Square-Planar Tetranuclear Cluster-Based High-Symmetry Coordination Metal-Organic Polymers for Efficient Electrochemical Nitrate Reduction to Ammonia.

Metal-organic polymers (MOPs) are gaining booming attention as atomically precise single-site catalysts for electrochemical nitrate-to-ammonia conversion owing to their regular structures and tunable functionalities. However, a molecular-level understanding is still lacking for the design of more efficient MOP electrocatalysts. Here, we report the construction of high-symmetry coordination MOPs (, , and ), utilizing square-planar tetranuclear building units [M(μ-O)(CO)] (M = Mn, Fe, or Co) bridged by 2,4,6-tris(4-carboxyphenyl)-1,3,5-triazine (HTATB) ligands. These MOPs possess distinct coordination motifs with well-defined porosity, high-density catalytic sites, accessible mass transfer channels, and nanoconfined chemical environments. Benefited from the unique metal-organic coordination framework, demonstrated a remarkable ammonia production Faradaic efficiency (FE) of ∼98% across a wide potential range (-0.7 to -1.0 V (vs RHE)) in the electrocatalytic nitrate reduction reaction (NITRR) and maintained stable performance over a long duration when tested in a flow cell at an industrially relevant current density of ∼332.1 mA cm. Furthermore, in situ spectroscopic analyses, combined with theoretical calculations, elucidate the intrinsic reaction pathway of the model during the NITRR process. These findings offer insightful perspectives on the strategic design of electrocatalysts with symmetrical configurations for the purification of nitrate-containing wastewater and the green synthesis of ammonia.