Preparation and Properties of Cross‐linked Sulphonated Poly(sulphide sulphone) Membranes for Fuel Cell Applications

A series of cross‐linked sulphonated poly(sulphide sulphone) (SPSSF) membranes have been prepared via a polyphosphoric‐acid‐catalysed condensation reaction at 180 °C for a period of time (1.5–5.0 h) and the resulting cross‐linking bonds are the highly stable sulphonyl groups. The cross‐linking density could be controlled by regulating the reaction time. Cross‐linking caused significant enhancement in the mechanical properties and large reduction in both water uptake (WU) and methanol permeability. The SPSSF‐60 membrane (the numeral 60 refers to the degree of sulphonation), e.g. had a tensile strength increased from 16 to 27 MPa (wet membranes) after cross‐linking for 5 h, while the WU substantially decreased from 320 to 58 wt.‐% and the methanol permeability decreased from 1.9 × 10 –6 to 2.7 × 10 –7 cm 2 s –1 (30 °C). Single cell test on hydrogen/oxygen revealed that the cross‐linked SPSSF‐50 (1.5 h) membrane displayed higher open circuit voltage (OCV, 1.02 V), higher maximum output power density (1.32 W cm –2 ) and significantly slower OCV decay rate than the uncross‐linked SPSSF‐40 membrane under the same operating conditions despite their similar ion exchange capacities. The cross‐linked SPSSF‐60 (5.0 h) and SPSSF‐50 (1.5 h) membranes showed significantly better fuel cell performance than Nafion 212.