Rare earth element doped carbon coated molybdenum phosphide bifunctional catalyst and preparation method thereof

Abstract

The invention belongs to the technical field of electro-catalysis and energy materials, and particularly relates to a rare earth element-doped carbon-coated molybdenum phosphide bifunctional catalyst and a preparation method thereof. The method comprises the following steps: 1) screening preparation raw materials, wherein the raw materials comprise rare earth metal salt, ammonium heptamolybdate tetrahydrate, a carbon source and a phosphorus-containing chelating agent; 2) weighing the raw materials obtained in the step 1) in proportion, uniformly mixing in a certain amount of deionized water, and then drying by distillation at the temperature of 60-100 DEG C to obtain a pre-product; and 3) grinding the pre-product obtained in the step 2), and performing pyrolysis treatment at 800-1000 DEG C to obtain the rare earth metal doped carbon coated molybdenum phosphide bifunctional catalyst. The introduction of the phosphorus-containing chelating agent effectively realizes uniform doping of rare earth elements into molybdenum phosphide crystal lattices. Due to introduction of rare earth elements, redistribution of surface charge density of the molybdenum phosphide is realized, the adsorption energy of intermediate adsorbates in the reaction is optimized, and the rare earth elements serve as reaction active sites to further activate the oxygen evolution activity of the molybdenum phosphide.

Description

Technical Field

[0001] This application belongs to the field of new energy materials and electrocatalysis technology, specifically relating to rare earth element-doped carbon-coated molybdenum phosphide bifunctional catalysts and their preparation methods. Background Technology

[0002] Hydrogen energy, with its advantages of being clean, renewable, and having high energy density, is a promising alternative to traditional fossil fuels. Hydrogen gas can be produced through water electrolysis. Water electrolysis consists of two half-reactions: the hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction (OER) at the anode, both of which require significant overpotentials to drive their multi-electron transfer processes. Therefore, constructing efficient catalysts to reduce overpotentials and improve overall energy conversion efficiency is urgently needed. Although Pt-based compounds and Ir / Ru-based oxides are recognized as the most efficient HER and OER catalysts, respectively, their low abundance, high cost, and limited bifunctional activity hinder their practical application.

[0003] Transition metal phosphides have shown great potential in alkaline water electrolysis due to their excellent conductivity and catalytic activity. Among them, molybdenum phosphide has been extensively studied due to its low cost, abundant reserves, and platinum-like electronic structure. However, its catalytic activity remains unsatisfactory due to its low active site content and excessively strong bonding ability with adsorbed hydrogen. Furthermore, most reported molybdenum phosphides currently exhibit only HER activity; their OER activity has been rarely studied to date.

[0004] Rare earth metals, due to their low electronegativity, unique f-block orbitals, and multiple valence states, can effectively modulate the electronic structure of catalyst surfaces. Studies have shown that the significant electronegativity difference between rare earth metals and transition metals can induce electron transfer between host and guest metal atoms, thereby effectively controlling the adsorption energy of intermediates on the catalyst. However, the ionic radii of rare earth metals are much larger than those of transition metals, making it difficult for them to insert into the transition metal phosphide lattice. Furthermore, the mechanism by which rare earth doping modulates molybdenum phosphide remains unclear and requires further development. Therefore, it is necessary to design a simple and controllable preparation method to synthesize rare earth-doped molybdenum phosphide electrocatalysts that simultaneously possess HER and OER catalytic activities. Summary of the Invention

[0005] The technical problem to be solved by the present invention is: in order to overcome the shortcomings of the prior art, the present invention provides a rare earth element-doped carbon-coated molybdenum phosphide bifunctional catalyst and its preparation method. The method provided by the present invention is simple and easy to operate, and the prepared rare earth element-doped molybdenum phosphide catalyst has good hydrogen evolution and oxygen evolution catalytic activity at the same time.

[0006] The technical solution adopted by the present invention to solve its technical problems is as follows: On the one hand, the present invention provides a preparation method of a rare earth metal-doped carbon-coated molybdenum phosphide bifunctional catalyst, comprising the following steps: 1) Screening raw materials for preparation, and the raw materials include rare earth metal salts, ammonium heptamolybdate tetrahydrate, carbon sources, and phosphorus-containing chelating agents; 2) Weighing rare earth metal salts, ammonium heptamolybdate tetrahydrate, phosphorus-containing chelating agents, and carbon sources in proportion, and uniformly mixing them in a certain amount of deionized water, and then evaporating to dryness at a temperature of 60-100 °C to obtain a pre-product; 3) Grinding the pre-product obtained in step 2) and performing pyrolysis treatment at a temperature of 800-1000 °C to obtain a rare earth metal-doped carbon-coated molybdenum phosphide bifunctional catalyst.

[0007] Further, the rare earth metal salts in step 1) include nitrates, acetylacetonates, and acetates of lanthanum, cerium, and ytterbium; the carbon sources include melamine, glucose, dicyandiamide, and sucrose; the phosphorus-containing chelating agents include phytic acid, phosphoric acid, and organic phosphonic acid.

[0008] Further, in step 2), the rare earth metal salts, ammonium heptamolybdate tetrahydrate, and phosphorus-containing chelating agents are fed in an atomic molar ratio of RE:Mo:P = x mmol:(1-x) mmol:1 mmol (0 < x ≤ 0.1), and the ratio of the rare earth metal salt to the carbon source is 1 mmol:(1-10) mmol; the ratio of the rare earth metal salt to deionized water is 1 mmol:(20-100) mL.

[0009] Further, in step 2), the uniform mixing and evaporation to dryness means adding all raw materials in proportion to a beaker containing a certain amount of deionized water, fully mixing by magnetic stirring, then raising the temperature of the water bath from room temperature to 60-100 °C and continuously stirring until completely evaporated to dryness to obtain a pre-product.

[0010] Further, the grinding of the pre-product in step 3) means placing the pre-product obtained by evaporation to dryness in a mortar or ball milling tank and fully mixing and grinding it by hand grinding or ball milling for 10-30 minutes.

[0011] Further, in step 3), the fully ground pre-product is heated from room temperature to 800-1000 °C under the protection of a protective gas, with a heating rate of 2-10 °C / min, then kept warm for 1-3 hours until the reaction is complete, and then naturally cooled to room temperature to obtain the rare earth metal-doped carbon-coated molybdenum phosphide catalyst.

[0012] Further, the protective gas is any one of argon-hydrogen gas, argon gas, or nitrogen gas.

[0013] On the other hand, the present invention also provides a number of rare earth-doped carbon-coated molybdenum phosphide bifunctional catalyst materials obtained by the above preparation method, and uses them as bifunctional catalysts for alkaline water electrolysis to produce hydrogen.

[0014] The beneficial effects of this invention are as follows: A rare-earth metal-doped carbon-coated molybdenum phosphide bifunctional catalyst was successfully prepared using the preparation method provided by this invention; the phosphorus-containing chelating agent can simultaneously coordinate with rare-earth metals and molybdenum ions, achieving successful incorporation of rare-earth metals into the molybdenum phosphide lattice; the introduced rare-earth metals have low electronegativity, which can adjust the surface electronic structure of molybdenum and phosphorus atoms, optimizing the adsorption energy of hydrogen adsorbate intermediates; more importantly, the rare-earth metals activate the OER activity of molybdenum phosphide and can themselves serve as reactive sites; carbon coating enhances the catalyst's conductivity, and the nanostructure facilitates the exposure of more active sites; the prepared rare-earth metal-doped molybdenum phosphide catalyst exhibits excellent hydrogen evolution and oxygen evolution reaction catalytic activity and stability.

[0015] The preparation method of this invention is simple and controllable, and the prepared catalyst is inexpensive and efficient, exhibiting excellent bifunctional catalytic activity and has great application potential in the field of alkaline water electrolysis for hydrogen production. Attached Figure Description

[0016] Figure 1 XRD patterns of a series of lanthanum-doped carbon-coated molybdenum phosphide bifunctional catalysts prepared in Examples 1, 2, and 3; Figure 2 These are scanning electron microscope (SEM) images of the lanthanum-doped carbon-coated molybdenum phosphide bifunctional catalysts prepared in Examples 1 and 2. Figure 3 Transmission electron microscope (TEM) image of the 2.5% lanthanum-doped carbon-coated molybdenum phosphide bifunctional catalyst prepared in Example 2. Figure 4 , 5 Figures 6, 7, and 8 show the electrochemical performance of a series of rare earth metal-doped carbon-coated molybdenum phosphide bifunctional catalysts prepared in Examples 1, 2, 3, 4, and 5 in alkaline electrolytes for HER and OER. Detailed Implementation

[0017] The principles and features of the present invention are described below. The embodiments given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0018] Example 1

[0019] A method for synthesizing a 1% La-doped carbon-coated MoP (La:Mo:P = 0.01:0.99:1) bifunctional catalyst includes the following steps: Step 1: First, prepare lanthanum nitrate, ammonium heptamolybdate tetrahydrate, melamine as a carbon source, and phytic acid as a phosphorus-containing chelating agent; Step 2: Dissolve 2 mmol of metal salt (0.283 mmol of ammonium heptamolybdate tetrahydrate and 0.02 mmol of lanthanum nitrate), 0.34 mmol of phytic acid and 5 mmol of melamine in 50 mL of deionized water and evaporate to dryness under continuous stirring at 80 °C to obtain preproduct I; Step 3: Place preproduct I in a mortar and grind it manually for 10 minutes. Then transfer it to a corundum boat and introduce 5 wt% argon-hydrogen gas. Set a tube furnace to heat the temperature from room temperature to 900℃ at a rate of 5℃ / min and hold it at that temperature for 2 hours. After complete carbonization, allow it to cool naturally to room temperature to obtain the desired sample 1% lanthanum-doped carbon-coated molybdenum phosphide bifunctional catalyst, i.e., 1% La-MoP@NC.

[0020] Example

[0021] A method for synthesizing a 2.5% La-doped carbon-coated MoP (La : Mo : P = 0.025 : 0.975 : 1) bifunctional catalyst includes the following steps: Step 1: First, prepare lanthanum nitrate, ammonium heptamolybdate tetrahydrate, melamine as a carbon source, and phytic acid as a phosphorus-containing chelating agent; Step 2: Dissolve 2 mmol of metal salt (0.279 mmol of ammonium heptamolybdate tetrahydrate and 0.05 mmol of lanthanum nitrate), 0.34 mmol of phytic acid and 5 mmol of melamine in 50 mL of deionized water and evaporate to dryness under continuous stirring at 80 °C to obtain preproduct I; Step 3: Place preproduct I in a mortar and grind it manually for 10 minutes. Then transfer it to a corundum boat and introduce 5 wt% argon-hydrogen gas. Set a tube furnace to heat the temperature from room temperature to 900℃ at a rate of 5℃ / min and hold it at that temperature for 2 hours. After complete carbonization, allow it to cool naturally to room temperature to obtain the desired sample, 2.5% lanthanum-doped carbon-coated molybdenum phosphide bifunctional catalyst, i.e., 2.5% La-MoP@NC.

[0022] Example 3: A method for synthesizing a 5% La-doped carbon-coated MoP (La:Mo:P = 0.05:0.95:1) bifunctional catalyst includes the following steps: Step 1: First, prepare lanthanum nitrate, ammonium heptamolybdate tetrahydrate, melamine as a carbon source, and phytic acid as a phosphorus-containing chelating agent; Step 2: Dissolve 2 mmol of metal salt (0.271 mmol of ammonium heptamolybdate tetrahydrate and 0.1 mmol of lanthanum nitrate), 0.34 mmol of phytic acid and 5 mmol of melamine in 50 mL of deionized water and evaporate to dryness under continuous stirring at 80 °C to obtain preproduct I; Step 3: Place preproduct I in a mortar and grind it manually for 10 minutes. Then transfer it to a corundum boat and introduce 5 wt% argon-hydrogen gas. Set a tube furnace to heat the temperature from room temperature to 900℃ at a rate of 5℃ / min and hold it at that temperature for 2 hours. After complete carbonization, allow it to cool naturally to room temperature to obtain the desired sample 5% lanthanum-doped carbon-coated molybdenum phosphide bifunctional catalyst, i.e., 5% La-MoP@NC.

[0023] Example 4: A method for synthesizing a 2.5% Ce-doped carbon-coated MoP (Ce : Mo : P = 0.025 : 0.975 : 1) bifunctional catalyst includes the following steps: Step 1: First, prepare cerium nitrate, ammonium heptamolybdate tetrahydrate, melamine as a carbon source, and phytic acid as a phosphorus-containing chelating agent. Step 2: Dissolve 2 mmol of metal salt (0.279 mmol of ammonium heptamolybdate tetrahydrate and 0.05 mmol of cerium nitrate), 0.34 mmol of phytic acid and 5 mmol of melamine in 50 mL of deionized water and evaporate to dryness under continuous stirring at 80 °C to obtain preproduct I; Step 3: Place preproduct I in a mortar and grind it manually for 10 minutes. Then transfer it to a corundum boat and introduce 5 wt% argon-hydrogen gas. Set a tube furnace to heat the temperature from room temperature to 900℃ at a rate of 5℃ / min and hold it at that temperature for 2 hours. After complete carbonization, allow it to cool naturally to room temperature to obtain the desired sample, 2.5% cerium-doped carbon-coated molybdenum phosphide bifunctional catalyst, namely 2.5% Ce-MoP@NC.

[0024] Example 5:

[0025] A method for synthesizing a 2.5% Yb-doped carbon-coated MoP (Yb : Mo : P = 0.025 : 0.975 : 1) bifunctional catalyst includes the following steps: Step 1: First, prepare ytterbium nitrate, ammonium heptamolybdate tetrahydrate, melamine as a carbon source, and phytic acid as a phosphorus-containing chelating agent; Step 2: Dissolve 2 mmol of metal salt (0.279 mmol of ammonium heptamolybdate tetrahydrate and 0.05 mmol of ytterbium nitrate), 0.34 mmol of phytic acid and 5 mmol of melamine in 50 mL of deionized water and evaporate to dryness under continuous stirring at 80 °C to obtain preproduct I; Step 3: Place preproduct I in a mortar and grind it manually for 10 minutes. Then transfer it to a corundum boat and introduce 5 wt% argon-hydrogen gas. Set a tube furnace to heat the temperature from room temperature to 900℃ at a rate of 5℃ / min and hold it at that temperature for 2 hours. After complete carbonization, allow it to cool naturally to room temperature to obtain the desired sample, 2.5% ytterbium-doped carbon-coated molybdenum phosphide bifunctional catalyst, i.e., 2.5% Yb-MoP@NC.

[0026] The raw material usage statistics for the above embodiments are shown below: In the above implementation examples, step two is only an exemplary operation and a large industrial stirred reactor can be used. Step three is only an exemplary operation and a large ball mill or sand mill can be used, thereby improving the overall production efficiency of the catalyst and the quantity of products.

[0027] like Figure 1 As shown, XRD patterns of a series of lanthanum-doped carbon-coated molybdenum phosphide bifunctional catalysts were obtained by referring to the method of the embodiment; it can be seen from the figure that all synthesized lanthanum-doped molybdenum phosphide are pure phase.

[0028] like Figure 4 , 5 As shown in Figures 6, 7, and 8, a series of rare earth-doped carbon-coated molybdenum phosphide bifunctional catalysts were obtained using the method described in the examples. The materials exhibited good electrocatalytic performance, including good hydrogen evolution and oxygen evolution overpotentials.

[0029] The rare earth-doped molybdenum phosphide catalysts prepared in Examples 1-5 were subjected to HER and OER tests in 1.0 M KOH solution. The test results are shown in the table below: The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a rare earth element-doped carbon-coated molybdenum phosphide bifunctional catalyst, characterized in that, The method comprises the following steps: 1) screening raw materials, which comprise rare earth metal salt, ammonium heptamolybdate tetrahydrate, carbon source and phosphorus-containing chelating agent; 2) weighing the rare earth metal salt, ammonium heptamolybdate tetrahydrate, phosphorus-containing chelating agent and carbon source according to the proportion, uniformly mixing them in a certain amount of deionized water, and then evaporating to dryness at a temperature of 60-100 ℃ to obtain a pre-product; 3) grinding the pre-product obtained in step 2) and pyrolyzing at a temperature of 800-1000 ℃ to obtain a rare earth element doped carbon-coated molybdenum phosphide bifunctional catalyst.

2. The method for preparing the rare earth doped carbon-coated molybdenum phosphide bifunctional catalyst according to claim 1, characterized in that: In step 1), the rare earth metal salt comprises nitrate, acetylacetone salt and acetate of lanthanum, cerium and ytterbium; the carbon source comprises melamine, glucose, dicyandiamide and sucrose; and the phosphorus-containing chelating agent comprises phytic acid, phosphoric acid and organic phosphonic acid.

3. The method for preparing the rare earth doped carbon-coated molybdenum phosphide bifunctional catalyst according to claim 1, characterized in that: In step 2), the rare earth metal salt, ammonium heptamolybdate tetrahydrate and phosphorus-containing chelating agent are fed according to the atomic molar ratio of RE: Mo: P = x mmol: (1-x) mmol: 1 mmol (0 < x ≤ 0.1), the ratio of the rare earth metal salt to the carbon source is 1 mmol: (1-10) mmol, and the ratio of the rare earth metal salt to deionized water is 1 mmol: (20-100) mL.

4. The method for preparing the rare earth doped carbon-coated molybdenum phosphide bifunctional catalyst according to claim 1, characterized in that: In step 2), the uniform mixing and evaporation to dryness refer to adding all raw materials according to the proportion into a beaker containing a certain amount of deionized water, fully mixing by magnetic stirring, then raising the temperature of the water bath from room temperature to 60-100 ℃ and continuously stirring until completely evaporated to obtain a pre-product.

5. The method for preparing the rare earth doped carbon-coated molybdenum phosphide bifunctional catalyst according to claim 1, characterized in that: In step 3), the grinding of the pre-product refers to placing the pre-product evaporated to dryness in a mortar or a ball mill jar, and fully mixing and grinding for 10-30 minutes by hand grinding or a ball mill.

6. The method for preparing the rare earth doped carbon-coated molybdenum phosphide bifunctional catalyst according to claim 1, characterized in that: The pre-product obtained in step 3) is heated from room temperature to 800-1000 ℃ under the protection of a protective gas, then kept at a temperature until the reaction is completed, and then naturally cooled to room temperature to obtain the rare earth element doped carbon-coated molybdenum phosphide bifunctional catalyst.

7. The method for preparing the rare earth doped carbon-coated molybdenum phosphide bifunctional catalyst according to claim 6, characterized in that: The heating rate is 2-10 ℃ / min, and the holding time is 1-3 hours.

8. The method for preparing the rare earth doped carbon-coated molybdenum phosphide bifunctional catalyst according to claim 6, characterized in that: The protective gas is any one of argon-hydrogen gas, argon gas or nitrogen gas.

9. A rare earth element doped carbon-coated molybdenum phosphide bifunctional catalyst prepared by the preparation method according to any one of claims 1-8.

10. Use of the rare earth doped carbon-coated molybdenum phosphide bifunctional catalyst according to claim 9, characterized in that: The catalyst is used as a bifunctional catalyst for electrolytic water hydrogen production.

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