Robust, flexible, freestanding and high surface area activated carbon and multi-walled carbon nanotubes composite material with outstanding electrode properties for aqueous-based supercapacitors

We report on multi-walled carbon nanotubes (MWCNTs) and an activated carbon (AC) composite material as an electrode for electrical double-layer capacitors (EDLCs). Material flexibility, robustness, and electrical conductivity are features that come from the MWCNTs, while a high specific surface area is an AC's intrinsic property. We prepared different MWCNT : AC ratios in solutions, which were filtered to form a buckypaper. We investigated the specific capacitance, equivalent series resistance, working voltage window (WVW), and the specific energy and power. The best electrochemical findings were obtained for the MWCNT : AC ratio of 1 : 3 with a specific capacitance reaching the theoretical limit. A high working voltage window of 1.4 V was verified in aqueous solution. Simultaneously, the symmetric cells were able to cycle for more than one million cycles in fast charge–discharge galvanostatic tests with 93% capacitance retention. Finally, the main criticism regarding the self-supported electrode materials is the difficulty of welding. In this sense, we presented a particular welding process as proof of concept for electrode scalability. Overall, this novel electrode material exhibits a set of exciting properties, which we now tested in EDLCs.