Octahedral Nanocrystals of Ru-Doped PtFeNiCuW/CNTs High-Entropy Alloy: High Performance towards pH-Universal Hydrogen Evolution Reaction.

Integrating high-entropy philosophy and nanocrystal-specific orientation into a single catalyst represents a promising strategy in the development of high-performance catalysts. Nonetheless, shape-controlled synthesis of high-entropy alloy (HEA) nanocrystals is a challenging task 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 the low Ru content in Ru-PtFeNiCuW/CNTs. As an electrocatalyst towards hydrogen evolution reaction (HER), Ru-PtFeNiCuW/CNTs exhibits a low overpotentials of 9, 16 and 34 mV at a current density of 10 mA cm -2 and Tafel slope 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 hours 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 the accelerated kinetics of H 2 O dissociation on W sites and *H desorption on hollow Cu-Cu-Cu and Cu-Cu-Pt sites. This article is protected by copyright. All rights reserved.