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Project Goals and Description:

High entropy oxides have generated a great deal of interest over the last few years because of the unique structural characteristics and associated opportunities for tailoring properties. The first report of “entropy-stabilized oxides” in 2015 demonstrated that five or more cations incorporated in equimolar ratios yielded a single-phase oxide.¹ Subsequent literature has established the more general nomenclature of “high-entropy oxides (HEOs)” for multi-cationic equimolar oxides.² Located at the center of a multi-nary phase diagram, HEOs represent an underexplored domain of material composition that display unexpected structural stability and electrochemical properties.^1-13

Over the last two decades, nanostructured, porous and two-dimensional (2D) materials have enabled fundamental new science^14-17 as well as tremendously diverse technological applications,^18-22 owing to a multitude of phenomena that occur when size is reduced to a few atomic layers in one or more dimensions.²³ An intriguing mix of challenges and opportunities is presented by high entropy nanostructured materials. In terms of opportunities, these materials (e.g., metals,^{24, 25} oxides,^26-28 sulfides^29-31) are poised to significantly advance catalysis, battery electrodes, energy storage, electronic devices, and nanosensors/detectors, as the initial reports in the literature reveal high catalytic activity and storage capacity, as well as interesting quantum and electronic properties.^{32, 33} To unleash these desired properties and enable their reliable use in applications, the materials should possess at least one dimension less than 10nm, high quality (crystallinity), and large surface area.^26-41  Focusing on oxides, we hypothesize that nanostructures with superior stability exist outside the currently established space of single oxide^{32, 33} nanomaterials: as such, we put forth the idea that nanomaterials made of high entropy oxides (HEOs, with >5 cations) can be synthesized by solution methods (enabling nanostructuring) and may lead to unique electrocatalytic properties and enhanced stability. This hypothesis is supported by exciting preliminary results demonstrating we have realized three HEOs. Further, we will use high-throughput computational approaches to guide the synthesis towards cation combinations most likely to be realized.

Entropic stabilization has been demonstrated for bulk (3D) oxides in various crystal structures (including 4+1 systems),^{1-4, 9}and we surmise that entropic-configurational effects can stabilize various nanostructures (2d thin films, meso/nano-porous materials, nanoparticles, etc) as well. As mentioned above, initial reports in the literature have demonstrated that high entropy systems in fact impart both stability and significantly increased catalytic activity to metal oxides.^{2, 7-11}

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