Far-from-equilibrium electrosynthesis ramifies high-entropy alloy for alkaline hydrogen evolution

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 manipulating the growth kinetics. While far-from-equilibrium synthesis of nanomaterials has been successful under 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 temperature. 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 ΔG=ΔH−TΔS+nFΔψ. 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 Fe0.22Co0.18Ni0.18Cr0.14Cu0.28 was fabricated and used as an electrocatalyst for the hydrogen evolution reaction in alkaline media. The noble-metal-free HEA exhibits an overpotential 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.