Acid-Stable High-Entropy Oxide Nanoparticles for Electrochemical Water Oxidation

Exploring cost-effective and acid-stable electrocatalysts for the oxygen evolution reaction (OER), which is the bottleneck for water-splitting reactions, has been recognized as the key to developing water-electrolysis technology. High-entropy oxides (HEOs) have recently been known as promising materials for water-electrolysis and exhibit excellent stability and activity toward electrochemical OER. However, a few compositions of acid-stable OER electrocatalysts have been studied so far, which means this attractive area has remained unexplored yet. Therefore, the present work emphasizes the synthesis of HEO nanoparticles (NPs) with the composition of (RuTiSnCrMn)O x by a simple sol–gel technique. Atomic ratios of the constituent elements in the HEOs were tuned during sol–gel synthesis to obtain a single-phase solid-solution of the HEO NPs. Moreover, the nanostructure and porosity of the synthesized HEO NPs were tuned by controlling the reaction parameters during the sol–gel synthesis. Detailed structural and microstructural studies of the developed HEO NPs were performed by X-ray diffraction and atomic-resolution scanning transmission electron microscopy studies. The optimized single-phase HEO NP with the composition of (Ru 1 Ti 1 Sn 0.5 Cr 1 Mn 1 )O x (with a particle size of about 12 nm and a pore size of 11.8 nm, and the small Tafel slope of 101 mV dec –1 ) showed an overpotential of 370 mV at 10 mA cm –2 current density for OER with a long-term stability of 12 h in 0.5 M H 2 SO 4 electrolyte, which was superior to that of the commercial RuO 2 catalyst. After 12 h of stability test, the sample showed only 90 mV increase in overpotential. The enhancement in OER performance was attributed to the synergistic effect caused by HEOs. This work provides an avenue for the development of acid-stable HEOs as electrocatalysts for OER.