Simple Mixed-Acid-Treated Carbon Fiber Electrodes with Oxygen-Containing Functional Groups for Flexible Supercapacitors

Flexible supercapacitors are demanded for energy storage of wearable electronics. In this paper, a simple strategy for preparing flexible carbon fibers (CFs) with good energy storage capacity using a mixed acid treatment process is reported. When the volume ratio of concentrated sulfuric acid to concentrated nitric acid is 3:1, the carbon fiber electrodes have the best electrochemical performance with a high capacitance of 27.83 F g−1at 15 mA g−1and extremely high capacitance retention of 79.9% after 500 cycles at 100 mA g−1. Furthermore, their energy density can reach 3.86 Wh kg−1with a power density of 7.5 W kg−1. Such an excellent electrochemical performance of carbon fiber electrodes is attributed to their surface rich oxygen-containing functional groups, rough surface, and a certain number of graphene quantum dots (GQDs). Importantly, the all-solid-state flexible supercapacitor performs excellent bending stability performance with a capacitance retention of almost 100% after 500 times of bending at 180°, showing good prospects and applications in the field of flexible energy storage devices.Keywords:carbon fibers;mixed acid treatment;oxygen-containing functional groups;electrochemical test;flexible supercapacitor