Composite polymer electrolytes for fuel cell applications: Filler-induced effect on water sorption and transport properties

Nafion- and sulfonated polysulfone (SPS)- based composite membranes were prepared by incorporation of SnO2 nanoparticles in a wide range of loading (0${ \div }$35 wt. %). The composites were investigated by differential scanning calorimetry, dynamic vapor sorption and electrochemical impedance spectroscopy to study the filler effect on water sorption, water mobility, and proton conductivity. A detrimental effect of the filler was observed on water mobility and proton conductivity of Nafion-based membranes. An increase in water mobility and proton conductivity was instead observed in SPS-based samples, particularly at low hydration degree. Analysis of the water sorption isotherms and states of water revealed that the presence of SnO 2 in SPS enhances interconnectivity of hydrophilic domains, while not affecting the Nafion microstructure. These results enable the design of suitable electrolyte materials that operate in proton exchange membrane fuel cell conditions. Materials for energy and sustainability: Composite membranes based on two different ionomers, Nafion and sulfonated polysulfone (SPS), can be used as electrolytes in polymer electrolyte membrane fuel cells (PEM-FCs). The analysis of water sorption and proton transport properties of composites illustrates the complex polymer-filler interaction, thus enabling the design of suitable electrolyte materials that operate in PEM-FC conditions.