Hierarchically porous carbon by activation of shiitake mushroom for capacitive energy storage

We present a facile yet effective two-step activation method to prepare a hierarchically porous carbon with natural shiitake mushroom as the starting materials. The first step involves the activation of shiitake mushroom with H3PO4, while the second step is to further activate the product with KOH. The resulting carbon is comprised of abundant micro-, mesopores and interconnected macropores that has a specific surface area up to 2988 m2 g−1 and pore volume of 1.76 cm3 g−1. With the unique porous nature, the carbon exhibited a specific capacitance of 306 and 149 F g−1 in aqueous and organic electrolyte, respectively. Moreover, this carbon also shows a high capacitance retention of 77% at large current density of 30 A g−1 and exhibited an outstanding cycling stability with 95.7% capacitance preservation after 15,000 cycles in 6 M KOH electrolyte. The far superior performance as compared with those of the commercially most used activated carbon RP20 in both aqueous and non-aqueous electrolyte demonstrates its great potential as high-performance supercapacitor electrode. The two-step method developed herein also represents a very attractive approach for scalable production of various functional carbon materials using diverse biomasses as starting materials.