Titania nanosheets (TNS)/Sulfonated poly ether ether ketone (SPEEK) nanocomposite proton exchange membranes for fuel cells

Sulfonated polyetherethcrketone (SPEEK)-based composite membranes containing various amounts of titania nanoshects (TNS) as inorganic filler have been prepared and investigated for proton exchange membrane applications. The SPEEK degree of sulfonation was DS = 0.58 and the TNS content was in the range 0.95-10.00 wt. %. The two-dimensional titanium oxide sheets, have been prepared as stable colloidal suspensions produced by the action of a quaternary ammonium ion, such as tetrabutylammonium, TBA+. SPEEK/TNS composites have been prepared by casting from DMA (dimethylacctamide). The samples have been characterized in terms of thermal stability (TG/ DTA, DSC), proton exchange capacity (P.E.C., by titration), water uptake, proton conductivity (EIS), and structural (XRD) and microstructural (SEM) features. Acid treated composites, at the lowest inorganic additive contents, exhibited improved properties in terms of proton conductivity and water uptake with respect to pure SPEEK. The best performing nanocomposite was the membrane containing only 1.67 wt.% TNS showing conductivity value of 4.14 10^-2 Scm^-1 at 140 °C and at 100% of relative humidity (RH), whereas pure SPEEK membrane exhibited a value of 1.76 x 10^-2 Scm^-1 at the same temperature and RH conditions. The volume swelling (VS), measured at 90 °C for the composite membrane containing 1.67 wt. % TNS, was reduced by ca. 80% with respect to that of a reference SPEEK membrane. The improved electrochemical properties of TNS nanocomposites have been associated to the unique nature of the two-dimensional nano structured inorganic additive.