Preparation And Characterizations Of High Performance&Low Pt Loading Catalysts For Fuelcells

Low temperature fuel cells have a wide range of advantages such as high energy conversion efficiency and quick start-up. They are also noiseless, environmentally friendly and available with variety of fuels, which have been considered as the most possibly large-scale industrialized fuel cells in the21st century. Low temperature fuel cells can be sub-classified as H2-O2fuel cells, direct alcohol fuel cells and direct acid fuel cells. These fuel cells commonly use noble metal platinum as the active component in the catalysts. Since its high price and resource scariety, the use of platinum has resulted in unacceptably high cell cost and consequently hindered the commercial development of fuel cells. Therefore, it is still a challenge to lower platinum loading to reduce catalysts cost while maintaining acceptable catalyst performance. It is of vital significance to develop high performance and low platinum loading fuel cell catalysts in order to promote fuel cell technology and commercialization.The thesis is targeted for the development of high performance and low platinum loading catalysts for low temperature fuel cells. A series of bimetallic carbon supported PtRu catalysts with good chemical and electrochemical stability has been designed and fabricated. These catalysts have been characterized as anode and cathode electrocatalysts at room temperature.Firstly, high catalytic activity with low platinum loading PtARu/C catalysts have been prepared. A two step hydrothermal method has been adopted to prepare20wt.%Pt^Ru/C with theoretic atomic PtRu ratio of1:1. The mass normalized specific activity for methanol oxidation reaction of PtARu/C out-performed E-TEK PtRu/C and home-made PtRu/C by240%and160%respectively.Secondly, core-shell structured Ru@Pt/C catalysts have been fabricated by pulse electrochemical deposition method using Ru/C substrate. The effects of different substrates, extent of platinum coverage (PtRu theoretic molar ratio) and different preparative methods on the Ru@Pt/C structure, methanol oxidation and oxygen reduction activity have been investigated. With the increase of PtRu theoretic molar ratio, the catalytic activity of Ru@Pt/C for methanol oxidation and oxygen reduction increased at the beginning and then decreased. A PtRu theoretic molar ratio of1:15resulted in the best catalytic performance. The electrochemically active surface area for Ru@Pt/C (PtRu theoretic molar ratio of1:15) is found to be238m2/g and its mass normalized methanol oxidation and oxygen reduction activity is10.8times and8.7times than that of commercial Hispec4100Pt/C, respectively. The home made Ru@Pt/C also displayed excellent CO tolerance capability.Lastly, CeO2has been used as additives to the carbon support to study its effects on catalytic activity. Pt-CeO2/C has been prepared by glycol reduction method and investigations have been made on the effects of substrate baking temperature on catalytic performance. It has been found that the addition of CeO2not only enhanced the methanol oxidation and oxygen reduction activity but also improved the CO tolerance capability.