Enhancing Hydrogen Evolution Reaction via Heterophase Boundaries and Stacking Faults in Molten Salt Electrodeposited Mg‐Ni Alloys

Abstract Heterophase boundaries and stacking faults have aroused deep concerns in electrocatalyst design for their unique capacity to modulate electronic structures and d ‐band centers. However, integrating these two structural features into catalysts remains challenging, primarily limited by the scarcity of mild synthetic approaches. Herein, a molten salt electrodeposition strategy is reported for in situ growth of stacking fault‐enriched heterogeneous Mg‐Ni alloys (Mg 2 Ni/MgNi 2 ) on Ni substrate. Phase boundaries between Mg 2 Ni and MgNi 2 act as ‘electronic bridges’ mediating the alignment of Fermi levels/d‐band centers between adjacent phases by interface electron transfer, thereby alleviating excessive H * adsorption on MgNi 2 and accelerating the desorption of OH on Mg 2 Ni. Concurrently, the broadly distributed stacking faults in MgNi 2 facilitate the diffusion of H * and enhance the hydrogen adsorption/desorption due to the strain effect, leading to significant HER improvements. Additionally, the porous structure of Mg 2 Ni/MgNi 2 catalysts facilitates efficient charge transfer and bubble detachment with small diameters. Consequently, the synergistic integration of alkaline earth metal Mg and transition metal Ni within the Mg 2 Ni/MgNi 2 system achieves exceptional HER performance, requiring only 69.2 mV overpotential at 10 mA cm −2 in 1.0 m KOH while demonstrating sustained operational stability at 600 mA cm −2 for 38 h without catalytic decay.