FeMnOx-Graphene Composites as High-Performance Bifunctional Electrocatalysts for Rechargeable Zinc-Air Batteries

Abstract

The development of efficient, stable, and cost-effective bifunctional electrocatalysts, particularly those based on earth-abundant elements, is essential for the advancement and large-scale deployment of rechargeable zinc–air batteries (ZABs). In this study, we report the synthesis and electrochemical evaluation of FeMnOx–graphene composites as bifunctional catalysts for the oxygen reduction (ORR) and oxygen evolution reactions (OER). Three catalysts were prepared using a patented process by Gnanomat SL with different graphene nanoplatelets of different physicochemical properties and characterized through XRD, TEM, STEM-EDS, XPS, TGA, and BET analyses. All samples exhibited poor crystallinity and, according to XPS analysis, showed similar surface phases attributed to Fe₂O₃ or Fe³⁺ oxyhydroxide species and Mn₃O₄. Meanwhile, the graphene support influenced the final surface area and oxide dispersion of the composite. Electrochemical testing using a three-electrode system revealed that FeMn-graphene composites, synthesized with high-surface-area graphene, exhibit promising bifunctional activity for both the ORR and OER. Full-cell ZAB testing confirmed improved charge-discharge performance and excellent cycling stability over 500 h at 10 mA cm⁻². These findings highlight the potential of FeMnOx–graphene composites as sustainable and efficient bifunctional air electrodes, providing an attractive alternative to bifunctional catalysts based on critical elements like Co.