Brian A. Litteer

Effect of Hydrogen and Oxygen Partial Pressure on Pt Precipitation within the Membrane of PEMFCs

Pt dissolution and further precipitation within the membrane of proton exchange membrane fuel cells (PEMFCs) was investigated at open-circuit voltage conditions. It was found that the location of Pt precipitation is affected by both H 2 and O 2 permeability through the membrane. A simple model is developed that can predict the location of the Pt precipitation band as a function of H 2 and O 2 partial pressure, which agrees well with measurements. The implications of Pt deposition on membrane chemical degradation are briefly discussed.

Membrane Degradation at Catalyst Layer Edges in PEMFC MEAs

Membrane failures at catalyst layer edges in proton exchange membrane fuel cell (PEMFC) membrane electrode assemblies (MEAs) were investigated using MEAs with segmented electrodes. A mathematical model was developed to predict the potential distribution at the edge of the MEA with misaligned electrodes. Control experiments were performed using an accelerated membrane durability test protocol and significant membrane degradation was observed in the region where the cathode overlaps the anode. The model-experiment comparisons suggest that a high cathode potential contributes to the membrane failure. A dependence of membrane degradation on relative humidity (RH) was observed in the experiments, regardless of the electrode overlap. The observed membrane degradation in the overlap region of MEAs with an anode catalyst overlap, run at low RH, is not explained by the model and needs further investigation.

Catalyst Degradation Mechanisms in PEM and Direct Methanol Fuel Cells

While much attention has been given to optimizing initial fuel cell performance, only recent research has focused on the various materials degradation mechanisms observed over the life-time of fuel cells under real-life operating conditions. This presentation will focus on fuel cell durability constraints produced by platinum sintering/dissolution, carbon-support oxidation, and membrane chemical and mechanical degradations. Over the past 10 years, extensive R&D efforts were directed towards optimizing catalysts, membranes, and gas diffusion layers (GDL) as well as combining them into improved membrane electrode assemblies (MEAs), leading to significant improvements in initial performance of H2/air-fed proton exchange membrane fuel cells (PEMFCs) and methanol/air-fed direct methanol fuel cells (DMFCs). 3 While the required performance targets have not yet been met, current PEMFC and DMFC performance are close to meeting entry-level applications and many prototypes have been developed for field testing. This partially shifted the R&D focus from performance optimization to more closely examining materials degradation phenomena which limit fuel cell durability under real-life testing conditions. The predominant degradation mechanisms are sintering/dissolution of platinum-based cathode catalysts under highly dynamic operating conditions, dissolution of ruthenium from DMFC anode catalysts, the oxidation of carbon-supports of the cathode catalyst during fuel cell startup and shutdown, and the formation of pinholes in proton exchange membranes if