Influence of Synthesis Conditions on Photo-Electrochemical Performances of CuGaO2

Abstract

In recent decades, our changing energy needs have significantly driven chemical research on metal oxides. The continuous innovation of new materials and the investigation of their properties for energy conversion devices are expected to deepen our understanding of the interesting electrochemical behavior of various metal oxides. This thesis explores the systematic design and synthesis of metal oxide and metal nanostructures, examining their roles in solar energy conversion and catalysis. The research covers a broad spectrum of materials chemistry, from fundamental aspects like the impact of synthesis conditions to more practical applications, including the design of dye-sensitized photoelectrochemical cells to evaluate the performance of the synthesized materials in p-type DSSCs. Chapter 2 presents an application using semitransparent CuGaO2 nanoplates as photocathodes in dye-sensitized photoelectrochemical cells. My research has focused on understanding the interfacial charge transfer properties and electronic structure of delafossite CuGaO2 nanoparticles produced via hydrothermal methods. This study utilized variations in synthesis parameters, such as precursor pH and post-synthetic annealing atmosphere, to passivate surface defects. An optimal thickness of 1.5-2 μm was achieved, yielding the highest charge collection efficiency for samples synthesized at pH 9. Additionally, H2 annealing further enhanced the photocurrent for samples synthesized at pH 9. In Chapter 3, a systematic investigation was conducted into the impact of synthesis temperature on CuGaO2 at pH 9. Employing Mott-Schottky analysis provided insights into acceptor state densities and apparent flat-band potentials (Efb). Notably, the Efb values of the CuGaO2 exhibited a gradual decrease with higher reaction temperature, indicating a decrease in the Fermi energy level of the charge carriers. In constructing p-type dye-sensitized photoelectrochemical cells using the CuGaO2 films, the photovoltage increased with the rising temperature up to 2300C. The optimal nominal temperature for the synthesis was determined to be 2300C, which contributed to enhancements in both carrier lifetimes and observed photocurrent as well as photovoltage within a three-electrode photoelectrochemical cell and reduced the carrier transport times within the nanoparticle semiconductor network. Finally, in Chapter 4, we explored the application of Surface Enhanced Raman Spectroscopy (SERS) to monitor the decarboxylation of 4-mercaptobenzoic acid (4-MBA) and its isomers. This method offers insights into chemical reactions occurring near metal nanostructures, helping to elucidate the reaction pathway and identify new species.