Breaking the Sabatier Limitation of Hydrogen Evolution via Spatial Decoupling on a Hollow Spherical Ru/TiO 2 /Ti 3 C 2 T x Heterostructure

Efficient alkaline hydrogen evolution reaction (HER) electrocatalysis requires simultaneously accelerating sluggish water dissociation and facile hydrogen desorption, yet integrating these kinetically incompatible steps within a single catalytic site remains fundamentally challenging. Here we report a hollow‐spherical multiphasic ruthenium (Ru)/TiO 2 /Ti 3 C 2 T x MXene heterostructure that spatially decouples the elementary HER steps through an interfacial hydrogen spillover mechanism. Through comprehensive in situ spectroscopic investigations and theoretical simulations, we demonstrate that the unconventional phase‐engineered architecture enables Ru sites to efficiently dissociate water, while the Ti 3 C 2 T x MXene surface serves as a thermodynamically favorable platform for hydrogen recombination and release. Importantly, an interfacial TiO 2 bridge acts as a relay medium that dramatically lowers the hydrogen‐transfer barrier between the distinct catalytic domains, thereby establishing a continuous dual‐site reaction pathway across the heterogeneous interfaces. Consequently, the optimized catalyst delivers an ultralow overpotential of 13 mV at 10 mA cm −2 , together with outstanding operational stability over 320 h. Moreover, the assembled anion‐exchange membrane water electrolyzer requires only 1.66 V to achieve a current density of 1 A cm −2 . This work establishes an interfacial relay strategy for regulating hydrogen spillover across heterogeneous catalytic phases and provides a general framework for constructing advanced electrocatalysts with spatially cooperative reaction pathways.