Fig. 1.

Schematic of sample preparation and transmission electron microscopic (TEM) studies. a Synthetic procedure of the Ru-NC-T samples. Te NWs denotes tellurium nanowires, Te@MF refers to tellurium nanowires with a melamine–formaldehyde resin shell, Ru-MF indicates the incorporation of ruthenium precursors into Te@MF, and Ru-NC-T signifies Ru,N-codoped carbon prepared by pyrolysis of the Ru-MF nanowires at different temperatures. b–d Representative TEM images of Ru-NC-800 at different magnifications. Scale bars are b 500 nm, c 50 nm, and d 5 nm. e High-angle annular dark-field scanning TEM image of the red area of c. The scale bar is 20 nm. f Cross-sectional elemental distributions by line scans along the red line in e. The colors of the elemental maps of C, N, O, Te, and Ru correspond to those in the line scan spectra. Scale bars are all 20 nm. g A zoom-in of e, where red arrows signify ruthenium single atoms. The scale bar is 1 nm