Preparation method, product and application of alkaline hydrogen evolution electrocatalyst

Abstract

The present invention relates to the fields of catalyst preparation and new energy, and in particular to a preparation method, product and application of an alkaline hydrogen evolution electrocatalyst. Co(OH)2 powder is kept at 240-400°C for 5-15 minutes, and then cooled at room temperature after the end of the heat preservation to obtain a Co(OH)2-Co3O4 heterojunction; the Co(OH)2-Co3O4 heterojunction and NaH2PO2·H2O powder are placed in an inert atmosphere and calcined, and then naturally cooled to room temperature to obtain a transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst. The catalyst contains two phases, CoP2 with high intrinsic catalytic activity and CoP with excellent electron transport ability. The synergistic effect between the different phases improves the reaction kinetics by regulating the adsorption / desorption process of the intermediate product, accelerates the electron transfer between the surface and the inner layer, and exhibits more outstanding electrochemical hydrogen evolution activity.

Description

Technical Field

[0001] The present invention relates to the fields of catalyst preparation and new energy, and in particular to a preparation method, product and application of a transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst. Background Art

[0002] As a secondary energy source with high-quality energy density and environmental friendliness, hydrogen energy has shown great potential to replace traditional fossil energy. However, there are no natural reserves of hydrogen energy on Earth, and it must be obtained through hydrogen production before it can be used. Using renewable energy sources such as wind or solar energy to provide electricity to produce hydrogen through water electrolysis has become the most promising way to produce green hydrogen. In the process of water electrolysis to produce hydrogen, the catalyst material on the electrode surface is an important factor affecting the electrochemical hydrogen evolution reaction (HER). The development of cheap, efficient, and stable water electrolysis catalysts can reduce the overpotential of the reaction and effectively improve the hydrogen evolution efficiency. Currently, the precious metal Pt is the best HER catalyst, but its reserves are scarce and its price is high, making it impossible to achieve large-scale hydrogen production applications. Therefore, it is necessary to study abundant, low-cost, and efficient non-precious metal catalysts to replace Pt group catalysts.

[0003] Transition metal phosphides (TMPs) share similar structures and properties to hydrogenases. They possess stable catalytic activity and the ability to serve as bifunctional catalysts for both hydrogen and oxygen evolution, making them promising candidates for HER (Heat-Excitation) reactions. TMPs are composed of phosphorus (P) and a transition metal (M). Due to their unique structure and properties, TMPs exhibit a wide variety of M / P stoichiometric ratios. Based on the M / P atomic ratio, TMPs can be classified into phosphorus-rich phosphides (M / P < 1), monophosphorus phosphides (M / P = 1), and metal-rich phosphides (M / P > 1). Monophosphorus and phosphorus-rich TMPs typically exhibit excellent electrical conductivity due to their relatively abundant M-M bonds, which result in a high number of free electrons and metal-like properties. While most phosphorus-rich TMPs are semiconductors or insulators, those in the phosphorus-rich phase often exhibit excellent intrinsic activity. This is mainly because P atoms can shrink the d band of metal atoms, resulting in an increase in the electronic state density near the Fermi level. Therefore, TMPs have the characteristics of noble metals and exhibit excellent catalytic performance. During the catalytic process, the phosphorus and metal sites in TMPs act as proton acceptor sites and hydride acceptor sites, respectively. P atoms carry a negative charge, which weakens the strength of the chemical bond between the metal and H, thereby promoting the desorption of H. In addition, the introduction of P atoms can also form a moderately strong chemical bond with the reaction product, reducing the strong adsorption of pure metal to H2, thereby accelerating the separation of H2. In order to balance the catalytic activity and conductivity of TMPs, most research work has focused on controlling the content of M and P in TMPs. However, this method makes it difficult to fully utilize the advantages of different metal phosphides.

[0004] By coupling TMPs with different M / P atomic ratios, a TMPs homo-heterojunction can be constructed. This material can significantly promote the HER catalytic performance of its phosphorus-rich compound component by leveraging the excellent electron transport ability and catalytic activity of single-phosphorus and phosphorus-rich TMPs electrode materials, thereby giving full play to the advantages of different metal phosphides. However, there is little research on the construction of TMPs homo-heterojunctions, and the heterojunction construction process is usually cumbersome, time-consuming and energy-consuming. Therefore, it is of great significance to develop a simple and efficient method for the rapid preparation of TMPs homo-heterojunction alkaline hydrogen evolution electrocatalysts.

[0005] A Chinese invention patent document, publication number CN114715864A, discloses a transition metal phosphide with non-metallic elements filling phosphorus vacancies, its preparation, and a lithium-sulfur battery, belonging to the field of inorganic compound preparation technology. This invention first prepares cobalt hydroxide nanosheets by electrodeposition. The cobalt hydroxide nanosheets are then calcined with sodium phosphite at the top and bottom ends of a tube furnace. After calcination, the nanosheets are treated with a sodium borohydride solution and washed with deionized water. Finally, different calcination conditions are used to calcine non-metallic elements such as sulfur, nitrogen, fluorine, chlorine, or boron with a transition metal phosphide containing phosphorus vacancies under an inert atmosphere to prepare a transition metal phosphide with non-metallic elements filling phosphorus vacancies. The cobalt hydroxide precursor prepared by electrodeposition in this invention suffers from low yield, high energy consumption, complex equipment, low efficiency, and inability to control the ratio of metal to phosphorus atoms.

[0006] Chinese invention patent publication number CN117861693A discloses a phosphorus-rich transition metal phosphide catalyst, its synthesis method, and its application. The invention first subjects NiCl2 to dynamic vacuum drying, followed by vacuum grinding and compression to tablets. The tablets are then placed in the closed end of a single-side sealed ampoule. Red phosphorus is then vacuum-weighed and placed in the other end of the ampoule, which is then sealed with a methane-oxygen torch. Finally, the ampoule is placed in the constant temperature section of a tube furnace and calcined at high temperature under an inert atmosphere to produce a phosphorus-rich transition metal phosphide (NiP2) solid. This phosphorus-rich metal phosphide preparation method is cumbersome and inefficient, and does not address the control of metal and phosphorus content.

[0007] The Chinese invention patent document with publication number CN101613097B discloses a carbon-supported transition metal phosphide (Fe2P, Co2P, Ni 12 P5) A method for preparing a new material. This invention first adds a soluble Group VIII metal salt to a resorcinol solution and stirs to dissolve it. Then, diammonium hydrogen phosphate is added to the solution in a specific proportion to form a precipitate. An appropriate amount of concentrated nitric acid is added dropwise until the precipitate is dissolved. Formaldehyde solution is then added dropwise while stirring, causing the solution to form a gel. After drying and high-temperature calcination under an inert atmosphere, a metal phosphide-modified gel carbon is obtained. While this method is simple to prepare, the product is single and does not involve controlling the ratio of transition metal to phosphorus. Furthermore, traditional calcination methods are time-consuming, energy-intensive, and inefficient.

[0008] Chinese invention patent publication number CN113772644A discloses a bimetallic phosphide, its preparation method, and application. This invention utilizes a coprecipitation method to prepare the bimetallic phosphide. Potassium ferrocyanide and a cobalt salt are first coprecipitated to produce iron-cobalt Prussian blue. The product is then transferred to a tube furnace and reacted at 600°C for 2 hours under an inert atmosphere. The iron-cobalt Prussian blue is then phosphated to produce the bimetallic phosphide. The traditional calcination method used to prepare the phosphide heterojunction requires a 2-hour reaction at 600°C, resulting in a long reaction time and high energy consumption. Furthermore, the composite material produced by this method does not involve homologous heterojunctions or the regulation of the transition metal to phosphorus ratio in the phosphide.

[0009] Chinese invention patent document CN115377605B discloses a hollow metal oxide-metal phosphide heterojunction material, its preparation method, and application. The invention first utilizes a sol-gel method to prepare metal compound-coated resorcinol-formaldehyde nanospheres. The resulting material is then calcined in air at 600°C for 3 hours to produce a hollow metal oxide precursor. The resulting hollow metal oxide precursor is then calcined at 350°C for 2 hours and phosphated to produce a hollow metal oxide-metal phosphide heterojunction. This method utilizes a traditional step-by-step calcination method, requiring inert gas incubation at 600°C and 350°C for 3 hours and 2 hours, respectively. This results in low catalyst preparation efficiency and high energy consumption. Furthermore, the catalyst support does not affect the ratio of transition metal to phosphorus in the heterojunction. Summary of the Invention

[0010] The present invention aims to provide a method for preparing a transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst, as well as a product and application thereof. This method can address the low intrinsic activity, slow charge transfer rate, poor stability, and long reaction time issues of transition metal phosphide electrocatalysts prepared by conventional methods. The present invention prepares a Co(OH)2-Co3O4 heterojunction through a rapid temperature ramp process, and then phosphates the Co(OH)2-Co3O4 heterojunction to prepare the transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst CoP2-CoP.

[0011] To achieve the above object, the present invention provides the following solutions:

[0012] One of the technical solutions of the present invention is a method for preparing a transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst, comprising the following steps:

[0013] The Co(OH)2 powder was kept at 240-400℃ for 5-15 minutes, and then cooled to room temperature to obtain a Co(OH)2-Co3O4 heterojunction.

[0014] The Co(OH)2-Co3O4 heterojunction and NaH2PO2·H2O powder are calcined in an inert atmosphere and then naturally cooled to room temperature to obtain the transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst (CoP2-CoP).

[0015] The second technical solution of the present invention is a transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst (abbreviated as: catalyst) prepared according to the above preparation method.

[0016] The third technical solution of the present invention is the application of the above-mentioned transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst in hydrogen production by water electrolysis.

[0017] The transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst prepared by the present invention is a highly active and stable HER catalyst, mainly because: (1) it contains two phases, CoP2 and CoP. CoP2 has a higher intrinsic catalytic activity due to its higher P content. At the same time, the presence of CoP can provide excellent electron transport capacity, so the heterojunction can balance the intrinsic catalytic activity and conductivity of TMPs; (2) the synergistic effect between different phases within the heterojunction improves the reaction kinetics by regulating the adsorption / desorption process of intermediate products, ensures the rapid transfer and timely consumption of electrons, reduces the electron accumulation in the phosphide, thereby inhibiting potential corrosion and improving the activity and stability of the catalyst.

[0018] The present invention discloses the following technical effects:

[0019] (1) The present invention can regulate the phase of the calcined product by controlling the calcination time of cobalt hydroxide, and further realize the preparation of transition metal phosphide homologous heterojunction through a simple one-step phosphiding method.

[0020] (2) Compared with single-phase Co2P and CoP catalysts, the transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst (CoP2-CoP) prepared in the present invention contains two phases, CoP2 with high intrinsic catalytic activity and CoP with excellent electron transport ability. The synergistic effect between different phases improves the reaction kinetics by regulating the adsorption / desorption process of intermediate products, accelerates the electron transfer between the surface and the inner layer, and exhibits more outstanding electrochemical hydrogen evolution activity.

[0021] (3) Compared with the traditional strategy of constructing phosphide-based composite materials, such as the growth-secondary growth-phosphiding strategy, the composite material synthesis method in the present invention is relatively simple and can simultaneously form homologous single phosphorus-phosphorus-rich heterojunction materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 X-ray powder diffraction (XRD) patterns of the Co(OH)2-Co3O4 heterojunction prepared in Example 1, the Co(OH)2 prepared in Comparative Example 1, and the Co3O4 prepared in Comparative Example 2.

[0024] Figure 2 The X-ray diffraction (XRD) patterns of the catalysts prepared in Example 1 and Comparative Examples 1-2 are shown.

[0025] Figure 3 This is a nitrogen adsorption-desorption (BET) curve of the catalyst prepared in Example 1.

[0026] Figure 4 The catalyst prepared in Example 1 and the commercial Pt / C catalyst were -2 Linear sweep voltammetry (LSV) curves of hydrogen evolution reaction (HER) at current density of .

[0027] Figure 5 The catalysts prepared in Example 1 and Comparative Examples 1-2 and the commercial Pt / C catalyst were -2 Overpotential diagram of hydrogen evolution reaction (HER) at current density of .

[0028] Figure 6 The catalysts prepared in Example 1 and Comparative Examples 1-2 were tested at 10 mA·cm -2 Cyclic stability test diagram of hydrogen evolution reaction (HER) at a current density of . DETAILED DESCRIPTION

[0029] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0030] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0031] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0032] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0033] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0034] The "room temperature" mentioned in the present invention, unless otherwise specified, refers to 20-30°C.

[0035] The first aspect of the present invention provides a method for preparing a transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst, comprising the following steps:

[0036] The Co(OH)2 powder was kept at 240-400℃ for 5-15min, and then cooled at room temperature to obtain a Co(OH)2-Co3O4 heterojunction.

[0037] The Co(OH)2-Co3O4 heterojunction and NaH2PO2·H2O powder are calcined in an inert atmosphere and then naturally cooled to room temperature to obtain the transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst (CoP2-CoP).

[0038] In a preferred embodiment of the present invention, the method of cooling the sample during the preparation of the Co(OH)2-Co3O4 heterojunction is to take the sample out and place it at room temperature for rapid cooling.

[0039] The conventional cooling method in this field is natural cooling in a muffle furnace. The muffle furnace itself has good thermal insulation effect, but the cooling rate is very slow, and it takes several hours to complete the cooling. Slow cooling will cause the sample to remain at a high temperature for a long time, which is easy to be completely converted into Co3O4, and the Co(OH)2-Co3O4 heterojunction cannot be obtained. The present invention uses a rapid cooling method. After the insulation is completed, the sample is taken out and placed at room temperature for cooling. The cooling rate is fast, and the sample is not completely converted into Co3O4, thereby obtaining a Co(OH)2-Co3O4 heterojunction.

[0040] If the heating rate is too slow, the Co(OH)2 powder will be completely converted into Co3O4, and the Co(OH)2-Co3O4 heterojunction cannot be obtained; the present invention directly transfers the Co(OH)2 powder to a 240~400℃ environment for a certain period of time, and the heating rate is fast, which can avoid the complete conversion of the Co(OH)2 powder into Co3O4, thereby obtaining a Co(OH)2-Co3O4 heterojunction.

[0041] In a preferred embodiment of the present invention, the mass ratio of the Co(OH)2-Co3O4 heterojunction to the NaH2PO2·H2O powder is 1:(5-20).

[0042] In a preferred embodiment of the present invention, the inert atmosphere is an argon atmosphere; the calcination is specifically carried out at a temperature of 1-10°C·min -1 Raise the temperature to 300~600℃ and keep it warm for 2h.

[0043] In a preferred embodiment of the present invention, the Co(OH)2-Co3O4 heterojunction and NaH2PO2.H2O powder are placed at the upper and lower ends of a tubular furnace heating device, respectively, and calcined in a high-purity argon atmosphere.

[0044] In a preferred embodiment of the present invention, the method for preparing Co(OH)2 comprises the following steps:

[0045] ZIF-67 powder is dispersed in a mixed solvent of ethanol and deionized water, followed by addition of Na2MoO4·2H2O and heating until the purple color disappears. The solution is then centrifuged, washed, and vacuum-dried to obtain Co(OH)2. Co(OH)2 with the same structure and elemental composition obtained through other sources, such as commercial purchase, is also suitable for use in the present invention.

[0046] In a preferred embodiment of the present invention, the volume ratio of the ethanol to the deionized water is 1:0.3-2; the mass ratio of the ZIF-67 powder to the Na2MoO4·2H2O is 1:(2-4); the heating temperature is 50-95°C; and the vacuum drying temperature is 50-100°C.

[0047] In a preferred embodiment of the present invention, when preparing Co(OH)2, the washing times are 2 to 5 times.

[0048] In a preferred embodiment of the present invention, the method for preparing the ZIF-67 powder comprises the following steps:

[0049] The 2-methylimidazole methanol solution is added to the cobalt nitrate hexahydrate methanol solution for reaction, and then centrifuged, washed, and vacuum-dried in sequence to obtain the ZIF-67 powder.

[0050] In a preferred embodiment of the present invention, the concentration of the 2-methylimidazole methanol solution is 0.16 M; the concentration of the cobalt nitrate hexahydrate methanol solution is 0.02 M; the volume ratio of the 2-methylimidazole methanol solution to the cobalt nitrate hexahydrate methanol solution is 5:3; the reaction temperature is room temperature, the reaction time is 2 to 24 hours; and the vacuum drying temperature is 50 to 100°C.

[0051] In some embodiments of the present invention, when preparing ZIF-67 powder, the washing frequency is 2 to 5 times.

[0052] A second aspect of the present invention provides a transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst prepared according to the above preparation method.

[0053] A third aspect of the present invention provides the use of the above-mentioned transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst in hydrogen production by water electrolysis.

[0054] The homologous heterojunction prepared by the present invention contains two phases, a monophosphorus compound and a phosphorus-rich compound. The phosphorus-rich compound CoP2 can improve the intrinsic activity of the catalyst, while the monophosphorus compound CoP has good conductivity and can provide the catalyst with excellent electron transport ability. In addition, the synergistic effect between the different phases improves the reaction kinetics by regulating the adsorption / desorption process of the intermediate product, accelerates the electron transfer between the surface and the inner layer, and exhibits more outstanding electrochemical hydrogen evolution performance. The transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst prepared by the method of the present invention can, under the synergistic effect of the two phases, achieve a constant current of 10 mA cm -2 It can maintain stable operation for 30 hours without obvious performance degradation and has excellent alkaline HER performance.

[0055] Unless otherwise specified, the technical solutions described in the present invention are all conventional solutions in the field, and the reagents or raw materials used, unless otherwise specified, are purchased from commercial channels or have been disclosed.

[0056] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0057] Example 1

[0058] Step 1: 50 mL of 0.16 M 2-methylimidazole methanol solution was quickly added to 30 mL of 0.02 M cobalt nitrate hexahydrate methanol solution. After reacting at room temperature for 16 h, the obtained suspension was centrifuged with methanol, washed with methanol four times, and dried in vacuo at 60° C. to obtain ZIF-67 powder.

[0059] In step 2, 40 mg of ZIF-67 powder was dispersed in a mixture of 20 mL of ethanol and 10 mL of deionized water. Then, 100 mg of Na₂MoO₄·2H₂O was added with stirring. The mixture was then heated at 80°C until the purple color disappeared. The resulting product was washed with deionized water, centrifuged three times, and dried in vacuo at 70°C to yield Co(OH)₂.

[0060] Step 3: preheat the muffle furnace to 300°C, then transfer the Co(OH)2 powder to the muffle furnace and keep it warm for 10 minutes. Then, take out the sample and quickly cool it down at room temperature to obtain a Co(OH)2-Co3O4 heterojunction.

[0061] Step 4: 40 mg of the above-obtained Co(OH)2-Co3O4 heterojunction and 0.4 g of NaH2PO2·H2O powder were placed at the upper and lower ends of a tube furnace heating device, respectively, and heated at 2°C·min under a high-purity argon atmosphere. -1 The tube furnace was heated to 450°C at a rate of 1000 nm, maintained for 2 h, and naturally cooled to room temperature to obtain a black powder, namely a transition metal phosphide homogeneous heterojunction alkaline hydrogen evolution electrocatalyst, recorded as CoP2-CoP-1.

[0062] Example 2

[0063] The only difference from Example 1 is that in step 2, 100 mg Na2MoO4·2H2O is replaced by 80 mg Na2MoO4·2H2O, and the remaining steps and parameters are the same as those in Example 1; the prepared catalyst is recorded as CoP2-CoP-2.

[0064] Example 3

[0065] The only difference from Example 1 is that in step 2, 100 mg Na2MoO4·2H2O is replaced by 150 mg Na2MoO4·2H2O, and heating at 80°C is replaced by heating at 60°C. The remaining steps and parameters are the same as those in Example 1; the prepared catalyst is recorded as CoP2-CoP-3.

[0066] Example 4

[0067] The only difference from Example 1 is that in step 3, the muffle furnace insulation for 10 minutes is replaced by the muffle furnace insulation for 5 minutes, and the remaining steps and parameters are the same as those in Example 1; the prepared catalyst is recorded as CoP2-CoP-4.

[0068] Example 5

[0069] The only difference from Example 1 is that in step 3, the muffle furnace insulation for 10 minutes is replaced by the muffle furnace insulation for 15 minutes, and the remaining steps and parameters are the same as those in Example 1; the prepared catalyst is recorded as CoP2-CoP-5.

[0070] Example 6

[0071] The only difference from Example 1 is that in step 4, the tubular furnace calcination heating temperature of 450°C is changed to 400°C, and the remaining steps and parameters are the same as those in Example 1; the prepared catalyst is recorded as CoP2-CoP-6.

[0072] Example 7

[0073] The only difference from Example 1 is that in step 4, the tubular furnace calcination heating temperature of 450°C is changed to 500°C, and the remaining steps and parameters are the same as those in Example 1; the prepared catalyst is recorded as CoP2-CoP-7.

[0074] Comparative Example 1

[0075] The only difference from Example 1 is that step 3 is omitted, and 40 mg of Co(OH)2 prepared in step 2 and 0.4 g of NaH2PO2·H2O powder are directly placed at the upper and lower ends of the tube furnace heating device, respectively, and heated at 2°C·min under high-purity argon atmosphere. -1 The tube furnace was heated to 450°C at a rate of , maintained for 2 h, and naturally cooled to room temperature to obtain a black powder; the prepared catalyst was recorded as CoP2.

[0076] Comparative Example 2

[0077] The only difference from Example 1 is that in step 3, the muffle furnace was kept warm for 120 min instead of 10 min to obtain Co3O4 black powder; in step 4, 40 mg of Co3O4 prepared in step 3 and 0.4 g of NaH2PO2·H2O powder were placed at the upper and lower ends of the tube furnace heating device, respectively, under a high-purity argon atmosphere, and heated at 2°C·min -1 The tube furnace was heated to 450°C at a rate of , maintained for 2 h, and naturally cooled to room temperature to obtain a black powder; the prepared catalyst was recorded as CoP.

[0078] Figure 1X-ray powder diffraction (XRD) patterns of the Co(OH)2-Co3O4 heterojunction prepared in Example 1, the Co(OH)2 prepared in Comparative Example 1, and the Co3O4 prepared in Comparative Example 2. The Co(OH)2 synthesized in Comparative Example 1 matches its standard card (PDF#45-0031), the Co3O4 synthesized in Comparative Example 2 matches its standard card (PDF#42-1467), and the Co(OH)2-Co3O4 heterojunction in Example 1 meets both standard cards, indicating that the heterojunction is composed of Co(OH)2 and Co3O4.

[0079] Figure 1 The results show that adjusting the holding time in the muffle furnace in step 3 can effectively control the phase of the calcined product. When no holding treatment is performed, the single-phase Co(OH)2 does not convert to Co3O4, and a heterojunction cannot be formed. However, if the holding time is too long, the Co(OH)2 will completely convert to Co3O4, and a heterojunction cannot be formed. Both situations are not conducive to the subsequent formation of the phosphide homo-heterojunction. Therefore, by precisely controlling the calcination time of Co(OH)2 in the muffle furnace, the phase of the calcined product can be effectively controlled, thereby achieving precise control over the formation of transition metal phosphide homo-heterojunctions.

[0080] Figure 2 X-ray diffraction (XRD) patterns of the catalysts prepared in Example 1 and Comparative Examples 1-2. The CoP2 synthesized in Comparative Example 1 matches its standard card (PDF#26-0481), while the CoP synthesized in Comparative Example 2 is consistent with its standard card (PDF#29-0497). The spectrum of CoP2-CoP-1 in Example 1 also corresponds to these two standard cards, indicating that the heterojunction is composed of CoP2 and CoP, while Comparative Examples 1 and 2 exhibit single-phase CoP2 and CoP, respectively.

[0081] The CoP2-CoP-1 in Example 1 contains both CoP2, which has high intrinsic catalytic activity, and CoP, which has excellent electron transport capabilities. The synergistic effect of the components within the heterojunction significantly enhances its electrocatalytic performance. Furthermore, the rapid surface reaction kinetics within the heterojunction ensure rapid electron transfer and timely consumption, reducing electron accumulation in the phosphide and inhibiting potential corrosion, thereby improving the stability of the catalyst.

[0082] Figure 3This is a nitrogen adsorption / desorption (BET) curve for CoP2-CoP-1 prepared in Example 1. The N2 adsorption-desorption isotherm and Barrett-Joyner-Halenda pore size distribution show that CoP2-CoP-1 prepared in Example 1 exhibits a typical type IV isotherm, indicating that the material has mesoporous properties, with a primary pore size distribution ranging from 2.0 to 4.0 nm. This pore structure facilitates the exposure of active sites, facilitating the adsorption of reactants and the desorption of products during the catalytic process, thereby improving catalytic efficiency.

[0083] The catalysts prepared in the examples and comparative examples and commercial Pt / C catalyst powder were used for alkaline electrocatalytic hydrogen evolution reaction, including the following application steps: 4 mg of catalyst and 1 mg of commercial carbon black were added to an ethanol-Nafion mixed solution (0.48 mL of ethanol and 0.02 mL of 0.5% Nafion solution), and after ultrasonication for 2 hours, a uniformly dispersed catalyst solution was obtained; 0.01 mL of catalyst solution was measured with a pipette and dripped onto a glassy carbon electrode, and after natural air drying, a catalyst-modified glassy carbon electrode was obtained; electrochemical tests were carried out on the American PINE rotating disk ring electrode apparatus (AFMSRCE) and CHI760E electrochemical workstation. The catalyst-modified glassy carbon electrode was used as the working electrode, the graphite rod was used as the counter electrode, and the saturated calomel was used as the reference electrode. The linear sweep voltammetry (LSV) test and cyclic stability test of the HER reaction were carried out in 1 M KOH aqueous solution, and the test results are shown in FIG. Figure 4-Figure 6 and Table 1.

[0084] Table 1 HER performance test results of the catalysts prepared in Examples 1-7 and Comparative Examples 1-2 and commercial Pt / C

[0085] name <![CDATA[Current density (mA·cm -2 )]]> Overpotential (mV) Example 1 10 59 Example 2 10 61 Example 3 10 62 Example 4 10 64 Example 5 10 62 Example 6 10 65 Example 7 10 65 Comparative Example 1 10 136 Comparative Example 2 10 151 Commercial Pt 10 53

[0086] Figure 4 The linear sweep voltammetry (LSV) performance test results of the catalyst prepared in Example 1 and commercial Pt / C materials in the hydrogen evolution reaction (HER) are used to further study the HER activity of the catalyst. Figure 4 It can be seen that the catalytic activity of Example 1 is close to that of commercial Pt / C, indicating that it has great potential in replacing Pt family catalysts to achieve hydrogen production by water electrolysis.

[0087] Figure 5 The catalysts prepared in Example 1, Comparative Examples 1-2, and commercial Pt / C catalysts were tested at 10 mA·cm -2 Overpotential diagram of hydrogen evolution reaction (HER) at current density of . Figure 5 As shown in Table 1, the transition metal phosphide homogeneous heterojunction alkaline hydrogen evolution electrocatalyst CoP2-CoP prepared in Example 1 has a high conductivity at 10 mA·cm-2 The overpotential at this current density is only 59~65 mV, which is comparable to commercial Pt / C (53mV@10mA·cm -2 ) and showed significantly enhanced hydrogen evolution reaction (HER) performance compared to the control sample. The fundamental reason for this performance difference is that, compared with the single-phase Co2P (136mV@10mA·cm -2 ) and CoP (151mV@10mA·cm -2 ) catalysts, the transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst CoP2-CoP contains both CoP2 with high intrinsic catalytic activity and CoP with excellent electron transport ability. Through the synergistic effect between different phases, it regulates the adsorption / desorption process of intermediates, thereby improving the reaction kinetics, accelerating the electron transfer between the surface and the inner layer, and exhibiting more excellent electrochemical hydrogen evolution activity.

[0088] Figure 6 The catalysts prepared in Example 1 and Comparative Examples 1-2 were shown to be -2 The hydrogen evolution reaction (HER) stability test results under 400 nm were used to further evaluate the long-term stability of the synthesized materials. Figure 6 As shown, Example 1 exhibited sustained stability and no significant performance degradation over a 30-hour electrocatalytic process, achieving the best stability, while both pure CoP2 and CoP exhibited significant activity degradation. This result demonstrates that the fast surface reaction kinetics within the heterostructure ensure rapid electron transfer and timely consumption, reducing electron accumulation in the phosphide, thereby inhibiting potential corrosion and improving the long-term stability of the catalyst.

[0089] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing a transition metal phosphide homogeneous heterojunction alkaline hydrogen evolution electrocatalyst, characterized in that: The following steps are involved: The Co(OH)2 powder was kept at 240-400℃ for 5-15min, and then cooled at room temperature to obtain a Co(OH)2-Co3O4 heterojunction. calcining the Co(OH)2-Co3O4 heterojunction and NaH2PO2·H2O powder in an inert atmosphere, and then naturally cooling to room temperature to obtain the transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst; The mass ratio of the Co(OH)2-Co3O4 heterojunction to the NaH2PO2·H2O powder is 1:(5-20); The inert atmosphere is an argon atmosphere; the calcination is specifically carried out at 1~10℃·min -1 Raise the temperature to 300~600℃ and keep it warm for 2h.

2. The method for preparing the transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst according to claim 1, characterized in that: The preparation method of Co(OH)2 comprises the following steps: ZIF-67 powder was dispersed in a mixed solvent of ethanol and deionized water, and then Na2MoO4·2H2O was added and heated until the purple color in the solution completely disappeared. The solution was then centrifuged, washed, and vacuum-dried to obtain Co(OH)2.

3. The method for preparing the transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst according to claim 2, characterized in that: The volume ratio of the ethanol to the deionized water is 1:0.3-2; the mass ratio of the ZIF-67 powder to the Na2MoO4·2H2O is 1:(2-4); the heating temperature is 50-95°C; and the vacuum drying temperature is 50-100°C.

4. A transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst prepared according to the preparation method according to any one of claims 1 to 3.

5. Use of the transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst as claimed in claim 4 in hydrogen production by electrolysis of water.

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