Design of efficient methanol impermeable membranes for fuel cell applications

Abstract

In this paper, the design of efficient composite membranes based on sulfonated polysulfone and acidic silica material with characteristics and properties such as methanol barrier, high proton conductivity and suitable fuel cells performance is presented. A positive influence of nanosized acidic silica powders, used as an additive filler in the preparation of composite membranes, due to an efficient hydrophilic inter-distribution inside the membrane when compared to pure silica, is found. A series of different techniques such as XRF, FT-IR, TGA, DSC, IEC and conductivity measurements are used to highlight the properties of acidic silica material and composite membranes. The composite membrane based on acidic silica (SPSf–SiO₂–S) shows the lowest crossover current (only 8 mA cm⁻²), which is 43% lower than that of a pure SPSf membrane and 33% lower compared to a composite membrane based on bare silica (SPSf–SiO₂). These significant differences are attributed to the increasing diffusion path length of MeOH/H₂O clusters in the composite membranes. The maximum DMFC performance at 30 °C is achieved with the SPSf–SiO₂–S membrane (23 mW cm⁻²), whereas the MEAs based on SPSf–SiO₂ and pure SPSf membranes reached 21 and 16 mW cm⁻², respectively. These significant results of the composite SPSf–SiO₂–S membrane are ascribed at a good compromise among high proton conductivity, low swelling and low methanol crossover compared to pure SPSf and (unmodified silica)-SPSf membranes. A preliminary short durability test of 100 h performed in a cell with the composite SPSf–SiO₂–S membrane shows remarkable performance stability during chrono-voltammetric measurements (60 mA cm⁻²) at 30 °C.