Electrocatalytic activity of Mn/Cu doped Fe2O3–PANI–rGO composites for fuel cell applications

Abstract

Low cost catalysts for the oxygen reduction reaction (ORR) have been successfully synthesized from a Mn/Cu doped Fe₂O₃–polyaniline (PANI) composite supported on reduced graphene oxide (rGO). The composite was prepared by oxidative polymerization followed by chemical reduction using hydrazine hydrate. The crystalline nature of Mn/Cu doped Fe₂O₃ was analyzed by X-ray diffraction (XRD) study. Surface morphology imaged by SEM shows the features of Mn/Cu doped Fe₂O₃ particles and PANI film on graphene sheets. The FT-IR studies revealed changes in the characteristic C–N and CN stretching vibrations of PANI which confirmed that PANI was bonded to the surface of the graphene sheets. The Raman spectrum showed the presence of PANI on the distorted graphene layers. TG/DTA studies revealed the thermal stability and extent of loading of Mn/Cu doped Fe₂O₃ in the composites. The electrocatalytic activity of the catalysts has been evaluated. Enhancements of ORR performance was observed in oxygen saturated 0.1 M KOH medium using the catalyst modified rotating disc electrode (RDE) and rotating ring disc electrode (RRDE). A maximum kinetic current density of −1.82 mA cm⁻² at −0.2 V was obtained for Cu doped Fe₂O₃–PANI–rGO. The Cu doped Fe₂O₃–PANI–rGO electrocatalyst has a Tafel slope of 156 mV dec⁻¹, onset potential of −46.4 mV and half wave potential of −225 mV. These values were obtained from the ORR response at 1600 rpm. To the best of our knowledge, this is the first work to study the enhancements of ORR using Mn/Cu doped Fe₂O₃ and PANI on a graphene support in an alkaline medium. The durability studies showed that the synthesized electrocatalyst has better stability and also higher methanol tolerance than the commercial 20 wt% Pt/C catalyst.