Surface-Functionalized Carbon Nanotube Yarn for High-Performing Flexible Supercapacitors

Carbon nanotube yarn (CNTY)-based fiber-shaped supercapacitors (FSCs) have shown great promise due to their light weight, flexibility, and wearability. However, their limited capacitance restricts broader applications. Additionally, the hydrophobic and chemically inert nature of CNT surfaces hinders the uniform growth and stable attachment of transition metal oxides such as MnO2, posing significant challenges to enhancing the overall performance. To address these issues, we propose a hydrogen peroxide (H2O2) pretreatment of CNTY to introduce hydrophilic functional groups (e.g., −OH and −COOH) and create structural defects. This modification improves MnO2 adhesion and enables uniform growth on the CNTY surface. The enhanced MnO2-CNT interface reduces resistance and facilitates charge transfer, resulting in a composite electrode with significantly improved specific capacitance and cycling stability. As a result, the MnO2@CNTY electrode achieves a specific capacitance of 227.64 mF cm–2 at a current density of 0.1 mA cm–2 and retains 95.8% of its initial capacitance after 10000 cycles. Furthermore, the integration of MnO2@CNTY SCs in series demonstrates its application potential in smart electronics. This study provides an effective approach for fabricating high-performing electrodes, advancing energy storage technologies.