Congratulations to Dr. John (Jake) McDonough, who successfully defended his thesis, “Carbon Onions for Electrochemical Capacitors,” on June 11. (See Jake’s abstract below, or visit the Publications page for some of his published papers.)
Best wishes to Jake in his future endeavors!
Abstract
Energy off the grid, whether it be generation, storage, or efficiency, is a worldwide problem that everyone can relate to, from a cell phone battery dying, to gas efficiency in a vehicle. An alternative system that is able to deliver much higher power than batteries is called an electric double layer capacitor (EDLC, also called supercapacitor or ultracapacitor). EDLCs are fundamentally different in their charge storage mechanism, which relies on the physical adsorption of ions on a high surface area material instead of chemical reactions. This system can deliver more than 10x the power density, be charged and discharged almost a million times, and has an excellent efficiency (~95%). The major obstacle is its lower energy density, with batteries having about 10x the energy density of an EDLC.
The low energy density of EDLCs has caused most research groups in the field to focus on improving this property. Unfortunately, it is a fundamental problem with the system, and may never be solved. For this reason, it is the goal of this work to further increase the power capabilities of EDLCs, approaching that of electrolytic capacitors, by exploring a new material, called carbon onions, or onion-like carbon (OLC). Never before has a thesis been focused solely on developing OLC for EDLC applications. OLC in its raw form has major advantages over traditional porous materials for EDLCs: it is nonporous allowing for exceptional charge- discharge rates, which translates into power densities more than 10x higher than traditional EDLC materials, although at the expense of a lower energy density.
This work focuses on understanding the effect of annealing conditions and precursor material on the OLC transformation mechanism and kinetics. The resulting structure and physical properties of OLC are correlated with electrochemical properties as OLC is used in EDLC electrodes. The capacitance of OLC was increased through chemical alteration of its surface and by coating the surface with redox active molecules. The unique structure of OLC allows for novel uses of the material with ionic liquid electrolytes and as a conductive additive to conventional EDLC materials.
