Figure 13.

Examples of how nitrogen atoms can be incorporated into the graphene layer: (1) and (3) deformational substitutions; (2) and (4) deformational substitutions with a vacancy; (6) “nitrogen gap” (three ‘pyridinic’-like nitrogen atoms, that all lead to a higher degree of freedom of the lattice); (5) molecules of nitrogen entrapped between adjacent graphene layers. The types of nitrogen-doping can be referred to ‘pyridinic-‘, ‘pyrrolic-‘ and ‘azepinic-like’ in analogy to the nomenclature of simple heterocyclic molecules.