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Carbon Supported Pd And Pd-based Composite Anode Catalyst In Direct Formic Acid Fuel Cell

Posted on:2009-05-19Degree:MasterType:Thesis
Country:ChinaCandidate:X WangFull Text:PDF
GTID:2192360245477047Subject:Physical chemistry
Abstract/Summary:PDF Full Text Request
In DMFC,Pt-based composite catalysts are usually used as the anodic catalyst. However,their electrocataltic activity for the methanol oxidation is low and is easy to be poisoned by the intermediate of the methanol oxidation.Especially,methanol is easy to penetrate the Nation membrane.Not only the fuel was wasted,but also the utilization efficiency of the fuel was reduced.The efficiency of the cathodal catalyst and the working voltage of the fuel cell are also reduced.In the recent years,it was found that DFAFC using formic acid as the methanol alternative fuel has many advantages comparing with DMFC.In DFAFC,the Pd catalyst is an anodic catalyst with the good electrocatalytic performance for the oxidation of formic acid. Therefore,this thesis mainly investigated the preparation methods and electrocatalytic performance of the carbon supported Pd and Pd based catalysts.The effect of the composition and structure of the catalysts on the electrocatalytic activity and stability of the catalysts for the oxidation of formic acid was investigated.The main results obtained are as follows:1.The structural characteristics and the electrocatalytic performance of the Pd/C catalyst prepared with the solid phase reaction method for the oxidation of formic acid were i(?)nvestigated.It was found that the average size and relative crystallinity of the Pd/C catalyst prepared with the solid phase reaction method are smaller than that of the Pd/C catalyst prepared with the liquid phase reduction method.Thus,the electrocatalytic activity and stability of the Pd/C catalyst is prepared with the solid phase reaction method are better than that of the Pd/C catalyst prepared with the liquid phase reduction method.Therefore,the solid phase reaction method is an excellent method for the preparation of the Pd/C catalyst and may obtain the practical application.2.The preparation method of the Pd-Ir/C catalyst and its electrocatalytic performance for the oxidation of formic acid were investigated.It was found that the Pd-Ir/C catalyst with a small average size and low relative crystallinity of the Pd-Ir particles can be prepared with a simple liquid phase reduction method.When the atomic ratio of Pd and Ir is suitable,the electrocatalytic activity of the Pt-Ir/C catalyst for the oxidation of formic acid is higher than that of the Pd/C catalyst prepared with the same method.The potential of the main anodic peak of formic acid at the Pd-Ir/C catalyst with the suitable atomic ratio of Pd and Ir is 50 mV more negative than that at the Pd/C catalyst and the peak current density at the Pd-Ir/C catalyst is 13%higher than that at the Pd/C catalyst.This is attributed to that Ir can promote the oxidation of formic acid at Pd through the direct pathway because Ir can decrease the adsorption strength of CO on Pd.However,when the content of Ir in the Pd-Ir/C catalyst is high the electrocatalytic activity of the Pd-Ir/C catalyst would be decreased because Ir has no the electrocatalytic activity for the oxidation of formic acid.3.The preparation method of the Pd-Au/C catalyst and its electrocatalytic performance for the oxidation of formic acid were investigated.(1)When the Pd-Au/C catalyst is prepared with the liquid phase reduction method in the aqueous solution,Pd and Au in the Pd-Au/C catalyst obtained do not form the alloy,because the onset reduction potentials of PdCl2 and HAuCl4 are not close and thus,they can not be reduced at the same time.However,when the Pd-Au/C catalyst is prepared with the liquid phase reduction method in the mixture solution of THF and H2O,Pd and Au in the Pd-Au/C catalyst prepared would form the alloy because the onset reduction potentials of PdCl2 and HAuCl4 are close and thus,they can be reduced at the same time.(2)The electrocatalytic activities and stabilities of the Pd-Au/C catalysts for the oxidation of formic acid are higher than that the Pd/C catalyst.It is attributed to that the addition of Au can reduce the adsorption strength of CO on Pd.(3)The Pd-Au alloy is formed in the Pd-Au/C-T catalyst and the Pd-Au alloy is not formed in Pd-Au/C-H catalyst.The adsorption strength of CO on the alloying Pd-Au/C catalyst is lower than that on the non-alloying Pd-Au/C catalyst.Thus,the electrocatalytic activity and stability of the alloying Pd-Au/C catalyst for the oxidation of formic acid are better than that of the non-alloying Pd-Au/C catalyst.This illustrated that the Pd-Au alloying is an important factor to affect the electrocatalytic performance of the Pd-Au/C catalyst for the oxidation of formic acid.
Keywords/Search Tags:Direct formic acid fuel cell, solid phase reaction, Pd/C catalyst, Pd-Ir/C catalyst, Pd-Au/C catalyst
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