CN114614061B - A kind of microbial fuel cell air cathode and preparation method thereof - Google Patents

Abstract

The invention provides an air cathode of a microbial fuel cell and a preparation method thereof. By using a metal-coated carbon material, the invention can not only improve the conductivity of the electrode carbon-based layer, but also utilize the synergistic effect between metals, thereby reducing the usage amount of the noble metal catalyst and reducing the preparation cost. In the preparation of the carbon base layer, deionized water is used as the solvent of the carbon powder in the carbon base layer instead of traditional organic solvents, which reduces the use of organic solvents, making the preparation cost lower and has the potential for large-scale industrial preparation; in the preparation of the catalytic layer, anhydrous ethanol is used as the solvent of the catalyst, avoiding the use of traditional organic solvents that are highly toxic to the human body, and reducing the poison to the operator's body.

Description

A kind of microbial fuel cell air cathode and preparation method thereof

technical field

The invention relates to the technical field of microbial fuel cells, in particular to an air cathode of a microbial fuel cell and a preparation method thereof.

Background technique

Microbial Fuel Cell (MFC for short) is a device that uses special microorganisms as catalysts to directly convert chemical energy in degradable organic matter in water samples into electrical energy. It can be used in wastewater treatment to achieve energy recovery while purifying the dual effects of energy and environment in sewage. It is a new type of green environmental protection technology with great application prospects.

In microbial fuel cells, electron acceptors near the cathode electrode receive free electrons released by the oxidation of organic matter by microorganisms at the anode and undergo a reduction reaction. Oxygen has become the most widely used electron acceptor in many microbial fuel cell systems in view of the advantages of easy access, cleanliness and high reaction overpotential of oxygen in the air. For an air cathode microbial fuel cell using oxygen as an electron acceptor, the performance of the cathode preparation will greatly affect the performance of the microbial fuel cell. The air cathode of microbial fuel cell mainly includes: catalytic layer, carbon base layer, cathode carrier, air diffusion layer and other parts. Among them, the catalyst layer is loaded with catalyst, facing the side of the proton exchange membrane, and is mainly used to catalyze the reaction of protons and oxygen; An oxygen reduction reaction occurs at the layer interface.

In the preparation process of traditional air cathodes, the catalyst in the catalytic layer generally uses expensive platinum-carbon catalysts. The amount of catalyst used determines the cost of the preparation. Therefore, how to reduce the amount of catalyst used as much as possible without affecting the performance of microbial fuel cells in the actual application process is also extremely critical. Conductive carbon black (such as XC-72 conductive carbon black) is generally used as a filler in the carbon base layer to improve the conductivity of the matrix. However, in the actual preparation process, the effect of pure carbon black on improving conductivity is limited. How to further improve the conductivity of the carbon base layer determines whether the performance of the microbial fuel cell can be further improved. In addition, in terms of preparation methods of traditional air cathodes, whether it is the preparation of the cathode diffusion layer or the preparation of the cathode catalytic layer, it is necessary to use highly toxic organic solvents, such as isopropanol, etc. The use of such organic solvents not only increases the cost of preparation, but also has a greater poisonous effect on the operator's body; secondly, the traditional preparation method requires the use of more professional large-scale equipment, which is slightly difficult for ordinary laboratories to implement; finally, the traditional preparation methods are more complicated. .

Contents of the invention

The purpose of the present invention is to overcome the shortcomings of the prior art and provide a microbial fuel cell air cathode and a preparation method thereof.

In order to achieve the above object, the technical scheme that the present invention takes is:

A method for preparing an air cathode of a microbial fuel cell, comprising the following steps:

(1) drop PTFE emulsion on one side of the support layer matrix to form the diffusion layer of the cathode;

(2) Mix polytetrafluoroethylene emulsion with deionized water, sonicate for 20 to 30 minutes, and then stir for 2 to 5 hours to obtain mixture A; then add cetyltrimethylammonium bromide to mixture A, and after ultrasonication for 10 to 15 minutes, continue to stir for 2 to 3 hours to obtain mixture B; The carbon load of the carbon powder is 1-3mg/cm ² , and the air cathode carbon-based layer is obtained after infrared drying and heating drying;

(3) Adding the Pt/C catalyst to deionized water, ultrasonicating for 10 to 15 minutes, to obtain a mixture D; then adding absolute ethanol and 5wt% Nafion solution to the mixture D, stirring for 8 to 10 hours, to obtain a slurry E; using a coating method to evenly coat the slurry D on one side of the air cathode carbon base layer prepared in step (2), so that the Pt loading of the Pt/C catalyst is 0.3 to 2 mg/cm ² , infrared drying, vacuum heating and drying.

The metal-coated carbon powder is prepared by reacting carbon powder with metal salt and sodium borohydride.

By using the metal-coated carbon material, the invention can not only improve the conductivity of the electrode carbon base layer, but also reduce the usage amount of the noble metal catalyst, lower the preparation cost, and utilize the synergistic effect between metals to improve the catalytic efficiency and service life of the catalyst. In the preparation of the diffusion layer, deionized water is used as the solvent of the carbon powder in the diffusion layer instead of traditional organic solvents, which reduces the use of organic solvents, makes the preparation cost lower, and has the potential for large-scale industrial preparation; in the preparation of the catalytic layer, absolute ethanol is used as the solvent of the catalyst, avoiding the use of traditional organic solvents that are highly toxic to the human body, and reducing the poison to the operator's body.

Preferably, the preparation method of the metal-coated carbon powder comprises the following steps:

(S1) Disperse the carbon powder in deionized water, and ultrasonically treat it for 0.5h; dissolve the metal salt and sodium borohydride in deionized water respectively, and set aside;

(S2) adding the metal salt solution into the carbon powder aqueous solution, and ultrasonically treating it for 0.5-1 hour;

(S3) Place the mixed solution prepared in step (S2) in a constant temperature water bath at 50-60°C, stir it magnetically, add sodium borohydride solution dropwise thereto while stirring, and then keep it warm for 2-3 hours;

(S4) Place the mixture prepared in step (S3) into a suction filter bottle for suction filtration, then wash it once with ethanol, and then wash it 2-3 times with deionized water; then place it in a vacuum drying oven to dry for 5-8 hours, after the drying is completed, take it out and grind it for later use.

Preferably, in the step (S1), the mass ratio of carbon powder, metal salt and sodium borohydride is 0.5:(0.1-1):(0.1-0.6); every 1g of carbon powder is dispersed in 50-100g of deionized water; every 0.1-1g of metal salt is dissolved in 40-80mL of deionized water, and every 0.1-0.6g of sodium borohydride is dissolved in 20-40mL of deionized water.

Preferably, the metal salt is selected from at least one of copper nitrate, copper sulfate, copper chloride, silver nitrate, ferrous sulfate, and ferric chloride. The invention utilizes the synergistic effect between metals, reduces the usage amount of the noble metal catalyst, lowers the preparation cost, and at the same time can improve the catalytic performance of the air cathode catalyst and the service life of the catalyst.

Preferably, in the step (1), the mass ratio of the metal-coated carbon powder, polytetrafluoroethylene emulsion and cetyltrimethylammonium bromide is 7:3: (0.5-2); the solid content of the polytetrafluoroethylene emulsion is 60 wt%.

Preferably, in the step (2), the Pt loading of the Pt/C catalyst is 20%.

Preferably, in the step (2), 0.8-0.9 μL of deionized water is added per 1 mg of Pt/C catalyst; 30-35 μL of absolute ethanol is added per 1 mg of Pt/C catalyst; 6-7 μL of 5wt% Nafion solution is added per 1 mg of Pt/C catalyst.

Preferably, the carbon powder is selected from at least one of XC-72 conductive carbon black, acetylene black, carbon nanotubes, and graphite oxide.

Preferably, the cathode support layer is selected from carbon paper or carbon cloth after hydrophobization treatment.

The present invention also provides the microbial fuel cell air cathode prepared by the above preparation method.

Compared with prior art, the beneficial effect of the present invention is:

(1) The preparation process of the present invention is simple, the cost is low, no large-scale professional equipment is needed, and electrode preparation can be realized in a general laboratory;

(2) In the preparation of the diffusion layer of the present invention, deionized water is used as the solvent of carbon powder in the diffusion layer, instead of traditional organic solvents, which reduces the use of organic solvents, makes the preparation cost lower, and has the potential for large-scale industrial preparation;

(3) In the preparation of the catalytic layer of the present invention, absolute ethanol is used as the solvent of the catalyst, which avoids the use of traditional organic solvents that have a greater poisonous effect on the human body, and reduces the poison to the operator's body;

(4) The present invention uses the metal-coated carbon material, which can not only improve the conductivity of the electrode carbon-based layer, but also utilize the synergistic effect between metals, thereby reducing the amount of noble metal catalyst used.

Description of drawings

Fig. 1 is each sample cyclic voltammetry scanning (CV) curve comparison of embodiment 2 in the present invention;

Fig. 2 is the LSV curve contrast of embodiment 2 and blank carbon paper in the present invention;

Fig. 3 is the comparison of the LSV curves of Example 2 and blank carbon cloth in the present invention;

Fig. 4 is the comparison of the LSV curves of the air cathode prepared in Example 4 of the present invention;

Fig. 5 is a schematic flow chart of the preparation process of the microbial fuel cell air cathode of the present invention.

Detailed ways

In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific examples.

Example 1

A kind of preparation method of metal-coated carbon powder of the present invention, comprises the following steps:

(1) Weigh 0.5g XC-72 conductive carbon black and place it in a beaker, then use a graduated cylinder to measure 10-20mL deionized water and pour it into the beaker, stir evenly, and ultrasonicate for 0.5h;

(2) Weigh 0.19g (10%), 0.57g (30%), and 0.95g (50%) of copper nitrate trihydrate solids respectively, and dissolve them in 40-80mL deionized water for subsequent use;

(3) Pour the metal salt solution prepared in step (2) into the beaker of step (1), and perform ultrasonic treatment for 0.5h;

(4) Place the homogeneously mixed solution in step (3) in a constant temperature water bath at 50-60°C, and put it into a magnetic stirring rotor with a rotating speed of 500-800rpm, and preheat the mixed solution while stirring;

(5) Weigh 0.11856g, 0.3496g, and 0.5928g of sodium borohydride solids respectively, dissolve them in 20-40mL deionized water, and set aside;

(6) Add the sodium borohydride solution prepared in step (5) dropwise into the mixed solution in step (4), while keeping stirring at a rotation speed of 800-1000 rpm. After the addition is completed, keep the rotation speed adjusted to 500-800 rpm and continue stirring. The temperature of the water bath is 50-60° C., and the insulation reaction is 2-3 hours;

(7) Put the metal-coated carbon powder prepared in step (6) into a suction filter bottle, first wash it once with ethanol, and then wash it 2 to 3 times with deionized water;

(8) Put the metal-coated carbon powder cleaned in step (7) in a vacuum drying oven to dry for 5-8 hours. After the drying is completed, take it out and grind it for later use.

Example 2

The preparation method of a kind of carbon paper supported carbon base layer of the present invention comprises the following methods:

(1) Adopting the carbon paper after hydrophobization treatment, first use 3.0 mg metal-coated carbon powder per square centimeter of carbon paper, and quantitatively weigh the metal-coated carbon powder with copper loadings of 0%, 10%, 30%, and 50% respectively;

(2) Take the metal-coated carbon powder as the mass ratio: PTFE=7:3, measure an appropriate amount of 60%wt polytetrafluoroethylene emulsion (PTFE) in a beaker, and then take deionized water with 65 times the weight of the metal-coated carbon powder, mix the two, and ultrasonically 30min to fully disperse the PTFE, put the magnetic stirring rotor, and place the beaker in a magnetic stirrer to stir for 2h;

(3) Metal-coated carbon powder according to the mass ratio: CTAB=7:1, weigh an appropriate amount of cetyltrimethylammonium bromide (CTAB), and after fully dissolving, add it to the mixed emulsion prepared in step (2), ultrasonicate for 15 minutes to make it fully mixed evenly, place it in a magnetic stirrer and continue stirring for 2 hours;

(4) Add the metal-coated carbon powder weighed in step (1) to the mixed solution in the above step (3), place it in a magnetic stirrer and stir overnight until the metal-coated carbon powder is completely dispersed and uniform, and finally a uniformly dispersed ink-like slurry can be obtained;

(5) Use a glass slide with both ends polished into rounded corners, and evenly coat the prepared slurry on one side of the carbon paper. During the scraping process, after each layer of slurry is loaded, the solvent is evaporated before loading the next layer. Repeat the above steps until the carbon load of the carbon powder reaches 2.5mg/cm2.

First, use a four-probe square resistance tester to select five different points on the surface of each carbon paper, test the surface resistance at each point, and calculate the average value. The results are shown in Table 1:

Table 1:

It can be seen from Table 1 that (1) simply coating conductive carbon black as the carbon base layer of carbon paper has a lower square resistance value than the carbon base layer prepared by loading metal-coated carbon powder, but the difference between the two is not large; (2) Compared with blank carbon paper, the surface resistance value of the carbon base layer prepared after coating metal-coated carbon powder has increased, but they are all in the same order of magnitude; Not huge, but homemade will cost less.

Fig. 1 is a cyclic voltammetry (CV) curve test chart of each sample in Example 2 using an electrochemical workstation (Shanghai Chenhua CHI 600E), wherein the scanning potential range is -0.4 to 0.4V, the scanning speed is 50mV/s, and the number of scanning cycles is 30.

It can be seen from Figure 1 that the integral areas of the CV curves of blank carbon paper, pure carbon black coating, 10% copper loading, 30% copper loading, and 50% copper loading are: 1.029×10 ^-4 , 2.227×10 ^-4 , 1.039×10 ^-3 , 3.234×10 ^-3 , 9.211×10 ^-4 .

Example 3

A kind of preparation method of microbial fuel cell air cathode of the present invention, comprises the following steps:

(1) The air cathode support layer of the microbial fuel cell adopts carbon paper after hydrophobization treatment, first uses 2.5mg of metal-coated carbon powder per square centimeter of carbon paper, and quantitatively weighs the metal-coated carbon powder;

(2) Take the metal-coated carbon powder as the mass ratio: PTFE=7:3, measure an appropriate amount of 60wt% polytetrafluoroethylene emulsion (PTFE) in a beaker, and then take deionized water with 65 times the weight of the metal-coated carbon powder, mix the two, and ultrasonically 30min to fully disperse the PTFE, put the magnetic stirring rotor, and place the beaker in a magnetic stirrer to stir for 2 hours;

(3) Metal-coated carbon powder according to the mass ratio: CTAB=7:1, weigh an appropriate amount of cetyltrimethylammonium bromide (CTAB), and after fully dissolving, add it to the mixed emulsion prepared in step (2), ultrasonicate for 15 minutes to make it fully mixed evenly, place it in a magnetic stirrer and continue stirring for 2 hours;

(4) Add the metal-coated carbon powder weighed in step (1) to the mixed solution in the above step (3), place it in a magnetic stirrer and stir overnight until the metal-coated carbon powder is completely dispersed and uniform, and finally a uniformly dispersed ink-like slurry can be obtained;

(5) Quantification is carried out by scraping film coating method. First, place a glass slide with rounded corners at one end on one side of the neatly cut carbon paper at ∠30-45°; then, use a pipette gun to quantitatively absorb PTFE (wt: 60%, ρ=1.51g/cm ³ ) emulsion and drop it between the carbon paper and the glass sheet; slowly pull the rounded glass sheet to the other side of the substrate, and form a uniform PTFE thin layer on the surface of the substrate, heat treatment at 350 ° C for 15 min, repeat the above-mentioned process 2 times; finally, make the diffusion layer of cathode through 3 coatings;

(6) Use a glass slide with both ends polished into rounded corners, and evenly coat the prepared slurry on the other side of the carbon paper. During the scraping process, after each layer of slurry is loaded, the solvent is evaporated and then the next layer is loaded. Repeat the above steps until the carbon load of the carbon powder reaches 2.5mg/ ^cm2 .

(7) Weigh 20% of the Pt/C catalyst with 1.0 mg of Pt/C catalyst per square centimeter of carbon paper, place the catalyst in a plastic bottle, and add 0.83 μL of deionized water per mg of catalyst, weigh and add deionized water, and sonicate for 15 minutes;

(8) Add 33.3 μL of absolute ethanol and 6.67 μL of Nafion solution with a mass concentration of 5% for each mg of catalyst, sequentially add absolute ethanol and Nafion solution with a mass concentration of 5%, put in a magnetic stirring rotor, place the plastic bottle in a magnetic stirrer and stir for 8 hours to obtain a viscous and smooth slurry;

(9) Use a stainless steel wire-wound rod to evenly coat the prepared slurry on the side with the carbon base layer. During the scrape coating process, after each layer of slurry is loaded, the solvent is evaporated to dryness before loading the next layer. Repeat the above steps until the Pt loading of the catalyst reaches 1.0 mg/cm ² , use infrared light to irradiate and dry for 3 hours, and then place it in a vacuum environment at 60 ° C for more than 12 hours to obtain a carbon paper cathode catalyst layer.

Test example 1

In order to verify that the use of metal-coated carbon powder on the carbon base layer can indeed reduce the amount of Pt/C catalyst used on the premise of ensuring the performance of the cathode, thereby reducing the cost of cathode preparation, the following comparative experiment is carried out: using carbon paper after hydrophobic treatment.

First, the carbon base layer was prepared on carbon paper, the preparation method was the same as that described in Example 2, and the carbon powder used included: pure carbon black carbon powder and 30% Cu loaded carbon black carbon powder. Then, prepare a catalytic layer on the carbon paper prepared with a carbon-based layer, and coat the catalytic layer on the carbon-based layer. The preparation method of the catalytic layer is consistent with the method described in Example 3. Among them, for the carbon paper prepared by using pure carbon black carbon powder for the carbon base layer, the amount of Pt/C catalyst is unchanged (the amount is assumed to be 100%); for the carbon paper prepared by using 30% Cu-loaded carbon black carbon powder for the carbon base layer, the amount of Pt/C catalyst is 100%, 70%, 50% and 30% in sequence.

sample Metal Cu load (mg/cm ² ) Pt final load (mg/cm ² ) C+Pt/C 0 1 Cu-C+Pt/C (70%) 0.75 0.7 Cu-C+Pt/C(50%) 0.75 0.5 Cu-C+Pt/C (30%) 0.75 0.3

Finally, electrochemical performance tests were performed on the prepared microbial fuel cell air cathodes using an electrochemical workstation (Shanghai Chenhua CHI 600E).

Test example 2

The oxygen reduction activity of the prepared microbial fuel cell air cathode is mainly measured to evaluate the performance of the prepared cathode.

The oxygen reduction activity was determined by using the linear sweep voltammetry (Linear Sweep Voltammetry, LSV) of the electrochemical workstation to characterize the oxygen reduction activity of the cathode, wherein the greater the slope of the LSV curve, the stronger the oxygen reduction activity.

Cathode performance test: In the three-electrode system, the performance of the prepared air cathode was evaluated by the linear sweep voltammetry (LSV) method using an electrochemical workstation (Shanghai Chenhua CHI 600E). The research electrode is the prepared cathode, the counter electrode is a Pt electrode, and Ag/AgCl is the reference electrode. The prepared air cathode is cut to the required size, and the cathode electrode is installed on the electrochemical test device according to the side where the cathode catalytic layer faces the electrolyte solution and the diffusion layer faces the air. A 100 mM phosphate buffer solution (pH=7.00) was injected into the electrochemical test device, the LSV scanning potential range was -0.3-0.2 V, and the scanning speed was 1.0 mV/s.

The LSV curve of the cathode is used as an index to characterize the oxygen reduction ability of the cathode. Under the same scanning voltage, the greater the current density, the greater the oxygen reduction ability of the cathode, and the better the performance of the prepared cathode.

It can be seen from Figure 2 that the limiting current density of the blank carbon paper is only 9.44×10 ^-3 A m ^-2 ; the limiting current density is increased to 12.96×10 ^-3 A m ^-2 after using pure carbon black as the carbon powder to prepare the carbon base; the limiting current density of the carbon base prepared by using 30% Cu-loaded carbon black mixed carbon powder can be increased to 89.58 × 10 ^-3 A m ^-2 , which is 6.9 times that of the carbon base prepared using pure carbon black. It can be seen that the carbon-based layer prepared by metal-loaded carbon powder has a higher oxygen reduction ability.

Figure 3 shows the oxygen reduction performance comparison of each stage of the carbon paper microbial fuel cell air cathode prepared by using nano-copper-loaded carbon black as carbon-based carbon powder. Among them, the limiting current density of the blank carbon paper is 9.44×10 ^-3 A·m ^-2 ; the limiting current density after coating the carbon base layer is 89.58×10 ^-3 A·m ^-2 ; the limiting current density after coating the catalytic layer is 388.50×10 ^-3 A·m ^-2 .

It can be seen from Figure 4 that the limiting current density corresponding to each sample is shown in the table below:

sample Limiting current density (A·m ^-2 ) C+Pt/C 0.69875 Cu-C+Pt/C (70%) 0.55475 Cu-C+Pt/C(50%) 0.40077 Cu-C+Pt/C (30%) 0.38600

It can be seen from the above table that the oxygen reduction performance of the air cathode prepared after coating the Pt/C catalyst is the best when the traditional carbon black is used as the carbon base layer; and when the carbon black coated with nano-copper is used as the carbon base layer, when the amount of the coated Pt/C catalyst is 70%, its oxygen reduction capacity can reach 79.39% of the oxygen reduction capacity of the electrode prepared by the traditional method.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than limiting the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims (9)

1. The preparation method of the microbial fuel cell air cathode is characterized by comprising the following steps of:

(1) Dropwise adding PTFE emulsion on one side of a supporting layer matrix to form a diffusion layer of a cathode;

(2) Mixing polytetrafluoroethylene emulsion with deionized water, performing ultrasonic treatment for 20-30 min, and then stirring for 2-5 h to obtain a mixture A; then adding cetyl trimethyl ammonium bromide into the mixture A, and continuing stirring for 2-3 hours after ultrasonic treatment for 10-15 min to obtain a mixture B; then adding metal coated carbon powder into the mixture B, and stirring for 12-24 hours to obtain uniformly dispersed slurry C; uniformly coating the slurry C on the other side of the cathode support layer by adopting a blade coating method to ensure that the carbon load of the metal-coated carbon powder is 1-3 mg/cm ² Infrared drying and heating drying to obtain an air cathode carbon base layer;

(3) Adding a Pt/C catalyst into deionized water, and performing ultrasonic treatment for 10-15 min to obtain a mixture D; then absolute ethyl alcohol and 5wt% Nafion solution are added into the mixture D, and stirring is carried out for 8-10 h, so as to prepare slurry E; uniformly coating the slurry D on one side of the air cathode carbon substrate prepared in the step (2) by adopting a coating method to ensure that the Pt loading capacity of the Pt/C catalyst is 0.3-2 mg/cm ² Infrared drying, and vacuum heating drying;

the metal-coated carbon powder is prepared by reacting carbon powder with metal salt and sodium borohydride;

the metal salt is at least one selected from copper nitrate, copper sulfate, copper chloride, silver nitrate, ferrous sulfate and ferric trichloride.

2. The method for preparing an air cathode of a microbial fuel cell according to claim 1, wherein the method for preparing the metal-coated carbon powder comprises the following steps:

(S1) dispersing carbon powder in deionized water, and respectively dissolving metal salt and sodium borohydride in the deionized water;

(S2) adding the metal salt solution into the carbon powder aqueous solution, and carrying out ultrasonic treatment for 0.5-1 h;

(S3) placing the mixed solution prepared in the step (S2) at 50-60 ℃ for stirring, dropwise adding sodium borohydride solution while stirring, and then preserving heat for 2-3 hours;

and (S4) filtering, washing and vacuum drying the mixture to obtain the metal-coated carbon powder.

3. The method for preparing an air cathode of a microbial fuel cell according to claim 2, wherein in the step (S1), the mass ratio of carbon powder, metal salt and sodium borohydride is 0.5: (0.1 to 1): (0.1 to 0.6); dispersing 1g of carbon powder into 50-100 g of deionized water; each 0.1-1 g of metal salt is dissolved in 40-80 mL of deionized water, and each 0.1-0.6 g of sodium borohydride is dissolved in 20-40 mL of deionized water.

4. The method for preparing an air cathode of a microbial fuel cell according to claim 1, wherein in the step (1), the mass ratio of the metal-coated carbon powder, polytetrafluoroethylene emulsion and cetyltrimethylammonium bromide is 7:3: (0.5-2); the solid content of the polytetrafluoroethylene emulsion is 60 weight percent.

5. The method for preparing an air cathode for a microbial fuel cell according to claim 1, wherein the Pt loading of the Pt/C catalyst in the step (2) is 20%.

6. The method for preparing an air cathode of a microbial fuel cell according to claim 1, wherein in the step (2), 0.8-0.9 μl of deionized water is added per 1mg of Pt/C catalyst; adding 30-35 mu L of absolute ethyl alcohol into each 1mg of Pt/C catalyst; 6-7 mu L of 5wt% Nafion solution is added to each 1mg of Pt/C catalyst.

7. The method for preparing an air cathode of a microbial fuel cell according to claim 1, wherein the carbon powder is at least one selected from XC-72 conductive carbon black, acetylene black, carbon nanotubes and graphite oxide.

8. The method for preparing an air cathode for a microbial fuel cell according to claim 1, wherein the cathode support layer is selected from carbon paper or carbon cloth after the hydrophobization treatment.

9. A microbial fuel cell air cathode made by the method of any one of claims 1-8.