Effect of Molar Ratio Modulation of Cobalt Precursors on Supercapacitor Behavior of Engineered Co–Co₃O₄ Nanocomposite Electrodes

Nanostructured Co–Co₃O₄ composite thin films deposited on nickel foam (NF) using combined cyclic voltammetry (CV) and pulse reverse potential (CV PRP) modes of electrodeposition from an electrolyte composed of CoCl₂ and Co(CH₃COO)₂ precursor salt solutions with varied molar ratios demonstrated a dependency of the supercapacitance performance over the precursor components’ molar ratios. The specific capacity and its retention were found to increase with increasing CoCl₂ in the electrolyte with a starting value of 474.6 C/g (791 F/g) at an applied current load of 1 A/g for a molar ratio of Co(CH₃COO)₂:CoCl₂ of 100:0. High specific capacity of 1548 C/g (2580 F/g) and large retention (90.5%) were obtained at a critical molar ratio of Co(CH₃COO)₂:CoCl₂ of 20:80. However, with 100% CoCl₂ in the electrolyte, the specific capacity lowered to 276 C/g (460 F/g) with poor retention of only 60%. Crystallinity and morphological features, driven by the electrolyte concentration with molar variations of the deposited films, have been found to influence the specific capacitance performance. The degree of crystallinity, and the presence of Co and Co₃O₄ phases for the different molar ratios have been revealed by X-ray diffraction (XRD) studies. The diverse morphological features obtained by scanning electron microscopy (SEM) and the varying quantities of Co and O in the Co–Co₃O₄ nanocomposite thin films as confirmed by energy-dispersive X-ray spectroscopy (EDX) spectra correlate well with the electrochemical performance. The phase composition was further confirmed by the presence of Co–O bonds via the attenuated total reflection–Fourier transform infrared (ATR-FTIR) spectra obtained on these films.