High-entropy nanoparticles (HENs), typically defined as multielemental nanoparticles composed of equal or near-equal quantities of no less than 5 metal elements in a solid-solution state, hold great potential for catalysis applications. Compared with conventional nanomaterials with simple compositions, HENs exhibit two unique features: (1) Due to the multielemental combination, HENs feature vast compositional space; (2) Due to the multielemental mixing, HENs have complex and tunable atomic structure and electronic states. While these two characteristics make HENs a unique and promising platform for property screening and optimization, these features also create grand challenges for controllable synthesis. This is because the wide span of physicochemical properties among various constituent elements can induce phase separation due to elemental immiscibility which undermines the multielemental synergy.<br/>We have invented a high temperature shock approach that can enable the synthesis of HENs under non-equilibrium conditions. This method features high heating and cooling rates of ~10<sup>5</sup> K/s, temperatures of up to 3000 K, and ultrafast synthesis time in milliseconds. The method can be used on various types of precursors (e.g., chloride, nitrate, etc.) and substrates (e.g., carbon, metal oxide, metal, etc.). We have demonstrated using the HTS method to synthesize a range of HENs including homogeneous alloys, intermetallics, oxides, sulfides, carbides, and metallic glasses. We showed in various model thermochemical (e.g., ammonia synthesis, ammonia decomposition, ammonia oxidation, and methane combustion) and electrochemical reactions (e.g., oxygen evolution, oxygen reduction, and nitrate reduction) that the HENs rendered superior activity due to the multielemental synergy as well as exhibiting excellent stability due to the entropy stabilization effect and the high diffusion barrier to prevent phase segregation and leaching.

High entropy nanoparticle catalysts by shock synthesis

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