One-pot synthesis of Sub-3 nm high-entropy alloy nanoparticles in hollow nanospheres for pH-universal hydrogen evolution.

The development of high-entropy alloy (HEA) nanocatalysts with ultrasmall size and hollow structures is vital yet challenging for efficient hydrogen evolution reaction (HER) across all pH conditions. Herein, we present a mild and facile hydrothermal strategy for synthesizing hollow PtRuRhCoCu HEA nanospheres (NSs) via self-assembly of sub-3 nm alloy nanoparticles directed by N, N'-methylenebisacrylamide (MBAA). The resulting PtRuRhCoCu HEA features a multielement composition, interconnected hollow architecture, and well-dispersed ultrafine particles, providing abundant active sites and strong synergistic electronic interactions. As a result, the PtRuRhCoCu HEA catalyst achieves remarkable HER activity with low overpotentials of 10 mV (1 M KOH), 15 mV (0.5 M HSO) and 30 mV (1 M phosphate-buffered saline, PBS) at 10 mA cm, outperforming commercial Pt black. Moreover, this catalyst also exhibits outstanding long-term stability across a broad pH range, operating continuously for 80 h under alkaline conditions at various current densities without noticeable degradation. The density functional theory (DFT) calculations confirm that this HEA exhibits optimized hydrogen adsorption energy and electronic structure. When integrated into a full electrolyzer, it delivers a cell voltage of 1.48 V at 10 mA cm, demonstrating great potential for water splitting. This work presents an effective design strategy for next-generation HEA electrocatalysts toward green hydrogen production.