Fully Aromatic Ionomers with Precisely Sequenced Sulfonated Moieties for Enhanced Proton Conductivity

Ion transport in sulfonated polymers

“…Given that ion transport across the PEM is rate-determining step in PEMFCs rather than the electron transfer between electrodes, PEMs are considered as a key component in PEMFCs to optimize the performance of these systems. [4][5][6] Among the wide range of existing PEMs, sulfonated polymers have been of particular interest, [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] which are a class of ionomers having been investigated over the last 30 years for diverse applications of thermoplastics, dispersants, and packing materials. 22 The specific ionic interactions in discrete regions of ionomers can yield significant changes in physical properties of polymers such as glass transition temperature (T g ) and water uptake.…”

“…[4][5][6][7][8] Hydrocarbon-based sulfonated polymers have also been extensively studied on account of their low cost in comparison to Nafion TM . [9][10][11] The most widely studied materials are sulfonated polyaromatic engineering plastics [12][13][14][15][16] and sulfonated polyimides. [17][18][19] Several studies have focused on the optimization of the amount of water absorbed in the PEMs so as to improve the conductivity.…”

“…[17][18][19] Several studies have focused on the optimization of the amount of water absorbed in the PEMs so as to improve the conductivity. [14][15][16][17][18] The aforementioned PEMs are often referred to as sulfonated random copolymers owing to the random location of the hydrophilic and hydrophobic moieties. [10][11][12][13][14] A simple means of improving the conductivity is to increase the sulfonation level (SL) in the PEMs.…”

“…The morphology-transport relationship in IL-integrated PEMs is discussed to highlight promising avenues for the rational design of new PEMs. [3][4][5][6][7] sulfonated polyaromatics, [12][13][14][15][16][48][49][50][51] and sulfonated polyimide derivatives. [17][18][19] Commercially available Nafion TM membranes have been the benchmark in the sulfonated PEM studies owing to their high conductivity (on order of 0.1 S/cm) under fully hydrated conditions, despite their low IEC value of 0.9 mmol/g.…”

“…37,60,61 Based on this consideration, the precise positioning of acid groups has recently been attempted, and the resultant PEMs having controlled ionic sequencing revealed well-defined ionic aggregates with a higher degree of organization in comparison to the conventional systems having a statistical distribution of acid groups. 16,[62][63][64] Although such issues in diverse sulfonated PEMs have clearly been elucidated, no consensus has thus far been reached concerning the role of the phase separation between the hydrophilic phases and hydrophobic domains in determining the membrane transport properties. The issue of phase separation should be fundamentally important in unraveling the structure-property relationship of sulfonated PEMs; however, the ill-defined, process-dependent, heterogeneous structures of many sulfonated PEMs have hampered the acquisition of quantitative information on them.…”