Covalently-Functionalized Graphene for Supercapacitor Application
A facile three-step synthesis to prepare covalently-grafted PANI/GO nanocomposites at room temperatures. The covalently-grafted composites formed a uniform hierarchical morphology of nanorod-like PANI grown on planar GO sheets, in contrast to a nonuniform morphology of nongrafted composites. The covalently-grafted PANI/GO composites exhibited higher surface area and larger pore volume compared with PANI and and noncovalently-grafted PANI/GO composites. These features allow the increased exposure of PANI to the electrolyte ions, resulting in a more accessible PANI surface for redox reaction species and faster ion transport. The covalently-grafted PANI/GO composites prepared with an aniline/GO ratio of 6:1 showed the highest capacitance of 422 F/g at a current density of 1 A/g. The capacitance can be retained at about 83% after 2000 cycles at 2 A/g. The excellent electrochemical performance can be attributed to the maximized synergistic effect between GO and PANI in the PANI/GO composites prepared via this covalent grafting approach.
Phenylbenzimidazole covalently-functionalized graphene was prepared by hyderthermal treatment of benzoic acid-functionalized graphene oxide and o-phenyldiamine in a teflon-lined autoclave for 16 h at 160 °C. Difference from pristine graphene oxide, carboxyl groups are present on both edge and basel plane of graphene oxide sheets in the benzoic acid-functionalized graphene oxide, which was prepared from diazonium reaction. The phenylbenzimidazole group can effectively act as the spacers to partially prevent the restacking/aggregation of the graphene sheets. The phenylbenzimidazole groups are also electrochemical active and can contribute to psedocapacitance. When used as supercapacitor electrodes, the functionalized graphene materials exhibit much better electrochemical performances (more than twice as much capacitance) than pure graphene, implying their potential for energy storage applications.
Figure 1. (a) CV curves of polyaniline and and covalently-grafted PANI/GO composites in 1 M H2SO4 at a scan rate of 10 mV/s; (b) CV curves of graphene and and Phenylbenzimidazole covalently-functionalized graphene in 1 M Na2SO4at a scan rate of 10 mV/s.
1. Conway, B. E., Electrochemical Supercapacitors: Scientific Fundamentals and Technological Applications. Springer: 1999.
2. Zhang, L. L.; Zhao, X. S., Chemical Society Reviews 2009, 38(9), 2520-2531.
3. Wang, L.; Fujita, M.; Inagaki, M., Electrochimica Acta 2006, 51(19), 4096-4102.
4. Pandolfo, A. G.; Hollenkamp, A. F., Journal of Power Sources 2006, 157(1), 11-27.
5. Allen, M. J.; Tung, V. C.; Kaner, R. B., Chemical Reviews 2009, 110(1), 132-145.