Ultra-small multifunctional CoNi-VN nanoparticle composite electrocatalyst, preparation method and application thereof

Abstract

The application discloses super-small multifunctional CoNi-VN nanoparticle composite electrocatalyst and a preparation method and application thereof, and belongs to the technical field of nanomaterials. A Co / Ni modified borovanadomolybdate is successfully designed and synthesized, and CoNi and VN nanodots encapsulated in B and N doped carbon nanotubes are prepared by a PEI soft template method as a three-function electrocatalyst. Super-small CoNi and VN nanoparticles with a particle size of about 4 nm are successfully prepared, have a large specific surface area and high curvature, and can generate strong LEFs at a catalytic center. The nanoparticle composite electrocatalyst effectively prevents the aggregation of catalyst particles in the synthesis process, thereby improving the exposure rate of active sites of the catalyst and the catalytic performance; meanwhile, the geometric stability of the catalyst is effectively enhanced by using a nanometer limiting effect, long-time catalytic stability is ensured, and the problem that existing catalysts can only be optimized for a single reaction is overcome, and the system complexity and manufacturing cost are reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nanomaterials, and particularly relates to a super-small multifunctional CoNi-VN nanoparticle composite electrocatalyst, a preparation method and application thereof. BACKGROUND

[0002] The rapid growth of global energy demand and increasing environmental pressure urgently require the development of sustainable energy conversion and storage technologies. Electrochemical technologies, such as water splitting for hydrogen production and metal-air batteries, have become the core of clean energy systems. However, the core reactions involved in these technologies, including the hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), face the dual challenges of slow reaction kinetics and high thermodynamic energy barrier. Traditional noble metal catalysts (such as platinum (Pt), ruthenium (Ru), iridium (Ir)) have excellent catalytic activity, but due to their high cost, scarcity and poor durability, their large-scale application is limited. In addition, traditional electrocatalysts usually focus on a single electrochemical reaction, increasing the complexity and manufacturing cost of the system. Therefore, the development of efficient, low-cost and stable multifunctional catalysts is crucial to break through the above bottlenecks.

[0003] Enhancing the electron transport, ion concentration and active site enrichment near the catalytic center is an effective strategy to improve catalytic activity, which can promote the catalytic reaction in kinetics and thermodynamics. Strong local electric field (LEF) enhances the electron transport and ion adsorption near the active site, significantly improves the adsorption / desorption behavior of intermediates, and adjusts the microenvironment of the reaction, thereby accelerating the multi-electron reduction process. Catalysts with high-curvature structures generate strong local electric fields and high surface ion concentrations, which help to couple proton and electron transfer and reduce the thermodynamic energy barrier of the reaction path. In addition, rational design of nanostructure and heteroatom doping can adjust the electronic state of the active site, making the bond breaking and adsorption process of intermediates more efficient. Vanadium nitride (VN) has a similar electronic state to noble metals, excellent electrical conductivity and high catalytic activity, so it has attracted widespread attention. Cobalt-nickel alloy (CoNi) provides significant intrinsic catalytic activity, which can be promoted by adjusting the electronic structure and composition ratio to facilitate the HER, OER and ORR reactions. Therefore, material design that combines microenvironment control with intrinsic material performance is crucial to overcome these limitations. The existing metal electrocatalysts currently have the following significant defects in practical applications, although they have good catalytic performance in theory:

[0004] 1. Poor stability of non-noble metal catalysts:

[0005] While research on non-precious metal materials such as VN and CoNi has made some progress, these materials are susceptible to side reactions at high current densities or in extreme environments. For example, VN easily undergoes side reactions with the electrolyte under acidic or alkaline conditions, causing the catalyst to transform into oxides, severely impacting catalytic performance and stability. Furthermore, cobalt-nickel alloy catalysts are prone to structural changes at high temperatures or current densities, further reducing their catalytic effectiveness.

[0006] 2. Nanoparticle aggregation problem:

[0007] Although researchers have attempted to increase the exposure of active sites by controlling catalyst particle size, VN nanoparticles tend to aggregate during the synthesis process, resulting in increased particle size and reduced active site exposure. Aggregated nanoparticles not only reduce the catalyst's reactivity but also lead to decreased catalyst stability after prolonged use.

[0008] 3. Insufficient regulation of the catalyst microenvironment:

[0009] Although the LEFs effect has been shown to play an important role in improving electrocatalytic performance, existing catalyst designs often fail to effectively regulate the electric field strength between the catalyst surface and the electrolyte. Conventional catalysts typically fail to accelerate electron transport, enhance ion enrichment, or optimize the adsorption / desorption behavior of intermediates through reasonable microenvironmental regulation, thereby limiting the rate of multi-electron reactions.

[0010] 4. Limitations of single-function catalysts:

[0011] Many current catalysts typically focus on a single electrocatalytic reaction (e.g., only one of the HER, OER, or ORR reactions) and are unable to provide efficient catalytic performance in different electrochemical reactions. Such single-function catalysts increase system complexity and manufacturing costs, hindering the realization of large-scale, low-cost energy conversion and storage.

[0012] 5. High cost and resource scarcity of precious metal catalysts:

[0013] Despite the excellent catalytic performance of noble metal catalysts (such as Pt, Ru, Ir, etc.), their high cost, scarcity, and unsustainability in large-scale applications have limited their practical application. In order to meet the large-scale demand for energy conversion and storage technologies, it is urgent to find low-cost and more stable alternative materials.

[0014] In summary, existing catalysts have problems such as high cost, low stability, nanoparticle aggregation, insufficient microenvironment regulation and single functionalization. These defects seriously limit the widespread application of catalysts in fields such as water splitting and metal-air batteries. SUMMARY

[0015] The present application aims to provide a new type of electrocatalyst, which can effectively overcome the problems existing in the prior art.

[0016] To achieve the above-mentioned purpose, the present application first provides a preparation method of ultra-small multifunctional CoNi-VN nanoparticle composite electrocatalyst, which comprises the following steps:

[0017] Step one: 4.6 mL of H2O and 0.96 mL of C6H 17 N3 are mixed to obtain a mixed solvent, 0.1053 g of NH4VO3, 0.29 g of Co(NO3)2·6H2O, 0.2846 g of H3BO3 and 0.625 g of NH4B5O 10 ·4H2O are dissolved in the mixed solvent, after stirring for 3 h, the solution is transferred to a reaction kettle, after heating at 180℃ for 72 h, it is cooled to room temperature at a temperature of 10℃ / h, ultrasonic treatment is performed, washing with MeCN is performed twice, and filtration is performed to obtain a cobalt-modified borovanadomolybdate nanocluster with a chemical formula of ([Co(H2O)2]3[V 12 O9(OH)9B 18 O 39 (OH)3]·3.5H2O); named as: 3D CoVB;

[0018] Step two: 0.0421 g of NH4VO3, 0.05815 g of Ni(NO3)2·6H2O, 0.1212 g of H3BO3 and 0.2725 g of NH4B5O 10 ·4H2O are dissolved in 2 mL of H2O, after stirring for 3 h, 0.11 mL of ethylenediamine is added to the mixed solution, then, the solution is transferred to a reaction kettle, after heating at 180℃ for 7 days, it is naturally cooled to room temperature, ultrasonic treatment is performed, washing with MeCN is performed twice, and filtration is performed to obtain a nickel-modified borovanadomolybdate nanocluster with a chemical formula of ([Ni(H2O)2]3[V 12 O9(OH)9B 18 O 39 (OH)3]·3.5H2O); named as: 3D NiVB;

[0019] Step three: 0.0421 g of NH4VO3, 0.026 g of Ni(NO3)2·6H2O, 0.026 g of Co(NO3)2·6H2O, 0.1212 g of H3BO3 and 0.2725 g of NH4B5O 10• 4H2O was dissolved in 2 mL of H2O, after stirring for 3 h, 0.11 mL of ethylenediamine was added to the mixed solution, then the solution was transferred to a reaction kettle, after heating at 180℃ for 7 days, natural cooling to room temperature, ultrasonic treatment, washing twice with MeCN, filtration, to obtain a cobalt nickel bimetallic modified borovanadate polyoxometalate nanocluster with the chemical formula: ([Co 0.5 Ni 0.5 Ni(H2O)2]3[V 12 O9(OH)9B 18 O 39 (OH)3]·3.5H2O);named as: 3D CoNiVB;

[0020] Step four: 10 g of PEI was dissolved in 10 mL of deionized water, then 50 mg of 3D CoNiVB prepared in step three was added, the obtained mixture was continuously heated in a crucible until water was removed; finally, heating to 800℃ at a heating rate of 5℃ min -1 -1 under Ar atmosphere, maintaining for 2 h to obtain a CoNi-VN nanoparticle composite electrocatalyst, named as: CoNi / VN / BNCNT.

[0021] Preferably, the cobalt modified borovanadate polyoxometalate nanocluster prepared in the above step one has a cubic Pn-3 crystal space group, and a unit cell parameter of: α = 90°, β = 90°, γ = 90°,

[0022] In addition, the present application also provides a CoNi-VN nanoparticle composite electrocatalyst prepared by the above preparation method.

[0023] Finally, the present application also provides the application of the above CoNi-VN nanoparticle composite electrocatalyst in hydrogen evolution reaction, oxygen evolution reaction or oxygen reduction reaction.

[0024] Advantages of the present application

[0025] The present application provides a new type of electrocatalyst, which has the following advantages:

[0026] 1. Overcoming the problem of nanoparticle aggregation: the present application innovatively designs polyethyleneimine (PEI) as a soft template and uses polyoxometalate (POMs) as a precursor, which effectively prevents the aggregation of catalyst particles during the synthesis process, ensures the uniform distribution of nanoparticles on the nanoscale, and thus improves the exposure rate of active sites of the catalyst and the catalytic performance.

[0027] 2. Improve the stability of the catalyst: The catalyst system of the present invention combines CoNi and VN materials and embeds them into N and B co-doped carbon nanotubes. The nanoconfinement effect is used to effectively enhance the geometric stability of the catalyst, avoiding side reactions or structural changes at high current density or in extreme environments, thereby ensuring long-term catalytic stability.

[0028] 3. Enhanced Local Electric Field Effects: This study successfully prepared ultrasmall CoNi and VN nanoparticles with a particle size of approximately 4 nm. These ultrasmall particles possess a large specific surface area and high curvature, enabling the generation of strong LEFs at the catalytic center. This local electric field effectively improves electron transport efficiency and ion enrichment, thereby accelerating the rate of multi-electron reduction reactions and enhancing the kinetics of the catalytic reaction.

[0029] 4. Achieve multifunctional catalysis: The catalyst designed in this invention can not only effectively promote HER, OER and ORR, but also has efficient trifunctional catalytic performance, overcoming the problem that existing catalysts can only be optimized for a single reaction, thereby reducing system complexity and manufacturing costs.

[0030] Through the above design, the present invention aims to provide a high-efficiency, low-cost and stable multifunctional electrocatalyst that can provide excellent electrocatalytic performance in fields such as water decomposition and zinc-air batteries, and significantly improve the long-term stability of the catalyst, thereby promoting the development of clean energy conversion and storage technologies. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagrams of the structures of 3D CoBV and 3D NiBV clusters provided by the present invention, wherein Figures a and b are ball-and-stick models of 3D CoBV and 3D NiBV clusters, respectively; Figures c and d are views of the crystal stacking structures of 3D CoBV and 3D NiBV clusters, respectively;

[0032] Figure 2 V6O in the crystal structure of 3D CoBV provided by the present invention 18 and V 12 O 60 Schematic diagram of the cluster structure and the coordination diagram of Co atoms, where Figure a is V6O 18 Schematic diagram of cluster; Figure b is B 18 Ring connected V 12 O 60 Ball-and-stick diagram of the cluster; Figure c is a schematic diagram of the coordination of Co atoms; Figure d is a crystal stacking view of 3D CoBV;

[0033] Figure 3The 3D CoBV, 3D NiBV and 3D CoNiBV structure characterization diagram provided by the present application, wherein figure a is the XRD diagram of 3D CoBV, 3D NiBV and 3D CoNiBV; figure b is the FT-IR spectrum diagram of 3D CoBV, 3D NiBV and 3D CoNiBV;

[0034] Figure 4 The CoNi / VN / BNCNT composite catalyst morphology characterization diagram provided by the present application, wherein figure a, b is the TEM image of CoNi / VN / BNCNT; figure c is the particle size distribution diagram of CoNi and VN; figure d, e, f is the HRTEM diagram of CoNi / VN / BNCNT;

[0035] Figure 5 The CoNi / VN / BNCNT composite catalyst structure characterization diagram provided by the present application, wherein figure a is the PXRD diagram of Ni / VN / BNCNT, Co / VN / BNCNT and CoNi / VN / BNCNT, and the insert in figure a is the local enlarged view of the range of 43.7° to 45.1° in the diffraction spectrum; figure b is the N2 adsorption-desorption isotherm diagram of Ni / VN / BNCNT, Co / VN / BNCNT and CoNi / VN / BNCNT, and the insert in figure b is the nanoparticle pore size distribution diagram; figure c, d are respectively the high-resolution Co 2p and Ni2p XPS spectrum diagram of CoNi / VN / BNCNT; figure e is the relative content diagram of N doping in CoNi / VN / BNCNT, wherein the insert in figure e is the high-resolution N1s XPS diagram of CoNi / VN / BNCNT; figure f is the relative content diagram of B doping in CoNi / VN / BNCNT, wherein the insert in figure f is the high-resolution B1s XPS diagram of CoNi / VN / BNCNT;

[0036] Figure 6 The high-resolution C1s XPS diagram of CoNi / VN / BNCNT provided by the present application;

[0037] Figure 7 The high-resolution V 2p XPS diagram of CoNi / VN / BNCNT provided by the present application;

[0038] Figure 8The catalytic performance diagram of CoNi / VN / BNCNT provided by the present invention, wherein Figure a is the HER LSV curve of Ni / VN / BNCNT, Co / VN / BNCNT, and CoNi / VN / BNCNT; Figure b is the OER LSV curve of Ni / VN / BNCNT, Co / VN / BNCNT, and CoNi / VN / BNCNT; Figure c is the RDE LSV curve of Ni / VN / BNCNT, Co / VN / BNCNT, CoNi / VN / BNCNT, and Pt / C at 1600rpm; Figure d is the LSV diagram of CoNi / VN / BNCNT‖CoNi / VN / BNCNT and IrO2‖Pt / C, wherein the inset of Figure d is a photo of the dual-electrode setup; Figure e is the discharge polarization curve and corresponding power density diagram of CoNi / VN / BNCNT and Pt / C-RuO2; Figure f is the discharge polarization curve of rechargeable Zn-air battery at 10mA cm -2 Long-term cycling performance diagram at different current densities;

[0039] Figure 9 COMSOL simulation electric field distribution diagram provided by the present invention, wherein Figures a1-e1 are electron field distribution diagrams of BNCNT, VN / BNCNT, CoNi / BNCNT, CoNi / VN / BNCNT-L and CoNi / VN / BNCNT during the HER process; Figures a2-e2 are electron field distribution diagrams of BNCNT, VN / BNCNT, CoNi / BNCNT, CoNi / VN / BNCNT-L and CoNi / VN / BNCNT during the OER process; Figure f is the electric field intensity and OH of BNCNT, CoNi / VN / BNCNT-L, VN / BNCNT, CoNi / BNCNT and CoNi / VN / BNCNT during the HER and OER processes. - Concentration distribution diagram; Figure g is a schematic diagram of the mechanism for improving alkaline water splitting performance;

[0040] Figure 10 COMSOL simulation OH provided by the present invention - Ion concentration distribution diagram, among which Figures a1-e1 show the OH concentration distribution of BNCNT, CoNi / VN / BNCNT-L, VN / BNCNT, CoNi / BNCNT and CoNi / VN / BNCNT during the HER process. - Concentration distribution diagram; Figures a2-e2 show the OH concentration of BNCNT, CoNi / VN / BNCNT-L, VN / BNCNT, CoNi / BNCNT and CoNi / VN / BNCNT in the OER process. - concentration distribution map;

[0041] Figure 11The HER, OER and overall water splitting stability performance diagrams of the catalyst provided by the present invention, wherein Figure a is the HER LSV curve of CoNi / VN / BNCNT before and after continuous cycling in 1.0M KOH, wherein the inset of Figure a is the HER LSV curve of CoNi / VN / BNCNT at 10mAcm -2 Figure b is a long-term stability test diagram of CoNi / VN / BNCNT in 1.0M KOH before and after continuous cycling; Figure b is the OER LSV curve of CoNi / VN / BNCNT in 1.0M KOH before and after continuous cycling, where the inset of Figure b is the OER LSV curve of CoNi / VN / BNCNT in 10mA cm -2 Figure 1 is a long-term stability test diagram under a fixed voltage; Figure c is a stability evaluation diagram of CoNi / VN / BNCNT under a fixed voltage for 15 hours during water decomposition; the inset of Figure c is a relationship diagram between the O2 and H2 gas production of CoNi / VN / BNCNT and the reaction time;

[0042] Figure 12 The ORR stability performance diagram of the catalyst provided by the present invention, wherein Figure a is the LSV diagram of CoNi / VN / BNCNT before and after 2000 CV cycles, wherein the inset of Figure a is a long-term stability test diagram of CoNi / VN / BNCNT at 0.85V and 1600rpm in an O2-saturated 0.1M KOH solution; Figure b is a current-time curve of CoNi / VN / BNCNT after adding 1M methanol in 0.1M KOH; DETAILED DESCRIPTION

[0043] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described here are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0044] Secondly, the present invention is described in detail with reference to the accompanying drawings. When describing the embodiments of the present invention in detail, for the convenience of explanation, the accompanying drawings are only examples and should not limit the scope of protection of the present invention.

[0045] The experimental characterization methods described in the following examples are conventional methods unless otherwise specified; the reagents, materials and instruments and equipment described are all commercially available unless otherwise specified.

[0046] The present invention provides a method for preparing an ultrasmall multifunctional CoNi-VN nanoparticle composite electrocatalyst based on enhancing the local electric field, and the multifunctional CoNi-VN nanoparticle composite electrocatalyst prepared according to the method, and provides the application of the multifunctional CoNi-VN nanoparticle composite electrocatalyst in hydrogen evolution reaction, oxygen evolution reaction or oxygen reduction reaction.

[0047] Example 1

[0048] First, a method for preparing an ultrasmall multifunctional CoNi-VN nanoparticle composite electrocatalyst is provided, the method comprising:

[0049] Step 1: Mix 4.6 mL of H2O and 0.96 mL of C6H 17 N3 mixed to obtain a mixed solvent, 0.1053g NH4VO3, 0.29g Co(NO3)2·6H2O, 0.2846g H3BO3 and 0.625g NH4B5O 10 4H2O was dissolved in the mixed solvent, stirred for 3 h, and the solution was transferred to a reactor, heated at 180°C for 72 h, cooled to room temperature at a rate of 10°C / h, ultrasonicated, washed twice with MeCN, and filtered to obtain a product with the chemical formula ([Co(H2O)2]3[V 12 O9(OH)9B 18 O 39 Cobalt-modified boron-vanadium polyoxometalate nanoclusters with a molten pool of 1.5 mmol / l (OH)3]·3.5H2O; named: 3D CoVB;

[0050] Step 2: Mix 0.0421g NH4VO3, 0.05815g Ni(NO3)2·6H2O, 0.1212g H3BO3 and 0.2725g NH4B5O 10 4H2O was dissolved in 2mL of H2O, stirred for 3h, and then 0.11mL of ethylenediamine was added to the mixed solution. Subsequently, the solution was transferred to a reactor, heated at 180℃ for 7 days, and then naturally cooled to room temperature. Ultrasonic treatment was performed, washed twice with MeCN, and filtered to obtain a product with the chemical formula ([Ni(H2O)2]3[V 12 O9(OH)9B 18 O 39 (OH)3]·3.5H2O) nickel-modified boron vanadium polyoxometalate nanoclusters; named: 3D NiVB;

[0051] Step 3: Mix 0.0421g NH4VO3, 0.026g Ni(NO3)2·6H2O, 0.026g Co(NO3)2·6H2O, 0.1212g H3BO3 and 0.2725g NH4B5O 10 4H2O was dissolved in 2mL of H2O, stirred for 3h, and then 0.11mL of ethylenediamine was added to the mixed solution. Subsequently, the solution was transferred to a reactor, heated at 180°C for 7 days, and then naturally cooled to room temperature, ultrasonically treated, washed twice with MeCN, and filtered to obtain a solution with the chemical formula: ([Co 0.5 Ni 0.5 Ni(H2O)2]3[V 12 O9(OH)9B18 O 39 3D CoNiVB is a cobalt-nickel bimetallic modified boron-vanadium polyoxometalate nanoclusters with the structure of (OH)3]·3.5H2O; it is named as 3D CoNiVB.

[0052] Step 4: 10 g of positively charged PEI was dissolved in 10 mL of deionized water, and then 50 mg of negatively charged 3D CoNiVB prepared in step 3 was added. The resulting mixture was continuously heated in a crucible until the water was removed and a black colloidal state was obtained. Finally, the mixture was heated in an Ar atmosphere at 5 °C min -1 The mixture was heated to 800 °C at a heating rate of 1000 °C and maintained for 2 h to obtain a CoNi-VN nanoparticle composite electrocatalyst named CoNi / VN / BNCNT.

[0053] The reagents used in the above preparation method were all purchased from the market. The reagents used, specifications and manufacturers are shown in Table 1.

[0054] Table 1

[0055]

[0056]

[0057] The present application provides a CoNi / VN / BNCNT catalyst material containing cobalt-nickel alloy nanoparticles. To demonstrate its catalytic performance and stability, Co / VN / BNCNT and Ni / VN / BNCNT were prepared for performance comparison.

[0058] Comparative Example 1

[0059] According to the preparation method described in step 1 of Example 1, 3D CoVB was prepared for use; 10 g of positively charged PEI was dissolved in 10 mL of deionized water, and then 50 mg of the negatively charged 3D CoVB prepared above was added. The resulting mixture was continuously heated in a crucible until the water was removed to obtain a black colloidal state; finally, the mixture was heated in an Ar atmosphere at 5°C min -1 The multifunctional electrocatalyst composite material was obtained by heating to 800 °C at a heating rate of 1000 ℃ and maintaining it for 2 h, and named as Co / VN / BNCNT.

[0060] Comparative Example 2

[0061] According to the preparation method described in step 2 of Example 1, 3D NiVB was prepared for use; 10 g of positively charged PEI was dissolved in 10 mL of deionized water, and then 50 mg of the negatively charged 3D NiVB prepared above was added. The resulting mixture was continuously heated in a crucible until the water was removed to obtain a black colloidal state; finally, the mixture was heated in an Ar atmosphere at 5°C min -1The multifunctional electrocatalyst composite material was obtained by heating to 800 °C at a heating rate of 1000 °C and maintaining it for 2 h, and named as Ni / VN / BNCNT.

[0062] Single crystal X-ray diffraction analysis showed that the 3D CoVB, 3D NiVB and 3D CoNiVB compounds prepared in Example 1 were isostructural, and each compound crystallized in the cubic Pn-3 space group (e.g. Figure 1 ). The crystal structure of 3D CoVB is used as a representative for description, as shown in Figure 2 As shown in a, oxygen atoms bridge six VO5 square pyramids to form a V6 cluster. Two V6 clusters are arranged face to face, and V is formed by bridging B and O atoms. 12 cluster, while V 12 The cluster is surrounded by a B composed of six [B3O7] units. 18 Surrounded by a ring. Figure 2 As shown in Figure b, two B atoms adopt tetrahedral coordination in the [B3O7] unit, while one B atom adopts planar trigonal coordination. Figure 2 As shown in c, the adjacent V 12 B 18 The clusters are connected by six-coordinated Co ions, four of which come from oxygen atoms in the cluster and two from water molecules. Finally, the structure extends along the a, b, and c crystal axes to form a V-based 12 B 18 The three-dimensional open framework of the cluster unit has the chemical formula [Co(H2O)2]3[V 12 O9(OH)9B 18 O 39 (OH)3]·3.5H2O, such as Figure 2 d, and its crystal data are shown in Table 2.

[0063] Table 2

[0064]

[0065]

[0066] Characterization of 3D NiVB crystals

[0067] The phase purity of the compound was determined by powder X-ray diffraction (PXRD) analysis. Figure 3 As shown in a, the simulated curves are highly consistent with the experimental curves, indicating that 3D NiVB, 3D CoVB, and 3D CoNiVB have high crystallinity and purity. The chemical composition of the obtained compounds was further analyzed by Fourier transform infrared spectroscopy (FT-IR). Figure 3As shown in b, the FT-IR spectrum shows the typical characteristics of POMs spectrum, in which the stretching vibration band of metal-oxygen bond appears in the range of 500-1200 cm -1 The asymmetric stretching vibration of the V–O–B group appears at approximately 457 cm -1 . Appears at 790, 717 and 664 cm -1 The signals correspond to the symmetric and asymmetric stretching vibrations of V–O–V. -1 and 1060-1070cm -1 The peaks observed at 1671, 1600 and 3461–2947 cm-1 are associated with the B–O stretching vibrations in the [BO3] and [BO4] units. -1 The signals at are assigned to N–H bonds and O–H groups, respectively.

[0068] Characterization of CoNi / VN / BNCNT catalyst

[0069] like Figure 4 Transmission electron microscopy (TEM) images show that the CoNi / VN / BNCNT material presents a hollow bamboo-like carbon nanotube structure ( Figure 4 a) This three-dimensional layered morphology facilitates rapid penetration of electrolyte into the electrocatalytic active sites, thereby improving reaction efficiency. Figure 4 b and Figure 4 c shows metallic Co and VN nanoclusters with an average diameter of 4 nm, uniformly dispersed and embedded in carbon nanotubes without significant aggregation, which helps to maintain high structural stability and durability in alkaline electrolytes. Figure 4 df High-resolution TEM (HRTEM) images show that the (111) planes of CoNi and VN have spacings of 0.204 and 0.242 nm, respectively. In addition, the spacing of the graphite C (002) lattice is 0.351 nm, indicating the high crystallinity of the carbon nanotubes in CoNi / VN / BNCNT.

[0070] Figure 5 a shows that the PXRD spectrum of CoNi / VN / BNCNT is very similar to that of Co / VN / BNCNT and Ni / VN / BNCNT samples. The diffraction peaks at 44.3°, 51.6° and 76.0° correspond to the characteristic (111), (200) and (220) planes of CoNi alloy, respectively, while the broad peak at 26.2° indicates the presence of graphitic carbon. In addition, the diffraction peaks at 37.7°, 43.7°, 63.5° and 76.2° are related to the cubic VN structure. Among them, Figure 5The inset of a shows a local magnification of the diffraction pattern from 43.7° to 45.1°, showing that the CoNi (111) diffraction peak is located between the diffraction peaks of pure cobalt (PDF#15-0806) and nickel (PDF#04-0850). This indicates that the alloying of Co and Ni leads to lattice expansion, confirming the formation of CoNi.

[0071] like Figure 5 The nitrogen adsorption-desorption isotherm shown in b shows that the Ni / VN / BNCNT (213.1m 2 / g) and Co / VN / BNCNT(165.3m 2 / g) compared with CoNi / VN / BNCNT, which has the highest specific surface area, reaching 630.8 m 2 / g. Figure 2 As shown in Figure 2b, the pore size distribution shows a pore size range of 2 to 10 nm, consistent with the nitrogen isotherm results. The mesoporous structure and high surface area of ​​CoNi / VN / BNCNT facilitate electrolyte penetration and diffusion to the active sites. Furthermore, large volume changes during charge and discharge are effectively mitigated.

[0072] The composition and valence state of the electrocatalysts were analyzed by X-ray photoelectron spectroscopy (XPS). Figure 6 As shown in Figure 2, in CoNi / VN / BNCNT, carbon species are represented by five different peaks (283.5, 284.8, 285.5, 286.5, and 288.0 eV), which correspond to different C–B, C–C, C–N, C–N / C–O, and COO– groups, respectively. Figure 7 As shown, V2p 3 / 2 The XPS spectrum shows peaks at 513.78, 515.5, and 517.3 eV, indicating the presence of V–N, V–N–O, and V–O species. In the Co2p XPS spectrum ( Figure 5 c) shows three chemical states of cobalt, including metallic Co, Co 2+ and Co 3+ The peaks at 777.9eV and 792.9eV are attributed to Co–Co bonds, while slight surface oxidation leads to the peaks at 779.7eV and 794.7eV for Co 3+ signal, and Co at 781.5eV and 796.5eV 2+ signal. Similarly, through Ni 2p 3 / 2 Peak deconvolution, Ni 0 、Ni 2+ and Ni 3+ They appear at 852.27eV, 854.13eV and 855.27eV respectively ( Figure 5d) The formation of CoNi alloy nanoparticles is further carried out by metal Co 0 and Ni 0 The existence of CoNi / VN / BNCNT was confirmed, which is consistent with the XRD results. 0 2p 3 / 2 Peak ratio Co / VN / BNCNT 0 2p 3 / 2 The binding energy of the peak is about 0.3eV lower. In contrast, the Ni 0 2p 3 / 2 Peak relative to Ni / VN / BNCNT 0 2p 3 / 2 The peak shows a positive shift of about 0.3 eV. These observations indicate that the incorporation of Ni affects the electronic structure of Co, highlighting the synergistic effect between the two metals. In CoNi, cobalt atoms are able to obtain d electrons from neighboring nickel atoms, which act as electron donors. The N 1s XPS spectrum shows seven peaks representing V–N (397.5 eV), B–N–C (398.3 eV), pyridinic nitrogen (398.9 eV), Co / Ni–N4 (399.8 eV), pyrrolic nitrogen (400.6 eV), graphitic nitrogen (401.2 eV) and oxidized nitrogen (402.2 eV). Histogram of nitrogen species ( Figure 5 e) shows a rich variety of active nitrogen species, especially pyridinic nitrogen (14.6%), graphitic nitrogen (16.81%) and Co / Ni–N4 (14.6%). Pyridinic nitrogen affects the electronic structure of the surrounding carbon atoms, affecting the spin and current density, as well as the p-state density at the Fermi level, thereby affecting the overall surface and electronic properties of the carbon material. Co / Ni–N4 acts as a catalytic anchor, optimizing the adsorption energy and accelerating the electrochemical reaction. Graphitic nitrogen enhances the limiting current density in the ORR process by promoting the adsorption of oxygen and dissociation intermediates. Figure 5 As shown in (f), the B 1s XPS spectrum can be decomposed into four peaks at 189.5, 190.8, 191.4, and 192.5 eV, corresponding to BC3, B–N, BC2O, and BCO2. The graphite-like structure of the active BC3 species represents an important active site for the ORR. The B–N species is crucial for enhancing catalytic activity through strong charge transfer effects with neighboring carbon atoms.

[0073] In addition, in this study, the trifunctional catalytic performance of the catalyst was analyzed using a classic three-electrode system. Figure 8As shown in a, the HER linear sweep voltammetry (LSV) curves of CoNi / VN / BNCNT were compared with those of Comparative Examples 1 and 2. The data show that CoNi / VN / BNCNT only needs an overpotential of 109 mV to reach 10 mA cm -2 In comparison, the overpotentials of Ni / VN / BNCNT (156 mV) and Co / VN / BNCNT (149 mV) are significantly higher.

[0074] like Figure 8 As shown in b, the OER catalytic performance of the catalyst was evaluated by -1 The LSV test was conducted in KOH solution to evaluate and compare the performance of the CoNi / VN / BNCNT catalyst. The overpotential of CoNi / VN / BNCNT was only 362 mV to achieve a 50 mA cm -2 The current density of the catalysts is better than that of Ni / VN / BNCNT (396 mV) and Co / VN / BNCNT (386 mV), as well as other reported catalysts (as shown in Table 3).

[0075] Table 3

[0076]

[0077]

[0078] The ORR activity of CoNi / VN / BNCNT was analyzed in an O2-saturated 0.1 M KOH solution at a rotation speed of 1600 rpm. Figure 8 c shows that CoNi / VN / BNCNT has a more positive onset potential (Eonset, 1 V) and half-wave potential (Eonset, 1 V) compared with Ni / VN / BNCNT, Co / VN / BNCNT and Pt / C. 1 / 2 , 0.85V).

[0079] Inspired by the excellent catalytic performance of CoNi / VN / BNCNT in HER and OER, a two-electrode system was constructed to promote the overall water splitting reaction. Figure 8 As shown in d, CoNi / VN / BNCNT only needs 1.52 V to achieve 10 mA cm -2 The current density can reach 50mA cm at 1.67V. -2 , which are significantly lower than IrO2||Pt / C (1.57 V and 1.78 V, respectively), and are superior to most of the multifunctional electrocatalysts reported so far (Table 4).

[0080] Table 4

[0081]

[0082]

[0083] Due to the excellent catalytic performance of CoNi / VN / BNCNT in OER and ORR, zinc-air batteries were constructed. Figure 8 As shown in e, the zinc-air battery based on CoNi / VN / BNCNT is -2 At a current density of 220 mW cm -2 The peak power density is about the same as that of zinc-air batteries using Pt / C-RuO2 (160 mW cm -2 , 108 mA cm -2 ) and outperforms the performance of recently reported electrocatalysts in zinc-air batteries (Table 5). Figure 8 As shown in f, by applying 10 mA cm -2 The battery's stability and long-term charge-discharge capability were verified by charge-discharge tests at a constant current. For a CoNi / VN / BNCNT-based zinc-air battery with an initial discharge voltage of 1.17V, a charge voltage of 2.06V, and a charge-discharge voltage difference of 0.89V, the charge-discharge voltage difference increased by only 0.94V after 1,000 long-term tests (20 minutes per cycle), a growth rate of less than 5%. Overall, these results indicate that the CoNi / VN / BNCNT electrocatalyst has great potential for application in rechargeable zinc-air batteries due to its excellent electrocatalytic reactivity and stability.

[0084] Table 5

[0085]

[0086]

[0087] To explore the potential mechanism behind the excellent electrocatalytic performance, this study used COMSOL Multiphysics simulation to analyze the charge and ion distribution near the catalyst surface. Two-dimensional models of different particle sizes and compositions were constructed to represent the electrodes immersed in 1.0 M KOH electrolyte. Figure 9 b and Figure 9 As shown in Figure c, there are high electric field regions (marked in red) around each CoNi and VN nanoparticle modified on the BNCNT surface. These hot spots are evenly distributed on the electrode surface, significantly affecting the reaction kinetics and serving as the main contributing factor to improving the overall catalytic efficiency. In addition, these hot spots expand the effective reaction surface area of ​​the BNCNT, providing more sites for the interaction between the reactants and the catalyst. Figure 10 As shown, during the HER and OER processes, OH around CoNi and VN nanoparticles -The concentration was significantly increased. This indicates that the local electric field generated by the nanoparticles plays a crucial role in promoting the ion concentration gradient required for efficient catalysis. The BNCNT structure loaded with CoNi or VN nanoparticles showed a stronger local electric field than the pure BNCNT, and the OH - The repulsion of ions is stronger, indicating that H + The enrichment of OH is enhanced. - Simulation data summary of concentration and electric field strength, combined with Figure 9 As shown in f, the simulation results further show that the electric field intensity near the surface of CoNi / VN / BNCNT can reach 0.04V / μm, and OH - The concentration of OH is 0.96 mol / L. Similar ion enhancement effect was also observed in the OER process. It is worth noting that in the HER process, as the electric field strength increases, the OH - The concentration of OH in OER decreased, while under the same conditions - To study the effect of nanoparticle size, a model was constructed in which the BNCNT surface was coated with larger nanoparticles (about 100 nm) synthesized by conventional methods. Figure 9 d and Figure 9 As shown in e, computational finite element simulations show that the local electric field strength generated by 4 nm CoNi-VN nanoparticles is 2.1 times that of larger nanoparticles. This enhanced local electric field creates an ion-rich environment that promotes the adsorption and activation of key species (such as Figure 9 g), ultimately improving the catalytic performance.

[0088] Table 6

[0089]

[0090] like Figure 11 As shown in Figure a, the current density of CoNi / VN / BNCNT remained relatively stable after 12 hours without significant attenuation. The overpotential of the LSV curve after 2000 CV cycles increased by only 2 mV, further confirming the excellent durability of the CoNi / VN / BNCNT catalyst in HER.

[0091] In the OER stability test, CoNi / VN / BNCNT maintained a relatively stable current density after 12 hours of continuous reaction, without any significant increase. Figure 11 As shown in b, after 2000 CV tests, the CoNi / VN / BNCNT catalyst only exhibited an activity loss of about 11 mV, demonstrating good electrochemical stability.

[0092] like Figure 11 As shown in Figure c, the constructed CoNi / VN / BNCNT full water splitting device shows almost no drop in current density after 15 hours, demonstrating its excellent durability. The Faradaic efficiency test shows that the linear growth of H2 and O2 gas volumes over time remains stable, with their gas ratio always around 2:1. The Faradaic efficiency of both gases is close to 100%, indicating that the electrolysis process has almost completed conversion.

[0093] like Figure 12 As shown in b, the methanol tolerance test of CoNi / VN / BNCNT and Pt / C was conducted by adding 10mL of methanol to 100mL of electrolyte. After adding methanol, the current density of Pt / C dropped sharply due to poisoning, while CoNi / VN / BNCNT almost did not lose current, indicating that it has better methanol tolerance. In addition, as Figure 12 As shown in the inset of a, the current density of CoNi / VN / BNCNT was maintained at 93.95% after continuous reaction at 0.85 V for 10 hours. Figure 12 As shown in a, after 1000 CV cycle tests, the E 1 / 2 Only a shift of about 2 mV occurred. These two results demonstrate the excellent durability of CoNi / VN / BNCNT in ORR.

[0094] In summary, this study successfully designed and synthesized Co / Ni modified boron vanadium polyoxometalates, and prepared CoNi and VN nanodots encapsulated in B- and N-doped carbon nanotubes as trifunctional electrocatalysts by the PEI soft template method. This strategy effectively solved the problem of nanoparticle aggregation by utilizing the electrostatic interaction between PEI and POMs, achieving uniform dispersion and controllable particle size. COMSOL simulation results show that the BNCNT structure loaded with CoNi or VN nanoparticles exhibits a stronger local electric field, which contributes to the enhanced adsorption of reaction intermediates compared with pure BNCNT. In a strong LEFs environment, coupled with the high specific surface area and efficient charge transfer characteristics of the carbon nanotube structure, the catalytic activity of CoNi / VN / BNCNT in HER, OER and ORR is excellent, reaching a level comparable to that of precious metal catalysts. In the overall water splitting reaction, CoNi / VN / BNCNT achieved 50 mA cm at a low applied voltage of 1.67 V. -2 The current density is better than that of most non-precious metal electrocatalysts. In addition, the CoNi / VN / BNCNT-based rechargeable zinc-air battery showed excellent performance with a peak power density of 220mWcm -2 , with a specific capacity of 810 mAh g -1 , and at 10mA cm -2The cycle stability of the Zn-air battery based on the Pt / C-RuO2 catalyst is over 1000 cycles, which is superior to the performance of the Zn-air battery based on the Pt / C-RuO2 catalyst.

Claims

1. A method for preparing an ultra-small multifunctional CoNi-VN nanoparticle composite electrocatalyst, characterized in that: The method includes: Step 1: Mix 4.6 mL of H2O and 0.96 mL of C6H 17 N3 mixed to obtain a mixed solvent, 0.1053g NH4VO3, 0.29g Co(NO3)2·6H2O, 0.2846g H3BO3 and 0.625g NH4B5O 10 4H2O was dissolved in the mixed solvent, stirred for 3 h, and the solution was transferred to a reactor, heated at 180°C for 72 h, cooled to room temperature at a rate of 10°C / h, ultrasonicated, washed twice with MeCN, and filtered to obtain a product with the chemical formula ([Co(H2O)2]3[V 12 O9(OH)9B 18 O 39 Cobalt-modified boron-vanadium polyoxometalate nanoclusters with a molten pool of 1.5 mmol / l (OH)3]·3.5H2O; named: 3D CoVB; Step 2: Mix 0.0421g NH4VO3, 0.05815g Ni(NO3)2·6H2O, 0.1212g H3BO3 and 0.2725g NH4B5O 10 4H2O was dissolved in 2mL of H2O, stirred for 3h, and then 0.11mL of ethylenediamine was added to the mixed solution. Subsequently, the solution was transferred to a reactor, heated at 180℃ for 7 days, and then naturally cooled to room temperature. Ultrasonic treatment was performed, washed twice with MeCN, and filtered to obtain a product with the chemical formula ([Ni(H2O)2]3[V 12 O9(OH)9B 18 O 39 (OH)3]·3.5H2O) nickel-modified boron vanadium polyoxometalate nanoclusters; named: 3D NiVB; Step 3: Mix 0.0421g NH4VO3, 0.026g Ni(NO3)2·6H2O, 0.026g Co(NO3)2·6H2O, 0.1212g H3BO3 and 0.2725g NH4B5O 10 4H2O was dissolved in 2mL of H2O, stirred for 3h, and then 0.11mL of ethylenediamine was added to the mixed solution. Subsequently, the solution was transferred to a reactor, heated at 180°C for 7 days, and then naturally cooled to room temperature, ultrasonically treated, washed twice with MeCN, and filtered to obtain a solution with the chemical formula: ([Co 0.5 Ni 0.5 Ni(H2O)2]3[V 12 O9(OH)9B 18 O 39 3D CoNiVB polyoxometalate nanoclusters modified with cobalt and nickel bimetallics (OH)3·3.5H2O) Step 4: 10 g of PEI was dissolved in 10 mL of deionized water, and then 50 mg of 3DCoNiVB prepared in step 3 was added. The resulting mixture was continuously heated in a crucible until the water was removed. Finally, the mixture was heated in an Ar atmosphere at 5 °C min -1 The mixture was heated to 800 °C at a heating rate of 1000 °C and maintained for 2 h to obtain a CoNi-VN nanoparticle composite electrocatalyst named CoNi / VN / BNCNT.

2. The method for preparing an ultra-small multifunctional CoNi-VN nanoparticle composite electrocatalyst according to claim 1, characterized in that: The cobalt-modified boron-vanadium polyoxometalate nanoclusters prepared in step 1 have a crystal space group of cubic Pn-3 and unit cell parameters of α=90°, β=90°, and γ=90°.

3. A CoNi-VN nanoparticle composite electrocatalyst prepared by the preparation method according to claim 1.

4. Use of the CoNi-VN nanoparticle composite electrocatalyst according to claim 3 in hydrogen evolution reaction, oxygen evolution reaction or oxygen reduction reaction.

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