Electrochemistry of electroless plating on optical fiber for sensors and vanadium sulfide cathodes for batteries
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The first part of this thesis proposes methods to monitor internal corrosion before catastrophic events occur. Internal corrosion accounts for about 60% of all natural gas transmission and gathering pipeline incidents caused by corrosion. In this work, first, nickel, copper, and iron were electrolessly coated on a single mode optical fiber and confirmed by Scanning Electron Microscope (SEM) and X-ray Photoelectron Spectroscopy (XPS). An Optical Backscatter Reflectometer (OBR) was then used to obtain optical measurements during electroless coating of corrosion proxy materials on the fiber, and their dissolution (corrosion). Three types of optical fiber-based sensors are proposed to monitor corrosion and water/humidity in natural gas transmission pipelines.
The second part of this thesis focuses on the study of vanadium sulfide compounds as potential cathode materials for battery applications. Recent theoretical predictions show high magnesium ion mobility in six-coordination, spinel close-packed frameworks. Mg-ion has been reported to favor octahedral environment in sulfides like vanadium sulfides. This project focuses on investigating vanadium sulfide compounds, AxV5S8, AxV6S8, and V5S8 (A = alkali metal or divalent, and x = 0 – 0.8) as candidate cathode materials for Mg-ion battery application.
Stoichiometric mixtures of vanadium sulfide compounds were synthesized in evacuated sealed quartz tubes and handled under argon. As-prepared samples of AxV6S8, AxV5S8, and V5S8 were characterized by powder XRD. The XRD patterns of RbxV5S8, RbxV6S8, and V5S8 matched with ICDD reference patterns without phase impurities. Cyclic voltammetry and chronopotentiometry data of the vanadium sulfide compounds with a lithium anode and the lithium-ion electrolyte suggest that KxV5S8 and RbxV5S8 are not electrochemically active. V5S8 was found to reversibly intercalate lithium and is a promising electrode material for further study.