Fluorine‐Induced Molybdate Trap‐and‐Buffer Enables Durable Intermittent Alkaline Seawater Electrolysis

Abstract Electrodes’ stability under intermittent operation remains a key bottleneck for alkaline seawater electrolysis. Especially, the cathode typically undergoes self‐oxidation under constant‐current operation, while this process intensifies during abrupt shutdown due to the presence of reverse current. Such accelerated cathodic degradation significantly undermines the long‐term durability of the electrolyzer during practical operating. Here a fluorine‐doped nickel‐molybdenum oxide cathode is reported that maintains stability under both constant‐current operation and startup‐shutdown transitions. This full‐cycle stability is achieved through a vacancy‐mediated molybdate trap‐and‐buffer strategy. Vacancies generated by fluorine leaching under constant‐current operation strongly trap molybdates, forming a negatively charged interfacial layer. This electron‐enriched layer effectively buffers the active sites against overoxidation during abrupt shutdown. Meanwhile, its strong electrostatic‐repulsion capability suppresses further dissolving of molybdenum and protects the electrode from chloride ion attack. As a result, an alkaline seawater electrolyzer assembled with the target catalyst operates stably for over 500 h at constant‐current densities of 0.5 and 1.0 A cm −2 . Notably, the electrolyzer maintains stable performance over 3900 startup‐shutdown cycles with a minimal voltage degradation of only 0.02 mV per cycle.