Unlocking Clean and Efficient Treatment of Hypersaline Wastewater via Synergistically Triggered Oxidation–Reduction Pathways on a Bifunctional Cathode

The electrochemical treatment of hypersaline wastewater is a double-edged sword: chloride-derived reactive chlorine species enhance oxidation but inevitably yield toxic chlorinated byproducts, limiting its environmental sustainability. To address this issue, we developed an advanced photoelectrochemical (PEC) system featuring a novel bifunctional Co 3 O 4 /g-C 3 N 4 (Co/CN) cathode that synergistically couples oxidative and reductive pathways to minimize chlorinated byproducts. The cathode simultaneously enables rapid H*-mediated dechlorination and the generation of H 2 O 2, which then reacts with anodic free chlorine to form 1 O 2, reducing chlorinated byproducts significantly. The developed Chlorination-Dechlorination-Mineralization (PEC/Cl/H 2 O 2 –CDM) system demonstrated a 1.86- to 2.38-fold enhancement in TOC removal efficiency, a 46.3–58.0% reduction in energy consumption, and a substantial decrease in acute toxicity relative to conventional PEC systems. Theoretical calculations further revealed that reductive dechlorination effectively lowers the energy barrier, making the dechlorinated intermediates more susceptible to radical attacks. Moreover, this system demonstrated a broad-spectrum degradation capability and was cost-effective for landfill leachate treatment to meet discharge standards. Guided by mechanistic insights, this study develops an advanced PEC process that enables the efficient and greener mineralization of hypersaline organic wastewater.