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 Al 2 O 3 /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 nm 2, 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.