Synthesis And Catalytic Mechanism Of Pd-based Anodic Catalysts For Direct Ethanol Fuel Cells

Direct ethanol fuel cells(DEFC)as a clean power source,have the advantages of high energy density and low pollutant emission,which has a very broad application prospect.The main reason for restricting the development of DEFC is the price of Pd and Pt noble metals with high catalytic activity are expensive.And they are very easy to be poisoned by the poisoning-intermediate species during the oxidation of ethanol.In this paper,the anode catalysts used to DEFC with high activity and anti poisoning ability were prepared by the modification of the support materials and Pd nanoparticles.The catalysts were characterized by physical and electrochemical methods.The main results were obtained as follows:The Pd/TiC-C(x:1 x=0.1,0.2,0.5 and 1)catalysts were prepared by a fast microwave polyol method.Their structure characterizations were carried out by fourier transform infrared spectrometry(FTIR),thermogravimetric analysis(TGA),X-ray diffraction(XRD),transmission electron microscope(TEM)and X-ray photoelectron spectroscopy(XPS).It is shown that Pd nanoparticles on Pd/TiC-C(x:1)are smaller and disperse more uniformly.The introduction of TiC into the composite support can inhibit the aggregation of Pd nanoparticles and make it more uniform.The majority of C support in the composite support are covered on the surface of the TiC.The Pd nanoparticles are more likely to be loaded on the surface of the C support due to the hydrophobicity of the TiC.TiC support can provide more oxygenated species,which can promote the oxidation of the intermediate toxic species during the oxidation of ethanol.However,too much TiC will reduce the activity of Pd catalysts because of the reduction of active carbon amount and the preferential deposit of Pd nanoparticles on the active carbon.The peak current density of ethanol oxidation on Pd/TiC-C(0.2:1)catalyst(125.6 mA cm-2)is 1.86 times higher than that on Pd/C catalyst(67.5 mA cm-2).The Pd/TiC-C(0.2:1)catalyst has the highest activity,stability and anti-poisoning ability,which is due to the synergistic effects of the oxygenated species on TiC support and the poisoning-intermediates on the Pd catalyst.The best mass ratio of TiC and C in the composite support is 0.2:1.PdAg/C and PdPtAg/C catalysts were synthesized by one-step microwave ethylene glycol method.XRD test results show that Pd Ag or PdPt Ag alloys can exist in the PdAg/C and PdPtAg/C catalysts.In the alkaline medium,the peak current densities of ethanol oxidation on PdPtAg/C and PdAg/C catalysts are 139.8 mA cm-2 and 87.6 mA cm-2 respectively,which are 2.2 and 1.4 times on Pd/C catalyst(62.4 mA cm-2).There is a strong“electronic effect”among Pd nanoparticles,Pt and Ag,and the catalytic activity of the catalyst is improved by the“double function mechanism”.At the same time,PdPtAg/C and PdAg/C catalysts can promote the formation of oxygenated species in the reaction process,and improve the ability of anti-poisoning.