Molybdenum Based 2D Conductive Metal–Organic Frameworks as Efficient Single-atom Electrocatalysts for N2 Reduction: A Density Functional Theory Study

Electrocatalytic nitrogen reduction reaction (NRR) is a sustainable and eco-friendly process to generate ammonia (NH3). However, there are significant challenges including low catalytic performance, instability, and poor selectivity, which hinder its rapid development. Herein, a series of two-dimensional (2D) conductive metal-organic frameworks (i.e., TM3(HHTT)2, TM = Sc, Ti, V, Cr, Mo, W, Mn, Fe, Co, Ni, Cu and Zn) are investigated as single atom catalysts (SACs) for NRR process by the density functional theory (DFT). The obtained results of Gibbs free energies of adsorption for N2, *NNH, *NH3, which are commonly used as activity descriptors to screen the effectiveness of catalysts, show that the Mo3(HHTT)2 monolayer (among all the TM3(HHTT)2 ones) can activate N≡N bonds, stabilize the adsorbed *NNH, and achieve the desorption of NH3. The Mo3(HHTT)2 monolayer also exhibits an excellent structural stability (with values of Ef = -2.96 eV and Udiss = 1.28 V). N2 can be effectively reduced into NH3 on the Mo3(HHTT)2 monolayer with a low limiting potential of -0.60 V along the distal pathway. Furthermore, the σ-donation and π* backdonation of N2 adsorbed onto the Mo3(HHTT)2 monolayer indicates an excellent electrical conductivity of Mo3(HHTT)2, which is beneficial for the effective electron transfer during the NRR process. Furthermore, the Mo3(HHTT)2 monolayer exhibits considerable selectivity for the NRR process over the hydrogen evolution reaction. Our study proved that this 2D c-MOFs carrying TM of the Mo3(HHTT)2 monolayer can be used as a promising catalyst for nitrogen fixation.