Oxide-modified bifunctional carbonaceous cathode: Oxygen-rich alkaline-like microenvironment strengthened hydrogen peroxide as an electron donor to enhance Fe3+ reduction in Fe(III) electro-Fenton

In this study, a novel Fe(III)-EF system was constructed with oxidized carbon black (OCB) modified carbon felt as the cathode and Fe(III) as the catalyst. X-ray photoelectron spectroscopy (XPS), N₂ adsorption-desorption isotherms and electrochemical analyses were used to characterize the materials. The results showed that the micro/mesoporous structure of the modified cathode could increase the local pH to form an oxygen-rich and locally alkaline-like microenvironment, accelerating the generation of intermediates (*O₂, *OOH) and thus realizing efficient H₂O₂ production. On the other hand, the oxygen-containing functional groups on the electrode surface increased the oxidation potential of Fe(III), making it easier for Fe(III) to gain electrons. With the complexation of -COOH with Fe(III), the electron density of Fe(III) migrated to the -COOH group, which decreased the charge transfer energy from H₂O₂ to Fe(III) and promoted the electron transfer from H₂O₂ to FeOH²⁺, enhancing the regeneration of Fe(II). Under the optimum conditions, 93.35 % Fe(II) conversion and 95 % Sulfamethazine removal were achieved within 1 hour. Finally, the application of Fe(III)-EF was investigated and the degradation of chemical oxygen demand (COD) in waste leachate by Fe(III)-EF system was 93.2 %. This indicates that the system is promising for the treatment of organic wastewater.