Preparation method of CTP-NS carbon-based electrocatalytic hydrogen evolution composite material

Abstract

The application relates to a preparation method of a CTP-NS carbon-based electrocatalytic hydrogen evolution composite material, which comprises the following steps: 1) mixing polyvinylpyrrolidone, styrene and deionized water and stirring to obtain an A solution; 2) deoxidizing the A solution under a nitrogen flow, heating, centrifuging with ethanol and deionized water, and drying to obtain PS balls; 3) mixing medium-temperature coal pitch and chloroform, ultrasonically treating, and stirring to obtain a B solution; 4) mixing the PS balls and the B solution and stirring to obtain a C solution; 5) drying the C solution, keeping the temperature at 750-850 DEG C, cooling to room temperature, and obtaining CTP; 6) ball-milling the CTP, MgSO4 and melamine, keeping the temperature at 700-800 DEG C, cooling to room temperature, washing the product with deionized water and drying. The advantages are that nitrogen and sulfur heteroatoms are embedded in the porous structure, the heteroatoms are arranged at different positions on the carbon framework, and the arrangement is helpful for the charge delocalization and migration of electrons.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of electrocatalytic hydrogen evolution materials, and particularly relates to a preparation method of a CTP-NS carbon-based electrocatalytic hydrogen evolution composite material. BACKGROUND

[0002] It is well known that with the rapid growth of population and the progress of science and technology, the energy demand is increasing dramatically, and hydrogen gas as a clean and pollution-free energy and energy carrier has an indispensable importance in the future energy structure. Producing hydrogen gas by electrolysis of water is considered as a green and effective way to meet the growing demand for renewable energy. However, it usually requires noble metal-based catalysts (i.e. Pt, Pd, RuO2, IrO2), which hinders the large-scale application of renewable energy technology due to the high cost of noble metals. Therefore, it is very desirable to develop efficient and low-cost alternative catalysts.

[0003] Since 2009, when it was reported that nitrogen-doped carbon nanotubes could be used as a high-efficiency carbon-based metal-free catalyst (C-MFEC) to replace Pt, (C-MFEC) has made many progress in the development of catalysts and the understanding of mechanism, Nitrogen-doped carbon nanotube arrays with high electrocatalytic activity for oxygen reduction. Science 2009, 323(5915), 760-4. Subsequently, various graphite carbon materials, including traditional porous carbon (ordered mesoporous carbon, carbon spheres, etc.), were found to exhibit good electrocatalytic performance Sustainable carbonaceous materials derived from biomass as metal-free electrocatalysts. Adv. Mater. 2019, 31(13), 1805718. In the original sp 2Doping of secondary elements in conjugated carbon networks can adjust their charge / spin distribution, thereby optimizing the adsorption and subsequent charge transfer of the main intermediates in the HER process. Doping of Carbon Materials for Metal-Free Electrocatalysis. Adv. Mater. 2019, 31(7), e1804672; Electronic and Structural Engineering of Carbon-Based Metal-Free Electronic catalysts for Water Splitting. Adv. Mater. 2019, 31(13), e1803625. Nitrogen doping on the carbon surface can effectively improve the reaction activity and electronic conductivity by generating external defects, Active sites of nitrogen-doped carbon materials for oxygen reduction reaction clarified using model catalysts. Science 2016, 351(6271), 361-365. Incorporation of sulfur can significantly increase the interlayer distance of carbon, mainly in the form of edge defects doped with thiophene, Highly crystalline sulfur doped carbon nitride as photocatalyst for efficient visible-light hydrogen generation. Appl. Catal., B 2018, 238, 592-598.

[0004] Studies have shown that the synergistic effect produced by the co-doping of graphite carbon materials with heteroatoms of different electronegativities can also achieve better hydrogen evolution electrocatalytic activity. By selecting high-activity S and N atoms as dopants, a double-doped N-S-C catalyst was obtained, and the spin and charge density redistribution caused by the double doping of S atoms and N atoms led to the enhancement of synergistic performance, which led to the integration of coexisting active centers into a three-dimensional conductive carbon skeleton with layered porous structure. The catalyst has excellent hydrogen evolution performance and long-term stability in alkaline environment. SUMMARY

[0005] To overcome the shortcomings of the prior art, the purpose of the present application is to provide a preparation method of CTP-NS carbon-based electrocatalytic hydrogen evolution composite material, which uses N, S double-doped medium temperature coal pitch / polystyrene ball to prepare a metal-free HER electrocatalyst, and the surface of the functionalized carbon exists fine pores, micro-layers and uniform distribution of heteroatoms, thereby exposing a large number of active sites and significantly improving the electrical conductivity and catalytic activity of the material.

[0006] To achieve the above object, the present application is realized by the following technical solutions:

[0007] A preparation method of a CTP-NS carbon-based electrocatalytic hydrogen evolution composite material, comprising the following steps:

[0008] 1) Preparation of A solution: polyvinylpyrrolidone, styrene are mixed according to a mass ratio of (1.5-2):10 and 80-100 mL of deionized water, stirred for 0.5-1 h to obtain A solution;

[0009] 2) The A solution is deoxygenated under nitrogen flow for 0.5-1 h, heated to 70-75 DEG C, and reacted for 20-24 h; the obtained product is centrifuged with ethanol and deionized water, dried at 60-70 DEG C for 8-10 h to obtain PS balls;

[0010] 3) Preparation of B solution: mix medium temperature coal tar and chloroform according to a mass ratio of (1-1.2):100, ultrasonic for 0.5-1 h, and stir at a speed of 200-300 r / min to make it completely dispersed into a brown solution;

[0011] 4) Preparation of C solution: mix the prepared PS balls with the B solution according to a mass ratio of (1-1.5):10, and stir for 6-8 h to obtain C solution;

[0012] 5) C solution is dried at 60-65 DEG C for 4-6 h, and kept at 750-850 DEG C for 2-3 hours under nitrogen atmosphere, and cooled to room temperature, marked as CTP;

[0013] 6) Mix CTP, MgSO4 and melamine according to a mass ratio of 1:(3-5):(3-5) by ball milling, keep at 700-800 DEG C for 2-2.5 hours under nitrogen atmosphere, and cool to room temperature, then wash and dry the product.

[0014] The particle size of the mixture after ball milling in step 6) is 70-80 mesh.

[0015] Compared with the prior art, the present application has the following beneficial effects:

[0016] The present application uses medium temperature coal tar as a precursor and adopts a simple method to prepare a layered nitrogen and sulfur double-doped porous carbon. The most important feature is that nitrogen and sulfur heteroatoms are embedded in the porous structure, and these heteroatoms are arranged at different positions on the carbon framework, which helps the charge delocalization and migration of electrons. The CTP-NS composite material is applied to the water electrolysis catalytic hydrogen evolution reaction, and the overpotential is 437 mV when the current density is 10 mA cm -2 , which exhibits excellent HER activity and superior stability (the overpotential is basically unchanged after 5000 cycles of CV). BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a preparation flow chart of CTP-NS composite material.

[0018] Figure 2 is an XRD chart of CTP-NS composite material.

[0019] Figure 3 is a scanning electron microscope chart and EDS energy spectrum chart of CTP-NS composite material.

[0020] Figure 4 is a cathode polarization curve chart of CTP-NS composite material.

[0021] Figure 5 is a Tafel slope chart of CTP-NS composite material.

[0022] Figure 6 is a stability chart of CTP-NS composite material. DETAILED DESCRIPTION

[0023] The present application will be described in detail below with reference to the accompanying drawings of the specification, but it should be pointed out that the implementation of the present application is not limited to the following embodiments.

[0024] Example 1

[0025] See Figure 1 , the preparation method of CTP-NS composite material, first, 10g of styrene, 1.5g of polyethylene and pyrrolidone are dissolved in 100mL of deionized water, stirred for 0.5h, named as A solution. Then the A solution is deoxidized under nitrogen flow for 0.5h, heated to 75℃ for 24h, the obtained product is centrifuged with ethanol and deionized water, dried at 60℃ for 8h, recorded as PS ball.

[0026] The medium temperature coal tar and chloroform are mixed according to the mass ratio of 1:100, ultrasonic for 0.5h, stirred at the speed of 200r / min, so that it is completely dispersed into brown solution, named as B solution. 8g of PS ball prepared above is mixed with B solution according to the mass ratio of 1:10, stirred for 6h, named as C solution.

[0027] The C solution is dried at 60℃ for 5h, kept at 800℃ for 2 hours under nitrogen atmosphere, cooled to room temperature, recorded as CTP-2; the material without PS is recorded as CTP. CTP-2, MgSO4, melamine are ball milled according to the mass ratio of 1:5:5, kept at 800℃ for 2 hours under nitrogen atmosphere, cooled to room temperature, the product is washed with deionized water for several times and dried, to obtain CTP-2-NS composite material.

[0028] Electrocatalytic hydrogen evolution test process, including catalyst ink, working electrode preparation and electrolyte preparation process, as follows:

[0029] Catalyst ink preparation: 5 mg of CTP-NS composite material was weighed and ground thoroughly, placed in a 5 mL glass bottle, and 700 μL of deionized water, 250 μL of isopropyl alcohol, and 50 μL of 5% Nafion binder were added dropwise using a pipette gun. The mixed catalyst suspension was ultrasonically treated for more than 60 min to ensure uniform dispersion.

[0030] Working electrode preparation: 10 μL of catalyst suspension was dropped onto the surface of a polished and ultrasonically cleaned glassy carbon electrode using a pipette gun, and it was allowed to dry naturally for later use.

[0031] Electrolyte preparation: 4.4888 g of KOH was weighed and dissolved in 80 mL of deionized water to prepare 1M KOH, and the solution was ultrasonically shaken to ensure complete dissolution. The prepared electrolyte solution was purged with nitrogen for 30 min.

[0032] Figure 2 The X-ray diffraction (XRD) pattern of the sample prepared in Example 1 showed two peaks near 2θ = 24° and 43°, corresponding to the (002) and (100) crystal planes of graphitized carbon.

[0033] Figure 3 The SEM and EDS spectra of the sample prepared in Example 1 showed a clear 3D porous network composed of a large number of spherical particles, which provided more nanochannels for intermolecular charge transfer induced by adsorbed electron acceptor / donor molecules between the graphite matrix. The element mapping image confirmed that N and S elements were successfully doped.

[0034] Figure 4 The cathode polarization curve of the sample prepared in Example 1 showed that CTP-2-NS had the best catalytic hydrogen evolution effect compared to the other two materials, with an initial potential close to 100 mV. Generally, the size of the overpotential value corresponding to a current density of 10 mA cm -2 is used to evaluate the activity of the catalyst. As shown in the figure, the overpotential of CTP-2-NS corresponding to a current density of 10 mA cm -2 was 437 mV, indicating that the hydrogen evolution catalytic effect on the surface of the CTP-2-NS electrode was higher.

[0035] Figure 5Tafel slope curves of the samples prepared in Example 1, Tafel slope is an important indicator to infer the electrocatalytic hydrogen evolution reaction path and reaction mechanism, which is related to the catalyst material itself. At the same current density, the smaller the Tafel slope, the faster the reaction kinetics rate, the more conducive to the reaction. The Tafel slope of sample CTP-2-NS is 71 mV decade -1 The Tafel slope is smaller than other samples, which determines the step rate of the electrocatalytic hydrogen evolution reaction, and the smaller it is, the more conducive to the reaction, therefore, the difference in Tafel slope in the figure reveals the influence of nitrogen and sulfur elements on the step rate, and the results show that the doping of nitrogen and sulfur elements makes the catalyst have more favorable kinetics.

[0036] Figure 6 The stability diagram of the sample catalyst prepared in Example 1, after 5000 cycles of cyclic voltammetry test, the overpotential of the material remains basically unchanged, indicating that the material can still maintain the catalytic activity before cycling, and it has excellent electrochemical cycle stability. In addition, the long-term stability of the material at 10 mA cm -2 The long-term stability of the material at 10 mA cm

[0037] The above electrochemical experimental results show that the nitrogen and sulfur double-doped in the layered porous carbon successfully improves the electrochemical properties of coal tar pitch, showing excellent hydrogen evolution performance and long-term stability, so that the CTP-NS composite material has certain application in the field of electrocatalysis.

[0038] Example 2

[0039] The preparation method of CTP-NS composite material, first, 10 g of styrene, 1.5 g of polyethylene and pyrrolidone were dissolved in 100 mL of deionized water, stirred for 0.5 h, and named as A solution. Then the A solution was deoxygenated under nitrogen flow for 0.5 h, heated to 75℃ for 24 h, the obtained product was centrifuged with ethanol and deionized water, dried at 60℃ for 8 h, and recorded as PS ball.

[0040] The medium temperature coal tar pitch and chloroform were mixed according to the mass ratio of 1:100, ultrasonic for 0.5 h, stirred at 200 r / min, so that it was completely dispersed into a brown solution, named as B solution. The medium temperature coal tar pitch and the PS ball prepared above were mixed according to the mass ratio of 1.2:10, stirred for 6 h, and named as C solution.

[0041] The C solution was dried at 60°C for 5h, and then kept at 800°C for 2h under nitrogen atmosphere, and cooled to room temperature, and was recorded as CTP-3. The material without PS was recorded as CTP. The CTP-3, MgSO4, and melamine were ball-milled at a mass ratio of 1:5:5, and then kept at 800°C for 2h under nitrogen atmosphere, and cooled to room temperature. The product was washed with deionized water for several times and dried to obtain the CTP-3-NS composite material.

[0042] Example 3

[0043] The C solution was dried at 60°C for 5h, and then kept at 800°C for 2h under nitrogen atmosphere, and cooled to room temperature, and was recorded as CTP-3. The material without PS was recorded as CTP. The CTP-3, MgSO4, and melamine were ball-milled at a mass ratio of 1:5:5, and then kept at 800°C for 2h under nitrogen atmosphere, and cooled to room temperature. The product was washed with deionized water for several times and dried to obtain the CTP-3-NS composite material.

[0044] The medium-temperature coal pitch and chloroform were mixed at a mass ratio of 1:100, and then ultrasonically treated for 0.5h, and stirred at a rotation speed of 200r / min to make them completely dispersed into a brownish solution, which was recorded as B solution. The medium-temperature coal pitch and the PS balls prepared above were mixed at a mass ratio of 1.5:10, and stirred for 6h, and recorded as C solution.

[0045] The C solution was dried at 60°C for 5h, and then kept at 800°C for 2h under nitrogen atmosphere, and cooled to room temperature, and was recorded as CTP-3. The material without PS was recorded as CTP. The CTP-3, MgSO4, and melamine were ball-milled at a mass ratio of 1:5:5, and then kept at 800°C for 2h under nitrogen atmosphere, and cooled to room temperature. The product was washed with deionized water for several times and dried to obtain the CTP-3-NS composite material.

Claims

1. A method for preparing a CTP-NS carbon-based electrocatalytic hydrogen evolution composite material, characterized in that, The method comprises the following steps: 1) preparing solution A: mixing polyvinylpyrrolidone, styrene and 80-100 mL of deionized water according to a mass ratio of (1.5-2):10:80-100, stirring for 0.5-1 h to obtain solution A; 2) deoxygenating solution A under a nitrogen flow for 0.5-1 h, heating to 70-75 °C, and reacting for 20-24 h, and then centrifuging the obtained product with ethanol and deionized water, and drying at 60-70 °C for 8-10 h to obtain PS balls; 3) preparing solution B: mixing medium-temperature coal tar pitch and chloroform according to a mass ratio of (1-1.2):100, and ultrasonically treating for 0.5-1 h, and stirring at a rotating speed of 200-300 r / min until the mixture is completely dispersed into a brownish-brown solution; 4) preparing solution C: mixing the prepared PS balls and solution B according to a mass ratio of (1-1.5):10, and stirring for 6-8 h to obtain solution C; 5) drying solution C at 60-65 °C for 4-6 h, and keeping the temperature at 750-850 °C for 2-3 h under a nitrogen atmosphere, and cooling to room temperature to obtain CTP; 6) ball-milling CTP, MgSO4 and melamine according to a mass ratio of 1:(3-5):(3-5), keeping the temperature at 700-800 °C for 2-2.5 h under a nitrogen atmosphere, and cooling to room temperature, and then washing and drying the product; the particle size of the mixture after ball-milling is 70-80 mesh.

Images