Methanol and gas crossover through modified Nafion membranes by incorporation of ionic liquid cations

Nafion membranes were modified by incorporation of ionic liquid (IL) cations, at controllable degrees, in order to assess the influence of this modification in both the methanol and gas crossover. The effect of using different degrees of incorporated IL cations, as well as the type of IL cation incorporated, in the transport of gases and methanol was studied in detail. The results obtained were compared with those obtained with an unmodified Nafion membrane. Depending on the IL cation incorporated, a reduction in methanol crossover in the range of 60-600 times was obtained in this work, when compared with a Nafion-112 membrane. This reduction was related both with the type of cation incorporated and its incorporation degree which determine the amount of water retained by the membrane and its degree of structuring inside the membrane. Pure H2, O2, N2 and CO2 permeabilities were also determined, and a lower gas crossover through all of the modified Nafion/IL cation membranes was obtained when compared with those obtained through the unmodified membrane (Nafion/H+). It was concluded that the electric properties, methanol and gas crossover as well the stability at high temperatures of these membranes can be tuned by controlling the degree of incorporation as well as the type of cation incorporated. The best compromise between all these properties has to be found in order to considerer their use in direct methanol fuel cells (DMFCs).