High-Entropy Alloy Aerogels with High-Density Solid–Solid Heterointerfaces for Alkaline Hydrogen Evolution

Constructing high-entropy alloy (HEA)-based solid–solid heterointerfaces offers a powerful route to creating catalytic materials with high structural complexity, particularly through the formation of grain-boundary-rich architectures. Such internal heterointerfaces provide diverse local atomic configurations that can enable interfacial synergy, circumvent scaling relations, and optimize multistep reaction pathways. However, the realization of HEA-based solid–solid heterostructures at the nanoscale remains challenging due to the stringent synthesis conditions and intrinsic atomic disorder of HEAs. Here, we report an epitaxial assembly strategy that drives the self-assembly of colloidal HEA nanoparticles into a self-supported three-dimensional aerogel, in which the particles are interconnected by epitaxially grown metal domains, forming extended heterostructures with abundant grain boundaries. Using alkaline hydrogen evolution as a model reaction, we show that the resulting HEA|Pt heterostructured aerogel exhibits significantly enhanced catalytic activity compared to isolated HEA nanoparticles, delivering overpotentials of 51 mV and 109 mV at 100 mA cm–2, respectively. Combined kinetic analyses and density functional theory calculations reveal that hydrogen coupling on the HEA surface is inhibited by strongly adsorbed hydroxyl species, whereas the HEA|Pt heterointerfaces lower the water dissociation barrier and enable interfacial hydrogen spillover from HEA to Pt, thereby facilitating efficient hydrogen recombination. This work establishes a general nanoscale strategy for engineering grain-boundary-dominated HEA heterostructures and opens new opportunities for assembling complex colloidal architectures with emergent interfacial functionalities.