Synthesis and characterization of (Fe0.2Ni0.2Co0.2Al0.2Zn0.2)3O4 high entropy oxide as electrocatalyst for oxygen evolution reaction

Abstract

In this work, the high entropy oxide (HEO) (Fe_0.2Ni_0.2Co_0.2Al_0.2Zn_0.2)₃O₄ was synthesized at 600 ºC (labeled as HEO-600) by sol-gel method assisted with polyvinylpyrrolidone (PVP). Additional samples were produced at higher temperatures and the spinel and rock-salt high entropy oxides were formed. The characterizations were carried out by XRD, EDS, XPS, TEM, Mössbauer spectroscopy, AC and DC magnetometry, UV-vis, FTIR, and electrochemical experiments. For sample HEO-600, the XPS analysis confirmed the equimolar composition of the sample. The EDS results showed homogeneous distribution of the cations within the sample. The TEM showed non-aggregated particles with size of 9.2 nm. The sample had superparamagnetic behavior at room temperature. The Mössbauer results showed Fe occupancies in the A and B sites of 43 and 57%, evidencing the formation of a partial inverse spinel. The DC and AC susceptibility data showed the presence of a spin glass phase with onset at 206 K, this magnetic phase was wiped under a field of about 4300 Oe. The electrochemical characterization showed the ability of this sample for oxygen evolution reaction applications. The HEO-600 sample showed overpotential of 358 mV at 10 mA cm^-2. This work brings new developments in the understanding of high entropy oxides and provides a useful application as an electrocatalyst in OER processes.