Investigation of the enhanced photocathodic activity of La 5 Ti 2 CuS 5 O 7 photocathodes in H 2 evolution by synchrotron radiation nanospectroscopy.

The local electronic structures of La5 Ti2 MS5 O7 (M = Cu, Ag) particulate photoelectrodes with and without Ga doping were investigated, using a photoemission spectroscopy system with a lateral resolution of approximately 100 nm. The band alignments for La5 Ti2 MS5 O7 were determined on the basis of pinpoint photoemission spectra acquired at optimal positions on the sample surfaces. A clear upward chemical potential shift of approximately 0.35 eV was observed in the case of Ga-doped La5 Ti2 CuS5 O7 . On the other hand, the electronic structure of La5 Ti2 AgS5 O7 remained almost unaffected by Ga doping. These results explain the enhanced photocathodic response of La5 Ti2 CuS5 O7 upon Ga doping.