Morphology-driven ionic pathway engineering in CuCo2O4/carbon nanotubes for high diffusion hybrid supercapacitors across diverse electrolyte conditions

Abstract

In tandem with conductive carbon nanomaterials, redox-active spinel oxides offer a promising strategy to improve the efficacy of electrochemical energy storage devices. Among them, CuCo₂O₄ (CCO) has attracted considerable attention; however, systematic evaluations of its controlled morphology and diffusion dynamics in varied electrolytes remain scarce. In this study, we engineered CCO nanorods, spherical particles, and their nanocomposites with carbon nanotubes (5, 10, and 15 wt%), named CCO-I, CCO-II, and CCO-III, to investigate diffusion behaviour using the galvanostatic intermittent titration technique across different electrolytic conditions, along with key performance parameters. Electron microscopy verified the successful formation of the desired morphologies, where nanorods provided large surface-active sites and spherical particles offered high volumetric energy density. Electrochemical measurements in 1 M KOH, coupled with theoretical investigation using Dunn's model and determination coefficients (R²), revealed a mixed capacitive-faradaic charge storage nature of the samples. Among all variants, CCO-II delivered the best performance, with a specific capacity of 1702.01 C g⁻¹ along with an energy density of 113.46 Wh kg⁻¹. It also retained 99.94% capacity after 4500 cycles at 0.4 A g⁻¹, while galvanostatic intermittent titration technique showed balanced diffusion coefficients of 3.9 × 10⁻¹¹ cm² s⁻¹ in 1 M KOH and 4.1 × 10⁻¹¹ cm² s⁻¹ in 3 M NaOH. Further, the optimized sample exhibited low internal resistance and high ionic conductivity. Overall, these results highlight the potential of the CCO-II as a promising candidate for high-performance energy storage electrodes.