Eco-friendly high entropy oxide rock-salt type structure for oxygen evolution reaction obtained by green synthesis

Abstract

Global energy consumption increases year after year, causing the depletion of non-renewable sources. According to the International Energy Agency (IEA), global demand for electrical energy is expected to increase by 3.3 % in 2024. Therefore, developing new renewable sources is urgent, including new devices for energy storage and conversion, particularly those based on electrochemical reactions. Water splitting is a clean and sustainable technology capable of facing this issue by producing oxygen and hydrogen from water and electricity. However, an issue related to this technology is the slow kinetics of oxygen evolution reaction, making it necessary to develop new electrocatalysts with high electrochemical performance. To meet this requirement, this work deals, for the first time, with a high entropy oxide with a rock-salt structure synthesized by a green sol–gel synthesis using red seaweed (Rhodophyta) as a polymerizing agent. Sol-gel synthesis allows the large-scale production of nanomaterials with high uniformity and dispersion of the involved chemical elements. The literature, which discussed the synthesis of these oxides, reveals that agents harmful to the environment are employed, including sodium hydroxide, acetic acid, hexadecyltrimethylammonium bromide, urea, and ammonium hydroxide. The composition of the high entropy oxide is (Mg0.2Ni0.2Co0.2Cu0.2Zn0.2)O. As electrocatalyst for oxygen evolution reaction, it exhibits a low overpotential (336 mV vs. RHE at 10 mA cm−2), a Tafel slope of 68 mV dec-1, and excellent durability. The electrochemical performance of the high entropy oxide prepared in this work is superior to other electrocatalysts of the same class that were produced using transition metal-based precursors.