Going beyond atom visualization—Characterization of supported two-atom single-cluster catalysts with scanning transmission electron microscopy

As an innovative development of single-atom catalysts (SACs), single-cluster catalysts (SCCs) such as dual-atom catalysts have attracted considerable interest due to their excellent performance in catalysis. As one of the most powerful and visualizable tools, scanning transmission electron microscopy (STEM) has been widely applied in the characterization of SCCs. Herein, the nitrogen-doped carbon-supported FeFe and CoFe, two representative examples of homonuclear and heteronuclear SCCs, are characterized by STEM. Furthermore, an image processing program is developed to analyze the STEM images and to obtain the locations of atoms, as well as the projected distances between atoms in possible dual-atom pairs. The dimer distances of both CoFe and FeFe catalysts exhibit a trimodal distribution, which can correspond to the energy-favorable atomic structures of the theoretical simulations. Our work offers an avenue for directly revealing the possible atomic configurations of dual-atom sites in SCCs via big data statistics of STEM images and strong theoretical simulations.