ALD-made noble metal high entropy alloy nanofilm with sub-surface amorphization for enhanced hydrogen evolution

Abstract

Noble metal-based high entropy alloys (NM-HEAs) have been shown to have optimized catalytic properties through compositional adjustments. Recently, an amorphous HEA, known as high-entropy metallic glass (HEMG), has gained attention for its potential in surface modification and atomic rearrangement. In this work, RhRuPtPdIr HEA thin films (Rh : Ru : Pt : Pd : Ir = 26.1 : 28.7 : 8.6 : 16.3 : 20.3) were synthesized on glassy carbon (GC) electrodes using precisely controlled sequential atomic layer deposition (ALD) process of each noble metal layer, followed by electrical Joule heating (EJH) alloying at 1000 °C for 5 seconds. Cross-sectional HR-TEM imaging revealed a thickness of 20 nm and the surface microstructure composed of nanocrystallites and amorphous structures, suggesting explosive crystallization during the EJH process. The HEA thin film achieved outstanding HER performance, exhibiting overpotentials of 13, 77, and 65 mV at a current density of 10 mA cm⁻² and Tafel slopes of 14, 45, and 78 mV dec⁻¹ in 0.5 M H₂SO₄, 1.0 M PBS, and 1.0 M KOH electrolytes, respectively. Remarkably, HEA/GC in an acidic environment reached strikingly top-level kinetics, which was mainly contributed by intrinsic activity and surface amorphization. The corresponding DFT study revealed a modified electronic structure of the HEA surface that facilitates surface–hydrogen interaction. The study demonstrates the potential of NM-HEA nanofilm as catalysts for highly efficient HER in harsh environments. This study also demonstrates that ALD-EJH is a novel and reliable method for synthesizing, manipulating, and tuning complex high-entropy nanomaterials.