Overview of Recent Advances in Rare-Earth High-Entropy Oxides as Multifunctional Materials for Next-Gen Technology Applications

Abstract

Rare-earth high-entropy oxides are a new promising class of multifunctional materials characterized by their ability to stabilize complex, multi-cationic compositions into single-phase structures through configurational entropy. This feature enables fine-tuning structural properties such as oxygen vacancies, lattice distortions, and defect chemistry, making them promising for advanced technological applications. While initial research primarily focused on their catalytic performance in energy and environmental applications, recent research demonstrated their potential in optoelectronics, photoluminescent materials, and aerospace technologies. Progress in synthesis techniques has provided control over particle morphology, composition, and defect engineering, enhancing their electronic, thermal, and mechanical properties. Rare-earth high-entropy oxides exhibit tunable bandgaps, exceptional thermal stability, and superior resistance to phase degradation, which positions them as next-generation materials. Despite these advances, challenges remain in scaling up production, optimizing compositions for specific applications, and understanding the fundamental mechanisms governing their multifunctionality. This review provides a comprehensive analysis of the recent developments in rare-earth high-entropy oxides as relatively new and still underrated material of the future.

Keywords: CO oxidation; CO2 hydrogenation; catalysis; configuration entropy; high-entropy oxides; hydrogen production; optoelectronics; rare-earth elements; sustainability.

Figure 1

Fluorite-type crystal structure of ceria-based high-entropy oxides showing the incorporation of 5 cations with similar ionic radius and oxidation state and the same coordination number into a single crystallographic position, with each cation occupying 1/5 of the position (each cation depicted in different color), while the anion remains untouched. The a, b, and c axes in the image represent the crystallographic orientation of the unit cell, as they define the three-dimensional lattice directions in the crystal structure.

Figure 2

General scheme of a solid oxide fuel cell (SOFC).

Figure 3

Schematic representation of the electrochemical water splitting reaction.

Figure 4

Photoelectrochemical (PEC) performance of CLPEY, CZLPY, CZLGY, CLPEG, and CLPGY was evaluated using LSV (a,b,d) under lights on (red arrow) and lights off (blue arrow) (a), photoswitching analysis (c), coating thickness-dependent LSV (d), ABPE efficiency plots (e), EIS (f), hydrogen evolution measurements (g,h), and stability testing (i), as reported by Nundy et al. [43].

Figure 5

Schematic overview of CO oxidation catalysis over the oxygen vacancies formed on the surface of RE-HEOs.

Figure 6

FTIR spectra of the gas phase over RECO GT 300 °C (RECO, RE = Y, La, Nd, Gd, Sm, C=Co, O=O₃); GT, synthesis temperature) at (a) 25 °C, (b) 50 °C, and (c) 100 °C (0–50 min). CO and CO₂ concentrations from FTIR analysis over time at (d) 25 °C, (e) 50 °C, and (f) 100 °C, as reported by Krawczyk et al. [105].

Figure 7

RE-HEO selectivity toward reaction products at (a) 21 min and (b) 189 min. Space–time yield for HEO catalysts of reaction products (c–e), as reported by Tatar et al. [22].