Heteroatom substitution boosts Electrocatalytic Ammonia synthesis in porous coordination network

Metal-organic frameworks (MOFs) have recently emerged as promising platforms for electrocatalytic investigations. Nevertheless, precisely tuning their electrocatalytic performance through heteroatom substitution remains a significant challenge. Herein, we employ the trinuclear MOF PCN-250 (PCN = Porous Coordination Network) as a structural model and partially substitute Fe sites with Co and Ni ions. Remarkably, the introduction of Co ions substantially enhances the electrocatalytic nitrate reduction reaction (NO₃RR) performance, achieving an NH₃ yield rate of 27.669 mg h^-1 mg_cat^-1 and a Faradaic efficiency (FE) of 97.5 %, nearly 1.9 times and 2.5 times higher than those of PCN-250(Fe₃) and PCN-250(Fe₂Ni), respectively. Combined electrochemical analyses and density functional theory (DFT) calculations reveal that Co substitution not only lowers the energy barrier for *NO hydrogenation but also suppresses the competing hydrogen evolution reaction (HER), thereby accounting for the superior NO₃RR performance. This study demonstrates that rational heteroatom substitution offers an effective strategy for optimizing the electrocatalytic activity of MOF-based materials.