Fig. 1: Physical characterization.

a TEM, scale bar: 200 nm; b HR-TEM, scale bar: 10 nm; and c, d Aberration-corrected STEM images; scale bar: 5 nm of c and 2 nm of d; e HAADF-STEM images of Co–N–C; STEM-mapping of N-K; C-K; Co-K, scale bar: 50 nm; f Normalized Co K-edge XANES spectra (inset is the magnified image of f in the range of 7718–7722 eV) and g Co K-edge EXAFS spectra of Co–N–C and references.