Platinum-Catalyzed Polymer Electrolyte Membrane for Fuel Cells
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ABSTRACT The objective of this research is to develop the combustion chemical vapor deposition (CCVD) process for low-cost manufacture of catalytic coatings for proton exchange membrane fuel cell (PEMFC) applications. The platinum coatings as well as the fabrication process for membrane-electrode-assemblies (MEAs) were evaluated in a single testing fuel cell using hydrogen/oxygen. It was found that increasing the platinum loading from 0.05 to 0.1 mg/cm 2 did not increase the fuel cell performance. The in-house MEA fabrication process needs to be improved to reduce the cell resistance. Significantly higher performance of Pt coating by the CCVD process has been obtained by MCT's fuelcell industry collaborators who are more experienced with MEA fabrication. The results can not be revealed due to confidentiality agreements. INTRODUCTION Proton exchange membrane (PEM) fuel cells typically use platinum or platinumbased materials as the catalysts for hydrogen conversion into electrical energy. The hydrogen/oxygen reactions occur at the catalyst layer of MEA. It is important to increase the effective contact of gases at the interface of three components (electrode-membranecatalyst). For cost-effective fuel cell application, industry must reduce the platinum 2 loading in MEAs to about 0.1 mg/cm2 and meanwhile increase their effective utilization-.1-4 In this study, we used the Combustion Chemical Vapor Deposition (CCVD) process 5 to deposit platinum coatings onto polymer membrane (NafionTM 115), or electrode (graphite Toray paper). The total platinum loadings studied are in a range of 0.05-0.1 mg/cm2. Membrane electrode fabrication processes are being developed inhouse for utilizing both the Pt-coated electrode and membrane. The goal of the assembly process development is to increase the effective utilization of platinum catalyst while maintaining low platinum loading. A single small fuel cell was used to test the resulting MEAs.
EXPERIMENTAL Deposition of platinum by the CCVDprocess In the CCVD process (Figure 1), platinum precursor, Pt-acetylacetonate, was dissolved in toluene which also acts as combustible fuel. The solution was atomized to
239 Mat. Res. Soc. Symp. Proc. Vol. 575 02000 Materials Research Society
Flame wVaporizer
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lSubstrate Inline Filter
Precursor Solution
Figure 1. Schematic representation of the CCVD process.
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form submicron droplets by means of the Nanomizer TM. An oxygen stream then carried the fine mist of the precursor droplets to a flame where they were combusted. The heat from the flame provided the energy required to evaporate the droplets and for the precursors to react. Vapor was deposited on the substrate in the open atmosphere by drawing it over the flame plasma. To coat the low temperature substrates, the CCVD process was modified to provide low temperature depositions. This process has been scaled up in the MCT's CCVD roll-to-roll web stock coater. The coating morphology can be controlled by adjusting the deposition parameters to achieve rough/porous or dense microstructur
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