(147c) PVDF-Acrylic Semi-Interpenetrating Network Proton Exchange Membranes

The proton exchange membrane (PEM) is a fundamental component of the polymer electrolyte membrane fuel cell (PEMFC); one of the most promising alternative energy conversion approaches for low to medium power applications. Existing commercially available PEMs are predominantly based on perfluorosulfonic acid polymers (PFSA) (e.g., Nafion®), which are characterized by elevated costs owing to convoluted manufacturing processes. In this study the viability of semi-interpenetrating ionomer-polymer networks from blends of poly(vinylidene fluoride) (PVDF) and covalently-crosslinked sulfonated acrylic polyelectrolytes (PE) as potential PEMs is examined. A total of 80 dissimilar PVDF/PE membranes, prepared from five different grades of Kynar® PVDF (homo- and copolymers) and two types of PE, were characterized in terms of proton conductivity and mechanical properties using custom-developed high-throughput screening tools. In addition to PE type and content, the crystalline characteristics (i.e., crystallinity and crystallite size) and melt viscosity of the inert PVDF phase were found to play a major role on proton conductivity. Particularly, membranes based on highly crystalline and viscous PVDF homopolymers exhibited the lowest proton conductivity due to precluded segmental motion of the PE chains during crosslinking. Mechanical properties of the membranes were dominated by the PVDF grade incorporated. Membranes based on stiffer PVDF homopolymers exhibited higher elastic modulus and tensile strength; while those based on the more flexible copolymers were tougher. In general PVDF/PE membranes compared favorably to Nafion®, having conductivities in excess of 130 mS/cm (vs. 84.5 mS/cm for Nafion®) and mechanical properties 2 to 5 times higher in some cases. The selection of a particular PVDF/PE membrane, however, implies a tradeoff between conductivity and mechanical properties and is determined by the requirements of the PEMFC final application.