Zi Wei

Graduation Semester and Year

2016

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Materials Science and Engineering

Department

Materials Science and Engineering

First Advisor

Fuqiang Liu

Abstract

In an attempt to explore a clean and renewable alternative to existing energy sources such as fossil fuel, we studied the feasibility of using vanadium redox species to store the inexhaustible solar energy via photoelectrochemical (PEC) reactions with photogenerated charge carriers from semiconductor photocatalysts such as TiO2. Based on our fundamental study of the compatibility of vanadium redox and TiO2, modification of TiO2 such as carbon coating and geometry enhancement, and development of a continuous-flow solar energy storage cell, we demonstrated high-efficiency solar energy storage cell.The research focuses on the following four directions. Firstly, a highly-efficient all-vanadium (all-V) PEC storage cell (PESC) has been developed. It showed a Faradaic efficiency of 95% without external bias and 12% incident photon-to-current efficiency (IPCE) at 350 nm. This PEC cell takes advantage of fast electrochemical kinetics of vanadium redox couples of VO²?/VO2? and V³?/V²?. The charge carriers created on the employed TiO2 photocatalyst have been demonstrated to be able to convert the two pairs of vanadium active species. Secondly, the amount of carbon coating on the surface commercial p25 TiO2 in the photoelectrode has been tuned through a facile high-temperature sintering procedure, which enhanced the photocurrent of the all-V PESC. The applied carbon coating was demonstrated to be beneficial to the conductivity of the photoelectrode in the all-V PESC, as it provides an interconnected layer for the transport of photogenerated charge carriers.Thirdly, a unique stirring-assisted hydrothermal synthesis method has been developed to create geometrically enhanced TiO2 nanobelts (TNBs), resulting a doubled photocurrent in the all-V PESC. The all-V PESC demonstrated a peak IPCE of ~22% without any external bias, double that of commercial P25 TiO2 (~11%) that we used in the previous case. Finally, an all-vanadium continuous-flow PEC cell was designed, resulting in 5 and 3 times increase in photocurrent and state of charge (SOC), respectively, compared to the all-V PESC with stagnant electrolytes. The improvement was mainly ascribed to the enhanced electrochemical charge transfer as well as boosted PEC reactions introduced by the forced convective flow.

Keywords

Solar energy storage, Vanadium battery

Disciplines

Engineering | Materials Science and Engineering

Comments

Degree granted by The University of Texas at Arlington

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