fig7

Figure 7. Models of ONPC-900 surface by DFT calculation. The adsorption models for K⁺ are (A) on an ideal carbon surface; (B-C) on an undoped defect carbon surface; (D-I) on various O, N co-doped defect carbon surfaces, respectively. ONPC: O, N co-doped hierarchical porous carbon; DFT: Density functional theory.