As a half-reaction in anion exchange membrane water electrolysis (AEMWE) technology, the hydrogen evolution reaction (HER) at the cathode is severely hindered by the sluggish reaction kinetics involved in additional water dissociation step, which results in large overpotentials and low energy conversion efficiency. Here, we develop a nano-heterostructure composed of ultra-thin W₅N₄ shells over Ni₃N nanoparticles (Ni₃N@W₅N₄) as efficient catalysts, in which built-in interfacial electric field (BIEF) is created owing to the distinct lattice arrangements and work functions of biphasic metal nitrides. The BIEF facilitates the electron localization around the interface and enables high valence W and more exposed binding sites in the surface W₅N₄ shell for accelerating the water dissociation step, ultimately leading to a remarkable reduction in the energy barriers of RDS from 1.40 eV to 0.26 eV. Theoretical calculations and operando X-ray absorption spectroscopy analysis results demonstrated that surface W₅N₄ serves as the active species for HER. Moreover, the ultra-thin shell characteristics enable the optimized W₅N₄ with enhanced intrinsic catalytic activity to be fully exposed as active sites. Consequently, the Ni₃N@W₅N₄ exhibits exceptional performance in alkaline HER (60 mV@10 mA cm^-2) and remarkable long-term stability (500 mA cm^-2 for 100 hours). When employed as the cathode in the AEMWE device, the synthesized Ni₃N@W₅N₄ demonstrates stable performance for 90 hours at a current density of 1 A cm^-2.

#	Concept	H-Index	Publications	Citations
1	Engineering	1	1	20
2	Natural Sciences	1	1	12
3	Applied Physics	1	1	20
4	Chemistry	1	1	12
5	Materials Science	1	1	20

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