Multimetallic synergy and interfacial regulation in MnCoFe-LDH cathode for efficient heterogeneous electro-Fenton...

The elimination of persistent antibiotic residues from water bodies poses a significant challenge for conventional advanced oxidation processes. Herein, an MnCoFe-LDH cathode was directly grown on graphite felt via a one-step hydrothermal method (MnCoFe-LDH@GF) to regulate the coupled generation and utilization of H₂O₂ for chlortetracycline (CTC) degradation. The incorporation of Mn, Co, and Fe created a more favorable interfacial environment for electro-Fenton reactions by regulating the material structure, surface chemical states, and charge-transfer behavior. In particular, the optimized MnCoFe-LDH contained relatively enriched low-valence Mn(II), Co(II), and Fe(II) centers together with abundant surface M-OH species, both of which were strongly correlated with H₂O₂ accumulation and CTC degradation, indicating their cooperative roles in oxygen reduction, interfacial redox cycling, and H₂O₂ activation. Consequently, MnCoFe-LDH@GF achieved a net H₂O₂ accumulation of 62.3 mg L^-1 and 93.3% CTC removal, outperforming the corresponding bimetallic cathodes. Mechanistic investigations further identified free •OH as the predominant oxidizing species, with high-valent metal-oxo species providing an auxiliary pathway, while divided-cell experiments distinguished the dominant cathodic ROS-mediated oxidation from the contribution of anodic oxidation. Combined DFT calculations and HPLC-MS analysis elucidated the susceptible reaction sites and transformation pathways of CTC. Moreover, the cathode exhibited good resistance to complex water matrices, low metal leaching, reduced effluent toxicity, and stable performance during continuous-flow operation. These findings demonstrate that coordinating H₂O₂ generation and activation through multimetallic redox centers and surface coordination regulation provides an effective strategy for designing efficient and durable HEF cathodes.