Self-supporting transition metal-doped mo-ni alloy electrocatalytic water splitting catalysts, methods of making and applications

Abstract

This invention relates to a self-supporting transition metal-doped Mo-Ni alloy electrocatalytic water splitting catalyst, its preparation method, and its application method, addressing the problems of low reserves and high prices of existing precious metals, as well as the poor catalytic activity of transition metal Mo-Ni alloys in alkaline solutions. By controlling the type and concentration of the transition metal doping and the high-temperature reduction temperature, a transition metal-doped Mo-Ni alloy electrocatalytic water splitting catalyst with a nano-hierarchical structure is prepared. This unique nano-hierarchy improves the utilization rate of the active material and effectively accelerates electron transfer and ion transport pathways. Furthermore, the introduction of transition metal elements into the Mo-Ni alloy significantly improves the adsorption Gibbs free energy of intermediate products, thereby enhancing the catalytic activity of the catalyst material, exhibiting lower overpotentials and faster kinetics. Therefore, the transition metal-doped Mo-Ni alloy exhibits high catalytic activity, faster kinetics, and good cycling stability in the alkaline solution water electrolysis reaction.

Description

Technical Field

[0001] This invention belongs to the fields of materials science and energy technology, and relates to a self-supporting transition metal-doped Mo-Ni alloy electrocatalytic water splitting catalyst, its preparation method, and its application. Background Technology

[0002] Currently, the excessive exploitation and use of fossil fuels have not only led to the rapid depletion of non-renewable energy sources but also caused numerous environmental problems. Therefore, vigorously developing renewable energy to achieve carbon peaking and carbon neutrality is of great significance for further energy transition and the construction of a diversified energy system. To this end, developing efficient energy conversion methods has become a current research hotspot, such as water electrolysis in the field of electrochemistry.

[0003] The electrolysis of water typically requires an additional potential to drive the reaction; therefore, developing efficient and stable catalysts is one of the main ways to improve the efficiency of water electrolysis. Currently, commonly used catalysts are precious metals such as platinum, iridium, and ruthenium, but their low reserves and high prices limit their large-scale application in industrial production. Non-precious metal materials not only overcome the disadvantages of low reserves and high prices associated with precious metals but also exhibit higher catalytic activity in water electrolysis. Among them, Mo-Ni alloys have received widespread attention due to their high metal synergistic effect and tunable electronic structure. However, the electrocatalytic activity of Mo-Ni alloys still lags behind that of precious metal-based catalysts.

[0004] The literature “Taotao Zhang, Xiaowang Liu, et al. Colloidal synthesis of Mo–Nialloy nanoparticles as bifunctional electrocatalysts for efficient overall water splitting[J]. Advanced Materials Interfaces, 2018, 5, 1800359” discloses a method for obtaining Mo through pyrolysis. 0.6 Ni 0.4 A method for preparing nanoparticle electrocatalysts. However, the Mo prepared by this method... 0.6 Ni 0.4 The material exhibits poor performance in electrolyzing water in alkaline solutions. Summary of the Invention

[0005] Technical problems to be solved

[0006] To overcome the shortcomings of existing technologies, this invention proposes a self-supporting transition metal-doped Mo-Ni alloy electrocatalytic water splitting catalyst, its preparation method, and its application method, thereby solving the problem of poor electrocatalytic activity of Mo-Ni alloy electrocatalysts prepared by existing processes in alkaline solutions.

[0007] Technical solution

[0008] The self-supporting transition metal-doped Mo-Ni alloy electrocatalytic water splitting catalyst is characterized by comprising nickel salt, molybdenum salt, doped transition metal, and pH adjuster, wherein the raw material for doped transition metal is various salts containing doped transition metal, and the molar ratio of nickel salt, molybdenum salt, doped transition metal salt, and pH adjuster is 0.5-1.5:0.06-0.2:0-0.1:10; the catalyst material has a macroscopic three-dimensional flower-like structure composed of two-dimensional sheets, and there are many channels in the microscopic sheets, and the material exhibits a nano-hierarchical structure.

[0009] The doped transition metal elements include, but are not limited to, iron or cobalt.

[0010] A method for preparing the self-supporting transition metal-doped Mo-Ni alloy electrocatalytic water splitting catalyst, characterized by the following steps:

[0011] Step 1: Dissolve nickel salt, molybdenum salt, doped transition metal salt and pH adjuster in ultrapure water and stir at room temperature to form a homogeneous mixed solution;

[0012] The molar ratio of the nickel salt, molybdenum salt, doped transition metal salt, and pH adjuster is 0.5–1.5: 0.06–0.2: 0–0.1: 10;

[0013] Among them, the metals in the transition metal salts doped with include, but are not limited to, iron or cobalt;

[0014] Step 2: Heat the prepared mixed solution to react at a temperature of 100–180°C;

[0015] Step 3: After the reaction is complete and the mixture is cooled to room temperature, wash the product several times and collect the precipitate.

[0016] Step 4: The collected precipitate is dried to obtain the self-supporting transition metal-doped Mo-Ni alloy precursor material.

[0017] Step 5: The precursor material is treated in an H2 / Ar mixed atmosphere at a temperature of 500-600℃ to obtain a self-supporting transition metal-doped Mo-Ni alloy material with a nano-hierarchical structure.

[0018] Stir at room temperature for 30–60 minutes in step 1.

[0019] The collected precipitate is obtained by centrifugation or filtration.

[0020] The anions of the nickel salts and doped transition metal salts include, but are not limited to, chlorides, nitrates, or sulfates.

[0021] The molybdenum salt is any molybdate containing cations including ammonium and alkali metal ions.

[0022] The pH adjuster includes, but is not limited to, urea, hexamethylenetetramine, or any reagent that adjusts the pH to alkaline.

[0023] The mixed solution prepared in step 1 is heated to react, using a closed or open reflux system.

[0024] The drying process in step 4 should have the ability to preserve the self-supporting morphology of the product.

[0025] A method for using the self-supporting transition metal-doped Mo-Ni alloy electrocatalytic water splitting catalyst, characterized in that the self-supporting transition metal-doped Mo-Ni alloy electrocatalytic water splitting catalyst is used as a catalyst for the water electrolysis reaction.

[0026] Beneficial effects

[0027] This invention proposes a self-supporting transition metal-doped Mo-Ni alloy electrocatalytic water splitting catalyst, its preparation method, and its application method, addressing the problems of low reserves and high prices of existing precious metals, as well as the poor catalytic activity of transition metal Mo-Ni alloys in alkaline solutions. This method prepares a transition metal-doped Mo-Ni alloy electrocatalytic water splitting catalyst with a nano-hierarchical structure by controlling the type and concentration of the doped transition metal and the high-temperature reduction temperature. This unique nano-hierarchy improves the utilization rate of the active material and effectively accelerates electron transfer and ion transport pathways. Furthermore, the introduction of transition metal elements into the Mo-Ni alloy significantly improves the adsorption Gibbs free energy of intermediate products, thereby enhancing the catalytic activity of the catalyst material, exhibiting lower overpotentials and faster kinetics. Therefore, the transition metal-doped Mo-Ni alloy exhibits high catalytic activity, faster kinetics, and good cycling stability in the alkaline solution water electrolysis reaction.

[0028] The beneficial effects of this invention are:

[0029] 1. Existing Mo-Ni alloy catalysts with large specific surface area and electrocatalytic activity are mostly constructed based on in-situ reaction on nickel foam substrates supplemented by thermal reduction precipitation methods. The resulting products have fixed phases and atomic ratios, making it difficult to further regulate the electrocatalytic activity. This invention uses nickel salts, molybdenum salts, doped transition metal salts, and pH adjusters as raw materials, and employs a hydrothermal-high temperature reduction method. It utilizes precursors with adjustable molybdenum-nickel atomic ratios as raw materials to construct a self-supporting Mo-Ni alloy-based nanocatalyst with a nano-hierarchical structure, which is significantly different from the morphology and composition of existing reported Mo-Ni alloy electrocatalysts. In addition, by changing the reduction treatment temperature (500-600℃), the morphology of the Mo-Ni alloy material can be further controlled, thereby controlling the number of active sites and improving the catalytic activity of the material.

[0030] 2. Based on the aforementioned precursor reaction strategy, this invention constructs a transition metal-doped Mo-Ni alloy electrocatalyst for water splitting with a self-supporting structure containing transition metal doped components. The doping of the transition metal alters the near-neighbor coordination environment of Mo and Ni atoms in the Mo-Ni alloy substrate, significantly affecting the activity of the catalytic sites and improving the adsorption Gibbs free energy of intermediate products, thereby enhancing the electrocatalytic activity of the catalyst and exhibiting lower overpotential and faster kinetics. Under existing optimized synthesis and metal doping conditions, a minimum electrocatalytic oxygen evolution overpotential of 187.18 mV and a Tafel slope of 56.40 mV dec are obtained. -1 It is comparable to commercial IrO2 catalysts (267.66mV, 53.16mV dec). -1 It also outperforms undoped Mo-Ni alloy electrocatalysts of the same type (261.47mV, 88.16mV dec). -1 ). Attached Figure Description

[0031] Figure 1 The flowchart below shows the preparation process of Fe-doped Mo-Ni alloy electrocatalytic water splitting catalyst in Example 1 of this invention. The material is prepared into a solution and subjected to a hydrothermal reaction, followed by a high-temperature reduction reaction under an H2 / Ar atmosphere to obtain the Fe-doped Mo-Ni alloy electrocatalytic water splitting catalyst material.

[0032] Figure 2 Fe-doped Mo-Ni alloy electrocatalyst MNF for water splitting was prepared in Example 1 of this invention. 2.5 X-ray diffraction patterns of CFs; MNF 2.5 The phase of CFs is MoNi4, where 43° and 51° correspond to the (121) and (002) crystal planes, respectively.

[0033] Figure 3Fe-doped Mo-Ni alloy electrocatalyst MNF for water splitting was prepared in Example 1 of this invention. 2.5 Scanning electron microscope images of CFs; MNF 2.5 CFs exhibit a three-dimensional flower-like structure on a macroscopic scale.

[0034] Figure 4 Fe-doped Mo-Ni alloy electrocatalyst MNF for water splitting was prepared in Example 1 of this invention. 2.5 (a) Transmission electron microscopy image and (b) elemental spectrum of energy-dispersive X-ray spectroscopy for CFs; MNF 2.5 The layers of CFs contain many channels, and the elements are evenly distributed.

[0035] Figure 5 Fe-doped Mo-Ni alloy electrocatalyst MNF for water splitting was prepared in Example 1 of this invention. 2.5 Linear voltammetric curves of CFs and IrO2 catalysts in 1M KOH electrolyte; by comparing the overpotential at a certain current density, the catalytic performance of the materials can be determined; the smaller the overpotential, the better the catalytic performance of the material. At a current density of 30 mA / cm²... -2 At that time, MNF 2.5 The overpotential of CFs is only 187.18 mV, which is much lower than the overpotential of IrO2 catalyst (267.66 mV).

[0036] Figure 6 Fe-doped Mo-Ni alloy electrocatalyst MNF for water splitting was prepared in Example 1 of this invention. 2.5 Tafel slope plots of CFs and IrO2 catalysts in 1M KOH electrolyte; the Tafel slope represents the kinetic rate of the catalyst material. The lower the Tafel slope, the faster the kinetics of the material, therefore MNF 2.5 CFs exhibit kinetics similar to those of IrO2 catalyst materials.

[0037] Figure 7 Fe-doped Mo-Ni alloy electrocatalyst MNF for water splitting was prepared in Example 1 of this invention. 2.5 Cyclic voltammetry curves for the stability test of CFs in 1M KOH electrolyte. The stability of the catalyst material can be characterized by comparing the repeatability of the curves before and after multiple cycles. As can be seen from the figure, MNF... 2.5 The CFs material remained in a similar position after 2000 cycles, indicating that the material has excellent catalytic stability. Detailed Implementation

[0038] The present invention will now be further described in conjunction with the embodiments and accompanying drawings:

[0039] Example 1

[0040] Fe-doped Mo-Ni alloy electrocatalytic water splitting catalyst MNF 2.5 The preparation steps for CFs materials are as follows:

[0041] 1) Add 0.8 mmol nickel nitrate hexahydrate, 0.11 mmol ammonium molybdate tetrahydrate, 0.05 mmol ferric nitrate nonahydrate and 10 mmol urea to 36 mL of ultrapure water and stir at room temperature for 30 min to form a homogeneous mixed solution.

[0042] 2) Transfer the mixed solution prepared in step 1) to a 50 mL hydrothermal reactor and place it in a heating oven. React the mixture at 150 °C for 6 h.

[0043] 3) After the hydrothermal reaction in step 2) is completed and cooled to room temperature, centrifuge 3 times at a speed of 6000 rpm for 5 min, and collect the precipitate.

[0044] 4) Place the precipitated reactants collected in step 3) in a freeze dryer and dry them at a freeze-drying temperature of -60°C for 24 hours. After the freeze-drying process is completed and the temperature is reduced to room temperature, collect the freeze-dried product. The freeze-dried product is a precursor material for Fe-doped Mo-Ni alloy.

[0045] 5) Place the precursor material from step 4) in a tube furnace and heat it at 500°C for 2 hours under a mixed H2 / Ar atmosphere. Once the temperature has cooled to room temperature, the Fe-doped Mo-Ni alloy material MNF with a nano-hierarchical structure can be obtained. 2.5 CFs. From Figure 2 The X-ray diffraction pattern shows that MNF 2.5 The CFs material phase is mainly MoNi4 alloy; due to the low Fe doping content, the presence of Fe was not detected. Figure 3 MNF can be seen in the scanning electron microscope image. 2.5 The CFs material exhibits a nano-hierarchical structure, which is further analyzed using transmission scanning electron microscopy (TEM). Figure 4 a) It can be seen that many porous structures exist within the layers constituting the nano-hierarchical structure. Although Fe was not detected in the X-ray diffraction pattern, it was found through... Figure 4 (b) The elemental images of energy-dispersive X-ray spectroscopy show that Fe has been successfully introduced into the MoNi4 alloy matrix material, and the elements are evenly distributed.

[0046] To further verify the above MNF 2.5 The electrochemical performance of CFs materials in alkaline solution was further investigated in step 6), as follows:

[0047] 6) Take the MNF obtained in step 5) 2.5 CFs materials were fabricated into electrode materials for the electrolysis of water in 1M KOH solution to produce oxygen. Figure 5 It can be seen that the catalyst material prepared in this embodiment exhibits excellent oxygen evolution activity in water electrolysis. At a current density of 30 mA cm⁻¹ -2 At that time, its overpotential was only 187.18 mV, far lower than the overpotential of the IrO2 catalyst (267.66 mV). (The text abruptly ends here.) Figure 6 It can be seen that MNF 2.5 CFs materials also exhibit relatively fast kinetic rates, with a Tafel slope of 56.40 mV dec. -1 After 2000 cycles of cyclic voltammetry stability testing, the test curve was basically in the same position as the initial test curve, therefore, the material has good cyclic stability.

[0048] Example 2

[0049] Co-doped Mo-Ni alloy water electrolysis catalyst MNC 1.0 The preparation steps for CFs materials are as follows:

[0050] 1) Add 0.6 mmol nickel nitrate hexahydrate, 0.08 mmol ammonium molybdate tetrahydrate, 0.02 mmol cobalt sulfate heptahydrate and 10 mmol urea to 36 mL of ultrapure water and stir at room temperature for 30 min to form a homogeneous mixed solution.

[0051] 2) Transfer the mixed solution prepared in step 1) to a 50 mL hydrothermal reactor and place it in a heating oven. React the mixture at 120 °C for 3 hours.

[0052] 3) After the hydrothermal reaction in step 2) is completed and cooled to room temperature, centrifuge 3 times at a speed of 6000 rpm for 5 min, and collect the precipitate.

[0053] 4) Place the precipitated reactants collected in step 3) in a freeze dryer and dry them at a freeze-drying temperature of -60°C for 24 hours. After the freeze-drying process is completed and the temperature is reduced to room temperature, collect the freeze-dried product. The freeze-dried product is a precursor material for Co-doped Mo-Ni alloy.

[0054] 5) Place the precursor material from step 4) in a tube furnace and heat it at 550°C for 2 hours under a mixed H2 / Ar atmosphere. Once the temperature has cooled to room temperature, the Co-doped Mo-Ni alloy material MNC with a nano-hierarchical structure can be obtained. 1.0 CFs.

[0055] 6) Take the MNC obtained in step 5) 1.0CFs materials were fabricated into electrode materials for the generation of oxygen in the electrolysis of water using 1M KOH solution. A current density of 30 mA / cm² was achieved with only 238.75 mV. -2 .

[0056] To verify the uniqueness of this preparation method, the present invention also conducted the following experiments:

[0057] Comparative Example 1:

[0058] In this comparative example, no transition metal salt was added in step 1), and the other process conditions were the same as in Example 1. The MN material prepared by this process exhibited the following catalytic activity in 1M KOH solution at a current density of 30 mA cm⁻¹. -2 At that time, its overpotential was 261.47 mV. Therefore, it can be determined that the doping of transition metal salts is the main factor improving the catalytic activity of the material in alkaline solutions for water electrolysis.

[0059] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the scope of the technology disclosed in the present invention, and such modifications or substitutions should all be covered within the scope of protection of the present invention.

Claims

1. A self-supporting transition metal-doped Mo-Ni alloy electrocatalytic water splitting catalyst, characterized in that, The preparation method of the catalyst material is: 0.8 mmol of nickel nitrate hexahydrate, 0.11 mmol of ammonium molybdate tetrahydrate, 0.05 mmol of iron nitrate nonahydrate and 10 mmol of urea are added into 36 mL of ultrapure water, stirred at room temperature for 30 min, and a uniform mixed solution is formed; The prepared mixed solution is transferred to a 50 mL hydrothermal reaction kettle and placed in a heating oven, and hydrothermal reaction is carried out at 150 ℃ for 6 h; After the hydrothermal reaction is completed and cooled to room temperature, centrifugation is carried out 3 times, the centrifugal separation speed is 6000 rpm, the centrifugal time is 5 min, and the precipitated reaction product is collected; The collected precipitated reaction product is placed in a freeze dryer, the freeze-drying temperature is -60 ℃, the freeze-drying time is 24 h, and after the freeze-drying program is completed to room temperature, the freeze-dried product is collected, which is the precursor material of Fe-doped Mo-Ni alloy; The above self-supporting transition metal-doped Mo-Ni alloy electrocatalytic water splitting catalyst is used as an electrolytic water reaction catalyst. The precursor material is placed in a tube furnace, and heated at 500 ℃ for 2 h under H2 / Ar mixed atmosphere, and the Fe-doped Mo-Ni alloy material MNF with nanoscale hierarchical structure is obtained after the temperature is reduced to room temperature 2.5 CFs.

2. A method of using the self-supporting transition metal-doped Mo-Ni alloy electrocatalytic water-splitting catalyst of claim 1, characterized in that, ​

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