Morphological and Spatial Aspects in Polymer Degradation: From Heterophasic Polymers to Proton Exchange

Membranes Used in Fuel Cells

Shulamith Schlick, University of Detroit Mercy, DMR 0412582

1. Danilczuk, M.; Schlick, S. Coms, F.D. Macromolecules 2009, 42, 8907-8913.2. Danilczuk, M.; Perkowski, A.J.; Schlick, S. Macromolecules 2010, 43, 3352-3358. 3. Spulber, M.; Schlick, S. J. Phys. Chem. A 2010, 114, 6217-6225.

(A)The stabilization of perfluorinated membranes by addition of Ce(III) has been studied in an In Situ fuel cell (FC) inserted in the resonator of an ESR spectrometer .1 Scheme 1 shows the deduced stabilization mechanism : Scavenging of the most aggressive oxygen radical, HO•, and generation of Ce(IV); and formation of Ce(III) and of the less reactive HOO• radical.

SCHEME 1HO• + Ce(III) + H+ → H2O + Ce(IV)

Ce(IV) + H2O2 ↔ Ce(III) + HOO• + H+

Ce(IV) + HOO• → Ce(III) + O2 + H+

(B) We have developed a kinetics approach that allowed ranking of membrane stability to attack of hydroxyl radicals, by monitoring the competition between the spin trap (DMPO) and the membrane for these radicals.2 Results indicated that the membranes’ stability depends on the structure of the side chain. Most stable: membrane without the ether bond in the side chain, for example the 3M and Aquivion membranes shown below.

(C) Inclusion in cyclodextrins (CDs) leads to the increase of the lifetime of short-lived spin adducts, for example DMPO/OH.3

The Figure shows the generation of the adduct and its decay at 300 K in the absence (line 1) and in the presence of increasing CD concentrations (lines 2 to 6). The red arrow in the inset indicates the signal whose intensity was monitored in the time scan.

(CF2CF2)nCF2CF

OCF2CF2CF2CF2SO3H

(CF2CF2)pCF2CF

OCF2CF2SO3H

0 500 1000 1500 2000 25000

10

20

30

40

3300 3320 3340 3360 3380 3400

Magnetic Field / G

Inte

nsi

ty /

a.u

.Time Scan / s

1 2 345 6

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Broader Impact Activities

Shulamith Schlick, University of Detroit Mercy, DMR 0412582 • The Group: Undergraduate A. J. Perkowski, graduate student Lu Lin, visiting graduate student L. Lancucki (University of Krakow, Poland), postdoctorals M. Danilczuk and M. Spulber (“Petru Poni” Institute, Yassy, Romania) and visiting scientist K. Kruczala (Krakow, Poland).

• 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 group2 for ranking membrane stability has encouraged efforts on the synthesis of more stable membranes.

• 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 ESR (Danilczuk et al. Fuel Cells 2008, 8(6), 436-452) .

• PI Schlick is 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 July 2011).

• The collaboration with scientists at the GM Research Lab continues, and we are looking forward to new equipment for In Depth Profiling by FTIR experiments.