Chitosan:poly (vinyl) alcohol composite alkaline membrane incorporating organic ionomers and layered silicate materials into a PEM electrochemical reactor

Mixed matrix membranes (MMM) are prepared from equivalent blends of poly (vinyl alcohol) (PVA) and chitosan (CS) polymers doped with organic ionomers 4VP and AS4, or inorganic layered titanosilicate AM-4 and stannosilicate UZAR-S3, by solution casting to improve the mechanical and thermal properties, hydroxide conductivity and alcohol barrier effect to reduce the crossover. The structural properties, thermal stability, hydrolytic stability, transport and ionic properties of the prepared composite membranes were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), thermo-gravimetric analysis (TGA), water uptake, water content, alcohol permeability, thickness, ion exchange capacity (IEC) and OH− conductivity measurements. The addition of both organic and inorganic fillers in a CS:PVA blend polymer enhances the thermal and ionic properties. All the membranes are homogenous, as revealed by the SEM and XRD studies, except when UZAR-S3 stannosilicate is used as filler, which leads to a dual layer structure, a top layer of UZAR-S3 lamellar particles bound together by the polymer matrix and a bottom layer composed mostly of polymer blend. The loss of crystallinity was especially remarkable in 4VP/CS:PVA membrane. Thus, the 4VP/CS:PVA membrane exhibits the best ionic conductivity, whereas the UZAR-S3/CS:PVA membrane the best reduced alcohol crossover. Finally, the performance of the CS:PVA-based membranes were tested in a Polymer Electrolyte Membrane Electrochemical Reactor (PEMER) for the feasibility use of alkaline anionic exchange membranes in electrosynthesis under alkaline conditions, showing the 4VP/CS:PVA and UZAR-S3/CS:PVA membranes the best performances in PEMER.We gratefully acknowledge the financial support from the Spanish Ministry of Economy and Competitiveness (MINECO) for CTQ2012-31229 project at the University of Cantabria, and MINECO-FEDER (Fondo Europeo de Desarrollo Regional (2014-2020)) through the CTQ2013-48280-C3-3-R project at the University of Alicante. C.C.C. also thanks the MINECO for the “Ramón y Cajal” program at the University of Cantabria (RYC2011-08550), and L.G.C. for her PhD fellowship BES-2011-045147 and the EEBB-14-09094 mobility grant for the research stay at the University of Cantabria, respectively