N, O-codoped porous carbon fiber cloth synthesized by molecular dispersed CaCl2·6H2O in situ activation for high performance supercapacitors

Abstract

In this study, a nitrogen/oxygen co-doped carbon fiber cloth with a hierarchical porous structure was synthesized by one-step carbonization and in situ activation method and acted as binder-free electrode materials for supercapacitors. Cotton fiber cloth served as the carbon precursor, while molecular dispersed CaCl2·6H2O and urea functioned as activator and N dopant, respectively. The influence of molar concentration of CaCl2·6H2O and urea on the microstructure and capacitive performance of the resulting products were investigated. CaCl2·6H2O has an expansion effect on pores, resulting in reduction of micropores. Hence, the specific surface area of the resulting porous carbon increased first and then decreased with the increase of CaCl2·6H2O concentration. In addition, the erosion of NH3 and CO2 (produced by the decomposition of urea) at high temperature on the surface of the samples promoted the formation of porous structure. Urea plays the dual role of doping and activation agent. The morphology and structure analysis shown that the activated samples exhibited hierarchical pore structure, large specific surface area, and high heteroatom content. The optimal sample NAC-20 exhibited good capacitive performance, including high specific capacitance of 260.9 F g−1 at 0.1 A g−1 and good rate performance. Moreover, the symmetric supercapacitor exhibited a maximum energy density and power density of 16.2 Wh kg−1 and 19.0 kW kg−1, respectively, in 6 M KOH electrolyte. In this work, a green, low-cost molten salt activation method was proposed to synthesis biomass derived porous carbon materials for energy storage devices.