Recent research is presented on graphene and its derivatives as electrodes of electrochemical storage systems including supercapacitors. The focus is on the rationalization of the nanostructure and architecture of these materials for enhancing their electrochemical performance.
Graphene is a material that offers a large charge-storage surface at a very light weight, which makes it a good candidate for supercapacitor electrodes. To increase energy density you need to use electrodes with higher specific capacitances.
Although the optimal material structure for graphene is not yet known, the trend today is to create structures that are tunable at the nano, micro, meso, and macro scales in order to optimize the performance of both the graphene electrodes as well as composite electrodes used for supercapacitors.
Chemical exfoliation is a cheap and effective way of producing a range of multi-dimensional, highly porous carbon materials that can be used to make electrodes for supercapacitors. The resulting layered graphene (EG) features a long-range ordered atomic layer structure, adjustable interlayer distance, abundant honeycomb and turbine microstructures, and a tunable mesoporous structure with a mean mesopore diameter of 4.27 nm. The tunable structural and architectural features of the EG allow it to offer an outstanding electrochemically active interface, speed up the deintercalation kinetics as well as achieve a high reversible capacitance.
In order to improve the performance and specific capacitance of EGs, different strategies were explored. These include the use conductive graphene fibres and high-conductivity coatings. Other methods included the doping of EGs with nitric acid, the incorporation of metal oxides onto EGs, and development of a multifunctional graphene-based nanocomposite material incorporating CNCs as well as a polymer binder. In order to plan for the end of life (EOL), a technology called pyrolysis has been created. It recovers valuable materials such as the electrolyte and metallic collectors as well as the dielectric papers which bind graphene.
An important challenge in the production of supercapacitors is their environmental impact. In order to address this issue, the EOL supercapacitors designed in the project were subjected to a Life Cycle Assessment (LCA). A life cycle assessment (LCA) was performed for the EOL supercapacitors developed in the project. This is mainly due to the use of a raw material that can be produced from waste products of the paper industry and the absence of the flammable and toxic solvents used in the production of activated carbon. The graphene-based matrix collector, as well as the polymer binder matrix have been repurposed using a newly developed method of recycling. This step is important to reduce the amount of virgin materials used and overall impact on the environment of production for EOL Supercapacitors. It is possible to extend this technology to include other recyclable components in a supercapacitor, like the metallic collector and graphene electrodes. LCA also suggests that a graphene based EOL Supercapacitor will require less energy to produce than current technologies.
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