Ultrafast Construct Local Acidic Microenvironment of Boron‐Intercalated Osmium with Anti‐Precipitation and Corrosion‐Resistant for Seawater‐splitting

Abstract Seawater electrolysis represents a promising avenue for hydrogen production, nevertheless, the Cl − corrosion and surface deposition of Ca(OH) 2 /Mg(OH) 2 hinder its practical application by deactivation. Herein, an interstitial boron doped osmium (B‐Os) is ultrafast (10 s) constructed by microwave quasi‐solid approach, where theoretical and experimental analysis proves that the interstitial boron triggers electron enrichment at the Os site and the formation of negative charge centers. The modified electronic structure electrostatically inhibits Cl − corrosion as well as promotes H 3 O + adsorption, creating a local acidic microenvironment in the natural seawater, neutralizing OH − and effectively avoiding Ca 2+ /Mg 2+ deposition. In situ spectroscopy and local pH monitoring confirm the pivotal role of the microenvironment in regulating reaction kinetics and stability. Therefore, B‐Os exhibits a remarkably low overpotential, for hydrogen evolution reaction (HER), of 7 mV@10 mA cm −2 in alkaline seawater, while maintaining stable performance over 400 h of stable operation in an anion exchange membrane (AEM) electrolyzer, significantly outperforming commercial Pt/C. Economic evaluation highlights its hydrogen production costs ($0.81 GGE −1 ) undercutting the U.S. DOE target.