Achieving a long-term stability by self-redox property between Fe and Mn ions in the iron-manganese spinel structured electrode in oxygen evolution reaction

Abstract The development of high-efficiency electrode for oxygen evolution reactions (OER) in water-electrolysis systems is an important challenge. Four types of spinel-structural materials (Mn3O4, Fe3O4, MnFe2O4, and Mn2FeO4) are prepared as OER electrocatalysts. The spinel MnFe2O4/NF electrode exhibits the best OER activity in a 1.0 M KOH alkaline electrolyte. The required electrode potential to reach a current density of 10 mA cm−2 is only 1.54 V (with η = 310 mV), and a low Tafel slope of 65 mV dec−1 is obtained. The X-ray photoelectron spectroscopy analysis of MnFe2O4/NF before and after OER found out that OER activity was promoted due to oxygen vacancies in the spinel lattice, and the high catalytic activity was maintained for a long time by the self-redox property between Mn and Fe ions. Finally, the corrosion resistance, which is directly related to the catalytic activity and stability of MnFe2O4/NF, is demonstrated through a 3000th-repeated OER acceleration stability and 1000 h-durability tests, with a high faradaic efficiency of 95.2%. Eventually, this study presents a new paradigm for energy production that enables the continuous and easy generation of hydrogen and oxygen via water electrolysis using high-performance and inexpensive iron-manganese-based electrocatalysts.