FeCoNiRhPt High-Entropy Alloy Catalyst Synthesized via Atmospheric Plasma-Ionic Liquid Reduction for Efficient Oxygen Evolution Reaction

Abstract

For the first time, FeCoNiRhPt high-entropy alloy (HEA) nanoparticles (NPs) were synthesized via atmospheric plasma-assisted reduction in an ionic liquid medium in ambient conditions.Structural characterization confirmed a single-phase FCC structure with uniformly distributed nanoparticles (average diameter of 4.28 ± 0.95 nm), exhibiting high crystallinity and phase stability. STEM-EDS mapping demonstrated a homogeneous distribution of Fe, Co, Ni, Rh, and Pt, indicating uniform alloying. Ultraviolet photoelectron spectroscopy analysis provided evidence of HEA formation, revealing a broad valence band structure with extensive d-orbital hybridization.The observed broadening, absence of sharp elemental features, and continuous density of states confirm the electronic characteristics of HEA systems. The measured work function of 5.8 ± 0.1 eV, evidenced by a single, sharp secondary electron cutoff and a well-defined Fermi edge, further supports the electronic homogeneity and favorable surface properties essential for catalytic activity.The FeCoNiRhPt HEA NPs exhibited excellent catalytic activity for oxygen evolution reaction (OER) in alkaline electrolyte, achieving a low overpotential of 150 mV at 10 mA cm⁻², significantly outperforming RuO₂ (340 mV). Electrochemical impedance spectroscopy revealed a lower charge transfer resistance (67.9 Ω vs. 96.4 Ω for RuO 2 ) and a higher electrochemical surface area (C dl : 17 × 10⁻³ vs. 8 × 10⁻³ mF/cm²). Chronoamperometric stability tests showed 80.01% current retention over 600 minutes, surpassing RuO 2 (78.69%). Our results establish FeCoNiRhPt HEA NPs as highly efficient and durable OER catalysts, with strong potential for hydrogen production and renewable energy technologies. The findings of this study lay a rigorous groundwork for the advancement of cost-effective electrocatalysts.