Metal heterostructure electrocatalyst as well as preparation method and application thereof

Abstract

The invention relates to the field of new energy, and discloses a metal heterostructure electrocatalyst and a preparation method and application thereof.The catalyst comprises a heterostructure composed of MoNi4 and MoO2 and metal elements doped in MoNi4 and MoO2, and the metal elements are selected from iron and / or manganese; based on the total amount of the catalyst, the amount of MoNi4 is 30-40 mol%, the amount of MoO2 is 40-50 mol%, and the amount of metal elements is 0.1-0.5 mol%. The catalyst provided by the invention does not use noble metal and is low in cost, and more importantly, the catalyst provided by the invention has excellent catalytic activity under an alkaline condition, has a relatively small Tafel slope value in HER, OER and HMOR reactions, is fast in reaction kinetics, is small in charge transfer resistance in a water electrolysis process, and has a good application prospect. And the electrochemical surface area and the electric double-layer capacitance Cdl are relatively large, the electrochemical active area is large, the stability is lasting, and the constant electrolysis lasts for at least 100 hours.

Description

Technical Field

[0001] This invention relates to the field of new energy, specifically to a metal heterostructure electrocatalyst, its preparation method, and its application. Background Technology

[0002] In recent years, hydrogen (H2), as a clean energy carrier with multiple functions and a renewable alternative to fossil fuels, has played a crucial role in achieving a low-carbon future and has become a global focus. Among the many methods for producing hydrogen, water electrolysis is considered a highly promising green hydrogen production route. However, the large-scale application of this technology is still limited by the kinetic slowness of the hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction (OER) at the anode. Against this backdrop, the strategic value of electrocatalytic water splitting for hydrogen production has received widespread attention from the scientific community. Although noble metal Pt-based and Ir / Ru-based materials are highly efficient electrocatalysts for HER and OER, respectively, their high cost and scarce reserves make it difficult to meet the needs of large-scale industrial applications and sustainable development. Summary of the Invention

[0003] The present invention aims to overcome the shortcomings of the prior art and solve the problem of high cost in existing water electrolysis hydrogen production, and provides a metal heterostructure electrocatalyst, its preparation method and application.

[0004] To achieve the above objectives, the first aspect of the present invention provides a metal heterostructure electrocatalyst, wherein the catalyst comprises a heterostructure composed of MoNi4 and MoO2, and a metal element doped in MoNi4 and MoO2, wherein the metal element is selected from iron and / or manganese; Based on the total amount of the catalyst, the amount of MoNi4 is 30-40 mol%, the amount of MoO2 is 40-50 mol%, and the amount of the metal element is 0.1-0.5 mol.

[0005] This invention provides a catalyst with a heterostructure doped with a metal element. This catalyst does not use precious metals, resulting in low cost. More importantly, the catalyst provided by this invention exhibits excellent catalytic activity under alkaline conditions, showing a small Tafel slope in the HER, OER, and HMFOR reactions, indicating fast reaction kinetics. It also exhibits low charge transfer resistance during water electrolysis and possesses a large electrochemical surface area and double-layer capacitance C. dl It has a large electrochemical active area, long-lasting stability, and constant electrolysis for at least 100 hours.

[0006] A second aspect of the present invention provides a method for preparing a metal heterostructure electrocatalyst, wherein the preparation method includes: preparing a catalyst comprising Ni... 2+A hydrothermal reaction is carried out on a mixed solution of soluble salts of [a substance], soluble salts of MoO4²⁻ and soluble salts of metal elements to obtain a precursor, and then the precursor is calcined to obtain a catalyst. The metal element is selected from iron and / or manganese, and Ni is present in the mixed solution. 2+ The molar ratio of Ni to MoO4²⁻ is 1:0.5-1.5. 2+ The molar ratio of the metal element is 1:0.02-0.25.

[0007] The catalyst provided by this invention has a simple preparation method, requires less reagent and has low cost, the preparation process is simple and convenient, the raw material cost is low, the required preparation conditions are low, and it is easy to commercialize.

[0008] The third aspect of this invention provides the application of the metal heterostructure electrocatalyst described in the first aspect of this invention or the catalyst prepared by the preparation method described in the second aspect of this invention in the electrolysis of water to produce hydrogen. Attached Figure Description

[0009] Figure 1 SEM images of the catalysts prepared in Examples 1 and 2; Figure 2 TEM image of the catalyst prepared in Example 1; Figure 3 EDS diagram of the material prepared in Example 1; Figure 4 XRD patterns of the catalysts prepared in Examples 1 and 2; Figure 5 XPS image of the catalyst prepared in Example 1; Figure 6 XPS image of the catalyst prepared in Example 2; Figure 7 LSV diagrams of the catalysts prepared in Examples 1 and 2; Figure 8 Tafel slope diagrams of the catalysts prepared in Examples 1 and 2; Figure 9 EIS diagrams of the catalysts prepared in Examples 1 and 2; Figure 10 CV plots of the catalysts prepared in Examples 1 and 2; Figure 11 CP diagrams of the catalysts prepared in Examples 1 and 2; Figure 12 The graphs show the polarization curves of the catalysts prepared in Examples 1 and 2. Detailed Implementation

[0010] The specific embodiments of this application will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit this application.

[0011] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0012] Furthermore, the term "and / or" in the specification and claims is used to describe the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0013] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0014] In this invention, a heterostructure refers to a composite structure formed by two or more phases that have significant differences in physical properties (such as crystal structure, band gap, work function) and / or chemical properties through close interfacial contact.

[0015] The first aspect of the present invention provides a metal heterostructure electrocatalyst, wherein the catalyst comprises a heterostructure composed of MoNi4 and MoO2, and a metal element doped in MoNi4 and MoO2, wherein the metal element is selected from iron and / or manganese; Based on the total amount of the catalyst, the amount of MoNi4 is 30-40 mol%, the amount of MoO2 is 40-50 mol%, and the amount of the metal element is 0.1-0.5 mol.

[0016] Binary MoNi intermetallic compounds are advanced electrocatalysts for hydrogen production, with the Ni-Mo synergistic effect allowing for flexible tuning of surface energy. However, existing binary MoNi intermetallic compounds still face challenges such as poor charge transfer performance at high current densities and difficulty in optimizing the adsorption / desorption process of HER intermediates. This invention addresses these challenges by initiating electron rearrangement around the active center through a heterojunction, optimizing the local electronic environment, and activating more active sites. The catalyst provided by this invention exhibits excellent catalytic activity under alkaline conditions, with a small Tafel slope value in HER, OER, and HMFOR reactions, resulting in fast reaction kinetics. It also demonstrates low charge transfer resistance during water electrolysis, a large electrochemical surface area, and a large double-layer capacitance (Cdl). Furthermore, it exhibits a large electrochemical active area, long-lasting stability, and constant electrolysis for at least 100 h.

[0017] When the amount of MoNi4 exceeds the range defined in this invention, particle agglomeration is likely to occur, resulting in insufficient exposure of active sites. Too low a proportion of MoNi4 will directly reduce the number of active sites. Insufficient MoO2 will lead to a lack of interfacial interactions with MoO2, preventing the full optimization of the electronic structure of MoNi4 and reducing the intrinsic activity of the active sites. Since MoO2 has weaker conductivity than MoNi4, an excessively high proportion will increase the overall resistance and reduce the charge transfer rate. Therefore, in the catalyst provided by this invention, based on the total amount of the catalyst, the amount of MoNi4 can be 30 mol%, 32 mol%, 34 mol%, 36 mol%, 38 mol%, 40 mol%, or any value between any two of these values, and the amount of MoO2 can be 40 mol%, 42 mol%, 44 mol%, 46 mol%, 48 mol%, 50 mol%, or any value between any two of these values. When the amount of metal element doping is below a certain range, it will affect the performance of the material. If it is above the certain range, the metal element may not exist in the form of doping. Therefore, the amount of metal element can be 0.1 mol%, 0.2 mol%, 0.3 mol%, 0.4 mol%, 0.5 mol%, and any value between any two of them.

[0018] Preferably, the oxygen 1s characteristic peak in the catalyst, after peak fitting, has three characteristic peaks: a characteristic peak corresponding to the metal-O bond at 530-531 eV, a characteristic peak corresponding to the oxygen vacancy at 531-532 eV, and a characteristic peak corresponding to the oxygen of surface-adsorbed water molecules at 532-533 eV. Based on the total amount of oxygen, the amount of oxygen vacancies is 25-35%. Preferably, the amount of oxygen vacancies is 30-35%. Oxygen vacancies can regulate the electron cloud density of surrounding atoms and weaken the HO bond strength to promote water molecule activation and stimulate more active sites. This invention increases the oxygen vacancy concentration in the heterostructure through metal doping, accelerating charge dynamics and optimizing the adsorption energy of hydrogen-containing intermediates in HER. The amount of oxygen vacancies can be 25%, 28%, 30%, 31%, 32%, 33%, 34%, 35%, or any value between any two of these values.

[0019] Preferably, the catalyst is in the form of nanorods with an average diameter of 80-85 nm. The average diameter of the catalyst can be 80 nm, 82 nm, 85 nm, or any value between any two of these numbers.

[0020] Preferably, the catalyst further includes a substrate, on which the catalyst is vertically grown. Vertical growth of the catalyst on the substrate maximizes the exposure of surface active sites and avoids obstruction caused by the stacking of nanorods.

[0021] Preferably, the substrate is selected from one or more of nickel mesh, carbon paper, carbon cloth, copper foam, carbonized wood, carbon nanotubes, and nickel fiber paper.

[0022] Preferably, the substrate is a nickel mesh. The present invention does not have special requirements for the choice of substrate; any substrate commonly used in the art that can grow catalysts is acceptable, with nickel mesh being preferred.

[0023] A second aspect of the present invention provides a method for preparing a metal heterostructure electrocatalyst, wherein the preparation method includes: preparing a catalyst comprising Ni... 2+ A hydrothermal reaction is carried out on a mixed solution of soluble salts of [a substance], soluble salts of MoO4²⁻ and soluble salts of metal elements to obtain a precursor, and then the precursor is calcined to obtain a catalyst. The metal element is selected from iron and / or manganese, and Ni is present in the mixed solution. 2+ The molar ratio of Ni to MoO4²⁻ is 1:0.5-1.5. 2+ The molar ratio of the metal element is 1:0.02-0.25.

[0024] The catalyst preparation method provided by this invention is simple, requires little reagent, is low in cost, has a simple and convenient preparation process, uses inexpensive raw materials, and requires relatively low preparation conditions, making it suitable for commercial application. Ni in the mixed solution2+ The molar ratio of Ni to the metallic element can be 1:0.2, 1:0.05, 1:0.1, 1:0.15, 1:0.2, 1:0.25, or any value between any two of these numbers. 2+ The molar ratio of 1:0.5, 1:0.8, 1:1, 1:1.2, 1:1.5 and any value between any two of these numbers.

[0025] Preferably, the preparation method further includes: adding a matrix to the mixed solution, and then carrying out the hydrothermal reaction. The matrix is ​​selected from one or more of nickel mesh, carbon paper, carbon cloth, copper foam, carbonized wood, carbon nanotubes, and nickel fiber paper. Nickel mesh is preferred as the matrix in this invention because the catalyst and nickel mesh are hydrothermally heated together, resulting in better bonding, avoiding the interfacial resistance introduced by traditional binders, and achieving a faster electron transport rate, thus accelerating the reaction efficiency.

[0026] The substrate can be cleaned before the hydrothermal reaction to remove the oxide layer on the surface, which facilitates the growth of the precursor. The present invention does not have any particular limitation on the cleaning method, and any commonly used methods in the art are acceptable. For example, acid washing can be used first, followed by alcohol washing and deionized water washing.

[0027] Preferably, the hydrothermal reaction temperature is 140-180℃, and the time is 4-8 hours. If the hydrothermal temperature is too low, the catalyst particles are small and poorly dispersed; if the temperature is too high, particle agglomeration will occur, resulting in insufficient exposure of active sites. Temperature also affects the morphology of the material. Time affects the doping effect and the formation of heterogeneous interfaces. Therefore, the hydrothermal reaction temperature can be any value between 140℃, 150℃, 160℃, 170℃, 180℃, and any two of these values, and the time can be any value between 4 hours, 6 hours, 8 hours, and any two of these values.

[0028] Preferably, the preparation method further includes drying after the hydrothermal reaction to obtain the catalyst, wherein the drying temperature is 50-80℃ and the time is 3-6h.

[0029] Preferably, the calcination temperature is 300-600℃, and the time is 1-4 hours. The calcination temperature can be any value between any two of the following: 300℃, 350℃, 400℃, 420℃, 450℃, 480℃, 500℃, 550℃, 600℃, and the time can be any value between any two of the following: 1 hour, 2 hours, 4 hours, and the time can be any value between any two of the following:

[0030] Preferably, the heating rate of the calcination is 2-5℃ / min.

[0031] Preferably, when the metal element is Fe, the calcination temperature is 400-500℃, and when the metal element is Mn, the calcination temperature is 300-400℃.

[0032] Preferably, the Ni 2+ The soluble salt is selected from one or more of nickel nitrate, nickel sulfate, nickel chloride, and their corresponding hydrates.

[0033] Preferably, the soluble salt of the MoO4²⁻ is selected from sodium molybdate and / or ammonium molybdate and their corresponding hydrates.

[0034] Preferably, the soluble salt of the metallic element iron is selected from one or more of ferrous sulfate, ferrous sulfate, ferrous ammonium sulfate, and ferrous chloride and their corresponding hydrates, and the soluble salt of the metallic element manganese is selected from one or more of manganese sulfate, manganese chloride, manganese nitrate and their corresponding hydrates.

[0035] The third aspect of this invention provides the application of the metal heterostructure electrocatalyst described in the first aspect of this invention or the catalyst prepared by the preparation method described in the second aspect of this invention in the electrolysis of water to produce hydrogen.

[0036] Compared with the prior art, the catalyst provided by the present invention has the following significant beneficial effects: This invention does not use precious metals, has low cost, and more importantly, the catalyst provided by this invention has excellent catalytic activity under alkaline conditions. It has a small Tafel slope value in HER, OER and HMFOR reactions, fast reaction kinetics, low charge transfer resistance during water electrolysis, and has a large electrochemical surface area and double layer capacitance Cdl. It also has a large electrochemical active area and long-lasting stability.

[0037] In particular, the iron-doped MoNi4 / MoO2 heterojunction electrocatalyst rich in oxygen vacancies (Fe-MoNi4 / MoO2 for short) provided by this invention exhibits excellent hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance, requiring only 92.8 and 295.8 mV overpotentials, respectively, to reach 100 mA cm⁻¹. -2 And at 100 mA cm −2The electrolyzer exhibited almost no degradation after 100 hours of continuous operation. Introducing iron / manganese into the MoNi4 / MoO2 heterostructure promotes lattice expansion and optimizes the d-band centers of MoNi4 / MoO2, thereby enhancing water dissociation and H* (* represents adsorbed hydrogen atoms, intermediates in the HER reaction) desorption. Furthermore, iron incorporation increases the oxygen vacancy concentration in MoNi4 / MoO2, correspondingly accelerating charge kinetics and optimizing the adsorption energy of hydrogen-containing intermediates in HER. In addition, the reconstructing of Fe-MoNi4 / MoO2 into a highly active Fe-MoO2 / Ni(OH)2 species for OER reduces the energy barrier for O intermediate formation and accelerates OER kinetics. Therefore, the anion exchange membrane electrolyzer equipped with bifunctional Fe-MoNi4 / MoO2 achieves high current densities of 500, 1000, and 2000 mA cm⁻¹. -2 At that time, only 1.59, 1.76, and 1.94 V were required, respectively, and at 100 mA cm⁻¹ −2 It exhibits excellent stability for over 100 hours under certain conditions, verifying its superior performance.

[0038] The catalyst of this invention can be used in a two-electrode electrolyzer, providing a good preparation route and strategy for the development of new and efficient non-precious metal catalysts, and making an important contribution to the important role of water electrolysis in green energy conversion systems.

[0039] The catalyst of this invention has a simple preparation and measurement method, requires little reagent and has low cost; the preparation process is simple and convenient, the raw materials are inexpensive, the required preparation conditions are low, and it is easy to commercialize.

[0040] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto. Unless otherwise specified, the test methods and testing equipment used in the following embodiments are conventional test methods and testing equipment in the art.

[0041] Example 1: Preparation of S1.Fe-NiMoO4∙xH2O nanorod electrodes: Cut a piece of nickel foam (2cm×3cm), place it in a 1mol / L HCl solution and sonicate for 15min, then sonicate it with anhydrous ethanol and deionized water for 3min in sequence, and dry it at 60℃ to obtain the NF electrode; The prepared NF electrode, along with Na2MoO4∙2H2O (2.0 mmol), Ni(NO3)2∙6H2O (2.0 mmol), Fe(NO3)2∙9H2O (0.1 mmol), and 30 ml of deionized water, were placed into a 50 mL polytetrafluoroethylene-lined autoclave and heated in an oven at 160°C for 8 hours to obtain an electrode with Fe-NiMoO4∙xH2O nanorods. After washing the electrode in deionized water and ethanol, it was vacuum dried at 60°C for 5 hours to obtain an electrode with Fe-NiMoO4∙xH2O nanorods.

[0042] Preparation of S2.Fe-MoNi4 / MoO2: An electrode with Fe-NiMoO4∙xH2O nanorods was placed in a tube furnace and heated to 450°C at 5°C / min under an H2 / Ar (5% / 95%) atmosphere and calcined for 2 hours to obtain a catalyst, denoted as Fe-MoNi4 / MoO2.

[0043] EDS (Electro-Dependent Sequencing) plots are obtained through TEM (Electro-Dependent Sequencing), and then the molar content of each element obtained from the EDS is used to calculate the content of each component based on the source of each element. Specifically: The EDS diagram of the material obtained in Example 1 is shown below. Figure 3 As shown, the results indicate that Mo is 84 mol, Ni is 167 mol, O is 92 mol, and Fe is 0.17 mol. O exists only in MoO2, and each 1 mol of MoO2 contains 2 mol of O atoms. Therefore, the total number of O atoms = 2 × the number of moles of MoO2. The original number of O atoms in EDS is 92 mol, so MoO2 is 46 mol. Mo exists only in MoNi4 and MoO2, and the number of Mo atoms in both is 1. Therefore, based on the source of the number of Mo atoms, MoNi4 is calculated to be 38 mol. The original number of Fe atoms is 0.17 mol, and after calibration, z = 0.1 mol. Finally, in this embodiment, based on the total amount of catalyst, MoNi4 is 38 mol%, MoO2 is 46 mol%, Fe is 0.1 mol%, and the balance is Ni.

[0044] Example 2: Preparation of S1. Mn-NiMoO4∙xH2O nanorod electrodes: Cut a piece of nickel foam (2cm×3cm), place it in a 1mol / L HCl solution and sonicate for 15min, then sonicate it with anhydrous ethanol and deionized water for 3min in sequence, and dry it at 60℃ to obtain the NF electrode; The treated NF, along with Na2MoO4∙2H2O (2.0 mmol), Ni(NO3)2∙6H2O (2.0 mmol), MnSO4∙6H2O (0.2 mmol), and 30 ml of deionized water, were placed in a 50 mL polytetrafluoroethylene-lined autoclave and heated in an oven at 140°C for 8 hours to obtain an electrode with Mn-NiMoO4∙xH2O nanorods. After cleaning the electrode with deionized water and ethanol, it was vacuum dried at 60°C for 5 hours to obtain an electrode with Fe-NiMoO4∙xH2O nanorods.

[0045] S2. Preparation of Mn-MoNi4 / MoO2: An electrode with Mn-NiMoO4∙xH2O nanorods was placed in a tube furnace and heated to 350°C at 5°C / min under an H2 / Ar (5% / 95%) atmosphere and calcined for 2 hours to obtain a catalyst, denoted as Mn-MoNi4 / MoO2.

[0046] In this embodiment, based on the total amount of catalyst, MoNi4 is 39 mol%, MoO2 is 46 mol%, Mn is 0.2 mol%, and the balance is Ni.

[0047] Examples 3 and 4: were carried out in the same manner as Example 2, except that the calcination temperature in Example 3 was 450°C and the calcination temperature in Example 4 was 550°C.

[0048] Comparative Example 1: The procedure was carried out in accordance with Example 1, except that Fe(NO3)2∙9H2O was not added in step S1.

[0049] In this embodiment, based on the total amount of catalyst, MoNi4 is 38 mol%, MoO2 is 46 mol%, Fe is 0 mol%, and the balance is Ni.

[0050] Comparative Example 2: The procedure was carried out in accordance with Example 1, except that Na2MoO4∙2H2O was 1.0 mmol and Ni(NO3)2∙6H2O was 3.0 mmol.

[0051] In this embodiment, based on the total amount of catalyst, MoNi4 is 21 mol%, MoO2 is 52 mol%, Fe is 0.1 mol%, and the balance is Ni.

[0052] Comparative Example 3: The procedure was carried out in accordance with Example 1, except that Na2MoO4∙2H2O was 3.0 mmol and Ni(NO3)2∙6H2O was 1.0 mmol.

[0053] In this embodiment, based on the total amount of catalyst, MoNi4 is 48 mol%, MoO2 is 28 mol%, Fe is 0.1 mol%, and the balance is Ni.

[0054] Comparative Example 4: The procedure was carried out in accordance with Example 1, except that the amount of Fe(NO3)2∙9H2O was 1 mmol.

[0055] In this embodiment, based on the total amount of catalyst, MoNi4 is 38 mol%, MoO2 is 46 mol%, Fe is 1 mol%, and the balance is Ni.

[0056] Performance testing (1) The catalysts prepared in Examples 1 and 2 were subjected to scanning electron microscopy (SEM), and the results are as follows: Figure 1 As shown. Figure 1 Images a and b are SEM images of the catalyst prepared in Example 1, while images c and d are SEM images of the catalyst prepared in Example 2. It can be seen that the catalyst exhibits a nanorod-like structure and is vertically distributed on the NF surface. Its average diameter was measured to be 81.3 nm.

[0057] (2) The catalyst prepared in Example 1 was scanned by transmission electron microscopy (TEM), and the results are as follows: Figure 2 As shown. Figure 2 Image a shows a transmission electron microscope (TEM) image of the Fe-MoNi4 / MoO2 catalyst; image b shows a high-resolution transmission electron microscope (HRTEM) image of the Fe-MoNi4 / MoO2 catalyst; image c shows a local HRTEM image of a region in image b; image d shows a multi-region HRTEM image of the Fe-MoNi4 / MoO2 catalyst; image e shows a magnified HRTEM image of the region corresponding to box e in image d; image j shows a magnified HRTEM image of the region corresponding to box d in image d; the mixed image "Mix" is a mapping diagram of the mixed element distribution, followed by mapping diagrams of Fe, Ni, Mo, and O in sequence. As can be seen from the images, the catalyst exhibits a rod-shaped nanostructure array with a smooth surface.

[0058] (3) X-ray diffraction (XRD) was performed on the catalysts prepared in Examples 1 and 2, and the results are as follows: Figure 4 As shown. Figure 4 Figure a shows the XRD pattern of the catalyst prepared in Example 1, and figure b shows the XRD pattern of the catalyst prepared in Example 2. As can be seen from the figures, neither catalyst prepared in the two examples exhibits diffraction peaks for Fe or Mn metals or composite phases. This result indicates that Fe or Mn, as ionic dopants in the MoNi4 / MoO2 heterojunction, did not form independent phases.

[0059] Combination Figure 2The smaller figures b and d show the interplanar spacing of the lattice fringes, which are 0.206 nm and 0.241 nm, respectively. Figure 4 It can be seen that the two correspond to the (121) crystal plane of MoNi4 and the (-202) crystal plane of MoO2, respectively. Elemental mapping analysis shows that Ni, Fe, Mo and O elements are uniformly distributed on the catalyst.

[0060] (4) X-ray photoelectron spectroscopy (XPS) analysis was performed on the catalysts prepared in Examples 1 and 2, and the results are as follows: Figure 5 , Figure 6 As shown. Among them. Figure 5 This is an XPS image of the catalyst prepared in Example 1. Figure 6 The image shows the XPS plot of the catalyst prepared in Example 2.

[0061] from Figure 5 In the diagram, small image a shows the high-resolution spectrum of Fe 2p, small image b shows the high-resolution spectrum of Ni 2p, small image c shows the high-resolution spectrum of Mo 3d, and small image d shows the high-resolution spectrum of O 1S. It can be seen that the high-resolution spectrum of Fe 2p contains two Fe 2p... 3 / 2 and Fe 2p 1 / 2 The peak of the spin orbit, and two other satellite peaks. Fe 2p 3 / 2 The peaks can be fitted to two peaks with binding energies of 712.6 eV and 706.1 eV, corresponding to Fe²⁺ and Fe²⁺, respectively. 0 Species. Similarly, Fe 2p 1 / 2 The peaks also include Fe²⁺ and Fe. 0 Species (723.9 eV and 720.7 eV, respectively) Figure 4 (a) indicates that metallic and oxidized iron coexist in the catalyst Fe-MoNi4 / MoO2.

[0062] Figure 6 In the smaller figures, a shows the high-resolution spectrum of Mn 2p, b shows the high-resolution spectrum of Ni 2p, c shows the high-resolution spectrum of Mo 3d, and d shows the high-resolution spectrum of O 1S. It can be seen that the high-resolution Mn 2p spectrum contains three pairs of doublets, as well as two additional satellite peaks, corresponding to Mn... 2+ (638.9 eV and 651.2 eV), Mn 3+ (641.1 eV and 653.2 eV) and Mn 6+ (232.77eV and 235.57eV) Figure 5 a). This indicates that Mn in the catalyst Mn-MoNi4 / MoO2 exists in an oxidized state.

[0063] Figure 5 and Figure 6In the study, through curve fitting of the Ni 2p spectrum, the binding energies were found to be 852.8 / 870 eV, 856.2 / 873.9 eV, and 862.2 / 880.7 eV. Figure 5 b and Figure 6 The peaks in b) correspond to Ni 0 Ni²⁺ and satellite peaks. The high-resolution 3d spectrum of Mo contains four pairs of doublets, corresponding to metallic Mo. 0 (228.6 eV and 231.5 eV), MoO2 (229.53 eV and 232.2 eV), Mo 5+ (230.54 eV and 234.1 eV) and Mo 6+ (232.77eV and 235.57eV) Figure 4 c and Figure 5 c). In both figures, the O 1s spectrum shows three peaks, at 530.6 eV (metal-O bond, O...). L ), 531.4 eV (oxygen vacancy, O v ) and 532.9 eV (surface-adsorbed H2O molecules, O a () Figure 5 d and Figure 6 d). Through O v / (O v +O a +O L The relative content of oxygen vacancies was calculated. By calculating the peak area of ​​oxygen in the O 1s spectrum in XPS, it was found that the oxygen vacancy content of Fe-MoNi4 / MoO2 was 32%, and that of Mn-MoNi4 / MoO2 was 31%.

[0064] It is evident that Fe and Mn have a strong electronic effect on the heterostructure, optimizing the electronic structure of MoNi4 / MoO2 and generating a large number of oxygen vacancies, which is beneficial for intermediate adsorption and desorption during the electrochemical reaction process.

[0065] (5) Three-electrode test The HER and OER reactions were carried out in a 1 mol / L KOH electrolyte using a three-electrode system, and the HMFOR reaction (5-hydroxymethylfurfural oxidation reaction) was carried out in a 1 mol / L KOH + 20 mM / L HMF (5-hydroxymethylfurfural) electrolyte.

[0066] The working electrodes for the HER, OER, and HMFOR reactions were all prepared with a geometric area of ​​1 × 1 cm. 2 The catalysts of Examples 1 and 2 were used with a platinum sheet as the counter electrode and a saturated calomel electrode (Hg / HgO / KOH) as the reference electrode. All tests were performed at room temperature (25°C) at a scan rate of 5 mV s. −1The correction rate is 90%. According to formula E... RHE (iR correction)=E Hg / HgO The potential is corrected by adding +0.927−iR×100%, where i is the current and R is the electrolyte resistance in the electrochemical impedance spectroscopy test. The test results are as follows: Figure 7-11 As shown.

[0067] in, Figure 7 For LSV curves, all electrochemical experiments were performed in 1 M KOH electrolyte using CHI750E and DH7003 electrochemical workstations with a typical three-electrode system. The working electrodes were Fe-MoNi4 / MoO2 and Mn-MoNi4 / MoO2 with a geometric area of ​​1 × 1 cm²; the counter electrode was Pt; and the reference electrode was a mercury oxide electrode. All tests were performed at room temperature. The linear sweep voltammetry (LSV) scan rate was 5 mV·s⁻¹, calibrated to 80%. The HER test potential ranged from -0.8 V to -1.8 V, while the OER and HMFOR test potentials ranged from 0 to 1 V. Figure 7 Inset a shows the LSV curves of the hydrogen evolution reaction (HER) for the Fe-MoNi4 / MoO2 catalyst; inset b shows the LSV curves of the oxygen evolution reaction (OER) for the Fe-MoNi4 / MoO2 catalyst; inset c shows the LSV curves of the hydrogen evolution reaction (HER) for the Mn-MoNi4 / MoO2 catalyst; and inset d shows the LSV curves of the 5-hydroxymethylfurfural reaction (HMFOR) for the Mn-MoNi4 / MoO2 catalyst. As can be seen from the figures, the catalysts Fe-MoNi4 / MoO2 and Mn-MoNi4 / MoO2 prepared in Examples 1 and 2, at a current density of 100 mA·cm⁻¹, exhibit better performance. −2 Under the given conditions, the overpotentials of HER were 92.8 mV and 79.9 mV, respectively. The catalyst prepared in Example 1, under a current density of 100 mA·cm⁻¹, exhibited the same overpotentials. −2 Under the given conditions, the overpotential of OER was 295.8 mV. The catalyst prepared in Example 2 exhibited an overpotential of 295.8 mV at a current density of 100 mA·cm⁻¹. −2 Under the given conditions, the voltage potential of HMFOR was 1.34 V, indicating that the Fe-MoNi4 / MoO2 and Mn-MoNi4 / MoO2 catalysts prepared in Examples 1 and 2 have excellent catalytic activity.

[0068] Figure 8 This is a Tafel slope plot, with the vertical axis representing overpotential. All Tafel slopes are within a current density range of 10-100 mAcm. -2The results were obtained by fitting within the kinetic control range, based on the Tafel equation η = a + b log∣j∣ (where b is the Tafel slope). In the figure, small plot a represents the Tafel curve for the hydrogen evolution reaction (HER) of the Fe-MoNi4 / MoO2 catalyst, small plot b represents the Tafel curve for the oxygen evolution reaction (OER) of the Fe-MoNi4 / MoO2 catalyst, small plot c represents the Tafel curve for the hydrogen evolution reaction (HER) of the Mn-MoNi4 / MoO2 catalyst, and small plot d represents the Tafel curve for the 5-hydroxymethylfurfural oxidation reaction (HMFOR) of the Mn-MoNi4 / MoO2 catalyst. As can be seen from the figures, the catalysts Fe-MoNi4 / MoO2 and Mn-MoNi4 / MoO2 prepared in Examples 1 and 2 both exhibit low Tafel slope values. The Tafel slope values ​​of the Fe-MoNi4 / MoO2 catalyst prepared in Example 1 during the HER and OER processes are 49.2 mV·dec. −1 and 36.3mV·dec −1 The Tafel slope values ​​of the catalyst Mn-MoNi4 / MoO2 prepared in Example 2 during the HER and HMFOR processes were 19.7 mV·dec. −1 and 48.1mV·dec −1 This indicates that the catalysts prepared in Examples 1 and 2 have relatively fast reaction kinetics in the water electrolysis system.

[0069] Figure 9 The figures show electrochemical impedance spectroscopy (EIS) diagrams with a frequency range of 0.1 Hz to 100 kHz and an amplitude of 5 mV. In the figures, small plot a represents the impedance diagram of the Fe-MoNi4 / MoO2 catalyst, and small plot b represents the impedance diagram of the Mn-MoNi4 / MoO2 catalyst. As can be seen from the figures, the catalysts prepared in Examples 1 and 2 both exhibit low impedance, indicating that the catalysts prepared in Examples 1 and 2 have low charge transfer impedance in the water electrolysis system, thereby achieving a faster electron transfer rate.

[0070] Figure 10 Cyclic voltammetry (CV) plots (recorded at different scan rates (20, 40, 60, 80, and 100 mV s) within the non-Radida potential range). −1The CV curves of the Fe-MoNi4 / MoO2 catalyst are shown. The slope of the straight line plotted between the current density (jc) and the scan rate (ν) on the CV curve is the Cdl value. The potential range of Example 1 is -0.9 to -0.8 V, and the potential range of Example 2 is -0.977 to -0.877 V. In the figure, small figure a is the cyclic voltammetry (CV) curve of the double layer region of the Fe-MoNi4 / MoO2 catalyst, small figure b is the cyclic voltammetry (CV) curve of the double layer region of the Mn-MoNi4 / MoO2 catalyst, and small figure c is the electrochemical double layer capacitance (Cdl) of the Fe-MoNi4 / MoO2 catalyst. dl The fitted curve, with the smaller plot d representing the electrochemical double-layer capacitance (C) of the Mn-MoNi4 / MoO2 catalyst. dl Fitting curves. As can be seen from the figure, the C values ​​of the catalysts prepared in Examples 1 and 2 are... dl The values ​​are 3.19 mF·cm -2 and 13.7 mF·cm -2 This indicates that the catalysts prepared in Examples 1 and 2 have a large active specific surface area, which can not only promote charge transfer, but also provide more active sites.

[0071] Figure 11 The figure shows the stability (CP) test results. In the figure, subplot a represents the HER stability of Fe-MoNi4 / MoO2, subplot b represents the OER stability of Fe-MoNi4 / MoO2, subplot c represents the OER stability of Mn-MoNi4 / MoO2, and subplot d represents the HMFOR stability of Mn-MoNi4 / MoO2 after ten cycles. As can be seen from the figure, in a 1 mol / L KOH electrolyte, the catalyst prepared in Example 1 exhibits stable stability at 100 mA·cm⁻¹. −2 The HER stability was maintained for 100 hours with a decay rate of 0.03 mV / h. -1 At 100 mA·cm −2 The OER stability was maintained for 100 hours with a decay rate of 0.015 mV / h. -1 In a 1 mol / L KOH electrolyte, the catalyst prepared in Example 2 showed a reaction rate of 100 mA·cm⁻¹. −2 The HER stability was maintained for 100 hours with a decay rate of 0.06 mV / h. -1 In a 1 mol / L KOH + 20 mM HMF electrolyte, the catalyst prepared in Example 2 showed almost no change in FE (Faraday efficiency), FDCA (HMF conversion rate), yield, and conversion rate after ten cycles. This indicates that the catalysts prepared in Examples 1 and 2 have good long-term stability.

[0072] (6) Two-electrode test The Fe-MoNi4 / MoO2 catalyst prepared in Example 1 was cut into 1×1cm pieces.2 The two electrodes were used as cathode and anode to assemble an MEA water electrolysis device for two-electrode performance testing. The cathode was a 1 mol / L KOH + 0.5 mol / L NaCl electrolyte, and the anode was a 1 mol / L KOH + 0.5 mol / L NaCl electrolyte. The hydrogen production performance of water electrolysis was studied under simulated industrial water electrolysis conditions.

[0073] The catalyst Mn-MoNi4 / MoO2 prepared in Example 2 was cut into 1×1cm pieces. 2 Geometric areas were used as cathode and anode electrodes, respectively, to assemble a MEA water electrolysis device for two-electrode performance testing. The cathode used a 1 mol / L KOH electrolyte, and the anode used a 1 mol / L KOH + 20 mM / L HMF (i.e., methanol) electrolyte. The hydrogen production performance of water electrolysis was studied under simulated industrial water electrolysis conditions. An alkaline anion exchange membrane was used as the membrane material, and the electrolyte flow rate was 10-20 ml / min. -1 The result is as follows Figure 12 As shown in the figure, small figure a is the polarization curve of Fe-MoNi4 / MoO2(HER+OER), and small figure b is the polarization curve of Mn-MoNi4 / MoO2(HER+HMFOR).

[0074] As shown in the figure, the anion exchange membrane MEA water electrolysis device (HER-OER) assembled with the Fe-MoNi4 / MoO2 catalyst prepared in Example 1 underwent complete water splitting in a 1 mol / L KOH electrolyte at room temperature. The Fe-MoNi4 / MoO2||Fe-MoNi4 / MoO2 MEA device performed well at a current density of 1000 mA·cm⁻¹. −2 The battery voltage was 1.76V. The MEA device (HER-HMFOR) assembled with the catalyst Mn-MoNi4 / MoO2 prepared in Example 2 underwent complete water splitting at room temperature in an electrolyte solution of 1 mol / L KOH + 20 mM / L HMF at the anode and 1 mol / L KOH at the cathode. An alkaline electrolyzer using the catalyst Mn-MoNi4 / MoO2 prepared in Example 2 as both cathode and anode was used at a current density of 1000 mA·cm⁻¹. −2 The battery voltage was 1.82 V. This indicates that the catalysts prepared in Examples 1 and 2 have excellent catalytic activity in the water electrolysis reaction and can be used for hydrogen production under experimental conditions of industrial water electrolysis.

[0075] The component analyses of the above embodiments and comparative examples are summarized in Table 1.

[0076] Table 1:

[0077] The same methods described above were used to perform performance tests on Examples 3 and 4, as well as Comparative Examples 1-4, and the test results of all examples and comparative examples are summarized in Table 2.

[0078] Table 2:

[0079] Table 2 continues:

[0080] It can be seen that the performance of each comparative example is lower than that of Example 1. In Comparative Example 2, the MoNi4 content is too low, the number of active sites is reduced, and thus the performance is worse. In Comparative Example 3, the MoNi4 content is too high, which makes it easy for particles to agglomerate, resulting in insufficient exposure of active sites and thus worsening its performance. In Comparative Example 4, the Fe doping is too high, and the Fe may exist in an undoped form, thus worsening its performance.

[0081] The contents not described in detail in this specification are existing technologies known to those skilled in the art, and will not be elaborated upon here.

[0082] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A metal heterostructure electrocatalyst, characterized in that, The catalyst comprises a heterostructure composed of MoNi4 and MoO2, and a metal element doped in MoNi4 and MoO2, wherein the metal element is selected from iron and / or manganese. Based on the total amount of the catalyst, the amount of MoNi4 is 30-40 mol%, the amount of MoO2 is 40-50 mol%, and the amount of the metal element is 0.1-0.5 mol.

2. The catalyst according to claim 1, wherein, The oxygen element O 1s characteristic peak in the catalyst has three characteristic peaks after peak fitting: the characteristic peak corresponding to the metal-O bond at 530-531 eV, the characteristic peak corresponding to the oxygen vacancy at 531-532 eV, and the characteristic peak corresponding to the oxygen of surface-adsorbed water molecules at 532-533 eV. Based on the total amount of oxygen element, the amount of oxygen vacancy is 25-35%.

3. The catalyst according to claim 1 or 2, wherein, The catalyst is in the form of nanorods with an average diameter of 80-85 nm.

4. The catalyst according to claim 3, wherein, The catalyst also includes a matrix, on which the catalyst is vertically grown; Preferably, the substrate is selected from one or more of nickel mesh, carbon paper, carbon cloth, copper foam, carbonized wood, carbon nanotubes, and nickel fiber paper, with nickel mesh being the most preferred.

5. A method for preparing a metal heterostructure electrocatalyst, characterized in that, The preparation method includes: preparing a mixture containing Ni 2+ A hydrothermal reaction is carried out on a mixed solution of soluble salts of MoO4²⁻ and soluble salts of metal elements to obtain a precursor, and then the precursor is calcined to obtain a catalyst. The metal element is selected from iron and / or manganese, and Ni is present in the mixed solution. 2+ The molar ratio of Ni to MoO4²⁻ is 1:0.5-1.

5. 2+ The molar ratio of the metal element is 1:0.02-0.

25.

6. The preparation method according to claim 5, wherein, The preparation method further includes: adding a matrix to the mixed solution and then carrying out the hydrothermal reaction, wherein the matrix is ​​selected from one or more of nickel mesh, carbon paper, carbon cloth, copper foam, carbonized wood, carbon nanotubes, and nickel fiber paper.

7. The preparation method according to claim 5 or 6, wherein, The hydrothermal reaction is carried out at a temperature of 140-180℃ for 4-8 hours.

8. The preparation method according to claim 5 or 6, wherein, The calcination temperature is 300-600℃, and the time is 1-4 hours; Preferably, the heating rate of the calcination is 2-5℃ / min.

9. The preparation method according to claim 8, wherein, The Ni 2+ The soluble salt is selected from one or more of nickel nitrate, nickel sulfate, nickel chloride and their corresponding hydrates; And / or, the soluble salt of the MoO4²⁻ is selected from sodium molybdate and / or ammonium molybdate and their corresponding hydrates; And / or, the soluble salt of the metal element iron is selected from one or more of ferrous sulfate, ferrous sulfate, ferrous ammonium sulfate, and ferrous chloride and their corresponding hydrates, and the soluble salt of the metal element manganese is selected from one or more of manganese sulfate, manganese chloride, manganese nitrate and their corresponding hydrates.

10. The application of a catalyst according to any one of claims 1-4 or a metal heterostructure electrocatalyst prepared by any one of claims 5-9 in the electrolysis of water to produce hydrogen.

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