Preparation method and application of transition metal oxide rich in cation vacancies

Abstract

The present invention relates to the technical field of electrocatalytic oxygen evolution reaction, specifically to a preparation method and application of a transition metal oxide rich in cation vacancies. First, a vacuum induction melting furnace is used to heat Mn and a transition metal to a molten state in a suitable proportion, and a single-roller quenching device is used to quickly throw out the alloy liquid to obtain a Mn-based initial alloy strip; secondly, the obtained initial alloy strip is placed in a weak acid solution for Mn removal treatment to obtain a Mn-doped porous transition metal precursor; finally, the obtained Mn-doped porous transition metal precursor is placed in a tubular furnace for high-temperature oxidation treatment to obtain a cation-rich porous transition metal oxide. The present invention can not only obtain an efficient, stable, and inexpensive oxygen evolution catalyst, but also the method is simple to operate, low in cost, and easy to apply on a large scale.

Description

Technical Field

[0001] The invention relates to the technical field of electrocatalytic oxygen evolution reaction, and in particular to a preparation method and application of a cation vacancy-rich transition metal oxide. Background Art

[0002] The oxygen evolution reaction (OER) is a key half-reaction in water electrolysis hydrogen production systems and rechargeable metal-air batteries (RMABs). However, since the reaction involves a complex four-electron transfer process and multiple oxygen-containing intermediates, it has problems such as slow kinetics and poor stability, which greatly limits the large-scale hydrogen production and the cycle life of RMBABs. Currently, the noble metal oxides IrO2 / RuO2 are the most effective OER electrocatalysts, but their high cost and low reserves are not conducive to commercial applications. Therefore, the development of efficient, stable and inexpensive OER catalysts is the primary goal of those skilled in the art.

[0003] In recent years, transition metal oxides (TMOs) have attracted widespread attention due to their diverse structures, stable performance, low cost, and environmental friendliness. However, their low electrical conductivity limits the further development of such materials in the field of electrocatalysis. To this end, doping or vacancy defects are usually used to regulate the electronic conductivity of TMOs and their adsorption / desorption capabilities for OER intermediates. At present, doped or defective catalysts are mainly prepared by "bottom-up" methods, such as hydrothermal / solvothermal methods, coprecipitation methods, and electrodeposition methods. However, these methods have more or less problems such as high process costs and slow synthesis speeds, which makes it difficult to achieve large-scale applications. Summary of the invention

[0004] In view of this, the present invention aims to solve the shortcomings of the prior art and provide a method for preparing a transition metal oxide rich in cation vacancies. The present invention can not only obtain an efficient, stable and inexpensive OER catalyst, but also has the advantages of simple operation, low cost and easy large-scale application.

[0005] It should be noted that the dealloying strategy ("top-down" method) adopted in the present invention only needs to selectively dissolve the more active elements in the system based on the potential difference between the alloy components, and the remaining inert elements can spontaneously form an electrode material with a controllable porous structure through diffusion / recombination. This method is simple, cheap, and easy to expand. The product has a continuous porous-ligament structure, which can provide a good mass transfer channel for the electrochemical reaction, thereby accelerating the electron transfer rate and improving the reaction efficiency.

[0006] In addition, the dealloyed sacrificial components will inevitably remain and be in-situ doped into the porous ligaments, promoting the transition of electrons between different metal valence states, thereby improving the electronic conductivity of the host material. Given that the atomic radius of the sacrificial components (such as Mn) is significantly larger than the atomic radius of the transition metals (such as Ni, Co, Fe, and Cu) in TMO, this will induce the corresponding metal-oxygen bonds to break, generating cation vacancy defects, thereby optimizing the catalyst's adsorption / desorption ability for OER intermediates.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A method for preparing a cation vacancy-rich transition metal oxide comprises the following steps:

[0009] Step 1: using a vacuum induction melting furnace to heat Mn and transition metal in a suitable proportion to a molten state, and using a single-roller quenching device to quickly throw out the alloy liquid to obtain a Mn-based initial alloy strip;

[0010] Step 2: placing the initial alloy strip obtained in step 1 in a weak acid solution for Mn removal to obtain a Mn-doped porous transition metal precursor;

[0011] Step 3: placing the Mn-doped porous transition metal precursor obtained in step 2 in a tube furnace for high-temperature oxidation treatment to finally obtain the cation vacancy-rich porous transition metal oxide.

[0012] It should be noted that there is a one-to-one correspondence between the Mn content of the initial alloy in step 1 and the Mn content of the porous transition metal precursor in step 2, and the Mn content is related to the final cation vacancy concentration.

[0013] Optionally, in step 1, the transition metal is one or more of Ni, Co, Fe, and Cu; and the atomic percentage of Mn is 70% to 95%. Usually, the Mn content of the initial alloy is higher than 70% to successfully remove the Mn, and there is a one-to-one correspondence between the initial alloy Mn content and the Mn doping after dealloying, and the Mn doping is also related to the final cation vacancy concentration.

[0014] Optionally, the weak acid solution in step 2 is (NH4)2SO4, dilute HCl or dilute H2SO4, and the concentration is 0.1-1 mol / L.

[0015] Furthermore, in step 2, the temperature for removing Mn is 25 to 100° C., and the time is 10 to 100 hours.

[0016] Optionally, in step three, the high temperature oxidation atmosphere is air or oxygen, the temperature is 500 to 1000° C., and the time is 1 to 48 hours.

[0017] The present invention also requests protection for the application of the cation vacancy-rich transition metal oxide, specifically adopting a three-electrode system, using the cation vacancy-rich transition metal oxide as a working electrode, a carbon rod as an auxiliary electrode, and Hg / HgO as a reference electrode to conduct an electrocatalytic oxygen evolution reaction test.

[0018] It can be seen from the above technical solution that, compared with the prior art, the preparation method and application of a cation vacancy-rich transition metal oxide provided by the present invention have the following excellent effects:

[0019] 1) Mn-based alloy is selected as the initial alloy, which has a wide range of raw materials, adjustable composition and low price;

[0020] 2) The dealloying strategy is used to construct a porous-ligament structure, which is not only energy-saving, time-saving, and easy to expand, but also can accurately control the pore size, pore morphology, ligament composition, etc. of the porous material according to the initial alloy composition, content, dealloying method and subsequent treatment method, thereby stimulating / inducing the surface to derive more active interfaces and sites;

[0021] 3) The dealloyed sacrificial component has a dual role. On the one hand, it can be used as a pore-forming agent to obtain a porous skeleton with a high specific surface area, which is beneficial to accelerate the OER kinetic process. On the other hand, it can be in-situ doped and induce cation vacancies, thereby optimizing the OER thermodynamic process.

[0022] 4) In-situ doping of dealloyed residual components can promote electron transitions and significantly improve the conductivity of spinel oxides. The induced cation vacancies can optimize the charge distribution on the material surface and reduce the energy barrier of the OER rate-determining step. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0024] Figure 1 This is the X-ray diffraction pattern of the cation vacancy-rich Cu-Co oxide prepared in Example 1.

[0025] Figure 2 This is a scanning electron microscope photograph of the cation vacancy-rich Cu-Co oxide prepared in Example 1.

[0026] Figure 3 This is a high-magnification transmission electron microscope photograph of the cation vacancy-rich Cu-Co oxide prepared in Example 1.

[0027] Figure 4This is a polarization curve of the electrocatalytic oxygen evolution of the cation vacancy-rich Cu-Co oxide prepared in Example 1 in 1 mol / L KOH solution.

[0028] Figure 5 This is the X-ray diffraction pattern of the cation vacancy-rich Ni-Fe oxide prepared in Example 2.

[0029] Figure 6 This is a scanning electron microscope photograph of the cation vacancy-rich Ni-Fe oxide prepared in Example 2. DETAILED DESCRIPTION

[0030] The following will be combined with the embodiments of the present invention and the drawings of the specification to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] The embodiment of the invention discloses a method for preparing a cation vacancy-rich transition metal oxide.

[0032] In order to better understand the present invention, the present invention is further specifically described below through the following examples, but it should not be understood as a limitation of the present invention. Some non-essential improvements and adjustments made by technicians in this field based on the above invention content are also considered to fall within the protection scope of the present invention.

[0033] The technical solution of the present invention will be further described below in conjunction with specific embodiments.

[0034] Example 1

[0035] A method for preparing a cation vacancy-rich Cu-Co oxide is carried out according to the following steps:

[0036] Step 1: Use a vacuum induction melting furnace to heat Mn, Cu and Co together in an atomic percentage of 70:10:20 to a molten state, and use a single-roll quenching device to quickly throw out the alloy liquid to obtain Mn 70 Cu 10 Co 20 Initial alloy strip;

[0037] Step 2: Mn obtained in step 1 70 Cu 10 Co 20 The initial alloy strip was placed in 1 mol / L (NH4)2SO4 solution for Mn removal treatment at a reaction temperature of 50°C for 72 h to obtain a Mn-doped porous Cu-Co alloy.

[0038] Step 3: Place the Mn-doped porous Cu-Co alloy obtained in step 2 in a tubular furnace for high-temperature oxidation treatment in an air atmosphere at a temperature of 600° C. for 2 h to obtain a cation vacancy-rich porous Cu-Co oxide.

[0039] The X-ray diffractometer (XRD) test found that the diffraction peak of the porous Cu-Co oxide was significantly negatively shifted relative to the standard diffraction peak, indicating that large atomic Mn was successfully doped into the Cu-Co oxide. At the same time, a large amount of spinel oxide Cu 0.95 Co 2.05 O4, confirming that it is rich in Cu vacancy defects (see Appendix Figure 1 ). Scanning electron microscopy (SEM) observations revealed that the cation vacancy-rich porous Cu-Co oxide has a worm-like porous-ligament structure (see Appendix Figure 2 ), which can significantly increase the effective contact area between the catalytic electrode and the electrolyte, promoting material transport and electron conduction. High-resolution transmission electron microscopy (HRTEM) observations revealed that there are clear Cu 0.95 Co 2.05 O4(311) lattice fringes, and the fringing spacing is slightly larger than the standard value (see Appendix Figure 3 ), which once again confirmed that the dealloyed residual Mn was successfully incorporated into the porous Cu-Co oxide and induced the generation of Cu vacancy defects.

[0040] Electrochemical tests were performed using cation vacancy-rich porous Cu-Co oxide as the working electrode, carbon rod as the auxiliary electrode, and Hg / HgO as the reference electrode. The results showed that the electrode has a current density of 10 mA / cm 2 Only 310mV oxygen evolution overpotential is required, showing electrocatalytic oxygen evolution activity beyond RuO2 (see Appendix Figure 4 ).

[0041] Example 2

[0042] A method for preparing a cation vacancy-rich Ni-Fe oxide is carried out according to the following steps:

[0043] Step 1: Use a vacuum induction melting furnace to heat Mn, Ni and Fe together in an atomic percentage of 85:5:10 to a molten state, and use a single-roll quenching device to quickly throw out the alloy liquid to obtain Mn 85 Ni5Fe 10 Initial alloy strip;

[0044] Step 2: Mn obtained in step 1 85 Ni5Fe 10 The initial alloy strip was placed in a 0.1 mol / L dilute HCl solution for Mn removal at a reaction temperature of 25°C for 24 h to obtain a Mn-doped porous Ni-Fe alloy.

[0045] Step 3: Place the Mn-doped porous Ni-Fe alloy obtained in step 2 in a tubular furnace for high-temperature oxidation treatment in an oxygen atmosphere at a temperature of 700° C. for 1 h to obtain a cation vacancy-rich porous Ni-Fe oxide.

[0046] XRD tests revealed that the diffraction peak of porous Ni-Fe oxide shifted significantly negatively relative to the standard diffraction peak, indicating that large atomic Mn was successfully doped into Ni-Fe oxide. At the same time, a large amount of spinel oxide Ni 1.25 Fe 1.85 O4, confirming that it is rich in Fe vacancy defects (see Appendix Figure 5 ).

[0047] SEM observation revealed that the cation vacancy-rich porous Ni-Fe oxide has a typical porous-ligament structure, and the ligament surface further derives secondary nanosheets (see Appendix Figure 6 ), which can significantly increase the effective contact area between the catalytic electrode and the electrolyte, promoting material transport and electron conduction.

[0048] Example 3

[0049] A method for preparing a cation vacancy-rich Co oxide is carried out according to the following steps:

[0050] Step 1: Use a vacuum induction melting furnace to heat Mn and Co together in an atomic percentage of 80:20 to a molten state, and use a single-roll quenching device to quickly throw out the alloy liquid to obtain Mn 80 Co 20 Initial alloy strip;

[0051] Step 2: Mn obtained in step 1 80 Co 20 The initial alloy strip was placed in 0.5 mol / L (NH4)2SO4 solution for Mn removal treatment at a reaction temperature of 60°C for 48 h to obtain Mn-doped porous Co.

[0052] Step 3: Place the Mn-doped porous Co alloy obtained in step 2 in a tubular furnace for high-temperature oxidation treatment in an air atmosphere at a temperature of 500° C. for 4 hours to obtain a cation vacancy-rich porous Co oxide.

[0053] Example 4

[0054] A method for preparing a cation vacancy-rich Ni-Co-Fe oxide is carried out according to the following steps:

[0055] Step 1: Use a vacuum induction melting furnace to heat Mn, Ni, Co and Fe in an atomic percentage of 70:10:10:10 to a molten state, and use a single-roll quenching device to quickly throw out the alloy liquid to obtain Mn 70 Ni 10 Co 10 Fe 10 Initial alloy strip;

[0056] Step 2: Mn obtained in step 1 70 Ni 10 Co 10 Fe 10 The initial alloy strip was placed in a 0.1 mol / L dilute H2SO4 solution for Mn removal treatment at a reaction temperature of 25°C for 24 h to obtain a Mn-doped porous Ni-Co-Fe alloy.

[0057] Step 3: Place the Mn-doped porous Ni-Co-Fe alloy obtained in step 2 in a tubular furnace for high-temperature oxidation treatment in an oxygen atmosphere at a temperature of 800°C for 2 hours to obtain a cation vacancy-rich porous Ni-Co-Fe oxide.

[0058] Example 5

[0059] A method for preparing a cation vacancy-rich Ni-Co-Fe-Cu oxide is carried out according to the following steps:

[0060] Step 1: Use a vacuum induction melting furnace to heat Mn, Ni, Co, Fe and Cu in an atomic percentage of 80:5:5:5:5 to a molten state, and use a single-roll quenching device to quickly throw out the alloy liquid to obtain Mn 80 Ni5Co5Fe5Cu5 initial alloy strip;

[0061] Step 2: Mn obtained in step 1 80 The Ni5Co5Fe5Cu5 initial alloy strip was placed in a 0.5 mol / L dilute HCl solution for Mn removal at a reaction temperature of 40°C for 12 h to obtain a Mn-doped porous Ni-Co-Fe-Cu alloy.

[0062] Step 3: Place the Mn-doped porous Ni-Co-Fe-Cu alloy obtained in step 2 in a tubular furnace for high-temperature oxidation treatment in an air atmosphere at a temperature of 700°C for 5 hours to obtain a cation vacancy-rich porous Ni-Co-Fe-Cu oxide.

[0063] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a cation vacancy-rich transition metal oxide, characterized in that: The specific steps include: Step 1: heating Mn and transition metal to a molten state, and then quickly spinning out the alloy liquid to obtain a Mn-based initial alloy strip; Step 2: placing the initial alloy strip obtained in step 1 in a weak acid solution for Mn removal to obtain a Mn-doped porous transition metal precursor; Step 3, subjecting the Mn-doped porous transition metal precursor obtained in step 2 to high-temperature oxidation treatment to finally obtain the cation vacancy-rich porous transition metal oxide; In step 1, the transition metal is one or more of Ni, Co, Fe, and Cu; and the atomic percentage of Mn is 70% to 95%; In step 2, the temperature for removing Mn is 25-100°C and the time is 10-100h; In step 3, the high temperature oxidation atmosphere is air or oxygen, the temperature is 500-1000° C., and the time is 1-48 hours.

2. The method for preparing a cation vacancy-rich transition metal oxide according to claim 1, characterized in that: The weak acid solution in step 2 is (NH4)2SO4, dilute HCl or dilute H2SO4, and the concentration is 0.1-1 mol / L.

3. Use of the cation vacancy-rich transition metal oxide prepared by the method of claim 1 in an electrocatalytic oxygen evolution reaction.

4. The use according to claim 3, characterized in that: A three-electrode system was adopted, with the cation vacancy-rich transition metal oxide as the working electrode, the carbon rod as the auxiliary electrode, and Hg / HgO as the reference electrode, to carry out an electrocatalytic oxygen evolution reaction test.

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