A transition metal molybdate-molybdenum trioxide heterojunction, preparation method and application thereof

Abstract

This invention relates to the field of electrocatalytic materials technology, and discloses a transition metal molybdate-molybdenum trioxide heterojunction, its preparation method, and its applications. This invention utilizes Cu... 2+ The Jan-Taylor effect induces lattice distortion, which, combined with the electronic regulation of Ir, forms a stable Ir-(NiCoFeCu)MoO4-MoO3 heterojunction. This heterojunction was synthesized in situ on a nickel foam substrate via a one-step hydrothermal method. The heterojunction described in this invention possesses a sea urchin-like microsphere structure, a large specific surface area, and abundant active sites. In alkaline seawater, the heterojunction serves as an electrocatalyst at 10 mA cm⁻¹. ‑2 The hydrogen evolution overpotential is 60 mV and the oxygen evolution overpotential is 239 mV, and it is within 500 mA cm⁻¹. ‑2 It can operate stably for more than 600 hours at industrial-grade current density, while effectively suppressing the chlorine evolution side reaction, with a Faraday efficiency of over 99%.

Description

Technical Field

[0001] This invention relates to the field of electrocatalytic materials technology, and more particularly to a Cu-based... 2+ Ginger-Taylor effect transition metal molybdate-molybdenum trioxide heterojunction and its application in alkaline seawater hydrolysis. Background Technology

[0002] Hydrogen, due to its high energy density and zero carbon emissions, is considered an ideal energy carrier to replace fossil fuels. Water electrolysis is a sustainable hydrogen production route, but currently, industrial applications mainly rely on methane steam reforming and coal gasification. Both methods consume non-renewable resources and emit large amounts of CO2. Water electrolysis accounts for less than 4% of hydrogen production, with the main bottleneck being the lack of efficient, stable, and low-cost electrocatalysts. Noble metals Pt and IrO2 / RuO2 are benchmark catalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively, but their high price and scarcity limit their large-scale application. Therefore, the development of non-noble metal bifunctional catalysts based on transition metals has become a research hotspot. Molybdate materials have attracted attention due to their unique electronic structure and good chemical stability, but single-component molybdates still have shortcomings in terms of catalytic activity and conductivity (Cheng J, Guan C, Sun M, Yang J, Guo H, Yuan B, Zhao Y, Lyu C, Geng D, Liu Y. From fundamental understanding to modification strategies of cobalt molybdates in electrocatalytic oxygenevolution reaction. Small, 2026, 22(13): e13722. DOI:10.1002 / smll.202513722). Especially in seawater electrolysis environments, high concentrations of Cl... - This can severely corrode the catalyst and trigger a competitive chlorine evolution reaction, reducing oxygen evolution selectivity. Constructing heterostructures is one of the effective strategies to improve catalytic performance.

[0003] Existing technologies attempt to improve catalytic performance by constructing molybdate-based heterostructures. Tian et al. prepared a core-shell heterostructure by electrodepositing CoFe-LDH on CoMoO4, achieving an OER overpotential of 245 mV, but its stability was less than 50 hours. This is mainly attributed to the weak interfacial bonding between LDH and molybdate, which is merely a physical coating, making it susceptible to Cl- oxidation in seawater. -The penetration leads to the stripping of the active layer, and the material only possesses OER monofunctional activity (Tian L, Wang Q, Li Y, Ren X, Wei Q, Wu D. A hierarchical CoMoO4@CoFe-LDH heterostructure as a highly effective catalyst to boost electrocatalytic water oxidation. Dalton Transactions, 2022, 51(27): 10552-10557. DOI:10.1039 / D2DT01257J). Wang et al. synthesized a three-phase heterostructure of NiSe2-NiMoO4-MoO3 using a two-step hydrothermal-calcination method. The HER overpotential in alkaline seawater was 105 mV. However, sulfides were easily oxidized and dissolved at high potentials, leading to interface degradation and stability testing showing a stability of only 15 hours (Wang H, Du X, Zhang X. Controlled synthesis of NiSe2-NiMoO4-MoO3 material on nickel foam as an efficient hydrogen evolution reaction catalyst in seawater and urealectrolytes. Sustainable Materials and Technologies, 2024, 42: e01158. DOI:10.1016 / j.susmat.2024.e01158). Regarding phosphide composite systems, Guo et al. reported a Ni2P@NiMoO4 / NF core-shell structure utilizing PO4 formed in situ on the surface. 3- / MoO4 2- Biionic layer to repel Cl - In alkaline seawater at 500 mA cm -2The overpotential for OER is 343 mV, and the stability can reach 500 h. However, this material fails to exhibit HER activity simultaneously and cannot be used as a bifunctional all-water splitting catalyst (Guo X, He X, Liu X, Sun S, Sun H, Dong K, Li T, Yao Y, Xie T, Zheng D. Arming amorphous NiMoO4 on nickel phosphide enables highly stable alkaline seawater oxidation. Small, 2024, 20(31): 2400141. DOI:10.1002 / smll.202400141). Regarding oxide heterostructures, Chen et al. prepared MoO3 / NiMoO4 nanorod arrays through a two-step method. The post-deposited MoO3 and the substrate NiMoO4 only have physical contact, and the interfacial bonding is not strong enough. After long-term operation at high current density, phase separation and performance degradation are prone to occur. Its all-water splitting stability is within 100 mA cm⁻¹. -2Only about 150 h (ChenC W, Zhang HX, Liu DQ, Xu ZF, Jing YN, Lin QX, Li LL, Yin DOI:10.1016 / j.apsusc.2025.163766). In the field of high-entropy materials, although the Ru single-atom supported high-entropy alloy prepared by Zou et al. exhibits certain HER activity, its preparation involves high-temperature metallurgical processes, which are complex and energy-intensive (Zou Y, Zhao H, ZhangWD, Gong Q, Liu J, Yang X, Wang J, Yan X. High entropy alloy supported ruthenium single-atoms for enhanced electrochemical hydrogen evolution reaction. Chemical Engineering Journal, 2025, 518: 164784. DOI:10.1016 / j.cej.2025.164784).

[0004] In summary, existing molybdate-based heterostructure electrocatalysts still face several common challenges. The preparation processes are mostly multi-step, cumbersome, and unsuitable for large-scale scaling. The heterostructure interface often relies on physical adhesion or added phase stacking, lacking atomic-scale chemical bonding, leading to interface degradation and performance decline during long-term operation. Most catalysts possess only a single HER or OER function, making it difficult to achieve efficient bifunctional water splitting in a single electrolyzer. In real seawater environments, their resistance to chlorine corrosion and long-term operational stability at industrial-grade current densities remain insufficient. Therefore, there is an urgent need to develop a seawater electrocatalyst with a simple preparation process, in-situ co-generated heterostructure interface, dual HER and OER activity, and long-term stable operation at industrial-grade current densities. Summary of the Invention

[0005] This invention aims to address the shortcomings of existing technologies by providing a transition metal molybdate-molybdenum trioxide heterojunction, its preparation method, and its application.

[0006] The technical solution of the present invention is as follows: A transition metal molybdate-molybdenum trioxide heterojunction, wherein the heterojunction uses nickel foam as a supporting framework, and the surface of the nickel foam has an interwoven sheet-like and / or needle-like heterojunction structure formed by the co-growth of (NiCoFeCu)MoO4 and MoO3.

[0007] Preferably, the preparation is carried out by a one-step hydrothermal method, in which nickel foam is subjected to a hydrothermal reaction with an aqueous solution of an iron source precursor, a cobalt source precursor, a copper source precursor, and a molybdenum source precursor. The hydrothermal reaction temperature is 120-180°C and the time is 4-8 hours. The iron source precursor is selected from one or more of ferric nitrate, ferric chloride, ferric sulfate, ferric acetate, and their hydrates. The cobalt source precursor is selected from one or more of cobalt nitrate, cobalt chloride, cobalt sulfate, cobalt acetate, and their hydrates. The copper source precursor is selected from one or more of copper nitrate, copper chloride, copper sulfate, copper acetate, and their hydrates. The molybdenum source precursor is selected from one or more of ammonium molybdate, sodium molybdate, potassium molybdate, phosphomolybdic acid, and their hydrates.

[0008] Preferably, the molar ratio of copper to molybdenum is 1:(0.4 to 0.6).

[0009] Preferably, it is prepared by the following steps: (1) Dissolve the iron source precursor, cobalt source precursor, copper source precursor and molybdenum source precursor in deionized water and stir until they are mixed evenly to obtain a mixed solution; in the mixed solution, the total molar concentration of the three metal ions of iron, cobalt and copper is 0.05 to 0.15 mol / L, and the molar ratio of iron, cobalt, copper and molybdenum is (0.8 to 1.2):(0.8 to 1.2):1:0.5; (2) The pretreated nickel foam was placed vertically in a polytetrafluoroethylene-lined reactor, and the mixed solution obtained in step (1) was added. The reaction was carried out at 150°C for 6 hours. (3) After the reaction is complete, cool naturally to room temperature, remove the nickel foam, rinse with ultrapure water, and dry to obtain the final product.

[0010] Preferably, the heterojunction is further doped with Ir. The heterojunction is prepared by adding an iridium source substance to an aqueous solution containing an iron source, a cobalt source, a copper source, and a molybdenum source precursor and carrying out a hydrothermal reaction. The iridium source substance is selected from one or more of iridium trichloride, iridium chloro-iridium acid, iridium tetrachloride, iridium acetate, iridium acetylacetonate, or their hydrates.

[0011] Preferably, the molar ratio of the iridium source material (calculated as iridium) to the copper source material (calculated as copper) is 1:50 to 1:20.

[0012] The above-mentioned heterojunctions are used as catalysts in the electrocatalytic hydrogen evolution reaction and oxygen evolution reaction.

[0013] Preferably, the heterojunction is used as a catalyst in the electrocatalytic complete water splitting process.

[0014] Preferably, the water is seawater, and the seawater is alkaline seawater.

[0015] The beneficial effects of this invention are as follows: (1) The preparation process is simple. It is synthesized in situ on nickel foam by a one-step hydrothermal method, which does not require a reducing atmosphere, has mild conditions, and is suitable for large-scale production.

[0016] (2) Unique structural design.

[0017] Since the radii of the three transition metal ions Fe, Co, and Ni are similar, they all react with MoO4 in a stable six-coordinate octahedral form. 2- Since the tetrahedrons share a common vertex, when only the above three transition metal ions are used for preparation, only a single-phase molybdate solid solution can be obtained, and the precipitation of the second phase of MoO3 cannot be induced.

[0018] This invention uses Cu 2+ The Jiang-Taylor effect was applied to the in-situ construction of heterogeneous interfaces. Cu was introduced. 2+ After that, its d 9 The electronic configuration in the octahedral coordination field produces a significant Jam-Taylor distortion, resulting in a significant elongation of the axial Cu-O bonds in the CuO6 octahedron and a relative shortening of the in-plane Cu-O bonds, forming an elongated octahedral coordination configuration. This local bond length asymmetry induces lattice stress that breaks the symmetry of the molybdate phase, driving partial Mo... 6+ The particles are expelled from the crystal lattice and crystallize in situ as orthorhombic MoO3, spontaneously forming a heterogeneous interface with interwoven two phases. Compared to physical contact interfaces formed by added MoO3 or stepwise deposition, this in-situ symbiotic interface has atomic-scale chemical bonding, strong interfacial adhesion, and tight electronic coupling, making it less prone to phase separation or structural degradation during long-term electrocatalysis.

[0019] This invention utilizes Cu 2+ The Ginger-Taylor effect induces lattice distortion, successfully achieving in-situ generation of stable heterostructures of (NiCoFeCu)MoO4 and MoO3.

[0020] This invention stabilizes Cu by further introducing Ir. 2+ The distorted coordination configuration, along with the optimization of interfacial charge transfer efficiency through electronic regulation, achieved a synergistic improvement in catalytic activity and structural stability.

[0021] (3) Excellent catalytic performance. In alkaline seawater, 10 mA cm -2The hydrogen evolution overpotential is only 60 mV and the oxygen evolution overpotential is only 239 mV, demonstrating bifunctional activity significantly superior to most reported metal catalysts. The catalyst described in this invention achieves Faraday efficiencies of over 99% for both hydrogen and oxygen evolution, indicating that almost all input charge is utilized for the target reaction.

[0022] (4) Excellent stability. At 500 mA cm⁻¹ -2 At industrial-grade current densities, it can operate stably for over 200 hours for hydrogen evolution and over 600 hours for oxygen evolution, and can effectively suppress the chlorine evolution side reaction, with a Faraday efficiency of over 99%. Attached Figure Description

[0023] Figure 1 The X-ray diffraction (XRD) patterns of the products obtained under different copper and molybdenum ratios in Example 1 are shown. Figure 2 The image shows scanning electron microscope (SEM) images of the products obtained under different copper and molybdenum ratios in Example 1. Figure 3 The results show the electrocatalytic performance of the products obtained in Example 1 with different copper and molybdenum ratios as catalysts in an alkaline seawater electrolyte composed of 1.0 M KOH and natural seawater. Figure 4 XRD patterns of samples obtained at different hydrothermal reaction times in Example 2; Figure 5 SEM images of samples obtained at different hydrothermal reaction times in Example 2.

[0024] Figure 6 The results show the electrocatalytic performance of samples obtained at different hydrothermal reaction times in Example 2 on an alkaline seawater electrolyte composed of 1.0 M KOH and natural seawater. Figure 7 The XRD patterns of the Ir-containing transition metal molybdate-MoO3 heterojunction and the Ir-free heterojunction of the present invention in Example 3 are shown. Figure 8 This is a SEM image of the Ir-(NiCoFeCu)MoO4-MoO3 heterojunction described in Example 3 of the present invention; Figure 9 The transmission electron microscope (TEM) and selected area electron diffraction (SED) characterization images of the Ir-(NiCoFeCu)MoO4-MoO3 heterojunction described in Example 3 of this invention are shown below. Figure 10 The TEM, elemental surface distribution map, and energy dispersive spectroscopy (EDS) results of the Ir-(NiCoFeCu)MoO4-MoO3 heterojunction described in Example 3 of this invention are shown. Figure 11The image shows the X-ray photoelectron spectroscopy (XPS) spectrum of the Ir-(NiCoFeCu)MoO4-MoO3 heterojunction described in Example 3 of this invention. Figure 12 The results of Cu K-edge X-ray absorption fine structure (XANES) analysis of the Ir-(NiCoFeCu)MoO4-MoO3 and (NiCoFeCu)MoO4-MoO3 heterojunctions described in Example 3 of this invention; Figure 13 The graph shows the hydrogen evolution reaction performance test results of different catalysts in an alkaline seawater electrolyte composed of 1.0 M KOH and natural seawater in Example 4. Figure 14 This is a test graph showing the hydrogen evolution stability of the Ir-(NiCoFeCu)MoO4-MoO3 catalyst described in this invention in alkaline seawater electrolyte in Example 4. Figure 15 The graph shows the oxygen evolution reaction performance of different catalysts in an alkaline seawater electrolyte composed of 1.0 M KOH and natural seawater in Example 5. Figure 16 The graph shows the oxygen evolution stability test results of different catalysts in the alkaline seawater electrolyte composed of 1.0 M KOH and natural seawater in Example 5. Figure 17 The image shows the microstructure and elemental distribution of the Ir-(NiCoFeCu)MoO4-MoO3 catalyst in Example 5 after a long-term oxygen evolution stability test. Figure 18 The image shows the in-situ Raman spectrum of the Ir-(NiCoFeCu)MoO4-MoO3 catalyst in Example 5 during the oxygen evolution process. Figure 19 This is a diagram illustrating the oxygen evolution reaction mechanism of the Ir-(NiCoFeCu)MoO4-MoO3 catalyst in Example 5. Figure 20 The results show the Faradaic efficiency and chlorine evolution side reaction test results of the Ir-(NiCoFeCu)MoO4-MoO3 catalyst in Example 5. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0026] A transition metal molybdate-molybdenum trioxide heterojunction is provided, with nickel foam as the supporting framework. The surface of the nickel foam has an interwoven sheet-like and / or needle-like heterojunction structure formed by the co-growth of (NiCoFeCu)MoO4 and MoO3.

[0027] The heterojunction of this invention is prepared by a one-step hydrothermal method, in which pretreated nickel foam is subjected to a hydrothermal reaction with aqueous solutions of iron, cobalt, copper, and molybdenum source precursors (preferably, the total molar concentration of the three metal ions, iron, cobalt, and copper, is 0.05–0.15%). The molar ratio of copper to molybdenum in the solution is 1:(0.4-1) (preferably 1:(0.4-0.6), more preferably 1:0.5). The hydrothermal reaction temperature is 120-180℃, and the reaction time is 4-8h (preferably 150℃ for 6h). The iron source precursor is selected from one or more of ferric nitrate, ferric chloride, ferric sulfate, ferric acetate, or their hydrates. The cobalt source precursor is selected from one or more of cobalt nitrate, cobalt chloride, cobalt sulfate, cobalt acetate, or their hydrates. The copper source precursor is selected from one or more of copper nitrate, copper chloride, copper sulfate, copper acetate, or their hydrates. The molybdenum source precursor is selected from one or more of ammonium molybdate, sodium molybdate, potassium molybdate, phosphomolybdic acid, or their hydrates.

[0028] Nickel foam pretreatment: The nickel foam is ultrasonically cleaned with acid to remove the surface oxide layer, and then ultrasonically cleaned with deionized water and anhydrous ethanol respectively, and dried for later use.

[0029] Preferably, the iron source precursor is selected from Fe(NO3)3, the cobalt source precursor is selected from Co(NO3)2, the copper source precursor is selected from Cu(NO3)2, and the molybdenum source precursor is selected from (NH4)6Mo7O. 24 .

[0030] In a specific example of the present invention, the heterojunction is prepared by the following steps: (1) Dissolve Fe(NO3)3·9H2O, Co(NO3)2·6H2O, and Cu(NO3)2·3H2O in equimolar ratio in 30 mL of deionized water, and stir until homogeneous to obtain a mixed solution. The total concentration of iron, cobalt, and copper ions in the mixed solution is 0.05–0.15 mol / L. Add 0.5 mmol of (NH4)6Mo7O 24 · Continue stirring with 4H2O, the molar ratio of iron, cobalt, copper and molybdenum is (0.8~1.2):(0.8~1.2):1:(0.4~0.6, preferably 0.5); (2) The pretreated nickel foam was placed vertically in a polytetrafluoroethylene-lined reactor, and the mixed solution obtained in step (1) was added. The reaction was carried out at 150°C for 6 h. (3) After the reaction is complete, cool naturally to room temperature, remove the nickel foam, rinse with ultrapure water, and dry (60℃, 12 h) to obtain the final product.

[0031] In a preferred embodiment of the present invention, the heterojunction is further doped with one or more metal ions selected from Mn, Zn, Ru, Ir, Ce, La, Cr, and V.

[0032] In a specific example of this invention, the heterojunction is further doped with Ir. The heterojunction is prepared by a hydrothermal reaction of adding an iridium source to an aqueous solution containing iron, cobalt, copper, or molybdenum source precursors. The iridium source is selected from one or more of iridium trichloride, iridium chloro-iridium acid, iridium tetrachloride, iridium acetate, iridium acetylacetonate, or their hydrates. Iridium trichloride is preferred as the iridium source.

[0033] Another object of the present invention is to provide the application of the heterojunction of the present invention as a catalyst in the electrocatalytic hydrogen evolution reaction and / or oxygen evolution reaction.

[0034] A specific example is the use of heterojunctions as catalysts for electrocatalytic water splitting.

[0035] Preferably, the water is seawater. More preferably, it is alkaline seawater. As a specific example, the alkaline seawater is a mixed solution of KOH (preferably 1.0M KOH) and natural seawater, which is taken from Bay No. 13 in Haikou City, Hainan Province, China, and filtered through a 0.22 μm filter membrane before use.

[0036] The heterojunction of this invention exhibits a sea urchin-like microsphere morphology, composed of an interwoven structure formed by the co-growth of outwardly radially extending sheet-like and / or needle-like structures, uniformly grown on a nickel foam framework. Four transition metals—Ni, Co, Fe, and Cu—are uniformly distributed in the catalyst, with Mo as the dominant metal. 6+ The structure forms an Ir-(NiCoFeCu)MoO4-MoO3 heterostructure, with Ir as the base material. 4+ With Ir 0 Mixed valence states exist. Cu 2+ The Ginger-Taylor effect induces local lattice distortion, forming an asymmetric Cu-O long and short bond coordination structure.

[0037] Example 1: Effect of the proportion of copper ions added on the structure, morphology and electrocatalytic performance of heterojunctions This embodiment investigates the effect of copper ion addition on heterostructure formation and catalytic performance, and uses a sample without copper ions as a comparison to verify the effect of Cu... 2+ The Ginger-Taylor effect is the key driving force for inducing MoO3 precipitation and constructing heterogeneous interfaces.

[0038] (1) Pretreatment of nickel foam: Nickel foam (3×4 cm) 2 The surface oxide layer was removed by ultrasonic cleaning with 3 M HCl for 15 min, followed by ultrasonic cleaning with deionized water and anhydrous ethanol for 15 min each, and then vacuum dried at 60℃ for later use.

[0039] (2) Dissolve 0.404 g Fe(NO3)3·9H2O (1 mmol) and 0.291 g Co(NO3)2·6H2O (1 mmol) in 30 mL of deionized water to prepare 5 parallel solutions. Add 0 g, 0.121 g (0.5 mmol), 0.242 g (1 mmol), 0.362 g (1.5 mmol) and 0.483 g (2.0 mmol) of Cu(NO3)2·3H2O respectively, and stir for 15 min to obtain mixed metal salt solutions with different amounts of copper ions added.

[0040] (3) Add 0.088 g (0.071 mmol of ammonium heptamolybdate tetrahydrate, approximately 0.5 mmol based on Mo element) of (NH4)6Mo7O to each of the mixed solutions obtained in step (2). 24 Add 4H2O and continue stirring for 15 minutes.

[0041] (4) Add 5 mg IrCl3·xH2O to the mixture obtained in step (3) and stir for 10 min until completely dissolved to obtain the hydrothermal reaction precursor solution.

[0042] (5) Place the pretreated nickel foam from step (1) vertically into a 50 mL polytetrafluoroethylene-lined reactor, pour in the hydrothermal reaction precursor liquid obtained in step (4), seal the reactor, and then place it in a 150℃ oven for 6 h.

[0043] (6) After the reaction is complete, cool naturally to room temperature, remove the nickel foam, rinse repeatedly with ultrapure water to remove residual solution on the surface, and dry in an oven at 60°C for 12 h to obtain the final product.

[0044] Figure 1 X-ray diffraction (XRD) patterns of products with different copper and molybdenum ratios are shown. Figure 1 It is evident that, without the addition of a copper source, the obtained Cu0 sample mainly exhibits diffraction peaks corresponding to the NiMoO4 standard card. No obvious MoO3 characteristic diffraction peaks were observed in the 2θ = 23°–28° range, indicating that without a Cu source, the diffraction peaks are within the range of 2θ = 23°–28°. 2+ Under the conditions specified, the product was mainly a single molybdate phase, without forming a distinct molybdate-MoO3 heterogeneous structure. When the molar ratio of copper to molybdenum was 0.5:0.5 (with an addition of 0.5 mmol of (NO3)2·3H2O), the sample Cu... 0.5 The XRD pattern initially showed weak MoO3-related diffraction signals, but the peak intensity was low, and non-target diffraction peaks could be observed in local areas. When the molar ratio of copper to molybdenum was 1:0.5 (the amount of Cu(NO3)2·3H2O added was 1.0 mmol), the sample Cu 1.0Clear diffraction peaks appeared near 2θ = 23.34°, 25.70°, and 27.30°, corresponding to the (021), (040), and (110) crystal planes of the orthorhombic MoO3 phase, respectively. Meanwhile, the characteristic diffraction peaks of the molybdate phase were retained, indicating that at this copper source addition, the molybdate and MoO3 phases could coexist well, forming a transition metal molybdate-MoO3 heterostructure with a relatively well-defined phase composition. When the molar ratio of copper to molybdenum was further increased to 1.5:0.5 and 2:0.5 (with Cu(NO3)2·3H2O addition further increased to 1.5 mmol and 2.0 mmol), non-target diffraction peaks could still be observed in local areas. The MoO3-related diffraction peaks were further enhanced and became sharper, while the molybdate phase diffraction peaks were relatively weakened, indicating that excess Cu... 2+ This could lead to excessive precipitation of the MoO3 phase in the system, affecting the molybdate framework structure and causing the product phase composition to deviate from the target heterostructure. Therefore, under the preparation conditions of this embodiment, a copper to molybdenum molar ratio of 1:0.5 is more conducive to obtaining a transition metal molybdate-MoO3 heterostructure with a suitable phase composition.

[0045] Figure 2 The images show scanning electron microscope (SEM) images of the products with different copper and molybdenum ratios. Figure 2 (a) and Figure 2 (b) Corresponding to Cu0 sample, Figure 2 (c) and Figure 2 (d) Corresponding to Cu 0.5 sample, Figure 2 (e) and Figure 2 (f) corresponds to Cu 1.0 sample, Figure 2 (g) and Figure 2 (h) corresponds to Cu 1.5 sample, Figure 2 (i) and Figure 2 (j) corresponds to Cu 2.0 Sample. From Figure 2 (a) and Figure 2 (b) As can be seen, without the addition of a copper source, the sample mainly exhibits a flower-like or bundle-like morphology formed by the accumulation of micron-sized rod-like structures, which is quite similar to common nickel molybdate-based materials. Figure 2 (c) and Figure 2 (d) It can be seen that when the molar ratio of copper to molybdenum is 0.5:0.5 (the amount of copper source added is 0.5 mmol), the morphology of the product begins to change, but the overall structure is relatively loose and lacks uniformity, indicating that a small amount of Cu 2+ It can influence the nucleation and growth process of the product, but is insufficient to induce the formation of a uniform target heterostructure. Figure 2 (e) and Figure 2(f) As can be seen, when the molar ratio of copper to molybdenum is 1:0.5 (copper source added 1.0 mmol), the product uniformly covers the surface of the nickel foam, forming a urchin-like microsphere morphology composed of radiating outward growth of sheet-like and / or needle-like nanostructures. This morphology facilitates the exposure of more active sites and also promotes electrolyte penetration and bubble release. Figure 1 XRD results showed that the addition of 1.0 mmol of copper source could promote the synergistic formation of the molybdate and MoO3 phases, thereby obtaining a molybdate-MoO3 heterojunction with uniform morphology and suitable phase composition. Figure 2 (g) to Figure 2 (j) It is evident that when the molar ratio of copper to molybdenum further increases to 1.5:0.5 and 2:0.5 (with the copper source added increasing to 1.5 mmol and 2.0 mmol), the product exhibits significant agglomeration, with the local structure becoming rough and heterogeneous, and the integrity of the urchin-like microsphere structure decreasing. This result indicates that excess Cu... 2+ This can alter the crystal growth behavior during the hydrothermal reaction, potentially leading to excessive precipitation or local aggregation of the MoO3 phase, which is detrimental to the formation of a uniform and stable target heterostructure. Therefore, an appropriate amount of Cu... 2+ The introduction of Cu(NO3)2·3H2O can influence the nucleation, growth, and local structural rearrangement of molybdate crystals through its coordination distortion effect, thereby promoting the in-situ precipitation of the MoO3 phase and the construction of a molybdate-MoO3 heterostructure. Under the conditions of this embodiment, the preferred molar ratio of copper to molybdenum is 1:0.5 (the amount of Cu(NO3)2·3H2O added is 1.0 mmol).

[0046] Figure 3 The electrocatalytic performance of products obtained with different copper and molybdenum ratios as catalysts for oxygen evolution reaction and hydrogen evolution reaction was tested. Figure 3 (a) shows the oxygen evolution reaction polarization curves for samples with different copper and molybdenum ratios. Figure 3 (b) shows the hydrogen evolution reaction polarization curves for samples with different copper and molybdenum element ratios. Figure 3 (a) It is evident that different ratios of copper and molybdenum significantly affect the oxygen evolution reaction performance of the samples. At a current density of 10 mA cm⁻¹ -2 At that time, Cu0, Cu 0.5 Cu 1.0 Cu 1.5 and Cu 2.0 The oxygen evolution overpotentials of the samples were 251 mV, 269 mV, 239 mV, 311 mV, and 319 mV, respectively. Among them, Cu... 1.0The sample exhibited the lowest oxygen evolution overpotential, indicating that the resulting transition metal molybdate-MoO3 heterojunction possessed optimal oxygen evolution catalytic activity when the copper-molybdenum molar ratio was 1:0.5 (Cu(NO3)2·3H2O added at 1.0 mmol). In contrast, without a copper source, the product was mainly a single molybdate phase, and its oxygen evolution overpotential was higher than that of Cu. 1.0 In the sample, when the molar ratio of copper to molybdenum was 0.5:0.5 (copper source added 0.5 mmol), the oxygen evolution performance was not effectively improved due to insufficient precipitation of the MoO3 phase and inadequate heterogeneous interface construction. However, when the molar ratio of copper to molybdenum was further increased to 1.5:0.5 and 2:0.5 (copper source added further increased to 1.5 mmol and 2.0 mmol), the oxygen evolution overpotential increased significantly, indicating that excessive copper source would cause the product phase composition and microstructure to deviate from the optimal state, which is not conducive to the oxygen evolution reaction. Figure 3 (b) It is evident that different molar ratios of copper and molybdenum also have a significant regulatory effect on the hydrogen evolution reaction performance. At a current density of 10 mA cm⁻¹ -2 At that time, Cu0, Cu 0.5 Cu 1.0 Cu 1.5 and Cu 2.0 The hydrogen evolution overpotentials of the samples were 153 mV, 123 mV, 60 mV, 136 mV, and 151 mV, respectively. Among them, Cu... 1.0 The sample only requires an overpotential of 60 mV to reach 10 mA cm⁻¹ -2 The concentration of Cu was significantly lower than that of other comparative samples, indicating that it has the best hydrogen evolution catalytic performance. 0.5 The hydrogen evolution performance of the sample was improved compared to the Cu0 sample, indicating that a small amount of Cu... 2+ The introduction of copper has been able to regulate the electronic structure and reaction interface of the material to some extent; however, due to insufficient copper source addition, the degree of heterostructure construction is limited, and its performance is still significantly weaker than Cu. 1.0 Samples. When the molar ratio of copper to molybdenum was further increased to 1.5:0.5 and 2:0.5 (when the amount of copper source added increased to 1.5 mmol and 2.0 mmol), the hydrogen evolution overpotential increased again, indicating that excess Cu... 2+ The resulting phase composition shift, crystal growth imbalance, or structural aggregation can reduce the utilization rate of effective active sites, thereby weakening hydrogen evolution performance.

[0047] Combining X-ray diffraction patterns and scanning electron microscopy characterization results, it can be seen that an appropriate amount of Cu... 2+The introduction of Cu(NO3)2·3H2O facilitates the in-situ precipitation of the MoO3 phase and promotes the formation of an effective heterogeneous interface between the transition metal molybdate phase and the MoO3 phase. This heterogeneous interface optimizes charge transport and adsorption behavior of reaction intermediates, while the urchin-like microsphere morphology exposes more active sites and promotes electrolyte diffusion. Therefore, under the conditions of this embodiment, the sample with a copper to molar ratio of 1:0.5 (Cu(NO3)2·3H2O added at 1.0 mmol) exhibits the best bifunctional electrocatalytic performance.

[0048] Example 2: Effects of different hydrothermal reaction times on the structure, morphology, and electrocatalytic performance of heterojunctions This embodiment investigates the effect of hydrothermal reaction time on the phase composition, microstructure, and electrocatalytic performance of low-Ir-doped transition metal molybdate-MoO3 heterojunctions to determine a suitable hydrothermal reaction time window. Except for the hydrothermal reaction time, all other preparation conditions remained consistent. The resulting samples were designated as 3h, 6h, and 12h, respectively, based on the different hydrothermal reaction times.

[0049] The method is the same as in Example 1, except that in step (2), 0.242 g Cu(NO3)2·3H2O (1 mmol) is added. In step (5), the mixture is placed in an oven at 150°C and reacted for 3 h, 6 h and 12 h respectively.

[0050] Figure 4 XRD patterns of samples obtained at different hydrothermal reaction times. Figure 4 As can be seen, the characteristic diffraction peaks of the transition metal molybdate phase were observed in the 3h, 6h, and 12h samples, with the NiMoO4 standard card PDF#24-7435 serving as a reference for the molybdate phase. Simultaneously, characteristic diffraction signals corresponding to the MoO3 standard card PDF#035-0609 were also observed in the samples, indicating that a heterostructure with the coexistence of the transition metal molybdate phase and the MoO3 phase could be formed at different hydrothermal reaction times. Among them, the 6h sample exhibited superior heterostructure characteristics in terms of both morphology and electrochemical performance.

[0051] Figure 5 SEM images of samples obtained at different hydrothermal reaction times are shown. Figure 5 (a) and Figure 5 (b) For the 3h sample, Figure 5 (c) and Figure 5 (d) Corresponding to the 6h sample, Figure 5 (e) and Figure 5 (f) Corresponds to the 12h sample. From Figure 5It is evident that the urchin-like microsphere structure of the 3-hour sample was not fully developed, and the nickel foam surface coverage was not uniform. The 6-hour sample formed a uniform and dense urchin-like microsphere morphology, with the sheet-like and / or needle-like nanostructures extending radially outwards. Although the 12-hour sample still maintained a certain microsphere structure, local stacking, aggregation, and structural coarsening occurred. These results indicate that an appropriate hydrothermal reaction time is beneficial for obtaining transition metal molybdate-MoO3 heterojunctions with uniform morphology and complete structure. Under the conditions of this embodiment, the sample obtained with a 6-hour hydrothermal reaction time exhibited the most uniform morphology and the most fully developed heterostructure.

[0052] Figure 6 To test the electrocatalytic performance of samples obtained at different hydrothermal reaction times on an alkaline seawater electrolyte composed of 1.0 M KOH and natural seawater for oxygen evolution and hydrogen evolution reactions, the results are as follows: Figure 6 As shown. Among them, Figure 6 (a) shows the oxygen evolution reaction polarization curves for different samples. Figure 6 (b) shows the hydrogen evolution reaction polarization curves for different samples, where 3h, 6h, and 12h represent the hydrothermal reaction times. The test electrolyte was an alkaline seawater electrolyte composed of 1.0 M KOH and natural seawater. Figure 6 (a) It is evident that different hydrothermal reaction times have a significant impact on the oxygen evolution reaction performance of the obtained samples. In an alkaline seawater electrolyte composed of 1.0 M KOH and natural seawater, when the current density is 10 mA cm⁻¹ -2 At 3h, 6h, and 12h, the oxygen evolution overpotentials of the samples were 248 mV, 239 mV, and 280 mV, respectively. The 6h sample exhibited the lowest oxygen evolution overpotential, indicating that a 6h hydrothermal reaction is more conducive to the formation of a transition metal molybdate-MoO3 heterojunction with high oxygen evolution activity. Figure 6 (b) It is evident that different hydrothermal reaction times also significantly affect the hydrogen evolution reaction performance of the samples. At 10 mA cm⁻¹ -2 At the specified current densities, the hydrogen evolution overpotentials for the 3h, 6h, and 12h samples were 92 mV, 60 mV, and 123 mV, respectively. Notably, the 6h sample required only a 60 mV overpotential to reach 10 mAcm⁻¹. -2 The concentration was significantly lower than that of the 3h and 12h samples, indicating that it has superior hydrogen evolution catalytic activity.

[0053] Example 3: Preparation and structural characterization of low Ir-doped transition metal molybdate-MoO3 heterojunction electrocatalysts This embodiment selects the Cu sample with low Ir-doped transition metal molybdate-MoO3 heterojunction from Example 1. 1.0The sample was designated as Ir-(NiCoFeCu)MoO4-MoO3, and its phase composition, microstructure, heterostructure interface, elemental distribution and surface chemical state were characterized. A control sample without Ir was prepared according to steps (1) to (3), (5) and (6) of Example 1, and was designated as (NiCoFeCu)MoO4-MoO3.

[0054] Figure 7 The figure shows the XRD patterns of the Ir-containing transition metal molybdate-MoO3 heterojunction catalyst and the Ir-free control sample. The NiMoO4 standard card PDF#24-7435 and the MoO3 standard card PDF#035-0609 are also listed as references. The red curve corresponds to Ir-(NiCoFeCu)MoO4-MoO3, and the black curve corresponds to the Ir-free (NiCoFeCu)MoO4-MoO3 control sample. As can be seen from the figure, both samples exhibit characteristic diffraction peaks corresponding to the transition metal molybdate phase and MoO3, indicating that a transition metal molybdate-MoO3 heterostructure can be formed under the stated preparation conditions. Therefore, the introduction of Ir is not a necessary condition for the formation of the heterostructure. 2+ The Ginger-Taylor distortion effect is an important factor in inducing the precipitation of MoO3 phase and the formation of heterojunction; at the same time, the sample still maintains the transition metal molybdate-MoO3 heterostructure after Ir doping, indicating that the introduction of low Ir content did not destroy the main crystal phase structure.

[0055] Figure 8 The image shows a SEM image of the heterojunction Ir-(NiCoFeCu)MoO4-MoO3. Figure 8 (a) is a low-magnification SEM image; Figure 8 (b) is a further magnified SEM image; Figure 8 (c) and Figure 8 (d) is a magnified view of a portion of the catalyst layer; Figure 8 (e) is a higher magnification SEM image. (From...) Figure 8 As can be seen, the heterojunction Ir-(NiCoFeCu)MoO4-MoO3 grows uniformly on the surface of the nickel foam framework, exhibiting a distinct sea urchin-like microsphere morphology. These sea urchin-like microspheres are composed of numerous outwardly radiating sheet-like and / or needle-like nanostructures interwoven together, exhibiting uniform overall coverage, a loose structure, and open three-dimensional porous characteristics. This structure, on the one hand, increases the contact area between the electrode and the electrolyte, exposing more catalytic active sites; on the other hand, it facilitates electrolyte penetration within the electrode, ion transport, and the rapid release of bubbles during hydrogen or oxygen evolution, thus providing a structural basis for improving the performance of alkaline seawater electrolysis.

[0056] Figure 9The images show high-resolution transmission electron microscopy (TEM) images and selected area electron diffraction (SAD) patterns of the heterostructure Ir-(NiCoFeCu)MoO4-MoO3. Figure 9 (a) is a TEM image; Figure 9 (b) is Figure 9 (a) High-resolution transmission electron microscope image of the selected area; Figure 9 (c) is the selected area electron diffraction pattern. (From...) Figure 9 (a) and Figure 9 (b) As can be seen, clear lattice fringes and interface regions between different crystalline phases can be observed in the sample, indicating that a close-contact heterogeneous interface has formed between the transition metal molybdate phase and the MoO3 phase. Specifically, lattice fringes with a lattice spacing of approximately 0.296 nm can be attributed to the relevant crystal planes of the transition metal molybdate phase, while lattice fringes with a lattice spacing of approximately 0.300 nm can be attributed to the relevant crystal planes of the MoO3 phase. The formation of the heterogeneous interface is beneficial for regulating the interfacial electronic structure, accelerating interfacial charge transport, and promoting the adsorption and transformation of key intermediates in the hydrogen evolution and oxygen evolution reactions. Figure 9 Multiple diffraction rings can be observed in the SAED diagram shown in (c), indicating that the sample has polycrystalline characteristics. At the same time, different diffraction rings can correspond to the transition metal molybdate phase and the MoO3 phase, respectively, further proving the existence of heterostructure.

[0057] Figure 10 The image shows the EDS elemental distribution of the heterojunction Ir-(NiCoFeCu)MoO4-MoO3. Figure 10 (a) is a TEM image of the catalyst microspheres, showing that the sample as a whole is a microsphere structure formed by interwoven nanosheets; Figure 10 (b) is a surface distribution map of EDS elements in the corresponding region; Figure 10 (c) shows the EDS energy spectrum and the corresponding atomic percentage results for each element. Figure 10 As can be seen, Ni, Co, Fe, Cu, Mo, Ir, and O elements are uniformly distributed in the sample, with no obvious elemental segregation or local enrichment observed, indicating that each metal element can participate well in the catalyst structure construction. EDS quantitative analysis results show that the transition metal contents are similar: Mo is 18.2%, O is 64.6%, and Ir is 0.2%, indicating that each element has been successfully introduced without segregation. It also indicates that Ir is introduced into the catalyst system in a low-content form. The introduction of low-content Ir, without significantly increasing the amount of noble metals, can adjust the local electronic structure of the polymetallic molybdate-MoO3 heterostructure and helps improve the long-term stability of the catalyst under high current density seawater electrolysis conditions.

[0058] Figure 11 The images show the full X-ray photoelectron spectroscopy (XPS) spectrum and high-resolution spectrum of the heterojunction Ir-(NiCoFeCu)MoO4-MoO3. Figure 11 (a) is the XPS full spectrum; Figure 11 (b) is the high-resolution spectrum of Co 2p; Figure 11 (c) is the high-resolution spectrum of Cu 2p; Figure 11 (d) is the high-resolution spectrum of Fe 2p; Figure 11 (e) is the high-resolution spectrum of Ni 2p; Figure 11 (f) is the high-resolution spectrum of Ir 4f; Figure 11 (g) is the high-resolution 3d spectrum of Mo. Characteristic signals of elements such as Cu, Ni, Co, Fe, Mo, Ir, and O can be detected in the full XPS spectrum, further proving that these elements have been successfully introduced into the sample. The high-resolution XPS spectrum shows that transition metal elements such as Co, Ni, Fe, and Cu all exhibit multi-valence state characteristics, indicating electronic interactions between the multi-metal components. Cu mainly exists as Cu... 2+ Equivalent states exist, where Cu 2+ Exhibiting Ginger-Taylor distortion characteristics, it can induce distortion of the local coordination environment, thereby promoting the precipitation of MoO3 phase from the multimetallic molybdate system and the construction of heterogeneous interfaces. Mo mainly exists as high-valence Mo. 6+ It exists in form, and Ir exists in the form of Ir. 4+ and Ir 0 Co exists in both its oxidized and / or lower valence states, with Co as Co 3+ and Co 2+ Existence, Fe as Fe 0 Fe 2+ and Fe 3+ Existence, Ni with Ni 2+ and Ni 0 Yes, it exists. The above results indicate that the multi-metallic composition and low Ir doping jointly regulate the surface electronic structure of the catalyst, providing a chemical basis for improving electrocatalytic activity and stability.

[0059] Figure 12 The extended X-ray absorption fine structure (EXAFS) fitting results are shown for the heterojunctions Ir-(NiCoFeCu)MoO4-MoO3 and (NiCoFeCu)MoO4-MoO3. Figure 12 (a) shows the Cu K-edge XANES spectrum, with Cu foil as a reference. Figure 12 (b) is the Cu K-edge EXAFS Fourier transform. R Spatial spectrum and fitting results. Figure 12 (c) shows the EXAFS fitting parameter table. The results show that in the (NiCoFeCu)MoO4-MoO3 sample, the disorder parameter σ of the Cu-O long bond is... 2 The value of 0.034 is significantly higher than the σ of the Cu-O short bond. 2(0.0053) indicates a strong Ginger-Taylor distortion in its local coordination environment. After introducing Ir, the σ corresponding to the Cu-O long bond... 2 The value of 0.021 indicates that the introduction of Ir helps stabilize the distorted coordination structure around Cu, reduces the degree of local structural disorder, and thus improves the stability of the heterojunction structure during long-term electrolysis. Therefore, Cu 2+ The Ginger-Taylor distortion effect is mainly responsible for inducing the precipitation of the MoO3 phase and constructing the transition metal molybdate-MoO3 heterostructure, while Ir doping mainly plays the role of stabilizing the local distortion structure and regulating the electronic structure of the interface, providing a structural basis for the long-term stable operation of the catalyst under high current density seawater electrolysis conditions.

[0060] Example 4: Hydrogen evolution performance of the heterojunction Ir-(NiCoFeCu)MoO4-MoO3 described in this invention This example is used to evaluate the hydrogen evolution reaction performance of the Ir-(NiCoFeCu)MoO4-MoO3 heterojunction electrocatalyst in alkaline seawater electrolyte.

[0061] The hydrogen evolution reaction was tested in a three-electrode system. An Ir-(NiCoFeCu)MoO4-MoO3 heterojunction catalyst electrode was used directly as the working electrode, cut to 1 cm × 1 cm before testing. A saturated calomel electrode was used as the reference electrode, and a platinum sheet was used as the counter electrode. The electrolyte was an alkaline seawater electrolyte composed of 1.0 M KOH and natural seawater. All test potentials were converted to the reversible hydrogen electrode potential. The linear sweep voltammetry was performed at a scan rate of 5 mV s. -1 And 85% iR compensation was performed. For performance comparison, the following samples were selected as comparative catalysts: (1) Ir-(NiCoFe)MoO4, as a Cu-free, single molybdate relative comparison sample; (2) (NiCoFeCu)MoO4-MoO3, used as a comparison sample without Ir heterojunction; (3) MoO3; (4) Commercial Pt / C.

[0062] In this study, Ir-(NiCoFe)MoO4 corresponds to CuO sample in Example 1, and (NiCoFeCu)MoO4-MoO3 is described in Example 3, with the metal salt type adjusted only according to the corresponding composition. MoO3 was prepared according to steps (1), (3), (5), and (6) of Example 1, and the resulting product was used for electrode preparation. Commercial Pt / C was a commercially available catalyst. For the powdered MoO3 and the commercial Pt / C comparative catalyst, 20 mg of the catalyst was weighed and added to a mixed solution consisting of 750 μL of ethanol, 230 μL of deionized water, and 30 μL of perfluorinated resin solution. The mixture was ultrasonically dispersed for 1 h to obtain a uniform catalyst ink. Subsequently, it was uniformly dripped onto the pretreated nickel foam surface and dried at room temperature for 12 h to serve as the working electrode.

[0063] Figure 13 The results show the hydrogen evolution reaction performance of different catalysts in an alkaline seawater electrolyte composed of 1.0 M KOH and natural seawater. Figure 13 (a) Linear sweep voltammetric curves of hydrogen evolution for Ir-(NiCoFeCu)MoO4-MoO3, (NiCoFeCu)MoO4-MoO3, Ir-(NiCoFeCu)MoO4, MoO3 and commercial Pt / C; Figure 13 (b) Tafel curves for different catalysts; Figure 13 (c) Electrochemical impedance spectroscopy for different catalysts; Figure 13 (d) shows the fitting plots of the capacitive current density for different catalysts at different scan rates. Figure 13 (a) As can be seen, the Ir-(NiCoFeCu)MoO4-MoO3 catalyst obtained in Example 3 exhibits excellent hydrogen evolution catalytic activity. At 10 mA cm⁻¹ -2 At the given current density, the hydrogen evolution overpotentials of Ir-(NiCoFeCu)MoO4-MoO3, (NiCoFeCu)MoO4-MoO3, Ir-(NiCoFeCu)MoO4, MoO3, and commercial Pt / C were 60 mV, 158 mV, 153 mV, 261 mV, and 31 mV, respectively. It can be seen that the hydrogen evolution overpotential of the catalyst in this embodiment is significantly lower than that of the sample without Ir heterojunction, the single molybdate phase sample, and the MoO3 sample, and is close to that of commercial Pt / C, indicating that Cu... 2+ The formation of polymetallic molybdate-MoO3 heterostructures induced by the Ginger-Taylor distortion exhibits a synergistic promoting effect with low Ir doping content. Figure 13 (b) As can be seen from the Tafel slope, the Tafel slope of Ir-(NiCoFeCu)MoO4-MoO3 is 70.49 mV dec. -1 It is close to the 69.73 mV dec of commercial Pt / C. -1The concentration was significantly lower than that of the comparative samples (NiCoFeCu)MoO4-MoO3, Ir-(NiCoFeCu)MoO4, and MoO3, indicating that this catalyst has faster hydrogen evolution reaction kinetics. Figure 13 As can be seen from the electrochemical impedance spectroscopy in (c), the catalyst in this embodiment has a small charge transfer resistance. R ct The Ω value is 2.43, indicating that its heterogeneous interface structure facilitates electron transport at the electrode / electrolyte interface. Figure 13 (d) It can be seen that the double-layer capacitance of Ir-(NiCoFeCu)MoO4-MoO3 C dl It is 2.29 mF cm -2 The Ir-doped transition metal molybdate-MoO3 heterojunction exhibits higher activity than the (NiCoFeCu)MoO4-MoO3, Ir-(NiCoFeCu)MoO4, and MoO3 comparative samples, indicating a larger electrochemical active area and more effective active sites for the hydrogen evolution reaction. These results demonstrate that the low-Ir-doped transition metal molybdate-MoO3 heterojunction can effectively optimize the hydrogen evolution reaction kinetics, reduce the hydrogen evolution overpotential, and exhibit excellent hydrogen evolution catalytic activity in alkaline seawater systems.

[0064] Figure 14 The results show the hydrogen evolution stability of the Ir-(NiCoFeCu)MoO4-MoO3 catalyst in alkaline seawater electrolyte. Figure 14 It can be seen that at 500 mA cm -2 Under constant current density, the catalyst was able to operate stably for over 200 hours continuously. The potential remained stable throughout the test without significant increase, indicating that the catalyst exhibits good long-term stability under high current density alkaline seawater hydrogen evolution conditions. Combined with the aforementioned hydrogen evolution activity test results, it can be seen that Ir doping does not simply enhance the initial hydrogen evolution activity, but rather helps stabilize the Cu-based catalyst. 2+ The heterogeneous interface structure induced by the Jiang-Taylor distortion improves the ability of active sites to maintain their structure during long-term electrolysis, thereby enhancing the durability of the catalyst in the high current density hydrogen evolution process.

[0065] Example 5: Oxygen evolution performance, selectivity and mechanism analysis of the heterojunction Ir-(NiCoFeCu)MoO4-MoO3 described in this invention This embodiment is used to evaluate the oxygen evolution reaction performance of Ir-(NiCoFeCu)MoO4-MoO3 heterojunction electrocatalyst in alkaline seawater electrolyte, and to further investigate its long-term stability, oxygen evolution selectivity and reaction mechanism.

[0066] The oxygen evolution reaction (OER) test was also conducted in a three-electrode system. An Ir-(NiCoFeCu)MoO4-MoO3 heterojunction catalyst electrode was used as the working electrode, cut to 1 cm × 1 cm before testing; a saturated calomel electrode was used as the reference electrode; and a platinum sheet was used as the counter electrode. The electrolyte was an alkaline seawater electrolyte composed of 1.0 M KOH and natural seawater. All test potentials were converted to the reversible hydrogen electrode potential.

[0067] The scan rate for the linear scan voltammetry test was 5 mV / s. -1 And with 85% iR compensation. Comparative catalysts include: (1) Ir-(NiCoFe)MoO4, as a Cu-free, single molybdate relative comparison sample; (2) (NiCoFeCu)MoO4-MoO3, used as a comparison sample without Ir heterojunction; (3) MoO3; (4) Commercial IrO2.

[0068] In this study, Ir-(NiCoFe)MoO4, (NiCoFeCu)MoO4-MoO3, and MoO3 were prepared according to Example 4; commercial IrO2 was a commercially available catalyst. The preparation methods of the working electrodes for the powdered MoO3 and commercial IrO2 comparative catalysts were the same as those for the Pt / C electrode in Example 4.

[0069] Figure 15 The results show the oxygen evolution reaction performance of different catalysts in an alkaline seawater electrolyte composed of 1.0 M KOH and natural seawater. Figure 15 (a) Linear sweep voltammetric curves of oxygen evolution for Ir-(NiCoFeCu)MoO4-MoO3, (NiCoFeCu)MoO4-MoO3, Ir-(NiCoFeCu)MoO4, MoO3 and commercial IrO2; Figure 15 (b) Tafel curves for different catalysts; Figure 15 (c) Electrochemical impedance spectroscopy for different catalysts; Figure 15 (d) shows the fitting plots of the capacitive current density for different catalysts at different scan rates. Figure 15 (a) As can be seen, the Ir-(NiCoFeCu)MoO4-MoO3 catalyst exhibits excellent oxygen evolution catalytic activity. At 10 mA cm⁻¹ -2At the specified current densities, the oxygen evolution overpotentials (OE) of Ir-(NiCoFeCu)MoO4-MoO3, (NiCoFeCu)MoO4-MoO3, Ir-(NiCoFeCu)MoO4, MoO3, and commercial IrO2 were 239 mV, 267 mV, 251 mV, 304 mV, and 317 mV, respectively. It can be seen that the OE overpotential of the Ir-(NiCoFeCu)MoO4-MoO3 catalyst is significantly lower than that of the sample without Ir heterojunction, the single molybdate phase sample, MoO3, and commercial IrO2, indicating its excellent OE reaction activity in alkaline seawater systems. Figure 15 (b) As can be seen from the Tafel slope, the Tafel slope of Ir-(NiCoFeCu)MoO4-MoO3 is 24.6 mV dec. -1 It is significantly lower than the 60.6 mV dec of (NiCoFeCu)MoO4-MoO3. -1 , 70.74 mV dec of Ir-(NiCoFeCu)MoO4 -1 70.01 mV dec of MoO3 -1 And commercial IrO2 with 81.08 mV dec -1 This indicates that the catalyst exhibits faster oxygen evolution reaction kinetics. Figure 15 (c) The electrochemical impedance spectroscopy shows that the charge transfer resistance of Ir-(NiCoFeCu)MoO4-MoO3 is... R ct The resistance was 1.11 Ω, lower than that of the comparative samples, indicating that its multi-metallic heterostructure is beneficial for reducing interfacial charge transport resistance and promoting the transformation of reaction intermediates. Figure 15 (d) It can be seen that the double-layer capacitance of Ir-(NiCoFeCu)MoO4-MoO3 C dl It is 4.18 mFcm -2 The value is higher than that of the (NiCoFeCu)MoO4-MoO3, Ir-(NiCoFeCu)MoO4, and MoO3 comparative samples, indicating that it has a higher electrochemical active area and more available active sites. These results demonstrate that the Ir-(NiCoFeCu)MoO4-MoO3 heterojunction can effectively promote the oxygen evolution reaction kinetics. 2+ The Ginger-Tyler distortion helps induce the formation of a polymetallic molybdate-MoO3 heterostructure and modulate the local electronic structure. Low-content Ir doping further optimizes the interfacial charge transport and the electronic environment of the active sites. The synergistic effect of these two factors enables the catalyst to exhibit superior oxygen evolution catalytic activity compared to commercial IrO2 in alkaline seawater systems.

[0070] Figure 16The graph shows the oxygen evolution stability test results of different catalysts in an alkaline seawater electrolyte composed of 1.0 M KOH and natural seawater. Figure 16 (a) is a graph showing the oxygen evolution stability of the Ir-(NiCoFeCu)MoO4-MoO3 catalyst. Figure 16 (b) is a graph showing the oxygen evolution stability of the (NiCoFeCu)MoO4-MoO3 catalyst. Figure 16 (a) It can be seen that Ir-(NiCoFeCu)MoO4-MoO3 at 500 mA cm -2 Under constant current density, the catalyst was able to operate stably for over 600 hours continuously, with only slight fluctuations in potential during the test and no continuous upward trend, indicating its excellent long-term stability under high current density alkaline seawater oxygen evolution conditions. Figure 16 (b) indicates that (NiCoFeCu)MoO4-MoO3 at 500 mA cm⁻¹ -2 At a constant current density, the catalyst exhibited a sharp decline in stability after approximately 370 hours of continuous stable operation. This indicates that the introduction of a low Ir content contributes to the stability of Cu. 2+ The polymetallic molybdate-MoO3 heterostructure induced by the Ginger-Tyler distortion (see...) Figure 12 This inhibits the loss of active components, damage to the interfacial structure, and excessive reconstruction during long-term oxygen evolution, thereby significantly improving the structural and electrochemical stability of the catalyst under alkaline seawater oxygen evolution conditions.

[0071] Figure 17 The images show the HRTEM image and EDS elemental distribution of the Ir-(NiCoFeCu)MoO4-MoO3 catalyst after oxygen evolution stability testing. Figure 17 (a) is the HRTEM image of the catalyst after stability testing; Figure 17 (b) is Figure 17 (a) Enlarged HRTEM image of the selected area; Figure 17 (c) shows the STEM image and corresponding elemental distribution of the catalyst after stability testing; Figure 17 (a) and Figure 17 (b) As can be seen, after a prolonged oxygen evolution reaction (OER), the catalyst surface exhibits the characteristics of a metal hydroxyl oxide active phase, with lattice fringes associated with M-OOH active species such as NiOOH, FeOOH, and CoOOH observed. This indicates that under OER conditions, in-situ reconstruction occurs on the catalyst surface, forming a true active phase favorable for OER. Figure 17The EDS elemental distribution results in (c) show that after a long period of high current density oxygen evolution reaction, elements such as Ni, Co, Fe, Cu, Mo, Ir, and O still maintain a relatively uniform spatial distribution, and no obvious element loss, severe segregation, or structural collapse was observed. This result further demonstrates that the catalyst in this embodiment has good structural retention under alkaline seawater oxygen evolution conditions, and that Ir doping and the multi-metal heterostructure interface structure have a positive effect on the long-term stability of the catalyst.

[0072] Figure 18 The image shows the in-situ Raman spectrum of the Ir-(NiCoFeCu)MoO4-MoO3 catalyst during the oxygen evolution process. Figure 18 As can be seen, at open-circuit potential and lower applied potentials, the spectrum mainly exhibits vibrational signals related to Mo-O-Mo, Mo-O, Mo=O, and metal-oxygen bonds, indicating that the initial catalyst retains the heterostructure characteristics of molybdate-MoO3. With the gradual increase of the applied potential, the spectrum at approximately 474 cm⁻¹... -1 and 555 cm -1 The new Raman peak gradually appears and intensifies. This peak can be attributed to the bending and stretching vibrations of Ni-O in γ-NiOOH, and also indicates that a polymetallic hydroxyl oxide M-OOH active phase, represented by NiOOH, has been formed on the surface.

[0073] Figure 19 The results show the oxygen evolution reaction mechanism analysis of the Ir-(NiCoFeCu)MoO4-MoO3 catalyst. Figure 19 (a) shows the oxygen evolution polarization curves of the Ir-(NiCoFeCu)MoO4-MoO3 catalyst under different pH conditions; Figure 19 (b) Oxygen evolution polarization curves of Ir-(NiCoFe)MoO4 comparative sample under different pH conditions; Figure 19 (c) Oxygen evolution polarization curves of MoO3 comparison samples under different pH conditions; Figure 19 (d)- Figure 19 (f) are comparison diagrams of oxygen evolution performance of Ir-(NiCoFeCu)MoO4-MoO3, Ir-(NiCoFe)MoO4 and MoO3 in 1 M KOH and 1 M TMAOH electrolytes, respectively, which are used to analyze the surface adsorption process and the characteristics of lattice oxygen participation; Figure 19 (g) is a fitting plot of the proton reaction order for different samples. (From...) Figure 19 (a)- Figure 19(c) As can be seen, the oxygen evolution polarization curves of Ir-(NiCoFeCu)MoO4-MoO3, Ir-(NiCoFe)MoO4, and MoO3 samples all exhibited a certain pH dependence under different pH conditions, indicating that the proton / hydroxyl-related reaction steps in the oxygen evolution process have a significant impact on the reaction kinetics. Compared with the control sample, the catalyst in this example exhibited a higher oxygen evolution current density under the same pH conditions, indicating that Cu 2+ The Ginger-Taylor distortion-induced heterostructure and Ir doping together improved the OER reaction kinetics. Figure 19 (d)- Figure 19 (f) It can be seen that the oxygen evolution current response of the catalyst differs in 1 M KOH and 1 M TMAOH electrolytes. Because TMA + Cations possess significant steric hindrance, which influences surface adsorption processes and the interfacial water / hydroxyl structure. Therefore, this comparative test can be used to analyze the degree of involvement of catalyst surface adsorption intermediates and lattice oxygen. The results show that the catalyst in this embodiment maintains high oxygen evolution activity in different electrolyte systems, indicating that its activity originates not only from the conventional surface adsorption intermediate pathway but also from the involvement of lattice oxygen. Figure 19 The proton reaction order calculation results of (g) show that the catalyst in this embodiment... ρ RHE The value was 0.87, higher than that of the Ir-(NiCoFe)MoO4 and MoO3 comparative samples, indicating that its oxygen evolution reaction is more sensitive to pH changes, suggesting that there may be a more significant non-cooperative proton-electron transfer process and lattice oxygen participation characteristics during the reaction. Combined with the in-situ Raman results, it can be seen that the catalyst in this embodiment first undergoes surface reconstruction during the oxygen evolution process, forming an M-OOH active phase. This active phase can complete the OH evolution through the traditional adsorbate evolution mechanism, i.e., the AEM pathway. O OOH Adsorption and transformation of intermediates; simultaneously, Cu 2+ The localized structural distortion induced by the Ginger-Taylor distortion, the synergistic electronic regulation of multiple metals, and the MoO3 heterostructure can enhance the tunability of metal-oxygen bonds, enabling some lattice oxygen to participate in the O-O bond formation process, thereby introducing LOM-assisted features. Therefore, the oxygen evolution process of the catalyst in this embodiment is not simply controlled by a single pathway of AEM or LOM, but rather by a reaction mechanism that couples the AEM pathway dominated by the surface M-OOH active phase with the LOM-assisted pathway induced by the heterostructure. This synergistic mechanism can optimize the adsorption strength of oxygen-containing intermediates, reduce the oxygen evolution reaction energy barrier, and accelerate the O-O bond formation process. Simultaneously, in alkaline seawater systems, this catalyst exhibits high selectivity for OER, preferentially promoting the oxygen evolution reaction while suppressing chloride ion-related side reactions, thereby improving the stability and safety of the seawater electrolytic oxygen evolution process.

[0074] Figure 20 The results show the Faradaic efficiency and chlorine evolution side reaction of the Ir-(NiCoFeCu)MoO4-MoO3 catalyst. Figure 20 (a) Photographs of the hydrogen and oxygen evolution gas collection device and the gas collection process at different reaction times, showing that hydrogen and oxygen can be continuously generated during the electrolysis process; Figure 20 (b) The actual hydrogen production, theoretical production, and Faraday efficiency test results during the hydrogen evolution process show that the Faraday efficiency of the hydrogen evolution reaction is 99.43%. Figure 20 (c) The actual oxygen production, theoretical oxygen production, and Faraday efficiency test results during the oxygen evolution process. The Faraday efficiency of the oxygen evolution reaction is 99.32%. Figure 20 (d) is a color comparison photograph of the electrolyte after the oxygen evolution reaction and NaClO standard solutions of different concentrations. No obvious pink color phenomenon was observed in the electrolyte after the oxygen evolution reaction. Figure 20 (e) shows the UV-Vis absorption spectrum of the corresponding solution. The absorption signal of the electrolyte after the oxygen evolution reaction is significantly lower than that of the NaClO standard solution. Figure 20 (a) It can be seen that the gases generated during hydrogen evolution and oxygen evolution are collected by water displacement gas collection method. Figure 20 (b) and Figure 20 (c) The gas yield and Faraday efficiency test results for the hydrogen evolution and oxygen evolution processes, respectively. The test results show that the Faraday efficiency of the hydrogen evolution reaction is 99.43% and the Faraday efficiency of the oxygen evolution reaction is 99.32%, both close to 100%, indicating that the input charge is mainly used for water splitting reaction, and the contribution of side reactions is relatively small. Figure 20 (d) and Figure 20 (e) shows the colorimetric test results of the chlorine evolution side reaction. Comparison with the colorimetric results of NaClO standard solutions of different concentrations reveals that the electrolyte after the oxygen evolution reaction did not exhibit a significant pink color, and its absorption spectrum signal was significantly lower than that of the NaClO standard solution, indicating that no significant hypochlorite formation was detected during electrolysis. This result demonstrates that the Ir-(NiCoFeCu)MoO4-MoO3 catalyst described in this invention exhibits high oxygen evolution selectivity during alkaline seawater oxygen evolution, effectively suppressing the chloride ion oxidation side reaction and contributing to improved efficiency and operational safety of the seawater electrolysis system.

[0075] In the description of this specification, the references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0076] The foregoing has shown and described the basic principles, main features, and advantages of this application. Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of this application. Various changes and modifications can be made to this application without departing from the spirit and scope thereof, and all such changes and modifications fall within the scope of the claims of this application.

Claims

1. A transition metal molybdate-molybdenum trioxide heterojunction, characterized in that, The heterojunction uses nickel foam as a supporting framework, and the surface of the nickel foam has a sheet-like and / or needle-like heterojunction structure formed by the co-growth of (NiCoFeCu)MoO4 and MoO3.

2. The heterojunction as described in claim 1, characterized in that, The product is prepared by a one-step hydrothermal method, in which foamed nickel is subjected to a hydrothermal reaction with aqueous solutions of iron, cobalt, copper, and molybdenum source precursors. The hydrothermal reaction temperature is 120–180°C, and the reaction time is 4–8 hours. The iron source precursor is selected from one or more of ferric nitrate, ferric chloride, ferric sulfate, ferric acetate, and their hydrates. The cobalt source precursor is selected from one or more of cobalt nitrate, cobalt chloride, cobalt sulfate, cobalt acetate, and their hydrates. The copper source precursor is selected from one or more of copper nitrate, copper chloride, copper sulfate, copper acetate, and their hydrates. The molybdenum source precursor is selected from one or more of ammonium molybdate, sodium molybdate, potassium molybdate, phosphomolybdic acid, and their hydrates.

3. The heterojunction as described in claim 2, characterized in that, The molar ratio of copper to molybdenum is 1:(0.4 to 0.6).

4. The heterojunction as described in claim 3, characterized in that, Prepared by the following steps: (1) Dissolve the iron source precursor, cobalt source precursor, copper source precursor and molybdenum source precursor in deionized water and stir until they are mixed evenly to obtain a mixed solution; in the mixed solution, the total molar concentration of the three metal ions of iron, cobalt and copper is 0.05 to 0.15 mol / L, and the molar ratio of iron, cobalt, copper and molybdenum is (0.8 to 1.2):(0.8 to 1.2):1:0.5; (2) The pretreated nickel foam was placed vertically in a polytetrafluoroethylene-lined reactor, and the mixed solution obtained in step (1) was added. The reaction was carried out at 150°C for 6 hours. (3) After the reaction is complete, cool naturally to room temperature, remove the nickel foam, rinse with ultrapure water, and dry to obtain the final product.

5. The heterojunction as described in claim 1, characterized in that, The heterojunction is also doped with Ir. The heterojunction is prepared by adding an iridium source substance to an aqueous solution containing an iron source, a cobalt source, a copper source, and a molybdenum source precursor and carrying out a hydrothermal reaction. The iridium source substance is selected from one or more of iridium trichloride, iridium chloroiridium acid, iridium tetrachloride, iridium acetate, iridium acetylacetonate, or their hydrates.

6. The heterojunction as described in claim 5, characterized in that, The molar ratio of the iridium source material (calculated as iridium) to the copper source material (calculated as copper) is 1:50 to 1:

20.

7. The application of the heterojunction as a catalyst according to any one of claims 1-6 in the electrocatalytic hydrogen evolution reaction and oxygen evolution reaction.

8. The application as described in claim 7, characterized in that, The application of the heterojunction as a catalyst in the electrocatalytic complete water splitting.

9. The application as described in claim 7, characterized in that, The water is seawater, and the seawater is alkaline seawater.

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