Transition Metal Selenide Nanostructures:Controllable Fabrication,Alternated Electronic And Structure Modulations For Application In Electrocatalysis And Charge Storage

Two-dimensional(2D)layered transition metal dichalcogenides(TMDs)are a group of extremely unique function materials that are high potential for technical applications in varied areas including catalysis,energy-transition and storage systems.With intensively reduced stacking density,the TMDs nanostructured selenides with ultrathin layers would possess highly increased specific areas and active sites,which are available for serving as catalysts to meet the multifaceted demands of energy technology with extendable feasibilities and enhanced properties.According to the differences in thermodynamics and bonding structure,selenides would be more favorable for the electrochemical applications as compared to the counterpart sulfides while their conductive property should be improved to meet the requirement for applications.To this end,in this dissertation,solution-phase synthetic routes were designed for the controllable growth of tungsten selenide(WSe2)-based heterostructured hybrid nanosheets typically via integrating some exotic components to improve their conductive property since they are promising and emerging for electrochemical energy applications.The main contents of this dissertation with novelties are described as below:First,WSe2/CoSe2 heterostructured hybrid nanosheets have been designed and controllably fabricated via hot-injection colloidal synthetic route,and their structure and electrocatalytic properties were intensively investigated.Characterizations using X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),etc.revealed that there are interactions between CoSe2 and WSe2 in the heterostructured nanohybrids,which exhibit improved acidic HER and basic OER electrocatalytic behavior as well as supercapacitor performance.The heterostructured nanohybrids perform a lower overpotential(η10)and Tafel slopes values of 157 mV and 79 mV dec-1 for HER and 330 mV and 76 mV dec-1 for OER,respectively.They also illustrated very high capacitance(2720 F g-1 at 1 A g-1),which is superior to most of reported counterparts.Second,using the dual strategy of phase-interface engineering,nanoscale heterostructures of 1L-1T-WSe2 with imbedded Ag2Se nanoparticles(NPs)are fabricated via a one-pot oleylamine-colloidal reaction through extending the system of hybrid nanosheets.The Ag2Se NPs as a superionic conductor state(over～133℃)growing and diffusing fast direct the growth forming quasi-monolayer Ag2Se/1L-1TWSe2 heterostructured hybrid nanosheets in situ in the synthetic process,and the nanosheets demonstrated excellent HER properties with overpotentials(η10)of 163 mV and 140 mV in acidic and basic conditions,respectively.The hybrid nanosheets exceled an alkaline supercapacitance of 1674 F g-1 at 1 A g-1.Meanwhile,XPS and ultraviolet photoelectron spectroscopy(UPS)determinations revealed the electronic modulation and mechanism of the quasi-monolayer hybrid nanosheets with enhanced electrochemical performances.And also,the synthetic route is also applied for the fabrication of selenium ad-atom tungsten selenide(Se-WSe2)nanosheets for the first time to optimize their electrochemical performances.Investigations revealed that there is a phase transformation from 2H to IT,which favors the improvement of electrochemical performances.In addition,a novel and highly active CoSe2/VSe2 system was developed optimally using the above developed solution-phase synthetic route for the improvement of electrocatalysis of water in HER and OER processes.With the assistance of conductive VSe2 substrate,CoSe2/VSe2 could be grown as a new type of van der Waal’s heterostructured hybrid nanocomposites.The hybrid nanostructures with dense exposed edges and interface electronic modulation between CoSe2 and VSe2 components could optimize their electrochemical properties and performances.A basic OER was succeeded with low overpotential of 290 and 440 mV for delivering current densities of 10 and 100 mA cm-2,respectively,at a Tafel slope value of 55 mV dec-1.Similarly,the electrocatalyst performed excellence for the acidic HER,at overpotentials of 142 and 249 mV for achieving current densities of 10 and 100 mA cm-2 with a smaller Tafel slope of 50.7 mV dec-1.HRTEM,XPS,and UPS revealed that the boosted electrocatalytic activities are endorsed to the electronic interaction and increased active sites from heterostructured architectures.As a whole,this dissertation on the designed fabrication,structure modulation and performance optimization of WSe2-like TMDs-based hybrid nanostructures would pace the steps for future technical utilizations in energy areas.