Interface-Density Regulation via quasi-in situ Reconstruction of NiFexP for Boosted Alkaline Hydrogen Evolution

Crystalline-amorphous heterointerfaces, enriched with unsaturated coordination sites and tunable electronic structures, hold great potential for accelerating the hydrogen evolution reaction (HER). However, conventional synthesis strategies provide little control over their density and spatial distribution. Here, by tailoring the Fe composition in NiFe x P, we achieve dynamic phase evolution that drives extensive dissolution-redeposition of Fe 2 P domains, producing dense defect-rich, sub-nanometer amorphous NiFeOOH on NiFe x P (NiFeOOH@NiFe x P). This process enables precise regulation of interface density and establishes intimate crystalline-amorphous junctions. Density functional theory calculations reveal that such interfaces synergistically activate a dual-pathway mechanism: amorphous NiFeOOH reduces the water dissociation barrier to 0.834 eV, while crystalline NiFe x P weakens H* binding via d-band modulation, jointly overcoming the kinetic bottleneck. As a result, the activated NiFeOOH@NiFe 0.2 P catalyst exhibits an ultralow overpotential (only 20 mV at 10 mA cm -2 ), a low Tafel slope of 35.86 mV dec -1 , and remarkable durability (20 mA cm -2 for over 60 h). This work highlights interface-density engineering as a powerful route to break the kinetic bottleneck of alkaline HER.