Design And Preparation Of Structure-controllable Porous Carbons And Their Capacitance Properties

In this paper, the newest development progress in research of supercapacitors and electrode materials of supercapacitors was reviewed, especially focused on the supercapacitor carbon materials controllable preparation and surface modification of structural control technology development status. For electric double layer capacitor, the effect of porosity, pore size distribution of the carbon materials on super capacitor performance is a very important fundamental scientific question. Unfortunately, this problem is basically limited to the qualitative description, no experimental verification, which is attributed to the complexity of the system and the structure of the carbon material. Accordingly, the new idea of preparing structure-controllable porous carbon is put forward, which is the high temperature carbonization of the block copolymer. At the same time, the electrochemical performance of electrode material is studied. Moreover, the relationship between the structure of block copolymer, pore structure and electrochemical performance of the carbon material is explored.The work has been carried out following generally the mainline as controlled syntheses of polymer-structure controllable carbon materials-high performance carbon electrode material of supercapacitor. The pore structure of the carbon material is regulated by controlling the flexibility of the block polymers segment, changing the molecular weight of the segment and the relative content of the different segments of the block copolymer morphology. The main contents are presented as follows:(1) The PAN-b-PMMA diblock copolymers were synthesized successfully by atom transfer radical polymerization(ATRP) with well-controlled molecular weight and narrow polydispersity, containing a reserved segment, i.e., polyacrylonitrile(PAN), and a sacrificial block, i.e., polymethylmethacrylate(PMMA). The PAN-Br macroinitiator(MnGPC = 22153 g mol-1, PDI = 1.04)was successfully prepared by ATRP. The PAN-b-PMMA diblock copolymer precursors(Mn PAN-b-PMMA = 26726 ~ 42234 g mol-1, PDI < 1.3) with various volume fractions of PMMA segment(f PMMA = 10.50 ~ 33.89%) were successfully obtained by precise controlling of the reaction conditions of ATRP, while the reserved segment(PAN) remained unchanged. The as-prepared carbon materials possessed highly well-controllable pore structure with DFT mesopore sizes of 5.96 ~ 17.64 nm and higher specific surface area of 274.6 ~ 427.36 m2g-1. The specific capacitance of the as-obtained carbon materials was firstly increased and then decreased with the increment of mesopore size. In particular, the as-obtained mesoporous carbon(13.64 nm) possessed the optimal supercapacitive performance.(2) The effects of HNO3 activation on pore structure and electrochemical properties were investigated systematically utilizing PAN418-b-PMMA169 diblock copolymer as a precursor. The oxygen- and nitrogen-containing functional groups were introduced into the carbon materials by surface activation of HNO3 solution, which can improve surface hydrophilicity and the ratio of specific surface area. The specific capacitance of as-obtained carbon materials was enhanced significantly, due to pseudocapacitance of these functional groups. Meanwhile, activated nitrogen-doped hierarchical porous carbon(A-NHPC) was successfully systhesized by HNO3 activation, which possessed spervior supercapacitive performance, due to more microporous and ultra-microporous structure, obvious hierarchical porous structure, and higher specific surface area. A-NHPC14-4-80 displayed high specific capacitance of 314 F g-1; it is mainly due to the introducing of oxygen- and nitrogen-containing functional groups, better conductivity, and more obvious hierarchical porous structure.(3) Highly electrochemically activated nitrogen-enriched carbons(HEANCs) were successfully prepared through a simple KOH activation process with suitable and controllable activating conditions: temperature(600 ~ 800 °C), ratio(0.5 ~ 4), and time(1 ~ 2 h), utilizing PAN418-b-PMMA111 diblock copolymer as a precursor. The obtained HEANCs showed tunable surface areas of 1 088 ~ 3 069 m2 g-1 and pore diameters of 1.68 ~ 3.45 nm with moderate nitrogen content of 2.3 ~ 7.5%. The well-controlled pore structure in such materials provided huge potential application as electrode materials for supercapacitors. The specific capacitance of the as-obtained carbon materials was increased with the increment of specific surface area. HEANC750-4-2h could achieve an extraordinary specific capacitance of 542 F g-1, an excellent cycle stability of 95% capacitance retention, and an outstanding rate capability of 78% capacitance retention in 6 M KOH aqueous electrolyte, due to the moderate mesoporous size of 3.45 nm, ultra-high surface area of up to 3 069 m2 g-1, total pore volume of 2.29 cm3 g-1, and appropriate nitrogen content of 2.39%. Meanwhile, HEANC750-4-2h//HEANC750-4-2h possessed a higher energy density of 12.1 Wh kg-1.