Edge-Selected Selenization of Subnanometer Amorphous NiFe Hydroxides for Efficient Alkaline Oxygen Evolution.

Crystalline-amorphous (c-a) heterointerfaces are a promising strategy to upgrade nanomaterials for catalysis. However, achieving precise control over c-a heterointerfaces at the subnanometer (subnm) scale for maximizing catalytic sites remains a formidable challenge. Here, we report a dual ligand-assisted synthesis strategy to engineer a hierarchically c-a heterostructure on subnanometer NiFe hydroxide, synergizing atomic-scale structural refinement with interfacial optimization for enhanced oxygen evolution reaction (OER) performance. Through the selective selenization of unstable edge sites in amorphous materials, the resulting crystalline Ni0.85Se@amorphous NiFe hydroxide catalysts, featuring edge-enriched Ni0.85Se domains and mismatched crystalline-amorphous heterointerfaces, deliver exceptional OER activity with an ultralow overpotential of 225 mV at 10 mA cm-2, surpassing most state-of-the-art NiFe-based catalysts. Spectroscopic techniques and theoretical calculations reveal that the crystalline Ni0.85Se outer layer modulates the d-band center of Ni/Fe active sites, enhances charge transfer kinetics, and optimizes oxygen intermediate adsorption, thereby accelerating the OER process. Furthermore, in the anion exchange membrane water electrolyzer (AEMWE), standout performance with an ultralow cell voltage of 1.78 V at a current density of 1.0 A cm-2 is achieved. This work establishes a universal blueprint for integrating atomic-level structural design with interfacial engineering to unlock high-performance c-a heterocatalysts for energy conversion technologies.