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.