We report a catechol-graphene composite hydrogel film that possess both the metallic conductivity of graphene and the redox activity of catechol. This catechol-graphene-composite film was prepared using a two-step electrofabrication process. In the first step, the graphene-entrapped chitosan film is electro-deposited onto the electrode due to a cathodic neutralization mechanism of chitosan (a pH-responsive film-forming polysaccharide). In the second step, an anodic oxidative grafting mechanism is used to conjugate catechol to the graphene-chitosan composite to form a catechol-graphene-chitosan film (Cat-Gr-Chit film).<br/> <br/>To characterize the mechanisms for electron flow through this Cat-Gr-Chit film, we prepared a film-coated electrode and performed various spectroelectrochemical measurements.  As expected, we observed that graphene confers metal-like conductivity to the film.  Our measurements also indicate that there are two functional forms of catechol: conductive-catechols that appear to be connected to graphene, and non-conductive catechols that are dis-connected from graphene. We provide spectroscopic evidence that the conductive-catechols can accept/donate electrons through graphene allowing its redox state to be directly switched between its oxidized (e.g., quinone) and reduced (e.g., catechol) states using an electrochemical method.  In contrast, the redox state of the non-conductive-catechols cannot be directly switched via graphene, but rather require diffusible mediators to shuttle electrons to/from the electrode to switch its redox state.<br/> <br/>Importantly, we show that the Cat-Gr-Chit composite film offers synergistic materials properties that represents both a graphene-based double layer capacitance and a catechol-based redox-capacitance. Further, the Cat-Gr-Chit hydrogel retains both the conducting properties of graphene and the molecular memory properties of catechol.  Finally, we demonstrate the important role that mediators can play in controlling electron flow through redox-active and conducting films. We envision this molecular-mechanism-level understanding of redox-activities will enhance our ability to design electronic materials for diverse technological applications.

Electron flow through catechol-graphene-composite hydrogel

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