TEM studies of Pt-NC and PtCo-NC nanowires. (a–c) HAADF-STEM images of Pt-NC-3. Insets of (b) are the EELS spectra at three selected areas. In (c), yellow circles signify Pt single atoms, blue circles highlight few-atom Pt2~7 clusters, and red circles denote Pt9 or larger clusters. (d) HAADF-STEM image of Pt-NC-4. (e) High-resolution TEM image of a Pt NP of Pt-NC-4. EDS elemental mapping studies of (f) Pt-NC-3 and (g) PtCo-NC-3. High-resolution TEM images of the (h) Pt-NC and (i) PtCo-NC samples.