Hierarchical Nanocomposites by Oligomer-Initiated Controlled Polymerization of Aniline on Graphene Oxide Sheets for Energy Storage

Hierarchical graphene oxide-g-polyaniline nanocomposites with a controlled nanostructure of uniformly oriented one-dimensional (1D) polyaniline (PANI) nanocylinders over two-dimensional (2D) graphene oxide (GO) surfaces are synthesized. PANI chains are grown from GO surface attached oligoaniline units following a grafting from approach, via chemical oxidative polymerization in aqueous acidic medium. Detailed kinetic analysis of aniline polymerization, both in the presence of oligoaniline attached graphene oxide and an equivalent amount of graphene oxide only, is presented for better understanding of the effect of oligoanilines over heterogeneous surface catalysis. The developed method involves a generalized approach, which holds potential for applications on various nanosurfaces irrespective of their dimensionality or nature. Significant control over the polyaniline chain growth helps to retain the basic morphology of the template nanomaterials, which is conducive for having improved synergy between the components. The nanostructured materials show further organization to generate unique, highly porous three-dimensional (3D) microstructures. These are presumably generated via supramolecular organization by the in situ developed higher oligoaniline nucleates, followed by controlled growth of polyaniline chains from them. The morphology of the developed nano/microstructures under controlled condition is in sharp contrast with the equivalent nanocomposite synthesized without imposing the control. Nanocomposites containing supramolecularly organized macroporous, three-dimensional microstructures have shown remarkably improved specific capacitance as high as 965 F/g (1 A/g) compared to 442 F/g (1 A/g) for the noncovalently attached uncontrolled nanocomposite under similar conditions. A thorough characterization of the nanocomposites using various spectroscopy, electron microscopy, X-ray crystallography, X-ray photoelectron spectrocscopy, surface area analysis, and electrochemical analysis techniques are conducted. A probable mechanistic interpretation for the microstructure formation considering supramolecular organization of the in situ developed, graphene oxide surface attached platelet like aniline oligomers has been proposed.