Structure‐Morphology‐Property Relationships of Non‐Perfluorinated Proton‐Conducting Membranes

Abstract

A fundamental understanding of structure-morphology-property relationships of proton exchange membranes (PEMs) is crucial in order to improve the cost, performance, and durability of PEM fuel cells (PEMFCs). In this context, there has been an explosion over the past five years in the volume of research carried out in the area of non-perfluorinated, proton-conducting polymer membranes, with a particular emphasis on exploiting phase behavior associated with block and graft copolymers. This progress report highlights a selection of interesting studies in the area that have appeared since 2005, which illustrate the effects of factors such as acid and water contents and morphology upon proton conduction. It concludes with an outlook on future directions.

Nanocomposite SPEEK-based membranes for Direct Methanol Fuel Cells at intermediate temperatures

“…Since swelling and water uptake increase with increasing temperature, especially above a critical temperature which depends on the IEC, it is inferred that the lower crosslinking degree reached at 110 ºC will promote a larger water uptake during the measurement at 90 ºC than at 60 ºC. Correspondingly, the larger fraction of water confined within the membrane will cause a diluting effect of the sulfonic acid groups thus decreasing the conductivity [54]. Crosslinking at 120 ºC seems to be optimal for the control of excessive water uptake while still not considerably reducing this parameter for the final achievement of a good proton conduction.…”

“…Proton conductivity and methanol permeability are associated with IEC, water uptake and swelling degree; both generally increasing with those parameters [50][51][52][53]. However, if water uptake and swelling degree surpass some critical value, it has been noticed that proton conductivity can be prone to diminish as a consequence of a dilution effect which decreases the local concentration of protons within the ionic channels [54]. Table 1 lists the swelling degree, water uptake and IEC parameters of the nanocomposite membranes as a function of crosslinking temperature.…”

Sulfonated fluorinated-aromatic polymers as proton exchange membranes

“…Qing et al (98) synthesized fluorinated sulfonated polybenzimidazoles (sPBI)s, whose structure is shown in Scheme 15 (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19). The sulfonated polymers showed good solubility in common organic solvents due to the presence of -CF 3 groups.…”

“…The structure of fluorinated SPI with naphthalene units is shown in Scheme 11 (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14). The DS was controlled by adjusting the mole ratio of diamines DSDSA to QA (DSDSA/QA) to obtain the SPI ionomers with controlled IEC.…”

“…Polymer electrolyte membrane fuel cells (PEMFCs), which usually operate at 60-80°C, have been extensively studied for applications to electric vehicles, residential power sources, and portable devices. PEMFCs convert chemical energy efficiently into electrical energy and are receiving considerable attention because of their low emission of pollutants and high energy conversion efficiency (1)(2)(3)(4)(5)(6)(7)(8). Because of their chemical and physical stability and high proton conductivity, perfluorosulfonic acid polymeric membranes such as Nafion ® (Dupont, Wilmington, Delaware, US) or Flemion ® (Asahi Glass, Marunouchi, Chiyoda-ku, Japan) have been mostly used as the electrolytes for PEMFCs.…”