Relationship Between Methanol Permeability and Structure of Different Radiation‐Grafted Membranes

Abstract

Styrene grafted and sulfonated poly(vinylidene fluoride) and poly(vinylidene fluoride‐co‐hexafluoropropylene) films are candidates as electrolytes in direct methanol fuel cells. Their behaviour in water, 1 and 3 mol dm–3 aqueous methanol, and pure methanol were studied. According to SAXS results, water and methanol‐water solutions have similar effects on the membranes, i.e., the lamellar period increases and the ionic domains enlarge. Furthermore, differences in the ionic domain structures in pure methanol and water were observed. These structural changes together with dissimilar liquid uptakes in water and in methanol are reflected as changes in the conductivities. An increase in the SAXS intensity and changes in the Bragg distance of the ionic peak were observed in methanol compared to aqueous solutions. This may be related to the hydrophobicity of the CH3 group on methanol. Dissimilarities in methanol permeability through the radiation‐grafted membrane can be related to structural differences in membranes observed with SAXS. Permeabilities were observed to be lower for the radiation‐grafted membranes compared to Nafion® 115, which compensates for the higher area resistance of the experimental membranes and thus improves their performance in a fuel cell.

Al2O3 coating grown on Nafion membranes by atomic layer deposition

“…Therefore, decrease in the liquid water uptake impedes methanol transport through the coated Nafion. Methanol diffusion coefficients and permeability have also been earlier shown to decrease with the decreasing water uptake of an ion exchange membrane [28]. Similar trend has been observed for oxygen transport through Nafion as it is faster through the hydrophilic water channel phase than through the another phase of the membrane comprising of the hydrophobic backbones of the Nafion molecule chains [37].…”

“…The drag correction factor kdl is taken from the data in ref. [28] as a function of temperature in 1 M MeOH: 0.8592 at 30°C…”

A 3D model for the free-breathing direct methanol fuel cell: Methanol crossover aspects and validations with current distribution measurements

“…On the other hand, some part of this gain is lost as the MeOH crossover also increases as a function of temperature [27,29].…”

“…In the case of the DMFC, the MeOH crossover (MeOH permeability through the membrane) is a very dominating loss mechanism [17] and it has been investigated widely [18][19][20][21][22][23][24][25][26][27][28][29]. However, most of these studies have been performed without current distribution measurements.…”

Partially fluorinated proton exchange membranes based on PVDF–SEBS blends compatibilized with methylmethacrylate block copolymers

“…Other research works, have demonstrated that sulfonated partially fluorinated PEMs based on styrene-grafted membranes have similar or higher performance in direct methanol fuel cells (DMFC) [4,8].…”