Preparation Of MoS₂@Nb₂CT_x（MXene） Composite And Its Application In Electrocatalytic Hydrogen Evolution And Lithium Sulfur Batteries

As energy issues become has become increasingly problems,the production of renewable energy has become a research hotspot in social development.Of all types of renewables,the development of unsustainable ones represented by solar energy has intensified the demand for energy storage devices,such as lithium-sulfur batteries and supercapacitors.On the other hand,green energy,represented by hydrogen energy,has become an ideal alternative to traditional energy due to its ability to be continuously generated through electrocatalysis or photocatalysis.Based on the above considerations,the development of high-performance and high-stability nanomaterials for the aforementioned devices has become a key factor in solving the problems.Among the various emerging nanomaterials,transition metal carbonitrides(MXene)have shown great potential in the energy field due to their unique high conductivity,functional group tunability,hydrophilicity and other characteristics.On the other hand,molybdenum disulfide(MoS2),a strong competitor to substitute for silicon in nanoelectronics,has caused increasing concern.However,the semiconductormetal heterostructures based on it are mostly n-type structures with high Schottky barriers owing to the low conductivity and high ionization energy of MoS2 as a semiconductor material,hindering the further application of MoS2-based composite materials.For all the above reasons,this paper successfully synthesized the MoS2@MXene composite and studied the hydrogen evolution revolution(HER)performance and the electrochemical performance in lithium-sulfur batteries.The main contents are summarized as follows:1.Through a simple two-step hydrothermal method,the MoS2@Nb2CTx composite was synthesized for the first time.Furthermore,a series of characterization methods such as XRD and SEM were used to explore their chemical composition and surface morphology.The characterization results exhibited that the composite material is a three-dimensional structure with two-dimensional layered Nb2CTx as the framework and MoS2 nanoflowers as the support material.2.This paper studies the performance of hydrogen electrolysis of composite materials with different mass ratios in different media.In the acidic medium,the 0.25MoS2-Nb2CTx sample shows lower overpotential(127 mV at 10 mA cm-1)and lower resistance(Rct=63.1Ω)and excellent stability.At the same time,the composite shows lower Tafel slope(56.3 mV dec-1),indicating a faster evolution rate.Furthermore,it also shows similar excellent electrocatalytic performance in alkaline environment.3.Combining the characterization results and theoretical calculations,this research offers a detailed analysis of the performance of the composite for hydrogen evolution.The characterization results show that Nb2CTx as the framework enhances the conductivity of the composite;and that the exposure of the flower-shaped MoS2 metal site further enlarges its electrochemically active surface area and gives rise to a faster hydrogen evolution rate.The theoretical results indicate that:1)the lattice mismatch between Nb2CO2 and MoS2 monolayer is extremely small(1.5%),which makes it possible to form a more stable heterostructure;2)the composite forms a p-type Schottky barrier contact-with a very small resistance value on the surface,which causes the redistribution of the charge,thereby further accelerating the electron transport characteristics at the interface;3)further calculations also proved that the composite has good hydrogen atom adsorption capacity.4.This research successfully synthesizes the lithium-sulfur battery with the composite material used as the sulfur host material and tests the battery performance of different sample materials as the cathode material.The composite uses Nb2CTx as the framework,which provides a short transmission path Li+diffusion.The interlaminar MoS2 nanoflower not only enlarges the gap between layers but also offers abundant active sites.Theoretical results show that the low p-type Schottky barrier on the surface further accelerates the interface electron transport characteristics.Therefore,the composite shows a smaller resistance(Rct=29.5Ω),a higher initial specific capacity(1147 mAh g-1 at 0.1C),and good cycle performance(the capacity attenuation is only 0.08%per cycle),revealing the great potential of the composite for lithium-sulfur batteries.