Enhancing the Photocatalytic Hydrogen Evolution and Decomposition by Optimizing the Elemental Ratios in High Entropy Oxides (Fe-Co-Ni-Cu-Zn-O)

Adjusting the amounts of different elements added can significantly affect various properties of high entropy oxides (HEOs), such as structural stability, optical, and electrochemical properties. In this work, HEO with equimolar ratios of elements was synthesized using a simple solvent thermal method and thermal annealing. Subsequently, the amounts of different elements added were sequentially adjusted to synthesize HEOs with different parameters, which were applied in photocatalytic hydrogen evolution reaction and photodegradation efficiencies of organic pollutants to find the most suitable HEO as a photocatalyst. The optimal HEO was compared with equimolar HEO in various aspects of properties through relevant analyses. For instance, X-ray diffraction (XRD) analysis confirmed the generation of new alloy oxides after adjusting the amounts of elements added, and the interaction between different alloy oxides enhanced the photocatalytic efficiency. Moreover, the electrochemical analysis also showed that HEOs with adjusted the amounts of elements added possessed superior charge transfer rates and hydrogen evolution capabilities, significantly improving the drawbacks when using semiconductors as photocatalysts. Furthermore, the relevant analysis indicated that adjusting the amounts of elements added changed the band gap, making it more versatile for applications in the visible light range. Finally, cyclic tests demonstrated that the HEO prepared in this work maintained excellent structural stability and reusability after multiple photocatalytic experiments. The interactions among metals in HEOs deserves further investigation, as they hold significant potential for development in the field of photocatalysis.