Iron Coordination in PtFeCoNiMo High-Entropy Alloys Modulates Platinum Local Environments for pH-Universal Hydrogen Evolution Reaction.

Developing cost-effective, stable hydrogen evolution reaction (HER) electrocatalysts effective across pH-Universal remains challenging. This work reports a one-pot synthesized Pt-Fe-Ni-Mo-Co high-entropy alloy catalyst supported on Ketjen Black (HEA@KB) featuring stacked nanoparticles. By systematically tuning the iron coordination, the optimized HEA@KB demonstrates outstanding HER activity with low overpotentials of 12.44 mV in acidic (0.5 m HSO), 61.35 mV in alkaline (1 m KOH), and 55.71 mV in neutral (1 m PBS) electrolytes at 10 mA cm, significantly outperforming commercial 20 wt.% Pt/C catalysts. Density functional theory (DFT) calculations reveal that Fe incorporation modulates the electronic structure of Pt active sites by downshifting the d-band center, weakening Pt-H bonds, and facilitating hydrogen desorption via the Tafel step. Concurrently, Fe enhances the density of states near the Fermi level and optimizes the local Pt coordination environment, increasing the hydrogen-targeted charge flux (HTCF) that accelerates electron transfer in the Volmer step. Electron microscopy confirms that Fe tuning governs nanoparticle stacking, thereby expanding the electrochemically active surface area. This work elucidates the dual kinetic promotion of Volmer and Tafel steps through electronic and structural synergy, offering a promising avenue for designing efficient, durable, and low-Pt HER electrocatalysts.