Halogen element F, Cl or Br doped cobalt phosphide / carbon paper composite electrode and preparation method and application thereof
Through the halogen-doped cobalt phosphide/carbon paper composite electrode, the problems of high cost and poor stability of Pt catalysts are solved, and the efficient electrocatalytic water decomposition effect is achieved, and the activity and stability of the catalyst are enhanced.
Patent Information
- Application Number
- CN202510430367.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-08
- Publication Date
- 2025-07-08
AI Technical Summary
Existing Pt catalysts have high cost and poor stability in electrocatalytic water decomposition, and transition metal phosphides such as CoP have a challenge of inefficiency in the adsorption and analysis of H*.
The cobalt phosphide/carbon paper composite electrode doped with halogen elements F, Cl or Br is prepared by hydrothermal and low-temperature phosphating methods to regulate the catalyst morphology and promote the formation of phosphorus vacancy, and improve the electronic structure and hydrogen adsorption performance.
It significantly improves catalytic activity and stability, reduces the overpotential, increases the specific surface area and number of active sites, optimizes the Gibbs free energy of hydrogen adsorption, and achieves efficient electrocatalytic water decomposition.
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Figure CN120272959A_ABST
Abstract
Description
Technical Field
[0001] The present disclosure relates to the technical field of catalysts, and particularly to a cobalt phosphide / carbon paper composite electrode doped with halogen elements F, Cl or Br, a preparation method thereof, and an application thereof. Background Art
[0002] Hydrogen is considered a clean energy source with zero carbon emissions, sustainability, and promise. However, currently, hydrogen mainly comes from the steam reforming process, which accelerates the consumption of fossil fuels and leads to a large amount of carbon dioxide emissions. Electrochemical water splitting technology driven by sustainable electricity has become a research hotspot in the field of efficient hydrogen production due to its unique advantages of being green and environmentally friendly. Among them, the alkaline hydrogen evolution reaction HER involves two steps: the dissociation of water molecules and the conversion of hydrogen intermediates H* to hydrogen gas H2. However, water dissociation requires the breaking of the hydrogen-oxygen bond H-OH, and the high energy barrier results in low water splitting efficiency, restricting its large-scale application. Although Pt exhibits excellent catalytic activity, it faces problems such as high cost and poor stability. Therefore, there is an urgent need to develop electrocatalysts with low cost and high efficiency.
[0003] Transition metal phosphides have received extensive attention from researchers due to their large number of active sites and unique electronic configurations. In particular, cobalt phosphide CoP has characteristics such as a suitable Fermi level and d-band center. When the P content increases and exceeds the Co content, the interaction force of the P-H bond will increase, but excessive P atoms will adsorb a large amount of H*, hindering the subsequent binding of H* and the desorption of H2. To regulate the overly strong H* adsorption, atomic doping engineering has been widely adopted, such as N-doped CoP, Ce-doped CoP, and Fe-doped CoP. A single doping strategy may only change the local electronic structure of the catalytic site. Coupling it with vacancy engineering can induce charge transfer and electron redistribution, which helps to improve the adsorption of intermediates. Summary of the Invention
[0004] To overcome the deficiencies of the above-mentioned prior art, the present disclosure provides a preparation method and an application of a chromium-iron bimetal-doped cobalt phosphide / nickel phosphide / nickel foam composite electrode.
[0005] According to a first aspect of the present disclosure, there is provided a preparation method of a cobalt phosphide / carbon paper composite electrode doped with halogen elements F, Cl or Br, characterized by including the following steps:
[0006] a. Sequentially add 2.5 - 3.5 mmol of cobalt nitrate hexahydrate Co(NO3)2·6H2O, 7.0 - 8.0 mmol of ammonium fluoride NH4F or ammonium chloride NH4Cl or ammonium bromide NH4Br, and 4.5 - 5.5 mmol of urea to deionized water and stir to form a uniform mixed solution; transfer the above mixed solution to a reaction kettle, and place a piece of washed 2 - 5 cm 2Carbon paper; the reaction kettle is placed in an oven for heat preservation, the heat preservation temperature is 100 - 150 °C, and the heat preservation time is 4 - 8 h to obtain cobalt hydroxyfluoride / carbon paper doped with halogen elements F, Cl or Br, (F,Cl,Br)-Co(OH)F / CP respectively; the obtained (F,Cl,Br)-Co(OH)F / CP is washed with deionized water and ethanol respectively, and placed in a drying oven at 40 - 80 °C for drying;
[0007] b. The prepared (F,Cl,Br)-Co(OH)F / CP is placed in a porcelain boat and positioned at the downstream of a tube furnace; 0.8 - 1.2 g of sodium hypophosphite contained in the porcelain boat is placed at the upstream of the tube furnace, and phosphating is carried out under an argon atmosphere, the heat preservation temperature is 250 - 350 °C, the heat preservation time is 1.5 - 2.5 h, and the heating rate is 2 - 5 °C / min –1 , and then it is naturally cooled to room temperature to obtain a cobalt phosphide / carbon paper composite electrode doped with halogen elements F, Cl or Br, (F,Cl,Br)-CoP / CP.
[0008] Preferably, in step a, the doped halogen elements F, Cl or Br can regulate the morphology of cobalt phosphide CoP, making it present structural characteristics similar to dandelion, pine needle and bouquet respectively. Among them, F doping increases the specific surface area of CoP and the number of its active sites; the introduction of F promotes the formation of phosphorus vacancies, induces charge redistribution, and regulates the Gibbs free energy of hydrogen adsorption; F also forms hydrogen bonds with H2O, increasing the adsorption of H2O.
[0009] Preferably, in step b, the (F,Cl,Br)-Co(OH)F / CP is subjected to phosphating treatment to obtain (F,Cl,Br)-CoP / CP, and the specific surface area of the (F,Cl,Br)-CoP / CP is larger than that of the (F,Cl,Br)-Co(OH)F / CP.
[0010] According to the second aspect of the present disclosure, there is provided a cobalt phosphide / carbon paper composite electrode doped with halogen elements F, Cl or Br.
[0011] According to the third aspect of the present disclosure, there is provided an application of a cobalt phosphide / carbon paper composite electrode doped with halogen elements F, Cl or Br, characterized in that the composite electrode is directly used as a working electrode for electrochemical testing.
[0012] Preferably, directly using as a working electrode for electrochemical testing includes the following steps:
[0013] a. The cobalt phosphide / carbon paper composite electrode doped with F, Cl or Br, (F,Cl,Br)-CoP / CP is cut into a size of 0.5 - 1.0 cm 2 in size;
[0014] b. Electrochemical tests are carried out in a standard three - electrode test system, where the (F, Cl, Br)-CoP / CP composite electrode prepared in step a serves as the working electrode, a carbon rod electrode serves as the counter electrode, a Hg / HgO electrode serves as the reference electrode, and a KOH solution with a concentration of 0.8 - 1.2 M serves as the electrolyte;
[0015] c. Electrochemical tests are carried out on an Ivium - n - Stat electrochemical workstation. When performing polarization curve tests, the potential scanning range relative to the Hg / HgO electrode is - 0.9 to - 1.9 V, and the scanning speed is 2 mV s –1 ; Electrochemical impedance tests are carried out at a potential of - 1.0 to - 1.4 V relative to the Hg / HgO electrode, and the scanning frequency is 100 K Hz - 0.01 Hz; Chronopotentiometry tests are carried out under the condition of a current density of 500 mA cm –2 for a duration of 600 h;
[0016] d. The prepared (F, Cl, Br)-CoP / CP composite electrode serves as the working electrode for the hydrogen evolution reaction. Among them, when the F - CoP / CP drives a current density of 100 mA cm –2 , only an overpotential of 79 mV is required, and the Tafel slope is only 58 mV dec –1 , and it can stably operate for 600 h at a current density of 500 mA cm -2 .
[0017] The purpose of the present disclosure is to provide a preparation method and application of a cobalt phosphide / carbon paper composite electrode doped with halogen elements F, Cl or Br. The composite electrode is prepared by combining hydrothermal and low - temperature phosphidation methods. Halogen elements have high directionality and are used as powerful structure regulators in crystal engineering and other fields. Incorporating F, Cl or Br during the hydrothermal process, they can regulate the morphology of the catalyst, making CoP exhibit structural characteristics similar to dandelions, pine needles and bouquets respectively. Among them, F doping significantly increases the specific surface area of CoP and the number of active sites. The introduction of F not only promotes the formation of phosphorus vacancies, induces electron redistribution, improves the Gibbs free energy of hydrogen adsorption, but also can form hydrogen bonds with H2O to enhance the adsorption of H2O. In addition, the subsequent phosphidation treatment improves the conductivity of the catalyst CoP and increases the specific surface area, which is beneficial to electron transfer and mass transfer. The present disclosure can be extended to the design of other Co - based catalysts doped with halogen elements, providing new ideas for the preparation of efficient and economical catalysts.
[0018] Beneficial effects of the technical solution of the present disclosure:
[0019] The cobalt phosphide / carbon paper composite electrode doped with halogen elements F, Cl or Br according to the present disclosure is prepared by combining hydrothermal and low-temperature phosphidation methods. F, Cl or Br, as powerful structure regulators, the modified CoP electrodes exhibit structural characteristics similar to dandelions, pine needles and bouquets respectively. Among them, F doping significantly increases the specific surface area of CoP and the number of active sites; electrons are enriched around F, promoting the formation of phosphorus vacancies, causing charge redistribution, and further regulating the electronic structure of adjacent P sites and the Gibbs free energy of hydrogen adsorption; F can also form hydrogen bonds with H2O, increasing the adsorption of H2O. Description of the Drawings
[0020] Combined with the drawings and referring to the following detailed description, the above and other features, advantages and aspects of the embodiments of the present disclosure will become more obvious. The drawings are used to better understand the solution and do not limit the present disclosure. In the drawings, the same or similar reference numerals represent the same or similar elements, where:
[0021] Figure 1 、The hydrogen evolution reaction polarization curves of different electrodes in Example 1 of the present disclosure.
[0022] Figure 2 、The FESEM photograph of the F-CoP / CP composite material prepared in Example 1 of the present disclosure.
[0023] Figure 3 、The FESEM photograph of the Cl-CoP / CP composite material prepared in Example 1 of the present disclosure.
[0024] Figure 4 、The FESEM photograph of the Br-CoP / CP composite material prepared in Example 1 of the present disclosure.
[0025] Figure 5 、The TEM photograph of the F-CoP / CP composite material prepared in Example 1 of the present disclosure.
[0026] Figure 6 、The HRTEM photograph of the F-CoP / CP composite material prepared in Example 1 of the present disclosure.
[0027] Figure 7 、The XRD pattern of the F-CoP / CP composite material prepared in Example 1 of the present disclosure.
[0028] Figure 8 、The EPR spectra of the F-CoP / CP composite material prepared in Example 1 of the present disclosure and the comparative sample.
[0029] Figure 9 、The high-resolution XPS spectrum of the Co 2p region of the F-CoP / CP composite material prepared in Example 1 of the present disclosure.
[0030] Figure 10 、High-resolution XPS spectrum of the P 2p region of the F-CoP / CP composite material prepared in Example 1 of the present disclosure.
[0031] Figure 11 、High-resolution XPS spectrum of the F 1s region of the F-CoP / CP composite material prepared in Example 1 of the present disclosure.
[0032] Figure 12 、Tafel curves of different electrodes in Example 1 of the present disclosure.
[0033] Figure 13 、Electrochemical impedance spectra of different electrodes in Example 1 of the present disclosure.
[0034] Figure 14 、Chronopotentiometry curves of the F-CoP / CP composite electrode prepared in Example 1 of the present disclosure.
[0035] Figure 15 、FESEM photographs of the F-CoP / CP composite material prepared in Example 2 of the present disclosure.
[0036] Figure 16 、FESEM photographs of the F-CoP / CP composite material prepared in Example 3 of the present disclosure. Detailed implementation manners
[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present disclosure clearer, the technical solutions in the embodiments of the present disclosure will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present disclosure. Apparently, the described embodiments are some, but not all, of the embodiments of the present disclosure. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present disclosure without creative efforts shall fall within the protection scope of the present disclosure.
[0038] Example 1
[0039] The preparation method of a cobalt phosphide / carbon paper composite electrode doped with a halogen element F, Cl, or Br of the present disclosure is as follows:
[0040] (1) 3.0 mmol of cobalt nitrate hexahydrate Co(NO3)2·6H2O, 7.5 mmol of ammonium fluoride NH4F or ammonium chloride NH4Cl or ammonium bromide NH4Br, and 10 mmol of urea are successively added to deionized water and stirred to form a uniform mixed solution; the above mixed solution is transferred to a reaction kettle, and a washed 6 cm 2Carbon paper; the reaction kettle was placed in an oven for heat preservation at a heat preservation temperature of 120 °C and a heat preservation time of 6 h to obtain cobalt hydroxyfluoride / carbon paper doped with halogen elements F, Cl or Br, (F,Cl,Br)-Co(OH)F / CP; the obtained (F,Cl,Br)-Co(OH)F / CP was washed with deionized water and ethanol respectively, and placed in a drying oven at 60 °C for drying;
[0041] (2) The prepared (F,Cl,Br)-Co(OH)F / CP was placed in a porcelain boat and positioned at the downstream of a tube furnace; 1.0 g of sodium hypophosphite loaded in the porcelain boat was placed at the upstream of the tube furnace and phosphorized under an argon atmosphere at a heat preservation temperature of 300 °C, a heat preservation time of 2 h, and a heating rate of 3 °C min –1 , and then naturally cooled to room temperature to obtain a cobalt phosphide / carbon paper composite electrode doped with halogen elements F, Cl or Br, (F,Cl,Br)-CoP / CP.
[0042] In some embodiments, the (F,Cl,Br)-CoP / CP composite electrode was cut into a size of 0.75 cm 2 and directly used as the working electrode, a carbon rod electrode as the counter electrode, a Hg / HgO electrode as the reference electrode, and a KOH solution with a concentration of 1.0 M as the electrolyte to form a standard three-electrode system for electrochemical testing.
[0043] In some embodiments, the (F,Cl,Br)-CoP / CP composite electrode was used as the working electrode for testing on an Ivium-n-Stat electrochemical workstation. When performing polarization curve testing, the potential scanning range relative to the Hg / HgO electrode was -0.9 to -1.9 V, and the scanning speed was 2 mV s –1 ; the electrochemical impedance test was carried out at a potential of -1.02 V relative to the Hg / HgO electrode, and the scanning frequency was 100 K Hz to 0.01 Hz; the chronopotentiometry test was carried out under the condition of a current density of 500 mAcm –2 for a duration of 600 h.
[0044] Taking Example 1 as an example, the morphology and structure characterization and the electrocatalytic performance characterization results of the composite electrode of the present disclosure are described.
[0045] (1) Morphology and structure characterization of the (F,Cl,Br)-CoP / CP composite electrode:
[0046] The surface morphology of the catalyst was characterized by field emission scanning electron microscopy (FESEM). Figure 2 The FESEM photograph of the F-CoP / CP composite material shows that it presents a dandelion-like structure composed of nanorods. Figure 3The FESEM image of the Cl-CoP / CP composite material shows that it presents a pine needle-like structure. Figure 4 The FESEM image of the Br-CoP / CP composite material shows that the micro / nanosheets are closely arranged to form a bouquet-like morphology. The well-dispersed nanorod structure in F-CoP / CP is beneficial for exposing more active sites. However, the nanoneedles of Cl-CoP / CP show a straighter and more divergent state, resulting in an increase in the diameter and a decrease in the number of nanoneedles. The increase or overlap of the Br-CoP / CP nanosheet sizes reduces the exposed surface area, thereby reducing their catalytic activity. Figure 5 The TEM image of the F-CoP / CP composite electrode shows that the diameter of the nanorods is 100 - 200 nm. Figure 6 The high-resolution transmission HRTEM image of the F-CoP / CP composite electrode shows that the interplanar spacing of 0.190 nm corresponds to the (211) crystal plane of CoP, which is smaller than the (211) crystal plane spacing of pure CoP at 0.188 nm. This is because the ionic radius of F is larger than that of Co resulting in the substitution of Co by F. Figure 7 The X-ray diffraction XRD pattern of the F-CoP / CP composite material shows that the diffraction peaks at 31.4°, 36.2°, 46.0°, 48.0° and 56.5° correspond to the (011), (111), (112), (211) and (013) crystal planes of CoP (JCPDS 65-2593), respectively. The diffraction peaks at 26.6° and 54.8° correspond to the peaks of the substrate C (JCPDS 26-1076). This indicates that CoP has been successfully synthesized without the formation of a hetero-phase of halogen F. Figure 8 The electron paramagnetic resonance EPR spectra of the F-CoP / CP and CoP / CP composite materials show that the phosphorus vacancy signal of the F-CoP / CP composite material is significantly stronger than that of CoP. This may be due to the fact that after the introduction of the F element, electrons are enriched around F, promoting the formation of phosphorus vacancies, causing charge redistribution, and further regulating the electronic structure of adjacent phosphorus sites and the Gibbs free energy of hydrogen adsorption. Figures 9 - 11 The high-resolution XPS spectra of Co 2p, P 2p and F 1s of the F-CoP / CP composite material are shown respectively. Figure 9 In it, the characteristic peak at 777.5 eV in the Co 2p 3 / 2 region corresponds to the Co-P bond, and the characteristic peaks at 780.4 eV and 781.9 eV correspond to the Co-O bond. Figure 10 In it, the characteristic peak at 128.7 eV in the P 2p 3 / 2 region corresponds to the P-Co bond. The above results confirm the formation of metal phosphides on the electrode surface, and at the same time indicate that oxidation inevitably occurs on the sample surface, forming metal oxides.Figure 11 In it, the characteristic peak at 687.7 eV in the F 1s XPS spectrum confirms the existence of the F-Co bond.
[0047] (2) Electrochemical performance characterization of cobalt phosphide / carbon paper composite electrodes doped with halogen elements F, Cl, or Br at room temperature:
[0048] Electrochemical tests were carried out in a standard three-electrode test system. Figure 1 is the polarization curve of the catalyst at a scanning rate of 2 mV s –1 . It can be seen that the F-CoP / CP composite electrode only requires an overpotential of 79 mV to reach a current density of 100 mA cm –2 , which is much lower than the overpotentials required by the Cl-CoP / CP (106 mV) and Br-CoP / CP (120 mV) electrodes. Thus, it can be seen that F doping significantly improves the HER performance of CoP. This may be because the doped F promotes the generation of phosphorus vacancies, thereby regulating the Gibbs free energy of hydrogen adsorption at the active sites around the phosphorus vacancies. At the same time, it forms hydrogen bonds with H2O to promote the adsorption of H2O, thus improving the electrochemical performance of the catalyst. Figure 12 is the corresponding Tafel curve. The Tafel slope of F-CoP / CP is 58 mV dec –1 , which is less than that of Cl-CoP / CP (67 mV dec –1 ) and Br-CoP / CP (76 mV dec –1 ), indicating that F-CoP / CP has excellent reaction kinetics. Figure 13 is the electrochemical impedance spectrum. The charge transfer resistance of F-CoP / CP is only 0.54 Ω, which is much lower than that of Cl-CoP / CP (0.78 Ω) and Br-CoP / CP (0.92 Ω), indicating that F-CoP / CP has fast charge transfer kinetics. Figure 14 is the chronopotentiometry curve of F-CoP / CP. At a current density of 500 mA cm –2 , this electrode can continuously work for 600 h, and the overpotential does not show obvious attenuation, confirming its excellent stability. In summary, F-CoP / CP exhibits excellent HER catalytic activity, and the main reasons are as follows: Halogen elements are powerful structure regulators. CoP modified by F, Cl, or Br shows structural characteristics similar to dandelions, pine needles, and bouquets respectively. Among them, F doping significantly increases the specific surface area of the catalyst and the number of active sites; The introduction of F not only promotes the formation of phosphorus vacancies, which is beneficial to inducing charge redistribution and regulating the electronic structure of adjacent P sites, and then regulating the Gibbs free energy of hydrogen adsorption; F can also form hydrogen bonds with H2O to increase the adsorption of H2O.
[0049] Example 2
[0050] The preparation method of a cobalt phosphide / carbon paper composite electrode doped with halogen elements F, Cl, and Br of the present disclosure is as follows:
[0051] (1) 3.0 mmol of cobalt nitrate hexahydrate Co(NO3)2·6H2O, 7.5 mmol of ammonium fluoride NH4F or ammonium chloride NH4Cl or ammonium bromide NH4Br, and 10 mmol of urea are successively added to deionized water and stirred to form a uniform mixed solution; the above mixed solution is transferred to a reaction kettle, and a washed 6 cm 2 carbon paper is placed; the reaction kettle is placed in an oven for heat preservation, the heat preservation temperature is 120 °C, and the heat preservation time is 6 h to obtain a halogen element F, Cl, or Br-doped cobalt hydroxyfluoride / carbon paper (F, Cl, Br)-Co(OH)F / CP; the obtained (F, Cl, Br)-Co(OH)F / CP is washed with deionized water and ethanol respectively, and placed in a drying oven at 60 °C for drying;
[0052] (2) The prepared (F, Cl, Br)-Co(OH)F / CP is placed in a porcelain boat and placed at the downstream position of a tube furnace; 1.0 g of sodium hypophosphite contained in the porcelain boat is placed at the upstream position of the tube furnace and phosphated in an argon atmosphere, the heat preservation temperature is 300 °C, the heat preservation time is 2 h, and the heating rate is 3 °C min –1 , and then it is naturally cooled to room temperature to obtain a halogen element F, Cl, or Br-doped cobalt phosphide / carbon paper (F, Cl, Br)-CoP / CP composite electrode.
[0053] In some embodiments, the (F, Cl, Br)-CoP / CP composite electrode is cut into a size of 0.75 cm 2 and directly used as a working electrode, a carbon rod electrode is used as a counter electrode, a Hg / HgO electrode is used as a reference electrode, and a KOH solution with a concentration of 1.0 M is used as an electrolyte to form a standard three-electrode system for electrochemical testing.
[0054] In some embodiments, the (F, Cl, Br)-CoP / CP composite electrode is used as a working electrode for testing on an Ivium-n-Stat electrochemical workstation. When performing a polarization curve test, the potential scanning range relative to the Hg / HgO electrode is -0.9 to -1.9 V, and the scanning speed is 2 mV s –1 ; the electrochemical impedance test is performed at a potential of -1.02 V relative to the Hg / HgO electrode, and the scanning frequency is 100 K Hz to 0.01 Hz; the chronopotentiometry test is performed under the condition of a current density of 500 mAcm –2 for 600 h.
[0055] The FESEM photograph of the F-CoP / CP composite electrode prepared in Example 2 is as Figure 15 shown. It can be seen from Figure 15 that the composite electrode prepared in Example 2 has a similar morphology to the composite electrode prepared in Example 1, both presenting a dandelion-like structure composed of nanorods.
[0056] Example 3
[0057] The preparation method of a cobalt phosphide / carbon paper composite electrode doped with halogen elements F, Cl, and Br of the present disclosure is as follows:
[0058] (1) 3.0 mmol of cobalt nitrate hexahydrate Co(NO3)2·6H2O, 7.5 mmol of ammonium fluoride NH4F or ammonium chloride NH4Cl or ammonium bromide NH4Br, and 10 mmol of urea are successively added to deionized water and stirred to form a uniform mixed solution; the above mixed solution is transferred to a reaction kettle, and a cleaned 6 cm 2 carbon paper is placed; the reaction kettle is placed in an oven for heat preservation, the heat preservation temperature is 120 °C, and the heat preservation time is 6 h to obtain cobalt hydroxyfluoride / carbon paper doped with halogen elements F, Cl, or Br (F,Cl,Br)-Co(OH)F / CP; the obtained (F,Cl,Br)-Co(OH)F / CP is washed with deionized water and ethanol respectively, and placed in a drying oven at 60 °C for drying;
[0059] (2) The prepared (F,Cl,Br)-Co(OH)F / CP is placed in a porcelain boat and placed at the downstream position of a tube furnace; 1.0 g of sodium hypophosphite contained in the porcelain boat is placed at the upstream position of the tube furnace and phosphated in an argon atmosphere, the heat preservation temperature is 300 °C, the heat preservation time is 2 h, and the heating rate is 3 °C min –1 , and then it is naturally cooled to room temperature to obtain a cobalt phosphide / carbon paper composite electrode doped with halogen elements F, Cl, or Br (F,Cl,Br)-CoP / CP.
[0060] In some embodiments, the (F,Cl,Br)-CoP / CP composite electrode is cut into a size of 0.75 cm 2 and directly used as a working electrode, a carbon rod electrode as a counter electrode, a Hg / HgO electrode as a reference electrode, and a 1.0 M KOH solution as an electrolyte to form a standard three-electrode system for electrochemical testing.
[0061] In some embodiments, the (F,Cl,Br)-CoP / CP composite electrode is used as the working electrode for testing on an Ivium-n-Stat electrochemical workstation. When performing polarization curve testing, the potential scanning range relative to the Hg / HgO electrode is -0.9 to -1.9 V, and the scanning speed is 2 mV s –1 ; Electrochemical impedance testing is carried out at a potential of -1.02 V relative to the Hg / HgO electrode, and the scanning frequency is 100 K Hz to 0.01 Hz; Chronopotentiometry testing is carried out under the condition of a current density of 500 mA cm –2 for 600 h.
[0062] The FESEM photograph of the F-CoP / CP composite electrode prepared in Example 3 is as Figure 16 shown. It can be seen from Figure 16 that the composite electrode prepared in Example 3 has a similar morphology to the composite electrodes prepared in Example 1 and Example 2, and both exhibit a dandelion-like structure composed of nanorods.
[0063] In summary, the halogen element F, Cl or Br-doped cobalt phosphide / carbon paper composite electrode involved in the present disclosure is prepared by combining hydrothermal and phosphidation methods. The F-CoP / CP composite electrode exhibits excellent catalytic activity, and the main reasons are as follows: Halogens are powerful structure regulators. CoP modified by F, Cl or Br presents structural characteristics similar to dandelions, pine needles and bouquets respectively. Among them, F doping greatly increases the specific surface area of the catalyst and the number of active sites; Phosphorus vacancies promote charge redistribution, which is beneficial to adjusting the electronic structure of adjacent P sites, and then regulating the Gibbs free energy of hydrogen adsorption; F can also form hydrogen bonds with H2O, increasing the adsorption of H2O.
[0064] The above embodiments are the preferred embodiments of the present disclosure, but the embodiments of the present disclosure are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present disclosure shall be equivalent replacement methods and are all included in the protection scope of the present disclosure.
Claims
1. A preparation method of a cobalt phosphide / carbon paper composite electrode doped with a halogen element F, Cl or Br, characterized in that, It includes the following steps: a. Sequentially add 2.5 - 3.5 mmol of cobalt nitrate hexahydrate Co(NO3)2·6H2O, 7.0 - 8.0 mmol of ammonium fluoride NH4F or ammonium chloride NH4Cl or ammonium bromide NH4Br, and 4.5 - 5.5 mmol of urea into deionized water and stir to form a homogeneous mixed solution; transfer the above mixed solution into a reaction kettle and place a piece of washed carbon paper with a size of 2 - 5 cm 2 into it; place the reaction kettle in an oven for heat preservation, with the heat preservation temperature being 100 - 150 °C and the heat preservation time being 4 - 8 h to respectively obtain halogen element F, Cl or Br doped cobalt hydroxyfluoride / carbon paper (F,Cl,Br)-Co(OH)F / CP; wash the obtained (F,Cl,Br)-Co(OH)F / CP with deionized water and ethanol respectively, and place it in a drying oven at 40 - 80 °C for drying; b. Place the prepared (F, Cl, Br)-Co(OH)F / CP in a porcelain boat and position it at the downstream of a tube furnace; place 0.8 - 1.2 g of sodium hypophosphite in the porcelain boat at the upstream of the tube furnace, perform phosphorization under an argon atmosphere, with the heat preservation temperature being 250 - 350 °C, the heat preservation time being 1.5 - 2.5 h, and the heating rate being 2 - 5 °C / min –1 , and then naturally cool it to room temperature to obtain a halogen element F, Cl or Br-doped cobalt phosphide / carbon paper (F, Cl, Br)-CoP / CP composite electrode.
2. The preparation method of the cobalt phosphide / carbon paper composite electrode doped with halogen elements F, Cl or Br according to claim 1, characterized in that, In step a, the doped halogen elements F, Cl or Br can regulate the morphology of cobalt phosphide CoP, making it exhibit structural characteristics similar to dandelion, pine needle and bouquet respectively. Among them, F doping increases the specific surface area of CoP and the number of its active sites; the introduction of F promotes the formation of phosphorus vacancies, induces charge redistribution, and regulates the Gibbs free energy of hydrogen adsorption; F also forms hydrogen bonds with H2O, increasing the adsorption of H2O.
3. The preparation method of the cobalt phosphide / carbon paper composite electrode doped with halogen elements F, Cl or Br according to claim 1, characterized in that, In step b, the (F,Cl,Br)-Co(OH)F / CP is subjected to phosphidation treatment to obtain (F,Cl,Br)-CoP / CP, and the specific surface area of the (F,Cl,Br)-CoP / CP is larger than that of the (F,Cl,Br)-Co(OH)F / CP.
4. A composite electrode of cobalt phosphide doped with halogen elements F, Cl or Br / carbon paper obtained by the preparation method according to any one of claims 1-3.
5. Use of the cobalt phosphide / carbon paper composite electrode doped with halogen elements F, Cl or Br according to claim 4, characterized in that The composite electrode is directly used as a working electrode for electrochemical testing.
6. Use of the cobalt phosphide / carbon paper composite electrode doped with halogen elements F, Cl or Br according to claim 5, characterized in that, Directly using it as a working electrode for electrochemical testing includes the following steps: a. Cut the F, Cl or Br-doped cobalt phosphide / carbon paper (F, Cl, Br)-CoP / CP composite electrode into pieces with a size of 0.5 - 1.0 cm 2 in size; b. Electrochemical testing is carried out in a standard three-electrode test system, where the (F,Cl,Br)-CoP / CP composite electrode prepared in step a is used as the working electrode, a carbon rod electrode is used as the counter electrode, a Hg / HgO electrode is used as the reference electrode, and a KOH solution with a concentration of 0.8-1.2 M is used as the electrolyte; c. Electrochemical tests were carried out on an Ivium-n-Stat electrochemical workstation. When performing polarization curve tests, the potential scanning range relative to the Hg / HgO electrode was -0.9 to -1.9 V, and the scanning speed was 2 mV s –1 ; Electrochemical impedance tests were carried out at a potential of -1.0 to -1.4 V relative to the Hg / HgO electrode, and the scanning frequency was 100 K Hz to 0.01 Hz; Chronopotentiometry tests were carried out under the condition of a current density of 500 mA cm –2 , and the duration was 600 h; d. The prepared (F, Cl, Br)-CoP / CP composite electrode is used as the working electrode for the hydrogen evolution reaction. Among them, when the F-CoP / CP drives a current density of 100 mA cm –2 , only an overpotential of 79 mV is required, and the Tafel slope is only 58 mV dec –1 , and it can operate stably for 600 h at a current density of 500 mA cm -2 .