Nanopartículas de Fe-Co-O para eletrocatálise: síntese verde, estrutura, magnetismo e aprimoramento da reação de evolução de oxigênio com campo magnético in-situ

Abstract

Nanostructured materials based on transition metal oxides have aroused great interest for application in electrocatalysis as potential substitutes for high cost noble metals. In this context, materials with a cubic structure of the spinel type, such as cobalt ferrite (CoFe2O4), discussed in the present work, show promising results for application as an electrocatalyst in the oxygen evolution reaction (OER). An aspect of great potential of this material and still little explored is the possibility of using an external magnetic field to improve its electrocatalytic activity. In this work, we studied the structural, magnetic and electrochemical properties of biphasic Co-Fe-O nanoparticles synthesized by a combination of sol-gel and hydrothermal synthetic routes, using agar-agar as chelating agent. Subsequently, the obtained powder was characterized by field emission beam scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, Mossbauer spectroscopy and magnetic measurements as a function of temperature and magnetic field (FC and ZFC). X-ray diffraction together with Mossbauer spectroscopy confirm the presence of biphasic nanoparticles (Fe-doped Co3O4 and CoFe2O4). The scanning electron microscopy technique shows nanostructures with a predominantly spherical morphology. From an electrocatalytic point of view, applying a magnetic field of 170 mT to the electrochemical cell improves the performance of nanoparticles as catalysts for OER. The nanostructured cobalt ferrite produced showed superior electrocatalytic performance, with an overpotential of 300 mV at 10 mA cm-2 , Tafel slope of 55 mV dec-1 , Cdl of 1.48 mF, ECSA of 37 cm², specific activity of 12.59 mA cm-2 and mass activity of 1165 A g-1 , with applied magnetic field. With no field applied, the measured overpotential was 320 mV, Tafel slope of 65 mV dec-1 and Cdl of 0.96 mF cm-2 , ECSA of 9.66 mA cm-2 , specific activity of 9.66 mA cm-2 and dough activity 580 A g-1.