Nitrogen-doped porous carbon loaded iron-selenium transition metal composite material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of battery materials, and discloses a nitrogen-doped porous carbon loaded iron-selenium transition metal composite material as well as a preparation method and application thereof. According to the method, Se atoms are innovatively introduced into a Fe monatomic catalyst, and components are uniformly distributed on a nitrogen-doped carbon-based material. By introducing Se, the electron structure and microenvironment of Fe sites can be hybridized and adjusted through a p-d orbit, so that the adsorption / desorption behavior between active sites and intermediates in the ORR process is optimized, the efficient utilization of the catalyst is ensured, and the catalytic efficiency is greatly enhanced through the synergistic effect among iron-selenium particles. In addition, the synthetic method of the composite material is simple and easy to implement, has high economical efficiency, and lays a solid foundation for achieving industrial mass production of the composite material. Compared with a traditional platinum-carbon catalyst, the composite material catalyst has remarkable advantages in electrochemical performance.

Description

Technical Field

[0001] The invention belongs to the technical field of battery materials, and particularly relates to a nitrogen-doped porous carbon-loaded iron-selenium transition metal composite material and a preparation method and application thereof. Background Art

[0002] Metal-air batteries, as a new type of energy conversion device that can directly convert chemical energy into electrical energy without combustion, have attracted widespread attention due to their high efficiency and environmental protection. This type of battery can not only significantly reduce greenhouse gas emissions and reduce environmental pollution, but also effectively improve energy efficiency, providing new possibilities for achieving global energy transformation and sustainable development goals. Metal-air batteries have the characteristics of high specific capacity, low cost, and low pollution, and have broad application prospects. Summary of the invention

[0003] In order to overcome the shortcomings and deficiencies in the prior art, the primary purpose of the present invention is to provide a method for preparing a nitrogen-doped porous carbon-loaded iron-selenium transition metal composite material; the preparation method has low preparation cost, simple preparation method, and the prepared composite material has excellent oxygen reduction electrocatalytic activity.

[0004] Another object of the present invention is to provide a nitrogen-doped porous carbon-loaded iron-selenium transition metal composite material prepared by the above preparation method.

[0005] Another object of the present invention is to provide an application of the above-mentioned nitrogen-doped porous carbon-loaded iron-selenium transition metal composite material.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A method for preparing a nitrogen-doped porous carbon-supported iron-selenium transition metal composite material comprises the following steps:

[0008] A magnesium zinc NC precursor and a selenium compound are ground and mixed together, and then put into a tube furnace together with a transition metal iron compound, and calcined by a vapor deposition method under nitrogen or an inert gas. The calcined product is ground and then acid-washed, filtered and dried, and then calcined twice to obtain a nitrogen-doped porous carbon-supported iron-selenium transition metal composite material; the molar ratio of the transition metal iron compound to the selenium compound is (0.1-5): (0.1-6); the molar ratio of the transition metal iron compound to the magnesium zinc NC precursor is (0.01-1): (0.1-5).

[0009] The present invention adopts a template synthesis strategy to form a porous doped carbon material loaded with a transition metal single atom catalyst. The present invention develops an electrocatalyst containing Fe single atom doped Se particles on N-doped porous carbon. Since there is a synergistic effect between FeSe particles, charge redistribution can be adjusted, the electronic structure and microenvironment can be optimized, the adsorption energy can be effectively reduced, and the catalytic activity can be synergistically improved, which significantly promotes the oxygen reduction reaction.

[0010] The magnesium zinc NC precursor is synthesized from magnesium chloride, p-phenylenediamine, sodium chloride and zinc chloride, and is specifically prepared according to the following steps:

[0011] (1) 1 mmol of anhydrous magnesium chloride and 20 mL of methanol were magnetically stirred until completely dissolved to obtain solution A;

[0012] (2) 10 mmol of p-phenylenediamine and 20 mL of methanol were magnetically stirred until completely dissolved to obtain solution B;

[0013] (3) 700 mg of sodium chloride, 1300 mg of zinc chloride and 20 mL of deionized water were magnetically stirred until they were completely dissolved to obtain solution C;

[0014] (4) Solution A was added to solution B, and after stirring for 10 min, solution C was also poured into the solution. The resulting mixed solution was magnetically stirred for more than 6 hours, and then frozen with liquid nitrogen, and then freeze-dried for 36 hours. After drying, the resulting solid was ground for 10 minutes, and the resulting powder particles were calcined at 900°C in a tubular furnace under a nitrogen atmosphere for 2 hours at a heating rate of 5°C / min; the calcined powder particles were ground again for 10 minutes, and then rinsed and filtered with deionized water to remove soluble salt ions; then acid-washed with 0.5 mol / L sulfuric acid for 12 hours, and then filtered with deionized water. After filtration, it was dried in an oven at 70°C for 12 hours; the dried sample was ground for 30 minutes, and then calcined for a second time, and calcined at 900°C in a tubular furnace under a nitrogen atmosphere for 2 hours at a heating rate of 5°C / min to obtain a MgZn NC precursor.

[0015] The molar ratio of the transition metal iron compound to the selenium compound is 1:1; the molar ratio of the transition metal iron compound to the magnesium zinc NC precursor is (0.01-0.5): (0.5-3).

[0016] The drying is carried out in an oven at a temperature of 20-100°C, preferably 75°C.

[0017] The calcination temperature is 600-1100° C. and the calcination time is 0.5-3 hours.

[0018] The secondary calcination was carried out at a temperature of 900° C. and for a time of 2 h.

[0019] A nitrogen-doped porous carbon-loaded iron-selenium transition metal composite material prepared by the above-mentioned preparation method, in which iron atoms and selenium atoms are uniformly distributed on the nitrogen-doped carbon-based material.

[0020] Application of the above-mentioned nitrogen-doped porous carbon-loaded iron-selenium transition metal composite material in metal-air batteries.

[0021] A metal-air battery positive electrode material comprises the above-mentioned nitrogen-doped porous carbon-loaded iron-selenium transition metal composite material.

[0022] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0023] (1) The present invention provides a method for preparing a nitrogen-doped porous carbon-supported iron-selenium transition metal composite material. The preparation method uses a template synthesis strategy to prepare an electrocatalyst containing Fe single-atom doped Se particles on a N-doped porous carbon. The catalyst innovatively introduces Se atoms into the Fe single-atom catalyst and the components are evenly distributed on the nitrogen-doped carbon-based material. The introduction of Se can make the pd orbital hybridization adjust the electronic structure and microenvironment of the Fe site, thereby optimizing the adsorption / desorption behavior between the active site and the intermediate in the ORR process; not only does it ensure the efficient use of the catalyst, but also through the synergistic effect between the iron-selenium particles, it greatly enhances the catalytic efficiency and significantly promotes the oxygen reduction reaction.

[0024] (2) The nitrogen-doped porous carbon-supported iron-selenium transition metal composite material prepared by the present invention has excellent oxygen reduction electrocatalytic activity, which is similar to that of Pt / C catalyst in alkaline electrolyte, with a half-wave potential of 0.89 V (vs. RHE), and shows higher power density and better 5 mA cm-2 than commercial Pt / C. -2 Long time discharge performance and step discharge performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 XRD of Fe-Se / NC, Fe / NC, Se / NC and NC prepared in Examples 1 to 4 of the present invention;

[0026] Figure 2 This is the SEM of Fe-Se / NC prepared in Example 1 of the present invention;

[0027] Figure 3 TEM of Fe-Se / NC prepared in Example 1 of the present invention;

[0028] Figure 4 The oxygen reduction activity test graphs of Fe-Se / NC, Fe / NC, Se / NC, NC and commercial Pt / C prepared in Examples 1 to 4 of the present invention;

[0029] Figure 5 This is a diagram showing the power test results of the magnesium metal air battery provided in Example 7 of the present invention;

[0030] Figure 6 The 10 mA cm of the magnesium metal air battery provided in Example 7 of the present invention -2 Constant current discharge test result diagram;

[0031] Figure 7 This is a graph showing the step discharge test results of the magnesium metal-air battery provided in Example 7 of the present invention.

[0032] Figure 8 This is a diagram showing the power test results of the zinc metal air battery provided in Example 8 of the present invention;

[0033] Fig. 9 The 10 mA cm of the zinc metal air battery provided in Example 8 of the present invention -2 Constant current discharge test result diagram;

[0034] Fig.10 This is a graph showing the step discharge test results of the zinc metal air battery provided in Example 8 of the present invention. DETAILED DESCRIPTION

[0035] The present invention is further described below with reference to specific embodiments, but they should not be construed as limiting the present invention.

[0036] Example 1

[0037] This example is the preparation of nitrogen-doped porous carbon-supported iron-selenium transition metal composite material Fe-Se / NC, and the specific preparation steps are as follows:

[0038] Solution A: Mix 1 mmol of magnesium chloride (anhydrous) and 20 mL of methanol, stir magnetically until completely dissolved to obtain solution A;

[0039] Solution B: 10 mmol of p-phenylenediamine and 20 mL of methanol were stirred magnetically until they were completely dissolved to obtain solution B;

[0040] Solution C: Add 700 mg of sodium chloride, 1300 mg of zinc chloride and 20 mL of deionized water and stir magnetically until they are completely dissolved to obtain Solution C.

[0041] The A solution was slowly added to the B solution, and after stirring for 10 minutes, the C solution was also slowly poured into it; the obtained mixed solution was magnetically stirred for more than six hours, and then frozen with liquid nitrogen, and then placed in a freeze dryer for freeze drying (36 hours). After drying, the obtained solid was ground for 10 minutes, and the obtained powder particles were calcined at 900°C for 2 hours in a nitrogen atmosphere in a tubular furnace, with a heating rate of 5°C / min; the calcined powder particles were ground again for 10 minutes, and then rinsed and filtered with a large amount of deionized water to remove the soluble salt ions therein; then acid-washed with 0.5 mol / L sulfuric acid for 12 hours, and then filtered with a large amount of deionized water. After the filtration was completed, it was dried at 70°C in an oven for 12 hours; the dried sample was ground for 30 minutes, and then calcined for a second time, and calcined at 900°C for 2 hours in a nitrogen atmosphere in a tubular furnace, with a heating rate of 5°C / min, to obtain a magnesium-zinc NC precursor.

[0042] The magnesium zinc NC precursor and diphenyl diselenide were ground and mixed at a molar ratio of 20:1 for 10 minutes, and then ferrocene (the molar ratio of ferrocene to magnesium zinc NC precursor was 1:20) was weighed and put into a tube furnace for calcination using a vapor deposition method, calcined at 950℃ in a nitrogen atmosphere, kept warm for 2 hours, and the heating rate was 5° / min. The obtained sample was ground for 10 minutes and then acid-washed with 0.5mol / L sulfuric acid for 12 hours, and then filtered with a large amount of deionized water. After the filtration was completed, it was dried in an oven at 70℃ for 12 hours. The dried and ground sample was calcined twice, calcined at 900℃ in a nitrogen atmosphere in a tube furnace, kept warm for 2 hours, and the heating rate was 5℃ / min, to obtain a nitrogen-doped porous carbon-supported iron-selenium transition metal composite material, recorded as Fe-Se / NC.

[0043] Example 2

[0044] This example is the preparation of nitrogen-doped porous carbon-supported iron transition metal composite material Fe / NC, and the specific preparation steps are as follows:

[0045] Solution A: Mix 1 mmol of magnesium chloride (anhydrous) and 20 mL of methanol, stir magnetically until completely dissolved to obtain solution A;

[0046] Solution B: 10 mmol of p-phenylenediamine and 20 mL of methanol were stirred magnetically until they were completely dissolved to obtain solution B;

[0047] Solution C: Add 700 mg of sodium chloride, 1300 mg of zinc chloride and 20 mL of deionized water and stir magnetically until they are completely dissolved to obtain Solution C.

[0048] The A solution was slowly added to the B solution, and after stirring for 10 minutes, the C solution was also slowly poured into it; the obtained mixed solution was magnetically stirred for more than six hours, and then frozen with liquid nitrogen, and then placed in a freeze dryer for freeze drying (36 hours). After drying, the obtained solid was ground for 10 minutes, and the obtained powder particles were calcined and kept warm at 900°C in a tubular furnace under a nitrogen atmosphere for 2 hours, with a heating rate of 5°C / min; the calcined powder particles were ground again for 10 minutes, and then rinsed and filtered with a large amount of deionized water to remove the soluble salt ions therein; then acid-washed with 0.5 mol / L sulfuric acid for 12 hours, and then filtered with a large amount of deionized water. After the filtration was completed, it was dried at 70°C in an oven for 12 hours; the dried sample was ground for 30 minutes, and then calcined for a second time, and calcined and kept warm at 900°C in a tubular furnace under a nitrogen atmosphere for 2 hours, with a heating rate of 5°C / min, to obtain a magnesium-zinc NC precursor.

[0049] Weigh ferrocene and the above-obtained magnesium zinc NC precursor in a molar ratio of 1:20, put them together in a tube furnace and calcine them using a vapor deposition method, calcine at 950°C in a nitrogen atmosphere, keep warm for 2 hours, and heat up at a rate of 5° / min. Grind the obtained sample for 10 minutes, then pickle it with 0.5 mol / L sulfuric acid for 12 hours, and then filter it with a large amount of deionized water. After the filtration is completed, dry it in an oven at 70°C for 12 hours. The dried and ground sample is calcined twice, calcined at 900°C in a tube furnace under a nitrogen atmosphere, keep warm for 2 hours, and heat up at a rate of 5°C / min to obtain a nitrogen-doped porous carbon-supported iron transition metal composite material, which is recorded as Fe / NC.

[0050] Example 3

[0051] This example is the preparation of nitrogen-doped porous carbon-supported selenium transition metal composite material Se / NC, and the specific preparation steps are as follows:

[0052] Solution A: Mix 1 mmol of magnesium chloride (anhydrous) and 20 mL of methanol, stir magnetically until completely dissolved to obtain solution A;

[0053] Solution B: 10 mmol of p-phenylenediamine and 20 mL of methanol were stirred magnetically until they were completely dissolved to obtain solution B;

[0054] Solution C: Add 700 mg of sodium chloride, 1300 mg of zinc chloride and 20 mL of deionized water and stir magnetically until they are completely dissolved to obtain Solution C.

[0055] The A solution was slowly added to the B solution, and after stirring for 10 minutes, the C solution was also slowly poured into it. The obtained mixed solution was magnetically stirred for more than six hours, and then frozen with liquid nitrogen, and then placed in a freeze dryer for freeze drying (36 hours). After drying, the obtained solid was ground for 10 minutes, and the obtained powder particles were calcined and kept warm at 900°C in a tubular furnace under a nitrogen atmosphere for 2 hours, with a heating rate of 5°C / min; the calcined powder particles were ground for 10 minutes, and then rinsed and filtered with a large amount of deionized water to remove the soluble salt ions therein; then acid-washed with 0.5 mol / L sulfuric acid for 12 hours, and then filtered with a large amount of deionized water. After the filtration was completed, it was dried at 70°C in an oven for 12 hours; the dried sample was ground for 30 minutes, and then calcined for a second time, and calcined and kept warm at 900°C in a tubular furnace under a nitrogen atmosphere for 2 hours, with a heating rate of 5°C / min, to obtain a magnesium-zinc NC precursor.

[0056] The magnesium zinc NC precursor and diphenyl diselenide were ground and mixed at a molar ratio of 20:1 for 10 minutes, and then placed in a tube furnace for calcination, calcined at 950℃ in a nitrogen atmosphere, kept warm for 2 hours, and the heating rate was 5° / min. The obtained sample was ground for 10 minutes and then acid-washed with 0.5mol / L sulfuric acid for 12 hours, and then filtered with a large amount of deionized water. After the filtration was completed, it was dried in an oven at 70℃ for 12 hours. The dried and ground sample was calcined twice, calcined at 900℃ in a tube furnace under a nitrogen atmosphere, kept warm for 2 hours, and the heating rate was 5℃ / min to obtain a nitrogen-doped porous carbon-supported selenium transition metal composite material, recorded as Se / NC.

[0057] Example 4

[0058] This example is the preparation of the precursor NC, and the specific preparation steps are as follows:

[0059] Solution A: Mix 1 mmol of magnesium chloride (anhydrous) and 20 mL of methanol, stir magnetically until completely dissolved to obtain solution A;

[0060] Solution B: 10 mmol of p-phenylenediamine and 20 mL of methanol were stirred magnetically until they were completely dissolved to obtain solution B;

[0061] Solution C: Add 700 mg of sodium chloride, 1300 mg of zinc chloride and 20 mL of deionized water and stir magnetically until they are completely dissolved to obtain Solution C.

[0062] Solution A was slowly added to solution B, and after stirring for 10 minutes, solution C was slowly poured into it; the resulting mixed solution was magnetically stirred for more than six hours, then frozen with liquid nitrogen, and then placed in a freeze dryer for freeze drying (36 hours). After drying, the resulting solid was ground for 10 minutes, and the resulting powder particles were calcined and kept warm for 2 hours at 900°C in a tube furnace under a nitrogen atmosphere, with a heating rate of 5°C / min; the calcined powder particles were ground for 10 minutes, and then rinsed and filtered with a large amount of deionized water to remove the soluble salt ions therein. Then, it was acid-washed with 0.5 mol / L sulfuric acid for 12 hours, and then filtered with a large amount of deionized water. After the filtration was completed, it was dried at 70°C in an oven for 12 hours. The dried sample was ground for 30 minutes, and then calcined for a second time, and calcined and kept warm for 2 hours at 900°C in a tube furnace under a nitrogen atmosphere, with a heating rate of 5°C / min, to obtain a magnesium zinc NC precursor, recorded as NC.

[0063] Example 5

[0064] 1. XRD characterization was performed on Fe-Se / NC, Fe / NC, Se / NC and NC prepared in Examples 1 to 4. The results are as follows: Figure 1 shown.

[0065] like Figure 1 As shown, Fe-Se / NC, Fe / NC, Se / NC and NC were successfully prepared in Examples 1 to 4. The main phases of Fe-Se / NC were FeSe and FeC phases; the main phases of Fe / NC and Se / NC were FeC and SeC phases respectively, and the main phase of NC was C phase.

[0066] 2. The Fe-Se / NC prepared in Example 1 was characterized by SEM and TEM. The results are as follows: Figure 2 , 3 shown.

[0067] like Figure 2 , 3 As shown in the figure, there are a large number of holes evenly distributed on the Fe-Se / NC material, which is highly porous. In the TEM, it can be seen that Fe-Se / NC has a very large surface area, which is conducive to providing sites for the anchoring of single atoms and also has a positive effect on promoting the contact between target molecules and active sites.

[0068] Example 6

[0069] The Fe-Se / NC, Fe / NC, Se / NC and NC prepared in Examples 1 to 4 and commercial Pt / C were tested for oxygen reduction activity. The specific preparation steps are as follows:

[0070] Weigh 8 mg of the samples prepared in Examples 1 to 4 into sample bottles, add 1 ml of ethanol, 1 ml of deionized water and 80 μl of Nafion, and perform ultrasound for 30 minutes to obtain a solution. After ultrasound is completed, use a pipette to drop 12.5 μL of the solution onto the glassy carbon electrode and use an infrared lamp to dry the water and alcohol (catalyst loading: 0.4 mg / cm 2 ). A glassy carbon electrode was used as the working electrode, graphite and Ag / AgCl were used as the counter electrode and reference electrode respectively, and 0.1M KOH solution was used as the electrolyte. A linear voltammetry test was performed at a speed of 1600 rpm, with a scanning interval of 0.2 to 1.0 V (vs. RHE). The test results are shown in Figure 2. Figure 4 shown.

[0071] like Figure 4 As shown, the oxygen reduction activities of Fe-Se / NC, Fe / NC, Se / NC and NC catalysts are close to that of Pt / C catalyst, but the best performance is that of Fe-Se / NC catalyst, with a half-wave potential of 0.88 V (vs. RHE).

[0072] Example 7

[0073] The metal-air battery was assembled as follows: the solution preparation process was consistent with the solution preparation process of Example 6 above, and a 6.5*2 cm hydrophilic and hydrophobic carbon cloth was cut. 562.5 μL of the prepared solution was evenly dripped onto the hydrophilic side of the 1.5*1.5 cm area (carbon cloth catalyst loading: 1 mg / cm 2 ), and then dried to obtain the air electrode. The air battery is assembled into an air battery using a specific mold, with magnesium sheet as the negative electrode and coated with 1mg / cm 2 The carbon cloth of Fe-Se / NC and Pt / C was used as the positive electrode, and an appropriate amount of 6M KOH was added as the electrolyte.

[0074] The magnesium-air battery assembled according to the above method was tested for power of Fe-Se / NC and Pt / C. The test results are shown in Figure 5 shown.

[0075] like Figure 5 As shown in Figure 2, the maximum power density of Fe-Se / NC is 53.73 mW cm -2 , which is higher than 36.82 mW cm of Pt / C. -2 , which further demonstrates the excellent oxygen reduction performance of Fe-Se / NC.

[0076] The magnesium-air battery assembled according to the above method was subjected to a current density of 10 mA cm-1 on Fe-Se / NC and Pt / C. -2 Constant current discharge test. The test results are as follows Figure 6 shown.

[0077] like Figure 6 As shown, the specific capacity of Fe-Se / NC is 1213 mAh g -1 Compared with commercial Pt / C (1140 mAh g - high.

[0078] The batteries assembled according to the above method were subjected to step discharge tests on Fe-Se / NC and Pt / C. The test results are shown in Figure 7 shown.

[0079] like Figure 7 As shown, Fe-Se / NC has good stability under open circuit, 2, 5 and 10 mA cm -2 The voltage values ​​under this condition are all higher than those of Pt / C.

[0080] Example 8

[0081] The metal-air battery was assembled as follows: the solution preparation process was consistent with the solution preparation process of Example 6 above, and a 6.5*2 cm hydrophilic and hydrophobic carbon cloth was cut. 562.5 μL of the prepared solution was evenly dripped onto the hydrophilic side of the 1.5*1.5 cm area (carbon cloth catalyst loading: 1 mg / cm 2 ), and then dried to obtain the air electrode. The air battery is assembled into a specific mold, with the zinc sheet as the negative electrode and coated with 1mg / cm 2 Fe-Se / NC and Pt / C carbon cloth were used as positive electrodes, and an appropriate amount of 3.5wt% NaCl was added as electrolyte.

[0082] The zinc-air batteries assembled according to the above method were tested for power of Fe-Se / NC and Pt / C. The test results are shown in Figure 8 shown.

[0083] like Figure 8 As shown in Figure 2, the maximum power density of Fe-Se / NC is 114.5 mW cm -2 , which is higher than 58.4 mW cm of Pt / C. -2 , which further demonstrates the excellent oxygen reduction performance of Fe-Se / NC.

[0084] The zinc-air battery assembled according to the above method was tested at a current density of 10 mA cm for Fe-Se / NC and Pt / C. -2 Constant current discharge test. The test results are as follows Fig. 9 shown.

[0085] like Fig. 9 As shown, the specific capacity of Fe-Se / NC is 818.9 mAh g -1 Compared with the 696.5mAh g of commercial Pt / C - high.

[0086] The batteries assembled according to the above method were subjected to step discharge tests on Fe-Se / NC and Pt / C. The test results are shown in Fig.10 shown.

[0087] like Fig.10 As shown in the figure, the Fe-Se / NC under open circuit, 2, 5, 10, 15 and 20 mA cm -2 The voltage values ​​under this condition are all higher than those of Pt / C.

[0088] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for preparing a nitrogen-doped porous carbon-supported iron-selenium transition metal composite material, characterized in that The steps include: A magnesium zinc NC precursor and a selenium compound are ground and mixed together, and then put into a tube furnace together with a transition metal iron compound, and calcined by a vapor deposition method under nitrogen or an inert gas. The calcined product is ground and then acid-washed, filtered and dried, and then calcined twice to obtain a nitrogen-doped porous carbon-supported iron-selenium transition metal composite material; the molar ratio of the transition metal iron compound to the selenium compound is (0.1-5): (0.1-6); the molar ratio of the transition metal iron compound to the magnesium zinc NC precursor is (0.01-1): (0.1-5).

2. The method for preparing a nitrogen-doped porous carbon-supported iron-selenium transition metal composite material according to claim 1, characterized in that: The magnesium zinc NC precursor is synthesized from magnesium chloride, p-phenylenediamine, sodium chloride and zinc chloride.

3. The method for preparing a nitrogen-doped porous carbon-supported iron-selenium transition metal composite material according to claim 1, characterized in that: The magnesium zinc NC precursor is prepared according to the following steps: (1) 1 mmol of anhydrous magnesium chloride and 20 mL of methanol were magnetically stirred until completely dissolved to obtain solution A; (2) 10 mmol of p-phenylenediamine and 20 mL of methanol were magnetically stirred until completely dissolved to obtain solution B; (3) 700 mg of sodium chloride, 1300 mg of zinc chloride and 20 mL of deionized water were magnetically stirred until they were completely dissolved to obtain solution C; (4) Add solution A to solution B, stir for 10 minutes, and then pour solution C into it. The obtained mixed solution was magnetically stirred for more than 6 hours, and then frozen with liquid nitrogen, and then freeze-dried for 36 hours. After drying, the obtained solid was ground for 10 minutes, and the obtained powder particles were calcined at 900°C for 2 hours in a nitrogen atmosphere in a tubular furnace, with a heating rate of 5°C / min; the calcined powder particles were ground again for 10 minutes, and then rinsed and filtered with deionized water to remove soluble salt ions; then acid-washed with 0.5 mol / L sulfuric acid for 12 hours, and then filtered with deionized water. After filtration, it was dried at 70°C in an oven for 12 hours; the dried sample was ground for 30 minutes, and then calcined for the second time, and calcined at 900°C for 2 hours in a nitrogen atmosphere in a tubular furnace, with a heating rate of 5°C / min, to obtain a magnesium-zinc NC precursor.

4. The method for preparing a nitrogen-doped porous carbon-supported iron-selenium transition metal composite material according to claim 1, characterized in that: The molar ratio of the transition metal iron compound to the selenium compound is 1:1; the molar ratio of the transition metal iron compound to the magnesium zinc NC precursor is (0.01-0.5): (0.5-3).

5. The method for preparing a nitrogen-doped porous carbon-supported iron-selenium transition metal composite material according to claim 1, characterized in that: The drying is carried out in an oven at a drying temperature of 20 to 100°C.

6. The method for preparing a nitrogen-doped porous carbon-supported iron-selenium transition metal composite material according to claim 5, characterized in that: The drying temperature is 75°C.

7. The method for preparing a nitrogen-doped porous carbon-supported iron-selenium transition metal composite material according to claim 1, characterized in that: The calcination temperature is 600-1100° C., and the time is 0.5-3 h; the secondary calcination temperature is 900° C., and the time is 2 h.

8. A nitrogen-doped porous carbon-supported iron-selenium transition metal composite material prepared by the preparation method according to any one of claims 1 to 7, characterized in that: In the composite material, iron atoms and selenium atoms are uniformly distributed on the nitrogen-doped carbon-based material.

9. Use of the nitrogen-doped porous carbon-supported iron-selenium transition metal composite material according to claim 8 in a metal-air battery.

10. A metal-air battery positive electrode material, characterized in that: The positive electrode material comprises the nitrogen-doped porous carbon-supported iron-selenium transition metal composite material as described in claim 8.

Images