Hexacyanoferrate-Complex-Derived NiFe₂O₄/CoFe₂O₄ Heterostructure–MWCNTs for an Efficient Oxygen Evolution Reaction

Abstract

Here, we have demonstrated the synthesis and characterization of hexacyanoferrate-complex-derived NiFe2O4/CoFe2O4 heterostructures (Ni/Co-HSs) blended with 10% multiwalled carbon nanotubes (MWCNTs) (C-Ni/Co-HS) as a composite for the first time to explore its performance in the electrocatalytic oxygen evolution reaction (OER). First, the structural and morphological analyses of the as-synthesized composite have been carried out using X-ray diffraction (XRD) patterns, Fourier-transform infrared (FT-IR) spectral studies, field emission-scanning electron microscopy (FE-SEM) with energy dispersive X-ray (EDAX), high-resolution transmission electron microscope (HR-TEM), X-ray photoelectron spectroscopy (XPS), and Brunauer–Emmett–Teller (BET) analyses. Second, C-Ni/Co-HS loaded at a 316 stainless steel (SSL) mesh electrode was studied as an efficient and stable electrocatalyst, which firmly initiated the OER at a low potential of 1.47 V (vs reversible hydrogen electrode (RHE)) compared to the benchmark catalyst such as RuO2 or other counterparts, ferrite-loaded electrodes such as iron oxide (Fe2O3), nickel ferrite (NiFe2O4), cobalt ferrite (CoFe2O4), etc. Accordingly, a very low overpotential of 240 mV was observed for OER at a current density of 10 mA cm–2 under alkaline 1.0 M KOH conditions where the Tafel slope was calculated as 42 mV dec–1 at the C-Ni/Co-HS-loaded 316 SSL mesh electrode when compared to the counterpart, NiFe2O4/CoFe2O4 heterostructure (Ni/Co-HS)-loaded electrode, i.e., in the absence of 10% MWCNTs under identical electrochemical conditions. Besides, an excellent faradic efficiency was measured for C-Ni/Co-HS, propounding that the carbon support has minimized the corrosion and the additional oxidation of the active electrocatalyst during the course of the electrocatalytic OER test. The stability of the active C-Ni/Co-HS composites was studied under continued oxygen evolution for several hours at an applied potential of 1.67 V (vs RHE) to interpret the heterostructure phenomenal long-term stability and higher electrocatalytic activity toward OER. Thus, the developed inorganic-complex-derived heterostructure-based electrocatalyst provides an alternative to noble metal systems to afford a simple, highly efficient, and stable process for OER.