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SUMMARY:Visualizing Ultrafast Electron Dynamics at Catalytic Surfaces
LOCATION:Chemistry A101
TZID:America/Denver
DTSTART:20189001T000000
UID:2026-05-16-21-01-09@natsci.colostate.edu
DTSTAMP:20260516T210109
Description:Directly observing electron dynamics at surfaces is required to
  reveal the material properties that determine efficiency during energy co
 nversion catalysis.  Toward this goal\, we have developed a tabletop inst
 rument for femtosecond X-ray spectroscopy of surfaces.  This method combi
 nes the benefits of X-ray absorption\, such as element\, oxidation\, and s
 pin state specificity\, with surface sensitivity and ultrafast time resolu
 tion\, having a probe depth of only a few nm and time resolution faster th
 an 100 fs.  Using this technique\, we study the electron dynamics in a nu
 mber of catalytically relevant metal oxides.  Specifically\, Fe2O3 is an 
 earth-abundant semiconductor with a band gap ideally suited for solar ligh
 t harvesting\, but its catalytic performance is low due to surface electro
 n trapping.  In these studies\, we show that surface trapping occurs in l
 ess than 1 ps.  Surprisingly this process is not sensitive to Fe2O3 surfa
 ce morphology\, indicating that electron trapping is not influenced by sur
 face defects.  Instead\, ultrafast trapping occurs by the interactions of
  the free electrons with the lattice nuclei via a process known as small p
 olaron formation.  In contrast to Fe2O3\, CuFeO2 is a closely related ear
 th-abundant photocatalyst\, which can reduce CO2 using sunlight.  Specifi
 cally\, we have recently shown that CuFeO2 is a selective catalyst for pho
 to-electrochemical CO2 reduction to acetate.  However\, the role of elect
 ronic structure and charge carrier dynamics in this process has not been w
 ell understood.  Using ultrafast X-ray spectroscopy\, it is possible to t
 rack electrons and holes independently in the Fe 3d\, Cu 3d\, and O 2p sta
 tes comprising the band structure of this photocatalyst.  Results show th
 at photocatalytic activity is related to ultrafast hole relaxation leading
  to spatial charge separation in the layered CuFeO2 lattice\, which cannot
  occur in Fe2O3.  This ability to elucidate site-specific charge carrier 
 dynamics in real time provides important criteria for the rational design 
 of catalysts for efficient solar energy harvesting based on their underlyi
 ng photophysics. 4:00 pm
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