A nickel coupling hybrid nanocarbon core-shell structure cocatalyst, a preparation method and application thereof

Abstract

The application discloses a nickel-coupled hybrid nanometer carbon core-shell structure cocatalyst, a preparation method and application thereof, and comprises the following steps: preparing a nickel salt N,N-dimethylformamide (DMF) solution (one); fully mixing ethylenediaminetetraacetic acid (EDTA), hybrid nanometer carbon (HC), trimethylamine and DMF to obtain a solution (two); fully mixing the solution (one) and the solution (two) to obtain a precursor of nickel (Ni) coupled with HC, and then centrifuging, washing, drying and heat treating by using a microwave tube furnace to obtain the Ni coupled with HC core-shell structure cocatalyst; the preparation method is simple, the non-noble metal Ni is compounded with the HC, and the cost is low; the prepared cocatalyst has a compact core-shell heterojunction interface, a high photo-generated carrier separation efficiency and a large number of hydrogen evolution active sites; after being compounded with graphite phase carbon nitride, the photocatalytic hydrogen production activity of the nickel cocatalyst coupled with the HC is significantly improved as compared with the nickel cocatalyst not coupled with the HC.

Description

Technical Field

[0001] This invention relates to the field of nanophotocatalyst preparation technology, specifically to a nickel-coupled hybrid nanocarbon core-shell structure cocatalyst, its preparation method, and its application. Background Technology

[0002] Photocatalytic water splitting for hydrogen production can directly convert inexhaustible solar energy into hydrogen energy and is considered one of the most promising hydrogen energy production technologies. Its core lies in high-performance photocatalytic materials.

[0003] Studies have shown that most single semiconductor photocatalysts (such as graphitic carbon nitride and TiO2) suffer from defects such as high recombination rates of photogenerated carriers, insufficient active sites for hydrogen evolution reaction on the surface, and high overpotentials, thus failing to exhibit ideal photocatalytic hydrogen production activity. Supported co-catalysts are the core approach to solving these problems. Co-catalysts can not only effectively promote the separation and transfer of photogenerated carriers but also provide abundant surface reactive sites, reducing the overpotential of the hydrogen evolution reaction, thereby significantly improving the photocatalytic hydrogen production performance of semiconductors.

[0004] Currently, most cocatalysts are precious metals such as platinum and palladium, which have excellent catalytic activity. However, their scarcity on Earth and high procurement costs severely limit the large-scale promotion and application of photocatalytic hydrogen production technology. In recent years, cocatalysts composed of low-cost non-precious metals (nickel, cobalt, iron, etc.) and carbon-based materials have become a research hotspot and have achieved certain research results. However, existing non-precious metal carbon-based cocatalysts still have obvious technical defects: First, the carbon source used cannot simultaneously achieve excellent electrical and optical properties, and cannot simultaneously achieve efficient transport of photogenerated carriers and full utilization of photons; Second, the interfacial bonding between metal and carbon materials is poor, and the interfacial structure is not ideal, resulting in high carrier transport resistance, low separation efficiency, and catalytic activity that cannot reach the expected level; Third, existing preparation methods have obvious shortcomings. Traditional tube furnace / muffle furnace calcination easily leads to nanoparticle agglomeration and poor product dispersion, while the liquid-phase reduction method has poor controllability of reduction degree, making it difficult to form a stable core-shell interface structure and achieve stable regulation of catalytic performance. Summary of the Invention

[0005] In view of the above-mentioned defects in the existing technology, the purpose of this invention is to provide a nickel-coupled hybrid nano-carbon core-shell structure cocatalyst and its preparation method. The preparation method is simple, the conditions are controllable, the product has good uniformity, the prepared cocatalyst does not use any precious metals, the cost is low, and it has excellent interfacial bonding performance, high photocatalytic hydrogen evolution activity and cycle stability.

[0006] The technical solution of this invention is as follows: A method for preparing a nickel-coupled hybrid nanocarbon core-shell structured cocatalyst, characterized by comprising the following steps: (1) Dissolve the nickel salt in N,N-dimethylformamide (DMF) and stir thoroughly until completely dissolved to obtain a homogeneous nickel salt solution; (2) Mix ethylenediaminetetraacetic acid (EDTA), hybrid nanocarbon (HC), trimethylamine, and DMF, and stir until uniformly dispersed; to obtain a precursor mixture of nickel (Ni) coupled HC composite material; (3) Add the nickel salt solution obtained in step (1) to the precursor mixture obtained in step (2), stir and react, collect the obtained powder by centrifugation, wash with DMF, dry in a microwave tube furnace at 50 ℃~80 ℃, then heat to 450 °C~550 °C at a heating rate of 10 ℃ / min~30 ℃ / min under an inert gas atmosphere, keep warm for 1 h~2 h, and cool naturally to room temperature to obtain the Ni-coupled HC core-shell structure cocatalyst.

[0007] Furthermore, in step (1), the nickel salt is one of nickel nitrate hexahydrate, nickel acetate tetrahydrate, nickel formate dihydrate, and nickel chloride hexahydrate.

[0008] Furthermore, in step (1), the molar ratio of Ni²⁺ to DMF in the nickel salt is n(Ni²⁺) / n(DMF) = 1 / (60~100).

[0009] Furthermore, in step (2), EDTA and Ni in step (1) 2＋ The molar ratio of EDTA to Ni²⁺ is n(EDTA) / n(Ni²⁺) = 1 / 2; The amount of HC is referenced from the amount of nickel salt in step (1). The mass ratio of nickel to HC in the nickel salt is m(Ni) / m(HC) = 1 / 0.2, 1 / 0.4, 1 / 0.6, 1 / 0.8, 1 / 1. The molar ratio of EDTA, trimethylamine, and DMF is n(EDTA) / n(trimethylamine) / n(DMF) = 1 / (4~10) / (280~400).

[0010] Furthermore, in step (2), HC is obtained by using commercially purchased nanodiamonds with a size of 3 nm to 5 nm as raw materials, which are acid-washed, and hydrogen is used as the reaction gas. The mixture is heated to 1000 ℃ to 1100 ℃ at a heating rate of 10 ℃ / min to 20 ℃ / min, kept at that temperature for 2 h to 4 h, and then naturally cooled to room temperature.

[0011] Furthermore, in step (3), the drying time is 0.5 h to 1 h; the inert gas is argon or nitrogen, and the gas flow rate is 50 mL / min to 200 mL / min.

[0012] The Ni-coupled HC core-shell structured cocatalyst was prepared according to the above-described method for preparing a nickel-coupled nano-carbon core-shell structured cocatalyst.

[0013] Application of the Ni-coupled HC core-shell structure cocatalyst described in the above claims in photocatalytic water splitting for hydrogen production.

[0014] The beneficial effects of this invention are as follows:

[0015] 1. This invention uses non-precious metal nickel and hybrid nano-carbon composite to prepare co-catalysts, without using precious metals such as platinum and palladium. The raw materials are widely available and inexpensive, which greatly reduces the production cost of photocatalytic hydrogen production co-catalysts and is suitable for large-scale promotion and application.

[0016] 2. The nickel-coupled hybrid nanocarbon core-shell structure cocatalyst prepared by the present invention has a core-shell structure of nickel-coated hybrid nanocarbon, and a tight heterojunction interface is formed between metallic nickel and hybrid nanocarbon. This interface structure is beneficial to reducing the interfacial charge transport impedance, promoting the separation and transfer of photogenerated carriers, and providing abundant active sites for hydrogen evolution reaction.

[0017] 3. This invention uses specially made hybrid nano-carbon as the carbon core. This material is prepared using nano-diamond as a precursor and combines the light scattering effect of sp³ hybrid diamond with the high conductivity of sp² hybrid carbon. It can achieve efficient transport of photogenerated carriers and has excellent optical performance. It can make full use of photon energy. After coupling with metallic nickel, it achieves a synergistic improvement in catalytic activity and structural stability.

[0018] 4. This invention uses a microwave tube furnace for heating, which utilizes its bulk heating characteristics to achieve rapid temperature rise. Nickel-coupled nano-carbon core-shell structures are prepared under an inert atmosphere, which is beneficial for obtaining uniform product morphology. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a transmission electron microscope (TEM) image of the Ni-coupled HC core-shell structured cocatalyst prepared in Example 3 of the present invention. Figure 2 shows the full X-ray photoelectron spectroscopy (XPS) spectrum of the Ni-coupled HC core-shell structure cocatalyst prepared in Example 3 of this invention; Figure 3 is a comparison of the photocatalytic hydrogen production activity of the Ni-coupled HC core-shell structure cocatalyst prepared in Example 3 of the present invention and other cocatalysts after being combined with graphitic carbon nitride. Figure 4 shows the cycle stability test of photocatalytic hydrogen production by Ni@HC / g-C3N4 in the embodiment of the present invention; Figure 5 This is a transient photocurrent response diagram of the sample in Example 3 of the present invention. Detailed Implementation

[0021] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0022] In this embodiment of the invention, the nickel salt is one of nickel nitrate hexahydrate, nickel acetate tetrahydrate, nickel formate dihydrate, and nickel chloride hexahydrate. The inert gas is argon or nitrogen. The HC used is prepared from nanodiamond as raw material. The preparation method is as follows: commercial nanodiamond (particle size 3~5 nm) is added to concentrated nitric acid, heated to 100 °C and boiled for 2 h. After cooling, it is centrifuged and washed until the filtrate is neutral. After drying, it is placed in a tube furnace and heated to 1000 °C at a heating rate of 15 °C / min under a hydrogen atmosphere (flow rate 100 mL / min). The temperature is held for 3 h and then naturally cooled to room temperature. Example 1

[0023] Step (a): Based on the molar ratio of Ni²⁺ to DMF in the nickel salt, n(Ni²⁺) / n(DMF)=1 / 60, weigh an appropriate amount of nickel salt and measure the corresponding volume of DMF. Add the nickel salt to the DMF and stir at room temperature until completely dissolved to obtain a homogeneous nickel salt solution.

[0024] Step (b): Based on EDTA and Ni in step (a) 2 The molar ratio of ⁺ is n(EDTA) / n(Ni²⁺) = 1 / 2. Weigh out the corresponding mass of EDTA. According to the mass ratio of nickel to HC in nickel salt in step (a) m(Ni) / m(HC)=1 / 0.2, weigh out the corresponding mass of HC; Based on the molar ratio of EDTA, trimethylamine, and DMF, n(EDTA) / n(trimethylamine) / n(DMF) = 1 / 4 / 280, measure the trimethylamine and DMF. EDTA, hybrid nano-carbon, trimethylamine, and DMF were mixed evenly and stirred thoroughly until uniformly dispersed to obtain a precursor mixture of Ni-coupled HC composite material.

[0025] Step (c) Composite and heat treatment: The nickel salt solution obtained in step (a) is slowly added dropwise to the precursor mixture obtained in step (b), and the mixture is stirred at room temperature for 2 h. The powder obtained is collected by centrifugation, washed three times with DMF, and the washed precipitate is placed in a microwave tube furnace. It is first dried at 50 ℃ for 0.5 h, and then heated to 450 ℃ at 10 ℃ / min under an inert gas atmosphere (flow rate 50 mL / min), held at that temperature for 1 h, and naturally cooled to room temperature to obtain the Ni-coupled HC core-shell structure cocatalyst. Example 2

[0026] Step (a): Based on the molar ratio of Ni²⁺ to DMF in the nickel salt, n(Ni²⁺) / n(DMF)=1 / 70, weigh an appropriate amount of nickel salt and measure the corresponding volume of DMF. Add the nickel salt to the DMF and stir at room temperature until completely dissolved to obtain a homogeneous nickel salt solution.

[0027] Step (b): Based on the molar ratio of EDTA to Ni²⁺ in step (a), n(EDTA) / n(Ni²⁺) = 1 / 2, weigh out the corresponding mass of EDTA; According to the mass ratio of nickel to HC in nickel salt in step (a) m(Ni) / m(HC)=1 / 0.4, weigh out the corresponding mass of HC; Based on the molar ratio of EDTA, trimethylamine, and DMF, n(EDTA) / n(trimethylamine): n(DMF) = 1 / 6 / 310, measure the trimethylamine and DMF. EDTA, HC, trimethylamine, and DMF were mixed evenly and stirred thoroughly until uniformly dispersed to obtain a precursor mixture of Ni-coupled HC composite material.

[0028] Step (c) Composite and heat treatment: The nickel salt solution obtained in step (a) was slowly added dropwise to the precursor mixture obtained in step (b). After stirring at room temperature for 2 hours, the powder was collected by centrifugation and washed three times with DMF. The washed precipitate was placed in a microwave tube furnace and dried at 60 °C for 1 hour. Then, it was heated to 450 °C at a heating rate of 20 °C / min under an inert gas atmosphere (flow rate 100 mL / min) and held for 1 hour. After naturally cooling to room temperature, it was removed to obtain the Ni-coupled HC core-shell structured cocatalyst. Example 3

[0029] Step (a): Based on the molar ratio of Ni²⁺ to DMF in the nickel salt, n(Ni²⁺) / n(DMF)=1 / 80, weigh an appropriate amount of nickel salt and measure the corresponding volume of DMF. Add the nickel salt to the DMF and stir at room temperature until completely dissolved to obtain a homogeneous nickel salt solution.

[0030] Step (b): Based on the molar ratio of EDTA to Ni²⁺ in step (a), n(EDTA) / n(Ni²⁺) = 1 / 2, weigh out the corresponding mass of EDTA; According to the mass ratio of nickel to HC in nickel salt in step (a) m(Ni) / m(HC)=1 / 0.6, weigh out the corresponding mass of HC; Based on the molar ratio of EDTA, trimethylamine, and DMF, n(EDTA) / n(trimethylamine) / n(DMF) = 1 / 7 / 340, measure the trimethylamine and DMF. EDTA, HC, trimethylamine, and DMF were mixed evenly and stirred thoroughly until uniformly dispersed to obtain a precursor mixture of Ni-coupled HC composite material.

[0031] Step (c) Composite and heat treatment: The nickel salt solution obtained in step (a) is slowly added dropwise to the precursor mixture obtained in step (b), and the mixture is stirred at room temperature for 2 h. The powder obtained is collected by centrifugation, washed three times with DMF, and the washed precipitate is placed in a microwave tube furnace. It is first dried at 80 °C for 1 h, and then heated to 550 °C at 20 °C / min under an inert gas atmosphere (flow rate 100 mL / min), held for 1 h, and then naturally cooled to room temperature to obtain the Ni-coupled HC core-shell structured cocatalyst. Example 4

[0032] Step (a): Based on the molar ratio of Ni²⁺ to DMF in the nickel salt, n(Ni²⁺) / n(DMF)=1 / 90, weigh an appropriate amount of nickel salt and measure the corresponding volume of DMF. Add the nickel salt to the DMF and stir at room temperature until completely dissolved to obtain a homogeneous nickel salt solution.

[0033] Step (b): Based on the molar ratio of EDTA to Ni²⁺ in step (a), n(EDTA) / n(Ni²⁺) = 1 / 2, weigh out the corresponding mass of EDTA; Based on the mass ratio of nickel to HC in step (a) m(Ni) / m(HC)=1 / 0.8, weigh the corresponding mass of hybrid nano-carbon. Based on the molar ratio of EDTA, trimethylamine, and DMF, n(EDTA) / n(trimethylamine) / n(DMF) = 1 / 8 / 370, measure the trimethylamine and DMF. EDTA, hybrid nano-carbon, trimethylamine, and DMF were mixed evenly and stirred thoroughly until uniformly dispersed to obtain a precursor mixture of Ni-coupled NC composite material.

[0034] Step (c) Composite and heat treatment: The nickel salt solution obtained in step (a) is slowly added dropwise to the precursor mixture obtained in step (b), and the mixture is stirred at room temperature for 2 h. The powder obtained is collected by centrifugation, washed three times with DMF, and the washed precipitate is placed in a microwave tube furnace. It is first dried at 70 °C for 1 h, and then heated to 500 °C at 20 °C / min under an inert gas atmosphere (flow rate 200 mL / min), held for 1 h, and naturally cooled to room temperature to obtain the Ni-coupled HC core-shell structure cocatalyst. Example 5

[0035] Step (a): Based on the molar ratio of Ni²⁺ to DMF in the nickel salt, n(Ni²⁺) / n(DMF)=1 / 100, weigh an appropriate amount of nickel salt and measure the corresponding volume of DMF. Add the nickel salt to the DMF and stir at room temperature until completely dissolved to obtain a homogeneous nickel salt solution.

[0036] Step (b): Based on the molar ratio of EDTA to Ni²⁺ in step (a), n(EDTA) / n(Ni²⁺) = 1 / 2, weigh out the corresponding mass of EDTA; According to the mass ratio of nickel to HC in nickel salt in step (a) m(Ni) / m(HC)=1 / 1, weigh the corresponding mass of hybrid nano-carbon. Based on the molar ratio of EDTA, trimethylamine, and DMF, n(EDTA) / n(trimethylamine) / n(DMF) = 1 / 10 / 400, measure the trimethylamine and DMF. EDTA, hybrid nano-carbon, trimethylamine, and DMF were mixed evenly and stirred thoroughly until uniformly dispersed to obtain a precursor mixture of Ni-coupled NC composite material.

[0037] Step (c) Composite and heat treatment: The nickel salt solution obtained in step (a) is slowly added dropwise to the precursor mixture obtained in step (b), and the mixture is stirred at room temperature for 2 h. The powder obtained is collected by centrifugation, washed three times with DMF, and the washed precipitate is placed in a microwave tube furnace. It is first dried at 80 °C for 1 h, and then heated to 550 °C at 30 °C / min under an inert gas atmosphere (flow rate 200 mL / min), held for 1 h, and naturally cooled to room temperature to obtain the Ni-coupled HC core-shell structure cocatalyst. Performance testing

[0038] The Ni-coupled NC core-shell structure cocatalyst was prepared using the steps described in the optimal embodiment 3 of this application for performance testing. In this embodiment, nickel acetate tetrahydrate was selected as the nickel salt, and argon was selected as the inert gas. In step (a), 0.99 g of nickel acetate tetrahydrate was weighed and 30 ml of DMF was measured. In step (b), 0.59 g of EDTA and 0.14 g of HC were weighed, and 1.5 ml of trimethylamine and 25 ml of DMF were measured.

[0039] 1. Microstructure and composition characterization The microstructure of the cocatalyst prepared in Example 3 was characterized using transmission electron microscopy (TEM), and the results are as follows: Figure 1 As shown in the figure, the prepared material exhibits a distinct core-shell structure, with hybrid carbon nanoparticles forming the core and nickel nanoparticles uniformly coated on the surface of the hybrid carbon nanoparticles, forming a complete core-shell structure. The nickel nanoparticles are uniformly dispersed without obvious agglomeration.

[0040] The elemental composition of the cocatalyst prepared in Example 3 was analyzed by X-ray photoelectron spectroscopy (XPS), and the results are as follows: Figure 2 As shown, the full spectrum exhibits distinct characteristic peaks for Ni, C, O, and N, confirming the successful introduction of nickel into the material, consistent with the expected elemental composition.

[0041] 2. Photocatalytic hydrogen production activity test The nickel-coupled hybrid carbon nanotubes (Ni@HC) obtained in Example 3 were used as co-catalysts and composited with graphitic carbon nitride. Different co-catalysts were prepared using the same method and composited with graphitic carbon nitride to obtain the following test groups: White control group: pure g-C3N4 (without any co-catalyst); Pure carbon material control group: HC / g-C3N4 (only HC is loaded, without the addition of metallic nickel component); Precious metal benchmark control group: Pt / g-C3N4 (supported with 1wt% Pt co-catalyst); Single-metal nickel control group: Ni / g-C3N4 (prepared using the exact same process as in Example 3 of this invention, except without the addition of HC, to prepare and support a pure nickel co-catalyst); Experimental group of this invention: Ni@HC / g-C3N4 (Ni@HC, a Ni-coupled HC core-shell structure cocatalyst prepared in Example 3 of this invention).

[0042] The photocatalytic hydrogen production activity was tested in a closed offline photocatalytic reaction system, with all groups tested under identical conditions: a 150 W xenon lamp with a visible light filter (λ≥420 nm) was used to simulate visible light; the reaction system was 100 mL of a 10% (v / v) triethanolamine aqueous solution (triethanolamine as a hole sacrificial agent); and the composite photocatalyst dosage was 50 mg. Before the reaction, the system was ultrasonically dispersed for 30 min, and high-purity argon gas was introduced for 30 min to completely remove air from the system. During the reaction, the system temperature was kept constant at 5 ℃ by circulating condensate water. Samples were taken every 1 h, and the hydrogen content generated was quantitatively detected using a gas chromatograph equipped with a thermal conductivity detector (TCD). The total duration of a single test was 8 h.

[0043] Test results are as follows Figure 3 As shown, in the pure carbon control group, without the addition of other co-catalysts, the photocatalytic water splitting hydrogen production activities of g-C3N4 and HC / g-C3N4 were very low. In contrast, the hydrogen production rate of Pt / g-C3N4 was 128 µmol·g. -1 ·h -1 The hydrogen production rate of Ni / g-C3N4 is 134 µmol·g. -1 ·h -1 The hydrogen production rate of Ni@HC / g-C3N4 in this invention reaches 244 µmol·g. -1 ·h -1 The photocatalytic hydrogen production activity was significantly improved, proving that the coupling of Ni and HC produced a significant synergistic catalytic enhancement effect, rather than the effect of carbon materials or nickel alone.

[0044] 3. Cyclic stability test The photocatalytic hydrogen production cycle stability of Ni@HC / g-C3N4 prepared in preferred embodiment 3 was tested. Each cycle lasted 4 hours, and a total of 6 cycles were performed. The results are as follows: Figure 4 As shown.

[0045] As can be seen from the figure, after 6 cycles of testing, the photocatalytic hydrogen production activity of the sample did not decrease significantly, and the cumulative hydrogen production retention rate reached more than 88%, proving that the cocatalyst prepared by this invention has excellent structural stability and cycle life.

[0046] 4. Photocurrent test The Ni@HC / g-C3N4 and Ni / g-C3N4 samples used in the photocatalytic hydrogen production activity test were subjected to photoelectrochemical tests. A three-electrode system was used, with the catalyst-coated FTO conductive glass as the working electrode, and the transient photocurrent response was measured under visible light irradiation.

[0047] The results are as follows Figure 5As shown, the photocurrent magnitudes of the two samples are in the order of Ni@HC / g-C3N4 > Ni / g-C3N4. The photocurrent density of Ni@HC / g-C3N4 is significantly higher than that of the control group, indicating that Ni coupling with HC helps to separate photogenerated carriers.

[0048] In summary, the cocatalyst prepared in the embodiments of the present invention has good photocatalytic hydrogen production activity and has broad application prospects in the field of photocatalytic water splitting for hydrogen production.

[0049] Although the present invention has been described in detail with reference to the accompanying drawings and preferred embodiments, the invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the invention should also be covered within the protection scope of the invention. Therefore, the protection scope of the invention should be determined by the scope defined in the claims.

Claims

1. A method for preparing a nickel-coupled hybrid nano-carbon core-shell structured cocatalyst, characterized in that, Includes the following steps: (1) Dissolve the nickel salt in N,N-dimethylformamide (DMF) and stir thoroughly until completely dissolved to obtain a homogeneous nickel salt solution; (2) Mix ethylenediaminetetraacetic acid (EDTA), hybrid nanocarbon (HC), trimethylamine, and DMF, and stir until uniformly dispersed to obtain a precursor mixture of nickel (Ni) coupled HC composite material; (3) Add the nickel salt solution obtained in step (1) to the precursor mixture obtained in step (2), stir and react, collect the obtained powder by centrifugation, wash with DMF, dry in a microwave tube furnace at 50 ℃~80 ℃, then heat to 450 ℃~550 ℃ at a heating rate of 10 ℃ / min~30 ℃ / min under an inert gas atmosphere, keep warm for 1 h~2 h, and cool naturally to room temperature to obtain Ni-coupled HC core-shell structure co-catalyst.

2. The method for preparing a nickel-coupled hybrid nano-carbon core-shell structured cocatalyst according to claim 1, characterized in that, In step (1), the nickel salt is one of nickel nitrate hexahydrate, nickel acetate tetrahydrate, nickel formate dihydrate, and nickel chloride hexahydrate.

3. The method for preparing a nickel-coupled hybrid nano-carbon core-shell structured cocatalyst according to claim 1, characterized in that, In step (1), the molar ratio of Ni²⁺ to DMF in the nickel salt is n(Ni²⁺) / n(DMF) = 1 / (60~100).

4. The method for preparing a nickel-coupled hybrid nano-carbon core-shell structured cocatalyst according to claim 1, characterized in that, In step (2), EDTA and Ni in step (1) 2＋ The molar ratio of EDTA and Ni²⁺ is n(EDTA) / n(Ni²⁺) = 1 / 2; The amount of HC is referenced from the amount of nickel salt in step (1). The mass ratio of nickel element to HC in the nickel salt is: m(Ni) / m(HC) = 1 / 0.2, 1 / 0.4, 1 / 0.6, 1 / 0.8, 1 / 1; The molar ratio of EDTA, trimethylamine, and DMF is n(EDTA) / n(trimethylamine) / n(DMF) = 1 / (4~10) / (280~400).

5. The method for preparing a nickel-coupled hybrid nano-carbon core-shell structured cocatalyst according to claim 1, characterized in that, In step (2), HC is obtained by using commercially purchased nanodiamonds with a size of 3nm~5nm as raw material, which are acid-washed, and then heated to 1000℃~1100℃ with hydrogen as the reaction gas at a heating rate of 10℃ / min~20℃ / min, held at the temperature for 2h~4h, and then naturally cooled to room temperature.

6. The method for preparing a nickel-coupled hybrid nano-carbon core-shell structured cocatalyst according to claim 1, characterized in that, In step (3), the drying time is 0.5 h to 1 h; the inert gas is argon or nitrogen, and the gas flow rate is 50 mL / min to 200 mL / min.

7. The Ni-coupled HC core-shell structured cocatalyst prepared by the method for preparing a nickel-coupled hybrid nano-carbon core-shell structured cocatalyst according to any one of claims 1-6.

8. The application of the Ni-coupled HC core-shell structure cocatalyst as described in claim 7 in photocatalytic water splitting for hydrogen production.

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