Controlled Lattice Distortion and Lattice‐Strain‐Engineered CoCuIr Alloy toward Preferential Chlorine Tolerant Direct Seawater Electrolysis

Direct seawater electrolysis (DSE) is a highly promising process for hydrogen production; however, the competing chlorine chemistry in seawater hinders the O 2 evolution reaction, and the corrosive environment poses major catalytic challenges. Herein, we meticulously design a lattice‐strain‐engineered Co–Cu–Ir trimetallic alloy nanoparticle (NP) electrocatalyst for efficient seawater electrolysis by carefully selecting and tuning the concentration of larger Ir into the smaller CoCu lattice. This insertion induces pronounced lattice distortion and compressive strain by shortening Cu─Co bond distances, generating rich active sites. Optimized Co 0.28 Cu 0.67 Ir 0.05 exhibits best performance, enabling DSE in untreated alkaline seawater with low cell voltage (<1.5 V at 10 mA cm ‒2 ), sustained ampere‐level current densities (>2.0 A cm ‒2 , 1.85 V), and long‐term stability at 500 mA cm ‒2 . Strain mapping suggests the coexistence of localized compressive and tensile strain. H 2 evolution occurs at the strain‐induced active sites (Ir/Cu), while O 2 evolution occurs at the Ir‐centered Ir/Co sites. Computational studies reveal Ir‐induced d‐band modulation that optimizes hydrogen adsorption and enhances both hydrogen and oxygen evolution. This work demonstrates that lattice‐strain engineering, coupled with particle‐size reduction, increased surface area, abundant active sites, and electronic modulation in trimetallic alloys, enables preferential chlorine‐tolerant seawater electrolysis.