Yatin P. Patil

Model Studies of the Durability of a Titania-Modified Nafion Fuel Cell Membrane

Nafion membranes degrade in polymer electrolyte membrane fuel cells due to the interplay of physical and chemical degradation. In the interest of mitigating this problem, Nafion membranes were modified via an in situ sol-gel polymerization of titanium isopropoxide to generate titania quasi-networks. These composite materials are viewed as model systems within the context of durability without an immediate concern for cell performance. The modification did not influence membrane equivalent weight but reduced its hydration capacity. Membrane modulus increased, dimensional stability improved, creep lessened, and the ability of constrained membranes to withstand contractile stresses due to humidity change was greatly enhanced. The damage surface morphology of unmodified Nafion, viewed using scanning electron microscopy, and of constrained samples showed significant failure, whereas the modified membranes showed considerably more structural integrity. Open-circuit voltage (OCV) testing showed that the inorganically modified membrane held voltage better with fluoride emission at least an order of magnitude lower than that of the unmodified membrane. However, the performance curve of the modified membrane before the OCV test is inferior to that of Nafion; but after the test it is slightly better. This in situ sol-gel-derived inorganic modification offers a simple way to enhance membrane durability by reducing both physical and chemical degradation.

Perfluorinated Polymer Electrolytes Hybridized with In situ Grown Titania Quasi-Networks

Perfluorinated Nafion membranes, neutralized to various extents, were hybridized with titania quasi-networks that were grown in situ via catalyzed sol-gel reactions of an titanium isopropoxide precursor. The formation of Ti-O-Ti groups within the ionomer was verified by FTIR-ATR spectroscopy. EDAX studies confirmed that the extent of propagation of titania quasi-networks into the bulk of the ionomer film increased with ionomer neutralization. Compared to the unmodified control membrane, the hybrid membranes exhibited superior dimensional stability, modulus, stress, and strain at break and gas barrier properties. All hybrid membranes exhibited superior resistance to degradation when subjected to an accelerated stress test in an operating fuel cell environment, as a resultant of the better dimensional stability and gas barrier properties induced through addition of the inorganic titania phase.