In situ investigation of the solid/electrolyte interface in photo-electrochemical conditions using surface X-ray diffraction

A custom setup was developed at Diamond Light Source for photo-electrochemical experiments probing the structure of solid/liquid interfaces in situ using surface X-ray diffraction (SXRD). Clean surfaces are prepared in ultra-high vacuum (UHV) by standard methods and pre-characterised using e.g. X-ray photoelectron spectroscopy and scanning tunnelling microscopy. Samples can be transferred under UHV into the chamber and mounted on a diffractometer for SXRD structure determination under UHV. The pristine surface is then contacted with a drop of electrolyte to study the solid/liquid interface with SXRD also under influence of an external potential and UV/visible light exposure.
The interface between the rutile TiO₂(110) and various electrolytes was investigated to evidence structural changes occurring during the water splitting reaction. Crystal truncation rod analysis showed that the TiO₂(110)/NaOH(0.1M) interface is composed of a Na layer adsorbed in a tetra-dentate site sandwiched between two layers of O species. In the case of TiO₂(110)/HCl(0.1M), Cl atoms are adsorbed directly on Ti_5c sites and covered by O atoms bridging between Cl atoms.