Vaporized Hydrothermal Functionalization of Carbon Fiber and Its Superior Supercapacitor Performance
Chongjun Zhao, Chongjun Zhao, Jiexin Zheng, Yixuan Wang, Pengfei Rui, Guang Yang, Chunhua Zhao, Chunhua Zhao, Sijia Xu
Abstract
Carbon fibers are promising in directly being used as a freestanding electrode in flexible and wearable devices due to their high conductivity and good mechanical performance. However, those micrometer-sized carbon fibers usually suffer from disadvantages including poor activity and a low surface area due to an inert surface, solid structure, and high diameter (7–15 μm). Traditional chemical activation methods in a liquid phase have a low efficiency and produce a vast waste solution. In this work, a vaporized hydrothermal oxidation process is proposed, in which vaporized functionalization of carbon fibers is completed during a hydrothermal process of 5 mL of aqueous solution containing 0.5 mL of nitric acid in a 100 mL autoclave. Combined with the subsequent aerobic pyrolysis process, this vaporized hydrothermal method converts smooth and inert carbon fibers into porous and activated carbon fibers, accompanied by a decrease of their diameter from 6.9 to 2.7 μm. Consequently, functionalized carbon fiber directly used as an electrode exhibits a high mass specific capacitance of 118.97 F g–1 (vs 0.217 F g–1 for pristine CF) whereas its symmetric supercapacitor delivers an energy density of 6.5 W h kg–1 and a maximum power density of 5000 W kg–1.