Evaluation of fluorine and sulfonic acid co-functionalized graphene oxide membranes under hydrogen proton exchange membrane fuel cell conditions

Abstract

Two-dimensional perfluorinated sulfonic acid represent an intriguing new proton exchange membrane concept.

Development of self-assembling sulfonated graphene oxide membranes as a potential proton conductor

“…Moving to sulfonated specimens, even the lowest acid-to-GO molar ratio displays a significant increase in the protonconducting ability as opposed to both Nafion ® 212 and virgin GO, since a value of 1.20 meq g −1 has been obtained ( Figure 8A), in agreement with those reported in literature [16,22,23]. A remarkable finding is that SGO-20 (1.97 meq g −1 ) appears to provide better features than SGO-200 (1.43 meq g −1 ) even though it has been prepared with a lower sulfonation ratio.…”

“…Consequently, sulfonation has improved the through-plane value by two orders of magnitude with respect to the ones measured by Bayer et al for bare GO [17,19], which is in agreement with a remarkable ion exchange capacity (1.1 meq g −1 ), even greater than for Nafion ® (0.93 meq g −1 ). Similar results have been found by Jiang et al [22] and by Sandström et al [23] but, despite an encouraging fuel cell performance, sulfonated GO's proton-conducting behavior, fuel impermeability, stability and durability are still unsatisfactory.…”

“…Hence, huge research efforts have been dedicated in the last few years to finding suitable alternatives that can outperform Nafion ® under conditions of high temperatures and low relative humidity (RH), which would substantially enhance both kinetics and efficiency of the redox reaction, while making water management and cell design simpler [20,21]. Among the most recent research trends, graphene oxide (GO) has gained significant interest for the production of both selfstanding [16,17,19,22,23] and hybrid electrolytes, which have been mostly tested for intermediate (80-130 °C) temperature applications. The latter may still be based on Nafion ® [24][25][26][27][28][29] or on more thermally stable polymers, such as sulfonated polyimide [30][31][32] and sulfonated poly(ether sulfones/ketones) [33][34][35][36][37][38], in which the addition of either virgin or functionalized GO is expected to improve mechanical, water-retaining and proton-conducting behaviors.…”

“…Therefore, innovative approaches involving the modification of GO flakes with alternative functionalities may be studied, with the aim of enhancing both ionic conductivity and structural cohesion of the material. A particularly interesting route consists in the introduction of some acid moieties more tightly bound to the skeleton of GO, such as sulfonic acid ones (-SO3H) analogous to those of Nafion ® , as proposed by several authors [16,[22][23][24][25][31][32][33][34]. Self-standing sulfonated graphene oxide membranes have been prepared by Kumar et al [16].…”

“…The aim is to produce self-assembling sulfonated graphene oxide (SGO-X) membranes with a simpler sulfonation procedure with respect to the multi-step ones reported in literature. These processes generally involve several precursors such as diazonium salts [16,23,25,28,37], silane molecules [24,31,32,34], chlorosulfonic acid [33,36] or sodium dodecylbenzenesulfonate [22], while the proposed one is based on a reaction with sulfuric acid. The prepared materials have been extensively characterized from the morphological viewpoint by employing scanning electron microscopy, infrared and energy-dispersive X-ray spectroscopies, thermogravimetry and static contact angle analyses.…”