Fig. 2: Characterization of single atom catalysts.

a High-resolution HAADF image of Mn1@PNC, together with the three-dimensional (3D) profile of the local structure of the Mn1 atoms (b). c Schematic illustration of the working mechanism of atomic probe tomography. d 3D atomic distribution of the elements: C, N, S, and Mn, and (e) their corresponding overlapped 3D atomic distribution map. (f) 3D profiles of the local structures of the Co1, Ni1, Fe1, Sn1, and Cu1 atoms.