Yttrium‐Doped MoS ₂ With Optimized Interface Charge Injection and Hydrogen Binding for Efficient Hydrogen Evolution

On‐chip electrocatalytic microdevices (OCEMs) are versatile platforms for probing the intrinsic kinetics of individual nanomaterials. However, their applications in evaluating 2D van der Waals materials often suffer from substantial interfacial contact resistance at the electrode/catalyst junction and sluggish catalytic reaction kinetics at the catalyst/electrolyte interface. Herein, we develop an yttrium‐doping strategy for monolayer MoS 2 (Y‐MoS 2 ) that simultaneously optimizes charge injection across the solid–solid (electrode/catalyst) interface and hydrogen binding on the basal plane of MoS 2 . The Y doping downshifts the conduction band minimum of MoS 2 , lowering the Schottky barrier from 0.47 to 0.23 eV and enhancing electron injection across the electrode/catalyst interface. The matching spatial orbital symmetry of Y and Mo 4 d xz/yz induces strong d‐d electronic coupling, driving the formation of a favorable bridge hydrogen intermediate () with an optimized binding energy of 0.36 eV for hydrogen evolution reaction (HER) at the catalyst/electrolyte interface. Benefiting from this synergistic optimization of band alignment and hydrogen binding, Y‐MoS 2 exhibits superior HER performance, delivering an overpotential of 187 mV at 10 mA cm −2 , competitive with recent 2D MoS 2 ‐based electrocatalysts. This work establishes an optimized OCEM platform for decoupled mechanistic analysis and an orbital‐level tuning strategy for efficient electrocatalyst design.