Synthesis And Catalytic Mechanism Of Anode Catalysts For Direct Ethanol Fuel Cells

Direct Ethanol Fuel Cells(DEFCs)are prospective clean energies with advantages of high energy density,low pollution and various sources,etc.However,the main factor to hinder the commercialization of DEFCs is the noble Pt and Pd metals with the rareness and high prices as well as the poisoning effects by the intermediate species of ethanol oxidation.In this work,carbon-supported PdCu,PtAg and PtPdAg nanoparticles were treated with electrochemical dealloying,which is a new approch to synthesize anodic catalysts in DEFCs with high activity and better anti-poisoning effect.The physical measurements were employed to characterize the compositions,structures,average particle sizes and electronic effects of the synthesized catalysts.And the structure-function relationship between physical properties and catalytic activity of ethanol oxidation was also studied.The main results are as follows:The dealloyed catalysts were synthesized via chemical reduction and following cyclic voltammetry(CV)in acidic solution.PdCu2/C was synthesized in ethanol because the Cu2+ ion was not reduced completely in the mixd solution of ethylene glycol and water.The PtAgx/C and PtPdxAgy/C were prepared in the mixture of ethylene glycol and water for their better catalytic activity of nanopartilces.It is found that PtAg2/C-D prepared by only 1 cycle pocesses the highest catalytic activity than those prepared by 5,10,20 cycles because of the existence of more Ag oxides.The PtPdAg3/C-D,PtPd2Ag4/C-D,PtPd3Ag5/C-D catalysts show far better catalytic acitity than PtAg2/C-D.And PtPd3Ag5/C-D pocesses the best anti-poisoning ability,but the activities of PtPd8Ag10/C-D and PdAg/C-D decline compared with PtAg2/C-D.The PtPd3Ag5/C-D catalyst with surface enriched Pt were fabricated via electrochemical dealloying and characterized by X-ray diffraction(XRD),transmission electron spectroscopy(TEM),atomic adsorption spectroscopy(AAS),X-ray electron spectroscopy(XPS).It is found that external Ag atoms are oxidized,dealloyed and leached out,and Pd can also be paritially leached out,both of which lead to lattice strain of the alloy phase,smaller average size of nanoparticles,larger ECSA as more Pt active sites were exposed on the surface.The Pt-rich surfaces protect the inner Pd and Ag atoms and thus the H adsorption/desorption and CO stripping curves are similar to the behavior on mono-Pt catalyst.The electronic effect between Pt and Pd in the bulk phase weakens the adsorption of COads on Pt sites and accelerate the electrooxidation of ethanol.43%of the near-surficial Pd atoms exists in oxidation states,so the remaining Pd atoms near the surface generate abundant oxygen-containing species,facilating the removal of poisoning species on Pt sites.The as-prepared PtAg2/C-D catalyst reaches a current density of 3.35 times as high as that on Pt/C.Even if the partially leached Pd atoms are counted,the PtPd3Ag5/C-D catalyst reaches the highest electrocatalytic activity of 4500 mA mg-1,which is 6.22 and 1.87 times as high as those on mono-component Pt/C and Pd/C,respectively.And the ratio of forward to backward peak current densities(If/Ib)is 1.62.PtPd3Ag5/C-D catalyst presents the current density of 750 mA mg-1 after 1800 s at-0.3 V vs.mercuric oxide electrode,and the charge-transfer kinetics for ethanol dehydrogenation and the anti-poisoning ability of PtPd3Ag5/C-D catalyst are markedly enhanced.