Toward the replacement of Nafion®: Innovative PBI-PGO composite membranes as prospective polymer electrolytes for the “conductivity gap” range

This work aims at addressing the limitations of Nafion®, the standard polymer electrolyte for Proton Exchange Membrane Fuel Cells, by proposing a set of novel self-assembling PBI-PGO composite membranes capable of sustaining the “conductivity gap” temperature range (80–120 °C). Morphological and microstructural analyses (SEM, XRD) highlight uniformity without visible defects and a predominantly amorphous layout. Compositional EDS analysis confirms the presence of all key elements, indicating the successful phosphonation of GO and the subsequent mixing with PBI in various mass proportions. Thermo-mechanical characterization demonstrates the thermal stability of the samples, especially below 120 °C, along with mechanical features in line with those of comparable materials reported in other researches. Electrochemical impedance spectroscopy unveils the effective combination of the thermal resistance of PBI with the water-holding and proton conduction-enhancing properties of PGO, eliminating the need for acid doping. The results recommend the potentiality of the PBI-PGO composite membranes with high PGO content, since PBI-PGO 1:3 provides the highest water retention (257%) combined with an acceptable swelling ratio (26.8%), the best IEC (0.53 meq g–1), and the maximum in-plane (σIP = 0.087 S cm–1) and through-plane proton conductivities (σTP = 0.036 S cm–1) at 100 °C.