Dynamic Amorphous Composite Shells on 3D Printed High‐Entropy Alloy Enable Stable and Active High‐Rate Seawater Oxidation

The corrosive chloride (Cl^-) in seawater challenges anode stability and compromises the efficiency of oxygen evolution reaction (OER), posing a barrier to high-rate seawater electrolysis. Herein, selective laser melting (SLM) 3D printing of a high-entropy NiFeCoCrMn alloy is combined with a 200 s mild anodic acid etching/reprecipitation, to form amorphous hydroxide-oxide composites on the printed scaffold (a-SLMH). The grain-boundary-free amorphous shells undergo dynamic in situ reconstruction into active NiFeCo oxyhydroxides, while immobilizing Mn/Cr oxides to suppress Cl^- attack during OER, as revealed by in situ Raman spectroscopy and ex situ microstructural characterizations. In 1 M KOH + 0.5 M NaCl, the a-SLMH exhibits leading seawater oxidation performances, such as reaching 500 and 1000 mA cm^-2 at low overpotentials of 310 and 328 mV, respectively, and maintaining a 100% O₂ selectivity at 500 mA cm^-2. Critically, the electrode operates stably for at least 500 h in alkaline natural seawater at 500 mA cm^-2, demonstrating its robustness. This work exemplifies that SLM 3D printing coupled with amorphous surface engineering yields durable and active anodes for high-rate seawater OER.