Composites Nafion-titania membranes for Polymer Electrolyte Fuel Cell (PEFC) applications at low relative humidity levels: Chemical physical properties and electrochemical performance

Abstract

The incorporation of inorganic compounds into the polymeric Nafion matrix represents a possible solution to improve the mechanical characteristics of the polymeric membranes when drastic operative conditions (higher temperatures and/or lower relative humidity levels) are adopted in a Polymer Electrolyte Fuel Cell (PEFC). On the basis of previous investigations, different commercial anatase titanium oxide (TiO2) loadings were used to prepare composite membranes with the aim of reducing the humidification levels for a PEFC stack. Membranes with three different TiO2 contents (5, 10, 15 wt.%) were cast and characterized in terms of chemical-physical and electrochemical behaviour. The influence of filler was highlighted resulting in a swelling reduction of the composite membranes if compared to a pristine recast Nafion membrane cast with the same method and used as a reference. A good proton conductivity was observed for all composite Nafion-titania (N-TiO2) membranes with values ranging 1.3–1.9·10−2 S cm−1 at 60 °C and 50%RH against a value of 1.5·10−2 S cm−1 related to the reference membrane. The composite membrane containing a 10 wt.% of TiO2 has shown an improved performance respect to the reference membrane, especially at low levels of humidification and a higher stability during the accelerated stress test (AST) carried out in drastic conditions (60 °C and 50%RH), probably due to the filler capability to reduce the swelling and give stiffness to the polymeric matrix.