Active electronic structure derived by Fe-Cl-C coordination of single-atom cathode applied in antibiotics degradation by electro-Fenton: Enhanced transformation of oxygen to hydroxyl radicals via 3-electron pathway

•Electronic structure of Fe-Cl-C catalytic sites was tuned to enhance EF reaction.•Fe-Cl2C2 and Fe-Cl2C3 configurations were constructed with Fe2+ and Fe3+ states.•Reactions from O2 to •OH were verified via 3-electron pathway by two configurations.•FeCl2Cx/PC showed efficient antibiotics removal from water and structure stability.••OH as a major ROS contributed on AMX decaying by opening β-lactam ring.