Durability enhancement of Nafion® fuel cell membranes via in situ sol-gel-derived titanium dioxide reinforcement

To improve durability of Nafion® membranes, samples were modified via an in situ sol-gel polymerization of titanium isopropoxide to generate titania quasi-networks in the polar domains. The incorporated titania reduced water uptake but equivalent weight was essentially unchanged. Fuel cell performance of the modified membrane was inferior to that of the unfilled membrane although these were considered as model studies with focus on mechanical durability. Mechanical analysis of contractile stress buildup during drying from a swollen state in samples clamped at constant length demonstrated considerable reinforcement of Nafion® by the titania structures. Tensile studies showed that at 80°C and 100% relative humidity the dimensional change of the composite membrane is one half and the initial modulus is three times higher than that of the unmodified membrane. During an open circuit voltage decay test the voltage decay rate for the modified membrane is 3.5 times lower than that of control Nafion®. Fluoride emission for the composite is at least an order of magnitude lower than that of the control Nafion® membrane indicating reduced chemical degradation. These model studies indicate that this in situ inorganic modification offers a way to enhance fuel cell membrane durability by reducing both physical and chemical degradation.