Strained Os nanoclusters on TaB2 for alkaline hydrogen evolution through hydroxyl management and interfacial water restructuring.

Alkaline hydrogen evolution is limited by sluggish water activation, unbalanced hydrogen (*H) adsorption, and hydroxyl (*OH)-related site blocking. Herein, highly dispersed Os nanoclusters are anchored on TaB2 (Os/TaB2) through an ultrafast quasi-solid microwave strategy, where strong metal-support interaction (MSI) couples Os-site regulation with interfacial water restructuring. The TaB2 support induces compressive strain and charge redistribution in the supported Os clusters, producing electron-enriched Os sites with moderated *H adsorption and faster *H conversion. Meanwhile, the *OH-affinitive TaB2 support preferentially accommodates *OH species, thereby protecting neighboring Os sites and potentially perturbing nearby hydration structures. In situ Raman spectroscopy reveals an increased fraction of weakly hydrogen-bonded water near the Os/TaB2 surface, providing a more labile water reservoir for water activation during the Volmer step. Benefiting from these coupled effects, Os/TaB2 delivers overpotentials of 25 and 100 mV at 10 and 100 mA cm-2 in 1.0 M KOH, respectively, with a Tafel slope of 37.19 mV dec-1. The anion exchange membrane water electrolysis (AEMWE) using Os/TaB2 as the cathode achieves cell voltages of 1.53 and 1.59 V at 0.5 and 1 A cm-2, respectively, and operates stably for over 230 h at 1 A cm-2. This work highlights an interface-engineering strategy for coupling active-site modulation with *OH management and interfacial water regulation in practical alkaline hydrogen production.