Research Interests

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

First, ion exchange polymers are commonly employed as separators in electrochemical cells, such as batteries and fuel cells. The best separators in inherently microstructured. The properties of microstructured matrices are often drastically different from 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 dictate the properties of microstructured materials. We form microstructured composites by sorbing ion exchange polymers onto high surface area substrates, where gradients at the interfaces between the ion exchanger and inert substrates enhance flux through the composites. Enhancements of twenty-fold over the flux through simple ion exchange polymers are common. We observe surface diffusion along straight interfaces, as well as transport along fractal interfaces formed with spherical, polymerized micelles. Here enhancements are driven by interfacial gradients in concentration. By reducing electrolyte concentration, intefacial potential gradients can enhance flux fifty-fold. Recently, we have cast density gradient polymers on an electrode, and the gradients in density and viscosity have altered the cyclic voltammetric response from that appropriate to linear diffusion to the sigmoidal response appropriate to radial diffusion. It should be possible to form ion exchange polymers with graded density of ion exchange sites.

Second, magnetic ion exchange composites are formed of ion exchange polymers and polystyrene coated magnetic particles, 1 to 2 um in diameter. These composites are formed in a magnetic field to orient the magnetic beads into columnar structures, which retain the magnetic field when the external magnet is removed. These composites influence the flux of redox species in two unusual ways: redox potentials are shifted positive, and flux enhancements are observed which depend on the magnetic susceptibilities of the halves of the redox couple. The flux through magnetic composites can be throttled by removing and replacing an external magnet. This opens the possibility of building flux switches. We are currently characterizing and modeling these composites, which have potential applications in separations, batteries, and fuel cells.

Third, we study electrochemistry in adsorbed solvent layers. Traditionally, high electrolyte concentrations are used 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, new 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, where questions about atmospheric corrosion and optimization of fuel cell electrodes can be addressed. The ability of an adsorbed solvent layer to support an electrolysis current is correlated with properties, such as autoprotolysis, acidity, and dielectric properties.

Fourth, projects undertaken in this group require a strong interplay between experiments and modeling. Modeling ranges from back-of-envelope calculations through transform and computational methods. Typically, computational models account for kinetics and mass transport, while analytical solutions describe solution phenomena.