Sol-Gel Synthesis and Electrochemical Applications of Graphite-Coated High Entropy Oxides

Abstract

High entropy oxide and a series of graphite-coated high entropy oxides (HEOs) were synthesized for use in water oxidation electrocatalysis. The synthesized compositions were used as a catalytic material for oxygen evolution reaction (OER). The selection of high entropy materials (HEMs) is based on their tailorable properties as compared to binary or ternary metal oxide nanomaterials. The high entropy oxides were synthesized by sol-gel method using citric acid as a chelating agent, where the gel was sintered for 9 hours at 800°C. HEOs were synthesized with 35 mol % Al and the other five cations constituted 65 mol % [Abs(MgFeCuNiCo)6s]O and coated with 5 to 20% by weight graphite (HEOs/C) that was achieved by ball milling. XRD, FTIR, SEM, and EDX characterization techniques were used for morphology and phase crystallinity in their structures. XRD pattern showed that HEOs/C belong to rock salt type high entropy oxide crystal structure. Moreover, the electrocatalytic behavior of all synthesized samples was evaluated by cyclic voltarnmetry (CV), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (ElS). The electro catalytic water splitting was performed in 1M KOH with methanol as a facilitator at room temperature employing three-electrode system in which Ag/ AgCI as a reference electrode, the modified glassy carbon electrode (GC) as working and platinum wire as a counter electrode were used. GC electrode modification with HEOs/C was carried out by the drop cast method. Different kinetic parameters like heterogenous rate constant (ko), diffusion coefficient (DO), and mass transport coefficient (mT) were determined from cyclic voltarnmetric data. Among all the compositions, one with 15% graphite-coated high entropy oxide (MT-3) showed excellent catalytic behavior for water oxidation which is evidenced by the high peak current responses, and with the addition of methanol a significant increase in peak current was observed. The electrochemical studies envisioned that all prepared HEOs/C showed promising activity and can be used as efficient catalyst for water oxidation and other electrolysis.