Proton Exchange Membrane Fuel Cells
Mechanisms of Water Sorption in Polymer Nanocomposite Electrolyte:
We are studying moisture diffusion characteristics (i.e. Fickian and Non-fickian) in polymer nanocomposites electrolytes with respect to various filler, polymer host, and environmental factors. We are exploring Nafion as well as other alternative polymers considered suitable for proton exchange membrane fuel cells (PEMFC).
Mitigating the “Dead-layer” Effect:
According to the classical capacitance theory, as the distance between the parallel plates is reduced to nanoscale length, the capacitance of a nanocapacitor is expected to increase by several orders of magnitude. However, experimental measurements show rather unexpected results and the capacitance of nanocapacitors are found to be much lower than that predicted from classical theories. It appears as if a layer of very low permittivity (“dead layer”) is present at the metal/dielectric interface causing a dramatic drop in the overall capacitance. Recently, the low capacitance in nanocapacitors was more precisely attributed to flexoelectricity and screening penetration. We have designed a graded dielectric film that can mitigate the so called “dead-layer” effect [Li et. al, 2011].
Lithium Ion Batteries
Novel Polymer Nanocomposite Electrolytes:
In recent years, there has been a growing shift from liquid electrolytes towards solid polymer electrolytes in lithium ion batteries. Polymer electrolytes offer several advantages including enhanced safety, less reactivity towards lithium, and suitability for thin film fabrication. However, the ion conductivity in polymers is much lower than in conventional liquid electrolytes. Nanoscale fillers are shown to enhance ion conductivity in polymer electrolytes. We are exploring novel polymer nanocomposite electrolytes by varying filler dimensions, shapes, size, material, and surface functionality to design electrolytes with optimum properties for lithium ion batteries.
Fundamental Mechanisms of Lithium Ion Conductivity:
We are developing models that address various parameters influencing ion conductivity in polymer nanocomposite electrolytes including filler properties (i.e. size, material, dispersion), polymer properties (free volume and segmental mobility), and lithium salt concentration. We are approaching this from both bulk level (continuum based models) and molecular level (MD simulations).