Electronic Metal–Support Interaction of Single‐Atom Catalysts and Applications in Electrocatalysis

Abstract

between the electronic structure and catalytic efficiency of heterogenous catalysts. Dating back to 1930s, the concept of "electronic factor" was proposed by G. M. Schwab to describe the influence of electronic interaction on catalytic behavior of supported catalyst and divided the interaction into two parts, structural and synergetic ones. [4] Electrons transferring between the metal and the support was first under consideration when it came to the catalysis. After that, S. J. Tauster used the term of "strong metal-support interaction" (SMSI) to describe the chemisorption properties of group VIII elements supported by a metal oxide (e.g. SiO 2 , MgO) in 1978. [5] Later the concept was broadened to interaction between any metallic species and support, based on the experimental phenomena. [6] Till that time, based on the early characterization of surface science, researchers had realized that the active site might change during the process from metallic to an SMSI state, which was indicated to be covered or encapsulated by the support. [7] Among many hypotheses concerning the mechanism of SMSI, electron transfer between the metal and the support has been adapted by many researchers, and was confirmed by Rodriguez based on X-ray crystallography and UV photoemission spectroscopy in 1990s. [8] Then almost at the same time that the term of SACs was formally put forward, C. T. Campbell proposed the concept of "electronic metal-support interaction" (EMSI). As Campbell described, the chemical and catalytic properties might be affected by the electronic perturbations (i.e., shifts in the energy of d-band center) due to the EMSI. [9] In other words, the EMSI gave a much more detailed explanation of the enhanced properties of supported catalysts than SMSI, indicating that the study on catalysis was finally pushed to the electronic scale after so many years. [9b,c,10] Unfortunately, for metal particles or clusters, the accurate identification of electronic state is often difficult or even impossible. [11] The most reliable way to overcome the barrier above is to develop the catalyst based on single-atom metal that avoids intrinsic metal effects, including the electronic quantum size effect as well as structure-sensitivity geometrical effect. [12] Therefore, the rise of SACs provides a nearly perfect model to study the EMSI. As the supported metal species downsize to the single atom, the interaction between active site and support is always uniform, which can be much easier to be characterized by both experiment and theoretical calculation. [13] With the help of advanced techniques, for instance, X-ray absorption spectroscopy (XAS), the information about electronic The electronic metal-support interaction (EMSI), which acts as a bridge between theoretical electronic study and the design of heterogenous catalysts, has attracted much attention. Utilizing the interaction between the metal and the support is one of the most essential strategies to enhance electrocatalytic efficiency due to structural and synergetic promotion. To ...

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