UC San Diego

The prospect of bridging the large energy density of batteries to the power densities of Electrochemical Capacitors (ECs) was explored. It has been demonstrated that nanostructuring of carbon electrodes significantly decrease the electrochemical capacitance of ECs due to density of states (DOS) related quantum and space charge effects. It is shown that the controlled generation of defects via Argo based plasma processing can substantially increase the electrochemical capacitance of a model nanostructured carbon electrode such as few layer graphene. Detailed consideration of the quantum and space charge capacitance was used delineate a new length scale, correlated to the active defects contributing to the enhanced capacitance and was found to be smaller than a structural correlation length determined through Raman spectroscopy. The study offers insight into a scalable method to improve the energy density of ECs.

An alternate approach to improving energy density and power density is shown via the use of redox additive electrolyte in macroporous carbon electrodes. The enhanced energy and power densities are initially, demonstrated on a model macroporous electrode such as vertically aligned carbon nanotube (CNT) arrays and then on a three-dimensional, hierarchically porous, reticulated vitreous carbon electrode with aligned CNTs within its macropores. Having demonstrated complete energy utilization at high current densities, cyclability studies were also conducted to test the longevity of the electrode system.

Electrochemical kinetics is investigated at the interface of single layer graphene and a redox electrolyte as an aqueous solution of potassium ferricyanide. It has been demonstrated that graphene’s variable DOS substantially alters the kinetics of electron transfer. It is shown that the kinetics does not follow the classic Butler- Volmer model but a modified Marcus- Hush-Chidsey model incorporating variable DOS.

The thesis is then concluded by summarizing the themes and findings presented in this work.