Enveloping of Catalyst Powder by Ionomer for Dry Spray Coating in Polymer Electrolyte Membrane Fuel Cells

Abstract

This study presents innovative concepts for improving performance of membrane electrode assemblies (MEAs) prepared by the dry-spraying method introduced by the German Aerospace center (DLR). Dry-spraying is a time and cost effective method that involves solvent-free spraying of catalyst powder on polymer electrolyte membrane. The issue which is resolved in this work is the large ionomer particle size in the conventional method. With mechanical grinding, particle size of the ionomer less than 100 nm were not been achieved. However, here the reactive interface of dry-sprayed MEA is optimized by improving ionic conductivity. Our approach is to modify a carbon support by partially enveloping with Nafion® ionomer followed by incorporating Pt black with it. Additionally, commercial catalyst powder was also modified by two-step preparation process with Nafion® dispersion. In this research, both of these modified powders are sprayed over membrane; hot-pressed; characterized, and have shown improved ionic network and distribution, which corresponds to their higher performances. The improvement in the performance does not correlate with electrode surface area but with the ionomer resistance of the catalytic layer. Therefore, with this study we demonstrate a pathway and methodology to further improve performance by optimizing ionomer structure and networks in the catalytic layer.