| Hydrogen generation through water electrolysis is proposed as an ideal method to store the renewable energy,which is promising to realize a clean and sustainable energy cycling in the future.Efficient and affordable electrocatalysts are critical to decrease the cost of hydrogen production through water electrolysis and thereby facilitate its large-scale application.With the unique 2D layer structure,molybdenum disulfide?Mo S2?is an appealing candidate,in which the configurationally unsaturated edges are high active that comparable to Pt.However,Mo S2conventionally occurs in a semiconducting phase?2H?,and the active sites are limited on edges.Both aspects are undesirable for efficient electrocatalysts.Compared with its 2H-Mo S2,the 1T phase Mo S2with different coordination structure is electroconductive.Moreover,the basal plane of 1T-Mo S2is electrochemically active,providing proliferated active sites.Therefore,1T-Mo S2is a more favorable alternative for the hydrogen evolution reaction?HER?.Nevertheless,the conventional synthesis of 1T-Mo S2involves highly inflammable agent?n-Butyllithium?and the reaction process is tedious.Besides,1T-Mo S2is metstable and tends to convert into 2H phase.Moreover,the catalytic activity of 1T-Mo S2basal plane is inferior to its edges,which hinders further improvement in catalytic performance.This thesis is focused on the facile synthesis and electrochemical applications of 1T-Mo S2.An aqueous solution synthesis of1T-Mo S2was developed,based on which we synthesized several highly efficient catalysts for the HER via modulating the microstructure and electronic structure.The mechanism underlying the efficient performance was revealed,and the influence factors were inspected,which provide guidance for the design of high-performance electrocatalysts based on 1T-Mo S2.With the favorable electrochemical features of1T-Mo S2,the as-obtained material were also applied for the lithium ion batteries and its Li+storage mechanism is investigated.The main research contents are listed as following:1.A hydrothermal synthesis of 1T-Mo S2in acid solution developed,which provides more facile approach to generating 1T-Mo S2with high purity.The influence factors on the 1T phase proportion in the product were inspected and a“reduction-sulfuration”mechanism concerning the formation of 1T-Mo S2in acid condition was proposed.On the basis of the results,the proportion of 1T-Mo S2can be adjusted in certain range?43%?72%?and a series of electrocatalysts were obtained.The catalytic activity is found to be enhanced as the proportion of 1T-Mo S2increases.In the optimized condition,the as-obtained 1T/2H-Mo S2heterogeneous catalyst exhibits remarkable active towards the HER with a overpotential of 220 m V at current density of 10 m A·cm-2and small Tafel slope of 61 m V·dec-1.Based on the electrochemical analysis,the remarkable catalytic performance of 1T/2H-Mo S2is origin from the proliferated active sites in 1T-Mo S2as well as its superior electroconductivity.2.A self-supported electrocatalyst with 1T-Mo S2?with a proportion of?70%?vertically oriented on carbon fibers was fabricated though the acidic solution hydrothermal synthesis approach with slight modulation.Experimental analysis indicates that vertical array of Mo S2is favorable to avoid accumulation of nanosheets and expose more active sites.Interweaved carbon fibers prove highways for electrons transfer throughout the architecture.Besides,the self-supported structure facilitates the mass transfer process between electrode and electrolyte.With these merits,the as-obtained 1T/2H-Mo S2/CC self-supported electrocatalysts delivered a high activity towards the HER with an overpotential of 160 m V at current density of 10 m A·cm-2,which is superior to that of powdery 1T/2H-Mo S2.Furthermore,the thermodynamic stability of 1T/2H-Mo S2/CC is obviously enhanced,which is correlated with its self-supported structure and the organic functional groups absorbed on surface.3.On the basis of optimized structure,we designed an in-plane heterogeneous electrocatalyst to enhance the intrinsic activity of 1T-Mo S2basal plane.Cobalt disulfide?Co S2?clusters were accommodated in the defects region of Mo S2nanosheets and formed interfaces with 1T-Mo S2.With distinct coordination at interfaces,the electronic state active sites can be modulated,which influences the corresponding hydrogen absorption energy??GH?and catalytic activity.Experimental and computational results indicate that electrons transfer from both Co S2and1T-Mo S2lattices to the interfaces,which makes the S atom on interfaces an electron-rich center.This electron migration effects the hydrogen absorption free energy of S atom on interfaces and optimized the corresponding catalytic activity.Consequently,the as-synthesized Co S2@1T-Mo S2/CC affords an excellent performance towards the HER with a small overpotential of 78 m V at current density of 10 m A·cm-2and facilitated kinetics,which is even comparable to the commercial Pt/C catalyst.4.With the unique electrochemical properties,1T-Mo S2is an ideal candidate as the anode for lithium ion batteries.However,the Li+storage mechanism in 1T-Mo S2,especially the origin of stable cycling performance is still ambiguous,which hinders the further development of 1T-Mo S2based anode materials.Thought solution approach,we directly assembled 1T-Mo S2nanosheets on Ti foil,which serves as a platform for the investigation of Li+storage mechanism where 1T-Mo S2is the only active substance.By comparing the different structural evolution and electrochemical performance between 1T-Mo S2/Ti and 2H-Mo S2/Ti upon cycling.We proposed the stable cycling performance of 1T-Mo S2is significantly correlated with its layer number.The intercalated Li+in multilayered 1T-Mo S2can be accommodated by forming Li-Mo-Sxternary compounds.The corresponding formation reaction is reversible,which benefits the retention of Mo S2lattices in Li+intercalation process.These Mo S2residues can serve as anchors to absorb polysulfide lithium?LixS?species and suppress the loss of active substance,thereby improves the cycling stability.Following the perspective,we further constructed a Co S2/1T-Mo S2/CC heterogeneous anode,where Co S2provides catalysis to the conversion reaction between LixS and Li2S.With the synergistic effect of Co S2and multilayered 1T-Mo S2,Co S2/1T-Mo S2/CC exhibits outstanding high rate performance with stable cycling under current density of 1 A·g-1,2 A·g-1and 5 A·g-1. |
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