Spectroscopic Investigation of Semiconductor Charge Carrier Dynamics and Semiconductor/electrolyte Catalytic Interface for Solar Energy Conversion Restricted; Files & ToC

Abstract

Utilizing semiconductor photoelectrode is a promising but challenging method to achieve direct energy conversion from solar energy to chemical energy stored in liquid fuels. A lot of fundamental questions need to be understood on semiconductor/electrolyte junction to achieve efficient energy conversion efficiency, for instance, how to understand the surface minority charge accumulation, the function of the surface co-catalyst and the catalytic interfacial electric field. In this thesis, we intend to investigate the semiconductor/electrolyte catalytic junction through time-resolved and in situ spectroscopic methods. In chapter 3 and 4, we introduced an in-situ bias-dependent Second Harmonic Generation (SHG) technique to investigate potential drop at the semiconductor electrode and solution double layer side without illumination and the minority charge accumulation at the surface under illumination condition for oxygen evolution reaction (OER). It is found that the TiO2 crystal angle and light polarization will have significant effect on its bias-dependent SHG behavior. Under photoexcitation, screening of built-in potential is observed, which is correlated to the surface hole accumulation. Studying accumulated holes provides crucial understanding of water oxidation rate-determining species. In chapter 8, in-situ Raman spectroscopy is developed to study the properties of a novel semiconductor-catalyst/electrolyte junction SMA/CNT/CoPc-NH2 during CO2 photoreduction condition.

In chapter 5, the synthesis of TiO2-Co9POM hybrid photoanode material showed a three-fold OER photocurrent enhancement compared to unmodified nanoporous TiO2, comprehensive transient absorption and photoelectrochemical characterization highlight the function of Co9POM catalyst. Chapter 6 uses transient reflectance spectroscopy to study the photocathode material GaP/TiO2, showcasing the importance of solution electrolyte concentration and potentiostat response in regulating interfacial recombination. Lastly, chapters 7 focused on the charge separation process of a CdS based CO2 reduction catalyst, clearly revealing the initial rapid charge separation process and later charge accumulation on the catalyst through transient absorption spectroscopy, providing mechanistic insight of this novel hybrid photocatalyst.

Table of Contents

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About this Dissertation

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School	Laney Graduate School
Department	Chemistry
Degree	Ph.D.
Submission	Dissertation
Language	English
Research Field	Chemistry, Physical
Keyword	Semiconductor photoelectrode Oxygen evolution reaction Raman spectroscopy Transient Absorption Spectroscopy Second Harmonic Generation CO2 reduction reaction
Committee Chair / Thesis Advisor	Heaven,Michael , Emory University Lian,Tianquan, Emory University Hill,Crain L. , Emory University

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