Self-assembly of polyhedral oligosilsesquioxane (POSS) into hierarchically ordered mesoporous carbons with uniform microporosity and nitrogen-doping for high performance supercapacitors

Polyhedral oligosilsesquioxanes (POSS), regarded as the smallest possible particles of silica , are used as carbon source and assembled into hierarchically porous carbon structures by a block copolymer-assisted method. The obtained carbon materials with high specific surface area of over 2000   m 2   g −1 and large pore volume of over 1.19   cm 3   g −1 possess both quite uniform micropores with the size of ~1   nm and highly ordered mesopores with the size of ~4   nm, owing to the molecular-scale templating effect of POSS siloxane cages as well as the good assembly compatibility between the block copolymers and the aminophenyl-functionalized POSS used. The mesopore arrangement can be two-dimensionally hexagonal ( p 6 m ) or body-centered cubic ( Im 3 ¯ m ) by simply adjusting different block copolymers. Nitrogen functionalities with a relatively high content (~4   wt%) can spontaneously be incorporated into those carbon materials. Benifiting from the uniform microporosity and the nitrogen doping, the specific capacitance of the POSS-derived hierarchically porous carbons can reach ~160   F   g −1 in ionic liquid electrolyte and ~210   F   g −1 in 1   M H 2 SO 4 aqueous electrolyte, when measured at a current density of 0.25   A   g −1 in a symmetrical two-electrode cell. More importantly, the highly ordered mesopores can facilitate ions fast transportion to the fine micropores to achieve the excellent power performance. The hierarchial carbon sample with a hexagonal mesostructure and a high mesoporosity displays the best rate capability with 94% and 97% of capacitance retention in ionic liquid and 1   M H 2 SO 4 , respectively, with the current density range from 0.25 to 10   A   g −1 . By combining self-assembly strategy with rich POSS chemistry, we believe that many other hierarchical hybrid materials or carbon materials with unique electrochemical properties can be synthesized.