Fig. 3.

a XPS survey spectra of PC, NC-1, NC-3, and NC-6. b Atomic ratio of O/C and N/C in PC, NC-1, NC-3, and NC-6. High-resolution XPS spectra of N 1 s for c NC-1, d NC-3, and e NC-6. f Schematic illustration of N-containing species incorporated in the graphene plane of the NC-X samples