Mesostructured-aluminosilicate-Nafion hybrid membranes for direct methanol fuel cells

Organic–inorganic hybrid membranes are prepared from Nafion and acid functionalized aluminosilicate with varying structures and surface areas. Acid-functionalized mesostructured aluminosilicate with cellular foam framework (Al-MSU-F type) of surface area 463 m2 g−1, acid-functionalized aluminosilicate molecular sieves (Al-HMS type) of surface area 651 m2 g−1 and acid-functionalized mesostructured aluminosilicate with hexagonal network (Al-MCM-41 type) of surface area 799 m2 g−1 have been employed as potential filler materials to form hybrid membranes with Nafion. The structural behavior, water uptake, ion-exchange capacity, proton conductivity and methanol permeability of the hybrid membranes are extensively investigated. Direct methanol fuel cells (DMFCs) with Al-HMS-Nafion and Al-MCM-41-Nafion hybrid membranes deliver respective peak power-densities of 170 mW cm−2 and 246 mW cm−2, while a peak power-density of only 48 mW cm−2 is obtained for the DMFC employing pristine recast-Nafion membrane under identical operating conditions. The unique properties associated with hybrid membranes could be exclusively attributed to the presence of pendant sulfonic-acid groups in the filler materials, which provide proton-conducting pathways between the filler and matrix in the hybrid membranes, and facilitate proton transport with adequate balance between proton conductivity and methanol permeability.