fig3

Figure 3. (A) Simplified schematic illustration of N₂ binding to single- and double-atom sites; (B) Computed molecular orbitals showing the electronic structure of free N₂ and N₂ absorbed on Pt₃/g-C₃N₃. The red dashed line is the d-band center; (C) The adsorption free energies ($$ \Delta G_{\ast \rm{N_{2}}} $$) of *N₂ on TM₃@C₃N₃. The number of CT of *N₂ with (D) side-on and (E) end-on configurations vs. its adsorption energies ($$ \Delta E_{\ast \rm{N_{2}}} $$); (F) The d-orbital center (ε_d) of TM₃@C₃N₃vs.$$ \Delta E_{\ast \rm{N_{2}}} $$. The inset is the differential charge density of N₂ on TM₃@C₃N₃ and TM₃@C₃N₃. CT: Charge transfers; DOS: density of states; TM: transition metal.