Self-supporting Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction composite material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of electro-catalysis seawater decomposition, and relates to a self-supporting Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction composite material as well as a preparation method and application thereof. The method comprises the following steps: firstly, sequentially synthesizing ultrathin NiFe-LDHs and Ni2Mo-LDHs on a foamed nickel carrier through two-step electrodeposition, so as to form a NiFe-LDHs / Ni2Mo-LDHs / NF precursor; then, the Fe-Ni5P4 / Ni-Mo4P3 heterojunction composite material is converted into corresponding Fe-Ni5P4 and Ni-Mo4P3 phosphides through high-temperature phosphating treatment, and finally, the Fe-Ni5P4 / Ni-Mo4P3 heterojunction composite material is constructed on a substrate. Benefited from a built-in electric field formed by a heterojunction interface, an efficient electron transmission channel and an optimized catalytic reaction interface are constructed in the material. According to the structure, high-speed transfer of charges is guaranteed, and the overall catalytic performance of the material is remarkably improved by enhancing the electron supply capacity of active sites. Furthermore, the electronic structure of the heterojunction interface can be effectively adjusted by adjusting and controlling the phosphorus content in the material, and then continuous adjustment and control of the built-in electric field intensity are achieved. The material shows excellent OER catalytic activity and long-term stability in an alkaline seawater environment.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrocatalytic seawater decomposition, and relates to a self-supporting Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction composite material and a preparation method and application thereof. BACKGROUND

[0002] Seawater electrolysis has become a promising green hydrogen production route due to its abundant resources and low cost. However, its practical application is limited by the slow kinetics of the anodic oxygen evolution reaction and the corrosion caused by chloride ions, which leads to a rapid decline in the activity and stability of most electrocatalysts. Nickel-based phosphides are widely concerned due to their good electrical conductivity and high activity. Among them, Fe-Ni5P4 can optimize the adsorption of intermediates through electronic regulation of Fe, but it is prone to corrosion in seawater environment, while Ni-Mo4P3 is structurally stable, but its intrinsic activity is limited due to its high initial potential. Existing single-component phosphorus-based catalysts are difficult to simultaneously achieve high activity, strong corrosion resistance and structural durability in seawater OER. In addition, traditional powder catalysts need to rely on adhesives for coating, which can easily shield active sites, increase interface contact resistance, and cause coating peeling at high current density, which seriously restricts their practical application. SUMMARY

[0003] To address the above bottlenecks, the present application proposes a composite of Fe-Ni5P4 and Ni-Mo4P3, which is in-situ constructed on a three-dimensional nickel foam substrate to form a self-supporting heterojunction electrode, which is expected to achieve synergistic enhancement of performance. This strategy induces an internal electric field through the heterojunction interface, effectively promoting electron transfer and improving the reaction path. Further, by adjusting the phosphorus vacancy concentration, the strength of the internal electric field can be precisely adjusted, thereby optimizing the interface reaction kinetics. At the same time, the self-supporting structure does not require adhesives, which can fully expose the active interface, enhance mass transfer efficiency, and improve mechanical stability, providing an effective technical approach for developing high-performance anodes suitable for industrial seawater electrolysis. Therefore, developing a method for controllable preparation of Fe-Ni5P4 / Ni-Mo4P3 heterojunction and interface regulation to fully utilize the synergistic mechanisms of internal electric field is an urgent need and feasible solution for developing industrial seawater electrolysis anodes.

[0004] The present application provides a Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction composite material and a preparation method and application thereof in electrocatalytic seawater decomposition. The catalyst induces an internal electric field by constructing a heterojunction structure with strong interface coupling, effectively promoting charge separation and transfer, and optimizing the reaction path, thereby exhibiting significantly enhanced oxygen evolution reaction activity and stability in seawater environment.

[0005] The core of the technical scheme of the present application is to construct a novel Fe-Ni5P4 / Ni-Mo4P3 heterojunction self-supporting electrode. By virtue of the band structure difference between the two phosphide materials Fe-Ni5P4 and Ni-Mo4P3, a significant built-in electric field is induced at the heterojunction interface, and at the same time, the adsorption energy barrier of the active sites to the reaction intermediates is optimized through the rearrangement of the electronic structure. The synergistic effect of the three-dimensional porous Ni substrate and the heterojunction structure not only ensures the full penetration of the electrolyte and the rapid adsorption / desorption of the reaction products / reaction intermediates / products, but also endows the electrode with excellent mechanical stability and structural integrity. By adjusting the phosphorus vacancy concentration, the present application can effectively adjust the interface electric field strength, which provides a new regulation dimension for optimizing the electronic structure of the heterojunction catalyst. Compared with single-component phosphide catalysts, the Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction electrode prepared by the present application exhibits significantly improved comprehensive performance in the simulated seawater environment: not only has a lower overpotential and a higher current density, but also exhibits excellent long-term stability and chlorine ion corrosion resistance. In addition, the preparation process adopted has the advantages of mild reaction conditions, simple operation and good repeatability, which provides a reliable material basis for promoting the practical application of seawater electrolysis technology.

[0006] In order to achieve the above-mentioned application purposes, the present application provides a preparation method of Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction composite material, comprising the following steps: (1) A three-electrode system is constructed with foam nickel (NF) as the working electrode, a graphite rod as the counter electrode, and an Ag / AgCl electrode as the reference electrode. Ni(NO3)2·6H2O and Fe(NO3)3·9H2O are dissolved in deionized water to prepare an electrolyte, and ultra-thin Ni1Fe1-LDHs are electrodeposited on the surface of NF at a specific voltage. After washing and drying, a Ni1Fe1-LDHs / NF precursor is obtained.

[0007] (2) The Ni1Fe1-LDHs / NF obtained in step (1) is used as the working electrode, a graphite rod is used as the counter electrode, and Ag / AgCl is used as the reference electrode, which is placed in deionized water containing Ni(NO3)2·6H2O and C 10 H 14 MoO6, and electrodeposition is carried out at a set voltage to in-situ grow Ni2Mo1-LDHs on the surface of Ni1Fe1-LDHs, forming a Ni1Fe1-LDHs / Ni2Mo1-LDHs / NF composite precursor, which is then washed with deionized water and ethanol and cold air dried.

[0008] (3) The Ni1Fe1-LDHs / Ni2Mo1-LDHs / NF and NaH2PO2·H2O obtained in step (2) are placed in two ceramic boats in a tube furnace and subjected to programmed temperature rise phosphating treatment under nitrogen atmosphere, and finally transformed into self-supporting Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction composite material.

[0009] Preferably, in step (1), the molar ratio of Ni(NO3)2·6H2O to Fe(NO3)3·9H2O is (0.8~1.2):(0.8~1.2), and the concentration of Ni(NO3)2·6H2O after dissolving in water is 0.225mol / L.

[0010] Preferably, in step (1), the voltage applied in step (1) is (-1.5-0) V relative to RHE.

[0011] Preferably, the electrodeposition time in step (1) is 200-500 s.

[0012] Preferably, in step (2), Ni(NO3)2·6H2O and C 10 H 14 The molar ratio of MoO6 is (1~2):(1~2), and the concentration of Ni(NO3)2·6H2O after dissolving in water is 0.6 mol / L.

[0013] Preferably, the voltage applied in step (2) is (-1.5-0) V relative to RHE.

[0014] Preferably, the electrodeposition time in step (2) is 200-500 s.

[0015] Preferably, in step (3), the mass ratio of Ni1Fe1-LDHs / Ni2Mo1-LDHs / NF to NaH2PO2·H2O is (0.1-1):(0.1-1).

[0016] Preferably, the heat treatment temperature in step (3) is 300~450 ℃.

[0017] Preferably, the heat treatment time in step (3) is 1 to 2 hours.

[0018] The present invention also provides Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction composite material prepared by the above method.

[0019] The present invention also provides the application of the above-mentioned Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction composite material in electrocatalytic seawater decomposition.

[0020] Compared with the prior art, the beneficial effects of the present invention are: The application can controllably prepare a Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction self-supporting electrode. The Ni-Mo4P3 is in-situ synthesized on the surface of the Fe-Ni5P4 through a simple two-step electrodeposition and in-situ phosphorization method, a strong built-in electric field is formed on the heterojunction interface, the directional migration of the interface charge is effectively promoted, and the electrode exhibits excellent resistance to chloride ion corrosion and long-term operation stability in seawater environment.

[0021] The application innovatively adjusts the concentration of the phosphorus vacancy in the Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction electrocatalyst, effectively adjusts the strength of the built-in electric field, and provides a new regulation dimension for optimizing the interface electronic structure and the reaction behavior of the catalytic active site. BRIEF DESCRIPTION OF DRAWINGS

[0022] The drawings accompanying the specification of this application serve to provide further understanding of the application, the illustrative embodiments of the application and the description thereof serve to explain the application, and do not constitute an improper limitation on the application. In the drawings: Figure 1 XRD results of the materials prepared for Example 8 and Comparative Examples 1 and 2; Figure 2 Scanning electron microscope pictures of the materials prepared for Example 8; Figure 3 High-magnification transmission electron microscope pictures and element distribution maps of the materials prepared for Example 8; Figure 4 Tauc plot graphs of the ultraviolet-visible diffuse reflectance absorption spectra of the materials prepared for Example 8 and Comparative Examples 1 and 2 after processing; Figure 5 XPS graphs of the materials prepared for Example 8 and Comparative Examples 1 and 2; Figure 6 Zeta results of the materials prepared for Example 8 and Comparative Examples 1 and 2; Figure 7 LSV curves of the materials prepared for Example 8 and Comparative Examples 1 and 2; Figure 8 i-t curves of the materials prepared for Example 8 and Comparative Examples 1 and 2; Figure 9 Cdl results of the materials prepared for Example 8 and Comparative Examples 1 and 2; Figure 10 EIS curves of the materials prepared for Example 8 and Comparative Examples 1 and 2; Figure 11 Liquid EPR results of the materials prepared for Examples 8-11; Figure 12Zeta results of the materials prepared in Examples 8-11, Comparative Examples 1, 2; In the figure, 8, 9, 10, 11, 12, 13 represent the samples prepared in Example 8, Comparative Example 1, 2, Example 9, Example 10, Example 11, respectively. DETAILED DESCRIPTION

[0023] The advantages and features of the present application will become more apparent with the description of specific embodiments. The embodiments are exemplary only, and do not constitute any limitation on the scope of the present application. Those skilled in the art should understand that the details and forms of the technical solutions of the present application can be modified or replaced without departing from the spirit and scope of the present application, and such modifications and replacements fall within the protection scope of the present application.

[0024] Example 1 This example is to synthesize Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction catalyst according to the following steps: (1) A three-electrode system was constructed with foam nickel (NF) as the working electrode, a graphite rod as the counter electrode, and an Ag / AgCl electrode as the reference electrode. 0.02 mol of Ni(NO3)2·6H2O and 0.022 mol of Fe(NO3)3·9H2O were dissolved in 200 mL of deionized water to prepare an electrolyte. The NF surface was electrodeposited at -1.2 V relative to RHE for 200 s, and after washing and drying, a Ni1Fe1-LDHs / NF precursor was obtained.

[0025] (2) The Ni1Fe1-LDHs / NF obtained in step (1) was used as the working electrode, a graphite rod was used as the counter electrode, and Ag / AgCl was used as the reference electrode. The system was placed in 100 mL of deionized water containing 0.06 mol of Ni(NO3)2·6H2O and 0.03 mol of C 10 H 14 MoO6, and electrodeposited at -1.0 V relative to RHE for 200 s to in situ grow Ni2Mo1-LDHs on the surface of Ni1Fe1-LDHs, forming a Ni1Fe1-LDHs / Ni2Mo1-LDHs / NF composite precursor, which was then washed with deionized water and ethanol and dried with cold air.

[0026] (3) The Ni1Fe1-LDHs / Ni2Mo1-LDHs / NF obtained in step (2) and 0.2 g of NaH2PO2·H2O were placed in two porcelain boats in a tube furnace, and heated at 2 ℃ / min to 350 ℃ for 2 h under a nitrogen atmosphere, finally converted into Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction composite material.

[0027] Example 2 This example is synthesized Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction catalyst according to the following steps: (1) The nickel foam (NF) as the working electrode, graphite rod as the counter electrode, Ag / AgCl electrode as the reference electrode, to build a three-electrode system. 0.045 mol Ni(NO3)2·6H2O and 0.045 mol Fe(NO3)3·9H2O were dissolved in 200 mL deionized water to prepare an electrolyte, and then electrodeposited on the surface of NF at-1.0 V relative to RHE for 200 s. After washing and drying, Ni1Fe1-LDHs / NF precursor was obtained.

[0028] (2) The Ni1Fe1-LDHs / NF obtained in step (1) was used as the working electrode, graphite rod as the counter electrode, Ag / AgCl as the reference electrode, and was placed in 100 mL deionized water containing 0.06 mol Ni(NO3)2·6H2O and 0.03 mol C 10 H 14 MoO6, and was electrodeposited at-1.0 V relative to RHE for 200 s. Ni2Mo1-LDHs was in-situ grown on the surface of Ni1Fe1-LDHs to form Ni1Fe1-LDHs / Ni2Mo1-LDHs / NF composite precursor, which was then washed with deionized water and ethanol and dried by cold air.

[0029] (3) The Ni1Fe1-LDHs / Ni2Mo1-LDHs / NF obtained in step (2) and 0.2 g NaH2PO2·H2O were placed in two porcelain boats in a tube furnace, and were heated at 2 ℃ / min to 350 ℃ for 2 h under nitrogen atmosphere. Finally, Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction composite material was obtained.

[0030] Example 3 This example is synthesized Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction catalyst according to the following steps: (1) The nickel foam (NF) as the working electrode, graphite rod as the counter electrode, Ag / AgCl electrode as the reference electrode, to build a three-electrode system. 0.045 mol Ni(NO3)2·6H2O and 0.045 mol Fe(NO3)3·9H2O were dissolved in 200 mL deionized water to prepare an electrolyte, and then electrodeposited on the surface of NF at-1.2 V relative to RHE for 300 s. After washing and drying, Ni1Fe1-LDHs / NF precursor was obtained.

[0031] (2) The Ni1Fe1-LDHs / NF obtained in step (1) was used as the working electrode, a graphite rod was used as the counter electrode, and Ag / AgCl was used as the reference electrode. The electrodes were placed in 100 mL of deionized water containing 0.06 mol of Ni(NO3)2·6H2O and 0.03 mol of C 10 H 14 Ni2Mo1-LDHs were in-situ grown on the surface of the Ni1Fe1-LDHs by electrodeposition at -0.9 V vs. RHE for 200 s in 100 mL of deionized water containing 0.06 mol of MoO6, to form a Ni1Fe1-LDHs / Ni2Mo1-LDHs / NF composite precursor, which was then washed with deionized water and ethanol and dried by cold air.

[0032] (3) The Ni1Fe1-LDHs / Ni2Mo1-LDHs / NF obtained in step (2) and 0.2 g of NaH2PO2·H2O were placed in two porcelain boats in a tube furnace, which was heated to 350°C at a rate of 2°C / min under a nitrogen atmosphere, and then heat-treated at 350°C for 2 h, to finally form a Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction composite material.

[0033] Example 4 This example is a synthesis of a Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction catalyst according to the following steps: (1) A three-electrode system was constructed using a nickel foam (NF) as the working electrode, a graphite rod as the counter electrode, and an Ag / AgCl electrode as the reference electrode. 0.045 mol of Ni(NO3)2·6H2O and 0.045 mol of Fe(NO3)3·9H2O were dissolved in 200 mL of deionized water to prepare an electrolyte, which was electrodeposited on the surface of the NF at -1.2 V vs. RHE for 400 s, washed and dried to obtain a Ni1Fe1-LDHs / NF precursor.

[0034] (2) The Ni1Fe1-LDHs / NF obtained in step (1) was used as the working electrode, a graphite rod was used as the counter electrode, and Ag / AgCl was used as the reference electrode. The electrodes were placed in 100 mL of deionized water containing 0.06 mol of Ni(NO3)2·6H2O and 0.03 mol of C 10 H 14 Ni2Mo1-LDHs were in-situ grown on the surface of the Ni1Fe1-LDHs by electrodeposition at -0.9 V vs. RHE for 300 s in 100 mL of deionized water containing 0.06 mol of MoO6, to form a Ni1Fe1-LDHs / Ni2Mo1-LDHs / NF composite precursor, which was then washed with deionized water and ethanol and dried by cold air.

[0035] (3) The Ni1Fe1-LDHs / Ni2Mo1-LDHs / NF obtained in step (2) was placed in two porcelain boats in a tube furnace, and 0.2 g of NaH2PO2·H2O was placed in each porcelain boat. The temperature was raised to 350°C at a rate of 2°C / min in a nitrogen atmosphere, and the sample was heat-treated for 2 h. Finally, the Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction composite material was obtained.

[0036] Example 5 In this example, the Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction catalyst was synthesized according to the following steps: (1) A three-electrode system was constructed using foam nickel (NF) as the working electrode, a graphite rod as the counter electrode, and an Ag / AgCl electrode as the reference electrode. 0.045 mol of Ni(NO3)2·6H2O and 0.045 mol of Fe(NO3)3·9H2O were dissolved in 200 mL of deionized water to prepare an electrolyte. The NF surface was electrodeposited at -1.2 V vs. RHE for 400 s, washed and dried to obtain the Ni1Fe1-LDHs / NF precursor.

[0037] (2) The Ni1Fe1-LDHs / NF obtained in step (1) was used as the working electrode, a graphite rod was used as the counter electrode, and Ag / AgCl was used as the reference electrode. The sample was placed in 100 mL of deionized water containing 0.06 mol of Ni(NO3)2·6H2O and 0.03 mol of C 10 H 14 MoO6, and electrodeposited at -0.9 V vs. RHE for 400 s. Ni2Mo1-LDHs were in-situ grown on the surface of Ni1Fe1-LDHs to form the Ni1Fe1-LDHs / Ni2Mo1-LDHs / NF composite precursor, which was then washed with deionized water and ethanol and dried with cold air.

[0038] (3) The Ni1Fe1-LDHs / Ni2Mo1-LDHs / NF obtained in step (2) was placed in two porcelain boats in a tube furnace, and 0.25 g of NaH2PO2·H2O was placed in each porcelain boat. The temperature was raised to 300°C at a rate of 2°C / min in a nitrogen atmosphere, and the sample was heat-treated for 2 h. Finally, the Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction composite material was obtained.

[0039] Example 6 In this example, the Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction catalyst was synthesized according to the following steps: (1) A three-electrode system was constructed with foam nickel (NF) as the working electrode, a graphite rod as the counter electrode, and an Ag / AgCl electrode as the reference electrode. An electrolyte was prepared by dissolving 0.045 mol of Ni(NO3)2·6H2O and 0.045 mol of Fe(NO3)3·9H2O in 200 mL of deionized water. The Ni1Fe1-LDHs / NF precursor was obtained by electrodeposition on the surface of NF at -1.2 V vs. RHE for 400 s, followed by washing and drying.

[0040] (2) The Ni1Fe1-LDHs / NF obtained in step (1) was used as the working electrode, a graphite rod was used as the counter electrode, and Ag / AgCl was used as the reference electrode. The Ni2Mo1-LDHs were in-situ grown on the surface of Ni1Fe1-LDHs by electrodeposition at -0.9 V vs. RHE for 300 s in 100 mL of deionized water containing 0.06 mol of Ni(NO3)2·6H2O and 0.03 mol of C 10 H 14 MoO6, to form a Ni1Fe1-LDHs / Ni2Mo1-LDHs / NF composite precursor, followed by washing with deionized water and ethanol and cold air drying.

[0041] (3) The Ni1Fe1-LDHs / Ni2Mo1-LDHs / NF obtained in step (2) and 0.25 g of NaH2PO2·H2O were placed in two porcelain boats in a tube furnace, respectively. The Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction composite material was finally converted by heat treatment at 300°C for 1 h at a heating rate of 2°C / min under a nitrogen atmosphere.

[0042] Example 7 This example is a synthesis of the Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction catalyst according to the following steps: (1) A three-electrode system was constructed with foam nickel (NF) as the working electrode, a graphite rod as the counter electrode, and an Ag / AgCl electrode as the reference electrode. An electrolyte was prepared by dissolving 0.045 mol of Ni(NO3)2·6H2O and 0.045 mol of Fe(NO3)3·9H2O in 200 mL of deionized water. The Ni1Fe1-LDHs / NF precursor was obtained by electrodeposition on the surface of NF at -1.2 V vs. RHE for 400 s, followed by washing and drying.

[0043] (2) The Ni1Fe1-LDHs / NF obtained in step (1) was used as the working electrode, a graphite rod was used as the counter electrode, and Ag / AgCl was used as the reference electrode. The Ni2Mo1-LDHs were in-situ grown on the surface of Ni1Fe1-LDHs by electrodeposition at -0.9 V vs. RHE for 300 s in 100 mL of deionized water containing 0.06 mol of Ni(NO3)2·6H2O and 0.03 mol of C 10 H14 Ni1Fe1-LDHs / Ni2Mo1-LDHs / NF composite precursor was formed by in-situ growth of Ni2Mo1-LDHs on the surface of Ni1Fe1-LDHs at -0.9 V (vs. RHE) for 300 s in 100 mL deionized water of MoO6, followed by washing with deionized water and ethanol and cold air drying.

[0044] (3) The Ni1Fe1-LDHs / Ni2Mo1-LDHs / NF obtained in step (2) and 0.25 g of NaH2PO2·H2O were respectively placed in two porcelain boats in a tube furnace, and heat-treated at 350°C for 2 h at a temperature rising rate of 2°C / min under a nitrogen atmosphere, to finally convert into Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction composite material.

[0045] Example 8 This example is to synthesize Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction catalyst according to the following steps: (1) A three-electrode system was constructed with foam nickel (NF) as the working electrode, a graphite rod as the counter electrode, and an Ag / AgCl electrode as the reference electrode. 0.045 mol of Ni(NO3)2·6H2O and 0.045 mol of Fe(NO3)3·9H2O were dissolved in 200 mL of deionized water to prepare an electrolyte, and electrodeposition was carried out on the surface of NF at -1.2 V (vs. RHE) for 400 s. After washing and drying, a Ni1Fe1-LDHs / NF precursor was obtained.

[0046] (2) The Ni1Fe1-LDHs / NF obtained in step (1) was used as the working electrode, a graphite rod was used as the counter electrode, and Ag / AgCl was used as the reference electrode. The working electrode was placed in a solution containing 0.06 mol of Ni(NO3)2·6H2O and 0.03 mol of C 10 H 14 Ni1Fe1-LDHs / Ni2Mo1-LDHs / NF composite precursor was formed by in-situ growth of Ni2Mo1-LDHs on the surface of Ni1Fe1-LDHs at -0.9 V (vs. RHE) for 300 s in 100 mL deionized water of MoO6, followed by washing with deionized water and ethanol and cold air drying.

[0047] (3) The Ni1Fe1-LDHs / Ni2Mo1-LDHs / NF obtained in step (2) and 0.25 g of NaH2PO2·H2O were respectively placed in two porcelain boats in a tube furnace, and heat-treated at 350°C for 2 h at a temperature rising rate of 2°C / min under a nitrogen atmosphere, to finally convert into Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction composite material.

[0048] Comparative Example 1 This example is to synthesize Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction catalyst according to the following steps: (1) A three-electrode system was constructed with foam nickel (NF) as the working electrode, a graphite rod as the counter electrode, and an Ag / AgCl electrode as the reference electrode. 0.045 mol of Ni(NO3)2·6H2O and 0.045 mol of Fe(NO3)3·9H2O were dissolved in 200 mL of deionized water to prepare an electrolyte. The Ni1Fe1-LDHs / NF precursor was obtained by electrodeposition on the surface of NF at -1.2 V relative to RHE for 400 s, followed by washing and drying. (2) The Ni1Fe1-LDHs / NF obtained in step (1) and 0.25 g of NaH2PO2·H2O were placed in two porcelain boats in a tube furnace, and heat-treated at 2 ℃ / min to 350 ℃ for 2 h under a nitrogen atmosphere. Finally, Fe-Ni5P4 / NF was obtained, denoted as sample 9.

[0049] Comparative Example 2 This example is to synthesize Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction catalyst according to the following steps: (1) A three-electrode system was constructed with foam nickel (NF) as the working electrode, a graphite rod as the counter electrode, and an Ag / AgCl electrode as the reference electrode. 0.06 mol of Ni(NO3)2·6H2O and 0.03 mol of C 10 H 14 MoO6 were dissolved in 100 mL of deionized water to prepare an electrolyte. The Ni2Mo1-LDHs / NF precursor was obtained by electrodeposition on the surface of NF at -0.9 V relative to RHE for 300 s, followed by washing and drying. (2) The Ni2Mo1-LDHs / NF obtained in step (1) and 0.25 g of NaH2PO2·H2O were placed in two porcelain boats in a tube furnace, and heat-treated at 2 ℃ / min to 350 ℃ for 2 h under a nitrogen atmosphere. Finally, Ni-Mo4P3 / NF was obtained, denoted as sample 10.

[0050] Example 9 This example is to synthesize Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction catalyst according to the following steps: (1) A three-electrode system was constructed with foam nickel (NF) as the working electrode, a graphite rod as the counter electrode, and an Ag / AgCl electrode as the reference electrode. An electrolyte was prepared by dissolving 0.045 mol of Ni(NO3)2·6H2O and 0.045 mol of Fe(NO3)3·9H2O in 200 mL of deionized water. The Ni1Fe1-LDHs / NF precursor was obtained by electrodeposition on the surface of NF at -1.2 V vs. RHE for 400 s, followed by washing and drying.

[0051] (2) The Ni1Fe1-LDHs / NF obtained in step (1) was used as the working electrode, a graphite rod was used as the counter electrode, and Ag / AgCl was used as the reference electrode. The Ni2Mo1-LDHs were in-situ grown on the surface of Ni1Fe1-LDHs by electrodeposition at -0.9 V vs. RHE for 300 s in 100 mL of deionized water containing 0.06 mol of Ni(NO3)2·6H2O and 0.03 mol of C 10 H 14 MoO6, to form the Ni1Fe1-LDHs / Ni2Mo1-LDHs / NF composite precursor, which was then washed with deionized water and ethanol and dried with cold air.

[0052] (3) The Ni1Fe1-LDHs / Ni2Mo1-LDHs / NF obtained in step (2) and 0.15 g of NaH2PO2·H2O were placed in two porcelain boats in a tube furnace, respectively. The Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction composite material was finally converted by heat treatment at 350°C at a rate of 2°C / min in a nitrogen atmosphere for 2 h, which is denoted as sample 11.

[0053] Example 10 In this example, the Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction catalyst was synthesized according to the following steps: (1) A three-electrode system was constructed with foam nickel (NF) as the working electrode, a graphite rod as the counter electrode, and an Ag / AgCl electrode as the reference electrode. An electrolyte was prepared by dissolving 0.045 mol of Ni(NO3)2·6H2O and 0.045 mol of Fe(NO3)3·9H2O in 200 mL of deionized water. The Ni1Fe1-LDHs / NF precursor was obtained by electrodeposition on the surface of NF at -1.2 V vs. RHE for 400 s, followed by washing and drying.

[0054] (2) The Ni1Fe1-LDHs / NF obtained in step (1) was used as the working electrode, a graphite rod was used as the counter electrode, and Ag / AgCl was used as the reference electrode. The Ni2Mo1-LDHs were in-situ grown on the surface of Ni1Fe1-LDHs by electrodeposition at -0.9 V vs. RHE for 300 s in 100 mL of deionized water containing 0.06 mol of Ni(NO3)2·6H2O and 0.03 mol of C 10 H14 Ni1Fe1-LDHs / Ni2Mo1-LDHs / NF composite precursor was formed by in-situ growth of Ni2Mo1-LDHs on the surface of Ni1Fe1-LDHs by electrodeposition of 300 s at -0.9 V vs. RHE in 100 mL deionized water containing MoO6, followed by washing with deionized water and ethanol and cold air drying.

[0055] (3) The Ni1Fe1-LDHs / Ni2Mo1-LDHs / NF obtained in step (2) and 0.35 g NaH2PO2·H2O were respectively placed in two porcelain boats in a tube furnace, and heat treated at 350℃ for 2 h at a temperature rising rate of 2℃ / min under nitrogen atmosphere, to finally convert into Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction composite material, recorded as sample 12.

[0056] Example 11 This example is to synthesize Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction catalyst according to the following steps: (1) A three-electrode system was constructed with foam nickel (NF) as the working electrode, graphite rod as the counter electrode, and Ag / AgCl electrode as the reference electrode. 0.045 mol Ni(NO3)2·6H2O and 0.045 mol Fe(NO3)3·9H2O were dissolved in 200 mL deionized water to prepare an electrolyte, and electrodeposited on the surface of NF at -1.2 V vs. RHE for 400 s, then washed and dried to obtain Ni1Fe1-LDHs / NF precursor.

[0057] (2) The Ni1Fe1-LDHs / NF obtained in step (1) was used as the working electrode, graphite rod as the counter electrode, and Ag / AgCl as the reference electrode, and was placed in a solution containing 0.06 mol Ni(NO3)2·6H2O and 0.03 mol C 10 H 14 Ni1Fe1-LDHs / Ni2Mo1-LDHs / NF composite precursor was formed by in-situ growth of Ni2Mo1-LDHs on the surface of Ni1Fe1-LDHs by electrodeposition of 300 s at -0.9 V vs. RHE in 100 mL deionized water containing MoO6, followed by washing with deionized water and ethanol and cold air drying.

[0058] (3) The Ni1Fe1-LDHs / Ni2Mo1-LDHs / NF obtained in step (2) and 0.5 g of NaH2PO2·H2O were respectively placed in two porcelain boats in a tube furnace, and heat-treated at 2 ℃ / min to 350 ℃ for 2 h under a nitrogen atmosphere, and finally converted into a Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction composite material, denoted as sample 13.

[0059] The products of Examples 8-11 and Comparative Examples 1 and 2 were respectively tested.

[0060] From the results of XRD of the sample prepared in Example 8, it can be seen that characteristic diffraction peaks of Ni5P4 and Mo4P3 phases appear, indicating that the main components of the sample prepared in Example 8 are Ni5P4 and Mo4P3. Figure 1 From the results of SEM of the sample prepared in Example 8, it can be seen that the morphology of the sample prepared in Example 8 is basically a two-dimensional composite heterostructure loaded on the substrate.

[0061] Figure 2 From the results of EDS of the sample prepared in Example 8, it can be seen that the sample prepared in Example 8 contains Fe, P, Mo and Ni elements, proving that Fe and Ni elements are successfully doped into the material.

[0062] From the results of XPS of the sample prepared in Example 8, it can be seen that the sample prepared in Example 8 contains Fe, P, Mo and Ni elements, proving that Fe and Ni elements are successfully doped into the material. Figure 3 From the results of UV-Vis of the samples prepared in Comparative Examples 1 and 2, it can be seen that the band gap of the samples prepared in Comparative Examples 1 and 2 is 1.8 eV and 2.23 eV, respectively.

[0063] Figure 4 From the results of UV-Vis of the samples prepared in Comparative Examples 1 and 2, it can be seen that the conduction band of the samples prepared in Comparative Examples 1 and 2 is 1.55 eV and 1.63 eV, respectively. Combined with the results of XPS, it can be proved that there is a built-in electric field in Fe-Ni5P4 / Ni-Mo4P3.

[0064] From the results of Zeta potential of the samples prepared in Example 8 and Comparative Examples 1 and 2, it can be seen that the Zeta potential of the samples prepared in Example 8 and Comparative Examples 1 and 2 is -24.3, -12.1 and -14.1 mV, respectively, and the results can prove that the built-in electric field of Fe-Ni5P4 / Ni-Mo4P3 / NF is the strongest. Figure 5 Figure 4

[0065] From the results of Zeta potential of the samples prepared in Example 8 and Comparative Examples 1 and 2, it can be seen that the Zeta potential of the samples prepared in Example 8 and Comparative Examples 1 and 2 is -24.3, -12.1 and -14.1 mV, respectively, and the results can prove that the built-in electric field of Fe-Ni5P4 / Ni-Mo4P3 / NF is the strongest. Figure 6

[0066] ​​​​​The electrocatalytic performance of the catalyst was tested using a standard three-electrode system. The working electrode was a sample grown on a nickel foam substrate, the counter electrode was a graphite rod, and the reference electrode was an Ag / AgCl electrode. The electrolytes were 1 M KOH and actual seawater solution. Before testing, the working electrode was activated by cyclic voltammetry (CV) within a potential window of 1.1–1.65 V (vs. RHE) until the curve stabilized. Subsequently, linear sweep voltammetry (LSV) was performed at a scan rate of 5 mV / s within the same potential range, and the LSV curve was recorded. The stability of the catalyst was evaluated using chronopotentiometry, i.e., at 10, 20, 50, and 100 mA cm⁻¹. -2 It was continuously operated at a constant current density. Electrochemical impedance spectroscopy (EIS) measurements were performed at open-circuit potentials, ranging from 100 kHz to 0.01 Hz, with a perturbation amplitude of 5 mV. All measured potentials were converted to potentials relative to the reversible hydrogen electrode.

[0067] Depend on Figure 7 It can be seen that, under the same current density, the overpotential of Example 8 is much lower than that of the samples prepared in Comparative Examples 1 and 2. This proves that the built-in electric field generated by the Fe-Ni5P4 and Ni-Mo4P3 composite enhances the electrocatalytic OER performance of the material.

[0068] Depend on Figure 8 It can be seen that the samples prepared in Example 8 showed good performance at 10, 20, 50, and 100 mA cm⁻¹. -2 The relatively stable current value at the specified current density demonstrates that Fe-Ni5P4 / Ni-Mo4P3 / NF has good stability.

[0069] Depend on Figure 9 It can be seen that the C of the samples prepared in Example 8 and Comparative Examples 1-2 dl The values ​​were 4.4, 2.7, and 2.5 mFcm, respectively. -2 This indicates that Fe-Ni5P4 / Ni-Mo4P3 / NF has the optimal active specific surface area. The characterization results confirm that the significant increase in the number of active sites at the heterojunction interface can be attributed to the optimization of the electronic structure by the built-in electric field and the induction effect of new active sites.

[0070] Depend on Figure 10 It can be seen that the diameter of the semicircle in the Nyquist plot of Example 8 is smaller than the diameter of the semicircle of the samples prepared in Comparative Examples 1-2, indicating that Fe-Ni5P4 / Ni-Mo4P3 / NF has the best charge transfer capability. This proves that the built-in electric field formed at the heterojunction interface effectively reduces the charge transfer impedance, accelerates the interface charge migration process, and significantly improves the electronic conduction efficiency and overall reaction kinetics performance of the material.

[0071] Depend on Figure 11It can be seen that the sample prepared in Example 8 has the most phosphorus vacancies, proving that the method can regulate the phosphorus vacancies in the heterojunction sample.

[0072] By Figure 12 It can be seen that the Zeta potentials of the samples prepared in Examples 8-11 and Comparative Examples 1-2 are -24.3, -20, -23.1, -21, -14.1, and -12.1 mV, respectively, indicating that the sample prepared in Example 8 has the strongest built-in electric field, proving that the phosphorus vacancies can regulate the strength of the built-in electric field.

Claims

1. A method for preparing a self-supported Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction composite material, characterized in that, Comprising the following steps: (1) A three-electrode system was constructed with nickel foam as the working electrode, a graphite rod as the counter electrode, and an Ag / AgCl electrode as the reference electrode. Ni(NO3)2·6H2O and Fe(NO3)3·9H2O were dissolved in deionized water to prepare an electrolyte. Ultra-thin Ni1Fe1-LDHs were electrodeposited on the surface of NF at a specific voltage. After washing and drying, the Ni1Fe1-LDHs / NF precursor was obtained; (2) The Ni1Fe1-LDHs / NF obtained in step (1) is used as a working electrode, a graphite rod is used as a counter electrode, and Ag / AgCl is used as a reference electrode, which is placed in a solution containing Ni(NO3)2·6H2O and C 10 H 14 MoO6 in deionized water, in-situ growth of Ni2Mo1-LDHs on the surface of Ni1Fe1-LDHs is carried out at a set voltage to form a Ni1Fe1-LDHs / Ni2Mo1-LDHs / NF composite precursor, and then the composite precursor is washed with deionized water and ethanol and dried by cold air. (3) The Ni1Fe1-LDHs / Ni2Mo1-LDHs / NF obtained in step (2) and NaH2PO2·H2O were placed in two porcelain boats in a tube furnace, and the phosphorization treatment was carried out under a nitrogen atmosphere by programmed temperature rising. Finally, the Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction composite material was obtained.

2. The production method according to claim 1, characterized by, In step (1), the molar ratio of Ni(NO3)2·6H2O to Fe(NO3)3·9H2O is (0.8-1.2):(0.8-1.2), and the concentration of Ni(NO3)2·6H2O after dissolving in water is 0.225 mol / L.

3. The production method according to claim 1, characterized by, In step (1), the voltage applied in step (1) is (-1.5-0) V relative to RHE; preferably, the electrodeposition time in step (1) is 200-500 s.

4. The production method according to claim 1, characterized by, The mass ratio of Ni(NO3)2·6H2O and C 10 H 14 The mass ratio of MoO6 is (1~2):(1~2), and the concentration of Ni(NO3)2·6H2O dissolved in water is 0.6 mol / L.

5. The production method according to claim 1, characterized by, The voltage applied in step (2) is (-1.5-0) V relative to RHE; preferably, the electrodeposition time in step (2) is 200-500 s.

6. The method of claim 1, wherein, In step (3), the mass ratio of Ni1Fe1-LDHs / Ni2Mo1-LDHs / NF to NaH2PO2·H2O is (0.1-1):(0.1-1).

7. The production method according to claim 1, characterized by, The heat treatment temperature in step (3) is 300-450 ℃.

8. The method of claim 1, wherein, The heat treatment time in step (3) is 1-2 hours.

9. The Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction composite material prepared by the method according to any one of claims 1-8.

10. The application of the Fe-Ni5P4 / Ni-Mo4P3 / NF heterojunction composite material according to claim 9 in electrocatalytic seawater splitting.

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