Ni-doped ferroferric oxide-molybdenum dioxide composite nano material, preparation method thereof and application of Ni-doped ferroferric oxide-molybdenum dioxide composite nano material as hydrogen and oxygen evolution electrocatalyst

Abstract

The invention discloses a Ni-doped ferroferric oxide-molybdenum dioxide composite nano material, a preparation method thereof and application of the Ni-doped ferroferric oxide-molybdenum dioxide composite nano material as a hydrogen and oxygen evolution electrocatalyst. According to the invention, the Ni-doped ferroferric oxide-molybdenum dioxide composite nano material is successfully prepared through a diversified material preparation process combining hydrothermal synthesis, high-temperature calcination and electro-deposition. The catalyst is a non-noble metal-based composite material, has the advantages of low raw material cost and green and controllable preparation process, and solves the industrial problems of high price and scarce resources of traditional noble metal catalysts (such as Pt and RuO2).

Description

Technical Field

[0001] This invention belongs to the fields of nanomaterials and catalyst preparation research, specifically relating to a Ni-doped iron tetroxide-molybdenum dioxide composite nanomaterial, its preparation method, and its application as an electrocatalyst for hydrogen and oxygen evolution. Background Technology

[0002] With the world facing numerous environmental and energy problems caused by the combustion of fossil fuels, the conversion and utilization of clean energy is urgently needed. Hydrogen energy, due to its high energy density and pollution-free combustion products, has become one of the most promising clean energy sources.

[0003] There are many methods for hydrogen production, among which water electrolysis is the simplest and produces high-purity hydrogen, making it the most suitable method for large-scale hydrogen production. Water electrolysis involves two half-reactions: the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Currently, the main electrocatalysts used in industrial water electrolysis for hydrogen production are platinum (Pt) for excellent performance in HER and ruthenium oxide (RuO2) for excellent performance in OER. However, these precious metals face challenges such as high price, limited resources, and insufficient stability, hindering large-scale industrial application. Therefore, using non-precious metals to prepare catalysts and synthesizing efficient, low-cost, and highly stable catalysts is not only a current research hotspot and challenge in this field, but more importantly, it provides a sound theoretical foundation for the industrial production of non-precious metal catalysts.

[0004] Currently, there are still a series of problems and challenges in the preparation of non-precious metal catalysts. For example, using a single transition metal can lead to insufficient stability and performance. Some composite catalysts, such as the reported NiFe-based catalysts, only show good OER performance, while their HER activity is insufficient, leaving considerable room for improvement. MoFe-based catalyst composites have limited electronic modulation capabilities and insufficient intrinsic activity. NiMo-based catalysts, on the other hand, face challenges such as easy catalyst particle detachment and insufficient catalytic stability.

[0005] Therefore, it is essential to provide a non-precious metal catalyst with high stability that can be used for hydrogen and oxygen evolution. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing Ni-doped iron tetroxide-molybdenum dioxide composite nanomaterials. Through hydrothermal, calcination and electrodeposition techniques, a highly efficient Ni-doped Fe3O4-MoO2 composite nanomaterial electrocatalyst for hydrogen and oxygen evolution can be obtained in just three steps. The required production cost is relatively low, the preparation process is short and the equipment is simple.

[0007] Another objective of this invention is to provide a Ni-doped iron tetroxide-molybdenum dioxide composite nanomaterial, which is prepared using the above-described method.

[0008] The final objective of this invention is to provide an application of Ni-doped iron(III) oxide-molybdenum(II) oxide composite nanomaterials as electrocatalysts for hydrogen and oxygen evolution (HEE). Specifically, the Ni-doped iron(III) oxide-molybdenum(II) oxide composite nanomaterials are used as highly efficient electrocatalysts for HEE in alkaline water splitting reactions. Applications include the use of the Ni-doped iron(III) oxide-molybdenum(II) oxide composite nanomaterials in the oxygen evolution reaction (OER); the use of the Ni-doped iron(III) oxide-molybdenum(II) oxide composite nanomaterials in the hydrogen evolution reaction (HER); and the application of the bifunctional properties of the Ni-doped iron(III) oxide-molybdenum(II) oxide composite nanomaterials at both the anode and cathode of the water splitting reaction, jointly promoting HEE and HE, exhibiting excellent catalytic performance.

[0009] The specific technical solution of this invention is as follows:

[0010] A method for preparing a Ni-doped iron(III) oxide-molybdenum(II) oxide composite nanomaterial includes the following steps:

[0011] 1) Add molybdenum source, nickel source and complexing agent to water, mix well, add nickel foam, perform hydrothermal reaction, and calcine the separated product to obtain the precursor Pre-Ni-MoO2 / NF;

[0012] 2) Dissolve the nickel source and iron source in water and mix them to form an electrolyte. Add the precursor Pre-Ni-MoO2 / NF prepared in step 1) as the working electrode and use a three-electrode system to perform electrodeposition to obtain Ni-doped iron tetroxide-molybdenum dioxide composite nanomaterials.

[0013] In step 1), the molar ratio of the nickel source, molybdenum source, and complexing agent is 20:5:12;

[0014] In step 1), the ratio of nickel source to water is 0.06-0.08 mmol / mL;

[0015] In step 1), the nickel source is selected from soluble nickel salts, preferably nickel nitrate hexahydrate Ni(NO3)2·6H2O;

[0016] In step 1), the molybdenum source is selected from soluble molybdenum salts, preferably ammonium molybdate tetrahydrate H2O. 24 Mo7N6O 24 ·4H2O;

[0017] In step 1), the complexing agent is selected from trisodium citrate dihydrate C6H5Na3O7·2H2O;

[0018] In step 1), the mixing is performed using an ultrasonic stirring process;

[0019] In step 1), the nickel foam needs to be pretreated before use to remove the oxide layer (nickel oxide) that has formed when exposed to air for a long time. The pretreatment method is as follows: first, soak in 6M HCl solution and sonicate for 15 minutes. After that, rinse repeatedly under tap water to remove surface hydrochloric acid. Then, soak in anhydrous ethanol and sonicate for 15 minutes. After that, rinse repeatedly under tap water and rinse 3 times with anhydrous ethanol. Then, dry in a vacuum drying oven for 1-2 hours, and then take it out and seal it for later use.

[0020] In step 1), the nickel foam is cut into 2cm × 3cm pieces for reuse;

[0021] In step 1), the hydrothermal reaction conditions are: hydrothermal reaction at 110℃ for 10 hours;

[0022] In step 1), the hydrothermal process employs a reaction vessel for heating;

[0023] In step 1), after the hydrothermal process is completed, the nickel foam is rinsed with ultrapure water, rinsed with anhydrous ethanol, dried, and then subjected to a calcination process.

[0024] In step 1), the calcination conditions are: calcination at 600℃ for 2 hours; wherein the calcination atmosphere is a mixed atmosphere with Ar volume percentage of 85% and H2 volume percentage of 15%.

[0025] In step 1), the calcination process uses a tube furnace for calcination;

[0026] The molar ratio of the nickel source in step 1) to the nickel and iron sources in step 2) is 2:1-4:1;

[0027] Step 2) The concentration of the iron source in the water is 0.010 mmol / mL;

[0028] In step 2), the nickel source is selected from soluble nickel salts, preferably nickel nitrate hexahydrate Ni(NO3)2·6H2O;

[0029] In step 2), the iron source is selected from soluble iron salts, preferably ferric nitrate nonahydrate Fe(NO3)3·9H2O;

[0030] In step 2), the mixing process involves ultrasonication and stirring.

[0031] In step 2), the electrodeposition refers to: current analysis method - Amperometric it Curve, voltage -3 to -6V, time 300s-1000s; preferably: voltage set to -3V, time set to 700s; the electrodeposition adopts a typical three-electrode system, using CHI660E / CHI760E (Shanghai Chenhua Instrument Co., Ltd.), the reference electrode is an Ag / AgCl electrode, the counter electrode is a carbon rod, and the working electrode is the precursor obtained in step 1).

[0032] In step 2), the applied voltage of -3 to -6V induces a reduction current on the surface of the working electrode (nickel foam), and the Fe in the electrolyte... 3+ and Ni 2+ Under continuous electron movement, the particles migrate to the surface of nickel foam and deposit there, which changes the morphology of the nanoparticles and ultimately forms a Ni-doped Fe3O4-MoO2 composite nanomaterial.

[0033] In step 2), after electrodeposition, the nickel foam is rinsed with ultrapure water, then rinsed with anhydrous ethanol, and then air-dried.

[0034] In steps 1) and 2), the water is ultrapure water.

[0035] The present invention provides a Ni-doped iron tetroxide-molybdenum dioxide composite nanomaterial, which is prepared by the above preparation method and has the morphology of an ultrathin nanosheet with a size of 100 nm ± 20 nm and a large specific surface area.

[0036] This invention employs a hydrothermal, calcination, and electrodeposition process to prepare a practical catalyst with dual functional properties. In the first step, under high temperature and pressure in a reactor, molybdate ions from ammonium molybdate and nickel ions from nickel nitrate undergo a complexation reaction with trisodium citrate dihydrate, resulting in rod-shaped molybdenum-nickel oxide that grows oriented along the crystal planes of nickel foam. Calcination further enhances the Ni content in the molybdenum-nickel oxide... 2+ and Mo 6+ Successfully reduced to Ni 0 The morphology of MoO2 remains that of nanorods; the second step involves electrodeposition, where electrons flowing out of the workstation flow back into the workstation via a three-electrode system constructed of nickel foam; under the influence of an external electric field, Fe in the electrolyte... 3+ and Ni 2+ Metal ions act as electrons - Reverse migration of movement, e - As the nickel foam flows out, the corresponding metal cations flow towards it. At this point, the Fe in the electrolyte... 3+ and Ni 2+ It will break through the limitations of the diffusion layer, continuously migrate to the electrode surface and undergo a reduction reaction, gradually depositing on the surface of Ni / MoO2 nanorods, Fe3+ and Ni 2+ Nucleation occurs again on the surface of the rod-shaped structure. New ions, unable to grow into rods in time, accumulate as sheets, resulting in uniform nanosheets of a certain thickness, thus avoiding excessive accumulation and uneven distribution. The nanosheets are primarily composite nanosheets composed of nickel, iron(III) oxide, and molybdenum dioxide, allowing for better synergistic effects and improved catalytic performance. A lower voltage does not alter the internal structure of the precursor Pre-Ni-MoO2 / NF, preserving excellent OER performance. High-valence metal ions contribute to the hydrogen evolution reaction (HER) at the cathode, providing more active sites. HRTEM, SEAD, and XRD analyses of the Ni-doped Fe3O4-MoO2 composite nanomaterial electrocatalyst confirm its crystal structure. HRTEM reveals distinct lattice fringes, SEAD shows crystal diffraction rings, and XRD results are consistent with HRTEM.

[0037] In the first step of this invention, ultrapure water is selected for hydrothermal treatment. This allows for efficient dissolution of the solute and ensures complete dispersion of the precursor metal ions. Ultrapure water is also chosen as the electrolyte solvent in the second step of electrodeposition because, compared to methanol, ethanol, and DMF, the composite nanosheet structure can grow in a pure water system. Non-pure water solvents may cause the sheet-like morphology to collapse or grow into amorphous particles. Furthermore, ultrapure water can prevent impurity ions from participating in the electrodeposition reaction, reducing unnecessary side reactions. The addition of trisodium citrate dihydrate to the hydrothermal solution in the first step of this invention is because the citrate ion is an excellent multidentate complexing agent, which can react with Ni… 2+ and MoO4 2- It forms stable water-soluble complexes, which can control hydrolysis and reaction rate.

[0038] This invention provides an application of Ni-doped iron(III) oxide-molybdenum dioxide composite nanomaterials as electrocatalysts for hydrogen and oxygen evolution reactions (HEER); including: the application of the Ni-doped iron(III) oxide-molybdenum dioxide composite nanomaterials in the oxygen evolution reaction (OER); the application of the Ni-doped iron(III) oxide-molybdenum dioxide composite nanomaterials as catalysts in the hydrogen evolution reaction (HER); and the application of the Ni-doped iron(III) oxide-molybdenum dioxide composite nanomaterials as catalysts with bifunctional properties at the anode and cathode of the water electrolysis process, jointly promoting hydrogen and oxygen evolution.

[0039] Application of Ni-doped iron(III) oxide-molybdenum(II) oxide composite nanomaterials in alkaline oxygen evolution reaction (OER, oxygen evolution reaction of total water splitting); at 10 mA cm⁻¹ -2 In the application of current density in the oxygen evolution reaction (OER), the overpotential required in 1M KOH electrolyte is only 162 mV, far lower than that of commercially available noble metal catalysts and most non-noble metal catalysts, while at 100 mA cm⁻¹... -2 and 200mA cm-2 The overpotentials at the current densities were 209 mV and 226 mV, respectively, exhibiting excellent oxygen evolution reaction (OER) catalytic activity. The low overpotential overcomes the 4e⁻ degradation. - The slow kinetic barrier of the transfer allows the oxygen evolution reaction of the same level to be driven with less energy supply; at the same time, it can promote the alkaline total hydrolysis decomposition rate, thereby indirectly increasing the hydrogen yield.

[0040] Application of Ni-doped iron(III) oxide-molybdenum(II) oxide composite nanomaterials in the alkaline hydrogen evolution reaction (HER, hydrogen evolution reaction by total water splitting); where, at 10 mA cm⁻¹... -2 Its application in the hydrogen evolution reaction (HER) at current density requires only 32 mV overpotential in 1M KOH electrolyte, which is comparable to commercial noble metal Pt-based catalysts. Furthermore, at 100 mA cm⁻¹... -2 and 200 mA cm -2 The overpotentials at current densities are 97.6 mV and 127 mV, respectively. The catalyst contains a large number of HER active sites, and the large surface area further accelerates hydrogen production. It is expected to replace high-cost precious metal catalysts and become a potential candidate for alkaline total water splitting cathode catalysts.

[0041] Ni-doped iron(III) oxide-molybdenum(II) oxide composite nanomaterials serve as bifunctional catalysts, participating in both the anodic and cathodic reactions of alkaline water splitting, thus promoting overall water splitting. In the alkaline water splitting process, a low potential energy of 1.4441 V is sufficient to reach 10 mA cm⁻¹. -2 Current density; while in alkaline seawater, 1.4447 V can yield 10 mA cm⁻¹. -2 The current density value, obtained at 1.4462 V in a simulated seawater solution, is 10 mA cm⁻¹. -2 The current density value is far superior to other catalysts. This invention provides a Ni-doped Fe3O4-MoO2 composite nanomaterial electrocatalyst for anodic oxidation, and at the same time, the catalyst is designed as a reduction reaction on the cathode to jointly promote alkaline total hydrolysis.

[0042] The design concept of this invention is as follows:

[0043] The inventors discovered that non-precious metal catalysts, commonly transition metal oxides such as iron oxides, molybdenum oxides, and nickel oxides, are widely found in nature, inexpensive, and readily available, possessing great potential to replace precious metal catalysts. Among iron oxides, Fe3O4 exhibits unique electronic and magnetic properties, and when combined with other materials, it produces a strong synergistic effect, promoting improved oxygen evolution performance. MoO2, a molybdenum element, possesses flexible electronic tunability and high conductivity, playing a crucial role in enhancing hydrogen evolution and oxygen evolution performance. Nickel is a good conductor with the ability to rapidly transfer electrons; its high position in the volcano diagram indicates intrinsic HER catalytic activity, and it is easily processed. By preparing structures such as nanosheets, nanowires, and nanorods, the specific surface area can be increased, thereby exposing more active sites and improving catalytic performance.

[0044] This invention designs a practical electrocatalyst based on Ni-doped Fe3O4-MoO2 composite nanomaterials, applicable to OER, HER, and alkaline water splitting. The specific preparation method is as follows: First, a hydrothermal reaction is performed by adding a nickel source, a molybdenum source, and trisodium citrate dihydrate. Water acts as a solvent, undergoing a complexation reaction to form a complex. After calcination, the complex on the surface of the nickel foam is reduced, generating a nanorod-like structure. Second, electrodeposition is performed by adding an external nickel source and an iron source. Utilizing the electron movement applied by an external electric field, Fe in the electrolyte is electrodeposited. 3+ and Ni 2+ Deposited onto the surface of the precursor Pre-Ni-MoO2 / NF nickel foam, a lamellar structure with high activity for HER is formed. The Ni-doped Fe3O4-MoO2 composite nanomaterial electrocatalyst exhibits bifunctional catalytic activity for two competing reactions and can be simultaneously applied to the anode and cathode of alkaline total hydrolysis, synergistically promoting overall water splitting. The preparation method provided by this invention overcomes the problems in the preparation of Ni-Mo-Fe ternary catalysts, such as the inability to effectively construct a stable and uniformly doped Fe3O4-MoO2 structure or the lack of precise control of the Ni nanostructure leading to insufficient exposure of active sites.

[0045] The nanomaterials provided by this invention overcome the shortcomings of existing water electrolysis catalysts and provide a Ni-doped Fe3O4-MoO2 nanocatalyst that not only has excellent bifunctional catalytic performance but also excellent stability. More importantly, it has low preparation cost and is expected to be applied in industrial hydrogen production.

[0046] Compared with existing technologies, this invention employs hydrothermal, calcination, and electrodeposition synthesis strategies, resulting in diverse synthesis approaches and a qualitative improvement in catalyst performance. Furthermore, the synthesized catalyst was applied to two competing reactions in alkaline water electrolysis, both exhibiting excellent catalytic properties, achieving dual-function application. The long-term stability of the material was tested under constant current. The hydrogen and oxygen produced by water electrolysis can serve as energy sources for other industrial production processes and provide electricity for the resynthesis of the catalyst, achieving a green circular industrial chain. Attached Figure Description

[0047] Figure 1 This is a scanning electron microscope image of the Ni-doped Fe3O4-MoO2 composite nanomaterial electrocatalyst Ni-Fe3O4-MoO2 / NF prepared in Example 1;

[0048] Figure 2 This is a transmission electron microscope (TEM) image of the Ni-doped Fe3O4-MoO2 composite nanomaterial electrocatalyst Ni-Fe3O4-MoO2 / NF prepared in Example 1.

[0049] Figure 3 The image shows an HRTEM image of the Ni-doped Fe3O4-MoO2 composite nanomaterial electrocatalyst Ni-Fe3O4-MoO2 / NF prepared in Example 1.

[0050] Figure 4 SAED image of Ni-Fe3O4-MoO2 / NF, the Ni-doped Fe3O4-MoO2 composite nanomaterial electrocatalyst prepared in Example 1;

[0051] Figure 5 The mapping diagram of Ni-Fe3O4-MoO2 / NF, the Ni-doped Fe3O4-MoO2 composite nanomaterial electrocatalyst prepared in Example 1;

[0052] Figure 6 The XRD diffraction pattern of the Ni-doped Fe3O4-MoO2 composite nanomaterial electrocatalyst Ni-Fe3O4-MoO2 / NF prepared in Example 1 is shown below.

[0053] Figure 7 Raman spectroscopy for the Ni-doped Fe3O4-MoO2 composite nanomaterial electrocatalyst Ni-Fe3O4-MoO2 / NF prepared in Example 1;

[0054] Figure 8 XPS image of Ni-Fe3O4-MoO2 / NF, the Ni-doped Fe3O4-MoO2 composite nanomaterial electrocatalyst prepared in Example 1;

[0055] Figure 9This is a scanning electron microscope image of the precursor Pre-Ni-MoO2 / NF prepared in Example 1;

[0056] Figure 10 Scanning electron microscope image of the Ni-MoO2 / NF control sample prepared in Comparative Example 1;

[0057] Figure 11 Scanning electron microscope image of the Fe3O4-MoO2 / NF control sample prepared in Comparative Example 2;

[0058] Figure 12 LSV polarization curves (OER) of the Ni-doped Fe3O4-MoO2 composite nanomaterial electrocatalyst Ni-Fe3O4-MoO2 / NF, precursor Pre-Ni-MoO2 / NF, Ni-MoO2 / NF comparative sample prepared in Comparative Example 1, and Fe3O4-MoO2 / NF comparative sample prepared in Comparative Example 2.

[0059] Figure 13 The LSV polarization curves (HER) of the Ni-doped Fe3O4-MoO2 composite nanomaterial electrocatalyst Ni-Fe3O4-MoO2 / NF, the precursor Pre-Ni-MoO2 / NF, the Ni-MoO2 / NF comparative sample prepared in Comparative Example 1, and the Fe3O4-MoO2 / NF comparative sample prepared in Comparative Example 2 are shown.

[0060] Figure 14 The LSV polarization curve (HER) of the Ni-doped Fe3O4-MoO2 composite nanomaterial electrocatalyst prepared in Example 1 during the complete water splitting process at KOH.

[0061] Figure 15 LSV polarization curves (OER) of the comparative samples prepared in Example 2 with different Ni:Fe ratios of 1:1, 2:1, 3:1, and 4:1.

[0062] Figure 16 The LSV polarization curves (HER) of the comparative samples prepared in Example 2 with different Ni:Fe ratios of 1:1, 2:1, 3:1, and 4:1 are shown.

[0063] Figure 17 The polarization curves (OER) of the control samples prepared by electrodeposition with different solvents as shown in Comparative Example 3 are as follows: methanol, ethanol, DMF, and ultrapure water.

[0064] Figure 18 The polarization curves (HER) of the control samples prepared by electrodeposition with different solvents as shown in Comparative Example 3 are as follows: methanol, ethanol, DMF, and ultrapure water.

[0065] Figure 19 The polarization curves (OER) of the control samples prepared in Comparative Example 4 with different electrodeposition times are shown. The control samples have electrodeposition times of 300s, 700s, and 1500s.

[0066] Figure 20 The polarization curves (HER) of the control samples prepared for different electrodeposition times in Comparative Example 4 are shown. The control samples were prepared for electrodeposition times of 300s, 700s, and 1500s. Detailed Implementation

[0067] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0068] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available.

[0069] Unless otherwise specified in the embodiments, the techniques or conditions described in the literature in this field or in accordance with the product manual may be followed.

[0070] Example 1

[0071] A method for preparing a Ni-doped iron(III) oxide-molybdenum(II) oxide composite nanomaterial includes the following steps:

[0072] 1) Pretreatment of nickel foam oxide layer: The nickel foam was purchased from Cyber ​​Electrochemical Materials Network with a porosity of 97.2%. It was cut into rectangles of 2cm×3cm and placed in a beaker. 6M HCl solution was added until it was completely submerged. Then, it was ultrasonically treated for 15min. After ultrasonic treatment, the hydrochloric acid was poured out and the surface of the nickel foam was repeatedly rinsed under a tap to remove residual HCl. Ethanol was added again for immersion and ultrasonic treatment for 15min. After completion, it was repeatedly rinsed under ultrapure water and then rinsed 3 times with anhydrous ethanol to completely remove the nickel foam oxide layer. After that, it was placed in a vacuum drying oven at 60℃ for 2h, and then removed and sealed for later use.

[0073] 2) Pre-Ni-MoO2 / NF precursor: 1 mmol nickel nitrate hexahydrate, 0.25 mmol ammonium molybdate tetrahydrate, 0.6 mmol trisodium citrate dihydrate and 15 mL ultrapure water were added to a beaker and ultrasonically stirred to form a homogeneous mixture. The mixture was then transferred to a reaction vessel and hydrothermally reacted at 110℃ for 10 h. The nickel foam was rinsed with ultrapure water and anhydrous ethanol, dried, and finally calcined at 600℃ for 2 h in an Ar / H2 atmosphere (85% Ar and 15% H2 by volume). The nanorod structure was determined by scanning electron microscopy, and the product was labeled as: Pre-Ni-MoO2 / NF.

[0074] 3) Preparation of Ni-doped iron(III) oxide-molybdenum(II) oxide composite nanomaterials: 0.5 mmol of ferric nitrate nonahydrate, 1.5 mmol of nickel nitrate hexahydrate, and 50 mL of ultrapure water were added to a beaker and ultrasonically stirred to form a homogeneous electrolyte. The electrolyte was then transferred to a clean three-electrode electrolytic cell, with an Ag / AgCl electrode as the reference electrode, a carbon rod as the counter electrode, and the Pre-Ni-MoO2 / NF precursor as the working electrode. A constant voltage of -3 V was applied for 700 s using current analysis. After electrodeposition, the nickel foam was removed, rinsed sequentially with ultrapure water and anhydrous ethanol, and allowed to air dry. The sheet-like structure was determined using scanning electron microscopy, and the product was labeled as Ni-Fe3O4-MoO2 / NF.

[0075] Figure 1 The image shows a scanning electron microscope (SEM) image of the Ni-doped Fe3O4-MoO2 composite nanomaterial electrocatalyst Ni-Fe3O4-MoO2 / NF prepared in Example 1. The morphology shows the interconnection of ultrathin nanosheets, and the staggered arrangement between the sheets greatly increases the electrocatalytic area and exposes more active sites.

[0076] Figure 2 The image shows a transmission electron microscope (TEM) image of the Ni-doped Fe3O4-MoO2 composite nanomaterial electrocatalyst Ni-Fe3O4-MoO2 / NF prepared in Example 1. This image confirms the actual distribution of nanosheets on the catalyst surface and matches the scanning electron microscope (SEM) image.

[0077] Figure 3 The image shows an HRTEM image of the Ni-doped Fe3O4-MoO2 composite nanomaterial electrocatalyst Ni-Fe3O4-MoO2 / NF prepared in Example 1. The HRTEM image shows obvious lattice fringes, indicating that the material has crystalline structural features.

[0078] Figure 4The image shows the SAED pattern of the Ni-doped Fe3O4-MoO2 composite nanomaterial electrocatalyst Ni-Fe3O4-MoO2 / NF prepared in Example 1. The diffuse ring diffraction pattern in the SAED pattern corresponds to the HRTEM, further confirming the characteristics of the crystal structure.

[0079] Figure 5 The image shows the mapping diagram of the Ni-doped Fe3O4-MoO2 composite nanomaterial electrocatalyst Ni-Fe3O4-MoO2 / NF prepared in Example 1. The elemental spots in the mapping diagram are uniformly distributed on the nanosheet structure.

[0080] Figure 6 The XRD diffraction patterns of the Ni-doped Fe3O4-MoO2 composite nanomaterial electrocatalyst Ni-Fe3O4-MoO2 / NF prepared in Example 1 are shown. The samples were prepared based on nickel foam, and Ni-Fe3O4-MoO2 powder was collected by ultrasound and XRD tests were performed to confirm that the catalyst has a crystalline structure and contains three substances: Ni, Fe3O4, and MoO2.

[0081] Figure 7 The image shows the Raman spectrum of the Ni-doped Fe3O4-MoO2 composite nanomaterial electrocatalyst Ni-Fe3O4-MoO2 / NF prepared in Example 1. The Fe-O / Mo-O vibrational peak was detected at 534 cm⁻¹. -1 At this point, the Mo=O vibration peak is at 692 cm⁻¹. -1 MoO4 was detected. 2- The vibration peak was detected at Mo=Mo.

[0082] Figure 8 The XPS plot of the Ni-doped Fe3O4-MoO2 composite nanomaterial electrocatalyst Ni-Fe3O4-MoO2 / NF prepared in Example 1 is shown. The XPS peak fitting results investigated the presence of Ni in the catalyst. 2+ and Ni 0 Fe element is in the form of Fe 3+ Fe 2+ and Fe 0 The Mo element exists in the form of Mo. 4+ Mo 6+ exist;

[0083] Figure 9 The image shown is a scanning electron microscope (SEM) image of the precursor Pre-Ni-MoO2 / NF prepared in Example 1. It shows a nanorod structure, which, compared to the nanosheet structure on the surface of Ni-Fe3O4-MoO2 / NF, indicates that the electrodeposition process effectively modified the morphology and properties of the precursor Pre-Ni-MoO2 / NF.

[0084] Comparative Example 1

[0085] The preparation method of Ni-MoO2 / NF control sample includes the following steps:

[0086] Preparation of Ni-MoO2 / NF: The first two steps of the preparation process are the same as in Example 1. The third step is to add 1.5 mmol of nickel nitrate hexahydrate and 50 mL of ultrapure water to a beaker, stir and mix evenly with ultrasonication to form an electrolyte, transfer it into a clean three-electrode electrolytic cell, connect the reference electrode - Ag / AgCl electrode, the counter electrode - carbon rod, and the working electrode - precursor Pre-Ni-MoO2 / NF. Using current analysis, a constant voltage of -3 V is set and maintained for 700 s. After electrodeposition, the nickel foam is taken out, rinsed with ultrapure water and anhydrous ethanol in sequence, and dried naturally. The product is labeled as: Ni-MoO2 / NF.

[0087] Figure 10 The image shows a scanning electron microscope (SEM) image of the Ni-MoO2 / NF control sample prepared in Comparative Example 1. The main structure is a nanorod structure, mixed with a small amount of nanosheet structure. The surface of the nanorods is covered with fine nanoparticles, which is a significant modification of the structure compared to the structure before electrodeposition.

[0088] Comparative Example 2

[0089] The preparation method of Fe3O4-MoO2 / NF control sample includes the following steps:

[0090] Preparation of Fe3O4-MoO2 / NF: The first two steps of the preparation are the same as in Example 1. The third step is to add 0.5 mmol of ferric nitrate nonahydrate and 50 mL of ultrapure water to a beaker, and mix them evenly by ultrasonic stirring to form an electrolyte. The electrolyte is then transferred to a clean three-electrode electrolytic cell, and the reference electrode - Ag / AgCl electrode, the counter electrode - carbon rod, and the working electrode - precursor Pre-Ni-MoO2 / NF are connected. The current analysis method is used, and a constant voltage of -3 V is set for 700 s. After electrodeposition, the nickel foam is removed, rinsed with ultrapure water and anhydrous ethanol in sequence, and then air-dried. The product is labeled as: Fe3O4-MoO2 / NF.

[0091] Figure 11 The scanning electron microscope image of the Fe3O4-MoO2 / NF control sample prepared in Comparative Example 2 shows that the overall structure is a nanorod structure. The surface of the nanorods is composed of tightly packed fine nanoparticles with a large number of pores between the particles. The surface roughness and porosity of the material are significantly improved compared with those before electrodeposition.

[0092] Example 2

[0093] The preparation method of Ni-Fe3O4-MoO2 / NF with different Ni and Fe ratios is the same as in Example 1, except that the Ni and Fe ratios in the electrodeposition are changed. The Ni and Fe ratios are 1:1, 2:1, 3:1, and 4:1, respectively.

[0094] Comparative Example 3

[0095] The preparation method of Ni-Fe3O4-MoO2 / NF involves electrodeposition using different solvents, following the same steps as in Example 1, except for the type of electrodeposition solvent. The solvents used were methanol, ethanol, DMF, and ultrapure water.

[0096] Comparative Example 4

[0097] The Ni-Fe3O4-MoO2 / NF was prepared by electrodeposition for different times, following the same steps as in Example 1, except that the electrodeposition time was changed. The electrodeposition times were 300s, 700s, and 1500s.

[0098] Application Example 1

[0099] The application of a Ni-doped iron(III) oxide-molybdenum(II) oxide composite nanomaterial as an electrocatalyst Ni-Fe3O4-MoO2 / NF in OER is as follows:

[0100] The catalysts prepared in the above embodiments and comparative examples were cut into 1cm × 1cm pieces before testing; they were clamped with electrode clips to serve as working electrodes; and the OER performance of the samples was tested. The same equipment as electrodeposition—electrochemical workstations CHI660E and CHI760E—was used, with a typical three-electrode system: Ag / AgCl electrode as the reference electrode, Pt sheet as the counter electrode, and the catalysts prepared in the above embodiments and comparative examples as the working electrode; 1M KOH solution was used as the electrolyte, and linear sweep voltammetry (LSV) was performed. The obtained OER polarization curves are shown in [the figures]. Figure 12 In the study, the Ni-doped Fe3O4-MoO2 composite nanomaterial electrocatalyst for the oxygen evolution reaction (OER) of Ni-Fe3O4-MoO2 / NF was 10 mA cm⁻¹. -2 The current density requires only 162 mV overpotential in 1 M KOH electrolyte, and only low potentials of 209 mV and 226 mV are needed to provide 100 mA cm⁻¹. -2 200 mA cm -2The current density is significantly lower than that of commercially available precious metal catalysts and most non-precious metal catalysts. The η10 values ​​for Pre-Ni-MoO2, Ni-MoO2 / NF, and Fe3O4-MoO2 / NF are 254 mV, 226 mV, and 195 mV, respectively, while the η100 values ​​are 351 mV, 287 mV, and 237 mV, respectively. Furthermore, the difference in current density provided at the same potential becomes more pronounced with increasing voltage.

[0101] Application Example 2

[0102] The application of a Ni-doped iron(III) oxide-molybdenum(II) oxide composite nanomaterial as an electrocatalyst in HER is as follows:

[0103] The catalysts prepared in the examples and comparative examples were cut into 1cm × 1cm pieces before testing; they were clamped with electrode clips to serve as working electrodes; the HER performance of these samples was then tested. The same equipment used for electrodeposition—electrochemical workstations CHI660E and CHI760E—was employed, with a typical three-electrode system: Ag / AgCl electrode as the reference electrode, a carbon rod as the counter electrode, and the catalysts prepared in the examples and comparative examples as the working electrode; 1M KOH solution was used as the electrolyte, and linear sweep voltammetry (LSV) was used for testing. The obtained HER polarization curves are shown below. Figure 13 In the process, the hydrogen evolution reaction HER occurs at 10 mA cm⁻¹. -2 The current density and overpotential of each catalyst in 1M KOH electrolyte, namely Pre-Ni-MoO2, Ni-MoO2 / NF, and Fe3O4-MoO2 / NF, were η10: 65 mV, 37 mV, and 49 mV, respectively; and η100: 167 mV, 134 mV, and 160 mV, respectively. Ni-Fe3O4-MoO2 / NF exhibited the best HER performance, requiring only 32 mV overpotential (η) to reach 10 mA·cm⁻¹. -2 An overpotential (η) of 97.6 mV can reach 100 mA·cm. -2 200 mA cm -2 The overpotential at the current density is 127 mV.

[0104] Application Example 3

[0105] Application of a Ni-doped iron(III) oxide-molybdenum(II) oxide composite nanomaterial as an electrocatalyst in alkaline water hydrolysis:

[0106] The catalysts according to the examples were cut into two pieces (1 cm × 1 cm) to serve as the anode and cathode for the total water splitting process. The total water splitting LSV performance of these samples was tested. On electrochemical workstations CHI660E and CHI760E, a standard three-electrode system was used with an Ag / AgCl electrode as the reference electrode. Two samples of the catalysts prepared in the examples and comparative examples were used as the anode and cathode, respectively. A 1 M KOH electrolyte was prepared, and the total water splitting polarization curves were obtained by linear sweep voltammetry (LSV). Figure 14 It exhibits excellent hydrogen and oxygen evolution characteristics, also at 10 mA cm⁻¹. -2 At the specified current density, only 1.4441 V is required in alkaline solution; in alkaline seawater, 1.4447 V yields 10 mA cm⁻¹. -2 Current density value; 1.4462 V yields 10 mA / cm² in simulated seawater solution. -2 The current density values ​​are consistent with the results of Application Example 1 and Application Example 2.

[0107] This invention utilizes an external molybdenum source, a nickel source, and a complexing agent, ultrasonically dissolved in water to construct a complex electrolyte that controls the ordered deposition of metal ions. This electrolyte is then subjected to hydrothermal treatment and calcination at 600°C for 2 hours to obtain a precursor, Pre-Ni-MoO2 / NF. This precursor is used as a novel working electrode for electrodeposition in an electrolyte containing an external iron and nickel source and ultrapure water to obtain a Ni-doped Fe3O4-MoO2 composite nanomaterial electrocatalyst. This invention utilizes Mo... 4+ and Ni 2+ The constructed complex system promotes the growth of nanorods; regulates Fe 3+ and Ni 2+ The deposition rate and order promote the growth of nanosheets, eventually becoming crystalline nanocatalysts. Ni-doped iron tetroxide-molybdenum dioxide composite nanomaterials exhibit excellent bifunctional properties, serving as both an anode for the oxygen evolution reaction and a cathode for the hydrogen evolution reaction. The two can work together to coordinate the application of alkaline water splitting, resulting in excellent catalytic performance for simultaneous hydrogen and oxygen evolution.

[0108] The applications of Ni-Fe3O4-MoO2 / NF electrocatalysts with different Ni / Fe ratios in OER and HER are as follows:

[0109] The catalysts prepared in Examples 1 and 2 were cut into 1cm × 1cm pieces before testing; these were then clamped with electrode clips to serve as working electrodes; the OER and HER performance of these samples were then tested. The same equipment used for electrodeposition—an electrochemical workstation CHI660E and CHI760E—was employed, with a typical three-electrode system: an Ag / AgCl electrode as the reference electrode, a carbon rod as the counter electrode, and the catalysts prepared in the above examples and comparative examples as the working electrode; 1M KOH solution was used as the electrolyte, and linear sweep voltammetry (LSV) was used for testing. The OER of the oxygen evolution reaction was measured at 10 mA cm⁻¹. -2 The current density and overpotential of each catalyst in a 1M KOH electrolyte, i.e., the η10 of electrodeposition solutions with Ni:Fe ratios of 1:1, 2:1, 3:1, and 4:1, are 177 mV, 174 mV, 162 mV, and 181 mV, respectively, and the η100 are 210 mV, 218 mV, 209 mV, and 220 mV, respectively. The hydrogen evolution reaction (HER) at 10 mA cm⁻¹... -2 The current density and overpotential of each catalyst in the 1M KOH electrolyte, i.e., the HER η10 of the hydrogen evolution reaction with Ni:Fe ratios of 1:1, 2:1, 3:1, and 4:1 were 49 mV, 38 mV, 32 mV, and 39 mV, respectively, and the η100 were 167 mV, 105 mV, 97.6 mV, and 119 mV, respectively. The obtained OER and HER polarization curves are shown in [the table / image ... Figure 15 , Figure 16 From the results, it can be concluded that the electrodeposition performance was best when the Ni:Fe ratio was 3:1 in Example 1. Catalysts prepared with other ratios were not subjected to further experiments.

[0110] The preparation methods of Ni-Fe3O4-MoO2 / NF using different solvents for electrodeposition and their application as electrocatalysts in OER and HER are as follows:

[0111] The catalysts prepared in Example 1 and Comparative Example 3 were cut into 1cm × 1cm pieces before testing; they were then clamped with electrode clips to serve as working electrodes; the OER and HER performance of these samples were then tested. The same equipment used for electrodeposition—electrochemical workstations CHI660E and CHI760E—was employed, with a typical three-electrode system: Ag / AgCl electrode as the reference electrode, a carbon rod as the counter electrode, and the catalysts prepared in the above examples and comparative examples as the working electrode; 1M KOH solution was used as the electrolyte, and linear sweep voltammetry (LSV) was used for testing. The obtained OER and HER polarization curves are shown in [images / descriptions]. Figure 17 , Figure 18 In the OER (oxygen evolution reaction), the value is 10 mA cm⁻¹. -2The current density and overpotential of each catalyst in the 1M KOH electrolyte, i.e., the η10 of the electrodeposition solutions using methanol, ethanol, DMF, and ultrapure water are 180 mV, 186 mV, 193 mV, and 162 mV, respectively, and the η100 are 242 mV, 231 mV, 236 mV, and 209 mV, respectively. The hydrogen evolution reaction (HER) at 10 mA cm⁻¹... -2 The current density and overpotential of each catalyst in the 1M KOH electrolyte, i.e., the η10 of the hydrogen evolution reaction HER using methanol, ethanol, DMF, and ultrapure water as electrodeposition solutions, were 88 mV, 100 mV, 92 mV, and 32 mV, respectively, and the η100 were 236 mV, 262 mV, 247 mV, and 97.6 mV, respectively. It can be concluded that ultrapure water as a solvent has the best performance for electrodeposition of OER and HER, and catalysts prepared with other solvents were not subjected to further experiments.

[0112] The preparation methods of Ni-Fe3O4-MoO2 / NF and the application of electrocatalysts with different electrodeposition times in OER and HER are as follows:

[0113] The catalysts prepared in Examples and Comparative Example 4 were cut into 1cm × 1cm pieces before testing; they were then clamped with electrode clips to serve as working electrodes; the OER and HER performance of these samples were then tested. The same equipment used for electrodeposition—electrochemical workstations CHI660E and CHI760E—was employed, with a typical three-electrode system: Ag / AgCl electrode as the reference electrode, a carbon rod as the counter electrode, and the catalysts prepared in the examples and comparative examples as the working electrode; 1M KOH solution was used as the electrolyte, and linear sweep voltammetry (LSV) was used for testing. The obtained OER and HER polarization curves are shown in [Figure / Table / Image]. Figure 19 , Figure 20 In the OER (oxygen evolution reaction), the value is 10 mA cm⁻¹. -2 The current density and overpotential of each catalyst in 1M KOH electrolyte, i.e., η10 for electrodeposition times of 300s, 700s, and 1500s, are 172 mV, 162 mV, and 168 mV, respectively, and η100 are 200 mV, 209 mV, and 211 mV, respectively. The hydrogen evolution reaction (HER) at 10 mAcm⁻¹... -2 The current density and overpotential of each catalyst in 1M KOH electrolyte, i.e., η10 for electrodeposition times of 300s, 700s, and 1500s, were 57 mV, 32 mV, and 61 mV, respectively, and η100 were 151 mV, 97.6 mV, and 157 mV, respectively. In comparison, the HER performance was superior with electrodeposition at 700s. Catalysts prepared at other electrodeposition times were not subjected to further experiments.

[0114] The above description of the embodiments is intended to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing Ni-doped iron(III) oxide-molybdenum(II) oxide composite nanomaterials, characterized in that, The preparation method includes the following steps: 1) Add molybdenum source, nickel source and complexing agent to water, mix well, add nickel foam, perform hydrothermal reaction, and calcine the separated product to obtain the precursor Pre-Ni-MoO2 / NF; 2) Dissolve the nickel source and iron source in water and mix them to form an electrolyte. Add the precursor Pre-Ni-MoO2 / NF prepared in step 1) as the working electrode and use a three-electrode system to perform electrodeposition to obtain Ni-doped iron tetroxide-molybdenum dioxide composite nanomaterials.

2. The preparation method according to claim 1, characterized in that, In step 1), the molar ratio of the nickel source, molybdenum source and complexing agent is 20:5:

12.

3. The preparation method according to claim 1, characterized in that, In step 1), the complexing agent is selected from trisodium citrate dihydrate.

4. The preparation method according to claim 1, characterized in that, In step 1), the hydrothermal reaction conditions are: hydrothermal reaction at 110℃ for 10 hours.

5. The preparation method according to claim 1, characterized in that, In step 1), the calcination conditions are: calcination at 600℃ for 2 hours; wherein the calcination atmosphere is a mixed atmosphere with Ar volume percentage of 85% and H2 volume percentage of 15%.

6. The preparation method according to claim 1, characterized in that, The ratio of the amount of nickel source mentioned in step 1) to the amount of nickel source and iron source mentioned in step 2) is 2:1-4:

1.

7. The preparation method according to claim 1, characterized in that, In step 2), the electrodeposition refers to: current analysis method - Amperometric it Curve, voltage -3 to -6V, time 300s-1000s; the electrodeposition adopts a typical three-electrode system with Ag / AgCl electrode as reference electrode, carbon rod as counter electrode, and precursor of step 1) as working electrode.

8. A Ni-doped iron tetroxide-molybdenum dioxide composite nanomaterial, prepared by the preparation method according to any one of claims 1-7, wherein the morphology of the Ni-doped iron tetroxide-molybdenum dioxide composite nanomaterial is an ultrathin nanosheet with a size of 100 nm ± 20 nm.

9. The application of the Ni-doped iron tetroxide-molybdenum dioxide composite nanomaterial as described in claim 8 as an electrocatalyst for hydrogen and oxygen evolution; characterized in that, The Ni-doped iron tetroxide-molybdenum dioxide composite nanomaterial is used in the oxygen evolution reaction (OER), the hydrogen evolution reaction (HER), and / or the total water splitting process.

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