fig2

Figure 2. XPS spectra of (A) Cu 2p; (B) O 1s for Cu SAC; (C) Normalized Cu K-edge XANES spectra; (D) FT-EXAFS spectra of Cu SAC; (E) EXAFS fitting and (inset) optimized model for Cu SAC; (F) Formation energy of Cu-N_xO_4-x (x=0-4) configurations with the coordination number of first-shell N/O species from DFT calculations. Color scheme: C atoms are grey, O atoms are red, N atoms are blue, and Cu atoms are orange. XPS: X-ray photoelectron spectroscopy; SAC: single atom catalyst; XANES: X-ray absorption near edge structure; EXAFS: extended X-ray absorption fine structure; DFT: density functional theory; FT-EXAFS: fourier transforms of extended X-ray absorption fine structure.