Ru‐Induced Defect Engineering in Co 3 O 4 Lattice for High Performance Electrochemical Reduction of Nitrate to Ammonium

Abstract Amidst these growing sustainability concerns, producing NH 4 + via electrochemical NO 3 − reduction reaction (NO 3 RR) emerges as a promising alternative to the conventional Haber‐Bosch process. In a pioneering approach, this study introduces Ru incorporation into Co 3 O 4 lattices at the nanoscale and further couples it with electroreduction conditioning (ERC) treatment as a strategy to enhance metal oxide reducibility and induce oxygen vacancies, advancing NH 4 + production from NO 3 RR. Here, supported by a suite of ex situ and in situ characterization measurements, the findings reveal that Ru enrichment promotes Co species reduction and oxygen vacancy formation. Further, as evidenced by the theoretical calculations, Ru integration lowers the energy barrier for oxygen vacancy formation, thereby facilitating a more energy‐efficient NO 3 RR‐to‐NH 4 + pathway. Optimal catalytic activity is realized with a Ru loading of 10 at.% (named 10Ru/Co 3 O 4 ), achieving a high NH 4 + production rate (98 nmol s −1 cm −2 ), selectivity (97.5%) and current density (≈100 mA cm −2 ) at −1.0 V vs RHE. The findings not only provide insights into defect engineering via the incorporation of secondary sites but also lay the groundwork for innovative catalyst design aimed at improving NH 4 + yield from NO 3 RR. This research contributes to the ongoing efforts to develop sustainable electrochemical processes for nitrogen cycle management.