Organic functionalization of graphene for applications in energy storage devices and optoelectronics

Licentiate thesis, 2024

The emergence of one-atom layer thick materials, exemplified by graphene following its first exfoliation by Geim and Novoselov, has sparked significant research interest. Owing to their unique electronic structure, 2D materials are regarded as promising candidates for diverse applications, including field-effect transistors (FETs), solar energy harvesting, biological systems, water purification, and energy storage devices. It has been demonstrated that the introduction of functional molecules onto the surface of 2D materials not only prevents the aggregation of the nanosheets but also enables fine-tuning of their physicochemical properties.

The widespread use of fossil fuels has propelled human society into a period of rapid industrial development. However, this progress has come with significant environmental challenges and concerns over the depletion of fossil energy sources. As a result, there is a pressing need for humanity to transition towards sustainable energy alternatives. Lithium-ion batteries (LIBs), as the predominant energy storage device in our daily lives, face limitations such as low power density, safety issues, and resource dependency. Aqueous supercapacitors utilizing 2D materials offer a promising solution to address these challenges. For instance, employing aqueous electrolytes can significantly enhance the safety of energy storage devices. In this thesis, we have developed asymmetric supercapacitors using graphene functionalized with pyrenetetraone derivatives as cathode and annealed Ti3C2Tx as anode, demonstrating a remarkable energy density of 38.1 Wh kg-1 at a power density of 950 W kg-1. Additionally, they exhibit outstanding stability, retaining more than 90% capacity after 15000 charge/discharge cycles. Furthermore, spectrophotometric titration was deployed to reveal the different interaction behaviors within the different functionalized 2D-materials. The rationally designed organic nanostructures exhibited excellent electrochemical performance, offering valuable insights in the design of organic-based electrode materials.

In addition, donor-acceptor system based on pyrenetetraone derivatives is designed and synthesized for the noncovalent functionalization of graphene. Further photophysical investigation on the hybrid material confirmed the interaction between the donor-acceptor system and graphene.