Plasma-Ionic Liquid Reduction for Synthesizing High-Entropy Alloy Nanoparticles

We report a novel cost-effective and scaling process for syntheses of the quinary IrPdPtRhRu HEA-NPs. The process is based on the plasma ionic liquid reduction strategy. The combination of PXRD, HRTEM, XPS, and EDX analyses confirms that the application of the developed wet plasma reduction method yields the IrPdPtRhRu HEA-NPs. HEA-NPs with the size of ≈5 nm were synthesized under mild temperature, and atmospheric pressure, and without support assistance. All elements constituting the as-prepared IrPdPtRhRu HEA-NPs are uniformly distributed in the FCC single-phase nanostructure. The valence band emission suggests the hybridization of the metal orbitals in the IrPdPtRhRu HEA-NPs. The work function (WF) of 4.63 eV for the HEA is determined by UPS. WF value is lower than the WFs of the metals from which the HEA consists, suggesting higher catalytic activity. The IrPdPtRhRu/C electrocatalyst shows excellent catalytic performance toward hydrogen evolution reaction (HER) with the overpotential of 60 mV at a current density of 10 mA cm^-2. Tafel slope of 40 mV dec^-1 was recorded in the alkaline electrolyte. HEA electrocatalyst exhibits long-term stability for 6 h without significant decay under a high constant current density of 100 mA cm^-2. The findings in this study contribute to the basic scientific understanding of catalysts and provide a platform for further development of HEA-NPs electrocatalysts for large-scale applications.