Synergizing Mo Single Atoms and Mo₂C Nanoparticles on CNTs Synchronizes Selectivity and Activity of Electrocatalytic N₂ Reduction to Ammonia

Abstract

Previous research of molybdenum-based electrocatalysts for nitrogen reduction reaction (NRR) has been largely considered on either isolated Mo single atoms (MoSAs) or Mo carbide particles (e.g., Mo₂ C) separately, while an integrated synergy (MoSAs-Mo₂ C) of the two has never been considered. The theoretical calculations show that the Mo single atoms and Mo₂ C nanoparticles exhibit, respectively, different catalytic hydrogen evolution reaction and NRR selectivity. Therefore, a new role-playing synergistic mechanism can be well enabled for the multistep NRR, when the two are combined on the same N-doped carbon nanotubes (NCNTs). This hypothesis is confirmed experimentally, where the MoSAs-Mo₂ C assembled on NCNTs (MoSAs-Mo₂ C/NCNTs) yields an ammonia formation rate of 16.1 µg h^-1 cm_cat ^-2 at -0.25 V versus reversible hydrogen electrode, which is about four times that by the Mo₂ C alone (Mo₂ C/NCNTs) and 4.5 times that by the MoSAs alone (MoSAs/NCNTs). Moreover, the Faradic efficiency of the MoSAs-Mo₂ C/NCNTs is raised up to twofold and sevenfold of the Mo₂ C/NCNTs and MoSAs/NCNTs, respectively. The MoSAs-Mo₂ C/NCNTs also demonstrate outstanding stability by the almost unchanged catalytic performance over 10 h of the chronoamperometric test. The present study provides a promising new prototype of synchronizing the selectivity and activity for the multistep catalytic reactions.