A Novel Composite Nafion/Anodized Aluminium Oxide Proton Exchange Membrane

The high proton conductivity of proton exchange membranes (PEMs) made of Nafion((R)) is attributed to a random 3D network of elongated water channels formed by bundles of rod-like inverted micelles. Alignment of bundles, e.g., by stretching, is known to significantly enhance the in-plane conductivity, yet achieving alignment normal to the membrane surface, desired for most applications, is challenging. A few attempts to obtain such alignment by confining Nafion in nanometric trans-membrane pores of solid anodized aluminium oxide (AAO) membranes were reported, so far with limited success. Here we demonstrate that considerable pore filling of AAO with 200nm pores by Nafion could be achieved through (i) use of Nafion concentrations below the threshold concentration C*, above which Nafion molecules form large aggregates; and (ii) control of filling rate through a combination of thermal and vacuum evaporation of Nafion solution through the membrane. The proton conductivity and NaCl diffusion permeability (sodium chloride diffusivity) tested by electrochemical impedance spectroscopy demonstrated superior intrinsic conductivity and selectivity of the composite membrane as compared to commercial Nafion membranes.