Dual redox-active bi-metallic oxide/nanoporous carbon nanotube hybrid architectures: probing diffusion dynamics and ionic conductivity for advanced supercapacitors

Abstract

Growing demand for sustainable energy storage drives the development of advanced materials and porous structures. Here, CrCo₂O₄ (CCO) and its composites with varying carbon-nanotube (CNT) content (3, 6, and 9%) are synthesized, termed as CCO-3%, CCO-6% and CCO-9%. X-ray diffraction confirms the spinel phase of CCO, while the morphology reveals higher CNT content, enhancing surface porosity. A cyclic voltammetry study demonstrates a battery-type hybrid charge storage mechanism, as evident by Dunn's model. Among these composites, CCO-9% exhibits the highest performance, achieving an impressive specific capacity (Q_sp) of 817.30 C g⁻¹ at 1.3 A g⁻¹. It delivers an energy density (E_d) of 56.75 Wh kg⁻¹ along with a power density (P_d) of 338.98 W kg⁻¹. The galvanostatic intermittent titration technique reveals the highest value of diffusion coefficient, ∼2.65 × 10⁻¹⁰ cm² s⁻¹, while electrochemical impedance spectroscopy reveals a reduced charge transfer resistance and an improved ionic conductivity of 4.02 × 10⁻⁴ S cm⁻¹. The electrode is utilized in an asymmetric device, where testing reveals a Q_sp of 129.48 C g⁻¹, corresponding to an E_d of 21.58 Wh kg⁻¹ at a P_d of 1016.94 W kg⁻¹. The electrode displays remarkable cycling stability, sustaining 98% of its initial capacity after 10k cycles. These results highlight CCO-9% as a viable contender for hybrid capacitors, portable electronic devices and regenerative braking systems.