Study On The Preparation And Properties Of Decorated Low-Platinum Electrocatalysts For Alcohol Fuel Cells

Considerable attention has been paid to alternative energy sources in an attempt to relieve the energy crisis. One of the promising fields of clean and sustainable power is direct alcohol Fuel Cells technology, based on direct conversation of fuel into electricity. Despite considerable advances in recent years, many technical barriers still need to overcome in the development of electrocatalysts for widespread commercialization.Pt is the most effective catalyst to facilitate both ethanol and methanol oxidation fuel cells. However, platinum is very expensive, resource limited and irreversibly inactivated by CO-like or oxidation of alcohol poisoning species. Therefore, it is essential that the utilization of platinum should be kept as low as possible without sacrificing the catalytic performance.The theses mainly focus on high utilization of platinum in the catalysts. To match this requirement, a series of decorated low-Pt electrocatalysts for ethanol and methanol oxidation are designed and prepared. And the catalysts were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), energy dispersive X-ray analysis (EDX) and electrochemical techniques. Additionally, the catalysts were tested in a micro fuel cell system by measuring the performance of MEA/s, which were made from our lab-made catalysts. The thesis is consists of three parts and the research details are as follows:Part â… :Amorphous CoSn alloys decorated by Pt as high efficiency electrocatalysts for ethanol oxidationThis study examines the electro-catalytic behaviour of Pt decorating amorphous alloys in the electro-oxidation of ethanol. Pt decorated CoSn nanoparticles on carbon (denoted as Pt-CoSn/C) are prepared using a two-stage chemical synthesis (sol-gel preparation and Steady-state replacement method). The structure of Pt-CoSn/C nanoparticles is confirmed by the transmission electron microscopy (TEM) and X-ray diffraction (XRD). Under the same quantity of platinum, the Pt-CoSn/C nanoparticles have higher activity in alcohol oxidation than the Pt/C, PtRu/C and PtSn/C nanoparticles in cyclic voltammetry tests. The structure of Pt decorating amorphous CoSn alloys notably decreases the usage of Pt and enhances its catalytic activity at the same time.Part â…¡:Electrooxidation of methanol on the Pt decorated amorphous CoSn alloyThe aim of this work is the study of the electro-catalytic behaviour of methanol electro-oxidation reaction with Pt decorating amorphous alloys. An effective and low-cost Pt decorating amorphous CoSn alloy catalyst, which supported on carbon (denote as Pt-CoSn/C), is prepared by the two-stage chemical synthesis (Sol-gel technology and Steady-state replacement method). The structure of Pt-CoSn/C catalyst is confirmed by the transmission electron microscopy (TEM) and X-ray diffraction (XRD). It exhibits face centered cubic structures and the nanoparticles disperse homogeneous with small size. Under the same quality of noble metal, the Pt-CoSn/C catalyst has higher mass activity than Pt/C and PtRu/C catalyst in cyclic voltammetry for methanol oxidation. The structure of Pt decorating amorphous CoSn alloys could obviously decrease the usage of Pt and enhance its catalytic activity at the same time.Part â…¢:Strain Effect of Core-Shell Co@Pt/C Nanoparticle Catalyst with Enhanced Electrocatalytic Activity for Methanol OxidationA surface engineering approach was adopted for the preparation of a core-shell structure of bimetallic PtCo nanoparticles to improve catalytic activity for methanol oxidation on a mass basis. Synthesis of core-shell Co@Pt/C nanocomposite catalysts with different Pt content was carried out by reducing platinum precursors using ethylene glycolcitrate (EG) in aqueous solution containing previously formed Co/C. Characterizations were carried out using transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectra (XPS) and electrochemical techniques. The synthesized core-shell Co@Pt/C nanocomposite catalysts showed enhanced catalytic activity in the methanol oxidation reaction. The enhancement may result from favorable strain effects related to the thickness of Pt shell formed on the non-noble metal substrate. Moreover, the electrocatalytic activity was optimized by tuning shell thickness. This result confirms that changing the Pt shell thickness has a significant effect on the catalytic activities of nonnoble core-noble shell bimetallic nanoclusters. The developed surface-modification method (i.e. by fine-tuning the thickness of Pt shell on the non-noble metal substrate) has great potential application for producing highly active electrochemical catalysts for methanol oxidation on a large scale. The work thus paves the way for further investigating the strain effect in core-shell bimetallic catalysts.