One-Step Synthesis of Nanostructured Spinel-Type High Entropy Oxide (HEO) Materials by the Flat Premixed Droplet-Seeded Flame (FPDSF) Method

OWEN S. FUHR, Serdar Yildirim, Xiao-Dong Zhou, Francesco Carbone, University of Connecticut

     Abstract Number: 548
     Working Group: Nanoparticles and Materials Synthesis

Abstract
High Entropy Oxides (HEOs) have emerged as promising materials in catalytic and energy storage applications due to their structural stability and compositional flexibility. In this study, a nanostructured spinel-type HEO material composed of Fe, Mn, Cu, Co, and Ni has been synthesized using the Flat Premixed Droplet-Seeded Flame (FPDSF) method, which enables rapid, scalable, and highly controllable synthesis and thermophoretic deposition of compositionally complex metal oxide nanoparticles. Thermophoretically deposited HEO films are analyzed using Transmission and Scanning Electron Microscopy (TEM and SEM) and X-ray Diffraction (XRD). Microscopy analyses reveal polycrystalline nanoparticle aggregates spanning multiple length scales, and XRD identifies clear diffraction peaks consistent with a single-phase spinel magnetite (Fe3O4) structure, confirming the successful incorporation of multiple transition metals into a homogeneous oxide lattice. Size Distribution Functions (SDFs), measured from 0.75 nm to 50 nm using dilution sampling followed by High-Resolution Differential Mobility Analysis (HR-DMA), reveal a particle mode centered around 1 nm to be predominant in number at a Height Above the Burner (HAB) of 30 mm. Further HR-DMA analyses at different HABs are ongoing to investigate particle growth kinetics with increasing flame residence times. In parallel, preliminary catalytic tests indicate promising activity of these HEO nanoparticles towards carbon monoxide oxidation. Additionally, HR-DMA results are being cross-validated with TEM analyses performed on samples collected directly on TEM grids over ~50 ms sampling intervals using a double-acting pneumatic actuator. This study demonstrates the potential of the FPDSF method as a cost-effective, rapid, and scalable synthesis route for producing nanosized high-entropy oxides with precise compositional control and promising catalytic performances.