wastewater treatment and new energy development. The cathode is a crucial component of the MFC, and its performance directly affects the MFC's output power and energy conversion efficiency.

[0003] The oxygen reduction reaction (ORR) is a key reaction at the MFC cathode, but its kinetics are slow, requiring highly efficient catalysts to accelerate the reaction rate. Currently, commonly used MFC cathode materials include platinum-carbon (Pt / C), activated carbon, and carbon cloth. Among these, Pt / C exhibits excellent ORR catalytic activity, but its high cost and poor stability limit its large-scale application. Activated carbon and carbon cloth are inexpensive, but their lower ORR catalytic activity limits the MFC's output power.

[0004] To improve the ORR catalytic activity of MFC cathodes, researchers have developed various modification methods, such as: heteroatom doping: Introducing heteroatoms such as nitrogen (N), sulfur (S), and phosphorus (P) into carbon materials can alter their electronic structure and enhance their ORR catalytic activity. Metal doping: Introducing transition metals such as iron (Fe), cobalt (Co), and nickel (Ni) into carbon materials can form active sites with heteroatoms, further improving ORR catalytic activity. Composite materials: Combining carbon materials with metal oxides, conductive polymers, and other materials can synergistically improve ORR catalytic activity.

[0005] However, ideal cathode materials with excellent bacterial adhesion, good conductivity, and excellent electroactive sites remain difficult to fabricate. Therefore, it is necessary to optimize the electroactive sites and surface functions of cathode materials to improve biofilm-cathode interactions and enhance ORR catalytic activity. Summary of the Invention

[0006] The technical problem solved by this invention is to provide a method for preparing a biosafe, green and renewable Fe-NSC catalyst, and to apply it to the cathode of a microbial fuel cell. When the Fe-NSC catalyst prepared by this method is used as a catalytic material for the air cathode of an MFC, it can improve the biofilm-cathode interaction, endow Bacillus subtilis cells with excellent electrocatalytic ORR activity and efficient power generation function of the microbial fuel cell.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for preparing an Fe-NSC catalyst includes the following steps:

[0009] S1. Preparation of Fe-NSC precursor: ZIF-8 is added to a solvent for dispersion, and then an iron salt is added; then a sulfur source is introduced to obtain the Fe-NSC precursor;

[0010] S2. The precursor obtained in step S1 is heated at 800-1000℃ for 2-4 hours under argon protection.

[0011] Preferably, in step S1, during the preparation of the Fe-NSC precursor, the mass ratio of ZIF-8: iron salt: sulfur source is 200:(5-20):(100-200).

[0012] More preferably, the mass concentration of ZIF-8 in the mixed system is 2.0 to 4.0 g / L.

[0013] More preferably, the iron salt is selected from Fe(NO3)3·9H2O, the sulfur source is selected from 4,4′-dihydroxydiphenyl sulfone, and the solvent is selected from methanol.

[0014] Preferably, the heating rate in step S2 is 2~5℃·min. -1 .

[0015] Preferably, in step S1, the mass ratio of ZIF-8 to iron salt to sulfur source is 20:1:16, the mass concentration of ZIF-8 is 2.8 g / L, the iron salt is selected from Fe(NO3)3·9H2O, and the sulfur source is selected from 4,4′-dihydroxydiphenyl sulfone.

[0016] Preferably, the heating rate in step S2 is 5°C·min. -1 .

[0017] Preferably, ZIF-8 is obtained by the following method: A 1.6M solution of 2-methylimidazolium in methanol and a 0.1M solution of Zn(NO3)2·6H2O in methanol are mixed at a volume ratio of 1:2–4, stirred at room temperature for 24 hours, washed, centrifuged, and the precipitate is collected and dried to obtain ZIF-8. (ZIF-8, short for zeolite imidazolium ester framework-8, is the most widely studied and common metal-organic framework material, and can also be obtained commercially; this application does not impose strict limitations on its availability.)

[0018] Preferably, the centrifugation process described above involves centrifuging at 8000 rpm for 5 minutes.

[0019] Preferably, in step S1, ZIF-8 is first dispersed in methanol, then an iron salt solution is injected, and then a methanol solution of 4,4′-dihydroxydiphenyl sulfone is added to the dispersion. The mixture is stirred at room temperature for 10–20 h. After washing three times with methanol, the mixture is vacuum dried at 60–80 °C for 12 h to obtain the Fe-NSC precursor.

[0020] When the Fe-NSC catalyst described in this invention is used for electrocatalytic ORR, the Fe-Nx active sites in the catalyst provide sufficient electrochemical active sites, which is beneficial to bacterial adhesion and biofilm formation. The Fe-Nx active sites are structurally similar to heme in c-Cyts, accelerating the EET process through the directional effect of flavin binding to c-Cyts. The Fe-Nx active sites in the Fe-NSC catalyst more readily gain electrons from c-Cyts and collect flavin through the π-π interaction of the isochloropyrazine ring, significantly improving the electrocatalytic ORR performance of Bacillus subtilis.

[0021] This invention also protects the Fe-NSC catalyst obtained by the preparation method described above.

[0022] Furthermore, it protects the application of the Fe-NSC catalyst in the preparation of air cathodes for microbial fuel cells.

[0023] Further, the catalyst is mixed with a binder and an electrolyte, and ultrasonically mixed to form a uniform dispersion; the dispersion is then coated onto a current collector and dried to obtain an electrode material modified with the Fe-NSC catalyst.

[0024] Furthermore, the amount of Fe-NSC catalyst added in step S4 is 3 mg.

[0025] Furthermore, Bacillus subtilis is attached to the electrode material as a cathode.

[0026] Furthermore, the cathode preparation process involves inoculating Bacillus subtilis into LB liquid medium and then placing the electrode in the liquid medium for co-incubation with the bacteria. The resulting Fe-NSC catalyst-modified electrode with an attached Bacillus subtilis biofilm serves as the cathode. The LB liquid medium comprises 10 g / L of... -1 Tryptone, 5g / L -1 Yeast extract and 5g L -1 Sodium chloride.

[0027] Furthermore, the catholyte is an M9 solution containing 30 mM glucose, a carbon cloth electrode coated with commercial Pt / C is used as the anode, and the anolyte is an M9 solution containing 1 M glucose. The two chambers are separated by a proton exchange membrane. The MFC is placed in an incubator at 30–37°C with an external resistor connected. Oxygen is introduced into the catholyte and nitrogen is introduced into the anolyte.

[0028] Further specifying, the co-incubation time is 24–48 hours.

[0029] This invention also claims the application of the Fe-NSC catalyst in the preparation of the working electrode of a three-electrode half-cell, in which a platinum sheet and a saturated silver / silver chloride electrode serve as the counter electrode and reference electrode, respectively.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] 1. This invention utilizes the Fe-Nx active sites in the Fe-NSC catalyst to provide sufficient electrochemical active sites, which is beneficial for bacterial adhesion and biofilm formation, and thus facilitates intercellular signal transduction and charge transfer, enhancing the extracellular electron transfer (EET) rate. The Fe-Nx active sites in the Fe-NSC catalyst are structurally similar to heme in c-Cyts, accelerating the EET process through the directional effect of flavin binding to c-Cyts. The Fe-Nx active sites in the Fe-NSC catalyst more readily acquire electrons from c-Cyts and collect flavin through the π-π interaction of the isochloropyrazine ring.

[0032] 2. The Fe-NSC catalyst-modified carbon cloth electrode with attached Bacillus subtilis biofilm provided by this invention not only has excellent electrocatalytic ORR activity in half-cells, but also exhibits good bio-power generation capability when assembled into a full cell as a catalytic material for MFC air cathode. Attached Figure Description

[0033] Figure 1 (a, b) SEM images of the Fe-NSC catalyst prepared in Example 1; (c, d) TEM images; (e) elemental mapping images;

[0034] Figure 2 (a) XRD pattern and (b) Raman spectrum of the Fe-NSC catalyst prepared in Example 1;

[0035] Figure 3 (a) XPS full spectrum of the Fe-NSC catalyst prepared in Example 1; (b) high-resolution N 1s peak fitting result; (c) high-resolution C 1s peak fitting result;

[0036] Figure 4 The following are (a) cyclic voltammetry (CV) and (b) linear sweep voltammetry (LSV) plots of the electrocatalytic ORR of the Fe-NSC catalyst-modified carbon cloth electrode with Bacillus subtilis biofilm prepared in Example 2.

[0037] Figure 5 The polarization curve-power density diagram is shown for the Fe-NSC catalyst-modified carbon cloth electrode with Bacillus subtilis biofilm prepared in Example 2, when used as the air cathode material of MFC. Detailed Implementation

[0038] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise specified, the experimental methods used in the embodiments of the present invention are conventional methods; the materials and reagents used, unless otherwise specified, are commercially available reagents and materials.

[0039] Example 1:

[0040] Step S1: Prepare a 1.6M 2-methylimidazolium methanol solution and a 0.1M Zn(NO3)2·6H2O methanol solution. Mix the two solutions at a volume ratio of 1:3 and stir vigorously at room temperature for 24 hours. Wash with methanol and centrifuge, repeating three times. Then, dry the collected precipitate under vacuum at 70°C for 12 hours to obtain ZIF-8.

[0041] Step S2: Disperse 200 mg of ZIF-8 in 20 mL of methanol, then inject 1 mL of Fe(NO3)3·9H2O methanol solution (10 mg·mL). -1 Add 50 mL of a methanol solution (3.2 M) of 4,4′-dihydroxydiphenyl sulfone to the above dispersion. Stir at room temperature for 15 h. Wash three times with methanol, and then vacuum dry at 70 °C for 12 h to obtain the Fe-NSC precursor.

[0042] Step S3: The Fe-NSC catalyst precursor was pyrolyzed at 900℃ for 3 hours in a tube furnace under a flowing Ar atmosphere (heating rate 5℃·min). -1 ), thus obtaining the Fe-NSC catalyst.

[0043] Step S4: Disperse 3 mg of Fe-NSC catalyst in a mixed solution of 50 μL Nafion (perfluoropolymer) and 1 mL ethanol, and sonicate for 1 h to generate a Fe-NSC catalyst mixed solution. Take an appropriate amount of the mixed solution and drop it onto carbon cloth (dropping volume: 40 μL·cm). -2 The electrode material of Fe-NSC catalyst-modified carbon cloth is prepared by drying with infrared light and repeating the process once.

[0044] SEM and TEM images of the Fe-NSC catalyst in Example 1 are shown below. Figure 1 As shown in the figure: the microstructure of the Fe-NSC catalyst was characterized by SEM and TEM. After high-temperature treatment, the Fe-NSC catalyst still maintains a polyhedral shape. Figure 1 X-ray energy dispersive spectroscopy (EDX) analysis showed that the Fe-NSC catalyst was mainly composed of a carbon framework, containing a certain amount of Fe, N, and S dopants. Figure 1 e).

[0045] The XRD and Raman patterns of the carbon dot material in Example 1 are as follows: Figure 2 As shown: The crystal structure of the Fe-NSC catalyst was analyzed by XRD characterization. Figure 2 a) The Fe-NSC catalyst exhibits two diffraction peaks at 2θ = 25° and 44°, which is due to the characteristic diffraction of the (002) and (101) crystal planes of graphitic carbon, indicating that the prepared Fe-NSC catalyst has a certain degree of crystallinity. In order to further study the internal structure of the Fe-NSC catalyst, Raman spectroscopy was performed. Figure 2 b), D peak (1364cm) -1 ) is sp 3 The disordered vibrations of carbon atoms represent defects in the C atom crystal; the G peak (1577 cm⁻¹) -1 ) represents the C atom sp 2 Hybrid in-plane stretching vibrations represent ordered structures and the degree of graphitization.

[0046] The XRD and Raman patterns of the carbon dot material in Example 1 are as follows: Figure 3 As shown: XPS analysis was used to analyze the elemental composition and valence state of the Fe-NSC catalyst. The full spectrum confirmed the coexistence of Fe, N, S, and C in the Fe-NSC catalyst. Figure 3a). N1s spectra show that the Fe-NSC catalyst simultaneously contains pyridine-N, pyrrole-N, graphite-N, and Fe-Nx ( Figure 3 b). C1s spectra show that the Fe-NSC catalyst contains CC / C=C, CN, and oxygen-containing groups. These data indicate that the Fe-Nx structure was successfully introduced into the Fe-NSC catalyst. Figure 3 c).

[0047] Application Examples

[0048] Application of Fe-NSC catalyst in the preparation of MFC air cathode biomaterials: Bacillus subtilis was inoculated into LB liquid medium (10 g L). -1 Tryptone, 5g / L -1 Yeast extract and 5g L -1 The Fe-NSC catalyst-modified carbon cloth electrode material prepared in Example 1 was placed in a culture medium and incubated with bacteria for 36 hours to obtain a Fe-NSC catalyst-modified carbon cloth cathode loaded with Bacillus subtilis biofilm.

[0049] Half-cell electrochemical performance testing: ORR performance testing was conducted on a Shanghai Chenhua CHI 760E electrochemical workstation using a typical three-electrode setup. The carbon cloth electrode (1cm × 1cm) prepared above was used as the working electrode, and a platinum sheet and a saturated silver / silver chloride electrode were used as the counter and reference electrodes, respectively. Electrochemical measurements were performed in 150 mL of M9 buffer solution (pH=7) composed of 22 mM KH2PO4, 42 mM Na2HPO4, 85.5 mM NaCl, 1.0 mM MgSO4, and 0.1 mM CaCl2. After O2 saturation, the ORR was measured at 50 mV s⁻¹. -1 Cyclic voltammetry (CV) measurements were performed at a scan rate of 5 mV / s. -1 Linear scan voltammetry (LSV) curves were tested at the scanning speed.

[0050] MFC full cell testing: A classic H-type dual-chamber MFC with an internal working volume of 50 mL was used, separated by a proton exchange membrane (Nafion 211 from DuPont). Carbon cloth (2 cm × 2 cm) served as the base electrode for both the cathode and anode. The cathode electrolyte was an M9 solution containing 30 mM glucose, purged with oxygen for 30 min to remove dissolved nitrogen. The anolyte was an M9 solution containing 1 M glucose. The Fe-NSC catalyst-modified carbon cloth electrode with the aforementioned Bacillus subtilis biofilm was used as the biocathode, and a commercially available 40% Pt / C coated carbon cloth electrode was used as the anode with a loading of 2 mg / cm³. -2The voltage of the assembled MFC was evaluated using a CHI 760E electrochemical workstation (Chenhua 760E, Shanghai, China). Once the MFC voltage reached a steady state, polarization and power density curves were obtained by varying the external resistance (10 ~ 300,000 Ω). The output performance of the MFC under long-term operation was tested using a Keithley 2700 data acquisition system with an external resistance of 1000 Ω. The MFC was operated at 37°C, and the operation was repeated three times.

[0051] Figure 4 shows the electrocatalytic ORR performance of the Fe-NSC catalyst-modified carbon cloth electrode supported on Bacillus subtilis biofilm in Example 2, with a maximum current density of 3.39 mA cm⁻¹. -2 Compared to conventional pure biocatalyst carbon cloth electrode (1.71 mA cm⁻¹), -2 The efficiency was nearly doubled compared to a catalyst-free carbon cloth electrode (1.03 mA cm⁻¹). -2 The current density is increased by nearly 2.3 times. The half-wave potential is 0.779 V (vs. RHE), which is much higher than the 0.511 V of conventional pure biocatalyst carbon cloth electrode and the 0.371 V of the catalyst-free system. This excellent performance is due to the synergistic effect of Fe-NSC catalyst and Bacillus subtilis biofilm, which achieves excellent performance in both current density and half-wave potential. It stands out among non-precious metal catalysts and provides a promising option for cathode materials of energy conversion devices such as microbial fuel cells.

[0052] Figure 5 The figure shows the polarization curve-power density diagram of the Fe-NSC catalyst-modified carbon cloth electrode with Bacillus subtilis biofilm prepared in Example 2, used as the air cathode material of MFC. As can be seen from the figure, the MFC assembled with this electrocatalyst achieves a maximum power density of 249.7 µW·cm⁻¹. -2 It is approximately 91.17 µW·cm⁻¹ of a conventional pure biocatalyst carbon cloth electrode. -2 The significant difference of 2.74 times that of Fe-NSC catalyst-modified carbon cloth and Bacillus subtilis clearly demonstrates that the synergistic effect of Fe-NSC catalyst-modified carbon cloth and Bacillus subtilis enables it to exhibit excellent power generation performance in MFC air cathode applications, greatly improving the energy output level of MFC.

[0053] Obviously, the specific implementation schemes described above are merely a further detailed explanation of the purpose, technical solution and beneficial effects of the present invention. It should be understood that the above descriptions are only specific examples of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing an Fe-NSC catalyst, characterized in that, Includes the following steps: S1. Preparation of Fe-NSC precursor: ZIF-8 is added to a solvent for dispersion, and then an iron salt is added; then a sulfur source is introduced to obtain the Fe-NSC precursor; S2. The precursor obtained in step S1 is heated at 800-1000℃ for 2-4 hours under argon protection.

2. The method for preparing the Fe-NSC catalyst according to claim 1, characterized in that, In step S1, during the preparation of the Fe-NSC precursor, the mass ratio of ZIF-8: iron salt: sulfur source is 200:(5-20):(100-200), the mass concentration of ZIF-8 in the mixed system is 2.0-4.0 g / L, the iron salt is selected from Fe(NO3)3·9H2O, the sulfur source is selected from 4,4′-dihydroxydiphenyl sulfone, and the solvent is selected from methanol.

3. The method for preparing the Fe-NSC catalyst according to claim 1, characterized in that, The heating rate in step S2 is 2~5℃·min -1 .

4. The method for preparing the Fe-NSC catalyst according to claim 1, characterized in that, ZIF-8 was obtained by the following method: 1.6M 2-methylimidazolium methanol solution and 0.1M Zn(NO3)2·6H2O methanol solution were mixed at a volume ratio of 1:2 to 4 and stirred at room temperature for 24 hours. After washing, the mixture was centrifuged, and the precipitate was collected and dried to obtain ZIF-8.

5. The Fe-NSC catalyst obtained by any of the preparation methods described in claims 1 to 4.

6. The application of the Fe-NSC catalyst according to claim 5 in the preparation of air cathode for microbial fuel cells.

7. The application according to claim 6, characterized in that, The catalyst is mixed with a binder and a solvent and ultrasonically dispersed to form a uniform dispersion. The dispersion is then coated onto a current collector and dried to obtain an electrode material modified with the Fe-NSC catalyst.

8. The application according to claim 7, characterized in that, Bacillus subtilis is attached to the electrode material to serve as the cathode.

9. The application according to claim 8, characterized in that, The cathode preparation process involves inoculating Bacillus subtilis into LB liquid medium and then placing the electrode in the liquid medium for co-incubation with the bacteria. The resulting Fe-NSC catalyst-modified electrode with an attached Bacillus subtilis biofilm is the cathode. The LB liquid medium consists of 10 g / L of LB liquid medium. -1 Tryptone, 5g / L -1 Yeast extract and 5g L -1 Sodium chloride.

10. The application according to claim 8 or 9, characterized in that, The catholyte is an M9 solution containing 30 mM glucose. A carbon cloth electrode coated with commercial Pt / C is used as the anode. The anolyte is an M9 solution containing 1 M glucose. The two chambers are separated by a proton exchange membrane. The MFC is placed in an incubator at 30–37°C with an external resistor connected. Oxygen is introduced into the catholyte and nitrogen is introduced into the anolyte.

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