Electrocatalytic Properties Of MWCNTs Supported Pd-based Bimetallic Anodic Catalysts

As an attractive candidate to replace methanol and hydrogen, formic acid (FA) has considerable advantages in polymer electrolyte membrane (PEM) fuel cells for powering portable devices. FA is nontoxic, nonflammable and has lower penetration efficiency through the Nafion membrane to methanol due to the repulsion between HCOO- and SO3- ions. These extraordinary properties of FA make it possible to use highly concentrated fuel solutions in DFAFCs, which compensates the low volumetric energy density of FA and improves the overall cell efficiency. In addition, FA has a higher electronic motive force (EMF,1.45 V) than either hydrogen or methanol. Recent studies showed that the electrocatalytic activity of Pd for FA oxidation is higher than that of Pt, because Pd catalysts can overcome the CO poisoning effect mainly through the direct pathway. In many studies, considerable effort has been made to develop the Pd and Pd-based binary metallic catalyst.In present work, Pd/f-MWCNTs, a series of bimetallic PdAu/f-MWCNTs catalysts and Pd/MWCNTs, PdRu/MWCNTs were synthesized by a mild impregnation reduction method. FA oxidation reaction of the catalysts were investigated, and compared with that of Pd catalyst.(1) PdAu nanocatalysts with different weight ratio of Pd and Au supported on functional multi-walled carbon nanotubes (f-MWCNTs) were prepared, and their electrocatalytic activity for the oxidation of formic acid was also studied. The electrocatalysts were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The electrochemical results showed that the 4PdlAu/f-MWCNTs (by weight) catalyst, exhibited distinctly higher activity and better stability in formic acid electrooxidation than the Pd/f-MWCNTs catalyst. So the suitable addition of Au to Pd/f-MWCNTs can promote the catalytic activity and poisoning tolerance of Pd catalyst for the electrooxidation of formic acid. The Au nanoparticles show potential in further improving the performance of Pd-based electrocatalysts for the direct formic acid fuel cells (DFAFCs).(2) We have developed nano-Pd, nano-PdRu catalysts supported on multi-walled carbon nanotubes. TEM and XRD studies indicated that so many fine Pd and Ru nanoparticles with well uniformed dispersion formed on the outer walls of the CNTs, and the coexistence of Pd and Ru particles in the catalyst. Further more, electrochemical results showed that the 4Pd1Ru/MWCNTs catalyst, weight ratio of 4Pd to 1Ru, exhibited distinctly higher catalytic activity and better stability on formic acid electrooxidation than the Pd/MWCNTs catalyst. So the nano-Ru improves potentially the performance of Pd-based electrocatalysts for the DFAFCs.