Interfacial Hydrogen Spillover in Partially Alloyed PdNi Electrocatalysts for Hydrogen Evolution

Hydrogen spillover can decouple elementary steps in the hydrogen evolution reaction (HER), yet conventional bimetallic catalysts often suffer from discontinuous interfaces that block spillover pathways. Herein, an interfacial hydrogen spillover mechanism is engineered in a Pd–PdNi–Ni catalyst via a partial interface alloying strategy for pH‐universal hydrogen evolution. The graded PdNi interface serves as a recombination sink integrating two synergistic pathways: primary spillover, in which strongly adsorbed H* generated on Ni spontaneously migrates across the interface, and secondary spillover, in which H* produced on Pd also diffuses to the same interfacial sites. The dual spillover is driven by a favorable hydrogen intermediate gradient resulting from Ni‐to‐Pd electron transfer and an optimized d‐band center. The optimal catalyst delivers ultralow overpotentials of 60 mV (alkaline) and 37 mV (acidic) at 10 mA cm −2 , with robust durability, and the corresponding anion exchange membrane electrolyzer exhibits 1.73 V at 0.5 A cm −2 and 452 h stability in simulated seawater. Operando Raman spectroscopy detects Pd–H and Ni–H vibrations, providing direct evidence for hydrogen migration from both domains to the interface, and theoretical calculations confirm the electronic origin and spillover pathways. This work demonstrates a rational design for high‐performance HER catalysts by harnessing dual hydrogen spillover.