Porphyrin enhancing performance of functionalized sPEEK membranes for Polymer Electrolyte Membranes portable applications

Fuel cells are clean and highly efficient electrochemical systems for energy conversion. In particular, polymer electrolyte fuel cells (PEFC) are more efficient and less bulky than currently available systems for the fabrication of portable systems, due to the high energy density with respect to the traditional batteries. In this field, one of the goal is to obtain low cost materials able to improve the performance of the device. The polyaromatic membranes based on sulphonated polyetheretherketone (sPEEK), due to its properties such as high solvent resistance, high thermo-oxidative stability, excellent mechanical properties, good proton conductivity, can be considered as an alternative and good candidate to conventional membrane. In order to stabilize the membranes maintaining a proton path for the conduction mechanism and improving the characteristics of the sPEEK material, opportunely selected porphyrins1 able to specifically interact with the polymeric matrix, were added. To identify the best composition as a function of the interactions between the components, membranes with different porphyrin load and functionalization polymer degree have been obtained by a standardized doctor-blade method. Spectroscopic investigation has been carried out to investigate the interactions among the chromophoric units and the polymeric matrix as well as the porphyrin aggregation state into the membranes. 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 investigating the role of the interaction between polymer and porphyrin on the proton transport mechanism. Moreover, the composite membranes were tested in a PEFC 25 cm2 single cell showing very good electrochemical performance and excellent stability operating in experimental conditions optimized for application in portable devices.