Preparation method and application of homonuclear non-noble metal diatomic catalyst

Abstract

The application discloses a preparation method and application of a homonuclear non-noble metal diatomic catalyst. The homonuclear non-noble metal diatomic catalyst is prepared by using a porous nitrogen-doped carbon material as a substrate, loading anions and cations in steps, removing a solvent by evaporation, and finally high-temperature calcination. x The homonuclear non-noble metal M-M-N described in the application has a synergistic and regulating mechanism, effectively reduces the potential of an oxygen reduction reaction process, improves the performance and stability of a fuel cell catalyst, and provides important theoretical and technical support for development of a new type of electrochemical catalyst and commercialization of a fuel cell.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of new energy materials and catalysis technology, and particularly relates to a preparation method of homonuclear non-noble metal diatomic catalyst and application of the homonuclear non-noble metal diatomic catalyst in oxygen reduction reaction and fuel cell. BACKGROUND

[0002] In order to solve the problem of increasing global energy consumption and environmental pollution caused by the use of fossil fuel energy, it is important to develop an advanced energy conversion and storage technology that can replace traditional fossil energy. Fuel cells have the advantages of high power density, high safety, wide use, etc. and have wide application prospects in the fields of transportation and energy storage. However, the traditional cathode catalyst of fuel cells is a platinum-based catalyst, which has the disadvantages of high price, poor stability and poor CO poisoning resistance, which hinders its large-scale commercial application.

[0003] Diatomic catalysts have wide application prospects in energy conversion due to their unique synergistic and regulatory mechanisms. The special structure of diatomic atoms can improve metal loading, optimize the adsorption configuration of reactants, change the reaction pathway and reduce the free energy of the rate-determining step. Especially for the oxygen reduction reaction, diatomic catalysts can effectively improve the activity and selectivity of the catalyst. Among them, homonuclear diatomic catalysts have received widespread attention due to their high catalytic performance, but the general synthesis is to mix metal salts, carbon sources and nitrogen sources together by mechanical stirring, which has a large randomness. Therefore, we need to design a method to accurately prepare homonuclear diatomic catalysts. SUMMARY

[0004] The application provides a preparation method of homonuclear non-noble metal diatomic catalyst and application thereof. The method uses a classic nitrogen-doped carbon material as a substrate, uses a step-by-step adsorption of anions and cations method to make metal ions pair up on the carrier, and after high-temperature calcination, a stable homonuclear diatomic catalyst is formed. The application solves the problem of easy occurrence of single atoms or agglomeration in the synthesis process of diatomic atoms in the prior art, and the prepared catalyst can be applied to the fields of oxygen reduction reaction, fuel cell, etc.

[0005] The homonuclear non-noble metal diatomic catalyst is a homonuclear diatomic catalyst that is paired in a monodispersed form on the carrier, and the distance between the paired metal atoms is about 0.24 nm, and the metal atoms have a synergistic regulatory mechanism to promote the occurrence of oxygen reduction reaction.

[0006] The preparation method of the homonuclear non-noble metal diatomic catalyst is as follows: uniformly dispersing the prepared porous nitrogen-doped carbon material in a solvent, using a step-by-step adsorption of anions and cations loading method, removing the solvent by evaporation, and finally high-temperature calcination under an inert atmosphere to form a homonuclear non-noble metal diatomic catalyst.

[0007] The nitrogen-doped carbon material is formed by high-temperature calcination taking ZIF-8 as a precursor.

[0008] The step-by-step adsorption is to first adsorb anions for a period of time and then adsorb cations for a period of time, which is beneficial to form a structure in which anions and cations are paired.

[0009] The anion metal salt is selected from any one or several of Fe(CN)6 3- , Fe(C2O4)3 3- , Co(CN)6 3- , Ni(CN)4 2- , Cu(CN)2 - , MnO4 2- , and the cation metal salt is selected from any one or several of Fe 3+ , Fe 2+ , Co 2+ , Cu 2+ , Cu + , Ni 2 , Mn 2+ .

[0010] The application of the homonuclear non-noble metal diatomic catalyst prepared above in an oxygen reduction reaction.

[0011] The application of the homonuclear non-noble metal diatomic catalyst prepared above in the preparation of a fuel cell.

[0012] Compared with the prior art, the present application has the following beneficial effects:

[0013] (1) The porous nitrogen-doped carbon material formed by calcination of ZIF-8 is preferably used as a substrate, and under the precursor with positive electricity, there are abundant pore structures and high conductivity, which ensure the necessary conditions for the substrate.

[0014] (2) The present application innovatively uses a step-by-step adsorption method to load anions and cations, so that metal ions can be adsorbed layer by layer on the surface of the substrate. This method can stably prepare a homonuclear diatomic catalyst with super-high activity. The preparation method is simple, highly repeatable, large in yield, cost-saving, easy to industrialize and mass-produce, and the prepared homonuclear diatomic catalyst is green and environmentally friendly.

[0015] (3) The present application can ensure the loading amount of metal by the method of evaporation drying, and single-atom or granular catalysts will not be formed due to changes in the adsorption performance of the substrate.

[0016] (4) The homonuclear non-noble metal diatomic catalyst prepared by the present application exhibits excellent performance and stability in oxygen reduction reaction (ORR). In fuel cells, it has high power density and high stability, which is conducive to promoting the development of high energy storage systems. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a transmission electron microscope (TEM) image of the Fe-Fe / NC catalyst obtained in Example 1.

[0018] Figure 2 is a high-resolution transmission electron microscope image (HR-TEM) of the Fe-Fe / NC catalyst obtained in Example 1.

[0019] Figure 3 is an energy dispersive X-ray spectroscopy (EDX) element map of the Fe-Fe / NC catalyst obtained in Example 1.

[0020] Figure 4 is a spherical aberration-corrected annular dark-field scanning transmission electron microscope image (HAADF-STEM) of the Fe-Fe / NC catalyst obtained in Example 1.

[0021] Figure 5 is an oxygen reduction linear voltammetry plot of the Fe-Fe / NC, 20wt% commercial Pt / C, the Fe / NC-SA and Fe / NC-NP described in Proportion 1 and Proportion 2 obtained in Example 1 in 0.1M HCIO4 as electrolyte.

[0022] Figure 6 is an oxygen reduction linear voltammetry plot of the Fe-Fe / NC and the Fe / NC-one step described in Proportion 3 obtained in Example 1 in 0.1M HCIO4 as electrolyte.

[0023] Figure 7 is an oxygen reduction linear voltammetry plot of the Fe-Fe / NC obtained in Example 1 before and after 10000 cycles in 0.1M HCIO4 as electrolyte.

[0024] Figure 8 is a H2O2 yield and electron transfer number plot of the Fe-Fe / NC, the Fe / NC-SA described in Proportion 1, Fe / NC-NP obtained in Example 1 in 0.1M HCIO4 as electrolyte.

[0025] Figure 9 is a polarization curve and power density curve of the fuel cell in hydrogen air of the Fe-Fe / NC, the Fe / NC-SA described in Comparative Example and 20wt% commercial Pt / C obtained in Example 1.

[0026] Figure 10is the current density curve of Fe-Fe / NC obtained in Example 1 at 0.5V constant voltage discharge.

[0027] Figure 11 is the linear voltammetry curve of Co-Co / NC obtained in Example 2-Example 4 in 0.1M HCIO4 as electrolyte. DETAILED DESCRIPTION

[0028] The technical solutions of the present application are further illustrated below in connection with the drawings, examples and comparative examples, but are not limited thereto, any modification or equivalent replacement to the technical solutions of the present application without departing from the spirit and essential scope of the present application shall be covered in the protection scope of the present application.

[0029] Example 1:

[0030] (a) Preparation of nitrogen-doped carbon material substrate: 875mg of 2-methylimidazole was taken in 15mL of methanol, which was then quickly poured into 15mL of methanol containing 793mg of Zn(NO3)2·6H2O, and crystal nucleation was carried out by stirring at room temperature for 30min. The nucleated solution was transferred to a reaction kettle, and was kept at 120℃ for 4h. The solution was centrifuged to obtain a solid, which was washed and dried to obtain a white powder. The sample was heated to 950℃ at a heating rate of 5℃ / min, and was kept at this temperature for 5h to obtain a black powder, which was the nitrogen-doped carbon material.

[0031] (b) 100mg of the nitrogen-doped carbon material was dispersed in ethanol, and 1.2wt% of Fe(CN)6 3- anion solution was adsorbed for 2h. Then 1.2wt% of Fe 3+ cation solution was adsorbed for 5h, and the solvent was evaporated at 75℃ to obtain a black material. The Fe-Fe / NC catalyst was obtained by calcining at 900℃ for 1.5h.

[0032] Example 2:

[0033] According to the operation method of Example 1, Fe 3+ was replaced by Co 2+ , Fe(CN)6 3- was replaced by Co(CN)6 3- , and Co-Co / NC was obtained.

[0034] Comparative Example 1:

[0035] According to the operation method of Example 1, only the cation solution was added during the stepwise adsorption to obtain Fe / NC-SA.

[0036] Comparative Example 2:

[0037] Fe / NC-onestep was obtained by mixing anions and cations directly without stepwise adsorption according to the operation method of Example 1.

[0038] Comparative Example 3:

[0039] Fe / NC-onestep was obtained by mixing anions and cations directly without stepwise adsorption according to the operation method of Example 1.

[0040] Application Example 1:

[0041] 4 mg of the catalysts obtained in Example 1, Example 2 and Comparative Examples 1-4 were respectively dispersed in a mixture of 685 μL of anhydrous ethanol, 295 μL of deionized water and 20 μL of 5 wt% Nafion, and after ultrasonic mixing, 0.8 mg cm-2of the catalysts were dropped on a rotating disc electrode. -2 The droplets were dried on the rotating disc electrode, and then the oxygen reduction electrocatalytic performance was determined on a Chenhua CHI660E electrochemical workstation.

[0042] In the electrochemical test, a saturated calomel electrode was used as a reference electrode, a graphite rod was used as a counter electrode, and 0.1 M KOH was used as an alkaline electrolyte. Before the test, the electrolyte was saturated with oxygen for 30 min, and then cyclic voltammetry was performed at a scan rate of 50 mV s-1to stabilize the catalyst. During the test, linear sweep voltammetry was performed at a scan rate of 10 mV s-1. -1 -1 -1

[0043] The ORR test results of Example 1, Comparative Examples 1-2 and 20 wt% commercial Pt / C in 0.1 M HClO4are shown in Table 1, which shows that Fe-Fe / NC has the best ORR performance, with a half-wave potential of 0.86 V vs RHE, which is much higher than that of Fe / NC-SA and Fe / NC-NP. Figure 6

[0044] The ORR test results of Example 1 and Comparative Example 3 in 0.1 M HClO4are shown in Table 2. Figure 7 From Table 2, it can be seen that under the same conditions, the oxygen reduction performance of Fe / NC-one step prepared by one-step loading is poorer, which proves the necessity of stepwise adsorption. Figure 10

[0045] The stability of the Fe-Fe / NC catalyst obtained in Example 1 in the oxygen reduction electrocatalytic reaction in 0.1 M HClO4as an electrolyte is shown in Table 3. Figure 8 The half-wave potential of the Fe-Fe / NC catalyst only decreased by 10 mV before and after 10,000 cycles, which shows that it has good cycle stability.

[0046] ​​​Example 2: Results of oxygen reduction electrocatalysis test in 0.1M HClO4 as electrolyte are as follows Figure 11 As shown, the Co-Co / NC homonuclear diatomic catalysts exhibit good performance in ORR.

[0047] Application Example 2:

[0048] 30 mg of the catalysts prepared in Examples 1, 2, 3, and Comparative Example 1 were dispersed in a mixed solution containing 3000 μL isopropanol, 50 μL H2O, and 300 μL 5% Nafion to form a uniform "ink" as the cathode catalyst. A 3 mg / cm³ Nafion 211 membrane was sprayed onto the cathode using a spraying method. 2 The catalyst sample was sprayed with 0.1 mg Pt / cm at the anode. 2 The Pt / C catalyst was hot-pressed at 130°C for 130 seconds under 1.5 bar pressure to obtain 5 cm⁻¹ of catalyst. 2 The membrane electrode assembly was completed. The PEMFC was tested under the following conditions: battery test temperature: 80℃; H2 / O2 gas flow rate: 0.4 L / min. -1 Anode and cathode back pressure: 2 bar; H2 / O2 gas flow rate for stability testing: 500 sccm. Performance testing was conducted after complete activation.

[0049] like Figure 10 As shown, the Fe-Fe / NC catalyst obtained in Example 1 exhibited an excellent peak power density of 983 mW / cm³ in a hydrogen-oxygen fuel cell. 2 This is far higher than that of Fe / NC catalyst hydrogen-oxygen fuel cells (580mW / cm). 2 The good stability of the Fe-Fe / NC catalyst can also be seen through constant voltage discharge experiments, which proves that the Fe-Fe diatomic catalyst has application prospects in practical fuel cells.

Claims

1. A homonuclear non-noble metal diatomic catalyst material, characterized in that, The material is a homonuclear non-noble metal M-M-N x wherein the metal elements and the same metal elements exist in a pairwise form; A same-nuclear non-noble metal bimetallic catalyst material is obtained by loading different metal ions with different charges on a nitrogen-doped carbon carrier by a stepwise adsorption method and calcining at high temperature. The preparation method of the same-nuclear non-noble metal bimetallic catalyst comprises the following steps: (1) prepare a methanol solution of zinc nitrate hexahydrate and 2-methyl imidazole respectively, mix them in a beaker, synthesize ZIF-8 by a solvothermal method after nucleation, and obtain a porous nitrogen-doped carbon material by calcining at high temperature; (2) uniformly disperse the nitrogen-doped carbon in an ethanol solution, add metal anions and metal cations step by step, and finally evaporate to obtain a composite material; The stepwise adsorption is to first adsorb metal anions for a period of time and then adsorb metal cations for a period of time, and the preparation steps comprise: uniformly disperse the hydrogen-doped carbon in an ethanol solution, add metal anions and metal cations step by step, and finally evaporate to obtain a composite material, and the composite material is calcined at high temperature to obtain a same-nuclear non-noble metal bimetallic catalyst; (3) calcine the composite material at high temperature to obtain a same-nuclear non-noble metal bimetallic catalyst; The metal anions in step (2) are selected from any one or several of Fe(CN)6 3- , Fe(C2O4)3 3- , Co(CN)6 3- , Ni(CN)4 2- , Cu(CN)4 2- . The metal cations are selected from any one or several of Fe 3+ , Fe 2+ , Co 2+ , Cu 2+ , Cu + , Ni 2+ .

2. A process for the preparation of the homonuclear non-noble metal diatomic catalyst material of claim 1, characterized by, A same-nuclear non-noble metal bimetallic catalyst material is obtained by loading different metal ions with different charges on a nitrogen-doped carbon carrier by a stepwise adsorption method and calcining at high temperature.

3. The production method according to claim 2, wherein The adsorption time is 2-10 h.

4. The production method according to claim 3, wherein The metal loading of the catalyst is 0.01-5 wt%.

5. Application of the catalyst with same-nuclear bimetallic active sites prepared by the method of any one of claims 2-4 in catalyzing an oxygen reduction reaction.

6. Application of the catalyst with same-nuclear bimetallic active sites prepared by the method of any one of claims 2-4 in preparing a fuel cell.

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