Noble Metal‐Based High Entropy Alloy Nanoparticles Prepared by Pulsed Electrodeposition: An Approach for Medium Throughput Studies

We present a medium-throughput synthesis approach for High Entropy Alloy (HEA) noble metal nanoparticles on conductive supports via electrodeposition. The presented method utilizes aqueous electrolyte solutions, exploiting high overpotentials to achieve mass transport-controlled deposition. This ensures electrodeposition independent from individual equilibrium potentials of the different elements. Hydrogen evolution which interferes with electrodeposition is suppressed by operating in a pulsed mode at a mildly acidic pH. Applying the approach to the Au–Ir–Pt–Pd–Rh–Ru composition space, this study demonstrates that the developed method is fast, adaptable, and enables compositional control while maintaining a homogeneous element distribution. The mechanism of HEA nanoparticle synthesis is further investigated by examining material-specific seed formation and diffusion phenomena. The results indicate that together with the electrolyte composition, seed formation as well as the diffusion of metal precursors in the aqueous phase govern the average composition of the synthesized HEA nanoparticles, while the formation enthalpies of element pairs explain the atomic-scale segregation observed.