X‐Ray Methods for the Study of Electrode Interaction

Abstract

X‐ray methods provide an excellent tool for the determination of the structure and composition of the electrode/solution interphase. The possibility of carrying out in situ experiments, because of the low absorbability of the X‐rays by the solution, allows direct correlation to be made between the structural changes observed in the sample and the potential applied. Depending on the interaction of the X‐rays with matter, these techniques can be classified in two main groups: X‐ray absorption techniques and X‐ray scattering techniques. Within the absorption techniques, extended X‐ray absorption fine structure (EXAFS) and X‐ray absorption near edge structure (XANES) will be considered. EXAFS allows determination of the short‐range order of the sample, i.e. it provides information about the nature and distances of the closest neighbors to the absorbing atom. On the other hand, identification of the oxidation state of the absorbing atom can be done with XANES. Grazing incident X‐ray diffraction (GIXD) and crystal truncation rod (CTR) measurements belong to the scattering techniques. The information obtained from these measurements can be considered complementary since GIXD allows precise determination of the long‐range order structure of the interphase whereas CTR analysis gives information about the out‐of‐plane structure of the interphase. The last technique covered, X‐ray standing waves (XSW), is not a pure scattering technique, but rather one that combines X‐ray scattering and X‐ray interference. With this last technique, the exact position of a foreign atom in the interphase can be determined.