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

The electrochemical nitrate reduction reaction (NO3RR) offers a sustainable pathway for ammonia (NH3) synthesis under ambient conditions, concurrently addressing nitrate-contaminated water remediation. Oxygen vacancies (VO) 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 NO3RR, particularly under practical electrochemical conditions, remains poorly understood. Herein, we report the development of morphology-controlled copper-doped cerium oxide (Cu/CeO2) catalysts featuring facet-dependent and tunable VO concentrations. Notably, the rod-shaped Cu/R-CeO2, enriched with highly regenerable VO, demonstrates exceptional NO3RR performance, achieving a Faradaic efficiency (FE) of 90% and an NH3 production rate of 7.8 × 102 mmol/(gcat.·h) at −1.02 V vs reversible hydrogen electrode (RHE). In situ spectroscopic analyses reveal that VO facilitates water dissociation, thereby enhancing surface *H coverage, accelerating N-terminal hydrogenation on Cu sites, and maintaining catalytic activity via dynamic VO regeneration. These findings underscore interfacial defect engineering as an effective strategy for the rational design of high-performance NO3RR electrocatalysts.