Engineering MnNiP x Cathode via Dual Role of Mn: Simultaneous Enhancement of Activity and Intermittent Operation Durability

Here, we propose Mn co‐deposition into phosphorus‐doped nickel (NiP x ) as a sacrificial strategy to protect active Ni–P phases while simultaneously improving catalytic activity. NiP x has been widely studied as an active cathode material for the hydrogen evolution reaction (HER) in alkaline water electrolysis. However, NiP x often suffers from irreversible surface oxidation during repeated on–off cycling, such as that caused by intermittent renewable energy. We found that Mn was preferentially oxidized during cycling, providing sacrificial protection against Ni oxidation. This sacrificial process also induced surface reconstruction and promoted the formation of a self‐formed porous Mn oxide layer. The morphology of this reconstructed layer was critical for durability, as only optimized Mn incorporation retained the porous and open surface structure. Besides, X‐ray and density functional theory (DFT) analysis confirmed that the metallic Mn incorporated in the Ni–P layer enhances HER activity through electronic modulation via charge donation to nearby Ni‐P sites. Optimized Mn incorporation (Mn:Ni = 1:9 in the deposition bath) enabled to achieve lower HER overpotential and markedly enhanced cycling stability. The feasibility of this approach was further verified in a single cell test. This study offers promising strategies for designing robust HER electrodes suitable for discontinuous water electrolysis operation.