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.