Conversion of Nitrate\nto Ammonia by Amidinothiourea-Coordinated\nMetal Molecular Electrocatalysts with d−π Conjugation

The electrochemical reduction of nitrate to ammonia (NO<sub>3</sub>RR) provides a desired alternative of the traditional Haber–Bosch\nroute for ammonia production, igniting a research boom in the development\nof electrocatalysts with high activity. Among them, molecular electrocatalysts\nhold considerable promise for the NO<sub>3</sub>RR, suppressing the\ncompeting hydrogen evolution reaction. However, the complicated synthesis\nprocedure, usage of environmentally unfriendly organic solvents, and\npoor stability of Cu-based molecular electrocatalysts greatly limit\ntheir employment in NO<sub>3</sub>RR, and the development of desired\nCu-based molecular catalysts remains challenging. Herein, a simple\nnonorganic solvent involving a one-step strategy was proposed to synthesize\nd−π-conjugated molecular electrocatalysts metal–amidinothiourea\n(M-ATU). Cu-ATU is composed of Cu coordinated with two S and two N\natoms, whereas Ni-ATU is formed by Ni with four N atoms from two ATU\nligands. Remarkably, Cu-ATU with a Cu–N<sub>2</sub>S<sub>2</sub> coordination configuration exhibits superior NO<sub>3</sub>RR activity\nwith a NH<sub>3</sub> yield rate of 159.8 mg h<sup>–1</sup> mg<sub>cat</sub><sup>–1</sup> (−1.54 V) and Faradaic\nefficiency of 91.7% (−1.34 V), outperforming previously reported\nmolecular catalysts. Compared to Ni-ATU, Cu-ATU transfers more electrons\nto the *NO intermediate, effectively breaking the strong sp<sup>2</sup> hybridization system and weakening the energy of NO bonds.\nThe increase in free energy of *NO reduced the energy barriers of\nthe rate-determining step, facilitating the further hydrogenation\nprocess over Cu-ATU. Our work opened up a new horizon for exploring\nmolecular electrocatalysts for nitrate activation and paved a way\nfor the in-depth understanding of catalytic behaviors, aligning more\nclosely with industrial demands.