High-entropy alloy electrocatalysts go to (sub-)nanoscale.

Alloying has proven power to upgrade metallic electrocatalysts, while the traditional alloys encounter limitation for optimizing electronic structures of surface metallic sites in a continuous manner. High-entropy alloys (HEAs) overcome this limitation by manageably tuning the adsorption/desorption energies of reaction intermediates. Recently, the marriage of nanotechnology and HEAs has made considerable progresses for renewable energy technologies, showing two important trends of size diminishment and multidimensionality. This review is dedicated to summarizing recent advances of HEAs that are rationally designed for energy electrocatalysis. We first explain the advantages of HEAs as electrocatalysts from three aspects: high entropy, nanometer, and multidimension. Then, several structural regulation methods are proposed to promote the electrocatalysis of HEAs, involving the thermodynamically nonequilibrium synthesis, regulating the (sub-)nanosize and anisotropic morphologies, as well as engineering the atomic ordering. The general relationship between the electronic structures and electrocatalytic properties of HEAs is further discussed. Finally, we outline remaining challenges of this field, aiming to inspire more sophisticated HEA-based nanocatalysts.