Oxygen Vacancy-Promoted Electrochemical Nitrate-to-Ammonia Conversion over Copper-Doped Cerium Oxide

The electrochemical nitrate reduction reaction (NO 3 RR) offers a sustainable pathway for ammonia (NH 3 ) synthesis under ambient conditions, concurrently addressing nitrate-contaminated water remediation. Oxygen vacancies (V O ) in metal oxides have been recognized as pivotal defect sites that modulate surface electronic structures, optimize the adsorption of reaction intermediates, and facilitate essential reaction steps. Nevertheless, their mechanistic role in the NO 3 RR, particularly under practical electrochemical conditions, remains poorly understood. Herein, we report the development of morphology-controlled copper-doped cerium oxide (Cu/CeO 2 ) catalysts featuring facet-dependent and tunable V O concentrations. Notably, the rod-shaped Cu/R-CeO 2, enriched with highly regenerable V O, demonstrates exceptional NO 3 RR performance, achieving a Faradaic efficiency (FE) of 90% and an NH 3 production rate of 7.8 × 10 2 mmol/(g cat. ·h) at −1.02 V vs reversible hydrogen electrode (RHE). In situ spectroscopic analyses reveal that V O facilitates water dissociation, thereby enhancing surface *H coverage, accelerating N-terminal hydrogenation on Cu sites, and maintaining catalytic activity via dynamic V O regeneration. These findings underscore interfacial defect engineering as an effective strategy for the rational design of high-performance NO 3 RR electrocatalysts.