On the proton conductivity of Nafion–Faujasite composite membranes for low temperature direct methanol fuel cells

Although zeolites are introduced to decrease methanol crossover of Nafion membranes for direct methanol fuel cells (DMFCs), little is known about the effect of their intrinsic properties and the interaction with the ionomer. In this work, Nafion–Faujasite composite membranes prepared by solution casting were characterized by extensive physicochemical and electrochemical techniques. Faujasite was found to undergo severe dealumination during the membrane activation, but its structure remained intact. The zeolite interacts with Nafion probably through hydrogen bonding between Si–OH and SO3H groups, which combined with the increase of the water uptake and the water mobility, and the addition of a less conductive phase (the zeolite) leads to an optimum proton conductivity between 0.98 and 2 wt% of zeolite. Hot pressing the membranes before their assembling with the electrodes enhanced the DMFC performance by reducing the methanol crossover and the serial resistance.

► Faujasite zeolite is dealuminated during Nafion's activation procedure.
► Few wt% of zeolite increase the mobility of water and proton conductivity (in- and through-plane directions).
► For high zeolite loadings, the interaction between Nafion and the zeolite results in a lower number of free –SO3H groups.