(218f) Functionalization Of Carbon Nanotubes And Carbon Nanofibers Via Supercritical Fluid Treatment For Use In Fuel Cells

Single walled carbon nanotubes (SWCNTs) and carbon nanofibers (CNFs) are presently being considered in the application areas of electron field-emission sources, functionalized sensor elements, electrochemical probes, scanning probe microscopy tips, nanoelectromechanical systems (NEMs), hydrogen and charge storage, and catalyst support [1]. These carbon 1-D materials are being evaluated as supports for fuel cells due to their exceptional mechanical, thermal, and electrical properties. Although the inertness of these materials is attractive for durability, this property makes it necessary to devise proper synthetic routes to load functional groups (i.e. Pt clusters) with high dispersion and controlled particle size onto the surface. We are investigating methods of using supercritical fluids (i.e. CO2 and Methanol) and selective heterogeneous nucleation (with ionic surfactants) to achieve these goals.

These methods eliminate the need for any harsh oxidative or UV treatments typically used to functionalize SWCNTs and CNFs [2, 3]. We have recently evaluated Pt functionalized SWCNTs and CNFs using this technique with anode Pt loadings of 0.57 mg/cm² and 0.55 mg/cm² respectively. Although the peak power density of the CNF membrane electrode assembly (MEA) was 334 mW/cm², which is slightly less than the SWCNT MEA (396 mW/cm²), the results are encouraging for the usage of CNFs as a substitute for the more expensive SWCNTs [4]. Improvements in synthesis conditions have revealed average Pt particle diameter of 3.1 nm with a standard deviation of 2.6 nm. With a goal of increasing the Pt utilization for these supports, we will characterize our synthesis conditions with the particle size, electrochemical active surface area, and fuel cell performance and compare our results to standard MEAs using conventional catalysts.

References:

1. Melechko, A.V., et al., Vertically aligned carbon nanofibers and related structures: Controlled synthesis and directed assembly. Journal of Applied Physics, 2005. 97(4).

2. Sun, Z.Y., et al., Synthesis of noble metal/carbon nanotube composites in supercritical methanol. Journal of Nanoscience and Nanotechnology, 2006. 6(3): p. 691-697.

3. Quinn, B.M., C. Dekker, and S.G. Lemay, Electrodeposition of noble metal nanoparticles on carbon nanotubes. Journal of the American Chemical Society, 2005. 127(17): p. 6146-6147.

4. Guo, J.S., et al., Carbon nanofibers supported Pt-Ru electrocatalysts for direct methanol fuel cells. Carbon, 2006. 44(1): p. 152-157.