The Micron‐Droplet‐Confined Continuous‐Flow Synthesis of Freestanding High‐Entropy‐Alloy Nanoparticles by Flame Spray Pyrolysis

Abstract Alloying multiple immiscible elements into a nanoparticle with single‐phase solid solution structure (high‐entropy‐alloy nanoparticles, HEA‐NPs) merits great potential. To date, various kinds of synthesis techniques of HEA‐NPs are developed; however, a continuous‐flow synthesis of freestanding HEA‐NPs remains a challenge. Here a micron‐droplet‐confined strategy by flame spray pyrolysis (FSP) to achieve the continuous‐flow synthesis of freestanding HEA‐NPs, is proposed. The continuous precursor solution undergoes gas shearing and micro‐explosion to form nano droplets which act as the micron‐droplet‐confined reactors. The ultrafast evolution (<5 ms) from droplets to <10 nm nanoparticles of binary to septenary alloys is achieved through thermodynamic and kinetic control (high temperature and ultrafast colling). Among them, the AuPtPdRuIr HEA‐NPs exhibit excellent electrocatalytic performance for alkaline hydrogen evolution reaction with 23 mV overpotential to achieve 10 mA cm −2 , which is twofold better than that of the commercial Pt/C. It is anticipated that the continuous‐flow synthesis by FSP can introduce a new way for the continuous synthesis of freestanding HEA‐NP with a high productivity rate.