Plasma-N-Doped Cobalt Sulfide: An Active and Robust OER Precatalyst for Ampere-Level Seawater Splitting

Developing active and robust electrocatalysts to boost the oxygen evolution reaction (OER) is a prerequisite for direct seawater splitting (DSS), yet it remains challenging. Here, we introduce a rapid and effective plasma treatment strategy to obtain nitrogen-doped cobalt sulfide, which builds an efficient catalytic platform for OER in DSS, delivering 100 mA cm–2 in alkaline seawater at an overpotential of only 230 mV, 70 mV lower than that of the undoped one. When applied in an anion exchange membrane water electrolyzer (AEMWE), it can drive 1 A cm–2 at 1.74 V and sustain this current density for over 100 h with no noticeable degradation. Also, the nitrogen incorporation is found to be well retained during the OER, elevates cobalt’s valence, nucleates a hierarchical nanosheet architecture, and upshifts the d-band center, collectively strengthening surface binding to oxygen intermediates, lowering the *OH-formation barrier (rate-determining step), while simultaneously suppressing chloride adsorption. This study highlights the significance of N dopants for TMS-based OER catalysts and opens up a feasible pathway for developing high-performance DSS catalysts by tuning composition and architectures via low-temperature N-plasma doping.