Synthesis Of Carbon Supported Pt, Pt-based Alloy And Pd Nanoparticles And Their Electrocatalytic Properties For Methanol And Formic Acid Oxidation

Fuel cells are a kind of green power source with high efficiency. Direct methanol fuel cells (DMFCs) and Direct formic acid fuel cells (DFAFCs) are believed to be the ideal small and mobile energy sources due to their high energy conversion efficiency. However, there are two major problems faced in DMFCs: one of which is that the electrocatalytic activity of methanol at anode is low at low termperature; the other is that the penetration of methanol from anode to cathode is quite severe. Therefore it is a urgent need to prepare a kind of anode catalyst with high electrocatalytic activity for methanol oxidation. Transition metal Pt and Pt alloys are the first candidates for anode catalysts of DMFCs due to their excellent catalytic activity. Foric acid has lower rate of fuel crossover through the membrane allows higher fuel concentrations to be used, and DFAFCs are attracting more interisting. As is well known, catalytic activity depends on the size and shape of the metal particles, and therefore the synthesis of well-controlled shapes and sizes of nanocatalysts could be critical for improving catalytic activity.In this article, research has been done mainly on preparation methods of Pt, Pt-based and Pd catalysts, highly dispersed carbon supported Pt, PtRu, PtNi, PtPd and Pd nanoparticle catalysts prepared by microwave polyol process and carbon supported hollow PtCo nanocatalysts prepared by a metal replacement reaction at room temperature. The structrue and composition of catalysts have been characterized bb energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and X-ray diffraction (XRD). And catalytic activity of methanol oxidation has been investigated by electrochemical analysis. The obtained results are as follows:(1) PtRu/C, PtNi/C and Pt/C nanoparticle catalysts have been prepared using microwave polyol process, and TEM image and X-ray diffraction (XRD) were used for characterizations of structure and morphology of the catalysts. The results showed that the as-synthesized PtRu, PtNi alloys and Pt nanoparticles are small and homogeneous and was highly dispersed on carbon. Compared with Pt/C catalysts, the PtRu/C and PtNi/C anode electrocatalysts had lower onset oxidation potential and more stable polaration current, which demonstrated that PtRu/C and PtNi/C catalysts exhitbited enhanced electrocatalytic performance, higher stability for methanol oxidation and better resistance for CO poisoning.(2) Loaded on carbon nanotubes, hollow PtCo alloy nanoshpere electrocatalyst was synthesized using a metal replacement mechanism, and was characterized in TEM image,â…©-ray diffraction (XRD) and Energy dispersionâ…©-ray spectra analysis (EDX). The TEM results showed that PtCo was typical hollow nanoshpere morphology with uniform out-diameters and were highly dispersed on carbon nanotubes. Electrochemical measurement demonstrated that the electrochemical active surface area of hollow PtCo/CNTs electrocatalyst is 93.5 m²/g, which is much higher than that of solid PtCo/CNTs catalyst. The hollow PtCo/CNTs anode electrocatalyst exhitbited enhanced electrocatalytic performance for methanol oxidation compared with solid PtCo/CNTs electrocatalyst.(3) Using a microwave polyol process, Pd/C and PtPd/C nanoparticle catalysts have been prepared. TEM image andâ…©-ray diffraction (XRD) were used for characterizations of structure and morphology of the electrocatalysts. The results showed that the as-synthesized Pd and PtPd alloys nanoparticles are small, homogeneous and highly dispersed on the surface of XC-72 carbon. Electrochemical measurements demonstrated that the PtRu/C and PtNi/C anode electrocatalysts had much lower onset oxidation potential compared with Pt/C anode electrocatalyst and exhitbited enhanced electrocatalytic performance for formic acid oxidation. Because of different reaction pathways of formic acid electro-oxidation reaction on palladium and platinum catalysts, PtRu/C and PtNi/C anode electrocatalysts exhitbited enhanced electrocatalytic performance for formic acid oxidation compared with Pt/C anode electrocatalyst. On platinum catalyst, formic acid is oxidized to CO₂ with the poisoning CO as the reactive intermediate and CO adsorbed on Pt surface can highly reduce the catalytic performance. Formic acid is directly oxidized to CO₂ on palladium catalyst, and had lower onset oxidation potential.