Preparation method of nickel-iron layered double hydroxide combined cobalt disulfide nickel combined multi-walled carbon nanotube catalyst

Abstract

The invention discloses a preparation method of a layered double hydroxide combined cobalt disulfide and nickel tetrasulfide combined multi-walled carbon nanotube catalyst, which comprises the following steps: firstly, preparing cobalt disulfide and nickel tetrasulfide combined multi-walled carbon nanotubes through a two-step hydrothermal method; and then successfully preparing the ferro-nickel layered double hydroxide and nickel dicobalt tetrasulfide combined multi-walled carbon nanotube. The invention also discloses an application of the ferro-nickel layered double hydroxide and nickel dicobalt tetrasulfide combined multi-walled carbon nanotube as a microbial fuel cell cathode catalyst. The prepared material has higher porosity, more reaction sites, better electrochemical stability and higher conductivity, so that when the material is used as a cathode catalyst of the microbial fuel cell, the efficiency of electric ion flow is improved, the stability of electrode circulation and the power generation efficiency are ensured, and the performance of the microbial fuel cell is improved.

Description

Background Art

[0001] Microbial fuel cells are a technology based on microbial electrochemical systems that provide energy and treat wastewater. They are now widely used in many fields. Due to its low energy consumption, environmental friendliness and high efficiency, it has attracted many scholars to study. However, low power density, long cycle, expensive materials and low cathode reaction efficiency have hindered its further development. In order to solve these problems, many scholars have focused on optimizing the materials of the air cathode with a simple structure. A large number of studies have found that layered double hydroxides, nickel cobalt tetrasulfide, multi-walled carbon nanotubes, etc. have become a hot spot in microbial fuel cell research due to their excellent properties such as huge specific surface area, numerous active sites and stable electrochemical properties.

[0002] Layered double hydroxide (LDH) is a type of two-dimensional nano-flower-like material with low price, high reduction reaction activity, and environmental friendliness. Its performance will be significantly improved after combining with metal ions, but it still has problems such as self-stacking and low ion transfer efficiency. In order to optimize this problem, many researchers combine it with porous materials such as carbon nanotubes and graphene.

[0003] NiCo2S4 is an important member of bimetallic transition metal sulfides. It has high conductivity and tunable morphology and is widely used in various fields. In addition, Ni and Co have multiple oxidation states, providing more reaction sites for redox. However, after long-term electrochemical reaction, the structure of NiCo2S4 will change, resulting in a decrease in its performance. Therefore, many scholars combine NiCo2S4 with other materials to improve its catalytic performance and stability. Multi-walled carbon nanotubes (MWCNTs) are a class of carbon nanomaterials with tubular structures. It has a high specific surface area and good conductivity, and has broad application prospects in catalysis. However, MWCNTs have low dispersibility and are easy to agglomerate. Therefore, MWCNTs are often compounded with other materials to solve the dispersibility problem and further improve the catalytic performance.

[0004] Therefore, it is necessary to propose further solutions to the above problems. Summary of the invention

[0005] The present invention aims to provide a method for preparing an oxygen reduction catalyst of nickel-iron layered double hydroxide combined with nickel dicobalt tetrasulfide and multi-walled carbon nanotubes. The prepared cathode catalyst of a microbial fuel cell can effectively improve the power generation performance of MFC.

[0006] The present invention is achieved through the following technical solutions: A method for preparing an oxygen reduction catalyst of nickel-iron layered double hydroxide combined with nickel dicobalt tetrasulfide and multi-walled carbon nanotubes, the method comprising the following steps: Step 1: 100 mg of MWCNT (multi-walled carbon nanotube) was dispersed in 50 mL of deionized water and stirred at room temperature, followed by the addition of 6 mmol of CoCl2·6H2O and 3 mmol of NiCl2·6H2O. After ultrasonic treatment, 4 ml of 0.5 mol / L CH5N3S solution was added. The resulting mixture was transferred to a high-pressure reactor for heating, cooled to room temperature, washed with deionized water and ethanol, centrifuged, and vacuum dried to obtain nickel tetrasulfide-cobalt combined multi-walled carbon nanotubes.

[0007] Step 2: Disperse 100 mg of nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes prepared in step 1 in 80 mL of deionized water, and then add 1.5 mmol Ni (NO3)2·6H2O, 5 mmol Fe (NO3)3·9H2O and 5 mmol urea. Stir at room temperature, transfer the resulting mixture to a high-pressure reactor for heating, cool to room temperature, wash with deionized water and ethanol, centrifuge, and vacuum dry to obtain nickel-iron layered double hydroxide combined with nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes.

[0008] Furthermore, the stirring in step 1 is stirring at room temperature for 10 min.

[0009] Furthermore, the ultrasonic treatment in step 1 is performed at room temperature for 1 h.

[0010] Furthermore, the heating in step 1 is heating at 180° C. for 12 h.

[0011] Furthermore, the drying in step 1 is performed at 60° C. for 2 h.

[0012] Furthermore, the stirring in step 2 is stirring at room temperature for 1 h.

[0013] Furthermore, the heating in step 2 is heating at 120° C. for 10 h.

[0014] Furthermore, the drying in step 2 is performed at 60° C. for 2 h.

[0015] The present invention provides a method for preparing an oxygen reduction catalyst of nickel-iron layered double hydroxide combined with nickel dicobalt tetrasulfide combined with multi-walled carbon nanotubes, and successfully prepares a composite material of nickel-iron layered double hydroxide combined with nickel dicobalt tetrasulfide combined with multi-walled carbon nanotubes constructed by a two-step simple hydrothermal method. First, NiCo2S4 and MWCNT are combined by a hydrothermal synthesis method to obtain NiCo2S4@MWCNT; then NiFe-LDH and NiCo2S4@MWCNT are combined by a hydrothermal synthesis method again to obtain NiFe-LDH@NiCo2S4@MWCNT, NiFe-LDH and NiCo2S4 are uniformly grown on the surface of MWCNT, and a unique nanostructure is thus prepared, which significantly improves the performance of nickel-iron layered double hydroxide combined with nickel dicobalt tetrasulfide combined with multi-walled carbon nanotubes as a cathode of a microbial fuel cell by providing a large number of ion transmission channels and active sites. Finally, using stainless steel mesh (SS) as the substrate, a two-layer polytetrafluoroethylene (PTEF) method was used to prepare the cobalt tetrasulfide-nickel-doped zinc-aluminum layered double hydroxide combined with titanium dioxide-doped two-dimensional transition metal carbide microbial fuel cell cathode, and its effect on improving the performance of microbial fuel cells was studied. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The present invention is a schematic flow chart of a method for preparing an oxygen reduction catalyst of nickel-iron layered double hydroxide combined with nickel dicobalt tetrasulfide and multi-walled carbon nanotubes.

[0017] Figure 2 This is a SEM image of the preparation method of the oxygen reduction catalyst of nickel-iron layered double hydroxide combined with nickel dicobalt tetrasulfide and multi-walled carbon nanotubes of the present invention. Figure 2 (a) is a scanning electron microscope image of multi-walled carbon nanotubes. Figure 2 (b) is a scanning electron microscope image of nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes. Figure 2 (c) and Figure 2 (d) is a scanning electron microscope image of nickel-iron layered double hydroxide combined with nickel cobalt tetrasulfide and multi-walled carbon nanotubes.

[0018] Figure 3 This is an EDS diagram of the preparation method of the oxygen reduction catalyst of nickel-iron layered double hydroxide combined with nickel dicobalt tetrasulfide and multi-walled carbon nanotubes of the present invention.

[0019] Figure 4 The invention relates to the XRD patterns of multi-walled carbon nanotubes, dicobalt nickel tetrasulfide combined with multi-walled carbon nanotubes, and nickel-iron layered double hydroxide combined with dicobalt nickel tetrasulfide combined with multi-walled carbon nanotubes in the preparation method of the oxygen reduction catalyst of the present invention.

[0020] Figure 5 The present invention is an FT-IR graph of multi-walled carbon nanotubes, dicobalt nickel tetrasulfide combined with multi-walled carbon nanotubes, and nickel-iron layered double hydroxide combined with dicobalt nickel tetrasulfide combined with multi-walled carbon nanotubes in the preparation method of the oxygen reduction catalyst of the present invention.

[0021] Figure 6 The XPS graph of nickel-iron layered double hydroxide combined with nickel dicobalt tetrasulfide and multi-walled carbon nanotubes in the preparation method of the oxygen reduction catalyst of nickel-iron layered double hydroxide combined with nickel dicobalt tetrasulfide and multi-walled carbon nanotubes of the present invention.

[0022] Figure 7 In the preparation method of the oxygen reduction catalyst of nickel-iron layered double hydroxide combined with cobalt tetrasulfide and nickel multi-walled carbon nanotubes of the present invention, multi-walled carbon nanotubes, cobalt tetrasulfide and nickel multi-walled carbon nanotubes, and nickel-iron layered double hydroxide combined with cobalt tetrasulfide and nickel multi-walled carbon nanotubes are used as CV curves (a) and LSV curves (b) of multi-walled carbon nanotubes, nickel-iron layered double hydroxide combined with cobalt tetrasulfide and nickel multi-walled carbon nanotubes as nanomicrobial fuel cathode catalysts.

[0023] Figure 8 The present invention is a method for preparing an oxygen reduction catalyst of nickel-iron layered double hydroxide combined with cobalt tetrasulfide nickel and multi-walled carbon nanotubes, and shows CV curves of nickel-iron layered double hydroxide combined with cobalt tetrasulfide nickel and multi-walled carbon nanotube nanomicrobial fuel cathode catalyst at different scan rates.

[0024] Fig. 9 In the preparation method of the oxygen reduction catalyst of nickel-iron layered double hydroxide combined with cobalt tetrasulfide nickel combined with multi-walled carbon nanotubes of the present invention, the power density curves of multi-walled carbon nanotubes, cobalt tetrasulfide nickel combined with multi-walled carbon nanotubes, and nickel-iron layered double hydroxide combined with cobalt tetrasulfide nickel combined with multi-walled carbon nanotubes nanomicrobial fuel cathode catalysts when the voltage is stable. DETAILED DESCRIPTION

[0025] The present invention is further described in detail below in conjunction with specific implementation modes.

[0026] Example 1 See also Figure 1 , Figure 1 The present invention is a schematic flow chart of a method for preparing an oxygen reduction catalyst of nickel-iron layered double hydroxide combined with nickel dicobalt tetrasulfide and multi-walled carbon nanotubes.

[0027] like Figure 1 As shown, the present invention provides a method for preparing an oxygen reduction catalyst of nickel-iron layered double hydroxide combined with nickel dicobalt tetrasulfide and multi-walled carbon nanotubes, comprising the following steps: Step 1: 100 mg of MWCNTs were dispersed in 50 mL of deionized water and stirred at room temperature, followed by the addition of 6 mmol CoCl2·6H2O and 3 mmol NiCl2·6H2O. After ultrasonic treatment, 4 ml of 0.5 mol / L CH5N3S solution was added. The resulting mixture was transferred to a high-pressure reactor for heating, cooled to room temperature, washed with deionized water and ethanol, centrifuged, and vacuum dried to obtain nickel tetrasulfide-cobalt combined multi-walled carbon nanotubes.

[0028] Step 2: Disperse 100 mg of nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes prepared in step 1 in 80 mL of deionized water, and then add 1.5 mmol Ni (NO3)2·6H2O, 5 mmol Fe (NO3)3·9H2O and 5 mmol urea. Stir at room temperature, transfer the resulting mixture to a high-pressure reactor for heating, cool to room temperature, wash with deionized water and ethanol, centrifuge, and vacuum dry to obtain nickel-iron layered double hydroxide combined with nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes.

[0029] Furthermore, the stirring in step 1 is stirring at room temperature for 10 min.

[0030] Furthermore, the ultrasonic treatment in step 1 is performed at room temperature for 1 h.

[0031] Furthermore, the heating in step 1 is heating at 180° C. for 12 h.

[0032] Furthermore, the drying in step 1 is performed at 60° C. for 2 h.

[0033] Furthermore, the stirring in step 2 is stirring at room temperature for 1 h.

[0034] Furthermore, the heating in step 2 is heating at 120° C. for 10 h.

[0035] Furthermore, the drying in step 2 is performed at 60° C. for 2 h.

[0036] After the above two steps, the prepared nickel-iron layered double hydroxide combined with nickel cobalt tetrasulfide combined with multi-walled carbon nanotube oxygen reduction catalyst is completed. After these two steps, the structure can also be tested, such as using the sample as a cathode to test the performance of a microbial fuel cell.

[0037] Step 3: Perform electrochemical performance tests on an electrochemical workstation using a three-electrode system, and perform microbial fuel cell performance tests using a composite material of nickel-iron layered double hydroxide combined with nickel cobalt tetrasulfide and multi-walled carbon nanotubes as a cathode catalyst.

[0038] The abbreviations mentioned in the present invention are all fixed abbreviations in the field, and some of the abbreviations are explained as follows: SEM: scanning electron microscope; FTIR: Fourier transform infrared spectroscopy; XRD: x-ray diffraction pattern, XPS: x-ray photoelectron spectroscopy; EDS: scanning electron microscope energy spectrum.

[0039] Example 2 This example demonstrates the implementation scheme of the oxygen reduction catalyst of nickel-iron layered double hydroxide combined with nickel dicobalt tetrasulfide combined with multi-walled carbon nanotubes according to the following scheme: In order to study the electrochemical performance of the oxygen reduction catalyst of nickel-iron layered double hydroxide combined with cobalt tetrasulfide nickel combined with multi-walled carbon nanotubes, the present invention uses multi-walled carbon nanotubes, cobalt tetrasulfide nickel combined with multi-walled carbon nanotubes, and nickel-iron layered double hydroxide combined with cobalt tetrasulfide nickel combined with multi-walled carbon nanotubes as MFC cathode catalysts. Both CV and LSV tests are carried out in 50mM PBS solution.

[0040] See also Figure 7 By comparing the cyclic voltammetry curves, it can be seen that at the same scanning speed, the cyclic voltammetry integrated area of ​​nickel-iron layered double hydroxide combined with nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes is significantly larger than the cyclic voltammetry integrated area of ​​other catalysts. The results show that the synthesized nickel-iron layered double hydroxide combined with nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes has good redox properties. The high specific surface area nickel-iron layered double hydroxide and the stable multi-walled carbon nanotubes synergistically increase the ion transport channels and enhance the redox activity, while nickel cobalt tetrasulfide effectively prevents their self-stacking. Figure 7 As shown in (a), the composite material of nickel-iron layered double hydroxide combined with nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes has an obvious redox peak in PBS solution, indicating the valence state transformation of nickel ions and cobalt ions in the nickel-iron layered double hydroxide combined with nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes, and further indicating the redox activity of nickel-iron layered double hydroxide combined with nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes as a cathode catalyst.

[0041] In order to further investigate the electrocatalytic activity of the composite catalyst, the present invention investigated the LSV curves of different catalysts, such as Figure 7(b). The results show that the order of the catalyst inclination is nickel-iron layered double hydroxide combined with nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes > nickel cobalt tetrasulfide > nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes > multi-walled carbon nanotubes. The slope of the voltammetric curve shows that at the same cathode potential, the nickel-iron layered double hydroxide combined with nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes has a larger current and higher conductivity. Overall, the oxygen reduction catalyst of nickel-iron layered double hydroxide combined with nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes has good redox performance and high catalytic performance.

[0042] Example 3 This embodiment shows the implementation scheme of the cobalt tetrasulfide nickel-doped zinc-aluminum layered double hydroxide combined with titanium dioxide-doped two-dimensional transition metal carbide oxygen reduction catalyst as follows: In order to study the electrochemical performance of the oxygen reduction catalyst of nickel-iron layered double hydroxide combined with nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes, multi-walled carbon nanotubes, nickel-iron layered double hydroxide combined with nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes were used as MFC cathode catalysts. The CV test was carried out in 50 mM PBS solution.

[0043] See also Figure 8 , Figure 8 The CV curves of nickel-iron layered double hydroxide combined with nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes oxygen reduction catalyst at different scan rates are shown. The scan rate is 25-100mV / s, the potential range is -0.85-0.85V, and when the current changes continuously, the CV curve still maintains a shape; when the current gradually increases, the CV curve remains smooth and stable, indicating the stability and reversibility of the composite material. Within a certain range, when the scan rate continues to increase, the composite material exhibits more obvious redox peaks and more stable redox reaction activity. The cyclic voltammetry curves at different scan rates show that nickel-iron layered double hydroxide combined with nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes can significantly improve the electrocatalytic performance of the MFC air cathode.

[0044] Example 4 This example demonstrates the implementation scheme of the oxygen reduction catalyst of nickel-iron layered double hydroxide combined with nickel dicobalt tetrasulfide combined with multi-walled carbon nanotubes according to the following scheme: See also Fig. 9, multi-walled carbon nanotubes, nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes, nickel iron layered double hydroxide combined with nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes were used as cathode catalysts of single-chamber MFC, and the anode state was kept consistent to evaluate the effect of different cathode catalysts on the power generation capacity of MFC. By gradually reducing the external resistance of MFC (from 2000 Ω to 20 Ω), the power density curve and voltage when the voltage was stable were evaluated.

[0045] See also Fig. 9 The maximum power density of nickel-iron layered double hydroxide combined with nickel dicobalt tetrasulfide and multi-walled carbon nanotube-MFC can reach 487.2 mW / m 2 , which is 1.79 times that of nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes-MFC (272.6 mW / m 2 ), which is 2.87 times that of multi-walled carbon nanotube-MFC (169.9 mW / m 2 ). The results show that the nickel-iron layered double hydroxide combined with nickel dicobalt tetrasulfide and multi-walled carbon nanotubes modified cathode has good power generation performance and redox activity.

[0046] Please refer to Table 1. The continuous output voltage of nickel-iron layered double hydroxide combined with nickel cobalt tetrasulfide combined with multi-walled carbon nanotube-MFC is 459.9 mV, which is 1.37 times (335.9 mV) of nickel cobalt tetrasulfide combined with multi-walled carbon nanotube-MFC and 1.44 times (319.6 mV) of multi-walled carbon nanotube-MFC. Higher voltage means faster consumption of organic matter, which further proves that nickel-iron layered double hydroxide combined with nickel cobalt tetrasulfide combined with multi-walled carbon nanotube is more effective as a cathode catalyst for ORR reaction. In addition, the output voltage of nickel-iron layered double hydroxide combined with nickel cobalt tetrasulfide combined with multi-walled carbon nanotube-MFC did not change much within 7 days, indicating that the catalyst has good durability and cycle stability.

[0047] Table 1 Maximum continuous output voltage and duration The specific conclusions of the oxygen reduction catalyst of nickel-iron layered double hydroxide combined with nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes described in the above examples are as follows: See also Figure 2 , Figure 2 This is a SEM image of the preparation method of the oxygen reduction catalyst of nickel-iron layered double hydroxide combined with nickel dicobalt tetrasulfide and multi-walled carbon nanotubes of the present invention. Figure 2 (a) is a scanning electron microscope image of multi-walled carbon nanotubes. Figure 2 (b) is a scanning electron microscope image of nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes. Figure 2 (c) and Figure 2(d) is a scanning electron microscope image of nickel-iron layered double hydroxide combined with nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes. The SEM image clearly observed the surface morphology of each element, further confirming that nickel-iron layered double hydroxide combined with nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes has been perfectly prepared. Figure 2 As shown in (a), multi-walled carbon nanotubes present a cross-linked network structure with abundant pores and high specific surface area. Figure 2 (b) shows that multi-walled carbon nanotubes and nickel cobalt tetrasulfide effectively form a composite material. The typical flower-like nanostructure of layered double hydroxide is Figure 2 It is obvious in (c)-2(d) that the multi-walled carbon nanotubes and the nickel cobalt tetrasulfide layer are wrapped on the surface to form a stable structure. This morphology gives the nickel-iron layered double hydroxide combined with nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes a wide specific surface area, while providing sufficient electroactive sites and pathways for electrochemical reactions. As can be seen from the figure, the nickel-iron layered double hydroxide combined with nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes was successfully synthesized. SEM testing further proves that the composite material has been perfectly prepared and has great catalytic potential.

[0048] See also Figure 3 , EDS diagram of the preparation method of the oxygen reduction catalyst of nickel-iron layered double hydroxide combined with cobalt tetrasulfide nickel combined with multi-walled carbon nanotubes of the present invention. EDS analysis obtained the distribution and proportion of elements in the nickel-iron layered double hydroxide combined with cobalt tetrasulfide nickel combined with multi-walled carbon nanotubes, such as Figure 3 As shown. The results show that O, C, S, Co, Ni and Fe are distributed throughout the structure of nickel-iron layered double hydroxide combined with nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes. This result further confirms the good synthesis of nickel-iron layered double hydroxide combined with nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes.

[0049] See also Figure 4 , Figure 4 The FT-IR images of multi-walled carbon nanotubes, dicobalt tetrasulfide nickel combined with multi-walled carbon nanotubes, and nickel-iron layered double hydroxide combined with dicobalt tetrasulfide nickel combined with multi-walled carbon nanotubes in the preparation method of the oxygen reduction catalyst of the present invention are shown in the figure. The composition of the surface functional groups of the composite material is clearly shown in the FT-IR image, and the 1628 cm -1 and 3434 cm -1 The peak at 1110 cm is caused by the stretching vibration of the -OH bond, and the hydrogen bond may be formed during the hydrothermal synthesis. -1 The peaks near 600 cm correspond to the symmetric and asymmetric stretching vibrations of the OCO bond, confirming the existence of multi-walled carbon nanotubes in the NiFe layered double hydroxide combined with NiCoS4.-1 The peak at 500-650cm is caused by the vibration of MS bond. -1 The peaks in the range represent stretching vibrations associated with MOM and MO (Ni-O-Fe, Ni-O, Fe-O), which correspond to the spectral characteristics of nickel-iron layered double hydroxide. However, it should be noted that the individual peaks of nickel-iron layered double hydroxide combined with cobalt tetrasulfide nickel combined with multi-walled carbon nanotubes disappear, and the peak intensity decreases significantly. This may be because after the addition of iron, some iron complexes are formed, which destroy the internal molecular structure of nickel-iron layered double hydroxide combined with cobalt tetrasulfide nickel combined with multi-walled carbon nanotubes.

[0050] See also Figure 5 , Figure 5 In the preparation method of the oxygen reduction catalyst of nickel-iron layered double hydroxide combined with nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes of the present invention, XRD patterns of multi-walled carbon nanotubes, nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes, and nickel-iron layered double hydroxide combined with nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes are provided. The characteristic peaks of the multi-walled carbon nanotubes are located at 11.19°, 20.99°, 34.37° and 55.15°, respectively, corresponding to (003), (111), (112) and (110) crystal planes, respectively. Some crystal plane diffraction angles also appear in the nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes, which are 19.10°, 32.66°, 38.09°, 51.67° and 58.39°, respectively. This indicates that the addition of nickel cobalt tetrasulfide changes the crystal structure of the multi-walled carbon nanotubes and forms new crystal planes. However, the number of XRD peaks of nickel-iron layered double hydroxide combined with nickel cobalt tetrasulfide and multi-walled carbon nanotubes decreased, the intensity weakened, and new characteristic peaks appeared. The possible reason for this phenomenon is that the incorporation of nickel-iron layered double hydroxide leads to an increase in the interlayer spacing of the material. The increase in the interlayer spacing triggers a phase change in the material structure, resulting in a change in the crystal structure.

[0051] See also Figure 6 , Figure 6 The XPS graphs of multi-walled carbon nanotubes, dicobalt nickel tetrasulfide combined with multi-walled carbon nanotubes, and nickel-iron layered double hydroxide combined with dicobalt nickel tetrasulfide combined with multi-walled carbon nanotubes in the preparation method of the oxygen reduction catalyst of the present invention are shown. The XPS graph clearly shows the content and valence state of each element in the composite material. Figure 6 (a) shows nickel-iron layered double hydroxide combined with nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes composed of C, O, S, Co, Fe and Ni. Figure 6In (b), the C 1s spectrum has three peaks at 289.87 eV, 286.44 eV, and 284.78 eV, corresponding to OC=O, CO, and CC bonds, respectively. Figure 6 In (c), the peak at 532 eV in the O 1s spectrum corresponds to O 2- .exist Figure 6 In (d), the S 2p spectra at 170.48 eV and 169.24 eV show the same 2+ and S 3+ The peaks observed at 163.63 eV and 162.38 eV represent the two satellite features of S. Figure 6 The Co 2p spectrum in (e) shows peaks at 797.31 eV and 782.34 eV, respectively, which are attributed to Co 2+ and Co 3+ .same, Figure 6 (f) is the Fe 2p spectrum, with peaks at 726.93 eV and 713.87 eV, corresponding to Fe 2+ and Fe 3+ In addition, the Ni 2p spectrum is shown in Figure 6 As shown in (g), peaks appear at 874.15 eV and 856.65 eV, corresponding to Ni 2+ and Ni 3+ , Ni shows further satellite features at 879.95 eV and 862.37 eV. Peak area analysis shows that Co and Fe elements have higher relative contents in nickel-iron layered double hydroxide combined with nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes. These results further prove the preparation of nickel-iron layered double hydroxide combined with nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes.

[0052] Compared with the prior art, the beneficial effects of the present invention are as follows: the composite material is based on multi-walled carbon nanotubes and combines nickel-iron layered double hydroxide and nickel dicobalt tetrasulfide. The huge specific surface area and a large number of active sites of the composite material promote ion transport. The special structure of the composite material has a high porosity, provides a channel for the transfer of ions between the multi-walled carbon nanotubes and the layered double hydroxide, and improves its redox ability. The nickel-iron layered double hydroxide combined with nickel dicobalt tetrasulfide combined with multi-walled carbon nanotubes increases the electron transfer rate, reduces the surface resistance, and enhances its electrochemical activity as a microbial fuel cell.

Claims

1. A method for preparing an oxygen reduction catalyst of nickel-iron layered double hydroxide combined with nickel dicobalt tetrasulfide and multi-walled carbon nanotubes, characterized in that: The following steps are involved: Step 1: MWCNTs are dispersed in deionized water, stirred at room temperature, and then CoCl2·6H2O and NiCl2·6H2O are added; after ultrasonic treatment, CH5N3S solution is added; the resulting mixture is transferred to a high-pressure reactor for heating, cooled to room temperature, washed with deionized water and ethanol, centrifuged, and vacuum dried to obtain nickel tetrasulfide-cobalt combined multi-walled carbon nanotubes; Step 2: Disperse the nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes prepared in step 1 in deionized water, then add Ni (NO3)2·6H2O, Fe (NO3)3·9H2O and urea, stir at room temperature, transfer the resulting mixture to a high-pressure reactor for heating, cool to room temperature, wash with deionized water and ethanol, centrifuge, and vacuum dry to obtain nickel-iron layered double hydroxide combined with nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes.

2. The method for preparing an oxygen reduction catalyst of nickel-iron layered double hydroxide combined with cobalt tetrasulfide and multi-walled carbon nanotubes according to claim 1, characterized in that: The added amounts of MWCNT, CoCl2·6H2O, and NiCl2·6H2O are 100 mg, 6 mmol, and 3 mmol, respectively.

3. The method for preparing an oxygen reduction catalyst of nickel-iron layered double hydroxide combined with cobalt tetrasulfide and multi-walled carbon nanotubes according to claim 1, characterized in that: The amount of CH5N3S solution added was 4 ml, and the concentration was 0.5 mol / L.

4. The method for preparing an oxygen reduction catalyst of nickel-iron layered double hydroxide combined with cobalt tetrasulfide and multi-walled carbon nanotubes according to claim 1, characterized in that: The stirring in step 1 is stirring at room temperature for 10 min; the ultrasonic treatment is ultrasonic treatment at room temperature for 1 h; the heating is heating at 180°C for 12 h; and the drying is drying at 60°C for 2 h.

5. The method for preparing the oxygen reduction catalyst of nickel-iron layered double hydroxide combined with cobalt tetrasulfide and multi-walled carbon nanotubes according to claim 1, characterized in that: The added amounts of nickel cobalt tetrasulfide combined with multi-walled carbon nanotubes, Ni (NO3)2·6H2O, Fe (NO3)3·9H2O, and urea were 100 mg, 1.5 mmol, 5 mmol, and 5 mmol, respectively.

6. The method for preparing the oxygen reduction catalyst of nickel-iron layered double hydroxide combined with cobalt tetrasulfide nickel combined with multi-walled carbon nanotubes according to claim 1, characterized in that: The stirring in step 2 is stirring at room temperature for 1 h; the heating is heating at 120° C. for 10 h; and the drying is drying at 60° C. for 2 h.

7. An oxygen reduction catalyst of nickel-iron layered double hydroxide combined with dicobalt tetrasulfide nickel combined with multi-walled carbon nanotubes prepared by the preparation method of the nickel-iron layered double hydroxide combined with dicobalt tetrasulfide nickel combined with multi-walled carbon nanotubes according to any one of claims 1 to 6.

8. Use of the nickel-iron layered double hydroxide combined with nickel dicobalt tetrasulfide and multi-walled carbon nanotube oxygen reduction catalyst according to claim 7 in a microbial fuel cell.

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