Surface Modification of Sulfonated Polystyrene Ethylene Butylene Polystyrene Membranes by Layer-by-layer Assembly of Polysulfone for Application in Direct Methanol Fuel Cell

Methanol permeability is a major drawback for application of sulfonated polystyrene ethylene butylenes polystyrene block copolymers (SPSEBS) in direct methanol fuel cells (DMFC). Modification of SPSEBS by layer-by-layer (LBL) assembly of aminated (APSU) and sulfonated polysulfone (SPSU) was attempted to reduce its methanol permeability. The LBL deposition of APSU and SPSU on SBSEBS was carried out by dipping in their solutions alternatively for 10min. The LBL assembly was confirmed by SEM analysis. The methanol permeability was lower than SPSEBS and Nafion 117. The proton conductivity, ion exchange capacity, and water absorption were lower than SBSEBS but higher than Nafion 117. Its selectivity ratio (0.70x105) was higher than both SBSEBS (0.54x105) and Nafion 117 (0.06x105). The maximum power density of LBL (62mW/cm2) was about five times higher than SBSEBS. These features of LBL confirm the LBL assembly method as a very simple procedure to modify SBSEBS for application in DMFC.