Size Controlled Monodisperse Alloy Nanocrystals via Colloidal Synthesis, from Medium to High Entropy and Their Excellent Catalytic Properties

High entropy alloy (HEA) nanocrystals (NCs) are solid solutions of 5 or more elements, while medium entropy alloy (MEA) NCs are solid solutions of 2 to 4 elements. Entropy alloy nanocrystals are an emerging class of materials which show intriguing properties such as enhanced resistance to oxidation and mixing of immiscible elements within nanocrystals. Furthermore, HEA NCs have recently been demonstrated as catalysts in various important reactions (e.g., water splitting and oxygen reduction reaction) with record or near-record activities, attributed to “synergistic” and “cocktail” effects originating from the combination of multiple metals within the NCs. Yet, the exact structure-activity relationships, leading to the excellent performance of high-entropy alloys in applications such as catalysis remain poorly understood. Furthermore, no synthesis method for highly monodisperse and size-controlled medium and high entropy alloy NCs exists yet. Here we show the colloidal synthesis of highly monodisperse entropy alloy NCs [1-2], employing oleylamine as a suitable reaction solvent and non-poisoning L-type ligand. Furthermore, we extend our synthetic method to achieve MEA NCs constituting of non-precious, environmentally benign metals (e.g., Ni-Zn) and we report the first size-tunable synthesis of HEA NCs (e.g., 1.8 nm, 2.5 nm, and 3.5 nm HEA NCs) [3]. The synthesis method is facile and easily scalable. We demonstrate that the resulting nanocrystals possess size-dependent catalytic properties and exhibit better catalytic performance compared to monometallic nanocrystals. We achieve MEA and HEA nanocrystals with excellent catalytic properties and study these for different reactions (e. g. semihydrogenation of alkynes and hydrogen-evolution reaction). We understand the crystallographic and electronic structure of the nanocrystals using a range of advanced characterization techniques (high resolution transmission electron microscopy and synchrotron-based X-ray diffraction, total X-ray scattering and X-ray absorption spectroscopy) and using density functional theory calculations and reveal the relationships between catalytic performance and structure of the MEA and HEA NCs.<br/><br/>[1] <i>J. Clarysse, A. Moser, O. Yarema, V. Wood, M. Yarema</i>; <b>Science advances</b>, 2021, 7 (31) eabg 1934.<br/>[2] <i>J. Clarysse, J. D. J. Silva, Y. Xing, S. Zhang, S. Docherty, N. Yazdani, C. Coperet, M. Yarema, C. Copéret, V. Wood; Submitted.</i><br/>[3] <i>J. Clarysse, Y. Xing, V. Wood et al.; In Preparation.</i>