Stabilizing proton exchange membranes using Cerium(III) ions

Proton Exchange Membrane Fuel Cells (PEMFCs) represent an innovative and promising technology for transportation applications due to their low weight, lower operative temperature, and pressure ranges. One of the most challenging limiting factors for the adoption of PEMFC in everyday life is the durability of the Proton Exchange Membrane (PEM), the true core of this type of device. The internal environment of PEMFCs is naturally rich in free radicals (such as HO• and HOO•), which react with the PEM backbone, damage the PEM, and ultimately lead to the PEMFC failure. One way to improve the stability of PEMs against these species is the incorporation of an additive that can act as a radical scavenger and become the preferential site for radical oxidation. One of the most used radical scavengers for this kind of application is cerium in its Ce3+ oxidation state. In this thesis work, a set of sulfophenylated polyphenylenes (sPPB) membranes were synthesized by introducing different amounts of Ce3+ (sPPB-Ce3+), and efforts were made to identify the multiple degradation pathways (chemical, thermal, mechanical). The stability of sPPB-Ce3+ membranes to radical degradation was enhanced almost threefold, they maintained their structural integrity, shape, and thickness and their proton conductivity was comparable to that of the pristine materials. Several other properties such as dimensional stability, polydispersity and solubility also underwent important changes. As observed through these analyses, the effects of Ce3+ on the original material properties can be advantageous in improving the characteristics of proton exchange membranes.