Development of Oil/Water/Surfactant Microemulsions as Templates for Micro and Nanostructured Metal Foams
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Development of Oil/Water/Surfactant Microemulsions as Templates for Micro and Nanostructured Metal Foams Catherine Cook1,2, Woo Renee2, Brenda O'Neil1,3, McKenzie Leigh1,3, Jason Manning1,2, and Martin Gerard Bakker1,2 1 Center for Materials for Information Technologies, The University of Alabama, Tuscaloosa, AL, 35487-0209 2 Chemistry, The University of Alabama, Tuscaloosa, AL, 35487-0336 3 Admiral Moorer Middle School, Eufala, AL, 36027
ABSTRACT There are a range of applications for bicontinuous metal micro and nanostructures including as porous electrodes for supercapacitors, in fuel cells and in advanced batteries. We have previously demonstrated a number of methods of generating metal nanostructures by electrodeposition into various templates including hexagonal surfactant phases and mesoporous silica. More recently we have been exploring the application of oil-in-water microemulsions as templates. We have found empirically that the formation of microstructure is strongly effected by the viscosity of the oil phase, the rate of metal electroreduction and the surface roughness of the substrate. We interpret these observations as reflecting a competition between growth of the metal around the oil droplet and the redistribution of the oil in front of the growing metal film. We are currently exploring bicontinuous and water-in-oil phases with the expectation that such templates will yield bicontinuous metal films with larger accessible surface areas. Preliminary results with water-in-oil phases appear to show the formation of bicontinuous nanostructured films on the 20 nm length scale. INTRODUCTION There is considerable interest in the fabrication of extremely high surface area porous electrodes for a wide range of applications including energy storage (super capacitors), energy conversion (fuel cells), separations (electrochemical chromatography), sensors and catalysis. We[1, 2] and a number of other groups[3-10] have demonstrated a variety of methods of generating nanoscale porous metal structures. For many potential applications macroscopic electrodes rather than thin films are desired, which presents two problems for purely nanostructuring methods. In order to function effectively as porous electrodes nanostructured metals are best electrodeposited. However, the templating methods used have very limited deposition rates and so are not capable of producing macroscopic electrodes within a reasonable time frame. Further, optimum flow characteristics dictate porosity at multiple length scales. Hence, there is a need for formation of microstructured films of thickness up to a 1 mm within a reasonable time. Methods of generating porous metallic microstructures have been much less extensively investigated than have nanoscale processes. For porous electrodes the microstructure needs to be completely electrically continuous and also compatible with addition of subsequent nanoporous layers. The combination of the two structuring methods should lead to rapid formation of extremely high surface area (> 100 m2
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