Chemical Identification of Catalytically Active Sites on Oxygen‐doped Carbon Nanosheet to Decipher the High Activity for Electro‐synthesis Hydrogen Peroxide

Electrochemical production of hydrogen peroxide (H 2 O 2 ) through two‐electron (2 e − ) oxygen reduction reaction (ORR) is an on‐site and clean route. Oxygen‐doped carbon materials with high ORR activity and H 2 O 2 selectivity have been considered as the promising catalysts, however, there is still a lack of direct experimental evidence to identify true active sites at the complex carbon surface. Herein, we propose a chemical titration strategy to decipher the oxygen‐doped carbon nanosheet (OCNS 900 ) catalyst for 2 e − ORR. The OCNS 900 exhibits outstanding 2 e − ORR performances with onset potential of 0.825 V (vs. RHE), mass activity of 14.5 A g −1 at 0.75 V (vs. RHE) and H 2 O 2 production rate of 770 mmol g −1  h −1 in flow cell, surpassing most reported carbon catalysts. Through selective chemical titration of C=O, C−OH, and COOH groups, we found that C=O species contributed to the most electrocatalytic activity and were the most active sites for 2 e − ORR, which were corroborated by theoretical calculations.