Oxygen Evolution Assisted Fabrication of Highly Loaded Carbon Nanotube/MnO₂ Hybrid Films for High-Performance Flexible Pseudosupercapacitors

To date, it has been a great challenge to design high-performance flexible energy storage devices for sufficient loading of redox species in the electrode assemblies, with well-maintained mechanical robustness and enhanced electron/ionic transport during charge/discharge cycles. An electrochemical activation strategy is demonstrated for the facile regeneration of carbon nanotube (CNT) film prepared via floating catalyst chemical vapor deposition strategy into a flexible, robust, and highly conductive hydrogel-like film, which is promising as electrode matrix for efficient loading of redox species and the fabrication of high-performance flexible pseudosupercapacitors. The strong and conductive CNT films can be effectively expanded and activated by electrochemical anodic oxygen evolution reaction, presenting greatly enhanced internal space and surface wettability with well-maintained strength, flexibility, and conductivity. The as-formed hydrogel-like film is quite favorable for electrochemical deposition of manganese dioxide (MnO₂) with loading mass up to 93 wt% and electrode capacitance kept around 300 F g^-1 (areal capacitance of 1.2 F cm^-2). This hybrid film was further used to assemble a flexible symmetric pseudosupercapacitor without using any other current collectors and conductive additives. The assembled flexible supercapacitors exhibited good rate performance, with the areal capacitance of more than 300 mF cm^-2, much superior to other reported MnO₂ based flexible thin-film supercapacitors. A high-performance carbon nanotube (CNT) film prepared via floating catalyst chemical vapor deposition method is expanded and activated by an electrochemically anodic method in H₂SO₄ aqueous solution. This activated CNT film can be used for depositing metallic oxide (such as MnO₂) with ultra-high loading mass (90 wt%) for flexible supercapacitors with superior areal capacitance.