Investigation of Iron-Doped Manganese Oxide Nanoparticles as Electrocatalysts for Oxygen Oxidation and Reduction

Abstract

Photoelectrochemical processes can facilitate the storage of solar energy in the form of chemical bonds via the water-splitting reaction: H\(_{2}\)O → ½ O\(_{2}\) + H\(_{2}\). Metal oxides and (oxy)hydroxides are known catalysts for oxygen evolution(OER) – the efficiency-limiting half-reaction of the solar-to-hydrogen energy conversion process. Similarly, metal oxides are also of interest as catalysts for the oxygen reduction reaction (ORR), specifically the 4-electron reduction pathway from O\(_{2}\) to H\(_{2}\)O for use in fuel cells. In this study, a series of gamma-MnO\(_{2}\) nanoparticles are synthesized, with varying amounts of Fe impurities introduced during the hydrothermal synthesis process. The efficiency of the nanoparticles as catalysts for oxygen evolution and oxygen reduction was studied via cyclic voltammetry in alkaline solution. Furthermore, a physiochemical study of the particles included characterization by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy(EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Analysis revealed that catalytic activity is related to crystallinity of each sample. Additionally, introduction of iron impurities caused in both the oxidation state and phase of manganese oxide.