N-doping activated carbon cathodes for electro-Fenton regeneration of benzene-loaded activated carbon: Mechanistic insights and performance enhancement

This work presents a systematic investigation of the electro-Fenton (EF) regeneration of benzene-saturated activated carbon (AC). Particular attention was given to elucidating how pre-adsorbed benzene molecules interfere with O 2 adsorption and the two-electron oxygen reduction reaction (2e-ORR) on AC cathodes, as well as to clarifying the mechanistic role of nitrogen doping (N-doping) in improving regeneration performance. The findings demonstrate that benzene molecules strongly inhibit O 2 uptake and H₂O₂ generation on pristine AC, thereby limiting its regeneration efficiency. In contrast, N-doping markedly enhances both O 2 adsorption and ORR activity in benzene-saturated carbons. Among different nitrogen functionalities, pyridinic nitrogen promotes synergistic benzene-O₂ adsorption and increases H₂O₂ yield. Graphitic nitrogen, although unfavorable for O₂ adsorption, still contributes to H₂O₂ generation. Pyrrolic nitrogen, by comparison, imposes a strong site competition effect that significantly suppresses the 2e-ORR. Notably, ACN-750 deliver superior regeneration efficiency, excellent cycling stability, and lower energy consumption. Overall, N-doping provides a highly effective strategy to boost the EF regeneration of spent AC, offering new opportunities for its efficient reuse and sustainable recycling.