Photoexcited Hole Transfer to a MnOx Cocatalyst on a SrTiO3 Photoelectrode during Oxygen Evolution Studied by In Situ X-ray Absorption Spectroscopy

Photoexcited hole transfer to MnOx cocatalysts on SrTiO3 photoelectrodes was examined under controlled potential conditions during UV irradiation using in situ Mn K-edge X-ray absorption fine structure (XAFS) spectroscopy. The absorption edges of spectra were found to shift to higher energies during irradiation, indicating that MnOx cocatalysts were oxidized by the migration of photoexcited holes accompanied by a positive potential shift of the MnOx cocatalysts. This oxidation process was promoted by the application of a positive applied potential, suggesting that the photoexcited hole transfer was enhanced by upward band bending at the cocatalystphotoelectrode interface. Structural changes of the MnOx cocatalyst were found to depend on the UV photon intensity; thus, the observations of photoexcited electron transfer by XAFS are associated with the photoelectrochemical activity during water splitting.