Vacancy-Mediated Control of Local Electronic Structure for High-Efficiency Electrocatalytic Conversion of N 2 to NH 3 .

Ambient electrocatalytic nitrogen (N 2 ) reduction has gained significant recognition as a potential substitute for producing ammonia (NH 3 ). However, N 2 adsorption and *NN protonation for N 2 activation reaction with the competing hydrogen evolution reaction remain a daunting challenge. Herein, a defect-rich TiO 2 nanosheet electrocatalyst with PdCu alloy nanoparticles (PdCu/TiO 2-x ) is designed to elucidate the reactivity and selectivity trends of N 2 cleavage path for N 2 -to-NH 3 catalytic conversion. The introduction of oxygen vacancy (OV) not only acts as active sites but also effectively promotes the electron transfer from Pd-Cu sites to high-concentration Ti 3+ sites, and thus lends to the N 2 activation via electron donation of PdCu. OVs-mediated control effectively lowers the reaction barrier of *N 2 H and *H adsorption and facilitates the first hydrogenation process of N 2 activation. Consequently, PdCu/TiO 2-x catalyst attains a high rate of NH 3 evolution, reaching 5.0 mmol g cat. -1  h -1 . This work paves a pathway of defect-engineering metal-supported electrocatalysts for high-efficient ammonia electrosynthesis.