EXAFS, XANES, SXS

This chapter describes the application of in situ surface X-ray scattering (SXS) and X-ray absorption spectroscopy (XAS) to the problems of fuel cell electrocatalysis. It is shown that SXS is well suited for studying single crystal electrode surfaces during electrocatalytic reactions. The structure of surfaces and surface adlayers which exhibit long range order can be probed with high accuracy and a quantitative measure of potential induced structural phase transitions can be obtained. XAS is sensitive to both structural and chemical information and can be applied to polycrystalline electrocatalysts under in situ conditions. A great advantage is that XAS is element-specific, and this permits investigation of the chemical environment of a constituent element in a composite material such as alloy catalysts. Since XAS probes only short-range order, it can provide structural information on amorphous materials, liquids, gases, adsorbed monolayers, as well as hydrated ions and complexes in aqueous solution. A major advantage of XAS in the study of electrocatalysts is its ability to probe the d states of Pt catalysts. Keywords: surface X-ray scattering; X-ray absorption spectroscopy; single crystal surfaces; adlayer structures; nanoparticle electrocatalysts; electrocatalytic reactions