Defect-rich transition metal nanostructure catalysts and methods for making same

Abstract

This invention belongs to the field of nanomaterial preparation and discloses a method for preparing a defect-rich transition metal nanostructure catalyst, comprising the following steps: weighing a transition metal compound and a binder, adding them to N-methylpyrrolidone and mixing to form a black solution; adding the black solution dropwise onto a current collector and vacuum drying to obtain a dried electrode; assembling the electrode as the electrode, an alkaline metal sheet as the counter electrode, and a solution containing Li ions as the electrolyte in a two-electrode electrolytic cell; connecting the two electrodes to both ends of a resistor, and using their own chemical energy to drive electron and ion migration for a reduction reaction until the reaction is complete; cleaning the electrodes after the reaction, and vacuum drying to obtain a defect-rich transition metal nanostructure catalyst. The prepared transition metal nanostructure is composed of metal nanocrystals of 2–8 nm in size, with a defect atom ratio of 30%–50%, exhibiting high electrocatalytic activity and good stability.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial preparation, and specifically relates to a defect-rich transition metal nanostructure catalyst and its preparation method. Background Technology

[0002] With the continuous depletion of fossil fuels and the increasing severity of environmental pollution, the search for efficient and clean energy sources is extremely necessary. Hydrogen, with its excellent energy density, high energy conversion efficiency, renewability, and zero-pollution characteristics, is an ideal choice as both a clean energy source and an energy storage carrier. Currently, platinum (Pt)-based materials are ideal and efficient catalysts for hydrogen evolution through water electrolysis. However, the limited reserves and high cost of precious metal materials restrict their further widespread application.

[0003] Transition metal-based catalysts, as promising materials for water electrolysis, have attracted widespread attention due to their advantages such as low cost, environmental friendliness, abundant resources, diverse types, rich electronic structures, and varied valence states. Among the many transition metal-based catalysts, single metals or transition metal alloys possess unparalleled conductivity and excellent intrinsic activity. However, the inevitable oxidation of metal elements and the difficulty in obtaining uniformly sized nanocrystals through high-temperature synthesis lead to a decrease in the catalytic activity of transition metal nanostructures.

[0004] To address this challenge, synthesizing transition metal nanocrystals with metal defects can increase active sites. These metal defects can improve the electronic structure of the nanostructure, accelerate electron transfer, and enhance both the catalytic activity and structural stability of the catalyst. However, methods such as hydrothermal growth, etching, dealloying, and ion intercalation are difficult to use to prepare catalysts with many metal defects, and the synthesis processes are costly and environmentally polluting. Summary of the Invention

[0005] The purpose of this invention is to provide a defect-rich transition metal nanostructure catalyst and its preparation method, which solves the problems that current preparation methods cannot synthesize catalysts containing many metal defects and it is difficult to obtain nanocrystals of uniform size.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] A method for preparing a defect-rich transition metal nanostructure catalyst includes the following steps:

[0008] 1) Weigh the transition metal compound and binder, add them to N-methylpyrrolidone and mix and stir to form a black solution; wherein, by mass percentage, the transition metal compound is 70% to 98% and the binder is 2% to 30%;

[0009] 2) Add the black solution dropwise onto the current collector and vacuum dry it at a temperature of 60-120℃ for 6-24 hours to obtain the dried electrode sheet;

[0010] 3) The dried electrode sheet is used as the electrode, the alkaline metal sheet is used as the counter electrode, and the solution containing Li ions is used as the electrolyte. The two electrodes are assembled in a double electrode electrolytic cell.

[0011] 4) Connect the two electrodes to the two ends of a resistor of 500-3000Ω, and use their own chemical energy to drive the migration of electrons and ions to carry out the reduction reaction until the reaction is completed;

[0012] 5) After cleaning the electrode after the reaction and drying it under vacuum, a defect-rich transition metal nanostructure catalyst is obtained.

[0013] Further, in step 1), the transition metal compound is a transition metal oxide, a transition metal sulfide, a transition metal hydroxide, or a transition metal halide.

[0014] Furthermore, the transition metals are Fe, Co, Ni, Cu, Mo, or Zn elements.

[0015] Furthermore, in step 1), the binder is polyvinylidene fluoride, polyacrylic acid, carboxymethyl chitosan, polypropylene, or polyvinyl alcohol.

[0016] Further, in step 1), stir for 5–48 hours.

[0017] Furthermore, in step 2), the current collector is foamed metal, metal sheet, or carbon cloth.

[0018] Furthermore, in step 3), the alkaline metal sheet is a lithium sheet, a sodium sheet, or a potassium sheet.

[0019] The present invention also discloses a defect-rich transition metal nanostructure catalyst prepared by the above preparation method. The transition metal nanostructure catalyst is composed of uniform metal nanocrystals with a size of 2-8 nm and a defect atomic ratio of 30%-50%.

[0020] Compared with the prior art, the present invention has the following beneficial technical effects:

[0021] This invention discloses a method for preparing defect-rich transition metal nanostructures. The method involves a reduction reaction between an electrode sheet made of a transition metal compound and a binder and an alkali metal electrode sheet via chemically driven electron and ion migration. The chemically driven transition metal nanocrystals are uniformly distributed in size between 3 and 8 nm. After the reaction, cleaning the electrode sheet to remove the alkali metal yields a clean metal surface without an oxide layer. The transition metal nanostructures contain 30% to 50% defect atoms, which optimizes the electronic structure and electrocatalytic performance of the material. The resulting metal nanostructures are attached to a current collector and can be directly applied to electrocatalytic water splitting, avoiding the electrode preparation process of traditional powder catalytic materials, which can lead to oxidation or organic encapsulation of the metal active surface, thus reducing performance. Therefore, the product of this invention exhibits higher catalytic activity and better electrocatalytic stability compared to metal nanostructures synthesized by other methods. The method for preparing transition metal nanostructures disclosed in this invention provides controllable material structure, a simple process, and eliminates the need for conventional synthesis equipment or external energy to excite the reaction, making it easy for large-scale production and application. This invention provides a low-cost, low-energy-consumption, and easily mass-producible chemical energy-driven reduction method for preparing transition metal nanostructures. The synthesized transition metal nanostructures are not only uniform and small in size, but also have a high proportion of metal defect atoms, which increases the electrochemical specific surface area and improves catalytic activity.

[0022] The advantages and features of this invention are: 1) The room temperature reaction prevents the rapid aggregation and growth of metal grains at high temperatures, thus obtaining uniformly sized ultrafine metal nanostructures; 2) Utilizing the slow crystallization kinetics at room temperature, abundant surface and interface defects are formed, causing changes in coordination number and surface stress, altering the electronic structure of the metal and the Gibbs free energy of hydrogen adsorption, creating excellent electrocatalytic properties; 3) The direct products of the reduction reaction are ultrafine metal nanocrystals and alkaline oxides. During storage, the alkaline oxides prevent the metal surface from oxidizing and reducing performance. During use, only water washing is needed to remove the alkaline oxides, exposing a fresh and clean metal surface and active sites; 4) Although the reaction apparatus is similar to traditional electrochemical preparation, the mechanism is different. The driving force of this reaction is the potential difference formed by the difference in its own chemical energy, not an externally applied potential. The inherent chemical energy driving force gradually weakens as the reaction proceeds. This has the advantage of spontaneously slowing down the reaction rate (ion mobility and metal growth rate), promoting the formation of ultrafine nanocrystals and a large number of defect atoms.

[0023] The transition metal nanocrystals prepared by this invention have a size of approximately 2–8 nm, possess a large electrochemical surface area and 30%–50% interface defect atoms, exhibiting high catalytic activity and good electrochemical stability. The provided preparation method is simple and convenient, requiring no conventional synthesis equipment or external energy, and is easy to mass-produce, offering advantages such as low energy consumption and low cost. Attached Figure Description

[0024] Figure 1 The image shows the XRD pattern of the iron nanostructure prepared in Example 1 of this invention.

[0025] Figure 2 The image shows the XRD pattern of the cobalt nanostructure prepared in Example 2 of this invention.

[0026] Figure 3 The image shows the XRD pattern of the nickel nanostructure prepared in Example 3 of this invention.

[0027] Figure 4 The image shows the XRD pattern of the copper nanostructure prepared in Example 4 of this invention.

[0028] Figure 5 The image shows the XRD pattern of the molybdenum nanostructure prepared in Example 5 of this invention.

[0029] Figure 6 This is a TEM image of the iron nanostructure prepared in Example 1 of the present invention;

[0030] Figure 7 This is a TEM image of the cobalt nanostructure prepared in Example 2 of the present invention;

[0031] Figure 8 This is a TEM image of the nickel nanostructure prepared in Example 3 of the present invention;

[0032] Figure 9 This is a TEM image of the copper nanostructure prepared in Example 4 of the present invention;

[0033] Figure 10 This is a TEM image of the molybdenum nanostructure prepared in Example 5 of the present invention;

[0034] Figure 11 The results show the electrocatalytic hydrogen evolution performance of the metal nanostructures prepared by the method of this invention. Detailed Implementation

[0035] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0036] Example 1

[0037] This invention discloses a method for preparing defect-rich transition metal nanostructures, comprising the following steps:

[0038] (1) Weigh 0.21g of iron oxide Fe2O3 and 0.09g of polyvinylidene fluoride PVDF respectively, add 5mL of N-methylpyrrolidone NMP, and stir for 5h to form a black solution.

[0039] (2) The black solution was added dropwise onto the nickel foam, with the loading controlled at 5 mg / cm³. 2 Vacuum drying for 12 hours at 80℃.

[0040] (3) Cut the dried electrode sheet into a circular piece with a radius of 0.8 cm as the positive electrode, and the lithium sheet as the counter electrode. Use 1M LiPF6 as the electrolyte to assemble a dual-electrode electrolytic cell.

[0041] (4) Use a 3000Ω resistor to connect two electrodes to start a chemical energy self-driven reaction.

[0042] (5) After the reaction was completed, the electrode sheet was removed and washed with deionized water. Finally, it was vacuum dried for 12 hours at 60°C to obtain a defect-rich iron nanostructure.

[0043] like Figure 1 As shown, the Fe after discharge corresponds exactly to the Fe PDF card (PDF#85-1410) in Jade, indicating that Fe2O3 has been completely reduced.

[0044] Figure 6 This is a TEM image of Fe2O3 after discharge. The particle diameter is about 2 nm. It is clear that there are many defects between the particles, and the proportion of defect atoms inside is about 50%.

[0045] The reaction equation of this invention is M x O y +Li→y / 2Li₂O+xM, where M x O y Represents transition metal oxides.

[0046] Example 2

[0047] This invention discloses a method for preparing defect-rich transition metal nanostructures, comprising the following steps:

[0048] (1) Weigh 0.225g of cobalt oxide (CoO) and 0.075g of polyvinyl alcohol (PVA), add 5.5mL of N-methylpyrrolidone (NMP), and stir for 48h to form a black solution.

[0049] (2) Add the black solution dropwise onto the copper foil, controlling the loading at 5 mg / cm². 2 Vacuum drying for 12 hours at 80℃.

[0050] (3) Cut the dried electrode into a circular piece with a radius of 0.8 cm as the positive electrode, and the lithium sheet as the counter electrode. Use 1M LiPF6 as the electrolyte to assemble a dual-electrode electrolytic cell.

[0051] (4) Use a 2500Ω resistor to connect two electrodes to start a chemical energy self-driven reaction.

[0052] (5) After the reaction is complete, the electrode is removed and washed with deionized water. Finally, it is vacuum dried for 12 hours at 80°C to obtain a cobalt nanostructure rich in defects.

[0053] like Figure 2 As shown, the Co after discharge corresponds exactly to the PDF card (PDF#89-4307) of Co in Jade, indicating that CoO has been completely reduced.

[0054] Figure 7 This is a TEM image of the CoO reaction. The particle diameter is about 4 nm. It is clear that there are many defects between the particles, and the proportion of defect atoms inside is about 42%.

[0055] Example 3

[0056] This invention discloses a method for preparing defect-rich transition metal nanostructures, comprising the following steps:

[0057] (1) Weigh 0.24g of nickel oxide (NiO) and 0.06g of polyacrylic acid (PAA), add 6mL of N-methylpyrrolidone (NMP), and stir for 10h to form a black solution.

[0058] (2) The black solution was added dropwise onto the carbon cloth, with the loading controlled at 3 mg / cm². 2 Vacuum drying for 6 hours at 120℃.

[0059] (3) Use the dried electrode as the electrode and the lithium sheet as the counter electrode, and use 1M LiPF6 as the electrolyte to assemble a dual-electrode electrolytic cell.

[0060] (4) Use a 2000Ω resistor to connect two electrodes to start a chemical energy self-driven reaction.

[0061] (5) After the reaction is complete, the electrode is removed and washed with deionized water. Finally, it is vacuum dried for 12 hours at 70°C to obtain a nickel nanostructure rich in defects.

[0062] like Figure 3 As shown, the Ni after discharge corresponds exactly to the Ni PDF card (PDF#70-1849) in Jade, indicating that NiO has been completely reduced.

[0063] Figure 8 This is a TEM image of NiO after the reaction. The particle diameter is about 6 nm. It is clear that there are many defects between the particles, and the proportion of defect atoms inside is about 40%.

[0064] Example 4

[0065] This invention discloses a method for preparing defect-rich transition metal nanostructures, comprising the following steps:

[0066] (1) Weigh 0.255g of copper oxide (CuO) and 0.045g of carboxymethyl chitosan respectively, add 6.5mL of N-methylpyrrolidone (NMP), and stir for 12h to form a black solution.

[0067] (2) The black solution was added dropwise onto the nickel foam, with the loading controlled at 7 mg / cm³. 2 Vacuum drying for 12 hours at 80℃.

[0068] (3) Use the dried electrode as the electrode and the lithium sheet as the counter electrode, and use 1M LiPF6 as the electrolyte to assemble a dual-electrode electrolytic cell.

[0069] (4) Use a 1500Ω resistor to connect two electrodes to start a chemical energy self-driven reaction.

[0070] (5) After the reaction was completed, the electrode was removed and washed with deionized water. Finally, it was vacuum dried for 12 hours at 80°C to obtain a copper nanostructure rich in defects.

[0071] like Figure 4 As shown, the discharged Cu completely corresponds to the Cu PDF card (PDF#70-3038) in Jade, indicating that CuO has been completely reduced.

[0072] Figure 9 This is a TEM image of CuO after the reaction. The particle diameter is about 7 nm. It is clear that there are many defects between the particles, and the proportion of internal defect atoms is about 35%.

[0073] Example 5

[0074] This invention discloses a method for preparing defect-rich transition metal nanostructures, comprising the following steps:

[0075] (1) Weigh 0.294g of molybdenum oxide (MoO3) and 0.006g of polyacrylonitrile (PAN) respectively, add 7.5mL of N-methylpyrrolidone (NMP), and stir for 12h to form a black solution.

[0076] (2) The black solution was added dropwise onto the nickel foam, with the loading controlled at 5 mg / cm³. 2 Vacuum drying for 24 hours at 70℃.

[0077] (3) Use the dried electrode as the electrode and the lithium sheet as the counter electrode, and use 1M LiPF6 as the electrolyte to assemble a dual-electrode electrolytic cell.

[0078] (4) Use a 500Ω resistor to connect two electrodes to start a chemical energy self-driven reaction.

[0079] (5) After the reaction was completed, the electrode was removed and washed with deionized water. Finally, it was vacuum dried for 12 hours at 80°C to obtain a molybdenum nanostructure rich in defects.

[0080] like Figure 5 As shown, the Mo after discharge corresponds exactly to the Mo PDF card (PDF#89-5023) in Jade, indicating that MoO3 has been completely reduced.

[0081] Figure 10 This is a TEM image of MoO3 after the reaction. The particle diameter is about 8 nm. It is clear that there are many defects between the particles, and the proportion of defect atoms inside is about 30%.

[0082] like Figure 11 As shown in Figure a, comparing the overpotential of the five metals at high current densities, Ni has the highest performance, followed by Co, Mo, Cu, and Fe.

[0083] like Figure 11 As shown in b, Co, Ni, Fe, Cu, and Mo at 100 mA / cm 2 The passing potentials are 208mV, 152mV, 329mV, 315mV, and 294mV, respectively.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a defect-rich transition metal nanostructure catalyst, characterized in that, Includes the following steps: 1) Weigh the transition metal compound and binder, add them to N-methylpyrrolidone and mix and stir to form a black solution; wherein, by mass percentage, the transition metal compound is 70%~98% and the binder is 2%~30%; 2) Add the black solution dropwise onto the current collector and vacuum dry it at a temperature of 60~120℃ for 6~24h to obtain the dried electrode sheet; 3) The dried electrode sheet is used as the electrode, the alkaline metal sheet is used as the counter electrode, and LiPF6 solution is used as the electrolyte. The two electrodes are assembled in a dual-electrode electrolytic cell. 4) Connect the two electrodes to the two ends of a resistor of 500~3000Ω, and use their own chemical energy to drive the migration of electrons and ions to carry out the reduction reaction until the reaction is completed; 5) After cleaning the electrode after the reaction and drying it under vacuum, a defect-rich transition metal nanostructure catalyst was obtained. The transition metal nanostructure catalyst is composed of uniform metal nanocrystals with a size of 2-8 nm and a defect atomic ratio of 30%-50%. Transition metal compounds are transition metal oxides, transition metal sulfides, transition metal hydroxides, or transition metal halides; The transition metals are Fe, Co, Ni, Cu, Mo, or Zn. In step 3), the alkaline metal sheet is a lithium sheet, a sodium sheet, or a potassium sheet.

2. The method for preparing the defect-rich transition metal nanostructure catalyst according to claim 1, characterized in that, In step 1), the binder is polyvinylidene fluoride, polyacrylic acid, carboxymethyl chitosan, polypropylene, or polyvinyl alcohol.

3. The method of claim 1, wherein the method is characterized by: In step 1), stir for 5 to 48 hours.

4. The method of claim 1, wherein the method is characterized by: In step 2), the current collector is foamed metal, metal sheet or carbon cloth.

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