Large-scale sonochemical fabrication of a Co₃O₄-CoFe₂O₄@MWCNT bifunctional electrocatalyst for enhanced OER/HER performances

Herein, we have prepared a mixed-phase Co₃O₄-CoFe₂O₄@MWCNT nanocomposite through a cheap, large-scale, and facile ultrasonication route followed by annealing. The structural, morphological, and functional group analyses of the synthesized catalysts were performed by employing various characterization approaches such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The resultant samples were tested for bifunctional electrocatalytic activity through various electrochemical techniques: cyclic voltammetry (CV), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS). The prepared Co₃O₄-CoFe₂O₄@MWCNT nanocomposite achieved a very high current density of 100 mA cm⁻² at a lower (290 mV and 342 mV) overpotential (vs. RHE) and a smaller (166 mV dec⁻¹ and 138 mV dec⁻¹) Tafel slope in the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively, compared to Co₃O₄-CoFe₂O₄. The excellent electrochemical activity of the as-prepared electrocatalyst was attributed to the uniform incorporation of Co₃O₄-CoFe₂O₄ over MWCNTs which provides high redox active sites, a greater surface area, better conductivity, and faster charge mobility. Furthermore, the enhanced electrochemical active surface, low charge-transfer resistance (R_ct), and higher exchange current density (J₀) of the Co₃O₄-CoFe₂O₄@MWCNT ternary composite are attributed to its superior behavior as a bifunctional electrocatalyst. Conclusively, this study demonstrates a novel and large-scale synthesis approach for bifunctional electrocatalysts with a high aspect ratio and abundance of active sites for high-potential energy applications.