Pt nanoparticle binding on functionalized multiwalled carbon nanotubes

To create new catalyst materials for fuel cell applications, multiwalled carbon nanotubes (CNTs) were functionalized with -C=O, -C-O-C-, -COO-, and -C-OH groups using a sonochemical treatment method under acidic aqueous solution (HNO3/H2SO4) conditions to make them amenable to deposition of highly dispersed, similar to 4 nm diameter Pt nanoparticles. The Pt-CNT inter-face was probed with X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure spectroscopy (EXAFS), and Raman and attenuated total reflection infrared (ATR-IR) spectroscopies to elucidate the nature of the Pt cluster-CNT surface binding. The degree of disorder of the sp(3)-hybridized C from the CNTs, as measured by the Raman D-to-G integrated peak area ratios, increased with the degree of surface oxidation of the CNTs. EXAFS of the Pt L-III edge showed Pt coordination with oxygen (in the form of PtOx) at the outermost perimeter of the Pt clusters while the majority of the bulk, as shown by the XPS Pt 4f core level, was in the metallic form. Infrared measurements showed that the carbonyl C=O stretching at 1700 cm(-1) red shifted to similar to 1550 cm(-1) following Pt cluster deposition. In addition, changes in the C-O structural features at similar to 1030 and 1150 cm(-1) were observed, indicative of Pt cluster binding with the ionic form of carboxylate, COO(Pt), or ester-like, C(=O)CO(Pt), O atoms.