Bimetal phosphide heterostructure composite electrode confined by superfine carbon nano tube, and preparation method and application of bimetal phosphide heterostructure composite electrode

Abstract

The invention relates to the field of catalysts for preparing green hydrogen by electrolyzing water, in particular to a bimetallic phosphide heterostructure composite electrode confined by superfine carbon nanotubes and a preparation method and application thereof. A cobalt-based zeolite imidazate framework structure / foamed nickel with a two-dimensional nanosheet structure is formed on a foamed nickel substrate through in-situ growth, and a cobalt phosphide-nickel phosphide heterostructure electrode material limited by an ultrafine carbon nanotube with the diameter of about 50nm is constructed through a phosphorization induction strategy. The phosphating induction strategy is used for finely regulating and controlling the tube diameter of the carbon nano tube, the initiated nano-size effect shows abundant active sites and electron transmission paths, and the characteristic obviously enhances the electro-catalysis intrinsic performance in the water electrolysis hydrogen production process. Besides, the carbon layer coated on the surface of the heterostructure effectively improves the stability of the cobalt phosphide-nickel phosphide heterostructure electrode, and lays a powerful support for long-term and efficient application of hydrogen production by water electrolysis.

Description

Technical Field

[0001] The present invention belongs to the technical field of green hydrogen production catalysts by electrolysis of water, and specifically relates to an ultrafine carbon nanotube-confined bimetallic phosphide heterostructure composite electrode, and a preparation method and application thereof. Background Art

[0002] Hydrogen energy is regarded as a potential substitute for traditional fossil energy due to its eco-friendly, clean and efficient characteristics. Among the many hydrogen production technologies, the use of renewable energy to generate electricity through electrocatalytic decomposition of water to produce hydrogen is hailed as a milestone technology in the new century's new energy field because of its abundant water resources and environmental friendliness. In recent years, with the continuous increase in the installed capacity of solar and wind power in my country, new opportunities have been brought to the production of green hydrogen from green electricity; however, the technology of hydrogen production by electrolysis of water involves hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), and the corresponding commercial electrocatalysts are usually Pt-based and Ru / Ir-based precious metal nanomaterials, which are limited in their wide application due to their high cost and low abundance. Therefore, the development of low-cost and highly active non-precious metal bifunctional electrocatalysts has become a hot spot for achieving efficient water electrolysis.

[0003] Transition metal phosphides, such as CoP and Ni 2 P, due to its remarkable catalytic activity and durability, has become a promising candidate for HER with a catalytic mechanism similar to that of hydrogenase, which is attributed to its highly electronegative phosphorus-rich structure and suitable hydrogen Gibbs free energy (ΔG H* ), which effectively promotes hydrogen proton adsorption and hydrogen desorption, thereby maximizing the catalytic activity. In addition, phosphides are recognized as excellent OER electrocatalysts, making them ideal candidate catalysts 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 the advantages of high specific surface area, ultra-high electronic conductivity and stable chemical properties, and are widely used in support materials for electrocatalytic hydrogen evolution (HER) electrodes. However, the electrocatalytic hydrogen evolution intrinsic activity of carbon nanotubes is low and the number of active sites caused by their outer surface is small.

[0004] Therefore, it is urgent to develop ultrafine carbon nanotube-confined heterojunction phosphides with adjustable nanosize, regulate the size of carbon nanotubes anchored by bimetallic phosphides, and study their nanosize effects to quickly reconstruct hydroxy oxides and promote OO coupling reactions, as well as their impact on the overall water splitting electrocatalytic activity. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art and to provide a bimetallic phosphide heterostructure composite electrode confined by ultrafine carbon nanotubes and a preparation method and application thereof. The nanosize effect of phosphating-induced regulation of the diameter of carbon nanotubes presents abundant active sites and electron transfer pathways, which contributes to the electrocatalytic intrinsic performance of hydrogen production by electrolysis of water.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A method for preparing an ultrafine carbon nanotube confined bimetallic phosphide heterostructure composite electrode comprises the following steps:

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

[0009] Step S2: The phosphorus source and the cobalt-based zeolite imidazolate framework structure / nickel foam are heated to a certain high temperature at a certain heating rate, and maintained in an argon inert atmosphere for a certain period of time, so that solid-phase metal ion exchange occurs under high temperature conditions; at the same time, multiphase catalysis is carried out to form carbon nanotubes by in-situ directional growth, and an ultrafine carbon nanotube-confined cobalt phosphide-nickel phosphide composite electrode is obtained.

[0010] Furthermore, the nickel foam in step S1 has an area of ​​1 to 100 cm 2 , electrodes with a thickness of 1 to 10 mm.

[0011] Furthermore, the organic ligand in step S1 is imidazole and its derivatives, such as at least one of dimethylimidazole, 1-methylimidazole, 2-ethylimidazole, 2-nitroimidazole and benzimidazole.

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

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

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

[0015] Furthermore, 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] Furthermore, the amount of the phosphorus source in step S2 is 1-20 times the molar amount of the metal salt.

[0017] The heterogeneous structure formed after phosphating is CoP, Ni 2 The crystal structure of P.

[0018] The phosphine etching produced by phosphating can limit the radial growth of carbon nanotubes, resulting in the formation of carbon nanotubes with a diameter of about 50nm, which is thinner than the diameter of carbonized carbon nanotubes (200nm). The present invention constructs a CoP-Ni confined ultrafine carbon nanotube with a three-dimensional interwoven network structure. 2 P bimetallic phosphide composite electrode material. This design not only induces a significant nano-size effect, presents a larger specific surface area, promotes the rapid transfer of electrons, and effectively increases the number of active sites. At the same time, the nanoscale-regulated CoP-Ni anchored on the carbon nanotubes with a smaller diameter 2 P heterostructure, whose heterogeneous interface can effectively regulate the d-band structure of the active site, redistribute the interface charge, accelerate electron transfer, and improve the electron cloud density redistribution, thereby improving its intrinsic catalytic activity.

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

[0020] Beneficial effects of the present invention:

[0021] 1. Electrocatalytic hydrogen evolution performance of the catalyst in a standard three-electrode system. CoP-Ni 2 P@U-NCNTs / NF exhibits superior performance (η 100 =184mV and η 200 =235mV), with the increase of current density, the gap between Pt / C and commercial Pt / C gradually narrowed; at 100mA·cm -2 When the above, the performance exceeds 20% of commercial Pt / C. The stability of the electrode material was tested under alkaline conditions using the chronoamperometry method, showing excellent stability;

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

[0023] 3. The stability of the catalyst under different voltages was tested by chronoamperometry, and it was found that it remained stable after 48 hours, indicating that the ultrafine carbon nanotube-confined bimetallic phosphide electrode material provided by the present invention has excellent electrochemical stability and has practical industrial production significance;

[0024] 4. The present invention constructs a "green electricity to green hydrogen" system. The green electricity generated by solar cells (voltage is 4.34V) drives the complete water splitting to produce hydrogen through bifunctional electrocatalysts. Since the process can achieve zero carbon emissions and does not produce any pollution, it is environmentally friendly and sustainable. The catalyst developed by the present invention has broad application prospects in the process of achieving "carbon neutrality". BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention will be further described below in conjunction with the accompanying drawings.

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

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

[0028] Figure 3 The EIS graphs are of cobalt-based zeolite imidazolate framework structure / nickel foam, cobalt-nickel@carbon nanotube / nickel foam, and cobalt phosphide-nickel phosphide@ultrafine carbon nanotube;

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

[0030] Figure 5 This is a diagram of the stable performance of cobalt phosphide-nickel phosphide heterostructure electrode materials confined by ultrafine carbon nanotubes under different current densities. DETAILED DESCRIPTION

[0031] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] Embodiment 1

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

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

[0035] (2) 1 g of ammonium dihydrogen phosphate was placed upstream of the tube furnace, and the nano-sheet-shaped cobalt-based zeolite imidazolate framework structure / nickel foam was placed downstream of the tube furnace. The mixture was heated at 1 °C min in an argon inert atmosphere. -1 The temperature was raised to 650 °C at a rate of 100 °C and maintained for 120 min. Solid-phase metal ion exchange occurred and heterogeneous catalysis in situ directional growth formed carbon nanotubes to obtain ultrafine carbon nanotube-confined cobalt phosphide-nickel phosphide bimetallic phosphide composite electrodes (CoP-Ni 2 P@U-NCNTs / NF).

[0036] Embodiment 2

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

[0038] (1) 0.4 mol of dimethyl imidazole and 0.05 mol of cobalt nitrate were prepared into two 40 mL homogeneous solutions, which were fully mixed and 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, and the sample was washed with deionized water for multiple times and dried overnight to obtain a nano-sheet-shaped cobalt-based zeolite imidazole ester framework structure / nickel foam;

[0039] (2) 2 g of diammonium hydrogen phosphate was placed upstream of the tube furnace, and the lamellae-shaped cobalt-based zeolite imidazolate framework structure / nickel foam was placed downstream of the tube furnace at 0.5 °C·min -1 The temperature was raised to 750 °C and maintained for 90 min, solid-phase metal ion exchange occurred, and heterogeneous catalysis in situ directional growth formed carbon nanotubes to obtain ultrafine carbon nanotube-confined cobalt phosphide-nickel phosphide composite electrodes (CoP-Ni 2 P@U-NCNTs / NF).

[0040] Embodiment 3

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

[0042] (1) 0.8 mol of dimethyl imidazole and 0.05 mol of cobalt nitrate were prepared into two 40 mL homogeneous solutions, which were fully mixed and reacted for 10 min to form a blue-purple colloidal liquid. The nickel foam was placed vertically in the solution and fully soaked for 8 h, and the sample was washed with deionized water for multiple times and dried overnight to obtain a nano-sheet-shaped cobalt-based zeolite imidazole ester framework structure / nickel foam;

[0043] (2) 2 g of diammonium hydrogen phosphate was placed upstream of the tube furnace, and the lamellae-shaped cobalt-based zeolite imidazolate framework structure / nickel foam was placed downstream of the tube furnace. The mixture was heated at 1 °C min in an argon inert atmosphere. -1 The temperature was raised to 850 °C and maintained for 90 min, solid-phase metal ion exchange occurred, and heterogeneous catalysis in situ directional growth formed carbon nanotubes to obtain ultrafine carbon nanotube-confined cobalt phosphide-nickel phosphide composite electrodes (CoP-Ni 2 P@U-NCNTs / NF).

[0044] Embodiment 4

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

[0046] (1) 0.8 mol of dimethyl imidazole and 0.05 mol of cobalt nitrate were prepared into two 40 mL homogeneous solutions, which were fully mixed and reacted for 10 min to form a blue-purple colloidal liquid. The nickel foam was placed vertically in the solution and fully soaked for 8 h, and the sample was washed with deionized water for multiple times and dried overnight to obtain a nano-sheet-shaped cobalt-based zeolite imidazole ester framework structure / nickel foam;

[0047] (2) 2 g of diammonium hydrogen phosphate was placed upstream of the tube furnace, and the lamellae-shaped cobalt-based zeolite imidazolate framework structure / nickel foam was placed downstream of the tube furnace. The mixture was heated at 1 °C min in an argon inert atmosphere. -1 The temperature was raised to 850 °C at a rate of 100 °C and maintained for 120 min. Solid-phase metal ion exchange occurred and carbon nanotubes were formed by in-situ directional growth of heterogeneous catalysis. Ultrafine carbon nanotube-confined cobalt phosphide-nickel phosphide composite electrodes (CoP-Ni 2 P@U-NCNTs / NF).

[0048] Embodiment 5

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

[0050] (1) 0.2 mol of dimethyl imidazole and 0.05 mol of cobalt nitrate were prepared into two 40 mL homogeneous solutions, which were fully mixed and reacted for 10 min to form a blue-purple colloidal liquid. The nickel foam was placed vertically in the solution and fully soaked for 8 h, and the sample was washed with deionized water for multiple times and dried overnight to obtain a nano-sheet cobalt-based zeolite imidazole ester framework structure / nickel foam;

[0051] (2) 1.5 g of diammonium hydrogen phosphate was placed upstream of the tube furnace, and the lamellae-shaped cobalt-based zeolite imidazolate framework structure / nickel foam was placed downstream of the tube furnace. The mixture was heated at 0.5 °C / min in an argon inert atmosphere. -1 The temperature was raised to 750 °C and maintained for 90 min, solid-phase metal ion exchange occurred, and heterogeneous catalysis in situ directional growth formed carbon nanotubes to obtain ultrafine carbon nanotube-confined cobalt phosphide-nickel phosphide composite electrodes (CoP-Ni 2 P@U-NCNTs / NF).

[0052] Comparative Example 1

[0053] (1) 0.05 mol of dimethyl imidazole and 0.05 mol of cobalt nitrate were prepared into two 40 mL homogeneous solutions, mixed and reacted for 10 min to form a blue-purple colloidal liquid. The nickel foam was placed vertically in the solution and fully soaked for 8 h, and the sample was washed with deionized water for multiple times and dried overnight to obtain a nano-sheet cobalt-based zeolite imidazole ester framework structure / nickel foam;

[0054] (2) The blade-shaped cobalt-based zeolite imidazolate framework structure / nickel foam was heated in an argon inert atmosphere at 1°C min -1 The temperature was raised to 750 °C at a rate of 1000 °C and maintained for 180 min, during which solid-phase metal ion exchange occurred and carbon nanotubes were formed by in-situ directional growth of heterogeneous catalysis to obtain a carbon nanotube-confined cobalt-nickel composite electrode (Co-Ni@NCNTs / NF).

[0055] Comparative Example 2

[0056] (1) 0.05 mol of dimethyl imidazole and 0.05 mol of cobalt nitrate were prepared into two 40 mL homogeneous solutions, which were fully mixed and 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, and the sample was washed with deionized water for multiple times and dried overnight to obtain a cobalt-based zeolite imidazole ester framework structure / nickel foam;

[0057] (2) The blade-shaped cobalt-based zeolite imidazolate framework structure / nickel foam was heated in an argon inert atmosphere at 1°C min -1The temperature was raised to 450 °C at a rate of 100 °C and maintained for 90 min, during which solid-phase metal ion exchange occurred and carbon nanotubes were formed by in-situ directional growth of heterogeneous catalysis to obtain an ultrafine carbon nanotube-confined cobalt-nickel composite electrode (Co-Ni@NCNTs / NF).

[0058] like Figure 1-Figure 5 The following are the performance characteristics of the above-mentioned embodiments and comparative examples. The heterogeneous structure formed after phosphating is CoP, Ni 2 The crystal structure of P Figure 1 ); the phosphine etching produced by phosphating can limit the radial growth of carbon nanotubes, resulting in the formation of carbon nanotubes with a diameter of about 50nm, which is thinner than the diameter of carbonized carbon nanotubes (200nm). The present invention constructs a cobalt phosphide-nickel phosphide composite electrode material (with a three-dimensional interwoven network structure) confined by ultrafine carbon nanotubes Figure 2 ). This design not only induces a significant nano-size effect, presents a 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 phosphide-nickel phosphide heterostructure anchored on a carbon nanotube with a thinner diameter, its heterogeneous interface can effectively regulate the d-band structure of the active site, redistribute the interface charge, accelerate electron transfer, and improve the redistribution of electron cloud density, thereby improving its intrinsic catalytic activity. In addition, combined with the attached figure, it can be seen that:

[0059] 1. Electrocatalytic hydrogen evolution performance of catalysts in a standard three-electrode system. Cobalt phosphide-nickel phosphide@ultrafine carbon nanotubes / nickel foam showed superior performance (η 100 =184mV and η 200 =235mV), with the increase of current density, the gap between it and commercial Pt / C gradually narrows; at 100mA cm -2 When the performance is above 20%, it exceeds that of commercial Pt / C by 20%. The stability of the electrode material was tested under alkaline conditions using the chronoamperometry method, showing excellent stability ( Figure 3 );

[0060] 2. The Tafel slopes of these catalysts further verified the Volmer-Heyrovesky pathway in the HER process. Figure 4 The electrochemical impedance directly reflects the charge transfer impedance of the catalytic material. The Nyquist plot value of cobalt phosphide-nickel phosphide@ultrafine carbon nanotubes / nickel foam (R = 7.1 ohm) is smaller than that of the reference sample (R 钴基沸石咪唑酯骨架结构 / 泡沫镍 >12ohm, R 钴-镍@碳纳米管 / 泡沫镍 =9.6ohm), 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 was tested by chronoamperometry. It was found that the catalyst remained stable after 48 hours, indicating that the ultrafine carbon nanotube-confined bimetallic phosphide electrode material provided by the present invention has excellent electrochemical stability and has practical industrial production significance ( Figure 5 ).

[0062] The above specific implementation method part specifically introduces the analytical method involved in the present invention. It should be noted that the above introduction is only to help those skilled in the art better understand the method and ideas of the present invention, rather than limiting the relevant content. Without departing from the principle of the present invention, those skilled in the art may also make appropriate adjustments or modifications to the present invention, and the above adjustments and modifications shall also fall within the scope of protection of the present invention.

Claims

1. A method for preparing a bimetallic phosphide heterostructure composite electrode confined by ultrafine carbon nanotubes, characterized in that: The following steps are involved: Step S1: After the organic ligand and the cobalt metal salt are uniformly mixed with the solvent respectively, two homogeneous solutions are formed, which are mixed and fully reacted to form a blue-purple colloidal liquid; the nickel foam is vertically placed in the solution and fully immersed for 4 hours, the sample is washed with deionized water for multiple times and dried overnight to obtain a cobalt-based zeolite imidazolate framework structure / nickel foam; Step S2: The phosphorus source and the cobalt-based zeolite imidazolate framework structure / nickel foam are heated to a certain high temperature at a certain heating rate, and maintained in an argon inert atmosphere for a certain period of time, so that solid-phase metal ion exchange occurs under high temperature conditions; at the same time, multiphase catalysis is carried out to form carbon nanotubes by in-situ directional growth, and an ultrafine carbon nanotube-confined cobalt phosphide-nickel phosphide composite electrode is obtained.

2. The method for preparing a bimetallic phosphide heterostructure composite electrode confined by ultrafine carbon nanotubes according to claim 1, characterized in that: The nickel foam in step S1 has an area of ​​1 to 100 cm 2 , electrodes with a thickness of 1 to 10 mm.

3. The method for preparing a bimetallic phosphide heterostructure composite electrode confined by ultrafine carbon nanotubes according to claim 1, characterized in that: The organic ligand in step S1 is imidazole and its derivatives.

4. The method for preparing an ultrafine carbon nanotube-confined bimetallic phosphide heterostructure composite electrode according to claim 1, characterized in that: The metal salt in step S1 is a cobalt salt.

5. The method for preparing an ultrafine carbon nanotube-confined bimetallic phosphide heterostructure composite electrode according to claim 1, characterized in that: The molar ratio of the organic ligand to the metal salt in step S1 is (1-10):

1.

6. The method for preparing an ultrafine carbon nanotube-confined bimetallic phosphide heterostructure composite electrode according to claim 1, characterized in that: The solvent in step S1 is at least one of deionized water, methanol and ethanol.

7. The method for preparing an ultrafine carbon nanotube-confined bimetallic phosphide heterostructure composite electrode according to claim 1, characterized in that: 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.

8. The method for preparing a bimetallic phosphide heterostructure composite electrode confined by ultrafine carbon nanotubes according to claim 1, characterized in that: The amount of the phosphorus source in step S2 is 1-20 times the molar amount of the metal salt.

9. An ultrafine carbon nanotube confined bimetallic phosphide heterostructure composite electrode, characterized in that: Prepared according to the preparation method according to any one of claims 1 to 8.

10. Application of the ultrafine carbon nanotube-confined bimetallic phosphide heterostructure composite electrode according to claim 9 in the field of hydrogen production by water electrolysis.

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