Surface Fluorinated Polymer Membranes with Low Interfacial Resistance for Fuel Cell

Abstract

Fuel cells have been attracted as alternative energy sources owing to their high energy efficiency and excellent power density. The fuel cell performances are significantly affected by electrochemical properties of membrane-electrode assemblies (MEAs), which is composed of proton exchange membrane (PEM) and the electrodes. Membrane electrode assembly (MEA) with Nafion� membrane, a commercially available PEM, has a very good compatibility with its catalyst layer containing Nafion� ionomer. This guarantees high electrochemical properties in long term operation. However, MEA with hydrocarbon membrane sandwiched between two Nafion�-based catalyst layers leads to rapid reduction of electrochemical performances of MEA. This may be due high contact resistance in the interface of membrane and catalyst layers. Moreover, difference in adsorption and desorption of PEM and binder materials to water-methanol mixture, and delamination of catalyst layers are additional causes for its lower performance. To solve the interfacial problems between MEA components, surface modification of sulfonated poly(arylene ether sulfone)-silica nanocomposite membrane was investigated by using direct fluorination. Membranes after 30 minutes surface fluorination showed about 20% conversion of C-H to C-F bonds on their surface. The surface fluorinated membranes exhibited high proton conductivity, high dimensional stability and low methanol permeability. Furthermore, this surface enrichment of fluorine atoms led to low interfacial resistance between membrane and catalyst layer with Nafion� ionomer. Thus, FSPAES-SiO2 membranes improved single cell performance (~200%) significantly at constant voltage of 0.4V comparing to pristine membrane and showed long-term durability over 1400 hr.