Reinforced Composite Proton Exchange Membranes Through Polytetrafluoroethylene Surface Modification

As the problems of environmental pollution and resource depletion become serious, fuel cells using hydrogen, an infinite resource that occupies most of the universe and does not emit pollution, are emerging as an alternative to solve these problems. Among fuel cell types, Polymer Electrolyte Membrane Fuel Cell (PEMFC) is attracting attention for its advantages such as high efficiency and high energy density, but it is difficult to commercialize it due to high price of fuel cell manufacturing materials. Nafion composed of a single polymer of perfluorosulfonic acid is currently the most widely used and considered a major reason for increasing the price of Membrane electrode assembly (MEA), which is a key component of a fuel cell that produces electrical energy through an electrochemical reaction. Therefore, the reinforced composite membrane is getting attention in that it can reduce the amount of ionomer impregnation and improve ionic conductivity through thinning based on the excellent mechanical properties of the support polymer. In this study, a reinforced composite membrane is produced by a surface modification of porous polytetrafluoroethylene (PTFE) through plasma-assisted silane treatment, followed by Nafion impregnation. The surface modification of PTFE is adjusted by time on plasma and silane treatments. The optimum conditions are observed at 1 min of 10 W, 100 kHz, Ar plasma and 0.5 vol% silane treatment at room temperature for 1 min. After surface modification, the surface of PTFE becomes hydrophilic with a contact angle of 65~75 ^o. The tensile strength and elongation at break of PTFE/Nafion were much higher than those of commercial homogeneous Nafion membranes. This PTFE/Nafion composite membrane has a tensile strength of 16 N mm^-1 and an elongation at break of 221 %. It also shows an ionic conductivity of 0.12 S cm^-1, similar to commercial homogeneous Nafion membranes.