Flexoelectric Catalysts Based on Hierarchical Wrinkling Surface of Centrosymmetric High-Entropy Oxide

Abstract

A high-entropy oxide nanocomposite with Ag(CuZn)(AlCr)₂O₄ and CuO phases is fabricated to form an abundantly hierarchical wrinkled surface. Application of a mechanical force to the nanocomposite resulted in a nonhomogeneous strain gradient at the interface between the Ag(CuZn)(AlCr)₂O₄ and CuO phases, changing the local charge distribution and creating flexoelectric polarization that delayed electron/hole recombination. Transmission electron microscopy energy-dispersive X-ray spectroscopy mapping revealed that the Ag, Cu, Zn, Al, Cr, and O elements were highly distributed throughout the nanocomposite. The nanocomposite produced 2116 μmol·g^-1 h^-1 of H₂ without external light irradiation, which is 980% higher than the H₂ produced by the same nanocomposite under the photocatalytic process. A strong electrical field is observed at the interface between the Ag(CuZn)(AlCr)₂O₄ and CuO phases, demonstrating that a flexoelectric potential (flexopotential) is established at the structural boundaries because the strain gradient is localized at these interfaces. The nanocomposite is a promising approach for environmentally friendly energy production.

Keywords: catalysts; flexoelectric; high-entropy oxide; hydrogen production; nanocomposite; strain gradient.