Understanding the Structural Evolution of IrFeCoNiCu High-Entropy Alloy Nanoparticles under the Acidic Oxygen Evolution Reaction

High-entropy alloy (HEA) nanoparticles are promisingcatalyst candidatesfor the acidic oxygen evolution reaction (OER). Herein, we reportthe synthesis of IrFeCoNiCu-HEA nanoparticles on a carbon paper substratevia a microwave-assisted shock synthesis method. Under OER conditionsin 0.1 M HClO4, the HEA nanoparticles exhibit excellentactivity with an overpotential of & SIM;302 mV measured at 10 mAcm(-2) and improved stability over 12 h of operationcompared to the monometallic Ir counterpart. Importantly, an activeIr-rich shell layer with nanodomain features was observed to formon the surface of IrFeCoNiCu-HEA nanoparticles immediately after undergoingelectrochemical activation, mainly due to the dissolution of the constituent3d metals. The core of the particles was able to preserve the characteristichomogeneous single-phase HEA structure without significant phase separationor elemental segregation. This work illustrates that under acidicoperating conditions, the near-surface structure of HEA nanoparticlesis susceptible to a certain degree of structural dynamics.