Direct Formic Acid Fuel Cell Carbon Contained Au-based Cathode Composite Catalyst

In more than 10 years,it was gradually found that the direct methanol fuel cell (DMFC)has some disadvanges.For example,the electrocataltic activity of the catalysts is low and is easy to be poisoned.Methanol is easy to penetrate the Nation membrane.Methanol is toxic.Thus,DMFC can not be commercialized in the near future.In recent years,it was found that DFAFC using formic acid as a fuel has some advantages comparing with DMFC.For example,formic acid has two orders of magnitude smaller crossover flux through the Nation membrane than methanol. However,a certain amount of formic acid would enter into the cathode and be oxidized at the cathode,leading the decrease in the cathidc performance.Therefore, the study on the cathodic catalysts with the high electrocatalytic activity for the oxygen reduction and high formic acid torelence ability is an important research direction in DFAFC.However,until now,there are no the reports about the cathodic catalysts for DFAFC.The cathodic catalysts in DMFC are generally the Pt,Pd and Pt-based or Pd-based composite catalysts.However,both Pt and Pd possess the high electrocatalytic activity for the oxidation of formic acid.Thus,they are not suitable to be used as the cathodic catalysts in DFAFC.Therefore,it is nessesary to investigate new cathodic catalysts in DFAFC.This thesis mainly investigated the preparation method of the cabon supported Au and Au-based cathodic composite catalysts and studied the effect of the component and structure of Au and Au-based cathodic catalysts on the electrocatalytic performances for the oxygen reduction and for the oxidation of formic acid as well as their mechanisms.The main results obtained are as follows:1.The average size and the relative relative crystallinity of the Au particles in the Au/C catalyst prepared by the PVA protection method are lower than that of the Au/C catalyst prepared with the pre-precipitation method.Thus,the electrocatalytic activity of the Au/C catalyst prepared by the PVA protection method is better than that of the Au/C catalyst prepared with the pre-precipitation method.In addition,it was found that the Au/C catalyst has no electrocatalytic activity for the oxidation of formic acid.Thus,the Au/C catalyst possesses high formic acid tolerance.2.After the CoTPP/C catalyst is heat-treated at 600℃,its electrocatalytic activity for the oxygen reduction is much better than that of the un-heat-treated CoTPP/C catalyst.Especially,it was found for the first time that formic acid not only decreases,but also slightly improves the electrocatalytic activity of the CoTPP/C catalyst heat-treated at 600℃for the oxygen reduction.3.Because the CoTPP-Au/C catalyst possesses small average size,low relative crystallinity and uniform distribution of the size of the Au particles as well as the interaction between Au and the N₄-Co moiety obtained form the heat decomposition of CoTPP,the electrocatalytic activity of the CoTPP-Au/C catalyst for the oxygen reduction is better than that of the CoTPP/C and Au/C catalysts.In addition,it was found that the CoTPP-Au/C catalyst has no electrocatalytic activity for the oxidation of formic acid.Therefore,the CoTPP-Au/C catalyst is a catalyst,which possesses the high electrocatalytic activity and the high formic acid tolerance.4.Au and Ir in the Au-Ir/C catalyst prepared with the THF complex reduction method cannot form the alloy.The Au particles possess the structure of the face centered cubic crystalline and Ir exists with amorphism.Because Au and Ir have no electrocatalytic activity for the oxidation of formic acid,the Au/C,Ir/C and Au-Ir/C catalysts possess the high formic acid tolerance.The electrocatalytic activity of the Au-Ir/C for the oxygen reduction reaction is much better than that of the Au/C catalyst and the Ir/C catalyst because of the interaction between Au and Ir.