Magnetic La0.7M0.3MnO3 (M= Mg, Ca, Sr and Ba) Catalysts for Next-Generation MFC Air-Cathodes

The production of energy from effluent via microbial fuel cells (MFCs) is a promising strategy for addressing the challenges of energy transition and sustainable waste treatment. However, the performance of these systems is limited by the slow kinetics of the oxygen reduction reaction (ORR) at the cathode. In this context, this study explores the potential of La₀.₇M₀.₃MnO₃ (M = Sr, Ca, Ba, and Mg) perovskite oxides as cathode catalysts for wastewater-fed MFCs, with a focus on the influence of magnetic properties on electrocatalytic activity. The catalysts were synthesized and characterized by X-ray diffraction, scanning electron microscopy coupled with energy-dispersive X-ray analysis, infrared spectroscopy, and magnetic measurements (PPMS DynaCool). Electrochemical performance was evaluated by cyclic voltammetry, chronoamperometry, polarization curves, power density, and electrochemical impedance spectroscopy. The results indicate that replacing lanthanum with divalent cations modifies the Mn³⁺/Mn⁴⁺ equilibrium, crystal structure, magnetic order, and electronic conductivity of manganites. The materials studied show that La₀.₇Sr₀.₃MnO₃ exhibits the most pronounced magnetic response, associated with the best electrocatalytic performance for ORR, with a maximum power superior to that of La₀.₇Ba₀.₃MnO₃, La₀.₇Ca₀.₃MnO₃, and La₀.₇Mg₀.₃MnO₃ catalysts. These results highlight a correlation between magnetic order and the efficiency of electron transfer and oxygen activation at the cathode.