阅读说明：本技术 一种二甲基咪唑钴联合镍铝层状双氢氧化物/氧化石墨烯的氧还原催化剂的制备方法 (Preparation method of oxygen reduction catalyst combining dimethyl imidazole cobalt with nickel-aluminum layered double hydroxide/graphene oxide ) 是由 陈峻峰 杨佳琪 刘彦彦 王雪梅 张译文 王仁君 杨月伟 杨道鑫 王永乐 魏庆营 于 2021-09-03 设计创作，主要内容包括：本发明公开了一种二甲基咪唑钴联合镍铝层状双氢氧化物/氧化石墨烯的氧还原催化剂的制备方法,包括以下步骤：以氧化石墨烯作为基底,在氧化石墨烯上垂直生长片状的镍铝层状双氢氧化物；多面立方体状的二甲基咪唑钴原位生长在镍铝层状双氢氧化物/氧化石墨烯上,从而成功制备出了二甲基咪唑钴联合镍铝层状双氢氧化物/氧化石墨烯。同时公开了其作为微生物燃料电池阴极催化剂的应用。本发明所制备的材料具有较大的比表面积、较多的活性位点、较高的电导率,因此作为微生物燃料电池阴极催化剂提高了电离子流的效率,保证了电极循环的稳定性和发电效率,从而改善了微生物燃料电池的性能。(The invention discloses a preparation method of an oxygen reduction catalyst of dimethylimidazole cobalt combined with nickel-aluminum layered double hydroxide/graphene oxide, which comprises the following steps: taking graphene oxide as a substrate, and vertically growing flaky nickel-aluminum layered double hydroxide on the graphene oxide; the polyhedral cubic dimethylimidazolium cobalt grows on the nickel-aluminum layered double hydroxide/graphene oxide in situ, so that the dimethylimidazolium cobalt combined nickel-aluminum layered double hydroxide/graphene oxide is successfully prepared. Also discloses the application of the catalyst as a cathode catalyst of a microbial fuel cell. The material prepared by the invention has larger specific surface area, more active sites and higher conductivity, so that the material used as the cathode catalyst of the microbial fuel cell improves the efficiency of ion flow, ensures the stability of electrode circulation and power generation efficiency, and improves the performance of the microbial fuel cell.)

1. The preparation method of the oxygen reduction catalyst of the dimethylimidazolium cobalt combined nickel-aluminum layered double hydroxide/graphene oxide is characterized by comprising the following steps of:

the method comprises the following steps: mixing 0.075mol of nickel chloride hexahydrate and 0.025mol of aluminum chloride hexahydrate to form 150ml of solution A; ultrasonically dispersing 0.22g of graphene oxide into 150ml of mixed solution containing 0.8g of sodium hydroxide and 0.53g of sodium carbonate to form mixed solution B, mixing and stirring the solution A and the solution B, and adding NaOH to adjust the pH value of the solution to 10; then heating the mixture in a water bath, then stirring strongly, quickly adding sodium sulfide, and finally cooling, centrifuging, washing and drying to obtain nickel-aluminum layered double hydroxide/graphene oxide;

step two: dissolving 3.28g of dimethylimidazole in 150ml of a methanol solution, and then slowly adding 150ml of a methanol solution in which 10mmol of cobalt chloride hexahydrate is dissolved into the dimethylimidazole solution and stirring to obtain a mixed solution;

step three: and (3) dissolving the nickel-aluminum layered double hydroxide/graphene oxide prepared in the first step into the mixed solution obtained in the second step, stirring for 1 h, sealing the mixture in a counter-pressure kettle, heating, naturally cooling to room temperature, collecting a product, washing, and carrying out vacuum treatment to obtain the dimethyl imidazole cobalt combined nickel-aluminum layered double hydroxide/graphene oxide.

2. The method for preparing the oxygen reduction catalyst of the layered double hydroxide/graphene oxide combined with nickel aluminum by dimethylimidazolium cobalt according to claim 1, which is characterized in that: in the first step, the water bath is heated to 65 ℃ for 5h, and the water bath is heated to 85 ℃ under the condition of intense stirring.

3. The method for preparing the oxygen reduction catalyst of the layered double hydroxide/graphene oxide combined with nickel aluminum by dimethylimidazolium cobalt according to claim 1, which is characterized in that: in the step one, the drying is carried out for 18 h at the temperature of 80 ℃.

4. The method for preparing the oxygen reduction catalyst of the layered double hydroxide/graphene oxide combined with nickel aluminum by dimethylimidazolium cobalt according to claim 1, which is characterized in that: in the second step, the stirring is performed at room temperature for 0.5 h.

5. The method for preparing the oxygen reduction catalyst of the layered double hydroxide/graphene oxide combined with nickel aluminum by dimethylimidazolium cobalt according to claim 1, which is characterized in that: in the third step, the heating is that the reaction kettle is heated to 125 ℃ in an oven and kept for 15 h.

6. The method for preparing the oxygen reduction catalyst of the layered double hydroxide/graphene oxide combined with nickel aluminum by dimethylimidazolium cobalt according to claim 1, which is characterized in that: the vacuum treatment described in step three was a treatment at 120 ℃ under high vacuum for 16 h.

7. The oxygen reduction catalyst of layered double hydroxide/graphene oxide of nickel aluminum combined with dimethylimidazolate prepared by the preparation method of oxygen reduction catalyst of layered double hydroxide/graphene oxide combined with nickel aluminum combined with dimethylimidazolate according to claims 1 to 6.

8. Use of the dimethylimidazolium cobalt combined nickel aluminum layered double hydroxide/graphene oxide oxygen reduction catalyst of claim 7 in a microbial fuel cell.

Technical Field

The invention relates to the technical field of microbial fuel cell cathode modification, in particular to a preparation method of an oxygen reduction catalyst of dimethylimidazole cobalt combined with nickel-aluminum layered double hydroxide/graphene oxide.

Background

The water pollution reduces the use function of the water body and aggravates the shortage of water resources. Under such severe environmental conditions, the control of water pollution is a major concern in the development of environmental work.

At present, the most common method in China is a microbial treatment method for treating industrial sewage and urban wastewater, and the method mainly utilizes the self metabolism of microbes to reduce the content of organic matters in the sewage. Wherein microbial fuel cells have come into the field of vision by virtue of their excellent range of properties.

A Microbial Fuel Cell (MFC) is a device that directly converts chemical energy in organic matter into electrical energy using microorganisms. Compared with other existing sewage treatment technologies, the microbial fuel cell has operational and functional advantages, however, the low output power density is a major bottleneck limiting the large-scale application thereof. It is well known that when MFC is used to treat wastewater, microorganisms on the anode release electrons and protons. When a suitable electron acceptor is present in the cathode, the electrons are transferred to the cathode through an external circuit to complete the reaction. In this process, the electricity generation performance of MFC is closely related to electrode material, anode environment, electricity generation microbes, cathode reaction efficiency, MFC structure and operation conditions. Among them, how to improve the efficiency of cathode reaction has become the key and difficult point of the research on the performance of the microbial fuel cell. To lower the cathode reduction potential and increase the cathode redox efficiency, the selection of a suitable cathode catalyst is crucial to improve the MFC performance.

In view of the above problems, a great deal of research finds that materials such as Layered Double Hydroxides (LDHs), graphene oxides (graphene oxides), metal organic framework Materials (MOFs) have become hot spots for research of microbial fuel cells because of their large surface area and many reaction sites. The layered double hydroxide is a typical two-dimensional nano material and has the characteristics of large specific surface area, high specific capacity, rich electroactive centers and the like. It plays a key role in energy storage, photocatalytic degradation, capacitors, adsorption, microbial fuel cells and other fields. However, the layered double hydroxide has slightly poor conductivity and greatly changes in volume during cycling, deteriorating cycling stability and multiplication rate of the electrode material. In recent years, studies have been made to improve the activity and stability of LDHs by modifying them. Several studies have shown that graphene oxide-modified LDHs can significantly improve their electrochemical performance as MFC cathode catalysts. Graphene (G) is an ideal two-dimensional nanomaterial appearing in recent years, graphene oxide is an oxide of graphene, reaction sites of the oxidized graphene are increased, so that the surface modification of the graphene is easier, and the modified nickel-aluminum layered double hydroxide/graphene oxide serving as an MFC cathode catalyst is expected to improve the electrochemical performance of the MFC cathode catalyst. Meanwhile, MOFs are also high-efficiency catalytic materials. MOFs are organic-inorganic hybrid materials with intramolecular pores formed by self-assembly of organic ligands with metal ions or clusters through coordination bonds. The arrangement of the organic ligand and the metal ions or clusters has obvious directionality, and different frame pore structures can be formed, so that different adsorption properties, optical properties, electromagnetic properties and the like are shown. Among many MOFs species, dimethylcobalt imidazolide, a porous crystalline material in which an organic imidazolide ester is crosslinked with a transition metal to form a polyhedral skeleton having a large specific surface area, has attracted considerable attention due to its unique properties. However, the low conductivity and large steric hindrance of MFC in power generation prevents its direct role as electrode material, so it is necessary to explore new strategies to improve its inherent electrocatalytic properties. Many researchers have focused on modifying layered double hydroxides to improve their activity, but there are few studies and some problems associated with the synthesized composite materials.

Therefore, it is necessary to provide a further solution to the above problems.

Disclosure of Invention

The invention aims to provide a preparation method of an oxygen reduction catalyst of dimethylimidazole cobalt combined with nickel-aluminum layered double hydroxide/graphene oxide, and the prepared cathode catalyst of a microbial fuel cell can effectively improve the electricity generation performance of an MFC.

The technical scheme of the invention is as follows:

a preparation method of an oxygen reduction catalyst of dimethylimidazole cobalt combined with nickel-aluminum layered double hydroxide/graphene oxide comprises the following steps:

the method comprises the following steps: mixing a certain amount of nickel chloride hexahydrate (0.075 mol) and aluminum chloride hexahydrate (0.025 mol) into 150ml of solution A; ultrasonically dispersing 0.22g of graphene oxide into a mixed solution of 150ml of sodium hydroxide (0.20M/0.8 g) and sodium carbonate (0.05M/0.53 g) to form a mixed solution B, mixing and stirring the solution A and the solution B, and adding NaOH to adjust the pH value of the solution to 10; then heating the mixture in a water bath, then stirring strongly, quickly adding sodium sulfide, and finally cooling, centrifuging, washing and drying to obtain nickel-aluminum layered double hydroxide/graphene oxide;

step two: dissolving 3.28g of dimethylimidazole in 150ml of a methanol solution, and then slowly adding 150ml of a methanol solution in which cobalt chloride hexahydrate (10mmol) is dissolved to the dimethylimidazole solution with stirring to obtain a mixed solution;

step three: and (3) dissolving the nickel-aluminum layered double hydroxide/graphene oxide prepared in the first step into the mixed solution obtained in the second step, stirring for 1 h, sealing the mixture in a counter-pressure kettle, heating, naturally cooling to room temperature, collecting a product, washing, and carrying out vacuum treatment to obtain the dimethyl imidazole cobalt combined nickel-aluminum layered double hydroxide/graphene oxide.

Further, in the first step, the water bath is heated to 65 ℃ for 5 hours, and the water bath is heated to 85 ℃ under the condition of intense stirring.

Further, in the step one, the drying is carried out for 18 hours at the temperature of 80 ℃.

Further, in the second step, the stirring is performed at room temperature for 0.5 h.

Further, in the third step, the heating is that the reaction kettle is heated to 125 ℃ in an oven and kept for 15 hours.

Further, the vacuum treatment in the third step is a high vacuum treatment at 120 ℃ for 16 h.

The invention provides a preparation method of an oxygen reduction catalyst of dimethylimidazolate cobalt combined with nickel-aluminum layered double hydroxide/graphene oxide, and the dimethylimidazolate cobalt combined with nickel-aluminum layered double hydroxide/graphene oxide is synthesized by a simple two-step hydrothermal method. Firstly, nickel-aluminum layered double hydroxide is stably grown on the surface of graphene oxide, and an ultrathin layered double hydroxide nanosheet is prepared by adjusting the pH value with alkali liquor. Then fixing polyhedral and stereoscopic dimethyl cobalt imidazolium on the surface of the flaky nickel-aluminum layered double hydroxide by adopting a direct growth method to synthesize the high-crystalline dimethyl cobalt imidazolium combined nickel-aluminum layered double hydroxide/graphene oxide. The synthesis process is simple to operate and easy to synthesize, and the synthesized dimethylimidazole cobalt combined nickel-aluminum layered double hydroxide/graphene oxide crystal has a large specific surface area, provides more active sites and greatly improves the efficiency of electron transfer. Not only shows stronger power generation performance, but also greatly improves the oxidation-reduction performance of the microbial fuel cell. And finally, a stainless steel wire mesh (ss) is used as a substrate, a two-layer Polytetrafluoroethylene (PTEF) method is adopted to prepare the cathode of the dimethylimidazole cobalt combined nickel-aluminum layered double hydroxide/graphene oxide microbial fuel cell, and the improvement effect of the cathode on the performance of the microbial fuel cell is researched.

Drawings

FIG. 1 is a schematic flow diagram of a preparation method of an oxygen reduction catalyst of dimethylcobaltous imidazole combined with nickel-aluminum layered double hydroxide/graphene oxide according to the present invention;

fig. 2 is an SEM image of the preparation method of the oxygen reduction catalyst of dimethylimidazolium cobalt combined with nickel aluminum layered double hydroxide/graphene oxide of the present invention. Fig. 2a is a scanning electron microscope image of Graphene Oxide (GO). FIG. 2b is a scanning electron microscope image of ZIF-67. FIGS. 2c and 2d are scanning electron microscope images of NiAl-LDH/GO @ ZIF-67.

FIG. 3 is an XRD diagram and an FTIR diagram of GO, NiAl-LDH/GO, ZIF-67 and NiAl-LDH/GO @ ZIF-67 in the preparation method of the oxygen reduction catalyst of the dimethylcobaltosic imidazole combined with nickel-aluminum layered double hydroxide/graphene oxide;

FIG. 4 is a CV curve diagram and an LSV curve diagram of a catalyst for an oxygen reduction of a layered double hydroxide/graphene oxide formed by combining cobalt dimethylimidazole with nickel aluminum, wherein NiAl-LDH/GO, ZIF-67 and NiAl-LDH/GO @ ZIF-67 are used as nano microbial fuel photocathode catalysts in the preparation method of the catalyst for an oxygen reduction of a layered double hydroxide/graphene oxide formed by combining cobalt dimethylimidazole with nickel aluminum according to the present invention;

FIG. 5 is a CV diagram and a linear fitting graph of a NiAl-LDH/GO @ ZIF-67 nano microbial fuel photocathode catalyst at different sweep rates in the preparation method of the oxygen reduction catalyst of dimethylcobaltous imidazole combined with nickel-aluminum layered double hydroxide/graphene oxide according to the present invention;

FIG. 6 is a power density curve of a NiAl-LDH/GO, ZIF-67, and NiAl-LDH/GO @ ZIF-67 nano microbial fuel electro-cathode catalyst in a preparation method of the oxygen reduction catalyst of the dimethylimidazolocobalt combined nickel-aluminum layered double hydroxide/graphene oxide, when the voltage is stable.

Detailed Description

The present invention will be described in further detail with reference to specific embodiments.

Referring to fig. 1, fig. 1 is a schematic flow chart of a preparation method of an oxygen reduction catalyst of dimethylimidazolium cobalt combined with nickel aluminum layered double hydroxide/graphene oxide according to the present invention. As shown in fig. 1, the invention provides a preparation method of an oxygen reduction catalyst of dimethylcobaltous imidazole combined with nickel-aluminum layered double hydroxide/graphene oxide, which comprises the following steps:

the method comprises the following steps: taking a certain amount of nickel chloride hexahydrate (0.075 mol) and aluminum chloride hexahydrate (0.025 mol) to mix into 150ml of solution A, ultrasonically dispersing 0.22g of graphene oxide into 150ml of mixed solution of sodium hydroxide (0.20M/0.8 g) and sodium carbonate (0.05M/0.53 g) to form mixed solution B, mixing and stirring the solutions A and B, and adding NaOH to adjust the pH value of the solution to 10; heating the mixture in a water bath to 65 ℃ for 5h, then heating to 85 ℃ under the condition of strong stirring, quickly adding 20ml of 34mg/ml sodium sulfide, and finally cooling, centrifuging, washing and drying at 80 ℃ for 18 h to obtain the nickel-aluminum layered double hydroxide/graphene oxide.

Step two: 3.28g of dimethylimidazole was dissolved in 150ml of a methanol solution, and then 150ml of a methanol solution in which cobalt chloride hexahydrate (10mmol) was dissolved was slowly added to the dimethylimidazole solution and stirred at room temperature for 0.5 h to obtain a mixed solution.

Step three: dissolving the nickel-aluminum layered double hydroxide/graphene oxide prepared in the first step into the mixed solution obtained in the second step and stirring for 1 h; and then sealing the mixture in a counter-pressure kettle, putting the reaction kettle in an oven, heating to 125 ℃ and keeping for 15h, naturally cooling to room temperature, collecting a product, washing, and treating at 120 ℃ under high vacuum for 16 h to obtain the composite material of the layered double hydroxide/graphene oxide of nickel and aluminum combined with dimethyl cobaltous imidazole.

And (3) completing the preparation of the oxygen reduction catalyst of the dimethylimidazole cobalt combined nickel-aluminum layered double hydroxide/graphene oxide after the three steps. After these three steps, the structure can also be tested, such as: the performance of the microbial fuel cell is tested by taking the sample as a cathode.

Step four: a three-electrode system is adopted to carry out electrochemical performance test on an electrochemical workstation, and a composite material of dimethyl cobalt imidazole combined with nickel aluminum layered double hydroxide/graphene oxide is used as a cathode catalyst to carry out performance test on the microbial fuel cell.

The short names of letters in the invention are all fixed short names in the field, wherein part of letter characters are explained as follows: SEM: a scanning electron microscope; FTIR: fourier transform infrared spectroscopy; XRD: x-ray diffraction pattern.

Example 1

The present embodiment shows an implementation of an oxygen reduction catalyst of dimethylcobaltimidazolate in combination with a nickel-aluminum layered double hydroxide/graphene oxide according to the following scheme:

in order to research the electrochemical performance of the oxygen reduction catalyst combining dimethyl cobaltosic imidazolium with nickel-aluminum layered double hydroxide/graphene oxide, dimethyl cobaltosic imidazolium and dimethyl cobaltosic imidazolium with nickel-aluminum layered double hydroxide/graphene oxide are respectively used as MFC cathode catalysts. Both CV and LSV assays were performed in 50mM PBS.

Referring to fig. 4, it can be seen by comparing the cyclic voltammetry curves that the cyclic voltammetry integrated area of the layered double hydroxide/graphene oxide of nickel aluminum combined with dimethylimidazolium cobalt is significantly larger than that of other catalysts at the same scanning speed. The result shows that the synthesized dimethylimidazole cobalt combined nickel-aluminum layered double hydroxide/graphene oxide nano structure has good oxidation-reduction performance. The three-dimensional structure and high conductivity of the dimethyl cobaltosic imidazole are coordinated with the ion transport of the nickel-aluminum layered double hydroxide/graphene oxide, and meanwhile, the graphene oxide is used as a substrate material, so that a larger specific surface area and an active center are provided for the combination of the dimethyl cobaltosic imidazole and the nickel-aluminum layered double hydroxide/graphene oxide. As shown in fig. 5, the composite material of cobalt dimethylimidazole combined with nickel aluminum layered double hydroxide/graphene oxide has a redox peak in PBS solution, which confirms higher electrical activity and conductivity and more active centers and functional groups. The structure of the electrode combining the dimethyl cobalt imidazolide with the nickel-aluminum layered double hydroxide/graphene oxide has the excellent properties of the nickel-aluminum layered double hydroxide/graphene oxide and the dimethyl cobalt imidazolide, and the electric active surface sites of oxidation reduction are increased by the dimethyl cobalt imidazolide existing in the periphery.

In order to further examine the electrocatalytic activity of the composite catalyst, LSV curves of different catalysts are examined under the condition that the scanning rates are all 10 mV/s. The result shows that the inclination sequence of the catalyst is NiAl-LDH/GO @ ZIF-67, NiAl-LDH/GO and ZIF-67. The slope of the voltammetry curve shows that under the same cathode potential, the NiAl-LDH/GO @ ZIF-67 has larger current and higher conductivity. In general, the oxygen reduction catalyst of the dimethylimidazole cobalt combined with the nickel-aluminum layered double hydroxide/graphene oxide has good oxidation-reduction performance and high-efficiency catalytic performance.

Example 2

The present embodiment shows an implementation of an oxygen reduction catalyst of dimethylcobaltimidazolate in combination with a nickel-aluminum layered double hydroxide/graphene oxide according to the following scheme:

in order to study the electrochemical performance of the oxygen reduction catalyst combining cobalt dimethylimidazolium with nickel-aluminum layered double hydroxide/graphene oxide, the oxygen reduction catalysts combining nickel-aluminum layered double hydroxide/graphene oxide, cobalt dimethylimidazolium, and cobalt dimethylimidazolium with nickel-aluminum layered double hydroxide/graphene oxide were used as MFC cathode catalysts, respectively. CV testing was performed in 50mM PBS.

Referring to fig. 5, fig. 5 shows CV curves of dimethylimidazolium cobalt in combination with nickel aluminum layered double hydroxide/graphene oxide oxygen reduction catalysts at different sweep rates. The scan rate was 10-100 mV/s, the potential ranged from-1.0 v, and the CV curves exhibited similar shapes as the scan rate increased to 100mV/s, indicating that the electrode had rate capability and electrochemical reversibility. As the scan rate increased, the redox current increased and the redox peak shifted slightly, indicating that the Ni-Co-Al ions associated with the Faraday reaction affected the diffusion process and electrochemical process of electron ion transport. Meanwhile, as the scanning rate increases, the internal resistance of the composite catalyst increases, which limits the transport of ions, resulting in the shift of the redox peak.

Based on the measurements in fig. 5, the linear fit of the oxidation peak current and reduction peak current of the cobalt dimethylimidazolide in combination with nickel aluminum layered double hydroxide/graphene oxide increased with increasing scan speed. The linear correlation coefficients of the oxidation peak current and the reduction peak current of the layered double hydroxide/graphene oxide combined by the dimethyl cobalt imidazolide and the nickel aluminum are 0.98939 and 0.97875 respectively. The result shows that the kinetic reaction catalyzed by the combination of the dimethyl imidazole cobalt and the nickel-aluminum layered double hydroxide/graphene oxide is the first-order kinetic reaction. The cyclic voltammetry curves and the fitting curves at different scanning speeds both show that the electrocatalytic performance of the MFC air cathode can be remarkably improved by combining dimethylimidazolium cobalt with nickel-aluminum layered double hydroxide/graphene oxide.

Example 3

The present embodiment shows an implementation of an oxygen reduction catalyst of dimethylcobaltimidazolate in combination with a nickel-aluminum layered double hydroxide/graphene oxide according to the following scheme:

referring to fig. 6, as cathode catalysts of the single-chamber MFC, i.e., dimethylcobaltimidazolate combined with nickel-aluminum layered double hydroxide/graphene oxide, and dimethylcobaltimidazolate are respectively used, anode states are kept consistent, so as to evaluate the influence of different cathode catalysts on the power generation capability of the MFC. The power density curve and voltage at voltage stabilization were evaluated by gradually decreasing the external resistance of the MFC (from 2200 Ω to 20 Ω).

Referring to FIG. 6, the maximum power density produced by NiAl-LDH/GO @ ZIF-67-MFC is 526.32 mW/m²Is NiAl-LDH/GO-MFC (401.02 mW/m)²) 1.31 times of that of ZIF-67-MFC (190.55 mW/m)²) 2.76 times of. The result shows that the modified cathode of the layered double hydroxide/graphene oxide combined by the dimethyl imidazole cobalt and the nickel aluminum has good power generation performance and redox activity.

Referring to Table 1, the maximum cell voltage generated by NiAl-LDH/GO @ ZIF-67-MFC is 541.8mV, and the maximum output voltages of NiAl-LDH/GO-MFC and ZIF-67-MFC are 320.25mV and 21.74 mV, respectively. Higher voltage means faster glucose consumption, which further demonstrates that ORR reaction using cobalt dimethylimidazole in combination with nickel aluminium layered double hydroxide/graphene oxide as cathode catalyst is more efficient. In addition, the output voltage of the dimethylimidazolium cobalt combined nickel-aluminum layered double hydroxide/graphene oxide MFC has small change within 8 days, which indicates that the catalyst has good durability and cycling stability.

The specific conclusions of the oxygen reduction catalyst of dimethylcobaltous imidazole combined with nickel aluminium layered double hydroxide/graphene oxide described in the above examples are as follows:

referring to FIG. 2, the morphological structure of NiAl-LDH/GO @ ZIF-67 was analyzed by scanning electron microscopy. NiAl-LDH/GO nanosheets and polyhedral ZIF-67 crystals are found in FIG. 2, where FIG. 2a is a scanning electron microscope image of Graphene Oxide (GO). FIG. 2b is a scanning electron microscope image of ZIF-67. FIGS. 2c and 2d are SEM images of NiAl-LDH/GO @ ZIF-67. The result shows that the NiAl-LDH/GO is stacked in a sheet shape, the ZIF-67 is a polyhedral crystal, and the particle distribution is relatively concentrated. Due to the adhesion effect, the synthesized NiAl-LDH/GO @ ZIF-67 has a stable structure, a unique space structure and high crystallinity. The surface of the synthetic material becomes rough, and the specific surface area and the activity of the material are improved to a certain extent. In addition, the ZIF-67 with the polyhedral structure enables the overall surface structure of the composite material to be firmer and provides more active centers in the process of combining with NiAl-LDH/GO. The large surface area and high porosity of the NiAl-LDH/GO @ ZIF-67 increase the contact area of the active material and electrons, and are beneficial to improving the electrochemical performance, and the scanning electron microscope result shows that the NiAl-LDH/GO @ ZIF-67 is successfully synthesized.

Referring to FIG. 3, FIG. 3a shows XRD profiles for materials GO, NiAl-LDH/GO, ZIF-67 and NiAl-LDH/GO @ ZIF-67, and FIG. 3b shows FT-IR profiles for each material, which indicate that highly crystallized NiAl-LDH/GO and ZIF-67 have been successfully prepared. The synthesized NiAl-LDH/GO is a sheet nano material, while ZIF-67 is a high-crystal dodecahedral structure. Graphene Oxide (GO) has a sharp peak at 12.3 °; the NiAl-LDH/GO has the characteristic peaks of (003), (006), (012), (018), (110) and (113), and the peaks are respectively 11.9, 21.4, 30.1, 42.6, 58.9 and 61.4; the XRD result of the ZIF-67 is consistent with the result of the crystal structure simulation, and no stray peak exists, which indicates that the prepared material is pure ZIF-67 crystal and is respectively pure ZIF-67 crystalHas two strong peaks of (011) and (112). In the NiAl-LDH/GO @ ZIF-67 composite material, diffraction crystal faces of (011), (022), (112), and (222) of the ZIF-67 almost completely disappear, which indicates that no ZIF-67 agglomeration exists in the composite material, and the addition of the ZIF-67 has no obvious influence on the structure of the NiAl-LDH/GO. The FT-IR curve of NiAl-LDH/GO @ ZIF-67 is shown in FIG. 3 b. 3444cm^-1And 1640cm^-1The characteristic infrared absorption peak of the compound is mainly-OH vibration, 1358cm^-1And 749cm^-1The characteristic infrared absorption peak of the composite is mainly CO in NiAl-LDH/GO₃ ^2-(V₃) And CO₃ ²-(V₂) And (5) vibrating. 583cm^-1The nearby absorption peak is C = N stretching vibration of dimethylimidazole. Furthermore, at 900cm^-1And 1500cm^-1The absorption peak therebetween was mainly the vibration of imidazole ring in ZIF-67, and 700cm^-1The following absorption peaks are mainly caused by the vibration characteristic peaks of Ni-O and Al-O in the NiAl-LDH/GO crystal lattice. The results show that the NiAl-LDH/GO @ ZIF-67 nanocomposite is successfully prepared, and the mechanical property of the nanocomposite is expected to be improved.

Compared with the prior art, the invention has the beneficial effects that: the oxygen reduction catalyst of the layered double hydroxide/graphene oxide of the nickel-aluminum combined with the dimethylimidazole cobalt is prepared by a simple two-step hydrothermal method. Nickel-aluminum layered double hydroxide nanoparticles vertically grow on the surface of graphene oxide, dimethyl cobaltosic imidazole is successfully modified on the surface of the nickel-aluminum layered double hydroxide/graphene oxide, and the oxygen reduction catalyst of the combination of the dimethyl cobaltosic imidazole and the nickel-aluminum layered double hydroxide/graphene oxide is successfully prepared. The high-conductivity graphene oxide is used as a substrate, so that the stability of electrode circulation and the power generation efficiency are ensured; the layered structure of the nickel-aluminum layered double hydroxide improves the ion flow efficiency and effectively reduces the transmission resistance; the polyhedral structure of the dimethyl cobalt imidazolide increases the specific surface area of the composite and provides more active centers. These characteristics are effective in improving the cycle stability and power generation efficiency of the microbial fuel cell electrode.

It should be noted that the above-mentioned embodiments are only for illustrating the technical solutions of the present invention and not for limiting, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, which should be covered by the claims of the present invention.