Solar pyrolysis of algae in molten salt for capacitive carbon preparation

Pyrolysis of algae in molten carbonates driven by concentrated solar energy is proposed as an economical and environmentally friendly method to obtain capacitive carbon for supercapacitors. The effects of molten car-bonates on pyrolysis process and electrochemical performance at different temperatures (800, 850 and 900 degrees C) are investigated. Na2CO3-K2CO3 leads to a relatively high carbon yield and superior microstructure at around 900 degrees C compared with other molten salts, which is beneficial for capacitive carbon production. The as-prepared carbon possesses a high specific surface area of 2009.26 m2/g and a hierarchical porous structure mainly con-sisting of micropores and mesopores. Moreover, it contains abundant oxygen-and nitrogen-containing functional groups, such as C--O, -OH, pyrrolic-N and quaternary-N. These features play an important multiple synergy for the preparation of desirable capacitive carbon, which has a high specific capacitance of 230.2 F/g at 0.25 A/g and a capacitance retention of 75.54% at 2 A/g. This work provides a green and promising approach for the production of heteroatom-doped capacitive carbon with superior porosity and specific surface area.