Chloride-Resistant CoO@Mo(OH)x Layered Heterostructure for Efficient Seawater Oxygen Evolution.

Seawater electrolysis for large-scale hydrogen production is severely hindered by chloride ion (Cl-) poisoning and the competing chlorine evolution reaction (CER) against the oxygen evolution reaction (OER). In this work, a layered CoO@Mo(OH)x heterostructure with a crystalline CoO inner layer and an amorphous Mo(OH)x outer layer forming a close interface, with possible oxygen-mediated Mo-O-Co interactions, was constructed. Systematic evaluation reveals distinct activity trends in alkaline vs simulated seawater electrolytes. The reference MoCoOx catalyst degrades severely in seawater due to MoO-mediated Cl- adsorption promoting CER at adjacent CoO sites. In contrast, the layered CoO@Mo(OH)x structure exhibits excellent chloride tolerance and OER performance, achieving 312 mV at 50 mA cm-2 and outstanding stability (98.1% retention after 170 h at 10 mA cm-2). Using experiments, in situ Raman, and DFT, we reveal that the outer Mo(OH)x layer captures chloride (Mo binding: -3.71 eV vs -3.32 eV on Co), protecting inner CoO sites and enabling durable OER.