UNIVERSITY OF SOUTHERN CALIFORNIA LOS ANGELES United States
We investigate carefully engineered metalsemiconductor nanostructures based on TiO2-passivated III-V compound semiconductors i.e., GaP, InP, GaAs to control the flow of electrons and intermediate species to catalytically active sites. The TiO2 passivation layer prevents photocorrosion of the III-V compound surface, providing a viable, long-term stable photocatalyst. Our primary reactions of interest include water splitting and the photocatalytic reduction of CO2 with H2O to various hydrocarbons, which is a complex reaction system requiring up to 8 electrons and many intermediate species, some of which have extremely high energy barriers. This system provides an interesting testbed for studying the control of energy transfer in catalytic processes. These carefully engineered structures provide control over the electron hole energy landscape, directing the flow of electrons to catalytically active sites through built-in fields, arising from a pn-junction formed between the III-V compound semiconductor and TiO2 passivation layer. These structures also enable us to control the adsorptiondesorption kinetics ofreactant, intermediates, and products to ensure that a high density of intermediates are present at the catalytically active sites. We use vibrational sum frequency generation vSFG spectroscopy to identify reaction intermediate species and catalytically active sites on these photocatalytic surfaces. In order to explore and separate various mechanisms of catalysis and enhancement, we will perform a systematic study of sample morphology by varying the surface coverage, size, and shape of metal co-catalyst nanoparticles, and controllably introducing defects to determine their effect on the reaction surface-bound intermediates.