An ultra-fine carbon nanotube confined bimetallic phosphide heterostructure composite electrode and a preparation method and application thereof

Abstract

The present application relates to the field of electrolytic water green hydrogen catalyst, specifically relates to a kind of superfine carbon nanotube limited bimetallic phosphide heterostructure composite electrode and its preparation method and application.The present application in situ growth forms two-dimensional nanosheet structure's cobalt-based zeolite imidazolate framework structure / foam nickel on foam nickel substrate, and by phosphating induction strategy, constructs the phosphide cobalt-phosphide nickel heterostructure electrode material limited by superfine carbon nanotube with about 50nm diameter.This phosphating induction strategy fine control carbon nanotube diameter, the nanometer size effect caused exhibits abundant active site and electron transport path, and this characteristic significantly enhances the intrinsic performance of electrocatalysis in the process of electrolytic water hydrogen production.In addition, the carbon layer coated on the surface of heterostructure effectively improves the stability of phosphide cobalt-phosphide nickel heterostructure electrode, and lays a strong support for long-term efficient electrolytic water hydrogen production application.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of water electrolysis green hydrogen catalysts, and particularly relates to an ultra-fine carbon nanotube confined bimetallic phosphide heterostructure composite electrode and a preparation method and application thereof. BACKGROUND

[0002] Hydrogen energy is regarded as a potential alternative to traditional fossil energy due to its ecological friendliness and clean and efficient characteristics. Among various hydrogen production technologies, the "green electricity to green hydrogen" technology is hailed as a milestone technology in the field of new energy in the new century, because it uses renewable energy to produce hydrogen through electrocatalytic water splitting, which is rich in water resources and environmentally friendly. In recent years, with the continuous increase of solar and wind power installed capacity in China, green electricity to green hydrogen has brought new opportunities. However, the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are involved in the process of water electrolysis, and the corresponding commercial electrocatalysts are usually noble metal nanomaterials such as Pt-based and Ru / Ir-based due to their high cost and low abundance, which limits their wide application. Therefore, it is urgent to develop low-cost and high-activity non-noble metal bifunctional electrocatalysts, which has become a hot spot for efficient water electrolysis.

[0003] Transition metal phosphides, such as CoP and Ni2P, have a catalytic mechanism similar to hydrogenase due to their significant catalytic activity and durability, making them promising candidates for HER, which is attributed to the high negative charge of the phosphorus-rich structure and the appropriate hydrogen Gibbs free energy (△G H* ), which effectively promotes hydrogen proton adsorption and hydrogen desorption, thereby maximizing catalytic activity. In addition, phosphides are also recognized as excellent OER electrocatalysts, making them ideal candidates for overall water splitting. In recent years, more and more nickel-cobalt-based electrocatalysts with excellent hydrogen evolution activity and stability have been widely studied. Carbon nanotubes (CNTs), as a new type of material in the carbon material family, have high specific surface area, ultra-high electronic conductivity and stable chemical properties, and are widely used as carrier materials for electrocatalytic hydrogen evolution (HER) electrodes. However, the intrinsic activity of carbon nanotubes for electrocatalytic hydrogen evolution is low, and the outer surface results in few active sites.

[0004] Therefore, it is urgent to develop nanoscale adjustable ultra-fine carbon nanotube confined heterojunction phosphides, to regulate the size of carbon nanotubes anchored by bimetallic phosphides, to study the nanoscale size effect to quickly reconstruct hydroxyl oxides, to promote O-O coupling reactions, and to study the influence on overall water splitting electrocatalytic activity. SUMMARY

[0005] The present application aims to overcome the shortcomings and deficiencies of the prior art, and provides an ultra-fine carbon nanotube confined bimetallic phosphide heterostructure composite electrode and a preparation method and application thereof.

[0006] The object of the present application can be achieved by the following technical solutions:

[0007] A preparation method of an ultra-fine carbon nanotube confined bimetallic phosphide heterostructure composite electrode comprises the following steps:

[0008] Step S1: The organic ligand and the cobalt metal salt are uniformly mixed with the solvent respectively to form two homogeneous solutions, which are mixed and fully reacted to form a blue-purple colloidal liquid. The foamed nickel is vertically placed in the solution and fully soaked for 4 hours. The above sample is washed with deionized water for multiple times and dried overnight to obtain a cobalt-based zeolitic imidazolate framework / foamed nickel;

[0009] Step S2: The phosphorus source and the cobalt-based zeolitic imidazolate framework / foamed nickel are heated to a certain high temperature at a certain heating rate, and kept in an argon inert atmosphere for a certain time. Solid-phase metal ion exchange occurs under high temperature conditions. At the same time, the carbon nanotubes are in-situ directionally grown by multi-phase catalysis to obtain an ultra-fine carbon nanotube confined cobalt phosphide-nickel phosphide composite electrode.

[0010] Further, the foamed nickel in step S1 is an electrode with an area of 1-100 cm 2 , and a thickness of 1-10 mm.

[0011] Further, the organic ligand in step S1 is at least one of imidazole and its derivatives, such as dimethyl imidazole, 1-methyl imidazole, 2-ethyl imidazole, 2-nitro imidazole, and benzimidazole.

[0012] Further, the metal salt in step S1 is a cobalt salt, specifically at least one of cobalt nitrate, cobalt sulfate, and cobalt chloride.

[0013] Further, the molar ratio of the organic ligand to the metal salt in step S1 is (1-10):1.

[0014] Further, the solvent in step S1 is at least one of deionized water, methanol, and ethanol.

[0015] Further, the phosphorus source in step S2 includes at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid, phosphorus trichloride, elemental phosphorus, and sodium hypophosphite.

[0016] Further, the amount of the phosphorus source in step S2 is 1-20 times the molar amount of the metal salt.

[0017] The heterostructure formed after phosphorization is the crystal structure of CoP and Ni2P.

[0018] The phosphine etching generated by phosphorization can limit the radial growth of carbon nanotubes, resulting in the formed carbon nanotubes with a diameter of about 50 nm, which is thinner than the carbonized carbon nanotubes (200 nm). The present application constructs an ultrafine carbon nanotube confined CoP-Ni2P bimetallic phosphide composite electrode material with a three-dimensional interwoven network structure. This design not only induces a significant nanosize effect, presents a larger specific surface area, promotes the rapid transfer of electrons, and thus effectively increases the number of active sites. At the same time, the nanoscale regulated CoP-Ni2P heterostructure anchored on the thinner diameter carbon nanotubes can effectively adjust the d-band structure of the active sites, redistribute the interface charge, accelerate the electron transfer, and improve the electron cloud density redistribution, thereby improving its intrinsic catalytic activity.

[0019] The present application also discloses an ultrafine carbon nanotube confined bimetallic phosphide heterostructure composite electrode prepared by the above preparation method and its application in the field of hydrogen production by electrolysis of water.

[0020] The beneficial effects of the present application are:

[0021] 1. The electrocatalytic hydrogen evolution performance of the catalyst in the standard three-electrode system. CoP-Ni2P@U-NCNTs / NF shows more superior performance (eta 100 = 184 mV and eta 200 = 235 mV), and the gap with the commercial Pt / C gradually narrows down with the increase of current density; at 100 mA·cm -2 above, the performance exceeds that of the commercial Pt / C by more than 20%. The chronoamperometry method is used to test the stability of the electrode material under alkaline conditions, and the electrode material shows excellent stability.

[0022] 2. The Tafel slope of these catalysts further verifies the Volmer-Heyrovesky pathway in the HER process. The electrochemical impedance directly reflects the charge transfer impedance of the catalytic material. The Nyquist plot value (R = 7.1 ohm) of CoP-Ni2P@U-NCNTs / NF is smaller than that of the reference sample (R Co-ZIF-L / NF > 12 ohm, R Co-Ni@NCNTs / NF = 9.6 ohm), which shows its excellent charge transfer performance, which is due to its excellent HER catalytic activity.

[0023] 3. The stability of the catalyst under different voltages is tested by the chronoamperometry method, and it is found that the catalyst still remains stable after 48 h, which indicates that the ultrafine carbon nanotube confined bimetallic phosphide electrode material provided by the present application has excellent electrochemical stability and practical industrial production significance.

[0024] 4, The application constructs a "green power to green hydrogen" system. The green electricity (voltage 4.34V) generated by solar cells drives the overall water splitting to produce hydrogen through a bifunctional electrocatalyst. Since this process can achieve zero carbon emission and does not produce any pollution, it has environmental friendliness and sustainability. The catalyst developed in this application has broad application prospects in the process of "carbon neutralization". BRIEF DESCRIPTION OF DRAWINGS

[0025] The application will be further described below in conjunction with the drawings.

[0026] Figure 1 XRD pattern of cobalt phosphide-nickel phosphide heterostructure electrode material confined by superfine carbon nanotubes;

[0027] Figure 2 Scanning electron microscope images: (a) precursor cobalt-based zeolitic imidazolate framework / nickel foam, (b) cobalt-nickel@carbon nanotube / nickel foam formed by carbonization, (c) cobalt-nickel@superfine carbon nanotube / nickel foam, transmission electron microscope images of cobalt-nickel@superfine carbon nanotube / nickel foam, (d, e) morphology images, (f) lattice fringe images;

[0028] Figure 3 EIS images of cobalt-based zeolitic imidazolate framework / nickel foam, cobalt-nickel@carbon nanotube / nickel foam, cobalt-nickel@superfine carbon nanotube;

[0029] Figure 4 HER performance images under different examples and comparative examples;

[0030] Figure 5 Stability performance images of cobalt-nickel phosphide heterostructure electrode material confined by superfine carbon nanotubes under different current densities. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the application will be clearly and completely described below in conjunction with the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, not all embodiments. Based on the embodiments in the application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of the application.

[0032] Example 1

[0033] The specific process of the preparation method of the bimetallic phosphide heterostructure composite electrode confined by superfine carbon nanotubes is as follows:

[0034] (1) 0.2 mol dimethylimidazole, 0.05 mol cobalt nitrate were mixed to form two homogeneous solutions and fully reacted for 15 min to form a 60 mL blue-purple colloidal liquid. The nickel foam was vertically placed in the solution and fully soaked for 4 h. The above sample was washed with deionized water for several times and dried overnight to obtain nanosheet cobalt-based zeolitic imidazolate framework / nickel foam;

[0035] (2) 1 g of ammonium dihydrogen phosphate was placed upstream of the tube furnace, and the nanosheet cobalt-based zeolitic imidazolate framework / nickel foam was placed downstream of the tube furnace. The temperature was raised to 650℃ at a rate of 1℃·min -1 -1 under an argon inert atmosphere and kept for 120 min. Solid-phase metal ion exchange occurred, and the carbon nanotubes were in-situ directionally grown by heterogeneous catalysis to form an ultra-fine carbon nanotube confined cobalt phosphide-nickel phosphide bimetallic phosphide composite electrode (CoP-Ni2P@U-NCNTs / NF).

[0036] Example Two

[0037] The specific process of the preparation method of the ultra-fine carbon nanotube confined bimetallic phosphide heterostructure composite electrode is as follows:

[0038] (1) 0.4 mol dimethylimidazole, 0.05 mol cobalt nitrate were mixed to form two 40 mL homogeneous solutions and fully reacted for 10 min to form a blue-purple colloidal liquid. The nickel foam was vertically placed in the solution and fully soaked for 8 h. The above sample was washed with deionized water for several times and dried overnight to obtain nanosheet cobalt-based zeolitic imidazolate framework / nickel foam;

[0039] (2) 2 g of ammonium dihydrogen phosphate was placed upstream of the tube furnace, and the nanosheet cobalt-based zeolitic imidazolate framework / nickel foam was placed downstream of the tube furnace. The temperature was raised to 750℃ at a rate of 0.5℃·min -1 -1 and kept for 90 min. Solid-phase metal ion exchange occurred, and the carbon nanotubes were in-situ directionally grown by heterogeneous catalysis to form an ultra-fine carbon nanotube confined cobalt phosphide-nickel phosphide composite electrode (CoP-Ni2P@U-NCNTs / NF).

[0040] Example Three

[0041] The specific process of the preparation method of the ultra-fine carbon nanotube confined bimetallic phosphide heterostructure composite electrode is as follows:

[0042] (1) 0.8 mol of dimethylimidazole and 0.05 mol of cobalt nitrate were mixed to form two 40 mL homogeneous solutions and fully reacted for 10 min to form a blue-purple colloidal liquid. The nickel foam was vertically placed in the solution and fully soaked for 8 h. The above sample was washed with deionized water for multiple times and dried overnight to obtain nanosheet-shaped cobalt-based zeolitic imidazolate framework / nickel foam;

[0043] (2) 2 g of diammonium hydrogen phosphate was placed upstream of the tube furnace, and the leaf-shaped cobalt-based zeolitic imidazolate framework / nickel foam was placed downstream of the tube furnace. Under an argon inert atmosphere, the temperature was raised to 850°C at a rate of 1°C·min -1 -1 and kept for 90 min. Solid-phase metal ion exchange occurred, and the in-situ directional growth of the multi-phase catalyst formed carbon nanotubes to obtain a superfine carbon nanotube confined cobalt phosphide-nickel phosphide composite electrode (CoP-Ni2P@U-NCNTs / NF).

[0044] Example Four

[0045] The specific process of the preparation method of the superfine carbon nanotube confined bimetallic phosphide heterostructure composite electrode is as follows:

[0046] (1) 0.8 mol of dimethylimidazole and 0.05 mol of cobalt nitrate were mixed to form two 40 mL homogeneous solutions and fully reacted for 10 min to form a blue-purple colloidal liquid. The nickel foam was vertically placed in the solution and fully soaked for 8 h. The above sample was washed with deionized water for multiple times and dried overnight to obtain nanosheet-shaped cobalt-based zeolitic imidazolate framework / nickel foam;

[0047] (2) 2 g of diammonium hydrogen phosphate was placed upstream of the tube furnace, and the leaf-shaped cobalt-based zeolitic imidazolate framework / nickel foam was placed downstream of the tube furnace. Under an argon inert atmosphere, the temperature was raised to 850°C at a rate of 1°C·min -1 -1 and kept for 120 min. Solid-phase metal ion exchange occurred, and the in-situ directional growth of the multi-phase catalyst formed carbon nanotubes to obtain a superfine carbon nanotube confined cobalt phosphide-nickel phosphide composite electrode (CoP-Ni2P@U-NCNTs / NF).

[0048] Example Five

[0049] The specific process of the preparation method of the superfine carbon nanotube confined bimetallic phosphide heterostructure composite electrode is as follows:

[0050] (1) 0.2 mol dimethylimidazole, 0.05 mol cobalt nitrate were mixed and reacted for 10 min to form a blue-purple colloidal liquid. The nickel foam was vertically placed in the solution and soaked for 8 h. The above sample was washed with deionized water for several times and dried overnight to obtain nanosheet cobalt-based zeolitic imidazolate framework / nickel foam;

[0051] (2) 1.5 g of diammonium hydrogen phosphate was placed upstream of the tube furnace, and the leaf-shaped cobalt-based zeolitic imidazolate framework / nickel foam was placed downstream of the tube furnace. The temperature was raised to 750°C at a heating rate of 0.5°C·min -1 under an argon inert atmosphere, and kept for 90 min. Solid-phase metal ion exchange occurred, and the carbon nanotubes were in-situ directionally grown by heterogeneous catalysis to form an ultrafine carbon nanotube confined cobalt phosphide-nickel phosphide composite electrode (CoP-Ni2P@U-NCNTs / NF).

[0052] Comparative Example One

[0053] (1) 0.05 mol dimethylimidazole, 0.05 mol cobalt nitrate were mixed and reacted for 10 min to form a blue-purple colloidal liquid. The nickel foam was vertically placed in the solution and soaked for 8 h. The above sample was washed with deionized water for several times and dried overnight to obtain cobalt-based zeolitic imidazolate framework / nickel foam;

[0054] (2) The leaf-shaped cobalt-based zeolitic imidazolate framework / nickel foam was heated to 750°C at a heating rate of 1°C·min -1 under an argon inert atmosphere, and kept for 180 min. Solid-phase metal ion exchange occurred, and the carbon nanotubes were in-situ directionally grown by heterogeneous catalysis to form a carbon nanotube confined cobalt-nickel composite electrode (Co-Ni@NCNTs / NF).

[0055] Comparative Example Two

[0056] (1) 0.05 mol dimethylimidazole, 0.05 mol cobalt nitrate were mixed and reacted for 10 min to form a blue-purple colloidal liquid. The nickel foam was vertically placed in the solution and soaked for 8 h. The above sample was washed with deionized water for several times and dried overnight to obtain cobalt-based zeolitic imidazolate framework / nickel foam;

[0057] (2) The leaf-shaped cobalt-based zeolitic imidazolate framework / nickel foam was heated to 750°C at a heating rate of 1°C·min -1The temperature was raised to 450℃ at a heating rate of 5℃ / min and maintained for 90 min, and solid-phase metal ion exchange occurred, and the multi-phase catalyst grew in situ to form carbon nanotubes, obtaining a superfine carbon nanotube confined cobalt-nickel composite electrode (Co-Ni@NCNTs / NF).

[0058] As shown in Figures 1-5 , the performance characterization diagram of the above examples and comparative examples. The heterostructure formed after phosphating is the crystal structure of CoP and Ni2P Figure 1 ; phosphine etching produced by phosphating can limit the radial growth of carbon nanotubes, resulting in carbon nanotubes with a diameter of about 50 nm, which is finer than the carbonized carbon nanotubes (200 nm). The present application constructs a superfine carbon nanotube confined cobalt-phosphorus-nickel composite electrode material Figure 2 ) with a three-dimensional interwoven network structure. This design not only induces significant nanoscale size effect, presents larger specific surface area, and promotes the rapid transfer of electrons, thereby effectively increasing the number of active sites. At the same time, the nanoscale regulated cobalt-phosphorus-nickel heterostructure anchored on the finer diameter carbon nanotubes can effectively adjust the d-band structure of the active sites, redistribute the interface charge, accelerate the electron transfer, and improve the electron cloud density redistribution, thereby improving its intrinsic catalytic activity. In addition, as can be seen from the accompanying drawings:

[0059] 1. The electrocatalytic hydrogen evolution performance of the catalyst in a standard three-electrode system. The cobalt-phosphorus-nickel@superfine carbon nanotube / foam nickel composite electrode shows more superior performance (η 100 = 184 mV and η 200 = 235 mV), and the gap with commercial Pt / C gradually narrows as the current density increases; at 100 mA cm -2 , the performance exceeds that of commercial Pt / C by more than 20%. Using chronoamperometry, the electrode material was tested for stability under alkaline conditions, and showed excellent stability Figure 3 ;

[0060] 2. The Tafel slope of these catalysts further verifies the Volmer-Heyrovesky pathway in the HER process. Figure 4 The electrochemical impedance in the Nyquist plot directly reflects the charge transfer impedance of the catalytic material. The Nyquist plot value (R = 7.1 ohm) of the cobalt-phosphorus-nickel@superfine carbon nanotube / foam nickel composite electrode is less than that of the reference sample (R 钴基沸石咪唑酯骨架结构 / 泡沫镍 > 12 ohm, R 钴-镍@碳纳米管 / 泡沫镍 = 9.6 ohm), showing its excellent charge transfer performance, which is due to its excellent HER catalytic activity Figure 4 ;

[0061] 3. The stability of the catalyst under different voltages is tested by chronocoulometry, and it is found that the catalyst remains stable after 48 h, indicating that the superfine carbon nanotube confined bimetallic phosphide electrode material provided by the application has excellent electrochemical stability, which has practical significance for industrial production. Figure 5

[0062] The above specific embodiment part specifically introduces the analysis method involved in the application. It should be noted that the above introduction is only to help those skilled in the art better understand the method and idea of the application, and is not a limitation on the related content. Those skilled in the art can also make appropriate adjustments or modifications to the application without departing from the principles of the application. The above adjustments and modifications should also belong to the protection scope of the application.​

Claims

1. A method for preparing a confined double-metal phosphide heterostructure composite electrode of ultrafine carbon nanotubes, characterized in that, Comprising the following steps: Step S1: uniformly mixing the organic ligand, the cobalt metal salt and the solvent respectively to form two homogeneous solutions, mixing and fully reacting to form a blue-purple colloidal liquid; vertically placing the foamed nickel in the solution and fully soaking for 4 hours, washing the above sample with deionized water for multiple times and drying overnight to obtain a cobalt-based zeolitic imidazolate framework / foamed nickel; Step S2: heating the phosphorus source and the cobalt-based zeolitic imidazolate framework / foamed nickel to a certain high temperature at a certain heating rate, and keeping in an argon inert atmosphere for a certain time, and under the condition of high temperature, solid-phase metal ion exchange occurs; at the same time, the multi-phase catalytic in-situ directional growth forms carbon nanotubes to obtain a superfine carbon nanotube confined cobalt phosphide-nickel phosphide composite electrode; The diameter of the superfine carbon nanotube is 50 nm.

2. The method of claim 1, wherein the method comprises the steps of: (a) mixing the carbon nanotubes, the metal phosphide, and the polymer to form a mixture; (b) applying the mixture to a substrate to form a film; and (c) annealing the film to form the composite electrode. The foamed nickel in step S1 is an electrode with an area of 1-100 cm2 and a thickness of 1-10 mm.

3. The method of claim 1, wherein the method comprises the steps of: (a) mixing the carbon nanotubes, the metal phosphide, and the surfactant to form a mixture; (b) sonicating the mixture; (c) adding the mixture to a solvent; (d) adding the mixture to a substrate; (e) drying the mixture; and (f) annealing the mixture. The organic ligand in step S1 is at least one of dimethyl imidazole, 1-methyl imidazole, 2-ethyl imidazole, 2-nitro imidazole and benzimidazole.

4. The method of claim 1, wherein the method is characterized by: The molar ratio of the organic ligand to the metal salt in step S1 is (1-10):

1.

5. The method of claim 1, wherein the method comprises the steps of: (a) mixing the carbon nanotubes, the metal phosphide, and the surfactant to form a mixture; (b) sonicating the mixture; (c) adding the mixture to a solvent; (d) adding the mixture to a substrate; (e) drying the mixture; and (f) annealing the mixture. The solvent in step S1 is at least one of deionized water, methanol and ethanol.

6. The method of claim 1, wherein the method is characterized by: The phosphorus source in step S2 includes at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid, phosphorus trichloride, elemental phosphorus and sodium hypophosphite.

7. The method of claim 1, wherein the method comprises the steps of: (a) mixing the carbon nanotubes, the metal phosphide, and the surfactant to form a mixture; (b) sonicating the mixture; (c) adding the mixture to a solvent; (d) adding the mixture to a substrate; (e) drying the mixture; and (f) annealing the mixture. The amount of the phosphorus source in step S2 is 1-20 times the molar amount of the metal salt.

8. A confined double-metal phosphide heterostructure composite electrode of ultrafine carbon nanotubes, characterized in that, Prepared according to the preparation method of any one of claims 1-7.

9. Application of the superfine carbon nanotube confined bimetallic phosphide heterostructure composite electrode of claim 8 in the field of electrolytic water hydrogen production.

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