Abstract: High-entropy alloys (HEAs) provide an ideal platform for developing highly active electrocatalysts and investigating the synergy of mixed elements. Far-from-equilibrium synthesis holds great potential for fabricating HEAs at the nanoscale by rapidly shifting the thermodynamic conditions and manipulat-ing the growth kinetics. While far-from-equilibrium synthesis of nanomaterials has been successful un-der thermochemical conditions, it is markedly challenging under electrochemical environments, as the use of an electrolyte limits the accessible temperature window and the temporal tunability of tem-perature. Herein, we demonstrate that applying a large electrochemical overpotential would create a far-from-equilibrium condition as changing the temperature of the system by considering the equation △G=△H-T△S+nF△ψ. An electrochemical far-from-equilibrium approach is thus setup for constructing hierarchical and self-supporting high-entropy alloy nanostructures. The large overpotential drives the simultaneous reduction of multiple cations and the subsequent formation of a single-phase alloy. As a proof-of-concept, hierarchical Fe_0.22Co_0.18Ni_0.18Cr_0.14Cu_0.28 was fabricated and used as an electrocatalyst for the hydrogen evolution reaction in alkaline media. The noble-metal-free HEA exhibits an overpoten-tial of 84 mV at a current density of 10 mA cm^-2, which is among the lowest even compared to noble metal-based electrocatalysts. This work opens a new avenue for building a variety of HEAs for energy and catalysis applications.

Key words: High-entropy alloys, Nanostructures, Electrocatalysis, Hydrogen evolution reaction, Far-from-equilibrium synthesis