Meso-Structured Silica-Nafion Hybrid Membranes for Direct Methanol Fuel Cells

Abstract

A series of novel organic-inorganic hybrid membranes have been prepared employing Nafion and acid-functionalized meso-structured molecular sieves (MMS) with varying structures and surface area. Acid-functionalized silica nanopowder of surface area 60 m2/g, silica meso-structured cellular foam (MSU-F) of surface area 470 m2/g and silica meso-structured hexagonal frame network (MCM-41) of surface area 900 m2/g have been employed as potential filler materials to form hybrid membranes with Nafion framework. The structural behavior, water uptake, proton conductivity and methanol permeability of these hybrid membranes have been investigated. DMFCs employing Nafion-silica MSU-F and Nafion-silica MCM-41 hybrid membranes deliver peak-power densities of 127 mW/cm2 and 100 mW/cm2, respectively; while a peak-power density of only 48 mW/cm2 is obtained with the DMFC employing pristine recast Nafion membrane under identical operating conditions. The aforesaid characteristics of the hybrid membranes could be exclusively attributed to the presence of pendant sulfonic acid groups in the filler, which provide fairly continuous proton-conducting pathways between filler and matrix in the hybrid membranes facilitating proton transport without any trade-off between its proton conductivity and methanol crossover.