Embodiments of nanostructures and nanocomposites and embodiments of
methods for forming and modifying these nanostructures and nanocomposites
are disclosed. The methods can include transporting a metal, metallic
compound or precursor to a surface of a nanostructure substrate in a
carrier while the carrier is in supercritical fluid form. Embodiments of
the disclosed methods can be used to form catalytic structures, such as
catalytic structures including nanostructure supports and catalytic
metallic nanoparticles attached to the nanostructure supports. These
catalytic structures are useful for catalyzing reactions in fuel cell
applications, such as oxygen reduction and methanol oxidation reactions.
Some of the disclosed nanostructures and nanocomposites include carbon
nanotubes.