Ammonia electro-oxidation is an extremely significant reaction with regards to the nitrogen cycle, hydrogen economy, and wastewater remediation. The design of efficient electrocatalysts for use in the ammonia electro-oxidation reaction (AOR) requires comprehensive understanding of the mechanism and intermediates involved. In this study, aggregation-induced emission (AIE), a robust fluorescence sensing platform, is employed for the sensitive and qualitative detection of hydrazine (N2H4), one of the important intermediates during the AOR. Here, we successfully identified N2H4 as a main intermediate during the AOR on the model Pt/C electrocatalyst using 4-(1,2,2-triphenylvinyl)benzaldehyde (TPE-CHO), an aggregation-induced emission luminogen (AIEgen). We propose the AOR mechanism for Pt with N2H4 being formed during the dimerization process (NH2 coupling) within the framework of the Gerischer and Mauerer mechanism. The unique chemodosimeter approach demonstrated in this study opens a novel pathway for understanding electrochemical reactions in depth.