Time resolved spectroscopic studies of iridium-based catalysts for water electrolysis
File(s)
Author(s)
Liang, Caiwu
Type
Thesis
Abstract
In this thesis, a series of time-resolved and operando spectroscopic techniques combined with mass spectrometry are used to understand the active states involved in water oxidation on iridium-based water oxidation catalysts and to link the active state density and their energetics with the intrinsic activity.
Chapter 1 introduces a broader motivation of the work in this thesis, discussing climate change, leading on to discussing the role of hydrogen for storing renewable energy in the transition toward carbon net-zero. Chapter 2 reviews the current developing understanding of water oxidation mechanism on iridium-based catalysts in particular. Chapter 3 describes the details of time-resolved and operando spectroscopic techniques used in this thesis. In Chapter 4, an operando optical absorption spectroscopy and a mathematical spectra deconvolution method are developed to investigate the redox active states on amorphous iridium oxide (IrOx) catalysts. Three different redox transitions are observed in optical absorption spectroscopy with increasing potential, with their densities quantified. The intrinsic kinetics are calculated and discussed based on the measured densities of these active states. Chapter 5 continues to study the nature of physiochemical nature of the optically detected redox states, by using a combination of hard X-ray absorption, soft X-ray absorption spectroscopies and density functional calculation. Chapter 6 switches to comparing the two most common iridium-based catalysts- amorphous IrOx versus rutile crystalline IrO2, using the methods developed in Chapter 4&5. Absorbate-absorbate interactions are observed in both oxides and play a key role in controlling the energetics of active states and thus the intrinsic reaction kinetics. Chapter 7 explores the origin of adsorbate-adsorbate interaction, the effects of electrolyte pH on this interaction and the resulting energetics of active states.
Finally, Chapter 8 presents the overall summary of this thesis and its limitations, and suggests some directions for future works.
Chapter 1 introduces a broader motivation of the work in this thesis, discussing climate change, leading on to discussing the role of hydrogen for storing renewable energy in the transition toward carbon net-zero. Chapter 2 reviews the current developing understanding of water oxidation mechanism on iridium-based catalysts in particular. Chapter 3 describes the details of time-resolved and operando spectroscopic techniques used in this thesis. In Chapter 4, an operando optical absorption spectroscopy and a mathematical spectra deconvolution method are developed to investigate the redox active states on amorphous iridium oxide (IrOx) catalysts. Three different redox transitions are observed in optical absorption spectroscopy with increasing potential, with their densities quantified. The intrinsic kinetics are calculated and discussed based on the measured densities of these active states. Chapter 5 continues to study the nature of physiochemical nature of the optically detected redox states, by using a combination of hard X-ray absorption, soft X-ray absorption spectroscopies and density functional calculation. Chapter 6 switches to comparing the two most common iridium-based catalysts- amorphous IrOx versus rutile crystalline IrO2, using the methods developed in Chapter 4&5. Absorbate-absorbate interactions are observed in both oxides and play a key role in controlling the energetics of active states and thus the intrinsic reaction kinetics. Chapter 7 explores the origin of adsorbate-adsorbate interaction, the effects of electrolyte pH on this interaction and the resulting energetics of active states.
Finally, Chapter 8 presents the overall summary of this thesis and its limitations, and suggests some directions for future works.
Version
Open Access
Date Issued
2024-07-07
Date Awarded
01/09/2024
License URL
Advisor
Stephens, Ifan E.L.
Durrant, James R.
Sponsor
Imperial College London
China Scholarship Council
Publisher Department
Materials
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)