Preparation and application of conductive molybdenum disulfide

Abstract

For applications of MoS2 in batteries, supercapacitors, electrocatalysts, solar cells and water quality sensors, a substantially increased conductivity is required in order to achieve reasonable currents. Popularly, the metallic 1T-MoS2 phase is used, which can be prepared via a lithium intercalation process, requiring inert atmosphere processing and safety procedures. In this thesis, I demonstrate a safer and more efficient process to yield conductive MoS2 (c-MoS2). This simple and effective way to prepare few layer c-MoS2 utilizes ambient conditions and 0.06 vol% aqueous hydrogen peroxide. Part of the research effort has been to enhance the conductivity of MoS2 using the idea of green solvents (like pure water). The bulk conductivities of both peroxide and water exfoliated MoS2 are up to seven orders of magnitude higher than that of the semiconducting 2H-MoS2 phase. The samples were characterized with Hall measurements, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Trace amounts of hydrogen molybdenum bronze (HxMoO3-y) and sub stoichiometric MoO3-y were shown to help tune the conductivity of the nanometer-scale thin films without impacting the sulfur-to-molybdenum ratio. c-MoS2 was further functionalized with thiols to determine the number of residual reactive sites. I also studied the mechanism of surface functionalization of MoS2 with diazonium molecules (both direct and in-situ approach) to understand the surface properties of our material and tune the chemical and mechanical properties of conductive MoS2.

An important goal of my work is to control the conductivity of the MoS2 thin films in safe and facile ways that enable their application in low-cost chemiresistive sensors for liquid environments. I fabricated chemiresistive sensors with centimeter channel lengths while maintaining low measurement voltages for pH sensing. I further measured the catalytic activity of c-MoS2 films in 0.5 M H2SO4 electrolyte solution using linear sweep voltammetry (LSV) which showed a lower Tafel value at 10 mA/cm2 current density. The lower Tafel value demonstrated that c-MoS2 has potential to use as catalyst for hydrogen evolution reaction. My study furthers the understanding of conductive forms of MoS2 and opens up a new pathway for next generation electronic and energy conversion devices.