Importance of Oxygen-Free Edge and Defect Sites for the Immobilization of Colloidal Pt Oxide Particles with Implications for the Preparation of CNF-Supported Catalysts

It was found that the Pt loading obtained by immobilization of colloidal Pt oxide particles on carbon nanofibers (CNFs) at a pH of 9-10 varied from 1.4 to 19.6 wt % (nominal loading 19.4 wt %). The amount of Pt deposited depended significantly on the CNF properties. The study targeted the identification of the determining carbon support properties for the successful preparation of Pt catalysts. CNFs, multiwall carbon nanotubes (MWNTs), and Vulcan XC-72R were utilized as supports. Platelet and fishbone CNFs with different surface areas, graphene layer stacking angles, and amount of surface oxygen groups were obtained by catalytic chemical vapor deposition. The carbon supports were thoroughly characterized by transmission electron microscopy (TEM), N-2-adsorption measurements, X-ray diffraction (XRD), temperature-programmed oxidation (TPO), zeta-potential measurements, and X-ray photoelectron spectroscopy (XPS). Characterization of the deposited Pt particles by TEM revealed similar sizes but differences with respect to particle location. Based on TEM, BET, XRD, and XPS, a clear indication of the importance of surface defects and edge sites for successful immobilization of Pt oxide colloid particles was found for all carbon supports. From XPS a linear relationship was found between the fraction of species originating at a binding energy of 285.1 eV and the final Pt loading. These species can be sp(3)-hybridized carbon, defects, and/or dangling bonds (edge structure). The surface oxygen groups were found to have a decisive effect on the immobilization of Pt. Negative linear trends were found between the Pt loading obtained on CNFs and the O 1s/C 1s ratio and number of carboxylic groups determined from XPS. It is based on the results believed that the oxygen-free defect and edge structure can play a vital and important role in the preparation of more effective CNF-supported catalysts.