We report the discovery of a dramatically enhanced N-2 electroreduction reaction (NRR) selectivity under ambient conditions via the Lit incorporation into poly(N-ethyl-benzene-1,2,4,5-tetracarboxylic diimide) (PEBCD) as a catalyst. The detailed electrochemical evaluation and density functional theory calculations showed that Li+ association with the O atoms in the PEBCD matrix can retard the HER process and can facilitate the adsorption of N-2 to afford a high potential scope for the NRR process to proceed in the "[O-Li+]center dot N-2-H-x" alternating hydrogenation mode. This atomic scale incorporation strategy provides new insight into the rational design of NRR catalysts with higher selectivity.