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

Abstract

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