Hierarchical heterostructure electrocatalyst for electrocatalytic oxidation of ethanol and preparation method and application thereof

Abstract

The present application belongs to the field of electrocatalytic material and energy conversion technology, and particularly relates to a hierarchical heterostructure electrocatalyst for electrocatalytic oxidation of ethanol and a preparation method and application thereof. The preparation method comprises the following steps: providing a conductive substrate; growing an amorphous porous transition metal sulfide layer on the surface of the conductive substrate in situ to obtain a composite intermediate; the transition metal sulfide is nickel sulfide; growing a two-dimensional metal organic framework nanosheet array on the surface of the composite intermediate in situ to obtain the target product. The catalyst of the present application can still maintain a low working voltage under high current density conditions, is conducive to electron transfer and reaction at the interface, and can solve the problems of weak interface coupling, harsh preparation conditions, easy destruction of structure and poor stability under high current density in the prior art. The present application has a good application prospect in ethanol-assisted water electrolysis for hydrogen production and anion exchange membrane electrolytic cell.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic materials and energy conversion technology, specifically relating to a hierarchical heterostructure electrocatalyst for the electrocatalytic oxidation of ethanol, its preparation method and application. Background Technology

[0002] Ethanol electrocatalytic oxidation (EOR), as a biomass energy conversion pathway, can replace the oxygen evolution reaction (OER) in water electrolysis, significantly reducing hydrogen production energy consumption. Developing efficient and stable anode catalysts is key to realizing this technology.

[0003] Metal-organic framework (MOF) materials are widely used in electrocatalysis due to their high specific surface area, tunable coordination structure, and abundant metal active centers. Existing anode catalyst technologies are mainly divided into three categories: first, obtaining metal oxide or sulfide catalysts through high-temperature calcination of MOFs; second, constructing heterostructures through physical composite methods; and third, constructing composite materials through multi-step hydrothermal methods. While these methods have improved catalytic performance to some extent, they still have the following problems: (1) the heterostructure interface coupling is weak, making it difficult to fully utilize the interface synergistic effect; (2) the preparation process is complex or requires high-temperature conditions, resulting in high energy consumption; (3) the material has poor structural stability during the reaction process; and (4) performance degradation is significant at high current densities. Therefore, how to construct non-noble metal-based heterostructure catalysts with strong interface coupling effects on conductive substrates under mild conditions, while ensuring high activity and stability, is a pressing technical problem that needs to be solved. Summary of the Invention

[0004] The present invention aims to overcome the shortcomings of the prior art by providing a hierarchical heterostructure electrocatalyst for the electrocatalytic oxidation of ethanol and its preparation method, so as to solve the problems of weak catalyst interface coupling, harsh preparation conditions, easy structural destruction and poor stability under high current density in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention is implemented as follows: A method for preparing a hierarchical heterostructure electrocatalyst for the electrocatalytic oxidation of ethanol, characterized by comprising the following steps: (1) Provide a conductive substrate; (2) An amorphous porous transition metal sulfide layer is grown in situ on the surface of the conductive substrate described in step (1) to obtain a composite intermediate; (3) A two-dimensional metal-organic framework nanosheet array is grown in situ on the surface of the composite intermediate described in step (2) to obtain the hierarchical heterostructure electrocatalyst for the electrocatalytic oxidation of ethanol.

[0006] Preferably, the transition metal sulfide in step (2) is nickel sulfide; the in-situ growth includes: first performing surface oxidation activation treatment on the conductive substrate, and then placing it in an aqueous solution containing a sulfur source for reaction.

[0007] Preferably, the two-dimensional metal-organic framework in step (3) is Co-ZIF-L, and its in-situ growth process includes preparing a precursor solution containing cobalt salt and 2-methylimidazole, immersing the composite intermediate in step (2) in it, and allowing it to react at room temperature.

[0008] Preferably, the conductive substrate is at least one of nickel foam, carbon cloth, carbon paper, or metal mesh.

[0009] Another objective of this invention is to provide a hierarchical heterostructure electrocatalyst prepared by the above-described preparation method.

[0010] Preferably, the hierarchical heterostructure electrocatalyst comprises: a. Conductive substrate; b. An amorphous porous transition metal sulfide layer, in situ bonded to the surface of the conductive substrate; c. A two-dimensional metal-organic framework nanosheet array is in situ bonded to the surface of the amorphous porous transition metal sulfide layer and forms a tight heterogeneous interface with the layer.

[0011] Preferably, the amorphous porous transition metal sulfide layer has a three-dimensional interconnected porous structure; the two-dimensional metal-organic framework nanosheet array is Co-ZIF-L nanosheets, grown on the surface of the amorphous porous transition metal sulfide layer, forming a hierarchical structure in which the three-dimensional framework and two-dimensional nanosheets work together.

[0012] The present invention also provides an application of the above-mentioned hierarchical heterostructure electrocatalyst in the electrocatalytic oxidation reaction of ethanol, wherein the catalyst is used as the working anode electrode in an alkaline ethanol oxidation reaction system.

[0013] The present invention also provides a method for producing hydrogen by ethanol-assisted electrolysis of water, which uses the above-mentioned hierarchical heterostructure electrocatalyst as the anode material and assembles it in an anion exchange membrane electrolyzer to catalyze the ethanol oxidation reaction, thereby reducing the electrolyzer voltage of the cathode hydrogen evolution reaction.

[0014] Preferably, the electrolyte used is a mixed aqueous solution containing 0.5–1.0 mol / L potassium hydroxide and 0.1–0.5 mol / L ethanol.

[0015] This invention does not rely on high-temperature pyrolysis, but instead employs a stepwise in-situ growth strategy to progressively construct a "three-dimensional-two-dimensional" hierarchical structure with a tight heterogeneous interface on a conductive substrate. Its core lies in using a highly conductive three-dimensional porous nickel foam as a framework, generating amorphous porous nickel sulfide (NiS) in situ on its surface as a transition layer, and then growing a two-dimensional Co-ZIF-L nanosheet array in situ on this transition layer, ultimately forming a NiS@Co-ZIF-L / NF hierarchical heterostructure electrocatalyst.

[0016] Compared with the prior art, the present invention has achieved the following substantial progress: (1) In this invention, due to the in-situ growth of the NiS layer and the Co-ZIF-L layer to form an atomic-level contact heterostructure interface, significant electron rearrangement occurs at the interface (see Figures 3-5 This electronic effect lowers the activation energy barrier of key steps in the ethanol oxidation reaction, allowing the catalyst to maintain a low operating voltage even under high current density conditions, which is beneficial for electron transfer and reaction at the interface.

[0017] (2) The amorphous NiS layer of the present invention can simultaneously anchor the conductive substrate and MOF nanosheets, thereby avoiding the shedding of active materials during the reaction process. At the same time, the multi-level channels formed by the foam pores, NiS pores and Co-ZIF-L interlayer pores can ensure the rapid transport of reactants to active sites and the timely release of gases, and have good stability and energy-saving effect.

[0018] (3) The present invention can complete MOF growth at room temperature. The maximum temperature of the entire preparation process is 60°C, which completely avoids the structural collapse and metal agglomeration problems caused by traditional high-temperature calcination. It effectively avoids material structure damage and reduces energy consumption. The two-dimensional morphology, crystal structure and coordination environment of Co-ZIF-L are completely preserved, ensuring the utilization rate of high-density active sites. Attached Figure Description

[0019] Figure 1 This is a scanning electron microscope image of the NiS@Co-ZIF-L / NF catalyst prepared in Example 1 of this invention; Figure 2 The image shows the X-ray diffraction (XRD) pattern of the catalyst prepared in Example 1 of this invention. Figure 3 The images show the Raman spectra of the NiS@Co-ZIF-L / NF catalyst of this invention and the comparative samples NiS / NF and Co-ZIF-L / NF. Figure 4 The Fourier transform infrared (FTIR) spectra of the NiS@Co-ZIF-L / NF catalyst and Co-ZIF-L / NF of this invention are shown below. Figure 5The image shows the X-ray photoelectron spectroscopy (XPS) spectrum of the catalyst of this invention. Figures 6-8 The graph shows the electrochemical performance test results of this invention. Figure 9 This is a performance comparison diagram between the AEM electrolyzer using the catalyst of this invention as the anode and a conventional oxygen evolution reaction electrolyzer. Detailed Implementation

[0020] The present invention will now be described in detail through specific embodiments. These embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art. As used throughout the specification and claims, the terms "comprising" or "including" are open-ended and are interpreted as "comprising but not limited to". The following description is a preferred embodiment for carrying out the invention; however, this description is intended to illustrate the general principles of the specification and is not intended to limit the scope of the invention. The scope of protection of the invention is determined by the appended claims. Unless otherwise specified, all reagents and materials used in the present invention are commercially available.

[0021] The term "Co-ZIF-L" as used in this invention refers to a product made of Co. 2+ The metal-organic framework nanosheets, consisting of metal nodes and 2-methylimidazole (2-MeIM) as organic ligands, self-assemble in aqueous solution at room temperature. These leaf-like two-dimensional metal-organic framework nanosheets belong to the layered MOF topology within the zeolitic imidazolate framework (ZIF) family. The nanosheets are approximately 10–50 nm thick and exhibit a high density of exposed metal active sites. The "amorphous NiS" referred to in this invention refers to a nickel sulfide layer obtained through sulfidation treatment. XRD analysis shows no obvious NiS crystalline phase characteristic diffraction peaks in the 10–80° range, indicating an amorphous (non-crystalline) structure, distinct from crystalline α-NiS or β-NiS. This structure facilitates the exposure of more coordination unsaturated sites and allows for a more uniform heterogeneous interface with the subsequently grown Co-ZIF-L.

[0022] This invention is implemented through the following specific steps: (1) Clean the conductive substrate (preferably nickel foam) to remove the surface oxide layer and contaminants, so as to provide a clean surface for subsequent in-situ growth.

[0023] (2) Active sites are introduced on the surface of nickel foam (NF) through surface oxidation activation treatment, followed by reaction in an aqueous solution containing sulfur source (about 60°C), so that amorphous NiS is generated in situ in the form of a three-dimensional interconnected porous structure and firmly bonded to the substrate surface. This layer has high conductivity, large specific surface area and open mass transfer channels, and at the same time provides a chemically compatible surface rich in nucleation sites for the subsequent growth of MOF.

[0024] (3) At room temperature, the substrate with the NiS layer was immersed in a precursor solution containing cobalt salt and 2-methylimidazole. Utilizing the abundant metal coordination unsaturated sites on the NiS surface, Co-ZIF-L nanosheets were induced to nucleate and grow in situ, forming a two-dimensional nanosheet array. This process does not require high temperature or an external electric field, and the ordered assembly of MOFs was achieved under mild conditions.

[0025] In the "three-dimensional-two-dimensional" hierarchical structure of the tight heterogeneous interface constructed in this invention, each layer is functionally irreplaceable and achieves tight coupling through in-situ chemical bonding, which is different from the physical mixing or multi-step independent synthesis in the prior art.

[0026] Example 1

[0027] A method for preparing a hierarchical heterostructure electrocatalyst includes the following steps: (1) Nickel foam pretreatment: Commercial nickel foam (porosity approximately 110 ppi, thickness 1.5 mm) was cut to appropriate sizes and then immersed in 3 mol / L hydrochloric acid solution for 10 min to remove the surface oxide layer. It was then ultrasonically cleaned with anhydrous ethanol and deionized water for 10 min each, and the process was repeated 3 times to thoroughly remove organic contaminants. The cleaned nickel foam was then dried in a vacuum drying oven at 60℃ for 2 h for later use.

[0028] (2) In-situ growth of amorphous NiS layer: The pretreated nickel foam was immersed in a 0.1 mol / L ammonium persulfate ((NH4)2S2O8) aqueous solution and left to stand at room temperature for 30 min to allow mild oxidation activation of the nickel foam surface, introducing abundant active nucleation sites. Subsequently, the activated nickel foam was transferred to a deionized aqueous solution (40 mL) containing 0.3 mol / L thiourea (CH4N2S) and reacted in a 60℃ constant temperature water bath for 6 h. After the reaction, the substrate was removed, rinsed thoroughly with deionized water 3 times, and dried in a 60℃ vacuum drying oven for 2 h to obtain a NiS / NF substrate with an amorphous nickel sulfide layer in situ generated on the nickel foam surface. The generated NiS layer showed no obvious characteristic diffraction peaks by XRD, confirming its amorphous morphology; scanning electron microscopy showed that it had a three-dimensional interconnected porous structure, which could provide good conductive channels, large specific surface area and open mass transfer channels.

[0029] (3) In-situ growth of Co-ZIF-L nanosheet array: Cobalt nitrate hexahydrate (Co(NO3)2·6H2O, 0.582 g, 2 mmol) was dissolved in 20 mL of deionized water to prepare a cobalt salt solution, and 2-methylimidazole (2-MeIM, 1.312 g, 16 mmol) was dissolved in 20 mL of deionized water to prepare a ligand solution. After the two solutions were mixed evenly, the NiS / NF substrate was quickly immersed vertically into the mixed precursor solution and allowed to stand at room temperature (25 °C) for 12 h to allow the Co-ZIF-L nanosheets to self-assemble and grow in situ on the NiS surface. After the reaction was completed, the substrate was removed and gently rinsed three times with deionized water to remove unbound precursors. It was then dried in a vacuum drying oven at 60 °C for 2 h to obtain the target catalyst NiS@Co-ZIF-L / NF. The prepared Co-ZIF-L nanosheet array had a complete two-dimensional morphology and maintained its crystalline structure and original coordination environment.

[0030] See attached diagram. Figure 1 This is a scanning electron microscope image of the NiS@Co-ZIF-L / NF catalyst prepared in this embodiment. Figure 2 Its XRD pattern. Figure 3 The image shows a Raman spectrum. Figure 4 For FTIR spectra, Figure 5 For XPS plots, Figures 6-8 The results show the electrochemical performance test results. The results indicate that the catalyst of this invention exhibits excellent electrocatalytic activity in the alkaline ethanol oxidation reaction system, maintaining a low operating potential even under high current density conditions, and possessing a small Tafel slope and low charge transfer impedance.

[0031] Example 2

[0032] Preparation of control samples To verify the contribution of the NiS interlayer and in-situ growth strategy to catalytic performance, the following two control samples were prepared for use. Figure 3 , Figures 6-8 A comparative analysis.

[0033] (1) Preparation of NiS / NF: The nickel foam pretreatment steps are the same as those in Example 1, step (1). Then, the in-situ growth of the amorphous NiS layer is completed according to step (2) of Example 1, without the subsequent Co-ZIF-L growth step, thus obtaining the NiS / NF control electrode. This sample is used to eliminate the contribution of NiS alone to the performance and to prove the effect of the introduction of Co-ZIF-L on the enhancement of catalytic activity.

[0034] (2) Preparation of Co-ZIF-L / NF: The nickel foam pretreatment steps are the same as step (1) in Example 1. The pretreated bare nickel foam is used directly to replace the NiS / NF substrate, and the remaining steps are the same as step (3) in Example 1 to obtain the Co-ZIF-L / NF control electrode. This sample is used to eliminate the contribution of the Co-ZIF-L component alone to the performance, and at the same time to verify the necessity of the NiS interlayer for the ordered growth of Co-ZIF-L and interface coupling.

[0035] Application examples

[0036] The catalyst of this invention exhibits excellent electrocatalytic performance in a typical alkaline system. The electrolyte can be a mixed solution of potassium hydroxide and ethanol, wherein the concentration of potassium hydroxide is 0.5–1.0 mol / L and the concentration of ethanol is 0.1–0.5 mol / L. In this system, the catalyst of this invention can achieve efficient ethanol oxidation at a relatively low potential and exhibits a small Tafel slope and low charge transfer impedance.

[0037] When used in membrane electrode assembly (MEA) electrolyzers, the catalyst of this invention, as an anode material, can operate stably under high current density conditions, significantly reducing the overall electrolysis voltage and exhibiting a clear energy-saving advantage compared to traditional oxygen evolution reaction (OER) systems. The performance of the catalyst of this invention compared to conventional OER anodes is shown in [link to relevant documentation]. Figure 9 .

[0038] The above embodiments are used to explain and illustrate the present invention, but not to limit the present invention. Any modifications and changes made to the present invention within the spirit and scope of the claims fall within the protection scope of the present invention.

Claims

1. A method for preparing a hierarchical heterostructure electrocatalyst for the electrocatalytic oxidation of ethanol, characterized in that, Includes the following steps: (1) Provide a conductive substrate; (2) An amorphous porous transition metal sulfide layer is grown in situ on the surface of the conductive substrate described in step (1) to obtain a composite intermediate; (3) A two-dimensional metal-organic framework nanosheet array is grown in situ on the surface of the composite intermediate described in step (2) to obtain the hierarchical heterostructure electrocatalyst for the electrocatalytic oxidation of ethanol.

2. The method for preparing the hierarchical heterostructure electrocatalyst for the electrocatalytic oxidation of ethanol according to claim 1, characterized in that, The transition metal sulfide mentioned in step (2) is nickel sulfide; the in-situ growth includes: first performing surface oxidation activation treatment on the conductive substrate, and then placing it in an aqueous solution containing sulfur source for reaction.

3. The method for preparing the hierarchical heterostructure electrocatalyst for the electrocatalytic oxidation of ethanol according to claim 2, characterized in that, The two-dimensional metal-organic framework mentioned in step (3) is Co-ZIF-L. Its in-situ growth process includes preparing a precursor solution containing cobalt salt and 2-methylimidazole, immersing the composite intermediate mentioned in step (2) in it, and allowing it to react at room temperature.

4. The method for preparing the hierarchical heterostructure electrocatalyst for the electrocatalytic oxidation of ethanol according to claim 1, characterized in that, The conductive substrate is at least one of nickel foam, carbon cloth, carbon paper, or metal mesh.

5. A hierarchical heterostructure electrocatalyst, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 4.

6. A hierarchical heterostructure electrocatalyst as described in claim 5, characterized in that, include: a. Conductive substrate; b. An amorphous porous transition metal sulfide layer, in situ bonded to the surface of the conductive substrate; c. A two-dimensional metal-organic framework nanosheet array is in situ bonded to the surface of the amorphous porous transition metal sulfide layer and forms a tight heterogeneous interface with the layer.

7. The hierarchical heterostructure electrocatalyst according to claim 6, characterized in that, The amorphous porous transition metal sulfide layer has a three-dimensional interconnected porous structure; the two-dimensional metal-organic framework nanosheet array is a Co-ZIF-L nanosheet grown on the surface of the amorphous porous transition metal sulfide layer, forming a hierarchical structure in which the three-dimensional framework and two-dimensional nanosheets work together.

8. The application of the hierarchical heterostructure electrocatalyst according to claim 6 or 7 in the electrocatalytic oxidation of ethanol, characterized in that, The catalyst is used as the working anode electrode in the alkaline ethanol oxidation reaction system.

9. A method for producing hydrogen through ethanol-assisted water electrolysis, characterized in that, The hierarchical heterostructure electrocatalyst described in claim 6 or 7 is used as the anode material and assembled in an anion exchange membrane electrolyzer to catalyze the ethanol oxidation reaction, thereby reducing the electrolyzer voltage of the cathode hydrogen evolution reaction.

10. The method for producing hydrogen by ethanol-assisted water electrolysis according to claim 9, characterized in that, The electrolyte is a mixed aqueous solution containing 0.5–1.0 mol / L potassium hydroxide and 0.1–0.5 mol / L ethanol.

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