fig4

Figure 4. (A) Schematic of the synthesis process and (B) N 1s of NPC. This figure is quoted with permission from Li et al.^[94]. The optimized model of a K ion adsorbed on (C) HPCNF, (D) N-HPCNF, (E) PN-HPCNF, and (F) corresponding barrier energy. This figure is quoted with permission from Hu et al.^[99]. The optimized model of a K ion adsorbed on (G) N-5, (H) N-6, (I) N-5-P, and (J) N-6-P; (K and L) DOS before and after a K ion absorption. This figure is quoted with permission from Wu et al.^[100].