Porous flower-shaped P-doped Co9S8 compound as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of catalyst preparation, and provides a porous flower-shaped P-doped Co9S8 compound as well as a preparation method and application thereof. The preparation method comprises the following steps: dispersing cobalt salt (including cobalt acetate) into a water-ethanol mixed solvent to obtain a cobalt salt solution; the preparation method comprises the following steps: dipping carbon cloth into a cobalt salt solution, adding a sulfur source into the cobalt salt solution after dipping is completed, and carrying out a hydrothermal reaction to obtain a carbon cloth Co9S8 compound; and mixing the carbon cloth Co9S8 compound with a phosphorus source, and phosphorizing to obtain the porous flower-shaped P-doped Co9S8 compound. The P-doped Co9S8 compound obtained by the preparation method disclosed by the invention is in a porous nano flower shape, and can provide a high specific surface area and abundant electron transmission channels. The P-doped Co9S8 compound shows the oxygen evolution performance and the hydrogen evolution performance of electrolyzed water under 10mA / cm < 2 >, and the oxygen evolution performance and the hydrogen evolution performance of electrolyzed water are 271 mV and 80 mV respectively.

Description

Technical Field

[0001] The present invention relates to the technical field of catalyst preparation, and particularly relates to a porous flower-like P-doped Co9S8 composite and its preparation method and application. Background Art

[0002] In recent years, transition metal sulfides have been used as excellent electrolytic water catalysts due to their low cost, good conductivity, easy synthesis and other advantages. Among them, cobalt sulfides (such as CoS, CoS2, Co9S8, etc.) have always been the research focus in the field of electrocatalysts due to their good catalytic activity. However, cobalt sulfide-based electrocatalysts still have many limitations in the field of electrolytic water, such as poor cycle stability, high Gibbs free energy of water decomposition, low catalytic active sites, etc. To overcome these challenges, researchers have adopted various strategies, including constructing heterostructures, doping foreign atoms, phase engineering, etc. Among them, doping foreign atoms into cobalt sulfide is considered a feasible way to optimize the catalytic activity of cobalt sulfide, because introducing foreign atoms into the cobalt sulfide structure can not only adjust the electronic structure, but also reduce the free energy of adsorbed hydrogen / oxygen during the water splitting process.

[0003] The prior art discloses the use of nitrogen-doped Co9S8 as a catalyst, but the obtained catalyst has low catalytic activity for hydrogen production by electrolytic water. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a porous flower-like P-doped Co9S8 composite and its preparation method and application. The porous flower-like P-doped Co9S8 composite prepared by the preparation method provided by the present invention has excellent catalytic activity for hydrogen production by electrolytic water.

[0005] In order to achieve the above invention purpose, the present invention provides the following technical solutions:

[0006] The present invention provides a preparation method of a porous flower-like P-doped Co9S8 composite, comprising the following steps:

[0007] Disperse cobalt salt in a water-ethanol mixed solvent to obtain a cobalt salt solution;

[0008] Immerse carbon cloth in the cobalt salt solution. After immersion, add a sulfur source to the cobalt salt solution, and perform hydrothermal reaction on the obtained mixed system to obtain a carbon cloth Co9S8 composite;

[0009] Mix the carbon cloth Co9S8 composite and a phosphorus source, and perform phosphidation to obtain the porous flower-like P-doped Co9S8 composite;

[0010] The cobalt salt includes cobalt acetate.

[0011] Preferably, in the water-ethanol mixed solvent, the volume ratio of water to ethanol is 3-10:1-2; the concentration of the cobalt salt solution is 0.025-0.1 mol / L.

[0012] Preferably, the dosage ratio of the cobalt salt to the carbon cloth is 0.1-1 mmol:0.01-0.2 g.

[0013] Preferably, the impregnation time is 30-60 min.

[0014] Preferably, the sulfur source includes thiourea and / or sodium sulfide; the molar ratio of the cobalt salt to the sulfur source is 1:1-15.

[0015] Preferably, the temperature of the hydrothermal reaction is 180-220 °C, and the time is 10-16 h.

[0016] Preferably, the phosphorus source is NaH2PO2, and the mass ratio of the carbon cloth Co9S8 composite to the phosphorus source is 1:1-4.

[0017] Preferably, the temperature of the phosphidation is 300-450 °C, the heating rate to the temperature of the phosphidation is 2-5 °C / min; the time of the phosphidation is 1.5-3.5 h; the phosphidation is carried out under a protective atmosphere.

[0018] The present invention also provides a porous flower-like P-doped Co9S8 composite prepared by the preparation method described in the above technical solution.

[0019] The present invention also provides the application of the porous flower-like P-doped Co9S8 composite described in the above technical solution in the field of water electrolysis.

[0020] The present invention provides a preparation method of a porous flower-like P-doped Co9S8 composite.

[0021] In the preparation method of the present invention, cobalt acetate is used as the cobalt salt and is uniformly dispersed in a water-ethanol mixed solvent to form a cobalt salt solution; then the carbon cloth is impregnated in the cobalt salt solution so that the cobalt salt can be deposited on the carbon cloth quickly and uniformly; then a sulfur source is added, and flower-like Co9S8 is formed under the conditions of a hydrothermal reaction; in the presence of a phosphating agent, the flower-like Co9S8 is phosphated, and while phosphorus is incorporated, a porous structure can also be introduced on the flower-like structure. The P-doped Co9S8 composite obtained by the preparation method provided by the present invention presents a porous nanoflower morphology, which can provide a high specific surface area and rich electron transport channels. The P-doped Co9S8 composite at 10 mA / cm 2The oxygen evolution and hydrogen evolution performances of electrolyzed water shown below are 271 mV and 80 mV respectively. Experimental and theoretical results show that introducing P atoms into Co9S8 can greatly adjust the electronic structure of Co9S8, promote the charge redistribution of Co9S8, and optimize the energy barrier of water splitting. Description of the Drawings

[0022] Figure 1 It is the preparation flow chart of the porous flower-like P-doped Co9S8 composite provided by the present invention;

[0023] Figure 2 They are the scanning electron microscope photos of P-Co9S8-1 (a), P-Co9S8-2 (b) and P-Co9S8-3 (c);

[0024] Figure 3 It is the structural characterization diagram of P-Co9S8-2;

[0025] Figure 4 They are the XRD diagrams of Co9S8, P-Co9S8-1, P-Co9S8-2 and P-Co9S8-3;

[0026] Figure 5 They are the XPS spectrograms of Co2p of Co9S8 and P-Co9S8-2;

[0027] Figure 6 They are the XPS spectrograms of S2p of Co9S8 and P-Co9S8-2;

[0028] Figure 7 They are the XPS spectrograms of P2p of Co9S8 and P-Co9S8-2;

[0029] Figure 8 They are the linear sweep voltammetry curves of commercially available RuO2, Co9S8, P-Co9S8-1, P-Co9S8-2 and P-Co9S8-3 after iR correction;

[0030] Figure 9 They are commercially available RuO2, Co9S8, P-Co9S8-1, P-Co9S8-2 and P-Co9S8-3 at 10 mA / cm 2 and 100 mA / cm 2 under the catalytic activity;

[0031] Figure 10 They are the Tafel slopes of commercially available RuO2, Co9S8, P-Co9S8-1, P-Co9S8-2 and P-Co9S8-3;

[0032] Figure 11C of Co9S8, P-Co9S8-1, P-Co9S8-2 and P-Co9S8-3 dl Figure

[0033] Figure 12 Electrochemical impedance spectroscopy diagrams of Co9S8, P-Co9S8-1, P-Co9S8-2 and P-Co9S8-3

[0034] Figure 13 Cyclic stability test diagram of P-Co9S8-2

[0035] Figure 14 Linear sweep voltammetry (LSV) curves of hydrogen evolution in water electrolysis for commercially available Pt / C, Co9S8, P-Co9S8-1, P-Co9S8-2 and P-Co9S8-3

[0036] Figure 15 For commercially available Pt / C, Co9S8, P-Co9S8-1, P-Co9S8-2 and P-Co9S8-3 at 10 mA / cm 2 and 100 mA / cm 2 Overpotential

[0037] Figure 16 Tafel slopes of commercially available Pt / C, Co9S8, P-Co9S8-1, P-Co9S8-2 and P-Co9S8-3

[0038] Figure 17 Electrochemical impedance spectroscopy diagrams of Co9S8, P-Co9S8-1, P-Co9S8-2 and P-Co9S8-3

[0039] Figure 18 Cyclic stability test diagram of P-Co9S8-2

[0040] Figure 19 Diagram of the application of P-Co9S8-2 and noble metal catalysts in water electrolysis

[0041] Figure 20 SEM diagram of the composite obtained in Comparative Example 1

[0042] Figure 21 SEM diagram of the composite obtained in Comparative Example 2

[0043] Figure 22 LSV curves of the composites obtained in Comparative Examples 1-2 and P-Co9S8-2 Detailed implementation mode

[0044] The present invention provides a preparation method of a porous flower-like P-doped Co9S8 composite, comprising the following steps:

[0045] Disperse cobalt salt in a water-ethanol mixed solvent to obtain a cobalt salt solution;

[0046] Immerse carbon cloth in the cobalt salt solution. After immersion, add a sulfur source to the cobalt salt solution, and perform a hydrothermal reaction on the obtained mixed system to obtain a carbon cloth Co9S8 composite;

[0047] Mix the carbon cloth Co9S8 composite and a phosphorus source, and perform phosphidation to obtain the porous flower-like P-doped Co9S8 composite;

[0048] The cobalt salt includes cobalt acetate.

[0049] Unless otherwise specified, the raw materials used in the present invention are preferably commercially available products.

[0050] Figure 1 is a preparation flow chart of the porous flower-like P-doped Co9S8 composite provided by the present invention. The following will be combined with Figure 1 to describe the preparation method provided by the present invention in detail.

[0051] The present invention disperses cobalt salt in a water-ethanol mixed solvent to obtain a cobalt salt solution.

[0052] In the present invention, the cobalt salt includes cobalt acetate, and is further preferably Co(CH3COO) 2· 6H2O. In the present invention, in the water-ethanol mixed solvent, the volume ratio of water to ethanol is preferably 3-10:1-2, further preferably 3-5:1, and specifically preferably 3:1, 4:1 or 5:1. In the present invention, using cobalt acetate as the cobalt salt can promote the formation of flower-like Co9S8; at the same time, using a water-ethanol mixed solvent as the solvent to disperse the cobalt salt can provide a hydrophilic environment for the uniform and rapid deposition of the cobalt salt on the surface of the carbon cloth; the uniform deposition of the cobalt salt on the surface of the carbon cloth will provide sufficient contact with sulfur atoms to form Co-S bonds, and then form a large area of Co9S8 through hydrothermal reaction.

[0053] In the present invention, the concentration of the cobalt salt solution is preferably 0.025-0.1 mol / L, and specifically preferably 0.025 mol / L, 0.03 mol / L, 0.035 mol / L, 0.04 mol / L, 0.045 mol / L, 0.05 mol / L, 0.055 mol / L, 0.06 mol / L, 0.065 mol / L, 0.07 mol / L, 0.075 mol / L, 0.08 mol / L, 0.085 mol / L, 0.09 mol / L, 0.095 mol / L or 0.1 mol / L.

[0054] In the present invention, the dispersion is preferably carried out under stirring conditions, and the stirring time is preferably 10 to 30 minutes, specifically preferably 10 minutes, 20 minutes or 30 minutes.

[0055] After obtaining the cobalt salt solution, the carbon cloth is impregnated in the cobalt salt solution in the present invention. After the impregnation is completed, a sulfur source is added to the cobalt salt solution, and the obtained mixed system is subjected to a hydrothermal reaction to obtain a carbon cloth Co9S8 composite.

[0056] In a specific embodiment of the present invention, the size of the carbon cloth is preferably 2 cm × 2 cm. In the present invention, the carbon cloth serves as a substrate for cobalt salt deposition. Using the carbon cloth as the substrate for Co9S8 has a low cost.

[0057] In the present invention, the dosage ratio of the cobalt salt to the carbon cloth is preferably 0.1 to 1 mmol: 0.01 to 0.2 g, specifically preferably 0.5 mmol: 0.062 g.

[0058] In the present invention, the impregnation time is preferably 30 to 60 minutes, further preferably 30 minutes, 40 minutes, 50 minutes or 60 minutes; the impregnation is preferably carried out at room temperature and under stirring conditions. In the present invention, during the impregnation process, the cobalt salt can be deposited on the carbon cloth quickly and uniformly.

[0059] In the present invention, the sulfur source preferably includes thiourea and / or sodium sulfide, further preferably thiourea. After the sulfur source is added, stirring is preferably further included in the present invention, and the stirring time is preferably 30 to 90 minutes, specifically preferably 30 minutes, 60 minutes or 90 minutes.

[0060] In the present invention, the molar ratio of the cobalt salt to the sulfur source is preferably 1:1 to 15, specifically preferably 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14 or 1:15.

[0061] In the present invention, the temperature of the hydrothermal reaction is preferably 180 to 220 °C, specifically preferably 180 °C, 190 °C, 200 °C, 210 °C or 220 °C; the time is preferably 10 to 16 hours, specifically preferably 10 hours, 12 hours, 14 hours or 16 hours. In the present invention, the hydrothermal reaction is preferably carried out in a high-pressure reaction kettle.

[0062] After the hydrothermal reaction is completed, the present invention preferably further includes: subjecting the obtained reaction system to vacuum drying to obtain the carbon cloth Co9S8 composite. In the present invention, the temperature of the vacuum drying is preferably 50 to 70 °C, specifically preferably 50 °C, 60 °C or 70 °C; the time is preferably 6 to 10 h, specifically preferably 6 h, 8 h or 10 h; the vacuum drying is preferably carried out in a vacuum oven.

[0063] In the present invention, the hydrothermal reaction can cause the sulfur source and the cobalt salt to react to form flower-like Co9S8.

[0064] After obtaining the carbon cloth Co9S8 composite, the present invention mixes the carbon cloth Co9S8 composite and a phosphorus source and performs phosphorization to obtain the porous flower-like P-doped Co9S8 composite.

[0065] In the present invention, the phosphorus source is preferably NaH2PO2, and the mass ratio of the carbon cloth Co9S8 composite to the phosphorus source is preferably 1:1 to 4, specifically preferably 1:1, 1:1.8, 1:2, 1:3 or 1:4.

[0066] In the present invention, the temperature of the phosphorization is preferably 300 to 450 °C, specifically preferably 300 °C, 350 °C, 400 °C or 450 °C; the heating rate for heating to the temperature of the phosphorization is preferably 2 to 5 °C / min, specifically preferably 2 °C / min, 3 °C / min, 4 °C / min or 5 °C / min; the time of the phosphorization is preferably 1.5 to 3.5 h, specifically preferably 1.5 h, 2 h, 2.5 h, 3 h or 3.5 h; the phosphorization is preferably carried out under a protective atmosphere, and the protective atmosphere is preferably argon.

[0067] In the present invention, the phosphorization is preferably carried out on a furnace; based on the air flow direction of the protective atmosphere, the phosphorizing agent is located upstream, and the carbon cloth Co9S8 composite is located downstream, where upstream refers to the position where the air flow passes first.

[0068] After the phosphorization is completed, the present invention preferably further includes: cooling the obtained product to room temperature to obtain the porous flower-like P-doped Co9S8 composite.

[0069] The present invention also provides a porous flower-like P-doped Co9S8 composite prepared by the preparation method described in the above technical solution.

[0070] In the present invention, the P-doped Co9S8 composite has a flower-like shape, and the flower-like structure has a porous structure. Introducing P atoms (P-Co9S8) into Co9S8 in the present invention can adjust the electronic structure of Co9S8, adjust its catalytic microenvironment, optimize the adsorption energy in the water separation process, and significantly improve the catalytic activity of Co9S8 in the future.

[0071] The present invention also provides an application of the porous flower-like P-doped Co9S8 composite described in the above technical solution in the field of electrolytic water.

[0072] The present invention does not specifically limit the application method of the porous flower-like P-doped Co9S8 composite, and those skilled in the art can set it according to actual needs.

[0073] The following combines examples to elaborate in detail on the porous flower-like P-doped Co9S8 composite provided by the present invention, its preparation method and application, but they cannot be construed as limiting the protection scope of the present invention.

[0074] Example 1

[0075] First, 0.5 mmol of Co(CH3COO) 2· 6H2O was added to a mixture of 15 mL of deionized water and 5 mL of ethanol, and stirred for 20 min to obtain a cobalt salt solution.

[0076] A piece of carbon cloth (with a size of 2 cm × 2 cm and a mass of 0.0620 g) was placed in the cobalt salt solution and stirred for another 30 min; then 1.5 mmol of thiourea was added to the cobalt salt solution and stirred for 60 min. Finally, the mixed system was transferred to a high-pressure reaction kettle and hydrothermally reacted at 190 °C for 12 h; the obtained reaction system was dried in a vacuum oven at 60 °C for 8 h to obtain a carbon cloth Co9S8 composite.

[0077] A piece of carbon cloth Co9S8 composite (with a mass of 0.0815 g) and 150 mg of NaH2PO2 were respectively placed at the downstream and upstream of a furnace. Then the furnace was heated to 350 °C (with a heating rate of 2 °C / min) under an argon gas flow for 2 h. After the furnace was cooled to room temperature, a porous flower-like P-doped Co9S8 composite was obtained, named P-Co9S8-1.

[0078] Using the same process, the furnace heating temperatures were 400 °C and 450 °C respectively to prepare P-Co9S8-2 and P-Co9S8-3.

[0079] Structure characterization

[0080] Figure 2 Scanning electron microscope photos of P-Co9S8-1 (a), P-Co9S8-2 (b) and P-Co9S8-3 (c), from Figure 2It can be seen that: 1) Different phosphating temperatures can significantly regulate the morphology of the porous flower-like P-doped Co9S8 composite; for example, the flower-like structure of P-Co9S8 phosphated at 350 °C (see (a)) is similar to that of pure Co9S8, but as the phosphating temperature increases, the morphology of the porous flower-like P-doped Co9S8 composite changes significantly and shows a uniform porous structure, as shown in (b) and (c). This porous structure can provide rich charge transfer channels during the electrolysis of water, and the high-temperature environment can transform the flower-like structure of Co9S8 into a porous nanoflower-like structure; different phosphating temperatures can significantly regulate the interfacial catalytic microenvironment of the porous flower-like P-doped Co9S8 composite, which can significantly control the catalytic activity of the porous flower-like P-doped Co9S8 composite.

[0081] Figure 3 Figure is the structural characterization diagram of P-Co9S8-2, where Figure 3 in (a) and (b) are the SEM images of P-Co9S8-2; (c)–(f) are the TEM and HRTEM images of P-Co9S8-2, where the inset in (e) is the SAED image; (g)–(k) are the elemental mapping diagrams of P-Co9S8-2. Figure 3 (a) and (b) in confirm the nanoflower-like structure of P-Co9S8-2. Importantly, the enlarged SEM image (b) of P-Co9S8-2 shows a large number of pores formed in the nanosheets; this unique structure not only provides a large surface area but also offers many channels for the transport of electrons between the electrolyte and the electrode. Figure 3 (c) in shows the nanoflower-like structure of the sample. Figure 3 (d) in shows that the lattice fringes with a spacing of 0.287 nm are consistent with the (222) plane of Co9S8. Figure 3 (e) in not only confirms the uniformity of the lattice but also indicates that it is a single-crystalline structure (see the inset in (e)). In addition, Figure 3 (f) in can also show that some defect structures are formed, which will provide more catalytic reaction centers. Figure 3 (g)–(k) in show the uniform distribution of Co, S, and P elements.

[0082] Figure 4 Figure is the XRD pattern of Co9S8, P-Co9S8-1, P-Co9S8-2, and P-Co9S8-3; as Figure 4 shown, the diffraction peaks located at 17.60°, 31.05°, and 36.13° correspond to the (200), (222), and (400) planes of Co9S8 (JCPDS No.: 19-0364), respectively.

[0083] Figure 5XPS spectra of Co 2p for Co9S8 and P-Co9S8-2; as Figure 5 shown, for Co9S8, Co 2p 2 / 3 and Co2p 1 / 2 peaks are located at 781.49 and 797.46 eV respectively, and the two satellite peaks are located at 786.45 and 803.06 eV respectively.

[0084] Figure 6 XPS spectra of S2p for Co9S8 and P-Co9S8-2; as Figure 6 shown, in Co9S8, S2p 2 / 3 and S2p 1 / 2 peaks are located at 161.80 and 162.96 eV respectively. In particular, the peaks of Co 2p and S2p in P-Co9S8-2 show a negative shift compared with Co9S8, indicating that the introduction of P atoms in Co9S8 can regulate the electronic structure of Co9S8.

[0085] Figure 7 XPS spectra of P2p for Co9S8 and P-Co9S8-2, as Figure 7 shown, P 2p of P-Co9S8-2 shows a peak at 134.03 eV. Comprehensive Figures 4 to 7 It can be seen that: the addition of P atoms in Co9S8 will greatly affect the electronic structure and local coordination environment of Co9S8.

[0086] Catalytic performance test

[0087] The electrochemical performance test uses a standard three-electrode system of CHI 760E electrochemical workstation. The polarization curve (LSV) is tested in 1M KOH solution with Hg / HgO as the reference electrode and a carbon rod as the auxiliary electrode. The working electrode is the sample prepared in the example or comparative example, and the scanning rate of the test is 5 mV / s.

[0088] Figure 8 Linear sweep voltammograms of commercially available RuO2, Co9S8, P-Co9S8-1, P-Co9S8-2 and P-Co9S8-3 after iR correction. From Figure 8 it can be seen that: compared with RuO2 and other samples, P-Co9S8-2 shows excellent oxygen evolution performance.

[0089] Figure 9 Catalytic activities of commercially available RuO2, Co9S8, P-Co9S8-1, P-Co9S8-2 and P-Co9S8-3 at 10 mA / cm 2 and 100 mA / cm 2 From Figure 9It can be seen that the overpotential of P-Co9S8-2 is 271 mV@10 mA / cm 2 , which is lower than that of RuO2 (362 mV), Co9S8 (325 mV), P-Co9S8-1 (298 mV) and P-Co9S8-3 (313 mV). At a current density of 100 mA / cm 2 , the overpotential of P-Co9S8-2 (345 mV) is also less than that of Co9S8 (423 mV), P-Co9S8-1 (382 mV) and P-Co9S8-3 (394 mV). The reasons for the enhanced oxygen evolution catalytic activity are as follows: 1) Injecting P atoms into Co9S8 will change the microenvironment and adjust the electronic structure of Co9S8; 2) The unique porous nanosheets can improve the electron transfer rate between the electrode and the electrolyte.

[0090] Figure 10 are the Tafel slopes of commercially available RuO2, Co9S8, P-Co9S8-1, P-Co9S8-2 and P-Co9S8-3. It can be seen from Figure 10 that the Tafel slopes of RuO2, Co9S8, P-Co9S8-1, P-Co9S8-2 and P-Co9S8-3 are 127, 112, 75, 64 and 79 mV / dec, respectively. Compared with other samples, the Tafel slope of P-Co9S8-2 is smaller, indicating its fast oxygen evolution kinetics.

[0091] Figure 11 are the C dl graphs of Co9S8, P-Co9S8-1, P-Co9S8-2 and P-Co9S8-3. It can be seen from Figure 11 that the C dl value of P-Co9S8-2 is 22.1 mF / cm 2 , which is much higher than that of Co9S8 (6.5 mF / cm 2 ), P-Co9S8-1 (13.8 mF / cm 2 ) and P-Co9S8-3 (12.1 mF / cm 2 ). The high C dl of P-Co9S8-2 indicates that it can provide abundant catalytic active sites during the OER process.

[0092] Figure 12 are the electrochemical impedance spectra of Co9S8, P-Co9S8-1, P-Co9S8-2 and P-Co9S8-3, as shown in Figure 12 . The charge transfer resistance (R ct)The trend presented is: Co9S8 > P-Co9S8-3 > P-Co9S8-1 > P-Co9S8-2, indicating that P-Co9S8-2 has excellent charge transfer characteristics.

[0093] Figure 13 This is the cyclic stability test diagram of P-Co9S8-2. As Figure 13 shown, P-Co9S8-3 still has excellent oxygen evolution activity after cyclic testing.

[0094] Figure 14 This is the linear sweep voltammetry (LSV) curves of commercial Pt / C, Co9S8, P-Co9S8-1, P-Co9S8-2, and P-Co9S8-3 for hydrogen evolution in electrolyzed water. It can be seen from Figure 14 that P-Co9S8-2 exhibits hydrogen evolution activity similar to that of commercial Pt / C. When the current density is greater than 200 mA / cm 2 , P-Co9S8-2 shows better hydrogen evolution activity than commercial Pt / C.

[0095] Figure 15 This is the overpotential of commercial Pt / C, Co9S8, P-Co9S8-1, P-Co9S8-2, and P-Co9S8-3 at 10 mA / cm 2 and 100 mA / cm 2 . It can be seen from Figure 15 that at a current density of 10 mA / cm 2 , the hydrogen evolution activities of Co9S8, P-Co9S8-1, P-Co9S8-2, P-Co9S8-3, and Pt / C are 298 mV, 131 mV, 80 mV, 190 mV, and 58 mV respectively. In addition, under the condition of 100 mA / cm 2 , the hydrogen evolution activity (207 mV) of P-Co9S8-2 is also lower than that of Co9S8 (395 mV), P-Co9S8-1 (249 mV), and P-Co9S8-3 (300 mV). This shows that P-Co9S8 also has higher hydrogen evolution activity.

[0096] Figure 16 This is the Tafel slope of commercial Pt / C, Co9S8, P-Co9S8-1, P-Co9S8-2, and P-Co9S8-3. It can be seen from Figure 16 that the Tafel slope of P-Co9S8-2 is 85 mV / dec, which is less than that of Co9S8 (192 mV / dec), P-Co9S8-1 (93 mV / dec), and P-Co9S8-3 (109 mV / dec). P-Co9S8-2 shows a lower Tafel slope, indicating that it has excellent catalytic kinetic performance in the process of hydrogen production.

[0097] Figure 17 Electrochemical impedance spectra of Co9S8, P-Co9S8-1, P-Co9S8-2, and P-Co9S8-3 are shown in Figure 17 Figure [X]. Compared with other samples, the R of P-Co9S8-2 is ct the lowest, indicating that P-Co9S8-2 has the performance of rapidly transferring electrons between the electrode and the electrolyte during the hydrogen evolution process.

[0098] Figure 18 Figure [X] shows the cyclic stability test of P-Co9S8-2. It can be seen from Figure 18 Figure [X] that the hydrogen evolution durability of P-Co9S8-2 is excellent, and P-Co9S8-2 still shows excellent hydrogen evolution catalytic activity after testing at a high current density.

[0099] Figure 19 Figure [X] shows the application of P-Co9S8-2 and noble metal catalysts in water electrolysis. As shown in Figure 19 Figure [X], the water electrolysis voltages of the P-Co9S8-2||P-Co9S8-2 electrode are 1.53 V@10 mA / cm 2 and 1.62 V@100 mA / cm 2 , which are lower than those of the Pt||RuO2 catalyst (1.58 V@10 mA / cm 2 and 1.79 V@100 mA / cm 2 ).

[0100] Comparative Example 1

[0101] The difference from Example 1 is that Co(CH3COO) 2· 6H2O was replaced with CoCl2·6H2O, and the phosphating temperature was 400 °C; other parameters were the same as in Example 1.

[0102] Figure 20 Figure [X] shows the SEM image of the composite obtained in Comparative Example 1. It can be seen from Figure 20 Figure [X] that when the cobalt salt was replaced from cobalt acetate to cobalt chloride, the morphology of the obtained composite was uneven nanoparticles with a size of 50-200 nm.

[0103] The hydrogen evolution performance of the obtained catalyst at 10 mA / cm 2 and 100 mA / cm 2 was 89 mV and 310 mV, respectively.

[0104] Comparative Example 2

[0105] S1) Pretreatment of cobalt foam: One piece of commercially available cobalt foam (1×3 cm 2) Immerse it in an acetone solution and ultrasonicate for 10 min, then ultrasonicate in a 3 mol / L hydrochloric acid solution for 10 min. Subsequently, rinse the surface residues with deionized water and absolute ethanol respectively, and place it in a vacuum drying oven to dry at 60 °C for 6 h;

[0106] S2) Immerse the pretreated cobalt foam into an aqueous solution of thiourea with a concentration of 30 mM, and then transfer it to a high-pressure reactor. After sealing the reactor, place it in a forced-air drying oven and react at 200 °C for 12 h. After the reaction ends, wait for the reactor to cool naturally, take out the reactant, wash it with deionized water and ethanol, and then dry it under vacuum to obtain the Co9S8 / CF electrode material grown in-situ on the cobalt foam.

[0107] S3) The parameters of phosphidation are the same as those in Example 1, and the phosphidation temperature is 400 °C

[0108] Figure 21 is the SEM image of the composite obtained in Comparative Example 2. From Figure 21 it can be seen that directly using cobalt foam as the substrate, the morphology of the obtained composite is nanoparticles, and the size of the nanoparticles is 30 - 100 nanometers.

[0109] The obtained catalyst at 10 mA / cm 2 and 100 mA / cm 2 has the hydrogen evolution performance of electrolyzing water of 85 mV and 289 mV respectively.

[0110] Figure 22 are the LSV curves of the composites obtained in Comparative Examples 1 - 2 and P-Co9S8-2. From Figure 22 it can be seen that the hydrogen evolution performance of the obtained P-Co9S8-2 catalyst is better than that of Comparative Example 1 and Comparative Example 2.

[0111] In summary, by introducing P atoms into Co9S8 to adjust the interfacial catalytic microenvironment of Co9S8, a cheap and efficient electrolytic water catalyst has been successfully prepared. This P-doped Co9S8 composite presents a porous nano-flower-like structure. This unique porous flower-like structure not only provides a large surface area but also provides rich electron transfer channels. The optimized P-doped Co9S8 composite has the oxygen evolution and hydrogen evolution performance of electrolyzing water reaching 271 mV and 80 mV respectively at 10 mA / cm 2 The research results show that introducing P atoms into Co9S8 can greatly adjust the electronic structure, promote the charge redistribution of Co9S8, and optimize its electrolytic water energy barrier. This research shows that regulating the catalytic microenvironment by introducing foreign atoms into metal sulfides is an effective strategy for constructing high-performance catalysts.

[0112] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a porous flower-shaped P-doped Co9S8 composite, comprising the following steps: dispersing the cobalt salt in a water-ethanol mixed solvent to obtain a cobalt salt solution; The carbon cloth is immersed in the cobalt salt solution, and after the immersion is completed, a sulfur source is added to the cobalt salt solution, and the obtained mixed system is subjected to a hydrothermal reaction to obtain a carbon cloth Co9S8 composite; The carbon cloth Co9S8 composite and a phosphorus source are mixed and phosphated to obtain the porous flower-shaped P-doped Co9S8 composite; The cobalt salt includes cobalt acetate.

2. The preparation method according to claim 1, characterized in that: In the water-ethanol mixed solvent, the volume ratio of water to ethanol is 3-10:1-2; the concentration of the cobalt salt solution is 0.025-0.1 mol / L.

3. The preparation method according to claim 1, characterized in that: The usage ratio of the cobalt salt and the carbon cloth is 0.1-1 mmol:0.01-0.2 g.

4. The preparation method according to claim 1 or 3, characterized in that: The immersion time is 30 to 60 minutes.

5. The preparation method according to claim 1, characterized in that: The sulfur source includes thiourea or sodium sulfide; the molar ratio of the cobalt salt to the sulfur source is 1:1-15.

6. The preparation method according to claim 1, 3 or 5, characterized in that: The temperature of the hydrothermal reaction is 180-220° C. and the time is 10-16 hours.

7. The preparation method according to claim 1, characterized in that: The phosphorus source is NaH2PO2, and the mass ratio of the carbon cloth Co9S8 composite to the phosphorus source is 1:1-4.

8. The preparation method according to claim 1 or 7, characterized in that: The phosphating temperature is 300-450° C., and the heating rate to the phosphating temperature is 2-5° C. / min. The phosphating time is 1.5-3.5 hours. The phosphating is carried out under a protective atmosphere.

9. The porous flower-shaped P-doped Co9S8 composite prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the porous flower-shaped P-doped Co9S8 composite according to claim 9 in the field of water electrolysis.

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