School of Physical and Chemical Sciences Seminar Series

Designing Graphene Supercapacitor Electrodes - Chemistry PhD Oral

Speaker

Anna Farquhar

Institute

School of Physical and Chemical Sciences

Time & Place

Wed, 06 Sep 2017 12:00:00 NZST in Room 531, level 5, Rutherford Building

All are welcome

Abstract

Graphene, a two-dimensional material comprised of sp2-hybridized carbon atoms arranged in a honeycomb lattice, has significant potential in energy storage applications as an electrode material for supercapacitor devices. Unfortunately, the strong intermolecular forces that exist between graphene sheets result in aggregation during assembly and use, thereby reducing the accessible surface area and the experimentally available capacitance. It is therefore necessary to prevent aggregation of the graphene sheets during electrode assembly, so materials with enhanced energy storage capacity can developed. In this thesis work, the use of molecular spacers grafted to few-layer graphene (FLG) was investigated as a way to prevent aggregation of graphene sheets. Initially, molecular spacers were grafted to FLG using three strategies: spontaneous reaction with aryldiazonium salts, the Diels Alder reaction of an aryne, and the addition of a primary amine. All three strategies were shown to successfully modify the graphene surface. Supercapacitor electrodes were assembled from aryldiazonium modified FLG using a layer-by-layer (LBL) strategy. A 7 hour spontaneous reaction with a 20 mM aryldiazonium salt solution was found to provide a phenyl film that could completely separate the FLG sheets during assembly and prevent restacking throughout cycling, with the full surface area remaining completely accessible even after 20,000 galvanostatic charge discharge cycles. Furthermore, the grafted film did not diminish the total capacitance of each graphene sheet or hinder ion movement to the surface of the sheets. To further enhance the capacitance of the FLG, metal hydroxide nanoparticles were electrochemically deposited on the FLG sheets prior to LBL assembly, which enhanced the total areal capacitance of the system, through additional pseudocapacitance contributions. This talk will discuss the successful development of a novel LBL protocol that allowed electrodes comprised of stacks of FLG to be assembled without diminishing the total accessible surface area and therefore capacitance of each graphene sheet, which is an essential step in the development of energy storage devices from graphene.

Biography

PhD student studying Chemistry at UC