Chloride-Induced Active Site Transfer and Mechanism Switching for Efficient and Stable Oxygen Evolution in Acidic Seawater Electrolysis

Abstract Direct seawater electrolysis for green hydrogen is hindered by Ca2+/Mg2+ precipitation in neutral/alkaline systems. Acidic electrolysis avoids this, yet suffers from sluggish oxygen evolution reaction (OER) kinetics, competitive chlorine evolution reaction (CER) from chloride ions, and severe catalyst corrosion. Herein, we construct a Ru/WO3 catalyst with abundant Ru–O–W interfacial bonds for simulated acidic seawater (0.5 M H2SO4 + 0.5 M NaCl). The catalyst requires only 153 mV overpotential to deliver 10 mA cm–2 and operates stably for over 600 h. Notably, excellent performance is also maintained in acidified natural seawater, achieving stable operation at 500 mA cm–2 for 200 h. Remarkably, the introduction of Cl– does not trigger severe chlorine evolution side reactions; instead, it enhances OER selectivity to 93.6% and reduces Ru and W dissolution by approximately 79% and 84%, respectively, relative to the pure acid condition. Mechanistic studies reveal that Cl– preferentially adsorbs on Ru sites to form a Ru–Cl protective layer, blocking OH– attack and high-valent Ru dissolution that occur in the conventional adsorbate evolution mechanism (AEM). Consequently, the active site transfers to adjacent W sites and Ru–O–W bridging oxygen, and the reaction proceeds via the lattice oxygen oxidation mechanism (LOM) to accomplish O–O coupling.