A preparation method and application of a fluorine and iron co-doped cobalt phosphide material

Abstract

A preparation method and application of a fluorine and iron co-doped cobalt phosphide material. The present invention aims to solve the problem that the recombination of the existing CoP catalyst only occurs in the surface layer during the OER process, and the reaction activity needs to be improved. Preparation method: First, soak and pretreat the carbon cloth in concentrated nitric acid at a temperature of 30-70 °C; Second, dissolve cobalt nitrate and iron nitrate in water, stir to obtain a reaction solution, and use a three-electrode system in the reaction solution for electrodeposition treatment; Third, place the carbon cloth growing with Fe-α-Co(OH)2 nanosheet arrays at the downstream of a high-temperature tube furnace, and sequentially place ammonium fluoride and sodium hypophosphite at the upstream of the tube furnace for calcination to obtain a fluorine and iron co-doped cobalt phosphide material. The fluorine and iron co-doped cobalt phosphide material of the present invention is used as an oxygen evolution electrode, and the introduction of F enhances the OER kinetics. The synergistic effect of F and Fe makes the recombination rate and recombination structure reach the optimal state. The fluorine and iron co-doped cobalt phosphide significantly improves the electrocatalytic performance.

Description

Technical Field

[0001] The present invention relates to a preparation method and application of a fluorine and iron co-doped cobalt phosphide material. Background Art

[0002] The excessive consumption of global fossil energy not only causes serious environmental pollution, but also brings an energy crisis. In order to achieve the goals of "carbon peak" and "carbon neutrality", the development of sustainable and clean energy has become the top priority to achieve this goal. In this regard, hydrogen (H2) is considered to be one of the most promising fuels. Hydrogen energy has the characteristics of high energy density, strong recyclability and no pollution, and is a potential candidate for future low-carbon energy systems. Electrochemical water splitting technology is considered a promising hydrogen production technology, which has the advantages of cleanliness, high efficiency and high purity, and has attracted people's attention. Moreover, from a thermodynamic perspective, its conversion efficiency is about 80%. The driving forces for the electrolytic water reaction are the hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction (OER) at the anode, respectively. However, OER involves a complex multi-electron transfer process and slow reaction kinetics, which will lead to a high overpotential in the actual reaction, making the electrolytic water consume a large amount of electric energy. Therefore, one of the important methods to solve the high energy consumption problem of electrolytic water is to research and produce efficient OER electrode catalytic materials.

[0003] It is reported that cobalt and its derivatives are the most promising catalysts in OER catalysis. Although cobalt metal and its oxides or hydroxides have been used for water splitting OER catalysis, the poor conductivity of these catalysts results in unsatisfactory catalytic performance and durability. Fortunately, cobalt phosphide (CoP) composed of transition metal cobalt and phosphorus through Co-P covalent bonds generates an electronic structure near the Fermi level and exhibits inherent metallicity. In recent years, under OER conditions, CoP forms a synergistic effect with cobalt oxide / hydroxide formed in-situ on CoP. Since CoP exposes more catalytic sites during the electrochemical cold working process of OER, CoP may have higher catalytic activity than the corresponding cobalt oxides or hydroxides. However, under alkaline conditions, the CoP catalyst undergoes surface reorganization during OER to form metal oxyhydroxide, which usually has a defective nanosheet structure and is called the "true" OER catalyst. However, this reorganization only occurs in the surface layer of the precatalyst CoP and the reorganization rate is slow. These problems limit the content and reactivity of the "true" catalyst. Summary of the Invention

[0004] The purpose of the present invention is to solve the problems of insufficient active sites and structure caused by the slow kinetics of the reconstruction process that only occurs in the surface layer of the precatalyst CoP during the OER process of the existing CoP catalyst, and the reactivity needs to be improved, and to provide a preparation method and application of a fluorine and iron co-doped cobalt phosphide material.

[0005] The preparation method of the fluorine and iron co-doped cobalt phosphide material of the present invention is realized according to the following steps:

[0006] I. Pretreatment of carbon cloth:

[0007] Put the carbon cloth into concentrated nitric acid at a temperature of 30-70 °C for soaking treatment, ultrasonically clean it with deionized water and absolute ethanol, and obtain the pretreated carbon cloth after drying;

[0008] II. Growth of iron-doped cobalt hydroxide nanosheet arrays on carbon cloth:

[0009] Dissolve 6-7 mmol of Co(NO3)2·6H2O and 0.07-0.7 mmol of Fe(NO3)3·9H2O in 80-120 mL of water, stir to obtain a reaction solution, adopt a three-electrode system in the reaction solution, use the pretreated carbon cloth as the working electrode, and perform electrodeposition treatment at a potential of -0.9 V (vs. SCE), and obtain the carbon cloth growing Fe-α-Co(OH)2 nanosheet arrays after washing and drying;

[0010] III. Preparation of fluorine and iron co-doped cobalt phosphide material:

[0011] Place the carbon cloth growing Fe-α-Co(OH)2 nanosheet arrays at the downstream of a high-temperature tube furnace, place NH4F at the upstream, calcine at a temperature of 400 °C for 0.8-1.2 hours in an Ar atmosphere to obtain a reaction product; then place NaH2PO2·H2O at the upstream of the high-temperature tube furnace, and place the reaction product at the downstream of the tube furnace, and calcine at a temperature of 350 °C for 1.5-2.5 hours in an Ar atmosphere, and obtain the fluorine and iron co-doped cobalt phosphide material after natural cooling.

[0012] The application of the fluorine and iron co-doped cobalt phosphide material of the present invention is to use the fluorine and iron co-doped cobalt phosphide material as an oxygen evolution electrode.

[0013] The preparation method of the fluorine and iron co-doped cobalt phosphide material of the present invention has the following beneficial effects:

[0014] 1. The fluorine and iron co-doped cobalt phosphide material obtained by the present invention grows on the carbon cloth. The carbon cloth serves as a conductive substrate (current collector), the active material has good contact with the carbon cloth, good stability, and the carbon cloth has high conductivity and strong proton transport ability.

[0015] 2. The obtained fluorine and iron co-doped cobalt phosphide material supported on the carbon cloth grows in-situ on the carbon cloth. Cobalt nitrate is used as the cobalt source. Since transition metals have empty orbitals and d-orbital electrons, they can easily gain or lose electrons in chemical reactions, have rich redox properties, and are prone to form intermediate transition states in the oxygen evolution reaction.

[0016] 3. The obtained cobalt phosphide material doped with fluorine and iron in the present invention is in-situ grown on carbon cloth. Using NaH2PO2·H2O as the phosphorus source, a low-temperature phosphidation method is adopted to replace the hydroxide groups in the precursor sample, and the morphology of the precursor will not be damaged under mild reaction conditions.

[0017] 4. For the cobalt phosphide material doped with fluorine and iron in the present invention, fluorine is successfully introduced with NH4F as the raw material. In the subsequent phosphidation reaction, since fluorine is unstable at high temperatures, it is replaced by phosphorus. Fluorine has the largest electronegativity and is easily approached by hydroxide groups in an alkaline environment. The fluorinated cobalt phosphide is prone to surface reorganization when used as a catalyst.

[0018] 5. For the cobalt phosphide material doped with fluorine and iron in the present invention, ferric nitrate is used as the iron source. Since cobalt metal and iron metal are both metals in the eighth main group and have similar structural characteristics, the iron content of the obtained cobalt phosphide material doped with fluorine and iron in the present invention is about 5% (iron accounts for the total metal content). The doping of Fe element improves the charge transfer ability.

[0019] 6. The cobalt phosphide material doped with fluorine and iron in the present invention is used as an oxygen evolution electrode. This material promotes surface structure reorganization in the electrocatalytic reaction. The introduction of F ensures the rapid progress of the reconstruction process and enhances the subsequent OER kinetics. Fe atoms further accelerate the charge transfer rate, strengthen the role of F, relieve the structural accumulation caused by insufficient kinetics during the reconstruction process, and reveal the activity-structure relationship of metal phosphides in the OER reaction to solve the problems of difficult recombination and slow kinetics in the reaction.

[0020] 7. The cobalt phosphide material doped with fluorine and iron in the present invention can exhibit significantly better excellent activity and good stability than each single component in the fields of catalytic energy storage, etc. The main reasons are as follows: (1) The cobalt phosphide composed of transition metal cobalt and phosphorus through Co-P covalent bonds generates an electronic structure near the Fermi level, showing inherent metallicity, promoting electron transfer at the material interface, and improving electrochemical activity. (2) Fluorine has the largest electronegativity (4.0) and is electrochemically easily accessible under OER conditions. It can not only more effectively regulate the electronic structure, but also may lead to more abundant oxygen vacancies or defects in the material compared with other non-metal elements, which is beneficial to catalysis. (3) On this basis, the further introduction of iron can accelerate the charge transfer rate and improve the reaction kinetics. (4) More importantly, the addition of iron strengthens the role of F, relieves the structural accumulation caused by insufficient kinetics during the reconstruction process, and helps to expose more active sites. The synergistic effect of F and Fe expands their respective roles synchronously, making the recombination speed and recombination structure reach the optimal state. The cobalt phosphide doped with fluorine and iron significantly improves the electrocatalytic performance compared with the single-doped ones.

[0021] 8. The fluorine and iron co-doped cobalt phosphide material of the present invention is used as an oxygen evolution electrode, and this material is prepared by low-temperature calcination using Fe-α-Co(OH)2 as a precursor. This method is ingeniously designed, has a simple process, low cost, and strong reproducibility.

[0022] 9. Through in-situ Raman and ex-situ structural analysis, the present invention clarifies the activity-structure relationship of F and Fe on metal phosphide catalysts in the OER reaction, providing a special reference for the design and research of low-cost and high-performance electrocatalysts. Description of the Drawings

[0023] Figure 1 is the scanning electron microscope image of the Fe-α-Co(OH)2 nanosheet array vertically grown on carbon cloth in the example;

[0024] Figure 2 is the X-ray diffraction spectrum of the Fe-α-Co(OH)2 nanosheet array vertically grown on carbon cloth in the example;

[0025] Figure 3 is the scanning electron microscope image of the F and Fe co-doped CoP nanosheet array obtained in the example;

[0026] Figure 4 is the X-ray diffraction spectrum of the F and Fe co-doped CoP nanosheet array obtained in the example;

[0027] Figure 5 is the transmission electron microscope image of the F and Fe co-doped CoP nanosheets obtained in the example;

[0028] Figure 6 is the high-resolution transmission electron microscope image of the F and Fe co-doped CoP nanosheets obtained in the example;

[0029] Figure 7 is the X-ray photoelectron spectroscopy of the F and Fe co-doped CoP nanosheet array obtained in the example;

[0030] Figure 8 is the elemental surface distribution map of the F and Fe co-doped CoP nanosheet array obtained in the example;

[0031] Figure 9 is the chronopotentiometry curve of the F and Fe doped CoP nanosheet array in the example, where 1 represents the F and Fe doped CoP nanosheets, and 2 represents the CoP nanosheets;

[0032] Figure 10 is the chronopotentiometry curve of the F doped CoP nanosheet array in the example, where 3 represents the F doped CoP nanosheets, and 2 represents the CoP nanosheets;

[0033] Figure 11 It is the chronopotentiometry curve of the Fe-doped CoP nanosheet array in the example, where 4 represents the Fe-doped CoP nanosheet and 2 represents the CoP nanosheet;

[0034] Figure 12 It is the X-ray diffraction spectrum of the F, Fe-doped CoP nanosheet array at different recombination times in the example;

[0035] Figure 13 It is the X-ray diffraction spectrum of the F-doped CoP nanosheet array at different recombination times in the example;

[0036] Figure 14 It is the X-ray diffraction spectrum of the Fe-doped CoP nanosheet array at different recombination times in the example;

[0037] Figure 15 It is the scanning electron microscope image of the F, Fe-doped CoP material during the recombination process in the example;

[0038] Figure 16 It is the scanning electron microscope image of the F-doped CoP material during the recombination process in the example;

[0039] Figure 17 It is the scanning electron microscope image of the Fe-doped CoP material during the recombination process in the example;

[0040] Figure 18 It is the electrochemical impedance spectroscopy diagram of the F, Fe-doped, F-doped, and Fe-doped CoP materials in the example, where 1 represents the F, Fe-doped CoP material, 2 represents the Fe-doped CoP material, 3 represents the F-doped CoP material, and 4 represents the CoP material;

[0041] Figure 19 It is the in-situ Raman diagram of the F, Fe-doped CoP material in the example;

[0042] Figure 20 It is the in-situ Raman diagram of the CoP material;

[0043] Figure 21 It is the OER linear sweep voltammogram of the F, Fe-doped, F-doped, and Fe-doped CoP materials in the example. Along the arrow direction, they are the F, Fe-doped CoP material, Fe-doped CoP material, F-doped CoP material, and CoP material in turn;

[0044] Figure 22 It is the function diagram of Δj / 2 versus scan rate of the F, Fe-doped, F-doped, and Fe-doped CoP materials in the example. Along the arrow direction, they are the F, Fe-doped CoP material, F-doped CoP material, Fe-doped CoP material, and CoP material in turn. Specific Embodiments

[0045] Specific Embodiment 1: The preparation method of the fluorine and iron co-doped cobalt phosphide material in this embodiment is implemented according to the following steps:

[0046] I. Pretreatment of carbon cloth:

[0047] Put the carbon cloth into concentrated nitric acid at a temperature of 30 - 70 °C for soaking treatment, ultrasonically clean it with deionized water and absolute ethanol, and obtain the pretreated carbon cloth after drying;

[0048] II. Growth of iron-doped cobalt hydroxide nanosheet arrays on the carbon cloth:

[0049] Dissolve 6 - 7 mmol of Co(NO3)2·6H2O and 0.07 - 0.7 mmol of Fe(NO3)3·9H2O in 80 - 120 mL of water, stir to obtain a reaction solution, adopt a three-electrode system in the reaction solution, use the pretreated carbon cloth as the working electrode, perform electrodeposition treatment at a potential of -0.9 V (vs. SCE), and obtain the carbon cloth growing Fe-α-Co(OH)2 nanosheet arrays after washing and drying;

[0050] III. Preparation of the fluorine and iron co-doped cobalt phosphide material:

[0051] Place the carbon cloth growing Fe-α-Co(OH)2 nanosheet arrays at the downstream of a high-temperature tube furnace, place NH4F at the upstream, calcine at a temperature of 400 °C for 0.8 - 1.2 hours in an Ar atmosphere to obtain a reactant; then place NaH2PO2·H2O at the upstream of the high-temperature tube furnace and the reactant at the downstream of the tube furnace, calcine at a temperature of 350 °C for 1.5 - 2.5 hours in an Ar atmosphere, and obtain the fluorine and iron co-doped cobalt phosphide material after natural cooling.

[0052] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is that the temperature of soaking in concentrated nitric acid in Step I is 60 °C.

[0053] Specific Embodiment 3: The difference between this embodiment and Specific Embodiment 1 or 2 is that the soaking treatment time in Step I is 4 - 8 hours.

[0054] Specific Embodiment 4: The difference between this embodiment and any one of Specific Embodiments 1 to 3 is that in the three-electrode system in Step II, a saturated calomel electrode is used as the reference electrode and a platinum sheet is used as the counter electrode.

[0055] Specific Embodiment 5: The difference between this embodiment and any one of Specific Embodiments 1 to 4 is that in Step II, electrodeposition treatment is carried out at a constant temperature of 30 °C for 20 - 30 minutes.

[0056] Specific Embodiment Six: The difference between this embodiment and one of Specific Embodiments One to Five is that in Step 3, the heating rate of the high-temperature tubular furnace is controlled at 10 °C / min.

[0057] Specific Embodiment Seven: The difference between this embodiment and one of Specific Embodiments One to Six is that it is calcined at a temperature of 350 °C for 2 hours under an Ar atmosphere of 100 sccm.

[0058] Specific Embodiment Eight: The difference between this embodiment and one of Specific Embodiments One to Seven is that in the fluorine and iron co-doped cobalt phosphide material obtained in Step 3, the iron accounts for 1.5 - 6 At% of the total metal content.

[0059] Specific Embodiment Nine: The difference between this embodiment and Specific Embodiment Eight is that in the fluorine and iron co-doped cobalt phosphide material obtained in Step 3, the doping amount of fluorine is 8 - 12 At%, and the doping amount of phosphorus is 40 - 60 At%.

[0060] Example: The preparation method of the fluorine and iron co-doped cobalt phosphide material in this example is implemented according to the following steps:

[0061] I. Pretreatment of carbon cloth:

[0062] Put the carbon cloth into concentrated nitric acid (mass concentration of 65 - 68%) at 60 °C and soak for 6 hours. After ultrasonic cleaning with deionized water and absolute ethanol and drying (drying temperature is 50 °C), the pretreated carbon cloth is obtained;

[0063] II. Growth of iron-doped cobalt hydroxide nanosheet arrays on the carbon cloth:

[0064] Dissolve 6.65 mmol of Co(NO3)2·6H2O and 0.35 mmol of Fe(NO3)3·9H2O in 100 mL of water, stir for 30 minutes to obtain a reaction solution. In the reaction solution, use a three-electrode system, with the pretreated carbon cloth as the working electrode, saturated calomel as the reference electrode, and a platinum sheet as the counter electrode. Electrodeposit at a constant temperature of 30 °C for 20 minutes at a potential of -0.9 V (vs. SCE). After alternately rinsing with ultrapure water and ethanol, dry in an oven at 60 °C for 6 hours to obtain the carbon cloth with Fe-α-Co(OH)2 nanosheet arrays grown;

[0065] III. Preparation of the fluorine and iron co-doped cobalt phosphide material:

[0066] The carbon cloth with Fe-α-Co(OH)2 nanosheet arrays grown thereon was placed downstream of a high-temperature tube furnace, 5 mmol of NH4F was placed downstream, and it was calcined at 400 °C for 1.0 hour in an Ar atmosphere to obtain a reactant; then 500 mg of NaH2PO2·H2O was placed upstream of the high-temperature tube furnace, and the reactant was placed downstream of the tube furnace, and it was calcined at 350 °C for 2 hours in an Ar atmosphere of 100 sccm, and after natural cooling, a fluorine- and iron-codoped cobalt phosphide material was obtained.

[0067] Figure 1 Figure 4 is a scanning electron microscope image of the Fe-α-Co(OH)2 nanosheet arrays vertically grown on carbon cloth in this example; it can be seen from the figure that the synthesized product has interconnected network nanosheets vertically growing on the surface of the carbon cloth to form an array. The surface of the nanosheets is smooth and evenly distributed, forming a multi-void network structure.

[0068] Figure 2 Figure 8 is the X-ray diffraction spectrum of the Fe-α-Co(OH)2 nanosheet arrays vertically grown on carbon cloth in this example. The broad diffraction signal at 25.8° in the spectrum comes from the carbon cloth. The other diffraction peaks all belong to the material α-Co(OH)2.

[0069] Figure 3 Figure 12 is a scanning electron microscope image of the F, Fe-codoped CoP nanosheet arrays (product) vertically grown on carbon cloth; it can be seen from the figure that there is no obvious change on the surface of the synthesized product compared with the precursor.

[0070] Figure 4 Figure 16 is the X-ray diffraction spectrum of the F, Fe-codoped CoP nanosheet arrays; the strong diffraction peak at 25.8° in the spectrum comes from graphite carbon. The other diffraction peaks at 31.6°, 36.3°, 46.2°, 48.1°, and 56.8° of CoP correspond to the (011), (111), (112), (211), and (301) planes of the CoP standard card (PDF#29-0497), respectively. The diffraction angles of F, Fe-codoped CoP, Fe-doped CoP, and F-doped CoP have not changed, indicating that the co-doping of F and Fe does not affect the crystal structure of CoP.

[0071] Figure 5 and Figure 6 Figures 22(a) and 22(b) are the transmission electron microscope image and high-resolution transmission electron microscope image of the F, Fe-codoped CoP nanosheets, respectively. It can be seen from the figure that the synthesized product has a flat nanosheet morphology, and the lattice fringe spacings of 0.279 and 0.283 nm are indexed to the (002) and (011) planes of CoP. According to the characteristics of the orthorhombic crystal structure (5.077×3.281×5.587), the two crystal planes form a 60° angle.

[0072] Figure 7This is the photoelectron spectrum of F and Fe co-doped CoP nanosheet array. It can be seen from the figure that iron accounts for about 5% of the total metal content, which is close to the initial molar ratio, fluorine accounts for 10% of the total content, and phosphorus accounts for 50% of the total content.

[0073] Figure 8 This is the element surface distribution diagram of F and Fe co-doped CoP nanosheet array; the figure shows the uniform distribution of Co, P, F and Fe elements in F and Fe co-doped CoP nanosheets, indicating that F and Fe elements have been successfully introduced into the nanosheet array.

[0074] Figures 9 - 11 is the chronovoltage curve of F-doped, Fe-doped, F-doped, Fe-doped CoP nanosheet array; Figure 9 The entire curve can be divided into three main steps: the first step represents the electrochemical oxidation of the intermediate F-Fe-CoP to F-Fe-Co(OH)2. The second step shows that F-Fe-Co(OH)2 completes the transformation to F-Fe-CoOOH before reaching the OER conditions. Finally, the surface-synthesized F-Fe-CoOOH, which took 2.6 hours, serves as the real catalytic component. For CoP and Fe-doped CoP, the reconstruction process is slower, and the final reconstruction time is 3.8 hours. This shows that the co-doping of F and Fe accelerates the reconstruction of CoP and accelerates the transition to the active substance F-Fe-CoOOH. In order to study the effects of F and Fe, the present invention studied the reconstruction phenomenon of F-CoP and Fe-CoP. When F is doped, the catalyst reconstruction time potential distribution diagram of F-CoP is significantly faster than CoP. Due to the relatively large electronegativity of F, the OH in the OER catalytic process is slower. - It is more easily adsorbed, thus accelerating the recombination of F-CoOOH, which is beneficial to the initiation of surface reconstruction and the optimization of OER performance.

[0075] Figures 12 - 14 Figure 2 shows X-ray diffraction spectra at different recombination times. The figure shows that for the F- and Fe-codoped CoP and F-doped CoP samples, the diffraction peaks attributable to CoP completely disappear after 2 hours. In contrast, when Fe is doped alone, only the Fe-CoP still contains CoP after 2 hours of electrochemical reconstruction, indicating incomplete conversion.

[0076] Figures 15 - 17 The following are scanning electron microscopy images of F-doped, Fe-doped, and Fe-doped CoP materials during the recombination process. The 3-hour scanning electron microscopy images show that F-doped CoP accelerates the reconstruction compared to CoP. However, a drawback is that the reconstructed nanosheets tend to stack, affecting the exposure of active sites. This is likely due to insufficient electron transfer rates during the reconstruction process. Furthermore, the introduction of Fe alleviates the stacking problem of F reconstruction. This is likely due to the accelerated charge transfer and reduced resistance caused by the addition of Fe.

[0077] Figure 18 is the electrochemical impedance spectrum of the sample; as can be seen from the figure, the charge transfer resistance of F, Fe-doped CoP is lower than that of CoP, Fe-CoP, and F-CoP, indicating that the injection of F and Fe can effectively promote charge migration.

[0078] Figure 19 and Figure 20 are the in-situ Raman spectra of F, Fe-doped CoP and CoP. In-situ Raman spectroscopy is used to capture the structural evolution between 0 and 1.8 V (vs. RHE) in 1.0 M KOH. The band near 488 cm -1 is caused by the E g mode, which is related to the stretching of the Co-O bond. The A -1 mode located at about 600 cm 1g is associated with the O-Co-O bond. It is worth noting that the spectra of F, Fe-doped CoP show that as the potential increases, the characteristic Raman peaks of F-Fe-CoOOH gradually broaden and strengthen starting from 1.6 V. However, CoP starts to change at 1.7 V, indicating that the co-doping of F and Fe accelerates the dynamic surface reconstruction. In addition, the F, Fe co-doped CoP electrocatalyst undergoes significant surface reconstruction during the activation process to generate more F-Fe-CoOOH active phases. It shows that F, Fe co-doped CoP exhibits fast OER kinetics and excellent performance.

[0079] Figure 21 are the OER linear sweep voltammograms of F, Fe-doped, F-doped, and Fe-doped CoP materials. As can be seen from the figure, F, Fe co-doped CoP has the smallest overpotential at the same current density. At a current density of 20 mA cm -2 , the overpotential is 259 mV, which is significantly smaller than that of F-CoP (270 mV), Fe-CoP (284 mV), and CoP (308 mV).

[0080] Figure 22 is a plot of Δj / 2 as a function of the scan rate for F, Fe-doped, F-doped, and Fe-doped CoP materials. The cyclic voltammograms in the non-Faradaic reaction region are tested at different scan rates, and a plot is made with Δj / 2 and the scan rate as the axes. The slope of the fitted curve is the double-layer capacitance value of the material. As can be seen from the figure, the slope of F, Fe-doped CoP is the largest, indicating that F, Fe-doped CoP has the largest double-layer capacitance, reflecting its largest active surface area.

Claims

1. Preparation method of fluorine- and iron-codoped cobalt phosphide material, characterized in that The preparation method is realized according to the following steps: I. Pretreatment of carbon cloth: The carbon cloth is immersed in concentrated nitric acid at a temperature of 30 - 70°C, ultrasonically cleaned with deionized water and absolute ethanol, and dried to obtain the pretreated carbon cloth; II. Growth of iron-doped cobalt hydroxide nanosheet arrays on the carbon cloth: 6 - 7 mmol of Co(NO3)2·6H2O and 0.07 - 0.7 mmol of Fe(NO3)3·9H2O are dissolved in 80 - 120 mL of water, stirred to obtain a reaction solution. In the reaction solution, a three-electrode system is adopted, with the pretreated carbon cloth as the working electrode, and electrodeposition treatment is carried out at a potential of -0.9 V. After washing and drying, the carbon cloth with Fe-α-Co(OH)2 nanosheet arrays grown is obtained; III. Preparation of fluorine- and iron-codoped cobalt phosphide material: The carbon cloth with Fe-α-Co(OH)2 nanosheet arrays grown is placed downstream of a high-temperature tube furnace, and NH4F is placed upstream. It is calcined at a temperature of 400°C for 0.8 - 1.2 hours in an Ar atmosphere to obtain a reaction product; then NaH2PO2·H2O is placed upstream of the high-temperature tube furnace, and the reaction product is placed downstream. It is calcined at a temperature of 350°C for 1.5 - 2.5 hours in an Ar atmosphere, and after natural cooling, the fluorine- and iron-codoped cobalt phosphide material is obtained.

2. The preparation method of the fluorine and iron co-doped cobalt phosphide material according to claim 1, wherein In step I, the temperature of the concentrated nitric acid immersion is 60°C.

3. The preparation method of the fluorine and iron co-doped cobalt phosphide material according to claim 1, characterized in that In step I, the immersion treatment time is 4 - 8 hours.

4. The preparation method of the fluorine and iron co-doped cobalt phosphide material according to claim 1, wherein In step II, a saturated calomel electrode is used as the reference electrode and a platinum sheet is used as the counter electrode in the three-electrode system.

5. The preparation method of the fluorine and iron co-doped cobalt phosphide material according to claim 1, characterized in that In step II, electrodeposition treatment is carried out at a constant temperature of 30°C for 20 - 30 minutes.

6. The preparation method of the fluorine and iron co-doped cobalt phosphide material according to claim 1, characterized in that In step III, the heating rate of the high-temperature tube furnace is controlled at 10°C / min.

7. The preparation method of the fluorine- and iron-codoped cobalt phosphide material according to claim 1, characterized in that It is calcined at a temperature of 350°C for 2 hours in an Ar atmosphere of 100 sccm.

8. The preparation method of the fluorine and iron co-doped cobalt phosphide material according to claim 1, wherein The iron doping amount in the fluorine- and iron-codoped cobalt phosphide material obtained in step III is 1.5 - 3 At%.

9. The method for preparing the fluorine and iron co-doped cobalt phosphide material according to claim 8, wherein The fluorine doping amount in the fluorine- and iron-codoped cobalt phosphide material obtained in step III is 8 - 12 At%, and the phosphorus doping amount is 40 - 60 At%.

10. Use of the fluorine- and iron-codoped cobalt phosphide material prepared as claimed in claim 1, characterized in that The fluorine- and iron-codoped cobalt phosphide material is used as an oxygen evolution electrode.

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