Systematic Development and Characterisation of Photoelectrodes for Light-Driven Water Splitting

Abstract

The research presented within this thesis aims to develop and expand procedures towards the fabrication of high performance photoelectrodes for light-driven water splitting in a systematic and rational manner. The nature of work within each chapter covers a broad range of techniques and objectives, exploring: bottom-up approaches to fabrication, optimal methods to increase the complexity of an electrode without changing the predominant material, and designing new methods to gain deeper understanding of materials and enable more informed optimisation.

Chapter 1. Introduction: Presented in alternative format, an introduction to the field and fundamentals of photoelectrochemical water splitting is provided, including semiconductor theory, photoelectrode materials and property requirements, chemical vapour deposition, and a particular emphasis on molecular precursor design.

Chapter 2. New Titanium Dioxide Precursors: Presented in alternative format, the synthesis and characterisation of a series of new TiO2 precursors is described. The two most promising are deposited via aerosol-assisted chemical vapour deposition (AACVD), and a full physical and photoelectrochemical analysis of the resulting thin films is performed. Remarkably high photocurrent densities are recorded, attributed to the presence of mixed rutile-anatase phase. A new Ge precursor based on the same ligand system is also synthesised, characterised, and trialled in AACVD.

Chapter 3. Dual-Source Aerosol-Assisted Chemical Vapour Deposition: In this chapter, the synthesis of an Fe2O3 precursor is optimised to enable its effective use in AACVD. This precursor is used in dual-source depositions with a Ti precursor from Chapter 2, and a known V precursor; all of which possess molecular structures based on the same ligand to enhance compatibility for deposition. Characterisation of the resulting films is performed, identifying the optimal deposition ratios.

Chapter 4. Plasma-Enhanced Atomic Layer Deposition of Hematite: More complex photoanode design is considered through the development of a plasma-assisted atomic layer deposition process for ultra-thin hematite films. The process has a high degree of control over film thickness and is proven to be highly conformal across a nanorod structured surface, making it effective at constructing heterojunctions on nanostructured and porous films.

Chapter 5. Titanium Dioxide Nanorods on Titanium Microwires: Presented in alternative format, a TiO2 nanorod system is grown onto a titanium wire substrate as an alternative to the commonly used 2D transparent conducting oxides, therefore significantly increasing the available surface area. Saturation of measured photocurrent for increasing nanorod lengths reveals a mass transport limitation associated with high surface area electrodes.

Chapter 6. Nanoscale Electrochemical Characterisation of Porous Materials: Presented in alternative format, this work details the development of a new scanning electrochemical cell microscopy protocol to quantitatively determine spatially-resolved electrochemical activity and electrochemical surface area within a single, high-throughput measurement. This protocol is applied to a porous, amorphous MoSx thin film to further the understanding of its structure-activity relations, and highlight the importance of local measurements for the systematic and rational design of thin film catalyst materials.

Chapter 7. Conclusions and Outlook: Final concluding remarks are made, and areas for future work are outlined.

Date of Award	2 Oct 2024
Original language	English
Awarding Institution	University of Bath
Supervisor	Andrew Johnson (Supervisor) & Frank Marken (Supervisor)