Spinel ferrite MFe2O4 (M = Ni, Co, or Cu) nanoparticles prepared by a proteic sol-gel route for oxygen evolution reaction

In this work, spinels of MFe2O4 (M = {Ni, Co, Cu}) were successfully prepared by proteic sol-gel method using commercial flavorless gelatin as a chelating agent. To break down aggregated particles, the samples were milled in alcohol at 400 rpm for 1 h. According to Rietveld refinements and transmission electron microscopy, the samples had crystallite and particle sizes in the range of 36-53 nm and 44-147 nm, respectively, confirming the as-prepared samples in a nanoscale. X-ray diffraction and Rietveld refinement confirmed that the samples are single phase. In addition, Mossbauer spectroscopy analysis and X-ray photoelectron spectroscopy revealed the mixed spinel composition. Besides, X-ray photoelectron spectroscopy showed surface oxygen vacancies, given by ratio areas between oxygen vacancies (O-V) and oxygen in the lattice (O-L), of 0.63, 0.27 and 0.10 for NiFe2O4, CuFe2O4 and CoFe2O4 powders, respectively. Magnetic measurements showed ferrimagnetic behavior for all samples. Toward oxygen evolution reaction (OER), copper-oxygenated groups on the CuFe2O4 nanoparticle surface may play an important role, once CuFe2O4 showed superior electrocatalytic performance, with overpotentials of 369 mV (CuFe2O4) < 386 mV (NiFe2O4) < 448 mV (CuFe2O4) at a current density of 10 mA cm(-2) and Tafel slopes of 76.3 mV dec(-1) (CuFe2O4), 85.7 mV dec(-1) (NiFe2O4) and 148.1 mV dec(-1) (CuFe2O4). All samples exhibited mechanical stability during the OER process. (C) 2021 The Society of Powder Technology Japan. Published by Elsevier BV and The Society of Powder Technology Japan. All rights reserved.

Automated summary

In this study, spinels of MFe2O4 (M = {Ni, Co, Cu}) were successfully synthesized using a proteic sol-gel method. The samples exhibited nanoscale characteristics, single-phase structure, and ferrimagnetic behavior. CuFe2O4 showed excellent electrocatalytic performance for the oxygen evolution reaction.