MOF-derived CoO@C electrocatalyst for atomic hydrogen-mediated reductive decomplexation of refractory Cu-complexes toward resource valorization

The electroplating industry generates massive volumes of wastewater laden with Cu-complexes, whose extraordinary stability renders conventional treatment methods ineffective and resource-wasting. Electrochemical reduction using atomic hydrogen (H*) has emerged as a promising alternative, yet its practical application is hampered by an inherent trade-off: catalytic surfaces must balance efficient H* generation from water splitting against suppression of H* recombination into H₂. Here, we overcome this dilemma by engineering a MOF-derived CoO@C composite with a nanoconfined architecture that spatially traps H* at the reactive interface, favoring its reaction with Cu-EDTA over parasitic H₂ evolution while enabling recovery of metallic Cu and intact ligands. Mechanistic investigations reveal that H* preferentially attacks coordinated Cu(II), forming a transient [Cu(I)-EDTA] intermediate that is subsequently reduced to metallic Cu, with the unaltered ligand released for potential reuse. This system achieves exceptional decomplexation efficiency for Cu-EDTA across a broad pH range (3-11) and demonstrates broad applicability to other Cu-complexes. When deployed in a laboratory-scale five-stage, series-connected flow-through reactor treating authentic electroplating effluent (0.55 mA/cm², initial Cu ∼50 mg/L, hydraulic retention time 2 h, the system maintains >97% Cu removal and reaches an EE_Cu of up to 196.3 g/kWh. A subsequent anodic stripping and acidification sequence yields high-purity Cu and H₄EDTA. Economic analysis projects a net profit of $1.27 per ton of wastewater, confirming commercial viability. Overall, this work offers an efficient solution for heavy metal complex remediation while establishing a resource-oriented paradigm that transforms hazardous effluents into recoverable assets.