Probe active sites of heterogeneous electrocatalysts by X-ray absorption spectroscopy: From single atom to complex multi-element composites

As the design of heterogeneous electrocatalysts is entering the 'atom' age, synchrotron radiation-based X-ray absorption spectroscopy (XAS) has started to expand its strategic presence in electrocatalysis. XAS has demonstrated its usefulness in determining the electronic and geometric structures of supported single atom catalysts thanks to its high sensitivities towards elemental, chemical, and orbital determination. Nowadays, it is expected that the role of XAS will further increase as current research interests are shifting to more complex size-selected single-or multi-element atomic clusters, including challenging electrochemical processes. This review discusses the latest applications of XAS in characterization of electrocatalysts with atomic dispersion, such as single atoms and clusters. Involved advanced analyses methods like wavelet transform, as well as outlooks and challenges for revealing the dynamic behaviours of catalytic active sites using in-situ XAS are also presented and discussed.