Modifying the platinum (Pt) local reaction microenvironment is a critical and complex challenge in enhancing electrochemical performances. Herein, amorphous Co(OH)2 and crystalline Pt (labeled as ac-Pt@Co(OH)2) featuring abundant crystalline-amorphous (c-a) interfaces are designed to boost hydrogen evolution reactions (HER). The engineered structure creates an advantageous chemical environment at the local level, enhancing hydrogen adsorption efficiency and resulting in exceptional HER performance. The ac-Pt@Co(OH)2 achieves a low Tafel slope of 28.5 mV dec-1 and requires merely 95 mV overpotential to reach 200 mA cm-2 in alkaline electrolyte (1 M KOH), surpassing those of conventional Pt/C catalysts (39.4 mV dec-1, 256 mV). Using in situ advanced characterization investigations revealing the dynamic electron rearrangement at the c-a interface, in which Co species initially accept electrons from Pt to optimize the adsorption of H species, then donate electrons to Pt for accelerating reduction kinetics. Theoretical calculation reveals that the amorphous Co(OH)2 promoted the dissociation of water molecules to produce active H, and electron rearrangement at c-a interface downshifts the d-band center and then optimizes the adsorption strength of *H for enhanced HER activity. The ac-Pt@Co(OH)2-based alkaline anion-exchange membrane water electrolyzer (AEMWE) maintains a current density of 500 mA cm−2 over 500 h.
