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A Spectroscopic Investigation of Photoelectrochemical Reactions at the Semiconductor - Electrolyte Interface for Artificial Photosynthesis


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.

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