Low Cost Commercially Available Block Copolymer Derived Highly Porous Carbon for Advanced Supercapacitors

Abstract

Increasing global warming and CO2 emission have created an urgent requirement of clean and green energy solutions which can resolve these issues. These energy solutions include fuel cells, batteries, and supercapacitors (SCs). Among them SCs are the devices of prime importance owing to their long cycle life (>106 charge discharge cycles) and wide applicability in variety of fields. Carbon based SC are commercialized and are being utilized worldwide, however their energy density (ED) is still limited to ~ 5 Wh.kg-1. Researchers have tried and reported various ways to improve its ED and overall performance. The surface area and porosity play a crucial role in deciding the overall performance of SCs. The higher specific surface area (SSA) and hierarchical pore structure with the good conductivity values are the desirable properties for the most suitable carbon electrode material. Block copolymers taking the advantage of structure directing property makes them suitable for tunning the surface area and porosity of product carbon material.Here, we have used the commercially available low-cost block copolymers including F127, and Brij-58 for the preparation of highly porous carbon materials. We have used low-cost glucose as the carbon precursor with KOH activation for improving the surface area values. The brief synthesis route includes the first step as the self-assembly of block copolymer template in the solvents like D.I. water and THF. Then the impregnation of carbon material is followed with the refluxing procedure followed by the hydrothermal treatment at 180 ºC for 5 h. Then the KOH activation and the further carbonization at various temperatures 700, 800 and 900 is performed. All the samples then washed with 5% HCl solution followed by repetitive D.I., methanol and ethanol washing. The final black colored powder is then utilized for various material and SC characterizations.The as synthesized material shows broad peaks around 25º in powder x-ray diffraction pattern. Moreover, the BET surface area measurement predicted the SSA in the range of 500-600 m2.g-1 for most of the samples. These SSA values are pretty much desirable for good capacitance storage. In addition to this the FESEM images shown in Figure 1 confirms the formation of spherical particles due to the structure direction of block copolymers. Along with this, the structural characterization including EDS and XPS further confirms the good carbon content in the developed material.The various developed materials were then tested for SC electrode in three electrode and two electrode measurements. The F127 directed carbon material has exhibited the maximum performance of ~ 250 F.g-1 at the scan rate of 5 mV.s-1, which is very good keeping in mind the low cost strategy for the synthesis of material. In two electrode packed device, the materials shows excellent specific energy of ~15 Wh.kg-1 with high specific power of 270 W.kg-1.Figure 1. a) low magnification FESEM image showing the formation of spherical shape particles directed by F127, b) high magnification image showing the single spherical particle directed by Brij 58, c) three electrode CV results at various scan rates for F127 derived spheres. Figure 1