fig9

Figure 9. (A) Top view of a single K atom absorbed in quaternary-N (N-Q), pyrrolic-N (N-5), and pyridinic-N (N-6). (B) The adsorption energy of different amounts of one N-6, two N-6, and three N-6. (C) The DOS of the defect site without N-doping, one, two, and three N-6 doping sites. (D) The barrier energy of one N-6, two N-6, and three N-6 doping sites. Copyright 2021, Electrochimica Acta^[75]. (E) The interlayer distances of different carbon structures before insertion of K⁺: pristine carbon, N-6 doped carbon, N-6/P-C co-doped carbon, and N-6/P-O co-doped carbon. (F) The layer spacing and adsorption energy of K⁺adsorbed by corresponding structures. (G) The DOS of different carbon structures. Copyright 2020, ACS Nano^[76].