3D Porous Hierarchical Microspheres of Activated Carbon from Nature through Nanotechnology for Electrochemical Double-Layer Capacitors

Porous activated carbons have attracted considerable attention as electrode material in energy storage devices, as they have high surface area and good conductivity. However, common processes to synthesize nanostructured electrodes of activated carbon only offer limited control on their morphology and structure. In this work, three-dimensional (3D) porous hollow microspheres of activated carbon are fabricated from various pollen grains (Camellia, Schisandra chinensis, lotus, rape and motherwort) through a facile, green and economic route. The sustainable and abundant carbon sources of pollens allow for mass production of nanostructured activated carbon microspheres (ACMs) with good electrochemical performances. The obtained ACMs retain the 3D hierarchical penetrable architecture of pollen grains, with vertically arranged nanorod-framework constructed shell and high volume of micropores/mesopores. Such activated carbon electrodes show remarkable electrical double-layer storage performances, such as high specific capacitance (250 F g^–1 in organic electrolyte), ultrafast rate capability (210 F g^–1 retained at a very high current density up to 40 A g^–1) and good cycling stability (93.8% retention after 10 000 charge/discharge cycles).