Identifying catalytic sites in oxygen-modified cobalt single atoms for H2O2 electrosynthesis and in situ realizing electro-Fenton process in acid

Cobalt single atom catalysts (Co SACs) have been extensively explored in catalyzing the two-electron oxygen reduction reaction (2e – ORR) into hydrogen peroxide (H 2 O 2 ). However, the contribution of active sites for 2e – ORR in different media remains elusive. Here, we synthesized epoxy-modified Co SACs through a chemical vapor deposition approach followed by an oxidation treatment, which provides a model catalyst to identify the distinct role of Co sites and oxygen species for 2e – ORR. It is found that Co sites dominantly function in acidic media and barely works in neutral solution. Introduction of epoxy groups in the vicinity of Co sites can enlarge interlayer spacing and reinforce Co–N strength, which facilitates O 2 transport and weakens Co–*OOH interaction, collectively contributing to a superior selectivity for acidic H 2 O 2 generation. While for neutral 2e – ORR, the O-containing groups distant from Co sites serve as the dominant active sites. Encouragingly, the onsite production of H 2 O 2 in the acidic solution can be efficiently utilized for pollutant removal.