fig1
![Regulating the electrocatalytic performance for nitrogen reduction reaction by tuning the N contents in Fe<sub>3</sub>@N<sub><i>x</i></sub>C<sub>20-<i>x</i></sub> (<i>x</i> = 0~4): a DFT exploration](https://image.oaes.cc/c34e0cfd-09e1-4115-bfa7-82756240306d/jmi3032.fig.1.jpg)
Figure 1. (A) Top and side views of the optimized 2D Fe3@C20 monolayer with the unit cell marked by black solid lines; (B) the partial density of states of the d orbitals of Fe atoms (red), and the DOS of the Fe3@C20 monolayer (black) with the Fermi level indicated by the red dashed line.