关键词: 紫菜, 多孔炭, 超级电容器, 碱活化, 氮掺杂

Abstract:

Porphyra is not only inexpensive and easily available but also rich in protein. Employing porphyra as raw material to provide carbon and nitrogen sources, crude carbon was first prepared by pre-carbonization. Subsequently, it was further activated by KOH to create numerous pores in the final product, thus achieving the fabrication of nitrogen-doped hierarchical porous carbon. When the ratio of KOH to crude carbon was 2∶1, the resulting nitrogen-doped porous carbon (NDHPC-2) possessed the most abundant porosity and the best honeycomb-like hierarchal porous structure, whose specific surface area, mesopore percentage and nitrogen doping content were 1975.2m²/g, 41.2% and 4.3%, respectively. Moreover, the electrochemical tests in a three-electrode system showed that the NDHPC-2 electrode released a maximum specific capacitance of 185.4F/g with splendid rate performance, coulombic efficiency and cycle stability. Based on this carbon material, a symmetric supercapacitor (NDHPC-2//NDHPC-2) was built, which offered a largest energy density of 6.7Wh/kg and still maintained outstanding rate capability, coulombic efficiency and cycling durability. For example, when consecutively charged/discharged at a high current density of 10A/g for over 10000 cycles, the coulombic efficiency of such device was close to 100% from beginning to end and its capacitance decay was almost negligible during the whole experiment as well. The supercapacitive properties of NDHPC-2 porous carbon, both in three- and two-electrode systems, were comparable or even superior to those of many reported porous biomass carbon materials, therefore exhibiting excellent advantages for energy storage and promising potential toward practical applications.

Key words: porphyra, porous carbon, supercapacitor, alkali activation, nitrogen doping