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How Charge Transforms Chemical Bonds at Solid-Liquid Interfaces

Event Details

Event Dates: 

Friday, September 15, 2017 - 4:00pm

Seminar Location: 

  • JILA Auditorium

Speaker Name(s): 

Tanja Cuk

Speaker Affiliation(s): 

CU Boulder
Seminar Type/Subject

Scientific Seminar Type: 

  • Phys Chem/Chem Phys Seminar

Event Details & Abstract: 

The principles that govern catalysis at solid-liquid interfaces are at the heart of energy storage technologies, enabling chemical reactions required to store energy in batteries, to release it in fuel cells, and to convert it in solar-to-fuel systems. Catalysis at these surfaces proceeds from the localization of charge onto surface atoms, forming a catalytic intermediate. My lab leads an effort in resolving the reaction pathway from the point of charge transfer to the surface. The experiments merge time-resolved (optical, mid-infrared) spectroscopy with efficient pulsed excitation of the photo-electrochemical oxidation of water on a model system, the n-SrTiO3/aqueous interface. Thus far, for the intermediates that precede the first chemical bond of the cycle (O-O), the following picture has emerged: photo-excited holes in the valence band of SrTiO3 localize perpendicular to the surface, in titanium oxyl (Ti-O•) radicals, and parallel to the surface, in bridge (Ti-O•-Ti) radicals. Aided by theoretical calculations, the oxyl radical was detected by its unique Ti-O stretch vibration in the plane right below Ti-O•1, and the bridge radical by an in-plane polarized optical dipole transition2. These experiments showed that the reorganization of water around the intermediates is critical to their surface stability, by the time constants with which the O-site radicals form and by the coupling of the oxyl radical’s vibration to water librations. Recently, the dynamics of these O-site radicals at microsecond time-scales of bond formation were probed and the results will be presented. Current and future work in my laboratory is to fully describe how the initial intermediates evolve to form the O-O bond and release O2 on model, wide band gap semiconductor systems. It is also to time-resolve the dynamics of catalysis while also tuning materials composition, electrolyte composition, and device architecture.