Novel Hydroxide-Conducting Polyelectrolyte Composed of an Poly(arylene ether sulfone) Containing Pendant Quaternary Guanidinium Groups for Alkaline Fuel Cell Applications

Abstract

Poly(arylene ether sulfone)s were functionalized with quaternary guanidinium groups in order to investigate their properties as novel polymeric hydroxide exchange membrane materials. The quaternized polymers were synthesized via chloromethylation of poly(arylene ether sulfone)s, followed by reactions with pentamethylguanidine. The resulting quaternized polymers PSGCl-x (where x represents the number of the quaternary guanidinium groups/repeat units) presented an elevated molecular weight and exhibited an outstanding solubility in polar aprotic solvents. Consequently flexible and tough membranes of PSGCl-x with varying ionic content could be prepared by casting from the DMSO solution. Novel anion exchange membranes, PSGOH-x, were obtained by an anion exchange of PSGCl-x with 1 M NaOH at room temperature. The membranes displayed a high ionic conductivity and an excellent chemical stability. The obtained alkaline anion exchange membranes (AEMs) showed conductivities almost above 10 -2 S cm -1 at room temperature; the hydroxide conductivity of PSGOH-1.4 was for instance found to be 6.7 Â 10 -2 S cm -1 .

Alkali resistant and conductive guanidinium-based anion-exchange membranes for alkaline polymer electrolyte fuel cells

“…2c) for GPPO-0.54 was used to measure the degree of the quaternization. Resonances due to guanidinium groups were detected as the new signals at δ = 2.6-3.3 [17]: The degree of conversion was close to 100%.…”

“…The alkali stabilities of GPPO-X AAEMs were investigated as reported previously [17]. Specifically, the samples were treated with aqueous KOH (1 mol dm -3 ) solution at room temperature for increasing lengths of time.…”

“…To achieve this aim, a series of AAEMs with pendant guanidinium groups were prepared, as recent reports suggest that this head-group exhibits appealing alkali stability and high anion (including hydroxide) conductivities (due to the high basicity and delocalized structure of the guanidinium functional groups) [17]. The AAEMs in the prior report were prepared using chloromethylation reactions followed by reaction with 1,1,2,3,3-pentamethylguanidine (PMG) [17]. It should be noted that PMG possesses a pK a = 13.8 [16], which is much higher than that of trimethylamine; this suggests that guanidinium hydroxides will express enhanced OH -anion dissociation.…”

“…It should be noted that PMG possesses a pK a = 13.8 [16], which is much higher than that of trimethylamine; this suggests that guanidinium hydroxides will express enhanced OH -anion dissociation. This higher alkalinity promises an augmentation of both the number of dissociated hydroxides and their associated water molecules, thereby facilitating hydroxide ion conduction [17].…”

“…In addition, the guanidinium groups can take part in conjugation and are strong electron donors, both of which enhance their alkaline and thermal stabilities [17].…”