NiCo-S / NiCo-OH-CL bifunctional catalyst with heterostructure and preparation method of NiCo-S / NiCo-OH-CL bifunctional catalyst

Abstract

The invention discloses a NiCo-S / NiCo-OH-CL bifunctional catalyst with a heterostructure and a preparation method of the NiCo-S / NiCo-OH-CL bifunctional catalyst, and belongs to the technical field of nano materials and electrochemical catalysis. The catalyst has a one-dimensional porous microrod structure, has a diameter of 0.8-2.5 [mu] m, contains rich sulfide / hydroxide heterogeneous interfaces, and shows significant hydrophilic and sulfur-repellent surface characteristics. Benefited from the interface and ligand dual-regulation effect, the catalyst disclosed by the invention shows excellent sulfur oxidation reaction (SOR) and hydrogen evolution reaction (HER) catalytic activity. The assembled SOR-HER coupling electrolysis system has the electrolysis voltage of only 0.62 V under the current density of 100 mA cm < 2 >, and can stably electrolyze for more than 3200 hours. Results show that the catalyst is excellent in electrochemical performance, the preparation process is simple and effective, and the catalyst has great application potential.

Description

Technical Field

[0001] The present invention belongs to the technical field of nanomaterials and electrocatalytic technologies, and particularly relates to a NiCo-S / NiCo-OH-CL bifunctional catalyst with a heterostructure and a preparation method thereof, and more particularly to a nickel-cobalt sulfide / carboxyl-modified nickel-cobalt hydroxide composite catalyst (NiCo-S / NiCo-OH-CL) designed based on an interface and ligand dual-regulation strategy, a preparation method thereof, and an application thereof. Background Art

[0002] Hydrogen energy (H 2 ), as a highly promising clean energy carrier, has become a key solution to address global carbon emission challenges, promote energy structure transformation, and reduce dependence on fossil fuels due to its high energy density (≈282 kJ·mol −1 ). However, traditional hydrogen production technologies, such as steam methane reforming, are plagued by severe environmental pollution, complex processes, high capital and operating costs, and excessive energy consumption. In contrast, electrochemical water splitting (OWS) is recognized for its green and renewable nature and is regarded as an ideal approach for large-scale hydrogen production. When powered by intermittent renewable energy sources such as solar and wind energy, the hydrogen evolution reaction (HER) at the cathode of OWS can efficiently produce high-purity H 2 , while being environmentally compatible and economically feasible. However, electrocatalytic water splitting still faces significant energy efficiency challenges, mainly restricted by the four-electron transfer mechanism of the oxygen evolution reaction (OER) at the anode. This process not only requires a high theoretical thermodynamic potential of 1.23 V vs. RHE, but also has a high overpotential in practical applications due to slow kinetics. The most advanced OER catalysts, such as Ru / Ir-based noble metal materials, further increase the hydrogen production cost due to scarce resources. In addition, the low economic value of the oxygen (O 2 ) generated at the anode, combined with the possible formation of explosive H 2 / O 2 mixtures when mixed with hydrogen at the cathode, poses a safety risk. Therefore, there is an urgent need to bypass the energy-intensive OER pathway and develop new alternative strategies to achieve safe and cost-effective hydrogen production.

[0003] Recent studies have proposed coupling HER with anodic small molecule (urea, alcohols, ethylene glycol, glucose, and hydrazine) oxidation reactions to improve the economic feasibility and environmental benefits of the electrolysis system by producing value-added chemicals or degrading pollutants at the anode. Among these alternatives, the sulfide oxidation reaction ( ) shows unique advantages because its thermodynamic energy barrier is significantly reduced compared to OER. Industrial sulfur-containing wastewater (from the paper, leather, textile, and petrochemical industries) contains abundant sulfide ions ( ), if discharged without treatment, it will pose a serious threat to the ecosystem, human health and crop growth. Traditional sulfur treatment processes, such as the Claus process, chemical precipitation and biological oxidation, are often hindered by high energy consumption, excessive reagent use, low efficiency and the risk of secondary pollution. Therefore, the SOR-HER coupled electrolysis system realizes the dual benefits of energy conservation and environmental protection by simultaneously treating sulfur-containing wastewater and co-producing hydrogen and elemental sulfur, thus achieving the recovery of resources from pollutants. Developing low-cost, highly active and durable bifunctional catalysts that can simultaneously catalyze the SOR and HER reactions is crucial for the wide application of this technology.

[0004] Currently, the catalyst systems for SOR mainly focus on metal chalcogenides, such as CoS 2 , Co 9 S 8 , NiS 2 , FeMoS 2 / Ru, NiSe, pa-Ru-CoSe and NiTe / NiMo. However, designing SOR catalysts faces the following challenges: (1) Sulfur deposition-induced inactivation occurs during the electrochemical reaction because the continuous deposition of sulfur species leads to active site coverage and high-resistance passivation layers, especially at high current densities ( Under such circumstances, the catalytic performance decreases rapidly. (2) The inhibition of HER activity stems from the strong interaction between sulfur species and metal sites, which significantly alters the electronic structure and reduces the HER activity, making it unfavorable for the construction of a low-cost membrane-free SOR-HER coupled electrolysis system. (3) Poor storage stability is a concern because metal chalcogenides, especially sulfides, are prone to oxidation in air due to their inherent structural characteristics, limiting practical applications. Therefore, the development of metal sulfide-based SOR electrodes with high catalytic activity, strong sulfur poisoning resistance, and long-term stability remains a focus of current research. In recent years, metal-organic frameworks (MOFs) have received attention in electrochemical energy conversion and storage. The designable frameworks formed by modular self-assembly are ideal material platforms. Compared with pristine MOFs and their composites, MOF derivatives have several advantages: (i) Structural tunability and design flexibility, where the active site distribution, pore structure, and morphology can be precisely adjusted by tuning metal nodes, organic ligands, and synthesis conditions. (ii) High specific surface area and ordered pore structure, which are beneficial for mass transfer and exposure of active sites. (iii) Flexible and scalable synthesis methods. (iv) Good chemical and structural stability. MOF-derived catalysts can be precisely regulated through metal site substitution, ligand modification, defect engineering, interface engineering, etc. In particular, ligand engineering optimizes the local environment of metal ions by introducing specific functional groups or tuning the electronic properties of ligands, thereby improving catalytic performance. However, systematic research on designing high-performance bifunctional catalysts for SOR-HER coupled hydrogen production systems - through the synergistic electronic structure regulation based on ligand and interface engineering of MOF materials - has not been explored yet. Summary of the Invention

[0005] In view of this, a NiCo-S / NiCo-OH-CL bifunctional catalyst with a heterostructure and its preparation method are provided. Benefiting from the porous network structure, sulfur-phobic and hydrophilic surface characteristics, as well as the dual-electron structure regulation of the heterointerfaces and ligands, the synthesized catalyst exhibits excellent SOR and HER activities. The constructed coupled electrocatalytic system has a working voltage of only 0.62 V at the current density, achieving a cathodic hydrogen Faraday efficiency of ≥95% and an electrolysis stability of over 3200 hours. The production rates of sulfur and hydrogen reach and . A synergistic interface ligand regulation strategy for the bifunctional catalyst is proposed, and a pathway for energy-saving hydrogen production and sulfur recovery is demonstrated.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A NiCo-S / NiCo-OH-CL bifunctional catalyst with a heterostructure, characterized in that the catalyst morphology is a porous micro-rod structure composed of porous nanosheets, and it is formed by assembling porous nanosheets, and the diameter of the micro-rods is 0.8-2.5 μm.

[0008] The catalyst of the present invention has a rich sulfide / hydroxide heterointerface. Thanks to the dual regulation effects of the heterointerface and ligands, it exhibits excellent electrocatalytic performance.

[0009] Preferably, the NiCo-S / NiCo-OH-CL micro-rods are loaded on a conductive substrate.

[0010] Another object of the present invention is to provide a preparation method of the NiCo-S / NiCo-OH-CL bifunctional catalyst with a heterostructure, including the following steps:

[0011] S1. Immerse nickel foam in a strong base solution, transfer it to a reaction kettle, take out the conductive substrate after heating and reacting, and obtain a nickel foam substrate (Ni-OH) treated with the alkali solution after washing and drying;

[0012] S2. Dissolve cobalt salt and 2,5-dihydroxyterephthalic acid ligand in N,N-dimethylformamide, then add a certain amount of deionized water and anhydrous ethanol and mix evenly, transfer it to a reaction kettle, add the substrate prepared in S1, and obtain a conductive substrate with Co-MOF-74 micro-rods grown on the surface after hydrothermal reaction;

[0013] S3. Dissolve the sulfur source in deionized water, then transfer it to a reaction kettle, add the substrate prepared in step S2, and obtain the NiCo-S / NiCo-OH-CL bifunctional catalyst loaded on the conductive substrate after hydrothermal reaction, washing and drying.

[0014] The present invention uses a hydrothermal sulfidation method based on a controllable ion exchange strategy to prepare NiCo-S / NiCo-OH-CL micro-rods, and the morphology is a porous micro-rod structure composed of porous nanosheets. During the hydrothermal process, Hydrolysis can produce , and then ion exchange with the organic ligand to produce hydroxide, and a sulfide / hydroxide composite catalyst can be prepared by controlling the reaction time. At the same time, the preparation method of the present invention has mild conditions, simple operation, low requirements for equipment, and is conducive to market promotion.

[0015] In the present invention, in step S1, the concentration of the strong base solution is 0.5-5 mol / L, the heating reaction temperature is 100-150 °C, and the time is 2-12 h.

[0016] In the present invention, in step S2, the amount of cobalt salt is 0.5 - 5 mmol, the amount of 2,5-dihydroxyterephthalic acid ligand is 0.5 - 5 mmol, the volume of N,N-dimethylformamide is 5 - 15 mL, the volume of deionized water is 1 - 6 mL, the volume of absolute ethanol is 1 - 6 mL, the heating reaction temperature is 80 - 200 °C, and the time is 2 - 12 h.

[0017] In the present invention, in step S3, the amount of sulfur source is 1 - 7 mmol, the heating reaction temperature is 80 - 200 °C, and the time is 2 - 24 h.

[0018] In the present invention, the strong base includes at least one of NaOH and KOH; the cobalt salt includes at least one of cobalt nitrate, cobalt sulfate, cobalt acetylacetonate, and cobalt chloride; the sulfur source includes at least one of thiourea, sodium sulfide, thioacetamide, and L-cysteine.

[0019] In the present invention, the conductive substrate can be one of carbon cloth, carbon paper, and nickel mesh.

[0020] In the present invention, based on the ion exchange strategy, samples such as Co-S / Co-OH-CL, NiCo-OH-CL, and Co-OH-CL can be correspondingly prepared by using the original conductive substrate without treatment with alkali solution and carrying out hydrothermal reaction with a strong base instead of a sulfur source.

[0021] Another object of the present invention is to provide the application of a NiCo-S / NiCo-OH-CL bifunctional catalyst with a heterostructure in auxiliary energy-saving hydrogen production and sulfur ion recovery, and the bifunctional catalyst is used in HER and SOR under alkaline conditions.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] (1) The morphology of the catalyst of the present invention is a porous micro-rod structure composed of nanoporous sheets. There are strong electronic interactions between the sulfide / hydroxide heterointerfaces and between the ligand / hydroxides, which can optimize the hydrogen atom adsorption behavior, promote the hydrogen evolution activity, and at the same time promote the generation and adsorption of sulfur intermediates, effectively catalyzing the sulfur oxidation reaction process. In addition, the catalytic electrode has the surface characteristics of being hydrophilic and hydrophobic to sulfur, further promoting the catalytic reaction.

[0024] (2) For the HER catalytic reaction, in a 1M NaOH + 2M Na 2 S solution, the linear sweep voltammetry results at a scan rate of 2 mV / s show that the overpotential of the NiCo-S / NiCo-OH-CL catalyst at the current density is only 169 mV. For the SOR catalytic reaction, the NiCo-S / NiCo-OH-CL catalyst at 10 and At the current density, the oxidation potentials are 0.254 and 0.263 V vs. RHE, respectively.

[0025] (3) The overall water splitting hydrogen production system assembled based on the NiCo-S / NiCo-OH-CL catalyst of the present invention has an ultra-low electrolysis voltage (0.62 V), a high Faraday efficiency (>95%), a low power consumption (1.48 kWh per m 3 H 2 ) and an ultra-high durability (3200 hours) at the current density. This material can be used as a catalyst for HER and SOR reactions in hydrogen production and environmental protection, with high catalytic activity and excellent durability.

[0026] (4) The present invention prepares a sulfide / ligand-modified hydroxide composite catalyst by a hydrothermal sulfidation method based on a controllable ion exchange strategy, enabling the catalyst to have a loose porous structure and abundant heterointerfaces, which can promote the rapid progress of catalytic reactions. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is the SEM image of the NiCo-S / NiCo-OH-CL bifunctional catalyst of Example 1 of the present invention; wherein Figure 1 a is the electron microscope image at a scale of 20 μm, Figure 1 b is the electron microscope image at a scale of 2 μm;

[0028] Figure 2 is the XRD pattern of the NiCo-S / NiCo-OH-CL bifunctional catalyst of Example 1 of the present invention;

[0029] Figure 3 is the HER performance of the NiCo-S / NiCo-OH-CL bifunctional catalyst of Example 1 of the present invention in 1M NaOH + 2M Na 2 S solution, polarization curve (3a), Tafel slope curve (3b), electrochemically active surface area (3c) and stability test (3d) at a scan rate of 2 mV / s;

[0030] Figure 4 is the SOR performance of the NiCo-S / NiCo-OH-CL bifunctional catalyst of Example 1 of the present invention in 1M NaOH + 2M Na 2 S solution, polarization curve (4a), Tafel slope curve (4b), comparison chart of polarization curves of SOR reaction and OER reaction (4c), and stability test curve (4d) at a scan rate of 2 mV / s;

[0031] Figure 5It is the overall water splitting performance of the NiCo-S / NiCo-OH-CL bifunctional catalyst of Example 1 of the present invention, including the overall water splitting diagram (5a), the overall water splitting polarization curve (5b), the ultraviolet-visible spectrum (5c), the XRD diagram of the collected sulfur product (5d) and photos, as well as the stability test curve (5e). Detailed implementation manners

[0032] Hereinafter, the applicant will further elaborate on the method of the present invention with specific examples, aiming to enable those skilled in the art to clearly understand the present invention. However, the following examples should not be construed in any way as limiting the scope of protection claimed in the claims of the present invention.

[0033] Example 1

[0034] This example provides a preparation method of a NiCo-S / NiCo-OH-CL bifunctional catalyst with a heterostructure, including the following steps:

[0035] S1. Prepare a NaOH solution with a concentration of 3M, transfer it to a reaction kettle, add a nickel foam substrate (2 cm × 2.5 cm), keep it at 120 °C for 6 h, and after washing and drying, obtain a Ni-OH substrate treated with the alkali solution;

[0036] S2. Dissolve 2 mmol of Co(NO) 3 ·6H 2 O and 0.5 mmol of 2,5-dihydroxyterephthalic acid ligand in 20 mL of N,N-dimethylformamide, then add 1.25 mL of deionized water and 1.25 mL of absolute ethanol and mix evenly, transfer it to a reaction kettle, add the substrate prepared in S1, keep it at 120 °C for 24 h, and after washing and drying, obtain a conductive substrate with Co-MOF-74 micro-rods grown on the surface;

[0037] S3. Dissolve 3 mmol of Na 2 S 9H 2 O in 25 mL of deionized water, then transfer it to a reaction kettle, add the substrate prepared in step S2, keep it at 120 °C for 3 h, and after washing and drying, obtain the NiCo-S / NiCo-OH-CL bifunctional catalyst supported on the conductive substrate.

[0038] Taking the NiCo-S / NiCo-OH-CL catalyst of this example as an example, its morphological characteristics are as Figure 1As shown, uniform array-structured micro-rods of NiCo-S / NiCo-OH with a size of 2 μm can be observed. This helps to enhance the structural stability, significantly increase the specific surface area of the catalyst, enabling more catalytic sites to be exposed to the electrolyte, improving the activity of the electrocatalytic reaction, and promoting the adsorption of reactants and the desorption of products. The XRD pattern is as follows Figure 2 shown, the NiCo-S / NiCo-OH-CL catalyst has distinct diffraction peaks. The characteristic diffraction peaks at 19.1°, 32.5°, 37.9°, and 51.4° respectively correspond to the (001), (100), (101), and (102) crystal planes of hexagonal Co(OH) 2 (PDF card number: 00-030-0443). Meanwhile, the characteristic peaks at 31.5°, 38.2°, 50.3°, and 55.1° respectively correspond to the (311), (400), (511), and (440) lattice planes of cubic Co 3 S 4 (PDF card number: 00-047-1738).

[0039] In this example, the electrocatalytic performance of the NiCo-S / NiCo-OH-CL catalyst was measured by an electrochemical workstation (CHI660E). In the electrocatalytic test, a self-supporting NiCo-S / NiCo-OH-CL catalytic electrode, a graphite rod electrode, and a mercury oxide electrode were used as the working electrode, counter electrode, and reference electrode respectively to form a standard three-electrode test system. By using the NiCo-S / NiCo-OH-CL electrode as the catalytic cathode (1.0 M NaOH) for the HER half-reaction and the catalytic anode (1.0 M NaOH + 2.0 M Na 2 S) for the SOR half-reaction to form an electrocatalytic coupling system, which was separated by an exchange membrane in the middle.

[0040] Taking the NiCo-S / NiCo-OH-CL catalytic electrode prepared in this example as the working electrode, its HER performance is as follows Figure 3 shown in a. The overpotentials of the NiCo-S / NiCo-OH heterostructure catalyst material for HER performance at 100 and are 239 mV and 287 mV, which are much smaller than those of Co-S / Co-OH-CL (258 mV and 330 mV), NiCo-OH-CL (249 mV and 317 mV), and Co-OH-CL (270 mV and 410 mV). The Tafel slope curve is usually used to characterize the kinetics of the catalytic reaction. As shown in Figure 3 b, the Tafel slope of the NiCo-S / NiCo-OH-CL catalyst is , which is much lower than that of Co-S / Co-OH-CL ( ), NiCo-OH-CL( ), and Co-OH-CL( ), showing faster HER reaction kinetics. The electrochemically active surface area (ECSA) was evaluated by measuring the double-layer capacitance (C dl ), which can be obtained by cyclic voltammetry (CV) measurements at different scan rates in the non-Faradaic region. As shown in Figure 3 c, the C value of NiCo-S / NiCo-OH-CL( dl ) is much larger than that of Co-S / Co-OH-CL( ), NiCo-OH-CL( ), and Co-OH-CL( ), indicating a larger electrochemically active surface area. In addition, a stability test was carried out at a current density for 120 h, showing excellent long-term durability with negligible decay ( Figure 3 d).

[0041] The SOR catalytic performance is shown in Figure 4 a. The NiCo-S / NiCo-OH heterostructure catalytic material only requires ultra-low oxidation potentials, namely 0.254 and 0.264 V vs. RHE, to achieve anodic current densities of 10 and , which is significantly better than the Co-S / Co-OH-CL, NiCo-OH-CL, and Co-OH-CL catalysts. This result indicates that constructing a heterostructure and Ni doping can greatly improve the SOR activity. The Tafel slope of the NiCo-S / NiCo-OH-CL heterostructure catalyst is , much lower than that of Co-S / Co-OH-CL( ), NiCo-OH-CL( ), and Co-OH-CL( ), showing faster SOR reaction kinetics ( Figure 4 b). Compared with the OER reaction, the potentials of the NiCo-S / NiCo-OH-CL catalyst at current densities of 100, 200, and are significantly reduced by 1.410, 1.497, and 1.657 V, further confirming the lower thermodynamic potential of the SOR reaction than the OER reaction ( Figure 4 c). In addition, a SOR stability test was carried out at a current density of for up to 100 h, and the NiCo-S / NiCo-OH-CL catalyst showed excellent stability ( Figure 4 d).

[0042] Figure 5Figure a shows the performance evaluation of overall water splitting in a two - electrode water electrolyzer that simultaneously uses NiCo - S / NiCo - OH - Cl as the anode and cathode. In the cathode region, a large number of hydrogen bubbles can be observed evolving from the cathode electrode; simultaneously, yellow substances are deposited at the anode, indicating the gradual accumulation of sulfides during the sulfur oxidation process. The LSV curve ( Figure 5 b) shows that at the same voltage, the SOR||HER electrolyzer can exhibit a higher current density compared to the traditional OER||HER electrolyzer (the reason is that the anode in the OER||HER electrolyzer is the OER reaction with slower kinetics), which also indicates that SOR plays a key role in reducing the electrolysis potential of water. The SOR||HER electrolysis system assembled with NiCo - S / NiCo - OH as the anode and cathode reaches the current density only requires 0.62 V. To determine the mechanism of the SOR process, UV - Vis spectroscopy was performed to analyze the products in the electrolyte, Figure 5 c shows obvious absorption peaks at 300 and 370 nm, which increase significantly with the extension of the electrolysis time, confirming the presence of short - chain polysulfides. The yellow product obtained by acidifying the anode electrolyte, centrifuging, washing, and drying ( Figure 5 d), according to the X - ray diffraction pattern, is confirmed to contain sulfur (JCPDS No. 01 - 089 - 2600). As shown in Figure 5 e, under the condition of a current density of , the chronopotentiometry was used to conduct a long - term stability test on the SOR||HER electrolysis system, which remained stable during the continuous 3200 - hour electrolysis process, demonstrating excellent long - term electrolysis durability.

[0043] Example 2:

[0044] Preparation method of NiCo - S / NiCo - OH - Cl catalytic electrode, which includes the following steps:

[0045] S1. Prepare a 2M NaOH solution, transfer it to a reaction kettle, add a nickel foam substrate (2 cm×2.5 cm), keep it at 100 °C for 4 h, and after washing and drying, obtain the Ni - OH substrate treated with the alkali solution;

[0046] S2. Dissolve 1 mmol of Co(NO) 3 ·6H 2 O and 2 mmol of 2,5 - dihydroxyterephthalic acid ligand in 20 mL of N,N - dimethylformamide, then add 1.25 mL of deionized water and 1.25 mL of absolute ethanol and mix evenly, transfer it to a reaction kettle, add the substrate prepared in S1, keep it at 120 °C for 12 h, and after washing and drying, obtain the conductive substrate with Co - MOF - 74 micro - rods grown on the surface;

[0047] S3. Dissolve 3 mmol of Na 2 S 9H 2 O in 25 mL of deionized water, then transfer it to a reaction kettle, add the substrate prepared in step S2, keep it warm at 120 °C for 12 h, and obtain the NiCo-S / NiCo-OH-CL bifunctional catalyst supported on the conductive substrate after washing and drying.

[0048] For the NiCo-S / NiCo-OH-CL catalyst prepared in this example, corresponding to the HER reaction, and the overpotentials at the current density are only 225 mV and 296 mV; for the SOR reaction, and the overpotentials at the current density are 0.31 and 0.39 V vs. RHE, respectively.

[0049] Example 3:

[0050] Preparation method of Co-S / Co-OH-CL catalytic electrode, which includes the following steps:

[0051] S1. Dissolve 1 mmol of Co(NO) 3 ·6H 2 O and 2 mmol of 2,5-dihydroxyterephthalic acid ligand in 20 mL of N,N-dimethylformamide, then add 1.25 mL of deionized water and 1.25 mL of absolute ethanol, mix evenly, transfer it to a reaction kettle, add the cleaned nickel foam substrate, keep it warm at 120 °C for 24 h, and obtain the conductive substrate with Co-MOF-74 micron rods grown on the surface after washing and drying;

[0052] S2. Dissolve 3 mmol of Na 2 S 9H 2 O in 25 mL of deionized water, then transfer it to a reaction kettle, add the substrate prepared in step S2, keep it warm at 120 °C for 3 h, and obtain the Co-S / Co-OH-CL bifunctional catalyst supported on the conductive substrate after washing and drying.

[0053] Using the Co-S / Co-OH-CL catalytic electrode prepared in this example as the working electrode, for the HER catalytic reaction, in 1M NaOH / 2M Na 2 S solution, the linear sweep voltammetry results at a scan rate of 2 mV / s show that for the NiCo-S / NiCo-OH-CL catalyst prepared in this example, corresponding to the HER reaction, and the overpotentials at the current density are only 258 mV and 330 mV; for the SOR reaction, and The oxidation potentials at the current densities are 0.26 and 0.38 V vs. RHE, respectively.

[0054] Example 4:

[0055] A preparation method of a NiCo-OH-CL catalytic electrode, which comprises the following steps:

[0056] S1. Prepare a NaOH solution with a concentration of 3 M, transfer it to a reaction kettle, add a nickel foam substrate (2 cm × 2.5 cm), keep it warm at 120 °C for 6 h, and obtain a Ni-OH substrate treated with an alkali solution after washing and drying;

[0057] S2. Dissolve 2 mmol of Co(NO) 3 ·6H 2 O and 0.5 mmol of 2,5-dihydroxyterephthalic acid ligand in 20 mL of N,N-dimethylformamide, then add 1.25 mL of deionized water and 1.25 mL of absolute ethanol and mix evenly, transfer it to a reaction kettle, add the substrate prepared in S1, keep it warm at 120 °C for 24 h, and obtain a conductive substrate with Co-MOF-74 micron rods grown on the surface after washing and drying;

[0058] S3. Dissolve 3 mmol of NaOH in 25 mL of deionized water, then transfer it to a reaction kettle, add the substrate prepared in step S2, keep it warm at 120 °C for 3 h, and obtain a NiCo-OH-CL bifunctional catalyst supported on a conductive substrate after washing and drying.

[0059] Using the NiCo-OH-CL catalytic electrode prepared in this example as the working electrode, for the HER catalytic reaction, in 1 M NaOH / 2 M Na 2 S solution, the linear sweep voltammetry results at a scan rate of 2 mV / s show that the NiCo-OH-CL catalyst prepared in this example, corresponding to the HER reaction, and the overpotentials at the current densities are only 249 mV and 317 mV; for the SOR reaction, and the oxidation potentials at the current densities are 0.26 and 0.55 V vs. RHE, respectively.

[0060] Example 5:

[0061] A preparation method of a Co-OH-CL catalytic electrode, which comprises the following steps:

[0062] S1. Dissolve 2 mmol of Co(NO) 3 ·6H 20 mmol and 0.5 mmol of 2,5-dihydroxyterephthalic acid ligand were dissolved in 20 mL of N,N-dimethylformamide, then 1.25 mL of deionized water and 1.25 mL of absolute ethanol were added and mixed evenly. The mixture was transferred to a reaction kettle, and a cleaned nickel foam substrate was added. It was kept at 120 °C for 24 h, and after washing and drying, a conductive substrate with Co-MOF-74 micron rods grown on the surface was obtained;

[0063] S2. 3 mmol of NaOH was dissolved in 25 mL of deionized water, then transferred to a reaction kettle, and the substrate prepared in step S2 was added. It was kept at 120 °C for 3 h, and after washing and drying, the Co-OH-CL bifunctional catalyst supported on the conductive substrate could be obtained.

[0064] Using the Co-OH-CL catalytic electrode prepared in this example as the working electrode, for the HER catalytic reaction, in 1M NaOH / 2M Na 2 S solution, the linear sweep voltammetry results at a scan rate of 2 mV / s showed that the NiCo-OH-CL catalyst prepared in this example, corresponding to the HER reaction, and the overpotentials of the current density were only 270 mV and 410 mV; for the SOR reaction, and the oxidation potentials at the current density were 0.27 and 0.49 V vs. RHE, respectively.

Claims

1. A NiCo-S / NiCo-OH-CL bifunctional catalyst with a heterogeneous structure, characterized in that: The catalyst has a one-dimensional porous microrod structure and is formed by assembling porous nanosheets. The diameter of the microrod is 0.8-2.5 μm.

2. The NiCo-S / NiCo-OH-CL bifunctional catalyst with heterogeneous structure according to claim 1, characterized in that: The microrods are attached to a conductive substrate.

3. The method for preparing a NiCo-S / NiCo-OH-CL bifunctional catalyst with a heterogeneous structure according to claim 1 or 2, characterized in that: The following steps are involved: S1. Immersing the nickel foam in a strong alkaline solution and transferring it to a reactor, taking out the conductive substrate after heating the reaction, washing and drying it to obtain an alkali-treated nickel foam substrate (Ni-OH); S2. dissolving the cobalt salt and 2,5-dihydroxyterephthalic acid ligand in N,N-dimethylformamide, then adding a certain amount of deionized water and anhydrous ethanol to mix evenly, transferring to a reactor, adding the substrate prepared in S1, and obtaining a conductive substrate with Co-MOF-74 microrods grown on the surface after a hydrothermal reaction; S3. The sulfur source is dissolved in deionized water, and then transferred to a reactor, and the substrate prepared in step S2 is added. After hydrothermal reaction, washing and drying, a NiCo-S / NiCo-OH-CL bifunctional catalyst supported on a conductive substrate can be obtained.

4. The method for preparing a NiCo-S / NiCo-OH-CL bifunctional catalyst with a heterogeneous structure according to claim 3, characterized in that: In step S1, the concentration of the strong alkaline solution is 0.5-5 mol / L, the heating reaction temperature is 100-150° C., and the time is 2-12 h.

5. The method for preparing a NiCo-S / NiCo-OH-CL bifunctional catalyst with a heterogeneous structure according to claim 3, characterized in that: In step S2, the amount of cobalt salt is 0.5-5 mmol, the amount of 2,5-dihydroxyterephthalic acid ligand is 0.5-5 mmol, the volume of N,N-dimethylformamide is 5-15 mL, the volume of deionized water is 1-6 mL, the volume of anhydrous ethanol is 1-6 mL, the heating reaction temperature is 80-200° C., and the time is 2-12 h.

6. The method for preparing a NiCo-S / NiCo-OH-CL bifunctional catalyst with a heterogeneous structure according to claim 3, characterized in that: In step S3, the amount of sulfur source is 1-7 mmol, the heating reaction temperature is 80-200° C., and the time is 2-24 h.

7. The method for preparing a NiCo-S / NiCo-OH-CL bifunctional catalyst with a heterogeneous structure according to claim 3, characterized in that: The strong base includes at least one of NaOH and KOH; the cobalt salt includes at least one of cobalt nitrate, cobalt sulfate, cobalt acetylacetonate and cobalt chloride; and the sulfur source includes at least one of thiourea, sodium sulfide, thioacetamide and L-cysteine.

8. According to the method for preparing a NiCo-S / NiCo-OH-CL bifunctional catalyst with a heterogeneous structure as described in claim 3, based on the ion exchange strategy, Co-S / Co-OH-CL, NiCo-OH-CL, and Co-OH-CL samples can be prepared correspondingly by using an original conductive substrate that is not treated with alkali solution and using a strong base instead of a sulfur source for hydrothermal reaction.

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