Modulation of the morphology, composition, and oxidation state of the spinel high-entropy oxides to boost their bifunctional catalytic activity for overall water splitting

Developing efficient, cheap, and stable bi-functional electrocatalysts is one of the most important keys to solve the current energy and environment issues. In this thesis, a novel high-entropy oxide (HEO) with special morphology is synthesized. Our results showed that the introduction of F − will effectually improve the morphology of the material. The 3D macro-flowers assembled through a series of nano-sheets increase the specific area of the materials obviously and thus offer more active sites for the catalytic reactions , being beneficial for the overall water splitting performance. Furthermore, the incorporation of well-behavior Zn and Cu elements and the non-equilibrium F − dopants results in a charge redistributions of the active metal sites, which are not fixed at a specific oxidation state but adaptable at (2±δ) + or (3±δ) + . This unique synergistic effect among multiple metal ions will facilitate the HER and OER performance of the catalysts simultaneously. As a result, HEO-F-30 sample exhibit the overpotentials of 67 mV and 245 mV respectively for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) under alkaline environment. In addition, the bi-functional electrode made by HEO-F-30 catalyst can realized the overall water decomposition at 1.65 V at 10 mA cm −2 . This study states a useful tactic to modulate the morphology and the synergetic effect of the HEOs to optimize their overall water splitting performance.