Operando Tracking of Hydrazine Intermediate Reveals the Gerischer–Marcus Pathway for Ammonia Electrooxidation on Oxygen‐Deficient CuO

The ammonia electrooxidation reaction (AOR) represents a pivotal process for sustainable energy technologies, yet its mechanism on non-precious metal catalysts remains ambiguous, primarily due to the elusive nature of key reaction intermediates. Specifically, the role of oxygen vacancies (Ov) in steering the AOR pathway is not well understood. Herein, we directly captured the hydrazine (N₂H₄) intermediate, which unequivocally confirms the operation of the Gerischer-Marcus (G-M) pathway on oxygen-deficient copper oxide (CuO). This breakthrough was enabled by an aggregation-induced emission electrochemiluminescence (AIE-ECL) probe, which allows quantitative, real-time detection of N₂H₄ with ultrahigh sensitivity (0.163 nM). The direct visualization of probe consumption via fluorescence microscopy imaging provided orthogonal validation. Combined with in situ spectroscopy and DFT calculations, we establish that oxygen vacancies (Ov) act as a "steering wheel" to preferentially stabilize N₂H₄ and channel the reaction preferentially along the G-M route. A direct correlation between Ov concentration and N₂H₄ accumulation is demonstrated, linking atomic-scale defect structure to macroscopic catalytic performance. This work not only presents a paradigm for probing elusive electrocatalytic intermediates but also delivers a fundamental principle for influencing reaction pathways through defect engineering.