Preparation method, product and application of alkali hydrogen evolution electrocatalyst

Abstract

The invention relates to the field of catalyst preparation and new energy, in particular to a preparation method, a product and application of an alkali hydrogen evolution electrocatalyst. The Co (OH) 2 powder is subjected to heat preservation for 5-15 min at the temperature of 240-400 DEG C, after heat preservation is finished, the Co (OH) 2 powder is placed under the room temperature condition to be cooled, and a Co (OH) 2-Co3O4 heterojunction is obtained; and calcining the Co (OH) 2-Co3O4 heterojunction and NaH2PO2.H2O powder in an inert atmosphere, and then naturally cooling to room temperature, so as to obtain the transition metal phosphide homologous heterojunction alkali hydrogen evolution electrocatalyst. The catalyst simultaneously contains two phases of CoP2 with relatively high intrinsic catalytic activity and CoP with excellent electron transmission capability, and the synergistic effect of different phases improves reaction kinetics and accelerates electron transfer of the surface and the inner layer by adjusting the adsorption / desorption process of an intermediate product, so that the catalyst shows more excellent electrochemical hydrogen evolution activity.

Description

Technical Field

[0001] The present invention relates to the fields of catalyst preparation and new energy, and particularly 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 exhibits great potential to replace traditional fossil fuels. However, there is no natural reserve of hydrogen energy on Earth, and it needs to be obtained through hydrogen production means before it can be utilized. Using renewable energy such as wind energy or solar energy to provide electricity for electrolytic water hydrogen production has become the most promising green hydrogen production route. During the electrolytic water hydrogen production process, the catalyst material on the electrode surface is an important factor affecting the electrochemical hydrogen evolution reaction (HER). Developing inexpensive, efficient, and stable electrolytic water catalysts can reduce the overpotential of the reaction and effectively improve the hydrogen evolution efficiency. Currently, noble metal Pt is the HER catalyst with the best performance, but its reserves are scarce and the price is high, making it impossible to achieve large-scale hydrogen production applications. Therefore, it is necessary to study non-noble metal catalysts with rich sources, low cost, and high efficiency to replace Pt-based catalysts.

[0003] Transition metal phosphides (TMPs) are similar in structure and properties to hydrogenases, with stable catalytic activity and the bifunctional property of being able to act as hydrogen evolution and oxygen evolution catalysts. They are considered HER catalyst materials with broad application prospects. TMPs are composed of phosphorus (P) and transition metals (M). Due to their special structure and properties, TMPs have a very diverse M / P stoichiometry. According to the M / P atomic ratio, TMPs can be divided into phosphorus-rich phosphides (M / P < 1), single-phosphorus phosphides (M / P = 1), and metal-rich phosphides (M / P > 1). Among them, single-phosphorus and phosphorus-rich TMPs usually have excellent electrical conductivity because they have relatively abundant M—M bonds, contain more free electrons, and usually exhibit properties similar to metals. Most phosphorus-rich TMPs are semiconductors or insulators, but phosphorus-rich TMPs often have excellent intrinsic activity. This is mainly because P atoms can cause the d-band of metal atoms to contract, resulting in an enhanced density of electronic states near the Fermi level. Therefore, TMPs possess 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. The negatively charged P atoms weaken the chemical bond strength between the metal and H, thus promoting the desorption of H. In addition, the introduction of P atoms can also form chemical bonds with moderate strength with the reaction products, reducing the strong adsorption of H2 by pure metals and thus accelerating the detachment of H2. In order to balance the catalytic activity and conductivity of TMPs, most research efforts have focused on controlling the content of M and P in TMPs. However, in this way, it is difficult to fully utilize the advantages of different metal phosphides.

[0004] By coupling TMPs with different M / P atomic ratios, TMPs homologous heterojunctions can be constructed. This material can significantly promote the HER catalytic performance of its phosphorus-rich compound components by virtue of the excellent electron transport ability and catalytic activity of single-phosphorus and phosphorus-rich TMPs electrode materials, and thus fully utilize the advantages of different metal phosphides. However, there are few research works on constructing TMPs homologous heterojunctions. Usually, the construction process of heterojunctions is also relatively cumbersome, time-consuming, and energy-consuming. Therefore, it is of great significance to develop a simple and efficient method for rapidly preparing TMPs homologous heterojunction alkaline hydrogen evolution electrocatalysts.

[0005] The Chinese invention patent document with the publication number CN114715864A discloses a transition metal phosphide filled with non-metallic elements in phosphorus vacancies, its preparation, and a lithium-sulfur battery, belonging to the technical field of inorganic compound preparation. In this invention, cobalt hydroxide nanosheets are first prepared by electrodeposition, and then the cobalt hydroxide nanosheets and sodium phosphite are calcined at the upper and lower ends of a tube furnace. After calcination, they are treated with a sodium borohydride solution and washed with deionized water. Finally, under different calcination conditions, non-metallic elements such as sulfur, nitrogen, fluorine, chlorine, or boron and transition metal phosphides containing phosphorus vacancies are calcined in an inert atmosphere to prepare transition metal phosphides filled with non-metallic elements in phosphorus vacancies. The cobalt hydroxide precursor prepared by the electrodeposition method in this invention has low yield, high energy consumption, complex equipment, low efficiency, and cannot achieve the regulation of the ratio of metal and P atoms.

[0006] The Chinese invention patent document with the publication number CN117861693A discloses a phosphorus-rich transition metal phosphide catalyst, its synthesis method, and application. In this invention, NiCl2 is first subjected to dynamic vacuum drying, then vacuum ground and compressed into tablets. Then, the tablets are placed at the closed end of an ampoule bottle with a single-side seal. Red phosphorus is weighed under vacuum and placed at the other end of the ampoule bottle, and then the ampoule bottle is sealed with a methane-oxygen torch. Finally, the ampoule bottle is placed in the constant temperature section of a tube furnace and calcined at a high temperature in an inert atmosphere to obtain a solid phosphorus-rich transition metal phosphide (NiP2). The preparation method of this phosphorus-rich metal phosphide is cumbersome, has low efficiency, and does not involve the regulation of the metal and phosphorus content.

[0007] The Chinese invention patent document with the publication number CN101613097B discloses a preparation method of a new material of carbon-supported transition metal phosphides (Fe2P, Co2P, Ni 12 P5). In this invention, a soluble Group VIII metal salt is first added to a resorcinol solution and stirred to dissolve. Subsequently, diammonium hydrogen phosphate is added to the above solution in a certain proportion to form a precipitate. An appropriate amount of concentrated nitric acid is added dropwise until the precipitate just dissolves. A formaldehyde solution is added dropwise under stirring, and the solution forms a gel. After drying and high-temperature calcination in an inert atmosphere, a gel carbon modified with metal phosphide can be obtained. Although this method is simple to prepare, the product is single, it does not involve the regulation of the ratio of transition metal and phosphorus, and the traditional calcination method takes a long time, has high energy consumption, and low efficiency.

[0008] The Chinese invention patent document with the publication number CN113772644A discloses a bimetallic phosphide, its preparation method and application. The invention prepares the bimetallic phosphide by the co-precipitation method. First, potassium ferricyanide and cobalt salt are subjected to a co-precipitation reaction to prepare iron-cobalt Prussian blue. The product is transferred to a tubular furnace and reacted at 600 °C for 2 h under an inert atmosphere. The iron-cobalt Prussian blue is subjected to phosphating treatment to prepare the bimetallic phosphide. When preparing the phosphide heterojunction, the traditional calcination method is used, which requires a reaction at 600 °C for 2 h. The reaction time is long and the energy consumption is high. Moreover, the composite material of this method does not involve the regulation of the ratio of transition metal and phosphorus in the homologous heterojunction and phosphide.

[0009] The Chinese invention patent document with the publication number CN115377605B discloses a hollow metal oxide-metal phosphide heterojunction material, its preparation method and application. The invention first prepares metal compound-coated resorcinol-formaldehyde nanospheres by the sol-gel method, and then calcines the obtained material in air at 600 °C for 3 h to obtain a hollow metal oxide precursor; then the obtained hollow metal oxide precursor is calcined at 350 °C for 2 h and phosphated to obtain a hollow metal oxide-metal phosphide heterojunction. This method uses the traditional step-by-step calcination method, which requires heat preservation at 600 °C and 350 °C in an inert gas for 3 h and 2 h respectively. The preparation efficiency of the catalyst is low and the energy consumption is high. In addition, the carrier of the catalyst does not involve the regulation of the ratio of transition metal and phosphorus in the heterojunction. Summary of the Invention

[0010] The purpose of the present invention is to provide a preparation method, product and application of a homologous heterojunction alkaline hydrogen evolution electrocatalyst of transition metal phosphide. The method of the present invention can solve the problems of low intrinsic activity, slow charge transfer rate, poor stability and long reaction time of the transition metal phosphide electrocatalyst prepared by the traditional method. The present invention prepares a Co(OH)2-Co3O4 heterojunction through a rapid heating and cooling process, and then phosphates the Co(OH)2-Co3O4 heterojunction to prepare a homologous heterojunction alkaline hydrogen evolution electrocatalyst CoP2-CoP of transition metal phosphide.

[0011] To achieve the above purpose, the present invention provides the following solutions: One of the technical solutions of the present invention, a preparation method of a homologous heterojunction alkaline hydrogen evolution electrocatalyst of transition metal phosphide, includes the following steps: Keep the Co(OH)2 powder at 240-400 °C for 5-15 min, and cool it to room temperature after the insulation ends to obtain a Co(OH)2-Co3O4 heterojunction; 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).

[0012] The second technical solution of the present invention is a transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst (abbreviation: catalyst) prepared according to the above preparation method.

[0013] 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 electrolyzing water.

[0014] The transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst prepared in the present invention is a HER catalyst with high activity and high stability, mainly due to: (1) it contains both CoP2 and CoP phases at the same time. Because CoP2 has a higher P content, the catalyst has higher intrinsic catalytic activity. At the same time, the presence of CoP can provide excellent electron transport ability. Therefore, the heterojunction can balance the intrinsic catalytic activity and conductivity of TMPs; (2) The synergistic effect between different phases inside 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.

[0015] The present invention discloses the following technical effects: (1) By controlling the calcination time of cobalt hydroxide in the present invention, the phase of the calcined product can be regulated, and then the preparation of the transition metal phosphide homologous heterojunction can be realized by a simple one-step phosphidation method.

[0016] (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 both CoP2 with higher intrinsic catalytic activity and CoP with excellent electron transport ability at the same time. The synergistic effect between different phases improves the reaction kinetics by regulating the adsorption / desorption process of intermediate products, accelerates the electron transfer on the surface and in the inner layer, and exhibits more excellent electrochemical hydrogen evolution activity.

[0017] (3) Compared with the traditional strategies for constructing phosphide-based composite materials, such as the growth-secondary growth-phosphidation strategy, the composite material synthesis method in the present invention is relatively simple and can simultaneously form a homologous single-phosphorus-rich phosphorus heterojunction material. Description of the Drawings

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can also be obtained based on these drawings.

[0019] Figure 1 X-ray powder diffraction (XRD) patterns of the Co(OH)2-Co3O4 heterojunction prepared in Example 1, Co(OH)2 prepared in Comparative Example 1, and Co3O4 prepared in Comparative Example 2.

[0020] Figure 2 X-ray diffraction (XRD) patterns of the catalysts prepared in Example 1 and Comparative Examples 1-2.

[0021] Figure 3 N2 adsorption-desorption (BET) isotherm curve of the catalyst prepared in Example 1.

[0022] Figure 4 Linear sweep voltammetry (LSV) curve of the hydrogen evolution reaction (HER) of the catalyst prepared in Example 1 and commercial Pt / C catalyst at a current density of 10 mA·cm -2 -2.

[0023] Figure 5 Overpotential diagram of the hydrogen evolution reaction (HER) of the catalysts prepared in Example 1 and Comparative Examples 1-2 and commercial Pt / C catalyst at a current density of 10 mA·cm -2 -2.

[0024] Figure 6 Cyclic stability test diagram of the hydrogen evolution reaction (HER) of the catalysts prepared in Example 1 and Comparative Examples 1-2 at a current density of 10 mA·cm -2 -2. Detailed Embodiments

[0025] The various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0026] It should be understood that the terms used in the present invention are only for describing specific embodiments and are not intended to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0027] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although only preferred methods and materials are described in this invention, any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of this invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the said documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0028] Without departing from the scope or spirit of this invention, various improvements and changes can be made to the specific embodiments of the description of this invention, which are obvious to those skilled in the art. Other embodiments obtained from the description of this invention are obvious to those skilled in the art. The description and examples of this invention are merely exemplary.

[0029] Regarding the use of "comprising", "including", "having", "containing", etc. herein, they are all open-ended terms, meaning including but not limited to.

[0030] As used in this invention, "room temperature" means 20 - 30 °C unless otherwise specified.

[0031] The first aspect of this invention provides a preparation method of a transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst, comprising the following steps: Keep the Co(OH)₂ powder at 240 - 400 °C for 5 - 15 min, and after the heat preservation, place it at room temperature to cool down to obtain a Co(OH)₂-Co₃O₄ heterojunction; Calcine the Co(OH)₂-Co₃O₄ heterojunction and NaH₂PO₂·H₂O powder in an inert atmosphere, and then naturally cool it to room temperature to obtain the transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst (CoP₂-CoP).

[0032] In a preferred embodiment of this invention, the way of cooling down during the preparation of the Co(OH)₂-Co₃O₄ heterojunction is to take out the sample and quickly cool it at room temperature.

[0033] The commonly used way of cooling down in the art is to naturally cool in a muffle furnace. The muffle furnace itself has good heat preservation effect and a very slow cooling rate, and it takes several hours to complete the cooling. Slow cooling will cause the sample to maintain at a high temperature for a long time and is easily completely converted into Co₃O₄, and it is impossible to obtain a Co(OH)₂-Co₃O₄ heterojunction; in this invention, by the way of quickly cooling, after the heat preservation, take out the sample and place it at room temperature to cool down. The cooling rate is fast, and the sample is not completely converted into Co₃O₄, thus obtaining a Co(OH)₂-Co₃O₄ heterojunction.

[0034] If the heating rate is slow, it will cause the complete conversion of Co(OH)2 powder into Co3O4, and the Co(OH)2-Co3O4 heterojunction cannot be obtained. In the present invention, the Co(OH)2 powder is directly transferred to an environment of 240-400 °C for heat preservation for a certain time, and the heating rate is fast, which can avoid the complete conversion of Co(OH)2 powder into Co3O4, thereby obtaining the Co(OH)2-Co3O4 heterojunction.

[0035] 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).

[0036] In a preferred embodiment of the present invention, the inert atmosphere is an argon atmosphere; the calcination specifically is to heat up to 300-600 °C at a rate of 1-10 °C·min -1 and keep warm for 2 h.

[0037] In a preferred embodiment of the present invention, the Co(OH)2-Co3O4 heterojunction and the NaH2PO2·H2O powder are respectively placed at the upper and lower ends of a tube furnace heating device and calcined in a high-purity argon atmosphere.

[0038] In a preferred embodiment of the present invention, the preparation method of the Co(OH)2 includes the following steps: Disperse the ZIF-67 powder in a mixed solvent of ethanol and deionized water, then add Na2MoO4·2H2O and heat until the purple color in the solution completely disappears, and then centrifuge, wash, and vacuum dry in sequence to obtain Co(OH)2. Co(OH)2 with the same specific structure and elemental composition obtained through other means such as the purchase route is also applicable to the present invention.

[0039] 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; the temperature of the vacuum drying is 50-100 °C.

[0040] In a preferred embodiment of the present invention, when preparing Co(OH)2, the number of washing times is 2-5 times.

[0041] In a preferred embodiment of the present invention, the preparation method of the ZIF-67 powder includes the following steps: Add the 2-methylimidazole methanol solution to the zinc nitrate hexahydrate methanol solution for reaction, and then centrifuge, wash, and vacuum dry in sequence to obtain the ZIF-67 powder.

[0042] In a preferred embodiment of the present invention, the concentration of the 2-methylimidazole methanol solution is 0.16 M; the concentration of the zinc nitrate hexahydrate methanol solution is 0.02 M; the volume ratio of the 2-methylimidazole methanol solution to the zinc nitrate hexahydrate methanol solution is 5:3; the temperature of the reaction is room temperature, and the time is 2 to 24 h; the temperature of the vacuum drying is 50 to 100 °C.

[0043] In some embodiments of the present invention, when preparing the ZIF-67 powder, the number of washing times is 2 to 5 times.

[0044] The second aspect of the present invention provides a transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst prepared by the above preparation method.

[0045] The third aspect of the present invention provides the application of the above-mentioned transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst in hydrogen production by electrolyzing water.

[0046] The homologous heterojunction prepared by the present invention contains both a single phosphorus compound and a phosphorus-rich compound. The phosphorus-rich compound CoP2 can improve the intrinsic activity of the catalyst, while the single phosphorus compound CoP has good electrical conductivity and can provide excellent electron transport ability for the catalyst; in addition, the synergistic effect between different phases adjusts the adsorption / desorption process of intermediate products, improves the reaction kinetics, accelerates the electron transfer on the surface and in the inner layer, and exhibits more excellent electrochemistry hydrogen evolution performance. Under the synergistic effect of two phases, the transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst prepared by the method of the present invention can maintain stable operation for 30 h at a constant current of 10 mA·cm -2 without obvious performance degradation and has excellent alkaline HER performance.

[0047] The technical solutions of the present invention are all conventional solutions in the art unless otherwise specified. The reagents or raw materials used are all purchased from commercial channels or have been made public unless otherwise specified.

[0048] The technical solutions provided by the present invention will be described in detail below with reference to the examples, but they cannot be construed as limiting the protection scope of the present invention.

[0049] Example 1 Step 1, quickly add 50 mL of 0.16 M 2-methylimidazole methanol solution to 30 mL of 0.02 M zinc nitrate hexahydrate methanol solution. After reacting at room temperature for 16 h, the obtained suspension is centrifuged with methanol and washed with methanol 4 times, and then dried in vacuum at 60 °C to obtain ZIF-67 powder.

[0050] Step 2: Disperse 40 mg of ZIF-67 powder in a mixed solution of 20 mL of ethanol and 10 mL of deionized water. Then, add 100 mg of Na2MoO4·2H2O under stirring, and then heat at 80 °C until the purple color completely disappears. The obtained product is washed with deionized water and centrifuged 3 times, and then vacuum dried at 70 °C to obtain Co(OH)2.

[0051] Step 3: Preheat the muffle furnace to 300 °C. Subsequently, transfer the Co(OH)2 powder to the muffle furnace and keep it warm for 10 min. Then, take out the sample and quickly cool it to room temperature to obtain the Co(OH)2-Co3O4 heterojunction.

[0052] Step 4: Place 40 mg of the obtained Co(OH)2-Co3O4 heterojunction and 0.4 g of NaH2PO2·H2O powder at the upper and lower ends of the heating device of the tubular furnace respectively. Under the atmosphere of high-purity argon, heat the tubular furnace to 450 °C at a rate of 2 °C·min -1 and keep it for 2 h, then naturally cool it to room temperature to obtain a black powder, that is, the transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst, denoted as CoP2-CoP-1.

[0053] Example 2 The difference from Example 1 is only that in Step 2, 100 mg of Na2MoO4·2H2O is replaced by 80 mg of Na2MoO4·2H2O, and the rest of the steps and parameters are the same as those in Example 1; the prepared catalyst is denoted as CoP2-CoP-2.

[0054] Example 3 The difference from Example 1 is only that in Step 2, 100 mg of Na2MoO4·2H2O is replaced by 150 mg of Na2MoO4·2H2O, and the heating at 80 °C is replaced by heating at 60 °C, and the rest of the steps and parameters are the same as those in Example 1; the prepared catalyst is denoted as CoP2-CoP-3.

[0055] Example 4 The difference from Example 1 is only that in Step 3, the 10-min heat preservation in the muffle furnace is replaced by a 5-min heat preservation in the muffle furnace, and the rest of the steps and parameters are the same as those in Example 1; the prepared catalyst is denoted as CoP2-CoP-4.

[0056] Example 5 The difference from Example 1 is only that in Step 3, the 10-min heat preservation in the muffle furnace is replaced by a 15-min heat preservation in the muffle furnace, and the rest of the steps and parameters are the same as those in Example 1; the prepared catalyst is denoted as CoP2-CoP-5.

[0057] Example 6 The difference from Example 1 is only that in Step 4, the calcination heating temperature of the tubular furnace is changed from 450 °C to 400 °C, and the remaining steps and parameters are the same as those in Example 1; the prepared catalyst is denoted as CoP2-CoP-6.

[0058] Example 7 The difference from Example 1 is only that in Step 4, the calcination heating temperature of the tubular furnace is changed from 450 °C to 500 °C, and the remaining steps and parameters are the same as those in Example 1; the prepared catalyst is denoted as CoP2-CoP-7.

[0059] Comparative Example 1 The difference from Example 1 is only 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 heating device of the tubular furnace. Under a high-purity argon atmosphere, the tubular furnace is heated to 450 °C at a rate of 2 °C·min -1 and maintained for 2 h, and then naturally cooled to room temperature to obtain a black powder; the prepared catalyst is denoted as CoP2.

[0060] Comparative Example 2 The difference from Example 1 is only that in Step 3, the holding time in the muffle furnace is replaced from 10 min to 120 min to obtain black Co3O4 powder; in Step 4, 40 mg of Co3O4 prepared in Step 3 and 0.4 g of NaH2PO2·H2O powder are respectively placed at the upper and lower ends of the heating device of the tubular furnace. Under a high-purity argon atmosphere, the tubular furnace is heated to 450 °C at a rate of 2 °C·min -1 and maintained for 2 h, and then naturally cooled to room temperature to obtain a black powder; the prepared catalyst is denoted as CoP.

[0061] Figure 1 Figure 23 is the X-ray powder diffraction (XRD) pattern of the Co(OH)2-Co3O4 heterojunction prepared in Example 1, Co(OH)2 prepared in Comparative Example 1, and Co3O4 prepared in Comparative Example 2. The Co(OH)2 synthesized in Comparative Example 1 matches its standard card (PDF#45-0031), and the Co3O4 synthesized in Comparative Example 2 is consistent with its standard card (PDF#42-1467). The Co(OH)2-Co3O4 heterojunction in Example 1 conforms to both of these two standard cards, indicating that this heterojunction is composed of Co(OH)2 and Co3O4.

[0062] Figure 1The results show that the phase of the calcined product can be effectively controlled by adjusting the holding time in the muffle furnace in step 3; when no holding treatment is carried out, the single-phase Co(OH)2 will not be converted into Co3O4 and no heterojunction can be formed; while too long holding time will lead to the complete conversion of Co(OH)2 into Co3O4 and also no heterojunction can be formed. Both of these situations are not conducive to the formation of the subsequent homologous heterojunction of phosphides. Therefore, by precisely controlling the calcination time of Co(OH)2 in the muffle furnace, the phase of the calcined product can be effectively regulated, and thus the precise control of the formation of the homologous heterojunction of transition metal phosphides can be achieved.

[0063] Figure 2 Figure 4 is the X-ray diffraction (XRD) pattern 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), and 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 the above two standard cards, indicating that this heterojunction is composed of CoP2 and CoP, while Comparative Example 1 and Comparative Example 2 are single-phase CoP2 and CoP respectively.

[0064] CoP2-CoP-1 in Example 1 contains both CoP2 with high intrinsic catalytic activity and CoP with excellent electron transport ability. Through the synergistic effect of the components inside the heterojunction, its electrocatalytic performance can be significantly enhanced. In addition, the fast surface reaction kinetics in the heterostructure ensures the rapid transfer and timely consumption of electrons, reduces the electron accumulation in the phosphide, and inhibits potential corrosion, thus improving the stability of the catalyst.

[0065] Figure 3 Figure 5 is the nitrogen adsorption-desorption (BET) curve of CoP2-CoP-1 prepared in Example 1. It can be seen from the N2 adsorption-desorption isotherm and the Barrett-Joyner-Halenda pore size distribution map that CoP2-CoP-1 prepared in Example 1 presents a typical Type IV isotherm, indicating that this material has mesoporous characteristics, and its main pore size distribution is in the range of 2.0 - 4.0 nm. This pore structure helps to expose the active sites and is conducive to the adsorption of reactants and the desorption of products during the catalytic process, thus improving the catalytic efficiency.

[0066] The catalysts prepared in the examples and comparative examples, as well as the commercial Pt / C catalyst powder, were respectively used for the alkaline electrocatalytic hydrogen evolution reaction, including the following application steps: 4 mg of the catalyst and 1 mg of commercial carbon black were added to an ethanol-Nafion mixed solution (a mixture of 0.48 mL of ethanol and 0.02 mL of 0.5% Nafion solution), and after ultrasonic treatment for 2 h, a uniformly dispersed catalyst solution was obtained; 0.01 mL of the catalyst solution was measured with a pipette and dropped onto a glassy carbon electrode, and after natural drying, a catalyst-modified glassy carbon electrode was obtained; the electrochemical tests were carried out on an American PINE rotating disk ring electrode device (AFMSRCE) and a CHI760E electrochemical workstation. The catalyst-modified glassy carbon electrode was used as the working electrode, a graphite rod as the counter electrode, and a saturated calomel electrode as the reference electrode. Linear sweep voltammetry (LSV) tests and cyclic stability tests of the HER reaction were carried out in 1 M KOH aqueous solution, and the test results are shown in Figures 4 - 6 and Table 1.

[0067] Table 1 HER performance test results of the catalysts prepared in Examples 1-7 and Comparative Examples 1-2 and commercial Pt / C 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 Figure 4 Figure Figure 4 shows the linear sweep voltammetry (LSV) performance test results of the catalyst prepared in Example 1 and the commercial Pt / C material in the hydrogen evolution reaction (HER), which are used for further studying the HER activity of the catalyst. As can be seen from

[0068] Figure 5 Figure -2 is the overpotential diagram of the hydrogen evolution reaction (HER) of the catalysts prepared in Example 1, Comparative Examples 1-2, and the commercial Pt / C catalyst at a current density of 10 mA·cm Figure 5 . As can be seen from -2 and Table 1, the overpotential of the transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst CoP2-CoP prepared in the example at a current density of 10 mA·cm -2 is only 59-65 mV, which is similar to that of commercial Pt / C (53 mV@10 mA·cm -2 ), and shows significantly enhanced hydrogen evolution reaction (HER) performance compared with the comparative samples. The fundamental reason for this performance difference is that compared with single-phase Co2P (136 mV@10 mA·cm -2Compared with the catalyst, the transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst CoP2-CoP simultaneously contains CoP2 with high intrinsic catalytic activity and CoP with excellent electron transport ability. Through the synergistic effect between different phases, the adsorption / desorption process of intermediate products is regulated, thereby improving the reaction kinetics, accelerating the electron transfer on the surface and in the inner layer, and showing more excellent electrochemically hydrogen evolution activity.

[0069] Figure 6 The hydrogen evolution reaction (HER) stability test results of the catalysts prepared in Example 1 and Comparative Examples 1-2 at a constant current density of 10 mA·cm -2 are shown below, which are used to further evaluate the long-term stability of the synthesized materials. As Figure 6 shown, Example 1 showed continuous stability during the 30-hour electrocatalytic process, and there was no obvious performance decay, with the best stability. While both pure CoP2 and CoP showed obvious activity decay. This result indicates that the fast surface reaction kinetics in the heterostructure can ensure the rapid transfer and timely consumption of electrons, reduce the electron accumulation in the phosphide, thereby inhibiting potential corrosion and improving the long-term stability of the catalyst.

[0070] The above-described embodiments are only descriptions of the preferred modes of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention should fall within the protection scope determined by the claims of the present invention.

Claims

1. A preparation method of a transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst, characterized in that, It includes the following steps: Keep the Co(OH)2 powder at 240 - 400 °C for 5 - 15 min, and after the heat preservation, let it cool to room temperature to obtain the Co(OH)2 - Co3O4 heterojunction; Calcine the Co(OH)2 - Co3O4 heterojunction and the NaH2PO2·H2O powder in an inert atmosphere, and then naturally cool to room temperature to obtain the transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst.

2. The preparation method of the transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst according to claim 1, characterized in that, The mass ratio of the Co(OH)2 - Co3O4 heterojunction to the NaH2PO2·H2O powder is 1∶(5 - 20).

3. The preparation method of the transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst according to claim 1, characterized in that, The inert atmosphere is an argon atmosphere; the calcination is specifically heating to 300-600 °C at a rate of 1-10 °C·min -1 and holding for 2 h.

4. The preparation method of the transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst according to claim 1, characterized in that, The preparation method of the Co(OH)2 includes the following steps: Disperse the ZIF-67 powder in a mixed solvent of ethanol and deionized water, then add Na2MoO4·2H2O and heat until the purple color in the solution completely disappears, and then centrifuge, wash, and vacuum dry in sequence to obtain Co(OH)2.

5. The preparation method of the transition metal phosphide homologous heterojunction alkali evolution hydrogen electrocatalyst according to claim 4, 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; the vacuum drying temperature is 50 - 100 °C.

6. The preparation method of the transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst according to claim 4, characterized in that, The preparation method of the ZIF-67 powder includes the following steps: Add the 2-methylimidazole methanol solution to the zinc nitrate hexahydrate methanol solution for reaction, and then centrifuge, wash, and vacuum dry in sequence to obtain the ZIF-67 powder.

7. The preparation method of the transition metal phosphide homologous heterojunction alkali evolution hydrogen electrocatalyst according to claim 6, characterized in that, The concentration of the 2-methylimidazole methanol solution is 0.16 M; the concentration of the zinc nitrate hexahydrate methanol solution is 0.02 M; the volume ratio of the 2-methylimidazole methanol solution to the zinc nitrate hexahydrate methanol solution is 5∶3; the reaction temperature is room temperature and the time is 2 - 24 h; the vacuum drying temperature is 50 - 100 °C.

8. A transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst prepared by the preparation method according to any one of claims 1 - 7.

9. The application of the transition metal phosphide homologous heterojunction alkaline hydrogen evolution electrocatalyst according to claim 8 in hydrogen production by electrolyzing water.

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