Effects of structure, composition, and carbon support properties on the electrocatalytic activity of Pt-Ni-graphene nanocatalysts for the methanol oxidation

The structure, composition, morphology, and support material significantly affect the catalytic characteristics of Pt-based nanocatalysts. Fine control of the structural and compositional features is highly favorable for the creation of new Pt-based nanocatalysts with enhanced catalytic performance and improved Pt utilization. This work reports on a systematic and comparative study of the effects of structure, composition, and carbon support properties on the electrocatalytic activity and stability of Pt-Ni bimetallic catalysts for methanol oxidation, particularly the promoting effect of Ni on Pt. Graphene-supported Pt-Ni alloy nanocatalysts were prepared by a facile, one-step chemical reduction of graphene oxide and the precursors of Ni2+ and PtCl62-. The nanocatalysts were characterized by transmission electron microscopy (TEM), ultraviolet-visible spectrophotometry (UV-vis), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). The electrocatalytic characteristics of the nanocatalysts were studied by voltammetry with methanol oxidation as a model reaction to evaluate the effects of the structure, surface composition, and electronic characteristics of the catalyst on the electrochemical activity. The catalyst with a Pt/Ni molar ratio of 1:1 exhibited the highest electrocatalytic activity for the methanol oxidation reaction with greatly lowered Pt utilization. The mechanism of the promoting effect of Ni on Pt is explained based on the modification of the electronic characteristics of the surface Pt atoms (Pt 4f) by Ni atoms due to the shift in the electron transfer from Ni to Pt and the synergistic roles of Pt and nickel hydroxides on the surfaces of the catalysts. The effects of the different carbon supports (i.e., graphene, single-walled carbon nanotubes, and Vulcan XC-72 carbon) on the electrocatalytic characteristics of the nanocatalysts are investigated by Raman and XPS experiments. The results demonstrate that the graphene-supported Pt-Ni catalyst has the highest electrocatalytic activity of the three carbon materials due to abundant oxygen-containing groups on the graphene surface, which can remove the poisoned intermediates and improve the electrocatalytic activity of the catalysts. (C) 2011 Elsevier B.V. All rights reserved.