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

Direct Ethanol Fuel Cell (DEFC) has been identified as a prospective fuel cell technology. And it is widely considered as promising power sources for portable electronic devices, fuel cell vehicles and power station in the future. However, the commercialization of DEFC is still inhibited by the sluggish kinetics of EOR on the anodic catalyst and the high cost of catalyst. The new material and synthesis methods for anodic catalysts in DEFC were developed in this work. The physical measurements were introduced to characterize the alloying degrees, average particle sizes, compositions and morphologies of different catalysts. The relationship between physical property and catalytic activity of ethanol oxidation was investigated. The main results are as follows:The Pt/MnOx-CNT catalyst with MnOx-CNT composite as a support was prepared by the microwave-polyol method. Pt nanoparticles are uniformly dispersed on MnOx-CNTs with the average particle size of about 2.2 nm. The Mn in the Pt/MnOx-CNT catalyst has various valence states, which can greatly enhance the exchange rate of H+ ions. The optimum mass ratio of MnOx to CNTs is 1:1 in the MnOx-CNT composite. Ethanol oxidation peak current on Pt/MnOx-CNTs is 1141.4 mA mg-1 Pt, which is 1.82 times higher than that on Pt/CNTs (626.4 mA mg=1 Pt). MnOx can not only accelerate the dehydrogenation reaction of ethanol oxidation on anodic catalyst, but also increase the formation of oxygenated species to eliminate the poisoning intermediates on the catalyst suface.For studying low-cost Pd-based catalyst, PdM/C (M=Te, Sb) bimetallic catalyst was prepared by the microwave-polyol method. There exist alloying phases in these two catalysts. The addition of Te or Sb into catalyst can improve the yield of oxygenated species on the catalyst surface, which can promote the removal of surface poisoning species, and facilitate the adsorption of ethanol for futher oxidation on catalyst surface. Ethanol oxidation peak currents on PdTe1.5/C and PdSb0.15/C are 190.3 mA cm-2 and 117.5 mA cm-2, which are 2.8 and 1.7 times higher than those on Pd/C, respectively.The PdBi/C and Cu@PdCu/C catalysts were prepared via the self-assemble method under room temperature. The results are as following:(1) In the solution, the Bi3+ ions can fast and irreversibly adsorb onto Pd surface to form PdBi/C catalyst. The average size of catalyst nanoparticles after adsorbed Bi is larger than that of Pd nanoparticles. Most Bi species deposited is in Bi (Ⅲ) state. The Bi has strongly electronic interaction with Pd, enhances the adsorption of OH" and thus improves the oxidation of poisonious intermediates on catalyst surface. Ethanol oxidation peak current density on Pd-Bi/C (20:1) catalyst is 180.5 mA cm-2, which is 2.4 times higher than that on Pd/C catalyst. (2) The Cu@PdCu core-shell nanoparticles were synthesized by the galvanic replacement of Pd2+ ions to Cu nanoparticle core. The catalyst is composed of the Cu core and PdCu alloying shell with ca.0.5 nm thickness. The catalyst with special core-shell structure enhances the Pd ultilization. The PdCu alloying promotes the formation of oxygenated species and enhances the oxidation of poisonious intermediates on catalyst surface. Thus the Cu@PdCu core-shell nanoparticles have great catalytic activity for ethanol oxidation. The catalytic activity of ethanol oxidation on Cu@PdCu/C catalyst is 166.0 mA cm-2, which is 2.8 times higher than that on Pd/C catalyst.