A C / MoS2-Co9S8-Co composite electrochemical catalyst and its preparation and application

Abstract

This invention discloses a C / MoS2-Co9S8-Co composite electrochemical catalyst, its preparation, and application. This material is synthesized using ammonium tetrathiomolybdate, cellulose, and a metal cobalt salt via a coating-pyrolysis method. The resulting composite material effectively enhances the electrocatalytic activity for oxygen evolution and reduction, making it a highly efficient electrocatalyst for oxygen evolution and reduction reactions.

Description

Technical Field

[0001] The present invention belongs to the field of metal-air batteries, and in particular relates to a C / MoS2-Co9S8-Co composite electrochemical catalyst and a preparation method thereof. Background Art

[0002] The rapid development of electric vehicles and new energy power generation technologies has urgently required the improvement of energy storage technology. Lithium-air batteries have gradually become a hot topic in energy storage technology research due to their extremely excellent specific capacity. Therefore, the preparation of electrocatalysts with excellent electrocatalytic activity and high catalytic efficiency has become the current research direction of many people. However, there are still some problems in practical applications that limit its development. Since the oxygen reduction reaction (ORR) during the discharge process of the battery oxygen electrode and the oxygen evolution reaction (OER) during the charging process involve many electron transfer electrochemical reactions, the process is slow and will cause Li2O2 dendrite accumulation, resulting in high polarization loss, low specific capacity and short cycle life of the battery during the charging process, affecting the battery performance. [1] In order to solve these problems, transition metal sulfides as excellent electrocatalysts have gradually attracted the attention of researchers.

[0003] The catalytic active sites at the edge of MoS2 have a strong adsorption capacity for intermediates such as O2 and Li2O2, which is beneficial to improving the efficiency of oxygen evolution and reduction reactions in lithium-air batteries and is conducive to the uniform deposition of Li2O2. Therefore, it has broad prospects in the application of lithium-air batteries. [2] However, MoS2 nanosheets do not have sufficient pore structure to support Li + The effective diffusion of O2 and its own low conductivity and aggregation limit the further improvement of electrochemical performance. Using carbonaceous materials as substrates to load MoS2 can effectively solve the above problems. Some researchers have proposed a MoS2@CNTs composite material for oxygen evolution and reduction reactions and lithium-air batteries, in which CNTs can improve conductivity and avoid the stacking of MoS2 nanosheets. [3,4] However, since carbon nanotubes only contain MoS2 nanosheets and lack catalytically active atoms, the catalytic performance of the material is not high, which in turn leads to poor performance in lithium-air batteries. Studies have shown that cobalt and its sulfide are also excellent and efficient catalysts for oxygen evolution and reduction reactions. Carbon-based molybdenum-cobalt bimetallic catalysts may have better catalytic performance for oxygen evolution and reduction reactions. [2] However, the catalytic activity of this carbon-based molybdenum-cobalt bimetallic catalyst is currently not high.

[0004] References:

[0005] 1.W.Liu,Y.Li,H.Yuan,X.Wu,D.Zhang,Synthesis ofC / MoS2-CoMo2S4 for application in Li-O2 batteries,Electrochimica Acta,409(2022)139790.

[0006] 2.S.Wu, D.Wu, D.Zhang, W.Liu, Boosting theActivity and Stability withDual-Metal-NCouplings for Li-O2 Battery[J].Energy&Environmental Materials, 0(2021)1–10.

[0007] 3.J.Long,A.Hu,C.Shu,S.Wang,J.Li,R.Liang,Three-Dimensional Flower-LikeMoS2@Carbon Nanotube Composites with Interconnected Porous Networks and HighCatalytic Activity as Cathode for Lithium-Oxygen Batteries,ChemElectroChem,5(2018)2816-2824.

[0008] 4. M. Song, H. Tan, X. Li, AIYTok, P. Liang, D. Chao, HJFan, Atomic-layer-deposited amorphous MoS2 for durable and flexible Li-O2 batteries, SmallMethods, 4(2020)1900274. Summary of the Invention

[0009] Based on the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a C / MoS2-Co9S8-Co composite electrochemical catalyst with simple preparation method and excellent performance and its preparation method. By coating MoS2 on porous carbon and cobalt, and forming a synergistic catalytic effect with Co9S8, the composite material has good conductivity, electrocatalytic activity and catalytic efficiency, thereby improving its electrochemical performance when used in metal-air batteries.

[0010] To achieve the above object, the present invention adopts the following technical solutions:

[0011] The present invention discloses a method for preparing a C / MoS2-Co9S8-Co composite electrochemical catalyst. The catalyst is prepared using ammonium tetrathiomolybdate, cellulose, and a metal cobalt salt as raw materials through a coating-pyrolysis method. The specific synthesis steps are as follows:

[0012] Step 1: dissolving cellulose in an alkaline solution containing urea, then adding a metal cobalt salt, stirring continuously for 1 to 4 hours, standing, centrifuging, and washing and drying the resulting precipitate;

[0013] Step 2, dissolving ammonium tetrathiomolybdate in an organic solvent, then adding the material obtained in step 1 and polyethylene glycol, stirring for 4 hours and then standing for 24 hours, filtering the obtained product, washing, and freeze-drying to obtain a precursor;

[0014] Step 3: placing the precursor in a tube furnace and calcining it under an inert atmosphere to obtain the target product C / MoS2-Co9S8-Co composite electrochemical catalyst.

[0015] Furthermore, in step 1, the mass ratio of urea, alkali and water in the alkaline solution containing urea is 7:12:81, and the usage ratio of cellulose, metal cobalt salt and alkaline solution containing urea is 2-5g:1-2.5g:50mL.

[0016] Furthermore, in step 1, the metal cobalt salt is cobalt chloride, cobalt bromide, cobalt carbonate, cobalt acetate or cobalt nitrate.

[0017] Furthermore, in step 1, the alkaline solution is a sodium hydroxide solution.

[0018] Furthermore, in step 2, the usage ratio of the ammonium tetrathiomolybdate, the organic solvent, the material obtained in step 1 and the polyethylene glycol is 0.005-0.03 g:50 mL: 0.1-0.3 g:5 mL.

[0019] Furthermore, in step 2, the organic solvent is methanol or ethanol.

[0020] Furthermore, in step 3: the inert atmosphere is N2 or Ar2; the calcination temperature is 600-900°C, and the calcination time is 2-6h.

[0021] The C / MoS2-Co9S8-Co composite electrochemical catalyst prepared by the above method is a black solid powder. Under a scanning electron microscope, it can be seen that the three-dimensional structure is basically maintained, and many atoms appear in the three-dimensional structure, which also has more catalytic sites.

[0022] The present invention achieves synergistic catalysis of the components through the composite of MoS2, Co9S8, Co and porous carbon, thereby obtaining a lithium-air battery cathode catalyst with high catalytic activity and catalytic efficiency. Specifically, utilizing the property of ammonium tetrathiomolybdate (NH4)2MoS4 being soluble in methanol or ethanol, (NH4)2MoS4 solutions of different concentrations are prepared, and (NH4)2MoS4 is evenly loaded on the surface of the Co and cellulose composite by an impregnation method, and then calcined at high temperature to obtain a C / MoS2-Co9S8-Co composite electrochemical catalyst. By changing the concentration of the (NH4)2MoS4 solution, the thickness of the MoS2 nanosheets is adjusted to further improve the performance of the catalyst.

[0023] Compared with the prior art, the beneficial effects of the present invention are embodied in:

[0024] The C / MoS2-Co9S8-Co catalyst provided by the present invention is composited with ammonium tetrathiomolybdate, cellulose, and a metallic cobalt salt via a coating-pyrolysis process. Active sulfur combines with Co and Mo metals to form Co9S8 and MoS2, respectively, thereby tightly binding Co and Mo and accelerating electron transfer between them. The carbon matrix within the porous carbon provides a large specific surface area and good electrical conductivity. Coating with ultrathin MoS2 nanosheets effectively preserves Co-S active sites, further improving catalytic efficiency.

[0025] 2. The catalytic active sites at the edge of MoS2 have a strong adsorption capacity for intermediates such as O2 and Li2O2, which is beneficial to improving the efficiency of oxygen evolution and reduction reactions in lithium-air batteries, and is beneficial to the uniform deposition of Li2O2, avoiding the formation of dendrites and improving cycle stability.

[0026] 3. The thickness of the MoS2 nanosheets in the coating layer of C / MoS2-Co9S8-Co was adjusted by changing the concentration of ammonium tetrathiomolybdate solution. The thinner the MoS2 nanosheets, the more exposed edge active sites, thus showing excellent electrocatalytic activity, which is conducive to the direct reduction of O2 to OH- instead of HO2. - , avoiding the generation of harmful intermediates and improving energy conversion efficiency and cycle stability.

[0027] 4. The preparation method of the present invention has simple process, easy operation and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 1 is the XRD pattern of the samples obtained in Examples 1-4, where ad corresponds to the samples obtained in Examples 1-4, respectively.

[0029] Figure 2 This is the Raman graph of the sample obtained in Example 1.

[0030] Figure 3 This is the SEM image of the sample obtained in Example 1.

[0031] Figure 4 This is the ORR polarization curve of the sample obtained in Example 1.

[0032] Figure 5 and Figure 6 They are comparison diagrams of the OER and ORR polarization curves of the samples obtained in Examples 1-4 at 1600 rpm, and ad corresponds to the samples obtained in Examples 1-4, respectively. DETAILED DESCRIPTION

[0033] The following is a detailed description of an embodiment of the present invention. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process. However, the protection scope of the present invention is not limited to the following embodiment.

[0034] Example 1

[0035] Step 1: Dissolve 2.45 g of cellulose in 50 mL of an alkaline solution containing urea (mixed with urea, sodium hydroxide, and water in a mass ratio of 7:12:81), stir for 1 hour, add 1.65 g of cobalt nitrate hexahydrate, stir for 4 hours, let stand for 24 hours, centrifuge, and wash and dry the resulting precipitate.

[0036] Step 2: Dissolve 0.01 g of ammonium tetrathiomolybdate in 50 mL of ethanol, then add 0.1 g of the material obtained in step 1 and 5 mL of polyethylene glycol. Stir for 4 h and let stand for 24 h. Filter the resulting product, wash it, and freeze-dry it for 24 h to obtain a precursor.

[0037] Step 3: Place the precursor in a tube furnace and calcine at 700°C for 2 h under argon protection to obtain the sample C / MoS2-Co9S8-Co, named EA-C / MoS2-Co9S8-Co-0.01.

[0038] Example 2

[0039] In this example, a composite material was prepared in the same manner as in Example 1, except that the dosage of ammonium tetrathiomolybdate in step 2 was changed to 0.02 g. The obtained product was named EA-C / MoS2-Co9S8-Co-0.02.

[0040] Example 3

[0041] In this example, a composite material was prepared by the same method as in Example 2, except that the solvent in step 2 was methanol. The obtained product was named MT-C / MoS2-Co9S8-Co-0.02.

[0042] Example 4

[0043] In this example, a composite material was prepared by the same method as in Example 3, except that the dosage of ammonium tetrathiomolybdate in step 2 was changed to 0.01 g. The obtained product was named MT-C / MoS2-Co9S8-Co-0.01.

[0044] Figure 1 Figures 2 and 3 are the XRD patterns of the samples obtained in Examples 1-4. Lines A and B correspond to the materials obtained in Examples 1-4, respectively. The four diffraction curves all exhibit distinct diffraction peaks at 44.2° and 75.8°, which are characteristic diffraction peaks of the (111) and (220) crystal planes of Co (PDF#15-0806). Crystal plane diffraction peaks belonging to Co9S8 (PDF#02-1459) appear at 29.8°, 31.1°, 44.8°, and 51.9°, and a characteristic diffraction peak belonging to MoS2 (PDF#17-0744) appears at 33°, demonstrating the successful recombination of MoS2 and Co9S8.

[0045] Figure 2 This is the Raman spectrum of the sample obtained in Example 1. After being immersed in ammonium tetrathiomolybdate solution and calcined, the sample has the following peaks at 260, 470, 512, and 674 cm -1 Four characteristic peaks attributed to Co particles appear at 2g 、E g 、F 2g and A 1g ), at 1500cm -1 The D peak and G peak of graphite carbon material appeared near the product. -1 There is E of MoS2 1 2g and A 1g Characteristic peaks. It can be inferred that the synthesized material is based on porous carbon, with MoS2 and Co9S8 coated on its surface.

[0046] Figure 3 This is the SEM image of the sample obtained in Example 1. It can be seen from the figure that the sample basically maintains a porous three-dimensional structure, and many atoms are loaded on the three-dimensional structure, exposing more catalytic sites.

[0047] To further compare the electrocatalytic performance of each sample, their ORR and OER activities were evaluated using a three-electrode system. Polarization curves were obtained by linear sweep voltammetry in an oxygen-saturated 0.1 M KOH solution using each sample as the working electrode. Figure 4 The ORR polarization curves of the sample in Example 1 at different rotation speeds are shown. At 1600 rpm, the limiting current density is as high as 6.65 mA cm -2 . Figure 5 and Figure 6The OER and ORR polarization curves of the samples obtained in Examples 1-4 are shown respectively. Both figures show that the sample obtained in Example 1 has the highest limiting current density.

[0048] From the above results, it can be seen that the electrocatalytic performance of C / MoS2-Co9S8-Co catalyst is mainly attributed to the following advantages: (1) the introduction of an appropriate amount of (NH4)2MoS4 to generate ultrathin MoS2 nanosheets exposes the Mo sites at the edge, enhancing the adsorption of O2; (2) the encapsulation of ultrathin MoS2 nanosheets can effectively protect the Co-S active sites and improve the catalytic activity, and the introduction of Mo-S bonds can further enhance the ORR activity; (3) the mesoporous structure of the porous carbon itself facilitates the Li + storage and improves the electrical conductivity of the composite material.

[0049] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a C / MoS2-Co9S8-Co composite electrochemical catalyst, characterized in that: The C / MoS2-Co9S8-Co composite electrochemical catalyst is prepared by using ammonium tetrathiomolybdate, cellulose and metal cobalt salt as raw materials through a coating-pyrolysis method, specifically according to the following steps: Step 1: dissolving cellulose in an alkaline solution containing urea, then adding a metal cobalt salt, stirring continuously for 1 to 4 hours, standing, centrifuging, and washing and drying the resulting precipitate; Step 2, dissolving ammonium tetrathiomolybdate in an organic solvent, then adding the material obtained in step 1 and polyethylene glycol, stirring for 4 hours and then standing for 24 hours, filtering the obtained product, washing, and freeze-drying to obtain a precursor; Step 3: placing the precursor in a tube furnace and calcining it under an inert atmosphere to obtain the target product C / MoS2-Co9S8-Co composite electrochemical catalyst.

2. The preparation method according to claim 1, wherein: In step 1, the mass ratio of urea, alkali and water in the alkaline solution containing urea is 7:12:81, and the usage ratio of cellulose, metal cobalt salt and alkaline solution containing urea is 2-5 g:1-2.5 g:50 mL.

3. The preparation method according to claim 1, wherein: In step 1, the metal cobalt salt is cobalt chloride, cobalt bromide, cobalt carbonate, cobalt acetate or cobalt nitrate, and the alkaline solution is sodium hydroxide solution.

4. The preparation method according to claim 1, wherein: In step 2, the usage ratio of the ammonium tetrathiomolybdate, the organic solvent, the material obtained in step 1, and the polyethylene glycol is 0.005-0.03 g:50 mL: 0.1-0.3 g:5 mL.

5. The preparation method according to claim 1, wherein: In step 2, the organic solvent is methanol or ethanol.

6. The preparation method according to claim 1, wherein: In step 3, the inert atmosphere is N2 or Ar2.

7. The preparation method according to claim 1, wherein: In step 3, the calcination temperature is 600-900° C. and the calcination time is 2-6 hours.

8. A C / MoS2-Co9S8-Co composite electrochemical catalyst prepared by the preparation method according to any one of claims 1 to 7.

9. Use of a C / MoS2-Co9S8-Co composite electrochemical catalyst prepared by the preparation method according to any one of claims 1 to 7 in a metal-air battery.

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