Mo-X ₄ (X = O, NH and S)-mediated triphenylene-based two-dimensional carbon-rich conjugate frameworks for an efficient nitrogen reduction reaction

The electrocatalytic nitrogen reduction reaction (NRR) is a highly competitive approach for the ammonia synthesis to overcome the problems of high energy consumption and air pollution by the traditional Haber-Bosch process. However, the challenges of inert N₂ molecule activation and the competitive hydrogen evolution reaction (HER) restrict the real utilization of the NRR. Herein, by means of density functional theory (DFT) calculations, we proposed three two-dimensional carbon-rich conjugate frameworks (2D-CCFs) with hexa-substituted triphenylene organic linkers with a metal atom Mo and functional groups X (X = O, NH, and S), namely Mo₃(HOTP)₂, Mo₃(HITP)₂ and Mo₃(THT)₂, to investigate their NRR performance. Our theoretical calculations reveal that Mo atoms in 2D-CCFs can efficiently capture and activate N₂ molecules. Among the three structures, Mo₃(HOTP)₂ exhibited the most superior performance toward the NRR with a favorable limiting potential of -0.41 V and good selectivity for the HER. Furthermore, the catalytic efficiency of 2D-CCFs can be regulated by changing the atoms X in Mo-X₄ motifs, providing a new scenario for the development of highly efficient NRR catalysts.