Low‐Valence Metal Single Atoms on Graphdiyne Promotes Electrochemical Nitrogen Reduction via M‐to‐N2 π‐Backdonation

Abstract The M‐to‐N 2 π‐backdonation weakens the triple bond of N 2 and shall promote the sluggish electrochemical nitrogen reduction reaction (ENRR). By using weak σ‐ and π‐donating graphdiyne (GDY) as a supporting material, herein, a versatile approach is described to stabilize low‐valence metal single atoms (SA) on GDY (M SA/GDY; M = Cr, Mo, W, Mn, and Re). Under the rigorous ENRR protocol, an activity trend of Re SA/GDY > Mo SA/GDY > Cr SA/GDY > W SA/GDY >> Mn SA/GDY (no activity) is delivered. Theoretical calculations reveal that the strong M‐to‐N 2 π‐backdonation of Re SA/GDY renders a low energy requirement of +0.39 eV for the reductive hydrogenation of *N 2 to *NNH, which is considered as the bottleneck of ENRR. A novel NH 3 desorption mechanism through N 2 or H 2 O aided ligand exchange mechanism is proposed to facilitate the NH 3 desorption from Re SA/GDY with a low energy input of +0.83 eV for the distal and mix pathways. This study expands the scope of low‐valance SA with boosted π‐backdonation capacity and offers new mechanistic insights for ENRR.