Design and preparation of highly structure-controllable mesoporous carbons at the molecular level and their application as electrode materials for supercapacitors

Highly structure-controllable mesoporous carbons (HSCMCs) were prepared through a simple carbonization procedure using well-controlled diblock copolymer precursors. We chose polyacrylonitrile-block-polymethylmethacrylate diblock copolymers as precursors, containing a source of carbon, i.e., polyacrylonitrile (PAN), and a sacrificial block, i.e., poly methyl methacrylate (PMMA). PAN-b- PMMA diblock copolymers were synthesized successfully by atom transfer radical polymerization (ATRP) in DMF at 90 degrees C with well-controlled molecular weight and narrow polydispersity. The as-synthesized PAN-b-PMMA diblock copolymers experienced a microphase-separation process to form a self-assembled nanostructure at 250 degrees C and then converted to a mesoporous carbon phase after carbonation at 800 degrees C. The mesoporous sizes of HSCMCs were increased with the increment of molecular weight of the sacrificial block (PMMA). In addition, the HSCMCs exhibited well-controlled mesoporous sizes of 5.96-17.42 nm and high specific surface areas of 427.6-213.1 m(2) g(-1). The well-controlled pore structure in such materials provided huge potential application as electrode materials for supercapacitors. In particular, HSCMC-5 with an optimal mesoporous size of 13.68 nm could achieve the highest specific capacitance of 254 F g(-1) at a current density of 0.5 A g(-1) in 2 M KOH aqueous electrolyte. Furthermore, it also possessed an excellent rate capability of 78% capacitance retention as the current density increased from 0.5 A g(-1) to 5 A g(-1) and a superior cycling performance of 96% capacitance retention after 10 000 cycles at a current density of 2 A g(-1). Besides, by precisely controlling the pore structure of HSCMCs, the mechanism of electric double layer capacitors could be investigated systematically.