fig4

Figure 4. Composition and surface analysis of ONPC materials. (A) FTIR spectra; (B) Raman spectra; (C) Full XPS survey; High-resolution XPS spectra of (D) C 1s, (E) N 1s, and (F) O1s; (G) Relative content of C, N, and O; (H) Relative content of O species; (I) Relative content of N species. ONPC: O, N co-doped hierarchical porous carbon; FTIR: Fourier transforms infrared; XPS: X-ray photoelectron spectroscopy.