Size‐adjustable High‐Entropy Alloy Nanoparticles as an Efficient Platform for Electrocatalysis

The high entropy alloy (HEA) possesses distinctive thermal stability and electronic characteristics, which exhibits substantial potential for diverse applications in electrocatalytic reactions. However, accurately controlling the size of HEA still remains a challenge, especially for the ultrasmall HEA nanoparticles. Herein, we firstly calculate and illustrate the size impact on the electronic structure of HEA and the adsorption energies of crucial intermediates in typical electrocatalytic reactions, such as the hydrogen evolution reaction (HER), oxygen reduction reaction (ORR), CO2 electroreduction (CO2RR) and NO3– electroreduction (NO3RR). Under the guidance of theoretical calculations, we synthesize a range of ultrasmall PtRuPdCoNi HEA nanoparticles with adjustable sizes (1.7, 2.3, 3.0, and 3.9 nm) using a one‐step spatially confined approach. Specifically, HEA nanoparticles with 1.7 nm size (HEA‐1.7) endows a 16 mV overpotential at current density of 10 mA cm−2, yielding a mass activity of 31.9 A mgNM‐1 of noble metal in HER, significantly outperforming commercial Pt/C catalyst. This strategy can also be easily applicable to other reduction reactions attributed to the richness of metal components and size adjustability, presenting a promising platform for various electrocatalytic applications as advanced catalysts.