Fe-Mn bimetallic oxides-catalyzed oxygen reduction reaction in alkaline direct methanol fuel cells

Two Fe-Mn bimetallic oxides were synthesized through a facile solvothermal method without using any templates. Fe₂O₃/Mn₂O₃ is made up of Fe₂O₃ and Mn₂O₃ as confirmed via XRD. TEM and HRTEM observations show Fe₂O₃ nanoparticles uniformly dispersed on the Mn₂O₃ substrate and a distinct heterojunction boundary between Fe₂O₃ nanoparticles and Mn₂O₃ substrate. MnFe₂O₄ as a pure phase sample was also prepared and investigated in this study. The current densities in CV tests were normalized to their corresponding surface area to exclude the effect of their specific surface area. Direct methanol fuel cells (DMFCs) were equipped with bimetallic oxides as cathode catalyst, PtRu/C as the anode catalyst and PFM as the electrolyte film. CV and DMFC tests show that Fe₂O₃/Mn₂O₃(3 : 1) exhibits higher oxygen reduction reaction (ORR) activity than Fe₂O₃/Mn₂O₃(1 : 1), Fe₂O₃/Mn₂O₃(1 : 3), Fe₂O₃/Mn₂O₃(5 : 1) and MnFe₂O₄. The much superior catalytic performance is due to its larger surface area, the existence of numerous heterojunction interfaces and the synergistic effect between Fe₂O₃ and Mn₂O₃, which can provide numerous catalytic active sites, accelerate mass transfer, and increase ORR efficiency.