Degradation and Stabilization of Ionomeric Membranes Used in Fuel Cells: Focus on Early Fragmentation Events and

Diffusion Processes Shulamith Schlick, University of Detroit Mercy, DMR 0964827

1. Spulber, M.; Schlick, S. (a) J. Phys. Chem. A 2010, 114, 6217-6225. (b) Manuscript in preparation. 2. Schlick, S. et al. , manuscript in preparation.

(A) Inclusion in cyclodextrins (CDs) leads to the increase of lifetimes of spin adducts.1a Recently we have exposed Aquivion membranes to hydroxyl radicals, using 2-methyl-2-nitrosopropane (MNP) as spin trap and showed that encapsulation in β-CD allows the detection of “Very Early Events”: very short-lived fragments.1b In the absence of β-CD, the carbon-centered radical (CCR) adduct is detected. As shown in Figure 1, the role of the CD host is to stabilize an initially generated short-lived oxygen-centered radical (OCR) and prevent its transformation into a more stable CCR. This approach is important for a more complete description of membrane fragmentation.

(B) FTIR measurements were performed with the Micro ATR FTIR spectrometer and line scans were collected from the cathode to the anode. The result: viewing in-depth degradation of Nafion in a fuel cell and assigning the FTIR bands; ovals in (C) show bands at 82 μ from the cathode.2

3300 3320 3340 3360 3380 3400

Aquivion, [-CD]= 2 mM

Experimental

Simulated

39 %

MNP/OCF2CF2R aN=16.4 G

aF=11.1 G (2F)

aN=17.1 GDTBN

61 %

Magnetic Field / G

Figure 1. Experimental and simulated spectra of MNP/OCF2CF2R adducts generated in the presence of Aquivion (0.01 wt %) and β-CD. DTBN stands for di-tert-butyl nitroxide, generated by MNP decomposition.

Figure 2. Nafion 115 membrane: non-degraded (A), and degraded during 52 h (B) and 180 h (C). FTIR spectra at the indicated distances from the cathode (D) . Assignment of FTIR bands. See notes for details.

(D)

Broader Impact Activities

Shulamith Schlick, University of Detroit Mercy, DMR 0964827 • The Group: Graduate student Lu Lin, visiting graduate student L. Lancucki (Jagiellonian University, Krakow, Poland), postdoctorals M. Danilczuk, M. Spulber, and L. Ghassemzadeh.

• Translational Research. Our collaboration with scientists and engineers from 3M, Ford Laboratories, and the Electrochemical Energy Research Lab of General Motors on the degradation and stabilization of membranes used in fuel cells is an example of the connectivity between fundamental research and applications: The kinetic approach developed by our group for ranking membrane stability has encouraged efforts on the synthesis of more stable membranes. In-depth profiling of degradation is a new imaging method that visualizes the effect of catalyst diffusion into the membrane and the reactivity of hydrogen atoms generated in a fuel cell.

• International Collaborations. PI Schlick has continued the collaboration with K. Kruczala (Krakow), with the group of Bogdan Simionescu at the Petru Poni Institute, Yassy, Romania, and most recently with Professor Willem H. Koppenol at the ETH, Zurich. The latest collaboration is centered on Pulse Radiolysis experiments in Zurich on the model compounds studied in our lab by spin trapping.

• PI Schlick was part of DOE7, a group of scientists and engineers at 3M Company in St. Paul, MN, and five professors at US universities. In annual meetings, teleconferences, and quarterly reports, the PI’s fundamental research on the degradation of fuel cell membranes has contributed to the recent “go” DOE decision (funding until 31 March 2011). A new proposal to DOE was submitted.

• In collaboration with scientists at the GM Research Lab, and S. Hamrock and colleagues at 3M, we have developed the new technique: In-Depth Profiling of membrane degradation by Micro ATR-FTIR.

L. Ghassemzadeh