Dual-cathode synergy in heterogeneous electro-Fenton: Copper-driven H2O2 activation for efficient leachate nanofiltration concentrate treatment

The heterogeneous electro-Fenton (EF) process is a promising advanced-oxidation technology for treating recalcitrant landfill leachate nanofiltration concentrate (LNC), yet single-cathode or homogeneous EF systems remain limited by iron-sludge generation, narrow pH windows and sub-optimal coupling between H₂O₂ production and activation. Here we engineer a dual-cathode heterogeneous EF (DEF) reactor that spatially decouples (i) high-rate in situ H₂O₂ electrosynthesis on a carbon-black modified Ni-foam gas-diffusion cathode, from (ii) efficient copper-activated Fenton-like decomposition of H₂O₂ on a Cu-coated Ni-foam cathode. The synergistic, reagent-free configuration operates from pH 3–7 without external Fe²⁺ dosing and produces negligible metal sludge. Under the optimum current (0.718 A) and pH 3.5 determined by response-surface methodology, the DEF removed 72.74 % COD and 65.31 % TOC from real LNC within 120 min at an energy demand of 128 kWh/kg TOC—54 % lower than anodic oxidation—and maintained >90 % activity after five reuse cycles with ∼0.715 mg/ Cu leaching. Electron paramagnetic resonance (EPR) spectroscopy verified ·OH and ·O₂⁻ as the dominant oxidant, generated via a surface Cu⁰/Cu⁺/Cu²⁺ redox cycle that accelerates H₂O₂ decomposition. Compared with homogeneous EF and single-cathode heterogeneous EF benchmarks, the DEF offers comparable mineralization yet superior energy efficiency and zero-sludge operation, providing a scalable strategy for treating refractory industrial effluents.