High‐Entropy Platinum‐Group Metal Phosphide Atomic Layers With Controlled Phosphorization for Electrocatalytic Alkaline Hydrogen Evolution

High‐entropy phosphides (HEP), derived from high‐entropy alloys (HEA), combine multimetallic active sites with phosphorus‐induced structural and electronic modulation, yet remain difficult to construct at the atomic‐layer scale. Here, a two‐step phosphorization and epitaxial‐growth strategy is developed to synthesize Pd@PdP@HEP nanocrystals with surface‐confined PdPtIrRhRuP HEP atomic layers. This design is further supported by density functional theory (DFT) formation‐energy calculations, which indicate that P preferentially occupies surface and near‐surface sites. Controlled phosphorization of Pd cubic seeds enables systematic regulation of P incorporation, lattice expansion, and structural disorder, while subsequent multimetallic growth produces compositionally complex surface layers. Electron microscopy and synchrotron‐based X‐ray absorption spectroscopy confirm the formation of P‐enriched HEP atomic layers and reveal strong electronic coupling between P and neighboring metal atoms. The optimized Pd@PdP@HEP catalyst exhibits higher alkaline hydrogen‐evolution activity than commercial Pt/C and the unphosphorized Pd@HEA counterpart, while maintaining excellent durability. DFT calculations show that P‐induced surface reconstruction and charge redistribution downshift the d‐band center, bring the hydrogen adsorption free energy (ΔG H* ) closer to thermoneutrality, and shift the hydroxyl adsorption free energy (ΔG OH* ) toward more positive values. These effects create a balanced adsorption environment, contribute to enhanced alkaline hydrogen‐evolution kinetics, and provide an effective strategy for engineering nonmetal‐modified high‐entropy catalysts.