Method for preparing multi-grain-boundary molybdenum carbide nano-particles through precise double-confinement path and application of multi-grain-boundary molybdenum carbide nano-particles

Abstract

The invention belongs to the technical field of nano confinement, and provides a method for preparing multi-grain-boundary molybdenum carbide nano-particles through a precise double-confinement path and application of the multi-grain-boundary molybdenum carbide nano-particles. The preparation method comprises the following steps of: coating polymer hydrogel on a carbon carrier in situ by taking a Ni-porphyrin cross-linking agent as a nickel source and phosphomolybdic acid as a molybdenum source, and preparing a Ni and PMo12 ortho-position double-confinement carbon-coated precursor by accurately controlling the ratio of the phosphomolybdic acid to the cross-linking agent and cross-linking through a self-confinement Ni-containing cross-linking agent Ni porphyrin cross-linking agent; the proportion of a Mo source to a cross-linking agent is precisely limited, and the multi-grain-boundary molybdenum carbide catalyst regulated and controlled by Ni atoms is prepared based on double-confinement pyrolysis. The molybdenum carbide catalyst containing a plurality of crystal boundaries is accurately prepared on the carbon substrate, and the OER catalytic performance of the molybdenum carbide catalyst is researched. Accurate regulation and control on the defect state of the molybdenum carbide nanosheet are realized, so that the intrinsic catalytic activity of molybdenum carbide is improved. The prepared catalyst shows excellent electrochemical performance in electro-catalysis oxygen evolution, and efficient water electrolysis oxygen evolution is achieved.

Description

Technical Field

[0001] The present invention belongs to the field of nanoconfinement technology, and specifically relates to a method for preparing multi-grain boundary molybdenum carbide nanoparticles by a precise dual-confinement path and its application. The grain boundary structure can be controlled in a general way to precisely manipulate the intrinsic electronic structure of Mo2C, thereby improving the electrochemical performance, and also provides a direction for the rational design and development of electrode materials for electrochemical catalytic oxygen evolution reaction. Background Art

[0002] Metal nanostructures are widely used in electrochemical hydrogen evolution, oxygen evolution and other related reactions due to their high conductivity, excellent dispersibility and chemical stability. However, these metal nanostructures also have some defects. For example, the metal loading is generally uneven, usually showing a mixed state of nanoparticles and nanoclusters. In addition, the surface of Mo2C will inevitably be corroded by oxygen evolution, resulting in poor activity and stability. And due to poor interfacial resistance, multi-component heterogeneous structure systems still have considerable energy barriers, which in turn increases the application cost.

[0003] In the process of water electrolysis, due to the limited resources of precious metals and the high production and use costs, it has become urgent to find alternative precious metal catalysts. Transition metal carbides, such as Mo2C, have shown excellent catalytic performance in redox reactions (OER) due to their electronic structure similar to that of platinum group metals. In addition, grain boundaries can effectively change the inherent reactivity of nanocrystalline materials by directly adjusting the surface atoms and electronic structure. The loose atomic arrangement and a large number of defects produced can moderately adjust the adsorption strength of intermediates, thereby accelerating the OER kinetic process. However, current research focuses on the construction of heterojunction materials, and the construction of multi-grain boundary stable catalysts by regulating the intrinsic structure of molybdenum carbide remains to be explored. Summary of the invention

[0004] The present invention aims to solve the problem that the current molybdenum carbide catalyst is easily corroded during the oxygen evolution process, and provides a method for preparing multi-grain boundary molybdenum carbide nanoparticles by a precise dual confinement path and its application. The purpose is to accurately synthesize molybdenum carbide catalysts with multiple grain boundary structures. The method simultaneously confines the molybdenum source and the nickel source, and further performs a pyrolysis treatment, so that the nickel single atom replaces the molybdenum atom in Mo2C, thereby generating an alternating multi-grain boundary structure. This structure increases the defects on the surface of the material and provides more highly active sites, thereby significantly improving the activity of the molybdenum carbide catalyst in the oxidation reaction (OER) and realizing efficient electrochemical applications.

[0005] The present invention is achieved by the following technical scheme: a method for preparing polycrystalline molybdenum carbide nanoparticles by a precise dual confinement path, a Ni-porphyrin crosslinker containing Ni atoms as a nickel source, phosphomolybdic acid as a molybdenum source, in-situ coating of a polymer hydrogel on a carbon carrier, based on the dual confinement of Ni atoms and phosphomolybdic acid in the hydrogel: by precisely controlling the ratio of phosphomolybdic acid to the crosslinker, and by crosslinking polypyrrole formed by a self-confined Ni-containing crosslinker and a pyrrole monomer, Ni and PMo are prepared. 12 Ortho-double-confined carbon-coated precursor; precisely limit the ratio of Mo source and cross-linker, and prepare polycrystalline molybdenum carbide catalyst regulated by Ni atoms based on double-confined pyrolysis.

[0006] The specific method is as follows: (1) Disperse 10-30 mg of acidified carbon nanotubes in 0.45-2 ml of deionized water containing 27-200 μL of pyrrole Py monomer to obtain solution A; (2) PMo 12 , 0.1-0.2 g FeCl3 powder and 0.007-0.028 g Ni-porphyrin crosslinker were dissolved in 0.8-3 mL deionized water and mixed thoroughly within 30 minutes to obtain solution B; control PMo 12 The mass ratio of Ni-porphyrin crosslinker is 15:7; (3) Solution A was added to solution B to quickly obtain a black hydrogel. After sufficient reaction, the solution was washed with ethanol and deionized water for more than three times respectively, and dried in an oven at 60 °C overnight to obtain a hydrogel. (4) The hydrogel obtained in step (3) is carbonized in an Ar atmosphere at 700-900° C. for 1-4 hours to obtain solid powder polycrystalline boundary molybdenum carbide nanoparticles.

[0007] Furthermore, the acidified carbon nanotubes in step (1) are multi-walled carbon nanotubes acidified with sulfuric acid and nitric acid in a volume ratio of 3:1.

[0008] The heteropoly acid is phosphomolybdic acid. The cross-linking agent is a cross-linking agent Ni-porphyrin containing Ni atoms.

[0009] The invention also provides multi-grain boundary molybdenum carbide nanoparticles obtained by the method.

[0010] The present invention also provides application of the polycrystalline boundary molybdenum carbide nanoparticles in electrochemical oxygen evolution reaction and anode materials.

[0011] The present invention has different product forms according to the different amounts of heteropolyacid and crosslinking agent ratios. Molybdenum carbide nanoparticles containing polycrystalline boundaries are prepared mainly through ortho-constrained confined pyrolysis strategies and applied to electrochemical oxygen evolution reactions and anode materials.

[0012] During the monomer gelation process of the present invention, the Ni porphyrin-doped "fishnet-like" positively charged polypyrrole (PPy) hydrogel is uniformly wrapped on the outer surface of the negatively charged carbon nanotubes, and a cage-like structure with nanopores of ~1.8 nm is formed, which is convenient for the storage of heteropolyacids (such as phosphomolybdic acid: diameter ~0.92 nm) of matching size; at the same time, the Ni atoms effectively constrained in the Ni porphyrin crosslinker separated by the PPy skeleton are kept in the PMo 12 Nearby, forming a precise adjacent double confinement domain.

[0013] Compared with the prior art, the present invention uses Ni porphyrin crosslinker to crosslink PPy to form a dual-confined hydrogel coating structure, which precisely confines heteropolyacids and Ni single atoms and constructs the ortho-spatial environment of the two. By controlling the ratio of precursor raw materials, polycrystalline molybdenum carbide materials are accurately prepared, which provides a direction for the subsequent rational design and preparation of adjacent constrained pyrolysis carbide electrocatalysts. The prepared catalyst has a high-density grain boundary structure, which provides an extremely high density of active sites, so that the catalyst exhibits excellent catalytic activity and excellent long-term durability. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 TEM image of the multi-grain boundary Mo2C nanosheet prepared in Example 1; Figure 2 High-resolution HADDF-STEM image of the multi-grain boundary Mo2C nanosheets prepared in Example 1; Figure 3 The Tafel slope diagram of the multi-grain boundary Mo2C nanosheets and pure molybdenum carbide prepared in Example 1; Figure 4 LSV polarization curves of the multi-grain boundary Mo2C nanosheets and pure molybdenum carbide prepared in Example 1; Figure 5 This is the OER stability chronopotentiometry diagram of the multi-grain boundary Mo2C nanosheets prepared in Example 1. DETAILED DESCRIPTION

[0015] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0016] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, and the disclosure and materials cited therein are hereby incorporated by reference.

[0017] Technical equivalents to the specific embodiments described that are apparent to those skilled in the art using no more than routine experimentation are intended to be encompassed by this application.

[0018] The experimental methods in the following examples are all conventional methods unless otherwise specified. The instruments and equipment used in the following examples are all conventional laboratory instruments and equipment unless otherwise specified; the experimental materials used in the following examples are all purchased from conventional biochemical reagent stores unless otherwise specified.

[0019] Example 1: A method for preparing polycrystalline molybdenum carbide nanoparticles by a precise dual confinement path, the specific method is as follows: (1) Multi-walled carbon nanotubes (15 mg) acidified with sulfuric acid and nitric acid (3:1) were dispersed in deionized water (2 mL) containing 84 μL of pyrrole (Py) monomer to obtain solution A. 12 (60 mg), FeCl3 powder (0.2 g) and cross-linking agent (0.028 g) were dissolved in deionized water (2 mL). After thorough mixing within 30 minutes, solution B was obtained. Solution A was added to solution B to quickly obtain a black hydrogel. After sufficient reaction, it was washed three times with ethanol and deionized water respectively, and dried in an oven at 60 °C overnight to obtain a precursor hydrogel loaded on carbon nanotubes.

[0020] (2) Carbonizing the hydrogel in an Ar atmosphere at 700-900° C. for 1-4 hours to obtain a molybdenum carbide material with a polycrystalline boundary.

[0021] When PMo 12 When the dosage and cross-linking agent ratio is 15:7, polycrystalline molybdenum carbide nanosheet material can be obtained.

[0022] Figure 1 This is a TEM image of the multi-boundary Mo2C nanosheets prepared in Example 1. From the image, it can be seen that the carbon tubes are deformed after pyrolysis, and multi-boundary molybdenum carbide nanoparticles are distributed on the carbon tubes, which are circled in red and blue respectively.

[0023] Figure 2 This is a high-resolution HADDF-STEM image of the multi-grain boundary Mo2C nanoparticles prepared in Example 1. It can be seen from the figure that carbon-supported molybdenum carbide nanosheets are obtained after pyrolysis of the hydrogel sample. Many twin boundary structures (TBs) appear on the surface due to the replacement of the yellow circled Mo by the red circled Ni single atom; Figure 3 The Tafel slope diagram of the polycrystalline Mo2C nanosheets and pure molybdenum carbide materials prepared in Example 1. The kinetic parameters from the Tafel slope show that the polycrystalline Mo2C nanosheets Ni@Mo2C@NC have a high -1The Tafel slope of , has higher OER catalytic activity than pure phase MoC materials; Figure 4 LSV polarization curves of the polycrystalline Mo2C nanosheets and pure MoC materials prepared in Example 1. Please note that all potentials in this work are referenced to the reversible hydrogen electrode. It can be seen from the figure that the polycrystalline MoC material has a high current density of 10 mA cm -2 The overpotential is small, 270 mV, which is lower than that of pure molybdenum carbide, verifying the excellent electrochemical oxygen evolution ability of polycrystalline boundary molybdenum carbide material.

[0024] Figure 5 This is a chronopotentiograph of the OER of the multi-grain boundary Mo2C nanosheets prepared in Example 1. It can be seen from the figure that after 71 hours of chronoamperometric measurement, the potential drop of the prepared material can also be ignored, verifying the high stability of the material.

[0025] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing polycrystalline molybdenum carbide nanoparticles by a precise dual confinement path, characterized in that: Ni-porphyrin crosslinkers containing Ni atoms were used as nickel sources and phosphomolybdic acid as molybdenum sources to in situ coat polymer hydrogels on carbon supports. Based on the double confinement of Ni atoms and phosphomolybdic acid in the hydrogels, Ni and PMo were prepared by precisely controlling the ratio of phosphomolybdic acid to crosslinkers and crosslinking polypyrroles formed by self-confined Ni-containing crosslinkers with pyrrole monomers. 12 Ortho-double-confined carbon-coated precursor; precisely limit the ratio of Mo source and cross-linker, and prepare polycrystalline molybdenum carbide catalyst regulated by Ni atoms based on double-confined pyrolysis.

2. The method for preparing multi-grain boundary molybdenum carbide nanoparticles by a precise dual confinement path according to claim 1, characterized in that: The specific method is as follows: (1) Disperse 10-30 mg of acidified carbon nanotubes in 0.45-2 ml of deionized water containing 27-200 μL of pyrrole Py monomer to obtain solution A; (2) PMo 12 , 0.1-0.2 g FeCl3 powder and 0.007-0.028 g Ni-porphyrin crosslinker were dissolved in 0.8-3 mL deionized water and mixed thoroughly within 30 minutes to obtain solution B; control PMo 12 The mass ratio of the Ni-porphyrin cross-linking agent is 15:7; (3) Solution A was added to solution B to quickly obtain a black hydrogel. After sufficient reaction, the solution was washed with ethanol and deionized water for more than three times respectively, and dried in an oven at 60 °C overnight to obtain a hydrogel. (4) The hydrogel obtained in step (3) is carbonized in an Ar atmosphere at 700-900° C. for 1-4 hours to obtain solid powder polycrystalline boundary molybdenum carbide nanoparticles.

3. The method for preparing polycrystalline molybdenum carbide nanoparticles by precise dual confinement path according to claim 2, characterized in that: The acidified carbon nanotubes in step (1) are multi-walled carbon nanotubes acidified with sulfuric acid and nitric acid in a volume ratio of 3:

1.

4. The method for preparing polycrystalline molybdenum carbide nanoparticles by precise dual confinement path according to claim 2, characterized in that: The heteropoly acid is phosphomolybdic acid.

5. The method for preparing multi-grain boundary molybdenum carbide nanoparticles by precise dual confinement path according to claim 2, characterized in that: The cross-linking agent is a cross-linking agent Ni-porphyrin containing Ni atoms.

6. Polycrystalline molybdenum carbide nanoparticles obtained by the method according to any one of claims 1 to 5.

7. Use of the polycrystalline molybdenum carbide nanoparticles according to claim 6 in electrochemical oxygen evolution reaction and anode materials.

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