Manganese Valence Modulation in δ-MnO2 via F-doping for Enhanced Electrocatalytic Oxygen Evolution Reaction

Abstract Manganese dioxide (MnO2) is recognized as a promising candidate for the oxygen evolution reaction (OER); however, its practical application is hindered by limited active sites and low electrical conductivity. Fluorine (F), known for its strong electron affinity and electronegativity, can modulate the surface electronic structure and physicochemical properties of catalysts. In this study, we synthesized MnO2 nanosheets and fluorine-doped MnO2 (F-MnO2) using simple hydrothermal and ion-exchange methods. We then assessed the influence of fluorine doping on the intrinsic OER activity and stability of these catalysts, as well as their underlying catalytic mechanisms. By manipulating the amount of fluorine introduced and the fluorination temperature, we explored the relationship between varying fluorine concentrations and OER performance. The experimental results show that F-MnO2 exhibits higher OER activity than pristine MnO2. At a current density of 10 mA cm⁻², the overpotential required for F-MnO2 is merely 320 mV, substantially lower than that of pristine MnO2. This enhanced performance is ascribed to fluorine doping, which leads to an increased quantity of active Mn³⁺ centers and oxygen vacancies (Vo), along with an expanded electrochemically active surface area. Furthermore, F-MnO2 displays improved stability during the testing period. It maintains long-term stability for over 25 hours, further corroborating the catalyst's excellent anti-oxidation and anti-corrosion properties in alkaline water electrolysis.