Narrowing the pH-Dependent HER Activity Gap via Synergistic Heteronuclear Dual-Single-Atom Sites and Compressive Strain in Sub-1.6 nm High-Entropy Alloy Clusters

Abstract

Developing electrocatalysts capable of narrowing the pH-dependent activity gap in hydrogen evolution reaction (HER) and revealing its mechanism remains a key challenge. Herein, we developed a facile and surfactant-free NaBH4 coreduction strategy for the rapid synthesis of sub-1.6 nm RuPtNiCuCo high-entropy alloy nanoclusters with a near-theoretical-maximum mixing entropy on presynthesized hollow nitrogen-doped carbon (RuPtNiCuCo-HEA/HNC). Detailed structural characterizations, combined with a series of in situ spectroscopic and isotopic experiments, collectively reveal that the ability of RuPtNiCuCo-HEA/HNC to narrow pH dependence originates from the synergistic effect between its heteronuclear Ru–Pt dual single-atom active sites and the compressive strain. This synergy promotes the formation of hydrogen-down water (OH2↓), accelerating interfacial water dissociation while balancing the adsorption and desorption of OH* and H* to enable rapid hydrogen release, thereby reducing the pH-dependent activity gap. Specifically, the RuPtNiCuCo-HEA/HNC exhibits low overpotentials (14, 27, and 9 mV at 10 mA cm–2) and delivers mass activities that are 8.11-, 3.54-, and 19.39-fold those of Pt/C in alkaline, neutral, and acidic electrolytes, respectively. Moreover, RuPtNiCuCo-HEA/HNC in an anion exchange membrane water electrolyzer (AEMWE) can operate continuously for over 260 h at 1 A cm–2, significantly outperforming RuPt/HNC and Pt/C.