Preparation via supercritical fluid route of Pd-impregnated nafion membranes which exhibit reduced methanol crossover for DMFC

Palladium (Pd)-impregnated Nafion membranes that reduce methanol crossover were synthesized via a supercritical fluid route. The method involved impregnation of Nafion membranes with palladium(II) hexafluoroacetylacetonate from a supercritical CO2 (scCO(2)) solution, followed by subjecting the impregnated membranes to hydrogen. Membrane morphology was characterized using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The obtained membranes had uniform surface morphology. The palladium particles were distributed both at the membrane surface and also extended deeper into the membrane. Membrane electrode assemblies with palladinized Nafion membranes were prepared and evaluated in direct methanol fuel cells (DMFCs) to determine methanol crossover, proton conductivity as well as DMFC performance. The Pd-impregnated Nafion membranes showed reduced methanol crossover and gave improved DMFC performance compared to that of a pure Nafion membrane, especially with higher concentration of methanol such as 5 M. The suppressed methanol crossover of Nafion membranes by the palladium impregnation improved DMFC efficiency. The successful preparation of palladium-impregnated membranes through the scCO(2) route demonstrated an effective alternative way for modifying membranes and for depositing electrode catalytic nanoparticles onto electrolyte. (c) 2005 The Electrochemical Society.