Cathodically intensified PFAS defluorination in a flow-through electrochemical reactor using a Cu/Mn–N–C lignin-derived gas-diffusion cathode

Per - and polyfluoroalkyl substances (PFAS) are highly persistent aquatic contaminants whose electrochemical destruction is often constrained by slow mass transfer, high energy demand, incomplete defluorination, and accumulation of short-chain fluorinated intermediates. Herein, a Fe-free Cu/Mn–N–C gas-diffusion cathode was developed from rice-straw lignin and integrated with a Ti₄O₇ anode in a three-dimensional flow-through electrochemical reactor for cathodically intensified PFOA and PFOS defluorination. The optimized CuMnNC-LC catalyst possessed a defect-rich porous carbon framework, N-coordinated metal sites, and multivalent Cu/Mn redox centers, enabling efficient O₂ delivery, rapid interfacial electron transfer, and enhanced two-electron oxygen reduction. The CuMnNC-LC@GDE cathode generated more than 150 mg L −1 H₂O₂ and produced multiple reactive oxygen species, including •OH, O₂• − , and 1 O₂. Coupling this cathode with Ti₄O₇ substantially improved PFAS degradation compared with adsorption, anode-only, cathode-only, and non-gas-diffusion controls. Under standard conditions, the full system achieved approximately 95% PFOA removal and 90% PFOS removal, while the optimized regime reached 99.1% PFOA removal, 99.3% PFOS removal, 66.3% PFOA defluorination, and 49.8% PFOS defluorination. Short-chain PFAS evolution, fluoride release, adsorbable organic fluorine reduction, and fluorine-balance analysis confirmed true destructive transformation rather than simple parent-compound disappearance. The cathode also exhibited stable operation over 100 h, limited Cu/Mn leaching, and good reusability over ten cycles. Energy analysis showed low EE/O and specific defluorination-energy demand, demonstrating a favorable balance between PFAS destruction and electrical input. This work provides a sustainable strategy for upgrading agricultural lignin waste into functional gas-diffusion cathodes for energy-efficient PFAS defluorination.