Spinel structure of activated carbon supported MFe2O4 composites as an economic and efficient electrocatalyst for oxygen reduction reaction in neutral media

Abstract

For more sustainability and marketing of microbial fuel cells (MFCs) in wastewater treatment, the sluggish kinetics of cathode oxygen reduction reaction (ORR) and platinum scarcity (with its high cost) should be swept away. So, this work aimed to synthesize metal ferrite (MFe2O4; M = Mn, Cu, and Ni) -based activated carbon composites as inexpensive ORR cathode catalysts. The composites were synthesized using a facile modified co-precipitation approach with low-thermal treatment and labeled as MnFe2O4/AC, CuFe2O4/AC, and NiFe2O4/AC. The as-synthesized catalysts are physicochemically characterized by X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared microscopy (FTIR), Barrett-Joyner-Halenda (BJH), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), and electron spin resonance (ESR). The electrochemical catalytic performance toward ORR was studied in a phosphate buffer solution (PBS) at neutral media via cyclic voltammetry (CV) and linear sweep voltammetry (LSV). MnFe2O4/AC has the highest onset potential (Eonset) value of − 0.223 V compared to CuFe2O4/AC (− 0.280 V) and NiFe2O4/AC (− 0.270 V). MnFe2O4/AC also has the highest kinetic current density (jK) and lowest Tafel slope (− 5 mA cm−2 and − 330 mV dec−1) compared to CuFe2O4/AC (− 3.05 mA cm−2 and − 577 mV dec−1) and NiFe2O4/AC (− 2.67 mA cm−2 and − 414 mV dec−1). The ORR catalyzed by MnFe2O4/AC at pH = 7 proceeds via a 4e− -kinetic pathway. The ESR is in good agreement with the electrochemical analysis due to the highest ∆Hppvalue for MnFe2O4/AC compared to CuFe2O4/AC and NiFe2O4/AC. Thus, MnFe2O4/AC is suggested as a promising alternative to Pt- electrocatalyst cathode for MFCs at neutral conditions.