High magnetic moment of nanoparticle-sphere-like Co, Fe based composites and alloys prepared by proteic sol-gel synthesis: Structure, magnetic study and OER activity

This work studies the magnetic behavior of a CoFe2/CoFe2O4 composite and a CoFe2 alloy obtained by proteic sol-gel synthesis as electrocatalysts for the oxygen evolution reaction (OER). Both samples were obtained through a two-step synthesis: (i) firstly, the preparation of CoFe2O4 nanoparticles using the protein sol-gel synthesis route and (ii) secondly, the reduction reaction of cobalt ferrite nanoparticles at 300 °C (CoFe2/CoFe2O4) and 500 °C (CoFe2) using H2 atmosphere. The morphological, structural, and magnetic properties were investigated by scanning and transmission electron microscopy (FESEM and TEM), X-ray diffraction (XRD), Mossbauer spectroscopy (MS) and magnetometry as a function of field and temperature. The FESEM and TEM analyses revealed that the nanoparticles have a sphere-like morphology. The nanostructured character of the samples was demonstrated through the Rietveld refinement of the XRD data. The Mössbauer spectra revealed the formation of the metallic phase of CoFe2 in the reduced samples. Magnetization versus field (M-H) curves obtained at 5 K reveal that CoFe2/CoFe2O4 and CoFe2 samples show saturation magnetizations (Ms) of 196 and 226 emu g−1, respectively. For OER applications, the CoFe2/CoFe2O4 and CoFe2 samples showed overpotentials of 304 and 291 mV vs RHE for 10 mA cm−2. Furthermore, the samples showed high electrochemical stability in chronopotentiometry studies for up to 15 h. These results suggest that materials based on transition metals, Co and Fe, are promising in developing electrodes for energy storage and conversion systems, due to their high performance and low manufacturing cost.