Since pristine CNTs are chemically inert, it is necessary to activate the graphitic surface of CNTs. Traditionally, CNTs are functionalized by harsh oxidative processes, such as refluxing in a concentrated mixture acid of HNO3 and H2SO4, thus generating functional groups on CNTs. However, this method generates a large number of defects and reduces the electrical conductivity and corrosion resistance of CNTs.

Alternative route

Researchers at Nanyang Technological University, Singapore, are developing milder methods of functionalizing the surface of CNTs for use as electrocatalyst support in fuel cells. In a recent study, which was published in Nanotechnology, the group demonstrated a novel and highly effective polyelectrolyte functionalization method for CNT using a positively charged polyelectrolyte, poly(diallyldimethylammonium chloride) (PDDA), which could homogeneously wrap/functionalize CNT surface in aqueous solution.

The strong adsorption of the positively charged PDDA on CNTs is due to the π-π interaction between PDDA and the basal plane of graphite of CNTs. This non-covalent polyelectrolyte functionalization not only leads to high density and homogeneous surface functional groups on CNT, but also preserves the intrinsic properties of CNTs without damaging their perfect surface structure. Consequently, the positively charged PDDA around CNT could electrostaticly interact with the negatively charged Pt precursors and nanoparticles, and the uniform distribution of surface functional groups leads to the well dispersed distribution of Pt nanoparticles on CNT, as shown in the figure.

The uniformly distributed Pt nanoparticles PDDA-functionalized CNTs show much higher electrochemically active surface area and the electrocatalytic activity for methanol oxidation than Pt electrocatalysts supported on the harsh acid-oxidized CNTs and the commercial E-TEK Pt/C electrocatalysts.

Further reading

[1] Nanotechnology 20 025605
[2] Nanotechnology 19 265601