A carbon-coated cobalt-based catalyst, its preparation method, and its application in water electrolysis.

Abstract

This invention discloses a carbon-coated cobalt-based catalyst, its preparation method, and its application in water electrolysis. The preparation method of the carbon-coated cobalt-based catalyst of this invention includes the following steps: S1, immersing nickel foam in a solution composed of a molybdenum source, a cobalt source, urea, a fluorine source, and water, and heating to carry out a hydrothermal reaction to obtain a nickel foam-supported Mo-Co LDH precursor; S2, annealing the product obtained in step S1 under inert gas protection to obtain a nickel foam-supported Mo-Co LDH nanowire array; S3, adding the product obtained in step S2 to a 2-methylimidazole solution for soaking treatment to load the metal-organic framework material ZIF-67 onto the nickel foam-supported Mo-Co LDH nanowire array; S4, pyrolyzing the product obtained in step S3 together with a phosphorus source under inert gas protection to form nickel foam-supported carbon-coated molybdenum-doped cobalt phosphide. The catalyst of this invention exhibits excellent hydrogen evolution activity and stability, and the preparation method is environmentally friendly, safe, and energy-efficient, making it suitable for large-scale preparation.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic hydrogen production catalyst technology, and particularly relates to a carbon-coated cobalt-based catalyst, its preparation method, and its application in water electrolysis. Background Technology

[0002] Water electrolysis is considered an environmentally friendly alternative that can reduce dependence on traditional fossil fuels and alleviate environmental problems. Large-scale industrial water electrolysis in alkaline media requires electrocatalysts capable of driving high current densities over long periods. Platinum and iron / ruthenium oxide-based nanomaterials, due to their favorable d-band centers, near-zero hydrogen adsorption free energy, and significant electronic conductivity, have long been considered benchmark materials for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). However, their poor stability, high cost, and natural scarcity have hindered their large-scale application.

[0003] It is well known that platinum-based materials are the most active electrocatalysts for HER, but their high cost and scarcity greatly hinder their large-scale application. Therefore, developing high-abundance, low-cost, and highly efficient HER electrocatalysts remains urgent and challenging. Current domestic research mainly focuses on non-precious metal catalysts, particularly cobalt-based catalysts, which possess empty d orbitals similar to those of precious metal catalysts, are inexpensive, and abundant, making them ideal alternatives to precious metal catalysts. In particular, cobalt phosphide, with its unique electronic properties, high electrocatalytic activity, and corrosion resistance, has attracted significant research attention and is considered a highly efficient and low-cost HER catalyst.

[0004] Cobalt-based electrocatalysts mainly include oxides, sulfides, hydroxides, carbides, and selenides. The structure and composition of these substances have a significant impact on the electrocatalytic performance of the materials. However, existing cobalt-based catalysts still require relatively high hydrogen evolution and oxygen evolution overpotentials to reach 500 and 1000 mA cm⁻¹, respectively. -2 The industrial current density is low, and the catalytic activity needs further improvement.

[0005] Incorporating electron-rich and electron-deficient heteroatoms of varying atomic radii and electronegativity into the cobalt phosphide lattice induces subtle lattice distortions and a redistribution of electron density, resulting in precise changes in the electronic structure, near-Fermi level d-band centers, favorable hydrogen adsorption Gibbs free energy, and enhanced intrinsic activity. Simultaneously, optimizing the electronic structure improves the adsorption energy for reaction intermediates, thereby enhancing the material's catalytic activity. However, how to dope cobalt phosphide to improve its catalytic activity at high current densities in alkaline media remains a significant challenge for current researchers. Summary of the Invention

[0006] The purpose of this invention is to provide a carbon-coated cobalt-based catalyst, its preparation method, and its application in water electrolysis. Through multilayer structure construction and heteroatom doping strategy, three-dimensional CoP nanospheres supported by nickel foam (NF) and doped with molybdenum were prepared and encapsulated in a nitrogen-doped carbon layer, realizing water electrolysis under simulated industrial conditions. This catalyst has excellent hydrogen evolution and oxygen evolution activities.

[0007] In a first aspect, the present invention provides a method for preparing a carbon-coated cobalt-based catalyst, comprising the following steps:

[0008] S1. Porous nickel foam is immersed in a solution composed of molybdenum source, cobalt source, urea, fluorine source and water, and heated to carry out a hydrothermal reaction to obtain nickel foam-supported Mo-Co LDH precursor.

[0009] S2. The product obtained in step S1 is annealed under inert gas protection to obtain a nickel foam-supported Mo-Co LDH nanowire array.

[0010] S3. The product obtained in step S2 is added to a 2-methylimidazole solution for soaking treatment to load the metal-organic framework material ZIF-67 on the nickel foam-supported Mo-Co LDH nanowire array.

[0011] S4. The product obtained in step S3 is pyrolyzed together with a phosphorus source under inert gas protection to form carbon-coated molybdenum-doped cobalt phosphide supported by nickel foam, thereby obtaining the carbon-coated cobalt-based catalyst.

[0012] Based on the above technical solutions, the more electronegative molybdenum doping in this invention leads to a redistribution of polarized electrons, thereby shifting the d-band center of CoP and generating appropriate hydrogen adsorption intensity, effectively improving water separation performance. Combined with density functional theory (DFT), Mo doping produces near-thermally neutral hydrogen adsorption energy, especially the dp hybridization of the Co-O bond lowers the reaction energy barrier for water dissociation. Notably, in-situ characterization verifies that the CoP species underwent structural reconstruction, forming an active CoOOH layer, thus accelerating the reaction rate. Furthermore, the superhydrophilicity of the CoP surface allows the electrolyte to completely penetrate the electrode surface and rapidly release bubbles to refresh the active surface, resulting in a high reaction rate of up to 3000 mA cm⁻¹ in alkaline media. -2 The high current density achieves excellent water separation results.

[0013] The obtained carbon-coated cobalt-based catalyst is a carbon-coated molybdenum-doped cobalt phosphide nanoflower material, in which molybdenum exists by replacing cobalt atoms in the cobalt phosphide lattice, and the carbon layer coating is formed by the anchoring effect of the metal-organic framework and cobalt, with an overall particle size of 10-15 micrometers. In this invention, the catalyst active sites are molybdenum-cobalt coupling sites. The three-dimensional nanoflower structure greatly increases the specific surface area and provides superior hydrophilicity and gas-repellency, making it suitable for high-current, high-rate operating modes. Furthermore, the carbon coating on the catalyst surface effectively protects the internal active sites, enhancing the material's stability and corrosion resistance. The obtained carbon-coated molybdenum-doped cobalt phosphide nanoflower catalyst exhibits excellent hydrogen evolution activity and stability, contains no precious metals, and its preparation method is environmentally friendly, safe, and energy-efficient, making it suitable for large-scale production.

[0014] In the above-mentioned method for preparing carbon-coated cobalt-based catalysts, the molybdenum source is further selected from at least one of ammonium heptamolybdate, ammonium molybdate, and sodium molybdate.

[0015] The mass of the molybdenum source does not exceed 30 wt% of the cobalt source, preferably 10 wt% to 30 wt%, such as 18%, 24%, or 14%.

[0016] The cobalt source is at least one of cobalt chloride hexahydrate and cobalt nitrate hexahydrate;

[0017] The fluorine source is at least one of ammonium fluoride and sodium fluoride;

[0018] The mass of the fluorine source fed into the feed shall not exceed 150 wt% of the cobalt source, preferably 50 wt% to 100 wt%, such as 77% or 66%.

[0019] The mass of urea fed into the feed shall not exceed 200 wt% of the cobalt source, preferably 150 wt% to 180 wt%, such as 158 wt%.

[0020] The concentration of the cobalt source in the solution is 10–15 mg / mL, such as 12.6 mg / mL;

[0021] Each 2cm*3cm*0.1cm porous nickel foam is immersed in 25-35mL (e.g., 30mL) of a solution composed of molybdenum source, cobalt source, urea, fluorine source and water.

[0022] In step S1, porous nickel foam (NF), molybdenum source, cobalt source, urea, and fluorine source form a layered bimetallic hydroxide precursor (LDH precursor) through a hydrothermal reaction. The addition of porous nickel foam provides a rough surface, offering greater mechanical strength compared to other supports such as carbon cloth, to withstand high-current operating conditions. The fluorine source regulates the anion coordination during LDH growth to obtain the desired morphology (larger specific surface area and gas diffusion pathways).

[0023] As an example, the nickel foam further includes the following pretreatment steps before addition: NF is washed sequentially with dilute hydrochloric acid, deionized water, and ethanol, and then vacuum dried. It is understood that the hydrothermal reaction is carried out in a closed autoclave.

[0024] In the above-mentioned method for preparing carbon-coated cobalt-based catalysts, the hydrothermal reaction temperature is 120-160°C and the time is 8-12 hours, such as heating at 120°C for 10 hours in a sealed high-pressure reactor.

[0025] In the above-described method for preparing carbon-coated cobalt-based catalysts, the annealing step involves a heating rate not exceeding 2°C / min, an annealing temperature of 300–350°C, a holding time of 1–3 hours, and a cooling rate not exceeding 5°C / min to room temperature. For example, the temperature may be raised to 350°C or 300°C at a heating rate of 2°C / min, annealed for 1 hour, and then cooled to room temperature at a cooling rate of 2°C / min. As an example, the inert gas is nitrogen.

[0026] In step S2, annealing the Mo-Co LDH precursor under an inert gas atmosphere to form a Mo-CoLDH nanowire array can enhance the mechanical strength of the Mo-Co LDH precursor surface, thus facilitating the subsequent growth of ZIF-67 on the surface.

[0027] In the above-mentioned method for preparing carbon-coated cobalt-based catalysts, the mass ratio of dimethylimidazole to the cobalt source does not exceed 8:1, preferably (3-6):1, such as 4.3:1 or 5.3:1;

[0028] The concentration of the 2-methylimidazole solution is 0.8–2.4 g / mL (e.g., 1.64 g / mL), and the solvent is deionized water and ethanol in a volume ratio of 1:1.

[0029] The soaking time is 12 to 24 hours, such as soaking for 12 hours at room temperature.

[0030] In step S3, a metal-organic framework material ZIF-67 is formed on the Mo-Co LDH nanowire array and a carbon coating layer is formed during subsequent pyrolysis phosphating. The carbon coating effectively protects the internal active sites and enhances the stability and corrosion resistance of the material.

[0031] In the above-mentioned method for preparing carbon-coated cobalt-based catalysts, the phosphorus source is at least one of sodium hypophosphite, sodium dihydrogen hypophosphite, ammonium dihydrogen hypophosphite, ammonium dihydrogen phosphate, and sodium dihydrogen phosphate.

[0032] The mass ratio of the phosphorus source to the cobalt source does not exceed 5:1, such as 1.3:1.

[0033] In the pyrolysis step, the heating rate is no higher than 2℃ / min, the pyrolysis temperature is 300℃~350℃, and the pyrolysis time is 2~3h. For example, at a rate of 2℃ / min... -1 The heating rate is such that pyrolysis is performed at 300℃ or 350℃ for 1 hour.

[0034] In step S4, the pyrolysis-phosphating coupling step can form a carbon coating layer while achieving phosphorus doping.

[0035] In a second aspect, the present invention provides a carbon-coated cobalt-based catalyst prepared by the method described in any of the preceding claims.

[0036] Thirdly, the present invention provides the application of the carbon-coated cobalt-based catalyst in the electrolysis of water for hydrogen evolution and / or oxygen evolution.

[0037] In the above applications, the electrolysis of water is carried out in an alkaline aqueous solution electrolyzer or an alkaline anion exchange membrane electrolyzer.

[0038] The present invention has the following beneficial effects:

[0039] (1) A carbon-coated molybdenum-doped cobalt phosphide nanoarray (Mo-CoP / NC) with a micron-scale three-dimensional nanoflower structure was prepared on nickel foam (NF) by in-situ assembly and subsequent phosphating. It has the characteristics of controllable synthesis and stable structural mechanical properties.

[0040] (2) The addition of porous nickel foam provides a rough surface and provides greater mechanical strength compared with other carriers such as carbon cloth to adapt to the operating conditions under high current. The introduction of fluorine source regulates the anion coordination in LDH growth to obtain the set morphology (larger specific surface area and gas diffusion path). The carbon coating layer is formed on the surface by cleverly using annealing and coordination of ZIF-67 to greatly extend the stable operation time under high current.

[0041] (3) Density functional theory (DFT) calculations show that doping with Mo shifts the d-band center of Co sites upward, resulting in hydrogen adsorption energy approaching zero, while the strong dp hybridization of Co-O species helps to achieve optimized Volmer steps.

[0042] (4) Mo-CoP / NC can operate at 3000 mA cm -2 HER and OER are achieved at high current densities; in a 6.0 M KOH solution at 60 °C, a low voltage of only 1.87 V is required to provide 1000 mA cm⁻¹. -2 It has a high current density and good stability over 100 hours. Attached Figure Description

[0043] Figure 1 This is a flowchart illustrating the preparation of a carbon-coated molybdenum-doped cobalt phosphide catalyst according to the present invention.

[0044] Figure 2 This is a scanning electron microscope image of carbon-coated molybdenum-doped cobalt phosphide prepared in Specific Embodiment 1 of the present invention.

[0045] Figure 3 This is a transmission electron microscope (TEM) image of carbon-coated molybdenum-doped cobalt phosphide prepared according to specific embodiment 1 of the present invention.

[0046] Figure 4 This is a contact angle test of carbon-coated molybdenum-doped cobalt phosphide prepared in specific embodiment 1 of the present invention.

[0047] Figure 5 These are the hydrogen evolution performance test results of carbon-coated molybdenum-doped cobalt phosphide prepared according to specific embodiment 1 of the present invention, wherein... Figure 5 a is the LSV curve. Figure 5 b represents long-term stability testing. Mo-CoP / NC-1 represents Comparative Example 3, Mo-CoP represents Comparative Example 2, CoP / NC represents Comparative Example 1, Mo-CoP / NC represents the carbon-coated molybdenum-doped cobalt phosphide prepared in Example 1, and Pt / C represents the commercial 20% Pt / C catalyst in Comparative Example 4.

[0048] Figure 6 These are the oxygen evolution performance test results of carbon-coated molybdenum-doped cobalt phosphide prepared according to specific embodiment 1 of the present invention, wherein... Figure 6 a is the LSV curve. Figure 6 b represents long-term stability testing. Mo-CoP / NC-1 represents Comparative Example 3, Mo-CoP represents Comparative Example 2, CoP / NC represents Comparative Example 1, Mo-CoP / NC represents the carbon-coated molybdenum-doped cobalt phosphide prepared in Example 1, and RuO2 represents the commercial RuO2 catalyst in Comparative Example 5.

[0049] Figure 7 The results are from the water splitting test of carbon-coated molybdenum-doped cobalt phosphide prepared in specific embodiment 2 of the present invention. Detailed Implementation

[0050] The present invention will now be described in further detail with reference to specific embodiments. The given embodiments are merely illustrative of the invention and not intended to limit its scope. The embodiments provided below can serve as a guide for further improvements by those skilled in the art and do not constitute a limitation on the invention in any way.

[0051] Unless otherwise specified, the methods used in the following embodiments are conventional methods, performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Unless otherwise specified, the materials and reagents used in the following embodiments are commercially available.

[0052] The nickel foam used in the following examples was purchased from Cyber ​​Electrochemical Materials Technology Co., Ltd., with a thickness of 1.0 mm and an areal density of 50 g / m³. 2 110 PPI.

[0053] Example 1

[0054] The carbon-coated molybdenum-doped cobalt phosphide catalyst for high-current water electrolysis was prepared according to the flowchart shown in Figure 1. The specific steps are as follows:

[0055] (1) The NF (3cm long × 2cm wide × 0.1cm thick) was washed successively with dilute hydrochloric acid, deionized water, and ethanol, and then vacuum dried. 0.380g of CoCl2·6H2O and 0.07g of (NH4)6Mo7O were then added. 24 0.6 g of urea and 0.296 g of NH4F were mixed into 30 mL of deionized water and stirred for 5 minutes. The mixture was then transferred to a 50 mL Teflon-lined stainless steel autoclave. A clean piece of NF was then immersed in the solution, and the autoclave was sealed. After heating the autoclave at 120 °C for 10 hours, the prepared sample was removed and washed with deionized water to obtain a pink, flake-like Mo-Co LDH precursor.

[0056] (2) The product obtained in step (1) is placed in a N2 atmosphere at 2℃ for 2 min. -1 The temperature was increased to 350℃, held for 1 hour, and then annealed, followed by a heating rate of 2℃ / min. -1 The cooling rate was reduced to room temperature to obtain a black sheet-like material, Mo-Co LDH nanowire array.

[0057] (3) The product obtained in step (2) was immersed in a homogeneous solution prepared by 1.64 g of 2-methylimidazole (2-MeIm), 5 mL of deionized water, and 5 mL of ethanol, and soaked at room temperature for 12 hours. Finally, strings of ZIF-67 were formed on the Mo-Co LDH array to obtain the purple sheet material Mo-Co LDH / ZIF-67.

[0058] (4) Place the product obtained in step (3) and 0.5 g of NaH2PO2 powder into porcelain boats and place them upstream and downstream of a tube furnace, respectively, and heat them in a N2 atmosphere at 2℃ for 1 minute. -1 The temperature was increased to 300℃ and held for 1 hour for pyrolysis, followed by a rate of 2℃ / min. -1 The cooling rate was reduced to room temperature, and then black flake-like carbon-coated molybdenum-doped cobalt phosphide Mo-CoP / NC was obtained.

[0059] The SEM image of the Mo-CoP / NC catalyst prepared in this embodiment is shown below. Figure 2Mo-CoP / NC consists of uniformly distributed micro-nanoflowers and surface-grown nanoarrays, with spheres approximately 10.9 micrometers in diameter. This nanosphere morphology provides a large specific surface area and gas diffusion channels for subsequent electrocatalytic reactions. HRTEM ( Figure 3 The results show that the Mo-CoP / NC nanoarray has a carbon layer on its surface. This surface carbon layer protects Mo-CoP, significantly enhancing its long-term stability and resistance to chloride ions. Furthermore, from... Figure 3 The lattice fringes at 2.48 nm and 2.15 nm correspond to the CoP(111) and Co2P(202) crystal planes, respectively. Then, we performed water and underwater bubble contact angle (CA) tests. Figure 4 The superhydrophilicity and gas-repellency of Mo-CoP / NC were monitored. The water contact angles of Mo-CoP / NC were 143.5° and 0°, respectively, indicating that Mo-CoP / NC possesses strong hydrophilicity, which is beneficial for close contact between the electrolyte aqueous solution and the solid electrode. During the OER process, the oxygen desorption capacity of the electrocatalyst surface was preliminarily determined by underwater bubble CA experiments. Significant gas-repellency allows bubbles to escape rapidly from the electrocatalyst surface, promoting the reconstruction and exposure of active sites, thereby accelerating reaction kinetics. The combination of superwetting and gas-repellency of Mo-CoP / NC promotes reactant diffusion, local electrolyte replenishment, and bubble detachment, which is crucial for efficient industrial electrocatalysis at ampere-level current densities.

[0060] Example 2

[0061] In this embodiment, the Mo-CoP / NC electrocatalyst was prepared using a method similar to that in Example 1, except that NH4F in step (1) was replaced with 0.252 g of sodium fluoride. The remaining steps were the same as in Example 1, resulting in the Mo-CoP / NC electrocatalyst.

[0062] Example 3

[0063] This embodiment prepares the Mo-CoP / NC electrocatalyst using a method similar to that of Example 1, except that step (1) involves adding 0.093 g of (NH4)6Mo7O. 24 The remaining steps are the same as in Example 1, yielding the Mo-CoP / NC electrocatalyst.

[0064] Example 4

[0065] This embodiment prepares the Mo-CoP / NC electrocatalyst using a method similar to that of Example 1, except that step (1) involves adding 0.056 g of (NH4)6Mo7O. 24 The remaining steps are the same as in Example 1, yielding the Mo-CoP / NC electrocatalyst.

[0066] Example 5

[0067] This embodiment prepares the Mo-CoP / NC electrocatalyst using a method similar to that of Example 1, except that step (1) involves adding 0.047 g of (NH4)6Mo7O. 24 The remaining steps are the same as in Example 1, yielding the Mo-CoP / NC electrocatalyst.

[0068] Example 6

[0069] In this embodiment, the Mo-CoP / NC electrocatalyst was prepared using a method similar to that in Example 1, except that the annealing temperature in step (2) was 300°C. The remaining steps were the same as in Example 1, resulting in the Mo-CoP / NC electrocatalyst.

[0070] Example 7

[0071] In this embodiment, the Mo-CoP / NC electrocatalyst was prepared using a method similar to that in Example 1, except that 2g of 2-methylimidazole was added in step (3). The remaining steps were the same as in Example 1, resulting in the Mo-CoP / NC electrocatalyst.

[0072] Example 8

[0073] In this embodiment, the Mo-CoP / NC electrocatalyst was prepared using a method similar to that in Example 1, except that in step (4), heating was performed at 350°C. The remaining steps were the same as in Example 1, resulting in the Mo-CoP / NC electrocatalyst.

[0074] Comparative Example 1

[0075] The preparation steps are the same as in Example 1, except that no molybdenum source is added. The specific steps are as follows:

[0076] (1) The NF (3cm long × 2cm wide × 0.1cm thick) was washed sequentially with dilute hydrochloric acid, deionized water, and ethanol, and then vacuum dried. 0.380g CoCl2·6H2O, 0.6g urea, and 0.296g NH4F were mixed into 30mL of deionized water and stirred for 5 minutes. The mixture was transferred to a 50mL Teflon-lined stainless steel autoclave. A clean piece of NF was then immersed in the solution, and the autoclave was sealed. After heating the autoclave at 120℃ for 10 hours, the prepared sample was removed and washed with deionized water to obtain the Co(OH)2 precursor.

[0077] (2) The product obtained in step (1) is placed in a N2 atmosphere at 2℃ for 2 min. -1 The temperature was increased to 350℃, held for 1 hour, and then annealed, followed by a heating rate of 2℃ / min. -1The cooling rate was reduced to room temperature to obtain a Co(OH)2 nanowire array.

[0078] (3) The product obtained in step (2) was immersed in a homogeneous solution prepared by 1.64 g of 2-methylimidazole (2-MeIm), 5 mL of deionized water, and 5 mL of ethanol, and soaked at room temperature for 12 hours. Finally, strings of ZIF-67 were formed on the Mo-Co LDH array to obtain Co(OH)2 / ZIF-67.

[0079] (4) Place the product obtained in step (3) and 0.5 g of NaH2PO2 powder into porcelain boats and place them upstream and downstream of a tube furnace, respectively, and heat them in a N2 atmosphere at 2℃ for 1 minute. -1 The temperature was increased to 300℃ and held for 1 hour for pyrolysis, followed by a rate of 2℃ / min. -1 The cooling rate is reduced to room temperature, and then CoP / NC is obtained.

[0080] Comparative Example 2

[0081] The preparation steps are the same as in Example 1, except that carbon coating is not used and a molybdenum source is added. The specific steps are as follows:

[0082] (1) The NF (3cm long × 2cm wide × 0.1cm thick) was washed successively with dilute hydrochloric acid, deionized water, and ethanol, and then vacuum dried. 0.380g of CoCl2·6H2O and 0.07g of (NH4)6Mo7O were then added. 24 0.6 g of urea and 0.296 g of NH4F were mixed into 30 mL of deionized water and stirred for 5 minutes. The mixture was then transferred to a 50 mL Teflon-lined stainless steel autoclave. A clean piece of NF was then immersed in the solution, and the autoclave was sealed. After heating the autoclave at 120 °C for 10 hours, the prepared sample was removed and washed with deionized water to obtain the Mo-Co LDH precursor.

[0083] (2) The product obtained in (1) and 0.5 g of NaH2PO2 powder were placed in porcelain boats and placed upstream and downstream of a tube furnace, and heated at 2 °C for 2 min in a N2 atmosphere. -1 The temperature was increased to 300℃ and held for 1 hour for pyrolysis, followed by a rate of 2℃ / min. -1 The cooling rate was reduced to room temperature, and then Mo-CoP was obtained.

[0084] Comparative Example 3

[0085] The preparation steps are the same as in Example 1, except that no fluorine source is added. The specific steps are as follows:

[0086] (1) The NF (3cm long × 2cm wide × 0.1cm thick) was washed successively with dilute hydrochloric acid, deionized water, and ethanol, and then vacuum dried. 0.380g of CoCl2·6H2O and 0.07g of (NH4)6Mo7O were then added. 24 Mix 0.6 g of urea with 30 mL of deionized water and stir for 5 minutes. Transfer the mixture to a 50 mL Teflon-lined stainless steel autoclave. Then, immerse a clean piece of NF in the solution and seal the autoclave. After heating the autoclave at 120 °C for 10 hours, remove the prepared sample and wash it with deionized water to obtain the Mo-Co LDH-1 precursor.

[0087] (2) The product obtained in step (1) is subjected to an incubation period of 2°C at 350°C in a N2 atmosphere for 2 minutes. -1 The temperature was increased to 350℃, held for 1 hour, and then annealed, followed by a heating rate of 2℃ / min. -1 The cooling rate was reduced to room temperature to obtain a Mo-Co LDH-1 nanowire array.

[0088] (3) The product obtained in step (2) was immersed in a homogeneous solution prepared by 1.64 g of 2-methylimidazole (2-MeIm), 5 mL of deionized water, and 5 mL of ethanol, and soaked at room temperature for 12 hours. Finally, strings of ZIF-67 were formed on the Mo-Co LDH array to obtain Mo-Co LDH-1 / ZIF-67.

[0089] (4) Place the product obtained in step (3) and 0.5 g of NaH2PO2 powder into porcelain boats and place them upstream and downstream of a tube furnace, respectively, and heat them in a N2 atmosphere at 2℃ for 1 minute. -1 The temperature was increased to 300℃ and held for 1 hour for pyrolysis, followed by a rate of 2℃ / min. -1 The cooling rate was reduced to room temperature, and then Mo-CoP / NC-1 was obtained.

[0090] Comparative Example 4

[0091] Commercial 20% Pt / C catalyst.

[0092] Comparative Example 5

[0093] Commercial RuO2 catalyst.

[0094] Test case

[0095] The catalyst materials from the above examples and comparative examples were cut into 1cm*1cm electrodes, and their electrochemical performance was tested.

[0096] Hydrogen evolution performance testing: The electrolyte was 1M KOH, the mercury / mercury oxide electrode was used as the reference electrode, and the graphite rod electrode was used as the counter electrode. In the test, cyclic voltammetry (scanning potential from -0.9V to -1.6V, scan rate 0.1V / s) was first used for 40 cycles to stabilize the catalyst performance, followed by linear voltammetry (scanning potential from -0.9V to -3V, scan rate 0.005V / s). All overpotentials were converted to overpotentials relative to the standard hydrogen electrode, using the conversion formula E. (RHE) =E (Hg / HgO) +0.098+0.0592*pH.

[0097] Oxygen evolution performance testing: The electrolyte was 1M KOH, the mercury / mercury oxide electrode was used as the reference electrode, and the graphite rod electrode was used as the counter electrode. In the test, cyclic voltammetry (scanning potential from 0V to 3V, scan rate 0.1V / s) was first used for 40 cycles to stabilize the catalyst performance, followed by linear voltammetry (scanning potential from 0V to 5V, scan rate 0.005V / s). All overpotentials were converted to overpotentials relative to the standard hydrogen electrode, using the conversion formula E. (RHE) =E (Hg / HgO) +0.098+0.0592*pH-1.23.

[0098] Stability test: at 500mA / cm 2 (Oxygen evolution) and -500mA / cm 2 The steady-state constant current polarization test was conducted at a constant current density for 100 hours to obtain the stability performance curves of oxygen evolution / hydrogen evolution.

[0099] The experimental results are shown in Tables 1 and 2.

[0100] Table 1. Electrochemical performance test results (hydrogen evolution)

[0101]

[0102]

[0103] Table 2. Electrochemical performance test results (oxygen evolution)

[0104]

[0105] Figure 5 These are the hydrogen evolution performance test results of the carbon-coated molybdenum-doped cobalt phosphide prepared in Example 1. Figure 5 As can be seen, Mo-CoP / NC requires overpotentials of 177mV and 198mV respectively to reach 500 and 1000mA cm⁻¹. -2The current densities were significantly higher than those of Mo-CoP (183 and 207 mV), CoP / NC (225 and 289 mV), Mo-CoP / NC-1 (279 and 403 mV), and commercial Pt / C (247 and 308 mV), indicating that molybdenum doping and carbon coating improved the hydrogen evolution reaction kinetics, thereby greatly enhancing HER performance. Figure 6 These are the oxygen evolution performance test results of the carbon-coated molybdenum-doped cobalt phosphide prepared in Example 1. Figure 6 As can be seen, Mo-CoP / NC requires overpotentials of 352 and 384 mV, respectively, to reach 500 and 1000 mA cm⁻¹. -2 The current density is superior to that of Mo-CoP (363 and 390 mV), CoP / NC (428 and 492 mV), Mo-CoP / NC-1 (458 and 547 mV), and commercial RuO2 (449 and 576 mV). The extremely low hydrogen evolution and oxygen evolution overpotentials of this invention enable the catalyst material to significantly reduce the reaction energy barrier and energy consumption in high-current water electrolysis reactions.

[0106] At 500m A cm -2 Chronopotential measurements (Et) of Mo-CoP / NC at industrial current densities validated its superiority and reliable prospects in industrial-grade water electrolysis. Figure 5 (b, 6b). After 100 hours of durability testing, Mo-CoP / NC showed only a slight decrease in potential in HER and OER, indicating its strong long-term electrochemical stability.

[0107] Figure 7 The results are from the total water splitting test of the carbon-coated molybdenum-doped cobalt phosphide prepared in Example 2. Figure 7 It can be seen that the assembled Mo-CoP / NC electrolyzer was initially tested in 1.0M KOH solution, and could provide 500, 1000, 2000 and 3000 mA cm⁻¹ at cell voltages of 1.80, 1.87, 1.92 and 1.93 V, respectively. -2 Its high current density is superior to RuO2||Pt / C (2.02, 2.30, 2.54 and 2.61 V).

[0108] Compared with the catalyst sample shown in Comparative Example 1, the catalyst in Example 1 had a molybdenum source added. As can be seen from the comparison results of Example 1 and Comparative Example 1 in Tables 1 and 2, the hydrogen production efficiency and oxygen production efficiency of Example 1 were significantly improved. This is because the doping of molybdenum species improved the water dissociation ability of cobalt phosphide material, optimized the hydrogen adsorption free energy, improved the carrier migration ability, and enhanced the reaction kinetics.

[0109] Compared with the catalyst sample shown in Comparative Example 2, the catalyst in Example 1 was carbon-coated. As can be seen from the comparison results of Example 1 and Comparative Example 2 in Tables 1 and 2, both the hydrogen production efficiency and oxygen production efficiency of Example 1 were improved. This is because annealing the Mo-Co LDH precursor under inert gas protection to form the metal-organic framework material ZIF-67 allows for the formation of a carbon coating layer during pyrolysis. The carbon coating is formed through the anchoring effect of the metal-organic framework and cobalt, effectively protecting the internal active sites and enhancing the catalytic activity, stability, and corrosion resistance of the material.

[0110] Compared with the catalyst sample shown in Comparative Example 3, the catalyst in Example 1 had a fluorine source added to the precursor. As can be seen from the comparison results of Example 1 and Comparative Example 3 in Tables 1 and 2, both the hydrogen production efficiency and oxygen production efficiency of Example 1 were improved. This is because the introduction of the fluorine source modulates the anion coordination in LDH growth, thereby controlling the morphology of the precursor to allow the final product to obtain a larger specific surface area and gas diffusion pathway, thus improving catalytic performance.

[0111] The comparison results with Comparative Examples 4-5 show that the catalytic activity of hydrogen evolution and oxygen evolution catalyzed by the present invention is far superior to that of current commercial catalysts. The present invention significantly reduces the cost of raw materials while improving catalytic activity.

[0112] The present invention has been described in detail above. Those skilled in the art will recognize that the invention can be practiced in a wide range of ways with equivalent parameters, concentrations, and conditions without departing from its spirit and scope. While specific embodiments have been provided, it should be understood that further modifications can be made to the invention. In summary, according to the principles of the invention, this application is intended to include any changes, uses, or improvements to the invention, including modifications made using conventional techniques known in the art that depart from the scope disclosed herein.

Claims

1. A method for preparing a carbon-coated cobalt-based catalyst, characterized in that, Includes the following steps: S1. Immerse nickel foam in a solution composed of molybdenum source, cobalt source, urea, fluorine source and water, and heat to carry out hydrothermal reaction to obtain nickel foam-supported Mo-Co LDH precursor. S2. The product obtained in step S1 is annealed under inert gas protection to obtain a nickel foam-supported Mo-CoLDH nanowire array. In the annealing process, the heating rate is no higher than 2 ℃ / min, the annealing temperature is 300 ℃~350 ℃, the holding time is 1~3 h, and the temperature is reduced to room temperature at a cooling rate of no higher than 5 ℃ / min. S3. The product obtained in step S2 is added to a 2-methylimidazole solution for soaking treatment to load the metal-organic framework material ZIF-67 on the nickel foam-supported Mo-Co LDH nanowire array. S4. The product obtained in step S3 is pyrolyzed together with a phosphorus source under inert gas protection to form carbon-coated molybdenum-doped cobalt phosphide supported by nickel foam, thereby obtaining the carbon-coated cobalt-based catalyst.

2. The method for preparing the carbon-coated cobalt-based catalyst according to claim 1, characterized in that: The molybdenum source is at least one of ammonium heptamolybdate, ammonium molybdate, and sodium molybdate. The mass of the molybdenum source fed into the feed does not exceed 30 wt% of the cobalt source. The cobalt source is at least one of cobalt chloride hexahydrate and cobalt nitrate hexahydrate; The fluorine source is at least one of ammonium fluoride and sodium fluoride; The feed mass of the fluorine source shall not exceed 150 wt% of the cobalt source; The mass of urea fed into the feed shall not exceed 200 wt% of the cobalt source. The concentration of the cobalt source in the solution is 10–15 mg / mL.

3. The method for preparing the carbon-coated cobalt-based catalyst according to any one of claims 1-2, characterized in that: The hydrothermal reaction is carried out at a temperature of 120–160°C for 8–12 hours.

4. The method for preparing the carbon-coated cobalt-based catalyst according to any one of claims 1-2, characterized in that: The mass ratio of the 2-methylimidazole to the cobalt source does not exceed 8:1; The concentration of the 2-methylimidazole solution is 0.8–2.4 g / mL, and the solvent is deionized water and ethanol in a volume ratio of 1:

1. The soaking treatment time is 12 to 24 hours.

5. The method for preparing the carbon-coated cobalt-based catalyst according to any one of claims 1-2, characterized in that: The phosphorus source is at least one of sodium hypophosphite, sodium dihydrogen hypophosphite, ammonium dihydrogen hypophosphite, and ammonium dihydrogen phosphate. The mass ratio of the phosphorus source to the cobalt source does not exceed 5:

1.

6. The method for preparing the carbon-coated cobalt-based catalyst according to any one of claims 1-2, characterized in that: In the pyrolysis step, the heating rate is no higher than 2 ℃ / min, the pyrolysis temperature is 300 ℃~350 ℃, and the pyrolysis time is 2~3 h.

7. The carbon-coated cobalt-based catalyst prepared by any one of claims 1-6.

8. The application of the carbon-coated cobalt-based catalyst according to claim 7 in the electrolysis of water for hydrogen evolution and / or oxygen evolution.

9. The application according to claim 8, characterized in that: The electrolysis of water is carried out in an alkaline aqueous solution electrolyzer or in an alkaline anion exchange membrane electrolyzer.

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