Decoupling Reaction Steps in Alkaline Hydrogen Evolution via a Ru/Mn 3 O 4− x Cascade Electrocatalyst

Decoupling the kinetically mismatched elementary steps in the alkaline hydrogen evolution reaction (HER) is crucial for developing efficient electrocatalysts. Herein, we report a Ru/Mn 3 O 4− x cascade electrocatalyst in which Ru nanoparticles are anchored onto an oxygen‐vacancy‐rich Mn 3 O 4− x support. Theoretical calculations and spectroscopic characterizations reveal an electronic metal–support interaction mediated cascade mechanism, where the Mn 3 O 4− x support serves as the primary site for water dissociation with a low energy barrier, while the generated hydrogen intermediates spontaneously spill over to adjacent Ru sites featuring a near‐optimal hydrogen adsorption free energy, finally enabling efficient proton coupling and H 2 evolution. This dual‐site synergy delivers exceptional alkaline HER activity with an overpotential of only 21.4 mV at 10 mA cm −2 , outperforming commercial Pt/C. When employed as a cathode in an anion exchange membrane water electrolyzer, the catalyst shows an ampere‐level current density of 1 A cm −2 at a low cell voltage of 1.85 V. This work provides a decoupling mechanistic paradigm for designing high‐performance alkaline HER electrocatalysts.