Kuiwen Shen

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 °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 °C and then converted to a mesoporous carbon phase after carbonation at 800 °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 m2 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.

A hierarchical porous carbon membrane from polyacrylonitrile/polyvinylpyrrolidone blending membranes: Preparation, characterization and electrochemical capacitive performance

Abstract Novel hierarchical porous carbon membranes were fabricated through a simple carbonization procedure of well-defined blending polymer membrane precursors containing the source of carbon polyacrylonitrile (PAN) and an additive of polyvinylpyrrolidone (PVP), which was prepared using phase inversion method. The as-fabricated materials were further used as the active electrode materials for supercapacitors. The effects of PVP concentration in the casting solution on structure feature and electrochemical capacitive performance of the as-prepared carbon membranes were also studied in detail. As the electrode material for supercapacitor, a high specific capacitance of 278.0 F/g could be attained at a current of 5 mA/cm 2 and about 92.90% capacity retention could be maintained after 2000 charge/discharge cycles in 2 mol/L KOH solution with a PVP concentration of 0.3 wt% in the casting solution. The facile hierarchical pore structure preparation method and the good electrochemical capacitive performance make the prepared carbon membrane particularly promising for use in supercapacitor.

Super long-life supercapacitor electrode materials based on hierarchical porous hollow carbon microcapsules

Remarkable supercapacitor electrodes with a high specific supercapacitance and a super long cycle life were achieved by using hierarchical porous hollow carbon microcapsules (HPHCMs) as active materials. HPHCMs were prepared by a facile chemical route based on pyrolysis of a soft sacrificial template involving a non-crosslinked core of poly(styrene-r-methylacrylic acid) and a crosslinked shell of poly(styrene-r-divinylbenzene-r-methylacrylic acid), which were synthesized by using traditional radical polymerization and emulsion polymerization. The results of scanning electron microscopy, transmission electron microscopy and Brunauer–Emmett–Teller characterizations revealed that HPHCM possessed the desired pore structure with apparent macro-/meso- and micropores, which not only provided a continuous electron-transfer pathway to ensure good electrical contact, but also facilitated ion transport by shortening diffusion pathways. As electrode materials for supercapacitor, a high specific capacitance of 278.0 F g−1 was obtained at the current density of 5 mA cm−2. Importantly, after 5000 potential cycles in 2 M KOH electrolyte at the discharge current density of 20 mA cm−2, the capacitance actually increased from 125 to 160 F g−1 and then remained 151 F g−1, corresponding to a capacitance retention of 120%, likely due to electrochemical self-activation.