Synthesis and characterization of manganese sulfide decorated molybdenum disulfide nanomaterials for energy storage applications

Abstract

The incorporationofMnSnanoparticlesonthesurface morphological,structural,chemical,optical,andelectrochemicalperformanceof2H-MoS2nanoflower(MoS2/MnS)synthesizedbyafacilehydrothermalmethodwasstudied.ThemorphologicalstudyperformedbyFESEMandHRTEMshowedthattheincorporationofMnSnanoparticlesdistortedthelatticefringeandincreasedtheinterlayerspacingoftheMoS2nanoflower.Thedifferentstructuralparametersofthecompositenanomaterials were investigated by XRD. The microstrain of the nanocomposites wasfound to vary with the concentration of MnS nanoparticles. The Raman spectra ofMoS2/MnS showed that interfacial interaction occurred between the MoS2 and MnSinterfacescausingn-typedopinginthenanocompositesduetotheincorporationofMnSnanoparticles.TheopticalstudywasperformedbyUV-Visspectroscopy,whichshowed a reduction of the optical band gap from 1.68 eV to 1.54 eV due to theincorporation of MnS nanoparticles. The XPS analysis revealed a partial conversionfrom2H-MoS2to1T-MoS2,togetherwiththeformationofdefectstatesinthenanoflowerduetothecreationofsulfurvacanciesbyincorporationofMnSnanoparticles. The electrochemical properties of the MoS2/MnS nanocomposites wasstudied by an electrochemical workstation. For MnS nanoparticles decorated MoS2nanoflower a highest specific capacitance of 351 Fg-1 at a current density of 0.3 Ag-1.Thecompositenanomaterialsexhibitacapacitiveretentionof80%after8,000charginganddischargingcycles.Thedensityfunctiontheory(DFT)revealedformationofdefectstatesintheforbiddenenergyregion duetothestronghybridizationbetweenMo-dandMn-dorbitalsoccurredduetotheincorporationofMnS.TheimprovedelectrochemicalperformanceofMoS2/MnSnanocompositecanbeattributedtothedefect-rich1T-MoS2phase,togetherwiththeenlargedsurfaceareaandincreasedinterlayerspacingoriginated from the decoration of MnS nanoparticles. The combined experimental andtheoretical approach used in this thesis work will open up an economic and sustainablerouteforthefabrication ofefficient energystoragedevices.