Precision Size Control of 1-Nm High-Entropy Alloy Nanoparticles Via Autocatalytic Reduction for HER Electrocatalysis

Since their discovery in 2004, solid-solution high-entropy alloys (HEAs), a class of solid-solution materials composed of at least five principal elements, have demonstrated remarkable versatility across various applications due to unique properties such as synergistic atomic interactions and limitless compositional design. In particular, nanoscale HEA particles have shown exceptional performance in electrocatalysis, photocatalysis, thermocatalysis, and energy storage. Achieving sub-1 nm HEA nanoparticles is critical for optimizing atomic utilization, but synthesizing such ultrasmall particles while maintaining high-entropy random mixing remains a major challenge due to complex multicomponent interactions. Herein, we report a novel template-confined synthesis strategy that employs mesoporous carbon (CMK-3) to fabricate a library of 1-nm HEA nanoparticles. By leveraging the confinement effect of the mesoporous framework and the autocatalytic reduction mechanism under reducing conditions, HEA nanoparticles with a narrow size distribution (1.12 ± 0.13 nm) and homogeneous element distribution were achieved. This library spans diverse compositions, including quinary to denary combinations, incorporating elements such as Pt, Pd, Ru, Rh, Fe, Co, Ni, Cu, Mo, and Zn. Notably, the temperature programmed reduction (TPR) experiments revealed that Pt and Ru significantly lower the reduction temperature of Fe(III), Co(II), and Ni(II), enabling the simultaneous reduction of multimetal precursors at a peak temperature of 189 o C. The electronic structures and coordination environments of PtRuFeCoNi HEA nanoparticles were also analyzed using synchrotron X-ray absorption spectroscopy (XAS), confirming the distinct orbital hybridizations of the HEA nanoparticles. These findings underscore the fine-tuned electronic structure and strongly indicate atomic mixing among the five elements within the PtRuFeCoNi HEA nanoparticles. The synthesized PtRuFeCoNi nanoparticles demonstrated outstanding catalytic performance in the hydrogen evolution reaction (HER), surpassing both other HEA systems and commercial Pt/C catalysts in mass activity and atom utilization. Operando XAS further uncovered a strong synergistic effect among constituent elements, with Pt and Ru identified as active centers for HER, facilitated by charge transfer from Fe. Complementary density functional theory (DFT) calculations revealed a hydrogen-adsorption free energy (ΔG H* ) of -0.15 eV, which is near the ideal value of 0 eV, demonstrating optimal hydrogen adsorption properties. This research highlights the benefits of combining template-confinement and autocatalytic reduction for synthesizing ultrasmall HEA nanoparticles. The resulting enhanced catalytic efficiency, coupled with a systematic understanding of multicomponent synergy, provides a promising approach for developing next-generation catalysts for hydrogen-related energy applications.