Membrane durability is a significant technical barrier for the commercialization of polymer electrolyte membrane (PEM) fuel cells, which are efficient and clean energy conversion devices that can produce electricity from hydrogen. The pinhole formation and mechanical embrittlement of fuel cell membranes lead to the frequently observed "sudden death" behavior, which limits the service life of PEM fuel cell devices. It is believed that the localized membrane decay is largely responsible for the weakening and the breach of the fuel cell membrane. The objective of this proposal is to explore the fundamental mechanisms of the localized or inhomogeneous membrane decay phenomena through novel in situ diagnostic methods, numerical modeling, and post-mortem analysis. Intellectual Merit: Preliminary evidence has shown that, depending on the operation history, the membrane decay can occur in different modes: uniform or localized. It is hypothesized that the localized membrane decay is a result of a sequence of events, which may include local flooding, local fuel starvation, perturbated membrane potential distribution, carbon corrosion and Pt dissolution, and inhomogeneous membrane decay. The localization of the decay phenomena is thought to be due to the self-amplifying (as against self-extinguishing) nature of the events in that they tend to create conditions that stabilize and reinforce the local membrane decay processes. To prove this hypothesis, novel in situ diagnostic methods are proposed to help reveal the local membrane decay processes in great details. These include confocal micro-Raman spectroscopy and high-resolution neutron imaging. Both techniques will be implemented to obtain in situ maps of the membrane degradation state in running PEM fuel cells. The map is expected to have a spatial (pixel) resolution on the order of 1 by 1 by 1 micron. The measured local intensive variables will be fed into simulation models that predict membrane potential distribution as well as regions that are susceptable to carbon corrosion, Pt dissolution and membrane thinning. These predictions will be further validated by post-mortem analysis. If succesful, the proposed method will result in the first in situ point-wise pictures of the membrane degradation processes in running fuel cells. The proposed in situ diagnostic methods offer significant advantages over traditional diagnostic techniques, and can be used to study various emerging and challenging problems that are related to ionomer membranes. The greater understanding of the mechanisms of the inhomogeneous membane degradation will suggest directions for engineering better materials, better cell/stack configuration, and innovative membrane degradation mitigation strategies to improve the service life of PEM fuel cells. Broader Impact: The proposed program will bring university professors, graduate and undergraduate students together in an exciting research effort, which has the potential to accelerate the commercialization of hydrogen and fuel cell technologies. As part of the education effort, female and minority students will be recruited to work on the project as summer interns. The PI and the students will help create and provide fuel cell enriched science curricula units to K-12 teachers. The adoption and dissemination of these curricula will hopefully intrigue and inspire a large number of K-12 students to pursue research in the broad area of energy for sustainability.
