Pseudocapacitive enhancement of VACNTs with SnO2 for next-generation supercapacitors

Abstract

Developing high-performance supercapacitors requires electrode materials that combine high energy density, rapid charge transport, and long-term stability. In this study, we report a binder-free hybrid SnO₂/vertically aligned carbon nanotubes (VACNTs) composite electrode by directly growing VACNTs on nickel foam via a plasma-enhanced chemical vapor deposition (PECVD) technique, followed by uniform SnO₂ nanoparticles coating through a wet-chemical method. The hierarchical structure integrates the electric double-layer capacitance (EDLC) of VACNTs with the pseudocapacitance of SnO₂, resulting in enhanced electrochemical performance. The SnO₂/VACNTs electrode exhibited a high specific capacitance (262.39 F g⁻¹ at 5 mV s⁻¹) in 1 M KOH, significantly exceeding pristine VACNTs (24.02 F g⁻¹). It delivered an energy density of 22.79 W h kg⁻¹ at a power density of 0.18 kW kg⁻¹ and retained 93% of its initial capacitance after 2000 cycles, demonstrating excellent rate capability and stability. Electrochemical impedance spectroscopy (EIS) revealed a low charge-transfer resistance (0.93 Ω) and small equivalent series resistance (1.65 Ω), indicating efficient electron and ion transport through the conductive VACNT framework. These results highlight the potential of SnO₂/VACNTs composites as promising binder-free electrodes for next-generation high-energy, high-power supercapacitors.