Modified anode for marine sediment microbial fuel cell, preparation method of modified anode and marine sediment microbial fuel cell

Abstract

The application discloses a modified anode for a marine sediment microbial fuel cell and a preparation method of the modified anode and the marine sediment microbial fuel cell, and the preparation method comprises the following steps: S1, obtaining a primary anode; S2, nitrogen is introduced into a first PBS buffer solution to perform nitrogen exposure treatment, and dopamine hydrochloride is added to obtain a first electrolyte; S3, the primary anode is immersed into the first electrolyte, and electro-deposition is performed on the primary anode by a first cyclic voltammetry scanning method to obtain a PDA modified anode; S4, Fe3O4 powder is added into a second PBS buffer solution to obtain a second electrolyte; and S5, the PDA modified anode is immersed into the second electrolyte, and electro-deposition is performed on the PDA modified anode by a second cyclic voltammetry scanning method to obtain a PDA / Fe3O4 modified anode. The PDA / Fe3O4 composite is used to modify the anode, the electrochemical performance of the anode is improved, and a proper amount of amino acid is added into the sediment, so that the organic matter conversion and electron transmission efficiency of the microbial fuel cell are improved, and the electricity generation performance of the microbial fuel cell is improved.

Description

Technical Field

[0001] This invention belongs to the field of microbial fuel cell technology, specifically relating to a modified anode for marine sediment microbial fuel cells, its preparation method, and marine sediment microbial fuel cells. Background Technology

[0002] Marine sediment microbial fuel cells (MSMFCs), as a green energy technology, can directly generate electricity from the organic matter and microbial metabolic activities in marine sediments, and have broad application prospects. However, their performance is limited by factors such as electrode materials and sediment characteristics. Existing MSMFCs typically have low conductivity, often requiring large conducting currents and voltages to achieve the desired effect, resulting in significant power losses.

[0003] As a crucial interface for microbial attachment and electron transfer, the selection and design of different anode materials and structures significantly impact the power generation capacity of microbial microbial fuel cells (MSMFCs). The surface properties of the anode material directly affect the start-up time, output power, and long-term operational stability of MSMFCs. In recent years, anode surface modification technology has become a key research direction for improving MSMFC performance. By optimizing electrode materials and structures, the adhesion ability of microorganisms and the efficiency of extracellular electron transfer can be significantly enhanced. Furthermore, the addition of exogenous organic matter is considered one of the effective means to improve MSMFC performance. Appropriate addition of exogenous organic matter can alter the composition and function of the microbial community, thereby improving electron generation and transfer efficiency. Currently, there are few studies, both domestically and internationally, on modifying anodes using electropolymerization and adding exogenous organic matter in the field of marine sediment microbial fuel cells. Modifying the anode of MSMFCs to improve electron transfer efficiency and microbial attachment is crucial for improving battery output power and stability.

[0004] Therefore, research on how to modify the anode surface to enhance its conductivity and biocompatibility, thereby improving the electrode's power generation performance, and how to improve battery performance through the addition of exogenous organic matter, is of great significance and value. Summary of the Invention

[0005] To address the problems in existing technologies, this invention provides a modified anode for marine sediment microbial fuel cells (MSMFCs), its preparation method, and the MSMFC itself. By modifying the anode with a PDA / Fe3O4 composite, the anode's adsorption capacity for microorganisms is enhanced, thereby improving its electrochemical performance. Furthermore, the addition of exogenous amino acids to the sediment optimizes the supply of organic nitrogen sources, selectively enriches electrogenic functional microbial communities, and enhances organic matter conversion and electron transfer efficiency, significantly improving the power generation performance of MSMFCs. This provides a new strategy for the regulation of the microbial-electrode interface in green energy technologies.

[0006] The primary objective of this invention is to provide a method for preparing a modified anode for marine sediment microbial fuel cells, the method comprising the following steps:

[0007] S1 Obtains a graphite carbon plate and sequentially grinds, washes, and dries the graphite carbon plate to obtain a primary anode;

[0008] S2 obtains the first PBS buffer, introduces nitrogen gas into the first PBS buffer for nitrogen aeration treatment, then adds dopamine hydrochloride, mixes evenly, and obtains the first electrolyte;

[0009] S3 immerses the primary anode in the first electrolyte and performs electropolymerization on the primary anode using the first cyclic voltammetry scanning method to obtain a PDA-modified anode;

[0010] S4 obtains the second PBS buffer, adds Fe3O4 powder to the second PBS buffer, mixes evenly, and obtains the second electrolyte;

[0011] S5. The PDA-modified anode is immersed in the second electrolyte, and electrodeposition is performed on the PDA-modified anode by the second cyclic voltammetry scanning method to obtain the PDA / Fe3O4 modified anode.

[0012] Specifically, in step S2, the concentration of the first PBS buffer is 0.01 mol / L.

[0013] Specifically, in step S2, the concentration of dopamine hydrochloride in the first electrolyte is 1 mg / mL.

[0014] Specifically, the first cyclic voltammetry scanning method in step S3 is as follows: using the primary anode as the working electrode, saturated silver-silver chloride as the reference electrode, and platinum wire as the counter electrode, the cyclic scanning is performed for 6 to 40 cycles under the conditions of a scanning rate of 20 mV / s and a potential range of -0.5 to 0.5V.

[0015] Specifically, in step S4, the concentration of the second PBS buffer is 0.01 mol / L.

[0016] Specifically, in step S4, the concentration of Fe3O4 powder in the second electrolyte is 15~60 mg / mL.

[0017] Specifically, the second cyclic voltammetry scanning method in step S5 is as follows: using a PDA modified anode as the working electrode, saturated silver-silver chloride as the reference electrode, and platinum wire as the counter electrode, pre-deposit for 10 min under the conditions of a scan rate of 20 mV / s and a potential range of -0.7~0.7 V, and then electrodeposit for 20 min at a constant potential of -1.4 V.

[0018] The second objective of this invention is to provide a PDA / Fe3O4 modified anode prepared by the method described above.

[0019] A third objective of this invention is to provide a marine sediment microbial fuel cell, comprising an anode chamber and a cathode chamber, wherein an anode and a cathode are respectively disposed in the anode chamber and the cathode are connected by an external circuit wire, and ion exchange is achieved between the anode chamber and the cathode chamber through a salt bridge. The anode chamber is supplied with filtered seawater, marine sediment and exogenous amino acids, and the cathode chamber is supplied with filtered seawater. The anode is the aforementioned PDA / Fe3O4 modified anode, and the cathode is a carbon brush.

[0020] Specifically, the exogenous amino acid is any one of aspartic acid, glutamic acid, or histidine; the volume ratio of filtered seawater to marine sediment in the anode chamber is 2:8; and the concentration of exogenous amino acid in the anode chamber is 0.001~0.1 μmol / mL.

[0021] Compared with the prior art, the present invention has the following beneficial technical effects:

[0022] (1) Based on the electrochemical deposition method, the present invention polymerizes biocompatible and adhesive polydopamine (PDA) on a graphite carbon plate and further deposits iron(III) oxide (Fe3O4) with good conductivity, forming a composite layered sandwich structure on the anode, which enhances the electron transfer efficiency and microbial attachment ability of the anode and promotes the adsorption and degradation of organic matter. In addition, when constructing the battery with the modified anode, the present invention optimizes the supply of organic nitrogen source by forming a stable biofilm formed by enriching a large number of electrogenic bacteria on the surface of the modified anode and forming a positive synergistic effect with the added deposited amino acids, thereby optimizing the supply of organic nitrogen source, directionally enriching electrogenic functional bacteria, and simultaneously enhancing the conversion efficiency of organic matter and electron transfer efficiency, effectively improving the electrochemical performance of the MSMFCs system.

[0023] (2) This invention employs a method combining electropolymerization of PDA with electrodeposition of Fe3O4 particles to composite modify the graphite carbon plate anode. First, an electrochemical deposition method is used to deposit a PDA film on the graphite carbon plate anode using potential oxidation of dopamine. The PDA binds to the graphite carbon plate through π−π conjugation, effectively introducing functional groups beneficial to electron transport, such as oxygen- and nitrogen-containing functional groups, providing a large number of active sites. This significantly improves the hydrophilicity and electron transport efficiency of the anode. Then, Fe3O4 is compositely deposited on the anode with the attached PDA film using electrodeposition. Fe3O4 has an Fd 3m spatial structure and contains Fe... 2+ and Fe 3+The electrons are arranged in a basically disordered manner at the octahedral positions, and can rapidly transfer between the two oxidation states of iron, exhibiting unique electrical properties. By using a PDA / Fe3O4 composite modified anode, through a triple synergistic mechanism of "interface hydrophilization - electron channel construction - functional microbial community regulation", the modified anode has improved electron transport capacity, stability and output voltage. At the same time, it also enhances the adsorption capacity of microorganisms, can regulate the sediment microenvironment, and promotes the degradation of organic matter in the sediment, making it more suitable for the growth of electrogenic bacteria and electron transport. Furthermore, by optimizing the ratio of PDA and Fe3O4, the biocompatibility of the anode interface and electron transport efficiency are balanced, so as to efficiently couple the organic matter oxidation metabolism and charge transfer process.

[0024] (3) In this invention, exogenous amino acids are added to the sediment in the anode chamber of a marine sediment microbial fuel cell. The added amino acids can change the microenvironment around the anode, accelerate the transfer rate of electrons between the electrode and the electrolyte, and effectively reduce the charge transfer resistance. This not only helps to improve the anode energy density and charge transfer efficiency, but also optimizes the microbial community structure and promotes the stable diffusion and degradation of organic matter amino acids. This improves the power generation performance and organic matter degradation efficiency of MSMFCs. By optimizing the amount of exogenous amino acids added, the dynamic balance of "metabolic intensity-electron transfer-environmental homeostasis" can be precisely controlled to achieve efficient synergy between organic matter degradation and energy output. Attached Figure Description

[0025] Figure 1 Images (a)-(c) are surface LSCM images of the unmodified anode in Comparative Example 1 and the PDA-modified anodes in Examples 1 and 3 of this invention.

[0026] Figure 2 Images (a)-(c) show the overall XPS spectrum and C1s peak profile of the unmodified anode in Comparative Example 1 and the PDA-modified anode in Example 1 of this invention.

[0027] Figure 3 This is a comparison diagram of the water contact angles between the unmodified anode in Comparative Example 1 and the PDA-modified anodes in Examples 1-4 of the present invention;

[0028] Figure 4 Images (a)-(c) are SEM images of the surface morphology of the unmodified anode in Comparative Example 1 and the PDA / Fe3O4 modified anodes prepared in Examples 1 and 6 of this invention.

[0029] Figure 5 Images (a)-(d) are surface LSCM images of the unmodified anode in Comparative Example 1, the PDA-modified anode prepared in Example 1, the PDA / Fe3O4-modified anode, and the PDA / Fe3O4-modified anode prepared in Example 6 of the present invention.

[0030] Figure 6 Images (a)-(b) show the overall XPS spectrum and Fe 2p peak profile of the unmodified anode surface in Comparative Example 1 and the PDA / Fe3O4 modified anode prepared in Example 1.

[0031] Figure 7 Comparison of CV curves of the PDA / Fe3O4 modified anodes prepared in Examples 1 and 5-7 of this invention, the unmodified anode in Comparative Example 1, and the PDA modified anode in Comparative Example 3;

[0032] Figure 8 Tafel curves comparing the PDA / Fe3O4 modified anodes prepared in Examples 1 and 5-7 of this invention with the unmodified anode in Comparative Example 1 and the PDA modified anode in Comparative Example 3;

[0033] Figure 9 The electrochemical impedance spectroscopy (EKQS) comparison diagrams of the PDA / Fe3O4 modified anodes prepared in Examples 1 and 5-7 of this invention, the unmodified anode in Comparative Example 1, and the PDA modified anode in Comparative Example 3 are shown.

[0034] Figure 10 Figures (a)-(b) show the power density and anodic polarization curves of the microbial fuel cells prepared in Examples 1 and 8-11 of this invention and the microbial fuel cells prepared in Comparative Example 2.

[0035] Figure 11 This is a comparison chart of the long-term discharge voltage curves of the microbial fuel cells prepared in Examples 1 and 8-11 of the present invention and the microbial fuel cell prepared in Comparative Example 2.

[0036] Figure 12 (a)-(c) are the distribution diagrams of total organic carbon and total nitrogen content in sediments near a fixed point after long-term load operation of the microbial fuel cell prepared in Comparative Example 2 and the microbial fuel cells prepared in Examples 1 and 9 of this invention.

[0037] Figure 13 Comparative diagrams showing the distribution of microbial community structures near the anode in the microbial fuel cell prepared in Comparative Example 2 of this invention and the microbial fuel cells prepared in Examples 1 and 9.

[0038] Figure 14 (a)-(d) are box plots of microbial α-diversity near the anode under different indices in the microbial fuel cell prepared in Comparative Example 2 and the microbial fuel cells prepared in Examples 1 and 9 of this invention;

[0039] Figure 15 This is a comparison chart showing the trend of total THAA content in the deposits near the anode in the microbial fuel cell prepared in Comparative Example 2 of this invention and the microbial fuel cells prepared in Examples 1 and 9.

[0040] Figure 16 This is a mechanism diagram of the operation and amino acid degradation of the microbial fuel cells (MSMFCs) prepared in Example 1 of the present invention. Detailed Implementation

[0041] The technical solutions 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 a part of the embodiments of the present invention, and not all of the embodiments. Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the present invention.

[0042] Example 1

[0043] Preparation of modified anodes for marine sediment microbial fuel cells:

[0044] S1. Obtain a graphite carbon plate and polish it with sandpaper of different grits until smooth. Then wash it with Milli-Q water and dry it in a vacuum drying oven at 60°C for 12 hours. After taking it out, drill a hole at the top, connect a silver-plated wire and seal it to obtain the primary anode.

[0045] S2. Take 20 mL of 0.01 mol / L PBS buffer solution, and purge the 20 mL PBS buffer solution with nitrogen gas for 10 min to remove oxygen; then add 20 mg of dopamine hydrochloride, mix well in a nitrogen atmosphere to obtain the first electrolyte solution.

[0046] S3 involves immersing the primary anode in the first electrolyte and performing polydopamine electrodeposition on the primary anode using a first cyclic voltammetry scanning method. Specifically, a three-electrode system is constructed using the primary anode as the working electrode, saturated silver-silver chloride as the reference electrode, and platinum wire as the counter electrode. The system is then cyclically scanned 20 times at a scan rate of 20 mV / s and a potential range of -0.5 to 0.5 V to obtain the PDA-modified anode, denoted as S20.

[0047] S4. Take 20 mL of 0.01 mol / L second PBS buffer, add 0.6 g of Fe3O4 powder to the 20 mL second PBS buffer, mix well, and obtain the second electrolyte.

[0048] S5. The PDA-modified anode was immersed in the second electrolyte, and electrodeposition was performed on the PDA-modified anode by the second cyclic voltammetry scanning method. The PDA-modified anode was used as the working electrode, saturated silver-silver chloride as the reference electrode, and platinum wire as the counter electrode to construct a three-electrode system. In the three-electrode system, the pre-deposition was carried out for 10 min at a scanning rate of 20 mV / s and a potential range of -0.7~0.7 V. Then, the electrodeposition was carried out for 20 min at a constant potential of -1.4 V to obtain the PDA / Fe3O4 modified anode, which is denoted as PDA / Fe3O4[0.6].

[0049] Preparation of marine sediment microbial fuel cells:

[0050] The seabed sediment used in Example 1 of this invention was collected from the waters near Maodao Island in Jiaozhou Bay (120.33°E, 36.19°N). Filtered seawater was placed on top of the marine sediment, with a volume ratio of filtered seawater to marine sediment of 2:8, totaling 1000 mL, forming an anode chamber. Exogenous amino acids at a concentration of 5 μmol were added to the anode chamber. The PDA / Fe3O4 modified anode prepared in Example 1 was then buried in the sediment to a depth of approximately 6 cm. A carbon brush connected to a titanium wire (Φ=1 mm) was used as the cathode, placed in the cathode chamber, which was supplied with filtered seawater. The anode and cathode were connected by an external circuit wire, and mass exchange between the cathode and anode was achieved through a salt bridge. The external circuit was loaded with a 500 Ω fixed resistor, forming the marine sediment microbial fuel cell prepared in Example 1, denoted as AA5. The microbial fuel cell includes an anode chamber and a cathode chamber, with an anode and a cathode respectively disposed in the anode chamber and the cathode chamber. The anode and cathode are connected by an external circuit wire. Ion exchange is achieved between the anode chamber and the cathode chamber through a salt bridge. The anode chamber is supplied with filtered seawater, marine sediments and exogenous aspartic acid, and the cathode chamber is supplied with filtered seawater.

[0051] Example 2

[0052] When preparing the modified anode for marine sediment microbial fuel cells, the only difference from Example 1 is that in step S3, the number of scans in the first cyclic voltammetry scan is 6, resulting in the PDA / Fe3O4 modified anode prepared in Example 2, denoted as S6.

[0053] The method for preparing marine sediment microbial fuel cells differs from Example 1 only in that the anode used is the PDA / Fe3O4 modified anode prepared in Example 2, resulting in the marine sediment microbial fuel cell prepared in Example 2.

[0054] Example 3

[0055] When preparing the modified anode for marine sediment microbial fuel cells, the only difference from Example 1 is that in step S3, the number of scans in the first cyclic voltammetry scan is 10, resulting in the PDA / Fe3O4 modified anode prepared in Example 3, denoted as S10.

[0056] The method for preparing marine sediment microbial fuel cells differs from Example 1 only in that the anode used is the PDA / Fe3O4 modified anode prepared in Example 3, resulting in the marine sediment microbial fuel cell prepared in Example 3.

[0057] Example 4

[0058] When preparing the modified anode for marine sediment microbial fuel cells, the only difference from Example 1 is that in step S3, the number of scans in the first cyclic voltammetry scan is 40, resulting in the PDA / Fe3O4 modified anode prepared in Example 4, denoted as S40.

[0059] In the method for preparing marine sediment microbial fuel cells, the only difference from Example 1 is that the anode used is the PDA / Fe3O4 modified anode prepared in Example 4, resulting in the marine sediment microbial fuel cell prepared in Example 3.

[0060] Example 5

[0061] When preparing the modified anode for marine sediment microbial fuel cells, the only difference from Example 1 is that the amount of Fe3O4 powder added in step S4 is 0.3 g, resulting in the PDA / Fe3O4 modified anode prepared in Example 5, denoted as PDA / Fe3O4[0.3].

[0062] The method for preparing marine sediment microbial fuel cells differs from Example 1 only in that the anode used is the PDA / Fe3O4 modified anode prepared in Example 5, resulting in the marine sediment microbial fuel cell prepared in Example 5.

[0063] Example 6

[0064] When preparing the modified anode for marine sediment microbial fuel cells, the only difference from Example 1 is that the amount of Fe3O4 powder added in step S4 is 0.9g, resulting in the PDA / Fe3O4 modified anode prepared in Example 6, denoted as PDA / Fe3O4[0.9].

[0065] The method for preparing marine sediment microbial fuel cells differs from Example 1 only in that the anode used is the PDA / Fe3O4 modified anode prepared in Example 6, resulting in the marine sediment microbial fuel cell prepared in Example 6.

[0066] Example 7

[0067] When preparing the modified anode for marine sediment microbial fuel cells, the only difference from Example 1 is that the amount of Fe3O4 powder added in step S4 is 1.2g, resulting in the PDA / Fe3O4 modified anode prepared in Example 7, denoted as PDA / Fe3O4 [1.2].

[0068] In the method for preparing marine sediment microbial fuel cells, the only difference from Example 1 is that the anode used is the PDA / Fe3O4 modified anode prepared in Example 7, resulting in the marine sediment microbial fuel cell prepared in Example 6.

[0069] Example 8

[0070] The preparation method for the modified anode used in marine sediment microbial fuel cells is exactly the same as that in Example 1.

[0071] The method for preparing marine sediment microbial fuel cells differed from that in Example 1 only in that the amount of exogenous amino acids added in the anode chamber was 1 μmol, resulting in the marine sediment microbial fuel cell prepared in Example 9, denoted as AA1.

[0072] Example 9

[0073] The preparation method for the modified anode used in marine sediment microbial fuel cells is exactly the same as that in Example 1.

[0074] The method for preparing marine sediment microbial fuel cells differs from that in Example 1 only in that the amount of exogenous amino acids added in the anode chamber is 20 μmol, resulting in the marine sediment microbial fuel cell prepared in Example 10, denoted as AA20.

[0075] Example 10

[0076] The preparation method for the modified anode used in marine sediment microbial fuel cells is exactly the same as that in Example 1.

[0077] The method for preparing marine sediment microbial fuel cells differs from that in Example 1 only in that the amount of exogenous amino acids added in the anode chamber is 50 μmol, resulting in the marine sediment microbial fuel cell prepared in Example 11, denoted as AA50.

[0078] Example 11

[0079] The preparation method for the modified anode used in marine sediment microbial fuel cells is exactly the same as that in Example 1.

[0080] The method for preparing marine sediment microbial fuel cells differed from that in Example 1 only in that the amount of exogenous amino acids added in the anode chamber was 100 μmol, resulting in the marine sediment microbial fuel cell prepared in Example 12, denoted as AA100.

[0081] Example 12

[0082] Preparation of modified anodes for marine sediment microbial fuel cells:

[0083] S1. Obtain a graphite carbon plate and polish it with sandpaper of different grits until smooth. Then wash it with Milli-Q water and dry it in a vacuum drying oven at 60°C for 12 hours. After taking it out, drill a hole at the top, connect a silver-plated wire and seal it to obtain the primary anode.

[0084] S2. Take 20 mL of 0.01 mol / L PBS buffer solution, and purge the 20 mL PBS buffer solution with nitrogen gas for 10 min to remove oxygen; then add 20 mg of dopamine hydrochloride, mix well in a nitrogen atmosphere to obtain the first electrolyte solution.

[0085] S3 immerses the primary anode in the first electrolyte and performs polydopamine electrodeposition on the primary anode using a first cyclic voltammetry scanning method. Specifically, a three-electrode system is constructed using the primary anode as the working electrode, saturated silver-silver chloride as the reference electrode, and platinum wire as the counter electrode. The three-electrode system is cyclically scanned for 15 cycles at a scan rate of 20 mV / s and a potential range of -0.5 to 0.5 V to obtain the PDA-modified anode.

[0086] S4. Take 20 mL of 0.01 mol / L second PBS buffer, add 0.8 g of Fe3O4 powder to the 20 mL second PBS buffer, mix well, and obtain the second electrolyte.

[0087] S5. The PDA-modified anode was immersed in the second electrolyte, and electrodeposition was performed on the PDA-modified anode using the second cyclic voltammetry scanning method. A three-electrode system was constructed with the PDA-modified anode as the working electrode, saturated silver-silver chloride as the reference electrode, and platinum wire as the counter electrode. In the three-electrode system, pre-deposition was performed for 10 min at a scan rate of 20 mV / s and a potential range of -0.7 to 0.7 V, followed by electrodeposition at a constant potential of -1.4 V for 20 min to obtain the PDA / Fe3O4 modified anode prepared in Example 13.

[0088] Preparation of marine sediment microbial fuel cells:

[0089] The seabed sediment used in Example 13 of this invention was collected from the waters near Maodao Island in Jiaozhou Bay. Filtered seawater was placed on top of the marine sediment, with a volume ratio of filtered seawater to marine sediment of 2:8, totaling 1000 mL, forming an anode chamber. Exogenous glutamic acid at a concentration of 15 μmol was added to the anode chamber. The PDA / Fe3O4 modified anode prepared in Example 13 was then buried in the sediment to a depth of approximately 7 cm. A carbon brush connected to a titanium wire served as the cathode, placed in the cathode chamber, which was supplied with filtered seawater. The anode and cathode were connected by external circuit wires, and mass exchange between the anode and cathode was achieved through a salt bridge. The external circuit was loaded with a 500 Ω fixed resistor, forming the marine sediment microbial fuel cell prepared in Example 13. This microbial fuel cell includes an anode chamber and a cathode chamber, each containing an anode and cathode respectively. The anode and cathode are connected by external circuit wires, and ion exchange is achieved between the anode and cathode chambers through a salt bridge. The anode chamber is supplied with filtered seawater, marine sediment, and exogenous glutamic acid, while the cathode chamber is supplied with filtered seawater.

[0090] Example 13

[0091] Preparation of modified anodes for marine sediment microbial fuel cells:

[0092] S1. Obtain a graphite carbon plate and polish it with sandpaper of different grits until smooth. Then wash it with Milli-Q water and dry it in a vacuum drying oven at 60°C for 12 hours. After taking it out, drill a hole at the top, connect a silver-plated wire and seal it to obtain the primary anode.

[0093] S2. Take 20 mL of 0.01 mol / L PBS buffer solution, and purge the 20 mL PBS buffer solution with nitrogen gas for 10 min to remove oxygen; then add 20 mg of dopamine hydrochloride, mix well in a nitrogen atmosphere to obtain the first electrolyte solution.

[0094] S3 immerses the primary anode in the first electrolyte and performs polydopamine electrodeposition on the primary anode using a first cyclic voltammetry scanning method. Specifically, a three-electrode system is constructed using the primary anode as the working electrode, saturated silver-silver chloride as the reference electrode, and platinum wire as the counter electrode. The three-electrode system is cyclically scanned for 30 cycles at a scan rate of 20 mV / s and a potential range of -0.5 to 0.5 V to obtain the PDA-modified anode.

[0095] S4. Take 20 mL of 0.01 mol / L second PBS buffer, add 0.5 g of Fe3O4 powder to the 20 mL second PBS buffer, mix well, and obtain the second electrolyte.

[0096] S5. The PDA-modified anode was immersed in the second electrolyte, and electrodeposition was performed on the PDA-modified anode using the second cyclic voltammetry scanning method. A three-electrode system was constructed with the PDA-modified anode as the working electrode, saturated silver-silver chloride as the reference electrode, and platinum wire as the counter electrode. In the three-electrode system, pre-deposition was performed for 10 min at a scan rate of 20 mV / s and a potential range of -0.7 to 0.7 V, followed by electrodeposition at a constant potential of -1.4 V for 20 min to obtain the PDA / Fe3O4 modified anode prepared in Example 14.

[0097] Preparation of marine sediment microbial fuel cells:

[0098] The seabed sediment used in Example 14 of this invention was collected from the waters near Maodao Island in Jiaozhou Bay. Filtered seawater was placed on top of the marine sediment, with a volume ratio of filtered seawater to marine sediment of 2:8, totaling 1000 mL, forming an anode chamber. Exogenous histidine at a concentration of 15 μmol was added to the anode chamber, and the PDA / Fe3O4 modified anode prepared in Example 14 was then buried in the sediment to a depth of approximately 7 cm. A carbon brush connected to a titanium wire served as the cathode, placed in the cathode chamber, which was supplied with filtered seawater. The anode and cathode were connected by external circuit wires, and mass exchange between the anode and cathode was achieved through a salt bridge. The external circuit was loaded with a 500 Ω fixed resistor, forming the marine sediment microbial fuel cell prepared in Example 14. This microbial fuel cell includes an anode chamber and a cathode chamber, each containing an anode and cathode respectively. The anode and cathode are connected by external circuit wires, and ion exchange is achieved between the anode and cathode chambers through a salt bridge. The anode chamber is supplied with filtered seawater, marine sediment, and exogenous histidine, while the cathode chamber is supplied with filtered seawater.

[0099] Comparative Example 1

[0100] Unmodified graphite carbon plates were used as the anode.

[0101] Preparation of marine sediment microbial fuel cells:

[0102] The seabed sediment used in Comparative Example 1 of this invention was collected from the waters near Maodao Island in Jiaozhou Bay (120.33°E, 36.19°N). Filtered seawater was placed on top of the marine sediment, with a volume ratio of filtered seawater to marine sediment of 2:8, and a total volume of 1000 mL, forming the anode chamber. An unmodified graphite carbon plate was buried in the sediment as the anode to a depth of approximately 6 cm. A titanium wire (Φ=1 mm) connected to a carbon brush served as the cathode, placed in the cathode chamber, which was supplied with filtered seawater. The anode and cathode were connected by an external circuit wire, and mass exchange between the cathode and anode was achieved through a salt bridge. The external circuit was loaded with a 500 Ω fixed resistor, forming the marine sediment microbial fuel cell prepared in Comparative Example 1, denoted as AA0.

[0103] Comparative Example 2

[0104] The preparation method for the modified anode used in marine sediment microbial fuel cells is exactly the same as that in Example 1.

[0105] In preparing the marine sediment microbial fuel cell, the only difference from Example 1 was that no exogenous amino acids were added to the anode chamber, resulting in the marine sediment microbial fuel cell prepared in Comparative Example 2, denoted as AA_Blank.

[0106] Comparative Example 3

[0107] The only difference between this modified anode and Example 1 in preparing the modified anode for marine sediment microbial fuel cells is that after preparing the PDA modified anode, it was not further modified with Fe3O4 composite, resulting in the PDA modified anode prepared in Comparative Example 3.

[0108] When preparing marine sediment microbial fuel cells, the only difference from Example 1 is that the anode in the anode chamber is the PDA-modified anode prepared in Comparative Example 3.

[0109] Structural characterization and performance testing

[0110] In this embodiment of the invention, the surface morphology, chemical composition, and hydrophilicity of the deposited PDA film were characterized sequentially using a laser microscope (LSCM), an X-ray photoelectron spectroscopy (XPS), and a contact angle meter, providing evidence for the effective deposition of the electropolymerized material. On the anode electrode surface after optimization treatment by polydopamine electropolymerization, Fe3O4 electrodeposition was further performed on the PDA using cyclic voltammetry, and the modified anode was physically characterized. The modified anode was electrochemically characterized by measuring open-circuit potential, cyclic voltammetry curves, Tafel curves, and electrochemical impedance spectroscopy. By adding exogenous amino acids to the deposits, various organic matter environments were simulated, a microbial fuel cell was constructed, and its performance was tested. Long-term power monitoring and organic matter collection were performed on the operating fuel cell to analyze the degradation and diffusion behavior of organic matter near the anode and the microbial community on the anode surface, and to analyze the impact of the modified anode on the succession of the microbial community.

[0111] Figure 1 Images (a)-(c) show the surface LSCM images of the unmodified anode in Comparative Example 1 and the PDA-modified anodes in Examples 1 and 3 of this invention; it can be seen that... Figure 1 (a) The anode surface is relatively rough, with natural textures and undulations, which are inherent morphologies formed during the preparation of the graphite carbon plate; such as Figure 1 As shown in (b), after 10 turns of PDA electrodeposition on the graphite carbon plate surface, a large number of relatively obvious PDA particles appeared on the graphite carbon plate surface, and were uniformly distributed on the surface of the graphite carbon plate, tightly bonded to the substrate material, providing more active sites for electrochemical reactions; Figure 1 As shown in (c), when the number of electrodeposition cycles is increased to 20, the particulate matter on the surface of the graphite carbon plate becomes more concentrated; it can be seen that the number of electrodeposition cycles of PDA has a significant impact on the morphology of the anode surface. By controlling the number of electrodeposition cycles, the distribution density and overall structure of the electrode surface can be adjusted, and the electrochemical performance of the anode can be optimized. Figure 2 Images (a)-(c) show the overall XPS spectrum and C1s peak profile of the unmodified anode in Comparative Example 1 and the PDA-modified anode in Example 1 of this invention; Figure 2 As shown in (a)-(c), after PDA modification, the oxygen and nitrogen content of the electrode was increased compared with that of the unmodified anode in Comparative Example 1, while the carbon content was significantly reduced. After processing the C 1s fitting peak, the surface of the unmodified anode in Comparative Example 1 was mainly composed of C−C bonds. After PDA modification, C−N bonds were introduced and the area of ​​C=O bonds increased. When dopamine is oxidized to PDA, a large number of phenol groups are oxidized to generate quinone groups. The adhesion of the attached PDA is largely related to the formation of hydrogen bonds between the hydroxyl groups of catechol and the material surface. Figure 3 This is a comparison diagram of the water contact angles between the unmodified anode in Comparative Example 1 and the PDA-modified anodes in Examples 1-4 of this invention; as shown... Figure 3As shown, the contact angle test results of the anode prepared in Comparative Example 1 and the anodes prepared in Examples 1-4 were 75.16°, 33.88°, 47.99°, 44.59° and 28.07°, respectively. After PDA modification, the contact angle of the anode surface was smaller than that of the unmodified anode, and the hydrophilicity of the modified anode was significantly improved. Figure 4 Images (a)-(c) are SEM images of the surface morphology of the unmodified anode in Comparative Example 1 and the PDA / Fe3O4 modified anodes prepared in Examples 1 and 6 of this invention; after PDA / Fe3O4 deposition, on Figure 4 In (b), spherical particles are clearly visible adhering to the anode surface. Furthermore, the spherical particles on the anode surface become more uniform as the molecular weight of Fe3O4 in the electrolyte increases. This indicates that, based on PDA electrodeposition, Fe3O4 was successfully doped onto the electrode using electrodeposition technology, and both are uniformly adhered to the anode surface. Figure 5 Images (a)-(d) are surface LSCM images of the unmodified anode in Comparative Example 1, the PDA-modified anode prepared in Example 1, the PDA / Fe3O4-modified anode, and the PDA / Fe3O4-modified anode prepared in Example 6 of this invention; Figure 5 As shown, the deposition of PDA causes a blackish-brown substance to adhere to the surface of the graphite carbon plate. With the addition of Fe3O4 deposition, the black color deepens and the surface of the graphite carbon plate shows a metallic luster, which is consistent with the scanning electron microscopy results. PDA and Fe3O4 can be effectively deposited on the anode surface. Figure 6 Images (a)-(b) show the overall XPS spectrum and Fe 2p peak profile of the unmodified anode surface in Comparative Example 1 and the PDA / Fe3O4 modified anode prepared in Example 1, respectively. Figure 6 As shown in (a), the PDA / Fe3O4 modified electrode prepared in Example 1 has four distinct characteristic peaks, corresponding to C 1s, N 1s, O 1s and Fe 2p, respectively, indicating that the prepared modified anode mainly contains four elements: carbon, nitrogen, oxygen and iron. Figure 6 (b) is the peak fractionation diagram of Fe 2p, showing peaks at 710.08, 723.28, 725.58, and 740.18 eV, corresponding to Fe(III) and Fe(O) , respectively. x Fe 2p, Fe 3p, and their anti-rotation peaks exist in the form of PDA / Fe3O4. The elemental composition of the anode surface was calculated, and compared with the unmodified anode in Comparative Example 1, after PDA / Fe3O4 composite modification, the carbon content was effectively reduced from 88.79% to 68.64%, while the oxygen and nitrogen contents increased accordingly. Iron content of 0.95% was also observed, indicating that PDA and Fe3O4 were successfully deposited on the anode surface using the electrodeposition method.

[0112] The specific capacitance is calculated based on the cyclic voltammetry curve of the anode, and the electrochemical activity of the anode is characterized. Figure 7The image shows a comparison of the CV curves of the PDA / Fe3O4 modified anodes prepared in Examples 1 and 5-7 of this invention, the unmodified anode in Comparative Example 1, and the PDA modified anode prepared in Comparative Example 3. Among the composite modified electrodes, the PDA / Fe3O4[0.6] anode in Example 1 has the highest specific capacitance of 34.31 F / m. 2 This is 1.33 times that of the unmodified anode in Comparative Example 1; the specific capacitances of other modified electrodes, including the PDA-modified anode prepared in Comparative Example 3, and the PDA / Fe3O4[0.3], PDA / Fe3O4[0.9], and PDA / Fe3O4[1.2] prepared in Examples 5-7, are 37.58 F / m. 2 31.68 F / m 2 32.66 F / m 2 and 15.92 F / m 2 The main reason for this improvement is that the electropolymerization of PDA increases the number of oxygen-containing functional groups on the electrode surface, and its good hydrophilicity and biocompatibility enhance the electrochemical performance of the electrode. Furthermore, the electrodeposition of Fe3O4 allows the electrochemically active surface area of ​​the anode to accept more electrons, effectively improving the anode's electron storage and transport capacity. The specific capacitance initially increases and then decreases with increasing molecular weight of deposited Fe3O4. This is because excessive deposition, with most of the carbon electrode surface covered by Fe3O4, hinders the accumulation and survival of microorganisms on the anode surface. Figure 8 This is a comparison chart of the Tafel curves of the PDA / Fe3O4 modified anodes prepared in Examples 1 and 5-7 of this invention, the unmodified anode in Comparative Example 1, and the PDA modified anode prepared in Comparative Example 3. By testing the Tafel curves of different anodes, the exchange current densities of the PDA modified anode prepared in Comparative Example 3, and the PDA / Fe3O4[0.3], PDA / Fe3O4[0.9], and PDA / Fe3O4[1.2] modified anodes prepared in Examples 5-7 were calculated to be 5.97 × 10⁻⁶. -5 A / cm 2 4.91×10 5 A / cm 2 5.24×10 5 A / cm 2 4.62×10 -5 A / cm 2 and 2.90×10 -5 A / cm 2 This is the unmodified anode (4.34 × 10⁻⁶) in Comparative Example 1. -5 A / cm 2The PDA / Fe3O4 deposition values ​​were 1.37, 1.13, 1.21, 1.06, and 0.67 times higher than those of the original PDA, indicating that PDA modification and appropriate modification of PDA / Fe3O4 facilitated the reaction on the anode, increased the reaction rate, and lowered the activation energy, making the anode system less prone to polarization. The hydrophilicity of the PDA-modified anode effectively promoted the exchange of matter and electrons between the electrode, sediment, and microorganisms, thereby effectively improving performance. Simultaneously, the deposition of Fe3O4 further enhanced electron transfer, improving the electrochemical performance of the electrode. In the composite modification, the PDA / Fe3O4[0.6] prepared in Example 1 exhibited the highest exchange current density, indicating the highest reversibility of the anode, consistent with the CV results. Therefore, modifying carbon electrodes using PDA / Fe3O4 composite deposition can enhance the electron transport capability of the electrode, resulting in superior electrochemical activity. Figure 9 This is a comparison of the electrochemical impedance spectroscopy (EQS) of the PDA / Fe3O4 modified anodes prepared in Examples 1 and 5-7 of this invention, the unmodified anode in Comparative Example 1, and the PDA modified anode prepared in Comparative Example 3. In these embodiments, an equivalent circuit diagram was fitted using impedance matching, and the EQS of the anode electrochemical impedance spectroscopy was obtained using Z-view software. The solution resistance Rs and charge transfer resistance Rct were then calculated. Figure 9 As shown, the Rct values ​​of the battery packs with PDA / PDA / Fe3O4[0.9] and PDA / PDA / Fe3O4[0.6] composite modified anodes are relatively low, at 3.48 Ω and 8.97 Ω, respectively. This is mainly because after the deposition of highly conductive Fe3O4, it works together with the hydrophilic and biocompatible PDA through electropolymerization. With the increase of Fe3O4 deposition, there are more and more iron ions in different valence states, the carrier concentration increases, and the conductivity of the anode is improved; the hydrophilicity of PDA increases the transfer of electrons at the interface between microorganisms and the electrode. At the same time, the electron transfer capability of the composite modified anode is greatly improved, the electron transfer resistance decreases, and more electrochemical active surface area is provided, indicating that PDA / Fe3O4 modification is conducive to the attachment reaction of microorganisms, thereby improving the conductivity of the electrode.

[0113] Figure 10 Figures (a)-(b) show the power density and anodic polarization curves of the microbial fuel cells prepared in Examples 1 and 8-11 of this invention and the microbial fuel cells (MSMFCs) prepared in Comparative Example 2; Figure 10 As shown, based on the PDA-modified anode, with the increase of Fe3O4 deposition, the maximum power density of AA5 prepared in Example 1 and AA1, AA20, AA50 and AA100 prepared in Examples 8-11 are 137.83 mW / m², respectively. 2 133.23 mW / m 2 133.02 mW / m 2 118.30 mW / m2 and 113.62 mW / m 2 The two fuel cells prepared in Comparative Example 2 have a combined capacity of 111.76 mW / m³. 2 The concentrations of amino acids added were 1.19, 1.23, 1.19, 1.06, and 1.02 times higher than those added to the fuel cell, indicating that the addition of amino acids effectively improved the output power of the fuel cell, with the power density reaching its optimum at an addition amount of 5 μmol. Appropriate addition of exogenous amino acids can improve the electrochemical properties of the electrodes and promote the electrostatic attraction between electroactive bacteria and the electrodes, thereby improving the electrochemical performance of the fuel cell. However, excessively high amino acid content inhibited the electrochemical behavior of the anode, possibly because the excessively high concentration of amino acids in the microenvironment had a negative effect on the electrogenic bacterial community in the short term, exceeding the maximum carrying capacity of the electron transport chain within the biomembrane, leading to an imbalance between electron generation and transfer rates.

[0114] Figure 11 This is a comparison of long-term discharge voltage curves of the microbial fuel cells (MSMFCs) prepared in Examples 1 and 8-11 of this invention and the microbial fuel cells (MSMFCs) prepared in Comparative Example 2; the output voltage was continuously monitored for 60 days after constructing the MSMFCs by connecting a 500 Ω resistor. Figure 11 As shown, the microbial fuel cell prepared in Comparative Example 2 had a voltage output of only 0.6 mV on day 60. After adding exogenous amino acids to the sediment, its output voltage increased significantly. The microbial fuel cells prepared in Examples 1 and 8-11 had output voltages of 6.0 mV, 5.2 mV, 10.4 mV, 10.9 mV, and 9.2 mV on day 60, respectively. With time, the higher the amino acid concentration, the higher the output voltage, reaching its highest at an addition of 50 μmol. Initially, the voltage was significantly better than the modified group, mainly because the amino acid-added marine mud group required stirring, disrupting its own community structure. As the battery operating time increased, the electrode cell stabilized, the microbial community structure was re-established, and its output voltage gradually increased. Figure 12 Images (a)-(c) show the distribution of total organic carbon (TOC) and total nitrogen (TN) content in sediments near a fixed location after long-term load operation of the microbial fuel cell (MSMFCs) prepared in Comparative Example 2 and Examples 1 and 9. During long-term resistance operation of the MSMFCs, samples were taken every 10 days at a distance of 2 cm (±0.1 cm) from the anode to test TOC and TN content. The data are as follows: Figure 5-7 As shown. The Blank group represents the microbial fuel cell prepared in Comparative Example 2; AA-5 represents the microbial fuel cell prepared in Example 1 by adding 5 μmol of exogenous amino acids; and AA-20 represents the microbial fuel cell prepared in Example 9 by adding 20 μmol of exogenous amino acids. Figure 12As shown, the TOC and TN content near the anode in the fuel cell constructed in Comparative Example 2 decreased at a slower rate because there were fewer microorganisms near the anode electrode in the sediment, resulting in less utilization of carbon and nitrogen. In contrast, in Examples 1 and 9, the TOC and TN decreased at a faster rate as the amount of amino acids added increased. The more organic matter that can be utilized by microorganisms during their production and metabolism, the stronger the microbial activity and the faster the degradation rate. Figure 13 This is a comparative diagram showing the distribution of microbial community structure near the anode in the microbial fuel cell prepared in Comparative Example 2 of this invention, and in the microbial fuel cells prepared in Examples 1 and 9. The abundance of microorganisms at the class level on different anode surfaces was tested, and the top 20 were plotted as a distribution histogram. AA_Bl_0 represents the experimental group (blank control group) without electrodes and without sediment treatment. Figure 13 As shown, the abundance ratio of microbial communities such as Gammaproteobacteria, Gemm-2, and Betaproteobacteria on the electrode surface increased relatively after sediment modification. This is because the addition of amino acids provided these microorganisms with additional carbon and nitrogen sources, promoting their growth and metabolic activities. Furthermore, PDA / Fe3O4 modified anodes improved the conductivity and hydrophilicity of the anode, promoting the attachment of electroactive microorganisms and electron transfer efficiency, thereby affecting the composition and function of the microbial community. Figure 14 (a)-(d) are box plots of microbial α-diversity near the anode under different indices in the microbial fuel cell prepared in Comparative Example 2 and the microbial fuel cells prepared in Examples 1 and 9 of this invention; Figure 14 As shown, the number of microbial species near the anode in the fuel cells prepared in Examples 1 and 9 was higher than that in Comparative Example 2, according to the Chao1 index and Observed_species index. This indicates that appropriate amounts of amino acids can provide additional energy sources for microorganisms, promoting their growth and reproduction, and improving the electrochemical performance of the electrode. Regarding diversity, both Examples 1 and 9 showed increases in the Shannon and Simpson indices (p values ​​were 0.033 and 0.025, respectively, p < 0.05). The addition of exogenous amino acids not only increased the richness of microbial species but also improved the evenness and diversity of the community, showing a more balanced species distribution and the stability of the microbial community. In contrast, the Shannon index of Example 9 was slightly lower than that of Example 1 but still higher than that of Comparative Example 2. This was mainly because the excessively high amino acid concentration negatively impacted community evenness, leading to an increase in the relative abundance of some species and a decrease in the relative abundance of others, indicating that moderate concentrations of amino acid modification had a more moderate effect on community structure. Figure 15 This is a comparison chart showing the trend of total THAA content in the deposits near the anode in the microbial fuel cell prepared in Comparative Example 2 and the microbial fuel cells prepared in Examples 1 and 9 of this invention; as shown. Figure 15As shown, the THAA content in Example 9 was highest initially (9.82 μmol / g), then rapidly decreased after 40 days, eventually reaching as low as 4.10 μmol / g. Under the synergistic effect of the modified anode, microorganisms effectively utilized amino acids as electron donors or carbon sources, accelerating amino acid decomposition and metabolism. Example 1 showed a relatively stable decreasing trend throughout the entire test (7.58–5.19 μmol / g), indicating that after the modification of the anode and sediment in Example 1, metabolic behavior in the sediment microenvironment stabilized, and MSMFCs maintained a stable voltage output. In contrast, the THAA content in Comparative Example 2 was relatively stable, indicating that without added amino acids, the amino acids in the sediment mainly originated from the decomposition of endogenous organic matter. Over time, some electroactive microorganisms or other microorganisms in the sediment utilized amino acids as carbon or nitrogen sources for metabolism, leading to a decrease in THAA and the release of electrons. Appropriate addition of amino acids promoted the rapid utilization of amino acids by sediment microorganisms, helping to maintain amino acid stability.

[0115] Figure 16 This is a mechanism diagram showing the operation and amino acid degradation of the microbial fuel cells (MSMFCs) prepared in Example 1 of this invention. Exogenous addition of amino acids can significantly improve the electrochemical performance of the anode and MSMFCs. On the one hand, the unique chemical properties of PDA, such as its hydrophilicity and adhesion, lead to the enrichment of a large number of microorganisms on the anode surface. As the electrochemical behavior of the electrode occurs, the microbial community structure changes, and electrogenic bacteria accumulate on the anode surface; Fe3O4 contains Fe 2+ / Fe 3+ The redox reaction generates electrons, and its magnetic properties and strong conductivity further accelerate electron transport. On the other hand, amino acids decompose under the amination of microorganisms to produce ammonium compounds, H2O, and CO2. The electrons generated in this process act on the anode, improving the electrochemical performance of the modified anode. The added amino acids also maintain the homeostasis of the anode environment, preserving its output performance. Furthermore, the acid products produced during amino acid metabolism react with minerals in the sediment to form new minerals. Simultaneously, the iron ions from Fe3O4 doping on the anode react with the generated CO2 to form iron carbonates and other minerals. Over a long period, these minerals participate in the diagenesis of Earth's oceans.

[0116] It is worth noting that in the embodiments of the present invention, a PDA-modified anode was prepared by scanning 20 times, and the anode was further electrodeposited with a Fe3O4 concentration of 30 mg / mL in the electrolyte to obtain the modified anode. The modified anode exhibited the best electron transfer efficiency and microbial adhesion ability. The fuel cell stack constructed using the modified anode, with the addition of 0.005 μmol / mL of exogenous amino acids in the anode chamber, enhanced the organic matter conversion and electron transfer efficiency, ultimately achieving a significant improvement in the power generation performance of MSMFCs.

[0117] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the present invention.

Claims

1. A method for preparing a modified anode for a marine sediment microbial fuel cell, characterized in that, The preparation method includes the following steps: S1 Obtains a graphite carbon plate and sequentially grinds, washes, and dries the graphite carbon plate to obtain a primary anode; S2 obtains the first PBS buffer, introduces nitrogen gas into the first PBS buffer for nitrogen aeration treatment, then adds dopamine hydrochloride, mixes evenly, and obtains the first electrolyte; S3 immerses the primary anode in the first electrolyte and performs electropolymerization on the primary anode using the first cyclic voltammetry scanning method to obtain a PDA-modified anode; S4. Obtain the second PBS buffer, add Fe3O4 powder to the second PBS buffer, mix well, and obtain the second electrolyte; the concentration of Fe3O4 powder in the second electrolyte is 15~45 mg / mL; S5. The PDA-modified anode is immersed in the second electrolyte, and electrodeposition is performed on the PDA-modified anode by the second cyclic voltammetry scanning method to obtain the PDA / Fe3O4 modified anode. Specifically, the second cyclic voltammetry scanning method in step S5 is as follows: using a PDA modified anode as the working electrode, saturated silver-silver chloride as the reference electrode, and platinum wire as the counter electrode, pre-deposit for 10 min under the conditions of a scan rate of 20 mV / s and a potential range of -0.7~0.7 V, and then electrodeposit for 20 min at a constant potential of -1.4 V.

2. The preparation method according to claim 1, characterized in that, In step S2, the concentration of the first PBS buffer is 0.01 mol / L.

3. The preparation method according to claim 1, characterized in that, In step S2, the concentration of dopamine hydrochloride in the first electrolyte is 1 mg / mL.

4. The preparation method according to claim 1, characterized in that, In step S3, the first cyclic voltammetry scanning method is specifically as follows: using the primary anode as the working electrode, saturated silver-silver chloride as the reference electrode, and platinum wire as the counter electrode, the cyclic scanning is performed for 6 to 40 cycles under the conditions of a scanning rate of 20 mV / s and a potential range of -0.5 to 0.5 V.

5. The preparation method according to claim 1, characterized in that, In step S4, the concentration of the second PBS buffer is 0.01 mol / L.

6. A PDA / Fe3O4 modified anode prepared by the preparation method according to any one of claims 1 to 5.

7. A marine sediment microbial fuel cell, characterized in that, It includes an anode chamber and a cathode chamber, each containing an anode and a cathode, which are connected by an external circuit wire. Ion exchange is achieved between the anode chamber and the cathode chamber through a salt bridge. The anode chamber is supplied with filtered seawater, marine sediments, and exogenous amino acids, while the cathode chamber is supplied with filtered seawater. The anode is the PDA / Fe3O4 modified anode as described in claim 6, and the cathode is a carbon brush.

8. The marine sediment microbial fuel cell according to claim 7, characterized in that, The exogenous amino acid is any one of aspartic acid, glutamic acid, or histidine; the volume ratio of filtered seawater to marine sediment in the anode chamber is 2:8; the concentration of exogenous amino acid in the anode chamber is 0.001~0.1μmol / mL.

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