Study on sulphonated polysulphone/polyurethane blend membranes for fuel cell applications

Abstract

The study of sulphonated polysulphone membranes (s-PSF) containing urethane groups was carried out, in order to improve the proton conductivity of a PEFC at T⩾80°C. Sulphonated polysulphone (s-PSF) polymers with a sulphonation degree (DS) ranging 40–70% were prepared following a standardised preparation procedure. An aliphatic polyurethane diol in oligomeric form (PU-Aldrich) was added to a s-PSFs with different sulphonation levels to prepare blend membranes, containing a 18%wt of PU, casting by the Doctor-Blade technique. The obtained membranes were characterised in terms of water uptake (Wup), ionic exchange capacity (IEC), swelling data, methanol permeability, scanning electron microscopy (SEM), thermo gravimetric analysis (TGA), proton conductivity measurements and electrochemical tests in a 5cm2 commercial single cell with humidified H2/air at 80°C.By adding a 18%wt of PU, a slight increase in the IEC values respect to the pristine polymers were obtained due to a ionic crosslinking, likewise, a slight increase of Wup values was observed for each DS between pristine and corresponding blend. For all prepared samples, a lower swelling than critical value of 2 was obtained also at 100°C. PU introduction determined an enhanced proton conductivity for each DS, due to an interaction between sulphonic and nitrogenous groups caused by a possible tautomerisation mechanism. The I−V curves at 80°C confirm that blend membranes performance is higher than bare membranes, in particular, an improvement was obtained with a blend membrane containing a 18% of PU and a medium PSF sulphonation degree (48%).