Synthesis method of carbon-coated phosphorus-rich vacancy cobalt phosphide and application thereof in electrolytic seawater

Abstract

This invention discloses a method for preparing high-performance and long-term durable high-current seawater electrolysis materials using Co-ZIF as a precursor. The ZIF precursor is converted into cobalt phosphide encapsulated in nitrogen-doped carbon through a phosphating process, and phosphorus vacancies are further introduced using a sodium borohydride reduction method, ultimately constructing a carbon-coated phosphorus-vacancy-rich cobalt phosphide material (Co-ZIF). x P v @NC). Utilizing this catalyst as a bifunctional electrocatalyst that serves as both the cathode and anode, under industrial seawater electrolysis conditions (electrolyte: 6M KOH seawater, temperature: 60℃), only a working voltage of 1.74V is required to achieve a 1.0A cm⁻¹ anode. ‑2 This invention provides a strategy for preparing a multi-level structured material based on ZIF, which possesses a multi-level structure composed of one-dimensional nanowires and three-dimensional ZIF polyhedra. This improves the electron transfer rate during the catalytic process and enhances the catalyst's durability. When applied to high-current electrolysis of seawater, it exhibits high activity and excellent stability.

Description

Technical Field

[0001] This invention belongs to the field of vacancy engineering materials, and particularly relates to a method for preparing carbon-coated phosphorus-rich vacancy cobalt phosphide material and its application in high-current electrolysis of seawater. Background Technology

[0002] Electrolysis systems incorporating the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are considered the most promising technology for obtaining clean hydrogen. Significant progress has been made to date in the research of water splitting systems using freshwater as the electrolyte. Due to the risk of freshwater scarcity, and with seawater accounting for 97% of the Earth's water resources, seawater has become the preferred alternative to freshwater. However, due to the presence of chloride ions, the chloride evolution reaction (CLER) occurs at high current densities, producing ClO₂. - Or Cl2, which can severely corrode the electrodes. Therefore, electrocatalytic activity is particularly important for seawater electrolysis catalysts. Furthermore, catalyst durability is another important reference factor, which has proven to be a crucial indicator for high current density industrial electrocatalysts. Specifically, the components of a three-dimensional hierarchical structure support each other, exhibiting high mechanical strength; therefore, this structure has become a typical configuration for high-durability electrocatalysts.

[0003] Transition metal phosphides (TMPs) are considered excellent bifunctional catalyst candidates due to their easily tunable electronic structure, excellent electronic conductivity, and outstanding catalytic performance. In recent years, increasingly sophisticated strategies have been proposed to improve TMP performance, with p-vacancy defects serving as active centers for catalytic reactions to further enhance the catalyst's internal properties. Summary of the Invention

[0004] 1. The purpose of this invention is to provide a carbon-coated phosphorus-rich vacancy cobalt phosphide (Co) x P v Synthesis method of @NC materials. Co containing P vacancies and encapsulated in an N-doped C layer. x p-nanowire arrays (Co) x P v @NC) addresses the issues of chlorine evolution and poor catalyst durability in seawater electrolysis through a multi-level structure and vacancy introduction strategy, and is equipped with Co x P v The alkaline electrolyzer with @NC electrode exhibits excellent high-current seawater electrolysis performance.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] The method for preparing the carbon-coated phosphorus-rich vacancy cobalt phosphide electrocatalyst provided by this invention can be achieved through the following preparation route:

[0007] (1) Treatment of nickel foam substrate: Cut the nickel foam substrate into appropriate size, then immerse it in dilute hydrochloric acid (1.0M), ethanol and deionized water in sequence, sonicate it and dry it overnight in a vacuum drying oven.

[0008] (2) The Co(OH)F array was prepared by mixing cobalt nitrate hexahydrate, urea and ammonium fluoride in deionized water and stirring for 5 minutes to form a clear solution. Then, the cleaned nickel foam was immersed in the solution and reacted at 100-150℃ for 5-15 hours. The prepared sample was taken out and washed with deionized water, and then annealed at 300-400℃ under N2 atmosphere for 0.5-2 hours.

[0009] (3) Preparation of Co(OH)F@ZIF-67: Co(OH)F was placed in a solution containing 1.4 to 1.9 g of 2-methylimidazole and reacted for 5 to 24 hours. After the reaction was completed, the sample was washed with ethanol.

[0010] (4) Co x Preparation of P@NC: Co(OH)F@ZIF-67 was phosphated under a nitrogen atmosphere for 0.5–2 h at a phosphating temperature of 250–350 °C at a heating rate of 1–3 °C / min. -1 .

[0011] (5) Co x P v Preparation of @NC: Co x The P@NC samples were immersed in sodium borohydride solution for 20–40 min. Finally, the samples were washed with deionized water and dried in an oven overnight.

[0012] According to the preparation method of the technical route, the characteristic is that: in step (1), the foamed nickel is cut into 2cm*3cm size, and the temperature of the vacuum drying oven is set to 40~80℃ to remove organic matter and oxides on the surface of the foamed nickel.

[0013] According to the preparation method of the technical route, the characteristic is that: the heating rate during annealing in step (2) is 2℃ / min. -1 To synthesize a Co(OH)F nanoarray precursor with uniform morphology.

[0014] According to the preparation method of the technical route, the characteristic is that the solvent for preparing the 2-methylimidazole solution in step (3) is a 1:1 mixture of water and ethanol.

[0015] According to the preparation method of the technical route, the characteristic is that the amount of sodium hypophosphite used in step (4) is 0.2-2g, and an appropriate amount of sodium hypophosphite is beneficial to the maintenance of sample morphology.

[0016] According to the preparation method of the technical route, the characteristic is that the concentration of sodium borohydride in step (5) is 0.1-2.5M.

[0017] This invention also provides the application of carbon-coated phosphorus-rich cobalt phosphide bifunctional electrocatalyst as the cathode and anode in alkaline industrial seawater electrolyzers.

[0018] As a further feature of the present invention: the carbon-coated phosphorus-vacancy-rich cobalt phosphide (Co) constructed in this invention... x P v The @NC method addresses a key challenge in preparing electrocatalysts for industrial seawater electrolysis at high current densities. We demonstrate that the introduction of phosphorus vacancies significantly enhances catalyst activity, and the establishment of a hierarchical structure ensures long-term stability during seawater electrolysis, thereby preventing complex chlorination reactions and guaranteeing long-term effective catalyst operation. The material obtained in this invention has low preparation cost, good performance, and broad application prospects in the industrial electrolysis of seawater. Detailed Implementation

[0019] Example 1

[0020] This invention relates to a method for preparing carbon-coated phosphorus-rich vacancy cobalt phosphide (Co). x P v The @NC method includes the following steps:

[0021] (1) Commercially available Co(NO3)2·6H2O, urea, and NH4F were selected as raw materials. The three were dissolved in 36 mL of water. The resulting solution was then transferred to a 100 mL stainless steel autoclave and heated at 120 °C for 10 hours, followed by a 2 °C / min incubation period at 350 °C. -1 The material was annealed at a heating rate of 1 hour in a N2 atmosphere, and the X-ray diffraction (XRD) results are shown in the figure. Figure 1 This proves that the material is a Co(OH)F phase.

[0022] (2) After the reaction was completed, the sample obtained in (1) was immersed in a homogeneous solution prepared with 1.64 g of 2-methylimidazole (2-MeIm) for 12 hours at room temperature, and then dried in an oven. The X-ray diffraction (XRD) results of the material are shown in the figure. Figure 2 This proves that the material is a composite phase of Co(OH)F and ZIF-67.

[0023] (3) Then, take an appropriate amount of the dried sample obtained in step (2) and carry out a phosphating reaction in a tube furnace. Place 0.5g of NaH2PO2 powder upstream and the obtained sample downstream. In a nitrogen atmosphere at 300℃, at a rate of 2℃ min... -1Phosphating was performed at a heating rate of 1 hour. The X-ray diffraction (XRD) results of this material are shown in the figure. Figure 3 This proves that the material is a CoP / Co2P phase.

[0024] (4) Finally, take an appropriate amount of the sample obtained in step (3), then soak it in 25 mL of 1.5 M NaBH4 solution for 40 minutes, then wash the sample with deionized water and dry it overnight at 60 °C to prepare sample Co. x P v @NC. The X-ray diffraction (XRD) results of this material are shown in the figure. Figure 4 This proves that the material is a CoP / Co2P phase. Figure 5 Co in Example 1 x P v The scanning electron microscope image of the @NC sample shows that nanosheet structures were grown on the surface of the nanoarray after treatment with sodium borohydride. Figure 6 For Co x P v High-resolution transmission electron microscopy (TEM) images of the @NC sample show nitrogen-doped carbon shells at the sample edges. In the electrolytic cell test using the catalyst, industrial seawater electrolysis conditions were employed (electrolyte: 6M KOH seawater, temperature: 60℃), with the prepared material serving as both the cathode and anode in the two-electrode system. The bifunctional electrocatalyst prepared above exhibits excellent hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activity. Figure 7 It requires only a 1.74V operating voltage to achieve a 1.0Acm output. -2 current density ( Figure 8 ), indicating Co x P v The two-electrode electrolysis system composed of @NC exhibits excellent catalytic activity and can achieve electrolysis at 0.2 and 1.0 Acm. -2 Stable operation for 100 hours at current density ( Figure 9 ), indicating Co x P v The two-electrode electrolysis system composed of @NC electrodes exhibits excellent long-term durability.

[0025] Example 2

[0026] This invention relates to a method for preparing carbon-coated phosphorus-rich vacancy cobalt phosphide (Co). x P v The @NC method includes the following steps:

[0027] (1) Commercially available Co(NO3)2·6H2O, urea, and NH4F were selected as raw materials. The three were dissolved in 36 mL of water. The resulting solution was then transferred to a 100 mL stainless steel autoclave and heated at 120 °C for 10 hours, followed by a 2 °C / min incubation period at 350 °C. -1 The material was annealed at a heating rate of 1 hour in a N2 atmosphere, and the X-ray diffraction (XRD) results are shown in the figure. Figure 1 This proves that the material is a Co(OH)F phase.

[0028] (2) After the reaction was completed, the sample obtained in (1) was immersed in a homogeneous solution prepared with 1.64 g of 2-methylimidazole (2-MeIm) for 12 hours at room temperature, and then dried in an oven. The X-ray diffraction (XRD) results of the material are shown in the figure. Figure 2 This proves that the material is a composite phase of Co(OH)F and ZIF-67.

[0029] (3) Then, take an appropriate amount of the dried sample obtained in step (2) and carry out a phosphating reaction in a tube furnace. Place 0.5g of NaH2PO2 powder upstream and the obtained sample downstream. In a nitrogen atmosphere at 300℃, at a rate of 2℃ min... -1 Phosphating was performed at a heating rate of 1 hour. The X-ray diffraction (XRD) results of this material are shown in the figure. Figure 3 This proves that the material is a CoP / Co2P phase.

[0030] (4) Finally, take an appropriate amount of the sample obtained in step (3), then soak it in 25 mL of 0.5 M NaBH4 solution for 40 minutes, then wash the sample with deionized water and dry it overnight at 60 °C to prepare sample Co. x P v @NC.

[0031] The bifunctional electrocatalysts obtained in the above embodiments exhibit excellent hydrogen evolution reaction and oxygen evolution reaction activity. Figure 10 ).

[0032] Example 3

[0033] This invention relates to a method for preparing carbon-coated phosphorus-rich vacancy cobalt phosphide (Co). x P v The @NC method includes the following steps:

[0034] (1) Commercially available Co(NO3)2·6H2O, urea, and NH4F were selected as raw materials. The three were dissolved in 36 mL of water. The resulting solution was then transferred to a 100 mL stainless steel autoclave and heated at 120 °C for 10 hours, followed by a 2 °C / min incubation period at 350 °C. -1The material was annealed at a heating rate of 1 hour in a N2 atmosphere, and the X-ray diffraction (XRD) results are shown in the figure. Figure 1 This proves that the material is a Co(OH)F phase.

[0035] (2) After the reaction was completed, the sample obtained in (1) was immersed in a homogeneous solution prepared with 1.64 g of 2-methylimidazole (2-MeIm) for 12 hours at room temperature, and then dried in an oven. The X-ray diffraction (XRD) results of the material are shown in the figure. Figure 2 This proves that the material is a composite phase of Co(OH)F and ZIF-67.

[0036] (3) Then, take an appropriate amount of the dried sample obtained in step (2) and carry out a phosphating reaction in a tube furnace. Place 0.5g of NaH2PO2 powder upstream and the obtained sample downstream. In a nitrogen atmosphere at 300℃, at a rate of 2℃ min... -1 Phosphating was performed at a heating rate of 1 hour. The X-ray diffraction (XRD) results of this material are shown in the figure. Figure 3 This proves that the material is a CoP / Co2P phase.

[0037] (4) Finally, take an appropriate amount of the sample obtained in step (3), then soak it in 25 mL of 2.5 M NaBH4 solution for 40 minutes, then wash the sample with deionized water and dry it overnight at 60 °C to prepare sample Co. x P v @NC.

[0038] The bifunctional electrocatalysts obtained in the above examples exhibit excellent hydrogen evolution reaction and oxygen evolution reaction activity. Figure 11 ). Attached Figure Description

[0039] Figure 1 This is an X-ray diffraction image of sample Co(OH)F from Example 1.

[0040] Figure 2 The image shows an X-ray diffraction pattern of sample Co(OH)F / ZIF-67 from Example 1.

[0041] Figure 3 Sample Co in Example 1 x X-ray diffraction image of P@NC.

[0042] Figure 4 Sample Co in Example 1 x P v X-ray diffraction image from @NC.

[0043] Figure 5 Sample Co in Example 1 x Pv Scanning electron microscope image from @NC.

[0044] Figure 6 Sample Co in Example 1 x P v High-resolution transmission electron microscope image from @NC.

[0045] Figure 7 Sample Co in Example 1 x P v @NC Properties of hydrogen evolution reaction and oxygen evolution reaction; the horizontal axis E (V) vs. RHE represents voltage (V), and the vertical axis Current density represents current density (A cm⁻¹). -2 ).

[0046] Figure 8 Sample Co in Example 1 x P v @NC electrode properties under industrial electrolysis conditions; the horizontal axis represents voltage (V), and the vertical axis represents current density (A cm⁻¹). -2 ).

[0047] Figure 9 Sample Co in Example 1 x P v @NC Two-electrode stability test under industrial seawater electrolysis conditions; the horizontal axis Time represents time (h), and the vertical axis E (V) vs. RHE represents voltage (V).

[0048] Figure 10 Sample Co in Example 2 x P v @NC Properties of hydrogen evolution reaction and oxygen evolution reaction; the horizontal axis E (V) vs. RHE represents voltage (V), and the vertical axis Current density represents current density (A cm⁻¹). -2 ).

[0049] Figure 11 Sample Co in Example 3 x P v @NC Properties of hydrogen evolution reaction and oxygen evolution reaction; the horizontal axis E (V) vs. RHE represents voltage (V), and the vertical axis Current density represents current density (A cm⁻¹). -2 ).

Claims

1. A method for preparing a carbon-coated cobalt phosphide electrocatalyst rich in phosphorus vacancies, characterized in that: The foam nickel substrate is simply cleaned and treated, and CoP is grown on the substrate by a hydrothermal method and a phosphating method x P@NC, and the CoP is further modified by a sodium borohydride reduction method to obtain a bimetallic CoP electrocatalyst, which can efficiently prepare hydrogen under the condition of industrial seawater and can maintain long-term stability, and the specific method is as follows: (1) The foamed nickel substrate was cut into 2 cm*3 cm size, and then it was immersed in 1.0 M dilute hydrochloric acid, ethanol and deionized water in turn, and dried in a vacuum drying oven at 40-80°C overnight after ultrasonic treatment; (2) Cobalt nitrate hexahydrate, urea and ammonium fluoride were mixed in deionized water and stirred for 5 minutes to form a clear solution; then, the washed foamed nickel was immersed in the solution for a solvothermal reaction; the temperature of the solvothermal reaction was 100-150°C, and the solvothermal reaction time was 5-15 h; the prepared sample was taken out and washed with deionized water, and then annealed at 300-400°C under N2 atmosphere for 0.5-2 h to obtain Co(OH)F; (3) Co(OH)F was placed in a solution in which 1.4-1.9 g of 2-methylimidazole was dissolved, and a reaction was carried out; the reaction temperature was room temperature, and the reaction time was 5-24 h; the product Co(OH)F@ZIF-67 of the Co(OH)F array on which ZIF-67 grew was obtained; (4) the Co(OH)F@ZIF-67 multi-level structure is subjected to phosphorization reaction in a nitrogen atmosphere for 0.5-2 h, the phosphorization temperature is 250-350 °C, and the temperature rising rate is 1-3 °C / min -1 , the amount of sodium hypophosphite used is 0.2-2 g, and finally CoxP@NC is obtained; (5) The obtained CoxP@NC sample was immersed in a 0.1-2.5 M NaBH4 solution for 20-40 min; finally, the sample was washed with deionized water and dried in an oven overnight to prepare the sample CoxPv@NC.

2. Use of the carbon-coated phosphorus-rich vacancy cobalt phosphide electrocatalyst prepared according to claim 1, characterized in that: The electrocatalyst can be used as a cathode and an anode at the same time in an alkaline industrial seawater electrolytic cell.

3. Use according to claim 2, characterized in that: The electrolyte of 6.0M KOH was prepared with natural seawater, and the temperature of the electrolyte was kept at 60°C during the electrolysis of seawater.

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