Synthesis And Electrocatalysis Towards Formic Acid Oxidation Of Platium-gold Catalysts

As many portable power devices such as cell phones, lap-top computers, emergency power equipments, etc. are rapidly developing, this facilitates the development of the direct formic acid fuel cells. Catalyts are the key factor governing the performace and cost of DFAFCs. In this thesis, we focused on the systhsis of both Pt Au alloy and core-shell catalysts in order to obtain best electrooxidation toward formic acid as well as analyze the relationship between Pt Au binary catalyst and performance of formic acid electrooxidation.We prepared binary Pt Au alloy catalysts using colloidal method. Firstly, the effects of stabilizers and coagulant agents on the performance of catalysts were investigated Based on the morphology and the activities of catalysts prepared by different stabilizer named as PDDA, sodium citrate and PSS, it can be concluded that the PDDA-Pt Au has the smallest particle size and the highest dispersion as well as the best catalyzing performance due to both electrostatic protection and steric effect, as well as its influence on electronic structure of Pt Au alloy atoms. At the same time, we found that(NH4)2SO4 can act as the best coagulant agent when assuring a high load of catalyst onto the supporter. And finally, Pt Au alloy catalysts with different Pt Au atom ratio were prepared. Pt Au-1:1 has the best electro-catalysis ability toward formic acid and its activity was 0.84 A/mg. The presence of Au in Pt Au alloy catalyst can change the reaction pathway on Pt of formic acid into mainly dehydrogenation reaction through ensemble effect and Au has no contribution to the suppression of CO formation.Then Au@Pt/C core-shell catalysts were facricated through underpotential deposition following by chemical replacement step. We used the chronoamperometry method to accomplish the process of underpotential depositon. The coverage range of Pt shell at nano Au core was found to be 20% ~ 69%. It turned out that Au@Pt-20% perform the best area specific activity toward electrooxidation of formic acid, which was better than the Pt Au alloy catalyst above. The mechanism of the Au@Pt/C core-shell catalyst is attributed to that Au can not only resultes in the ensemble effect, it can also promote the oxidation of CO intermediate through electronic effect.