A cobalt composite nickel phosphide nanotube array and a preparation method and application thereof

Abstract

The present application relates to a kind of cobalt composite phosphorus nickel nanotube array and its preparation method and application, specifically, zinc oxide template electrodeposition and phosphating heat treatment preparation cobalt composite phosphorus nickel nanotube array method is used to improve the performance of hydrogen production by alkaline water electrolysis.The present application uses conductive material as substrate, by constant current electrodeposition, zinc oxide nanorod array loaded on conductive substrate is obtained, further constant current co-deposition is carried out to prepare elemental cobalt composite elemental nickel nanorod array, after phosphating heat treatment, zinc oxide template is removed by alkaline solution, and cobalt composite phosphorus nickel nanotube array is obtained.The elemental cobalt with lower composite oxidation potential can effectively reduce anode overpotential, coupled with cathode hydrogen evolution reaction, the cell voltage of alkaline water hydrogen evolution reaction can be reduced, and the harmful urea pollutants to the environment can be consumed.The process is simple and low in cost, and green and efficient, and the cobalt composite phosphorus nickel nanotube array prepared has excellent electrocatalytic oxidation performance.

Description

Technical Field

[0001] This invention relates to the field of electrocatalytic oxidation technology, specifically to a method for preparing cobalt-based nickel phosphide nanotubes and its application in promoting efficient urea electrooxidation and hydrogen production via alkaline water electrolysis. Background Technology

[0002] Hydrogen, due to its high energy density and lack of greenhouse gas emissions after depletion, is considered the most promising and practical energy carrier. Vigorously developing and promoting hydrogen energy can effectively reduce carbon emissions and is of great significance to achieving sustainable development for human society. Hydrogen production through water electrolysis, using water molecules as the hydrogen source and electricity as the power source to obtain high-purity hydrogen products, can largely avoid pollutants and achieve zero carbon emissions. However, the high cost due to massive energy consumption remains a bottleneck restricting its application. In typical water electrolysis, the hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction (OER) at the anode are coupled. Compared to HER, OER, due to its complex four-electron transfer process, is always slow, and its theoretical potential is 1.23V vs. HER, leading to high voltage-driven, high-efficiency hydrogen production. Although efforts have been made to develop effective OER catalysts to reduce overpotential, the energy consumption of water electrolysis remains high. In contrast, coupling HER with thermodynamically more favorable organic oxidation reactions not only effectively reduces the overpotential of the anode reaction but also reduces environmental pollution by oxidizing organic pollutants in nature. The thermodynamic potential required for the urea oxidation reaction (UOR) is only 0.37 V (vs. RHE), significantly lower than that for the oxygen evolution reaction (OER) at 1.23 V (vs. RHE), theoretically saving 70% of energy (Advanced Functional Materials, 2020, 30(21):2000556). Furthermore, urea production in industry and its use as a nitrogen fertilizer in agriculture, along with the generation of urea-containing wastewater from human and animal urine, lead to serious environmental problems. Untreated urea-containing wastewater also pollutes the atmosphere, groundwater, and soil, causing severe health issues for humans. The urea oxidation reaction can not only effectively treat urea-containing wastewater but also produce hydrogen, a clean energy source. However, due to the inherent six-electron transfer process in the urea oxidation reaction, the reaction kinetics are slow, requiring a high overpotential to overcome the reaction barrier, resulting in greater energy consumption. Therefore, highly active, stable, and inexpensive catalysts are essential for the widespread application of these technologies in the future (Small, 2020, 16, 1906133). Currently reported UOR catalysts generally suffer from low catalytic activity and high overpotential, urgently requiring highly active, low-overpotential, stable, and efficient urea oxidation electrocatalysts. Previous studies have shown that non-noble metal transition metal nickel (Ni)-based compounds exhibit higher urea oxidation catalytic activity than other metal compounds, among which Ni...3+ (NiOOH) was identified as the catalytic active site. Unfortunately, these urea oxidation catalysts still exhibit unsatisfactory catalytic activity (Angewandte Chemie, 2021, 133, 10671-10676). The urea oxidation mechanism involves electrocatalytic dehydrogenation and spontaneous urea oxidation; the key to improving urea oxidation activity is to reduce NiOOH. 3+ The formation potential of (NiOOH) is reduced. Because cobalt has a lower oxidation potential than metallic nickel, the catalyst formed by combining cobalt and nickel can effectively reduce the oxidation potential of Ni. 3+ The generation potential of (NiOOH) is reduced by this electrocatalyst design strategy, which not only greatly reduces energy consumption but also improves electrolysis efficiency (Angewandte Chemie International Edition, 2021, 60, 7297-7307). Summary of the Invention

[0003] The purpose of this invention is to provide a cobalt-nickel phosphide composite nanotube array and its preparation method, and to use it as a nickel-based catalytic electrode for the electrocatalytic oxidation of urea. The process is simple and low-cost, and the prepared cobalt-nickel phosphide nanotube array exhibits excellent electrocatalytic oxidation performance. By combining it with cobalt, which has a low oxidation potential, the anodic overpotential can be effectively reduced. Coupled with the cathodic hydrogen evolution reaction, the battery voltage of the alkaline water hydrogen evolution reaction can be reduced. At the same time, it can consume urea pollutants that are harmful to the environment, exhibiting green and efficient characteristics.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] This invention provides a method for preparing cobalt-nickel phosphide composite nanotube arrays through constant current electrodeposition and phosphating heat treatment, the specific steps of which are as follows:

[0006] (1) The conductive substrate was immersed in a mixed aqueous solution of zinc nitrate and ammonium nitrate. At 70~90 °C, in a two-electrode electrolytic cell, the conductive electrode was used as the counter electrode, and constant current electrodeposition was used to obtain an array of zinc oxide nanorods grown vertically on the conductive substrate.

[0007] (2) The zinc oxide nanorod array obtained in step (1) is placed in a mixed solution containing nickel sulfate, cobalt sulfate, ammonium chloride and sodium hypophosphite, and at room temperature, a constant current co-deposition is performed using a conductive electrode as the counter electrode to obtain a zinc oxide nanorod array loaded with nickel and cobalt.

[0008] (3) The zinc oxide nanorod array loaded with nickel and cobalt obtained in step (2) is subjected to phosphating heat treatment in an inert atmosphere, and then naturally cooled to obtain a cobalt composite nickel phosphide nanorod array self-supported on a conductive substrate.

[0009] (4) Remove the zinc oxide template from the nanorod array obtained in step (3) in an alkaline solution to obtain a cobalt composite nickel phosphide nanotube array self-supported on nickel foam.

[0010] Furthermore, the conductive substrate used in step (1) includes nickel foam, titanium sheet, copper sheet, copper mesh, carbon cloth, carbon paper, or conductive glass, with nickel foam being preferred. For example, the processing method for nickel foam is as follows: first, the nickel foam is cut into pieces with an area of ​​2~9 cm². 2 Surface impurities are removed with acetone, then washed with dilute hydrochloric acid, and finally washed with ultrapure water and ethanol. The treated nickel foam is then stored in anhydrous ethanol.

[0011] Furthermore, in the mixed aqueous solution of step (1), the concentration of zinc nitrate is 0.01~1 M, preferably 0.01 M, and the concentration of ammonium nitrate is 0.01 M~1 M, preferably 0.05 M.

[0012] Furthermore, the current used for constant current electrodeposition in step (1) is -0.5 mA / cm. 2 ~-5 mA / cm 2 Preferred value: -1.5mA / cm 2 The electrodeposition time is 30~180 min, preferably 90 min. The ZnO nanorods prepared under these conditions have a hexagonal prism morphology.

[0013] Furthermore, in the mixed solution of step (2), the concentration range of nickel sulfate is 0.001~0.01 M, the concentration range of cobalt sulfate is 0.001~0.01 M, the concentration range of ammonium chloride is 0.001~0.05 M, preferably 0.018 M, and the concentration range of sodium hypophosphite is 0.001~0.02 M, preferably 0.002 M.

[0014] Furthermore, the electrodeposition current in step (2) is -0.3 mA / cm. -2 ~ -1 mA / cm -2 0.5 mA / cm is preferred. 2 The electrodeposition time is 100~150 min, preferably 120 min.

[0015] Furthermore, in step (3), the high-temperature phosphating atmosphere is argon, the temperature is 300~350 ℃, preferably 320 ℃, the constant temperature time is 1~3 h, preferably 2 h, and the heating rate is 1~20 ℃ / min, preferably 5 ℃ / min.

[0016] Furthermore, in step (4), the alkaline solution is an ammonia solution with a concentration of 0.01~5 M.

[0017] This invention provides a cobalt-nickel phosphide nanotube array prepared using the above method. This invention also provides the application of the cobalt-nickel phosphide nanotube array in promoting alkaline water electrolysis for hydrogen production through urea electrooxidation. The cobalt-nickel phosphide nanotube array achieves 200 mA / cm² at a potential of 1.49–1.59 V (vs. RHE). -2 The current density.

[0018] The beneficial effects of this invention are as follows: This invention effectively reduces the anolyte overpotential by combining cobalt, which has a low oxidation potential, with the coupling effect of the cathode hydrogen evolution reaction, thus lowering the battery voltage of the alkaline water hydrogen evolution reaction. Simultaneously, it consumes environmentally harmful urea pollutants, exhibiting green and efficient characteristics. The process of this invention is simple and low-cost, and the prepared cobalt-nickel phosphide nanotube array exhibits excellent electrocatalytic oxidation performance. The cobalt-nickel phosphide synthesized in this invention requires a low electrode potential at high current densities and has high catalytic urea oxidation efficiency. Attached Figure Description

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

[0020] Figure 1 The images show the X-ray diffraction patterns of the catalysts prepared in Example 1, Comparative Example 1, and Comparative Example 2 of this invention.

[0021] Figure 2 This is a scanning electron microscope image of the Co / Ni4-P nanotube array prepared in Example 1 of the present invention.

[0022] Figure 3 Polarization curves of the catalysts prepared in Examples 1-5 and Comparative Examples 1-3 of this invention in 1 M potassium hydroxide and 0.33 M urea.

[0023] Figure 4 Polarization curves of the catalyst prepared in Example 1 of this invention in 1 M potassium hydroxide (dashed line) and 1 M potassium hydroxide plus 0.33 M urea (solid line). Detailed Implementation

[0024] The present invention will be further described below with reference to specific embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make some non-essential improvements and adjustments based on the above-described invention.

[0025] Example 1 (Co / Ni4-P)

[0026] The preparation method of the cobalt-nickel phosphide (Co / Ni4-P) nanotube array in this embodiment is as follows:

[0027] (1) A 1.0 cm * 2.0 cm piece of treated nickel foam was immersed in a mixed aqueous solution of 0.01 M zinc nitrate and 0.05 M ammonium nitrate. At 70 °C, a graphite rod was used as the counter electrode, and a current of -1.5 mA / cm was applied. 2 Zinc oxide nanorod arrays can be obtained by constant current electrodeposition for 90 min.

[0028] (2) The obtained zinc oxide nanorod array was placed in an electrolyte of 0.0072 M nickel sulfate, 0.0018 M cobalt sulfate, 0.018 M ammonium chloride, and 0.002 M sodium hypophosphite (pH adjusted to 6 using an alkaline solution). At room temperature, with graphite rods as the counter electrode, a current of -0.5 mA / cm was applied. 2 Nickel and cobalt were simultaneously loaded onto a zinc oxide nanorod array by constant current deposition for 120 min.

[0029] (3) The nanorod array of elemental nickel and cobalt loaded on zinc oxide obtained in step (2) was subjected to phosphating heat treatment with sodium hypophosphite as phosphorus source under argon atmosphere. The heating rate was 5℃ / min, and the temperature was kept constant at 320℃ for 2 h. After natural cooling, it was taken out to obtain the elemental cobalt composite nickel phosphide nanorod array loaded on zinc oxide.

[0030] (4) The nanorod array obtained in step (3) was placed in ammonia water with a concentration of 0.01 M to remove the zinc oxide template and obtain elemental cobalt composite nickel phosphide nanotubes (in the name Co / Ni4-P, it means that the concentration ratio of nickel sulfate to cobalt sulfate in the electrolyte is 4:1. The catalyst naming method in the following examples is the same as in Example 1).

[0031] Table 1. ICP detection results of the catalyst prepared in Example 1

[0032] catalyst Co / Ni4-P(Ni) Co / Ni4-P(Ni) Deposition mass (mg) 1.21 0.14

[0033] Table 1 shows the mass of elemental nickel and elemental cobalt deposited on the conductive substrate in Example 1.

[0034] Example 2 (Co@Ni6-P)

[0035] The preparation method of the cobalt-nickel phosphide (Co / Ni6-P) nanotube array in this embodiment is as follows:

[0036] (1) A 1.0 cm * 2.0 cm piece of treated nickel foam was immersed in a mixed aqueous solution of 0.01 M zinc nitrate and 0.05 M ammonium nitrate at 70 °C, using a graphite rod as the counter electrode, and a current of -1.5 mA / cm was applied.2 Zinc oxide nanorod arrays can be obtained by constant current electrodeposition for 90 min.

[0037] (2) The obtained zinc oxide nanorod array was placed in an electrolyte of 0.0078 M nickel sulfate, 0.0013 M cobalt sulfate, 0.018 M ammonium chloride, and 0.002 M sodium hypophosphite (pH adjusted to 6 using an alkaline solution). At room temperature, a graphite rod was used as the counter electrode, and a current of -0.5 mA / cm was applied. 2 Nickel and cobalt were simultaneously loaded onto a zinc oxide nanorod array by constant current deposition for 120 min.

[0038] (3) The nanorod array of elemental nickel and cobalt loaded on zinc oxide obtained in step (2) was subjected to phosphating heat treatment with sodium hypophosphite as phosphorus source under argon atmosphere. The heating rate was 5℃ / min, and the temperature was kept constant at 320℃ for 2 h. After natural cooling, it was taken out to obtain the elemental cobalt composite nickel phosphide nanorod array loaded on zinc oxide.

[0039] (4) The nanorod array obtained in step (3) is placed in ammonia water with a concentration of 0.1 M to remove the zinc oxide template, and then the elemental cobalt composite nickel phosphide nanotubes are obtained.

[0040] Example 3 (Co / Ni2-P)

[0041] The preparation method of the cobalt-nickel phosphide (Co / Ni2-P) nanotube array in this embodiment is as follows:

[0042] (1) A 1.0 cm * 2.0 cm piece of treated nickel foam was immersed in a mixed aqueous solution of 0.01 M zinc nitrate and 0.05 M ammonium nitrate at 70 °C, using a graphite rod as the counter electrode, and a current of -1.5 mA / cm was applied. 2 Zinc oxide nanorod arrays can be obtained by constant current electrodeposition for 90 min.

[0043] (2) The obtained zinc oxide nanorod array was placed in an electrolyte of 0.006 M nickel sulfate, 0.003 M cobalt sulfate, 0.018 M ammonium chloride, and 0.002 M sodium hypophosphite (pH adjusted to 6 using an alkaline solution). At room temperature, with graphite rods as the counter electrode, a current of -0.5 mA / cm was applied. 2 Nickel and cobalt were simultaneously loaded onto a zinc oxide nanorod array by constant current deposition for 120 min.

[0044] (3) The nanorod array of elemental nickel and cobalt loaded on zinc oxide obtained in step (2) was subjected to phosphating heat treatment with sodium hypophosphite as phosphorus source under argon atmosphere. The heating rate was 5℃ / min, and the temperature was kept constant at 320℃ for 2 h. After natural cooling, it was taken out to obtain the elemental cobalt composite nickel phosphide nanorod array loaded on zinc oxide.

[0045] (4) The nanorod array obtained in step (3) is placed in ammonia water with a concentration of 1 M to remove the zinc oxide template, and then the elemental cobalt composite nickel phosphide nanotubes are obtained.

[0046] Example 4 (Co3 / Ni2-P)

[0047] The preparation method of the cobalt composite nickel phosphide (Co3 / Ni2-P) nanotube array in this embodiment is as follows:

[0048] (1) A 1.0 cm * 2.0 cm piece of treated nickel foam was immersed in a mixed aqueous solution of 0.01 M zinc nitrate and 0.05 M ammonium nitrate at 70 °C, using a graphite rod as the counter electrode, and a current of -1.5 mA / cm was applied. 2 Zinc oxide nanorod arrays can be obtained by constant current electrodeposition for 90 min.

[0049] (2) The obtained zinc oxide nanorod array was placed in an electrolyte of 0.0036 M nickel sulfate, 0.0054 M cobalt sulfate, 0.018 M ammonium chloride, and 0.002 M sodium hypophosphite (pH adjusted to 6 using an alkaline solution). At room temperature, with graphite rods as the counter electrode, a current of -0.5 mA / cm was applied. 2 Nickel and cobalt were simultaneously loaded onto a zinc oxide nanorod array by constant current deposition for 120 min.

[0050] (3) The nanorod array of elemental nickel and cobalt loaded on zinc oxide obtained in step (2) was subjected to phosphating heat treatment with sodium hypophosphite as phosphorus source under argon atmosphere. The heating rate was 5℃ / min, and the temperature was kept constant at 320℃ for 2 h. After natural cooling, it was taken out to obtain the elemental cobalt composite nickel phosphide nanorod array loaded on zinc oxide.

[0051] (4) The nanorod array obtained in step (3) is placed in ammonia water with a concentration of 2 M to remove the zinc oxide template, and then the elemental cobalt composite nickel phosphide nanotubes are obtained.

[0052] Example 5 (Co2 / Ni-P)

[0053] The preparation method of the cobalt-nickel phosphide (Co2 / Ni-P) nanotube array in this embodiment is as follows:

[0054] (1) A 1.0 cm * 2.0 cm piece of treated nickel foam was immersed in a mixed aqueous solution of 0.01 M zinc nitrate and 0.05 M ammonium nitrate at 70 °C, with a graphite rod as the counter electrode, using -1.5 mA / cm 2 Zinc oxide nanorod arrays can be obtained by constant current electrodeposition for 90 min.

[0055] (2) The obtained zinc oxide nanorod array was placed in an electrolyte of 0.003 M nickel sulfate, 0.006 M cobalt sulfate, 0.018 M ammonium chloride, and 0.002 M sodium hypophosphite (pH adjusted to 6 using an alkaline solution). At room temperature, the graphite rod was used as the counter electrode, and a voltage of -0.5 mA / cm was applied. 2 Nickel and cobalt were simultaneously loaded onto a zinc oxide nanorod array by constant current deposition for 120 min.

[0056] (3) The nanorod array of elemental nickel and cobalt loaded on zinc oxide obtained in step (2) was subjected to phosphating heat treatment with sodium hypophosphite as phosphorus source under argon atmosphere. The heating rate was 5℃ / min, and the temperature was kept constant at 320℃ for 2 h. After natural cooling, it was taken out to obtain the elemental cobalt composite nickel phosphide nanorod array loaded on zinc oxide.

[0057] (4) The nanorod array obtained in step (3) is placed in ammonia water with a concentration of 5 M to remove the zinc oxide template, and then the elemental cobalt composite nickel phosphide nanotubes are obtained.

[0058] Comparative Example 1 (Ni-P)

[0059] (1) A 1.0 cm * 2.0 cm piece of treated nickel foam was immersed in a mixed aqueous solution of 0.01 M zinc nitrate and 0.05 M ammonium nitrate at 70 °C, with a graphite rod as the counter electrode, using -1.5 mA / cm 2 Zinc oxide nanorod arrays can be obtained by constant current electrodeposition for 90 min.

[0060] (2) The obtained zinc oxide nanorod array was placed in an electrolyte containing 0.009 M nickel sulfate, 0.018 M ammonium chloride, and 0.002 M sodium hypophosphite (pH adjusted to 6 using an alkaline solution). At room temperature, graphite rods (1.8 cm) were used to... 2 () as the counter electrode, using -0.5 mA / cm 2 Nickel was loaded onto a zinc oxide nanorod array by constant current deposition for 120 min.

[0061] (3) The elemental nickel nanorod array loaded on zinc oxide obtained in step (2) was subjected to phosphating heat treatment with sodium hypophosphite as phosphorus source under argon atmosphere. The heating rate was 5℃ / min, and the temperature was kept constant at 320℃ for 2 h. After natural cooling, the array was taken out to obtain the nickel phosphide nanorod array loaded on zinc oxide.

[0062] (4) The nanorod array obtained in step (3) is placed in ammonia water with a concentration of 1 M to remove the zinc oxide template and obtain a nickel phosphide nanotube array.

[0063] Comparative Example 2 (Co-P)

[0064] (1) A 1.0 cm * 2.0 cm piece of treated nickel foam was immersed in a mixed aqueous solution of 0.01 M zinc nitrate and 0.05 M ammonium nitrate at 70 °C, with a graphite rod as the counter electrode, using -1.5 mA / cm 2 Zinc oxide nanorod arrays can be obtained by constant current electrodeposition for 90 min.

[0065] (2) The obtained zinc oxide nanorod array was placed in an electrolyte of 0.009 M cobalt sulfate, 0.018 M ammonium chloride, and 0.002 M sodium hypophosphite (pH adjusted to 6 using an alkaline solution). At room temperature, the graphite rod was used as the counter electrode, and a current of -0.5 mA / cm was applied. 2 Cobalt was loaded onto a zinc oxide nanorod array by constant current deposition for 120 min.

[0066] (3) The elemental nickel nanorod array loaded on zinc oxide obtained in step (2) was subjected to phosphating heat treatment with sodium hypophosphite as phosphorus source under argon atmosphere. The heating rate was 5℃ / min, and the temperature was kept constant at 320℃ for 2h. After natural cooling, the array was taken out to obtain cobalt phosphide nanorod array loaded on zinc oxide.

[0067] (4) The nanorod array obtained in step (3) is placed in ammonia water with a concentration of 1 M to remove the zinc oxide template and obtain cobalt phosphide nanotubes.

[0068] Comparative Example 3 (Co-Ni4)

[0069] (1) A 1.0 cm * 2.0 cm piece of treated nickel foam was immersed in a mixed aqueous solution of 0.01 M zinc nitrate and 0.05 M ammonium nitrate at 70 °C, with a graphite rod as the counter electrode, using -1.5 mA / cm 2 Zinc oxide nanorod arrays can be obtained by constant current electrodeposition for 90 min.

[0070] (2) The obtained zinc oxide nanorod array was placed in an electrolyte of 0.0072 M nickel sulfate, 0.0018 M cobalt sulfate, 0.018 M ammonium chloride, and 0.002 M sodium hypophosphite (pH adjusted to 6 using an alkaline solution). At room temperature, the graphite rod was used as the counter electrode, and a voltage of -0.5 mA / cm was applied. 2 Nickel and cobalt were simultaneously loaded onto a zinc oxide nanorod array by constant current deposition for 120 min.

[0071] (3) The nanorod array obtained in step (2) was placed in ammonia water with a concentration of 1 M to remove the zinc oxide template, and elemental nickel composite elemental cobalt nanotubes were obtained.

[0072] Electrochemical performance tests of electrocatalysts prepared in Examples 1-5 and Comparative Examples 1-3

[0073] Electrochemical measurements were evaluated using a three-electrode setup with a self-supported nickel foam electrode as the working electrode, an Ag / AgCl electrode as the reference electrode, and a platinum sheet electrode as the counter electrode. The potential reference was a reversible hydrogen electrode (RHE): E RHE =E Ag / AgCl +0.098 +0.059 × pH (1 M KOH solution). Polarization curves of all examples and comparative examples in 1 M KOH and 0.33 M urea solutions were tested at a scan rate of 50 mV / s. Analysis showed that Examples 1–5 achieved a polarization rate of 200 mA / cm². 2 The electrode potentials at the current densities of all examples were lower than those of Comparative Examples 1-3, demonstrating that their catalytic performance was superior to that of Comparative Examples 1-3. Among them, Example 1 had the lowest electrode potential of 1.49 V (vs. RHE) and exhibited the best catalytic performance. See [link to relevant documentation]. Figure 3 The polarization curves of Example 1 in 1 M KOH and 1 M KOH in 0.33 M urea were tested at a scan rate of 50 mV / s. Analysis showed that at 200 mA / cm²... 2 At the specified current density, the catalyst described in Example 1 can reduce the electrode potential by 234 mV in an electrolyte containing urea compared to an electrolyte without urea. (Reference) Figure 4 None of the electrode potential data were compensated for voltage drop.

[0074] Figure 1 The images show the X-ray diffraction patterns of the catalysts prepared in Example 1, Comparative Example 1, and Comparative Example 2 of this invention. Figure 1 It can be seen that Example 1 has a clear Ni2P peak, but since the peak value of elemental Co in Example 1 is small, it is inferred from the XRD pattern and ICP results of Comparative Example 2 that the example is elemental Co.

[0075] Figure 2 This is a scanning electron microscope (SEM) image of the Co / Ni4-P nanotube array prepared in Example 1 of this invention. The image shows that the morphology of Example 1 consists of nanotubes interleaved and grown on nickel foam.

[0076] Figure 3 Polarization curves of the catalysts prepared in Examples 1-5 and Comparative Examples 1-3 of this invention in 1 M potassium hydroxide and 0.33 M urea. The graphs show that at 200 mA / cm², the polarization curves are... 2 At the given current density, the electrode potentials for urea oxidation in the embodiments are all lower than those in the embodiments, and the electrode potential required for urea oxidation in Embodiment 1 is the smallest, resulting in the best performance.

[0077] Figure 4The polarization curves of the catalyst prepared in Example 1 of this invention are shown in the figures for 1 M potassium hydroxide (dashed line) and 1 M potassium hydroxide with 0.33 M urea (solid line). The figures show that the catalyst reaches 200 mA / cm². 2 At the given current density, the electrode potential in urea solution in Example 1 is significantly lower than that in alkaline solution without urea.

[0078] The foregoing has shown and described the basic principles and main features of the present invention, as well as its advantages. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a cobalt-nickel phosphide composite nanotube array, characterized in that... Includes the following steps: (1) The conductive substrate was immersed in a mixed aqueous solution of zinc nitrate and ammonium nitrate. At 70~90℃, in a two-electrode electrolytic cell, the conductive electrode was used as the counter electrode, and constant current electrodeposition was used to obtain an array of zinc oxide nanorods grown vertically on the conductive substrate. (2) The zinc oxide nanorod array obtained in step (1) is placed in a mixed solution containing nickel sulfate, cobalt sulfate, ammonium chloride and sodium hypophosphite. At room temperature, with a conductive electrode as the counter electrode, nickel and cobalt are simultaneously loaded onto the zinc oxide nanorod array by constant current co-deposition. (3) The zinc oxide nanorod array loaded with nickel and cobalt obtained in step (2) is subjected to phosphating heat treatment in an inert atmosphere, and then naturally cooled to obtain a cobalt composite nickel phosphide nanorod array self-supported on a conductive substrate. (4) Remove the zinc oxide template from the nanorod array obtained in step (3) in an alkaline solution to obtain a cobalt composite nickel phosphide nanotube array that is self-supported on a conductive substrate. The concentration of nickel sulfate in the mixed solution of step (2) is 0.001~0.01M, the concentration of cobalt sulfate is 0.001~0.01M, the concentration of ammonium chloride is 0.001~0.1M, and the concentration of sodium hypophosphite is 0.001~0.1M.

2. The method for preparing the cobalt composite nickel phosphide nanotube array according to claim 1, characterized in that: The conductive electrode in step (1) is a graphite rod, platinum sheet or platinum wire; the conductive substrate is nickel foam, titanium sheet, copper sheet, copper mesh, carbon cloth, carbon paper or conductive glass.

3. The method for preparing the cobalt composite nickel phosphide nanotube array according to claim 1, characterized in that: When the conductive substrate is made of nickel foam, it is first cut into pieces with an area ranging from 2 to 9 cm². 2 Surface impurities were removed with acetone, then washed with dilute hydrochloric acid, and finally washed with ultrapure water and ethanol. The treated conductive substrate was then stored in anhydrous ethanol.

4. The method for preparing the cobalt composite nickel phosphide nanotube array according to claim 1, characterized in that: The concentration of zinc nitrate in the mixed aqueous solution of step (1) is 0.01 M ~ 1 M, and the concentration of ammonium nitrate is 0.01 M ~ 1 M.

5. The method for preparing the cobalt composite nickel phosphide nanotube array according to claim 1, characterized in that: The reaction conditions for the phosphating heat treatment in step (3) are as follows: using sodium hypophosphite as the phosphorus source, holding at 300~350℃ for 1~3 h under an inert atmosphere, with a heating rate of 1~20℃ / min.

6. The method for preparing the cobalt composite nickel phosphide nanotube array according to claim 1, characterized in that: In step (4), the alkaline solution used is ammonia water with a concentration of 0.01~5 M.

7. The cobalt composite nickel phosphide nanotube array prepared by the method according to any one of claims 1-6.

8. The application of the cobalt composite nickel phosphide nanotube array according to claim 7 in urea electro-oxidation to promote alkaline water electrolysis for hydrogen production.

9. The application according to claim 8, characterized in that: Cobalt-nickel phosphide nanotube arrays achieved a potential of 200 mA relative to the reversible hydrogen electrode (RHE) at a potential of 1.49–1.59 V. -2 The current density.

Images