Octahedral Nanocrystals of Ru‐Doped PtFeNiCuW/CNTs High‐Entropy Alloy: High Performance Toward pH‐Universal Hydrogen Evolution Reaction

Abstract Integrating high‐entropy philosophy and nanocrystal‐specific orientation into a single catalyst represents a promising strategy in development of high‐performance catalysts. Nonetheless, shape‐controlled synthesis of high‐entropy alloy (HEA) nanocrystals is challenging owing to the distinct redox potentials and growth dynamics of metal elements. Herein, a one‐pot co‐reduction method is developed to fabricate ruthenium (Ru)‐doped PtFeNiCuW octahedral HEA nanocrystals onto carbon nanotubes (Ru–PtFeNiCuW/CNTs). It is demonstrated that Ru dopants and W(CO)₆ promote the concurrent reduction and growth of other metal precursors to obtain higher yield and larger size of HEA nanocrystals, despite low Ru content in Ru–PtFeNiCuW/CNTs. As an electrocatalyst toward hydrogen evolution reaction (HER), Ru–PtFeNiCuW/CNTs exhibits low overpotentials of 9, 16, and 34 mV at a current density of 10 mA cm⁻² and Tafel slopes of 19.2, 27.9, and 23.1 mV dec⁻¹ in acidic, alkaline, and neutral electrolytes, respectively. As a cathodic catalyst, Ru–PtFeNiCuW/CNTs operates for up to 1500 and 1200 h in acidic and alkaline electrolyte, respectively, at a current density of 50 mA cm⁻² in a two‐electrode system for full water splitting. Theoretical calculations reveal accelerated kinetics of H₂O dissociation on W sites and *H desorption on hollow Cu–Cu–Cu and Cu–Cu–Pt sites.