Silicon nanowire-confined nitrogen-doped carbon / transition metal nanocomposite electrocatalysts and their preparation and application

Abstract

The present invention belongs to the technical field of hydrogen production by electrolysis of water, and specifically relates to a silicon nanowire-constrained nitrogen-doped carbon / transition metal nanocomposite electrocatalyst, and its preparation and application. The preparation method adopts a directional coupling strategy to in-situ graft porous nitrogen-doped carbon hollow nanocages embedded with ultrafine transition metal nanoparticles onto silicon nanowires. The present invention not only forms a multi-threaded conductive network and improves the electron transfer capacity through the coupling constraint of silicon nanowires on nitrogen-doped carbon / transition metal porous hollow nanocages; at the same time, it effectively stabilizes the skeleton of the nanocage, curbs the random stacking between different nanocages, and the corresponding masking of surface active areas (sites). In addition, the porous and hollow structure of the nitrogen-doped carbon / transition metal nanocage helps to promote the transfer of hydrogen evolution reaction intermediates and gases. Therefore, the electrocatalyst exhibits excellent activity and stability in the hydrogen evolution reaction under high current.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydrogen production by electrolysis of water, and in particular relates to a silicon nanowire-constrained nitrogen-doped carbon / transition metal nanocomposite electrocatalyst and its preparation and application. Background Art

[0002] Water electrolysis is considered one of the most promising hydrogen production pathways. Its advantages include simple operation, the absence of harmful greenhouse gas emissions during hydrogen production, and its flexible coupling with renewable energy sources (such as wind or solar energy). Therefore, it has gradually become one of the most promising approaches to replace fossil fuel reforming-based hydrogen production. As the core half-reaction of electrocatalytic water splitting, the hydrogen evolution reaction (HER) involves a two-electron transfer process, and its reaction kinetics significantly influence the ultimate hydrogen production efficiency. Therefore, efficient electrocatalysts are needed to slow down the HER kinetics and lower the reaction energy barrier, thereby improving the overall hydrogen production capacity of water electrolysis. Currently, the benchmark commercial HER electrocatalysts are mainly based on the precious metal platinum (Pt). While their catalytic performance is satisfactory, the high price and scarce availability of Pt hinder the further large-scale application of such catalysts. For this reason, the development of non-precious metal-based HER catalysts that are inexpensive, simple to prepare, and yet offer superior performance has become a focus of research and industry.

[0003] Among the non-precious metal-based hydrogen evolution catalysts that have been developed, transition metal (e.g., iron (Fe), cobalt (Co), nickel (Ni))-based nanocomposites derived from metal-organic frameworks (MOFs) and coupled with porous nitrogen-doped carbon (NC) are particularly favored due to their simple and controllable preparation methods and the presence of more exposed and acid- and alkali-resistant surface active sites.

[0004] Composite carbonaceous materials with transition metal-based nano hydrogen evolution electrocatalysts can prevent the corrosion of simple transition metal-based nanomaterials in strong acid / alkaline electrolytes, and effectively realize electronic interactions, optimize the adsorption / desorption capacity of hydrogen evolution intermediates, increase their specific surface area, and expose surface active sites. Using MOFs materials (network structures constructed by metal centers and organic connectors), such as the commonly used zeolitic imidazolate frameworks (ZIFs) and Prussian blue analogues (PBAs), as precursors and annealing them is considered to be the most convenient, simple, and easily scalable method for preparing carbonaceous materials / transition metal nanocomposite catalysts (Prog. Mater. Sci. 2020, 108, 100618). In particular, thanks to the various properties of MOFs precursors, the derived carbonaceous materials / transition metal nanocomposite catalysts often have advantages such as diverse morphologies, easy composition modulation, and controllable surface structure, thereby improving the electrocatalytic hydrogen evolution activity at the final display (Prog. Mater. Sci. 2020, 108, 100618). Unfortunately, although this method has been maturely developed and widely used, there are still some bottlenecks. For example, the MOFs precursor itself is a nanostructure, which is often disordered when prepared, causing the derived composite catalyst particles to easily agglomerate, submerging the true catalytically active surface and the catalytically active sites thereon; and during the subsequent heat treatment process, due to the lack of organic ligands, the original skeleton structure of MOFs is prone to collapse, resulting in the loss of the final active sites (Adv. Funct. Mater. 2018, 28, 1801554); At the same time, the currently developed carbonaceous material / transition metal nanocomposite catalysts derived from MOFs precursors also have relatively poor mass transfer capabilities (such as slow transfer of reaction intermediates, affecting the reaction progress; and insufficient escape ability of the generated gas product H2, which in turn blocks the surface active sites). The ensuing problem is that when such materials are used as catalysts under the conditions of the high current density required for industrial water electrolysis to produce hydrogen, their hydrogen evolution catalytic activity is often unsatisfactory. Therefore, the further large-scale industrial application of such materials has always been hindered. Summary of the Invention

[0005] The present invention aims to solve the above problems and provides a silicon nanowire-constrained nitrogen-doped carbon / transition metal nanocomposite electrocatalyst and its preparation and application. The electrocatalyst has high catalytic activity and high stability and is suitable for large-scale practical production.

[0006] According to the technical solution of the present invention, the method for preparing the silicon nanowire-constrained nitrogen-doped carbon / transition metal nanocomposite electrocatalyst comprises the following steps:

[0007] S1: dispersing silicon nanowires, a surfactant, and a transition metal salt I in methanol in sequence to obtain a mixed solution I;

[0008] S2: adding 2-methylimidazole to the mixed solution I, stirring and reacting to obtain a mixed solution II;

[0009] S3: separating the mixed solution II to obtain a precipitate;

[0010] S4: dispersing the precipitate and transition metal salt II in methanol to obtain a mixed solution III;

[0011] S5: adding 2-methylimidazole to the mixed solution III, stirring and reacting to obtain a mixed solution IV;

[0012] S6: separating the mixed solution IV to obtain a precursor;

[0013] S7: thermally treating the precursor to obtain the silicon nanowire-constrained nitrogen-doped carbon / transition metal nanocomposite electrocatalyst.

[0014] Furthermore, the mass ratio of the silicon nanowires, surfactant and transition metal salt I is 1:6-9:7-12.

[0015] Furthermore, the surfactant is polyvinyl pyrrolidone (PVP). By adding the surfactant, the particle surface is stabilized to control the growth and dispersion rate of the nanoparticles.

[0016] Specifically, in step S1, silicon nanowires, polyvinyl pyrrolidone and transition metal salt I are sequentially added to methanol, and ultrasonicated for 0.5-1.5 hours to obtain a mixed solution I;

[0017] Furthermore, in step S4, the mass ratio of the precipitate to the transition metal salt II is 1:8-15.

[0018] Specifically, in step S4, the precipitate is dispersed in methanol, mixed with a methanol solution of the transition metal salt II, and ultrasonicated for 0.5-1.5 h to obtain a mixed solution III.

[0019] Furthermore, the transition metal salt I and the transition metal salt II are independently selected from one or more of cobalt salts, zinc salts, nickel salts and manganese salts.

[0020] Furthermore, the transition metal salt I and the transition metal salt II are independently selected from one or more of nitrates, acetates and hydrochlorides of transition metals.

[0021] Furthermore, in step S2, the amount of 2-methylimidazole added is 15-40 times the mass of the silicon nanowires.

[0022] Furthermore, in step S5, the amount of 2-methylimidazole added is 8-16 times the mass of the precipitate.

[0023] Furthermore, in steps S2 and S4, 2-methylimidazole is added in the form of a solution, and the solvent is methanol; the stirring reaction time is 1-3 hours and 12-36 hours, respectively.

[0024] Furthermore, in steps S3 and S5, the specific separation operations are as follows: centrifugation, removal of the supernatant, washing the obtained precipitate by multiple centrifugations, and freeze-drying for 1-3 days.

[0025] Furthermore, in step S7, the heat treatment is performed under an inert atmosphere at a temperature of 850-950° C. for 2-4 hours, and the surface of the precursor is roughened by the heat treatment.

[0026] The second aspect of the present invention provides a silicon nanowire-constrained nitrogen-doped carbon / transition metal nanocomposite electrocatalyst prepared by the above preparation method.

[0027] A third aspect of the present invention provides a three-electrode electrolytic cell comprising a working electrode, a counter electrode, a reference electrode and an electrolyte, wherein the silicon nanowire-constrained nitrogen-doped carbon / transition metal nanocomposite electrocatalyst is deposited on the working electrode.

[0028] Furthermore, the working electrode is carbon cloth, the counter electrode is a carbon rod, and the reference electrode is a saturated calomel electrode.

[0029] Furthermore, the electrolyte is a hydrogen-saturated H2SO4 solution, and specifically a hydrogen-saturated 0.5MH2SO4 solution.

[0030] Furthermore, the deposition method of the silicon nanowire-constrained nitrogen-doped carbon / transition metal nanocomposite electrocatalyst is as follows: dispersing the silicon nanowire-constrained nitrogen-doped carbon / transition metal nanocomposite electrocatalyst in water containing Nafion (perfluorosulfonic acid polymer) to obtain a dispersion, and dropping the dispersion onto the working electrode until the loading mass reaches 3-5 mg cm -2 .

[0031] A fourth aspect of the present invention provides the use of the silicon nanowire-constrained nitrogen-doped carbon / transition metal nanocomposite electrocatalyst or the three-electrode electrolytic cell in water electrolysis.

[0032] The present invention directly directionally couples a double-layer zeolite imidazolate framework (ZIFs) nanopolyhedron precursor on a silicon nanowire through simple in-situ growth at room temperature; then the precursor is subjected to a simple and mild heat treatment to obtain in situ a porous nitrogen-doped carbon hollow nanocage embedded with ultrafine transition metal (such as Co) nanoparticles, which is tightly coupled in series with the silicon nanowire. Due to the series constraint of the silicon nanowire on the cobalt / nitrogen-doped carbon nanocomposite, the overall catalyst not only forms a multi-threaded conductive network with enhanced electron transfer ability; at the same time, it improves the stability of the nanocage catalyst and significantly curbs the stacking between nanocages and the masking of the corresponding surface active area (site). The porous and hollow structure of the cobalt / nitrogen-doped carbon nanocage catalyst itself facilitates the transfer of reaction intermediates and generated gas products in the hydrogen evolution reaction, and has higher reaction kinetics. These advantages enable the catalyst to exhibit excellent performance in the electrocatalytic hydrogen evolution reaction, especially at a high current density (≥500mA cm) that meets the actual industrial production level. -2 ), showing satisfactory activity and stability. In 0.5 mol / L H2SO4 electrolyte, the overpotentials of the catalyst during hydrogen evolution reaction are η 10mAcm-2 ≈57mV and η 500mAcm-2 ≈430mV. And can maintain 500mA cm -2 The current density only decays slightly after 24 hours.

[0033] Compared with the prior art, the present invention has the following advantages:

[0034] 1) The present invention provides a silicon nanowire-constrained nitrogen-doped carbon / transition metal nanocomposite electrocatalyst for the hydrogen evolution reaction (HER) at high current densities. Due to the serial confinement of the transition metal / nitrogen-doped carbon nanocomposite by the silicon nanowires, the overall catalyst not only forms a multithreaded conductive network with enhanced electron transfer capacity, but also improves the stability of the nanocage catalyst, significantly preventing the stacking of nanocages and the masking of corresponding surface active areas (sites). The porous and hollow structure of the transition metal / nitrogen-doped carbon nanocage catalyst facilitates the transfer of reaction intermediates and generated gaseous products in the HER, resulting in higher reaction kinetics.

[0035] 2) The preparation method provided by this invention features simple process, inexpensive and readily available raw materials, ease of operation, environmental friendliness, low production cost, high reproducibility, and strong universality. This method can be extended to synthesize various binary and ternary transition metal nanocomposites embedded in nitrogen-doped carbon (or other carbonaceous materials) coupled to silicon nanowires; or hollow (or solid) porous nanocages of nitrogen-doped carbon (or other carbonaceous materials) / transition metals with adjustable thickness and number of layers coupled to silicon nanowires, demonstrating considerable universality and scalability.

[0036] 3) The electrocatalyst obtained by the present invention can exhibit excellent hydrogen evolution catalytic activity and stability at high current density, which is conducive to larger-scale commercial applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a scanning electron microscope (SEM) image of the H-Co / NC@Si electrocatalyst prepared in Example 1 of the present invention.

[0038] Figure 2 This is a transmission electron microscopy (TEM) image of the H-Co / NC@Si electrocatalyst prepared in Example 1 of the present invention.

[0039] Figure 3 HER linear sweep voltammetry curve of the H-Co / NC@Si electrocatalyst prepared in Example 1 of the present invention in 0.5 mol / L H2SO4 electrolyte at a scan rate of 5 mV / s

[0040] Figure 4 The H-Co / NC@Si electrocatalyst prepared in Example 1 of the present invention was loaded with 500 mA cm -2 Current density, HER current density-time curve in 0.5 mol / L H2SO4 electrolyte. DETAILED DESCRIPTION

[0041] The present invention will be further described below with reference to the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0042] Example 1

[0043] The preparation of silicon nanowire-confined nitrogen-doped carbon / cobalt hollow nanocomposite (H-Co / NC@Si) electrocatalyst includes the following steps:

[0044] (1) 40 mg of Si nanowires, 300 mg of polyvinyl pyrrolidone (PVP), and 361 mg of Zn(NO3)2·6H2O were added to 20 mL of methanol solvent in sequence and ultrasonicated for 1 h to obtain a homogeneous solution. Subsequently, 815 mg of 2-methylimidazole solution dissolved in 4 mL of methanol solvent was added and stirred at room temperature for 2 h to obtain a homogeneous mixture. The mixture was then centrifuged and the resulting precipitate was washed with methanol three times. The product was then freeze-dried for 2 days. 110 mg of the freeze-dried product was dispersed in 40 mL of methanol solvent and mixed with 1.165 g of Co(NO3)2·6H2O dissolved in 10 mL of methanol solvent. The mixture was ultrasonicated for 1 h to obtain a homogeneous mixture. Subsequently, 1.28 g of 2-methylimidazole solution dissolved in 10 mL of methanol solvent was added and stirred for 24 h to obtain a homogeneous mixture. After that, centrifugation was performed, and the precipitate after centrifugation was further washed with methanol, which was repeated three times. Finally, the product was freeze-dried for 2 days to obtain a double-layer zeolite imidazolate framework nanopolyhedron precursor with directionally coupled on silicon nanowires (Zn-ZIF(core)@Co-ZIF(shell)@Si).

[0045] (2) The precursor was subjected to a simple and mild heat treatment to obtain in situ silicon nanowire-constrained nitrogen-doped carbon / cobalt hollow nanocomposite (H-Co / NC@Si) electrocatalyst: the prepared Zn-ZIF@Co-ZIF@Si precursor was placed in a tube furnace at 5°C min -1 The temperature was raised to 900°C at a rate of 0.5 ℃, kept at this temperature for 3 h in flowing Ar, and then naturally cooled to room temperature to obtain the final target product H-Co / NC@Si electrocatalyst.

[0046] Example 2

[0047] The preparation of silicon nanowire-confined nitrogen-doped carbon / cobalt nickel hollow nanocomposite (H-CoNi / NC@Si) electrocatalyst includes the following steps:

[0048] (1) 40 mg of Si nanowires, 300 mg of polyvinyl pyrrolidone (PVP), and 361 mg of Zn(NO3)2·6H2O were added to 20 mL of methanol solvent in sequence and ultrasonicated for 1 h to obtain a homogeneous solution. 815 mg of 2-methylimidazole solution dissolved in 4 mL of methanol was then added and stirred at room temperature for 2 h to obtain a homogeneous mixture. The mixture was then centrifuged and the resulting precipitate was washed with methanol three times. The product was then freeze-dried for 2 days. 110 mg of the freeze-dried product was then dispersed in 40 mL of methanol solvent and mixed with 874 mg of Co(NO3)2·6H2O and 291 mg of Ni(NO3)2·6H2O dissolved in 10 mL of methanol (molar ratio of Co source to Ni source 3:1). The mixture was ultrasonicated for 1 h to obtain a homogeneous mixture. 1.28 g of 2-methylimidazole solution dissolved in 10 mL of methanol was then added and stirred for 24 h to obtain a homogeneous mixture. After that, centrifugation was performed, and the precipitate after centrifugation was further washed with methanol, which was repeated three times. Finally, the product was freeze-dried for 2 days to obtain a double-layer zeolite imidazolate framework nanopolyhedron precursor with directionally coupled on silicon nanowires (Zn-ZIF(core)@CoNi-ZIF(shell)@Si).

[0049] (2) The precursor was subjected to a simple and mild heat treatment to obtain in situ silicon nanowire-constrained nitrogen-doped carbon / cobalt nickel hollow nanocomposite (H-CoNi / NC@Si) electrocatalyst: the prepared Zn-ZIF@CoNi-ZIF@Si precursor was placed in a tube furnace at 5°C min -1 The temperature was raised to 900°C at a rate of 0.5 ℃ and kept at that temperature for 3 h under flowing Ar, and then naturally cooled to room temperature to obtain the final target product H-CoNi / NC@Si electrocatalyst.

[0050] Example 3

[0051] The preparation of silicon nanowire-confined nitrogen-doped carbon / cobalt-manganese hollow nanocomposite (H-CoMn / NC@Si) electrocatalyst includes the following steps:

[0052] (1) 40 mg of Si nanowires, 300 mg of polyvinyl pyrrolidone (PVP), and 361 mg of Zn(NO3)2·6H2O were added to 20 mL of methanol solvent in sequence and ultrasonicated for 1 h to obtain a homogeneous solution. Subsequently, 815 mg of 2-methylimidazole solution dissolved in 4 mL of methanol solvent was added and stirred at room temperature for 2 h to obtain a homogeneous mixture. The mixture was then centrifuged and the resulting precipitate was washed with methanol three times. The product was then freeze-dried for 2 days. 110 mg of the freeze-dried product was dispersed in 40 mL of methanol solvent and mixed with 874 mg of Co(NO3)2·6H2O and 251 mg of Mn(NO3)2·4H2O dissolved in 10 mL of methanol solvent (molar ratio of Co source to Mn source 3:1). The mixture was ultrasonicated for 1 h to obtain a homogeneous mixture. Subsequently, 1.28 g of 2-methylimidazole solution dissolved in 10 mL of methanol solvent was added and stirred for 24 h to obtain a homogeneous mixture. After that, centrifugation was performed, and the precipitate after centrifugation was further washed with methanol, which was repeated three times. Finally, the product was freeze-dried for 2 days to obtain a double-layer zeolite imidazolate framework nanopolyhedron precursor with directionally coupled on silicon nanowires (Zn-ZIF(core)@CoMn-ZIF(shell)@Si).

[0053] (2) The precursor was subjected to a simple and mild heat treatment to obtain in situ silicon nanowire-constrained nitrogen-doped carbon / cobalt manganese hollow nanocomposite (H-CoMn / NC@Si) electrocatalyst: the prepared Zn-ZIF@CoMn-ZIF@Si precursor was placed in a tube furnace at 5°C min -1 The temperature was raised to 900°C at a rate of 0.5 ℃ and kept at that temperature for 3 h under flowing Ar, and then naturally cooled to room temperature to obtain the final target product H-CoMn / NC@Si electrocatalyst.

[0054] Example 4

[0055] Preparation of silicon nanowire-confined nitrogen-doped carbon / cobalt nickel manganese hollow nanocomposite (H-CoNiMn / NC@Si) electrocatalyst includes the following steps:

[0056] (1) 40 mg of Si nanowires, 300 mg of polyvinyl pyrrolidone (PVP), and 361 mg of Zn(NO3)2·6H2O were added to 20 mL of methanol solvent in sequence and ultrasonicated for 1 h to obtain a homogeneous solution. Subsequently, 815 mg of 2-methylimidazole solution dissolved in 4 mL of methanol solvent was added and stirred at room temperature for 2 h to obtain a homogeneous mixed solution. The mixture was then centrifuged and the obtained precipitate was washed with methanol three times. The product was then freeze-dried for 2 days. 110 mg of the sample was freeze-dried and dispersed in 40 mL of methanol. The sample was then mixed with 874 mg of Co(NO₃)₂·6H₂O, 145 mg of Ni(NO₃)₂·6H₂O, and 126 mg of Mn(NO₃)₂·4H₂O dissolved in 10 mL of methanol (Co, Ni, Mn molar ratio 3:0.5:0.5). The mixture was sonicated for 1 h to obtain a homogeneous solution. A solution of 1.28 g of 2-methylimidazole dissolved in 10 mL of methanol was then added, and the mixture was stirred for 24 h to obtain a homogeneous solution. The solution was then centrifuged, and the precipitate was washed with methanol three times. Finally, the product was freeze-dried for 2 days to obtain a double-layer zeolitic imidazolate framework nanopolyhedron precursor (Zn-ZIF(core)@CoNiMn-ZIF(shell)@Si) with a directionally coupled double-layer zeolitic imidazolate framework on a silicon nanowire.

[0057] (2) The precursor was subjected to a simple and mild heat treatment to obtain in situ silicon nanowire-constrained nitrogen-doped carbon / cobalt nickel manganese hollow nanocomposite (H-CoNiMn / NC@Si) electrocatalyst: the prepared Zn-ZIF@CoNiMn-ZIF@Si precursor was placed in a tube furnace at 5°C min -1 The temperature was raised to 900°C at a rate of 1000 ℃, kept at this temperature for 3 h in flowing Ar, and then naturally cooled to room temperature to obtain the final target product H-CoNiMn / NC@Si electrocatalyst.

[0058] Example 5

[0059] The preparation of silicon nanowire-confined nitrogen-doped carbon / cobalt solid nanocomposite (S-Co / NC@Si) electrocatalyst includes the following steps:

[0060] (1) 40 mg of Si nanowires, 300 mg of polyvinyl pyrrolidone (PVP), and 353 mg of Co(NO3)2·6H2O were added to 20 mL of methanol solvent in sequence and ultrasonicated for 1 h to obtain a uniform solution. Subsequently, 815 mg of 2-methylimidazole solution dissolved in 4 mL of methanol solvent was added and stirred at room temperature for 2 h to obtain a uniform mixed solution. The mixture was then centrifuged and the obtained precipitate was washed with methanol, repeated three times, and the product was freeze-dried for 2 days to finally obtain a zeolite imidazolate framework nanopolyhedron precursor (Co-ZIF@Si) directionally coupled on silicon nanowires.

[0061] (2) The precursor was subjected to a simple and mild heat treatment to obtain in situ silicon nanowire-constrained nitrogen-doped carbon / cobalt solid nanocomposite (S-Co / NC@Si) electrocatalyst: the prepared Co-ZIF@Si precursor was placed in a tube furnace at 5°C min -1 The temperature was raised to 900°C at a rate of 1000 ℃, kept at this temperature for 3 h under flowing Ar, and then naturally cooled to room temperature to obtain the final target product S-Co / NC@Si electrocatalyst.

[0062] Example 6

[0063] The preparation of a thick nitrogen-doped carbon / cobalt solid nanocomposite (S-Co / TNC@Si) electrocatalyst confined by silicon nanowires comprises the following steps:

[0064] (1) 40 mg of Si nanowires, 300 mg of polyvinyl pyrrolidone (PVP), and 353 mg of Co(NO3)2·6H2O were added to 20 mL of methanol solvent in sequence and ultrasonicated for 1 h to obtain a homogeneous solution. Subsequently, 815 mg of 2-methylimidazole solution dissolved in 4 mL of methanol solvent was added and stirred at room temperature for 2 h to obtain a homogeneous mixture. The mixture was then centrifuged and the resulting precipitate was washed with methanol three times. The product was then freeze-dried for 2 days. 110 mg of the freeze-dried product was dispersed in 40 mL of methanol solvent and mixed with 1.191 g of Zn(NO3)2·6H2O dissolved in 10 mL of methanol solvent. The mixture was ultrasonicated for 1 h to obtain a homogeneous mixture. Subsequently, 1.28 g of 2-methylimidazole solution dissolved in 10 mL of methanol solvent was added and stirred for 24 h to obtain a homogeneous mixture. After that, centrifugation was performed, and the precipitate after centrifugation was further washed with methanol, which was repeated three times. Finally, the product was freeze-dried for 2 days to obtain a double-layer zeolite imidazolate framework nanopolyhedron precursor, Co-ZIF (core) @ Zn-ZIF (shell) @ Si, which was directionally coupled on silicon nanowires.

[0065] (2) The precursor was subjected to a simple and mild heat treatment to obtain in situ Si nanowire-constrained thick nitrogen-doped carbon / cobalt solid nanocomposite (S-Co / TNC@Si) electrocatalyst: the prepared Co-ZIF@Zn-ZIF@Si precursor was placed in a tube furnace at 5°C min -1 The temperature was raised to 900°C at a rate of 0.5 ℃, kept at that temperature for 3 h under flowing Ar, and then naturally cooled to room temperature to obtain the final target product S-Co / TNC@Si electrocatalyst.

[0066] Example 7

[0067] The preparation of a double-layer nitrogen-doped carbon / cobalt hollow nanocomposite (H-Co / NC@Co / NC@Si) electrocatalyst confined by silicon nanowires comprises the following steps:

[0068] (1) 40 mg of Si nanowires, 300 mg of polyvinyl pyrrolidone (PVP), and 353 mg of Co(NO3)2·6H2O were sequentially added to 20 mL of methanol solvent and ultrasonicated for 1 h to obtain a homogeneous solution. 815 mg of 2-methylimidazole solution dissolved in 4 mL of methanol solvent was then added and stirred at room temperature for 2 h to obtain a homogeneous mixture. The mixture was then centrifuged and the resulting precipitate was washed with methanol three times. The product was then freeze-dried for 2 days. 110 mg of the freeze-dried product was then dispersed in 40 mL of methanol solvent and mixed with 1.191 g of Zn(NO3)2·6H2O dissolved in 10 mL of methanol solvent. The mixture was ultrasonicated for 1 h to obtain a homogeneous mixture. 1.28 g of 2-methylimidazole solution dissolved in 10 mL of methanol solvent was then added and stirred for 24 h to obtain a homogeneous mixture. The mixture was then centrifuged and the precipitate was washed with methanol three times. The product was finally freeze-dried for 2 days. 110 mg of the freeze-dried sample was then dispersed in 40 mL of methanol and mixed with 1.165 g of Co(NO₃)₂·6H₂O dissolved in 10 mL of methanol. The mixture was sonicated for 1 hour to obtain a homogeneous mixture. 1.28 g of 2-methylimidazole dissolved in 10 mL of methanol was then added, and the mixture was stirred for 24 hours to obtain a homogeneous mixture. Centrifugation was then performed, and the precipitate was washed with methanol three times. The product was then freeze-dried for 2 days to obtain a three-layer zeolitic imidazolate framework nanopolyhedron precursor directed coupled to a silicon nanowire (Co-ZIF(core)@Zn-ZIF(first shell)@Co-ZIF(second shell)@Si).

[0069] (2) The precursor was subjected to a simple and mild heat treatment to obtain an in situ double-layer nitrogen-doped carbon / cobalt hollow nanocomposite (H-Co / NC@Co / NC@Si) electrocatalyst constrained by silicon nanowires: the prepared Co-ZIF@Zn-ZIF@Co-ZIF@Si precursor was placed in a tube furnace at 5°C min -1 The temperature was raised to 900°C at a rate of 0.5 ℃ and kept at this temperature for 3 h under flowing Ar, and then naturally cooled to room temperature to obtain the final target product H-Co / NC@Co / NC@Si electrocatalyst.

[0070] Result Analysis

[0071] When the H-Co / NC@Si electrocatalyst prepared in Example 1 is used in the electrochemical hydrogen evolution reaction, the electrocatalyst is deposited on carbon cloth as the working electrode; at the same time, a saturated calomel electrode is used as the reference electrode, and a carbon rod is used as the counter electrode. The specific steps for depositing the electrocatalyst on the carbon cloth are as follows: 10 mg of the prepared sample is dispersed in a mixture of 970 μL of deionized water and 30 μL of Nafion, and after ultrasonication until uniform dispersion, the ultrasonicated liquid is dropped on the carbon cloth until the loading mass reaches 4 mg cm -2 Afterwards, the electrocatalytic HER performance test was carried out in a 0.5M H2SO4 solution saturated with hydrogen as the electrolyte, mainly including linear sweep voltammetry test and time-current density test.

[0072] Depend on Figure 1 It can be seen from the SEM image that H-Co / NC@Si is composed of nano-silicon wires (Si) coupled in series with NC hollow porous multifaceted nanocages (Co / NC) embedded with Co nanoparticles. Due to the constraint effect of nano-Si wires, the H-Co / NC nanocages show a relatively orderly series arrangement.

[0073] Depend on Figure 2 TEM images (a-b) show that H-Co / NC is composed of Co nanoparticles embedded in the porous hollow NC nanocages. In addition, ultrafine nano-Si wires penetrate the nanocages. Figure 2 The high-magnification transmission electron microscopy (HRTEM) images (cd) clearly show the Co nanoparticles embedded in the NC matrix and the nano-Si wires penetrating the NC bulk phase; among them, the Si nanowires, NC matrix, and Co nanoparticles show clear lattice fringes, which are 0.314, 0.34, and 0.205 nm, corresponding to the (111) planes of Si, (002) of C, and (111) of Co, respectively, indicating the successful preparation of the catalyst.

[0074] Depend on Figure 3 It can be seen that the H-Co / NC@Si electrocatalyst reaches 10 mA cm -2The current density required is only 57 mV overpotential; and to reach 500 mA cm -2 The high current density only requires an overpotential of 430 mV, demonstrating excellent hydrogen evolution catalytic activity.

[0075] Depend on Figure 4 It can be seen that the H-Co / NC@Si electrocatalyst can maintain 500 mA cm -2 The high current density can be maintained for 24 h without obvious decay, which reflects the excellent catalytic stability of hydrogen evolution and indicates its practical application potential.

[0076] When the catalysts prepared in Examples 2-7 were used in the electrochemical hydrogen evolution reaction, the results obtained were comparable to those in Example 1.

[0077] The present invention utilizes silicon nanowires to couple and constrain nitrogen-doped carbon / transition metal porous hollow nanocages, forming a multi-threaded conductive network and improving electron transfer. Simultaneously, it effectively stabilizes the nanocage framework, preventing random stacking between different nanocages and the masking of corresponding surface active areas (sites). Furthermore, the porous and hollow structure of the nitrogen-doped carbon / transition metal nanocages facilitates the transfer of hydrogen evolution reaction intermediates and gases. Consequently, the electrocatalyst exhibits excellent activity and stability in the hydrogen evolution reaction under high currents.

[0078] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing a silicon nanowire-constrained nitrogen-doped carbon / transition metal nanocomposite electrocatalyst, characterized in that: The following steps are included: S1: dispersing silicon nanowires, a surfactant, and a transition metal salt I in methanol in sequence to obtain a mixed solution I; the mass ratio of the silicon nanowires, the surfactant, and the transition metal salt I is 1:6-9:7-12; the surfactant is polyvinyl pyrrolidone; S2: adding 2-methylimidazole to the mixed solution I, stirring and reacting to obtain a mixed solution II; the amount of 2-methylimidazole added is 15-40 times the mass of the silicon nanowires; S3: separating the mixed solution II to obtain a precipitate; S4: dispersing the precipitate and transition metal salt II in methanol to obtain a mixed solution III; the mass ratio of the precipitate to the transition metal salt II is 1:8-15; S5: adding 2-methylimidazole to the mixed solution III, stirring and reacting to obtain a mixed solution IV; the amount of 2-methylimidazole added is 8-16 times the mass of the precipitate; S6: separating the mixed solution IV to obtain a precursor; S7: thermally treating the precursor to obtain the silicon nanowire-constrained nitrogen-doped carbon / transition metal nanocomposite electrocatalyst; The heat treatment is carried out in an inert atmosphere at a temperature of 850-950 °C for 2-4 h. The transition metal salt I is a zinc salt; the transition metal salt II is a cobalt salt, a mixture of a cobalt salt and a nickel salt, a mixture of a cobalt salt and a manganese salt, or a mixture of a cobalt salt, a nickel salt and a manganese salt.

2. A silicon nanowire-constrained nitrogen-doped carbon / transition metal nanocomposite electrocatalyst prepared by the preparation method according to claim 1.

3. A three-electrode electrolytic cell comprising a working electrode, a counter electrode, a reference electrode and an electrolyte, characterized in that: The silicon nanowire-constrained nitrogen-doped carbon / transition metal nanocomposite electrocatalyst according to claim 2 is deposited on the working electrode.

4. The three-electrode electrolytic cell according to claim 3, wherein The electrolyte is a H2SO4 solution saturated with hydrogen.

5. Use of the silicon nanowire-constrained nitrogen-doped carbon / transition metal nanocomposite electrocatalyst according to claim 2, or the three-electrode electrolytic cell according to claim 3 or claim 4 in water electrolysis.

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