Photoelectrochemical mechanisms may be characterised by potential-dependent structural changes of the photoactive interfaces. These may include stoichiometric changes (e. g. intercalation or excalation of ionic species), phase changes or dynamic molecular changes of photocatalytic species. In all these cases, time-dependent structural information is desirable. This may be accomplished with in-situ X-ray and EXAFS (X-ray absorption fine structure) techniques. For such measurements, the electrochemical cell is integrated into a ‘Plexiglass’ body covered with Capton layers that are penetrated by the X-rays from the diffractometer source or the synchrotron (EXAFS), which are incident at a low grazing angle, as shown in Fig. 12.38.
Schubert et al. (1996) undertook in-situ X-ray studies to determine the origin of H2O2 production during oxygen reduction at transition-metal cluster materials. They observed that H2O2 generation increased from an originally very low level due to oxidation of the material and excalation of inserted metal species from inside of the material. Alonso-Vante and Borthen (1997) performed in-situ EXAFS studies to investigate whether a RuMo-cluster catalyst changes its structure during oxygen reduction. They found that the Ru-Ru distance changes, but not the Mo-Mo distance.
Figure 12.38 Cell for in-situ X-ray and EXAFS studies of interfacial electrochemical processes.