Modulating the Bipolaronic Units in the Graphene/Polyaniline Heterostructure by Metal Ion Doping

High Resolution Image Download MS PowerPoint Slide Hybrid systems combining carbonaceous materials, conducting polymers, and transition metal cations exhibit pronounced synergistic effects in energy-related and electrochemical applications. To elucidate the origin of this synergistic behavior, a two-dimensional graphene/polyaniline heterostructure (on a Si/SiO 2 support) was synthesized, and for known intense effects, cobalt(II) chloride was used to subsequently modify the electronic structure of polyaniline. Raman and XPS spectroscopies confirm the formation of the graphene/polyaniline heterostructure and the incorporation of cobalt(II) cations. In situ Raman spectroelectrochemistry reveals the redox activity of the polyaniline modified by cobalt(II) cations and the reversible potential-dependent charge doping of graphene. XPS spectroscopy indicates a nitrogen-to-cobalt ratio of ∼6:1, a comparable population of charged and uncharged nitrogen atoms in polyaniline, and the polaron lattice as the prevailing electronic state. The results show that cobalt(II) incorporation into the graphene/polyaniline heterostructure induces the formation of additional charge-carrier states in polyaniline; an increased content of the bipolaronic structure of various delocalization lengths is identified by resonance Raman spectroscopy at excitation wavelengths of 568, 633, and 647 nm. These findings emphasize the general role of metal–polymer interactions in governing charge states at graphene-conducting polymer interfaces, providing a mechanistic basis for designing systems utilizing the synergy observed in polyaniline and metal salt systems for supercapacitors and sensors.