A Spectroscopic Investigation of Photoelectrochemical Reactions at the Semiconductor - Electrolyte Interface for Artificial Photosynthesis
- Author(s): Herlihy, David Michael
- Advisor(s): Harris, Charles B
- et al.
The mechanism of water oxidation to molecular oxygen at the surface of strontium
titanate, a representative transition-metal oxide photocatalyst, was investigated
using ultrafast pump-probe spectroscopy and accompanying characterization methods.
The dependence of the rate of initial charge transfer on applied potential was investigated
with transient absorption spectroscopy, revealing a phenomenological transfer coefficient
for this single step of the multi-step water oxidation reaction. Time resolved
infrared spectroscopy provided the first direct evidence of the molecular character of the
first intermediate to be a titanium-bound oxyl radical, and revealed interfacial Fano coupling
between the electrolyte, surface species, and catalyst electronic continuum. Further
work combining both transient absorption and time-resolved mid-infrared spectroscopy
exposed a minimum of three distinct surface states at the strontium titanate surface,
providing insight into the rich chemistry mediated at the catalyst surface. These results
highlight the intricacies of charge transfer at the surface of these promising materials,
provide insight into an important but difficult reaction necessary for any artificial
photosynthetic system, and offer a generalizable paradigm for considering heterogeneous
photochemistry. Finally, preliminary groundwork was done to uncover the mechanism
of the carbon dioxide reduction half reaction in a novel inorganic-biological bacterial
system with potential to produce green chemicals such as carbon-neutral liquid fuels.