Recent Developments of High Energy Resolution X-Ray Spectroscopic Methods for Energy Materials at NSLS-II

X-ray absorption spectroscopy (XAS), first used to be applied in the field of energy materials, such as catalysts, over 50 years ago, has evolved into an indispensable tool in the arsenal of characterization techniques. XAS is element-specific method which compatible with a variety of sample environments, enabling in situ and operando experiments. An extension of XAS spectroscopy, high energy resolution (HR) X-ray spectroscopy, a collection of techniques which resolves the energy of the fluorescence photons with high accuracy, opened new opportunities in the field [1]. Among these methods is a high-energy resolution fluorescence detection (HERFD) XAS allows to overcome the limitations of traditional XAS by selectively detecting fluorescence photon within narrow energy band. Another is Valence-to-Core X-ray Emission Spectroscopy (VtC XES) which probes electronic states in the valence band, making is a far more sensitive to subtle electronic changes than the traditional Extended X-ray Absorption Fine Structure (EXAFS). In this contribution we review recent innovations at the National Synchrotron Light Source II (NSLS-II) which enable applications of HR XAS to energy-relevant systems as well as several examples to demonstrate the advantages of these techniques.