Hollow carbon microtubes from kapok fiber: structural evolution and energy storage performance

Hollow carbon microtubes, with tunable porosity and surface chemistry, are highly desired for advanced energy conversion and storage applications. Although most natural fibers possess a hollow tubular structure, their original morphology is easily destroyed when they are carbonized directly due to the pyrolysis reactions. In this study, using kapok fiber as a precursor, hollow carbon microtubes were obtained by pre-stabilization and subsequent carbonization–activation in the presence of (NH4)2HPO4. During structural evolution from an organic biomass fiber to a hollow carbon fiber, (NH4)2HPO4 acts not only as a porogen and nitrogen/phosphorus source for in situ activation and doping but also as a crosslinking agent for chemical stabilization. The material exhibited good electrochemical performance in an organic electrolyte when evaluated as a supercapacitor electrode due to highly accessible surface area, convenient ion diffusion, and electron transfer. This study provides insights for the design of an anisotropic porous carbon structure towards next-generation high-power smart devices.