Fluorinated Cobalt Sites Enable Solar-Enhanced Neutral Active Chlorine Electrosynthesis for In Situ Seawater...

The electrocatalytic chlorine evolution reaction (ClER) provides a sustainable approach for converting abundant seawater chloride into highly reactive chlorine species for in situ marine purification. However, the practical implementation remains limited by the need for precious-metal-based electrodes to achieve high selectivity, while under neutral conditions, intense competition from the oxygen evolution reaction (OER) and severe anode dissolution compromise both efficiency and stability. Here, we demonstrate a solar-driven strategy employing surface-fluorinated cobalt hydroxide nanosheets (Co(OH)_xF_y) as an efficient, highly selective, and precious-metal-free catalyst for neutral-pH ClER. This catalyst enables rapid degradation of a broad spectrum of prevalent marine contaminants within seconds, including antibiotics, phenols, and endocrine disruptors. In situ surface-interrogation scanning electrochemical microscopy (SI-SECM) and scanning electrochemical cell microscopy (SECCM) combined with theoretical calculations reveal that surface fluorination optimizes the coordination and electronic structure of Co(III) active sites, significantly enhancing intrinsic activity and selectivity, particularly at edge regions. Furthermore, the catalyst uniquely leverages photo-activation to selectively amplify chlorine generation. Integrated into a membrane-free photoelectrochemical flow reactor, this approach achieves direct seawater purification with significantly reduced energy demand and carbon emissions, demonstrating compelling promise for scalable, environmentally benign marine water treatment.