Functionalized graphene oxide (FGO) was incorporated into polyvinyl alcohol/ poly(diallyldimethylammonium chloride) semiinterpenetrating polymer networks (PVA/PDA SIPNs) in order to create novel nanocomposite anion-exchange membranes (AEMs) with improved OH − conductivity and good thermo-mechanical stability at high relative humidity. The nanocomposites were fabricated by a solvent-casting method and subsequently thermally crosslinked to improve their mechanical stability in the hydrated state. The effects of PVA/PDDA ratio, cross-linking method, cross-linking temperature, and FGO content were studied in order to determine the optimal conditions to fabricate AEMs with improved material properties. The membranes were characterized by XRD, FTIR, TGA, FE-SEM, and impedance spectroscopy to assess the material properties of FGO and the nanocomposite membranes. The membranes were also evaluated as polymer electrolytes in anion exchange membrane fuel cells. The results reveal that the membrane fabricated at a PVA/PDDA weight ratio of 70/30 and 20 wt% FGO possesses the highest value of OH − conductivity (12.1 mS cm −1 @ 30 • C and 21 mS cm −1 @ 80 • C), as well as improved thermo-mechanical stability at 100% R.H. However, the fuel cell performance reaches a maximum using the membrane fabricated at 10 wt% FGO. Anion exchange membrane fuel cells (AEMFCs) have attracted considerable attention during the last few years due to some advantages that these kinds of systems offer compared to proton exchange membranes fuel cells (PEMFCs).1,2 For example, thanks to the facile kinetics for electrochemical charge transfer in alkaline environments, it is possible to use less expensive catalysts like nickel and silver in AEM-based fuel cells. 3 In terms of the fuel management, it is also possible to use concentrated fuels to operate these devices, because of the often reduced fuel crossover in AEMs. 4 Unfortunately, AEMFCs have some issues, specifically related to the polyelectrolyte performance. In general, AEMs have lower ionic conductivity than PEMs, mostly due to the fact that conductivity of OH − is intrinsically lower than H + . 5 Another concern with the use of AEMs is the degradation of their cationic groups in strong alkaline media. 6 In addition, AEMs usually exhibit poor solubility in low boiling point and inexpensive solvents, leading to less environmentallyfriendly fabrication processes with high costs and high degree of complexity. 7In order to overcome these limitations, a wide variety of membranes have been proposed during the last few decades as AEMs, including homopolymers, heterogeneous membranes and semi-interpenetrating polymer networks (SIPNs). [8][9][10][11] Among the various options available, SIPNs have gained relevance due to ease of fabrication, acceptable ionic conductivities, and excellent mechanical properties.12-14 More specifically, poly(vinyl alcohol)/poly(diallyldimethylammonium chloride) (PVA/PDDA) SIPNs are promising membranes for applications in electrochemical energy systems mainly because PVA is ...

Anion-exchange membranes (AEMs) are promising materials for a wide variety of applications including among others, fuel cells, electrolyzers, and membrane separation processes. However, development of AEMs with improved hydroxyl conductivity and selectivity as well as excellent thermo-mechanical stability, remains an absolute necessity, now more urgent than ever, due to the global climate change and energy crisis. The main objective of the present study is to synthesize novel AEMs with excellent hydroxyl conductivity and mechanical stability from hyperbranched polyester polymers. More specifically, poly (vinyl pyridine) (PVP) was grafted onto bis-MPA polyester-64-hydroxyl via graft copolymerization and subsequently quaternized using different alkylating agents. The effects of some variables such as grafting degree and alkylating agent on the morphology as well as on the materials properties of these new-developed membranes were evaluated. The cation stability in alkaline media and the water uptake of these AEMs were also investigated. Some characterization techniques such as NMR, SAXS, FTIR, TEM, TGA, DSC and impedance spectroscopy were used to assess the materials properties of these membranes.

In the last few years, direct borohydride/hydrogen peroxide fuel cells (DB/HPFC) have attracted considerable attention due to their potential use as air-independent power sources in undersea vehicles. In general, a DB/HPFC system can be built using either a cation exchange membrane (CEM) or an anion exchange membrane (AEM) as a polymer electrolyte. Unfortunately, to date, these systems exhibited low efficiency, mainly due to some problems related to the intrinsic properties of the polymer electrolyte themselves. Bipolar membranes are promising candidates to improve the efficiency of DB/HPFC systems, since these incorporate advantageous features of both AEM and CEM, and also mitigate the loss of fuel. The present work focuses on the fabrication and characterization of a novel bipolar membrane for DB/HPFC applications. The first goal is to fabricate water-soluble PVA-based AEM and CEM with both high ionic conductivity and excellent mechanical stability. For this purpose, a variety of AEMs are prepared via polymer blending of PVA and poly(diallyldimethylammonium chloride) (PDDA) or poly(acrylamide-co-diallyldimethylammonium chloride) (PACoDDA). Similarly, CEMs are fabricated via polymer blending of PVA and acid polymer ((poly (styrene sulfonic acid) (PSSA) or poly (acrylic acid) (PAA)). Subsequently, the membranes are cross-linked using a chemical or physical method. The chemical cross-linking is performed at different concentrations of glutaraldehyde (GA), whereas the physical cross-linking is performed at different temperatures. The electrical, mechanical and morphological properties of these membranes are evaluated as a function of PVA content and cross-linking process conditions. Some of the material characterization techniques used in this study include, but are not limited to: Fourier transform infrared spectroscopy (FTIR), four-electrode impendence measurement, transmission electron microscopy (TEM), and tensile tests. Preliminary results indicate that PVA-PDDA and PVA-PSS membranes have excellent mechanical and alkaline stability. Also, the maximum OH− conductivity of 8.57E-3 S cm−1 was achieved for physically cross-linked PVA/PDDA membrane with a polymer composition of 70/30 as shown in Figure 1a. In the case of CEM, the high H+ conductivity of 1.77E-2 S cm−1 corresponds to the chemically cross-linked PVA-PSS membrane with a polymer composition of 70:30 (see Fig. 1b). Figure 1. Ionic conductivity as a function of PVA content for (a) PVA/PDDA membranes and (b) PVA/PSS membranes.