Devproshad K. Paul

Understanding the Ionomer Structure and the Proton Conduction Mechanism in PEFC Catalyst Layer: Adsorbed Nafion on Model Substrate

To understand the structure/property of the ionomer in the CL, adsorbed Nafion thin films were prepared on model substrate, SiO2 terminated silicon wafer, by spontaneous adsorption of Nafion from its 0.1 to 5 wt% solution. Fitting of Variable Angle Spectroscopic Ellipsometry (VASE) data yielded thickness of adsorbed films ranging from 4 nm at low concentrations (0.1 wt% film) to 306 nm at high concentrations (5wt% film). Contact angle measurements indicated that the low (0.1 wt%) and high (3 wt%) films to posses hydrophobic surface but the intermediate concentration (0.5 wt% and 1.0 wt%) film surface to be hydrophilic. Conductivity measurements of adsorbed films over a range of RH showed that all films prepared from 1 wt% and lower concentrations solutions to possess similar conductivities at high RH. However, the 5wt% film showed much higher conductivity indicating a different proton conduction mechanism for low and high concentration films.

Preparation of Ultra-Thin Catalyst Layers by Piezo-electric Printer for PEMFCs Applications

Introduction One of the main technical barriers to commercialization of Proton Exchange Membrane Fuel Cells (PEMFCs) operated at low temperatures (up to 90 °C) is the material cost, which is in major part attributed to the cost of platinum metal [1]. From the perspective of electrode performance, the cost problem can be tackled in two ways: reduction of the catalyst loading and improvement of the catalyst utilization and performance. Electrodeposition and sputter deposition have been used to manufacture membrane-electrode assemblies (MEAs) of low catalyst loadings [2-4]. However, these techniques have several drawbacks to overcome, including film homogeneity/size of the particle deposited and MEA life time. Theoretical studies have shown that the utilization of the Pt catalyst in these thicker films is low and desirable performance can be attained without using high amounts of platinum if thin catalyst layers are used wherein the catalytic utilization of platinum is higher. The objective of this work is to present an improved catalyst deposition methodology, based on a piezo-electric printing technique [5], that can overcome many of the current limitations and that can to produce MEAs having (i) very low precious metal (Pt) loading and (ii) better utilization of the precious metal present on the electrode in PEMFCs. This procedure for manufacturing catalyst coated membrane (CCM) resulted in the enhanced performance of state-of-the-art experimental fuel cells.