Sulfonation of PIM-1-towards highly oxygen permeable binders for fuel cell application

The development of alternative, non-fluorinated membranes for polymer electrolyte membrane fuel cells necessitates the co-development of a non-fluorinated electrode catalyst binder to ensure compatibility between membrane and electrode. However, most hydrocarbon based polymers have lower gas permeability than perfluorinated Nafion. In this work we tried to obtain a sulfonated, non-fluorinated binder based on PIM-1 (polymer of intrinsic microporosity 1) which has up to 2000 times higher permeability than Nafion. However, sulfonation was not straightforward and often led to degradative side reactions. Sulfonated polymers were too brittle to give stable membranes and the highest experimental IEC was 1.03 meq/g, significantly lower than the theoretical IEC of 3.2 meq/g (2 sulfonic acid groups per repeat unit).