[ materials ]
Even after decades of research into PEM alternatives ( investigating modified PFSA , partially perfluorinated , fluoride free , sulfonated hydrocarbon polymers ), PFSA membranes remain the benchmark PEM material in the industry .
PFSA-based membranes ( with their most commonly used representatives from Nafion ® and GORE ® ) have been the materials of choice for commercial fuel cells .
PFSA is a semi-crystalline copolymer with poly ( tetrafluoroethylene ) ( PTFE ) backbone ( providing the membrane with thermal , chemical and mechanical stability due to fluorine presence ) and perfluorovinyl ether side chains terminated with sulfonic acid groups ( responsible for the ionic
conductivity due to the presence of ionic groups ). ( See Figure 2 ).
Barrier , chemical , and mechanical properties of PEM result from PFSA ’ s phase separated morphology , microstructure ( nano-domains , ionomer conformation ), multiscale structure ( connectivity , crystallinity , tortuosity , or surface properties ), and physicochemical characteristics . And PEM ’ s morphology and chemistry are a strong function of PFSA materials properties , including the dual phase-separated nature .
Given the aforementioned , the most prominent way to control the PFSA morphology is via the ionomer chemistry . Side chains length and EW ( that is inversely proportional to the PFSA ’ s ion exchange capacity , IEC ) are two underlying
Fig . 2 . ( a ) Chemical formula of Nafion ® ionomer with PTFE backbone ( blue ) and sulfonate acid-terminated side chains ( green ). ( b ) Schematic representation of Nafion ® with proton-conducting channels . Adapted from : Topics in Catalysis 61 ( 2018 ): 2064 – 2084
Hydrogen Tech World | Issue 15 | April 2024 21