Research Interests

Professor Leddy's research is in the area of electrochemistry. Electrochemical techniques allow the investigation of solid/solution interfaces as well as bulk solution phases. Heterogeneouselectron transfer, mass transport processes, homogeneous reaction kinetics and solution properties are among the phenomena which can be investigated electrochemically. The general areas of interest, as outlined below, mix both experimental and theoretical studies.

1. Microstructure and Its Effect on the Transport and Selectivity Properties of Composite Ion Exchange Polymers

Ion exchange polymers are commonly employed as separators in electrochemical cells, such as batteries and fuel cells. The best separators are those which are inherently microstructured. The properties of microstructured matrices are often drastically different from those of bulk materials. As microstructured matrices are characterized by a high ratio of surface area to volume, interfacial gradients of no significance in bulk materials can alter and even dictated the properties of microstructured materials. Our efforts have focused on the cation exchanger, Nafion. By absorbing Nafion into the small diameter (15 to 600 nm), cylindrical pores of neutron track etched polycarbonate, the flux of cations and neutrals through Nafion can be enhanced twenty-fold by surface diffusion. In addition, a fifty-fold reduction in electrolyte concentration further enhances the flux twenty-fold. This arises from migration, driven radially in the pores by an interfacial potential gradient. Our efforts are now turning to the identification of additiorfal interfacial gradients, such as magnetic fields and density gradients, which can be capitalized upon to enhance transport in composites, and to the study of composites formed with other ion exchange polymers and microstructured supports.

2. Electrochemistry in Adsorbed Solvent Layers

Traditionally, high electrolyte concentrations have been necessary in electrochemical systems to reduce solution resistance, and, thus, voltage drops. With the advent of microelectrodes, added electrolyte is no longer necessary because the extremely small currents passed at microelectrodes generate negligible voltage drops. Thus, a whole new range of systems are now open to electrochemical inspection, including frozen solvents, pure redox materials, and low dielectric solvents. We have focused on the electrochemistry of adsorbed solvent layers with no added electrolyte. Questions about atmospheric corrosion and optimization of fuel cell electrodes can be addressed with these studies. Our studies have shown that the ability of an adsorbed solvent layer to support an electrolysis current is correlated with the properties of the solvent; these include autoprotolysis, acidity, and dielectric properties. Future studies will use quartz crystal microbalances and microelectrode arrays to better quantify the amount of adsorbed solvent and map the potential profile through solvent layer. As standard theories of the interfacial electron transfer events, such as Guoy Chapman Stern and Frumkin models, fail catastrophically for these systems, new models will have to be developed.

3. Modeling

All of the projects undertaken in this group require a strong interplay between experiments and systems modeling. Modeling ranges from back of the envelope calculations, through transform techniques and computational methods. Typical computational models account for heterogeneous and homogeneous kinetics, and mass transport, while analytical solutions are more typical in describing solution properties.