Reduced Graphene Oxide-Based Nanoassemblies for Energy Storage Applications

Reduced graphene oxide provides an alternative route to the use of single-layer graphene in functional devices as a result of its ability to be synthesized and functionalized via solution-based processing in large quantities. Graphene oxide serves as a versatile precursor to reduced graphene oxide by offering unique opportunities to anchor nanostructured materials onto its surface and serve as a 2-D conductive support. The high surface area and excellent conductivity of reduced graphene oxide provide a suitable foundation for shuttling charges to redox-active materials such as those used in lithium ion batteries while maximizing the interfacial contact between the conductor (reduced graphene oxide) and redox-active nanomaterial.

This dissertation first describes the progress in elucidating the fundamental characteristics that drive the enhancements offered to electrode designs incorporating reduced graphene oxide so that more rational designs are possible. The use of reduced graphene oxide as conductive support for active cathode material in lithium ion batteries led to significantly improved electrode kinetics, faster Li+ diffusion to the electrode surface, and increased double layer charging. Further, the strong electrostatic interactions between the electronegative oxygen functional groups inherent to graphene oxide and the transition metal precursors influenced dopant concentration in the active material.

Pivoting from the finding that reduced graphene oxide improves the diffusion of electroactive species, a new graphene morphology, holey graphene, was synthesized that offers potentially further improvement of transport characteristics in energy storage electrodes. Through a catalytic oxidation process, gold nanoparticles and hydroxyl radicals work in tandem to etch holes into reduced graphene oxide sheets in solution. This new approach provides secondary, solution-based control over the reduced graphene oxide morphology, providing a range of opportunities to tune electrode transport characteristics.

Based on the new insights obtained regarding the fundamental role of reduced graphene oxide in improving electrode characteristics in lithium ion batteries, the work described in this dissertation serves as a basis for further exploration of graphene-based nanoassemblies. Finally, the development of a solution-based process for tuning the morphology and degree of oxidation of reduced graphene oxide potentially opens the door to its use in other energy or optoelectronic applications.