(54b) Functionalization of Carbon Nanotubes Via Supercritical Fluid Treatment

Due to their relative inertness, it is difficult to produce homogenous metal deposits on the surfaces of carbon nanotubes (CNTs). In addition, CNTs are hydrophobic which makes it difficult to wet their surfaces using liquids with surface tensions higher than 100-200 mN/m [1]. We report the functionalization of single-wall CNTs (SWCNT) using surface activation with sulfonic acid intermediates [2] and treatment with super-critical CO2 or methanol [3]. This method avoids the harsh oxidative pretreatments typically used to functionalize CNTs [4] and avoids the ambiguity associated with the concurrent reduction of H+ during the electrodeposition of Pt particles [5]. A series of Pt functionalized SWCNTs were prepared. A representative sample is illustrated in Figures 1.

The Pt particles ranged in size from 2 ? 15 nm with an average particle size of 5 nm. We are using a variety of different Pt precursors (i.e. Pt(Acac)2, PtCl2 etc.), surface activation intermediates (i.e. (2(4-chlorosulfonylphenyl) ethyl trichlorosilane)), and conditions in our effort to produce 2-3 nm Pt particles for fuel cell applications. The talk will describe details of the Pt functionalized SWCNTs as well as the performance of these materials in a Micro-PEM fuel cell.

References:

1. Hogarth, M.P. and T.R. Ralph, Catalysis for low temperature fuel cells - Part III: Challenges for the direct methanol fuel cell. Platinum Metals Review, 2002. 46(4): p. 146-164.

2. Sun, X., et al., Composite electrodes made of Pt nanoparticles deposited on carbon nanotubes grown on fuel cell backings. Chemical Physics Letters, 2003. 379(1-2): p. 99-104.

3. 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.

4. 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.

5. Lin, Y.H., et al., Platinum/carbon nanotube nanocomposite synthesized in supercritical fluid as electrocatalysts for low-temperature fuel cells. Journal of Physical Chemistry B, 2005. 109(30): p. 14410-14415.