Effect of photochemically oxidized carbon nanotubes on the deposition of platinum nanoparticles for fuel cell catalysts

The applicability of photochemically oxidized multi-walled carbon nanotubes (MWCNTs) to support materials for fuel cell catalysts has been examined in comparison with the MWCNTs treated and untreated by nitric acid. The photochemical oxidation of MWCNTs under vacuum ultraviolet (VUV, λ = 172 nm) irradiation introduces oxygen functional groups onto the surface of the nanotubes with generating new defects on their structure. The VUV-induced photochemical oxidation more preferentially introduces carbonyl and carboxyl groups, compared with nitric acid oxidation. The deposition manner of platinum (Pt) nanoparticles from their precursor ions (PtCl62-) is positively correlated with the proportion of surface oxygen groups. This implies that the anchoring sites for the PtCl62- are not the π electron regions of the basal plane but the surface oxygen groups. For the electrochemical evaluation of Pt-deposited MWCNT catalysts, the photochemically oxidized MWCNTs have enhanced the active surface area and the performance of methanol oxidation, which is due to the high dispersion and dense deposition of Pt nanoparticles on the oxygen groups-rich surface.