Chemically Bonded Carbon Nanotubes to Au Films for Robust High-Performance Electrochemical Double-Layer Supercapacitors

As energy storage devices, electrochemical double-layer capacitors (EDLCs) are a potential alternative to traditional batteries owing to their higher charge-discharge capability, higher power density, and longer life span; however, EDLCs typically lack energy density. Carbon nanotubes (CNTs), which have a high surface area and excellent conductivity, are promising for improving the energy density in EDLCs. In this study, an innovative approach was adopted to fabricate CNT-metal electrodes, in which chemical bonds between vertically aligned carbon nanotubes (VACNTs) and Au metal were formed via a linker molecule, resulting in robust, highly electrically conductive CNT-Au bonds without compromising the free-standing nature and quality of the VACNT array. Specifically, VACNT arrays prepared through chemical vapor deposition on an Al₂O₃/Si substrate were transferred onto Au metal while maintaining their free-standing arrangement. The average resistance at the CNT-Au interface was 0.5 kΩ over an area of 1 nm², as measured using an atomic force microscopy-based technique. Supercapacitors fabricated using the prepared VACNT-Au electrodes had a specific capacitance of 50 mF cm^-2 (9.5 F g^-1), thereby outperforming most pure VACNT-based EDLCs. Moreover, these devices exhibited outstanding stability, with 74% capacitance retention after 100,000 charge-discharge cycles.