Multithermal Pulse-Controlled Synthesis of Sub-3 nm High-Entropy Intermetallic Nanoparticles for Ordering Degree-Dependent Oxygen Reduction Electrocatalysis.

Abstract

Ultrafine high-entropy intermetallics (HEIs), which synergistically combine high-entropy effect, size effect, and ordered intermetallic structure, have attracted considerable attention as promising candidates for highly active and durable catalysts. However, the sluggish diffusion inherent to the complex multielement environment of high-entropy systems necessitates high temperatures to drive atomic ordering, which typically leads to severe nanoparticle sintering in the traditional thermal process. Here, we address this challenge via a multithermal-pulse control strategy that effectively suppresses long-range atomic diffusion-mediated interparticle sintering and intraparticle phase separation during short-range atomic ordering, enabling the synthesis of uniform sub-3 nm HEI nanoparticles. By varying the number of thermal pulses to precisely control the chemical ordering degree of PtFeCuCoNi alloy nanoparticles, we discover a clear positive correlation between the ordering degree and oxygen reduction performance. The HO-PtFeCuCoNi nanoparticles with the highest ordering degree exhibit the best catalytic activity (MA of 0.95 A mg_Pt^-1 and SA of 1.18 mA cm_Pt^-2) and stability (MA retention of 70.8%, SA retention of 70.4%, and Δ<i>E</i>_1/2 of 6 mV) compared to their less ordered counterparts and commercial Pt/C. This multipulse strategy provides a feasible route to utilize pulse dynamics for capturing ordered structures and regulating the sintering-ordering trade-off and offers useful guidance for the structural design of multicomponent alloys.