| Transition metal chalcogenides(TMCs),due to its abundant atomic structures and distinctive physical or chemical properties,are widely studied and have great potential applications in electronic devices,electrocatalysis,energy storage,etc.In electrocatalysis,the improvement of the electrocatalytic performance of TMCs has entered a bottleneck stage.A new strategy is highly desired to further improve the electrocatalytic activity of TMCs.In this thesis,molybdenum sulfide and chromium sulfide are prepared by chemical vapor deposition.By using structural engineering,magnetic properties of molybdenum sulfide and chromium sulfide are successfully modulated,and its electrocatalytic performance are improved.This thesis will include the following parts:(1)By introducing magnetic field into electrocatalytic reaction,the mass transfer on the electrode surface can be effectively improved and the reaction kinetics is energetically changed,which provides additional degrees of freedom in the design of electrochemical process.It has become a new-rising research direction in the field of electrochemistry.Magnetic field assisted electrocatalysis will make it possible to break the bottleneck for further improvement of electrocatalytic performance.However,there is no intrinsic long-range magnetic order in MoS2.It is difficult to obtain any expected response in nonmagnetic MoS2 under the external magnetic field.Therefore,in this work,the structure of MoS2 is regulated by stepby-step chemical vapor deposition,and the ferromagnetic bowl-like MoS2 nanoflakes are successfully synthesized.Theoretical calculations show that the magnetism of bowl-like MoS2 mainly comes from the unpaired spin,which concentrates on the edge Mo terminations.Based on theoretical calculations and experiments,it is proved that ferromagnetic bowl-like MoS2 nanoflakes can afford efficient electrons transfer from glassy carbon electrode to active sites to participate the hydrogen evolution reaction(HER),leading to an enhanced HER performance.This work may provide a new pathway to break the bottleneck for further improvement of HER performance and also paves the way to utilize the magnetic enhancement in wide catalytic applications.(2)Subsequently,this thesis also focuses on the alternating magnetic field(AMF)assisted electrocatalytic reaction.Eddy current is a magnetic field effect generated in AMF.And it can realize continuous local heating without affecting the energy consumption and service life of catalyst or reactor,which brings new vitality to electrocatalytic reactions.In this work,by utilizing structural engineering of chemical vapor deposition to regulate the vertical stacking growth mode,step pyramid(layer by layer stacking growth)and screw pyramid(screw dislocation driven growth)MoS2 nanoflakes with rich edge active sites are successfully synthesized.Unlike the step pyramid MoS2,the screw pyramid MoS2 presents better HER performance than the step pyramid MoS2,which can be attributed to the fact that the electrons of screw pyramid MoS2 are directly transmitted along the spiral track,thereby significantly improves the electron transfer efficiency.More importantly,the HER performance of screw pyramid MoS2 is greatly improved compared with step pyramid MoS2 under AMF,which can be attributed to that the micro eddy current is formed inside the screw pyramid MoS2 nanosheets under AMF and thus maximizes utilization of magnetic heating.This work provides a promising guideline for eddy current played in promoting the HER activity of multilayered TMCs and a new thinking to design magnetic field-assisted electrocatalytic reactions in the future.(3)In this thesis,except for utilizing structural engineering to induce magnetism in nonmagnetic TMCs,modulating the magnetism of two-dimensional(2D)intrinsic magnetic TMCs by structural engineering are vying for attention,which can enrich the 2D magnetic material family and cater to the different needs of practical applications.Exploration for the new members of air-stable 2D antiferromagnetic magnets has drawn great attention due to its potential applications in spintronic devices.In addition to seek the intrinsic antiferromagnets,externally introducing antiferromagnetic ordering in existing 2D materials by structural engineering,may be a promising way to modulate antiferromagnetism in the 2D limit.In this work,based on the large-scale synthesis of air-stable 2D ferromagnetic Cr2S3 nanoflakes,the in situ nitrogen doping growth of ultrathin 2D Cr2S3 nanoflakes has been achieved.Theoretical calculations and magnetic measurements prove the achievement of anti ferromagnetic ordering in Cr2S3 by nitrogen doping induced new phase.This work may provide a new approach to manipulate antiferromagnetism in atomically thin 2D magnets.(4)Next,the preparation technique of Cr2S3 nanoflakes is improved,and stable 1T phase CrS2 nanoflakes with intrinsic magnetism are successfully synthesized.Combining 2D intrinsic magnetic CrS2 and zero dimensional single atoms(SAs)through structural engineering can not only possess the excellent electrocatalytic performance of single atom catalysts(SACs),but also take advantage of the good stability of 2D materials to prevent the agglomeration of SAs and avoid the attenuation of electrocatalytic performance.It will be a new strategy to further improve the electrocatalytic performance.Therefore,in this work,Mo atoms are directly anchored on the metallic basal plane of CrS2 nanoflakes by laser molecular beam epitaxy,forming the single-atom tip structure.This Mo SAs@1T-CrS2 with single-atom tip structure could possess an enhanced electric field surrounding Mo atoms and a teeny hydrogen adsorption free energy closed to zero,resulting superior HER performance together with high stability.This work provides a reliable and universal approach to obtain varieties of SACs confined in 2D intrinsic magnetic TMCs,which lays a foundation for the application of magnetic field assisted electrocatalysis in the field of SACs. |
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