Phosphorus-doped high-entropy oxide HER electrocatalyst as well as preparation method and application thereof

Abstract

The invention discloses a phosphorus-doped high-entropy oxide HER electrocatalyst as well as a preparation method and application thereof, and belongs to the technical field of electrocatalytic materials and preparation thereof. The invention solves the problems that the existing high-entropy oxide is difficult to realize phosphorization and cannot be used as an HER electrocatalyst. According to the preparation method, firstly, a high-entropy oxide precursor is prepared through a biomass template method, so that the high-entropy oxide precursor has a three-dimensional porous morphology, metal active sites can be fully exposed in the heat treatment process, and reduction of sodium hypophosphite on the active sites is facilitated; and then through two heat treatment processes, the precursor is pre-oxidized, so that a substrate with higher chemical activity is provided for subsequent phosphorization, phosphorization can be smoothly carried out, and the problem that high-entropy oxide is difficult to phosphorize is solved. By doping phosphorus, the electronic structure of the high-entropy oxide is improved, the adsorption capacity of the high-entropy oxide to hydrogen atoms is optimized, the speed of the hydrogen evolution reaction of electrolyzed water is increased, and the obtained phosphorus-doped high-entropy oxide shows relatively high hydrogen evolution reaction catalytic activity.

Description

Technical Field

[0001] The present invention relates to a phosphorus-doped high-entropy oxide HER electrocatalyst, a preparation method thereof, and an application thereof, belonging to the technical field of electrocatalytic materials and their preparation. Background Art

[0002] The hydrogen evolution reaction (HER) plays a crucial role as a key half-reaction in the electrolysis of water. However, due to its multi-step electron transfer process, and each step of the electron transfer process will introduce a reaction kinetic energy barrier, which severely restricts the efficiency of hydrogen production by electrolysis of water. Currently, the most effective HER electrocatalyst in industry is still a noble metal-based platinum (Pt) electrocatalyst. However, the natural resources of noble metals on the earth are limited and the price is expensive, which limits their large-scale application in the field of electrolysis of water. Therefore, the development of non-noble metal-based HER electrocatalysts with low cost, high activity, and long life has become a research hotspot today.

[0003] Among the many reported non-noble metal-based electrocatalysts, high-entropy oxides have received extensive attention from researchers due to their unique physical and chemical properties, such as single-phase structure, high mixing entropy, lattice distortion, slow diffusion, and the synergistic catalytic effect of multi-metal centers. High-entropy oxides refer to oxides in which five or more metal elements are uniformly distributed in an equimolar ratio or near-equimolar ratio. The complex combination of multiple elements will have an impact on the overall performance of high-entropy oxides while maintaining their own characteristics, and different element components will interact with each other to finally form unexpected properties. Such a combination method can significantly expand the possible high-entropy material system and show great development potential. However, unfortunately, high-entropy oxides are currently mainly applied in the OER field, and the research in the HER aspect is still in its infancy, and its electrocatalytic performance is far from satisfactory. And due to the complex electronic structure of high-entropy oxides, it is also difficult to dope and modify them, and there is no relatively successful research report yet. Summary of the Invention

[0004] The present invention provides a phosphorus-doped high-entropy oxide HER electrocatalyst, a preparation method thereof, and an application thereof in order to solve the above technical problems existing in the existing HER electrocatalysts.

[0005] The technical solution of the present invention:

[0006] One of the purposes of the present invention is to provide a preparation method of a phosphorus-doped high-entropy oxide, and the method includes the following steps:

[0007] (1) Dissolve ferric salt, cobalt salt, nickel salt, zinc salt, and manganese salt in deionized water, and perform ultrasonic treatment to obtain Solution I;

[0008] (2) Use soybeans as raw materials, add deionized water, and perform grinding and heating treatment to obtain Suspension I;

[0009] (3) Slowly drip Solution I into Suspension I, heat it in a water bath while stirring until no more precipitate forms, let it stand, filter, dry the solid product, and grind it to obtain powdery Product I;

[0010] (4) Heat-treat powdery Product I in a tube furnace while passing air through it to obtain powdery Product II;

[0011] (5) Thoroughly grind and mix powdery Product II with sodium hypophosphite to obtain powdery Product III;

[0012] (6) Heat-treat powdery Product III in a tube furnace while passing a hydrogen-argon mixture through it to obtain powdery Product IV. Wash the obtained powdery Product IV with deionized water and absolute ethanol multiple times, and dry it to obtain phosphorus-doped high-entropy oxide.

[0013] Further specify that in (1), the molar ratio of iron salt, cobalt salt, nickel salt, zinc salt, and manganese salt in the obtained Solution I is 1:1:1:1:1.

[0014] Further specify that in (1), the solute concentration of the obtained Solution I is 0.4 - 0.8 g / mL.

[0015] Further specify that in (2), the mass ratio of soybeans to deionized water in the obtained Suspension I is 1:(8 - 12).

[0016] Further specify that in (2), the grinding and heat-treatment conditions are: heat to 50 - 60 °C and grind for 10 - 15 min.

[0017] Further specify that in (3), the volume ratio of Solution I to Suspension I is 1:(8 - 12).

[0018] Further specify that in (3), the water bath heating temperature is 60 - 80 °C.

[0019] Further specify that in (3), the standing time is 5 - 10 min.

[0020] Further specify that in (3), the drying temperature is 40 - 80 °C and the drying time is 1 - 2 h.

[0021] Further specify that in (4), the heat-treatment conditions are: heat at a heating rate of 5 °C / min to 400 - 700 °C and hold for 2 - 4 h.

[0022] Further specify that in (5), the mass ratio of powdery Product II to sodium hypophosphite is 1:(0.5 - 4).

[0023] Further specify that in (6), the volume fraction of hydrogen in the hydrogen-argon mixture is 10%.

[0024] Further limitation: the heat treatment conditions in (6) are as follows: heating up to 400 - 700 °C at a heating rate of 5 °C / min and holding for 2 - 4 h.

[0025] The second object of the present invention is to provide an application of the phosphorus-doped high-entropy oxide prepared by the above method, specifically as a HER electrocatalyst.

[0026] Beneficial effects of the present invention:

[0027] (1) First, the present invention prepares a high-entropy oxide precursor by a biomass template method, and then performs high-temperature phosphidation on the high-entropy oxide precursor in a tube furnace through secondary heat treatment to obtain a phosphorus-doped high-entropy oxide electrocatalyst. This electrocatalyst can accelerate the rate of the hydrogen evolution reaction in water electrolysis and is used as a HER electrocatalyst, filling the research gap of existing high-entropy oxide electrocatalysts in the field of water electrolysis HER.

[0028] (2) The present invention innovatively combines the biomass template method with secondary heat treatment. First, a high-entropy oxide precursor is prepared by the biomass template method, making it have a three-dimensional porous morphology, which can fully expose metal active sites during the heat treatment process, facilitating the reduction of these active sites by sodium hypophosphite; through two heat treatment processes, the precursor can be pre-oxidized to provide a more chemically active substrate for subsequent phosphidation, enabling phosphidation to proceed smoothly and solving the problem of difficult phosphidation of high-entropy oxides. Moreover, the doping of phosphorus improves the electronic structure of the electrocatalyst, optimizes the adsorption ability of the electrocatalyst to hydrogen atoms, accelerates the rate of the hydrogen evolution reaction in water electrolysis, and makes the obtained phosphorus-doped high-entropy oxide exhibit high catalytic activity for the hydrogen evolution reaction.

[0029] (3) Compared with the existing commonly used noble metal electrocatalysts, the present invention prepares a phosphorus-doped high-entropy oxide HER electrocatalyst with high catalytic activity at a lower cost, and the preparation process is simple, the conditions are mild, it is green and environmentally friendly, and the raw materials are cheap and easily available, facilitating large-scale industrial production and being more suitable as a HER electrocatalyst for industrial electrolytic cells. Description of the drawings

[0030] Figure 1 SEM image of 1P-HEO@BTM-400 °C prepared in Example 1;

[0031] Figure 2 TEM image of 1P-HEO@BTM-400 °C prepared in Example 1;

[0032] Figure 3 HRTEM image of 1P-HEO@BTM-400 °C prepared in Example 1;

[0033] Figure 4Comparison chart of LSV curves of 1P-HEO@BTM-400℃ prepared in Example 1, unphosphated high-entropy oxide HEO@BTM prepared in Comparative Example 1, and traditional high-entropy oxide HEO@SGM;

[0034] Figure 5 Comparison chart of Tafel slopes of HER performance of 1P-HEO@BTM-400℃ prepared in Example 1, unphosphated high-entropy oxide HEO@BTM prepared in Comparative Example 1, and traditional high-entropy oxide HEO@SGM;

[0035] Figure 6 Impedance diagram of HER performance of 1P-HEO@BTM-400℃ prepared in Example 1, unphosphated high-entropy oxide HEO@BTM prepared in Comparative Example 1, and traditional high-entropy oxide HEO@SGM;

[0036] Figure 7 Comparison chart of LSV curves of HER performance of 2P-HEO@BTM-500℃ prepared in Example 2, unphosphated high-entropy oxide HEO@BTM prepared in Comparative Example 1, and traditional high-entropy oxide HEO@SGM;

[0037] Figure 8 Comparison chart of Tafel slopes of HER performance of 2P-HEO@BTM-500℃ prepared in Example 2, unphosphated high-entropy oxide HEO@BTM prepared in Comparative Example 1, and traditional high-entropy oxide HEO@SGM;

[0038] Figure 9 Impedance diagram of HER performance of 2P-HEO@BTM-500℃ prepared in Example 2, unphosphated high-entropy oxide HEO@BTM prepared in Comparative Example 1, and traditional high-entropy oxide HEO@SGM. Detailed implementation manners

[0039] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following describes the detailed implementation manners of the present invention in conjunction with the embodiments of the specification.

[0040] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0041] Secondly, the "one embodiment" or "embodiment" referred to herein means a specific feature, structure, or characteristic that may be included in at least one implementation manner of the present invention. The "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor is it an individual or alternative embodiment that is mutually exclusive with other embodiments.

[0042] The experimental methods used in the following embodiments are all conventional methods unless otherwise specified. The materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in this field, and those skilled in the art can obtain them through commercial channels without special instructions.

[0043] Example 1

[0044] The method for preparing the phosphorus-doped high-entropy oxide HER electrocatalyst in this embodiment is carried out according to the following steps:

[0045] Step 1: Dissolve 0.015 mol of Fe(NO3)3·9H2O, 0.015 mol of Co(NO3)2·6H2O, 0.015 mol of Ni(NO3)2·6H2O, 0.015 mol of Zn(NO3)2·9H2O, and 0.015 mol of Mn(NO3)2·4H2O in 50 mL of deionized water, and ultrasonically treat for 15 min to obtain Solution I;

[0046] Step 2: Heat 80 g of soybeans and 1000 mL of deionized water to 60 °C and grind for 15 min to obtain Suspension I;

[0047] Step 3: Slowly add 50 mL of Solution I to 600 mL of Suspension I, stir under the condition of water bath heating at 80 °C, ensure uniform stirring until the precipitate no longer precipitates, let it stand for 5 min, filter, separate the solid product, and put the solid product into an oven at 80 °C to dry for 2 h. Pour the dried product into an agate mortar and grind for 10 min to obtain powdery Product I;

[0048] Step 4: Put the powdery Product I into a quartz boat, and place the quartz boat in a tube furnace. Heat it to 400 °C at a heating rate of 5 °C / min and keep it warm for 4 h to obtain powdery Product II;

[0049] Step 5: Thoroughly grind and mix the powdery Product II and sodium hypophosphite in a mass ratio of 1:1 to obtain powdery Product III;

[0050] Step 6: Put the powdery product III into a quartz boat, place the quartz boat in a tube furnace, introduce a hydrogen-argon mixed gas (the volume ratio of hydrogen is 10%), heat it to 400 °C at a heating rate of 5 °C / min and keep it warm for 4 h to obtain a powdery product IV. Wash the obtained powdery product IV 3 times each with deionized water and absolute ethanol in turn, and dry it in an oven at 80 °C for 2 h to obtain a phosphorus-doped high-entropy oxide HER electrocatalyst, named 1P-HEO@BTM-400 °C.

[0051] Example 2

[0052] The method for preparing the phosphorus-doped high-entropy oxide HER electrocatalyst in this example is carried out according to the following steps:

[0053] Step 1: Dissolve 0.2 mol of Fe(NO3)3·9H2O, 0.02 mol of Co(NO3)2·6H2O, 0.02 mol of Ni(NO3)2·6H2O, 0.02 mol of Zn(NO3)2·9H2O, and 0.02 mol of Mn(NO3)2·4H2O in 60 mL of deionized water, and ultrasonically treat for 15 min to obtain solution I;

[0054] Step 2: Heat 60 g of soybeans and 500 mL of deionized water to 55 °C and grind for 10 min to obtain suspension I;

[0055] Step 3: Slowly add 50 mL of solution I to 500 mL of suspension I, stir under the condition of water bath heating at 80 °C, ensure uniform stirring until the precipitate no longer precipitates, stand for 5 min, filter, separate the solid product, and put the solid product into an oven at 80 °C for 2 h. Pour the dried product into an agate mortar and grind for 12 min to obtain a powdery product I;

[0056] Step 4: Put the powdery product I into a quartz boat, place the quartz boat in a tube furnace, heat it to 600 °C at a heating rate of 5 °C / min and keep it warm for 2 h to obtain a powdery product II.

[0057] Step 5: Thoroughly grind and mix the powdery product II and sodium hypophosphite in a mass ratio of 1:2 to obtain a powdery product III;

[0058] Step 6: Put the powdery product III into a quartz boat, place the quartz boat in a tube furnace, introduce 10% hydrogen-argon mixed gas, heat it to 500 °C at a heating rate of 5 °C / min and keep it warm for 3 h to obtain a powdery product IV. Wash the obtained powdery product IV 3 times each with deionized water and absolute ethanol in turn, and dry it in an oven at 80 °C for 2 h to obtain a phosphorus-doped high-entropy oxide HER electrocatalyst, named 2P-HEO@BTM-500 °C.

[0059] Comparative Example 1

[0060] The method for preparing unphosphated high-entropy oxide HEO@BTM in this example was carried out according to the following steps:

[0061] Step 1: Dissolve 0.015 mol of Fe(NO3)3·9H2O, 0.015 mol of Co(NO3)2·6H2O, 0.015 mol of Ni(NO3)2·6H2O, 0.015 mol of Zn(NO3)2·9H2O, and 0.015 mol of Mn(NO3)2·4H2O in 50 mL of deionized water, and ultrasonically treat for 15 min to obtain Solution I;

[0062] Step 2: Heat 80 g of soybeans and 1000 mL of deionized water to 60 °C and grind for 15 min to obtain Suspension I;

[0063] Step 3: Slowly add 50 mL of Solution I to 600 mL of Suspension I, stir under the condition of water bath heating at 80 °C, ensure uniform stirring until the precipitate no longer precipitates, stand for 5 min, filter, separate the solid product, and put the solid product into an oven at 80 °C for drying for 2 h. Pour the dried product into an agate mortar and grind for 10 min to obtain powdery Product I;

[0064] Step 4: Put the powdery Product I into a quartz boat, and place the quartz boat in a tube furnace. Heat it to 400 °C at a heating rate of 5 °C / min and hold for 4 h to obtain powdery Product II; Wash the obtained powdery Product II 3 times each with deionized water and absolute ethanol in turn, and dry it in an oven at 80 °C for 2 h to obtain unphosphated high-entropy oxide, named HEO@BTM.

[0065] Effect Example

[0066] (1) Characterize the microstructure of the phosphorus-doped high-entropy oxide HER electrocatalyst 1P-HEO@BTM-400 °C prepared in Example 1, and the results are as Figures 1 to 3 shown. It can be seen from Figures 1 to 3 that the phosphorus-doped high-entropy oxide HER electrocatalyst 1P-HEO@BTM-400 °C is composed of a large number of metal nanoparticles loaded on the carbon surface. The nanoparticles agglomerate into spheres and the surface is very rough, which is beneficial to increasing the active surface area. In addition, the TEM image also shows a large number of randomly distributed lattice fringes and amorphous regions, which are all beneficial to the electron transfer process in the hydrogen evolution reaction.

[0067] (2) The phosphorus-doped high-entropy oxide HER electrocatalyst 1P-HEO@BTM-400 °C prepared in Example 1, the unphosphated high-entropy oxide HEO@BTM prepared in Comparative Example 1, and the traditional high-entropy oxide HEO@SGM prepared according to the method described in the literature (A new class of spinel high-entropy oxides with controllable magnetic properties in the Journal of Magnetism and Magnetic Materials) were respectively loaded on carbon paper with an area of 1 cm 2 ². The loading amount was 0.5 mg for all. Then, the carbon paper, carbon rod, and saturated Ag / AgCl electrode were used as the working electrode, counter electrode, and reference electrode respectively to form a three-electrode system. An oxygen-saturated 1 mol / L KOH solution was used as the electrolyte solution, and the HER electrochemical performance of 1P-HEO@BTM-400 °C, HEO@BTM, and HEO-SGM was tested by an electrochemical workstation respectively. The test results are as Figures 4 to 6 shown. At a current density of 10 mA / cm 2 ², the overpotential of the 1P-HEO@BTM-400 °C electrocatalyst was 218.1 mV, and the Tafel slope was -129.5 mV / dec. The overpotential of the HEO@BTM electrocatalyst was 364.2 mV, and the Tafel slope was -334.8 mV / dec. The overpotential of HEO-SGM was 367.8 mV, and the Tafel slope was -385.1 mV / dec. The hydrogen evolution performance of the HEO@BTM and HEO-SGM electrocatalysts was similar, while the overpotential, Tafel slope, and impedance of 1P-HEO@BTM-400 °C were lower than those of HEO@BTM and HEO-SGM, proving that the phosphorus-doped high-entropy oxide HER electrocatalyst 1P-HEO@BTM-400 °C prepared in Example 1 was successfully phosphated and had higher HER catalytic activity than traditional high-entropy oxides.

[0068] (3) The phosphorus-doped high-entropy oxide HER electrocatalyst 2P-HEO@BTM-500 °C prepared in Example 2, the unphosphated high-entropy oxide HEO@BTM prepared in Comparative Example 1, and the traditional high-entropy oxide HEO@SGM prepared according to the literature were respectively loaded on carbon paper with an area of 1 cm 2On the carbon paper with a loading of 0.5 mg, the carbon paper, carbon rod, and saturated Ag / AgCl electrode were used as the working electrode, counter electrode, and reference electrode, respectively, to form a three-electrode system. A 1 mol / L KOH solution saturated with oxygen was used as the electrolyte solution, and the HER electrochemical performance of 2P-HEO@BTM-500℃ and HEO-SGM was tested by an electrochemical workstation. The test results are as Figures 7 to 9 shown. At a current density of 10 mA / cm 2 , the overpotential of the 2P-HEO@BTM-500℃ electrocatalyst was 237.2 mV, and the Tafel slope was -135.4 mV / dec. The overpotential of the HEO@BTM electrocatalyst was 364.2 mV, and the Tafel slope was -334.8 mV / dec. The overpotential of the HEO-SGM was 367.8 mV, and the Tafel slope was -385.1 mV / dec. The hydrogen evolution performance of the HEO@BTM and HEO-SGM electrocatalysts was similar, while the overpotential, Tafel slope, and impedance of 2P-HEO@BTM-500℃ were lower than those of HEO@BTM and HEO-SGM, proving that the phosphorus-doped high-entropy oxide HER electrocatalyst 2P-HEO@BTM-500℃ prepared in Example 2 was successfully phosphorized and had higher HER catalytic activity than traditional high-entropy oxides.

[0069] The above are only the preferred embodiments of the present invention. Given that those skilled in the art to which the present invention pertains can make appropriate changes and modifications to the above-described embodiments, the present invention is not limited to the specific embodiments described above, and some modifications and changes to the present invention should also fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a phosphorus-doped high entropy oxide, characterized in that: include: (1) dissolving an iron salt, a cobalt salt, a nickel salt, a zinc salt and a manganese salt in deionized water, and performing ultrasonic treatment to obtain a solution I; (2) using soybean as a raw material, adding deionized water, grinding and heating to obtain a suspension I; (3) slowly dripping solution I into suspension I, heating in a water bath while stirring until no more precipitate is precipitated, letting stand, filtering, drying and grinding the solid product to obtain a powdered product I; (4) heating the powdered product I in a tube furnace by passing air to obtain a powdered product II; (5) grinding and mixing the powdered product II and sodium hypophosphite to obtain a powdered product III; (6) The powdered product III is heated in a tube furnace by passing a hydrogen-argon mixed gas to obtain a powdered product IV. The obtained powdered product IV is washed with deionized water and anhydrous ethanol for multiple times and dried to obtain a phosphorus-doped high-entropy oxide.

2. The preparation method according to claim 1, characterized in that: (1) The solute concentration in the obtained solution I is 0.4-0.8 g / mL, wherein the molar ratio of the iron salt, the cobalt salt, the nickel salt, the zinc salt and the manganese salt is 1:1:1:1:

1.

3. The preparation method according to claim 1, characterized in that: (2) The mass ratio of soybean to deionized water is 1:(8-12); the grinding and heating treatment conditions are: heating to 50-60°C and grinding for 10-15 minutes.

4. The preparation method according to claim 1, characterized in that: (3) The volume ratio of the solution I to the suspension I is 1:(8-12); the water bath adding temperature is 60-80°C; the standing time is 5-10 min; the drying temperature is 40-80°C, and the drying time is 1-2 h.

5. The preparation method according to claim 1, characterized in that: The heating treatment conditions in (4) are: heating to 400-700°C at a heating rate of 5°C / min and keeping the temperature for 2-4h.

6. The preparation method according to claim 1, characterized in that: (5) The mass ratio of the powdered product II to sodium hypophosphite is 1:(0.5-4).

7. The preparation method according to claim 1, characterized in that: (6) The volume proportion of hydrogen in the hydrogen-argon mixture is 10%.

8. The preparation method according to claim 1, characterized in that: The heating conditions in (6) are: heating to 400-700°C at a heating rate of 5°C / min and keeping the temperature for 2-4h.

9. A phosphorus-doped high entropy oxide prepared by the method according to any one of claims 1 to 8.

10. An application of the phosphorus-doped high entropy oxide according to claim 9, characterized in that: Used as HER electrocatalyst.

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