Letter Cite This: ACS Macro Lett. 2019, 8, 331−336
pubs.acs.org/macroletters
Solution Self-Assembly of an Alternating Copolymer toward Hollow Carbon Nanospheres with Uniform Micropores Chuanlong Li, Tahir Rasheed, Hao Tian, Ping Huang, Yiyong Mai,* Wei Huang,* and Yongfeng Zhou* School of Chemistry and Chemical Engineering, State Key Laboratory of Metal Matrix Composites, Shanghai Key Laboratory of Electrical Insulation and Thermal Ageing, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China ACS Macro Lett. Downloaded from pubs.acs.org by UNIV OF TEXAS AT DALLAS on 03/09/19. For personal use only.
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ABSTRACT: Controllable preparation of porous hollow carbon spheres (HCSs) has attracted considerable attention due to their potential applications, e.g., in energy conversion and storage. We report for the first time the synthesis of narrowly size-distributed HCSs with uniform micropores in the wall, through a simple template-free approach, which employs the solution self-assembly of an alternating copolymer (poly(9,9′-bis(4-glycidyloxyphenyl)fluorene-alt2,3-dihydroxy-butylene dithioether) (P(BGF-a-DHBDT))). This alternating copolymer first self-assembled into previously undocumented hollow polymeric spheres (HPSs) in an N,Ndimethylformamide (DMF)/H2O solvent mixture. After the cross-linking of the BGF segments in the spheres, the stabilized HPSs (CL-HPSs) were carbonized at 800 °C under N2 atmosphere, yielding porous HCSs with uniform micropores of very narrow size distribution (0.4−0.8 nm) in the wall, benefiting from the uniform DHBDT block length in the alternating copolymer. Through KOH activation, which made the internal pores fully interconnected, uniform micropores (0.5−1.0 nm) of a narrow size distribution were retained within the activated HCSs (A-HCSs), while their specific surface areas (SSAs) were much increased to 2580 m2 g−1. As a proof of concept, the A-HCSs were applied as electrode materials of supercapacitors. They exhibited superior electrochemical performance with a high specific capacitance (292 F g−1 at 0.2 A g−1), good rate capability, and outstanding cycling stability with no apparent capacitance loss after 10 000 cycles.
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method is advantageous to the template-assisted approach, as the former can avoid the tedious process of template removal and the possible impurity introduction during this course.14−16 However, it still remains challenging for the template-free method to prepare HCSs with relatively uniform micropores in the wall, as pores generally form randomly with uncontrollable structures and sizes ranging from zero to tens of nanometers without template assistance. Self-assembly of amphiphilic copolymers in solution has been considered as a versatile approach for the preparation of various ordered nanostructures.17−28 Among different types of polymer precursors, alternating copolymers exhibit a unique alternating monomeric unit structure in the backbone. This allows the self-assembly of alternating copolymers into nanostructures with hydrophobic or hydrophilic domains of uniform dimension in spite of the dispersity of the copolymers.29−34 By taking advantage of the peculiarity of alternating copolymers, we developed the first template-free method toward porous HCSs with uniform micropores in the
orous hollow carbon spheres (HCSs) have attracted considerable attention due to a wide range of their potential applications such as in energy storage and conversion.1−10 For instance, when serving as electrode materials of supercapacitors, the porous structure in the shell of HCSs may facilitate the mass transport to the cavity and afford the electrode high specific surface areas (SSAs). Meanwhile, the hollow cavity can reserve the electrolyte and shorten the ion diffusion distances from the exterior to the interior surfaces.11 In contrast, solid carbon spheres do not have lumens that can reserve electrolyte, and thus the electrolyte cannot transport smoothly into or even cannot reach their interior.1,8 Thereby, the pore structure significantly affects the electrochemical performance. In aqueous electrolytes, the micropores (
