Publication Date

8-2018

Date of Final Oral Examination (Defense)

4-17-2018

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Materials Science and Engineering

Department

Materials Science and Engineering

Supervisory Committee Chair

Hui (Claire) Xiong, Ph.D.

Supervisory Committee Member

Rick Ubic, Ph.D.

Supervisory Committee Member

Dmitri Tenne, Ph.D.

Abstract

The effects of various heat treatments on the physical and electrochemical properties of anatase TiO2 nanotubes were studied in this work. Well-ordered TiO2 nanotubes were grown via electrochemical anodization and annealed at 450°C to induce a phase transformation to anatase. The heat treatments were conducted under atmospheres of O2, Ar, N2, and water vapor (WV) to create different point defects. The oxygen-deficient atmospheres were used to generate oxygen vacancies in the TiO2 nanotubes, while the water vapor treatment was used to create Ti vacancies by stabilizing them via the protonation of O sites. Computational models of anatase TiO2 with oxygen or titanium vacancies were created to predict the effect of the defects on the band structure and electrical properties. Two-point conductivity measurements and Mott-Schottky characterizations were conducted to evaluate the electrical conductivity and charge carrier concentration of TiO2 nanotube samples and compared to the predicted effects of the heat treatments. Scanning electron microscopy and x-ray diffraction were used to study the nanostructure morphology. Additional characterization techniques such as Raman spectroscopy were used to study the generation of the respective point defects. The anatase nanotubes synthesized under different atmospheres were then used as anodes in lithium-ion batteries. The N2- and WV-treated samples exhibited the largest increase in capacity, while the Ar-treated sample had a slight capacity increase compared to the stoichiometric O2-treated control sample. Further electrochemical testing revealed that the WV-treated sample had the highest Li diffusivity.

DOI

10.18122/td/1439/boisestate

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