Adjusting hydrophily and aromaticity strategy for pitch-based hierarchical porous carbon and its application in flexible supercapacitor

Abstract

Coal tar pitch (CTP), residue of coal tar distillation process, is regarded as one promising precursor of porous carbon (PC). However, almost all the polycyclic aromatic hydrocarbons (PAHs) in CTP are hydrophobic, their poor dispersion in aqueous solution and insufficient contact with activating agents restrict the activation effect and cause uneven activation easily. Moreover, these PAHs possess easy polycondensation feature in heat-treatment process, which also obstruct the development of pore structures seriously. In this work, we proposed both introducing hydrophilic functional groups and adjusting aromatic structure strategy to modify its activation property. CTP was modified by H2O2 (CTP (O)) and HNO3 (CTP (N,O)), respectively. After activation, the modified samples derived porous carbon (PC-CTP (O) and PC-CTP (N,O)) had more developed pore structure, especially for PC-CTP (N,O), which possessed high specific surface area (2087 m2/g), hierarchical pore structure and certain N content (3.13 wt%). The mechanism was disclosed by analyzing structure changes of PAHs before and after different modifications. Specific capacitance of PC-CTP (N,O) attained 318.1 F/g at 0.5 A/g in three-electrodes system. Two equal PC-CTP (N,O) electrodes were further assembled into flexible cells using PVA/KOH solid electrolyte, and LED lights were lit for more than 4 min by three cells connected in series.