Supramolecularly engineered sPEEK membranes via cationic porphyrins for intermediate temperature PEM fuel cells

A novel sulfonated poly(etheretherketone) (sPEEK) composite membrane incorporating the cationic meso-tetrakis(N-methyl-4-pyridinium)porphyrin TMPyP was developed for intermediate temperature polymer electrolyte membrane fuel cells (PEMFC). TMPyP acts as a supramolecular modulator of the ionic architecture through electrostatic interactions with sPEEK sulfonic groups. Spectroscopic and SAXS analyses demonstrated that TMPyP remains chemically stable and monomeric within the polymer matrix while inducing a controlled reorganization of the ionic domains. The ionomer spacing increased from 2.41 nm for sPEEK to 2.71 nm for the composite membrane, indicating enhanced nanoscale organization without excessive swelling. Compared with pristine sPEEK and membranes containing other porphyrins, the sPEEK/TMPyP membrane exhibited an improved balance between proton conductivity, dimensional stability, and mechanical robustness under intermediate humidity and temperature conditions. The membrane maintained stable electrochemical performance above 100 °C, achieving current densities above 650 mA cm−2 at 0.6 V and 110 °C. Importantly, the membrane was successfully scaled up to a 250 cm2 active area and implemented in a stack-relevant single-cell configuration. To the best of our knowledge, this represents the first demonstration of a porphyrin-based sPEEK membrane at this scale for intermediate temperature PEMFC applications, highlighting the potential of supramolecular electrostatic stabilization as a new strategy for fluorine-free proton exchange membranes.