Synthesis Of 2D Iron Sulfide Nanosheets For Applications In New Energy

Two-dimensional（2D）ion sulfide（FeS_x）nanosheets have promising applications in sodium ion storage and water electrolysis,owing to the large surface area,ultra-thin thickness,and a large number of active sites on the surface.However,the sodium storage and electrocatalytic performance of 2D FeS_xnanosheets are affected by the morphology,crystallinity,composition and surface coating.Therefore,modulation of composition,morphology,and crystallinity of 2D FeS_xnanosheets is a promising route to optimize the device performance.In this thesis,carbon-coated hexagonal FeS nanosheets and amorphous FeS nanosheets were designed and prepared for enhanced performance in sodium ion batteries and electrolyzed water.The main results are as follows:1.We report a simple solvothermal method to synthesize pyrite FeS₂nanosheets（FeS₂NS）with a cubic phase.The hexagonal FeS nanosheets coated with amorphous carbon（FeS/C NS）are then synthesized by using the FeS₂NS as template.The phase transition process from FeS₂NS to FeS/C NS was investigated.The FeS/C NS was demonstrated as a roubst anode material of SIBs with high rate performance.The excellent performance of FeS/C NS benefits from the surface carbon coating and the two-dimensional morphology with large lateral dimensions and thin thickness.This structure shortens the ion diffusion distance,enriches the electrochemical reaction activity and accelerates the reaction kinetics.Therefore,compared with FeS₂and FeS anodes,FeS/C NS anode exhibits significantly improved cycling stability and high rate performance.The FeS/C NS anode can maintain a reversible capacity of 388 m Ah g^-1after 300 cycles at the current density of 1 A g^-1.Even at the high current densities of 5and 10 Ag^-1,it can deliver amazing capacities of 438 and 391 m Ah g^-1,respectively,showing outstanding high-rate capability.The high pseudocapacitance contribution is also the reason for the high rate performance of FeS/C NS for sodium storage.2.Amorphous FeS nanosheets were synthesized by a solvothermal method to work as an advanced electrocatalyst for electrochemical water splitting.The amorphous FeS nanosheets can be converted to polycrystalline hexagonal FeS nanosheets by post annealing.Compared with the polycrystalline FeS nanosheets obtained by annealing at300 and 500?C,the amorphous FeS nanosheets exhibit significantly improved hydrogen evolution reaction（HER）kinetics with a low Tafel slope of 43 m V dec^-1and a low overpotential of 67 m V at the current density of 10 m A cm^-2.The outstanding electrocatalytic performance of amorphous FeS is attributed to disordered atomic arrangement,which provides abundant defects as active sites.