Study On Electronic Structure Control And Electrolytic Performance Of MoS₂-Based Materials

In this thesis,MoS₂ was chosen as the substrate material,and the electronic structure of intrinsic MoS₂ was adjusted by a series of means including morphology control,atomic doping and construction of heterogeneous interfaces to accelerate the kinetic process of acidic hydrogen precipitation,and the key role of highly active catalytic sites in energy conversion was revealed through theoretical calculations and model building.The details are as follows:（1）Homogeneous and monodisperse MoS₂ microspheres assembled with nanosheets were prepared by microemulsion technology and a series of Ru-MoS₂ nanostructures were also obtained by systematically adjusting the addition of Mo and Ru salts during the microemulsion process.Ru doping had no effect on the geometrical configuration of the microspheres.EPR data confirmed the sulphur defects in MoS₂ and Ru-MoS₂.The results showed that 2Ru-MoS₂ has the lowest overpotential and Tafel slope,superior to most MoS₂-based catalysts.The collected TEM images show the structural advantages of the microspheres in the HER process.DFT calculations demonstrat that 2Ru-MoS₂ has the best electronic structure and revealed a mechanism for the highly enhanced catalytic performance.（2）The yolk-shell MoS₂-（CTAB）₂S_z with covalent S₂^2-was prepared by micellar limited microemulsion technique.Different from the traditional preparation methods,the proposed bifunctional S strategy includes the in-situ reaction of pre-encapsulated S₂²-in the precursor with M（M=Fe,Co,Ni,Cu,Zn,Mn,Sn,Cd）ions to synthesize covalently linked MoS₂/M_xS_y-BS nanoreactors.Thanks to the unique configuration and covalent heterogeneous interface,the optimized MoS₂/Cd S-BS showed better hydrogen evolution activity than the traditional MoS₂/Cd S and MoS₂-based heterogeneous catalysts reported at present.The results of in-situ XRD,XPS and TEM confirmed its excellent durability.The results of DFT calculations show that the enhanced electrocatalytic mechanism is attributed to the formation of an“electron bridge”at the covalent interface of the MoS₂/Cd S-BS nanoreactor and the catalytic center transforming from S site to Cd site,thus reducing the thermodynamic barrier of the adsorption-desorption intermediate.（3）A universal sub-nanoreactor strategy was used for the synthesis of yolk-shell structured MoS₂-based SACs with a unique double-anchored microenvironment of S vacancies and embedded carbon to achieve excellent hydrogen-evolution reaction.Theoretical calculations revealed that the“E-Lock”and“E-Channel”were conducived to stabilize and activate metal single-atoms（M=M=Fe,Co,Ni,Cu,Zn,Mn,W,Cd）.A group of SACs was subsequently produced with the assistance of sulfur vacancy and intercalation carbon in the yolk–shell sub-nanoreactor.The optimized C-Co-MoS₂ yielded the lowest overpotential(η₁₀=17 m V)compared with previously reported MoS₂-based electrocatalysts to date,and also afforded a 5?9 fold improvement in activity even comparing with those as-prepared single–anchored analogues.The finite element analysis results showed that the intensity and distribution of the current density on the double anchored electrode are much better than those on the single anchored electrode.The results of density functional theory calculation and in-situ characterization revealed the actual active center and durability of C-Co-MoS₂.