High-magnification TEM and corrected HAADF-STEM images for CuSA@HNCNx. The white dots are Cu single atoms. Inset (a) is the HRTEM image (upper left) and SAED pattern (bottom left), Partial density of states (PDOS) of b) Fe, c) Co, and d) Cu in FeSA@HNCNx, CoSA@HNCNx, and CuSA@HNCNx, respectively. The blue and black dashed lines represent the d-band center of Fe, Co and Cu, respectively, and the Fermi level. (Reprinted with permission;[41]Copyright 2020, Elsevier Ltd.).
