Preparation of porous carbon electrodes from semen cassiae for high-performance electric double-layer capacitors

A series of sponge-like hierarchical porous carbons are prepared using semen cassiae as the precursor and potassium oxalate monohydrate as the activation agent. These sponge-like carbon materials have high surface areas, wide distributions of pore size, and the appropriate forms of nitrogen/oxygen derivatives. All these advantages in structures and surface states contribute to the outstanding performances of such materials as electrodes for high performance electric double-layer capacitors, which include high specific capacitance, high cycling stability, and high energy density. For example, the optimal sample exhibits a high specific capacitance of 401 F g(-1), excellent cycling stability (94.5% retention after 10 000 cycles), high energy density (12.01 W h kg(-1)) and a high power density (10200 W kg(-1)) in 1 M H2SO4 solution.