Synthesis of platinum-based nanostructures and metal-organic framework-derived carbon for electrocatalytic applications
2016 i Acknowledgement First and foremost, I would like to express my most sincere gratitude to my supervisor, Assoc. Prof. Wang Xin, for providing patient supervision, continuous support and encouragement throughout the whole courses of my study and research. His patience, wisdom, enthusiasm, and serious attitude towards research deeply influence me. This thesis would not have been successfully carried out without his great help. I would also like to extend my thanks to Dr. Xia Bao Yu for his
... Xia Bao Yu for his generous time and effort. My thanks are extended to all of the former and present colleagues for their precious friendship in daily life, and helpful discussion and collaboration in research. I also thank all of my friends, especially those who are also pursuing a PhD degree, for our mutual faith and passion in science, their encouragement and sharing their knowledge with me. Also, I highly appreciate our technical executives for their help in analytical instrument and purchasing, and NTU for providing me the opportunity for this degree. Last but most importantly, I would like to express my sincere gratitude to my families especially my mum and my sister for their deep love and support that enables me to concentrate on my pursuits. ii iii Abstract Fuel cell is one of the most promising candidates of renewable energy that have been highlighted in many researches these days. The main reason for this is the depleting non-renewable energy resources and the skyrocketing demand for energy in various applications to support current situation of technology development in a variety of fields. However, the main challenge of commercializing usage of fuel cells is the electrodes used in fuel cells. This major challenge revolves around the materials used as electrodes and their corresponding catalytic activities. It was discovered that nanoparticles can be used in construction of these electrodes. Thereby, large number of researches is going on investigating on various morphologies and crystal structures of nanoparticles. Among the so many kinds of nanostructured materials, platinum nanostructures have been broadly used for catalysis and fuel cells, owing to that Pt could catalyze both the oxidation and reduction reactions. Many researches have seen different synthetic routes proposed and carried out by researchers from around the world attempting to synthesize Pt nanoparticles since Pt could function as electrocatalyst for not only the oxygen reduction reaction (ORR) but also the fuel oxidation reactions, for example, formic acid oxidation reaction (FAOR), with the highest efficiency. As the demand for Pt grows while the Pt resource is scarce, the price of Pt has increased, and it could be predicted that the price will keep climbing later on. Finding new ways to lessen Pt utilized in a specific application by improving its catalytic activity is in need so as to overcome the prohibitive cost barrier. iv In this project, we focus on the rational design and synthesis of Pt-based nanostructures and MOF-derived carbon for electrocatalytic performance. In the first part of the research work, 3D Pt nanodendrites with clean surface and good catalytic performance were synthesized by a facile inorganic species assisted strategies. The possible specific adsorption of iron and nitrate ions would assist the growth of this 3D Pt nanostructure. Thanks to their unique 3D morphology composed of interconnected 1D Pt nanorods/wires, the clean unsupported 3D Pt NDs exhibit higher stability and enhanced activity than commercial carbon black supported Pt nanoparticles and Pt black electrocatalyst for the oxygen reduction reaction and oxidation of small fuel molecules. Incorporation of the transition metals with Pt during the preparation of Pt-based catalysts could significantly improve the activity and the poisoning tolerance while reducing the cost of catalysts. Of all the bimetallic Pt-based catalysts examined hitherto including PtRu, PtSn, PtPb, PtCo etc., PtBi exhibits the powerful activity for formic acid oxidation. Inspired by this, PtBi nanosheets with tunable composition and 2D structure is prepared with an effective thermal decomposition method and investigate the composition effect on the catalytic activity for formic acid oxidation reaction (FAOR). The addition of NH4Cl plays an important role on the formation of well-defined nanosheet structures. Due to the unique nanosheet structures and optimized composition, the as-prepared PtBi catalyst demonstrates the excellent electrocatalytic performance of FAOR. v In addition to synthesizing bimetallic/trimetallic electrocatalysts by introducing transition metal, various support materials for Pt and Pt contained nanocatalysts have also been investigated in depth and employed widely with the mutual purpose of significantly reducing of Pt cost while gaining fantabulous electrochemical performance. Nitrogen-doped CNT@Co-Pt composite using zeolitic imidazole framework-67 (ZIF-67) derived hierarchical nitrogen-doped CNT@Co frameworks as the carbon matrix was prepared with a facile method in our research work. The unique structure of the framework enables the catalyst with excellent structural merits including high accessibility, strong structural stability and sufficient loading site for the Pt nanoparticles. Meanwhile, the small amounts of carbon-nitrogen species would generate some extrinsic defects and active sites. In addition, the inner wrapped cobalt nanocrystals might provide extra conductivity. When applied as an advanced catalyst of ORR, the hybrid displays superior performance compare with commercial Pt/CB catalyst.