Proton conducting sulfonated polysulfone and polyphenylsulfone multiblock copolymers with improved performances for fuel cell applications

A series of proton exchange membranes based on sulfonated multiblock copolymers with three polysulfone (PSU) and polyphenylsulfone (PPSU) ratios (50/50, 60/40 and 75/25) are prepared following a synthesis strategy that aims to achieve a microphase separation. A selective sulfonation of PSU blocks was observed in copolymers with a high proportion of PSU. The water uptake is higher in these materials (31% and 57% for SPES 50/50 and SPES 75/25, respectively at 60 °C) while the tensile strength was lower (56.0 MPa and 40.6 MPa for SPES 50/50 and SPES 75/25 in the H form, respectively). Ionic conductivity of SPES 75/25 membranes measured both ex situ and in situ at 80 °C is 25 and 31 mS·cm, respectively. Fuel cell tests reveal that SPES 75/25 shows the highest value for the maximum power density (670 mW·cm at 70 °C and 100% of RH) which is higher than that achieved for SPES 50/50 (400 mW·cm). In addition, the high current density obtained for SPES 75/25 (1000 mA·cm at 0.6 V and 70 °C) compared with SPES50/50 (600 mA·cm) and Nafion 112 (450 mA·cm at 75 °C) shows its promising properties as solid electrolyte in polymeric fuel cells.