Revealing the Role of Brønsted Basicity by the Electrocatalytic Reaction via Li Insertion in the MgFe2O4 Lattice

Abstract

In this work, the impact of improving Brønsted basicity of the MgFe2O4 spinel lattice through Li substitution has been explored to ease out hydrogen evolution reaction (HER) or methanol oxidation reaction (MOR) by the unique compositions of electrocatalytic materials synthesized using a solvothermal method by varying the ratios of Li and Mg precursors. The substitution of Li+ at the Mg2+ lattice in the MgFe2O4 spinel was deliberated by X-ray diffraction, X-ray photoelectron spectroscopy, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, and Brunauer–Emmett–Teller analyses. The smaller-sized Li+ (alkali metal) ion substitution was enabled with ease as LixMg1–xFe2O4 led to increase in the Brønsted basicity as confirmed by pH studies. Among the prepared different electrocatalysts, the 3-D polyhedron chain-like Li0.5Mg0.5Fe2O4 loaded at a 316 stainless steel mesh electrode exhibits an enhanced electrocatalytic activity for HER or MOR. Importantly, the developed electrocatalyst needs an unresolved overpotential of 27 mV for HER activity which is very near to that of the bench mark Pt/C catalyst to reach a current density of 10 mA cm–2 and an excellent electrochemical activity for MOR with a current density of 171.3 mA cm–2. Besides, the faradaic efficiency for the Li0.5Mg0.5Fe2O4-loaded electrode was calculated as 97% that significantly revealed the existence of a synergistic effect between Li+ and Mg2+ ions where the effective participation of the Li and Mg lattice has enabled the spinel lattice to increase the Brønsted basicity and to enhance the electrocatalytic activities for HER or MOR.