|Enhanced Photocatalytic Activity Induced by Surface Structural Changes in Strontium Titanate Electrodes: An Operando Study|
|Presenter||Joel Donald Brock, Cornell High Energy Synchrotron Source and School of Applied and Engineering Physics, Cornell University,|
A major objective of energy research is to employ light to cleave water directly, without an applied bias, into hydrogen and oxygen. Since the initial reports of the ultraviolet activity of TiO2 and SrTiO3 in the 1970’s, researchers have pursued the development of photo-active materials and a fundamental understanding of the mechanistic and molecular-level phenomena involved in photo-catalysis.[1-7] While surface science, utilizing ultrahigh vacuum (UHV) techniques to study well-defined materials (e.g., single crystals), has provided many insights, we still know relatively little about molecular-level processes near electrodes in contact with electrolytes under operating conditions. Here, we report observations of the surface-structure dependent photocatalytic activity of SrTiO3 towards the water splitting reaction under active potential control. Pre-treating the electrode surface, by biasing to potentials where oxygen evolution occurs in basic medium, irreversibly reorders the surface and nearly triples the photo-induced water splitting activity at open circuit, as measured by scanning electrochemical microscopy (SECM). Using in situ x-ray reflectivity, we obtain the history-dependent structure factor along the (001) face of a SrTiO3 electrode/electrolyte interface during photoassisted electro-catalysis. First-principles joint density-functional theory (JDFT) interpretation of the x-ray data suggests a biaxially strained anatase-like structure as the active operando surface.
 A. Fujishima and K. Honda, "Electrochemical Photolysis of Water at a Semiconductor Electrode," Nature 238 (5358), 37-38 (1972).