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 La5Ti2MS5O7 (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 La5Ti2MS5O7 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 La5Ti2CuS5O7. On the other hand, the electronic structure of La5Ti2AgS5O7 remained almost unaffected by Ga doping. These results explain the enhanced photocathodic response of La5Ti2CuS5O7 upon Ga doping.