Effective role of calcination environments in the design of manganese oxide-based nanostructured catalysts for fuel cell applications

The development of cost-effective and high-performance catalysts for the ORR is essential to advance next generation fuel cell technologies. In this work, nanostructured manganese oxides (MnOx) were synthesized through direct electrospinning deposition onto carbon paper, Atmosphere-controlled calcination enabled selective formation of Mn3O4, Mn2O3, or mixed-phase MnOx while preserving the nanofiber (NF) and nanobead (NB) morphologies of the electrospun precursors. Raman spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy revealed that oxygen partial pressure strongly influences phase composition in final MnOx nanostructures and surface oxygen-vacancy concentration. Rotating ring–disk electrode measurements demonstrated enhanced ORR activity for catalysts obtained under mixed-atmosphere conditions, achieving up to 3.95 electrons exchanged and peroxide formation below 10 %. NBs displayed intrinsically lower charge-transfer resistance, whereas NFs performance benefited the most from atmosphere modulation. These results demonstrated that atmosphere-controlled-calcination represents an effective strategy to engineer noble-metal-free MnOx nanostructured-catalysts with ORR performances approaching those of commercial catalyst, based on platinum.