CN114016057B - MXenes compound catalyst and preparation method and application thereof - Google Patents

MXenes compound catalyst and preparation method and application thereof Download PDF

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CN114016057B
CN114016057B CN202111248585.5A CN202111248585A CN114016057B CN 114016057 B CN114016057 B CN 114016057B CN 202111248585 A CN202111248585 A CN 202111248585A CN 114016057 B CN114016057 B CN 114016057B
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CN114016057A (en
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王得丽
黄晓
张建
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Huazhong University of Science and Technology
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Abstract

The invention belongs to the technical field of catalysts, and particularly relates to an MXenes compound catalyst and a preparation method and application thereof, wherein the preparation method comprises the following steps: (1) Adding the MXenes powder and the transition metal salt into a solvent, and uniformly mixing to obtain an MXenes solution adsorbing the transition metal; m in the MXenes powder is one of Ti, nb and Mo, and X is C or N; (2) Adding the organic ligand solution into the MXenes solution adsorbing the transition metal, uniformly mixing to obtain a suspension, and separating and precipitating to obtain a precursor; (3) And calcining and acid-washing the precursor to obtain the MXenes composite catalyst. The invention effectively adjusts the catalyst to O by improving the preparation process of the MXenes compound 2 And due to the adsorption capacity of OOH, the transition metal and MXenes have strong interaction, the electrochemical synthesis of hydrogen peroxide has excellent performance, the preparation process is simple, the cost is low, and the method is suitable for industrial large-scale production.

Description

MXenes compound catalyst and preparation method and application thereof
Technical Field
The invention belongs to the technical field of catalysts, and particularly relates to an MXenes compound catalyst, and a preparation method and application thereof.
Background
Hydrogen peroxide H 2 O 2 Is one of the most important 100 chemicals in the world, is a recognized environment-friendly oxidant, and is widely applied to various industries such as chemical synthesis, food disinfection, pulp bleaching, sewage treatment and the like. H 2 O 2 The traditional synthetic method of the anthraquinone method has high energy consumption and great pollution, and the produced H 2 O 2 High concentration and potential safety hazard, and is inconvenient to transport. Electrochemical process for producing H 2 O 2 The method has the advantages of environmental protection, no pollution, field production and the like, and is widely concerned by researchers at home and abroad. Among them, the oxygen cathodic reduction (ORR) is currently the most promising H 2 O 2 An electrochemical synthesis method.
Essentially the ORR mechanism can be divided into two categories: direct 4e - Process and Indirect 2e - And (4) processing. Using 2e - Process for producing H 2 O 2 The reaction formulae of (1) and (2), in an acidic medium: o is 2 +2e - +2H + →H 2 O 2 (1) (ii) a In an alkaline medium: o is 2 +H 2 O+2e - →HO 2 - +OH - (2). The activity, selectivity and stability of the catalyst are the effects of electrochemical synthesis of H 2 O 2 Key factors for performance. Currently, noble metals and their alloys, such as Pd, pt-Hg, pt-Ni, pd-Hg, etc., are electrochemically synthesized H 2 O 2 The most effective catalyst of (1). However, the disadvantages of high price, easy poisoning, etc. limit its large-scale application. Therefore, a two-electron oxygen reduction catalyst with low cost and high activity is urgently needed.
The two-dimensional transition metal carbide, nitride or carbonitride MXenes is a transition metal carbon/nitride with a two-dimensional layered structure, has the advantages of good electrical conductivity, hydrophilicity, rich surface functional groups and the like, and is widely applied to the fields of energy storage and catalysis. MXenes are prepared by etching an A layer of MAX with HF or in situ generated HF, wherein M represents a transition metal element such as Ti, nb, mo, etc., A represents a group III or IV element such as Al, and X is C or N. The MXenes obtained after etching have rich functional groups on the surface and are marked as MXene T x T represents a functional group such as-OH, -O, -F, etc.
Among the numerous non-noble metal catalysts studied at present, the MNC material has the advantages of low cost and high activity and is considered as the most potential electrochemical H synthesis 2 O 2 Catalyst, but oxygen reduction reaction 2e - The selectivity is low. Through a reasonable preparation method, the electron structure of the transition metal can be regulated and controlled by utilizing abundant functional groups on the surface of MXenes, and the oxygen reduction reaction O is changed 2 The adsorption mode and OOH adsorption energy of the catalyst are to improve the electrochemical synthesis of H by the MNC catalyst 2 O 2 Effective way of performance. Therefore, the oxygen functional group on the surface of MXenes is utilized to influence the electronic structure of the transition metal so as to regulate and control the adsorption energy of OOH, and the problem needs to be solvedThe technical problem is that the transition metal must have strong interaction with MXenes, and the MXenes remain in a layered structure during high temperature sintering.
An Integrating MXene nanosheets with cobalt-doped carbon nanotubes for an influencing oxygen reduction reaction is disclosed 3 C 2 Preparation and its use in oxygen reduction reactions. The technique adopts Ti 3 C 2 MXenes as substrate, co (NO) 3 ) 2 Added to 20mL of a solution containing Ti 3 C 2 Adding dimethyl imidazole into MXenes solution by ultrasonic treatment, stirring for 4h, centrifuging, separating precipitate, and vacuum drying at 60 ℃ for one night to obtain Co-CNT/Ti 3 C 2 Precursor, then H 2 /N 2 (5% v/v) atmosphere, calcining at 800 deg.C, holding for 2h, and naturally cooling to room temperature to obtain Co-CNT/Ti 3 C 2 。Co-CNT/Ti 3 C 2 When used as an oxygen reduction electrocatalyst, the electrocatalyst has high electrocatalytic activity and is expressed in 4e - The reaction pathway is dominant.
However, this solution has the following problems: first, MXenes based Ti 3 C 2 Easily oxidized and Co-CNT in Ti 3 C 2 The surface distribution is not uniform; second, catalyst Co-CNT/Ti 3 C 2 H used in high-temperature calcination in preparation process 2 /N 2 The mixed gas causes a large amount of Co particles to exist; third, catalyst Co-CNT/Ti 3 C 2 The transition metal is not adsorbed on Ti in the preparation process 3 C 2 Surface of Co and Ti 3 C 2 Has weak interaction and cannot effectively regulate Co-CNT/Ti 3 C 2 For O 2 OOH adsorption capacity of Co-CNT/Ti 3 C 2 When used as an oxygen reduction catalyst, 4e is still used - The reaction path is dominant.
In review, the prior art is still lacking a highly active two-electron oxygen reduction reaction for producing H 2 O 2 MXenes complex catalyst of (1).
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides an MXenes compositeThe object of the catalyst is to effectively adjust the catalyst to O by improving the preparation process of MXenes compound 2 And due to the adsorption capacity of OOH, the transition metal and MXenes have strong interaction, the electrochemical synthesis of hydrogen peroxide has excellent performance, the preparation process is simple, the cost is low, and the method is suitable for industrial large-scale production.
To achieve the above object, according to one aspect of the present invention, there is provided a method for preparing an MXenes composite catalyst, comprising the steps of:
(1) Adding MXenes powder and transition metal salt into a solvent, and uniformly mixing to obtain MXenes solution adsorbing transition metal; m in the MXenes powder is one of Ti, nb and Mo, and X is C or N;
(2) Adding the organic ligand solution into the MXenes solution adsorbing the transition metal, uniformly mixing to obtain a suspension, and separating and precipitating to obtain a precursor;
(3) And calcining and acid-washing the precursor to obtain the MXenes composite catalyst.
Preferably, in the step (1), the mass ratio of the substance of the transition metal salt to the MXenes powder is 1 (20-60).
Preferably, the transition metal in the transition metal salt in the step (1) is one of Co, fe and Ni, and the concentration of the transition metal salt solution is 0.05-1.5mol/L.
Preferably, M in the MXenes powder is Nb, X is C, and the transition metal in the transition metal salt is Co.
Preferably, the organic ligand in the step (2) is one of dimethyl imidazole, dopamine hydrochloride and melamine, and the concentration of the organic ligand is 0.05-1.5mol/L.
Preferably, the ratio of the amount of the transition metal to the amount of the organic ligand is 1: (5-10).
Preferably, the calcining temperature in the step (3) is 700-900 ℃, and the calcining time is 2-4h; the acid in the acid washing is hydrochloric acid or nitric acid, the acid concentration is 1-2mol/L, and the acid washing time is 12-48h.
Preferably, in the step (1), the MXenes powder is prepared by etching MAX phase powder, wherein M in MAX is one of Ti, nb and Mo, A is a III or IV main group element, and X is C or N;
preferably, the etching is specifically performed by using a hydrofluoric acid solution, the mass fraction of the hydrofluoric acid solution is 10-50%, the etching temperature is 10-30 ℃, and the etching time is 24-48h.
According to another aspect of the invention, the MXenes composite catalyst prepared by the preparation method is provided.
According to another aspect of the invention, the MXenes composite catalyst prepared by the preparation method is applied to electrochemical preparation of a hyperoxidant.
The invention has the following beneficial effects:
(1) The invention effectively adjusts the catalyst to O by improving the preparation process of the MXenes compound 2 And due to the adsorption capacity of OOH, the transition metal and MXenes have strong interaction, the electrochemical synthesis of hydrogen peroxide has excellent performance, the preparation process is simple, the cost is low, and the method is suitable for industrial large-scale production.
(2) The MXenes composite material is obtained by adopting a strategy of dual regulation and control of the shape and the electronic structure of MNC (sodium niobate), and is used as acidic electrochemical synthesis H 2 O 2 Catalyst for electrochemical synthesis of H from conventional acids 2 O 2 Compared with the catalyst design, the synthesis process has mild conditions and extremely low cost, the morphology and the electronic structure of MNC are regulated and controlled by virtue of MXenes layered structure and oxygen functional groups with abundant surfaces, the effective design of the atomic structure of the active site of the catalyst can be quickly and accurately realized, and the large-scale industrial preparation is easy to realize.
(3) The MXenes composite material catalyst obtained by the invention can synchronously realize the obvious optimization of oxygen molecule adsorption and OOH adsorption capacity in the catalytic process, and can prepare H by acid oxygen reduction 2 O 2 The catalyst has excellent catalytic activity and oxygen reduction selectivity in the reaction. 0.1M HClO 4 In the electrolyte, the initial potential is 0.80V, and H is prepared by reducing H compared with the reported oxygen 2 O 2 High initial potential of catalyst and simultaneous oxygenThe reduction selectivity reaches 80 percent, which shows that the MXenes composite material is used for preparing H by acid oxygen reduction 2 O 2 Excellent catalytic activity and oxygen reduction selectivity in the reaction process. In addition, in a self-made flow battery, oxygen is reduced to produce H 2 O 2 After 24H of reaction, H was accumulated 2 O 2 The concentration reaches 8wt%, can completely meet the commercial application, and embodies the excellent electrochemical synthesis of H by the catalyst 2 O 2 And (4) performance. And the current attenuation is not obvious after the circulation for 24 hours, which shows that the MXenes composite material catalyst is used for preparing H by acid oxygen reduction 2 O 2 Excellent catalytic durability during the reaction. Therefore, the MXenes composite material catalyst is used for electrochemical synthesis of H in acidity 2 O 2 The technical field has obvious large-scale application prospect.
Drawings
FIG. 1 is an SEM image of the material prepared in example 1;
FIG. 2 is a TEM image of the material prepared in example 1;
FIG. 3 is CoNC/Nb prepared in example 1 2 CT x And oxygen reduction reaction polarization profile of pure CoNC material;
FIG. 4 is CoNC/Nb prepared in example 1 2 CT x And oxygen reduction reaction process of pure CoNC Material the number of electrons transferred and H 2 O 2 The left diagram is the electron transfer number, and the right diagram is H 2 O 2 A selectivity profile;
FIG. 5 is CoNC/Nb prepared in example 2 2 CT x And oxygen reduction reaction polarization profile of pure CoNC material;
FIG. 6 is CoNC/Nb prepared in example 2 2 CT x And oxygen reduction reaction process of pure CoNC Material the number of electrons transferred and H 2 O 2 Selectivity graph, wherein the left graph is electron transfer number and the right graph is H 2 O 2 A selectivity profile;
FIG. 7 is CoNC/Nb prepared in example 3 2 CT x And oxygen reduction reaction polarization profile of pure CoNC material;
FIG. 8 is CoNC/Nb prepared in example 3 2 CT x And pure CoNC materialElectron transfer number and H in oxygen reduction reaction 2 O 2 Selectivity graph, wherein the left graph is electron transfer number and the right graph is H 2 O 2 A selectivity profile;
FIG. 9 shows FeNC/Nb prepared in example 4 2 CT x And oxygen reduction reaction polarization curve diagram of pure FeNC material;
FIG. 10 is a FeNC/Nb strain prepared in example 4 2 CT x And electron transfer number and H in oxygen reduction reaction of pure FeNC material 2 O 2 Selectivity graph, wherein the left graph is electron transfer number and the right graph is H 2 O 2 A selectivity profile;
FIG. 11 is a NiNC/Nb strain prepared in example 5 2 CT x And oxygen reduction reaction polarization curve diagram of pure NiNC material;
FIG. 12 shows the NiNC/Nb strain prepared in example 5 2 CT x And oxygen reduction reaction Process of pure NiNC Material the number of electrons transferred and H 2 O 2 Selectivity graph, wherein the left graph is electron transfer number and the right graph is H 2 O 2 A selectivity profile;
FIG. 13 is CoNC/Ti prepared in comparative example 3 C 2 T x And oxygen reduction reaction polarization profile of pure CoNC material;
FIG. 14 is CoNC/Ti prepared in comparative example 3 C 2 T x And oxygen reduction reaction process electron transfer number and H of pure CoNC material 2 O 2 The left diagram is the electron transfer number, and the right diagram is H 2 O 2 And (4) a selectivity graph.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
Examples
Example 1CoNC/Nb 2 CT x Preparation of the Material
(1) Weighing 1g of Nb 2 Placing AlC powder (produced by Jilin science and technology limited Co., ltd.) in 20mL HF solution with mass fraction of 40%, stirring the solution at room temperature, etching for 48h, washing with water, centrifuging for 7 times, and freeze-drying the product for 12h to obtain layered Nb 2 CT x MXenes substrate.
(2) Taking 40mg of Nb 2 CT x Adding the powder into 20ml of anhydrous methanol, performing ultrasonic treatment for half an hour, and adding 0.182g of Co (NO) according to the metal content of 1mmol 3 ) 2 To Nb 2 CT x Stirring the solution for 24 hours to obtain Nb adsorbing Co 2 CT x And (3) solution.
(3) Then, 20ml of dimethyl imidazole solution with the concentration of 0.4mol/L is slowly added, the mixture is continuously stirred for 4 hours and then kept stand for 12 hours, and after centrifugation and washing are carried out for 6 times, the mixture is dried for 12 hours in a vacuum drying oven at the temperature of 60 ℃ to obtain the precursor.
(4) Calcining the dried precursor at 800 ℃ for 2h in argon atmosphere to obtain CoNC/Nb containing a large amount of Co particles 2 CT x Washing the powder with 2mol/L hydrochloric acid solution for 12h to remove large-particle Co simple substance, filtering, washing, and vacuum drying at 60 ℃ for 12h to obtain CoNC/Nb 2 CT x A material.
Example 2CoNC/Nb 2 CT x Preparation of the Material
This example is substantially the same as example 1 except that Nb is added 2 CT x The amount is different, specifically 20mg of Nb powder is taken in the step (2) 2 CT x Added to 20ml of anhydrous methanol.
Example 3CoNC/Nb 2 CT x Preparation of the Material
This example is substantially the same as example 1 except that Nb is added 2 CT x The amount is different, specifically, 60mg of powdered Nb is taken in the step (2) 2 CT x Added to 20ml of anhydrous methanol.
Example 4FeNC/Nb 2 CT x Preparation of the Material
This example is substantially the same as example 1 except that a transition metal salt species is addedThe difference is that 0.242g Fe (NO) is taken in the step (2) 3 ) 3 Adding to Nb 2 CT x Stirring the solution for 24 hours to obtain Nb adsorbing Fe 2 CT x And (3) solution.
Example 5NiNC/Nb 2 CT x Preparation of the Material
This example is substantially the same as example 1 except that the kind of the transition metal salt to be added is different, specifically, 0.183g of Ni (NO) was taken in step (2) 3 ) 3 Adding to Nb 2 CT x Stirring the solution for 24 hours to obtain Nb adsorbing Ni 2 CT x And (3) solution.
Comparative example CoNC/Nb 2 CT x Preparation of the Material
(1) Weighing 1g of Nb 2 Placing AlC powder (produced by Jilin science and technology limited Co., ltd.) in 20mL HF solution with mass fraction of 40%, stirring the solution at room temperature, etching for 48h, washing with water, centrifuging for 7 times, and freeze-drying the product for 12h to obtain layered Nb 2 CT x MXenes substrate.
(2) Taking 40mg of Nb 2 CT x Powder and 0.182g Co (NO) 3 ) 2 Adding the mixture into 20ml of anhydrous methanol, performing ultrasonic treatment for half an hour, slowly adding 20ml of 0.4mol/L dimethyl imidazole solution, continuously stirring for 4 hours, standing for 12 hours, centrifuging, washing for 6 times, and drying in a vacuum drying oven at 60 ℃ for 12 hours to obtain the precursor.
(4) Putting the dried precursor in a mixed atmosphere of argon and hydrogen (H) 2 (5%) CoNC/Nb) was obtained after calcination at 800 ℃ for 2h 2 CT x And (3) powder.
FIG. 1 is a CoNC/Nb blend prepared in example 1 2 CT x Scanning electron micrograph (c).
As can be seen from FIG. 1, coNC is uniformly distributed in Nb 2 CT x A surface.
FIG. 2 is the CoNC/Nb prepared in example 1 2 CT x A projection electron microscope image of (a).
As can be seen from FIG. 2, nb is obtained after high-temperature sintering 2 CT x The layered structure is still maintained, which shows that the CoNC can protect Nb 2 CT x In layers ofThe structure is not oxidized during the high temperature sintering process.
FIG. 3 is the CoNC/Nb strain prepared in example 1 2 CT x And oxygen reduction reaction polarization profiles of pure CoNC materials. Weighing CoNC/Nb 2 CT x Dispersing in Nafion isopropanol solution (Nafion 117, wt0.1%) to obtain ink with uniformly dispersed catalyst, dropping the ink on electrode, naturally drying, using as working electrode for oxygen reduction reaction, and testing catalyst in 0.1M HClO saturated with oxygen by using three-electrode system 4 Oxygen reduction polarization curve in electrolyte. CoNC/Nb when 0.1V can be read from the oxygen reduction polarization curve 2 CT x The disk current of (2) was 0.79mA, and the loop current was 0.33mA.
FIG. 4 is the CoNC/Nb strain prepared in example 1 2 CT x And oxygen reduction reaction process of pure CoNC Material the number of electrons transferred and H 2 O 2 Selectivity graph, wherein the left graph is electron transfer number and the right graph is H 2 O 2 And (4) a selectivity graph.
As can be seen from the left diagram in FIG. 4, nb is added 2 CT x Then, coNC/Nb 2 CT x The electron transfer number of the catalyst was about 2.5, indicating that Nb was present 2 CT x Can regulate and control CoNC/Nb 2 CT x Oxygen reduction reaction pathway of (1), from 4e - Reaction to 2e - Reacting; as can be seen from the right diagram of FIG. 4, nb is added 2 CT x Then, coNC/Nb 2 CT x Catalyst H 2 O 2 The selectivity increased to 80%, indicating that Nb was added 2 CT x Is favorable for CoNC/Nb 2 CT x Electrocatalytic production of H by catalyst 2 O 2 。
FIG. 5 is the CoNC/Nb prepared in example 2 2 CT x And oxygen reduction reaction polarization profiles of pure CoNC materials.
As can be seen from the comparison of FIGS. 5 and 4, the CoNC/Nb prepared in example 2 is compared with that of example 1 2 CT x The current at 0.1V for catalysis was 0.93mA, which is higher than that (0.79 mA) for the catalyst prepared in example 1, indicating that the catalyst prepared in example 2 has higher catalytic activity.
FIG. 6 is CoNC/Nb prepared in example 2 2 CT x And oxygen reduction reaction process electron transfer number and H of pure CoNC material 2 O 2 Selectivity graph, wherein the left graph is electron transfer number and the right graph is H 2 O 2 And (4) a selectivity graph.
As can be seen from the left image of FIG. 6, coNC/Nb prepared in example 2 2 CT x The electron transfer number n of the catalyst is 3.50, which is higher than that of the CoNC/Nb prepared in example 1 2 CT x The number of catalyst electron transfers (2.5); as can be seen from the right panel of FIG. 6, coNC/Nb prepared in example 2 2 CT x H of the catalyst 2 O 2 The selectivity is 30%, which is much lower than the CoNC/Nb prepared in example 1 2 CT x H of catalyst 2 O 2 Selectivity (80%).
FIG. 7 is CoNC/Nb prepared in example 3 2 CT x And oxygen reduction reaction polarization profile of pure CoNC material.
As can be seen from FIG. 7, in contrast to example 1, coNC/Nb prepared in example 3 2 CT x The current at 0.1V for catalysis was 0.65mA, which is lower than the current (0.79 mA) for the catalyst prepared in example 1, indicating a significant decrease in catalytic activity for the catalyst prepared in example 3.
FIG. 8 is CoNC/Nb prepared in example 3 2 CT x And oxygen reduction reaction process electron transfer number and H of pure CoNC material 2 O 2 The left diagram is the electron transfer number, and the right diagram is H 2 O 2 And (4) a selectivity graph.
As can be seen from the left image of FIG. 8, coNC/Nb prepared in example 3 2 CT x The electron transfer number n of the catalyst is 2.9, which is higher than that of the CoNC/Nb prepared in example 1 2 CT x Catalyst electron transfer number (2.5); as can be seen from the right panel of FIG. 8, coNC/Nb prepared in example 3 2 CT x H of catalyst 2 O 2 Selectivity of 60% lower than that of CoNC/Nb prepared in example 1 2 CT x H of catalyst 2 O 2 Selectivity (80%).
FIG. 9 is a FeNC/Nb strain prepared in example 4 2 CT x And pure FeNC materialOxygen reduction reaction polarization curve diagram of material.
As can be seen from FIG. 9, in contrast to example 1, feNC/Nb prepared in example 4 2 CT x The current at 0.1V for catalysis was 1.01mA, higher than that of CoNC/Nb prepared in example 1 2 CT x The current (0.79 mA) of the catalyst, which indicates a significant increase in the catalytic activity of the catalyst prepared in example 4.
FIG. 10 is a FeNC/Nb strain prepared in example 4 2 CT x And oxygen reduction reaction process electron transfer number and H of pure FeNC material 2 O 2 Selectivity graph, wherein the left graph is electron transfer number and the right graph is H 2 O 2 And (4) a selectivity graph.
As can be seen from the left diagram of FIG. 10, feNC/Nb prepared in example 4 2 CT x The electron transfer number n of the catalyst is 3.85, which is higher than that of the CoNC/Nb prepared in example 1 2 CT x The number of catalyst electron transfers (2.5); as shown in the right diagram of FIG. 10, feNC/Nb prepared in example 4 2 CT x H of catalyst 2 O 2 The selectivity is 13%, which is much lower than that of CoNC/Nb prepared in example 1 2 CT x H of catalyst 2 O 2 Selectivity (80%).
FIG. 11 is a NiNC/Nb strain prepared in example 5 2 CT x And the oxygen reduction reaction polarization profile of pure NiNC material.
FIG. 11 shows that, in contrast to example 1, niNC/Nb prepared in example 5 2 CT x The current at 0.1V for catalysis was 0.73mA, lower than that of CoNC/Nb prepared in example 1 2 CT x Current of catalyst (0.79 mA).
FIG. 12 shows the NiNC/Nb strain prepared in example 5 2 CT x And oxygen reduction reaction process electron transfer number and H of pure NiNC material 2 O 2 The left diagram is the electron transfer number, and the right diagram is H 2 O 2 And (4) a selectivity graph.
As can be seen from FIG. 12, niNC/Nb prepared in example 5 2 CT x When used as an oxygen reduction electrocatalyst, H 2 O 2 CoNC/Nb selectivity ratio prepared in example 1 2 CT x The material is low. As can be seen from the left drawing of FIG. 12, niNC/Nb prepared in example 5 2 CT x The electron transfer number n of the catalyst is 3.21, which is higher than that of the CoNC/Nb prepared in example 1 2 CT x Catalyst electron transfer number (2.5); as can be seen from the right drawing of FIG. 12, niNC/Nb prepared in example 5 2 CT x H of catalyst 2 O 2 The selectivity is 43%, lower than that of CoNC/Nb prepared in example 1 2 CT x H of catalyst 2 O 2 Selectivity (80%).
FIG. 13 is CoNC/Nb prepared in comparative example 2 CT x And oxygen reduction reaction polarization profiles of pure CoNC materials.
As can be seen from FIG. 13, in contrast to example 1, coNC/Nb prepared in comparative example 2 CT x The current at 0.1V for catalysis was 0.89mA, which is higher than that of CoNC/Nb prepared in example 1 2 CT x Current of catalyst (0.79 mA). This shows that the CoNC/Nb prepared in the comparative example 2 CT x The material has high electrocatalytic activity.
FIG. 14 is a CoNC/Nb plot of that prepared in the comparative example 2 CT x And oxygen reduction reaction process electron transfer number and H of pure CoNC material 2 O 2 Selectivity graph, wherein the left graph is electron transfer number and the right graph is H 2 O 2 And (4) a selectivity graph.
As can be seen from the left image of FIG. 14, coNC/Nb prepared in the comparative example 2 CT x The electron transfer number n of the material as an oxygen reduction electrocatalyst was 3.81, which is higher than that of CoNC/Nb prepared in example 1 2 CT x Catalyst electron transfer number (2.5); as can be seen from the right image of FIG. 14, coNC/Nb prepared in comparative example 2 CT x H of catalyst 2 O 2 Selectivity of 12% lower than CoNC/Nb prepared in example 1 2 CT x H of the catalyst 2 O 2 Selectivity (80%).
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (5)

1. A preparation method of an MXenes composite catalyst is characterized by comprising the following steps:
(1) Adding the MXenes powder and the transition metal salt into a solvent, and uniformly mixing to obtain an MXenes solution adsorbing the transition metal; m in the MXenes powder is Nb, X is C, and transition metal in the transition metal salt is Co; the mass ratio of the mass of the transition metal salt to the mass of the MXenes powder is 1; the concentration of the transition metal salt solution is 0.05-1.5 mol/L;
(2) Adding the organic ligand solution into the MXenes solution adsorbing the transition metal, uniformly mixing to obtain a suspension, and separating and precipitating to obtain a precursor; the organic ligand is one of dimethyl imidazole, dopamine hydrochloride and melamine, and the concentration of the organic ligand is 0.05-1.5 mol/L;
(3) Calcining and acid-washing the precursor to obtain the MXenes compound catalyst; the calcining temperature is 700-900 ℃, and the calcining time is 2-4h; the acid in the acid washing is hydrochloric acid or nitric acid, the acid concentration is 1-2mol/L, and the acid washing time is 12-48h.
2. The method according to claim 1, wherein the ratio of the amount of the transition metal to the amount of the organic ligand is 1: (5-10).
3. The preparation method according to claim 1, wherein in the step (1), the MXenes powder is prepared by etching MAX phase powder;
the etching is performed by using a hydrofluoric acid solution, the mass fraction of the hydrofluoric acid solution is 10-50%, the etching temperature is 10-30 ℃, and the etching time is 24-48h.
4. An MXenes complex catalyst prepared by the method of any one of claims 1-3.
5. Use of the MXenes composite catalyst prepared by the method of any one of claims 1-3 in electrochemical preparation of hydrogen peroxide.
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