Enhancing electrochemical performance of PECVD-fabricated MWCNTs: Influence of electrolyte selection on electrochemical traits and device functionality

This study investigates the impact of electrolytes on MWCNTs synthesized through PE-CVD, aiming to bridge the critical knowledge gap in selecting the most suitable electrolyte for MWCNT-based supercapacitor electrodes by performing a comparative electrochemical study. The structural analysis was carried out using X-ray diffraction (XRD), Raman spectroscopy, and high-resolution transmission electron microscopy (HR-TEM). The reflection at 2θ ∼25.40° in the XRD pattern, while two intense bands at 1324 cm⁻¹ and 1576 cm⁻¹ in Raman spectroscopy confirm the single-phase nature of MWCNTs. The FE-SEM image demonstrates dense tubular-type nanostructures. The interplanar spacing of ∼0.348 nm further validates the successful growth of MWCNTs. The MWCNTs had a high adsorption capacity with a specific surface area (SSA) of 68.73 m²/g and a 44.12 Å of average pore size. Electrochemical impedance spectroscopy (EIS), galvanostatic charge-discharge (GCD), and cyclic voltammetry (CV) were used to evaluate the electrochemical characteristics in 1 M KCl, KOH, Na₂SO₄, and NaOH electrolyte solutions. The GCD analysis revealed that the MWCNTs exhibited the highest specific capacitance in 1 M NaOH, which was 65.23 F/g at 1 A/g. In addition, the CV analysis indicated the specific capacitance of 61.51, 67.38, 71.63, and 72.17 F/g at a scan rate of 5 mV/s in 1 M KCl, KOH, Na₂SO₄, and NaOH electrolytes, respectively. According to the cyclic stability studies, the electrodes remained highly stable over 1000 cycles in 1 M NaOH, which shows 98 % retention. Furthermore, a symmetric supercapacitor device designed using MWCNTs exhibited a specific capacitance of 26.75 F/g and 23.57 F/g from GCD (0.25 A/g current density) and CV (5 mV/s scan rate), respectively. The observed energy and power densities were 3.71 Wh/Kg and 5000 W/kg, respectively, with a retention of 89 % after 1000 cycles, indicating its potential for future energy storage applications.