Experimental Validation of Novel Fluorite-Type Rare Earth High-Entropy Oxides for Photocatalytic Water Splitting Applications

Five different rare-earth-based nanocrystalline high-entropy oxides (HEOs) with fluorite type of structure and average crystallite sizes between 6 and 8 nm were prepared and their photocatalytic behaviour towards AZO dye degradation and photoelectrochemical water splitting for hydrogen generation was examined. The cationic site in the fluorite lattice consists of five equimolar elements selected from the group of rare-earth elements, including La, Ce, Pr, Eu, and Gd and second-row transition metals, Y and Zr. They reveal high photocatalytic activity which is mostly attributed to the accessibility of more photocatalytically active sites [1] which provided radicals responsible for the AZO dye degradation [1-3]. The materials successfully produce hydrogen by photocatalytic water splitting, suggesting the potential of HEOs as new photocatalysts. The photocatalytic performances of all studied HEOs outperform the single fluorite oxides or equivalent mixed oxides. The Ce0.2Zr0.2La0.2Pr0.2Y0.2O2 (CZLPY) engender hydrogen in the quantity of 9.2 µmol mg–1 per hour, which is much higher content than for pristine CeO2 material which amounts to 0.8 µmol mg–1 per hour.