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

摘要：

紫菜不仅廉价易得，而且富含蛋白质。以紫菜为原料，提供炭源和氮源，先预炭化获得粗炭，再以KOH活化造孔实现氮掺杂分级多孔炭材料的制备。当KOH与粗炭比为2∶1时所获得的氮掺杂多孔炭材料（NDHPC-2）具有最丰富孔隙和最佳蜂窝状分级孔结构，其比表面积高达1975.2m²/g，介孔占比41.2%，掺氮原子含量4.3%。此外，电化学测试表明，三电极体系中NDHPC-2的最大比电容为185.4F/g，同时兼具良好倍率性能、库仑效率和循环稳定性。基于此炭材料，进一步组装了NDHPC-2//NDHPC-2对称超级电容器，单个器件最大能量密度为6.7Wh/kg，并依旧保持了出色的倍率性质、库仑效率和反复充放电稳定性。比如在10A/g高电流密度下连续充放电10000次，整个实验过程的库仑效率始终接近100%，电容损失亦几乎可忽略不计。无论三电极还是两电极体系，NDHPC-2多孔炭材料的超级电容性能均可媲美甚至超过许多已报道的生物质多孔炭材料的电化学表现，展现了较好的储能优势和实际应用潜能。

关键词: 紫菜, 多孔炭, 超级电容器, 碱活化, 氮掺杂