Date of Award

1-27-2026

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Applied Science

First Advisor

John Nichols

Abstract

The synthesis of tungsten oxide (WO3−δ, 0 ≤ δ ≤ 1) nanostructures with controlled phase and morphology remains a significant challenge, particularly for applications in energy conversion and storage. This dissertation presents an eco-friendly and time-efficient method for synthesizing tungsten oxide nanostructures with tailored stoichiometry and crystal phases through the Resistive Hot Wire Oxidation (RHWO) technique. In this method, a tungsten wire is heated via resistive heating in an oxygen environment, and by precisely controlling the growth conditions, we successfully synthesized WO2.72, WO2.76, WO2.80, WO2.83, WO2.90, and WO2.98 phases with controlled morphologies using simple instrumentation. This approach eliminates the need for sophisticated equipment, complex procedures, and an costly precursors thereby offering a scalable solution for nanomaterial synthesis. An arsenal of characterization techniques including scanning electron microscopy (SEM), x-ray diffraction (XRD), Raman spectroscopy (RS), x-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and electrochemical characterization methods such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) was employed to reveal the morphological, compositional, and electrochemical properties of the synthesized tungsten oxides. The electrochemical performance of synthesized tungsten oxide nanostructures and microstructures highlights the critical role of phase and morphology in influencing ionic transport and charge storage behavior. Phase-controlled material exhibit significant variations in their electrochemical responses. Specifically, the non-stoichiometric phase WO2.76 demonstrates promising electrocatalytic activity for the hydrogen evolution reaction (HER) in acidic environments, exhibiting an overpotential of approximately −0.42 V versus standard hydrogen electrode (SHE) and a favorable Tafel slope of 115 mV/dec. This performance suggests efficient H+ ion intercalation suggesting for potential energy storage applications. Similarly, a detailed electrochemical energy storage investigation across a series of non-stoichiometric tungsten oxides (WO3−δ, 0 < δ < 1) reveals stiochiometric and morphology dependent energy storage properties. Fine nanostructured WO2.90 exhibits enhanced double-layer capacitance, while WO2.72, characterized by large open channels and higher carrier concentration, demonstrates enhanced hybrid energy storage with combined diffusion-controlled and pseudocapacitive behavior. These results indicate that tungsten oxide nanostructures, particularly in the WO3−δ phases, serve as effective electrodes for high-performance supercapacitors and energy conversion applications. The study validates the RHWO synthesis technique as an eco-friendly, time-efficient, and scalable alternative to traditional nanomaterial synthesis methods, offering both enhanced performance and practical scalability.

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