MnFe2O4 thin film electrodes via AACVD: A facile route for enhanced oxygen evolution reaction

Abstract

CO₂ emissions from existing non-renewable energy sources pose serious environmental consequences, making it a major global concern. There is an urgent need to develop eco-friendly alternative energy resources. Efficient electrocatalysts represent a promising solution due to their zero emissions of CO₂. In this study, we synthesized sustainable electrocatalysts based on transition metal oxides, designed to offer high current densities, superior stability, and a lower onset potential. Therefore, individual thin film electrodes of Fe₃O₄ and Mn₃O₄ and their binary composite MnFe₂O₄ were fabricated using an aerosol-assisted chemical vapor deposition (AACVD) method for water-splitting applications. Bimetallic thin film electrodes were developed by varying the deposition temperatures of 425, 450, 475, and 500 °C. The synthesized thin film electrodes underwent comprehensive characterization to evaluate their structure, properties, composition, and morphology using techniques such as X-ray diffractometry (XRD), scanning electron microscopy (SEM), elemental mapping, and X-ray photoelectron spectroscopy (XPS). Among the tested electrodes, the MnFe₂O₄ binary thin film electrode synthesized at 500 °C showed promising results for the oxygen evolution reaction compared to individual thin films and other binary composites prepared at different temperatures. It exhibited the lowest charge transfer resistance (R_ct) of 1.56 Ω and achieved current densities of 50 and 100 mA/cm² at remarkably low overpotentials of 390 and 480 mV, respectively. Further, the MnFe₂O₄@500 possess electrochemical active area of 269.2 cm² and Tafel slope value of 54 mV/dec. Moreover, following electrochemical efficiency, the film fabricated at 500 °C has the highest N_D value of 8.12 × 10²⁰ with the lowest flat band potential of 0.96 V. In addition, the same film showed excellent durability of 15 h at the potential of 1.35 V analyzed by chronoamperometry.