Composite porphyrin nafion and s-peek polymeric membranes

The ability to control the spatial arrangement of porphyrins, through non covalent intermolecular interactions, is very important for accessing advanced functional materials with peculiar properties. Recently, 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. Furthermore, in order to overcome the Nafion limitations such as high production cost and low performance at low temperature, pressure and humidity we explored porphyrin modified sulphonated polyetheretherketone (sPEEK) membranes. Generally, sPEEK-membranes possess good mechanical properties, reduced hydrogen cross-over, similar unit area resistance to Nafion, improved stability to radical species and reduced production cost. Opportunely selected porphyrins embedded in the membranes allowed to increase the proton transmissibility of the material forming a hydrogen ion sieve structure.2 Here, we report on composite membranes based on highly sPEEK and different weight percentage (0 - 5wt%) of 5,10,15,20-tetra(4-pyridyl)porphyrin (TPyP)3 and meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) developed and tested for their use in portable applications. The aim is to exploit the ability of two different porphyrins, containing polar functional groups, to create specific interactions in a polymeric matrix, in order to stabilize the membranes maintaining a proton path for the conduction mechanism. The membranes have been obtained by a standardized doctor-blade method, thermally and chemically treated. UV-Vis and Fluorescence emission were carried out to investigate the porphyrin aggregation state. Physical-chemical characterizations in terms of ionic exchange capacity, water uptake, dimensional variations and swelling, structural and morphological analyses have been performed. Proton conductivity measurements at low temperatures allowed to investigate the role of the interaction between polymer and porphyrin on the proton transport mechanism. Furthermore, the composite membranes were tested in a PEFC 25 cm2 single cell to verify the electrochemical performance at the selected operative conditions. We anticipate that sPEEK-TPPS membranes operating at 30°C, dry H2/ 100%RH air and 1 abs. bar showed the best fuel cell performance with a limiting current approaching 1A/cm2.