| Transition metal dichalcogenides?TMDs?with the formula of MX2?M=Mo,W,Re;X=S,Se?become the most important two-dimensional semiconductors after the discovery of graphene.Due to their unique electrical,optical,mechanical,catalytic,electrochemical properties,TMDs have great potential applications in the fields of microelectronics,optoelectronics,sensors,energy storages and catalysis,and rapidly become the international research frontier and hotspots.In this dissertation,we focus on the synthesis and properties of rhenium disulfide?Re S2?,rhenium diselenide?Re Se2?,and tungsten disulfide?WS2?.Firstly,the controllable synthesis of Re S2 and its composites was investigated,and the effects of microstructure,reduced graphene oxide?r GO?and carbon nanotubes?CNTs?on the electrochemical and electrocatalytic properties were further investigated.Then,the synthesis and electrochemical property of Re Se2,and the comparision of electrocatalytic behaviors?hydrogen evolution reactive,HER?in Re S2and Re Se2 was investigated.Finally,the effects of three-dimensional?3D?graphene foam on the HER of WS2 were investigated.The main research content and results are as follows.1. A physical vapor deposition method was presented to synthesize large-area Re S2film.The results show that the Re S2 film can be grown on objective substrates by thermal evaporation of Re S2 powder at 900 oC.The thickness of prepared Re S2 film is2.30 nm,corresponding to trilayer Re S2.Furthermore,the Re S2 film is contiguous,uniform,and polycrystalline with a average grain size of about 250 nm.2.A one-pot hydrothermal method was presented to prepare nanostructured Re S2,whose electrochemical and electrocatalytic properties were investigated.The results show that the unique,chrysanthemums-like,three-dimensional,porous Re S2 spheres with a diameter of 12?m were self-assembled by few-layered Re S2 nanosheets.At 0.2 C,the initial specific capacity of Re S2 microspheres is about 843.0 m Ah g-1,and it can maintain at 422.1 m Ah g-1 after 30 cycles,which are much better than those of commercial Re S2powders.The excellent electrochemical performance is attributed to the porous microsphere structure,which can provide many more reactive sites and increase the contact area between the active material and electrolyte.Additionally,the Re S2microspheres exhibit an onset potential of-100 m V vs RHE and a Tafel slope of 153.5m V dec-1 for electrocatalytic HER.3.The in-situ synthesis of Re S2 and r GO composite and corresponding electrochemical properties were investigated.The results show that without r GO,Re S2will remain 3D porous microsphere structure and when r GO was introduced,instead of3D porous microsphere structure,the r GO/Re S2/r GO hierarchical structure was obtained.When the Re S2/r GO composite was used as a anode of lithium-ion battery,it delivers an reversible specific capacity of 885 m Ah g-1 at 0.2 C,and the reversible specific capacity can remain 745 m Ah g-1 after 50 cycles,which are much better than those of bare Re S2.The Re S2/r GO composite also has excellent rate performance.Besides,the Re S2/r GO composite exhibits much better electrocatalytic performance than that of bare Re S2:it has an onset potential of-100 m V vs RHE,a Tafel slope of 107.4 m V dec-1,and a well cycling stability.4.The in-situ synthesis of Re S2 and CNTs composite and corresponding electrochemical and electrocatalytic properties were investigated.The results show that when CNTs were introduced,instead of microsphere structure,the assembled Re S2/CNTs composite with tubular structure was obtained.Compared to bare Re S2,the Re S2/CNTs composite delivers much better electrochemical performance:its discharge specific capacity at 0.5 C is as large as 847 m Ah g-1,and it can remain 793 m Ah g-1 after 100cycles with a retention of 93.6%;it also shows excellent rate performance.The Re S2/CNTs composite also shows much better electrocatalytic performance than that of bare Re S2:it has a low onset potential of-80 m V vs RHE,a smaller Tafel slope of 93.5m V dec-1,and a superior cycling stability.5.A one-pot hydrothermal method was presented to synthesize Re Se2nanostructured material and corresponding HER properties were investigated.The results show that chrysanthemums-like,three-dimensional,porous Re Se2 microspheres with a diameter of 1?m were self-assembled by few-layered Re Se2 nanosheets.Compared to Re S2 microspheres,the Re Se2 microspheres show much better electrocatalytic performance:it has a low onset potential of-80 m V vs RHE,a smaller Tafel slope of 67.5m V dec-1,and a excellent cycling stability.In addition,the Re Se2 microspheres deliver the reversible specific capacity of 340.4 m Ah g-1 at 400 m A g-1 and only maintain the reversible specific capacity of 62.6 m Ah g-1 after 100 cycles.It shows low rate performance.There is greater optimized space for improving the electrochemical performance of Re Se2.6.WS2 was directly grown on 3D nickel foam?3DNi?and 3D graphene foam?3DGF?,respectively,and corresponding HER properties were investigated.The results show that compared to WS2/Ni,WS2/graphene/Ni delivers much better HER performance:it delivers a much lower onset potential of-40 m V vs RHE,a smaller Tafel slope of 79m V dec-1,a lower potential of-87 m V vs RHE at 10 m A cm-2,a larger current density of119.1 m A cm-2 at-250 m V vs RHE;it also exhibits much better cycling stability.The superior HER performances of WS2/graphene/Ni can be attributed to its unique structure:the highly conductive three-dimensional graphene network can not only be used as the template for WS2 growth to enhance the bonding strength between the 3DGF and WS2and increase the mass loading of WS2 catalyst,but also effectively prevent the corrosion of nickel by the electrolyte. |
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