Study On Fabrication And Electrochemical Performance Of Ti₃C₂T_x MXene-Based Composites

Developing novel energy storage and conversion technology is of profound significance to the social development of human beings.Today,lithium-ion battery with graphite anode is widely utilized,while the low lithium-storage capacity and power density of graphite can be difficult to fulfill the prospective demand.Thus,the exploitation of advanced anode materials with high specific capacity and power density performance is current top priority.Meanwhile,as carbon-free hydrogen energy carrier with high energy density,ammonia is expected to play an important role in the energy structure in the future.In this context,electrocatalytic nitrogen reduction reaction is a very attractive strategy to accomplish continuous ammonia generation under mild conditions.The key to high-efficiency ammonia synthesis is appropriate catalyst with extraordinary nitrogen adsorption and activation capacity.Aiming at above issues,this thesis starts from the design and preparation of Ti₃C₂T_x MXene-based composite materials under mild condition,and takes full advantage of the functional characteristics of MXene.The electrochemical performance is improved by synergistically optimize the structure and constituent of composite material,and its improvement mechanism is investigated as well.Few-layer Ti₃C₂T_x MXene nanosheets and ultrafine Co₃O₄ quantum dots are synthesized via HCl/Li F etching and solvothermal methods,respectively.Then the MXene/Co₃O₄ QDs composites with different ingredient proportions can be obtained via self-assembly strategy under sonication and inert atmosphere protection.Then,physical characterizations and lithium-ion storage activity evaluations are carried out.As multifunctional substrate,MXene nanosheet protects the great dispersity of Co₃O₄quantum dots and buffer the volume change accompanied with the rapid cycling process.Meanwhile,Co₃O₄ quantum dot as spacer can protect MXene nanosheet from restacking.The mutual assistances thereby endow the composites with great structural robustness.Co₃O₄ constituent can provide high lithium storage capacity,and the MXene constituent can provide certain capacity and accelerate the electron transfer in the meantime.Based on above methodology,MXene/Co₃O₄ QDs-1:2 maintains a discharge capacity of 525.3m Ah g^-1 after 500 cycles at a current desnity of 1000 m A g^-1.Considering that Ti₃C₂T_x MXene nanosheet possesses great electron transport and special film-making property,freestanding MXene/Mo S₂ composite film can be obtained via vacuum-assisted alternate aqueous solution filtration method at room temperature.The introduction of Mo S₂ nanotubes renders the freestanding film architecture open and further expands the nanosheet layer spacing.The freestanding film electrode without any inactive conductive agent,binder and current collector acquires great electrochemical performance,delivering a high discharge capacity of 704.8 m Ah g^-1 after 500charge/discharge cyclings at 1000 m A g^-1.Additionally,freestanding MXene/Mn O₂composite film is fabricated according to the above method and exhibits great lithium-ion storage performance,attesting the validity and universality of this hybrid strategy.The above studies cover the separate preparation and following hybrid of two individual components.To further simplify the preparation procedure,the negatively-charged Ti₃C₂T_x MXene nanosheets can attract the cations in aqueous media,which can be subsequently reduced into MXene@boride composite material by Na BH₄.The electrostatic effect of cations helps MXene nanosheet to further form three-dimensional MXene network structure,which serves as substrate to synthesis boride nanoparticles through reduction reaction.The binary heterostructure is equipped with decent specific surface area and rich pores.As lithium-ion battery anode material,MXene@Co₂B composite exhibits a discharge capacity of 826.7 m Ah g^-1 after 100 cycles at 100 m A g^-1and remains a discharge capacity of 620.4 m Ah g^-1 after 500 cycles at 1000 m A g^-1.In addition,to extend the application field of Ti₃C₂T_x MXene and exploite the orbit superiority of transition metal and boron elements,MXene@NiCo B composite is synthesized with the referenc of above preparation route.Theoretical calculations prove that this catalyst can efficiently adsorb and activate the nitrogen molecules,and the ammonia generation reaction proceeds in accordance with associative distal pathway.The tests reveal that MXene@NiCo B catalyst accomplishes ammonia yield rate of 38.7μg h^-1 mg_cat.^-1and Faradaic efficiency of 6.92%at applied voltage of-0.4 V with superior selectivity,repeatability and stability.