Faujasite zeolites as solid electrolyte for low temperature fuel cells

In this work, the potential use of faujasite zeolites as a solid electrolyte material was evaluated with a particular focus on their endurance in acid environment, and on the influence played by the zeolites' chemical and textural properties on the degree of hydration and proton conductivity. Three faujasites with different initial Si/Al ratio were exposed to 6 mol dm⁻³ HCl solution and the exposure time was varied up to 7000 h for selected samples. Faujasite dealumination is a very fast process occurring mainly within 24 h of exposure. X-ray diffraction patterns show the faujasite structure was preserved, although N₂ sorption measurements indicate a possible partial collapse of the pore structure for samples dealuminated for 4500 and 7000 h.The proton conductivity of the faujasites is in the order of 10⁻⁸ S cm^-1 at 10% relative humidity, 10⁻⁶ S cm^-1 at 90% relative humidity, and 10⁻⁴ S cm^-1 for samples immersed in liquid water. The correlation between the proton conductivity and the zeolites' properties shows the predominant influence of the Al content at low relative humidity, and of the water content and micropore and mesopore volumes at high relative humidity. In particular, the expected increase of the proton conductivity with the mesopore volume at high relative humidity and for samples saturated with water was not observed.