Impedance Spectroscopy and Performance of Cross-Linked New Naphthalenic Polyimide Acid Membranes

This paper reports the synthesis, characterization, and thermal stability of cation-exchange membranes based on naphthalenic copolyimides. To improve the mechanical stability, the membranes were cross-linked through the reaction of sulfonic acid groups with hydrogen atoms of activated phenyl groups located in neighboring chains using appropriate catalysts. The ion-exchange capacity of the membranes is higher than 2 meq/(g of dry membrane), and the number of molecules of water per ion-exchange group lies in the vicinity of 20. The response of the membrane electrode assembly (MEA) to electrical perturbation fields in a wide range of frequencies was measured, and the equivalent electrical circuit governing the response is discussed. The conductivity of the MEAs at 75 °C is of the order of 10 −2 S/cm. Hydrogen crossover in the membranes was determined by electrochemical measurements and the permeability coefficient of the gas in the membranes determined. Finally, the single cell exhibits a fair performance, the power of the cell at 75 °C being only 225 mW/cm 2 or lower, at 0.5 V.