In The main parameters of the three models are listed in which is larger than the cohesion energy of atomic iron (-1.9 eV) and bulk iron (-4.12 eV), indicating that single iron atom can be anchored firmly by nitrogen atoms on the catalyst substrate. The binding energy of Fe atoms on FeSA-N5-C catalyst is -10.05 eV, which is higher than that of Fe atoms on FeSA-N3-C (-4.79 eV) and FeSA-N4-C (-7.00 eV). It is shown that FeSA-N5-C is more structurally stable than the other two catalysts.