The incorporation of oxygen functional groups (OFGs) into cobalt-nitrogen-carbon (CoNC) catalysts is widely regarded as a promising strategy for enhancing hydrogen peroxide (H₂O₂) electrosynthesis via the two-electron oxygen reduction reaction (2e⁻ ORR). However, the roles and effects of OFGs in CoNC catalysts on H₂O₂ electrosynthesis, especially on the actual production, remain unclear. Herein, we conducted a comprehensive investigation into a series of typical CoNC catalysts with or without OFGs for H₂O₂ electrosynthesis. Contrary to the traditional insight, our finding demonstrates that the incorporation of OFGs into CoNC leads to a notable decline in actual H₂O₂ productivity. Remarkably, this phenomenon occurs across diverse oxidizing agents and CoNC catalysts, indicating its generality. Mechanistic investigations reveal that the OFGs regulate the surface chemical states and interfacial hydrophobicities of CoNC, resulting in hindered O₂ diffusion, thus harming H₂O₂ productivity. This study not only clarifies the complex role of OFGs in CoNC catalysts for H₂O₂ electro-synthesis but also promotes their more extensive application in the field of electrocatalyst development.