Sulfur vacancies mediated high-valent cobalt for selective seawater oxidation

Currently, seawater electrolysis is an effective technology for the large-scale production of green hydrogen, but the issues of poisoning active sites and catalyst corrosion caused by chloride ions in seawater urgently need to be addressed. This paper reports a non-precious metal cobalt sulfide with sulfur vacancies (v-Co₉S₈) catalyst, where the presence of sulfur vacancies can accelerate the formation of metal hydroxyl oxides and induce the generation of high-valent Co, enabling v-Co₉S₈ to exhibit long-term stability and excellent oxygen evolution reaction (OER) activity in seawater electrolysis. At the same time, the high-valent Co acts as a Lewis acid, providing stronger OH⁻ adsorption and Cl⁻ repulsion capabilities during the seawater OER process. Therefore, v-Co₉S₈ catalyst achieves an overpotential of only 420 mV at 1000 mA·cm⁻² in alkaline seawater. At the same time, the assembled alkaline seawater anion exchange membrane (AEM) electrolyzer operates stably for over 130 h under the condition of 500 mA·cm⁻². This work reports a mechanism where anion vacancy-induced metal sulfide reconstruction forms high-valent metals, which is expected to provide effective guidance for the development of seawater electrocatalysts.