Effect of manganese oxide with its discrete valencies on Fe2O3/C to form (MnOx–Fe2O3/C) hybrid nanocomposite electrodes for enhanced ORR activity

Abstract

Electrocatalysts play a vital role in emerging energy conversion devices. The present study aimed to synthesize non-precious metal oxides, namely manganese oxide–iron oxide/carbon (MnO_x–Fe₂O₃/C) hybrid nanocomposites, as high-performance electrocatalysts for oxygen reduction reaction (ORR). The synthesis involved a simple and low-cost co-precipitation method, where MnO_x (MnO₂, Mn₂O₃, and Mn₃O₄) served as dopants to Fe₂O₃ supported on carbon derived from chitosan. The biopolymer-derived carbon provided a highly conductive framework, facilitating uniform dispersion of metal oxides and enhancing electron transfer. The physiochemical and electrochemical investigations conducted via XRD, Raman spectroscopy, SEM/EDX, cyclic voltammetry (CV), linear scan voltammetry (LSV) and chronoamperometry (CA) revealed that MnO₂–Fe₂O₃/C demonstrated superior ORR activity with higher current density, lower onset potential, fast kinetics, better methanol tolerance and stability compared with other tested samples. The synthesized MnO₂–Fe₂O₃/C nanocomposite conferred lower charge-transfer resistance (R_ct) and higher electrocatalytic efficiency when subjected to electrochemical impedance spectroscopy (EIS). The enhanced ORR performance of the MnO₂–Fe₂O₃/C composite could be attributed to the synergistic interaction between MnO_x and Fe₂O₃ alongside the conductive behavior of the chitosan-derived carbon matrix. These findings suggest that MnO₂–Fe₂O₃/C is a promising non-precious metal electrocatalyst for ORR, offering a sustainable, low-cost alternative to noble metal catalysts for fuel cells.