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• A facile strategy to construct a similar coordination environment around the metal atom center using CB particles as substrates; • Both a high yield rate of 110.2 mmol g metal −1 h−1 at the potential of 0.3 V vs RHE and a high positive onset potential of 0.65 V vs RHE were achieved. • The active center was revealed for 2e−-ORR, including the Co-C 3 O 1 moiety as the first coordination and the epoxy group at ⑥ site in the second coordination sphere. • The practical application of CB-based SACs was evaluated in a wastewater treatment system including an H 2 O 2 electrolyzer and a Fenton filter. The coordination environment of transition metals in single-atom catalysts (SACs) is crucial for tuning the pathway of the electrocatalytic oxygen reduction reaction (ORR). However, it is significantly difficult to simultaneously and precisely control the first and second coordination structure near the metal active center. Herein, we report that the activated carbon black was used to anchor transition metals' single atoms with a similar first and second coordination structure. As a result, Co-SACs exhibit an extraordinary performance for ORR to produce H 2 O 2 , where a current density of around ∼2.8 mA cm−2 at 0.1 V vs RHE by rotating ring-disk electrodes and a high yield rate of 110.2 mmol g metal −1 h−1 at the potential of 0.3 V vs RHE in a gas diffusion electrodes (GDEs) cell, with a high positive onset potential of 0.65 V vs RHE and a >80% selectivity of H 2 O 2 at the potential range from 0.25 to 0.65 V vs RHE, respectively. The combined experimental observations and theoretical calculations indicate that the catalytic active center lies in the Co-C 3 /O 1 moiety of the adjacent epoxy group. The possible position of the epoxy group in the second coordination sphere was further revealed. Moreover, Co-SACs were employed in an electrocatalytic GDEs cell for distributed generation of H 2 O 2 in the acidic media, and coupling Fe-SACs-based Fenton filter or electro-Fenton setup with the H 2 O 2 electrolytic generator delivers an efficient and distributable wastewater treatment system. Our study provides a promising and alternative route for on-site H 2 O 2 production coupling the practical application process. [ABSTRACT FROM AUTHOR]