Porphyrin/sPEEK Membranes With Improved Conductivity And Durability For PEFC Technology

The ability to control the spatial arrangement of porphyrins, through non covalent intermolecular interactions, is very important for accessing to advanced functional materials with peculiar properties. In the past we reported on the ability to easily tune porphyrin J-aggregates optical features using inner channels of Nafion membranes as confined environment to arrange and orient the chromophores.[1] Since Nafion is usually involved as electrolyte in fuel cells applications, also the contribution of the porphyrin aggregates on the membranes proton conduction mechanism has been investigated. Moreover, in order to overcome the Nafion limitations, recently, advanced composite membranes have been obtained by incorporation of the meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) into a sulfonated poly(etheretherketone) (sPEEK). The presence of porphyrins in their monomeric, dimeric, and aggregated forms into the membrane ionic domains have been investigated by static and time-resolved spectroscopic techniques. In particular, we succeeded in modulating the percentage of the different porphyrin species present into the proton-conducting channels acting on the dye load in the range 0.35−5 wt % porphyrin/polymer. The nanostructure of all the composite membranes has been investigated by small-angle X-ray scattering. This latter shows how the presence of TPPS porphyrins into the membrane ionic domains induces a reorganization of polymer chains in a more stable and organized lamellar-like structure with respect to the pristine polymeric matrix. Finally, the composite membranes have been used as proton exchange membrane for fuel cells (PEFCs) technology. The presence of porphyrins improved the performance of the membranes in terms of proton conductivity and stability. In particular, the 0.77 wt % composite membrane has been tested in a PEFC single cell simulating the operative conditions typical for portable applications, highlighting an improved stability compared to that of the sPEEK pristine membranes.[2]