| dc.description.abstract | Photoelectrochemical water splitting provides a promising way for solar-to-hydrogen conversion to address energy and environmental crisis. Hematite (α-Fe2O3) is an attractive photoanode material due to its natural abundance, narrow bandgap for visible light absorption, and excellent photo and chemical stability. However, its photoelectrochemical efficiency remains inefficient, mainly because of the multiple pathways of charge recombination at its interface and surface. Also, the sluggish oxygen evolution reaction at the hematite surface contributes to inefficient efficiency. Therefore, suppressing interface/surface charge recombination and facilitating surface oxygen evolution reaction is essential for developing an efficient hematite photoanode. Thus, some new strategies aiming to address the above concerns by using recent emerging materials, including carbon dots, molecular water oxidation catalysts, and single-atom catalysts, were explored in this thesis, along with mechanism investigation by advanced material characterizations, photoelectrochemical technologies, and in-situ transient absorption spectroscopy complemented with density functional theory calculations. Chapter 1 is an introduction to this thesis, including the background and motivation for this thesis, fundamentals of photoelectrochemical water splitting, basics of hematite photoanodes, the state-of-art interface/surface modulation strategies for hematite photoanodes, background knowledge and application in photoelectrochemical devices of recent emerging carbon dots, molecular water oxidation catalysts, and single-atom catalysts, followed by the objectives of this thesis research. Chapter 2 presents experiment details and characterization techniques used for this thesis. This chapter starts by giving a detailed description of synthesis approaches for hematite films, carbon dots, iridium molecular water oxidation catalysts, and single iridium catalysts. Then the specific information of the instruments used for characterization of these as-prepared materials, along with a brief description of their critical fundamentals and principles, is provided. Finally, photoelectrochemical-related concepts, measurements, and mechanism studies are described. Chapter 3 focuses on the engineering of a carbon underlayer produced from carbon dots using biomass as raw material through a facile hydrothermal process accompanied by a thorough exploration of its role in the structural and photoelectrochemical properties of hematite photoanodes by combining structural, compositional, and electrochemical characterisation techniques, including photoelectrochemical impedance spectroscopy, intensity-modulated photocurrent spectroscopy, and Mott-Schottky measurements. Chapter 4 explores the effects of the ligands in Ir complexes on the interfacial charge transfer by adjusting the electronic structure of the organic ligands and coordination environment of iridium active centre on hematite photoanodes in an attempt to reveal whether structurally induced electronic differences of the ligand would translate into different charge transfer efficiencies. Chapter 5 unravels the precise role of Ir single-atom catalysts on hematite by in-situ transient absorption spectroscopy, ultraviolet photoelectron spectroscopy, and intensity-modulated photoelectrochemical spectroscopy coupled with density-functional theory calculations. Chapter 6 summarises the main conclusion of this thesis research and provides an outlook for future work related to this thesis research. | en_US |
