Theoretical study of N2 adsorption and dissociation on Ir/Cu loaded Ir(100) catalyst

Abstract

Electrocatalytic nitrogen reduction (NRR) is a promising method for NH3 synthesis. However, the design of catalysts with high activity for N2 dissociation remains a key challenge. Herein, we have designed several catalysts based on Ir, including pure Ir(100), and Ir(100) with Ir (Cu) atom loaded on it (denoted as Ir(a)@Ir(100) and Cu(a)@Ir(100)), to study the reactivity of N2 dissociation. The results showed that Ir(a)@Ir(100) and Cu(a)@Ir(100) can effectively activate NN bond with ultralow dissociation barriers of 0.31 eV and 0.61 eV. However, the adsorption strength of N2 is significantly poor on Ir(a)@Ir(100) (−0.24 eV) compared to that on Cu(a)@Ir(100) (−0.62 eV). This can be interpreted from the electronic properties: The Ir-5d states can hybridize with N-2π* states significantly near the Fermi level, which is absence for Cu-3d states. Therefore, the loaded Cu atom on Cu@Ir(100) can effectively decrease the occupation of N2 antibonding orbitals (ICOHP = −7.68) compared to the situation on Ir@Ir(100) (ICOHP = −7.35). Therefore, Cu(a)@Ir(100) can be screened as the favorable candidate although a little higher dissociation barrier of N2 (0.61 eV), compared to the situation on Ir(a)@Ir(100) (0.31 eV). However, a barrier of 0.61 eV can also be easily overcome at room temperature as 0.31 eV on Ir(a)@Ir(100). We firmly believe that this work can not only open a novel way for the design of Ir-based catalysts, but also provide a promising strategy of N2 dissociation for experimental works.