Comparative study of sPIM with Nafion as binder for Proton Exchange Membrane Fuel Cells

Binders are crucial elements for the efficient functioning of fuel cells. Their role is to keep the catalyst tied to the electrode, but they must possess precise characteristics, in order to facilitate the work of a fuel cell (FC): these binders must show that they have good adhesion to electrodes, good resistance to corrosion and they have to facilitate electron transfer within the electrode through a high electrical conductivity. The most widely used binder is Nafion, a polymeric material that has consolidated operation and it is clearly recognized by the entire scientific community. Tests reported in this thesis will compare a sulfur-containing Polymer of Intrinsic Microporosity (sPIM) to see if it could be a good substitute for Nafion. The object of this research is to evaluate if sPIM characteristics are better than Nafion. Through this research, it was determined that Nafion remains the most competitive material working as a binder, but sPIM has a very promising future due to its performance. sPIM was analyzed in two different forms: in the following paragraphs there are tests with a sulfur-containing polymer of intrinsic microporosity with a different degree of sulphonation, one with 16 hours of sulphonation, the other one with 72 hours. In the first set of tests with RRDE, Nafion was compared with sPIM 16h and sPIM 72h. Results showed that in an acid environment sPIM 72h has a better performance than its sPIM 16h, but not like Nafion. A totally different result was obtained in an alkaline environment, in fact sPIM reached almost the same performance of Nafion and the sPIM with the best performance is the one with 16h of sulfonation. In the second set of tests with GDE, the behavior is similar: in acid environment the sPIM with the best characteristics is the sPIM 72h, while in alkaline environment is sPIM 16h. The greatest difference with the RRDE system is that results between Nafion and sPIM are not the same in an alkaline environment, their performances are not very similar as in RRDE setup. There also are accelerated degradation tests (ADT) to evaluate the performance of a material in a long period of time, by simulating stress conditions. With the RRDE device, ADT in acid environment showed the best performance for Nafion, followed by sPIM 72h and finally sPIM 16h. In alkaline environment, the trend seems to be the same. About the analysis made with the GDE cell, ADT in acid environment showed that Nafion maintains its leading role, but the second best one is sPIM 16h (and not 72h as before, for RRDE). In alkaline environment, ADT exhibited a performance quite similar for Nafion and sPIM 16h. In both environments, sPIM 72h has a very low resistance to stress conditions.