Synthesis and Characterization of Ni-Doped Fe₃O₄/Go Nanoparticles by Co-Precipitation Method for Electrocatalytic Oxygen Reduction Reaction in Microbial Fuel Cells

Nickel-doped Fe3O4/graphene oxide powders were synthesized by the co-precipitation method varying the Ni/Fe ratio, and the activity of the materials towards the oxygen reduction reaction in a microbial fuel cell (MFC) was studied. The samples presented X-ray diffraction peaks associated with magnetite, maghemite and Ni ferrite, as well as evidence of Fe2O3. Scanning electron micrographs showed exfoliated sheet decorated with nanoparticles and transmission electron micrographs showed spherical nanoparticles about 10 nm diameter well distributed onto the individual graphene sheet. The electrocatalytic activity for the oxygen reduction reaction (ORR) was studied by cyclic voltammetry in an air saturated electrolyte, finding that the best catalyst was the sample with a 1:2 Ni/Fe ratio, using a catalyst concentration of 15 mg/cm2 onto a graphite felt. The 1:2 Ni/Fe catalyst provided an oxygen reduction potential of 397 mV and a maximum oxygen reduction current of -0.13 mA; for comparison, an electrode prepared with GO/Fe3O4 showed a maximum ORR of 369 mV and a maximum current of -0.03 mA. The MFC’s with vertical proton membrane were prepared with Ni-doped Fe3O4 and Fe3O4/graphene oxide and tested for 24 h; reached a stable OCV of +400 mV and +300 mV OCV, respectively.