Highly N2 dissociation catalyst: Ir(100) and Ir(110) surfaces

Density functional theory (DFT) was performed to systematically study the adsorption and dissociation of N2 on Ir(100) and Ir(110) surfaces. By analyzing the properties, including adsorption energies, reaction barriers, and optimal adsorption sites, the hollow (H) sites were finally identified as favorable dissociation sites for N2. The dissociation barriers of N2 are 0.87 eV on Ir(100) and 1.12 eV on Ir(110), which can be overcome at around 348 and 448 K, respectively. Therefore, Ir(100) is screened as a promising catalyst for N2 dissociation compared to Ir(110). This can be attributed to the significantly higher adsorption energy of N2 on the H site of Ir(100) (-0.48 eV) compared to that on Ir(110) (-0.22 eV), leading to different dissociation mechanisms on Ir(100) and Ir(110). Ir(100) can dissociate N2 directly on H site and Ir(110) should firstly capture N2 via bridge site and further transfer the adsorbed N2 to the H site, which will dramatically deteriorate the reactivity of N2 dissociation. In addition, the following protonation processes of dissociated *N atoms are all exothermal at 348 K on Ir(100), indicating that the ammonia synthesis can occur spontaneously as the temperature higher than 348 K. These results have provided a reasonable materials design scheme for subsequent ammonia synthesis.