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.
High entropy oxides composed of Ag, Al, Zn, Cr, and Cu are synthesized through sol-gel method. The metal nitrates, including silver nitrate, aluminum nitrate, zinc nitrate, chromium nitrate, and copper nitrate, are firstly dissolved in distilled water and stirred for one hour at room temperature. After mixing thoroughly, citric acid will be added into the solution as the coordinating agent to catch all metal atoms and stirred for another half an hour. Then, by adding ammonia, the pH value of the solution is adjusted to seven and the solution is dried in the oven at 90oC for 48 hours. After that, the powder was annealed at 300oC for one hour to obtain the final product. The x-ray diffraction pattern shows that AgAlZnCrCuO exhibited a single-phase spinel structure with the second phase of CuO. Interestingly, based on the scanning electron microscope image, the AgAlZnCrCuO nanoparticles show highly porous morphologies, suggesting that the AgAlZnCrCuO may possess the unique potential application for electrochemical process.
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