3.6 Selectivity and thermostability of filtrated TM2@sitex (x = 1, 2, 3, 4) systems
For eNRR performance in many studies, the competitive hydrogen evolution reaction (HER) is the major hamper for ammonia yield. Thus, it is necessary to compare N2 and H atom adsorption strength. As depicted in Figure 7 , for all the selected systems, the Gibbs free energy of *N2 is smaller than the corresponding *H (mean the ΔG*N2 is more negative) and can be regarded as efficient adsorption of N2, thus inhibiting the competitive HER. Therefore, the Ru2@site1, W2@site2, and W2@site4 may not be suitable for the eNRR of the HER competition. Therefore, they are excluded from eNRR exploration. Among the rest systems with high activity eNRR performance, high stability is required for Mn2@site1, Co2@site2, Os2@site3, V2@site4, and Cr2@site4 systems. Herein, the AIMD simulation is performed at 300 K for 9 ps within a step of 1.5 fs are employed. As shown in Figure 7 (b)-(f) , after simulation, the structures of the selected systems are well maintained, meaning that the systems chosen could keep their geometry under 300 K. At the same time, the changes in temperature and energy are slightly, further revealing the thermostability of the selected systems. Thus, the Mn2@site1, Co2@site2, Os2@site3, V2@site4, and Cr2@site4 would keep stable during the eNRR process.