Transition metal-tetracyanoquinodimethane monolayers as single-atom catalysts for the electrocatalytic nitrogen reduction reaction

Converting earth-abundant nitrogen into value-added chemical ammonia is a significant yet challenging topic. The electrocatalytic nitrogen reduction reaction (NRR), compared with the conventional Haber-Bosch process, is an energy-saving and environmentally friendly approach. Finding electrocatalysts which can activate nitrogen effectively and exhibit high selectivity and stability for the electrocatalytic NRR is a major task. Single-atom catalysts can act as a good solution. In this work, by means of first-principles density functional theory, molecular dynamics calculations, and a two-step screening process, we have studied 17 transition metal single atoms supported on tetracyanoquinodimethane monolayers (TM-TCNQ), and among them, Sc-TCNQ and Ti-TCNQ are found to be excellent candidates for NRR electrocatalysts. N-2 adsorption and activation are effective due to the 'acceptance-donation' mechanism and suitable electronic structure of TM-TCNQ. The Gibbs free energy diagram shows that Sc-TCNQ and Ti-TCNQ exhibit a low NRR overpotential of 0.33 and 0.22 V, respectively, through an enzymatic-consecutive mixed pathway. In addition, the selectivity of the NRR over the HER and stability of the Sc-/Ti-TCNQ monolayers are also validated. This work opens a new avenue for designing novel single-atom catalysts for the NRR as well as other catalytic applications.