Fig. 2

Structural characterizations of single-Ni-atom catalyst by X-ray absorption spectroscopy. a Normalized Ni K-edge XANES spectra. b k3-weighted Fourier transform spectra from Ni K-edge EXAFS. c WT-EXAFS of Ni foil. d WT-EXAFS of NiO. e WT-EXAFS of Ni-NCNT/AC.