Facile synthesis of nanosized spinel high entropy oxide (FeCoNiCrMn)₃O₄ for efficient oxygen evolution reaction

The sluggish reaction kinetics of oxygen evolution reaction (OER) and the high price of noble metal catalysts hinder the wide application of water electrolysis for hydrogen generation. High-entropy oxides (HEOs) with multi-components and high entropy stabilized structures have attracted great research interests due to their efficient and durable performance in electrolytic water splitting reactions. However, the development of efficient HEO electrocatalysts are often hindered by the limited surface exposed active sites because high temperature is usually required to form a high entropy stabilized structure. Herein, a flaky high-entropy oxide with a spinel structure, (FeCoNiCrMn)₃O₄, was synthesized by using the sacrificial layered carbon template in situ prepared by the volatile reaction between ammonium sulfate and molten glucose. High-resolution TEM results show the as-prepared (FeCoNiCrMn)₃O₄ flakes are composed of nanosized HEO particles. The nanosized (FeCoNiCrMn)₃O₄ HEO electrocatalysts exhibit excellent OER activity, with an overpotential of 239 mV at 10 mA/cm² and a Tafel slope of 52.4 mV/dec. The electrocatalyst has excellent stability. Even at a high current density of 100 mA/cm², the activity remains unchanged during the stability test for 24 h. The results here shed a new light in the design and fabrication of highly efficient HEO electrocatalysts.