A NF / Co8FeS8-Co2P-Fe2P composite material with a three-phase heterogeneous structure and its preparation method and application

Abstract

The present invention discloses a NF / CoFeS-CoP-FeP composite material with a three-phase heterogeneous structure. The composite material uses nickel foam as a substrate and a self-supporting skeleton. Cobalt nitrate hexahydrate and ferric nitrate nonahydrate are used as raw materials, and thiourea is used as a sulfur source. Partially sulfided cobalt iron sulfide and cobalt iron hydroxide are grown on the nickel foam. Sodium hypophosphite is used as a phosphorus source to convert the cobalt iron hydroxide into cobalt iron phosphide. Co8FeS8 is a spherical magic cube structure; Co2P is a spherical nanosheet structure; Fe2P is a nanosheet structure; Co8FeS8 combines with Co2P and Fe2P to form a three-phase heterogeneous structure. The preparation method includes the following steps: 1. Preparation of NF / CoFeS-CoOH-FeOH; 2. Preparation of NF / CoFeS-CoP-FeP. When used as a hydrogen evolution catalyst material, it reacts in a 1M KOH solution and reacts in the range of 0 to 0.1V when the current density is 10mA·cm ‑2 When NF / CoFeS‑CoP‑FeP is used, the overpotential is 61‑67 mV and the Tafel slope is 99.51‑105.23 mV·dec ‑1 ; Under the condition of a cycle time of 24h, the current retention rate of NF / CoFeS‑CoP‑FeP is 98%.

Description

Technical Field

[0001] The present invention relates to the technical field of electrocatalytic hydrogen evolution, and in particular to a NF / Co8FeS8-Co2P-Fe2P composite material with a three-phase heterogeneous structure, a preparation method and applications thereof. Background Art

[0002] Platinum-based precious metal materials have low overpotential, large exchange current density and good stability, and are currently the most attractive HER electrocatalysts. However, the scarcity and high price of precious metals limit the commercial application of such materials. There are also problems such as susceptibility to corrosion and reduced life under strong acid or strong base conditions. Therefore, the current common solution is to use low-cost non-precious metal HER electrocatalysts, such as transition metal sulfides, which have been widely used as materials for hydrogen evolution in alkaline water electrolysis. Among them, the S atoms in single-component transition metal sulfides usually regulate the electronic configuration of the transition metal by generating S vacancies to promote the dissociation of water molecules, and have good HER performance. However, single-component transition metal sulfides as hydrogen evolution reaction catalysts have problems such as fewer active components and low intrinsic catalytic activity.

[0003] In order to solve the problem of poor catalytic performance of single-component transition metal catalysts due to low intrinsic activity of the catalyst, the synergistic enhancement effect can be reflected at different active sites and electronic reconstruction interfaces through the synergistic effect of multiple components, so as to improve the adsorption capacity of the catalyst for hydrogen atoms and promote the electrochemical hydrogen evolution reaction. For example, the existing document 1 (Ni-Mo-STernary Chalcogenide Thin Film for Enhanced Hydrogen Evolution Reaction [J]. Catalysis Letters, 2021.) uses a two-step method of co-sputtering and thermal sulfurization of Ni-Mo alloy films to prepare Ni-Mo-S ternary sulfide films with different Ni concentrations. The Ni-Mo-S film obtained by this technical solution has a Ni concentration of 50 at.%, and a current density of 10 mA cm -2 Under the conditions of , the overpotential is 400mV. The reason is that the introduction of Ni element can change the morphology and electronic structure of the MoS2 film, thereby promoting the HER kinetics, and can improve the adsorption of H ions, thereby improving the performance of the electrocatalytic hydrogen evolution reaction. However, since the basic morphology of the material obtained by this technical solution is a thin film, it directly leads to a small double-layer capacitance value caused by the planar two-dimensional structure, as well as the instability of the structure itself, which is specifically reflected in the obvious attenuation of the potential when the number of CV cycles is 1000.

[0004] In order to solve the problems of small electrochemical active surface area and poor structural stability of multi-element transition metals, the catalyst morphology can be regulated by anion synergistic doping, the electrochemical active surface area can be increased, and the HER performance can be improved. Among them, the introduction of P element can form a synergistic effect through S element and P element, which can promote the adsorption of thermoneutral electrons and realize electron redistribution, thereby increasing the electrochemical active area, and realizing activation when adsorbing hydrogen ions, that is, obtaining activated hydrogen ions, thereby reducing the energy barrier of the hydrogen evolution reaction and accelerating the hydrogen evolution reaction rate. For example, the existing document 2 (Facile hydrothermal synthesis of combined MoSe2PS nanostructures on nickel foam with superior electrocatalytic properties for hydrogen evolution reaction [J]. International Journal of Hydrogen Energy, 2023.) synthesized a MoSe2PS composite nanomaterial with a petal structure covered with slender nanoleafs on the surface of nickel foam by a three-step hydrothermal method. This technical solution achieved a high performance at 10 mA cm -2 The overpotential reaches 90mV at a current density of 1000 Å. The reason is as mentioned above, that is, the P and S elements effectively increase the electrochemical active sites of MoSe2 and improve the adsorption and desorption of hydrogen atoms on the catalyst surface. However, this structural morphology also leads to new technical problems. That is, the petal-shaped MoSe2PS composite nanomaterial covered with slender nanoblades is in direct contact with the electrolyte during the hydrogen evolution reaction. After a long period of circulation, the catalyst partially falls off, resulting in poor stability of this technical solution.

[0005] In order to improve the stability of multi-transition metal catalysts, the stability of the composite material can be improved by constructing a heterostructure and through the strong coupling of heterogeneous interfaces. Existing literature 3 (High activity and stabilityin Ni2P(Co,Ni)OOH heterointerface with a multiple-hierarchy structure foralkaline hydrogen evolution reaction[J].Nano Research,2023.) First, nickel foam is used as the working electrode, Hg / HgO is used as the reference electrode, graphite rod is used as the counter electrode, and cobalt chloride hexahydrate aqueous solution is used as the electrolyte to obtain (Co,Ni)OOH by electrodeposition. Then, phosphorus powder is used as the raw material and Ni2P(Co,Ni)OOH is obtained by annealing. This technical solution obtains the reaction temperature at a current density of 100mA·cm-2 Under the conditions of 100 nm, the overpotential is only 169 mV, and the current decay is negligible after 36 hours of chronopotentiometry. The reason for the improved performance of this technical solution is that the strong charge transfer at the Ni2P(Co,Ni)OOH heterojunction eliminates the spin asymmetry and enables the thermoneutral adsorption of active H atoms. The resulting Coulomb attraction firmly stacks the two materials together, while improving the stability and hydrogen evolution catalytic performance.

[0006] In order to improve the performance of electrocatalytic hydrogen evolution, a third phase component can also be introduced. For example, the previous work results of the research group of the inventor of the present invention, the existing document 4 (NF / rGO / CoNi2S4-MoO2 nanosheets with a core-shell structure formed: An efficient electrocatalyst for the hydrogen evolution reaction [J]. Journal of Alloys and Compounds, 2024, i.e. application number: 2024110685776, a NFrGOCo-Ni-SMo-O self-supporting composite material and its preparation method and application) is based on nickel foam, cobalt nitrate hexahydrate, nickel nitrate hexahydrate, urea and ammonium fluoride as raw materials, and reduced graphene oxide is also introduced as a third phase component. The specific preparation method is to obtain NF / rGO / CoNi2O4 by hydrothermal preparation, and then use ammonium molybdate tetrahydrate and thiourea as raw materials to hydrothermally prepare NF / rGO / CoNi2S4-MoO2 again. The hydrogen evolution catalytic performance is achieved at a current density of 10mA·cm -2 Under the conditions of , the overpotential is only 65mV. The purpose of this technical solution is to simplify the preparation process and reduce the loss of active substances. Therefore, the purpose of selecting the third phase component as rGO, that is, its role in the technical solution is to use the active sites and adjustable micromorphology of rGO itself to composite with the self-supporting material NF with a smooth surface to anchor the active substance on the surface of NF and reduce agglomeration. Therefore, rGO does not form a three-phase heterogeneous structure with the other two components. This technical solution shows that not any preparation method can construct a three-phase heterogeneous structure by combining any three-phase components.

[0007] Therefore, the technical problem existing in the prior art is that, although a three-phase component or even a multi-phase component can be formed by introducing multiple transition metal cations or sulfur and phosphorus anions, a three-phase heterogeneous structure cannot be constructed. Summary of the Invention

[0008] The present invention aims to provide a NF / CoFeS-CoP-FeP composite material with a three-phase heterogeneous structure, a preparation method and an application thereof.

[0009] The basic principle involved in the present invention is that in a heterogeneous structure, the strong coupling effect between the interfaces of the heterogeneous interface can enhance the binding force between the materials, accelerate the rapid transfer of electrons and ions in the entire electrocatalyst, and improve the cyclic stability and hydrogen evolution efficiency of the catalyst. In order to obtain the above-mentioned effect, the technical problem to be solved by the present invention is to construct a three-phase heterogeneous structure by a simple two-step method. The specific method is to control the addition amount of sulfur element when the surface of nickel foam NF is loaded with binary transition metal elements to achieve partial sulfurization, and then phosphide the unsulfurized transition metal to construct a three-phase heterogeneous structure.

[0010] Among them, binary transition metal elements promote HER kinetics by changing the electron distribution through the interaction between different metals, thereby improving the adsorption of H ions, reducing the charge transfer resistance, and enhancing the electrocatalytic hydrogen evolution performance;

[0011] The sulfides and phosphides formed after sulfidation and phosphiding promote the adsorption of thermally neutral electrons / ions through the synergistic effect of sulfur and phosphorus, realize the redistribution of electrons, increase the electrochemical active area, and obtain activation when adsorbing hydrogen ions, that is, obtain activated hydrogen ions, thereby reducing the energy barrier of the hydrogen evolution reaction and promoting the performance of the hydrogen evolution reaction;

[0012] The present invention can be simply summarized as follows: by performing phosphating on the basis of partially sulfided cobalt iron hydroxide, a dual-doping synergistic effect is obtained while constructing a three-phase heterojunction structure. That is, through a simple preparation process, the micromorphology of the composite material can be regulated to improve the hydrogen evolution performance and cycle performance of the catalyst.

[0013] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is as follows:

[0014] A NF / CoFeS-CoP-FeP composite material with a three-phase heterogeneous structure is described. The composite material uses nickel foam as a substrate and a self-supporting skeleton. Cobalt nitrate hexahydrate and ferric nitrate nonahydrate are used as raw materials, and thiourea is used as a sulfur source. A partially sulfurized cobalt iron sulfide and cobalt iron hydroxide (NF / CoFeS-CoOH-FeOH) are grown on the nickel foam via a hydrothermal method. Sodium hypophosphite is then used as a phosphorus source. A one-step phosphating method is then used to convert the cobalt iron hydroxide into cobalt iron phosphide, thereby obtaining cobalt iron sulfide and cobalt iron phosphide NF / CoFeS-CoP-FeP grown on the nickel foam.

[0015] The micromorphology of the Co8FeS8 is a spherical Rubik's cube structure; the micromorphology of the Co2P is a spherical nanosheet structure; the micromorphology of the Fe2P is a nanosheet structure; and the spherical Rubik's cube-shaped Co8FeS8 and the spherical nanosheet-shaped Co2P are combined together and grown on the Fe2P nanosheet to form a three-phase heterogeneous structure.

[0016] A method for preparing a NF / CoFeS-CoP-FeP composite material with a three-phase heterogeneous structure comprises the following steps:

[0017] Step 1, preparation of NF / CoFeS-CoOH-FeOH: First, cobalt nitrate hexahydrate, ferric nitrate nonahydrate, and thiourea are dissolved in deionized water to obtain solution A, which is then stirred under certain conditions. Then, under certain conditions, nickel foam NF is immersed in solution A for a hydrothermal reaction. Finally, after washing and drying, a nickel foam simultaneously loaded with cobalt iron sulfide and cobalt iron hydroxide is obtained, referred to as NF / CoFeS-CoOH-FeOH.

[0018] In the step 1, the mass ratio of cobalt nitrate hexahydrate, ferric nitrate nonahydrate and thiourea is 2:3:2;

[0019] In step 1, the stirring condition of solution A is that the stirring time is 0.5-1h;

[0020] In step 1, the conditions for the hydrothermal reaction are: hydrothermal temperature is 160° C., and hydrothermal time is 5 h;

[0021] In step 1, the NF needs to be washed before immersion. The washing method is to wash the NF with acetone, hydrochloric acid, deionized water and anhydrous ethanol in sequence, and then dry it at a drying temperature of 60°C.

[0022] Step 2, preparation of NF / CoFeS-CoP-FeP: first, sodium hypophosphite is placed upstream of a tube furnace, and NF / CoFeS-CoOH-FeOH obtained in step 1 is placed downstream of the tube furnace. Then, calcination and phosphating are performed under certain conditions. After the phosphating is completed, the obtained product is cooled, washed, and dried to obtain a nickel foam simultaneously loaded with cobalt iron sulfide and cobalt iron phosphide, referred to as NF / CoFeS-CoP-FeP.

[0023] In the step 2, the mass ratio of sodium hypophosphite to cobalt nitrate hexahydrate in step 1 is 17:5;

[0024] In step 2, the calcination and phosphating conditions are as follows: in an argon atmosphere, the temperature is increased at a rate of 1°C min -1 , the calcination temperature is 300℃ and the calcination time is 1h.

[0025] A NF / CoFeS-CoP-FeP composite material with a three-phase heterogeneous structure is used as a hydrogen evolution catalyst material. When the current density is 10 mA cm in a 1M KOH solution, the reaction is carried out in the range of 0 to -0.1 V. -2 When NF / CoFeS-CoP-FeP is used, the overpotential is 61-67 mV, and the Tafel slope is 99.51-105.23 mV·dec -1 ; In 1M KOH solution, the current density is 10mA·cm in the range of 0~-0.1V. -2 When the cycle time is 24h, the current retention rate of NF / CoFeS-CoP-FeP is 98%.

[0026] The technical effects of the present invention have been tested and the specific contents are as follows:

[0027] XRD testing of the present invention shows that the NF / Co-Fe-S / Co-P / Fe-P simultaneously exhibits characteristic peaks of Co8FeS8, Co2P, and Fe2P. Comparing the test results with those of step 1, it is clear that step 2 successfully produces Co2P and Fe2P, i.e., successfully preparing NF / Co-Fe-S / Co-P / Fe-P.

[0028] TEM and EDS tests show that the NF / Co-Fe-S / Co-P / Fe-P of the present invention successfully synthesized uniformly distributed Co8FeS8, Co2P and Fe2P, and the spherical cube-shaped Co8FeS8 was combined and grown together with the nanoflower-shaped Co2P and nanosheet-shaped Fe2P to form a three-phase heterogeneous structure with rich morphology.

[0029] SEM testing shows that the present invention shows that: Fe2P nano-sheet structures are directly grown on the NF surface, and then Co8FeS8 spherical cube-shaped structures and Co2P nano-spherical structures are grown on the Fe2P nano-sheet structures, and the spherical cube-shaped Co8FeS8 is combined with the spherical Co2P and the sheet-like Fe2P to form a three-phase heterojunction structure with rich morphology.

[0030] The electrochemical performance test of the present invention shows that: in 1M KOH solution, in the range of 0 to -1.0V, when the current density is 10mA·cm -2 When NF / Co-Fe-S / Co-P / Fe-P is 1.57-2.50 mV, the overpotential is 61-67 mV, and the Tafel slope is 99.51-105.23 mV·dec. -1 , after 24h it test, the current retention rate is 98%.

[0031] Therefore, the present invention has the following advantages over the prior art:

[0032] 1. When constructing the NF / CoFeS-CoP-FeP composite catalyst, the synergistic effect of multiple components is achieved at different active sites and electronic reconstruction interfaces, thereby improving the catalyst's ability to adsorb hydrogen atoms and promoting the electrochemical hydrogen evolution reaction;

[0033] 2. In the NF / CoFeS-CoP-FeP composite catalyst, the synergistic effect of sulfur and phosphorus can adsorb more thermally neutral electrons / ions, promote the redistribution of electrons, increase the electrochemical active area, and achieve activation when hydrogen ions are adsorbed, that is, obtaining activated hydrogen ions, thereby reducing the energy barrier of the hydrogen evolution reaction and promoting the performance of the hydrogen evolution reaction;

[0034] 3. In the NF / CoFeS-CoP-FeP composite catalyst, a three-phase heterojunction structure is formed between the Co-Fe-S / Co-P / Fe-P loaded on the conductive substrate. The strong coupling effect between the interfaces enhances the bonding force between the materials, greatly reduces the material shedding phenomenon, improves the stability of the catalyst, and extends its service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is the XRD test pattern of Example 1;

[0036] Figure 2 This is the SEM test image of the NF / CoFeS-CoOH-FeOH precursor prepared in Example 1;

[0037] Figure 3 This is the linear sweep voltammetry curve of Example 1;

[0038] Figure 4 The Tafel diagrams are shown for Example 1, Comparative Example 1, Reference Example 1, Comparative Example 2, and Comparative Example 3;

[0039] Figure 5 This is the EDS test image of NF / CoFeS-CoP-FeP prepared in Example 1;

[0040] Figure 6 TEM image of NF / CoFeS-CoP-FeP prepared in Example 1;

[0041] Figure 7 This is the SEM test image of NF / CoFeS-CoP-FeP prepared in Example 1;

[0042] Figure 8 This is the IT stability test diagram of Example 1;

[0043] Figure 9 The XRD test patterns of Comparative Example 1, Comparative Example 2, and Comparative Example 3 are shown;

[0044] Figure 10 This is the SEM test image of NF / CoFeS prepared in Comparative Example 1;

[0045] Figure 11 The LSV diagrams of Comparative Example 1, Reference Example 1, Comparative Example 2, and Comparative Example 3 are shown;

[0046] Figure 12 This is the SEM test image of pure NF prepared in Reference Example 1;

[0047] Figure 13 This is the SEM test image of NF / CoP prepared in Comparative Example 2;

[0048] Figure 14 This is the SEM test image of NF / FeP prepared in comparative example 3. DETAILED DESCRIPTION

[0049] The present invention is further described in detail through embodiments and in conjunction with the accompanying drawings, but the present invention is not limited thereto.

[0050] Example 1

[0051] A method for preparing a NF / CoFeS-CoP-FeP composite material with a three-phase heterogeneous structure comprises the following steps:

[0052] Step 1, preparation of NF / CoFeS-CoOH-FeOH: first, 0.291 g of cobalt nitrate hexahydrate, 0.452 g of ferric nitrate nonahydrate, and 0.304 g of thiourea were dissolved in 60 mL of deionized water to obtain solution A, and solution A was stirred for 30 minutes. Then, a nickel foam NF with a size of 2 mm × 3 mm was immersed in solution A for hydrothermal reaction at a hydrothermal temperature of 160° C. for 5 hours. Finally, after washing and drying, a nickel foam simultaneously loaded with cobalt iron sulfide and cobalt iron hydroxide was obtained, referred to as NF / CoFeS-CoOH-FeOH.

[0053] In step 1, the NF needs to be washed before immersion. The washing method is to wash the NF with acetone, hydrochloric acid, deionized water and anhydrous ethanol in sequence, and then dry it at a drying temperature of 60°C.

[0054] In order to prove the composition of NF / CoFeS-CoOH-FeOH obtained in step 1, XRD test was performed. The test results are as follows Figure 1 As shown in Figure 3, the characteristic peaks of Co8FeS8, Co(OH)2 and Fe(OH)2 coexist in NF / CoFeS-CoOH-FeOH. The test results show that step 1 successfully prepared Co8FeS8, Co(OH)2 and Fe(OH)2.

[0055] In order to verify the microstructure of NF / CoFeS-CoOH-FeOH, SEM test was carried out. The test results are shown in Figure 2. Figure 2 As shown in the figure, Co8FeS8, Co(OH)2 and Fe(OH)2 are grown on the NF surface at the same time, among which Co8FeS8 is a spherical Rubik's cube structure, Co(OH)2 is a nanoflower-like structure, and Fe(OH)3 is a nanosheet-like structure. Moreover, the Fe(OH)3 nanosheet structure grows directly on the NF surface, and then the Co8FeS8 spherical Rubik's cube structure and Co(OH)2 nanoflower-like structure are grown on the Fe(OH)3 nanosheet structure.

[0056] In order to demonstrate the electrochemical performance of NF / CoFeS-CoOH-FeOH, electrochemical performance tests were conducted. The specific method of electrochemical performance test is to conduct electrochemical performance tests in a three-electrode system consisting of the material to be tested as the working electrode, the mercury oxide electrode as the reference electrode, the graphite electrode as the counter electrode, and 1M KOH solution as the electrolyte. The linear sweep voltammetry curve test results are shown in Figure 2. Figure 3 As shown, in the range of 0 to -1.0 V, at a current density of 10 mA cm -2 When , the overpotential of NF / CoFeS-CoOH-FeOH is 202 mV;

[0057] The Tafel slope can be calculated by current polarization test. The test results are as follows: Figure 4 As shown, the Tafel slope of NF / CoFeS-CoOH-FeOH is 112.86 mV·dec -1 .

[0058] Step 2, preparation of NF / CoFeS-CoP-FeP, first, place 1.0 g of sodium hypophosphite upstream of the tube furnace, place the NF / CoFeS-CoOH-FeOH with a size of 2 mm × 3 mm obtained in step 1 downstream of the tube furnace, and then, under an argon atmosphere, heat the mixture at a rate of 1 °C min -1 The calcination temperature is 300°C and the calcination time is 1 hour. The calcination and phosphating are carried out. After the phosphating is completed, the obtained product is cooled, washed and dried to obtain a nickel foam simultaneously loaded with cobalt iron sulfide and cobalt iron phosphide, that is, a NF / CoFeS-CoP-FeP composite material with a three-phase heterogeneous structure, abbreviated as NF / CoFeS-CoP-FeP.

[0059] In order to prove the composition of NF / CoFeS-CoP-FeP, XRD test was carried out. The test results are as follows Figure 1As shown in Figure 3, the characteristic peaks of Co8FeS8, Co2P, and Fe2P coexist in NF / CoFeS-CoP-FeP. The test results show that the phosphating step 2 converts Co(OH)2 and Fe(OH)3 into Co2P and Fe2P, respectively, while Co8FeS8 remains unchanged as a cobalt iron sulfide.

[0060] Since NF / CoFeS-CoP-FeP is composed of three components, it may have a three-phase heterogeneous structure. Therefore, EDS and TEM tests were performed to prove that NF / CoFeS-CoP-FeP has a three-phase heterogeneous structure.

[0061] EDS test results are as follows Figure 5 As shown in Figure 3, NF / CoFeS-CoP-FeP contains Co, Fe, S, and P elements at the same time, but the main distribution areas of S and P elements do not overlap;

[0062] TEM test results are as follows Figure 6 As shown, NF / CoFeS-CoP-FeP has three independent lattice fringes of different materials, and the boundaries of the regions where the lattice fringes are located are clear, indicating the existence of a three-phase heterojunction structure. Further specific analysis shows that the lattice fringes with a spacing of 0.2030nm match the (422) crystal plane of Co8FeS8, the lattice fringes with a spacing of 0.2147nm match the (220) crystal plane of Co2P, and the lattice fringes with a spacing of 0.1920nm match the (210) crystal plane of Fe2P. In other words, the test results also prove the successful synthesis of Co8FeS8, Co2P, and Fe2P.

[0063] The combination of EDS and TEM tests shows that NF / CoFeS-CoP-FeP has a three-phase heterogeneous structure formed by Co8FeS8, Co2P and Fe2P.

[0064] In order to verify the microstructure of NF / CoFeS-CoP-FeP, SEM test was carried out. The test results are shown in the figure below. Figure 7 As shown in the figure, the basic micromorphology of NF / CoFeS-CoP-FeP has no substantial difference from that of NF / CoFeS-CoOH-FeOH, that is, Co8FeS8, Co2P and Fe2P grow on the NF surface at the same time, among which Co8FeS8 maintains a spherical magic cube structure, while when Co(OH)2 is converted to Co2P, the micromorphology changes from a nanoflower-like structure to a nanosphere structure, and when Fe(OH)3 is converted to Fe2P, the micromorphology still maintains a nanosheet structure, but wrinkles appear; SEM test results also support the conclusion that NF / CoFeS-CoP-FeP has a three-phase heterogeneous structure.

[0065] In order to prove the electrochemical performance of NF / CoFeS-CoP-FeP, electrochemical catalytic performance tests were carried out. The test results are shown in Figure 2. Figure 3 As shown, in the range of 0 to -1.0 V, at a current density of 10 mA cm -2 When phosphating, the overpotential of NF / CoFeS-CoP-FeP is 61.8mV. Compared with step 1, under the same conditions, the overpotential of NF / CoFeS-CoP-FeP is significantly reduced, indicating that the Co2P and Fe2P generated by phosphating in step 2 can produce a synergistic effect with Co8FeS8.

[0066] The Tafel slope can be calculated by current polarization test. The test results are as follows: Figure 4 As shown, the Tafel slope of NF / CoFeS-CoP-FeP is 99.51 mV·dec -1 Compared with step 1, under the same conditions, the Tafel slope of NF / CoFeS-CoP-FeP decreases, indicating that the three-phase heterostructure formed in step 2 can accelerate the charge transfer rate, that is, increase the reaction rate.

[0067] In order to prove the stability of NF / CoFeS-CoP-FeP, stability performance test was carried out. The test results are as follows Figure 8 As shown, the current density is 10 mA cm -2 Under the condition of 24h cycle time, the current retention rate is 98%. The test results show that NF / CoFeS-CoP-FeP has good stability.

[0068] In order to demonstrate the role of each component, namely Co8FeS8, Co2P and Fe2P in the technical solution,

[0069] Comparative Example 1 is provided, in which only Co8FeS8 is grown on NF, i.e., NF / Co-Fe-S is prepared without introducing Co2P and Fe2P, and the role of Co8FeS8 in the technical solution is demonstrated in combination with Example 1;

[0070] Provide reference example 1 and comparative example 2, comparative example 3,

[0071] Reference Example 1: pure NF without any loading as the basic reference example;

[0072] Comparative Example 2 is a NF / Co-P prepared by growing only Co2P on NF, i.e., without introducing Co8FeS8 and Fe2P. This is combined with Reference Example 1 to demonstrate the role of Co2P in the technical solution.

[0073] Comparative Example 3 is to grow only Fe2P on NF, that is, NF / Fe-P prepared without introducing Co8FeS8 and Co2P, and to demonstrate the role of Fe2P in the technical solution in combination with Reference Example 1.

[0074] Comparative Example 1

[0075] A method for preparing NF / CoFeS. Since NF / CoFeS in which only Co8FeS8 grows on NF cannot be obtained by directly adopting the preparation method of step 1 of Example 1, in order to obtain NF / CoFeS, it is necessary to increase the amount of thiourea added in step 1 to suppress the formation of cobalt iron hydroxide. That is, the steps not specifically described in the preparation method are the same as those in Example 1, except that step 2 is not required, and in step 1, the amount of thiourea added is twice that of Example 1. The obtained material is referred to as NF / CoFeS.

[0076] The XRD test results of NF / CoFeS are as follows: Figure 9 As shown, NF / CoFeS only has the characteristic peaks of Co8FeS8. The test results show that Co8FeS8 was successfully prepared and the formation of cobalt iron hydroxide was suppressed. The test results also prove that the composition can be adjusted by adjusting the amount of thiourea added.

[0077] The SEM test results of NF / CoFeS are as follows Figure 10 As shown, the basic microscopic morphology of Co8FeS8 is not substantially different from that in Example 1, that is, a spherical Rubik's cube structure.

[0078] The electrochemical performance test results of NF / CoFeS are as follows Figure 11 As shown, in the range of 0 to -1.0 V, at a current density of 10 mA cm -2 When , the overpotential of NF / CoFeS is 202mV.

[0079] Compared with the NF / CoFeS-CoOH-FeOH obtained in step 1 of Example 1, it can be seen that increasing the amount of S element added to convert all Co and Fe elements into CoFeS has no substantial effect on reducing the overpotential, that is, CoFeOH has no substantial effect on reducing the overpotential.

[0080] Compared with the NF / CoFeS-CoP-FeP obtained in step 2 of Example 1, it can be seen that the introduction of the P element to form CoFeP can improve the electrocatalytic activity and further reduce the reaction overpotential. The reason is that the P element has a high electronegativity and can extract electrons from adjacent transition metal atoms to form negatively charged P atoms, which in turn helps to capture protons. Therefore, the introduction of the P element can increase the adsorption of reaction intermediates on the catalyst surface, increase the electron transfer rate on the catalyst surface, and ultimately achieve improved electrocatalytic hydrogen evolution performance;

[0081] The Tafel slope test results of NF / CoFeS are as follows Figure 4 As shown, the Tafel slope of NF / CoFeS is 106.01 mV·dec -1 .

[0082] Compared with the NF / CoFeS-CoOH-FeOH obtained in step 1 of Example 1, it can be seen that increasing the amount of S element added and converting all the Co and Fe elements into CoFeS slightly decreases the Tafel slope, indicating that the charge transfer capacity becomes lower, that is, CoFeOH has the effect of inhibiting the decrease in the Tafel slope;

[0083] Compared with the NF / CoFeS-CoP-FeP obtained in step 2 of Example 1, it can be seen that the introduction of P element to form CoFeP can accelerate the hydrogen evolution reaction rate. The reason is that the introduction of P element can increase the active sites of the catalyst, and the synergistic effect of S element and P element will lead to more thermoneutral electron / ion adsorption, electron redistribution, increase the electrochemical active area, and achieve activation when hydrogen ions are adsorbed, that is, activated hydrogen ions are obtained, thereby reducing the energy barrier of the hydrogen evolution reaction and accelerating the hydrogen evolution reaction rate.

[0084] Reference Example 1

[0085] A method for preparing pure NF, which does not require the preparation of any load, and therefore does not require the addition of any raw materials, and only requires conventional processing of the pure NF.

[0086] The SEM test results of pure NF are as follows Figure 12 As shown in Figure 3, the microstructure of pure NF is smooth without any protruding structures.

[0087] The electrochemical performance test results of pure NF are as follows Figure 11 As shown, in the range of 0 to -1.0 V, at a current density of 10 mA cm -2 When , the overpotential of pure NF is 266mV.

[0088] The Tafel slope test results of pure NF are as follows: Figure 4 As shown, the Tafel slope of pure NF is 142.02 mV·dec-1 .

[0089] Comparative Example 2

[0090] A method for preparing NF / CoP. Since only hydroxide needs to be prepared and then phosphated, no sulfide needs to be prepared. Therefore, in the preparation method of step 1 of Example 1, thiourea does not need to be added, that is, the hydroxide can be prepared by conventional methods. That is, the steps not specifically described in the preparation method are the same as those in Example 1, except that: in step 1, ferric nitrate nonahydrate and thiourea are not added. Instead, ammonium fluoride and urea are added as raw materials by conventional methods, and the mass ratio of ammonium fluoride to urea to cobalt nitrate hexahydrate in step 1 is 4:15:21. The resulting material is referred to as NF / CoP.

[0091] The XRD test results of NF / CoP are as follows: Figure 9 As shown in Figure 3, NF / CoP only has the characteristic peak of Co2P. The test results show that the successful preparation of Co2P means the successful preparation of NF / CoP.

[0092] The SEM test results of NF / CoP are as follows: Figure 13 As shown in the figure, spherical nanosheet structures are grown on the surface of NF. Combined with the reference example 1 and the XRD test results, it can be seen that the spherical nanosheet structures are Co2P. Compared with the NF / CoFeS-CoP-FeP obtained in Example 1, the Co2P obtained by Co(OH)2 conversion has a nano-spherical structure in its microstructure. That is, the microstructure of Co2P can be adjusted by the preparation method of Example 1.

[0093] The electrochemical performance test results of NF / CoP are as follows: Figure 11 As shown, in the range of 0 to -1.0 V, at a current density of 10 mA cm -2 When , the overpotential of NF / CoP is 117mV.

[0094] Compared with the pure NF obtained in Reference Example 1, it can be seen that the introduction of Co and P elements to form Co2P can reduce the reaction overpotential. The reason is that the electron cloud of the Co atom will be biased towards the P atom under the action of electronegativity. The electronegative P atom can capture positively charged protons, which is conducive to the adsorption of active hydrogen on the surface of the metal phosphide and the desorption of hydrogen molecules. In addition, the nanosheet Co2P can expose abundant catalytic active sites, thereby achieving high electron transfer and effectively improving the electrocatalytic hydrogen evolution performance.

[0095] Compared with the NF / CoFeS-CoP-FeP obtained in Example 1, it can be seen that when the Fe element is introduced to form CoFeP, the reaction overpotential can be reduced and the electrocatalytic hydrogen evolution performance can be improved. The reason is that for the hydrogen adsorption Gibbs free energy, the D band center of the Fe2P adsorption site is farther away from the Fermi level than Co2P, and the adsorption of hydrogen is weaker, which is more conducive to the analysis of hydrogen, thereby effectively improving the electrocatalytic activity of the catalyst. At the same time, the Co8FeS8 spherical magic cube structure is introduced to make the originally dispersedly grown spherical Co2P nanosheets become nanospheres and evenly dispersed and grown on its surface, effectively improving the hydrogen evolution catalytic activity. The reason is that the spherical magic cube-shaped Co8FeS8 provides a large number of active sites for the growth of Co2P nanospheres, reduces the occurrence of agglomeration, and increases the effective contact area of ​​Co2P with the electrolyte.

[0096] The Tafel slope test results of NF / CoP are as follows: Figure 4 As shown, the Tafel slope of NF / CoP is 107.97 mV·dec -1 .

[0097] Compared with the pure NF obtained in Example 1, the introduction of Co and P elements to form Co2P can reduce the Tafel slope of the reaction. The reason is that Co2P can redistribute the electrons inside the catalyst, reduce the reaction energy barrier, and facilitate the adsorption and reduction of hydrogen ions, thereby improving the hydrogen evolution efficiency.

[0098] Compared with the NF / CoFeS-CoP-FeP obtained in Example 1, it can be seen that when the Fe element is introduced to form CoFeP, the reaction overpotential can be significantly reduced and the electrocatalytic hydrogen evolution performance can be improved. The reason is that the binding energy of the density of states Fe2P is lower than Co2P. It can be seen that Fe2P has a weaker adsorption of hydrogen and is more conducive to the resolution of hydrogen, thereby effectively improving the electrocatalytic activity of the catalyst. At the same time, the introduction of Co8FeS8 spherical magic cube structure forms a NF / CoFeS-CoP-FeP three-phase heterojunction structure, which can effectively improve the hydrogen evolution reaction rate. The reason is that the interface coupling effect between CoFeS and CoP and FeS can accelerate the charge transfer rate, further accelerate the hydrogen evolution reaction process, thereby effectively reducing the Tafel slope of the reaction.

[0099] Comparative Example 3

[0100] A method for preparing NF / FeP. Since only hydroxide needs to be prepared and then phosphating is performed, no sulfide needs to be prepared. Therefore, in the preparation method of step 1 of Example 1, thiourea does not need to be added, that is, the hydroxide can be prepared by conventional methods. That is, the steps not particularly described in the specific steps are the same as those in Example 1, except that: in the step 1, cobalt nitrate hexahydrate and thiourea are not added. Instead, ammonium fluoride and urea are added as raw materials by conventional methods, and the mass ratio of ammonium fluoride to urea and ferric nitrate nonahydrate in step 1 is 4:15:32. The obtained material is referred to as NF / FeP.

[0101] The XRD test results of NF / FeP are as follows: Figure 9 As shown in Figure 3, NF / FeP only has the characteristic peak of Fe2P. The test results show that the successful preparation of Fe2P means the successful preparation of NF / FeP.

[0102] The SEM test results of NF / FeP are as follows Figure 14 The results of the XRD analysis of the NF show that nanosheet structures have grown on the NF surface. This is consistent with the results of Reference Example 1 and XRD analysis, which indicate that the nanosheet structures are Fe2P. A comparison with the NF / CoFeS-CoP-FeP obtained in Example 1 shows that the Fe2P obtained by Fe(OH)3 conversion exhibits a wrinkled nanosheet microstructure, demonstrating that the preparation method of Example 1 can adjust the microstructure of Fe2P.

[0103] The electrochemical performance test results of NF / FeP are as follows Figure 11 As shown, in the range of 0 to -1.0 V, at a current density of 10 mA cm -2 When , the overpotential of NF / FeP is 104mV.

[0104] Compared with the pure NF obtained in Reference Example 1, the introduction of Fe and P elements to form Fe2P can reduce the reaction overpotential. This is because the metal-rich structure of Fe2P increases the active sites for hydrogen adsorption, accelerating charge transfer. Fe2P also improves the contact between the catalyst and the electrode, thereby reducing electron transport resistance and ultimately increasing the hydrogen evolution reaction rate.

[0105] Compared with the NF / CoFeS-CoP-FeP obtained in Example 1, it can be seen that the introduction of Co element to form CoFeP can significantly reduce the reaction overpotential and improve the electrocatalytic hydrogen evolution performance. The reason is that the multi-component structure shows synergistically enhanced activity at different active sites and electronic reconstruction interfaces, and has excellent electrocatalytic activity compared with single-component CoP. At the same time, the introduction of Co8FeS8 spherical magic cube structure changes the originally straight Fe2P nanosheets into wrinkled nanosheet structures, effectively improving the hydrogen evolution catalytic activity. The reason is that the wrinkled Fe2P nanosheets increase the electrochemical active surface area, thereby expanding the effective contact area between the catalyst and the electrolyte, improving the hydrogen evolution reaction performance, and effectively reducing the hydrogen evolution reaction overpotential.

[0106] The Tafel slope test results of NF / FeP are as follows: Figure 4 As shown, the Tafel slope of NF / FeP is 138.94 mV·dec -1 .

[0107] Compared to the pure NF obtained in Reference Example 1, the introduction of Fe and P to form Fe2P significantly reduces the Tafel slope of the reaction. This is because Fe2P enhances the charge transfer capability within the catalyst, thereby lowering the energy barrier for hydrolysis. Furthermore, the nanosheet structure of Fe2P increases the effective contact area with the electrolyte, accelerating the electron transfer rate and further enhancing the catalyst's hydrogen evolution performance.

[0108] Compared with the NF / CoFeS-CoP-FeP obtained in Example 1, it can be seen that when the Co element is introduced to form CoFeP, the reaction overpotential can be significantly reduced, and the electrocatalytic hydrogen evolution performance can be improved. The reason is that the multi-component structure shows synergistically enhanced activity at different active sites and electronic reconstruction interfaces, and has excellent electrocatalytic activity compared with single-component FeP. At the same time, the introduction of Co8FeS8 spherical magic cube structure to form NF / CoFeS-CoP-FeP three-phase heterojunction structure can effectively improve the hydrogen evolution reaction rate. The reason is that S and P synergistically adsorb more thermoneutral electrons, thereby playing an indirect role in the alkaline HER process, further improving the electrocatalytic hydrogen evolution performance.

[0109] The following conclusions can be drawn from the above Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3:

[0110] Multi-element transition metal sulfides have a large number of active sites, which can increase the specific surface area of ​​the composite material on the one hand, and provide growth sites for Co2P and Fe2P on the other hand, so that the phosphide can grow uniformly and reduce agglomeration;

[0111] 2. Multi-element transition metal phosphides not only have a metal-rich structure that increases active sites for hydrogen adsorption and has good conductivity and chemical stability, but can also regulate the morphology of Co8FeS8 and improve hydrogen evolution catalytic performance. The P atoms, as stable proton carriers, can enhance the adsorption of reaction intermediates on the catalyst surface and accelerate the electron transfer rate on the catalyst surface, ultimately achieving enhanced electrocatalytic hydrogen evolution performance.

[0112] 3. There is a synergistic effect between S and P elements, which can adsorb thermally neutral electrons / ions, promote the redistribution of electrons, increase the electrochemical active area, and achieve activation when adsorbing hydrogen ions, that is, obtain activated hydrogen ions, thereby reducing the energy barrier of the hydrogen evolution reaction and accelerating the hydrogen evolution reaction rate;

[0113] 4. The spherical cube-shaped Co8FeS8 is combined with spherical Co2P and flake Fe2P to form a three-phase heterostructure. The interfacial coupling effect between the three phases can accelerate the charge transfer rate, further accelerate the hydrogen evolution reaction process, and significantly improve the HER performance and stability of the catalyst.

Claims

1. A NF / Co8FeS8-Co2P-Fe2P composite material with a three-phase heterogeneous structure, characterized by: Using nickel foam as a substrate and a self-supporting skeleton, using cobalt nitrate hexahydrate and ferric nitrate nonahydrate as raw materials and thiourea as a sulfur source, a hydrothermal method is used to grow partially sulfided cobalt iron sulfide and cobalt iron hydroxide on the nickel foam. Then, using sodium hypophosphite as a phosphorus source, a one-step phosphating method is used to convert the cobalt iron hydroxide into cobalt iron phosphide, thereby obtaining cobalt iron sulfide and cobalt iron phosphide grown on the nickel foam. The mass ratio of the cobalt nitrate hexahydrate, the ferric nitrate nonahydrate and the thiourea is 2:3:2; The mass ratio of the sodium hypophosphite to cobalt nitrate hexahydrate is 17:

5.

2. The NF / Co8FeS8-Co2P-Fe2P composite material according to claim 1, characterized in that: The micromorphology of the Co8FeS8 is a spherical Rubik's cube structure; the micromorphology of the Co2P is a spherical nanosheet structure; the micromorphology of the Fe2P is a nanosheet structure; and the spherical Rubik's cube-shaped Co8FeS8 and the spherical nanosheet-shaped Co2P are combined together and grown on the Fe2P nanosheet to form a three-phase heterogeneous structure.

3. The method for preparing the NF / Co8FeS8-Co2P-Fe2P composite material according to claim 1, characterized in that The following steps are involved: Step 1: First, cobalt nitrate hexahydrate, ferric nitrate nonahydrate, and thiourea are dissolved in deionized water to obtain solution A, and solution A is stirred under certain conditions. Then, under certain conditions, nickel foam NF is immersed in solution A for hydrothermal reaction. Finally, after washing and drying, nickel foam loaded with both cobalt iron sulfide and cobalt iron hydroxide can be obtained; In the step 1, the mass ratio of cobalt nitrate hexahydrate, ferric nitrate nonahydrate and thiourea is 2:3:2; Step 2: First, sodium hypophosphite is placed upstream of a tube furnace, and the nickel foam simultaneously loaded with cobalt iron sulfide and cobalt iron hydroxide obtained in step 1 is placed downstream of the tube furnace. Then, calcination and phosphating are performed under certain conditions. After the phosphating is completed, the obtained product is cooled, washed, and dried to obtain a nickel foam simultaneously loaded with cobalt iron sulfide and cobalt iron phosphide, referred to as NF / Co8FeS8-Co2P-Fe2P. In the step 2, the mass ratio of sodium hypophosphite to cobalt nitrate hexahydrate in the step 1 is 17:

5.

4. The preparation method according to claim 3, wherein: In step 1, the stirring condition of solution A is that the stirring time is 0.5-1h; In step 1, the conditions for the hydrothermal reaction are: hydrothermal temperature is 160° C., and hydrothermal time is 5 h; In step 1, the NF needs to be washed before immersion. The washing method is to wash the NF with acetone, hydrochloric acid, deionized water and anhydrous ethanol in sequence. After washing, the NF is dried at a drying temperature of 60°C.

5. The preparation method according to claim 3, wherein: In step 2, the calcination and phosphating conditions are as follows: in an argon atmosphere, the temperature is increased at a rate of 1°C min -1 , the calcination temperature is 300℃ and the calcination time is 1h.

6. Use of the NF / Co8FeS8-Co2P-Fe2P composite material according to claim 1 as a hydrogen evolution catalyst material, characterized in that: In 1M KOH solution, the current density is 10mA·cm in the range of 0~-0.1V. -2 When NF / Co8FeS8-Co2P-Fe2P has an overpotential of 61-67 mV, the Tafel slope is 99.51-105.23 mV·dec -1 .

7. Use of the NF / Co8FeS8-Co2P-Fe2P composite material according to claim 1 as a hydrogen evolution catalyst material, characterized in that: In 1M KOH solution, the current density is 10mA·cm in the range of 0~-0.1V. -2 When the cycle time is 24h, the current retention rate of NF / Co8FeS8-Co2P-Fe2P is 98%.

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