The characterization of new fluorinated ionomers for use in polymer electrolyte membrane (PEM) fuel cells

Proton exchange membrane (PEM) fuel cells were fabricated using a novel class of bis[(perfluoalkyl)sulfonyl] imide ionomer materials synthesized by Professor Darryl D. DesMarteau and coworkers at Clemson University. These imide materials were incorporated in catalyst layers and used as membranes in fuel cell membrane electrode assemblies (MEAs). Corresponding fuel cells that used the structurally related industry standard DuPont Naflon were also assembled and tested as benchmarks.; Assembled MEAs were characterized on a device level using multiple techniques including voltage-current discharge curves, current output at a static load potential, and measurement of cell resistance. Characterization was performed at a number of different cell temperatures (80, 100, and 110°C) and under a range of cell humidification conditions. The performance of MEAs with imide-based catalyst layers was found to be highly dependent upon the equivalent weight of the ionomer and the operating temperature. For MEAs where membrane material was the variable, performance was observed to be highly dependent upon membrane thickness and equivalent weight of the membrane ionomer.; A representative number of these fuel cells were also characterized ex situ with scanning electron microscopy (SEM) and X-ray dispersive analysis (EDX). SEM micrographs were obtained that clearly displayed the distinct layers of MEAs. The transitions between the MEA layers were also visible in EDX elemental line scans.; An investigation into the effect of catalyst poisoning from low levels of carbon monoxide in the hydrogen fuel stream was undertaken at Los Alamos National Laboratory (LANL). Anodic stripping voltammetry was used to electrochemically oxidize CO from Pt, Pt-Ru, and Pt-Mo catalyst surfaces. Results from this study corroborated earlier work at LANL for CO stripping voltammetry from Pt. Pt-Mo results were similar to those seen in literature. Pt-Ru showed CO desorption at the lowest overpotential of the three materials, indicating the highest feasibility as a fuel cell catalyst in the presence of CO.